ИСТИНА

Procoagulant platelets are a subpopulation of activated platelets formed upon potent activation and characterized by high phosphatidylserine externalization, surface retention of alpha-granule proteins, decreased adhesivity, disrupted cytoskeleton, balloon-like shape and other specific traits. To get insight into the dynamics of their formation during thrombosis and their impact on thrombus architecture, we investigated the fate of individual procoagulant platelets during ex vivo thrombus formation in human blood under arterial flow conditions. Real-time confocal microscopy showed that procoagulant platelets which formed inside a thrombus migrated towards its surface leaving a trace of microvesicles behind. This locomotion resulted in a ring-like distribution of procoagulant platelets around the base of the thrombus near collagen. Three-dimensional computational model of heterogeneous aggregate contraction suggested that mechanical contraction driven by consolidation of non-procoagulant platelets can lead to mechanical expulsion of poorly adhesive procoagulant platelets to its surface. In agreement with this, procoagulant platelets were irregularly distributed and did not migrate to the surface of thrombi formed in blood of platelet MYH9-deficient mice. Primary fibrin generation sites determined with an anti-fibrin antibody agreed with the procoagulant platelet localization: in WT mice, fibrin originated at the surface of thrombi, while for MYH9-deficient mice, fibrin generation sites were distributed all over the thrombus. Inhibition of procoagulant platelets formation with cyclosporin A resulted in thrombi which lacked both procoagulant platelets and fibrin. Our results suggest that outward migration of procoagulant platelets driven by the thrombus contraction process plays an important role in the determination of spatial thrombus structure and fibrin distribution.