Abstract 273: Smooth Muscle Cell Specific Beclin-1 Deficiency Accelerates Aortic Aneurysms In Male And Female Normolipidemic And Hypercholesterolemic Mice

Abstract

Background and Objective: Ascending and abdominal aortic aneurysms (AAs) are permanent dilations of the aorta with 80% mortality after rupture. Vascular smooth muscle cell (SMC)-rich aortic media is disrupted in AAs. Autophagy is a process by which cell recycles their cytoplasmic materials for energy purposes under stress. Recent clinical studies highlighted that Beclin-1, an autophagy induction gene, is upregulated in AA tissues from patients. Using Angiotensin II (AngII) infusion model of AAs, we examined the functional role of SMC-derived Beclin-1 during AA development in normolipidemic and hypercholesterolemic mice. Methods and Results: Mice with inducible deletion of Beclin-1 in SMCs were produced by breeding male Acta2-Cre ERT2 hemizygous mice female Beclin-1 floxed mice in normolipidemic and hypercholesterolemic (LDLR-/-) background. At 8 weeks of age, Beclin-1 x Acta2-Cre ERT2 (Cre+) and non-Cre littermates (Cre-) mice were injected with tamoxifen (75 mg/kg, i.p.) for 5 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 SMC-Beclin-1, normolipidemic or hypercholesterolemic male Cre+ and Cre- (N=7 per group) mice were fed either chow or fat-enriched diet (21% fat; 0.15% cholesterol) for 5 weeks. After 1 week of diet feeding, mice were infused with saline or low dose of AngII (500 ng/kg/min) by osmotic mini-pumps for 4 weeks. SMC-Beclin-1 deficiency in either normolipidemic or hypercholesterolemic mice spontaneously but significantly accelerated ascending (Cre-: 1.2 ± 0.07 vs Cre+: 1.8 ± 0.04 mm; P <0.001), arch (Cre-: 1.1 ± 0.04 vs Cre+: 1.8 ± 0.03 mm; P <0.001), descending (Cre-: 1.1 ± 0.04 vs Cre+: 1.5 ± 0.04 mm; P <0.001), and abdominal (Cre-: 1.0 ± 0.02 vs Cre+: 1.5 ± 0.14 mm; P <0.001) aortic expansion. AngII-infusion had no additional influence on SMC-Beclin-1 deficiency accelerated aortic expansion. In addition, SMC-Beclin-1 deficiency significantly increased aortic medial hypertrophy and elastin breaks (P<0.001 Cre- vs Cre+) associated with complete loss of medial alpha-SMC actin positive area. Conclusion: These findings demonstrate that SMC-Beclin-1 plays a critical role in suppressing aortic aneurysmal formation in mice.