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  • 1.
    Aboulaich, Nabila
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Ortegren, Unn
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vener, Alexander V
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Association and insulin regulated translocation of hormone-sensitive lipase with PTRF2006In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 350, no 3, p. 657-661Article in journal (Refereed)
    Abstract [en]

    Polymerase I and transcript release factor (PTRF) is in human adipocytes mainly localized at the plasma membrane. This localization was under control of insulin, which translocated PTRF to the cytosol and nucleus, indicating a novel role for PTRF in insulin transcriptional control. In the plasma membrane PTRF was specifically bound to a triacylglycerol-metabolizing subclass of caveolae containing hormone-sensitive lipase (HSL). In response to insulin PTRF was translocated to the cytosol in parallel with HSL. PTRF and HSL were quantitatively immunoprecipitated from the cytosol by antibodies against either PTRF or HSL. The findings indicate also a novel extranuclear function for PTRF in the control of lipolysis.

  • 2.
    Aboulaich, Nabila
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vainonen, Julia P
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vener, Alexander V
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vectorial proteomics reveal targeting, phosphorylation and specific fragmentation of polymerase I and transcript release factor (PTRF) at the surface of caveolae in human adipocytes2004In: The Biochemical journal, ISSN 1470-8728, Vol. 383, no Pt 2, p. 237-248Article in journal (Refereed)
    Abstract [en]

    Caveolae, the specialized invaginations of plasma membranes, formed sealed vesicles with outwards-orientated cytosolic surface after isolation from primary human adipocytes. This morphology allowed differential, vectorial identification of proteins at the opposite membrane surfaces by proteolysis and MS. Extracellular-exposed caveolae-specific proteins CD36 and copper-containing amine oxidase were concealed inside the vesicles and resisted trypsin treatment. The cytosol-orientated caveolins were efficiently digested by trypsin, producing peptides amenable to direct MS sequencing. Isolation of peripheral proteins associated with the cytosolic surface of caveolae revealed a set of proteins that contained nuclear localization signals, leucine-zipper domains and PEST (amino acid sequence enriched in proline, glutamic acid, serine and threonine) domains implicated in regulation by proteolysis. In particular, PTRF (polymerase I and transcript release factor) was found as a major caveolae-associated protein and its co-localization with caveolin was confirmed by immunofluorescence confocal microscopy. PTRF was present at the surface of caveolae in the intact form and in five different truncated forms. Peptides (44 and 45 amino acids long) comprising both the PEST domains were sequenced by nanospray-quadrupole-time-of-flight MS from the full-length PTRF, but were not found in the truncated forms of the protein. Two endogenous cleavage sites corresponding to calpain specificity were identified in PTRF; one of them was in a PEST domain. Both cleavage sites were flanked by mono- or diphosphorylated sequences. The phosphorylation sites were localized to Ser-36, Ser-40, Ser-365 and Ser-366 in PTRF. Caveolae of human adipocytes are proposed to function in targeting, relocation and proteolytic control of PTRF and other PEST-domain-containing signalling proteins.

  • 3.
    Aboulaich, Nabila
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vener, Alexander V
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Hormonal control of reversible translocation of perilipin B to the plasma membrane in primary human adipocytes2006In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 281, no 17, p. 11446-11449Article in journal (Refereed)
    Abstract [en]

    In adipocytes, perilipin coats and protects the central lipid droplet, which stores triacylglycerol. Alternative mRNA splicing gives rise to perilipin A and B. Hormones such as catecholamines and insulin regulate triacylglycerol metabolism through reversible serine phosphorylation of perilipin A. It was recently shown that perilipin was also located in triacylglycerol-synthesizing caveolae of the plasma membrane. We now report that perilipin at the plasma membrane of primary human adipocytes was phosphorylated on a cluster of threonine residues (299, 301, and 306) within an acidic domain that forms part of the lipid targeting domain. Perilipin B comprised <10% of total perilipin but was the major isoform associated with the plasma membrane of human adipocytes. This association was controlled by insulin and catecholamine: perilipin B was specifically depleted from the plasma membrane in response to the catecholamine isoproterenol, while insulin increased the amount of threonine phosphorylated perilipin at the plasma membrane. The reversible translocation of perilipin B to and from the plasma membrane in response to insulin and isoproterenol, respectively, suggests a specific function for perilipin B to protect newly synthesized triacylglycerol in the plasma membrane.

  • 4.
    Ahmad, Faiyaz
    et al.
    NHLBI, Translat Med Branch, NIH, Bethesda, MD 20892 USA .
    Lindh, Rebecka
    Lund University, Department Expt Med Science, S-22184 Lund, Sweden .
    Tang, Yan
    NHLBI, Translat Med Branch, NIH, Bethesda, MD 20892 USA .
    Ruishalme, Iida
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Sahachartsiri, Bobby
    NHLBI, Translat Med Branch, NIH, Bethesda, MD 20892 USA .
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Degerman, Eva
    Lund University, Department Expt Med Science, S-22184 Lund, Sweden .
    C Manganiello, Vincent
    NHLBI, Translat Med Branch, NIH, Bethesda, MD 20892 USA .
    Differential regulation of adipocyte PDE3B in distinct membrane compartments by insulin and the beta(3)-adrenergic receptor agonist CL316243: effects of caveolin-1 knockdown on formation/maintenance of macromolecular signalling complexes2009In: BIOCHEMICAL JOURNAL, ISSN 0264-6021, Vol. 424, no 3, p. 399-410Article in journal (Refereed)
    Abstract [en]

    In adipocytes, PDE3B (phosphodiesterase 3B) is an important regulatory effector in signalling pathways controlled by insulin and cAMP-increasing hormones. Stimulation of 3T3-L1 adipocytes with insulin or the beta(3)-adrenergic receptor agonist CL316243 (termed CL) indicated that insulin preferentially phosphorylated/activated PDE3B associated with internal membranes (endoplasmic reticulum/Golgi), whereas CL preferentially phosphorylated/activated PDE3B associated with caveolae. siRNA (small interfering RNA)-mediated KD (knockdown) of CAV-1 (caveolin-1) in 3T3-L1 adipocytes resulted in down-regulation of expression of membrane-associated PDE3B. Insulin-induced activation of PDE3B was reduced, whereas CL-mediated activation was almost totally abolished. Similar results were obtained in adipocytes from Cav-1-deficient mice. siRNA-mediated KID of CAV-1 in 3T3-L1 adipocytes also resulted in inhibition of CL-stimulated phosphorylation of HSL (hormone-sensitive lipase) and perilipin A, and of lipolysis. Superose 6 gel-filtration chromatography of solubilized membrane proteins from adipocytes stimulated with insulin or CL demonstrated the reversible assembly of distinct macromolecular complexes that contained P-32-phosphorylated PDE3B and signalling molecules thought to be involved in its activation. Insulin- and CL-induced macromolecular complexes were enriched in cholesterol, and contained certain common signalling proteins [14-3-3, PP2A (protein phosphatase 2A) and cav-1]. The complexes present in insulin-stimulated cells contained tyrosine-phosphorylated IRS-1 (insulin receptor substrate 1) and its downstream signalling proteins, whereas CL-activated complexes contained beta(3)-adrenergic receptor, PKA-RII [PKA (cAMP-dependent protein kinase)-regulatory subunit] and HSL. Insulin- and CL-mediated macromolecular complex formation was significantly inhibited by CAV-1 KID. These results suggest that cav-1 acts as a molecular chaperone or scaffolding molecule in cholesterol-rich lipid rafts that may be necessary for the proper stabilization and activation of PDE3B in response to CL and insulin.

  • 5. Al Hilli, S.M.
    et al.
    Willander, Magnus
    Linköping University, The Institute of Technology. Linköping University, Department of Science and Technology.
    Öst, Anita
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
    ZnO nanorods as an intracellular sensor for pH measurements2007In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 102, no 8Article in journal (Refereed)
    Abstract [en]

    ZnO nanorods with 80 nm diameter and 700 nm length and grown on the tip of a borosilicate glass capillary (0.7 μm in diameter) were used to create a highly sensitive pH sensor for monitoring in vivo biological process within single cells. The ZnO nanorods, functionalized by proton H3 O+ and hydroxyl O H- groups, exhibit a pH -dependent electrochemical potential difference versus a AgAgCl microelectrode. The potential difference was linear over a large dynamic range (4-11), which could be understood in terms of the change in surface charge during protonation and deprotonation. These nanoelectrode devices have the ability to enable analytical measurements in single living cells and have the capability to sense individual chemical species in specific locations within a cell. © 2007 American Institute of Physics.

  • 6.
    Asif, Muhammad H
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Fulati, Alimujiang
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nor, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Johansson, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Börjesson, Sara I.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Functionalized zinc oxide nanorod with ionophore-membrane coatingas an intracellular Ca2+ selective sensor2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 2, p. 23703-Article in journal (Refereed)
    Abstract [en]

    The tip of a borosilicate glass capillary with functionalized hexagonal ZnO nanorods was used to make a sensitive electrochemical intracellular Ca2+ sensor. To adjust the sensor for Ca2+ measurements with sufficient selectivity and stability, polyvinyl chloride (PVC) membrane containing Ca2+ ionophores were coated on the surface. The membrane covered ZnO nanorods exhibited a Ca2+-dependent electrochemical potential difference versus an Ag/AgCl reference electrode. The potential difference was linear over a large concentration range (100 nM to 10 mM). The measurements of Ca2+ concentrations using our ZnO nanorods sensor in human fat cells or in frog egg cells were consistent with values of Ca2+ concentrations reported in the literature. This nanoelectrode device paves the way to measurements of intracellular biochemical species in specific locations within single living cells.

  • 7.
    Asif, Muhammad H.
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Englund, Ulrika H
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Lu, Jun
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Hultman, Lars
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Growth and Structure of ZnO Nanorods on a Sub-Micrometer Glass Pipette and Their Application as Intracellular Potentiometric Selective Ion Sensors2010In: Materials, ISSN 1996-1944, Vol. 3, p. 4657-4667Article in journal (Refereed)
    Abstract [en]

    This paper presents the growth and structure of ZnO nanorods on a sub-micrometer glass pipette and their application as an intracellular selective ion sensor. Highly oriented, vertical and aligned ZnO nanorods were grown on the tip of a borosilicate glass capillary (0.7 μm in diameter) by the low temperature aqueous chemical growth (ACG) technique. The relatively large surface-to-volume ratio of ZnO nanorods makes them attractive for electrochemical sensing. Transmission electron microscopy studies show that ZnO nanorods are single crystals and grow along the crystal’s c-axis. The ZnO nanorods were functionalized with a polymeric membrane for selective intracellular measurements of Na

     

    +. The membrane-coated ZnO nanorods exhibited a Na+-dependent electrochemical potential difference versus

    an Ag/AgCl reference micro-electrode within a wide concentration range from 0.5 mM to 100 mM. The fabrication of functionalized ZnO nanorods paves the way to sense a wide range of biochemical species at the intracellular level.

  • 8.
    Asif, Muhammad H
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Usman Ali, Syed M
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Nur, Omer
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Englund H, Ulrika
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Danielsson, Bengt
    Pure and Applied Biochemistry, Lund University, Box 124, SE-221 00 Lund, Sweden.
    Functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose2010In: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 25, no 10, p. 2205-2211Article in journal (Refereed)
    Abstract [en]

    In this article, we report a functionalised ZnO-nanorod-based selective electrochemical sensor for intracellular glucose. To adjust the sensor for intracellular glucose measurements, we grew hexagonal ZnO nanorods on the tip of a silver-covered borosilicate glass capillary (0.7 mu m diameter) and coated them with the enzyme glucose oxidase. The enzyme-coated ZnO nanorods exhibited a glucose-dependent electrochemical potential difference versus an Ag/AgCl reference microelectrode. The potential difference was linear over the concentration range of interest (0.5-1000 mu M). The measured glucose concentration in human adipocytes or frog oocytes using our ZnO-nanorod sensor was consistent with values of glucose concentration reported in the literature; furthermore, the sensor was able to show that insulin increased the intracellular glucose concentration. This nanoelectrode device demonstrates a simple technique to measure intracellular glucose concentration.

  • 9.
    Asif, Muhammad H.
    et al.
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology, Physics and Electronics. Linköping University, The Institute of Technology.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Danielsson, Bengt
    Lund University, Sweden.
    Zinc Oxide Nanorods and their Application to Intracellular Glucose Measurements2012In: Nanotechnology and Nanomedicine in Diabetes / [ed] Lan-Anh Le, Ross J. Hunter, Victor R. Preedy, CRC Press, 2012, p. 126-146Chapter in book (Other academic)
  • 10.
    Brannmark, Cecilia
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Palmer, Robert
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Mass and Information Feedbacks through Receptor Endocytosis Govern Insulin Signaling as Revealed Using a Parameter-free Modeling Framework2010In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 285, no 26, p. 20171-20179Article in journal (Refereed)
    Abstract [en]

    Insulin and other hormones control target cells through a network of signal-mediating molecules. Such networks are extremely complex due to multiple feedback loops in combination with redundancy, shared signal mediators, and cross-talk between signal pathways. We present a novel framework that integrates experimental work and mathematical modeling to quantitatively characterize the role and relation between coexisting submechanisms in complex signaling networks. The approach is independent of knowing or uniquely estimating model parameters because it only relies on (i) rejections and (ii) core predictions (uniquely identified properties in unidentifiable models). The power of our approach is demonstrated through numerous iterations between experiments, model-based data analyses, and theoretical predictions to characterize the relative role of co-existing feedbacks governing insulin signaling. We examined phosphorylation of the insulin receptor and insulin receptor substrate-1 and endocytosis of the receptor in response to various different experimental perturbations in primary human adipocytes. The analysis revealed that receptor endocytosis is necessary for two identified feedback mechanisms involving mass and information transfer, respectively. Experimental findings indicate that interfering with the feedback may substantially increase overall signaling strength, suggesting novel therapeutic targets for insulin resistance and type 2 diabetes. Because the central observations are present in other signaling networks, our results may indicate a general mechanism in hormonal control.

  • 11.
    Bronnikov, Gennady
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Aboulaich, Nabila
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Vener, Alexander
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Acute effects of insulin on the activity of mitochondrial GPAT1 in primary adipocytes2008In: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 367, no 1, p. 201-207Article in journal (Refereed)
    Abstract [en]

    The mitochondrial enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase (mtGPAT1) catalyzes a rate-limiting step in triacylglycerol and glycerophospholipid biosynthesis, which can be modulated by protein kinases in cell free analyses. We report that treatment of primary rat adipocytes with insulin acutely affects the activity of mtGPAT1 by increasing VMAX and KM for the substrates glycerol-3-phosphate and palmitoyl-CoA. Proteolytic cleavage of isolated mitochondrial membranes and mass spectrometric peptide sequencing identify in vivo phosphorylation of serine 632 and serine 639 in mtGPAT1. These phosphorylation sites correspond to casein kinase-2 consensus sequences and are highly conserved in chordate animal, but not fly, fungal or plant, mtGPAT1. © 2007 Elsevier Inc. All rights reserved.

  • 12.
    Brännmark, Cecilia
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Nyman, Elin
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Bergenholm, Linnéa
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Ekstrand, Eva-Maria
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Insulin Signaling in Type 2 Diabetes: Experimental and Modeling Analyses Reveal Mechanisms of Insulin Resistance in Human Adipocytes2013In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 288, no 14, p. 9867-9880Article in journal (Refereed)
    Abstract [en]

    Type 2 diabetes originates in an expanding adipose tissue that for unknown reasons becomes insulin resistant. Insulin resistance reflects impairments in insulin signaling, but mechanisms involved are unclear because current research is fragmented. We report a systems-level mechanistic understanding of insulin resistance in humans. We developed a dynamic mathematical model of insulin signaling – normally and in diabetes – based on quantitative steady-state and dynamic time-course data on signaling intermediaries in human mature adipocytes. At the core of insulin resistance is attenuation of a positive feedback from mammalian target of rapamycin in complex with raptor (mTORC1) to the insulin receptor substrate-1 (IRS1), which explains reduced sensitivity and signal strength throughout the signaling network. We demonstrate the potential of the model for identification of drug targets, e.g. increasing the feedback restores insulin signaling. Our findings suggest that insulin resistance in an expanded adipose tissue results from cell growth restriction to prevent cell necrosis.

  • 13.
    Bäck, Karolina
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Arnqvist, Hans
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Endocrinology and Gastroenterology UHL.
    Differential effects of IGF-I, IGF-II and insulin in human preadipocytes and adipocytes - Role of insulin and IGF-I receptors2011In: Molecular and Cellular Endocrinology, ISSN 0303-7207, E-ISSN 1872-8057, Vol. 339, no 02-jan, p. 130-135Article in journal (Refereed)
    Abstract [en]

    We compared insulin and IGF effects in adipocytes expressing IR (insulin receptors), and preadipocytes expressing IR and IGF-IR (IGF-I receptors). Treatment of adipocytes with insulin, IGF-II or IGF-I resulted in phosphorylation of IR. Order of potency was insulin greater thanIGF-IIgreater than IGF-I. In preadipocytes IR, IGF-IR and insulin/IGF-I hybrid receptors (HR) were detected. Treatment of preadipocytes with IGF-I and IGF-II 10(-8) M resulted in activation of IGF-IR and IR whereas insulin was more potent in activating IR, with no effect on IGF-IR. In adipocytes glucose transport was 100-fold more sensitive to insulin than to IGFs and the maximal effect was higher with insulin. In preadipocytes glucose accumulation and DNA synthesis was equally sensitive to insulin and IGFs but the maximal effect was higher with IGF-I. In conclusion, insulin and IGF-I activate their cognate receptors and IGF-I also HR. IGF-II activates IR, IGF-IR and HR. Insulin and IGF-I are partial agonists to each others receptors.

  • 14.
    Cedersund, Gunnar
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Roll, Jacob
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ulfhielm, Erik
    Linköping University, Department of Electrical Engineering. Linköping University, The Institute of Technology.
    Danielsson, Anna
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Tidefelt, Henrik
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Model-Based Hypothesis Testing of Key Mechanisms in Initial Phase of Insulin Signaling2008In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 4, no 6Article in journal (Refereed)
    Abstract [en]

    Type 2 diabetes is characterized by insulin resistance of target organs, which is due to impaired insulin signal transduction. The skeleton of signaling mediators that provide for normal insulin action has been established. However, the detailed kinetics, and their mechanistic generation, remain incompletely understood. We measured time-courses in primary human adipocytes for the short-term phosphorylation dynamics of the insulin receptor (IR) and the IR substrate-1 in response to a step increase in insulin concentration. Both proteins exhibited a rapid transient overshoot in tyrosine phosphorylation, reaching maximum within 1 min, followed by an intermediate steady-state level after approximately 10 min. We used model-based hypothesis testing to evaluate three mechanistic explanations for this behavior: (A) phosphorylation and dephosphorylation of IR at the plasma membrane only, (B) the additional possibility for IR endocytosis, (C) the alternative additional possibility of feedback signals to IR from downstream intermediates. We concluded that (A) is not a satisfactory explanation, that (B) may serve as an explanation only if both internalization, dephosphorylation, and subsequent recycling are permitted, and that (C) is acceptable. These mechanistic insights cannot be obtained by mere inspection of the datasets, and they are rejections and thus stronger and more final conclusions than ordinary model predictions.

  • 15.
    Cedersund, Gunnar
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors , Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Putting the pieces together in diabetes research: Towards a hierarchical model of whole-body glucose homeostasis2009In: European Journal of Pharmaceutical Sciences, ISSN 0928-0987, E-ISSN 1879-0720, Vol. 36, no 1, p. 91-104Article in journal (Refereed)
    Abstract [en]

    Type 2 diabetes is one of the most widespread and rapidly spreading diseases world-wide and has been subject of extensive research efforts. However, understanding the molecular basis of the disease is increasing piecemeal and a consensus regarding the overall picture of normal metabolic regulation and malfunction in diabetes has not emerged. A systems biology approach, combining mathematical modelling with simultaneous high-throughput measurements, can be of considerable help. On the whole-body level, this has been done in pharmacokinetic and pharmacodynamic models, which recently have started to mature into more physiologically realistic organ-based models. At the other end of the spectrum, detailed models for crucial cellular processes are starting to mature into complete modules that potentially can be fitted into such whole-body organ-based models. The result of such a merge is a multi-level hierarchical model, which is a model type that has been common in technical systems. In this review, we report and exemplify some of the recent progress that has been made to achieve such a hierarchical model, and we argue why it is only through such a model that a Complete picture of diabetes mellitus can be obtained.

  • 16.
    Cedersund, Gunnar
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Jirstrand, Mats
    Fraunhofer-Chalmers Research Centre for Industrial Mathematics, Chalmers Teknikpark, 41288 Gothenburg, Sweden.
    Core-Box Modeling in the Biosimulation of Drug Action2008In: Biosimulation in Drug Development / [ed] Martin Bertau, Erik Mosekilde, Hans V. Westerhoff, Weinheim, Germany: Wiley-VCH Verlagsgesellschaft, 2008, p. 115-139Chapter in book (Other academic)
  • 17.
    Danielsson, Anna
    et al.
    Linköping University, Department of Medicine and Health Sciences, Nursing Science. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Franck, Niclas
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Health Sciences.
    Kjölhede, Preben
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Obstetrics and gynecology . Östergötlands Läns Landsting, Centre of Paediatrics and Gynecology and Obstetrics, Department of Gynecology and Obstetrics in Linköping.
    Nyström, Fredrik H
    Linköping University, Department of Medicine and Health Sciences, Cardiology . Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Short-Term Overeating Induces Insulin Resistance in Fat Cells in Lean Human Subjects2009In: Molecular medicine (Cambridge, Mass. Print), ISSN 1076-1551, E-ISSN 1528-3658, Vol. 15, no 7-8, p. 228-234Article in journal (Refereed)
    Abstract [en]

    Insulin resistance and type 2 diabetes (T2D) are closely linked to obesity. Numerous prospective studies have reported on weight gain, insulin resistance, and insulin signaling in experimental animals, but not in humans. We examined insulin signaling in adipocytes from lean volunteers, before and at the end of a 4-wk period of consuming a fast-food, high-calorie diet that led to weight gain. We also examined adipocytes from patients with T2D. During the high-calorie diet, subjects gained 10% body weight and 19% total body fat, but stayed lean (body mass index = 24.3 kg/m2) and developed moderate systemic insulin resistance. Similarly to the situation in T2D subjects, in subjects on the high-calorie diet, the amount of insulin receptors was reduced and phosphorylation of IRS1 at tyrosine and at serine-307 (human sequence, corresponding to murine serine-302) were impaired. The amount of insulin receptor substrate protein-1 (IRS1) and the phosphorylation of IRS1 at serine-312 (human sequence, corresponding to murine serine-307) were unaffected by the diet. Unlike the T2D subjects, in subjects on the high-calorie diet, likely owing to the ongoing weight-gain, phosphorylation of MAP-kinases ERK1/2 became hyperresponsive to insulin. To our knowledge this study is the first to investigate insulin signaling during overeating in humans, and it demonstrates that T2D effects on intracellular insulin signaling already occur after 4 wks of a high-calorie diet and that the effects in humans differ from those in laboratory animals.

  • 18.
    Danielsson, Anna
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cellbiology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Medicine and Health Sciences, Internal Medicine . Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cellbiology. Linköping University, Faculty of Health Sciences.
    Phosphorylation of IRS1 at serine 307 and serine 312 in response to insulin in human adipocytes2006In: Biochemical and biophysical research communications, ISSN 0006-291X, Vol. 342, no 4, p. 1183-1187Article in journal (Refereed)
    Abstract [en]

    Feedback control in insulin signaling involves serine phosphorylation of insulin receptor substrate-1 (IRS1). By analyzing the insulin-induced phosphorylation of IRS1 at serine 307, serine 312, and tyrosine in the same primary human adipocytes, we now report that negative feedback phosphorylation of serine 312 (corresponding to murine serine 307) required relatively high concentrations of insulin (EC50 = 3 nM) for a long time (t1/2 ca. 30 min) and reduced the steady-state tyrosine phosphorylation, without affecting the cellular concentration, of IRS1. In contrast, positive feedback phosphorylation of serine 307 was a rapid (t1/2 ca. 2 min) event at physiological concentrations of insulin (EC50 = 0.2 nM).

  • 19.
    Danielsson, Anna
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Lystedt, Erika
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Kjölhede, Preben
    Linköping University, Department of Clinical and Experimental Medicine, Obstetrics and gynecology . Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Insulin resistance in human adipocytes occurs downstream of IRS1 after surgical cell isolation but at the level of phosphorylation of IRS1 in type 2 diabetes2005In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 272, no 1, p. 141-151Article in journal (Refereed)
    Abstract [en]

    Insulin resistance is a cardinal feature of type 2 diabetes and also a consequence of trauma such as surgery. Directly after surgery and cell isolation, adipocytes were insulin resistant, but this was reversed after overnight incubation in 10% CO2 at 37 °C. Tyrosine phosphorylation of the insulin receptor and insulin receptor substrate (IRS)1 was insulin sensitive, but protein kinase B (PKB) and downstream metabolic effects exhibited insulin resistance that was reversed by overnight incubation. MAP-kinases ERK1/2 and p38 were strongly phosphorylated after surgery, but was dephosphorylated during reversal of insulin resistance. Phosphorylation of MAP-kinase was not caused by collagenase treatment during cell isolation and was present also in tissue pieces that were not subjected to cell isolation procedures. The insulin resistance directly after surgery and cell isolation was different from insulin resistance of type 2 diabetes; adipocytes from patients with type 2 diabetes remained insulin resistant after overnight incubation. IRS1, PKB, and downstream metabolic effects, but not insulin-stimulated tyrosine phosphorylation of insulin receptor, exhibited insulin resistance. These findings suggest a new approach in the study of surgery-induced insulin resistance and indicate that human adipocytes should recover after surgical procedures for analysis of insulin signalling. Moreover, we pinpoint the signalling dysregulation in type 2 diabetes to be the insulin-stimulated phosphorylation of IRS1 in human adipocytes.

  • 20.
    Danielsson, Anna
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Attenuation of insulin-stimulated insulin receptor substrate-1 serine 307 phosphorylation in insulin resistance of type 2 diabetes2005In: Journal of biological chemistry, ISSN 0021-9258, Vol. 280, no 41, p. 34389-3492Article in journal (Refereed)
    Abstract [en]

    Insulin resistance is a primary characteristic of type 2 diabetes and likely causally related to the pathogenesis of the disease. It is a result of defects in signal transduction from the cell surface receptor of insulin to target effects. We found that insulin-stimulated phosphorylation of serine 307 (corresponding to serine 302 in the murine sequence) in the immediate downstream mediator protein of the insulin receptor, insulin receptor substrate-1 (IRS1), is required for efficient insulin signaling and that this phosphorylation is attenuated in adipocytes from patients with type 2 diabetes. Inhibition of serine 307 phosphorylation by rapamycin mimicked type 2 diabetes and reduced the sensitivity of IRS1 tyrosine phosphorylation in response to insulin, while stimulation of the phosphorylation by okadaic acid, in cells from patients with type 2 diabetes, rescued cells from insulin resistance. EC50 for insulin-stimulated phosphorylation of serine 307 was about 0.2 nM with a t1/2 of about 2 min. The amount of IRS1 was similar in cells from non-diabetic and diabetic subjects. These findings identify a molecular mechanism for insulin resistance in non-selected patients with type 2 diabetes.

  • 21.
    Fagerholm, Siri
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Örtegren Kugelberg, Unn
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Karlsson, M.
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Ruishalme, I.
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Rapid insulin-dependent endocytosis of the insulin receptor by caveolae in primary adipocytes2009In: PLoS ONE, ISSN 1932-6203, Vol. 4, no 6, p. e5985-Article in journal (Refereed)
    Abstract [en]

    Background: The insulin receptor is localized in caveolae and is dependent on caveolae or cholesterol for signaling in adipocytes. When stimulated with insulin, the receptor is internalized. Methodology/Principal Findings: We examined primary rat adipocytes by subcellular fractionation to examine if the insulin receptor was internalized in a caveolae-mediated process. Insulin induced a rapid, t1/2 less than3 min, endocytosis of the insulin receptor in parallel with receptor tyrosine autophosphorylation. Concomitantly, caveolin-1 was phosphorylated at tyrosine(14) and endocytosed. Vanadate increased the phosphorylation of caveolin-1 without affecting insulin receptor phosphorylation or endocytosis. Immunocapture of endosomal vesicles with antibodies against the insulin receptor co-captured caveolin-1 and immunocapture with antibodies against tyrosine(14)-phosphorylated caveolin-1 co-captured the insulin receptor, demonstrating that the insulin receptor was endocytosed together with tyrosine(14)-phosphorylated caveolin-1. By immunogold electron microscopy the insulin receptor and caveolin-1 were colocalized in endosome vesicles that resembled caveosomes. Clathrin was not endocytosed with the insulin receptor and the inhibitor of clathrin-coated pit-mediated endocytosis, chlorpromazine, did not inhibit internalization of the insulin receptor, while transferrin receptor internalization was inhibited. Conclusion: It is concluded that in response to insulin stimulation the autophosphorylated insulin receptor in primary adipocytes is rapidly endocytosed in a caveolae-mediated process, involving tyrosine phosphorylation of caveolin-1.

  • 22.
    Franck, Niclas
    et al.
    Linköping University, Department of Medicine and Health Sciences, Internal Medicine . Linköping University, Faculty of Health Sciences.
    Stenkula, Karin G.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Lindström, Torbjörn
    Linköping University, Department of Medicine and Health Sciences, Internal Medicine . Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Medicine and Health Sciences, Internal Medicine . Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Insulin-induced GLUT4 translocation to the plasma membrane is blunted in large compared with small primary fat cells isolated from the same individual2007In: Diabetologia, ISSN 0012-186X, E-ISSN 1432-0428, Vol. 50, no 8, p. 1716-1722Article in journal (Refereed)
    Abstract [en]

    Aims/hypothesis: Several studies have suggested that large fat cells are less responsive to insulin than small fat cells. However, in these studies, large fat cells from obese individuals were compared with smaller fat cells from leaner participants, in effect making it impossible to draw conclusions about whether there is a causal relationship between fat cell size and insulin sensitivity. We hypothesised that small fat cells might be more insulin-responsive than large adipocytes when obtained from the same individual.

    Materials and methods: We developed a method of sorting isolated primary human fat cells by using nylon filters of two different pore sizes. The cells were stained to visualise DNA, which allowed discrimination from artefacts such as lipid droplets. The sorted cells were left to recover overnight, since we had previously demonstrated that this is necessary for correct assessment of insulin response.

    Results: We found similar amounts of the insulin receptor (IR), IRS-1 and GLUT4 when we compared small and large adipocytes from the same volunteer by immunoblotting experiments using the same total cell volume from both cell populations. Activation of IR, IRS-1 and Akt1 (also known as protein kinase B) by insulin was similar in the two cell populations. However, immunofluorescence confocal microscopy of plasma membrane sheets did not reveal any increase in the amount of GLUT4 in the plasma membrane following insulin stimulation in the large fat cells, whereas we saw a twofold increase in the amount of GLUT4 in the small fat cells.

    Conclusions/interpretation: Our results support a causal relationship between the accumulation of large fat cells in obese individuals and reduced insulin responsiveness.

  • 23.
    Fulati, Alimujiang
    et al.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Usman Ali, Syed M.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Asif, Muhammad H.
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology. Pakistan.
    Hassan Alvi, Naveed Ul
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Willander, Magnus
    Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Börjesson, Sara I.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Elinder, Fredrik
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Danielsson, Bengt
    Lund University, Sweden.
    An intracellular glucose biosensor based on nanoflake ZnO2010In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 150, no 2, p. 673-680Article in journal (Other academic)
    Abstract [en]

    In this study, an improved potentiometric intracellular glucose biosensor was fabricated with immobilization of glucose oxidase on a ZnO nanoporous material. The ZnO nanoporous material with a wall thickness around 200 nm was grown on the tip of a borosilicate glass capillary and used as a selective intracellular glucose sensor for the measurement of glucose concentrations in human adipocytes and frog oocytes. The results showed a fast response within 4 s and a linear glucosedependent electrochemical response over a wide range of glucose concentration (500 nM-10 mM). The measurements of intracellular glucose concentrations with our biosensor were consistent with the values of intracellular glucose concentrations reported in the literature. The sensor also demonstrated its capability by detecting an increase in the intracellular glucose concentration induced by insulin. We found that the ZnO nanoporous material provides sensitivity as high as 1.8 times higher than that obtained using ZnO nanorods under the same conditions. Moreover, the fabrication method in our experiment is simple and the excellent performance of the developed nanosensor in sensitivity, stability, selectivity, reproducibility and anti-interference was achieved. All these advantageous features of this intracellular glucose biosensor based on functionalised ZnO nanoporous material compared to ZnO nanorods demonstrate a promising way of enhancing glucose biosensor performance to measure reliable intracellular glucose concentrations within single living cells.

  • 24.
    Gustavsson, Johanna
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Parpal, Santiago
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Karlsson, Margareta
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Ramsing, Cecilia
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Thorn, Hans
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Borg, Marie
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Lindroth, Margaretha
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Holmgren Peterson, Kajsa
    Linköping University, Department of Molecular and Clinical Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
    Magnusson, Karl-Eric
    Linköping University, Department of Molecular and Clinical Medicine, Medical Microbiology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Localization of the insulin receptor in caveolae of adipocyte plasma membrane1999In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 13, no 14, p. 1961-1971Article in journal (Refereed)
    Abstract [en]

    The insulin receptor is a transmembrane protein of the plasma membrane, where it recognizes extracellular insulin and transmits signals into the cellular signaling network. We report that insulin receptors are localized and signal in caveolae microdomains of adipocyte plasma membrane. Immunogold electron microscopy and immunofluorescence microscopy show that insulin receptors are restricted to caveolae and are colocalized with caveolin over the plasma membrane. Insulin receptor was enriched in a caveolae-enriched fraction of plasma membrane. By extraction with β-cyclodextrin or destruction with cholesterol oxidase, cholesterol reduction attenuated insulin receptor signaling to protein phosphorylation or glucose transport. Insulin signaling was regained by spontaneous recovery or by exogenous replenishment of cholesterol. β-Cyclodextrin treatment caused a nearly complete annihilation of caveolae invaginations as examined by electron microscopy. This suggests that the receptor is dependent on the caveolae environment for signaling. Insulin stimulation of cells prior to isolation of caveolae or insulin stimulation of the isolated caveolae fraction increased tyrosine phosphorylation of the insulin receptor in caveolae, demonstrating that insulin receptors in caveolae are functional. Our results indicate that insulin receptors are localized to caveolae in the plasma membrane of adipocytes, are signaling in caveolae, and are dependent on caveolae for signaling.

  • 25.
    Johansson, Rickard
    et al.
    Linköping University, Department of Biomedical Engineering, Medical Informatics.
    Kreutz, Clemens
    Physics Department, University of Freiburg, Germany.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Timmer, Jens
    Physics Department, University of Freiburg, Germany.
    Cedersund, Gunnar
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    A two-dimensional bootstrap approach to model discriminationManuscript (preprint) (Other academic)
  • 26.
    Johansson, Rikard
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Kreutz, Clemens
    University of Freiburg, Department of Physics.
    Bartolomé Rodríguez, M. M.
    University of Freiburg, Department of Medicine.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Timmer, Jens
    University of Freiburg, Department of Physics.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Elucidating mechanisms of early insulin signaling in primary adipocytes and hepatocytes: a joint systems biology effort2009Conference paper (Other academic)
    Abstract [en]

    Type II diabetes is one of the most common diseases afflicting people today. Understanding how this disease works, not only on a cellular level and between different organs and tissues, but also how it affects whole body level homeostasis is crucial for enhancement of its treatment. We use model-bases analysis as a tool for distinguishing different biological hypothesis on the system behavior.

    The Insulin Receptor (IR), is located in the cell membrane as a dimer, and thus has the potential two bind two different insulin molecules. It can also undergo a series of phosphorylations, as well as having the ability to become internalized, and thus be removed from the cell’s censing area. However, it can then be recycled back to the membrane again. The major target of IR is the Insulin Receptor Substrate 1 (IRS1). IRS1 in turn mediates the signal further downstream through Protein Kinase B (PBK) and mammalian Target of Rapamycin (mTOR).  In adipocytes the end result is the translocation of internal vesicles containing Glucose Transporters (GLUT4) to the membrane, thus increasing the uptake of glucose. The liver, on the other hand, responds by down regulating the endogenous glucose production.

    The activity of IRS1 is determined by its phospho-tyrosine composition. This in turn is regulated by at least two serine-phosphorylations, on ser307 and ser312. The serine levels of this protein are regulated by downstream kinases, of which only one is known, S6K. The ser307 phosphorylation appears to allow for a short term positive feedback while the ser312 phosphorylation has the dynamics of a more long term negative feedback.

    The overall dynamics of the IRS1 tyrosine phosphorylation is a mirror of that of the Insulin Receptor. They both have a quick response to insulin within minutes, manifested as a high overshoot before declining to a steady state level. The overshoot behavior of this system can be explained either by a downstream negative feedback, or by having an advanced internalization and recycling model. Several hypotheses of the negative feedback mechanisms necessary to allow for the receptor to adopt such a behavior have previously been rejected by us. So has the hypothesis of internalization (unpublished data). The internalized Insulin Receptors can account for only a small fraction of the total amount of receptors, it however seems to be necessary for its own down regulation, since without it the overshoot behavior disappears.

    The complexity of this system is immense and hence we keep to as minimal models as possible, only considering adding complexity to the system when data indicates so, or when a simpler model structure has been rejected. We model the system with a series of Ordinary Differential Equations (ODEs), optimize and estimate the parameters of a given model structure with the Systems Biology Toolbox (SBTB) and reject, or fail to reject, models based on their statistical agreement with our data. We search the entire approximated parameter space for a sample of all acceptable parameter values for any given parameter. We then look for commonalities shared between model simulations of all parameter sets in the sample. That is, a behavior of e.g. a state in the model that has to be above a certain threshold for it to be able to explain the data, while other states might be of arbitrary sizes. If we find such a commonality, we call it a core prediction. Assuming your data is correct and your analysis thorough, a Core Prediction has the same strength as a model rejection. The common aspect, shared between all acceptable parameter etc, is something that has to be true, no matter how much more data you acquire. One such core prediction, which led to the rejection of the internalization hypothesis, was that the amount of internalized IR had to be above 80% of the total receptor pool.  We subsequently rejected this experimentally.

  • 27.
    Johansson, Rikard
    et al.
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Health Sciences.
    Combining test statistics and models in bootstrapped model rejection: it is a balancing act2014In: BMC Systems Biology, ISSN 1752-0509, E-ISSN 1752-0509, Vol. 8, no 46Article in journal (Refereed)
    Abstract [en]

    Background: Model rejections lie at the heart of systems biology, since they provide conclusive statements: that the corresponding mechanistic assumptions do not serve as valid explanations for the experimental data. Rejections are usually done usinge.g. the chi-square test (χ2) or the Durbin-Watson test (DW). Analytical formulas for the corresponding distributions rely on assumptions that typically are not fulfilled. This problem is partly alleviated by the usage of bootstrapping, a computationally heavy approach to calculate an empirical distribution. Bootstrapping also allows for a natural extension to estimation of joint distributions, but this feature has so far been little exploited.

    Results: We herein show that simplistic combinations of bootstrapped tests, like the max or min of the individual p-values, give inconsistent, i.e. overly conservative or liberal, results. A new two-dimensional (2D) approach based on parametric bootstrapping, on the other hand, is found both consistent and with a higher power than the individual tests, when tested on static and dynamic examples where the truth is known. In the same examples, the most superior test is a 2D χ2 vs χ2, where the second χ2-value comes from an additional help model, and its ability to describe bootstraps from the tested model. This superiority is lost if the help model is too simple, or too flexible. If a useful help model is found, the most powerful approach is the bootstrapped log-likelihood ratio (LHR). We show that this is because the LHR is one-dimensional, because the second dimension comes at a cost, and because LHR has retained most of the crucial information in the 2D distribution. These approaches statistically resolve a previously published rejection example for the first time.

    Conclusions: We have shown how to, and how not to, combine tests in a bootstrap setting, when the combinatio is advantageous, and when it is advantageous to include a second model. These results also provide a deeper insight into the original motivation for formulating the LHR, for the more general setting of nonlinear and non-nested models. These insights are valuable in cases when accuracy and power, rather than computational speed, are prioritized.

  • 28.
    Jufvas, Åsa
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Sjödin, Simon
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Lundqvist, Kim
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Amin, Risul
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Vener, Alexander V
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Global differences in specific histone H3 methylation are associated with overweight and type 2 diabetes.2013In: Clinical Epigenetics, E-ISSN 1868-7083, Vol. 5, no 1, article id 15Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Epidemiological evidence indicates yet unknown epigenetic mechanisms underlying a propensity for overweight and type 2 diabetes. We analyzed the extent of methylation at lysine 4 and lysine 9 of histone H3 in primary human adipocytes from 43 subjects using modification-specific antibodies.

    RESULTS: The level of lysine 9 dimethylation was stable, while adipocytes from type 2 diabetic and non-diabetic overweight subjects exhibited about 40% lower levels of lysine 4 dimethylation compared with cells from normal-weight subjects. In contrast, trimethylation at lysine 4 was 40% higher in adipocytes from overweight diabetic subjects compared with normal-weight and overweight non-diabetic subjects. There was no association between level of modification and age of subjects.

    CONCLUSIONS: The findings define genome-wide molecular modifications of histones in adipocytes that are directly associated with overweight and diabetes, and thus suggest a molecular basis for existing epidemiological evidence of epigenetic inheritance.

  • 29.
    Jufvas, Åsa
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Vener, Alexander
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Histone Variants and Their Post-Translational Modifications in Primary Human Fat Cells2011In: PLOS ONE, ISSN 1932-6203, Vol. 6, no 1Article in journal (Refereed)
    Abstract [en]

    Epigenetic changes related to human disease cannot be fully addressed by studies of cells from cultures or from other mammals. We isolated human fat cells from subcutaneous abdominal fat tissue of female subjects and extracted histones from either purified nuclei or intact cells. Direct acid extraction of whole adipocytes was more efficient, yielding about 100 mu g of protein with histone content of 60%-70% from 10 mL of fat cells. Differential proteolysis of the protein extracts by trypsin or ArgC-protease followed by nanoLC/MS/MS with alternating CID/ETD peptide sequencing identified 19 histone variants. Four variants were found at the protein level for the first time; particularly HIST2H4B was identified besides the only H4 isoform earlier known to be expressed in humans. Three of the found H2A potentially organize small nucleosomes in transcriptionally active chromatin, while two H2AFY variants inactivate X chromosome in female cells. HIST1H2BA and three of the identified H1 variants had earlier been described only as oocyte or testis specific histones. H2AFX and H2AFY revealed differential and variable N-terminal processing. Out of 78 histone modifications by acetylation/trimethylation, methylation, dimethylation, phosphorylation and ubiquitination, identified from six subjects, 68 were found for the first time. Only 23 of these modifications were detected in two or more subjects, while all the others were individual specific. The direct acid extraction of adipocytes allows for personal epigenetic analyses of human fat tissue, for profiling of histone modifications related to obesity, diabetes and metabolic syndrome, as well as for selection of individual medical treatments.

  • 30.
    Jullesson, David
    et al.
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology. Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Johansson, Rikard
    Linköping University, Department of Biomedical Engineering. Linköping University, The Institute of Technology. Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Rohini Rajan, Meenu
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Dominant negative inhibition data should be analyzed using mathematical modeling - re-interpreting data from insulin signaling.2015In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 282, no 4, p. 788-802Article in journal (Refereed)
    Abstract [en]

    As our ability to measure the complexity of intracellular networks has evolved, it has become increasingly clear that we need new methods for data analysis: methods involving mathematical modeling. Nevertheless, it is still uncontroversial to publish and interpret experimental results without a model-based proof that the reasoning is correct. In the present study, we argue that this attitude probably needs to change in the future. We illustrate this need for modeling by considering the common experimental technique of using dominant-negative constructs. More specifically, we consider published time-series and dose-response data which previously have been used to argue that the protein S6 kinase does not phosphorylate insulin receptor substrate-1 at a specific serine residue. Using a presented general approach to interpret such data, we now demonstrate that the given dominant-negative data are not conclusive (i.e. that in the absence of other proofs, S6 kinase still may be the kinase). Using simulations with uncertainty analysis and analytical solutions, we show that an alternative explanation is centered around depletion of substrate, which can be tested experimentally. This analysis thus illustrates both the necessity and the benefits of using mathematical modeling to fully understand the implications of biological data, even for a small system and relatively simple data.

  • 31.
    Karlsson, Margareta
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Thorn, Hans
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Danielsson, Anna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Karin G., Stenkula
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    In human adipocytes the insulin receptor and IRS1 are localized in caveolae, and caveolae destruction makes cells resistant to insulin signaling for metabolic and mitogenic controlManuscript (preprint) (Other academic)
    Abstract [en]

    Caveolae are plasma membrane invaginations with several functions, one of which appears to be to organize receptor mediated sigoaling. Here we show that in human adipocytes the iosulin receptor is localized in caveolae: by electron microscopy and immunogold detection and by isolating caveolae from plasma membranes. We similarly demonstrate that significant part of the immediate downstream signal mediator IRS1 is localized at the plasma membrane and caveolae. A detailed image shows the caveola as a bulb, protroding into the cell interior, with a neck attaching it to the plasma membrane. The caveolar structural protein caveolin is localized in the neck aod not in the bulb of the caveola. The receptor is active in caveolae since insulin stimulation caused tyrosine specific phosphorylation of the receptor recovered in isolated caveolae. Caveolae contain a major part of the free cholesterol in the plasma membrane and cholesterol is a stroctural component of caveolae. Depletion of cholesterol from the cells using B-cyclodextrio blocks insulin stimulation of glucose uptake, insulin inhibition of perilipin phosphorylation in response to isoproterenol, and insulio stimulation of protein kinase B and Map-kinases ERK1/2 phosphorylation- in effect making the human adipocytes insulin resistant. The insulin-stimulated phosphorylation of the insulin receptor and IRS1 are, however, not affected, indicating that caveolae integrity is required downstream of IRS1, consistent with its colocalization with the insulin receptor io caveolae in human adipocytes.

  • 32.
    Karlsson, Margareta
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Thorn, Hans
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Danielsson, Anna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Stenkula, Karin
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Öst, Anita
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik
    Linköping University, Department of Medicine and Care. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Colocalization of insulin receptor and insulin receptor substrate-1 to caveolae in primary human adipocytes2004In: European Journal of Biochemistry, ISSN 0014-2956, E-ISSN 1432-1033, Vol. 271, no 12, p. 2471-2479Article in journal (Refereed)
    Abstract [en]

    Caveolae are plasma membrane invaginations with several functions, one of which appears to be to organize receptor mediated signalling. Here we report that in primary human subcutaneous adipocytes the insulin receptor was localized to caveolae by electron microscopy/immunogold detection and by isolating caveolae from plasma membranes. Part of insulin receptor substrate 1 (IRS1), the immediate downstream signal mediator, was colocalized with the insulin receptor in the plasma membrane and caveolae, as demonstrated by immunofluorescence microscopy, immunogold electron microscopy, and immunogold electron microscopy of transfected recombinant HA-IRS1. In contrast, rat epididymal adipocytes lacked IRS1 at the plasma membrane. Depletion of cholesterol from the cells using β-cyclodextrin blocked insulin stimulation of glucose uptake, insulin inhibition of perilipin phosphorylation in response to isoproterenol, and insulin stimulation of protein kinase B and Map-kinases extracellular signal-related kinase (ERK)1/2 phosphorylation. Insulin-stimulated phosphorylation of the insulin receptor and IRS1 was not affected, indicating that caveolae integrity is required downstream of IRS1. In conclusion we show that insulin receptor and IRS1 are both caveolar proteins and that caveolae are required for both metabolic and mitogenic control in human adipocytes. Our results establish caveolae as foci of insulin action and stress the importance of examining human cells in addition to animal cells and cell lines.

  • 33.
    Karlsson, Margareta
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Thorn, Hans
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Parpal, Santiago
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Insulin induces translocation of glucose transporter GLUT4 to plasma membrane caveolae in adipocytes2002In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 16, no 2, p. 249-251Article in journal (Refereed)
    Abstract [en]

    Insulin-stimulated glucose uptake in muscle and adipose tissue is the result of translocation of insulin-regulated glucose transporters (GLUT4) from intracellular vesicles to the plasma membrane. Here we report that GLUT4 in the plasma membrane of 3T3-L1 adipocytes were located predominantly in caveolae invaginations: by immunogold electron microscopy of plasma membranes, 88% of GLUT4 were localized to caveolae structures and this distribution within the plasma membrane was not affected by insulin. By immunofluorescence microscopy, a major part of GLUT 4 was colocalized with caveolin. The total amount of GLUT4 in the plasma membrane increased 2.2-fold in response to insulin as determined by immunogold electron or immunofluorescence microscopy. GLUT4 were enriched in caveolae fractions isolated without detergents from plasma membranes of rat adipocytes. In these fractions, GLUT4 were largely confined to caveolin-containing membranes of the caveolae preparation isolated from insulin-stimulated cells, determined by electron microscopy. Insulin increased the amount of GLUT4 2.7-fold in this caveolae fraction. Caveolae were purified further by immunoisolation with antibodies against caveolin. The amount of GLUT4 increased to the same extent in the immunopurified caveolae as in the cruder caveolae fractions from insulin-stimulated cells. We conclude that insulin induces translocation of GLUT4 to caveolae.

  • 34.
    Karlsson, Margareta
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Örtegren, Unn
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Blomqvist, Maria
    Department of Clinical Neuroscience, Sahlgrenska University Hospital/Mölndal, Göteborg University, Mölndal, Sweden.
    Blazic, Natascha
    Department of Clinical Neuroscience, Sahlgrenska University Hospital/Mölndal, Göteborg University, Mölndal, Sweden.
    Nyström, Fredrik H.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Fredman, Pam
    Department of Clinical Neuroscience, Sahlgrenska University Hospital/Mölndal, Göteborg University, Mölndal, Sweden.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Lipid composition of caveolae and of surrounding plasma membrane in rat adipocytesManuscript (preprint) (Other academic)
    Abstract [en]

    Caveolae are invaginations of the plasma membrane that may arise from so called rafts in the presence of the structural protein caveolin. We have isolated caveolae from purified plasma membrane of primary rat adipocytes using ultrasonication to disrupt the membrane followed by density gradient ultracentrifugation. This caveolae fraction was further purified by adsorption to antibodies against caveolin. As a comparison we also isolated a detergent-insoluble fraction of the plasma membrane, utilizing the detergent insolubility of caveolae and rafts. Caveolae were strongly enriched in cholesterol and sphingomyelin, the concentration was 3.5 and 2.8-fold, respectively, higher in the caveolar membrane than in the surrounding plasma membrane. Phosphoacylglycerols were also concentrated in caveolae, while proteins were depleted compared to the surrounding plasma membrane. We have calculated that an average adipocyte caveola contains 18000 molecules of cholesterol, 6000 of sphingomyelin, 18000 of phosphoacylglycerol, 350 protein molecules, and about I 00 glycolipid molecules.

    We analyzed for a range of glycolipids and especially gangliosides. Of these GM3 and GD3 are the most prevalent and both were enriched in caveolae, together with GM1 and GDla. GDlb and GTib were present in the plasma membrane at low levels, while GM2, GD2, GQ1b, sulphatide, and lactosylceramide sulphate were not detected. None of them were detected in caveolae. As a first comprehensive and quantitative analysis of purified caveolae from primary cells, our results provide a firm basis for the examination of caveolae formation using artificial membranes.

  • 35.
    Klionsky, Daniel J
    et al.
    Life Sciences Institute; Department of Molecular, Cellular and Developmental Biology; Department of Biological Chemistry; University of Michigan; Ann Arbor, MI, USA .
    Abdalla, Fabio C
    Laboratory of Structural and Functional Biology; Federal University of São Carlos (UFSCar); Campus Sorocaba; São Paulo State, Brazil .
    Abeliovich, Hagai
    Department of Biochemistry and Food Science; Hebrew University; Rehovot, Israel .
    Abraham, Robert T
    Acevedo-Arozena, Abraham
    Adeli, Khosrow
    Agholme, Lotta
    Linköping University, Department of Clinical and Experimental Medicine, Geriatric. Linköping University, Faculty of Health Sciences.
    Agnello, Maria
    Agostinis, Patrizia
    Aguirre-Ghiso, Julio A
    Ahn, Hyung Jun
    Ait-Mohamed, Ouardia
    Ait-Si-Ali, Slimane
    Akematsu, Takahiko
    Akira, Shizuo
    Al-Younes, Hesham M
    Al-Zeer, Munir A
    Albert, Matthew L
    Albin, Roger L
    Alegre-Abarrategui, Javier
    Aleo, Maria Francesca
    Alirezaei, Mehrdad
    Almasan, Alexandru
    Almonte-Becerril, Maylin
    Amano, Atsuo
    Amaravadi, Ravi
    Amarnath, Shoba
    Amer, Amal O
    Andrieu-Abadie, Nathalie
    Anantharam, Vellareddy
    Ann, David K
    Anoopkumar-Dukie, Shailendra
    Aoki, Hiroshi
    Apostolova, Nadezda
    Auberger, Patrick
    Baba, Misuzu
    Backues, Steven K
    Baehrecke, Eric H
    Bahr, Ben A
    Bai, Xue-Yuan
    Bailly, Yannick
    Baiocchi, Robert
    Baldini, Giulia
    Balduini, Walter
    Ballabio, Andrea
    Bamber, Bruce A
    Bampton, Edward T W
    Bánhegyi, Gábor
    Bartholomew, Clinton R
    Bassham, Diane C
    Bast, Robert C
    Batoko, Henri
    Bay, Boon-Huat
    Beau, Isabelle
    Béchet, Daniel M
    Begley, Thomas J
    Behl, Christian
    Behrends, Christian
    Bekri, Soumeya
    Bellaire, Bryan
    Bendall, Linda J
    Benetti, Luca
    Berliocchi, Laura
    Bernardi, Henri
    Bernassola, Francesca
    Besteiro, Sébastien
    Bhatia-Kissova, Ingrid
    Bi, Xiaoning
    Biard-Piechaczyk, Martine
    Blum, Janice S
    Boise, Lawrence H
    Bonaldo, Paolo
    Boone, David L
    Bornhauser, Beat C
    Bortoluci, Karina R
    Bossis, Ioannis
    Bost, Frédéric
    Bourquin, Jean-Pierre
    Boya, Patricia
    Boyer-Guittaut, Michaël
    Bozhkov, Peter V
    Brady, Nathan R
    Brancolini, Claudio
    Brech, Andreas
    Brenman, Jay E
    Brennand, Ana
    Bresnick, Emery H
    Brest, Patrick
    Bridges, Dave
    Bristol, Molly L
    Brookes, Paul S
    Brown, Eric J
    Brumell, John H
    Brunetti-Pierri, Nicola
    Brunk, Ulf T
    Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
    Bulman, Dennis E
    Bultman, Scott J
    Bultynck, Geert
    Burbulla, Lena F
    Bursch, Wilfried
    Butchar, Jonathan P
    Buzgariu, Wanda
    Bydlowski, Sergio P
    Cadwell, Ken
    Cahová, Monika
    Cai, Dongsheng
    Cai, Jiyang
    Cai, Qian
    Calabretta, Bruno
    Calvo-Garrido, Javier
    Camougrand, Nadine
    Campanella, Michelangelo
    Campos-Salinas, Jenny
    Candi, Eleonora
    Cao, Lizhi
    Caplan, Allan B
    Carding, Simon R
    Cardoso, Sandra M
    Carew, Jennifer S
    Carlin, Cathleen R
    Carmignac, Virginie
    Carneiro, Leticia A M
    Carra, Serena
    Caruso, Rosario A
    Casari, Giorgio
    Casas, Caty
    Castino, Roberta
    Cebollero, Eduardo
    Cecconi, Francesco
    Celli, Jean
    Chaachouay, Hassan
    Chae, Han-Jung
    Chai, Chee-Yin
    Chan, David C
    Chan, Edmond Y
    Chang, Raymond Chuen-Chung
    Che, Chi-Ming
    Chen, Ching-Chow
    Chen, Guang-Chao
    Chen, Guo-Qiang
    Chen, Min
    Chen, Quan
    Chen, Steve S-L
    Chen, WenLi
    Chen, Xi
    Chen, Xiangmei
    Chen, Xiequn
    Chen, Ye-Guang
    Chen, Yingyu
    Chen, Yongqiang
    Chen, Yu-Jen
    Chen, Zhixiang
    Cheng, Alan
    Cheng, Christopher H K
    Cheng, Yan
    Cheong, Heesun
    Cheong, Jae-Ho
    Cherry, Sara
    Chess-Williams, Russ
    Cheung, Zelda H
    Chevet, Eric
    Chiang, Hui-Ling
    Chiarelli, Roberto
    Chiba, Tomoki
    Chin, Lih-Shen
    Chiou, Shih-Hwa
    Chisari, Francis V
    Cho, Chi Hin
    Cho, Dong-Hyung
    Choi, Augustine M K
    Choi, DooSeok
    Choi, Kyeong Sook
    Choi, Mary E
    Chouaib, Salem
    Choubey, Divaker
    Choubey, Vinay
    Chu, Charleen T
    Chuang, Tsung-Hsien
    Chueh, Sheau-Huei
    Chun, Taehoon
    Chwae, Yong-Joon
    Chye, Mee-Len
    Ciarcia, Roberto
    Ciriolo, Maria R
    Clague, Michael J
    Clark, Robert S B
    Clarke, Peter G H
    Clarke, Robert
    Codogno, Patrice
    Coller, Hilary A
    Colombo, María I
    Comincini, Sergio
    Condello, Maria
    Condorelli, Fabrizio
    Cookson, Mark R
    Coombs, Graham H
    Coppens, Isabelle
    Corbalan, Ramon
    Cossart, Pascale
    Costelli, Paola
    Costes, Safia
    Coto-Montes, Ana
    Couve, Eduardo
    Coxon, Fraser P
    Cregg, James M
    Crespo, José L
    Cronjé, Marianne J
    Cuervo, Ana Maria
    Cullen, Joseph J
    Czaja, Mark J
    D'Amelio, Marcello
    Darfeuille-Michaud, Arlette
    Davids, Lester M
    Davies, Faith E
    De Felici, Massimo
    de Groot, John F
    de Haan, Cornelis A M
    De Martino, Luisa
    De Milito, Angelo
    De Tata, Vincenzo
    Debnath, Jayanta
    Degterev, Alexei
    Dehay, Benjamin
    Delbridge, Lea M D
    Demarchi, Francesca
    Deng, Yi Zhen
    Dengjel, Jörn
    Dent, Paul
    Denton, Donna
    Deretic, Vojo
    Desai, Shyamal D
    Devenish, Rodney J
    Di Gioacchino, Mario
    Di Paolo, Gilbert
    Di Pietro, Chiara
    Díaz-Araya, Guillermo
    Díaz-Laviada, Inés
    Diaz-Meco, Maria T
    Diaz-Nido, Javier
    Dikic, Ivan
    Dinesh-Kumar, Savithramma P
    Ding, Wen-Xing
    Distelhorst, Clark W
    Diwan, Abhinav
    Djavaheri-Mergny, Mojgan
    Dokudovskaya, Svetlana
    Dong, Zheng
    Dorsey, Frank C
    Dosenko, Victor
    Dowling, James J
    Doxsey, Stephen
    Dreux, Marlène
    Drew, Mark E
    Duan, Qiuhong
    Duchosal, Michel A
    Duff, Karen
    Dugail, Isabelle
    Durbeej, Madeleine
    Duszenko, Michael
    Edelstein, Charles L
    Edinger, Aimee L
    Egea, Gustavo
    Eichinger, Ludwig
    Eissa, N Tony
    Ekmekcioglu, Suhendan
    El-Deiry, Wafik S
    Elazar, Zvulun
    Elgendy, Mohamed
    Ellerby, Lisa M
    Eng, Kai Er
    Engelbrecht, Anna-Mart
    Engelender, Simone
    Erenpreisa, Jekaterina
    Escalante, Ricardo
    Esclatine, Audrey
    Eskelinen, Eeva-Liisa
    Espert, Lucile
    Espina, Virginia
    Fan, Huizhou
    Fan, Jia
    Fan, Qi-Wen
    Fan, Zhen
    Fang, Shengyun
    Fang, Yongqi
    Fanto, Manolis
    Fanzani, Alessandro
    Farkas, Thomas
    Farré, Jean-Claude
    Faure, Mathias
    Fechheimer, Marcus
    Feng, Carl G
    Feng, Jian
    Feng, Qili
    Feng, Youji
    Fésüs, László
    Feuer, Ralph
    Figueiredo-Pereira, Maria E
    Fimia, Gian Maria
    Fingar, Diane C
    Finkbeiner, Steven
    Finkel, Toren
    Finley, Kim D
    Fiorito, Filomena
    Fisher, Edward A
    Fisher, Paul B
    Flajolet, Marc
    Florez-McClure, Maria L
    Florio, Salvatore
    Fon, Edward A
    Fornai, Francesco
    Fortunato, Franco
    Fotedar, Rati
    Fowler, Daniel H
    Fox, Howard S
    Franco, Rodrigo
    Frankel, Lisa B
    Fransen, Marc
    Fuentes, José M
    Fueyo, Juan
    Fujii, Jun
    Fujisaki, Kozo
    Fujita, Eriko
    Fukuda, Mitsunori
    Furukawa, Ruth H
    Gaestel, Matthias
    Gailly, Philippe
    Gajewska, Malgorzata
    Galliot, Brigitte
    Galy, Vincent
    Ganesh, Subramaniam
    Ganetzky, Barry
    Ganley, Ian G
    Gao, Fen-Biao
    Gao, George F
    Gao, Jinming
    Garcia, Lorena
    Garcia-Manero, Guillermo
    Garcia-Marcos, Mikel
    Garmyn, Marjan
    Gartel, Andrei L
    Gatti, Evelina
    Gautel, Mathias
    Gawriluk, Thomas R
    Gegg, Matthew E
    Geng, Jiefei
    Germain, Marc
    Gestwicki, Jason E
    Gewirtz, David A
    Ghavami, Saeid
    Ghosh, Pradipta
    Giammarioli, Anna M
    Giatromanolaki, Alexandra N
    Gibson, Spencer B
    Gilkerson, Robert W
    Ginger, Michael L
    Goncu, Ebru
    Gongora, Céline
    Gonzalez, Claudio D
    Gonzalez, Ramon
    González-Estévez, Cristina
    González-Polo, Rosa Ana
    Gonzalez-Rey, Elena
    Gorbunov, Nikolai V
    Gorski, Sharon
    Goruppi, Sandro
    Gottlieb, Roberta A
    Gozuacik, Devrim
    Granato, Giovanna Elvira
    Grant, Gary D
    Green, Kim N
    Gregorc, Aleš
    Gros, Frédéric
    Grose, Charles
    Grunt, Thomas W
    Gual, Philippe
    Guan, Jun-Lin
    Guan, Kun-Liang
    Guichard, Sylvie M
    Gukovskaya, Anna S
    Gukovsky, Ilya
    Gunst, Jan
    Gustafsson, Asa B
    Halayko, Andrew J
    Hale, Amber N
    Halonen, Sandra K
    Hamasaki, Maho
    Han, Feng
    Han, Ting
    Hancock, Michael K
    Hansen, Malene
    Harada, Hisashi
    Harada, Masaru
    Hardt, Stefan E
    Harper, J Wade
    Harris, Adrian L
    Harris, James
    Harris, Steven D
    Hébert, Marie-Joseé
    Heidenreich, Kim A
    Helfrich, Miep H
    Helgason, Gudmundur V
    Henske, Elizabeth P
    Herman, Brian
    Herman, Paul K
    Hetz, Claudio
    Hilfiker, Sabine
    Hill, Joseph A
    Hocking, Lynne J
    Hofman, Paul
    Hofmann, Thomas G
    Höhfeld, Jörg
    Holyoake, Tessa L
    Hong, Ming-Huang
    Hood, David A
    Hotamisligil, Gökhan S
    Houwerzijl, Ewout J
    Høyer-Hansen, Maria
    Hu, Bingren
    Hu, Chien-An A
    Hu, Hong-Ming
    Hua, Ya
    Huang, Canhua
    Huang, Ju
    Huang, Shengbing
    Huang, Wei-Pang
    Huber, Tobias B
    Huh, Won-Ki
    Hung, Tai-Ho
    Hupp, Ted R
    Hur, Gang Min
    Hurley, James B
    Hussain, Sabah N A
    Hussey, Patrick J
    Hwang, Jung Jin
    Hwang, Seungmin
    Ichihara, Atsuhiro
    Ilkhanizadeh, Shirin
    Inoki, Ken
    Into, Takeshi
    Iovane, Valentina
    Iovanna, Juan L
    Ip, Nancy Y
    Isaka, Yoshitaka
    Ishida, Hiroyuki
    Isidoro, Ciro
    Isobe, Ken-ichi
    Iwasaki, Akiko
    Izquierdo, Marta
    Izumi, Yotaro
    Jaakkola, Panu M
    Jäättelä, Marja
    Jackson, George R
    Jackson, William T
    Janji, Bassam
    Jendrach, Marina
    Jeon, Ju-Hong
    Jeung, Eui-Bae
    Jiang, Hong
    Jiang, Hongchi
    Jiang, Jean X
    Jiang, Ming
    Jiang, Qing
    Jiang, Xuejun
    Jiang, Xuejun
    Jiménez, Alberto
    Jin, Meiyan
    Jin, Shengkan
    Joe, Cheol O
    Johansen, Terje
    Johnson, Daniel E
    Johnson, Gail V W
    Jones, Nicola L
    Joseph, Bertrand
    Joseph, Suresh K
    Joubert, Annie M
    Juhász, Gábor
    Juillerat-Jeanneret, Lucienne
    Jung, Chang Hwa
    Jung, Yong-Keun
    Kaarniranta, Kai
    Kaasik, Allen
    Kabuta, Tomohiro
    Kadowaki, Motoni
    Kågedal, Katarina
    Linköping University, Department of Clinical and Experimental Medicine, Experimental Pathology. Linköping University, Faculty of Health Sciences.
    Kamada, Yoshiaki
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    Kumar, Raj
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    Kurz, Tino
    Linköping University, Department of Medical and Health Sciences, Pharmacology. Linköping University, Faculty of Health Sciences.
    Kwon, Ho Jeong
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    Mograbi, Baharia
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    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
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    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
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    Guidelines for the use and interpretation of assays for monitoring autophagy2012In: Autophagy, ISSN 1554-8627, Vol. 8, no 4, p. 445-544Article, review/survey (Refereed)
    Abstract [en]

    In 2008 we published the first set of guidelines for standardizing research in autophagy. Since then, research on this topic has continued to accelerate, and many new scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Accordingly, it is important to update these guidelines for monitoring autophagy in different organisms. Various reviews have described the range of assays that have been used for this purpose. Nevertheless, there continues to be confusion regarding acceptable methods to measure autophagy, especially in multicellular eukaryotes. A key point that needs to be emphasized is that there is a difference between measurements that monitor the numbers or volume of autophagic elements (e.g., autophagosomes or autolysosomes) at any stage of the autophagic process vs. those that measure flux through the autophagy pathway (i.e., the complete process); thus, a block in macroautophagy that results in autophagosome accumulation needs to be differentiated from stimuli that result in increased autophagic activity, defined as increased autophagy induction coupled with increased delivery to, and degradation within, lysosomes (in most higher eukaryotes and some protists such as Dictyostelium) or the vacuole (in plants and fungi). In other words, it is especially important that investigators new to the field understand that the appearance of more autophagosomes does not necessarily equate with more autophagy. In fact, in many cases, autophagosomes accumulate because of a block in trafficking to lysosomes without a concomitant change in autophagosome biogenesis, whereas an increase in autolysosomes may reflect a reduction in degradative activity. Here, we present a set of guidelines for the selection and interpretation of methods for use by investigators who aim to examine macroautophagy and related processes, as well as for reviewers who need to provide realistic and reasonable critiques of papers that are focused on these processes. These guidelines are not meant to be a formulaic set of rules, because the appropriate assays depend in part on the question being asked and the system being used. In addition, we emphasize that no individual assay is guaranteed to be the most appropriate one in every situation, and we strongly recommend the use of multiple assays to monitor autophagy. In these guidelines, we consider these various methods of assessing autophagy and what information can, or cannot, be obtained from them. Finally, by discussing the merits and limits of particular autophagy assays, we hope to encourage technical innovation in the field.

  • 36. Lindberg, Jan
    et al.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Cell biology.
    Konradsson, Peter
    Synthesis of inositol phosphoglycans containing thiol-terminated spacers for efficient coupling to maleimide functionalized solid phases or proteins2002In: Tetrahedron, ISSN 0040-4020, E-ISSN 1464-5416, Vol. 58, no 21, p. 4245-4254Article in journal (Refereed)
    Abstract [en]

    The synthesis of inositol phosphoglycans (IPGs), analogous to second messengers of insulin, to provide a small targeted library of compounds is described. These derivatives contain the glucosamine(a1-6)myo-inositol 1,2-cyclic phosphate motif. A thiol-terminated spacer was introduced, for their immobilization, by a radical elongation of an allyl ether with benzyl mercaptane. ⌐ 2002 Elsevier Science Ltd. All rights reserved.

  • 37.
    Lystedt, Erika
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care.
    Westergren, Hanna
    Brynhildsen, Jan
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Obstetrics and gynecology. Östergötlands Läns Landsting, Centre of Paediatrics and Gynecology and Obstetrics, Department of Gynecology and Obstetrics in Linköping.
    Lindh-Åstrand, Lotta
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Obstetrics and gynecology. Östergötlands Läns Landsting, Centre of Paediatrics and Gynecology and Obstetrics, Department of Gynecology and Obstetrics in Linköping.
    Gustavsson, Johanna
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
    Nyström, Fredrik
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Internal Medicine. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
    Hammar, Mats
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Molecular and Clinical Medicine, Obstetrics and gynecology. Östergötlands Läns Landsting, Centre of Paediatrics and Gynecology and Obstetrics, Department of Gynecology and Obstetrics in Linköping.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedicine and Surgery, Division of cell biology.
    Subcutaneous adipocytes from obese hyperinsulinemic women with polycystic ovary syndrome exhibit normal insulin sensitivity but reduced maximal insulin responsiveness2005In: European Journal of Endocrinology, ISSN 0804-4643, E-ISSN 1479-683X, Vol. 153, no 6, p. 831-835Article in journal (Refereed)
    Abstract [en]

    Background: Polycystic ovary syndrome (PCOS) has a high prevalence in women and is often associated with insulin resistance and hence with aspects of the so-called metabolic syndrome. Methods: Ten women diagnosed with PCOS were consecutively included (aged 21-39 years, average 30.2±1.9 years, body mass index 28.4-42.5 kg/m2, average 37.5±1.7 kg/m2 (mean±S.E.)). Adipocytes were isolated from the subcutaneous fat and, after overnight incubation to recover from insulin resistance due to the surgical cell isolation procedures, they were analyzed for insulin sensitivity. Results: The patients with PCOS exhibited marked clinical hyperinsulinemia with 3.6-fold higher blood levels of C-peptide than a healthy lean control group (1.7±0.2 and 0.5±0.02 nmol/l respectively, P < 0.0001). The patients with PCOS also exhibited 2.4-fold higher concentrations of serum triacylglycerol (2.1±0.3 and 0.9±0.06 mmol/l respectively, P < 0.0001), but only slightly elevated blood pressure (118±12/76±6 and 113±7/72±6 mmHg respectively, P = 0.055/0.046). However, insulin sensitivity for stimulation of glucose transport in the isolated adipocytes was indistinguishable from a non-PCOS, non-diabetic control group, while the maximal insulin effect on glucose uptake was significantly lower (2.2±0.2- and 3.8±0.8-fold respectively, P = 0.02). Conclusions: Subcutaneous adipocytes from patients with PCOS do not display reduced insulin sensitivity. The findings show that the insulin resistance of PCOS is qualitatively different from that of type 2 diabetes. © 2005 Society of the European Journal of Endocrinology.

  • 38.
    Nyman, Elin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Palmér, Robert
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Brugård, Jan
    MathCore Engn.
    Nyström, Fredrik
    Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Centre, Department of Endocrinology and Gastroenterology UHL.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    A Hierarchical Whole-body Modeling Approach Elucidates the Link between in Vitro Insulin Signaling and in Vivo Glucose Homeostasis2011In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 29, p. 26028-26041Article in journal (Refereed)
    Abstract [en]

    Type 2 diabetes is a metabolic disease that profoundly affects energy homeostasis. The disease involves failure at several levels and subsystems and is characterized by insulin resistance in target cells and tissues (i.e. by impaired intracellular insulin signaling). We have previously used an iterative experimental-theoretical approach to unravel the early insulin signaling events in primary human adipocytes. That study, like most insulin signaling studies, is based on in vitro experimental examination of cells, and the in vivo relevance of such studies for human beings has not been systematically examined. Herein, we develop a hierarchical model of the adipose tissue, which links intracellular insulin control of glucose transport in human primary adipocytes with whole-body glucose homeostasis. An iterative approach between experiments and minimal modeling allowed us to conclude that it is not possible to scale up the experimentally determined glucose uptake by the isolated adipocytes to match the glucose uptake profile of the adipose tissue in vivo. However, a model that additionally includes insulin effects on blood flow in the adipose tissue and GLUT4 translocation due to cell handling can explain all data, but neither of these additions is sufficient independently. We also extend the minimal model to include hierarchical dynamic links to more detailed models (both to our own models and to those by others), which act as submodules that can be turned on or off. The resulting multilevel hierarchical model can merge detailed results on different subsystems into a coherent understanding of whole-body glucose homeostasis. This hierarchical modeling can potentially create bridges between other experimental model systems and the in vivo human situation and offers a framework for systematic evaluation of the physiological relevance of in vitro obtained molecular/cellular experimental data.

  • 39.
    Nyman, Elin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Insulin signaling - mathematical modeling comes of age2012In: Trends in endocrinology and metabolism, ISSN 1043-2760, E-ISSN 1879-3061, Vol. 23, no 3, p. 107-115Article, review/survey (Refereed)
    Abstract [en]

    Signaling pathways that only a few years ago appeared simple and understandable, albeit far from complete, have evolved into very complex multi-layered networks of cellular control mechanisms, which in turn are integrated in a similarly complex whole-body level of control mechanisms. This complexity sets limits for classical biochemical reasoning, such that a correct and complete analysis of experimental data while taking the full complexity into account is not possible. In this Opinion we propose that mathematical modeling can be used as a tool in insulin signaling research, and we demonstrate how recent developments in modeling - and the integration of modeling in the experimental process - provide new possibilities to approach and decipher complex biological systems more efficiently.

  • 40.
    Nyman, Elin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Jullesson, David
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Mechanistic explanations for counter-intuitive phosphorylation dynamics of the insulin receptor and insulin receptor substrate-1 in response to insulin in murine adipocytes2012In: The FEBS Journal, ISSN 1742-464X, E-ISSN 1742-4658, Vol. 279, no 6, p. 987-999Article in journal (Refereed)
    Abstract [en]

    Insulin signaling through insulin receptor (IR) and insulin receptor substrate-1 (IRS1) is important for insulin control of target cells. We have previously demonstrated a rapid and simultaneous overshoot behavior in the phosphorylation dynamics of IR and IRS1 in human adipocytes. Herein, we demonstrate that in murine adipocytes a similar overshoot behavior is not simultaneous for IR and IRS1. The peak of IRS1 phosphorylation, which is a direct consequence of the phosphorylation and the activation of IR, occurs earlier than the peak of IR phosphorylation. We used a conclusive modeling framework to unravel the mechanisms behind this counter-intuitive order of phosphorylation. Through a number of rejections, we demonstrate that two fundamentally different mechanisms may create the reversed order of peaks: (i) two pools of phosphorylated IR, where a large pool of internalized IR peaks late, but phosphorylation of IRS1 is governed by a small plasma membrane-localized pool of IR with an early peak, or (ii) inhibition of the IR-catalyzed phosphorylation of IRS1 by negative feedback. Although (i) may explain the reversed order, this two-pool hypothesis alone requires extensive internalization of IR, which is not supported by experimental data. However, with the additional assumption of limiting concentrations of IRS1, (i) can explain all data. Also, (ii) can explain all available data. Our findings illustrate how modeling can potentiate reasoning, to help draw nontrivial conclusions regarding competing mechanisms in signaling networks. Our work also reveals new differences between human and murine insulin signaling.

  • 41.
    Nyman, Elin
    et al.
    Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Health Sciences.
    Rohini Rajan, Meenu
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences. Linköping University, Department of Biomedical Engineering.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    A Single Mechanism Can Explain Network-wide Insulin Resistance in Adipocytes from Obese Patients with Type 2 Diabetes2014In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 289, no 48, p. 33215-33230Article in journal (Refereed)
    Abstract [en]

    The response to insulin is impaired in type 2 diabetes. Much information is available about insulin signaling, but understanding of the cellular mechanisms causing impaired signaling and insulin resistance is hampered by fragmented data, mainly obtained from different cell lines and animals. We have collected quantitative and systems-wide dynamic data on insulin signaling in primary adipocytes and compared cells isolated from healthy and diabetic individuals. Mathematical modeling and experimental verification identified mechanisms of insulin control of the MAPKs ERK1/2. We found that in human adipocytes, insulin stimulates phosphorylation of the ribosomal protein S6 and hence protein synthesis about equally via ERK1/2 and mTORC1. Using mathematical modeling, we examined the signaling network as a whole and show that a single mechanism can explain the insulin resistance of type 2 diabetes throughout the network, involving signaling both through IRS1, PKB, and mTOR and via ERK1/2 to the nuclear transcription factor Elk1. The most important part of the insulin resistance mechanism is an attenuated feedback from the protein kinase mTORC1 to IRS1, which spreads signal attenuation to all parts of the insulin signaling network. Experimental inhibition of mTORC1 using rapamycin in adipocytes from non-diabetic individuals induced and thus confirmed the predicted network-wide insulin resistance.

  • 42.
    Nyman, Elin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Rohini Rajan, Meenu
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Brännmark, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Health Sciences.
    The insulin-signaling network in human adipocytes, normally and in diabetes: role of signaling through ERK1/22014Manuscript (preprint) (Other academic)
    Abstract [en]

    Insulin acutely controls metabolism in adipocytes, but also nuclear transcription through the “mitogenic” signaling pathway mediated by Map-kinases ERK1/2 (ERK). The cellular metabolic response to insulin is attenuated in insulin resistance and type 2 diabetes, but whether this involves also signaling through ERK is unclear. Based on experimental data from primary mature human adipocytes from diabetic and nondiabetic individuals, we demonstrate a network-wide, model-based analysis of insulin signaling through ERK to phosphorylation of transcription factor Elk1 integrated with signaling for “metabolic” control. We use minimal modeling to analyze the idiosyncratic phosphorylation dynamics of ERK, i.e. a slow phosphorylation response that returns to basal in response to insulin, and conclude that sequestration of ERK is the simplest explanation to data. We also demonstrate a significant cross-talk between ERK and mTORC1 signaling to ribosomal protein S6 for control of protein synthesis. A reduced sensitivity and reduced maximal phosphorylation of ERK in response to insulin in the diabetic state can be explained by the same mechanisms that generate insulin resistance in the control of metabolism.

  • 43.
    Nyman, Elin
    et al.
    Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, Faculty of Science & Engineering. CVMD iMed DMPK AstraZeneca R&D, Gothenburg, Sweden.
    Rozendaal, Yvonne J W
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Helmlinger, Gabriel
    AstraZeneca, Pharmaceuticals LP, Waltham, MA, USA.
    Hamrén, Bengt
    AstraZeneca, Gothenburg, Sweden.
    Kjellsson, Maria C
    Uppsala University, Uppsala, Sweden.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    van Riel, Natal A W
    Eindhoven University of Technology, Eindhoven, The Netherlands.
    Gennemark, Peter
    AstraZeneca R&D, Gothenburg, Sweden.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology.
    Requirements for multi-level systems pharmacology models to reach end-usage: the case of type 2 diabetes2016In: Interface Focus, ISSN 2042-8898, E-ISSN 2042-8901, Vol. 6, no 2, p. 1-14Article, review/survey (Refereed)
    Abstract [en]

    We are currently in the middle of a major shift in biomedical research: unprecedented and rapidly growing amounts of data may be obtained today, from in vitro, in vivo and clinical studies, at molecular, physiological and clinical levels. To make use of these large-scale, multi-level datasets, corresponding multi-level mathematical models are needed, i.e. models that simultaneously capture multiple layers of the biological, physiological and disease-level organization (also referred to as quantitative systems pharmacology-QSP-models). However, today's multi-level models are not yet embedded in end-usage applications, neither in drug research and development nor in the clinic. Given the expectations and claims made historically, this seemingly slow adoption may seem surprising. Therefore, we herein consider a specific example-type 2 diabetes-and critically review the current status and identify key remaining steps for these models to become mainstream in the future. This overview reveals how, today, we may use models to ask scientific questions concerning, e.g., the cellular origin of insulin resistance, and how this translates to the whole-body level and short-term meal responses. However, before these multi-level models can become truly useful, they need to be linked with the capabilities of other important existing models, in order to make them 'personalized' (e.g. specific to certain patient phenotypes) and capable of describing long-term disease progression. To be useful in drug development, it is also critical that the developed models and their underlying data and assumptions are easily accessible. For clinical end-usage, in addition, model links to decision-support systems combined with the engagement of other disciplines are needed to create user-friendly and cost-efficient software packages.

  • 44.
    Nyman, Elin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Cedersund, Gunnar
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Multilevel-Modeling, Core Predictions, and the Concept of Final Conclusions2012In: Biosimulation in Biomedical Research, Health Care and Drug Development / [ed] Mosekilde, Erik; Sosnovtseva, Olga; Rostami-Hodjegan, Amin, Wien: Springer, 2012, p. 311-328Chapter in book (Other academic)
  • 45. Nystrom, FH
    et al.
    Strålfors, Peter
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Stenkula, Karin
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Transfection of human fatcells by electroporation2002In: Diabetologia, ISSN 0012-186X, E-ISSN 1432-0428, Vol. 45, p. 592-Conference paper (Other academic)
  • 46.
    Parpal, Santiago
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Karlsson, Margareta
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Gustavsson, Johanna
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Ramsing, Cecilia
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Reduced content of cholesterol in caveolae of adipocytes from insulin resistant, obese, and diabetic Zucker fa/fa ratsManuscript (preprint) (Other academic)
    Abstract [en]

    The Zucker fa/fa rat has a mutation in the leptin receptor and therefore over-eats and becomes grossly obese. The animal develops insulin resistance and tumor necrosis factor a (TNFa) has been implicated in the pathogenesis of the insulin resistance that thls animal model of type 2 diabetes exhibits. We have shown that the insulin receptor is located in caveolae of the plasma membrane and that reduction of caveolar cholesterol content makes adipocytes insulin resistant (Parpal et a., J. Biol. Chem. 276 (2001)9670-9678). Here we show that adipocytes from the Zucker fa/fa rat are insulin resistant and that this can be explained by a 50 % lower content of cholesterol in the caveolae compared to lean rats. Moreover, TNFa treatment reduces the caveolar content of cholesterol in normal rat adipocytes. An enhanced production of TNFa may thus reduce caveolar cholesterol levels and make the Zucker fa/fa rat insulin resistant.

  • 47.
    Parpal, Santiago
    et al.
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Karlsson, Margareta
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Thorn, Hans
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Cholesterol Depletion Disrupts Caveolae and Insulin Receptor Signaling for Metabolic Control via Insulin Receptor Substrate-1, but Not for Mitogen-activated Protein Kinase Control2001In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 276, no 13, p. 9670-9678Article in journal (Refereed)
    Abstract [en]

    Insulin exerts its cellular control through receptor binding in caveolae in plasmalemma of target cells (Gustavsson, J., Parpal, S., Karlsson, M., Ramsing, C., Thorn, H., Borg, M., Lindroth, M., Peterson, K. H., Magnusson, K.-E., and Strålfors, P. (1999) FASEB. J. 13, 1961–1971). We now report that a progressive cholesterol depletion of 3T3-L1 adipocytes with β-cyclodextrin gradually destroyed caveolae structures and concomitantly attenuated insulin stimulation of glucose transport, in effect making cells insulin-resistant. Insulin access to or affinity for the insulin receptor on rat adipocytes was not affected as determined by 125I-insulin binding. By immunoblotting of plasma membranes, total amount of insulin receptor and of caveolin remained unchanged. Receptor autophosphorylation in response to insulin was not affected by cholesterol depletion. Insulin treatment of isolated caveolae preparations increased autophosphorylation of receptor before and following cholesterol depletion. Insulin-increased tyrosine phosphorylation of an immediate downstream signal transducer, insulin receptor substrate-1, and activation of the further downstream protein kinase B were inhibited. In contrast, insulin signaling to mitogenic control as determined by control of the extracellular signal-related kinases 1/2, mitogen-activated protein kinase pathway was not affected. Insulin did not control Shc phosphorylation, and Shc did not control extracellular signal-related kinases 1/2, whereas cholesterol depletion constitutively phosphorylated Shc. In conclusion, caveolae are critical for propagating the insulin receptor signal to downstream targets and have the potential for sorting signal transduction for metabolic and mitogenic effects.

  • 48.
    Rajan, Meenu Rohini
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Nyman, Elin
    Linköping University, Department of Biomedical Engineering, Medical Informatics. Linköping University, Faculty of Science & Engineering. Cardiovascular and Metabolic Diseases, Innovative Medicines, and Drug Metabolism and Pharmacokinetics, AstraZeneca Research and Development, Gothenburg, Sweden .
    Kjölhede, Preben
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center of Paediatrics and Gynaecology and Obstetrics, Department of Gynaecology and Obstetrics in Linköping.
    Cedersund, Gunnar
    Linköping University, Department of Biomedical Engineering. Linköping University, Faculty of Science & Engineering. Linköping University, Faculty of Medicine and Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Systems-wide Experimental and Modeling Analysis of Insulin Signaling through Forkhead Box Protein O1 (FOXO1) in Human Adipocytes, Normally and in Type 2 Diabetes2016In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 291, no 30, p. 15806-15819Article in journal (Refereed)
    Abstract [en]

    Insulin resistance is a major aspect of type 2 diabetes (T2D), which results from impaired insulin signaling in target cells. Signaling to regulate forkhead box protein O1 (FOXO1) may be the most important mechanism for insulin to control transcription. Despite this, little is known about how insulin regulates FOXO1 and how FOXO1 may contribute to insulin resistance in adipocytes, which are the most critical cell type in the development of insulin resistance. We report a detailed mechanistic analysis of insulin control of FOXO1 in human adipocytes obtained from non-diabetic subjects and from patients with T2D. We show that FOXO1 is mainly phosphorylated through mTORC2-mediated phosphorylation of protein kinase B at Ser(473) and that this mechanism is unperturbed in T2D. We also demonstrate a cross-talk from the MAPK branch of insulin signaling to stimulate phosphorylation of FOXO1. The cellular abundance and consequently activity of FOXO1 are halved in T2D. Interestingly, inhibition of mTORC1 with rapamycin reduces the abundance of FOXO1 to the levels in T2D. This suggests that the reduction of the concentration of FOXO1 is a consequence of attenuation of mTORC1, which defines much of the diabetic state in human adipocytes. We integrate insulin control of FOXO1 in a network-wide mathematical model of insulin signaling dynamics based on compatible data from human adipocytes. The diabetic state is network-wide explained by attenuation of an mTORC1-to-insulin receptor substrate-1 (IRS1) feedback and reduced abundances of insulin receptor, GLUT4, AS160, ribosomal protein S6, and FOXO1. The model demonstrates that attenuation of the mTORC1-to-IRS1 feedback is a major mechanism of insulin resistance in the diabetic state.

  • 49.
    Rohini Rajan, Meenu
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Fagerholm, Siri
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Jonsson, Cecilia
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
    Kjölhede, Preben
    Linköping University, Department of Clinical and Experimental Medicine, Obstetrics and gynecology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre of Paediatrics and Gynecology and Obstetrics, Department of Gynecology and Obstetrics in Linköping.
    Turkina, Maria
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Phosphorylation of IRS1 at Serine 307 in Response to Insulin in Human Adipocytes Is Not Likely to be Catalyzed by p70 Ribosomal S6 Kinase2013In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 8, no 4Article in journal (Refereed)
    Abstract [en]

    The insulin receptor substrate-1 (IRS1) is phosphorylated on serine 307 (human sequence, corresponding to murine serine 302) in response to insulin as part of a feedback loop that controls IRS1 phosphorylation on tyrosine residues by the insulin receptor. This in turn directly affects downstream signaling and is in human adipocytes implicated in the pathogenesis of insulin resistance and type 2 diabetes. The phosphorylation is inhibited by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR) in complex with raptor (mTORC1). The mTORC1-downstream p70 ribosomal protein S6 kinase (S6K1), which is activated by insulin, can phosphorylate IRS1 at serine 307 in vitro and is considered the physiological protein kinase. Because the IRS1 serine 307-kinase catalyzes a critical step in the control of insulin signaling and constitutes a potential target for treatment of insulin resistance, it is important to know whether S6K1 is the physiological serine 307-kinase or not. We report that, by several criteria, S6K1 does not phosphorylate IRS1 at serine 307 in response to insulin in intact human primary adipocytes: (i) The time-courses for phosphorylation of S6K1 and its phosphorylation of S6 are not compatible with the phosphorylation of IRS1 at serine 307; (ii) A dominant-negative construct of S6K1 inhibits the phosphorylation of S6, without effect on the phosphorylation of IRS1 at serine 307; (iii) The specific inhibitor of S6K1 PF-4708671 inhibits the phosphorylation of S6, without effect on phosphorylation of IRS1 at serine 307. mTOR-immunoprecipitates from insulin-stimulated adipocytes contains an unidentified protein kinase specific for phosphorylation of IRS1 at serine 307, but it is not mTOR or S6K1.

  • 50.
    Sauma, Lilian
    et al.
    Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Medicine, Department of Endocrinology and Gastroenterology UHL.
    Franck, Niclas
    Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences.
    Paulsson, Johan F
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Westermark, Gunilla T.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Kjølhede, Preben
    Linköping University, Department of Molecular and Clinical Medicine. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Söderström, Mats
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Nyström, Fredrik H.
    Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences.
    Peroxisome proliferator activated receptor gamma activity is low in mature primary human visceral adipocytes2007In: Diabetologia, ISSN 0012-186X, E-ISSN 1432-0428, Vol. 50, no 1, p. 195-201Article in journal (Refereed)
    Abstract [en]

    AIMS/HYPOTHESIS: The amount of visceral fat mass strongly relates to insulin resistance in humans. The transcription factor peroxisome proliferator activated receptor gamma (PPARG) is abundant in adipocytes and regulates genes of importance for insulin sensitivity. Our objective was to study PPARG activity in human visceral and subcutaneous adipocytes and to compare this with the most common model for human disease, the mouse.

    MATERIALS AND METHODS: We transfected primary human adipocytes with a plasmid encoding firefly luciferase controlled by PPARG response element (PPRE) from the acyl-CoA-oxidase gene and measured PPRE activity by emission of light. RESULTS: We found that PPRE activity was 6.6-fold higher (median) in adipocytes from subcutaneous than from omental fat from the same subjects (n = 23). The activity was also 6.2-fold higher in subcutaneous than in intra-abdominal fat cells when we used a PPARG ligand-binding domain-GAL4 fusion protein as reporter, demonstrating that the difference in PPRE activity was due to different levels of activity of the PPARG receptor in the two fat depots. Stimulation with 5 micromol/l rosiglitazone did not induce a PPRE activity in visceral adipocytes that was as high as basal levels in subcutaneous adipocytes. Interestingly, in mice of two different strains the PPRE activity was similar in visceral and subcutaneous fat cells.

    CONCLUSIONS/INTERPRETATION: We found considerably lower PPARG activity in visceral than in subcutaneous primary human adipocytes. Further studies of the molecular mechanisms behind this difference could lead to development of drugs that target the adverse effects of visceral obesity.

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