PROJECT SUMMARY Obesity is a major risk factor for chronic diseases, such as cardiovascular and metabolic diseases, and its global prevalence parallels the overconsumption of calorie-dense diets. Gastric bypass surgery is currently the only effective treatment for maintaining weight loss. However, surgery is expensive, invasive, and reserved for people with severe obesity. The effectiveness of gastric bypass surgery is partly attributed to a shift in the composition of the gut microbiota and microbial metabolites, and to the increased production of peripheral satiety hormones. Vagal afferent neurons (VANs) are located in the gut wall, express receptors for peripheral hormones and microbial metabolites, and transmit satiety signals from the gastrointestinal tract to the brain to inhibit food intake. The G-protein coupled receptor 35 (GPR35) is activated by microbial metabolites and is highly expressed on VANs. Recent evidence demonstrates GPR35 on VANs is co-localized with CCKAR, the receptor for mediating the satiety-inducing effects of the enteroendocrine hormone, cholecystokinin (CCK). Desensitization of VANs to intestinal satiety signals, including CCK, precedes high-fat diet-induced weight gain and hyperphagia in mouse models of human obesity and leads to increased food intake. High-fat diet has been shown to reduce plasma levels of kynurenic acid, a microbial metabolite that is an endogenous GPR35 ligand. However, the role of GPR35 in peripheral satiety signaling is unknown. Preliminary data show that activation of GPR35 using the GPR35 agonist, zaprinast, decreases food intake in mice and in vitro experiments demonstrate that GPR35 inhibition decreases the sensitivity of VANs to CCK. Therefore, we hypothesize that high-fat diet decreases the production of microbially-derived GPR35 ligands, leading to reduced VAN sensitivity to CCK, suppression of intestinal satiety signaling thereby increasing energy intake. The hypothesis will be tested in two aims. Aim 1 will determine the interaction of CCKAR and GPR35 in activation of VANs and second order neurons in the brain, and in inhibiting food intake. Aim 2 will determine whether increasing availability of GPR35 ligands, either by administration of prebiotics or probiotics, can restore HF-diet induced impairment of VANs and control food intake. The hypothesis will be tested using a combination of in vitro, intravital, and in vivo techniques including calcium imaging, RNA interference knockdown of GPR35 in VANs, and automated feeding behavior monitoring. Successful completion of these studies will demonstrate the role of GPR35 in peripheral satiety signaling and reveal a potential therapeutic target for treating obesity. The training plan will be facilitated by the mentorship of my sponsor and the exceptional facilities at UC Davis. This proposal describes an integrative and comprehensive training plan to support scientific and professional development and propel me toward my long-term goal of bec...