The activation of NLRP3 inflammasome and its function in anti-infection immunity of largemouth bass (Micropterus salmoides).

As an intracellular sensor, NLRP3 can recognize a variety of pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Upon activation, it assembles with the adaptor protein ASC and the effector molecule pro-Caspase-1 to form inflammasome complex, which is closely associated with various infectious and inflammatory diseases. However, the NLRP3 inflammasome has only been identified in a few teleost species, and its activation mechanism remains unclear. In the present study, four NLRP3 genes (MsNLRP3) were cloned and identified from the largemouth bass (Micropterus salmoides), and their roles in the assembly of inflammasome as well as anti-infection immune responses were investigated. It was found that there were significant differences in the number of LRR domains among these MsNLRP3. The four MsNLRP3 had the highest expression levels in the foregut and spleen of healthy largemouth bass, and the expression of MsNLRP3a was higher than others. In addition, the four MsNLRP3 genes could respond to Aeromonas hydrophila stimulation, and their expression levels in the spleen and foregut of largemouth bass were significantly increased. Notably, the four MsNLRP3 proteins could directly interact with MsASC and promote its oligomerization, among which MsNLRP3a had the strongest effect. They could activate MsCaspase-1 in a MsASC-dependent or MsASC-independent manner; however, the enzymatic activity was further enhanced in the presence of MsASC. Moreover, the four MsNLRP3 could induce pyroptosis and enhance cytotoxicity, among which MsNLRP3d had the strongest effect. Taken together, the results could enrich the research on the molecular diversity of NLRP3, and provide theoretical support for the prevention and control of infectious diseases in teleost.