A Possible Role of Crustacean Cardioactive Peptide in Regulating Immune Response in Hepatopancreas of Mud Crab

Crustacean cardioactive peptide (CCAP), a cyclic amidated non-apeptide, is widely found in arthropods. The functions of CCAP have been revealed to include regulation of heart rate, intestinal peristalsis, molting, and osmotic pressure. However, to date, there has not been any report on the possible involvement of CCAP in immunoregulation in crustaceans. In this study, a CCAP precursor (designated as -CCAP) was identified in the commercially important mud crab , which could be processed into four CCAP-associated peptides and one mature peptide (PFCNAFTGC-NH ). Bioinformatics analysis indicated that -CCAP was highly conserved in crustaceans. RT-PCR results revealed that was expressed in nerve tissues and gonads, whereas the -CCAP receptor gene ( ) was expressed in 12 tissues of , including hepatopancreas. hybridization further showed that an -positive signal is mainly localized in the F-cells of hepatopancreas. Moreover, the mRNA expression level of in the hepatopancreas was significantly up-regulated after lipopolysaccharide (LPS) or polyriboinosinic polyribocytidylic acid [Poly (I:C)] challenge. Meanwhile, the mRNA expression level of , nuclear transcription factor NF-κB homologs ( and ), member of mitogen-activated protein kinase (MAPK) signaling pathway ( ), pro-inflammatory cytokines factor ( and ), and antimicrobial peptide ( , and ) in the hepatopancreas were all up-regulated after the administration of synthetic -CCAP mature peptide both and . The addition of synthetic -CCAP mature peptide also led to an increase in nitric oxide (NO) concentration and an improved bacterial clearance ability in the hepatopancreas culture medium. The present study suggested that -CCAP signaling system might be involved in the immune responses of by activating immune molecules on the hepatopancreas. Collectively, our findings shed new light on neuroendocrine-immune regulatory system in arthropods and could potentially provide a new strategy for disease prevention and control for mud crab aquaculture.