Arterial shear stress downregulates thrombin receptor expression and attenuates thrombin-induced response in endothelial cells

Due to the important role of thrombin receptor (protease activated receptor-1: PAR-1), in inflammatory and thrombotic processes, the authors investigated effect of shear stress on PAR-1 expression in human umbilical vein endothelial cells (HUVECs) and microvascular endothelial cells (HMECs). HUVECs and HMECs were exposed to different shear stresses in a parallel plate flow system. Northern blot analysis showed that high shear stress (25 dyn/cm²) downregulated PAR-1 mRNA in both HUVECs and HMECs (2- and 3-fold decrease compared to static controls). Moderate shear (15 dyn/cm²) also reduced PAR-1 mRNA in HMECs, but not in HUVECs whereas low shear (5 dyn/cm²) did not affect PAR-1 mRNA in either HUVECs or HMECs. Moreover, flow cytometry analysis indicated that high shear stress decreased surface PAR-1 expression by 45% in HUVECs and by 60% in HMECs compared to that of static controls. Furthermore, exposure to high shear stress caused significant decreases of endothelin-1 production from HUVECs and HMECs and nitric oxide release from HUVECs in response to thrombin. These findings indicate that shear stress not only downregulates PAR-1 expression in HUVECs and HMECs but also attenuates endothelial cell functional responses to thrombin