title: Complementary roles of glycoprotein VI and alpha2beta1 integrin in collagen-induced thrombus formation in flowing whole blood ex vivo.
abstract: Platelets interact vigorously with subendothelial collagens that are exposed by injury or pathological damage of a vessel wall. The collagen-bound platelets trap other platelets to form aggregates, and they expose phosphatidylserine (PS) required for coagulation. Both processes are implicated in the formation of vaso-occlusive thrombi. We previously demonstrated that the immunoglobulin receptor glycoprotein VI (GPVI), but not integrin alpha2beta1, is essential in priming platelet-collagen interaction and subsequent aggregation. Here, we report that these receptors have yet a complementary function in ex vivo thrombus formation during perfusion of whole blood over collagen. With mice deficient in GPVI or blocking antibodies, we found that GPVI was indispensable for collagen-dependent Ca2+ mobilization, exposure of PS, and aggregation of platelets. Deficiency of integrin beta1 reduces the GPVI-evoked responses but still allows the formation of loose platelet aggregates. By using mice deficient in G(alpha)q or specific thromboxane A2 and ADP antagonists, we show that these autocrine agents mediated aggregation but not collagen-induced Ca2+ mobilization or PS exposure. Collectively, these data indicate that integrin alpha2beta1 facilitates the central function of GPVI in the platelet activation processes that lead to thrombus formation, whereas the autocrine thromboxane A2 and ADP serve mainly to trigger aggregate formation.
authors.affiliation: Department of Biochemistry, CARIM, Maastricht University, 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: Wolfgang
authors.initials: W
authors.lastname: Bergmeier
authors.forename: Theo
authors.initials: T
authors.lastname: Lindhout
authors.forename: Cord
authors.initials: C
authors.lastname: Brakebusch
authors.forename: Stefan
authors.initials: S
authors.lastname: Offermanns
authors.forename: Reinhard
authors.initials: R
authors.lastname: Fässler
authors.forename: Johan W M
authors.initials: JW
authors.lastname: Heemskerk
authors.forename: Bernhard
authors.initials: B
authors.lastname: Nieswandt
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D003094:Collagen / Q000008:administration & dosage / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000502:physiology; D038982:Integrin alpha2beta1 / Q000097:blood / Q000235:genetics / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D010973:Platelet Adhesiveness / Q000187:drug effects / Q000502:physiology; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D017452:Receptors, IgG / Q000235:genetics / Q000502:physiology; D013927:Thrombosis / Q000378:metabolism*; D013928:Thromboxane A2 / Q000378:metabolism
chemical_list: D038982:Integrin alpha2beta1; D010980:Platelet Membrane Glycoproteins; D017452:Receptors, IgG; C098341:platelet membrane glycoprotein VI; D013928:Thromboxane A2; D000244:Adenosine Diphosphate; D003094:Collagen; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; D002118:Calcium