Asparagine Availability Is a Critical Limiting Factor for Infectious Spleen and Kidney Necrosis Virus Replication

Infectious spleen and kidney necrosis virus (ISKNV) has brought huge economic loss to the aquaculture industry. Through interfering with the viral replication and proliferation process that depends on host cells, its pathogenicity can be effectively reduced. In this study, we investigated the role of asparagine metabolites in ISKNV proliferation. The results showed that ISKNV infection up-regulated the expression of some key enzymes of the asparagine metabolic pathway in Chinese perch brain (CPB) cells. These key enzymes, including glutamic oxaloacetic transaminase 1/2 (GOT1/2) and malate dehydrogenase1/2 (MDH1/2) associated with the malate-aspartate shuttle (MAS) pathway and asparagine synthetase (ASNS) involved in the asparagine biosynthesis pathway, were up-regulated during ISKNV replication and release stages. In addition, results showed that the production of ISKNV was significantly reduced by inhibiting the MAS pathway or reducing the expression of ASNS by 1.3-fold and 0.6-fold, respectively, indicating that asparagine was a critical limiting metabolite for ISKNV protein synthesis. Furthermore, when asparagine was added to the medium without glutamine, ISKNV copy number was restored to 92% of that in the complete medium, indicating that ISKNV could be fully rescued from the absence of glutamine by supplementing asparagine. The above results indicated that asparagine was a critical factor in limiting the effective replication of ISKNV, which provided a new idea for the treatment of aquatic viral diseases.