Enhancement of reactive oxygen species metabolism by antioxidant enzyme Cu/Zn-SOD can block betanodavirus-induced necroptosis and suppress viral replication in fish cells

Very little is known about oxidative stress as a modulator of signaling between the host and virus in viral nervous necrosis (VNN) within the aquaculture field. In the present study, we examined whether blocking ROS signaling using mitochondrial Cu/Zn-SOD could affect host cell death and the viral replication of RGNNV during infection in fish cells. Upon the overexpression of Cu/Zn-SOD in fish GF-1 cells, superoxide generation in RGNNV infection was reduced 0.6-fold, which correlated to host cell viability in the middle–late stages. Regarding the regulation of reactive oxygen species (ROS) signaling by superoxide, Cu/Zn-SOD overexpression can enhance superoxide's metabolism to hydrogen peroxide, which suppresses the RIPK3-mediated cell death signals at 48 hpf. On the other hand, ROS-mediated signal suppression can enhance Bcl-2 family Bcl-2/Bcl-xL expression in the early and middle replication stages. Furthermore, the enhancement of superoxide metabolism can reduce the virus' replication ability and expression of the non-structural genes B1 and B2, as well as the genome replication gene Protein A and the major capsid protein protein α, which were correlated with the viral load dropping by two log viral titers at 48 and 72 hpf. Taken together, these data suggest that ROS signals trigger host stress responses related to cell death/necroptosis in RGNNV infection. Then, ROS-mediated stress signals can modulate anti-cell death signals through the Bcl-2/Bcl-xL pathway. In conclusion, an ROS-mediated stress response is required for viral expression and replication cycles, providing new insights into controlling RNA viruses.