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

• 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
• Journal Title: BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR BASIS OF DISEASE
• Volume: Volume 1867, Number 8
• Publisher: ELSEVIER | 2021-04-30, Pages 166153-166153
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1016/j.bbadis.2021.166153
• Subjects: Health Sciences, Medicine and Surgery; Health Sciences, Nutrition
• Keywords: Science & Technology; Life Sciences & Biomedicine; Biochemistry & Molecular Biology; Biophysics; Cell Biology; Nuclear receptors; Bile acids; Enterohepatic, cholestasis, gene expression; Metabolism; FARNESOID-X-RECEPTOR; ISO-BILE ACIDS; DEOXYCHOLIC-ACID; ISOURSODEOXYCHOLIC ACID; URSODEOXYCHOLIC ACID; METABOLISM; MICROBIOTA; EXPRESSION; BINDING; CHOLESTASIS

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.