Hypertension overrides the protective effect of female hormones on the development of aortic aneurysm secondary to Alk5 deficiency via ERK activation.

The prevalence of aortic aneurysm is five times higher in men than women among the general population. Similar sexual dimorphism also exists in syndromic aortic aneurysms triggered by TGF-ß signaling disorders. To understand the responsible mechanisms, we developed an animal model where inducible deletion of the type I TGF-ß receptor, Alk5, specifically in smooth muscle cells (Alk5iko) causes spontaneous aortic aneurysm formation. This model recapitulated an extreme scenario of the dimorphism in aortic aneurysm development between genders. In a comparative experiment, all Alk5iko males (n=42) developed aortic aneurysms and 26% of them died prematurely from aortic rupture. In contrast, the Alk5iko females (n=14) presented only a subclinical phenotype characteristic of scarcely scattered elastin breaks. Removal of male hormones via orchiectomy (n=7) resulted in only minimal influence on aortic pathology. However, reduction of female hormones via ovariectomy (n=15) increased the phenotypic penetrance from zero to 53%. Finally, an elevation of systolic blood pressure by 30 points unmasked the subclinical phenotype of Alk5iko females (n=17) to 59%. This exaggerated phenotypic penetrance was coupled with an early intensification of ERK signaling, a molecular signature that correlated to 100% phenotypic penetrance in normotensive Alk5iko males. In conclusion, aortic aneurysm induced by Alk5iko exhibits dimorphic incidence between genders with females less susceptible to aortic disease. This sexual dimorphism is partially the result from the protective effects of female hormones. Hypertension, a known risk factor for aortic aneurysm, is able to break the female sex protective effects through mechanisms associated with enhanced ERK activity.