Hippo-YAP pathway regulates antimicrobial immune response in obscure puffer <i>Takifugu obscurus</i>

The Hippo signaling pathway plays an important role in regulating host immune responses. However, few studies have explored its role in fish. Therefore, this study aimed to investigate the mechanism by which the Hippo pathway regulates the expression of antimicrobial peptides (AMPs) in obscure puffer Takifugu obscurus. After infection with Staphylococcus aureus or Vibrio harveyi, the expression of mammalian STE20-like protein kinase (ToMst) and Yes-associated protein (ToYap) was significantly upregulated in the liver, heart, and kidney of T. obscurus. Additionally, the phosphorylation level of ToMst increased. When ToMst phosphorylation was inhibited, the expression of inhibitor of kappa B (ToIκB) was upregulated, the translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (ToNF-κB) from the cytoplasm to the nucleus was inhibited, and the expression of AMPs (ToLyz, ToFerritin, and ToPerforin-1) was downregulated. Conversely, when ToMst was overexpressed, the expression of ToLyz, ToFerritin, and ToPerforin-1 increased. After bacterial stimulation, ToYap was translocated from the nucleus to the cytoplasm. When the expression of ToYap was knocked down by RNA interference, the expression of ToIκB in the kidney was downregulated, and the expression of ToLyz, ToFerritin, and ToPerforin-1 was upregulated. However, ToYap overexpression inhibited the expression of the three AMP genes. These findings indicate that ToYap negatively regulates the expression of AMPs by regulating the transcriptional activity of ToIκB. These findings reveal the molecular mechanism of the Hippo pathway in the antimicrobial immunity of T. obscurus and contribute to the development of new methods and strategies for treating diseases.