Energy response and modulation of AMPK pathway of the olive flounder Paralichthys olivaceus in low-temperature challenged

Cold resistance is important for fish in natural and aquaculture environments. Modulation of energy metabolism has been proved to be vital for fish in cold. However, the interaction of energy response and the known AMPK pathway remains vague in fish coping with cold stress. In the present study, the olive flounders Paralichthys olivaceus were subject to low-temperature condition (0.2 ± 0.2 °C). The energy metabolism and modulation of AMPK pathway were analyzed. Results showed that flounders increased ATP-coupled ion transport, as indicated by Na+/K+-ATPase and Ca2 +/Mg2 +-ATPase activities. Nevertheless, higher levels of aerobic and anaerobic metabolism, respectively indicated by the elevation of COX and LDH activities, contributed to the stable energy homeostasis during cold exposure. The three subunits of AMPK responded differently to cold, and AMPKα and AMPKβ might be more sensitive in the early stage while AMPKγ might be more sensitive in the later stage. The transcriptional response of LKB1/CaMKKβ-AMPK-NRF1 axis might play an important role in helping flounders against the early cold stress. However, flounders differentiated in cold resistance with the stress time elapsed. Concomitantly a greater reliance on LKB1-AMPK-NRF1 axis for cold-tolerant flounders compared to those sensitive ones to cold was observed, and this axis was speculated to be related with flounder cold resistance. To our knowledge, this is the first time to explore the possible response of AMPK pathway to cold in fish. Our data showed that the flounder relied on metabolic regulation and modulation of AMPK pathway including not only higher expression levels of genes in this pathway but also changes in its related function axes to maintain energy homeostasis.