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Blood, 16 July 2009, Vol. 114, No. 3, pp. 663-666. Prepublished online as a Blood First Edition Paper on April 22, 2009; DOI 10.1182/blood-2009-01-200345.
PLATELETS AND THROMBOPOIESIS Two distinct pathways regulate platelet phosphatidylserine exposure and procoagulant function![]() ![]() 1 Australian Centre for Blood Diseases, Monash University, Melbourne; Divisions of 2 Molecular Medicine, 3 Molecular Genetics of Cancer, and 4 Cancer and Hematology, The Walter and Eliza Hall Institute (WEHI) of Medical Research, Parkville, Australia
Procoagulant platelets exhibit hallmark features of apoptotic cells, including membrane blebbing, microvesiculation, and phosphatidylserine (PS) exposure. Although platelets possess many well-known apoptotic regulators, their role in regulating the procoagulant function of platelets is unclear. To clarify this, we investigated the consequence of removing the essential mediators of apoptosis, Bak and Bax, or directly inducing apoptosis with the BH3 mimetic compound ABT-737. Treatment of platelets with ABT-737 triggered PS exposure and a marked increase in thrombin generation in vitro. This increase in procoagulant function was Bak/Bax- and caspase-dependent, but it was unaffected by inhibitors of platelet activation or by chelating extracellular calcium. In contrast, agonist-induced platelet procoagulant function was unchanged in Bak–/–Bax–/– or caspase inhibitor–treated platelets, but it was completely eliminated by extracellular calcium chelators or inhibitors of platelet activation. These studies show the existence of 2 distinct pathways regulating the procoagulant function of platelets.
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