Shear stress regulates angiotensin type 1 receptor expression in endothelial cells
Rationale: Shear stress (SS) has an established role in atherosclerotic plaque localization, but how it exerts its protective effect is not fully understood. Objective: To test the hypothesis that SS may downregulate angiotensin type 1 receptors (AT1,Rs). Angiotensin II has been shown to be proinflammatory and to promote atherosclerosis. Methods and Results: Using immunohistochemistry, we found a pronounced expression of AT1R in the inner, atheroprone regions of the aortic arch of C57BL/6 and endothelial NO synthase-deficient (eNOS-/-) mice but not eNOS-overexpressing mice. In human umbilical vein endothelial cells (HUVECs), laminar SS (15 dyn/cm2) induced a biphasic decrease in AT1R protein expression characterized by a first reduction at 1 hour (31 ±4% of static control, P<0.01), partial recovery at 3 hours (65±9%), and a second more prolonged decline at 6,12, and 24 hours (48±9%, 36±9%, 33±5%, respectively, P<0.05). One and 24 hours of SS significantly reduced fluorescent angiotensin binding compared to static HUVECs. Shear-induced downregulation of AT1R was abolished by treatment with protein kinase A and G inhibitors or A-nitro-L-arginine methyl ester (L-NAME). Fittingly, stimulating static HUVECs with an NO donor decreased AT1R protein levels. RT-PCR revealed a significant (P<0.05) decrease of AT1R mRNA in HUVECs exposed to SS during 3 (6±2% of static control), 6 (4±1%), 12 (4±1%), and 24 hours (15±4%), suggesting a transcriptional downregulation of AT1R at length. Finally, angiotensin-induced vascular cell adhesion molecule was abated in HUVECs exposed to SS and in the outer aortic arch of mice. Conclusions: Our results demonstrate that SS may convey some of its atheroprotective effects through downregulation of AT1R in endothelial cells.