Herbal extracts interfere with bacterial adhesion and support apoptosis-dependent exfoliation to protect mammals against bacterial infection. In this study, juvenile yellow catfish were fed with control diet or Acanthopanax senticosus extracts (AS)supplemented diet. After 60 days, AS (180 ml/kg feed) significantly elevated fish growth and feed utilization, with higher weight gain and feed efficiency. After challenged with Edwardsiella ictaluri, survival rate of AS-supplemented fish (65%) was significantly higher than control fish (30%). Control fish exhibited obvious skin lesions since 1 day post-infection (dpi) and decreased thickness of epidermis with prolonged days, while AS-supplemented fish skin structure showed better integrity. Moreover, length of secondary branchial filaments of AS-supplemented fish was higher than control fish that showed obvious occlusion between adjacent lamellae. Unlike its proinflammatory role in spleen, AS significantly inhibited gill inflammation at 4 dpi via regulating TLRs-NFκB pathway. Moreover, haematoxylin-eosin staining exhibited that AS delayed the liver vasculitis and necrotic hepatitis of yellow catfish. Further study by TUNEL assay, caspase-3 activity and mRNA expression indicated that AS significantly promoted hepatic apoptosis at 1 dpi to prevent further necrosis, which process was regulated by JAK/STAT pathway. All results demonstrated AS modulated inflammation and apoptosis to protect yellow catfish against Edwardsiella ictaluri infection.

The susceptibility of animals to pathogenic infection is significantly affected by nutritional status. The present study took yellow catfish (Pelteobagrus fulvidraco) as a model to test the hypothesis that the protective roles of glutamine during bacterial infection are largely related to its regulation on the immune and antioxidant system, apoptosis and autophagy. Dietary glutamine supplementation significantly improved fish growth performance and feed utilization. After a challenge with Flavobacterium columnare, glutamine supplementation promoted il-8 and il-1β expression via NF-κB signaling in the head kidney and spleen, but inhibited the over-inflammation in the gut and gills. Additionally, dietary glutamine inclusion also enhanced the systematic antioxidant capacity. Histological analysis showed the protective role of glutamine in gill structures. Further study indicated that glutamine alleviated apoptosis during bacterial infection, along with the reduced protein levels of caspase-3 and the reduced expression of apoptosis-related genes. Moreover, glutamine also showed an inhibitory role in autophagy which was due to the increased activation of the mTOR signaling pathway. Thus, our study for the first time illustrated the regulatory roles of glutamine in the fish immune and antioxidant system, and reported its inhibitory effects on fish apoptosis and autophagy during bacterial infection.