Abstract

BackgroundAbdominal aortic aneurysms (AAAs) occur predominately in males. However, AAAs in females have rapid growth rates and rupture at smaller sizes. Mechanisms contributing to AAA progression in females are undefined. We defined effects of ovariectomy, with and without 17-β estradiol (E2), on progression of established angiotensin II (AngII)-induced AAAs in female mice.MethodsWe used neonatal testosterone exposures at 1 day of age to promote susceptibility to AngII-induced AAAs in adult female Ldlr−/− mice. Females were infused with AngII for 28 days to induce AAAs, and then stratified into groups that were sham, ovariectomized (Ovx, vehicle), or Ovx with E2 administration for 2 months of continued AngII infusions. Aortic lumen diameters were quantified by ultrasound and analyzed by linear mixed model, and maximal AAA diameters were analyzed by one-way ANOVA. Atherosclerosis was quantified en face in the aortic arch. AAA tissue sections were analyzed for cellular composition. We quantified effects of E2 on abdominal aortic smooth muscle cell (SMC) growth, α-actin and transforming growth factor-beta (TGF-β) production, and wound healing.ResultsSerum E2 concentrations were increased significantly by E2. Aortic lumen diameters increased over time in sham-operated and Ovx (vehicle) females, but not in Ovx females administered E2. At day 70, E2 administration decreased significantly aortic lumen diameters compared to Ovx vehicle and sham-operated females. Compared to Ovx females (vehicle), maximal AAA diameters were reduced significantly by E2. AAA tissue sections from Ovx females administered E2 exhibited significant increases in α-actin and decreases in neutrophils compared to Ovx females administered vehicle. In abdominal aortic SMCs, E2 resulted in a concentration-dependent increase in α-actin, elevated TGF-β, and more rapid wound healing. E2 administration to Ovx females also significantly reduced atherosclerotic lesions compared to sham-operated females. This effect was accompanied by significant reductions in serum cholesterol concentrations.ConclusionsE2 administration to Ovx females abolished progressive growth and decreased severity of AngII-induced AAAs. These effects were accompanied by increased SMC α-actin, elevated TGF-β, and reduced neutrophils. Similarly, E2 administration reduced AngII-induced atherosclerosis. These results suggest that loss of E2 in post-menopausal females may contribute to progressive growth of AAAs.Electronic supplementary materialThe online version of this article (doi:10.1186/s13293-015-0030-1) contains supplementary material, which is available to authorized users.

Highlights

  • Abdominal aortic aneurysms (AAAs) occur predominately in males

  • Abdominal aortic smooth muscle cell (SMC) respond to 17-β estradiol (E2) with increased α-actin and transforming growth factor-beta (TGF-β) and exhibit more rapid wound healing To define mechanisms for protective effects of E2 on AAA progression, we examined concentration-dependent effects of E2 on abdominal aortic SMC proliferation, on proteins associated with AAA development, and on wound healing as an index of cell repair

  • While ovariectomy of female mice had no significant effect on aortic lumen or external AAA diameters, AAA tissue sections from Ovx females exhibited tissue remodeling that was reversed by E2 administration

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Summary

Introduction

Abdominal aortic aneurysms (AAAs) occur predominately in males. We defined effects of ovariectomy, with and without 17-β estradiol (E2), on progression of established angiotensin II (AngII)-induced AAAs in female mice. Male hypercholesterolemic mice exhibit a two- to threefold higher prevalence of angiotensin II (AngII)-induced AAA formation compared to females [3]. Adult female mice administered testosterone exhibited increased incidence of AngII-induced AAAs [4]. Few studies have incorporated interventions after an AAA is established and monitored effects of interventions on AAA progression This is significant because as AAA size increases, so does the propensity for aneurysm rupture which results in >80 % mortality [6,7,8,9,10]

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