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.

Non‐coding genetic variation in regulatory elements determines thrombosis and hemostasis phenotypes

“…This approach is used to connect variants to genes and phenotypes, to identify molecular and cellular phenotypes (e.g., transcription levels) that are relevant for more complex traits (e.g., GWAS‐associated disease) and to determine the mechanism by which the GWAS variants are influencing the phenotype. Colocalization of GWAS and eQTL variants in tissues implicated in thrombosis and hemostasis has been reported in various studies 10–13 . Among others, rs1175170 was identified as a regulator of RGS18 transcription in platelets, linking this gene to arterial thrombosis 12 .…”

“…For instance, Downes and colleagues identified rs10886430, in a GRK5 intron, as a regulator of platelet activation through the protease‐activated receptor‐1 pathway. The alternative nucleotide in rs10886430 locus alters GATA1 and MEIS1 binding sites in a megakaryocyte‐specific enhancer (Table 1) and alters GRK5 expression level 13 …”

Biomaterials-Mediated Tumor Infarction Therapy

“…Thrombin is a key enzyme in the coagulation cascade that can cleave the plasma fibrinogen into fibrin monomers that can then spontaneously form insoluble polymers ( Wells and Di Cera, 1992 ). Thrombin can also activate coagulation factors VIII (to VIIIa) and V (to Va) as well as platelets to aggregate platelets and block blood vessels ( Downes et al, 2022 ). Of course, the role of thrombin is not limited to coagulation events.…”

GRK2 regulates ADP signaling in platelets via P2Y1 and P2Y12

“…Emerging studies from our group and others strongly suggest that GPCR kinases (GRKs) are critical negative regulators for platelet activation. [3][4][5][6][7] GRKs are a group of serine/threonine kinases that typically terminate agonist-occupied GPCR signaling in a phosphorylation-dependent manner. In cells other than platelets, GRKs phosphorylate agonistbound GPCRs, triggering arrestin binding followed by clathrinmediated endocytosis.…”

“…Emerging studies from our group and others strongly suggest that GPCR kinases (GRKs) are critical negative regulators for platelet activation. 3, 4, 5, 6, 7 …”