Interleukin-6 regulates hepatic transporters during acute-phase response

https://doi.org/10.1016/j.bbrc.2004.07.102Get rights and content

Abstract

Cholestasis develops during inflammatory conditions characterized by the release of cytokines like interleukin-6 (IL-6), which is the major player in the hepatic acute-phase response. However, the exact contribution of IL-6 to transporter down-regulation is unclear. Therefore, we compared wild-type and IL-6-deficient mice after IL-6-injection and induction of an aseptic (turpentine-injection) or septic (LPS-injection) acute-phase response. Down-regulation of basolateral (Ntcp, Oatp1, and Mrp3) and canalicular (Mrp2, Bsep) transporter mRNA occurred after treatment with IL-6, turpentine, and LPS. In IL-6-deficient mice, turpentine failed to decrease mRNA-levels of basolateral and canalicular transporters, whereas LPS-mediated down-regulation of Ntcp, Mrp3, and Mrp2 was abolished at later time points (24 h). In conclusion, induction of an aseptic and septic acute-phase response leads to the down-regulation of basolateral and canalicular organic anion transporters. IL-6 is required for transporter down-regulation during aseptic inflammation. Furthermore, IL-6 also contributes to transporter regulation during LPS-induced cholestasis at more delayed time points.

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Materials and methods

Cytokines and reagents. Recombinant human IL-6 with a specific activity of 5 × 106 B-cell stimulatory factor 2 U/mg protein was produced in the Escherichia coli expression system, purified to homogeneity by gel filtration and ion exchange high-performance liquid chromatography as described [21]. Endotoxin content was less than 3.5 pg/mg as measured in the Limulus assay, which is far below the concentration of LPS needed to induce an acute-phase protein production [22]. Steam distilled turpentine

Transporter mRNA expression in IL-6-treated wild-type mice

To determine whether an inflammatory response induced by IL-6 affects the mRNA expression of hepatobiliary organic anion transporters in wild-type mice in vivo, we quantified the steady-state mRNA levels of transport proteins exclusively localized either at the basolateral (Ntcp, Oatp1, and Mrp3) or canalicular (Bsep, Mrp2) plasma membrane of hepatocytes by Northern blotting (Figs. 1A and B). There was a reduction in the mRNA levels of all basolateral transporters analyzed: Ntcp mRNA declined

Discussion

The acute-phase reaction is an orchestrated complex response to tissue injury, infection or inflammation leading either to the induction of acute-phase proteins involved in the restoration of homeostasis (positive acute-phase proteins) or down-regulation of acute-phase proteins not required for host defense (negative acute-phase proteins) [3], [26]. Cytokines, particularly interleukin-6, are important mediators of the acute-phase response [2], [3]. However, the patterns of cytokine production

Acknowledgments

The authors thank Sonja Strauch, Petra Schmitz, Aline Müller, Sabine Beutelspacher, and Claudia Thomsa for their excellent technical assistance and H. Bluethmann (Roche, Basel/Switzerland) for providing BL/6 wild-type and homozygous IL-6 knock-out mice. Grant support: Sonderforschungsbereich 542 der Deutschen Forschungsgemeinschaft, Project C1 (2nd period) to C.G., A.G., and S.M.; Grants DFG SI 633/3-1 to E.S., DI 729/3-1 to C.G.D., and LA 997/3-1 to F.L.

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