RIG-I Mediates Innate Immune Response in Mouse Neurons Following Japanese Encephalitis Virus Infection

Abstract

BackgroundNeuroinflammation associated with Japanese encephalitis (JE) is mainly due to the activation of glial cells with subsequent release of proinflammatory mediators from them. The recognition of viral RNA, in part, by the pattern recognition receptor retinoic acid-inducible gene I (RIG-I) has been indicated to have a role in such processes. Even though neurons are also known to express this receptor, its role after JE virus (JEV) infections is yet to be elucidated.Methodology/Principal FindingsUpon infecting murine neuroblastoma cells and primary cortical neurons with JEV the expression profile of key proinflammatory cyto/chemokines were analyzed by qRT-PCR and bead array, both before and after ablation of RIG-I. Immunoblotting was performed to evaluate the levels of key molecules downstream to RIG-I leading to production of proinflammatory mediators. Changes in the intracellular viral antigen expression were confirmed by intracellular staining and immunoblotting. JEV infection induced neuronal expression of IL-6, IL-12p70, MCP-1, IP-10 and TNF-α in a time-dependent manner, which showed significant reduction upon RIG-I ablation. Molecules downstream to RIG-I showed significant changes upon JEV-infection, that were modulated following RIG-I ablation. Ablation of RIG-I in neurons also increased their susceptibility to JEV.Conclusions/SignificanceIn this study we propose that neurons are one of the potential sources of proinflammatory cyto/chemokines in JEV-infected brain that are produced via RIG-I dependent pathways. Ablation of RIG-I in neurons leads to increased viral load and reduced release of the cyto/chemokines.

Innate Immune Mechanisms in Japanese Encephalitis Virus Infection: Effect on Transcription of Pattern Recognition Receptors in Mouse Neuronal Cells and Brain Tissue

“…Delineating the differential roles of MDA5 and RIG-I in recognition of double-stranded RNA viruses, Kato et al (14) observed that RIG-I is essential for eliciting protection against JEV through a robust interferon production, whereas MDA5 played a similar role in picornavirus infection. These observations, as well as recent studies by Nazmi et al (17,18) suggest that RIG-I could be a key pathway in controlling JEV infection. Studying the transcriptome profile in the brains of mice following JEV infection, Gupta and Rao (13) noted that there is an increased expression of mRNAs of TLR2, TLR3, and TLR7, suggesting that they have an important role in mediating inflammation and immune response to the virus.…”

“…The present study also revealed that these three TLRs are upregulated following JEV infection in suckling mice. Nazmi et al (17) reported that JEV infection results in increased expression of RIG-I in the neurons of mice. Further, they noted that virus infection resulted in activation of RIG-I leading to modulation in the downstream pathways that cause the infected neurons to participate in the inflammatory milieu in the CNS, which ultimately leads to their own demise (18).…”

“…Nazmi et al (2011) used GP78 strain of JEV, BALB/c mice and an MOI of 5, while in the present study, P20778 strain of JEV, C57BL6/J mice and an MOI of 0.1 were used. Although these studies (13,17,18) have added new information and thrown some light on the role of a few PRRs in JEV infection, they were not designed to comprehensively address the gamut of innate immune events that occur following JEV infection, especially delineating the role of all the PRRs. Furthermore, the cascade events that result following JEV infection in vitro as well as in vivo have not been identified.…”

MicroRNA-15b Modulates Japanese Encephalitis Virus–Mediated Inflammation via Targeting RNF125

“…Although we showed that RNF125 was targeted by miR-15b to regulate the JEV-induced inflammatory response, RNF125 is not the only target of miR-15b. Given that RIG-I plays essential roles in JEV-induced inflammation (46,55,56), we focused our current study on miR-15b-regulated RIG-I pathways. Further exploration of other potential targets of miR15b and more detailed mechanisms are required in future studies.…”

“…RIG-I, a cytoplasmic sensor for viral RNA, was shown to be essential in the mediation of the proinflammatory response following JEV infection (46,55,56). Many proteins are known to modify the RIG-I pathway and the subsequent cytokine signal transduction (34,51,57,58), but the role of miRNA-mediated regulation is only beginning to emerge.…”