Screening of Natural Extracts for Inhibitors against Japanese Encephalitis Virus Infection

Guo, Jiao; Jia, Xiaoying; Liu, Yang; Wang, Shaobo; Cao, Junyuan; Zhang, Bo; Xiao, Gengfu; Wang, Wei

Cardiac glycoside acts via inhibiting the sodium-potassium ion pump, leading to changes in the intracellular concentration of sodium, potassium, and calcium, which have been shown to play essential roles in many cellular biosynthetic signaling and vesicular sorting pathways (26) . In this study, ouabain exhibited therapeutic effects on JEV infection in an adult mouse model by decreasing viral loads and alleviating pathological injuries in the brain, which significantly improved the survival rate of JEV-infected mice. We proposed two mechanisms that may contribute to the antiviral effects. First, ouabain may block JEV infection by inducing the cellular stress response. Ouabain treatment in mammalian cells causes the interaction between the inositol 1,4,5-trisphosphate (IP3) receptor and Na ϩ /K ϩ -ATPase to induce calcium oscillations and further activate calcium-dependent transcription factors, such as the NF-B and activator protein (27) . Some evidence suggested that cardiac glycosides mediate inflammatory processes via the activation of the phosphoinositide 3-kinase/Akt pathway and the Src/mitogen-activated protein kinase pathway (28, 29) . These signaling pathways also cause the activation of NF-B. Many of the genes expressed were elicited by activation of NF-B, including innate immune response, growth, and differentiation, which stimulate an antiviral state that might block JEV infection in the end (30) . Second, JEV could replicate in the central nervous system (CNS), and infections result in the breakdown of the blood-brain barrier (BBB) along with an influx of inflammatory cells; the breakdown of BBB caused by JEV infection may have allowed BBB-nonpermissive ouabain to enter the brain, bind the murine ATPase ␣2 and ␣3 isoforms (31) , and inhibit viral replication in neurons.