Published online before print September 17, 2009, doi: 10.1161/CIRCRESAHA.109.204040
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Submitted on August 6, 2008
Revised on September 3, 2009
Accepted on September 8, 2009
Shear Stress Regulates Angiotensin Type 1 Receptor Expression in Endothelial Cells
Bhama Ramkhelawon ;
From the Paris Cardiovascular Research Center (B.R., J.V., A.T., S.L.), Institut National de la Santé et de la Recherche Médicale U970, Hôpital Européen Georges Pompidou, France; Lady Davis Institute for medical Research (D.R., S.L.), McGill University, Montreal, Canada; and Department of Vascular Surgery (B.M., R.d.C.) and Cell Biology & Genetics (B.M.), Erasmus University medical Center, Rotterdam, The Netherlands.
* To whom correspondence should be addressed. E-mail: stephanie.lehoux{at}mcgill.ca.
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 (AT1Rs). 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 cell (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 NG-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.
Key words: shear stress • angiotensin • nitric oxide • endothelium • atherosclerosis