Angiotensin II signaling mechanisms involved in the elevation of arginase activity/expression and vascular dysfunction

Abstract

Vascular endothelial dysfunction is a major cause of morbidity and mortality in · patients with cardiovascular diseases such as hypertension, atherosclerosis and diabetes. Nitric oxide (NO) produced by endothelial nitric oxide synthase (NOS) is· needed for norm.al vascular function. During hypertension, diabetes or -atherosclerosis, elevated levels of arginase can compete with NOS for available L-arginine thus reducing vascular NO production. Elevated angiotensin II (Ang II) is a key participant of endothelial dysfunction in many cardiovascular diseases and has been linked to elevated arginase activity. In this· study we explored the signaling pathway leading to increased arginase expression/activity in responses to Ang II.in bovine aortic endothelial cells (BAEC). Treatment of BAEC with Ang II (10-7 _M, 24 hrs) caused a 40±6% increase in arginase activity. This was accompanied by 30±8% decrease in NO production. Our studies indicate involvement of the RhoA/ROCK-p38 mitogen activated protein kinase (MAPK) in Ang 11.,induced arginase upregulation and reduced NO production, as inhibitors of ROCK or p38 MAPK prevented the Ang II-induced increase in arginase activity. Our studies in mice also show involvement of p38 MAPK in Ang II-induced vascular dysfunction associated with elevated arginase activity and expression. Ang 11 (42 · μg/kg/h) caused impaired EC-dependeht vasorelaxation in mouse . aorta (55±7~ vs. -75±8% for control}. This ·impairment was prevented by treatment with p38 inhibitor S8203580. (5 μg/kg/day). Ang II also caused a 6.2 fold increase in vascular arginase activity/expression that was complete_ly prevented by p38 MAPK inhibition. Additionally, treatment of BAEC with Ang II causes phosphorylation of activating transcription factor-2 (ATF-2) and -enhancement of the binding of ATF-2 to arginase promoter through an AP-1 site . as evident from electrophoretic mobility shift assay experiments. Transfection of BAEC with ATF-2 siRNA prevents Ang II-induced increases in arginase activity/expression and maintains NO production. These results indicate that. ATF-2 is necessary for enhanced expression of arginase by Ang II. Collectively, our results indicate that Ang 11 increases endothelial arginase activity/expression through a RhoA/ROCK-p38 MAPK-ATF-2 pathway leading to reduced NO production and endothelial dysfunction. Targeting these signaling steps might be therapeutic points for preventing vascular endothelial dysfunction_ associated with · elevated arginase activity/expression.