ROS induced by spring viraemia of carp virus activate the inflammatory response via the MAPK/AP-1 and PI3K signaling pathways

Spring viraemia of carp virus (SVCV) can cause a high mortality in common carp (Cyprinus carpio), and its main pathological processes include the inflammatory response. However, the detailed mechanism is still unclear. Reactive oxygen species (ROS) have been shown to play critical roles in the immune response, including inflammation, in different models. Our previous studies have demonstrated that SVCV infection results in the accumulation of ROS, including H2O2, in epithelioma papulosum cyprini (EPC) cells. In this study, we aimed to explore the relationship between H2O2 accumulation and inflammation during SVCV infection. After EPC cells were infected with SVCV, the expression levels of the inflammatory factors tumor necrosis factor (TNF)-alpha, cyclooxygenase (COX)-2, and interleukin (IL)-8 were up-regulated, while the expression of the anti-inflammatory factor interleukin (IL)-10 was down-regulated, compared with that in mock-infected EPC cells. The antioxidant N-acetyl-c-cysteine (NAC) could dampen the increased TNF-alpha and COX-2 expression induced by SVCV and H2O2, suggesting a relationship between ROS accumulation and inflammation during SVCV infection. Dual luciferase reporter assays demonstrated that SVCV could not activate the NF-kappa B pathway. In addition, inhibition of NF-kappa B by pyrrolidine dithiocarbamate (PDTC) treatment had no effect on the expression of inflammatory factors. Furthermore, inhibition of the ERK, JNK, and p38MAPK signaling pathways by U0126, 5P600125, and 5B203580, respectively, reduced the expression of TNF-alpha, COX-2, and IL-8, indicating that these three signaling pathways were all involved in the inflammatory response after SVCV infection. In addition, the PI3K signaling pathway was involved in the expression of the chemokine IL-8 in the SVCV-induced inflammatory response. We also showed that inhibition of the MAPK or PI3K signaling pathway facilitated the expression of SVCV-G as well as increased the SVCV viral titer. Altogether these results reveal the mechanism of the SVCV-mediated inflammatory response. Thus, targeting these signaling pathways may provide novel treatment strategies for SVCV-mediated diseases.