Roles of TLR3 and RIG-I in mediating the inflammatory response in mouse microglia following Japanese encephalitis virus infection.

Rong Jiang,Bibo Zhu,Yunfeng Song,Huanchun Chen,Jing Ye,Shengbo Cao

doi:10.1155/2014/787023

Abstract

Japanese encephalitis virus (JEV) infection can cause central nervous system disease with irreversible neurological damage in humans and animals. Evidence suggests that overactivation of microglia leads to greatly increased neuronal damage during JEV infection. However, the mechanism by which JEV induces the activation of microglia remains unclear. Toll-like receptor 3 (TLR3) and retinoic acid-inducible gene I (RIG-I) can recognize double-stranded RNA, and their downstream signaling results in production of proinflammatory mediators. In this study, we investigated the roles of TLR3 and RIG-I in the inflammatory response caused by JEV infection in the mouse microglial cell line. JEV infection induced the expression of TLR3 and RIG-I and the activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38MAPK). Knockdown of TLR3 and RIG-I attenuated activation of ERK, p38MAPK, activator protein 1 (AP-1), and nuclear factor κB (NF-κB). Secretion of TNF-α, IL-6, and CCL-2, which was induced by JEV, was reduced by TLR3 and RIG-I knockdown and inhibitors of phosphorylated ERK and p38MAPK. Furthermore, viral proliferation was increased following knockdown of TLR3 and RIG-I. Our findings suggest that the signaling pathways of TLR3 and RIG-I play important roles in the JEV-induced inflammatory response of microglia.

Highlights

Japanese encephalitis, one of the leading forms of endemic encephalitis in Eastern and Southern Asia, is caused by Japanese encephalitis virus (JEV), which belongs to the family Flaviviridae [1]
To determine whether microglial cells use these pattern recognition receptors (PRRs) for JEV recognition and induction of inflammatory mediators, the expression of retinoic acid-inducible gene I (RIG-I) and Toll-like receptor 3 (TLR3) in JEV- or mock-infected BV-2 cells was analyzed with western blotting
The levels of both RIG-1 and TLR3 were markedly increased in JEVinfected and poly(I : C)-treated cells compared with controls (Figure 1), suggesting that JEV infection stimulates the expression of RIG-I and TLR3 in microglia

Summary

Introduction

One of the leading forms of endemic encephalitis in Eastern and Southern Asia, is caused by Japanese encephalitis virus (JEV), which belongs to the family Flaviviridae [1]. JEV targets the central nervous system (CNS), leading to neuroinflammation with typical features of immune cell infiltration, neuronal death, and the activation of resident glial cells. Various mechanisms including virus-mediated killing and cytokine-mediated cytotoxicity have been reported as the causes of neuronal death. Uncontrolled overactivation of microglia may play an important role in inducing neuron death owing to the production of proinflammatory mediators [2]. These factors, including inducible nitric oxide synthase, cyclooxygenase-2, interleukin- (IL-) 6, IL-1β, tumor necrosis factor- (TNF-) α, chemokine (C-C motif) ligand 2 (CCL2), and CCL5, are significantly increased in microglia following JEV infection [7]. The cross-talk between neurons and microglia often influences the outcome of JEV pathogenesis [8]

Methods

Results

Conclusion