SHP-dependent and -independent induction of peroxisome proliferator-activated receptor-γ by the bile acid sensor farnesoid X receptor counter-regulates the pro-inflammatory phenotype of liver myofibroblasts

Inflamm Res. 2011 Jun;60(6):577-87. doi: 10.1007/s00011-010-0306-1. Epub 2011 Jan 29.

Abstract

Objective: The regulation of hepatic stellate cells (HSCs) by bacterial lipopolysaccharide (LPS) represents a recently-discovered and novel mechanism for hepatic injury and fibrosis. Stimulation of HSCs with LPS results in a rapid and marked induction of interleukin (IL)1β, IL6 and tumor necrosis factor α. These events lead to the development of the activated phenotype in the HSCs associated with fibrosis and inflammation in the injured liver. We have previously demonstrated that farnesoid X receptor (FXR) activation increases transcription of rat peroxisome proliferator-activated receptor-γ (PPARγ) gene in HSCs. We aimed at evaluating the molecular mechanism of the transcriptional regulation of the PPARγ gene by FXR.

Methods: Real-time PCR, ELISA, transactivations, EMSA and ChIP experiments were performed in HSC-T6 cells, in primary HSCs, in HEK293T cells and in CCl(4)-treated rats.

Results: In vivo and in vitro activation of FXR downregulates cytokines and collagen(α)1 while inducing PPARγ and small heterodimer partner (SHP). NUBIScan analysis of rat PPARγ promoter revealed the presence of a putative FXR response element. Cotransfection with FXR/retinoic acid receptor significantly enhanced chenodeoxycholic acid-induced luciferase activity. EMSA experiments demonstrated that FXR was able to bind to an inverted repeat-1 sequence and ChIP experiments confirmed that FXR is recruited on the PPARγ promoter.

Conclusion: The present study provides a molecular basis for the physiological cross-talk between FXR and PPARγ pathways in HSCs.

MeSH terms

  • Animals
  • Carbon Tetrachloride
  • Cell Line
  • Chemical and Drug Induced Liver Injury / metabolism*
  • Chemical and Drug Induced Liver Injury / pathology
  • Chenodeoxycholic Acid / pharmacology*
  • Gene Expression Regulation / drug effects
  • HEK293 Cells
  • Hepatic Stellate Cells / drug effects
  • Hepatic Stellate Cells / metabolism
  • Humans
  • Interleukin-1beta / metabolism
  • Male
  • Myofibroblasts / drug effects
  • Myofibroblasts / metabolism
  • PPAR gamma / genetics*
  • Phenotype
  • Rats
  • Rats, Wistar
  • Receptors, Cytoplasmic and Nuclear / genetics*
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Tumor Necrosis Factor-alpha / metabolism

Substances

  • Interleukin-1beta
  • PPAR gamma
  • Receptors, Cytoplasmic and Nuclear
  • Tumor Necrosis Factor-alpha
  • nuclear receptor subfamily 0, group B, member 2
  • farnesoid X-activated receptor
  • Chenodeoxycholic Acid
  • Carbon Tetrachloride