Aryl hydrocarbon receptor-dependent induction of liver fibrosis by dioxin

Toxicol Sci. 2014 Jan;137(1):114-24. doi: 10.1093/toxsci/kft236. Epub 2013 Oct 23.


The contribution of environmental pollutants to liver fibrosis is an important and poorly explored issue. In vitro studies suggest that the environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other aryl hydrocarbon receptor (AhR) ligands induce several genes that are known to be upregulated during liver fibrosis. Our aim was to determine whether exposure to such pollutants can lead to liver fibrosis and to characterize the mechanisms of action. Mice were treated for 2, 14, or 42 days, once a week with 25 µg/kg of TCDD. Gene and protein expression, in vitro and in vivo, as well as liver histology were investigated for each treatment. Treatment of mice with TCDD for 2 weeks modified the hepatic expression of markers of fibrosis such as collagen 1A1 and α-smooth muscle actin. This is not observed in AhR knockout mice. Following 6 weeks of treatment, histological features of murine hepatic fibrosis became apparent. In parallel, the levels of inflammatory cytokines (interleukin-1 beta, tumor necrosis factor α) and of markers of activated fibroblasts(fibroblast-specific protein 1) were found to be upregulated. Interestingly, we also found increased expression of genes of the TGF-β pathway and a concomitant decrease of miR-200a levels. Because the transcription factors of the Snail family were shown to be involved in liver fibrosis, we studied their regulation by TCDD. Two members of the Snail family were increased, whereas their negative targets, the epithelial marker E-cadherin and Claudin 1, were decreased. Further, the expression of mesenchymal markers was increased. Finally, we confirmed that Snai2 is a direct transcriptional target of TCDD in the human hepatocarcinoma cell line, HepG2. The AhR ligand, TCDD, induces hepatic fibrosis by directly regulating profibrotic pathways.

Keywords: AhR; dioxin; inflammation.; liver diseases; mice.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / agonists*
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Chemical and Drug Induced Liver Injury / etiology*
  • Chemical and Drug Induced Liver Injury / genetics
  • Chemical and Drug Induced Liver Injury / metabolism
  • Chemical and Drug Induced Liver Injury / pathology
  • Dose-Response Relationship, Drug
  • Environmental Pollutants / toxicity*
  • Epithelial-Mesenchymal Transition / drug effects
  • Gene Expression Regulation
  • Hep G2 Cells
  • Humans
  • Inflammation Mediators / metabolism
  • Ligands
  • Liver / drug effects*
  • Liver / metabolism
  • Liver / pathology
  • Liver Cirrhosis / chemically induced*
  • Liver Cirrhosis / genetics
  • Liver Cirrhosis / metabolism
  • Liver Cirrhosis / pathology
  • Mice
  • Polychlorinated Dibenzodioxins / toxicity*
  • Receptors, Aryl Hydrocarbon / agonists*
  • Receptors, Aryl Hydrocarbon / genetics
  • Receptors, Aryl Hydrocarbon / metabolism
  • Snail Family Transcription Factors
  • Time Factors
  • Transcription Factors / genetics
  • Transcription Factors / metabolism


  • AHR protein, human
  • Ahr protein, mouse
  • Basic Helix-Loop-Helix Transcription Factors
  • Environmental Pollutants
  • Inflammation Mediators
  • Ligands
  • Polychlorinated Dibenzodioxins
  • Receptors, Aryl Hydrocarbon
  • SNAI2 protein, human
  • Snai2 protein, mouse
  • Snail Family Transcription Factors
  • Transcription Factors