Platelet dysfunction associated with the novel T rp29 C ys thromboxane A 2 receptor variant

Summary Background Genetic variations that affect the structure of the thromboxane  A 2 receptor ( TP receptor) provide insights into the function of this key platelet and vascular receptor, but are very rare in unselected populations. Objectives To determine the functional consequences of the TP receptor T rp29 C ys ( W 29 C ) substitution. Patients/Methods We performed a detailed phenotypic analysis of an index case ( P 1) with reduced platelet aggregation and secretion responses to TP receptor pathway activators, and a heterozygous TP receptor W 29 C substitution. An analysis of the variant W 29 C TP receptor expressed in heterologous cells was performed. Results Total TP receptor expression in platelets from P 1 was similar to that of controls, but there was reduced maximum binding and reduced affinity of binding to the TP receptor antagonist [ 3 H ] SQ 29548. HEK 293 cells transfected with W 29 C TP receptor c DNA showed similar total TP receptor expression to wild‐type ( WT ) controls. However, the TP receptor agonist U 46619 was less potent at inducing rises in cytosolic free C a 2+ in HEK 293 cells expressing the W 29 C TP receptor than in WT controls, indicating reduced receptor function. Immunofluorescence microscopy and cell surface ELISA showed intracellular retention and reduced cell surface expression of the W 29 C TP receptor in HEK 293 cells. Consistent with the platelet phenotype, both maximum binding and the affinity of binding of [ 3 H ] SQ 29548 to the W 29 C TP receptor were reduced compared to WT controls. Conclusion These findings extend the phenotypic description of the very rare disorder TP receptor deficiency, and show that the W 29 C substitution reduces TP receptor function by reducing surface receptor expression and by disrupting ligand binding.