Identification of the Nrf2–Keap1 pathway in the European eel Anguilla anguilla: Role for a transcriptional regulation of antioxidant genes in aquatic organisms

• Nrf2 and Keap1 sequences have been characterized in A. anguilla.
• Nrf2–Keap1 pathway modulates antioxidant genes in marine organisms.
• Transcription of Nrf2 sustains protracted induction of antioxidant genes.
• Keap1 variations act to switch off antioxidant responses.
• Regulation mechanisms are conserved between mammalian and marine organisms.

Antioxidant defences play a central role in cell protection against a wide variety of environmental stressors, their variations being thus frequently studied to reveal oxidative stress conditions in fish. The Nrf2–Keap1 pathway is among the main mechanisms of transcriptional regulation in mammalians, but its involvement in modulation of antioxidant system of aquatic organisms is still largely unexplored. The present study focused on the identification of Nrf2 and Keap1 in the European eel Anguilla anguilla using liver slices as an in vitro model during an oxidative challenge. The mRNA levels of Nrf2, Keap1 and typical Nrf2 target genes (catalase, glutathione peroxidase 1 and glutathione S-transferase pi) were analyzed at different H2O2 exposure times to investigate the time course activation of these molecular responses. Obtained results showed a coordinated transcriptional regulation of CAT, GPx1 and GSTpi, also suggesting that Nrf2 de novo synthesis is required for the protracted induction of such antioxidant genes. Further, Keap1 variations would support its role in switching off these molecular responses, providing novel insight on the importance of the Nrf2–Keap1 pathway in the regulation of antioxidant genes in marine species.