Regulation of Ahr signaling by Nrf2 during development: Effects of Nrf2a deficiency on PCB126 embryotoxicity in zebrafish (Danio rerio)

Rousseau, M.E., Sant, K.E., Borden, L.R., Franks, D.G., Hahn, M.E., Timme-Laragy, A.R.
Aquatic toxicology (Amsterdam, Netherlands)   167: 157-171 (Journal)
Registered Authors
Hahn, Mark E.
Dioxin-like compound, Embryonic development, Gene expression, Swim bladder, Transcription factor, Yolk
MeSH Terms
  • Animals
  • Embryo, Nonmammalian/drug effects*
  • Gene Expression Regulation, Developmental/drug effects
  • NF-E2-Related Factor 2/deficiency
  • NF-E2-Related Factor 2/genetics
  • NF-E2-Related Factor 2/metabolism*
  • Oxidative Stress/drug effects
  • Oxidative Stress/genetics
  • Polychlorinated Biphenyls/toxicity*
  • Receptors, Aryl Hydrocarbon/metabolism*
  • Signal Transduction/drug effects
  • Signal Transduction/genetics*
  • Water Pollutants, Chemical/toxicity*
  • Zebrafish/embryology
  • Zebrafish/physiology*
  • Zebrafish Proteins/deficiency
  • Zebrafish Proteins/genetics
  • Zebrafish Proteins/metabolism*
26325326 Full text @ Aquat. Toxicol.
The embryotoxicity of co-planar PCBs is regulated by the aryl hydrocarbon receptor (Ahr), and has been reported to involve oxidative stress. Ahr participates in crosstalk with another transcription factor, Nfe2l2, or Nrf2. Nrf2 binds to antioxidant response elements to regulate the adaptive response to oxidative stress. To explore aspects of the crosstalk between Nrf2 and Ahr and its impact on development, we used zebrafish (Danio rerio) with a mutated DNA binding domain in Nrf2a (nrf2a(fh318/fh318)), rendering these embryos more sensitive to oxidative stress. Embryos were exposed to 2nM or 5nM PCB126 at 24h post fertilization (prim-5 stage of pharyngula) and examined for gene expression and morphology at 4 days post fertilization (dpf; protruding - mouth stage). Nrf2a mutant eleutheroembryos were more sensitive to PCB126 toxicity at 4dpf, and in the absence of treatment also displayed some subtle developmental differences from wildtype embryos, including delayed inflation of the swim bladder and smaller yolk sacs. We used qPCR to measure changes in expression of the nrf gene family, keap1a, keap1b, the ahr gene family, and known target genes. cyp1a induction by PCB126 was enhanced in the Nrf2a mutants (156-fold in wildtypes vs. 228-fold in mutants exposed to 5nM). Decreased expression of heme oxygenase (decycling) 1 (hmox1) in the Nrf2a mutants was accompanied by increased nrf2b expression. Target genes of Nrf2a and AhR2, NAD(P)H:quinone oxidoreductase 1 (nqo1) and glutathione S-transferase, alpha-like (gsta1), showed a 2-5-fold increase in expression in the Nrf2a mutants as compared to wildtype. This study elucidates the interaction between two important transcription factor pathways in the developmental toxicity of co-planar PCBs.
Genes / Markers
Mutations / Transgenics
Human Disease / Model
Sequence Targeting Reagents
Engineered Foreign Genes