Distinguishing inflammatory Th17 subsets through using an autoimmune Th17-selective inhibitor

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Project Summary Th17 cells are a subset of IL-17-producing T helper CD4+ T cells and play a pivotal role in the pathogenicity of a variety of autoimmune diseases, which are affecting over 23 million Americans with no cure. Knowledge about regulatory mechanisms of Th17 cells might offer new opportunities for treating these diseases. Based on the requirement of IL-23 for the development, Th17 cells are currently divided into IL-23-independent homeostatic and IL-23-dependent inflammatory Th17 cells, of which the latter execute both physiological (clearing extracellular pathogen infections) and pathogenic (eliciting autoimmunity) functions. Substantial efforts have been made to define gene regulatory networks that discriminate homeostatic and inflammatory Th17 cells. However, how to dissect the subsets of inflammatory Th17 cells is largely unknown. This knowledge is critically needed because non-selective suppression of inflammatory Th17 cells, as by the newly approved IL- 23 monoclonal antibody-based therapy for autoimmune diseases, inevitably increases susceptibility to fungal and bacterial infections. Herein, autoimmune and anti-infection Th17 subsets display differential responses to the small molecule Clofazimine: the autoimmune effect of Th17 subsets was repressed while the anti-infection function of Th17 subsets was not disturbed. Our overall objectives in this application are to elucidate the gene expression and metabolic programs discriminating autoimmune and anti-infection Th17 subsets. The central hypothesis is that autoimmune and anti-infection Th17 subsets are distinguishable and SHMT1 is a checkpoint of intracellular serine levels in autoimmune Th17 cells. The rationale for this project is that determination of the differences between autoimmune and anti-infection Th17 subsets is likely to offer a strong scientific framework whereby new strategies to autoimmune diseases therapy with substantially increased selectivity and reduced adverse effects can be developed. The central hypothesis will be tested by pursuing two specific aims: Aim 1) To identify gene expression signatures of anti-infection and autoimmune Th17 subsets in vivo; and Aim 2) To determine the role of SHMT1 in regulating intracellular serine in autoimmune Th17 cells. Under Aim 1, single- cell RNA-seq analysis will be utilized with verification using Cas9-based knockout assay. For Aim 2, the pathogenicity of autoimmune Th17 cells and their intracellular serine levels will be evaluated in the presence of SHMT1 modulation: pharmacologic inhibition, genetic knockout, and point mutation with inactive enzymatic activities. The research proposed in this application is innovative, because it focuses on the regulatory network discriminating anti-infection and autoimmune Th17 subsets, a heretofore-unexamined mechanism. The proposed research is significant because it is expected to provide novel opportunities to develop autoimmune Th17-selective therapeutics for autoimmune diseases. This would be extraordinarily important for patients that have been infected or exposed to certain pathogens, such as tuberculosis, since existing Th17 inhibitors cannot be used due to the risks of decreasing the patients’ control of the infection.