This project focuses on understanding a fundamental cellular mechanism underlying the control of feeding and obesity in humans. The mechanism uses an ancient cellular signaling organelle, the primary cilium, to control responses to satiety signals generated following feeding. Bardet-Biedl syndrome (BBS) is a rare human syndrome called a ciliopathy because of mutations in genes encoding components of the primary cilium. Patients with mutations in BBS genes have inherited mutations in genes linked to a complex called the BBSome, discovered in our laboratory, that fail to present G-protein coupled receptors critical to controlling feeding after a meal. An additional pathway organized by the Tubby/TULP3-IFT-A complex is essential for entry of GPCRs and other signaling molecules into cilia. These trafficking pathways control essential GPCRs that regulate feeding and satiety in the hypothalamus and defects in cilia cause a loss of feeding control. Our work has found that cilia also control the generation of fat tissue and the secretion of insulin via the pancreas, adding peripheral control to CNS regulation. We have found in ciliopathies, monogenic obesity syndromes and now GWAS studies that mutations in structural or signaling components, or in the receptors themselves can cause strong defects in ciliary signaling. Our current hypothesis is that the sum of these diverse mutations in ciliary genes underlie some of the complex, polygenic nature of obesity and metabolic disease. We have previously searched GPCRs known to be linked to metabolism and found many localized to cilia including three new receptors described here GPR45, GPR63 and GPR135. These receptors have specific links to obesity and metabolic disease including preliminary mouse data and human Genome Wide Associations Studies. Finding one or more these receptors linked to metabolic disease may offer new understanding and new targets for much needed therapeutics for obesity or diabetes. Creating these first models will also facilitate intercrossing of these mice and other ciliary drivers of obesity to build a better picture of the complex polygenic drivers of obesity and diabetes. The preliminary studies proposed here would thus serve as a bridge to later funding focused on the best candidates discovered in these screening studies here. The specific aims are: Aim 1 Construct mouse KOs of GPR45, GPR63 and GPR135 and test for obesity phenotypes; Aim 2 Use newly produced antibodies to determine the target tissues for these orphan GPCRs; and Aim 3 Use tissue proteomics of KO mice to understand the molecular phenotypes of signaling. By identifying signaling pathways defective in obesity and diabetes, we can identify targets to protect or restore these tissues and molecular profiles of patients to facilitate patient selection.

Project Narrative This project seeks to understand fundamental mechanisms controlling feeding and obesity in humans, organized in part by the primary cilium, an ancient signaling organelle in the cell. We have found three new conserved G-protein coupled receptors (GPCRs) localized to cilia in tissues important for metabolism in brain and endocrine organs and these GPCRs are linked to human genetic mutations involved in obesity, diabetes and metabolic disease. Here we will knockout the mouse genes for these receptors to test obesity and metabolic defects, determine the key tissues expressing these receptors and the effect on tissues using proteomics technology, thus identifying new potential targets for metabolic disease and building our diagnostic profile for drivers of metabolic disease and obesity to allow precision medicine for patients.