SUPPRESSION OF ANGIOTENSIN-CONVERTING ENZYME EXPRESSION AND ACTIVITY BY SHEAR-STRESS

Shear stress caused by the frictional forces of a fluid moving over a cell monolayer is an important regulator of gene expression. In this s tudy, we investigated the effect of shear stress on angiotensin-conver ting enzyme (ACE) expression and promoter activity in vitro and on loc al vascular ACE activity in vivo. ACE activity measured in bovine pulm onary artery endothelial (BPAE) cells was reduced by 49.5% after expos ure to a shear stress of 20 dyne/cm(2) for 18 hours. Short-term sheari ng (2 hours) elevated ACE activity in BPAE cells, whereas long-term sh earing produced a time-dependent reduction in ACE activity by 23.3%, 3 3.5%, and 48.9% at 8, 12, and 18 hours, respectively. Northern blot an alysis revealed that shear stress (20 dyne/cm(2) for 18 hours) signifi cantly reduced ACE mRNA expression by 82%. To determine the mechanism of ACE activity and message reduction, the effect of shear on transcri ptionally related events was determined in a rabbit aortic endothelial cell line (W3LUC) stably transfected with 1.3 kb of a rat ACE promote r/luciferase construct. Different shear stress magnitudes (5 to 20 dyn e/cm(2)) caused suppression of luciferase activity by an average of 40 .7%. ACE promoter activity was suppressed by 2 hours of shear stress ( 24.7%) and was further inhibited at time periods >8 hours. In vivo ele vations in shear stress were created by placing a stainless steel clip over a 12-mm region of the rat abdominal aorta. Restriction of vessel diameter increased blood flow velocity and caused reduction in vascul ar ACE activity by 40%. These studies suggest that elevations in the l evel of shear stress alter endothelial cell function by suppressing AC E gene and protein expression in vitro and in vivo.