Role of Microbial Tryptophan Metabolism in Th17 Activation and Multiple Sclerosis 2260431

Abstract Introduction The relationship between diet, the gut microbiota, and immune cells influences autoimmune diseases such as multiple sclerosis (MS). In a mouse model of MS, a ketogenic diet (KD) reduced disease severity in a microbiota-dependent manner. In further studies, a KD-enriched microbe, Lactobacillus murinus, and its metabolite indole lactate (ILA) both independently conferred disease protection without need for a KD. ILA is a tryptophan metabolite known to inhibit Th17 cells, key immune drivers of MS. However, whether ILA is required for Lactobacillus mediated Th17 inhibition is unclear. Methods To investigate the necessity of microbial ILA production, a microbe deficient in ILA production was tested to determine if it retained the ability to inhibit Th17 activity in vitro and modulate disease in the Experimental Autoimmune Encephalomyelitis (EAE) mouse model of MS. Specifically, a human strain of Lactobacillus reuteri lacking the key enzyme, aromatic aminotransferase (ArAT), involved in tryptophan conversion to ILA was utilized. Naïve mouse CD4+ T cells were treated with cell-free supernatants from wild-type L. murinus, L. reuteri, or L. reuteri ArAT knockout (KO) strains during a Th17 differentiation assay, followed by IL-17A quantification using an ELISA. For EAE studies, mice were orally gavaged with wild-type L. reuteri, L. reuteri ArAT KO, or PBS preceding and throughout disease course. Results ILA producing microbes significantly inhibited IL-17a production in vitro, while the ILA deficient L. reuteri ArAT KO strain did not. Furthermore, L. reuteri ArAT KO treated mice had higher EAE disease scores compared to those receiving wild-type L. reuteri, indicating that ILA is required for disease protection. Conclusion These findings suggest that ILA plays a critical role in microbial-mediated Th17 inhibition and protection against EAE. This work highlights the potential for targeting microbial tryptophan metabolism as a therapeutic for IL-17-driven autoimmune diseases like MS. Funding Source University of Wisconsin-Madison Genetics and Genomics Undergraduate Distinguished Research Fellowship Topic Categories Mucosal and Regional Immunology (MUC)