Inhibition of the transcriptional regulation of CDCA-induced BSEP expression by IL-1β involves the IL-1β triggered activation of autocrine chemokine circuits

* corresponding author

Introduction: The liver as central regulator of multiple metabolic processes is indispensable for proper systemic function and survival. One important function is the synthesis and transport of bile acids for lipid digestion and adsorption. The malfunction of this machinery leads to accumulation of cytotoxic bile acids in hepatocytes and a subsequent severe damage of the liver. Modulation of transcriptional programs for bile acid homeostasis is achieved by activation of nuclear receptors such as the farnesoid X receptor (FXR), which plays a key role in bile synthesis, secretion, and detoxification by regulation of transporter expression levels in the polarized hepatocytes. Thereby the bile salt export pump BSEP is critical for the transport of bile salts from the hepatocyte into the canaliculus. Its expression is mainly controlled by CDCA stimulated activation of FXR. The inhibition of the expression of BSEP by inflammatory cytokines such as IL-1β has been identified as a critical factor for the development of cholestasis under septic conditions or LPS-inducible inflammation. The molecular mechanisms, which are responsible for down-regulation of BSEP expression by inflammatory factors, are incompletely understood. Objectives – The present study analysis the role of chemokine circuits and its intra-cellular signal-transduction for the inhibition of the transcriptional regulation of CDCA induced BSEP expression in primary murine hepatocytes and the human hepatoma cell line HepaRG which displays several characteristics of polarized hepatocytes. Materials and

Methods: The study involves transcriptional analysis of BSEP expression in primary hepatocytes from 8 – 12 week old C57/BL6J male mice and the well-established human hepatoma cell line HepaRG. The cells were grown in Sandwich or Monolayer culture and treated with IL1β, CDCA and the CXCR2 Inhibitor SB225002 in a cell culture based stimulation assay for defined periods of time. Results – The time resolved analysis of the concentration dependent effects of IL-1β on CDCA-inducible expression of the BSEP gene indicates that even concentrations of less than 0.1 ng/ml of IL-1β efficiently suppress expression of the BSEP gene. The inhibitory effect of IL-1β on BSEP gene expression can be partially resolved by inhibition of the CXCR2 receptor. These data suggest that inhibition of CDCA-inducible BSEP expression by IL-1β involves an autocrine circuit mediated via production of CXCR2 ligands. Indeed the analysis of the expression of the CXCR2 ligands CXCL1, 2 and 3 indicates that IL-1β induces the expression of these ligands in hepatocytes.

Conclusion: In summary the data suggest that the inhibitory effects of IL1β on BSEP gene expression are at least part due to autocrine effects of CXCR2 ligands released from hepatocytes upon exposure to IL-1β.

Corresponding author: Bode, Johannes G.

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