Cortisol signaling and stress-induced gene expressions in response to copper toxicity through heat stress during zebrafish embryogenesis
Abstract Climate change is leading to an increase in temperatures, which has a stressful impact on the aquatic environment. Cortisol signaling is involved in enhancing metabolic processes such as anti-oxidation, immune defense, and osmoregulation, under stress conditions in fish. The present study aimed at evaluating the effects of copper (Cu) toxicity along with an increase in temperature during zebrafish embryogenesis, based on the transcriptional responses of cortisol and stress-related genes. A decreased survival rate was observed following combined exposure to high temperature and Cu. Heart rates of zebrafish embryos significantly increased only during heat stress. An abnormal morphology was induced by exposure to a combination of Cu and heat stress. Furthermore, heat stress also triggered Cu-induced intracellular reactive oxygen species production with upregulation of superoxide dismutase (SOD) and glutathione s-transferase (GST) and cell death with modified expressions of p53 and B-cell lymphoma-2 (Bcl-2) in the zebrafish embryo. Finally, increased cortisol level and altered expressions of cortisol-signaling genes were observed following exposure to Cu and high temperature. These results highlight that the realistic exposure to combined stressors disturbs cortisol-related defense pathways as well as the stress-induced processes of anti-oxidation and cell death in fish.