Dihydromyricetin switches pyroptosis to apoptosis during Aeromonas hydrophila infection in Mylopharyngodon piceus.

Ampelopsis grossedentata is a traditional Chinese medicine used to treat fever, anti-inflammatory and parasitic infections. Dihydromyricetin is one of the flavonoids with high content, which has been proved to have certain antibacterial and anti-inflammatory effects. However, its antibacterial mechanism is still unclear. In this study, the mechanisms by which A. grossedentata extract and dihydromyricetin promote the organism's defence against A. hydrophila were investigated. The results showed that both A. grossedentata grape extract and dihydromyricetin (DMY) promoted the expression of IL1β in MPK cells. A. hydrophila infection resulted in a significant increase in the expression of caspase1, IL1β, and GSDME, and a significant enhancement of IL1β and LDH release, which were slowed down by DMY. Differently, on the basis of the up-regulation of A. hydrophila, DMY treatment further enhanced the expression of caspase3 and BAX and the activity of caspase3 resulting in stronger apoptosis. And at the same time, the titer of A. hydrophila was decreased by DMY treatment. In black carp (Mylopharyngodon piceus), injections of A. grossedentata extract and DMY also significantly reduced the lethality of A. hydrophila. The up-regulation of the expression of genes associated with pyroptosis due to A. hydrophila infection in splenocytes was attenuated by dihydromyricetin treatment, whereas the expression of apoptosis-associated genes was significantly enhanced. Tissue sections showed significant damage to splenic tissue following A. hydrophila infection, whereas splenic damage was alleviated and its apoptosis-associated DNA breaks were enhanced by dihydromyricetin injection. DMY may regulate multiple modes of cell death in cells. Further studies revealed that TBK1 may be a molecular target of DMY because of their high structural binding potential and as well as functional synergy and relevance. Therefore, these data implied that DMY potentially regulates TBK1 to transform A. hydrophila-induced pyroptosis into apoptosis. This provides a theoretical basis for the application of dihydromyricetin as an antibiotic alternative and feed additive in aquaculture.