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  • 1.
    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.

  • 2.
    Karlsson, Margareta
    Linköping University, Department of Biomedicine and Surgery, Cell biology. Linköping University, Faculty of Health Sciences.
    Caveolae in insulin signalling in human and rat adipocytes2003Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The pancreatic hormone insulin is a key hormone in maintenance of metabolic homeostasis but it also exerts control on gene expression and cell growth. This thesis presents results on fhe role of caveolae in insulin signalling in human and rat adipocytes. Caveolae are invaginations of the plasma membrane, characterised by the structural protein caveolin. Caveolae and caveolin have been implicated in a variety of functions, like uptake of molecular cargo into the cell, cholesterol transport and signal transduction. After isolation of caveolae and using electron microscopy on cell membranes, the insulin receptor was demonstrated to be localised in caveolae of human adipocytes. We also used biochemical and morphological methods to show that the glucose transporter GLUT4 was translocated to caveolae in response to insulin in rat adipocytes, indicating fhat the caveola is the locale for glucose uptake in adipocytes.

    Adipocytes fhat were depleted of cholesterol using ß-cyclodextrin lacked caveolae invaginations. In cells fhus depleted of cholesterol and caveolae, fhe insulin receptor itself was not affected, but insulin signalling to metabolic control was inhibited. In rat adipocytes, insulin signalling to mitogenic control was not affected. In human fat cells, however, insulin's mitogenic signalling was dependent on caveolae/cholesterol. In contrast to other cells studied, including rat adipocytes, where the insulin receptor substrate (IRS-1) is mainly cytosolic, in human adipocytes IRS-1 was found in the plasma membrane and in caveolae. These results show the importance of choosing the relevant system to work with, since there are clear species differences.

    We performed an analysis of the lipid composition of purified caveolae from rat adipocytes. As expected, cholesterol constitutes a major part of caveolae, but there is also an enrichment of sphingomyelin and the gangliosides GM1, GM3, GD3 and GD1a, while there is less protein, compared to the surrounding plasma membrane.

    Taken together, caveolae appear as hnbs for insulin signalling. Caveolae seem necessary for fhe maintenance of metabolic signalling, like glucose uptake, and defects in caveolae may thus be the cause of insulin resistance.

    List of papers
    1. Cholesterol Depletion Disrupts Caveolae and Insulin Receptor Signaling for Metabolic Control via Insulin Receptor Substrate-1, but Not for Mitogen-activated Protein Kinase Control
    Open this publication in new window or tab >>Cholesterol Depletion Disrupts Caveolae and Insulin Receptor Signaling for Metabolic Control via Insulin Receptor Substrate-1, but Not for Mitogen-activated Protein Kinase Control
    2001 (English)In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 276, no 13, p. 9670-9678Article in journal (Refereed) Published
    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.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-47429 (URN)10.1074/jbc.M007454200 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13Bibliographically approved
    2. Insulin induces translocation of glucose transporter GLUT4 to plasma membrane caveolae in adipocytes
    Open this publication in new window or tab >>Insulin induces translocation of glucose transporter GLUT4 to plasma membrane caveolae in adipocytes
    Show others...
    2002 (English)In: The FASEB Journal, ISSN 0892-6638, E-ISSN 1530-6860, Vol. 16, no 2, p. 249-251Article in journal (Refereed) Published
    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.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-25037 (URN)10.1096/fj.01-0646fje (DOI)9461 (Local ID)9461 (Archive number)9461 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13Bibliographically approved
    3. 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 control
    Open this publication in new window or tab >>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 control
    Show others...
    (English)Manuscript (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.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-84462 (URN)
    Available from: 2012-10-09 Created: 2012-10-09 Last updated: 2013-09-10Bibliographically approved
    4. Lipid composition of caveolae and of surrounding plasma membrane in rat adipocytes
    Open this publication in new window or tab >>Lipid composition of caveolae and of surrounding plasma membrane in rat adipocytes
    Show others...
    (English)Manuscript (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.

    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-84464 (URN)
    Available from: 2012-10-09 Created: 2012-10-09 Last updated: 2013-09-10Bibliographically approved
  • 3.
    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.

  • 4.
    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.

  • 5.
    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.

  • 6.
    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.

  • 7.
    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.

  • 8.
    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.

  • 9.
    Stenkula, Karin G.
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Said Suma, Lilian
    Linköping University, Department of Medical and Health Sciences, Internal Medicine. Linköping University, Faculty of Health Sciences.
    Karlsson, Margareta
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cell Biology.
    Thorn, Hans
    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. Östergötlands Läns Landsting, Center of Paediatrics and Gynaecology and Obstetrics, Department of Gynaecology and Obstetrics in Linköping.
    Gustavsson, Johanna
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
    Söderström, Mats
    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.
    Nyström, Fredrik H
    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.
    Expression of a mutant IRS inhibits metabolic and mitogenic signalling of insulin in human adipocytes2004In: Molecular and Cellular Endocrinology, ISSN 0303-7207, Vol. 221, no 1-2, p. 1-8Article in journal (Refereed)
    Abstract [en]

    Adipose tissue is a primary target of insulin, but knowledge about insulin signalling in human adipocytes is limited. We developed an electroporation technique for transfection of primary human adipocytes with a transfection efficiency of 15% ± 5 (mean ± S.D.). Human adipocytes were co-transfected with a mutant of IRS-3 (all four potential PI3-kinase binding motifs mutated: IRS-3F4) and HA-tagged protein kinase B (HA-PKB/Akt). HA-PKB/Akt was immunoprecipitated from cell lysates with anti-HA antibodies, resolved with SDS-PAGE, and immunoblotted with phospho-specific antibodies. We found that IRS-3F4 blocked insulin stimulation of HA-PKB/Akt phosphorylation and in further analyses also translocation of recombinant HA-tagged glucose transporter to the plasma membrane. IRS-3F4 also blocked insulin-induced activation of the transcription factor Elk-1. Our results demonstrate the critical importance of IRS for metabolic as well as mitogenic signalling by insulin. This method for transfection of primary human adipocytes will be useful for studying insulin signalling in human adipocytes with molecular biological techniques.

  • 10.
    Thorn, Hans
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. 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.
    Karlsson, Margareta
    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.
    Nyström, Fredrik H.
    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.
    Gustavsson, Johanna
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
    Strålfors, Peter
    Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
    Cell surface orifices of caveolae and localization of caveolin to the necks of caveolae in adipocytes2003In: Molecular Biology of the Cell, ISSN 1059-1524, E-ISSN 1939-4586, Vol. 14, no 10, p. 3967-3976Article in journal (Refereed)
    Abstract [en]

    Caveolae are noncoated invaginations of the plasma membrane that form in the presence of the protein caveolin. Caveolae are found in most cells, but are especially abundant in adipocytes. By high-resolution electron microscopy of plasma membrane sheets the detailed structure of individual caveolae of primary rat adipocytes was examined. Caveolin-1 and -2 binding was restricted to the membrane proximal region, such as the ducts or necks attaching the caveolar bulb to the membrane. This was confirmed by transfection with myc-tagged caveolin-1 and -2. Essentially the same results were obtained with human fibroblasts. Hence caveolin does not form the caveolar bulb in these cells, but rather the neck and may thus act to retain the caveolar constituents, indicating how caveolin participates in the formation of caveolae. Caveolae, randomly distributed over the plasma membrane, were very heterogeneous, varying in size between 25 and 150 nm. There was about one million caveolae in an adipocyte, which increased the surface area of the plasma membrane by 50%. Half of the caveolae, those larger than 50 nm, had access to the outside of the cell via ducts and 20-nm orifices at the cell surface. The rest of the caveolae, those smaller than 50 nm, were not open to the cell exterior. Cholesterol depletion destroyed both caveolae and the cell surface orifices.

  • 11.
    Örtegren, Unn
    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.
    Blazic, Natascha
    Department of Clinical Neuroscience, Sahlgrenska University Hospital/Mölndal, Göteborg University, Mölndal, Sweden.
    Blomqvist, Maria
    Department of Clinical Neuroscience, Sahlgrenska University Hospital/Mölndal, Göteborg University, Mölndal, Sweden.
    Nyström, Fredrik
    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.
    Lipids and glycosphingolipids in caveolae and surrounding plasma membrane of primary rat adipocytes2004In: European Journal of Biochemistry, ISSN 0014-2956, E-ISSN 1432-1033, Vol. 271, no 10, p. 2028-2036Article in journal (Refereed)
    Abstract [en]

    We have made a comprehensive and quantitative analysis of the lipid composition of caveolae from primary rat fat cells and compared the composition of plasma membrane inside and outside caveolae. We isolated caveolae from purified plasma membranes using ultrasonication in carbonate buffer to disrupt the membrane, or extraction with nonionic detergent, followed by density gradient ultracentrifugation. The carbonate-isolated caveolae fraction was further immunopurified using caveolin antibodies. Carbonate-isolated caveolae were enriched in cholesterol and sphingomyelin, and the concentration was three- and twofold higher, respectively, in caveolae compared to the surrounding plasma membrane. The concentration of glycerophospholipids was similar suggesting that glycerophospholipids constitute a constant core throughout the plasma membrane. The composition of detergent-insoluble fractions of the plasma membrane was very variable between preparations, but strongly enriched in sphingomyelin and depleted of glycerophospholipids compared to carbonate-isolated caveolae; indicating that detergent extraction is not a suitable technique for caveolae preparation. An average adipocyte caveola contained about 22 × 103 molecules of cholesterol, 7.5 × 103 of sphingomyelin and 23 × 103 of glycerophospholipid. The glycosphingolipid GD3 was highly enriched in caveolae, whereas GM3, GM1 and GD1a were present inside as well as outside the caveolae membrane. GD1b, GT1b, GM2, GQ1b, sulfatide and lactosylceramide sulfate were not detected in caveolae.

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