Immune, inflammatory, autophagic and DNA damage responses to long-term HO exposure in different tissues of common carp (Cyprinus carpio).

Hydrogen peroxide (HO) is a stable reactive oxygen species (ROS) in aquatic environment, and high concentration of ambient HO may directly or indirectly affect aquatic animal health. However, the response mechanism of fish to ambient HO has not been well studied yet. Therefore, the aim of the study was to investigate the immune, inflammatory, autophagic and DNA damage responses to long-term HO exposure in different tissues of common carp. The results showed that HO exposure induced a significant immune response, with alterations in the levels of immune parameters including AKP, ACP, LZM, C3, HSP90 and HSP70 in different tissues. The inflammatory response evoked by HO exposure was associated with the activations of TLRs and NF-κB (P65) in the majority of tested tissues. The autophagy process was significantly affected by HO exposure, evidenced by the upregulations of the autophagy-related genes in liver, gills, muscle, intestines, heart and spleen and the downregulations in kidney. Meanwhile, the mRNA level of atm, a primary transducer of DNA damage response, was upregulated in liver, gills, intestines and spleen, and the DNA damage was evidenced by increased 8-OHdG level in intestines after HO exposure. Moreover, cell cycle regulation-related genes, including cyclin A1, B and/or E1, highly expressed in all tested tissues except heart after HO exposure. Interestingly, IBR analysis exhibited that immune, inflammatory, autophagic and DNA damage responses to HO exposure were in a dose-dependent and tissue-specific manner. These data may contribute to understanding HO toxicity for fish and assessing potential risk of HO in aquatic environment.