Grass carp superoxide dismutases exert antioxidant function and inhibit autophagy to promote grass carp reovirus (GCRV) replication

Superoxide dismutases (SODs) are potent antioxidants crucial for neutralizing reactive oxygen species (ROS) and protecting organisms from oxidative damage. In this study, we successfully cloned and analyzed two SOD genes, CiSOD1 and CiSOD2, from grass carp (Ctenopharyngodon idellus). CiSOD1 consists of two CuZn signature motifs and two conserved cysteine residues, while CiSOD2 contains a single Mn signature motif. The expression of CiSODs was found to be ubiquitous across all examined tissues, with their expression levels significantly altered after stimulation by grass carp reovirus (GCRV) or pathogen-associated molecular patterns (PAMPs). CiSOD1 was observed to be uniformly distributed in the cytoplasm, whereas CiSOD2 localized in the mitochondria. Escherichia coli transformed with both CiSODs demonstrated enhanced host resistance to H2O2 and heavy metals. Additionally, purified recombinant CiSOD proteins effectively protected DNA against oxidative damage. Furthermore, overexpression of CiSODs in fish cells reduced intracellular ROS, inhibited autophagy, and then resulted in the promotion of GCRV replication. Knockdown of CiSODs showed opposite trends. Notably, these roles of CiSODs in autophagy and GCRV replication were reversed upon treatment with an autophagy inducer. In summary, our findings suggest that grass carp SODs play an important role in decreasing intracellular ROS levels, inhibiting autophagy, and subsequently promoting GCRV replication.