The occurrence of hepatopancreatic
necrosis syndrome (
HPNS) has seriously affected the sustainable development of Chinese mitten crab (Eriocheir sinensis) farming industry. Limited studies have focused on the immune responses in crabs with
HPNS.
Serine proteases (SPs) and SP homologs (SPHs) play important roles in the innate immunity of crustaceans. This study investigated the effects of
HPNS on the expression levels of genes related to
prophenoloxidase (proPO) activation system, and the relationship between Runt
transcription factor and the transcriptions of these genes. Eight SPs and five SPHs (SPH1-4, Mas) were identified from E. sinensis. SPs contain a catalytic triad of "HDS", while SPHs lack a catalytic residue. SPs and SPHs all contain a conservative Tryp_SPc domain. Evolutionary analysis showed that EsSPs, EsSPHs, EsPO, and EsRunt were clustered with SPs, SPHs, POs, and Runts of other arthropods, respectively. In crabs with
HPNS, the expression levels of six SPs (1, 3, 4, 6, 7, and 8), five SPHs, and PO were significantly upregulated in the hepatopancreas. The knockdown of EsRunt could evidently decrease the expression levels of four SPs (3, 4, 5 and 8), five SPHs (SPH1-4, Mas), and PO. Therefore, the occurrence of
HPNS activates the proPO system. Furthermore, the expression levels of partial genes related to proPO system were regulated by Runt. The activation of innate immune system may be a strategy for crabs with
HPNS to improve immunity and fight diseases. Our study provides a new understanding of the relationship between
HPNS and innate immunity.