Menopause represents a shift from a period of cardiovascular protection to cardiovascular risk, and thus provides an opportunity to define mechanisms that confer cardiovascular protection. Increased cardiovascular risk after menopause is associated with the metabolic complications of obesity arising from hepatic insulin resistance. Hepatic insulin resistance contributes to hyperglycemia and dyslipidemia characterized by increased very low density lipoprotein (VLDL) and low levels of high density lipoprotein (HDL). The transcription factor forkhead box O1 (FoxO1) acts as an energy sensor in the liver to help coordinate glucose and lipid metabolism. Insulin signaling inactivates FoxO1, which decreases hepatic glucose production and VLDL secretion. With high-fat feeding, insulin resistance arises in the liver, and insulin fails to inactivate FoxO1, resulting in increased glucose production, and secretion of VLDL. We have found that female mice with intact estrogen signaling are able to inactive FoxO1 in the liver despite high-fat feeding and decreased insulin action to AKT, but that after surgical menopause by ovariectomy this protection from insulin resistance is lost. Additionally, inactivation of FoxO1 in the liver prevents triglyceride elevations after ovariectomy. Our overarching hypothesis is that hepatic estrogen signaling mediated by estrogen receptor alpha (ER1) promotes insulin sensitivity by bypassing the signaling defect to FoxO1 created by high-fat feeding. In our first AIM, we use metabolic clamp techniques in mice with a liver-specific deletion of the ER1 gene to assess if hepatic estrogen signaling can promote insulin sensitivity. In our second AIM, we determine if hepatic estrogen signaling is sufficient to prevent, ameliorate, or delay high fat diet-induced insulin resistance. In our third AIM, we determine if genetic inactivation of FoxO1 can prevent glucose intolerance caused by high-fat feeding after surgical menopause by ovariectomy. These experiments apply an innovative approach to simultaneously quantify whole-body and liver insulin sensitivity, trace hepatic handling of glucose, and define molecular targets which may augment glucose metabolism after menopause. Obesity and insulin resistance affect the Hispanic and African American community in a disproportionate manner. This award will not only make it possible for me as an under- represented minority to pursue a research career but may also impact the disparities in cardiovascular disease for minority populations. The support of the Ruth L. Kirchstein National Research Service Award to promote diversity in health related research will make it possible to understand the mechanisms of cardiovascular disease associated with diabetes and obesity.
At menopause, women have a rapid increase in the risk of cardiovascular disease related to the complications of obesity, but the mechanisms of how menopause increases the risk of cardiovascular disease are not well defined. In this project we define how estrogen signaling in the liver protects from metabolic complications of insulin resistance arising from obesity. Understanding molecular pathways by which estrogen confers protection against cardiovascular disease may lessen the impact of obesity for both women and men.
|Cappel, David A; Palmisano, Brian T; Emfinger, Christopher H et al. (2013) Cholesteryl ester transfer protein protects against insulin resistance in obese female mice. Mol Metab 2:457-67|