Common variants in the human platelet PAR4 thrombin receptor alter platelet function and differ by race

Abstract

• White individuals have a high frequency of the common PAR4 gene (F2RL3) variant Ala120; blacks have a high frequency of Thr120.• PAR4 Thr120 induces greater signaling and is associated with greater platelet aggregation and reduced inhibition by a PAR4 antagonist.Human platelets express 2 thrombin receptors: protease-activated receptor (PAR)-1 and PAR4. Recently, we reported 3.7-fold increased PAR4-mediated aggregation kinetics in platelets from black subjects compared with white subjects. We now show that platelets from blacks (n 5 70) express 14% more PAR4 protein than those from whites (n 5 84), but this difference is not associated with platelet PAR4 function. Quantitative trait locus analysis identified 3 common single nucleotide polymorphisms in the PAR4 gene (F2RL3) associated with PAR4-induced platelet aggregation. Among these single nucleotide polymorphisms, rs773902 determines whether residue 120 in transmembrane domain 2 is an alanine (Ala) or threonine (Thr). Compared with the Ala120 variant, Thr120 was more common in black subjects than in white subjects (63% vs 19%), was associated with higher PAR4-induced human platelet aggregation and Ca 21 flux, and generated greater inositol 1,4,5-triphosphate in transfected cells. A second, less frequent F2RL3 variant, Phe296Val, was only observed in blacks and abolished the enhanced PAR4-induced platelet aggregation and 1,4,5-triphosphate generation associated with PAR4-Thr120. PAR4 genotype did not affect vorapaxar inhibition of platelet PAR1 function, but a strong pharmacogenetic effect was observed with the PAR4-specific antagonist YD-3 [1-benzyl-3(ethoxycarbonylphenyl)-indazole]. These findings may have an important pharmacogenetic effect on the development of new PAR antagonists. (Blood. 2014;124(23):3450-3458)

A pharmacokinetics and safety phase 1/1b study of oral ixazomib in patients with multiple myeloma and severe renal impairment or end‐stage renal disease requiring haemodialysis

“…The safety, tolerability, pharmacokinetics (PK), pharmacodynamics and clinical activity of the oral proteasome inhibitor ixazomib have been assessed previously in phase 1 and phase 1–3 studies in relapsed and/or refractory MM (RRMM) and newly diagnosed MM, relapsed or refractory systemic light‐chain amyloidosis (RRAL), lymphoma and solid tumours (Assouline et al , 2014; Kumar et al , 2014a,b; Merlini et al , 2014; Richardson et al , 2014; Gupta et al , 2015a; Moreau et al , 2015a; Smith et al , 2015). Among these cancer types, the efficacy of ixazomib has been particularly noted in MM.…”

Protease-activated receptors in hemostasis

“…107 The recently described difference in reactivity between PAR4 sequence variants provides the most compelling evidence that single nucleotide polymorphisms can influence a physiological response downstream of PARs. 104,105 Edelstein and colleagues identified 2 single nucleotide polymorphisms (rs773902 and rs2227346) that result in sequence variants at positions 120 (Ala/Thr) in transmembrane helix 2 (TM2) and 296 (Phe/Val) in TM6, respectively ( Figure 4A). 104 The PAR4 variants correlate with platelet reactivity and are distributed by race.…”

“…[101][102][103][104][105][106] The challenge is establishing a direct link from the identified polymorphisms to receptor expression or function, and ultimately to a physiological output. For example, a polymorphism in an intron of the PAR1 gene (f2r) results in a lower density of PAR1 on the platelet surface and decreased aggregation in response to PAR1 agonists.…”

Genomics and transcriptomics of megakaryocytes and platelets: Implications for health and disease

“…These racial differences are dependent in part, on thrombin protease‐activated receptors (PARs), most specifically PAR4 activation 57. Black individuals were shown to have a 4‐fold higher expression of phosphatidylcholine transfer protein (PCTP) mRNA correlating with increased PAR4 mediated aggregation.…”