Signaling pathways of oxidative stress in aquatic organisms exposed to xenobiotics

Oxidative stress is frequently generated in cells of organisms exposed to environmental pollutants. The production of reactive oxygen species can have either adaptive or maladaptive consequences for the organism as well as for the entire population. However, regarding fish species and other invertebrates exposed to aquatic xenobiotics, the signaling pathways of oxidative stress still lacks a comprehensive characterization. After reviewing the recent literature, we show that important pathways described in mammals are also activated in aquatic species in response to a variety of xenobiotics. A central actor is the Nrf2/Keap1 pathway, which regulates the expression of ARE-driven genes including Gr, Gpx, or Cat. Other important activated pathways concern PPAR, MAPKs, NF-κB, and even AhR. Moreover, the autophagy and apoptosis pathways are also involved in the cellular response to oxidative stress. Importantly, there exists crosstalks between these pathways, which together activate a complex cellular antioxidative machinery in response to different xenobiotics. However, our knowledge of these responses in aquatic organisms is still fragmentary. Efforts should be made to extend the number of studied species and better characterize the organ-dependency and age-dependency of the responses. However, the huge number and variety of chemicals present in the environment makes the task difficult. Deciphering these key pathways can help to understand the mode of action of pollutants and consequently help to assess the environmental risk in aquatic ecosystems.