Alteration characteristics of intestinal mucosal immunity and transcriptome in Songpu mirror carp (Cyprinus carpio Songpu) exposed to acute cadmium exposure

This study focused on the acute toxic effects of cadmium (Cd) on Songpu mirror carp ( Cyprinus carpio Songpu) with an average body mass of (35.4 ± 0.4) g. Changes in intestinal immunity function and intestinal transcriptome were observed at 0, 6, 12, 24, 48, 72, and 96 h post-exposure to Cd at the low concentration (0.005 mg/L) and safe mass concentration (SMC) of Cd (1.25 mg/L). Results showed that 1.25 mg/L Cd exposure significantly reduced the activity of intestinal digestive enzymes. After 96 h, intestinal villi shedding was observed in both Cd exposure groups, with the 1.25 mg/L Cd group showing more severe damage. For the early stage of 0.005 mg/L Cd exposure, higher superoxide dismutase (SOD) activity and the expression of Nrf2 , CuMnSOD , GPX1a , ZO-1, claudin3 , claudin7, IL-6 and TNF-α occurred in 6–12 h, while the higher glutathione peroxidase (GSH-Px) activity and lower malondialdehyde (MDA) content occurred in 6–12 h. For the 1.25 mg/L Cd exposure, higher SOD and GSH-Px activities occurred in 24–48 h, while the lower MDA content and the expression of Nrf2 , CuMnSOD , GPX1a , occcludin , ZO-1, claudin3, IL-1β, IL-6 and TNF-α occurred in 12–24 h. Transcriptome data revealed that Cd exposure (close to or exceed SMC) could interfere with intestinal energy metabolism (such as lipid metabolism and amino acid metabolism), thereby leading to the generation and development of excessive oxidative stress. Overall, 6–12 h might become a sensitive time bucket for launching the intestinal immune response triggered by low-concentration Cd toxicity; whereas exposure to Cd at the safe mass concentration will delay the effective period of immunity until 12–24 h.