1. Secondary (iso)BAs cooperate with endogenous ligands to activate FXR under physiological and pathological conditions.
- Author
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Zaufel A, van de Wiel SMW, Yin L, Fauler G, Chien D, Dong X, Gilmer JF, Truong JK, Dawson PA, van de Graaf SFJ, Fickert P, and Moustafa T
- Subjects
- Animals, Caco-2 Cells, Cell Line, Cell Line, Tumor, Cholestasis drug therapy, Cholestasis metabolism, Disease Models, Animal, Fibroblast Growth Factors metabolism, HEK293 Cells, Hep G2 Cells, Humans, Ileum drug effects, Ileum metabolism, Isoxazoles pharmacology, Ligands, Liver drug effects, Liver metabolism, Male, Mice, RNA, Messenger metabolism, Signal Transduction drug effects, Signal Transduction physiology, Transcription Factors metabolism, Bile Acids and Salts pharmacology, Receptors, Cytoplasmic and Nuclear metabolism
- 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., (Copyright © 2021 The Author(s). Published by Elsevier B.V. All rights reserved.)
- Published
- 2021
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