Fibulin-1 mediates platelet adhesion via a bridge of fibrinogen.
Fibulin-1 is a component of the extracellular matrix that surrounds vascular smooth muscle. This observation, along with the recent finding that fibulin-1 can bind fibrinogen (J Biol Chem 270:19458, 1995), prompted investigation into the potential role of fibulin-1 as a thrombogenic agent. In perfusion chamber assays, platelets in whole blood under flow conditions attached and spread on surfaces coated with fibulin-1. This adhesion was completely blocked by fibulin-1 antibodies. Platelets free of plasma did not attach to fibulin-1 coated surfaces; however, with the addition of fibrinogen, platelet adhesion to fibulin-1 took place. When detergent extracts of platelets were subjected to fibulin-1-Sepharose affinity chromatography, the integrin alpha IIb beta 3 was selected. Solid phase binding assays using purified components showed that integrin alpha IIb beta 3 could not bind directly to fibulin-1 but in the presence of fibrinogen the integrin bound to fibulin-1-coated surfaces. Monoclonal alpha IIb beta 3 antibodies capable of blocking its interaction with fibrinogen completely blocked platelet adhesion to fibulin-1 in both whole blood perfusion and static adhesion assays. The results show that fibulin-1 can support platelet attachment via a bridge of fibrinogen to the platelet integrin alpha IIb beta 3. When fibroblast monolayers containing extracellular matrix-incorporated fibulin-1 were used as adhesion substrates, platelet adhesion in the presence of fibrinogen could be inhibited by 30% using antibodies to fibulin-1. Following vascular injury, fibulin-1 present in the extracellular matrix of the vessel wall may therefore interact with plasma fibrinogen and promote platelet adhesion, leading to the formation of a platelet plug. Thus, fibulin-1 joins the list of matrix proteins including collagens I and IV and fibronectin that mediate platelet adhesion via a plasma protein bridge. This bridging phenomenon may represent a general mechanism by which platelets interact with exposed subendothelial matrices following vascular injury.
Godyna
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Biochemistry Department, J.H. Holland Laboratory, American Red Cross, Rockville, MD, USA.
Diaz-Ricart
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Argraves
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WS
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D002478:Cells, Cultured; D002846:Chromatography, Affinity; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism; D018056:Hemorheology; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D010973:Platelet Adhesiveness / Q000187:drug effects*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors / Q000276:immunology / Q000302:isolation & purification
D000911:Antibodies, Monoclonal; D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; D046911:Macromolecular Substances; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; C060820:fibulin; D005340:Fibrinogen