Effects of Janus kinase (JAK) on hemocyte proliferation and disease resistance in Scylla paramamosain

Abstract

Janus kinase (JAK), a nonreceptor tyrosine kinase, is the JAK-signal transducer and activator of transcription (STAT) signaling pathway. In this study, RNA interference technology was used to knockdown the expression of JAK to explore the immune function of JAK in Scylla paramamosain. JAK expression was relatively high in the intestine and relatively low in the heart and hemocytes of S. paramamosain. JAK was highly expressed in all examined tissues of S. paramamosain after infection with white spot syndrome virus (WSSV) or Vibrio alginolyticus. The expression levels of Astakine, STAT, CAP, TLR, proPO, and CTL were downregulated, while MCM7, Myosin and Relish expression was upregulated in hemocytes at 24 h after injection of JAK-dsRNA. Astakine expression was significantly downregulated within 72 h after injection of JAK-dsRNA. The total hemocyte count and hemocyte proliferation were significantly decreased after treatment with Astakine-dsRNA or JAK-dsRNA. The results showed that JAK may promote hemocyte proliferation, probably by regulating Astakine expression. The activities of phenoloxidase, superoxide dismutase, and lysozyme were decreased significantly, while production of reactive oxygen species was increased significantly in hemocytes after treatment with JAK-dsRNA. After JAK knockdown, the phagocytosis rate of WSSV or V. alginolyticus in hemocytes was increased. After WSSV challenge, the WSSV copy number in the JAK-dsRNA-treated group was higher than that in the WSSV group. After V. alginolyticus challenge, the apoptosis rate of hemocytes in the JAK-dsRNA group was higher than that in the V. alginolyticus group. The mortality rate of WSSV or V. alginolyticus-infected crabs after JAK knockdown was higher than that of the infection group. These results suggest that JAK can regulate the expression of some immune-related genes, such as Astakine, to influence the innate immune response of S. paramamosain against pathogens (WSSV or V. alginolyticus), mostly by regulating enzyme activities, hemocyte phagocytosis and apoptosis.