Abstract 313: Protective Roles of Small GTP-Binding Protein GDP Dissociation Stimulator Against Angiotensin II-Induced Thoracic Aortic Aneurysm Formation and Rupture in Mice -A Possible Novel Therapeutic Target

Background: Statins reduce the incidence and development of thoracic aortic aneurysm (TAA) and rupture. We have previously identified that small GTP-binding protein GDP dissociation stimulator (SmgGDS) is a crucial mediator of the pleiotropic effects of statins. Methods and Results: To examine the role of SmgGDS in TAA formation, Apoe -/- and Apoe -/- SmgGDS +/- (DKO) mice were infused with angiotensin II (AngII, 1,000 ng/min/kg) for 4 weeks. There was no significant difference in blood pressure between the 2 genotypes in response to the AngII treatment. However, during the follow-up, 36% of DKO mice died suddenly due to TAA rupture, whereas there was no TAA rupture in Apoe -/- mice ( P n =14 each). Histological analysis of DKO mice showed dissections of major thoracic aorta in the early phase of AngII infusion (day 3~5). We performed ultrasound imaging every week to follow the serial changes in aortic diameters. Diameter of the ascending aorta was progressively and significantly increased in DKO mice compared with Apoe -/- mice (1.64±0.06 vs. 1.43±0.05 mm at 4 weeks, P n =14 each), whereas that of the abdominal aorta was comparable between the 2 genotypes. Indeed, there was no significant difference in the incidence of AngII-induced abdominal aortic aneurysm (AAA) formation between the 2 genotypes (both 75%). Western blotting demonstrated that AngII-induced activations of JNK and ERK were significantly higher in the thoracic aorta of DKO mice compared with Apoe -/- mice ( P n =6 each). For mechanistic analyses, we primary cultured aortic smooth muscle cells (AoSMCs) from the 2 genotypes. After AngII (100 nM) treatment for 24 hours, DKO AoSMCs showed significantly increased JNK activity, cyclophilin A secretion, and oxidative stress levels compared with Apoe -/- AoSMCs ( P n =6 each). Interestingly, AngII-induced upregulation of Nrf2, a master regulator of cellular responses against environmental stresses, was significantly less in DKO AoSMCs compared with Apoe -/- AoSMCs ( P n =6). Finally, expressions of matrix metalloproteinase-2 and -9 were significantly increased in DKO AoSMCs compared with Apoe -/- AoSMCs. Conclusions: These results suggest that SmgGDS is a novel therapeutic target for the prevention and treatment of TAA.