Megalobrama amblycephala IL-22 attenuates Aeromonas hydrophila induced inflammation, apoptosis and tissue injury by regulating the ROS/NLRP3 inflammasome axis

Mammalian interleukin-22 (IL-22) attenuates organismal injury by inhibiting reactive oxygen species (ROS) and impeding the NLRP3 inflammasome activation. However, the role of fish IL-22 in this process remains unclear. We characterized MaIL-22, an IL-22 homolog in blunt snout bream (<i>Megalobrama amblycephala</i>). Despite its low sequence identity, it shares conserved structures and close evolutionary relationships with other teleost IL-22s. Furthermore, <i>Aeromonas hydrophila</i> (<i>A. hydrophila</i>) infection leads to tissue injury in <i>M. amblycephala</i> immune organs and concomitantly altered <i>Mail-22</i> mRNA expression, suggesting that MaIL-22 was involved in the antimicrobial immune response. To explore MaIL-22's biological functions, we produced recombinant MaIL-22 (rMaIL-22) protein and demonstrated it significantly enhanced the survival of <i>M. amblycephala</i> post-<i>A. hydrophila</i> infection. To unravel its protective mechanisms, we explored the ROS/NLRP3 inflammasome axis and its downstream signaling responses. The results showed that rMaIL-22 treatment significantly elevated antioxidant enzyme (T-SOD, CAT and GSH-PX) activities to inhibit MDA activity and scavenge ROS in visceral tissues. Meanwhile, rMaIL-22 impeded the activation of NLRP3 inflammasome by suppressing NLRP3 protein and mRNA expression. This indicated that rMaIL-22 contributed to inhibit <i>A. hydrophila</i>-induced activation of the ROS/NLRP3 inflammasome axis. Consistent with these findings, rMaIL-22 treatment attenuated the expression of proinflammatory cytokines (<i>il-1β</i>, <i>tnf-α</i> and <i>il-6</i>) and proapoptotic genes (<i>caspase-3</i> and <i>caspase-8</i>) while promoting antiapoptotic genes (<i>bcl-2b</i> and <i>mcl-1a</i>) expression, ultimately mitigating tissue injury in visceral tissues. In conclusion, our research underscores MaIL-22's key role in microbial immune regulation, offering insights for developing IL-22-targeted therapies and breeding programs.