Mechanistic role of Nrf2-Keap1 and JNK/p38 MAPK signaling in mercury-induced oxidative stress and apoptosis in monocytes/macrophages of Channa punctatus Bloch.

BACKGROUND: Mercury (Hg) is a hazardous environmental contaminant that presents significant threats to aquatic life via oxidative stress-induced cellular damage. This study examined mercury-induced oxidative stress and its influence on the regulation of antioxidant and apoptotic signaling pathways in the monocytes/macrophages of Channa punctatus Bloch. METHODS: Acclimatized fish were split into control and treatment groups are exposed to HgCl₂ (0.3 mg/L) for 7 days. Monocytes/macrophages were extracted and evaluated for ultrastructural modifications, oxidative stress indicators, antioxidant enzyme activity, and DNA damage. Reactive oxygen species (ROS), respiratory burst activity, lipid peroxidation, superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) concentrations were quantified. The expression of antioxidant signaling molecules (Nrf2, Keap1, and HO-1) was assessed, whereas apoptotic responses were examined via flow cytometry for caspase-3, caspase-8, caspase-9, TNF-α, p38, and p53, in conjunction with variations in cytochrome c protein levels. RESULTS: Mercury exposure resulted in considerable ultrastructural damage and increased reactive oxygen species (ROS) formation, respiratory burst activity, lipid peroxidation, DNA fragmentation, and superoxide dismutase (SOD) activity, alongside reduced catalase (CAT) and glutathione (GSH) levels. Dysregulation of the Nrf2–Keap1 signaling pathway and diminished HO-1 expression signify compromised antioxidant defense. The elevated expression of caspase-3, caspase-8, caspase-9, TNF-α, p38, and p53 confirmed the activation of apoptotic pathways. Alterations in cytochrome c and the activation of the JNK/p38 MAPK pathway further evidenced mitochondrial malfunction and the induction of apoptosis. CONCLUSIONS: Mercury exposure causes oxidative stress-related immune cell damage in C. punctatus by inhibiting antioxidant signaling and facilitating apoptosis through intrinsic and extrinsic pathways, with the JNK/p38-MAPK pathway acting as a crucial mechanistic connection.