Secondary (iso)BAs cooperate with endogenous ligands to activate FXR under physiological and pathological conditions

• Type of Material: Article
• Authors: Alex Zaufel, Medical University of Graz; Sandra MW van de Wiel, University of Amsterdam; Lu Yin, Trinity College Dublin; Günter Fauler, University of Graz, Austria; Daphne Chien, Johns Hopkins University; Xinzhong Dong, Johns Hopkins University; John F Gilmer, Trinity College Dublin; Jennifer K Truong, Emory University; Paul Dawson, Emory University; Stan FJ van de Graaf, University of Amsterdam; Peter Fickert, Medical University of Graz; Tarek Moustafa, Medical University of Graz
• Language: English
• Date: 2021-04-30
• Publisher: ELSEVIER
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2021 The Author(s). Published by Elsevier B.V.
• License: Creative Commons Attribution 4.0 International
• Final Published Version (URL): http://dx.doi.org/10.1016/j.bbadis.2021.166153
• Title of Journal or Parent Work: BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE
• Volume: 1867
• Issue: 8
• Start Page: 166153
• End Page: 166153
• Grant/Funding Information: TM is the recipient of the Andrew K. Burroughs fellowship. This work was supported by the Doctoral College “Metabolic and Cardiovascular Disease” (AZ) of the Austrian Science Fund (FWF, DK-MCD W1226). JKT and PAD were supported by the National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases grant DK047987.
• Keywords: Biophysics; FARNESOID-X-RECEPTOR; Nuclear receptors; EXPRESSION; DEOXYCHOLIC-ACID; Cell Biology; ISOURSODEOXYCHOLIC ACID; Science & Technology; CHOLESTASIS; Bile acids; Biochemistry & Molecular Biology; ISO-BILE ACIDS; METABOLISM; MICROBIOTA; BINDING; Life Sciences & Biomedicine; Metabolism; URSODEOXYCHOLIC ACID; Enterohepatic, cholestasis, gene expression

Abstract

IsoBAs, stereoisomers of primary and secondary BAs, are found in feces and plasma of human individuals. BA signaling via the nuclear receptor FXR is crucial for regulation of hepatic and intestinal physiology/pathophysiology. Aim: Investigate the ability of BA-stereoisomers to bind and modulate FXR under physiological/pathological conditions. Methods: Expression-profiling, luciferase-assays, fluorescence-based coactivator-association assays, administration of (iso)-BAs to WT and cholestatic mice. Results: Compared to CDCA/isoCDCA, administration of DCA/isoDCA, UDCA/isoUDCA only slightly increased mRNA expression of FXR target genes; the induction was more evident looking at pre-mRNAs. Notably, almost 50% of isoBAs were metabolized to 3-oxo-BAs within 4 h in cell-based assays, making it difficult to study their actions. FRET-based real-time monitoring of FXR activity revealed that isoCDCA>CDCA stimulated FXR, and isoDCA and isoUDCA allowed fully activated FXR to be re-stimulated by a second dose of GW4064. In vivo co-administration of a single dose of isoBAs followed by GW4064 cooperatively activated FXR, as did feeding of UDCA in a background of endogenous FXR ligands. However, in animals with biliary obstruction and concomitant loss of intestinal BAs, UDCA was unable to increase intestinal Fgf15. In contrast, mice with an impaired enterohepatic circulation of BAs (Asbt−/−, Ostα−/−), administration of UDCA was still able to induce ileal Fgf15 and repress hepatic BA-synthesis, arguing that UDCA is only effective in the presence of endogenous FXR ligands. Conclusion: Secondary (iso)BAs cooperatively activate FXR in the presence of endogenous BAs, which is important to consider in diseases linked to disturbances in BA enterohepatic cycling.