Complex formation of platelet thrombospondin with fibrinogen.

TLDR

Inhibitors that block thrombin- and thrombospondin-mediated platelet lectin activity, as well as the fibrinogen-binding glycoproteins IIb/IIIa, do not prevent fibrinogen–thrombospondin complex formation on activated platelets. ELISA demonstrates that fibrinogen specifically and saturably binds adsorbed platelet thrombospondin, a complex partially inhibited by sugar analogues and arginine, and that this interaction—stronger than with fibronectin—likely contributes to platelet aggregation.

Abstract

Using an enzyme-linked immunosorbent assay, we have demonstrated that purified human fibrinogen forms a complex with adsorbed platelet thrombospondin. The formation of the fibrinogen-thrombospondin complex was specific, saturable, and partially inhibited by mannosamine, glucosamine, and arginine. These same inhibitors have been previously shown to block thrombin-induced platelet lectin activity and platelet thrombospondin lectin activity. Adsorbed thrombospondin also formed a complex with fibronectin, although the extent of complex formation was significantly less than the extent of formation of the fibrinogen-thrombospondin complex. Platelet membrane glycoproteins IIb and IIIa, which have been previously shown to bind fibrinogen, did not inhibit the formation of the fibrinogen-thrombospondin complex. The present study supports the hypothesis that the interaction of fibrinogen with thrombospondin on the activated platelet surface may be an important step in the platelet aggregation process.