ИСТИНА

Background: Procoagulant platelets are highly activated subpopulation with high level of phosphatidylserine externalization, decreased adhesivity, balloonlike shape and other specific traits. Their (patho)physiological role continues to be debated. Aims: To get insight into dynamics of procoagulant platelets formation and their impact on thrombus architecture we investigated fates of individual procoagulant platelets during thrombosis. Methods: Realtime imaging with confocal and epifluorescence microscopes was used for analysis of thrombus formation on collagen under microvascular flow conditions in a flow chamber system. A computational model for studying dynamics of nonadhesive spheres within contracting thrombus was developed. Results: Realtime microscopy showed that procoagulant platelets formed inside a thrombus moved towards its surface. This resulted in a ringlike distribution of procoagulant platelets around the base of the thrombi near collagen. We assumed that this motion was driven by thrombus contraction along with reduced adhesivity of procoagulant platelets. This hypothesis was in line with results obtained using blood of MYH9 mice (with deficient nonmuscle myosin and, therefore, no thrombus contraction): for knockouts, procoagulant platelets were distributed within the thrombus and did not migrate to its outer surface. Computational modeling demonstrated that mechanical contraction of thrombus consisting of adhesive spheres leads to mechanical extrusion of nonadhesive spheres to its surface. Analysis of primary fibrin generation sites distribution yielded some correlation with procoagulant platelets localization: in WT mice fibrin originated at the surface of thrombi, while for MYH9 mice fibrin generation sites were distributed throughout the thrombi. Conclusions: Procoagulant platelets are mechanically expelled to thrombus surface by thrombus contraction process. Surface distribution of procoagulant platelets might be responsible for observed spatial features of fibrin generation.