Abstract 358: Smooth Muscle Cell Specific Beclin-1 Deficiency Accelerates Ascending And Abdominal Aortic Aneurysms In Male Hypercholesterolemic Mice Infused With Angiotensin Ii

Abstract

Background and Objective: Ascending and abdominal aortic aneurysms (AAs) are permanent dilations of the ascending and abdominal aorta with a mortality greater than 80% after rupture. Vascular smooth muscle cells (SMCs) are pivotal in maintaining aortic structural integrity and function, and SMC-rich aortic medial stability is highly disrupted in AAs. Autophagy is a self-regulatory process by which cell digest, and recycles their cytoplasmic materials for energy purposes under stress. Recent clinical studies highlighted that Beclin-1, a gene indispensable for autophagy induction, is highly upregulated in AA tissues from patients. However, the functional contribution of SMC-derived Beclin-1 in the development of AAs is unknown. Using the well-established Angiotensin II infusion model of AAs, we examined the role of SMC-Beclin-1 during the development of AAs in hypercholesterolemic mice. Methods and Results: Mice with inducible deletion of Beclin-1 in SMCs were produced by breeding male mice hemizygous for Acta2-Cre ERT2 (Cre+) to female Beclin-1 floxed mice in an LDLR -/- background. At 8 weeks of age, male Beclin-1 x Acta2-Cre ERT2 (Cre+) and non-Cre littermates (Cre-) mice were injected with tamoxifen (75mg/kg, i.p.) for 5 consecutive days. After 2 weeks, Western blot analyses showed depletion of Beclin-1 protein in the aortic media from Cre+ mice compared to Cre- littermates. To study the role of Beclin-1in SMCs, male Cre+ and Cre- (N=5-6/group) mice were fed a fat-enriched diet (21% fat; 0.15% cholesterol) for 5 weeks. After 1 week of diet feeding, mice were infused subcutaneously with low dose of AngII (500 ng/kg/min) by osmotic mini-pumps for 4 weeks. Interestingly, depletion of Beclin-1 in SMCs significantly accelerated AngII-induced aortic luminal dilation (Cre-: 1.0 ± 0.02 mm, Cre+: 1.5 ± 0.14 mm; P < 0.001), and expansion of ex-vivo maximal diameters of abdominal aortas in mice (Cre-: 1.1 ± 0.1 mm, Cre+: 1.52 ± 0.1 mm; P < 0.05). In addition, SMC- Beclin-1 depletion significantly increased AngII-induced ascending aortic aneurysms (Cre-: 12.6 ± 0.4 mm 2 , Cre+: 20.9 ± 1.2 mm 2 ; P=0.008 ). Conclusion: These findings demonstrate that SMC-Beclin-1 plays a critical role in suppressing AngII-induced ascending and abdominal aortic aneurysm formation in mice.