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  • 1.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Studies on interfaces between primary and secondary hemostasis2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Our conceptual understanding of hemostasis is still heavily influenced by outdated experimental models wherein the hemostatic activity of platelets and coagulation factors are understood and studied in isolation. Although perhaps convenient for researchers and clinicians, this reductionist view is negated by an ever increasing body of evidence pointing towards an intimate relationship between the two phases of hemostasis, marked by strong interdependence. In this thesis, I have focused on factual and proposed interfaces between primary and secondary hemostasis, and on how these interfaces can be studied.

    In my first project, we zoomed in on the mechanisms behind the well-known phenomenon of thrombin-induced platelet activation, an important event linking secondary to primary hemostasis. In our study, we examined how thrombin makes use of certain domains for high-affinity binding to substrates, called exosite I and II, to activate platelets via PAR4. We show that thrombin-induced platelet activation via PAR4 is critically dependent on exosite II, and that blockage of exosite II with different substances virtually eliminates PAR4 activation. Apart from providing new insights into the mechanisms by which thrombin activates PAR4, these results expand our knowledge of the antithrombotic actions of various endogenous proteins such as members of the serpin superfamily, which inhibit interactions with exosite II. Additionally, we show that inhibition of exosite II could be a feasible pharmacological strategy for achieving selective blockade of PAR4.

    In my second project, we examined the controversial issue of whether platelets can initiate the coagulation cascade by means of contact activation, a hypothesis which, if true, could provide a direct link between primary and secondary hemostasis. In contrast to previous results, our findings falsify this hypothesis, and show that some of the erroneous conclusions drawn from earlier studies can be explained by inappropriate experimental models unsuitable for the study of plateletcoagulation interfaces.

    My third project comprised an assessment of the methodological difficulties encountered when trying to measure the ability of platelets to initiate secondary hemostasis by the release of microparticles expressing tissue factor. Our study shows that the functional assays available for this purpose are highly susceptible to error caused by artificial contact activation. These results could help to improve the methodology of future research and thus pave the way for new insights into the roles of tissue factor-bearing microparticles in the pathophysiology of various thrombotic disorders.

    From a personal perspective, my PhD project has been a fascinating scientific odyssey into the largely unexplored interfaces between primary and secondary hemostasis. Looking forward, my ambition is to continue our work exploring platelet-coagulation interactions and to translate these insights into clinically meaningful information, which may someday improve the treatment of patients with bleeding and/or thrombosis.

    List of papers
    1. Thrombin-induced platelet activation via PAR4: pivotal role for exosite II
    Open this publication in new window or tab >>Thrombin-induced platelet activation via PAR4: pivotal role for exosite II
    Show others...
    2014 (English)In: Thrombosis and Haemostasis, ISSN 0340-6245, Vol. 112, no 3, p. 558-565Article in journal (Refereed) Published
    Abstract [en]

    Thrombin-induced platelet activation via PAR1 and PAR4 is an important event in haemostasis. Although the underlying mechanisms responsible for ensuring efficient PAR1 activation by thrombin have been extensively studied, the potential involvement of recognitions sites outside the active site of the protease in thrombin-induced PAR4 activation is largely unknown. In this study, we developed a new assay to assess the importance of exosite I and II for PAR4 activation with alpha- and gamma-thrombin. Surprisingly, we found that exosite II is critical for activation of PAR4. We also show that this dependency on exosite II likely represents a new mechanism, as it is unaffected by blockage of the previously known interaction between thrombin and glycoprotein Ib alpha.

    Place, publisher, year, edition, pages
    Schattauer Gmbh, 2014
    National Category
    Clinical Medicine
    Identifiers
    urn:nbn:se:liu:diva-111269 (URN)10.1160/TH13-12-1013 (DOI)000341547000015 ()24990072 (PubMedID)
    Note

    Funding Agencies|Swedish Research Council [K2010-65X-15060-07-3, K2013-65X-15060-10-3]; Swedish Heart and Lung Foundation [20100219, 20120263]

    Available from: 2014-10-15 Created: 2014-10-14 Last updated: 2017-12-05Bibliographically approved
    2. Putting polyphosphates to the test: evidence against platelet-induced activation of factor XII
    Open this publication in new window or tab >>Putting polyphosphates to the test: evidence against platelet-induced activation of factor XII
    Show others...
    2013 (English)In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 122, no 23, p. 3818-3824Article in journal (Refereed) Published
    Abstract [en]

    The recent claim that stimulated platelets activate the intrinsic pathway of coagulation by the release of polyphosphates has been considered a breakthrough in hemostasis research. In little more than 3 years, the original publication by Muller et al has been cited greater than100 times. However, none of the citing articles has sought to independently validate this potentially paradigm-shifting concept. To this end, we performed extensive experimentation in vitro and in vivo in an attempt to verify the claim that factor XII (FXII) is primarily activated by stimulated platelets. In contrast to the original assertion, platelet-derived polyphosphates were found to be weak activators of FXII, with a FXIIa-generating activity of less than10% compared with equivalent concentrations of kaolin. Using different coagulation assays, it was shown that platelet contribution to whole blood coagulation was unrelated to the generation of activated FXII in vitro. Additionally, key results used to verify the hypothesis in the original study in vivo were found to be irreproducible. We conclude that platelet-derived polyphosphates are not physiologically relevant activators of FXII.

    Place, publisher, year, edition, pages
    American Society of Hematology, 2013
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-104301 (URN)10.1182/blood-2013-05-499384 (DOI)000329735000021 ()
    Available from: 2014-02-17 Created: 2014-02-14 Last updated: 2017-12-06
    3. Response: platelets do not generate activated factor XII--how inappropriate experimental models have led to misleading conclusions
    Open this publication in new window or tab >>Response: platelets do not generate activated factor XII--how inappropriate experimental models have led to misleading conclusions
    Show others...
    2014 (English)In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 124, no 10, p. 1692-1694Article in journal, Letter (Other academic) Published
    Place, publisher, year, edition, pages
    American Society of Hematology, 2014
    National Category
    Clinical Medicine
    Identifiers
    urn:nbn:se:liu:diva-111531 (URN)10.1182/blood-2014-04-566067 (DOI)000342762300027 ()25190755 (PubMedID)
    Available from: 2014-10-22 Created: 2014-10-22 Last updated: 2017-12-05Bibliographically approved
    4. Contact activation: important to consider when measuring the contribution of tissue factor-bearing microparticles to thrombin generation using phospholipid-containing reagents
    Open this publication in new window or tab >>Contact activation: important to consider when measuring the contribution of tissue factor-bearing microparticles to thrombin generation using phospholipid-containing reagents
    2014 (English)In: Journal of Thrombosis and Haemostasis, ISSN 1538-7933, E-ISSN 1538-7836, Vol. 12, no 4, p. 515-518Article in journal (Refereed) Published
    Abstract [en]

    Background A commercial MP reagent containing phospholipids is used for thrombin generation (TG) measurements to estimate the procoagulant activity of microparticles (MPs). Previous reports have shown that contact activation affects TG when TF levels are low, and that addition of phospholipids might augment this effect. Objectives To quantify the impact of contact activation on TG in the presence of phospholipids and low/no TF, as is the case using a commercially available MP-reagent. Methods Thrombin generation was analyzed using MP- or platelet-rich plasma (PRP)-reagent in the presence and absence of corn trypsin inhibitor and anti-TF antibodies, respectively. To quantify the impact of different experimental parameters on contact activation, microparticle-depleted plasma was analyzed in the presence of different concentrations of phospholipids, TF and/or contact activating agents (kaolin). Results Even with low contact activating blood collection tubes, substantial thrombin generation was observed with the MP-reagent, but this was completely inhibited by addition of corn trypsin inhibitor. Control experiments illustrate that the phospholipids in the reagent play a major role in enhancing TG initiated by FXIIa. Even with the PRP-reagent, which is recommended for determining the content of phospholipids from MPs, TG was partly dependent on contact activation. Conclusions Contact activation plays a major role in TG when using reagents/samples containing phospholipids but little or no tissue factor. This needs to be considered and accounted for in future clinical studies using TG to assess the procoagulant activity of MPs.

    Place, publisher, year, edition, pages
    Wiley, 2014
    Keywords
    cell-derived microparticles; thromboplastin; blood coagulation; thrombin; factor XII
    National Category
    Medical and Health Sciences
    Identifiers
    urn:nbn:se:liu:diva-106682 (URN)10.1111/jth.12503 (DOI)000334157000012 ()
    Available from: 2014-05-21 Created: 2014-05-19 Last updated: 2017-12-05
  • 2.
    Boknäs, Niklas
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Lindahl, Tomas L
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Contact activation: important to consider when measuring the contribution of tissue factor-bearing microparticles to thrombin generation using phospholipid-containing reagents2014In: Journal of Thrombosis and Haemostasis, ISSN 1538-7933, E-ISSN 1538-7836, Vol. 12, no 4, p. 515-518Article in journal (Refereed)
    Abstract [en]

    Background A commercial MP reagent containing phospholipids is used for thrombin generation (TG) measurements to estimate the procoagulant activity of microparticles (MPs). Previous reports have shown that contact activation affects TG when TF levels are low, and that addition of phospholipids might augment this effect. Objectives To quantify the impact of contact activation on TG in the presence of phospholipids and low/no TF, as is the case using a commercially available MP-reagent. Methods Thrombin generation was analyzed using MP- or platelet-rich plasma (PRP)-reagent in the presence and absence of corn trypsin inhibitor and anti-TF antibodies, respectively. To quantify the impact of different experimental parameters on contact activation, microparticle-depleted plasma was analyzed in the presence of different concentrations of phospholipids, TF and/or contact activating agents (kaolin). Results Even with low contact activating blood collection tubes, substantial thrombin generation was observed with the MP-reagent, but this was completely inhibited by addition of corn trypsin inhibitor. Control experiments illustrate that the phospholipids in the reagent play a major role in enhancing TG initiated by FXIIa. Even with the PRP-reagent, which is recommended for determining the content of phospholipids from MPs, TG was partly dependent on contact activation. Conclusions Contact activation plays a major role in TG when using reagents/samples containing phospholipids but little or no tissue factor. This needs to be considered and accounted for in future clinical studies using TG to assess the procoagulant activity of MPs.

  • 3.
    Boknäs, Niklas
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Sanchez Centellas, Daniel
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Wallstedt, Maria
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Grenegård, Magnus
    University of Örebro, Sweden.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Thrombin-induced platelet activation via PAR4: pivotal role for exosite II2014In: Thrombosis and Haemostasis, ISSN 0340-6245, Vol. 112, no 3, p. 558-565Article in journal (Refereed)
    Abstract [en]

    Thrombin-induced platelet activation via PAR1 and PAR4 is an important event in haemostasis. Although the underlying mechanisms responsible for ensuring efficient PAR1 activation by thrombin have been extensively studied, the potential involvement of recognitions sites outside the active site of the protease in thrombin-induced PAR4 activation is largely unknown. In this study, we developed a new assay to assess the importance of exosite I and II for PAR4 activation with alpha- and gamma-thrombin. Surprisingly, we found that exosite II is critical for activation of PAR4. We also show that this dependency on exosite II likely represents a new mechanism, as it is unaffected by blockage of the previously known interaction between thrombin and glycoprotein Ib alpha.

  • 4.
    Boknäs, Niklas
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Ström, Jakob O
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Tengvall, Pentti
    Sahlgrenska Academy, University of Gothenburg, Sweden.
    Theodorsson, Elvar
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Lindahl, Tomas L
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Response: platelets do not generate activated factor XII--how inappropriate experimental models have led to misleading conclusions2014In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 124, no 10, p. 1692-1694Article in journal (Other academic)
  • 5.
    Boknäs, Niklas
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Haematology.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry. Orebro Univ, Sweden.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Flow cytometry-based platelet function testing is predictive of symptom burden in a cohort of bleeders2018In: Platelets, ISSN 0953-7104, E-ISSN 1369-1635, Vol. 29, no 5, p. 512-519Article in journal (Refereed)
    Abstract [en]

    Platelet function disorders (PFDs) are common in patients with mild bleeding disorders (MBDs), yet the significance of laboratory findings suggestive of a PFD remain unclear due to the lack of evidence for a clinical correlation between the test results and the patient phenotype. Herein, we present the results from a study evaluating the potential utility of platelet function testing using whole-blood flow cytometry in a cohort of 105 patients undergoing investigation for MBD. Subjects were evaluated with a test panel comprising two different activation markers (fibrinogen binding and P-selectin exposure) and four physiologically relevant platelet agonists (ADP, PAR1-AP, PAR4-AP, and CRP-XL). Abnormal test results were identified by comparison with reference ranges constructed from 24 healthy controls or with the fifth percentile of the entire patient cohort. We found that the abnormal test results are predictive of bleeding symptom severity, and that the greatest predictive strength was achieved using a subset of the panel, comparing measurements of fibrinogen binding after activation with all four agonists with the fifth percentile of the patient cohort (p=0.00008, hazard ratio 8.7; 95% CI 2.5-40). Our results suggest that whole-blood flow cytometry-based platelet function testing could become a feasible alternative for the investigation of MBDs. We also show that platelet function testing using whole-blood flow cytometry could provide a clinically relevant quantitative assessment of platelet-related hemostasis.

  • 6.
    Faxälv, Lars
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    PAR1, PAR4 and GPIB form functional interdependent units in a receptor complex mediating platelet activation by thrombin in JOURNAL OF THROMBOSIS AND HAEMOSTASIS, vol 9, issue SI, pp 11-112011In: JOURNAL OF THROMBOSIS AND HAEMOSTASIS, Wiley-Blackwell , 2011, Vol. 9, no SI, p. 11-11Conference paper (Refereed)
    Abstract [en]

    n/a

  • 7.
    Faxälv, Lars
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Ström, Jakob
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
    Tengvall, Pentti
    University of Gothenburg, Gothenburg, Sweden .
    Theodorsson, Elvar
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Center for Diagnostics, Department of Clinical Chemistry.
    Putting polyphosphates to the test: evidence against platelet-induced activation of factor XII2013In: Blood, ISSN 0006-4971, E-ISSN 1528-0020, Vol. 122, no 23, p. 3818-3824Article in journal (Refereed)
    Abstract [en]

    The recent claim that stimulated platelets activate the intrinsic pathway of coagulation by the release of polyphosphates has been considered a breakthrough in hemostasis research. In little more than 3 years, the original publication by Muller et al has been cited greater than100 times. However, none of the citing articles has sought to independently validate this potentially paradigm-shifting concept. To this end, we performed extensive experimentation in vitro and in vivo in an attempt to verify the claim that factor XII (FXII) is primarily activated by stimulated platelets. In contrast to the original assertion, platelet-derived polyphosphates were found to be weak activators of FXII, with a FXIIa-generating activity of less than10% compared with equivalent concentrations of kaolin. Using different coagulation assays, it was shown that platelet contribution to whole blood coagulation was unrelated to the generation of activated FXII in vitro. Additionally, key results used to verify the hypothesis in the original study in vivo were found to be irreproducible. We conclude that platelet-derived polyphosphates are not physiologically relevant activators of FXII.

  • 8.
    Lindahl, Tomas
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Caveats in studies of the physiological role of polyphosphates in coagulation2016In: Biochemical Society Transactions, ISSN 0300-5127, E-ISSN 1470-8752, Vol. 44, p. 35-39Article, review/survey (Refereed)
    Abstract [en]

    Platelet-derived polyphosphates (polyP), stored in dense granule and released upon platelet activation, have been claimed to enhance thrombin activation of coagulation factor XI (FXI) and to activate FXII directly. The latter claim is controversial and principal results leading to these conclusions are probably influenced by methodological problems. It is important to consider that low-grade contact activation is initiated by all surfaces and is greatly amplified by the presence of phospholipids simulating the procoagulant membranes of activated platelets. Thus, proper use of inhibitors of the contact pathway and a careful choice of materials for plates and tubes is important to avoid artefacts. The use of phosphatases used to degrade polyP has an important drawback as it also degrades the secondary activators ADP and ATP, which are released from activated platelets. In addition, the use of positively charged inhibitors, such as polymyxin B, to inhibit polyP in platelet-rich plasma and blood is problematic, as polymyxin B also slows coagulation in the absence of polyP. In conclusion we hope awareness of the above caveats may improve research on the physiological roles of polyP in coagulation. © 2016 Authors; published by Portland Press Limited.

  • 9.
    Macwan, Ankit
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Chemistry. Linköping University, Faculty of Medicine and Health Sciences.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Chemistry. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Haematology.
    Ntzouni, Maria
    Linköping University, Department of Clinical and Experimental Medicine, Division of Cell Biology. Linköping University, Faculty of Medicine and Health Sciences.
    Ramström, Sofia
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Chemistry. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry. Orebro Univ, Sweden.
    Gibbins, Jonathan M.
    Univ Reading, England.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Chemistry. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Clinical Chemistry. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Gradient-dependent inhibition of stimulatory signaling from platelet G protein-coupled receptors2019In: Haematologica, ISSN 0390-6078, E-ISSN 1592-8721, Vol. 104, no 7Article in journal (Refereed)
    Abstract [en]

    As platelet activation is an irreversible and potentially harmful event, platelet stimulatory signaling must be tightly regulated to ensure the filtering-out of inconsequential fluctuations of agonist concentrations in the vascular milieu. Herein, we show that platelet activation via G protein-coupled receptors is gradient-dependent, i.e., determined not only by agonist concentrations per se but also by how rapidly concentrations change over time. We demonstrate that gradient-dependent inhibition is a common feature of all major platelet stimulatory G protein-coupled receptors, while platelet activation via the non-G protein-coupled receptor glycoprotein VI is strictly concentration-dependent. By systematically characterizing the effects of variations in temporal agonist concentration gradients on different aspects of platelet activation, we demonstrate that gradient-dependent inhibition of protease-activated receptors exhibits different kinetics, with platelet activation occurring at lower agonist gradients for protease-activated receptor 4 than for protease-activated receptor 1, but shares a characteristic bimodal effect distribution, as gradient-dependent inhibition increases over a narrow range of gradients, below which aggregation and granule secretion is effectively shut off. In contrast, the effects of gradient-dependent inhibition on platelet activation via adenosine diphosphate and thromboxane receptors increase incrementally over a large range of gradients. Furthermore, depending on the affected activation pathway, gradient-dependent inhibition results in different degrees of refractoriness to subsequent autologous agonist stimulation. Mechanistically, our study identifies an important role for the cyclic adenosine monophosphate-dependent pathway in gradient-dependent inhibition. Together, our findings suggest that gradient-dependent inhibition may represent a new general mechanism for hemostatic regulation in platelets.

  • 10.
    Tunströmer, Kjersti
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences.
    Faxälv, Lars
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Haematology.
    Lindahl, Tomas L.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Chemistry.
    Quantification of Platelet Contractile Movements during Thrombus Formation2018In: Thrombosis and Haemostasis, ISSN 0340-6245, Vol. 118, no 09, p. 1600-1611Article in journal (Refereed)
    Abstract [en]

    Imaging methods based on time-lapse microscopy are important tools for studying the dynamic events that shape thrombus formation upon vascular injury. However, there is a lack of methods to translate the vast amount of visual data generated in such experiments into quantitative variables describing platelet movements that can be subjected to systematic analysis. In this study, we developed experimental and computational protocols allowing for a detailed mathematical analysis of platelet movements within a developing thrombus. We used a flow chamber-based model of thrombosis wherein a collagen strip was used to initiate platelet adhesion and activation. Combining the use of a platelet staining protocol, designed to enable identification of individual platelets, and image processing, we tracked the movements of a large number of individual platelets during thrombus formation and consolidation. These data were then processed to generate aggregate measures describing the heterogeneous movements of platelets in different areas of the thrombus and at different time points. Applying this model and its potential, to a comparative analysis on a panel of platelet inhibitors, we found that total platelet intra-thrombus movements are only slightly reduced by blocking the interactions between glycoproteins IIb/IIIa and Ib and their ligands or by inhibiting thromboxane synthesis or P2Y12 signalling. In contrast, whereas 30 to 40% of the platelets movements (for the CD42a-labelled platelets) and 20% (for the pro-coagulant platelets), within a thrombus, are contractile, i.e., towards the centre of the thrombus, this contractile component is almost totally abolished in the presence of agents inhibiting these pathways.

  • 11.
    Tynngård, Nahreen
    et al.
    Linköping University, Department of Medical and Health Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Regional Board, Research and Development Unit.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Haematology.
    Trinks, Marie
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Immunology and Transfusion Medicine.
    Dreimane, Arta
    Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Haematology.
    Berlin, Gösta
    Linköping University, Department of Clinical and Experimental Medicine, Division of Neuro and Inflammation Science. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Clinical Immunology and Transfusion Medicine.
    Storage-induced change in platelet transfusion response evaluated by serial transfusions from one donor to one patient2019In: Transfusion, ISSN 0041-1132, E-ISSN 1537-2995, Vol. 59, no 2, p. 723-728Article in journal (Refereed)
    Abstract [en]

    BACKGROUND

    Storage of platelet concentrates (PCs) results in storage lesions with possible detrimental effects on platelet recovery after transfusion, which might affect their ability to prevent or arrest bleeding. The aim of this study was to compare the quality of PCs stored for 1 to 3 or 5 to 7 days by assessing the corrected count increment (CCI) after transfusion. To isolate the effects of storage time, we studied serial transfusions of PCs obtained from one donor and one donation, and transfused to one single recipient after storage for 1 to 3 days and 5 to 7 days.

    STUDY DESIGN AND METHODS

    Platelets were obtained from one donor by apheresis, divided into two units (>240 × 109platelets/unit) and stored for 1 to 3 and 5 to 7 days, respectively, before transfusion. The PCs were transfused on normal indications to patients undergoing treatment at the hematology ward. Platelet count was measured before and after transfusion.

    RESULTS

    Thirty patients concluded the study according to the protocol. The mean storage time was 2.4 ± 0.7 and 5.7 ± 0.8 days for platelets transfused on Days 1 to 3 and 5 to 7, respectively. Storage for 5 to 7 days decreased the 1‐hour transfusion response as compared to platelets stored 1 to 3 days, from a CCI of 17 ± 7 to 13 ± 5. Despite this decrease, 86% of the 5 to 7 days stored PCs resulted in a CCI above the cutoff value for a successful transfusion of 7.5, which was not significantly different to PCs stored for 1 to 3 days.

    CONCLUSION

    Storage of PCs for 5 to 7 days only slightly altered the transfusion response.

  • 12.
    Vretenbrant Öberg, Karin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
    Boknäs, Niklas
    Linköping University, Department of Clinical and Experimental Medicine, Division of Microbiology and Molecular Medicine. Linköping University, Faculty of Health Sciences.
    Kalsum, Sadaf
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences.
    Ramström, Sofia
    Molecular & Cellular Therapeutics, Royal College of Surgeons in Ireland, Dublin, Ireland.
    Lindahl, Tomas
    Linköping University, Department of Clinical and Experimental Medicine, Clinical Chemistry. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Laboratory Medicine, Department of Clinical Chemistry.
    Platelet thrombin receptors PAR1 and PAR4 act in a synergistic mannerManuscript (preprint) (Other academic)
    Abstract [en]

    n/a

1 - 12 of 12
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