ABSTRACT IBDs affect 1.3% of U.S. adults. Despite the success of antibody therapies targeting TNFα and IL-23, a significant fraction of patients does not achieve remission, necessitating the search for novel pathogenic pathways that can be targeted. The pathogenesis of IBD is dependent on proper regulation of intestinal immunity. Given their constitutive presence in the intestinal mucosa, group 3 innate lymphoid cells (ILC3) play a pivotal role in maintaining intestinal homeostasis. ILC3 are vital for defense against extracellular bacteria through the secretion of IL-17 and IL-22. However, in mouse models of innate immune colitis, inappropriate activation of ILC3 is a main driver of pathology. Thus, a comprehensive understanding of ILC3 biology is crucial for potentially targeting their role in IBD. Due to their proximity to the intestinal lumen, ILC3 make a number of metabolic adaptations to accommodate the surrounding environment. To systematically characterize these adaptations, we performed untargeted metabolomic profiling of the major intestinal ILC subsets. In combination with analysis of previously generated RNA- sequencing data from intestinal ILCs, we identified a significant enrichment of polyamines and polyamine metabolic enzymes in ILC3. Polyamines are products of arginine metabolism with diverse functions in cancer, aging, and autoimmunity. Mechanistically, they participate in proliferation, chromatin accessibility, as well as translation elongation and termination. Preliminary data shows that dietary polyamines positively regulate the abundance of ILC3. We also found that inhibition of polyamine synthesis using the drug DFMO impairs IL-22 production by ILC3. Furthermore, administration of DFMO in vivo has been shown to exacerbate infection by the intestinal pathogen C. rodentium. Considering these premises, we hypothesize that polyamines positively regulate ILC3 function and contribute to the immunoregulatory role of ILC3 in colitis. We will interrogate these hypotheses in the following aims: Aim 1: To evaluate the impact of intracellular polyamines on ILC3 function at steady state. Synthesis of polyamines is dependent on the rate-limiting enzyme ODC1. We have generated RorcCreOdc1flox/flox mice, in which polyamine biosynthesis is genetically ablated in all conventional T cells and ILC3. By studying these mice (Odc1ΔILC3/T), we will selectively interrogate the importance of polyamines in abundance, functional capacity and proliferation of ILC3. Aim 2: To assess the contribution of ILC3-intrinsic polyamine metabolism in a model of infectious colitis. We will assess the function of Odc1-deficient ILC3 during a model of attaching effacing bacterial colitis, the C. rodentium model, which is highly dependent on ILC3-derived IL-22 for protection. These studies will further our understanding of the metabolic adaptations of ILC3 as well as the potential role for targeting these metabolic pathways to treat inflammatory bowel diseases.

PROJECT NARRATIVE Inflammatory bowel diseases affect 1.3% of U.S. adults. Despite the success of antibody therapies that attenuate excessive intestinal inflammation and immune responses, a significant fraction of patients does not achieve remission, necessitating the search for novel pathways that can be targeted. Here we propose to temper the inflammatory potential of intestinal immune cells by targeting their metabolism, which relies on the production of metabolites known as polyamine.