Endothelial Mineralocorticoid Receptors: Novel Mechanism for Sex-Discrepancies in Vascular Disorders Associated with Obesity

Project Summary The rising obesity epidemic affects more women than men and obese premenopausal women are at higher risk for development of cardiovascular disease (CVD) than men. The mechanisms that underlie this loss of protection from CVD in young obese women are unknown. The adipose-derived hormone leptin plays a significant role in CVD in obesity. Leptin-mediated sympatho-activation in obese male animals specifically increases blood pressure. In contrast, our lab has published that leptin-induced CVD in females involves activation of the aldosterone-mineralocorticoid receptor (MR) axis. Preliminary data in this proposal demonstrates that there is a sex-discrepancy in aldosterone sensitivity. Our results show that vessels from female mice develop endothelial dysfunction in response to acute aldosterone exposure, whereas those from males do not. In addition, female mice have ~3-4-fold higher expression of the endothelial cell mineralocorticoid receptor (ECMR). In addition, the sex-difference in ECMR expression is exacerbated in obese females compared to obese males. Suppression of female sex hormones by ovariectomy ablates the sex difference in ECMR expression, which is restored with the female sex hormone progesterone. Furthermore, female mice with deletion of ECMR do not develop leptin-induced endothelial dysfunction. Collectively, these data suggest that ECMR mediates the increased sensitivity to aldosterone in obese premenopausal females. We, therefore, hypothesize that ECMR mediate obesity-associated, leptin-induced endothelial dysfunction and hypertension in obese female mice. We will test this hypothesis in two Specific Aims. Experiments described for Specific Aim 1 will determine if ECMR expression is increased in female mice when progesterone levels are endogenously elevated as well whether progesterone receptor inhibition in female obese mice ablates the sex-difference in ECMR expression. We will also determine if progesterone activates MR promoter activity up- or down-regulates microRNAs. The results of this aim will determine whether progesterone inhibition downregulates ECMR in females. Specific Aim 2 will determine if increases in ECMR expression in females mediates leptin-induced hypertension and endothelial dysfunction. We will assess blood pressure and endothelial dysfunction in ECMR knockout mice. In addition, we will investigate whether conditional ECMR overexpression ablates the sex difference in leptin-induced endothelial dysfunction and hypertension. Collectively, these studies will assess if progesterone mediates increased ECMR activation in obese females and if ECMR is required for leptin-induced CVD in females. These data will increase our knowledge of mechanisms that contribute to CVD in obese premenopausal women, and will give evidence for whether pharmacological progesterone inhibition is a potential treatment strategy for CVD in obese women.