Platelet Activation through GPVI Receptor: Variability of the Response

Abstract

Platelets are nuclear-free cell fragments responsible for preventing blood loss in case of the vascular wall injury. After a contact with collagen exposed when the vessel is damaged, platelets become activated through the receptor glycoprotein GPVI. This leads to platelet shape change, degranulation, aggregation, and procoagulant responses. The aim of this study was to observe changes in the concentration of Ca2+ in the cytosol and functional responses of platelets upon stimulation through the GPVI receptor. The study involved healthy adult volunteers and house mice Mus musculus of the C57Bl6 line (wild type). Calcium signaling was monitored by Fura-Red fluorophore fluorescence using BD FACS Canto II flow cytometer. Functional responses were observed on a flow cytometer by binding of human fibrinogen conjugated to a fluorescent label or by Biola optical aggregometry. When tested on a cytometer, platelets were activated by collagen-related peptide CRP and when tested by aggregometry, platelets were activated using collagen. As a result of the study, the following phenomenon was revealed: despite a significant variability in the human platelet cytosolic Ca2+ levels in response to stimulation, the variability in activation of platelet integrins, shape change, and the aggregation response was significantly lower. No variability in the platelet cytosolic Ca2+ levels in response to stimulation was observed in mice. The observed variability of the calcium response of platelets could be caused by differences in the GPVI expression or polymorphisms of the GPVI receptor gene in the studied donors. Similarities in the functional responses of platelets with different signaling suggest a variable contribution of the phosphoinositide branch of intracellular signaling in platelets in response to activation of GPVI.