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ABT-737 triggers caspase-dependent inhibition of platelet procoagulant extracellular vesicle release during apoptosis and secondary necrosis in vitro

Published version
Peer-reviewed

Type

Article

Change log

Authors

Wei, Hao 

Abstract

Platelet lifespan is limited by activation of intrinsic apoptosis. Apoptotic platelets are rapidly cleared form the circulation in vivo. ABT-737 triggers platelet apoptosis and is a useful tool for studying this process. However, in vitro experiments lack clearance mechanisms for apoptotic platelets. To determine whether apoptotic platelets progress to secondary necrosis, apoptosis was triggered in human platelets with ABT-737, a BH3 mimetic. Platelet annexin V (AnV) binding, release of AnV+ extracellular vesicles (EVs) and loss of plasma membrane integrity were monitored by flow cytometry. ABT-737 triggered AnV binding, indicating phosphatidylserine exposure, release of AnV+ EVs, and a slow loss of plasma membrane integrity. The latter suggests that apoptotic platelets progress to secondary necrosis in vitro. These responses were dependent on caspase activation and Ca2+ entry. Surprisingly, although intracellular Ca2+ concentration increased, AnV+ EV release was not dependent on the Ca2+-dependent protease, calpain. On the contrary, ABT-737 downregulated the ability of the Ca2+ ionophore, A23187, to trigger calpain-dependent release of AnV+ EVs. This was dependent on caspase activity as, when caspases were inhibited, ABT-737 increased the ability of A23187 to trigger AnV+ EV release. These data suggest that apoptotic platelets progress to secondary necrosis unless they are cleared. This may affect the interpretation of ABT-737 triggered signalling in platelets in vitro. Ca2+-dependent AnV+ EV release is downregulated during apoptosis in a caspase-dependent manner, which may limit the potential consequences of secondary necrotic platelets.

Description

Keywords

Animals, Apoptosis, Biphenyl Compounds, Blood Platelets, Calcimycin, Calcium, Caspase Inhibitors, Caspases, Cells, Cultured, Down-Regulation, Extracellular Vesicles, Humans, Mice, Necrosis, Nitrophenols, Phosphatidylserines, Piperazines, Platelet Activation, Signal Transduction, Sulfonamides

Journal Title

Thrombosis and Haemostasis

Conference Name

Journal ISSN

0340-6245
2567-689X

Volume Title

119

Publisher

Schattauer GmbH
Sponsorship
Wellcome Trust (105602/Z/14/Z)
Isaac Newton Trust/ Wellcome Trust ISSF/University of Cambridge Joint Research Grant