Novel assays shows that coronary artery disease patients have heightened procoagulant potential and implicates the Cyclophilin D dependent necrosis pathway

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• Dr Vivien Chen, ANZAC Research Institute, University of Sydney
• Tuesday 12 July 2016, 11:00-12:00
• Sackler Lecture Theatre, MRC/Wellcome Building, Addenbrookes Hospital.

If you have a question about this talk, please contact Katja Kivinen.

Host: Willem Ouwehand / Kate Downes

A subpopulation of platelets fulfil a procoagulant role in haemostasis and thrombosis by enabling the thrombin burst required for fibrin formation and clot stability at the site of vascular injury. Excess procoagulant activity is linked with pathological thrombosis. The identity of the procoagulant platelet has been elusive. The cell death marker GSAO rapidly enters a subpopulation of agonist-stimulated platelets via an organic anion-transporting polypeptide and is retained in the cytosol through covalent reaction with protein dithiols. Labelling with GSAO together with exposure of P-selectin distinguishes necrotic from apoptotic platelets. Use of GSAO labelling in vitro and in vivo identifies that the major subpopulation of phosphatidylserine positive platelets involved in thrombus formation are formed via cyclophilin D dependent regulated necrosis, not apoptosis. GSAO platelets form in occluding murine thrombi after ferric chloride stimulation, are attenuated with megakaryocyte directed deletion of the cyclophilin D gene. These platelets form a procoagulant surface supporting fibrin formation in vivo and reduction in GSAO platelets is associated with reduction in platelet thrombus size and fibrin formation. Analysis of platelets from human subjects on aspirin therapy indicates that these procoagulant platelets form despite aspirin therapy, but are attenuated by inhibition of the necrosis pathway. This indicates that necrotic platelets may be targeted independently of platelet activation indicating a potential therapeutic target in cardiovascular patients.

To facilitate investigation of the role of procoagulant platelets in patient samples, we then developed a flow cytometry based assay based on GSAO /Pselectin labelling of platelets using whole blood collected in standard citrate collection tubes. Using this assay we demonstrated the strong platelet agonists, thrombin and collagen, induce formation of procoagulant platelets via a mechanism that is largely independent of protease activated receptors. Patients with coronary artery disease have a heightened procoagulant platelet potential and are sensitised to thrombin and ADP stimulation. The procoagulant platelet potential in these patients is insensitive to aspirin, which targets platelet aggregation, but modified by P2Y12 antagonists. This assay has potential prognostic and predictive potential in patients with platelet-based thrombosis disorders, as well as potential screening tool for identifying future anti-platelet therapies.

This talk is part of the Cambridge Cardiovascular Seminar Series series.

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• Cambridge Cardiovascular Seminar Series
• Cardiovascular Epidemiology Unit Special Seminars
• Sackler Lecture Theatre, MRC/Wellcome Building, Addenbrookes Hospital
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