title: Rate-limiting roles of the tenase complex of factors VIII and IX in platelet procoagulant activity and formation of platelet-fibrin thrombi under flow.
abstract: The importance of factor Xa generation in thrombus formation has not been studied extensively so far. Here, we used mice deficient in either factor VIII or factor IX to determine the role of platelet-stimulated tenase activity in the formation of platelet-fibrin thrombi on collagen. With tissue factor present, deficiency in factor VIII or IX markedly suppressed thrombus growth, fibrin formation and platelet procoagulant activity (phosphatidylserine exposure). In either case, residual fibrin formation was eliminated in the absence of tissue factor. Effects of factor deficiencies were antagonized by supplementation of the missing coagulation factor. In wild-type thrombi generated under flow, phosphatidylserine-exposing platelets bound (activated) factor IX and factor X, whereas factor VIII preferentially co-localized at sites of von Willebrand factor binding. Furthermore, proteolytic activity of the generated activated factor X and thrombin was confined to the sites of phosphatidylserine exposure. With blood from a hemophilia A or B patient, the formation of platelet-fibrin thrombi was greatly delayed and reduced, even in the presence of high concentrations of tissue factor. A direct activated factor X inhibitor, rivaroxaban, added to human blood, suppressed both thrombin and fibrin formation. Together, these data point to a potent enforcement loop in thrombus formation due to factor X activation, subsequent thrombin and fibrin generation, causing activated factor X-mediated stimulation of platelet phosphatidylserine exposure. This implies that the factor VIII/factor IX-dependent stimulation of platelet procoagulant activity is a limiting factor for fibrin formation under flow conditions, even at high tissue factor concentrations.
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, The Netherlands.
authors.forename: Frauke
authors.initials: F
authors.lastname: Swieringa
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, The Netherlands.
authors.forename: Marijke J E
authors.initials: MJ
authors.lastname: Kuijpers
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, The Netherlands.
authors.forename: Moniek M E
authors.initials: MM
authors.lastname: Lamers
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, The Netherlands.
authors.forename: Paola E J
authors.initials: PE
authors.lastname: van der Meijden
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht (CARIM), Maastricht University, The Netherlands jwm.heemskerk@maastrichtuniversity.nl.
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
mesh_terms: D000818:Animals; D001777:Blood Coagulation / Q000502:physiology*; D001792:Blood Platelets / Q000378:metabolism* / Q000473:pathology; D003546:Cysteine Endopeptidases / Q000502:physiology*; D015949:Factor IXa / Q000378:metabolism; D015944:Factor VIIIa / Q000378:metabolism; D005337:Fibrin / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009363:Neoplasm Proteins / Q000502:physiology*; D013927:Thrombosis / Q000097:blood* / Q000473:pathology
chemical_list: D009363:Neoplasm Proteins; D015944:Factor VIIIa; D005337:Fibrin; D015949:Factor IXa; D003546:Cysteine Endopeptidases; C030910:cancer procoagulant