miR-144 affects the immune response and activation of inflammatory responses in Cynoglossus semilaevis by regulating the expression of CsMAPK6.

MicroRNAs are increasingly recognized for their pivotal role in the immune system, yet the specific regulatory functions of fish-derived microRNAs remain largely unexplored. In this research, we discovered a novel miRNA, Cse-miR-144, in the Chinese tongue sole (Cynoglossus semilaevis), characterized by a 73-base pair precursor and a 21-nucleotide mature sequence. Our findings revealed that the expression of Cse-miR-144 was notably inhibited by various Vibrio species. Utilizing bioinformatics and dual-luciferase assay techniques, we established that the pro-inflammatory cytokine gene CsMAPK6 is a direct target of Cse-miR-144. Subsequent in vitro and in vivo western blotting analyses confirmed that Cse-miR-144 can effectively reduce the protein levels of CsMAPK6 post-transcriptionally. Moreover, CsMAPK6 is known to be involved in the activation of the Nuclear Factor kappa-light-chain-enhancer of activated B cells (NF-kB). Additional investigations using qPCR and ELISA demonstrated that suppression of Cse-miR-144 leads to an upsurge in the liver mRNA levels of various immune genes (including MYD88, TRAF6, NF-κB, TRAF2, TRAF3, and TNF), alongside a marked increase in the production and secretion of pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) in the bloodstream of C. semilaevis. These findings collectively underscore the potential of Cse-miR-144 as a key inhibitor of CsMAPK and its crucial role in modulating the immune and inflammatory responses in teleost fish. Compared to the siRNA, miRNA is a better tool in controlling the expression of target gene with a lower cost.