Peptide neurotransmitters play important roles in the neuronal networks regulating appetite in several brain regions, including brainstem feeding centers such as the nucleus tractus solitarius (NTS) and hypothalamus. One such peptide, cocaine- and amphetamine-regulated transcript (CART), appears to act as a downstream mediator integrating peripheral metabolic signals including glucagon like peptide 1 and cholesytokinin. Central injection of CART inhibits food intake in multiple animal models and global deletion of CART leads to exaggerated food intake and increased susceptibility to a high fat diet in mice. Additionally, central CART neurons appear to play a role in whole body glucose homeostasis and meal patterning. To date, the identity of the CART receptor(s) has remained elusive, thus limiting the therapeutic potential of CART analogs for the treatment of obesity and associated eating disorders. CART activates downstream signaling cascades typical of those associated with G protein coupled receptors (GPCRs). Using our unique Deductive Reasoning Ligand-Receptor matching strategy, we identified the orphan GPCR, GPR160, to be a receptor for CART. In this Research Plan, we propose to test the overall hypotheses that activation of GPR160 is necessary for the biologic effect of CART peptides and that endogenous GPR160 plays a significant role in the regulation of appetite and metabolic function. We will test these hypotheses in four Specific Aims using a combination of cutting edge molecular techniques and innovative animal models. S.A. 1: Examine the functional and physical relationship between CART and GPR160. S.A. 2: Investigate the role of endogenous GPR160 in the short-term regulation of appetite and metabolism. S.A. 3: Investigate the role of endogenous GPR160 in the hypothalamic regulation of appetite and stress hormone secretion. S.A. 4: Establish a genetic model of GPR160 absence to investigate the importance of the receptor in the long term regulation of metabolic function. The proposed studies will further evaluate the functional and physical relationship between GPR160 and CART, establish CART and GPR160 as an important ligand-receptor pair in the short term and long term regulation of metabolic function, and produce innovative research tools, such as the GPR160-flox rat.
Obesity and metabolic disease are common health issues that have grave implications and broad impact on individual patients and the healthcare system in general. Our discovery of the protein that receives feedback signals from the gut and thus functions to curb appetite, promises the possible development of novel therapeutic approaches for the treatment of obesity and metabolic disease. The proposed work will establish that target and begin the development of those novel therapeutics.