Immune function of cytosolic manganese superoxide dismutase from Macrobrachium rosenbergii in response to bacterial infection

Abstract

An excess of reactive oxygen species (ROS) usually disrupts the balance of the antioxidant system and impairs the homeostasis of cells, resulting in serious oxidative damage. Therefore, a better understanding of how the immune system protects itself against such excessive oxidative stress is crucial. SODs play an indispensable role in antioxidant defense and the innate immune system. Among those, MnSOD is one of the most being. Previous studies using crustaceans have focused much on the gene expression changes underlying pathogenic infections, which generally indicate that MnSOD is involved in the antibacterial immune process of crustaceans. Yet the detailed biological properties of MnSOD and mechanism by which it counters pathogen infection in Macrobrachium rosenbergii remain unclear. Here we first cloned the cytosolic MnSOD from M. rosenbergii (MrcMnSOD), and then analyzed its distribution in tissues and expression patterns under bacterial infection with Staphylococcus aureus and Vibrio parahaemolyticus. The results revealed MrcMnSOD widely distributed in the tested tissues, whose expression level was highest in the hepatopancreas, followed by the stomach and intestine. Infection with S. aureus and V. parahaemolyticus significantly up-regulated both total SOD activity and transcription level of MrcMnSOD. To further investigate the possible mechanism of MrcMnSOD's participation in that antibacterial immune response, an RNA knockdown assay in vivo was performed. After knocking down MrcMnSOD, a higher mortality rate and more residual bacteria in haemocytes were recorded than for control group. Furthermore, an in vitro bacterial agglutination assay of MrcMnSOD demonstrated MrcMnSOD harbors broad bacterial agglutination to both gram-negative and gram-positive bacteria. Overall, our findings strongly suggest that MrcMnSOD is only capable of modulating the host's redox state but also exerting an antibacterial function in M. rosenbergii, thus shedding new light on the immune functioning of MrcMnSOD in crustaceans. Importantly, this work provides a new perspective for disease prevention and control in farmed crustaceans.