24-Nor-ursodeoxycholic acid counteracts TH17/Treg imbalance and ameliorates intestinal inflammation by restricting glutaminolysis in differentiating TH17 cells

Objective: 24-Nor-ursodeoxycholic acid (NorUDCA) is a novel therapeutic bile acid for treating primary sclerosing cholangitis (PSC), an immune-mediated cholestatic liver disease. Since PSC strongly associates with inflammatory bowel diseases (IBD) driven by TH17/Treg imbalance, we aimed to explore NorUDCA's immunomodulatory potential on intestinal TH17/Treg balance. Design: NorUDCA's impact on TH17/Treg tissue distribution was first assessed in Mdr2-/- mouse model of PSC. We specifically investigated NorUDCA's effect on modulating TH17/Treg balance in a CD4+ T cell driven colitis model induced by adoptive transfer of CD25-CD44lowCD45RBhighCD4+ TNaive cells into Rag2-/- mice, mimicking human IBD. Mechanistic studies were performed using molecular approaches, flow cytometry and metabolic assays in murine TH17 cells in vitro. NorUDCA's signaling effects observed in murine system were further validated in circulating CD4+ T cells from PSC patients with co-existing IBD. Results: NorUDCA promoted Treg generation in both liver and intestine in the Mdr2-/- model. In the experimental IBD model, NorUDCA attenuated intestinal immunopathology. Mechanistically, NorUDCA demonstrated strong immunomodulatory efficacy in counteracting TH17/Treg imbalance by restricting glutaminolysis in differentiating TH17 cells, thus suppressed a-Ketoglutarate-dependent mTORC1 activation, glycolysis and enhanced FOXP3 expression. NorUDCA's impact on mTORC1 signaling was further confirmed in circulating CD4+ T-cells from PSC patients with IBD. Conclusion: NorUDCA possesses direct immunometabolic modulatory potency to counteract TH17/Treg imbalance and ameliorate excessive TH17 cell driven intestinal immunopathology. These findings extend future clinical applications of NorUDCA for treatment of TH17 cell-mediated disorders along the gut-liver axis and beyond. ### Competing Interest Statement Michael Trauner has served as speaker for Falk Foundation, Gilead, Intercept and MSD; he has advised for Albireo, BiomX, Boehringer Ingelheim, Falk Pharma GmbH, Genfit, Gilead, Intercept, Jannsen, MSD, Novartis, Phenex, Regulus andShire. He further received travel grants from Abbvie, Falk, Gilead and Intercept and research grants from Albireo, Almylam, Cymabay, Falk, Gilead, Intercept, MSD, Takeda and Ultragenyx. He is also co-inventor of patents on the medical use of NorUDCA filed by the Medical Universities of Graz and Vienna. All the other authors declare no conflict of interest.