title: Function of glycoprotein VI and integrin alpha2beta1 in the procoagulant response of single, collagen-adherent platelets.
abstract: Various collagen-based materials were used to assess the structural requirements of collagen for inducing the procoagulant response of adhering platelets, as well as the collagen receptors involved. Cross-linked or monomeric collagen-related peptide (CRP), Gly-Cys-Hyp-(Gly-Pro-Hyp)10-Gly-Cys-Hyp-Gly was highly adhesive for platelets in a glycoprotein VI-(GpVI-)dependent manner. Adhesion was followed by a prolonged increase in cytosolic [Ca2+]i, formation of membrane blebs, exposure of phosphatidylserine (PS) and generation of prothrombinase-stimulating activity. Fibrils of type-I collagen were less adhesive but, once adhered, many of the platelets presented a full procoagulant response. Monomeric type-I collagen was unable to support adhesion, unless Mg(2+)-dependent integrin alpha2beta1 interactions were facilitated by omission of Ca2+ ions. With all surfaces, however, post-addition of CaCl2 to adhering platelets resulted in a potent Ca(2+)-influx signal, followed by PS exposure and bleb formation. The procoagulant response elicited by binding to CRP was inhibited by anti-GpVI Fab fragments, but not by impeding integrin alpha2beta1-mediated events. With fibrillar collagen, it was inhibited by blocking either the GpVI- or integrin alpha2beta1-mediated interactions. This suggests that the triple-helical Gly-Pro-Hyp repeat in CRP and analogous sequences in fibrillar collagen stimulate the procoagulant response of adherent platelets by acting as ligands for GpVI. Influx of Ca2+ is required for this response, and adhesion via integrin alpha2beta1 serves to potentiate the signaling effects of GpVI.
authors.affiliation: Department of Biochemistry, University of Maastricht, The Netherlands. JWM.Heemskerk@Bioch.UniMaas.nl
authors.forename: J W
authors.initials: JW
authors.lastname: Heemskerk
authors.forename: P
authors.initials: P
authors.lastname: Siljander
authors.forename: W M
authors.initials: WM
authors.lastname: Vuist
authors.forename: G
authors.initials: G
authors.lastname: Breikers
authors.forename: C P
authors.initials: CP
authors.lastname: Reutelingsperger
authors.forename: M J
authors.initials: MJ
authors.lastname: Barnes
authors.forename: C G
authors.initials: CG
authors.lastname: Knight
authors.forename: R
authors.initials: R
authors.lastname: Lassila
authors.forename: R W
authors.initials: RW
authors.lastname: Farndale
mesh_terms: D001665:Binding Sites / Q000235:genetics; D001777:Blood Coagulation; D001792:Blood Platelets / Q000166:cytology / Q000502:physiology*; D003094:Collagen; D006801:Humans; D016023:Integrins / Q000502:physiology*; D018613:Microscopy, Confocal; D010973:Platelet Adhesiveness; D010980:Platelet Membrane Glycoproteins / Q000502:physiology*; D038981:Receptors, Collagen
chemical_list: D016023:Integrins; D010980:Platelet Membrane Glycoproteins; D038981:Receptors, Collagen; C098341:platelet membrane glycoprotein VI; D003094:Collagen