Project Summary The intestine serves both as a conduit for the uptake of food-derived nutrients and as a barrier that prevents host invasion by microorganisms. This barrier function is important to maintain intestinal integrity and it is promoted by immune cells, which can quickly respond to microbial presence in intestinal lumen coordinating protective functions. Alterations in timing of food intake and diet composition have been associated with the development of immune-mediated intestinal dysfunctions (e.g. irritable bowel syndrome). However, despite its profound biological and clinical relevance, there is a major gap in our understanding of how intestinal immune responses are modulated by food presence in the intestinal tract. The long-term goal of this proposal is to determine how, during feeding, dietary-derived signals are sensed in the intestine and promote alterations in intestinal immune responses. Recently, we uncovered a neuroimmune circuit that coordinates intestinal immune- mediated barrier functions in response to food consumption. This neuroimmune circuit is formed by the interaction of vasoactive intestinal peptide-producing enteric neurons (VIPens) and type 3 innate lymphoid cells (ILC3s). VIPens are activated by the presence of food in the intestinal tract, they directly inhibit ILC3 functions. Although VIPen-mediated inhibition of ILC3 during feeding reduces intestinal barrier functions, it also increases efficiency of fat absorption from the diet (immune-nutritional trade-off). Importantly, in experimental mouse models, perturbations in this neuroimmune circuit alters host resistance to enteropathogens and host-microbiota interactions. We propose to study the mechanism of activation of VIPens by dietary signals as an entry point to understand how feeding promotes alterations in intestinal immunity. A combination of cutting-edge technologies to measure neuronal activation in vivo (genetically encoded calcium indicators and intravital imaging), manipulate neuronal activity (chemogenetic tools and AAV-assisted CRISPR/Cas9-based genetic manipulation), dissect molecular profiles of cellular circuits (monosynaptic viral tracing and single cell genomics), and control ingestion of specific dietary signals (diet engineering), will allow us to acquire a mechanistic understanding of how food consumption can affect intestinal immunity through neuroimmune circuits. The Specific Aims of this proposal are: 1) to determine the nature of food-derived signals that, by triggering activation of VIPens, coordinate intestinal immune-nutritional trade-offs, and 2) to dissect the cellular and molecular pathways of VIPens activation by food-derived signals. These studies will provide the molecular underpinnings of how intestinal immune responses are being modulated by food consumption, as well as provide new insights of the intestinal mechanisms for sensing food-derived signals and orchestrating immune-nutritional trade-offs. These studies will also...