Low retinol levels differentially modulate bile salt–induced expression of human and mouse hepatic bile salt transporters

Authors

  • Martijn O. Hoeke,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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    • These authors contributed equally to this work.

  • Jacqueline R.M. Plass,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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    • These authors contributed equally to this work.

  • Janette Heegsma,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Mariska Geuken,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Duncan van Rijsbergen,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Julius F.W. Baller,

    1. Department of Pediatrics, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Folkert Kuipers,

    1. Department of Pediatrics, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Han Moshage,

    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
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  • Peter L.M. Jansen,

    1. Department of Gastroenterology and Hepatology, Academic Medical Center, Amsterdam, The Netherlands
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  • Klaas Nico Faber

    Corresponding author
    1. Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
    • Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands
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    • fax: (31)-50-3614756.


  • Potential conflict of interest: Nothing to report.

Abstract

The farnesoid X receptor/retinoid X receptor-alpha (FXR/RXRα) complex regulates bile salt homeostasis, in part by modulating transcription of the bile salt export pump (BSEP/ABCB11) and small heterodimer partner (SHP/NR0B2). FXR is activated by bile salts, RXRα by the vitamin A derivative 9-cis retinoic acid (9cRA). Cholestasis is associated with vitamin A malabsorption. Therefore, we evaluated the role of vitamin A/9cRA in the expression of human and mouse bile salt export pump (hBSEP/mBsep), small heterodimer partner (hSHP/mShp), and mouse sodium-dependent taurocholate co-transporting polypeptide (mNtcp). HBSEP and hSHP transcription were analyzed in FXR/RXRα-transfected HepG2 cells exposed to chenodeoxycholic acid (CDCA) and/or 9cRA. BSEP promoter activity was determined by luciferase reporter assays, DNA-binding of FXR and RXRα by pull-down assays. Serum bile salt levels and hepatic expression of Bsep, Shp, and Ntcp were determined in vitamin A–deficient (VAD)/cholic acid (CA)-fed C57BL/6J mice. Results indicated that 9cRA strongly repressed the CDCA-induced BSEP transcription in HepG2 cells, whereas it super-induced SHP transcription; 9cRA reduced DNA-binding of FXR and RXRα. The 9cRA repressed the CDCA-induced BSEP promoter activity irrespective of the exact sequence of the FXR-binding site. In vivo, highest Bsep messenger RNA (mRNA), and protein expression was observed in CA-fed VAD mice. Shp transcription was highest in CA-fed vitamin A–sufficient mice. Ntcp protein expression was strongly reduced in CA-fed VAD mice, whereas mRNA levels were normal. CA-fed control and VAD mice had similarly increased serum bile salt levels. Conclusion: We showed that 9cRA has opposite effects on bile salt–activated transcription of FXR/RXRα target genes. Vitamin A deficiency in CA-fed mice leads to high BSEP expression. Clearance of serum bile salts may, however, be limited because of post-transcriptional reduction of Ntcp. The molecular effects of vitamin A supplementation during cholestasis need further analysis to predict a therapeutic effect. (HEPATOLOGY 2009;49:151–159.)

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