ABSTRACT Research Project Leader - Lin Imbalanced gut microbiome (i.e., dysbiosis) and altered intestinal mucosal immunity are leading factors for developing several chronic diseases, including obesity and type 2 diabetes mellitus (T2DM). Proper dietary patterns can promote healthy microbial community composition, metabolism, and function, thereby preventing and/or slowing the progression of these diseases. Dietary carotenoids are beneficial food bioactive compounds for human health. For example, zeaxanthins are essential pigments for macula in the human eye. Low plasma levels of carotenoids, such as zeaxanthins, are associated with the progression of obesity and T2DM in humans. Therefore, there is an urgent need to determine the roles zeaxanthin plays in the development of obesity and T2DM. The Research Project Leader’s preliminary findings in animal models indicate that dietary zeaxanthins reduce pro-inflammatory cytokines (such as IL-17A), increase colonic goblet cell numbers, and alter the cecal microbiota composition. Germ-free C57BL/6J (GF) recipient mice gained significantly less weight and had a decreased elevation of blood glucose levels when colonized with fecal microbiota from diabetic db/db mice fed a zeaxanthin diet, compared to GF mice receiving fecal microbiota from db/db mice fed a chow diet. Despite the recent progress outlined above, a substantial knowledge gap regarding the interplay of dietary zeaxanthin, gut microbiota, and the host intestinal mucosal immunity during the progression of obesity and T2DM remains. The central hypothesis of this proposal is that dietary zeaxanthin effectively reduces intestinal immune response and inflammation by the gut microbiota. This project’s objective is to determine the underlying mechanism by which the zeaxanthin diet, gut microbiome, and host intestinal mucosal immunity interact to prevent the progression of obesity and T2DM through the following two specific aims: 1) Determine how dietary zeaxanthins modulate intestinal mucosal immunity through the gut microbiome in the early stages of obesity and diabetes. 2) Determine mechanistically how the gut microbiota alters the chemistry of dietary zeaxanthins. The results from this research are expected to provide a deeper understanding of the bidirectional interaction between dietary zeaxanthins and the gut microbiota-immune axis in regulating gut health and diseases. These studies will also reveal the importance of the interplay of zeaxanthin-gut microbiota on host intestinal immunity. Thus, this research will significantly impact public health by advancing our understanding of dietary intervention of carotenoids in these high-risk populations of obesity and T2DM. Moreover, completing these studies will further empower RPL's program in microbiology and immunology and ultimately elevate his career to become an independent NIH PI (e.g., with a funded R01).