The long range goal of the proposed research is to elucidate the mechanisms by which 17?-estradiol (E2) signals in hypothalamic neurons to control energy homeostasis. At the core of the regulation of energy homeostasis, and hence the central feedback of insulin (and leptin), are the hypothalamic arcuate proopiomelanocortin (POMC) and neuropeptide Y/agouti related peptide (NPY/AgRP) neurons. These neurons form a reciprocal circuit that controls energy homeostasis. We have recently discovered that both leptin and insulin depolarize POMC neurons via activation of canonical transient receptor potential (TRPC) channels, and hyperpolarize NPY/AgRP neurons via activation of KATP channels. Moreover, E2 exerts rapid effects through a putative Gq coupled membrane estrogen receptor (GqmER) that either attenuates or augments GABAB mediated inhibition to increase POMC or decrease NPY/AgRP neuronal excitability, respectively. Given the functional convergence of E2 and insulin in the hypothalamus, we propose the novel hypothesis that E2 signaling pathways act in concert with the insulin signaling pathway to upregulate POMC and downregulate NPY/AgRP neuronal excitability and gene expression in a cell specific manner. These estrogenic actions protect against the development of diet induced insulin resistance in POMC neurons. Elucidating the cell specific signaling pathways and gene expression at the single cell level will help in developing new therapies for targeting hormone actions in CNS neurons and also for countering insulin resistance in CNS neurons that leads to diabetic neuropathy and stroke. Our multidisciplinary approach incorporates a unique array of cellular, molecular and optogenetic tools and our combined expertise in electrophysiology, chemical genetics, molecular biology, histochemistry and whole animal physiology.
Our specific aims are the following: (1) To elucidate the cellular/molecular mechanisms by which insulin activates TRPC channels in POMC neurons;(2) to elucidate the mechanism by which E2 augments insulin signaling in POMC neurons;(3) to elucidate the direct inhibitory effects of POMC synaptic input to NPY/AgRP neurons using optogenetic stimulation of POMC neurons and recording of postsynaptic inhibitory responses in NPY/AgRP neurons;and (4) to elucidate the changes in insulin signaling in POMC neurons associated with diet induced insulin resistance. Women show increased risk of insulin resistance in hypoestrogenic states (e.g., with the onset of menopause), which in turn can lead to severe injury to the nervous system as seen in diabetic neuropathies and stroke. Therefore, a greater understanding of how E2 protects against insulin resistance and specifically how E2 signaling cross talks with insulin signaling wil provide unique insights and novel approaches to prevent insulin resistance in the CNS.
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