The p.T216R mutation of the thromboxane A2 receptor disrupts platelet function by selectively altering the G12/13 signaling pathway.

The thromboxane A2 receptor (TBXA2R) is a platelet receptor that binds to 2 distinct G protein signaling pathways (Gq and Gα12/13) and plays a major role in platelet activation. Mutations in the TBXA2R gene can alter platelet aggregation and cause bleeding disorders. Until now, only mutations affecting the Gq pathway have been reported. This study aimed to characterize a new TBXA2R gene mutation discovered in a family with moderate bleeding syndrome. After identifying the mutation through gene sequencing, the function of the platelets was evaluated using aggregation tests after stimulation with the thromboxane analogue U46619, arachidonic acid, and collagen. The functional consequences of the mutation were then examined through the studies of intracellular calcium signaling and RhoA signaling pathway. Defective aggregation responses were observed when the platelets were stimulated by U46619, arachidonic acid, or collagen. In contrast to other described TBXA2R mutations, the p.T216R mutation did not affect the Gq signaling pathway that regulates intracellular calcium. Rather, it selectively impaired the Gα12/13 signaling pathway, which is associated with RhoA and myosin light chain activation, thereby affecting actin-myosin contractility. This study is the first to demonstrate the selective impact of TBXA2R mutation on Gα12/13-dependent signaling, providing new insights into the molecular mechanisms underlying platelet dysfunction.