Interactive effects of temperature and salinity on the apoptosis, antioxidant enzymes, and MAPK signaling pathway of juvenile pufferfish (Takifugu fasciatus)

Takifugu fasciatus is an anadromous fish widely distributed in East Asia and often experiences fluctuations in temperature and salinity. This study investigated the effects of the interactions between temperature and salinity on apoptosis, antioxidant enzymes, and mitogen-activated protein kinase (MAPK) signaling pathways in the liver of T. fasciatus. The temperature (25, 21, 17, and 13 ℃) and salinity (0, 10, and 20 ppt salinity) were conducted with three replicates for each treatment. Quantitative reverse transcription-PCR (qRT-PCR), western blotting, and TdT-mediated dUTP Nick-End Labeling (Tunel) assays were used to detect mRNA expression, protein levels, and apoptosis levels. The expressions of caspase 3, 7, 9, and the apoptosis index increased in T. fasciatus as the temperature decreased, while the expression of B-cell lymphoma-2 (BCL-2) decreased. The correlation results in this study showed that after the exposure to 10 ppt salinity at 13 and 17 ℃, the glutathione peroxidase (GSH-PX) activity and malondialdehyde (MDA) concentration, caspase3, 7, and 9 expressions, and apoptosis index were decreased as compared with those in the control. In addition, there were no deaths and no significant change in apoptosis in the group at 21 ℃, and there were a small number of deaths in the 20 ppt, 25 ℃ groups. Correspondingly, MDA concentration and total superoxide dismutase (T-SOD) activity, caspase7 and 9 expressions, and apoptosis index in the liver were significantly higher in the 20 ppt, 25 ℃ groups than in the 0 ppt, 25 ℃, and 10 ppt, 25 ℃ groups. In addition, salinity had no significant influence on the expression of p-p38 MAPK and its phosphorylation ratio (p-p38/p38) at low temperatures but significantly affected its downstream transcription factors (ATF2, ElK-1, MEF2, and P53). Our study provides a reference for healthy cultures of T. fasciatus.