Elsevier

Biochemical Pharmacology

Volume 74, Issue 11, 3 December 2007, Pages 1665-1676
Biochemical Pharmacology

Regulation of hepatic bile acid transporters Ntcp and Bsep expression

https://doi.org/10.1016/j.bcp.2007.08.014Get rights and content

Abstract

Sodium-taurocholate cotransporting polypeptide (Ntcp) and bile salt export pump (Bsep) are two key transporters for hepatic bile acid uptake and excretion. Alterations in Ntcp and Bsep expression have been reported in pathophysiological conditions. In the present study, the effects of age, gender, and various chemicals on the regulation of these two transporters were characterized in mice. Ntcp and Bsep mRNA levels in mouse liver were low in the fetus, but increased to its highest expression at parturition. After birth, mouse Ntcp and Bsep mRNA decreased by more than 50%, and then gradually increased to adult levels by day 30. Expression of mouse Ntcp mRNA and protein exhibit higher levels in female than male livers. No gender difference exists in BSEP/Bsep expression in human and mouse livers. Hormone replacements conducted in gonadectomized, hypophysectomized, and lit/lit mice indicate that female-predominant Ntcp expression in mouse liver is due to the inhibitory effect of male-pattern GH secretion, but not sex hormones. Ntcp and Bsep expression are in general resistant to induction by a large battery of microsomal enzyme inducers. Administration of cholestyramine increased Ntcp, whereas chenodeoxycholic acid (CDCA) increased Bsep mRNA expression. In conclusion, mouse Ntcp and Bsep are regulated by age, gender, cholestyramine, and bile acid, but resistant to induction by most microsomal enzyme inducers.

Introduction

Bile acids secreted into bile undergo enterohepatic circulation (97%). Both hepatic uptake and biliary excretion of bile acids are driven by transport proteins. Bile acid uptake from blood into liver is mediated mainly by the Na+-taurocholate cotransporting polypeptide (Ntcp), and efflux from liver into bile by the bile salt export pump (Bsep).

Ntcp (gene symbol Slc10a1) has been cloned in various species [1], [2], [3], [4], and localized to the basolateral membrane of hepatocytes. Ntcp transports all physiological bile acids [5], [6], [7]. Bsep (gene symbol Abcb11) is responsible for the canalicular excretion of bile acids [8], [9]. Targeted inactivation of the mouse Bsep gene results in mild, non-progressive, but persistent intrahepatic cholestasis [10]. In contrast, a mutation in human BSEP gene is responsible for progressive familial intrahepatic cholestasis subtype 2 (PFIC-2) [11], [12].

Ntcp mRNA and protein expression is uniformly down-regulated in all experimental models of cholestasis and liver disease [13], [14], [15], [16], [17]. In contrast, Bsep expression is only modestly impaired during cholestasis even with complete bile-duct obstruction [16], [18].

Bile acids in general are thought to decrease Ntcp expression through farnesoid X receptor (FXR)-small heterodimer partner (Shp) pathway, and increase Bsep expression through direct FXR activation [19], [20], [21].

In rats, Ntcp mRNA expression is male-predominant, which is due to the inhibitory effect of female-pattern GH secretion [22]. However, it is not known whether mouse, rat, and human Ntcp/NTCP expression share similar gender predominance and underlying regulatory mechanisms. Except for the influence of bile acids, the regulation of Ntcp and Bsep is not complete. A few studies have been performed in rats, some in humans, but less in mice. Therefore, in the present study, we determined the effects of age, gender, and various chemicals, including microsomal enzyme inducers, cholestyramine, and chenodeoxycholic acid (CDCA) on the regulation of Ntcp and Bsep mRNA expression in mouse livers and evaluate their human relevance.

Section snippets

Materials

Sodium chloride, HEPES sodium salt, HEPES free acid, lithium lauryl sulfate, EDTA, and d-(+)-glucose were purchased from Sigma–Aldrich (St. Louis, MO). Micro-O-protect was purchased from Roche Diagnostics (Indianapolis, IN). Formaldehyde, 3-(N-morpholino)propanesulfonic acid, sodium citrate, and NaHCO3 were purchased from Fischer Chemicals (Fairlawn, NJ). Chloroform, agarose, and ethidium bromide were purchased from AMRESCO Inc. (Solon, OH). 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was a gift

Constitutive expression of Ntcp and Bsep in adult male and female mouse and human livers

Both Ntcp/NTCP and Bsep/BSEP have been shown to be highly expressed in mouse and human livers [1], [18], [29], [30]. Ntcp protein expression is 60% higher in female than male mouse liver (Fig. 1a), and Ntcp mRNA is 70% higher in female than male mouse livers (Fig. 1b). In human livers, NTCP mRNA is 43% higher in women than men; however, it is not statistically different due to high variation in individual human NTCP expression. In contrast, no gender differences exist in mouse Bsep expression

Discussion

The goal of the present study was to obtain systematic information on the regulation of Ntcp and Bsep, two critical bile acid transporters in mouse and human livers. There are numerous reports on the regulation of Ntcp [19], [32], [33], [34] and Bsep [20], [32], [34] by bile acids. The focus of this study was to characterize the ontogenic and gender-related constitutive expression of these two hepatic bile acid transporters, as well as examine the regulation of Ntcp and Bsep by microsomal

Acknowledgements

This work was supported by NIH grants RR021940, ES09649, and ES09716.

References (65)

  • M. Ananthanarayanan et al.

    Human bile salt export pump promoter is transactivated by the farnesoid X receptor/bile acid receptor

    J Biol Chem

    (2001)
  • J.R. Plass et al.

    Farnesoid X receptor and bile salts are involved in transcriptional regulation of the gene encoding the human bile salt export pump

    Hepatology

    (2002)
  • G.L. Guo et al.

    Complementary roles of farnesoid X receptor, pregnane X receptor, and constitutive androstane receptor in protection against bile acid toxicity

    J Biol Chem

    (2003)
  • M.Z. Dieter et al.

    Expression and regulation of the sterol half-transporter genes ABCG5 and ABCG8 in rats

    Comp Biochem Physiol C Toxicol Pharmacol

    (2004)
  • D.R. Johnson et al.

    Expression of rat multidrug resistance protein 2 (Mrp2) in male and female rats during normal and pregnenolone-16alpha-carbonitrile (PCN)-induced postnatal ontogeny

    Toxicology

    (2002)
  • P. Fickert et al.

    Effects of ursodeoxycholic and cholic acid feeding on hepatocellular transporter expression in mouse liver

    Gastroenterology

    (2001)
  • E.C. Torchia et al.

    Coordinate regulation of bile acid biosynthetic and recovery pathways

    Biochem Biophys Res Commun

    (1996)
  • H. Wolters et al.

    Effects of bile salt flux variations on the expression of hepatic bile salt transporters in vivo in mice

    J Hepatol

    (2002)
  • H.L. Chen et al.

    Developmental expression of canalicular transporter genes in human liver

    J Hepatol

    (2005)
  • W. Hardikar et al.

    Differential ontogenic regulation of basolateral and canalicular bile acid transport proteins in rat liver

    J Biol Chem

    (1995)
  • A. Abrahamsson et al.

    Feedback regulation of bile acid synthesis in human liver: importance of HNF-4alpha for regulation of CYP7A1

    Biochem Biophys Res Commun

    (2005)
  • M. Crestani et al.

    Transcriptional activation of the cholesterol 7alpha-hydroxylase gene (CYP7A) by nuclear hormone receptors

    J Lipid Res

    (1998)
  • S. Gupta et al.

    LXR alpha is the dominant regulator of CYP7A1 transcription

    Biochem Biophys Res Commun

    (2002)
  • S. Shibata et al.

    Roles of nuclear receptors in the up-regulation of hepatic cholesterol 7alpha-hydroxylase by cholestyramine in rats

    Life Sci

    (2007)
  • B. Hagenbuch et al.

    Functional expression cloning and characterization of the hepatocyte Na+/bile acid cotransport system

    Proc Natl Acad Sci USA

    (1991)
  • B. Hagenbuch et al.

    Molecular cloning, chromosomal localization, and functional characterization of a human liver Na+/bile acid cotransporter

    J Clin Invest

    (1994)
  • P.J. Meier et al.

    Bile salt transporters

    Annu Rev Physiol

    (2002)
  • G.A. Kullak-Ublick et al.

    Hepatic transport of bile salts

    Semin Liver Dis

    (2000)
  • M. Trauner et al.

    Bile salt transporters: molecular characterization, function, and regulation

    Physiol Rev

    (2003)
  • S. Childs et al.

    Identification of a sister gene to P-glycoprotein

    Cancer Res

    (1995)
  • R. Wang et al.

    Targeted inactivation of sister of P-glycoprotein gene (spgp) in mice results in nonprogressive but persistent intrahepatic cholestasis

    Proc Natl Acad Sci USA

    (2001)
  • S.S. Strautnieks et al.

    A gene encoding a liver-specific ABC transporter is mutated in progressive familial intrahepatic cholestasis

    Nat Genet

    (1998)
  • Cited by (0)

    View full text