Selective and cytokine-dependent regulation of hepatic transporters and bile acid homeostasis during infectious colitis in mice

Abstract

Various disease models have been shown to alter hepatic drug-metabolizing enzyme (DME) and transporter expression and to induce cholestasis through altered enzyme and transporter expression. Previously, we detailed the regulation of hepatic DMEs during infectious colitis caused by Citrobacter rodentium infection. We hypothesized that this infection would also modulate hepatic drug transporter expression and key genes of bile acid (BA) synthesis and transport. Mice lacking Toll-like receptor 4 (TLR4), interleukin-6 (IL-6), or interferon-gamma (IFNγ) and appropriate wild-type animals were orally infected with C. rodentium and sacrificed 7 days later. In two wild-type strains, drug transporter mRNA expression was significantly decreased by infection for Slc22a4, Slco1a1, Slco1a4, Slco2b1, and Abcc6, whereas the downregulation of Abcc2, Abcc3, and Abcc4 were strain-dependent. In contrast, mRNA expressions of Slco3a1 and Abcb1b were increased in a strain-dependent manner. Expression of Abcb11, Slc10a1, the two major hepatic BA transporters, and Cyp7a1, the rate-limiting enzyme of BA synthesis, was also significantly decreased in infected animals. None of the above effects were caused by bacterial lipopolysaccharide, since they still occurred in the absence of functional TLR4. The downregulation of Slc22a4 and Cyp7a1 was absent in IFNγ-null mice, and the downregulation of Slco1a1 was abrogated in IL-6-null mice, indicating in vivo roles for these cytokines in transporter regulation. These data indicate that C. rodentium infection modulates hepatic drug processing through alteration of transporter expression as well as DMEs. Furthermore, this infection downregulates important genes of BA synthesis and transport and may increase the risk for cholestasis.

Fig. 1.

Effect of C. rodentium infection on hepatic mRNA expression of uptake transporters. Seven days following oral infection with C. rodentium, female mice were sacrificed, livers harvested, and mRNA isolated from (A) HeOuJ and HeJ (TLR4-null) mice (n = 6) and (B) C57BL/6, IL-6-null, and IFNγ-null mice (n = 8). mRNA was quantified by qRT-PCR and resulting values are expressed as relative levels of mRNA expression after normalization to GAPDH, with uninfected wild-type (HeOuJ or C57BL/6) set to 1. Values represent mean ± S.E.M. Significant differences are in comparison with uninfected control groups. *P < 0.05 by t test.

Fig. 2.

Effect of C. rodentium infection on hepatic mRNA expression of efflux transporters. Seven days following oral infection with C. rodentium, female mice were sacrificed, livers harvested, and mRNA isolated from (A) HeOuJ and HeJ (TLR4-null) mice (n = 6) and (B) C57BL/6, IL-6-null, and IFNγ-null mice (n = 8). mRNA was quantified by real-time qRT-PCR and resulting values are expressed as relative levels of mRNA expression after normalization to GAPDH, with uninfected wild type (HeOuJ or C57BL/6) set to 1. Values represent mean ± S.E.M. Significant differences are in comparison with uninfected control groups. *P < 0.05 by t test.

Fig. 3.

Effect of C. rodentium infection on hepatic mRNA expression of bile acid–associated genes. Seven days following oral infection with C. rodentium, female mice were sacrificed, livers harvested, and mRNA isolated from (A) HeOuJ and HeJ (TLR4-null) mice (n = 6) and (B) C57BL/6, IL-6-null, and IFNγ-null mice (n = 8). mRNA was quantified by real-time qRT-PCR and resulting values are expressed as relative levels of mRNA expression after normalization to GAPDH, with uninfected wild-type (HeOuJ or C57BL/6) set to 1. Values represent mean ± S.E.M. Significant differences are in comparison with uninfected control groups. *P < 0.05 by t test.

Fig. 4.

Effect of C. rodentium infection on hepatic protein expression of efflux transports. Seven days following oral infection with C. rodentium, female mice were sacrificed, livers harvested, and whole-cell lysates prepared from (A) HeOuJ and HeJ (TLR4-null) mice (n = 6) and (B) C57BL/6, IL-6-null, and IFNγ-null mice (n = 8). Protein levels of specific transporters were detected by western blotting and quantified using Image Laboratory software (Bio-Rad). Resulting values are expressed as relative levels of protein expression after normalization to Erk1/2, with uninfected wild-type (HeOuJ or C57BL/6) set to 1. Values represent mean ± S.E.M. Significant differences are in comparison with uninfected control groups. *P < 0.05 by t test.