Abstract 5222: Genetic Deficiency of Arginase II Reduces Endothelial Dysfunction and Atherosclerosis in ApoE-Knockout Mice

Abstract

Introduction: Arginase II is known to be one of the key mediator in vascular pathophysiology of cholesterol-medicated endothelial dysfunction by reciprocal regulation of NOS and NO production through substrate competition. We aimed to investigate whether the transgenic Arginase II inhibition could reduce the endothelial dysfunction and atherosclerosis in apolipoprotein E-knockout (ApoE-KO) mice. Methods and Results: ApoE-KO mice were bred on an arginase II KO (ArgII-KO) background. Mice that were homozygous deleted at both alleles were used in the study. Male 8 – 12 wk old Arg-KO mice, ApoE-KO mice, Arg/ApoE-KO (Dbl-KO) mice fed high cholesterol diet for 16 weeks, and age-matched wild type (WT) mice fed normal diet were enrolled. Arginase activity was significantly higher in the aorta of ApoE-KO mice than compared to WT mice (1612.2±445.9 pmol Urea/mg protein/min vs. 836.3±12.2 pmol Urea/mg protein/min, n=5, p < 0.01), but not detected in Arg-KO and Dbl-KO mice. We measured NO an ROS in vascular strips pinned down endothelial side up using the fluorescent probes DAF-FM diacetate and DHE. Dbl-KO mice showed significantly higher NO production (0.0737±0.0056 intensity/sec vs. 0.0256±0.0029 intensity/sec, n=6, p < 0.05) and lower ROS production than ApoE-KO mice (0.0676±0.0065 intensity/sec vs. 0.1147±0.01619 intensity/sec, n=6, p < 0.05). We tested endothelial dependent vasorelaxation in aortic rings in organ chambers. The vasorelaxation response to acetylcholine (Ach) in Dbl-KO mice was greater than in ApoE-KO mice (log EC 50 , −5.68 vs. −5.13, p <0.05), although it was less than in Arg-KO and WT mice. N G -nitro-L-arginine methyl ester (L-NAME) incubation didn’t only impair Ach response, but also abolished the inter-group difference. The aortic atheromatous plaque burden as measured by Sudan IV staining was significantly reduced in Dbl-KO group compared to ApoE-KO group (38.4±3.8% vs. 52.0±2.8%, n=6, p <0.01), No significant plaque was detectable in Arg-KO and WT mice. Conclusion: The genetic inhibition of Arginase II enhanced NO production, reduced ROS produnction restored endothelial function and lowered atheromatous plaque burden. Therefore, Arginase II represents a crtical novel target for atherosclerosis therapy.