Caspase-8 promotes innate immunity in the Chinese mitten crab by regulating the expression of antimicrobial peptides and apoptosis in hemocyte

In mammals, caspase-8 primarily functions as an initiator caspase that regulates apoptosis, while in Drosophila, the caspase-8 ortholog DREDD not only induces apoptosis during development but also regulates antimicrobial peptides (AMPs) expression during Gram-negative bacterial infection-induced immune responses. However, the immune-related function of caspase-8 in the crustacean remains unknown. In the present study, the open reading frame of EsCaspase-8 was cloned from the Chinese mitten crab (Eriocheir sinensis). The deduced EsCaspase-8 protein sequence contained only one death effector domain (DED) and a cysteine aspartase cysteine structural domain. The EsCaspase-8 expression was significantly induced after 6 h of Vibrio parahaemolyticus infection and continued to 24 h in hemocyte. Knocking down EsCaspase-8 expression in hemocytes significantly inhibited Relish's nuclear translocation and suppressed the expression of AMPs, including Crustin 1, Crustin 2, Lysosome, and double WAP domain, after V. parahaemolyticus infection. Furthermore, the knockdown of EsCaspase-8 in vivo significantly inhibited hemocyte apoptosis post-bacterial infection. These results demonstrated that EsCaspase-8 can promote antibacterial activities by regulating the expression of AMPs through activation of Relish nuclear translocation in Chinese mitten crabs, thus acting as a critical positive regulator in innate immunity. In addition, EsCaspase-8 also has the function of inducing hemocyte apoptosis. These findings expand our understanding of the molecular mechanisms underlying crustacean immune responses and provide a foundation for future research to improve disease resistance.