Reich M, Spomer L, Klindt C, Fuchs K, Stindt J, Deutschmann K, Höhne J, Liaskou E, Hov JR, Karlsen TH, Beuers U, Verheij J, Ferreira-Gonzalez S, Hirschfield G, Forbes SJ, Schramm C, Esposito I, Nierhoff D, Fickert P, Fuchs CD, Trauner M, García-Beccaria M, Gabernet G, Nahnsen S, Mallm JP, Vogel M, Schoonjans K, Lautwein T, Köhrer K, Häussinger D, Luedde T, Heikenwalder M, and Keitel V
Background & Aims: Primary sclerosing cholangitis (PSC) is characterized by chronic inflammation and progressive fibrosis of the biliary tree. The bile acid receptor TGR5 (GPBAR1) is found on biliary epithelial cells (BECs), where it promotes secretion, proliferation and tight junction integrity. Thus, we speculated that changes in TGR5-expression in BECs may contribute to PSC pathogenesis., Methods: TGR5-expression and -localization were analyzed in PSC livers and liver tissue, isolated bile ducts and BECs from Abcb4 -/- , Abcb4 -/- /Tgr5 Tg and ursodeoxycholic acid (UDCA)- or 24-norursodeoxycholic acid (norUDCA)-fed Abcb4 -/- mice. The effects of IL8/IL8 homologues on TGR5 mRNA and protein levels were studied. BEC gene expression was analyzed by single-cell transcriptomics (scRNA-seq) from distinct mouse models., Results: TGR5 mRNA expression and immunofluorescence staining intensity were reduced in BECs of PSC and Abcb4 -/- livers, in Abcb4 -/- extrahepatic bile ducts, but not in intrahepatic macrophages. No changes in TGR5 BEC fluorescence intensity were detected in liver tissue of other liver diseases, including primary biliary cholangitis. Incubation of BECs with IL8/IL8 homologues, but not with other cytokines, reduced TGR5 mRNA and protein levels. BECs from Abcb4 -/- mice had lower levels of phosphorylated Erk and higher expression levels of Icam1, Vcam1 and Tgfβ2. Overexpression of Tgr5 abolished the activated inflammatory phenotype characteristic of Abcb4 -/- BECs. NorUDCA-feeding restored TGR5-expression levels in BECs in Abcb4 -/- livers., Conclusions: Reduced TGR5 levels in BECs from patients with PSC and Abcb4 -/- mice promote development of a reactive BEC phenotype, aggravate biliary injury and thus contribute to the pathogenesis of sclerosing cholangitis. Restoration of biliary TGR5-expression levels represents a previously unknown mechanism of action of norUDCA., Lay Summary: Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease-associated with progressive inflammation of the bile duct, leading to fibrosis and end-stage liver disease. Bile acid (BA) toxicity may contribute to the development and disease progression of PSC. TGR5 is a membrane-bound receptor for BAs, which is found on bile ducts and protects bile ducts from BA toxicity. In this study, we show that TGR5 levels were reduced in bile ducts from PSC livers and in bile ducts from a genetic mouse model of PSC. Our investigations indicate that lower levels of TGR5 in bile ducts may contribute to PSC development and progression. Furthermore, treatment with norUDCA, a drug currently being tested in a phase III trial for PSC, restored TGR5 levels in biliary epithelial cells., Competing Interests: Conflict of interest MR, LS, CK, KF, JS, KD, JH, EL, JV, SFG, GH, SJF, IE, DN, CDF, MGB, GG, SV, JPM, MV, KS, TL, KK, DH, TL, MH have nothing to disclose.VK has served as speaker for Falk Foundation, Albireo and Abbvie. JRH has served on the advisory board for Novartis and Orkla Health. JRH has received research support from Biogen unrelated to the current work. THK has received consulting/speaker reimbursement from Gilead and Intercept unrelated to the current work. CS has served as speaker for Falk Foundation. MT 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 and Shire. MT further received travel grants from Abbvie, Falk, Gilead and Intercept and research grants from Albireo, Cymabay, Falk, Gilead, Intercept, MSD and Takeda. MT is also co-inventor of patents on the medical use of NorUDCA filed by the Medical Universities of Graz and Vienna (WO2006119803, WO20099013334). PF received norUDCA, an unrestricted research grant, travel grants and advisory board fees from Dr. Falk Pharma GmbH. PF is listed as co-inventor of patents for the medical use of norUDCA filed by the Medical University of Graz (WO2006119803, WO20099013334). UB received grants for investigator-initiated studies by Dr Falk GmbH, Freiburg, and Intercept, San Diego., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)