G protein-coupled receptor kinase 5 regulates thrombin signaling in platelets via PAR-1.

Abstract

The interindividual variation in the functional response of platelets to activation by agonists is heritable. Genome-wide association studies (GWAS) of quantitative measures of platelet function have thus far identified fewer than 20 distinctly associated variants, some with unknown mechanisms. Here, we report GWAS of pathway specific functional responses to agonism by ADP, a glycoprotein VI-specific collagen mimetic and thrombin receptor-agonist peptides, each specific to one of the G protein-coupled receptors PAR-1 and PAR-4, in subsets of 1,562 individuals. We identified an association (P=2.75x10-40) between a common intronic variant, rs10886430 in the G protein-coupled receptor kinase 5 gene (GRK5), and the sensitivity of platelets to activate through PAR-1. The variant resides in a megakaryocyte-specific enhancer bound by the transcription factors GATA1 and MEIS1. The minor allele (G) is associated with fewer GRK5 transcripts in platelets and greater sensitivity of platelets to activate through PAR-1. We show that thrombin mediated activation of human platelets causes binding of GRK5 to PAR-1 and that deletion of the mouse homologue Grk5 enhances thrombin induced platelet activation sensitivity and increases platelet accumulation at the site of vascular injury. This corroborates evidence that the human G-allele of rs10886430 associates with greater risks of cardiovascular diseases. In summary, by combining the results of pathway specific GWAS and eQTL studies in humans with the results of platelet function studies in Grk5-/- mice, we obtain evidence that GRK5 regulates the human platelet response to thrombin via the PAR-1 pathway.