title: Both TMEM16F-dependent and TMEM16F-independent pathways contribute to phosphatidylserine exposure in platelet apoptosis and platelet activation.
abstract: Scott syndrome, a bleeding disorder caused by defective phospholipid scrambling, has been associated with mutations in the TMEM16F gene. The role of TMEM16F in apoptosis- or agonist-induced phosphatidylserine (PS) exposure was studied in platelets from a Scott syndrome patient and control subjects. Whereas stimulation of control platelets with the BH3-mimetic ABT737 resulted in 2 distinct fractions with moderate and high PS exposure, the high PS-exposing fraction was markedly delayed in Scott platelets. High, but not moderate, PS exposure in platelets was suppressed by chelation of intracellular Ca(2+), whereas caspase inhibition completely abolished ABT737-induced PS exposure in both Scott and control platelets. On the other hand, high PS exposure induced by the Ca(2+)-mobilizing agonists convulxin/thrombin fully relied on mitochondrial depolarization and was virtually absent in Scott platelets. Finally, PS exposure induced by collagen/thrombin was partly affected in Scott platelets, and the residual PS positive fraction was insensitive to inhibition of caspases or mitochondrial depolarization. In conclusion, TMEM16F is not required for, but enhances, caspase-dependent PS exposure; convulxin-/thrombin-induced PS exposure is entirely dependent on TMEM16F, whereas collagen/thrombin-induced PS exposure results from 2 distinct pathways, one of which involves mitochondrial depolarization and is mediated by TMEM16F.
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht, University of Maastricht, Maastricht, The Netherlands.
authors.forename: Roger
authors.initials: R
authors.lastname: van Kruchten
authors.forename: Nadine J A
authors.initials: NJ
authors.lastname: Mattheij
authors.forename: Christine
authors.initials: C
authors.lastname: Saunders
authors.forename: Marion A H
authors.initials: MA
authors.lastname: Feijge
authors.forename: Frauke
authors.initials: F
authors.lastname: Swieringa
authors.forename: Jef L N
authors.initials: JL
authors.lastname: Wolfs
authors.forename: Peter W
authors.initials: PW
authors.lastname: Collins
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
authors.forename: Edouard M
authors.initials: EM
authors.lastname: Bevers
mesh_terms: D000075368:Anoctamins; D017209:Apoptosis; D001778:Blood Coagulation Disorders / Q000378:metabolism / Q000473:pathology*; D001792:Blood Platelets / Q000378:metabolism / Q000473:pathology*; D002118:Calcium / Q000378:metabolism*; D016022:Case-Control Studies; D020169:Caspases / Q000378:metabolism; D003435:Crotalid Venoms / Q000494:pharmacology; D021983:Cyclophilins / Q000378:metabolism; D005434:Flow Cytometry; D006490:Hemostatics / Q000494:pharmacology; D006801:Humans; D037181:Lectins, C-Type; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins / Q000378:metabolism*; D015539:Platelet Activation; D013917:Thrombin / Q000494:pharmacology; D000097322:Peptidyl-Prolyl Isomerase D
chemical_list: D000075368:Anoctamins; D002118:Calcium; D020169:Caspases; D003435:Crotalid Venoms; D021983:Cyclophilins; D006490:Hemostatics; D037181:Lectins, C-Type; D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D013917:Thrombin; C555078:ANO6 protein, human; C028890:convulxin; C114456:PPID protein, human; D000097322:Peptidyl-Prolyl Isomerase D