Sphingolipid Metabolism Controls Regulatory T cell Function and Intestinal Homeostasis - PROJECT ABSTRACT Inflammatory bowel disease (IBD) is characterized by inconsistent response to current therapies and persistent activation of pathogenic effector CD4+ T cells, implying that regulatory T cells (Tregs) are potentially dysfunctional. Recent evidence suggests that inflammatory-like Tregs are present in the intestinal lesions of individuals suffering from refractory IBD; however, the underlying mechanism and its contribution to IBD are poorly understood. Thus, the OVERALL OBJECTIVE of this proposal is to aid in the generation of more preliminary data for a planned R01 application that will explore the molecular mechanisms by which lipid metabolites enforce Treg phenotype and immunosuppressive function during chronic intestinal inflammation. These insights will facilitate the development of therapeutic strategies for manipulating Tregs to treat IBD. Untargeted metabolomics revealed that certain sphingolipids accumulate in human Tregs. This proposal aims to then explore how these lipids are synthesized and elucidate the importance of these lipids to metabolic homeostasis, cell signaling, and Treg function. Building on the unbiased metabolomics data, we also found that the abundance of these lipids in Tregs can be modulated by physiologically and pathophysiologically relevant signals. Therefore, we hope to explore the functionality of Tregs depleted of these lipids in the setting of experimental mouse models of chronic intestinal inflammation to establish the function of these lipids in Tregs in a manner that mirrors human IBD. Based on these observations, we formulated the CENTRAL HYPOTHESIS that long-chain ceramides promote metabolic homeostasis and resistance against the acquisition of effector-like phenotype in Tregs, resulting in the preservation of immunosuppressive function. The following independent SPECIFIC AIMS are designed to test two integrated hypotheses. First, we will directly test the hypothesis that ceramides prevent excessive oxidation of fatty acids linked to the glycolytic-lipogenic metabolism and effector IL-17-producing T helper (Th)17 cell-like phenotype. Furthermore, we will test the hypothesis that ceramides inhibit the activation of the nutrient-sensing signaling pathway associated with effector type T helper (Th1) cell-like phenotype. Second, we will test the hypothesis that Tregs depleted of ceramides exhibit poor resolution of IBD in an animal model. We propose to utilize sophisticated approaches relevant to health and IBD pathophysiology to test our central hypothesis. This proposal, which is technically and conceptually innovative, is also significant because it presents a novel concept in Treg biology and identifies new mechanisms for therapeutically optimizing Tregs to halt the refractory IBD.
