Affiliation: School of Medicine, Department of Pharmacology
Understanding and manipulating thrombosis and blood hemostasis is critical for the effective treatment of patients at risk for heart attack and stroke. ADP is an important modulator of platelet function and vascular tone that acts by binding to and activating the P2Y1 and P2Y12 receptors. Deletion or inhibition of either receptor results in nearly a total loss of ADP-promoted aggregation. Interestingly, the P2Y1 receptor desensitizes extremely rapidly, with a half-life of approximately 18 sec, whereas the P2Y12 receptor continuously signals minutes after initial activation. We hypothesized that the rapid desensitization of the P2Y1 receptor in platelets prevents excess thrombosis and unwanted aggregation at lower concentrations of ADP. We have used ex vivo platelet activation experiments to demonstrate that the observed desensitization is specific to the P2Y1 receptor compared to other Gq-coupled receptors in platelets and is recapitulated in mouse platelets. We focused on serine and threonine residues on the C-terminus because of the involvement of various Ser and Thr phosphorylation on the regulation of the P2Y1 receptor in cell culture systems. Using an optimized viral transduction model to introduce variants of the P2Y1 receptor into bone marrow, we show preliminary data suggesting that mutating multiple serine and threonine residues in the C-terminus of the P2Y1 receptor (“340-0P”) results in prolonged activation of platelets in the absence of the P2Y12 receptor pathway, thus eliminating the observed desensitization in the wild type P2Y1 receptor. Furthermore, creation of a knock-in mouse for the 340-0P variant of the P2Y1 receptor revealed a loss of desensitization in platelets upon ADP stimulation in 340-0P heterozygous mice. These data suggest that the loss of Ser and Thr residues on the C-terminus of the P2Y1 receptor nullifies the observed desensitization and provides insights regarding the physiological relevance of this process in platelets.