Interaction of Estrogen and AMPK in the Hypothalamus

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DESCRIPTION (provided by applicant): The goal of this project is to determine the mechanism by which estradiol affects the food intake pathway in the mammalian hypothalamus. Obesity is of growing concern in Western society, mainly due to its associated pathologies, including diabetes, atherosclerosis, and heart disease. In women, decreases in estradiol occur during menopause and may lead to hyperphagia and obesity. Estradiol is anorexigenic in rodents and humans. Food intake is regulated by a variety of exigenic neuropeptides (neuropeptide Y, NPY; agouti-related protein, AgRP) and anorexigenic neuropeptides (pro- opiomelanocortin, POMC) that act in the hypothalamus. All of these neuropeptides appear to be estrogen-regulated and neurons expressing these peptides also express estrogen receptors. NPY, AgRP, and POMC are also regulated by the cellular energy sensing enzyme AMP-activated protein kinase (AMPK), which is phosphorylated (pAMPK) by the enzyme liver kinase B1 (LKB1) and activated when a decrease in the AMP:ATP ratio signals low endogenous energy. Activation of AMPK results in an increase in food intake. Ovariectomized female rats (lacking estradiol) become obese and have increased expression of hypothalamic pAMPK; however, the mechanism by which estradiol affects hypothalamic AMPK is unknown. The hypothesis of this proposal is that estradiol, acting through estrogen receptor ¿ (ER¿), decreases expression of LKB1, thereby decreasing phosphorylation and activation of AMPK and reducing food intake. To test this hypothesis, changes in gene and protein expression of LKB1 and AMPK will be examined both in vitro and in vivo in the presence and absence of estradiol, utilizing cell culture, transfection, Western blotting, quantitative RT-PCR, ovariectomy and intracerebroventricular injection. Preliminary data suggest that estradiol treatment in N-38 hypothalamic cells decreases the proportion of active to inactive AMPK, and decreases relative abundance of NPY, in effect signaling an environment of high available energy. These data point to a potential mechanism for estradiol to impact energy balance by preventing the phosphorylation and activation of AMPK. Therefore, the purpose of this project is to test the hypothesis that estradiol impacts the hypothalamic food intake pathway through its actions on AMPK, thereby shedding light on the cellular pathways underlying obesity and providing information for possible pharmacological interventions on the pathologies associated with the condition of obesity. PUBLIC HEALTH RELEVANCE: As of 2010, approximately one third of the U.S. population was considered obese (BMIe30), and no state had less than 20% obesity in its adult population (CDC BRFSS 2010). Obese individuals are at increased risk for heart disease, diabetes, certain cancers, stroke and reproductive problems, and health problems related to obesity cost about $147 billion per year (Finkelstein et al. 2009). The proposed project will investigate the cellular mechanisms underlying the interaction between food intake and reproductive hormones, and the results may be useful in mitigating the pathological effects of certain types of obesity.