Mitochondrial Calcium and Reactive Oxygen Species Regulate Agonist-Initiated Platelet Phosphatidylserine Exposure

• Type of Material: Article
• Authors: Hyo-Jung Choo, Emory University; Talib B. Saafir, Emory University; Laura Mkumba, Emory University; Mary B Wagner, Emory University; Shawn M. Jobe, Emory University
• Language: English
• Date: 2012-12
• Publisher: American Heart Association
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2012, Wolters Kluwer Health
• Final Published Version (URL): http://atvb.ahajournals.org/content/32/12/2946.long
• Title of Journal or Parent Work: Arteriosclerosis, Thrombosis, and Vascular Biology
• ISSN: 1079-5642
• Volume: 32
• Issue: 12
• Start Page: 2946
• End Page: 2955
• Grant/Funding Information: This work was supported by grants from the National Institutes of Health/National Heart, Lung, and Blood Institute (R01 HL095858, S.M.J.) and the American Heart Association (Fellow-to-Faculty Transition Award, S.M.J.).
• Keywords: calcium; phosphatidylserine; platelets; mPTP; Mitochondria
• Research Categories: Health Sciences, Obstetrics and Gynecology; Health Sciences, General; Health Sciences, Pathology

Abstract

Objective To study the interactions of cytoplasmic calcium (Ca2+cyt) elevation, mitochondrial permeability transition pore (mPTP) formation, and reactive oxygen species (ROS) formation in the regulation of phosphatidylserine (PS) exposure in platelets. Methods and results mPTP formation, but not the degree of Ca2+cyt elevation, was associated with PS exposure in wild-type, CypD null, ionomycin-treated and ROS-treated platelets. In the absence of the mPTP regulator cyclophilin D agonist-initiated mPTP formation and high-level PS exposure were markedly blunted, but Ca2+cyt transients were unchanged. Mitochondrial calcium (Ca2+mit) transients and ROS, key regulators of mPTP formation, were examined in strongly-stimulated platelets. Increased ROS production occurred in strongly-stimulated platelets and was dependent on extracellular calcium entry, but not the presence of CypD. Ca2+mit increased significantly in strongly-stimulated platelets. Abrogation of Ca2+mit entry either by inhibition of the mitochondrial calcium uniporter or mitochondrial depolarization prevented mPTP formation and exposure, but not platelet aggregation or granule release. Conclusions Sustained Ca2+cyt levels are necessary, but not sufficient, for high-level PS exposure in response to agonists. Increased Ca2+mit levels are a key signal initiating mPTP formation and PS exposure. Blockade of Ca2+mit entry allows the specific inhibition of platelet procoagulant activity.