title: Facilitating roles of murine platelet glycoprotein Ib and alphaIIbbeta3 in phosphatidylserine exposure during vWF-collagen-induced thrombus formation.
abstract: Vessel wall damage exposes collagen fibres, to which platelets adhere directly via the collagen receptors glycoprotein (GP) VI and integrin alpha(2)beta(1) and indirectly by collagen-bound von Willebrand factor (vWF) via the GPIb-V-IX and integrin alphaIIbbeta3 receptor complexes. Platelet-collagen interaction under shear stimulates thrombus formation in two ways, by integrin-dependent formation of platelet aggregates and by surface exposure of procoagulant phosphatidylserine (PS). GPVI is involved in both processes, complemented by alpha2beta1. In mouse blood flowing over collagen, we investigated the additional role of platelet-vWF binding via GPIb and alphaIIbbeta3. Inhibition of GPIb as well as blocking of vWF binding to collagen reduced stable platelet adhesion at high shear rate. This was accompanied by delayed platelet Ca(2+) responses and reduced PS exposure, while microaggregates were still formed. Inhibition of integrin alphaIIbbeta3 with JON/A antibody, which blocks alphaIIbbeta3 binding to both vWF and fibrinogen, reduced PS exposure and aggregate formation. The JON/A effects were not enhanced by combined blocking of GPIb-vWF binding, suggesting a function for alphaIIbbeta3 downstream of GPIb. Typically, with blood from FcR gamma-chain +/- mutant mice, expressing 50% of normal platelet GPVI levels, GPIb blockage almost completely abolished platelet adhesion and PS exposure. Together, these data indicate that, under physiological conditions of flow, both adhesive receptors GPIb and alphaIIbbeta3 facilitate GPVI-mediated PS exposure by stabilizing platelet binding to collagen. Hence, these glycoproteins have an assistant procoagulant role in collagen-dependent thrombus formation, which is most prominent at reduced GPVI activity and is independent of the presence of thrombin.
authors.affiliation: Department of Biochemistry, Cardiovascular Research Institute Maastricht, University of Maastricht, Maastricht, The Netherlands.
authors.forename: Marijke J E
authors.initials: MJ
authors.lastname: Kuijpers
authors.forename: Valerie
authors.initials: V
authors.lastname: Schulte
authors.forename: Cécile
authors.initials: C
authors.lastname: Oury
authors.forename: Theo
authors.initials: T
authors.lastname: Lindhout
authors.forename: Jos
authors.initials: J
authors.lastname: Broers
authors.forename: Marc F
authors.initials: MF
authors.lastname: Hoylaerts
authors.forename: Bernhard
authors.initials: B
authors.lastname: Nieswandt
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
mesh_terms: D000818:Animals; D018955:CD36 Antigens / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D010718:Phosphatidylserines / Q000494:pharmacology; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism*; D019038:Platelet Glycoprotein GPIb-IX Complex / Q000378:metabolism*; D013047:Specific Pathogen-Free Organisms; D013314:Stress, Mechanical; D013927:Thrombosis / Q000378:metabolism*; D014841:von Willebrand Factor / Q000378:metabolism*
chemical_list: D018955:CD36 Antigens; D010718:Phosphatidylserines; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D019038:Platelet Glycoprotein GPIb-IX Complex; D014841:von Willebrand Factor; D003094:Collagen; D002118:Calcium