PROJECT SUMMARY Osteoarthritis (OA) is a major public health problem and leads to long-term pain, disability, and huge healthcare costs, for which there is a substantial therapeutic gap. The closely linked manifestations of OA with metabolic syndrome and its shared pathophysiological basis in activation of systemic inflammation through innate immune pathways, have predicated recognition of a highly prevalent ‘metabolic’ phenotype of OA that is associated with persistent pain. Consonant with metabolic syndrome, there is evidence for the interaction of the gut microbiome with occurrence and severity of OA pain that is mediated through innate immune activation by gut microbial flora. A large population-based cohort study further demonstrates an association of alterations in gut microbiota, specifically an increase in the relative abundance and quantity of Streptococcus species with osteoarthritis-related knee pain. These observations suggest that opportunities may exist to influence the natural history of OA by targeting the microbiome; and to better understand the biology of effective interventions of OA by studying their effects on the microbiome in the context of pain pathways. Randomized trials have demonstrated that Tai Chi, a multi-dimensional mind-body exercise, shows benefits for OA for 3 to 12 months or longer. However, limited knowledge of the underlying mechanisms has restricted further optimization of the clinical efficacy and implementation of this promising mind-body therapy. Our long-term goal is to elucidate the mechanistic basis of the effect of Tai Chi in treating OA pain. The aim of this exploratory study is to determine the effect of Tai Chi mind-body exercise on gut microbiota in patients with metabolic OA and estimate the effect size. We will randomize 80 eligible individuals who meet the American College of Rheumatology criteria for knee OA into Tai Chi or wellness education interventions for 12 weeks. Using 16S rRNA amplicon sequencing of fecal DNA samples we will compare the changes in gut microbiota profiles (composition, relative and differential abundance, alpha and beta diversity) using 16S rRNA gene amplicon sequencing, and quantity of Streptococcus species using quantitative PCR10, as well as their association with clinical outcomes. This proposal will provide crucial preliminary knowledge of the mechanism underlying Tai Chi mind-body therapy for metabolic OA. These results are necessary to guide the design of future studies to elucidate mechanistic interactions between Tai Chi, gut microbiota, pain and behavioral pathways underlying the potential disease-modifying role of mind-body approaches, ultimately advancing arthritis treatment.