ИСТИНА

Introduction. Strong platelet activation by agonists of protease-activated receptors (PARs) and/or GPVI lead to segregation of platelets into two subpopulations. One of them exposes phosphatidylserine, thus accelerating blood plasma coagulation reactions on platelet surface (“procoagulant platelets”). The levels of procoagulant platelets formed upon stimulation with thrombin in vitro vary between donors by order of magnitude without any observable difference in donor’s hemostatic phenotype. Aims. To explain, by means of computational modeling and PARs genotyping, the observed individual differences in the dynamics of procoagulant platelet formation in response to thrombin. Methods. Twenty healthy volunteers, both men and women aged 18 to 35 years were recruited into the study. Dynamics of procoagulant platelet formation was observed by means of continuous flow cytometry of washed annexin-V labeled human platelets. A multicompartmental stochastic computational systems biology model of dual-receptor thrombin signaling in platelets was developed to gain insight into the roles of PAR1 and PAR4 in procoagulant platelet subpopulation formation. Activity of PAR receptors in donors was evaluated by mRNA measurement and by polymorphism sequencing. Donors were genotyped for rs168753 (IVSn−14 A/T transition in PAR1 gene) and rs773902 (Ala120Thr substitution in PAR4 gene) SNPs. Investigations were performed in accordance with the Declaration of Helsinki, and written informed consent was obtained from all donors. Results. Activation with thrombin produced step-like procoagulant response or, in other donors, led to linear growth of the fraction of procoagulant platelets with time over the first 5-10 minutes after activation. Computational analysis predicted that such difference could be explained by elevation of PAR4 activity and decrease in PAR1 activity by 25%. We have shown that the linear time-course is associated with Ala120Thr polymorphism in the F2RL3 gene encoding PAR4. Conclusions. The platelet PAR4 receptor activity determines whether the population procoagulant response will be quick step-like or prolonged in time.