Recent work has continued to challenge and expand our views on the neural control of body weight. Leptin receptors have been shown to engage multiple signaling pathways in a neuron-specific pattern. The overall goals of our proposal are to decipher the crosstalk between the cAMP/PKA signaling system and the leptin receptor-initiated signals in neuronal pathways that regulate feeding and energy expenditure. Mouse genetic techniques allow us to investigate this problem in a physiological setting and also provide us with novel tools for defining regulation at the molecular level. We propose to use our newly developed ribosome-tagging approaches (RiboTag) to quantitate the translatome (mRNAs actively engaged on polyribosomes) in specific subtypes of hypothalamic neurons. Our focus will be on those groups of neurons that respond to the adipocyte-synthesized hormone, leptin, and also express the RIIb regulatory subunit of PKA. The RIIb-PKA KO mouse line is lean and resistant to diet-induced obesity and our recent results indicate that this is because of an increase in leptin sensitivity in the hypothalamus.
The specific aims of this proposal are: (1) Analyze the regulation of mRNA expression/translation in specific hypothalamic cell types by diet and hormones (2) Identify the nutritional regulators of PKA activation in the hypothalamus (3) Develop a strategy to increase the sensitivity of hypothalamic neurons to leptin by pharmacological regulation of the cAMP/PKA pathway. At the conclusion of these studies we will have completed a comprehensive analysis of mRNA transcripts in key hypothalamic neuronal populations as they respond to nutritional signals. We also expect to gain a better understanding of the mechanisms by which PKA activity can modulate leptin signaling and adiposity. The sensitivity of the hypothalamic response network to leptin is one of the ultimate determinants of how much energy an organism will store as fat. The cAMP/PKA system is well suited to pharmacological manipulation by agonists and antagonists of G-protein coupled receptors, phosphodiesterase inhibitors, and kinase activators and inhibitors. Our proposal seeks to identify potential targets within hypothalamic neurons that might be exploited to modulate leptin sensitivity as a therapeutic approach to the treatment of obesity.
The combination of high caloric diets and lack of exercise leads to obesity and greatly increases the risk of adult onset diabetes, hypertension, and other adverse cardiovascular problems. Using a mouse model we have discovered a mutation in the cAMP/PKA signaling system that enhances the response of the brain to a hormone, leptin that is produced in fat cells and tells us to stop eating and increase metabolism. Mice with this mutation are resistant to diet-induced obesity and our proposal will study the mechanism of this protective effect with the goal of developing a therapy that will induce resistance to diet-induced obesity in humans.
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