Dietary AiiO-AIO6 mitigated Aeromonas hydrophila-induced intestinal inflammation in juvenile grass carp (Ctenopharyngodon idella) involving in NF-κB signaling and pyroptosis.

AiiO-AIO6 is a quorum-sensing quenching enzyme that could decrease the virulence of pathogenic bacteria, and improve animal immunity. However, the precise regulatory mechanism of AiiO-AIO6 on intestinal immunity remains unknown. Thus, this study aimed to reduce this knowledge gap. After feeding with graded levels of AIO-AIO6 (0.0 (un-supplemented group), 2.5, 5.0, 7.5, 10.0, and 12.5 U/g) for 70 days, juvenile grass carp was selected from each group for a 6-day Aeromonas hydrophila challenge test. Meanwhile, some other fish selected from un-supplemented control group were injected with saline as un-challenged control. Results showed that A. hydrophila infection increased enteritis morbidity, and caused intestinal inflammation in grass carp compared with saline group, while AiiO-AIO6 supplementation decreased enteritis morbidity, mitigated inflammatory cell infiltration, pyroptosis, and apoptosis in the intestine after A. hydrophila infection. Furthermore, both 5.0 and 7.5 U/g AiiO-AIO6 decreased gene expressions of tumor necrosis factor-α and interleukin-1β, and elevated gene expressions of transforming growth factor-β1 and IL-10, potentially associating with decreased NF-κB p65 and increased PPARγ signaling in the intestine. Supplementing 5.0 or 7.5 U/g AiiO-AIO6 also mitigated intestinal pyroptosis, as indicated by reduced mRNA levels of NLRP3, PYCARD, caspase-1, GSDME a, and GSDME b, and decreased protein levels of N-GSDME and IL-1β. Additionally, AiiO-AIO6 alleviated intestinal apoptosis, demonstrated by reduced gene expressions of pro-apoptotic genes apoptotic protease activating factor-1, Bcl-2 associated X protein, Fas ligand, and caspase-3, as well as c-Jun N-terminal kinase and mitogen-activated protein kinase p38, and elevated gene expressions of anti-apoptotic factors, B-cell lymphoma-2, myeloid cell leukemia 1, and inhibitor of apoptosis protein. Altogether, optimal levels of AiiO-AIO6 attenuated intestinal inflammation probably relating to down-regulated NF-κB signaling, and reduced NLRP3 and GSDME-mediated pyroptosis, and finally reduced apoptosis in the intestine of grass carp.