Chemokine profiling of Japanese encephalitis virus-infected mouse neuroblastoma cells by microarray and real-time RT-PCR: implication in neuropathogenesis

Japanese Encephalitis Virus-Infected Cells

RNA virus infections have been a leading cause of pandemics. Aided by global warming and increased connectivity, their threat is likely to increase over time. The flaviviruses are one such RNA virus family, and its prototypes such as the Japanese encephalitis virus (JEV), Dengue virus, Zika virus, West Nile virus, etc., pose a significant health burden on several endemic countries. All viruses start off their life cycle with an infected cell, wherein a series of events are set in motion as the virus and host battle for autonomy. With their remarkable capacity to hijack cellular systems and, subvert/escape defence pathways, viruses are able to establish infection and disseminate in the body, causing disease. Using this strategy, JEV replicates and spreads through several cell types such as epithelial cells, fibroblasts, monocytes and macrophages, and ultimately breaches the blood-brain barrier to infect neurons and microglia. The neurotropic nature of JEV, its high burden on the paediatric population, and its lack of any specific antivirals/treatment strategies emphasise the need for biomedical research-driven solutions. Here, we highlight the latest research developments on Japanese encephalitis virus-infected cells and discuss how these can aid in the development of future therapies.

Recent advances to overcome the burden of Japanese encephalitis: A zoonotic infection with problematic early detection

Japanese encephalitis (JE) is a vector-borne neurotropic disease caused by Japanese encephalitis virus (JEV) associated with high mortality rate distributed from Eastern and Southern Asia to Northern Queensland (Australia). The challenges in early detection and lack of point-of-care biomarkers make it the most important Flavivirus causing encephalitis. There is no specific treatment for the disease, although vaccines are licenced. In this review, we focussed on point-of-care biomarkers as early detection tools and developing the effective therapeutic agents that could halt JE. We have also provided molecular details of JEV, disease progression, and its pathogenesis with recent findings which might bring insights to overcome the disease burden.

Pathobiology of Japanese encephalitis virus infection

Japanese encephalitis virus (JEV) is a flavivirus, spread by the bite of carrier Culex mosquitoes. The subsequent disease caused is Japanese encephalitis (JE), which is the leading global cause of virus-induced encephalitis. The disease is predominant in the entire Asia-Pacific region with the potential of global spread. JEV is highly neuroinvasive with symptoms ranging from mild fever to severe encephalitis and death. One-third of JE infections are fatal, and half of the survivors develop permanent neurological sequelae. Disease prognosis is determined by a series of complex and intertwined signaling events dictated both by the virus and the host. All flaviviruses, including JEV replicate in close association with ER derived membranes by channelizing the protein and lipid components of the ER. This leads to activation of acute stress responses in the infected cell-oxidative stress, ER stress, and autophagy. The host innate immune and inflammatory responses also enter the fray, the components of which are inextricably linked to the cellular stress responses. These are especially crucial in the periphery for dendritic cell maturation and establishment of adaptive immunity. The pathogenesis of JEV is a combination of direct virus induced neuronal cell death and an uncontrolled neuroinflammatory response. Here we provide a comprehensive review of the JEV life cycle and how the cellular stress responses dictate the pathobiology and resulting immune response. We also deliberate on how modulation of these stress pathways could be a potential strategy to develop therapeutic interventions, and define the persisting challenges.

Upregulated expression of the antioxidant sestrin 2 identified by transcriptomic analysis of Japanese encephalitis virus-infected SH-SY5Y neuroblastoma cells

Japanese encephalitis virus (JEV) exerts a profound burden of viral encephalitis. We have investigated the differentially expressed transcripts in the neuronal transcriptome during JEV infection by RNA sequencing (RNA-Seq) of virus-infected SH-SY5Y human neuroblastoma cells. Gene ontology analysis revealed significant enrichment from two main pathways: endoplasmic reticulum (ER)-nucleus signaling (P value: 5.75E-18; false discovery rate [FDR] 3.11E-15) and the ER unfolded protein response (P value: 7.58E-18; FDR 3.11E-15). qPCR validation showed significant upregulation and differential expression (P < 0.01) of ER stress-signaling transcripts (SESN2, TRIB3, DDIT3, DDIT4, XBP1, and ATF4) at 24 h post-infection for both low (LN) and high (HN) neurovirulence JEV strains. Immunoblot analysis following JEV infection of SH-SY5Y cells showed an increase in levels of SESN2 protein following JEV infection. Similarly, Zika virus (MR766) infection of SH-SY5Y showed a titer-dependent increase in ER stress-signaling transcripts; however, this was absent or diminished for DDIT4 and ATF4, respectively, suggestive of differences in the induction of stress-response transcripts between flaviviruses. Interestingly, SLC7A11 and SLC3A2 mRNA were also both deregulated in JEV-infected SH-SY5Y cells and encode the two constituent subunits of the plasma membrane xCT amino acid antiporter that relieves oxidative stress by export of glutamate and import of cystine. Infection of SH-SY5Y and HEK293T cells by the JEV HN strain Sw/Mie/40/2004 lead to significant upregulation of the SLC7A11 mRNA to levels comparable to DDIT3. Our findings suggest upregulation of antioxidants including SESN2 and, also, the xCT antiporter occurs to counteract the oxidative stress elicited by JEV infection.

Neuronal transcriptomic responses to Japanese encephalitis virus infection with a special focus on chemokine CXCL11 and pattern recognition receptors RIG-1 and MDA5

Japanese encephalitis virus (JEV) causes central nervous system neuronal injury and inflammation. A clear understanding of neuronal responses to JEV infection remains elusive. Using the Affymetrix array to investigate the transcriptome of infected SK-N-MC cells, 1316 and 2737 dysregulated genes (≥ 2/-2 fold change, P < 0.05) were found at 48 hours post-infection (hpi) and 60 hpi, respectively. The genes were mainly involved in anti-microbial responses, cell signalling, cellular function and maintenance, and cell death and survival. Among the most highly upregulated genes (≥ 10 folds, P < 0.05) were chemokines CCL5, CXCL11, IL8 and CXCL10. The upregulation and expression of CXCL11 were confirmed by qRT-PCR and immunofluorescence. Pathogen recognition receptors retinoic acid-inducible gene-1 (RIG-1) and melanoma differentiation-associated protein 5 (MDA5) were also upregulated. Our results strongly suggest that neuronal cells play a significant role in immunity against JEV. CXCL11, RIG-1 and MDA5 and other cytokines may be important in neuropathogenesis.

Nitrosporeusine analogue ameliorates Chandipura virus induced inflammatory response in CNS via NFκb inactivation in microglia

Chandipura Virus (CHPV), a negative-stranded RNA virus belonging to the Rhabdoviridae family, has been previously reported to bring neuronal apoptosis by activating several factors leading to neurodegeneration. Following virus infection of the central nervous system, microglia, the ontogenetic and functional equivalents of macrophages in somatic tissues gets activated and starts secreting chemokines, thereby recruiting peripheral leukocytes into the brain parenchyma. In the present study, we have systemically examined the effect of CHPV on microglia and the activation of cellular signalling pathways leading to chemokine expression upon CHPV infection. Protein and mRNA expression profiles of chemokine genes revealed that CHPV infection strongly induces the expression of CXC chemokine ligand 10 (CXCL10) and CC chemokine ligand 5 (CCL5) in microglia. CHPV infection triggered the activation of signalling pathways mediated by mitogen-activated protein kinases, including p38, JNK 1 and 2, and nuclear factor κB (NF-kappaB). CHPV-induced expression of CXCL10 and CCL5 was achieved by the activation of p38 and NF-kappaB pathways. Considering the important role of inflammation in neurodegeneration, we have targeted NF-kappaB using a newly synthesised natural product nitrosporeusine analogue and showed incapability of microglial supernatant of inducing apoptosis in neurons after treatment.

Chemokine receptor antagonist block inflammation and therapy Japanese encephalitis virus infection in mouse model

Japanese encephalitis (JE) is a viral encephalitis disease caused by infection with the Japanese encephalitis virus (JEV). The virus can cross the blood-brain barrier and cause death or long-term sequela in infected humans or animals. In this study, we first investigated the distribution of JEV infection in brain and further analyzed the dynamic change in inflammation related genes, chemokines, as well as pathological characteristics. Results demonstrated that CCR2 and CCR5 antagonist could significantly inhibit the inflammation. The mice treated with CCR2 and CCR5 antagonists had a higher survival rate between 60% and 70%, respectively. In summary, our study thoroughly illustrated the characteristics of the dynamic change in inflammation related genes and chemokines induced by JEV infection. We further indicated that CCR5 and CCR2 are potential targets for treatment of JE.

Respiratory syncytial virus prolifically infects N2a neuronal cells, leading to TLR4 and nucleolin protein modulations and RSV F protein co-localization with TLR4 and nucleolin

BACKGROUND

Respiratory syncytial virus (RSV) infects the central nervous system, resulting in neurological symptoms. However, the precise underlying pathogenic mechanisms have not been elucidated. In the present study, the infectivity of RSV on N2a neuronal cells and the possible roles of Toll-like receptor 4 (TLR4) and nucleolin (C23) during RSV infection were investigated.

METHODS

We compared two experimental groups (infected and non-infected) and monitored the RSV viral titers in the culture supernatant by a viral plaque assay. We also inspected the morphology of the nucleus in infected N2a cells. We measured the level of RSV F protein and studied its co-localization with TLR4 and nucleolin using immunofluorescence assays and laser confocal microscopy. The potential interaction of RSV F protein with TLR4 and nucleolin was examined by coimmunoprecipitation. The expression changes of TLR4, nucleolin, TLR3 and TLR7 proteins in N2a cells and IL-6 and TNF-α in the culture supernatant were investigated by Western Blot analysis and ELISA assay. Changes in neuronal cell apoptosis status was examined by flow cytometry.

RESULTS

The results demonstrated prolific RSV infection of N2a cells, which triggered a decrease of NeuN protein expression, coinciding with an increase of nuclear lesions, F protein expression, RSV viral titers, and late apoptotic levels of N2a cells. RSV infection induced co-localization of RSV F protein with TLR4 and nucleolin, which could potentially lead to a direct interaction. Furthermore, it was found that TLR4 and nucleolin levels increased early after infection and decreased subsequently, whereas TLR3 and TLR7 expression increased throughout RSV infection.

CONCLUSION

The RSV Long strain can prolifically infect N2a neuronal cells, modulating the expression of TLR4 and nucleolin, as well as TLR3, TLR7 and their downstream inflammatory factors, and inducing the co-localization of the RSV F protein with TLR4 and nucleolin.

Interferon regulated gene (IRG) expression-signature in a mouse model of chikungunya virus neurovirulence

Interferon regulated genes (IRGs) are critical in controlling virus infections. Here, we analyzed the expression profile of IRGs in the brain tissue in a mouse model of chikungunya virus (CHIKV) neurovirulence. Neurovirulence is one of the newer complications identified in disease caused by re-emerging strains of CHIKV, an alphavirus with positive-strand RNA in the Togaviridae family. In microarray analysis, we identified significant upregulation of 269 genes, out of which a predominant percentage (76%) was IRGs. The highly modulated IRGs included Ifit1, Ifi44, Ddx60, Usp18, Stat1, Rtp4, Mnda, Gbp3, Gbp4, Gbp7, Oasl2, Oas1g, Ly6a, Igtp, and Gbp10, along with many others exhibiting lesser changes in expression levels. We found that these IRG mRNA transcripts are modulated in parallel across CHIKV-infected mouse brain tissues, human neuronal cell line IMR-32 and hepatic cell line Huh-7. The genes identified to be highly modulated both in mouse brain and human neuronal cells were Ifit1, Ifi44, Ddx60, Usp18, and Mnda. In Huh-7 cells, however, only two IRGs (Gbp4 and Gbp7) showed a similar level of upregulation. Concordant modulation of IRGs in both mice and human cells indicates that they might play important roles in regulating CHIKV replication in the central nervous system (CNS). The induction of several IRGs in CNS during infection underscores the robustness of IRG-mediated innate immune response in CHIKV restriction. Further studies on these IRGs would help in evolving possibilities for their targeting in host-directed therapeutic interventions against CHIKV.

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

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.

Gene-expression patterns in the cerebral cortex of mice infected with porcine haemagglutinating encephalomyelitis virus detected using microarray

Porcine haemagglutinating encephalomyelitis virus (PHEV) is the main causative agent of porcine coronavirus-associated disease, which is characterized by encephalomyelitis and involves the central nervous system. Little is known about the molecular mechanisms of brain injury caused by PHEV. To gain insight into the interaction between the virus and host cells, changes in global gene expression in the cerebral cortex of PHEV- or mock-infected mice were investigated using DNA microarray analysis and quantitative real-time PCR. The results of the microarray analysis showed that 365 genes on day 3 post-infection (p.i.) and 781 genes on day 5 p.i. were differentially expressed in response to PHEV infection in the cerebral cortex. The upregulated genes were mainly involved in immune system processes, antigen processing and presentation, the Jak-STAT signalling pathway, the RIG-I-like receptor signalling pathway, Toll-like receptor signalling and apoptosis-related proteases. Significantly downregulated genes were mainly involved in nervous-system development, synaptic transmission, neuron-projection development, the transmission of nerve impulses and negative regulation of glial cell differentiation. The differential expression of these genes suggests a strong antiviral host response, but may also contribute to the pathogenesis of PHEV resulting in encephalomyelitis.

Etanercept reduces neuroinflammation and lethality in mouse model of Japanese encephalitis

BACKGROUND

Japanese encephalitis virus (JEV) is a neurotropic flavivirus that causes Japanese encephalitis (JE), which leads to high fatality rates in human. Tumor necrosis factor alpha (TNF-α) is a key factor that mediates immunopathology in the central nervous system (CNS) during JE. Etanercept is a safe anti-TNF-α drug that has been commonly used in the treatment of various human autoimmune diseases.

METHODS

The effect of etanercept on JE was investigated with a JEV-infected mouse model. Four groups of mice were assigned to receive injections of phosphate-buffered saline, etanercept, JEV, or JEV plus etanercept. Inflammatory responses in mouse brains and mortality of mice were evaluated within 23 days post infection.

RESULTS

The in vitro assay with mouse neuron/glia cultures showed that etanercept treatment reduced the inflammatory response induced by JEV infection. In vivo experiments further demonstrated that administration of etanercept protected mice from JEV-induced lethality. Neuronal damage, glial activation, and secretion of proinflammatory cytokines were found to be markedly decreased in JEV-infected mice that received etanercept treatment. Additionally, etanercept treatment restored the integrity of the blood-brain barrier and reduced viral load in mouse brains.

CONCLUSIONS

Etanercept effectively reduces the inflammation and provides protection against acute encephalitis in a JEV-infected mouse model.

Transcriptome profiling of brain edemas caused by influenza infection and lipopolysaccharide treatment

Influenza A virus-associated encephalopathy triggered by influenza virus infection often occurs in children aged five and younger in Japan. However, the mechanisms behind Influenza A virus-associated encephalopathy are not yet well understood. This study developed an Influenza A virus-associated encephalopathy-like model using mice infected with Influenza A virus and given lipopolysaccharide treatment. The results showed that the mice used in the model suffered from brain edemas nearly three times more severe, as well as having higher cytokine levels in sera compared to those of the control groups. Using gene expression profiling, cytokine-related genes were found not to be up-regulated in the brain in situ, while protein coding genes, which are known to be involved in blood-brain barrier disruption, were up-regulated. Categorizing the functional groups using gene ontology revealed the terms "ion channels," "calcium oscillation," and "membrane transporter activities." The blood-brain barrier disruption found in this Influenza A virus-associated encephalopathy model can therefore be assumed to be due to a cellular electrolyte imbalance of the neuronal tissue, in addition to a cytokine storm.

Th1 immune response takeover among patients with severe Japanese encephalitis infection

The present study was intended to explore the dynamics of viral and host factors determining the outcome of Japanese encephalitis viral infection. 223 patients with acute encephalitic syndrome, 126 with febrile illness suspected of JE and 79 apparently healthy individuals as control were enrolled. Elevated levels of TNF-α and IL-6 in encephalitis patients and IFN-γ in febrile JE patients without encephalitis were observed. A cutoff value of >55pg/ml of TNF-α and >370pg/ml of IL-6 in CSF was found as poor prognostic marker. Th1 shift (IFN-γ/IL-4: >1) was observed in encephalitis patients.

Identification of host proteins involved in Japanese encephalitis virus infection by quantitative proteomics analysis

Japanese encephalitis virus (JEV) enters host cells via receptor-mediated endocytosis and replicates in the cytoplasm of infected cells. To study virus-host cell interactions, we performed a SILAC-based quantitative proteomics study of JEV-infected HeLa cells using a subcellular fractionation strategy. We identified 158 host proteins as differentially regulated by JEV (defined as exhibiting a greater than 1.5-fold change in protein abundance upon JEV infection). The mass spectrometry quantitation data for selected proteins were validated by Western blot and immunofluorescence confocal microscopy. Bioinformatics analyses were used to generate JEV-regulated host response networks consisting of regulated proteins, which included 35 proteins that were newly added based on the results of this study. The JEV infection-induced host response was found to be coordinated primarily through the immune response process, the ubiquitin-proteasome system (UPS), the intracellular membrane system, and lipid metabolism-related proteins. Protein functional studies of selected host proteins using RNA interference-based techniques were carried out in HeLa cells infected with an attenuated or a highly virulent strain of JEV. We demonstrated that the knockdown of interferon-induced transmembrane protein 3 (IFITM3), Ran-binding protein 2 (RANBP2), sterile alpha motif domain-containing protein 9 (SAMD9) and vesicle-associated membrane protein 8 (VAMP8) significantly increased JEV replication. The results presented here not only promote a better understanding of the host response to JEV infection but also highlight multiple potential targets for the development of antiviral agents.

The role of chemokines in the pathogenesis of neurotropic flaviviruses

Neurotropic flaviviruses are important emerging and reemerging arthropod-borne pathogens that cause significant morbidity and mortality in humans and other vertebrates worldwide. Upon entry and infection of the CNS, these viruses can induce a rapid inflammatory response characterized by the infiltration of leukocytes into the brain parenchyma. Chemokines and their receptors are involved in coordinating complex leukocyte trafficking patterns that regulate viral pathogenesis in vivo. In this review, we will summarize the current literature on the role of chemokines in regulating the pathogenesis of West Nile, Japanese encephalitis, and tick-borne encephalitis virus infections in mouse models and humans. Understanding how viral infections trigger chemokines, the key cellular events that occur during the infection process, as well as the immunopathogenic role of these cells, are critical areas of research that may ultimately guide a much needed effort toward developing specific immunomodulators and/or antiviral therapeutics.

The involvement of microglial cells in Japanese encephalitis infections

Despite the availability of effective vaccines, Japanese encephalitis virus (JEV) infections remain a leading cause of encephalitis in many Asian countries. The virus is transmitted to humans by Culex mosquitoes, and, while the majority of human infections are asymptomatic, up to 30% of JE cases admitted to hospital die and 50% of the survivors suffer from neurological sequelae. Microglia are brain-resident macrophages that play key roles in both the innate and adaptive immune responses in the CNS and are thus of importance in determining the pathology of encephalitis as a result of JEV infection.

Innate immune response gene expression profiles in central nervous system of mice infected with rabies virus

The present study was focused on the modulation of innate immune response genes in CNS of mouse in response to rabies virus (RABV) infection. The global gene expression changes in brains of RABV- or mock-infected mice were investigated using DNA microarray analysis and quantitative real-time PCR. Then functional enrichment of the differentially expressed mRNAs was performed. Microarray analysis showed that 390 genes in brain were significantly (P<0.01) regulated in response to RABV infection, with obviously up-regulated genes like interferon (IFN) stimulated genes (ISGs), IFN inducible transcription factors, cytokines and complement, etc. The significant pathways of differentially expressed genes are mainly involved in JAK-STAT signaling pathway, antigen processing and presentation, ubiquitin mediated proteolysis and complement cascades. The results suggest that the modulated genes in infected CNS were possibly involved in pathogenesis of rabies. Conversely, they may have protective effects.

Gene expression analysis in the thalamus and cerebrum of horses experimentally infected with West Nile virus

Gene expression associated with West Nile virus (WNV) infection was profiled in the central nervous system of horses. Pyrosequencing and library annotation was performed on pooled RNA from the CNS and lymphoid tissues on horses experimentally infected with WNV (vaccinated and naïve) and non-exposed controls. These sequences were used to create a custom microarray enriched for neurological and immunological sequences to quantitate gene expression in the thalamus and cerebrum of three experimentally infected groups of horses (naïve/WNV exposed, vaccinated/WNV exposed, and normal).From the sequenced transcriptome, 41,040 sequences were identified by alignment against five databases. 31,357 good sequence hits (e<10(-4)) were obtained with 3.1% of the sequences novel to the equine genome project. Sequences were compared to human expressed sequence tag database, with 31,473 equine sequences aligning to human sequences (69.27% contigs, 78.13% seed contigs, 80.17% singlets). This indicated a high degree of sequence homology between human and equine transcriptome (average identity 90.17%).Significant differences (p<0.05) in gene expression were seen due to virus exposure (9,020), survival (7,395), and location (7,649). Pathways analysis revealed many genes that mapped to neurological and immunological categories. Involvement of both innate and adaptive components of immunity was seen, with higher levels of expression correlating with survival. This was highlighted by increased expression of suppressor of cytokine signaling 3 in horses exposed to WNV which functions to suppress innate immunity. Pentraxin 3 was most increased in expression for all horses exposed to WNV.Neurological pathways that demonstrated the greatest changes in gene expression included neurotransmitter and signaling pathways. Decreased expression of transcripts in both the glutamate and dopamine signaling pathways was seen in horses exposed to WNV, providing evidence of possible glutamate excitotoxicity and clinical signs associated with decreased dopamine. Many transcripts mapped to non-infectious neurological disease functions, including mental disorders and degenerative neuropathies.

Characterization of nonstructural protein 3 of a neurovirulent Japanese encephalitis virus strain isolated from a pig

BACKGROUND

Japanese encephalitis virus (JEV), as a re-emerging virus that causes 10,000-15,000 human deaths from encephalitis in the world each year, has had a significant impact on public health. Pigs are the natural reservoirs of JEV and play an important role in the amplification, dispersal and epidemiology of JEV. The nonstructural protein 3 (NS3) of JEV possesses enzymatic activities of serine protease, helicase and nucleoside 5'-triphosphatase, and plays important roles in viral replication and pathogenesis.

RESULTS

We characterized the NS3 protein of a neurovirulent strain of JEV (SH-JEV01) isolated from a field-infected pig. The NS3 gene of the JEV SH-JEV01 strain is 1857 bp in length and encodes protein of approximately 72 kDa with 99% amino acid sequence identity to that of the representative immunotype strain JaGAr 01. The NS3 protein was detectable 12 h post-infection in a mouse neuroblastoma cell line, Neuro-2a, and was distributed in the cytoplasm of cells infected with the SH-JEV01 strain of JEV. In the brain of mice infected with the SH-JEV01 strain of JEV, NS3 was detected in the cytoplasm of neuronal cells, including pyramidal neurons of the cerebrum, granule cells, small cells and Purkinje cells of the cerebellum.

CONCLUSIONS

The NS3 protein of a neurovirulent strain of JEV isolated from a pig was characterized. It is an approximately 72 kDa protein and distributed in the cytoplasm of infected cells. The Purkinje cell of the cerebellum is one of the target cells of JEV infection. Our data should provide some basic information for the study of the role of NS3 in the pathogenesis of JEV and the immune response.

Transcriptomic profile of host response in Japanese encephalitis virus infection

BACKGROUND

Japanese encephalitis (JE) is one of the leading causes of acute encephalopathy with the highest mortality rate of 30-50%. The purpose of this study was to understand complex biological processes of host response during the progression of the disease. Virus was subcutaneously administered in mice and brain was used for whole genome expression profiling by cDNA microarray.

RESULTS

The comparison between viral replication efficiency and disease progression confirms the active role of host response in immunopathology and disease severity. The histopathological analysis confirms the severe damage in the brain in a time dependent manner. Interestingly, the transcription profile reveals significant and differential expression of various pattern recognition receptors, chemotactic genes and the activation of inflammasome. The increased leukocyte infiltration and aggravated CNS inflammation may be the cause of disease severity.

CONCLUSION

This is the first report that provides a detailed picture of the host transcriptional response in a natural route of exposure and opens up new avenues for potential therapeutic and prophylactic strategies against Japanese encephalitis virus.

Japanese encephalitis virus infection induces changes of mRNA profile of mouse spleen and brain

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus, leading to an acute encephalitis and damage to the central nervous system (CNS). The mechanism of JEV pathogenesis is still unclear. DNA microarray analyses have been recently employed to detect changes in host gene expression, which is helpful to reveal molecular pathways that govern viral pathogenesis. In order to globally identify candidate host genes associated with JEV pathogenesis, a systematic mRNA profiling was performed in spleens and brains of JEV-infected mice.

RESULTS

The results of microarray analysis showed that 437 genes in spleen and 1119 genes in brain were differentially expressed in response to JEV infection, with obviously upregulated genes like pro-inflammatory chemokines and cytokines, apoptosis-related proteases and IFN inducible transcription factors. And the significant pathways of differentially expressed genes are involved in cytokine-cytokine receptor interaction, natural killer cell mediated cytotoxicity, antigen processing and presentation, MAPK signaling, and toll-like receptor signaling, etc. The differential expression of these genes suggests a strong antiviral response of host but may also contribute to the pathogenesis of JEV resulting in encephalitis. Quantitative RT-PCR (RT-qPCR) assay of some selected genes further confirmed the results of microarray assay.

CONCLUSIONS

Data obtained from mRNA microarray suggests that JEV infection causes significant changes of mRNA expression profiles in mouse spleen and brain. Most of differentially expression genes are associated with antiviral response of host, which may provide important information for investigation of JEV pathogenesis and therapeutic method.

TNF-α and IL-1β mediate Japanese encephalitis virus-induced RANTES gene expression in astrocytes

Infection with Japanese encephalitis virus (JEV) causes neuroinfection and neuroinflammation characterized by profound neuronal destruction/dysfunction, concomitant microgliosis/astrogliosis, and production of various molecules that initiate the recruitment of immune cells to the sites of infection. Previously, we reported that glial cells expressed RANTES (regulated upon activation, normal T cell expressed and secreted) with chemotactic activity in response to JEV infection. In this study, we further demonstrated that JEV-infected microglia had an additional activity in regulating RANTES production. Both astrocytes and microglia responded to JEV infection by releasing RANTES through a process likely related to viral replication. Independent of infectious virus, supernatants of JEV-infected microglia, but not JEV-infected astrocytes, caused additional RANTES production from astrocytes. Antibody neutralization studies suggested the potential involvement of tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) in mediating additional RANTES production. Treatment of astrocyte cultures with TNF-α and IL-1β caused activation of several signaling molecules and transcription factors crucial to RANTES gene expression, including reactive oxygen species, extracellular signal-regulated kinase, NF-κB, and NF-IL6, increased RANTES gene promoter activity, and provoked RANTES production. As with RANTES, neutralization of bioactive TNF-α and IL-1β caused an attenuation of chemotactic activity from supernatants of mixed glia containing astrocytes and microglia during the course of JEV infection. In conclusion, TNF-α and IL-1β produced by JEV-infected microglia might trigger another mechanism which induces a secondary wave of RANTES gene expression by activating astrocytes. The released RANTES from glial cells might play a role in the recruitment of immune cells during JEV infection.