Fibrinolysis regulation by platelets retaining plasminogen and tissue-type plasminogen activator on their surface

Platelets play a key role in hemostasis as cofactors of thrombin generation, fibrin polymerization centers , and initiators of clot retraction, while their ability to modulate clot dissolution remains less understood. The aim of this study was to investigate the interaction of plasminogen and tissue plasminogen activator with native and activated platelets, to determine the amount of plasmin generated by various activators in the presence of platelets, and the ability of platelets to modulate the rate of polymer fibrin hydrolysis. spectrometric and immunofluorometric methods were used in the study. it was shown that intact circulating platelets carry a small amount of plasminogen on their surface, whereas thrombin-induced activation led to the exposure of plasminogen-binding sites on their plasma membrane. activated platelets stimulated plasminogen activation by tissue plasminogen activator, urokinase, and streptokinase. Components of prothrombin complex enhanced plasminogen activation by tissue plasminogen activator on the surface of activated platelets. Model system with desaB-fibrin revealed the ability of platelets to stimulate fibrinolysis. These results suggest that the regulation of fibrinolysis by platelets is provided by the binding of plasminogen and plasminogen activators on their surface, acceleration of plasmin generation and, consequently, acceleration of the onset of fibrin lysis and reducing of the clot lifetime, which is important to maintain hemostatic balance.