<scp>NAD</scp> ⁺ Homeostasis Attenuates Japanese Encephalitis Virus Infection Progression

Nicotinamide adenine dinucleotide (NAD⁺) is a crucial molecule involved in numerous interconnected metabolic processes. Due to its implication in multiple viral infection responses, maintaining NAD⁺ homeostasis has become a promising target for host-directed therapies. Japanese encephalitis virus (JEV) causes severe, fatal encephalitis with irreversible brain damage and long-lasting neurological deficits in survivors. However, the potential interaction between JEV infection and NAD⁺ metabolism remains largely unclear. In this study, we found that JEV infection dysregulates NAD⁺ metabolism and the expression of its pathway enzyme genes in Type I interferon (IFN-α/β) receptor-deficient (A129) mice and human glioblastoma (T98G) cells. Specifically, JEV infection altered the expression of de novo/kynurenine pathway (IDO, KATII, KMO) and salvage pathway (NAMPT, NMNATs) NAD⁺ biosynthetic enzymes, as well as NAD⁺-consuming enzymes (PARPs, SIRTs), culminating in a substantial decrease in NAD⁺ levels. Furthermore, NAD⁺ depletion and JEV production increased when salvage biosynthesis was restrained through NAMPT knockdown, but these effects were reversed by supplementing nicotinamide riboside (NR) in NAMPT knockdown T98G cells. Importantly, restoring NAD⁺ levels with NR supplementation as an anti-JE strategy in A129 mice reduced JEV production and improved infection outcomes. In conclusion, this study demonstrates that JEV infection disrupts NAD⁺ metabolism, and restoring NAD⁺ levels inhibits JE progression. Therefore, maintaining NAD⁺ homeostasis and regulating its metabolic pathway could be a promising therapeutic approach for JE.