High Glucose Regulation of Human Vascular Thrombin Receptor PAR-4

Diabetes is associated with enhanced thrombin generation, atherothrombosis and vascular remodelling. Clotting factor thrombin could modify these pathologies via protease-activated receptors- PAR-1, PAR-3 and PAR-4, exerting pleiotropic effects on vascular cells. This study investigates the possible regulation of thrombin receptors by high glucose in vascular smooth muscle cells (SMC). Treatment of human saphenous vein SMCs with high glucose selectively increased PAR-4 but not PAR-1 and PAR-3 expression, which was mediated via PKC and NFκB. High glucose mediated-ROS generation via NAD(P)H oxidase or other pro-oxidants such as Ang-II or exogenous H2O2 also enhanced PAR-4 expression. PAR-4 upregulation was associated with enhanced SMC migration, calcium signaling and inflammatory gene expression in responses to thrombin or PAR-4AP. The positive staining for PAR-4 and its colocalization with SMC was seen in the vicinity of the intimal plaque region of diabetic atherosclerotic plaques. This study highlights a unique role of PAR-4 in hyperglycemic settings, which might contribute to the enhanced cellular effects of thrombin and exaggerated cardiovascular complications of diabetes.