Gastroenterology

Gastroenterology

Volume 126, Issue 3, March 2004, Pages 756-764
Gastroenterology

Clinical-liver, pancreas, and biliary tract
Progressive familial intrahepatic cholestasis, type 1, is associated with decreased farnesoid X receptor activity

https://doi.org/10.1053/j.gastro.2003.12.013Get rights and content

Abstract

Background & Aims: The mechanisms by which mutations in the familial intrahepatic cholestasis-1 gene cause Byler’s disease (progressive familial intrahepatic cholestasis type 1) are unknown. Methods: Interactions among the apical sodium-dependent bile acid transporter, the farnesoid X receptor (FXR), and familial intrahepatic cholestasis-1 were studied in the ileum of children with progressive familial intrahepatic cholestasis type 1 and in Caco-2 cells. Results: Increased ileal apical sodium-dependent bile acid transporter messenger RNA (mRNA) expression was detected in 3 patients with progressive familial intrahepatic cholestasis type 1. Paradoxically, ileal lipid-binding protein mRNA expression was repressed, suggesting a central defect in bile acid response. Ileal FXR and short heterodimer partner mRNA levels were reduced in the same 3 patients. In Caco-2 cells, antisense-mediated knock-down of endogenous familial intrahepatic cholestasis-1 led to up-regulation of apical sodium-dependent bile acid transporter and down-regulation of FXR, ileal lipid-binding protein, and short heterodimer partner mRNA. In familial intrahepatic cholestasis-1-negative Caco-2 cells, the activity of the human apical sodium-dependent bile acid transporter promoter was enhanced, whereas the human FXR and bile salt excretory pump promoters’ activities were reduced. Overexpression of short heterodimer partner but not of the FXR abrogated the effect of familial intrahepatic cholestasis-1 antisense oligonucleotides. FXR cis-element binding and FXR protein were reduced primarily in nuclear but not cytoplasmic extracts from familial intrahepatic cholestasis-1-negative Caco-2 cells. Conclusions: Loss of familial intrahepatic cholestasis-1 leads to diminished nuclear translocation of the FXR, with the subsequent potential for pathologic alterations in intestinal and hepatic bile acid transporter expression. Marked hypercholanemia and cholestasis are predicted to develop, presumably because of both enhanced ileal uptake of bile salts via up-regulation of the apical sodium-dependent bile acid transporter and diminished canalicular secretion of bile salts secondary to down-regulation of the bile salt excretory pump.

Section snippets

Materials and methods

ASBT,10 FIC1,2 ileal lipid-binding protein (ILBP),11 short heterodimer partner (SHP),12 farnesoid X receptor (FXR),13 ATP8B2,14 and 28S15 messenger RNA (mRNA) levels were quantified by PhosphorImager (Molecular Dynamics, Sunnyvale, CA) analysis of Northern blots of total RNA from excess ileal tissue obtained at the time of ileal exclusion in 5 children with intractable pruritus associated with intrahepatic cholestasis (Table 1). Endogenous FIC1 expression in Caco-2 cells was knocked down by

Results

Quantitative Northern blot analysis of ASBT mRNA found that levels in ileum from the 3 children with PFIC1 were 4-fold higher than those found in the children with FIC1-positive cholestasis (Figure 1). FIC1 mRNA could not be shown in the 3 children with PFIC1, but it was found in the other 2 children (one with high γ-glutamyl transpeptidase cholestasis and the other with PFIC2). Northern analysis of intestinal expression of FIC1 may thus, in certain cases, be a rapid means of diagnosing FIC1

Discussion

These studies provide fundamental insights into the novel mechanisms by which defects in FIC1 may lead to human disease. FIC1, an apical membrane protein, seems to activate the FXR gene product, presumably via posttranslational modifications that lead to nuclear translocation of FXR (Figure 8). In the absence of FIC1, either in human disease or in Caco-2 cell knock-down studies, FXR activity is reduced. This is noted in both circumstances by the downstream effects of its reduced activity,

Acknowledgements

The authors would like to acknowledge the technical assistance of Xiaoping Li, Julie Vargas, and Venus Mahmoodi.

References (33)

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Supported by grants NIH DK 54165 (to B.L.S.) and HD 20632 (to F.J.S.).

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