Revka O. Coordination of thrombus formation and fibrinolysis by blood cells

PhD thesis highlights the investigation of the role of blood cells - monocytes, neutrophils and platelets - in coordination of thrombus formation and thrombolysis. For the first time it has been shown that monocytes have a direct impact on the formation of a fibrin clot, shifting the hemostatic balance of the coagulation/lysis process towards thrombus formation. Neutrophils equally accelerate the formation and lysis of fibrin clots, reducing the overall lifetime of the fibrin clot by half. Using the method of real-time confocal microscopy, it has been shown for the first time that platelets act as centers of fibrin polymerization and organization of the fibrin clot structure, which promotes the acceleration and spatiotemporal coordination of coagulation and fibrinolysis and limits the size and lifetime of thrombus. By using flow cytometry and enzymatic activity determination methods it has been shown that platelets circulating in the bloodstream do not carry Glu-plasminogen on their surface but are able to bind it after activation. Confocal microscopy and spectrofluorimetry have demonstrated for the first time that native platelets are able to bind tissue plasminogen activator, and it has been shown that the interaction of tissue plasminogen activator with platelets is possible through fibrin-dependent and fibrin-independent mechanisms. The amount of plasmin generated on the surface of activated platelets by the action of endogenous (tissue plasminogen activator and urokinase) and exogenous (streptokinase) activators has been established. For the first time new molecular mechanisms by which blood cells coordinate the formation and lysis of fibrin clots have been identified. These mechanisms include: - endothelium-independent pathway of protein C activation, in which protein C activation occurs directly on the surface of platelets, monocytes and neutrophils; - stimulation of plasminogen activation by tissue plasminogen activator by components of the prothrombin complex in the presence of activated platelets, and, accordingly, enhancement of plasmin generation; - structuring of fibrin clot by platelets, and accumulation of fibrin on their surface, where plasminogen and tissue plasminogen activator can be bound to form centers of lysis initiation. For the evaluation of the complex effects of different platelet activities, a new method has been proposed, using platelet-rich plasma in clot waveform analysis. Investigation on platelet-rich plasma samples from patients with arterial hypertension have shown the suitability of such an approach for more adequate evaluation of the balance between procoagulant and anticoagulant processes in the plasma (including platelet-mediated) and, as a consequence, for more reliable differentiation of healthy donors and hypertension patients which should improve therapeutic approaches. The obtained results are important for understanding the role of blood cells in coordination of thrombus formation and dissolution, which can be used to improve existing and develop new methods for the diagnosis and treatment of pathological conditions associated with the development of cardiovascular diseases.