Determination of PAR4 numbers on the surface of human platelets: no effect of the single nucleotide polymorphism rs773902

Abstract

The thrombin receptor, protease-activated receptor 4 (PAR4), is important for platelet activation and is the target of emerging anti-thrombotic drugs. A frequently occurring single nucleotide polymorphism (SNP; rs773902) causes a function-altering PAR4 sequence variant (NC_000019.10:p.Ala120Thr), whereby platelets from Thr120-expressing individuals are hyper-responsive to PAR4 agonists and hypo-responsive to some PAR4 antagonists than platelets from Ala120-expressing individuals. This altered pharmacology may impact PAR4 inhibitor development, yet the underlying mechanism(s) remain unknown. We tested whether PAR4 surface expression contributes to the altered receptor function. Quantitative flow cytometry was used to determine the absolute number of PAR4 on platelets from individuals subsequently genotyped at rs773902. We detected 539 ± 311 PAR4 per platelet (mean ± SD, n = 84). This number was not different across rs773902 genotypes. This first determination of cellular PAR4 numbers indicates variations in platelet surface expression do not explain the altered pharmacology of the rs773902 PAR4 sequence variant.

Keywords:

• Platelets
• protease-activated receptors
• thrombin

Acknowledgements

We thank G. Paukovics and team from the Alfred Research Alliance Flow Cytometry Core, P. Larsson for help with the study, N. Finn for insights, and all of our wonderful volunteer blood donors for their participation in this study.

Declaration Of Interest Statement

The authors declare no conflict of interest.

Author Contributions

SL and VT performed experiments, analyzed data, and co-wrote the paper; RBIC and SLF performed experiments and analyzed data; JRH designed and supervised the study, analyzed data, and wrote the paper.

Additional information

Funding

This work was supported by grants to J.R.H. from the National Health Medical Research Council of Australia (1137508 & 1187595).