title: Influence of fibrillar collagen structure on the mechanisms of platelet thrombus formation under flow.
abstract: We have used real-time video microscopy to study the mechanisms of platelet adhesion to type I collagen fibrils of distinct structure exposed to flowing blood. Electron microscopy analysis by surface replication demonstrated morphological differences between acid-insoluble fibrils, displaying a regularly repeating striated pattern (banded collagen), and acid-soluble fibrils generated by pepsin treatment of insoluble collagen, smaller in size with a helical configuration (nonbanded collagen). These structural differences proved to be related to the role of platelet integrin alpha(2)beta(1) in stabilizing adhesion to collagen under a variety of flow conditions. Blocking alpha(2)beta(1) function with a monoclonal antibody had no effect on platelet adhesion to insoluble type I collagen coated at high density on a glass surface, whereas there was an absolute dependence of alpha(2)beta(1) function for the initial permanent arrest of platelets and subsequent thrombus formation on pepsin-solubilized type I collagen under the same conditions. In contrast, reconstituted, banded fibrils prepared from pepsin-solubilized type I collagen supported platelet adhesion and thrombus development even when platelet alpha(2)beta(1) function was blocked, a process that was greatly accelerated by pre-exposure of this substrate to autologous plasma under flow. These results implicate a collagen receptor(s) on platelets other than alpha(2)beta(1) that can selectively engage domains in banded, but not nonbanded type I collagen when alpha(2)beta(1) function is blocked. In addition, collagen structure may regulate the extent and affinity of the binding under flow of plasma components such as von Willebrand factor and/or other alpha(IIb)beta(3) ligands.
authors.affiliation: Roon Research Center for Arteriosclerosis and Thrombosis, Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, CA 92037, USA. brian@scripps.edu
authors.forename: B
authors.initials: B
authors.lastname: Savage
authors.forename: M H
authors.initials: MH
authors.lastname: Ginsberg
authors.forename: Z M
authors.initials: ZM
authors.lastname: Ruggeri
mesh_terms: D000328:Adult; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001777:Blood Coagulation / Q000502:physiology*; D002417:Cattle; D003094:Collagen / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D005898:Glass; D006801:Humans; D016023:Integrins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D018715:Microscopy, Video; D010434:Pepsin A / Q000494:pharmacology; D010973:Platelet Adhesiveness / Q000502:physiology*; D010974:Platelet Aggregation / Q000502:physiology*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000378:metabolism; D011485:Protein Binding; D038981:Receptors, Collagen; D012212:Rheology; D012995:Solubility; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D016023:Integrins; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D038981:Receptors, Collagen; D014841:von Willebrand Factor; D003094:Collagen; D010434:Pepsin A