title: Dual mechanism of integrin αIIbβ3 closure in procoagulant platelets.
abstract: BACKGROUND
  Inactivation of integrin αIIbβ3 reverses platelet aggregate formation upon coagulation.
  
  
  CONCLUSIONS
  Platelets from patient (Scott) and mouse (Capn1(-/-) and Ppif(-/-)) blood reveal a dual mechanism of αIIbβ3 inactivation: by calpain-2 cleavage of integrin-associated proteins and by cyclophilin D/TMEM16F-dependent phospholipid scrambling.
  
  
  CONCLUSIONS
  These data provide novel insight into the switch mechanisms from aggregating to procoagulant platelets. Aggregation of platelets via activated integrin αIIbβ3 is a prerequisite for thrombus formation. Phosphatidylserine-exposing platelets with a key role in the coagulation process disconnect from a thrombus by integrin inactivation via an unknown mechanism. Here we show that αIIbβ3 inactivation in procoagulant platelets relies on a sustained high intracellular Ca(2+), stimulating intracellular cleavage of the β3 chain, talin, and Src kinase. Inhibition of calpain activity abolished protein cleavage, but only partly suppressed αIIbβ3 inactivation. Integrin αIIbβ3 inactivation was unchanged in platelets from Capn1(-/-) mice, suggesting a role of the calpain-2 isoform. Scott syndrome platelets, lacking the transmembrane protein TMEM16F and having low phosphatidylserine exposure, displayed reduced αIIbβ3 inactivation with the remaining activity fully dependent on calpain. In platelets from Ppif(-/-) mice, lacking mitochondrial permeability transition pore (mPTP) formation, agonist-induced phosphatidylserine exposure and αIIbβ3 inactivation were reduced. Treatment of human platelets with cyclosporin A gave a similar phenotype. Together, these data point to a dual mechanism of αIIbβ3 inactivation via calpain(-2) cleavage of integrin-associated proteins and via TMEM16F-dependent phospholipid scrambling with an assistant role of mPTP formation.
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht, Maastricht University, 6200 MD Maastricht, The Netherlands.
authors.forename: Nadine J A
authors.initials: NJ
authors.lastname: Mattheij
authors.forename: Karen
authors.initials: K
authors.lastname: Gilio
authors.forename: Roger
authors.initials: R
authors.lastname: van Kruchten
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Jobe
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Wieschhaus
authors.forename: Athar H
authors.initials: AH
authors.lastname: Chishti
authors.forename: Peter
authors.initials: P
authors.lastname: Collins
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
authors.forename: Judith M E M
authors.initials: JM
authors.lastname: Cosemans
mesh_terms: D000818:Animals; D000075368:Anoctamins; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018955:CD36 Antigens / Q000378:metabolism; D020013:Calcium Signaling; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003435:Crotalid Venoms / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D006801:Humans; D037181:Lectins, C-Type; D051379:Mice; D057507:Mice, 129 Strain; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D010718:Phosphatidylserines / Q000378:metabolism; D049294:Phospholipid Transfer Proteins / Q000378:metabolism; D010974:Platelet Aggregation; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D020836:Protein Structure, Quaternary; D059748:Proteolysis; D016608:Talin / Q000378:metabolism; D013917:Thrombin / Q000494:pharmacology / Q000502:physiology; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: C555078:ANO6 protein, human; D000075368:Anoctamins; D018955:CD36 Antigens; D003435:Crotalid Venoms; D004151:Dipeptides; D037181:Lectins, C-Type; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C518832:TLN1 protein, human; D016608:Talin; C071482:calpeptin; C028890:convulxin; D019061:src-Family Kinases; D013917:Thrombin; D002154:Calpain; C569870:CAPN2 protein, human; C058076:calpain inhibitor III
keywords: Calpain; Cyclophilin D; Integrins; Mitochondria; Phosphatidylserine; Platelets; Procoagulant Activity