title: Mitochondrially mediated integrin αIIbβ3 protein inactivation limits thrombus growth.
abstract: When platelets are strongly stimulated, a procoagulant platelet subpopulation is formed that is characterized by phosphatidylserine (PS) exposure and epitope modulation of integrin αIIbβ3 or a loss of binding of activation-dependent antibodies. Mitochondrial permeability transition pore (mPTP) formation, which is essential for the formation of procoagulant platelets, is impaired in the absence of cyclophilin D (CypD). Here we investigate the mechanisms responsible for these procoagulant platelet-associated changes in integrin αIIbβ3 and the physiologic role of procoagulant platelet formation in the regulation of platelet aggregation. Among strongly stimulated adherent platelets, integrin αIIbβ3 epitope changes, mPTP formation, PS exposure, and platelet rounding were closely associated. Furthermore, platelet mPTP formation resulted in a decreased ability to recruit additional platelets. In the absence of CypD, integrin αIIbβ3 function was accentuated in both static and flow conditions, and, in vivo, a prothrombotic phenotype occurred in mice with a platelet-specific deficiency of CypD. CypD-dependent proteolytic events, including cleavage of the integrin β3 cytoplasmic domain, coincided closely with integrin αIIbβ3 inactivation. Calpain inhibition blocked integrin β3 cleavage and inactivation but not mPTP formation or PS exposure, indicating that integrin inactivation and PS exposure are mediated by distinct pathways subsequent to mPTP formation. mPTP-dependent alkalinization occurred in procoagulant platelets, suggesting a possible alternative mechanism for enhancement of calpain activity in procoagulant platelets. Together, these results indicate that, in strongly stimulated platelets, mPTP formation initiates the calpain-dependent cleavage of integrin β3 and associated regulatory proteins, resulting in integrin αIIbβ3 inactivation, and demonstrate a novel CypD-dependent negative feedback mechanism that limits platelet aggregation and thrombotic occlusion.
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Fang
authors.initials: F
authors.lastname: Liu
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Graciela
authors.initials: G
authors.lastname: Gamez
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322,; the Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30322, and.
authors.forename: David R
authors.initials: DR
authors.lastname: Myers
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322.
authors.forename: Wayne
authors.initials: W
authors.lastname: Clemmons
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322,; the Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30322, and; the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Atlanta, Georgia 30322.
authors.forename: Wilbur A
authors.initials: WA
authors.lastname: Lam
authors.affiliation: From the Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia 30322,; the Aflac Cancer and Blood Disorders Center, Children's Healthcare of Atlanta, Atlanta, Georgia 30322. Electronic address: shawn.jobe@bcw.edu.
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Jobe
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology; D002154:Calpain / Q000235:genetics / Q000378:metabolism; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D059748:Proteolysis; D013927:Thrombosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology
chemical_list: D000081406:Peptidyl-Prolyl Isomerase F; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C000631446:PPIF protein, mouse; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D002154:Calpain; D021983:Cyclophilins
keywords: Calpain; Integrin; Mitochondria; Platelets; Thrombosis