Testosterone inhibits aneurysm formation and vascular inflammation in male mice

Abdominal aortic aneurysm (AAA), one of the pathological phenotypes of vascular aging, is characterized by aortic dilation with impaired arterial wall integrity. Recent epidemiologic studies have shown that men with AAA have lower serum testosterone compared to men without. However, the underlying mechanisms remain unclear. In this study, we investigated the effects of testosterone on AAA formation using a murine AAA model under the conditions of depletion and administration of testosterone. In wild-type male mice (C57BL/6J), AAA was induced by CaCl2 application and angiotensin II infusion at 5 weeks after castration. Exacerbated AAA formation was seen in castrated mice, compared with sham-operated mice. Histological analysis revealed marked infiltration of macrophages in the destroyed aorta and IL-6/pSTAT3 expression was significantly elevated, suggesting that AAA development by castration is attributable to pronounced inflammation. Conversely, both 4-week and 9-week administration of testosterone significantly prevented AAA formation, and improvement of histological findings was confirmed. Aortic F4/80, Il-1b and Il-6 expression were significantly inhibited both by testosterone administration. Indeed, mice with implanted flutamide exhibited exacerbated AAA formation and aortic F4/80, Il-1b and Il-6 expression were significantly increased. Taken together, these results demonstrate that testosterone depletion and AR blockade precede AAA formation, and conversely, testosterone administration could suppress AAA formation by regulating macrophage-mediated inflammatory responses. This anti-inflammatory action of testosterone/AR on AAA formation might provide a mechanistic insight into the vascular protective actions of testosterone and suggest that its proper administration or selective AR modulators might be novel therapeutic strategies for this aortic pathology.