fru-miR-138 targeting SOCS3 modulates the immune response of Japanese pufferfish (Takifugu rubripes) upon Vibrio harveyi infection.

MicroRNAs (miRNAs), a subclass of non-coding small RNA molecules, exert pivotal functions in regulating the immune responses of fish during pathogen infections. The Japanese pufferfish (Takifugu rubripes), a prominent commercial fish species in China, has experienced substantial economic losses due to infections caused by Vibrio harveyi. However, research on the immune modulatory effects of miRNAs in conferring resistance to Vibrio infections in the Japanese pufferfish remains scarce. In this study, high-throughput sequencing was applied to characterize the miRNA profile within the spleen of Japanese pufferfish following V. harveyi infection. The analysis revealed the identification of 106 conserved miRNAs alongside 170 putative novel miRNAs, amounting to a collective of 110 miRNAs exhibiting statistically significant differential expression in the spleen subsequent to infection. Target prediction analysis revealed that differentially expressed miRNA target genes were enriched in various immune-related signaling pathways. Furthermore, dual-luciferase reporter assays combined with both in vivo and in vitro overexpression experiments consistently demonstrated that fru-miR-138 directly targets and suppresses SOCS3 expression. Bacterial clearance assays showed that fru-miR-138 increased bacterial load in the spleen. These results establish a foundation for future investigations into the functions of miRNAs in immune responses during V. harveyi infection in Japanese pufferfish.