THROMBIN STIMULATES HUMAN ENDOTHELIAL ARGINASE ACTIVITY VIA RHOA/ROCK PATHWAY: INHIBITION BY THE HMG-COA REDUCTASE INHIBITOR FLUVASTATIN

XF. Ming (1), C. Barandier (1), H. Viswambharan (1), S. Rusconi (2), JP. Montani (1), Z. Yang (1).
Vascular Biology, Department of Medicine, Division of Physiology (1) and Biochemistry (2), University of Fribourg, Switzerland.

Background: Endothelial nitric oxide (NO), the important protective factor in cardiovascular system, is synthesized from L-arginine via endothelial NO-synthase (eNOS). L-arginine can be hydrolyzed to L-ornithine and urea by arginase. Therefore, an enhanced arginase activity in endothelial cells would decrease bioavailability of L-arginine for NO production. The aim of the study is to investigate regulatory mechanisms of arginase activity in endothelial cells and in atherosclerosis.
Methods and results: Human endothelial cells (HUVECs) were isolated from umbilical veins. Arginase activity was measured by urea production. Protein expression of two arginase isoforms I and II was analyzed by immunoblotting using specific antibodies. In HUVECs, thrombin at a concentration of 1 U/ml for 24 hours significantly increased arginase activity (2-fold, p<0.001) without affecting arginase gene expression. Moreover, the thrombin-induced increase in arginase activity was suppressed by the HMG-CoA reductase inhibitor fluvastatin which inhibits RhoA or Y-27632, an ROCK inhibitor. In addition, adenoviral overexpression of active RhoA or ROCK mutant enhanced arginase activity in endothelial cells. Furthermore, an increased arginase activity (150% increase), which is co-incided with an overexpression of RhoA (4-fold increase), was observed in aorta of ApoE-/- mice as compared to wild-type mice.
Conclusions: Thrombin enhances arginase activity via RhoA/ROCK in human endothelial cells. In atherosclerosis, arginase activity is significantly increased, associated with an increased RhoA expression. Inhibition of arginase activity may represent another novel beneficial mechanism for protective role of statins in endothelial function.