CNS EFFECTS OF ADIPOKINES ON METABOLISM

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Obesity has reached epidemic proportions and poses serious public health challenges, in particular type 2 diabetes, cardiovascular disease, sleep apnea, osteoarthritis and cancer. Adipocyte hormones may provide key insights into the pathogenesis of obesity-related diseases. Leptin and adiponectin stimulate fatty acid oxidation, decrease lipid levels and increase insulin sensitivity. In contrast, resistin decreases insulin sensitivity, and increases glucose and lipids. Leptin acts in the CMS to suppress appetite and increase energy expenditure, but also has direct effects on peripheral tissues. Adiponectin and resistin have direct actions on liver and muscle, but recent observations suggest that these adipokines also have central effects. We hypothesize that the divergent effects of these adipocytes on metabolism are mediated, at least in part, through distinct neuronal targets and signaling pathways in the hypothalamus. Specific Aim 1 will compare the effects of CMS administration of leptin, adiponectin and resistin on energy and glucose metabolism. We will examine the regulation of peripheral glucose fluxes using insulin clamp and radioactive tracer kinetics. Based on our preliminary studies showing an attenuation of the CMS effects of leptin and adiponectin in agouti mice, we will determine whether the opposite effects of leptin/adiponectin versus resistin on glucose levels is mediated through melanocortin (MC)4 receptor signaling. Specific Aim 2 will determine the sites of action of these adipocyte hormones in the hypothalamus, using Fos immunohistochemistry and in situ hybridization. Finally, Specific Aim 3 will determine whether the opposing metabolic effects of leptin, adiponectin and resistin occur through AMP-kinase and SOCS-3 in the hypothalamus. We will test the hypothesis that central administration of resistin antagonizes the central effects of leptin and adiponectin on metabolism, through reciprocal regulation of AMPK, SOC-3, or both signaling pathways. Understanding the hypothalamic and signaling pathways that mediate the effects of leptin, adiponctin and resistin will provide novel insights into the pathophysiology of obesity and diabetes that will facilitate novel diagnostic and treatment strategies.