Upregulation of RANTES gene expression in neuroglia by Japanese encephalitis virus infection

Japanese Encephalitis virus infection in astrocytes modulate microglial function: Correlation with inflammation and oxidative stress

BACKGROUND

Japanese Encephalitis Virus (JEV) is a neurotropic virus which has the propensity to infect neuronal and glial cells of the brain. Astrocyte-microglia crosstalk leading to the secretion of various factors plays a major role in controlling encephalitis in brain. This study focused on understanding the role of astrocytic mediators that further shaped the microglial response towards JEV infection.

METHODS

After establishing JEV infection in C8D1A (mouse astrocyte cell line) and primary astrocyte enriched cultures (PAEC), astrocyte supernatant was used for preparation of conditioned media. Astrocyte supernatant was treated with UV to inactivate JEV and the supernatant was added to N9 culture media in ratio 1:1 for preparation of conditioned media. N9 microglial cells post treatment with astrocyte conditioned media and JEV infection were checked for expression of various inflammatory genes by qRT-PCR, levels of secreted cytokines in N9 cell supernatant were checked by cytometric bead array. N9 cell lysates were checked for expression of proteins - pNF-κβ, IBA-1, NS3 and RIG-I by western blotting. Viral titers were measured in N9 supernatant by plaque assays. Immunocytochemistry experiments were done to quantify the number of infected microglial cells after astrocyte conditioned medium treatment. Expression of different antioxidant enzymes was checked in N9 cells by western blotting, levels of reactive oxygen species (ROS) was detected by fluorimetry using DCFDA dye.

RESULTS

N9 microglial cells post treatment with JEV-infected astrocyte conditioned media and JEV infection were activated, showed an upsurge in expression of inflammatory genes and cytokines both at the transcript and protein levels. These N9 cells showed a decrease in quantity of viral titers and associated viral proteins in comparison to control cells (not treated with conditioned media but infected with JEV). Also, N9 cells upon conditioned media treatment and JEV infection were more prone to undergo oxidative stress as observed by the decreased expression of antioxidant enzymes SOD-1, TRX-1 and increased secretion of reactive oxygen species (ROS).

CONCLUSION

Astrocytic mediators like TNF-α, MCP-1 and IL-6 influence microglial response towards JEV infection by promoting inflammation and oxidative stress in them. As a result of increased microglial inflammation and secretion of ROS, viral replication is lessened in conditioned media treated and JEV infected microglial cells as compared to control cells with no conditioned media treatment but only JEV infection.

Replication of Rocio virus in primary cultures of mouse neural cells

OBJECTIVE

This study verified the replication efficiency of the Rocio virus in a primary culture of mouse neural cells.

METHODS

Mixed primary cultures (neurons/glia) obtained from the brains of newborn isogenic BALB/c mice were inoculated with Rocio virus on the 7 th day of culture, and the development of cytopathogenic effects was monitored. The infection was confirmed via immunocytochemistry (anti-ROCV), while viral replication was quantified in infected primary cultures. The titration method used depended on the infection period.

RESULTS

Rocio virus efficiently infected primary cultured neural cells, with the highest viral titer causing cytopathic changes was observed at 2 days post infection. The virus-infected primary culture survived for up to 7 days post infection, and viral load quantitation showed viral replication kinetics compatible with the cell death kinetics of cultures.

CONCLUSION

The findings of this study suggest that mouse neural cell primary cultures support Rocio virus replication and could be used as an alternative system for studying Flavivirus infection in the central nervous system.

Mice as an Animal Model for Japanese Encephalitis Virus Research: Mouse Susceptibility, Infection Route, and Viral Pathogenesis

Japanese encephalitis virus (JEV), a zoonotic flavivirus, is principally transmitted by hematophagous mosquitoes, continually between susceptible animals and incidentally from those animals to humans. For almost a century since its discovery, JEV was geographically confined to the Asia-Pacific region with recurrent sizable outbreaks involving wildlife, livestock, and people. However, over the past decade, it has been detected for the first time in Europe (Italy) and Africa (Angola) but has yet to cause any recognizable outbreaks in humans. JEV infection leads to a broad spectrum of clinical outcomes, ranging from asymptomatic conditions to self-limiting febrile illnesses to life-threatening neurological complications, particularly Japanese encephalitis (JE). No clinically proven antiviral drugs are available to treat the development and progression of JE. There are, however, several live and killed vaccines that have been commercialized to prevent the infection and transmission of JEV, yet this virus remains the main cause of acute encephalitis syndrome with high morbidity and mortality among children in the endemic regions. Therefore, significant research efforts have been directed toward understanding the neuropathogenesis of JE to facilitate the development of effective treatments for the disease. Thus far, multiple laboratory animal models have been established for the study of JEV infection. In this review, we focus on mice, the most extensively used animal model for JEV research, and summarize the major findings on mouse susceptibility, infection route, and viral pathogenesis reported in the past and present, and discuss some unanswered key questions for future studies.

Chemokines in patients with Alzheimer's disease: A meta-analysis

Background

Alzheimer's disease (AD) is the most common neurodegenerative disease in elderly people. Many researches have reported that neuroinflammation is related to AD. Chemokines are a class of small cytokines that play important roles in cell migration and cell communication, which involved in neuroinflammation. Up to now there is no meta-analysis to explore the difference of chemokines between AD patients and healthy elderly individuals.

Method

We searched PubMed, Web of science, Cochrane library, EMBASE and Scopus databases from inception to January 2022. Data were extracted by two independent reviewers, and the Review Manager 5.3 was used for the meta-analysis.

Result

Thirty-two articles were included and analyzed. The total number of participants in the included study was 3,331. We found that the levels of CCL5 (SMD = 2.56, 95% CI: 1.91–3.21), CCL15 (SMD = 3.30, 95% CI: 1.48–5.13) and IP-10 (SMD = 3.88, 95% CI: 1.84–5.91) in the plasma of AD patients were higher than healthy people. MCP-1 protein (SMD = 0.67, 95% CI: 0.29–1.05) in the AD patients' CSF was higher than healthy controls.

Conclusion

These results suggested that chemokines may play an important role in AD. These findings could provide evidences for the diagnosis and treatment of AD.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021278736, identifier: CRD42021278736.

Immune Functions of Astrocytes in Viral Neuroinfections

Neuroinfections of the central nervous system (CNS) can be triggered by various pathogens. Viruses are the most widespread and have the potential to induce long-term neurologic symptoms with potentially lethal outcomes. In addition to directly affecting their host cells and inducing immediate changes in a plethora of cellular processes, viral infections of the CNS also trigger an intense immune response. Regulation of the innate immune response in the CNS depends not only on microglia, which are fundamental immune cells of the CNS, but also on astrocytes. These cells align blood vessels and ventricle cavities, and consequently, they are one of the first cell types to become infected after the virus breaches the CNS. Moreover, astrocytes are increasingly recognized as a potential viral reservoir in the CNS; therefore, the immune response initiated by the presence of intracellular virus particles may have a profound effect on cellular and tissue physiology and morphology. These changes should be addressed in terms of persisting infections because they may contribute to recurring neurologic sequelae. To date, infections of astrocytes with different viruses originating from genetically distinct families, including Flaviviridae, Coronaviridae, Retroviridae, Togaviridae, Paramyxoviridae, Picomaviridae, Rhabdoviridae, and Herpesviridae, have been confirmed. Astrocytes express a plethora of receptors that detect viral particles and trigger signaling cascades, leading to an innate immune response. In this review, we summarize the current knowledge on virus receptors that initiate the release of inflammatory cytokines from astrocytes and depict the involvement of astrocytes in immune functions of the CNS.

Exaggerated levels of some specific TLRs, cytokines and chemokines in Japanese encephalitis infected BV2 and neuro 2A cell lines associated with worst outcome

Japanese encephalitis (JE) disease, a viral brain fever is caused by Japanese encephalitis virus (JEV). Despite the availability of effective vaccines against this deadly infection, JE is the leading cause of epidemic viral encephalitis in children in South-east Asia. There is no treatment available for the JE disease which might be due to incomplete understanding of the pathogenesis of JE virus. The JEV infections lead to permanent neurological deficits even in those who survive from the infection. Activated microglia may play a potentially detrimental role by eliciting the expression of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α) influencing the surrounding brain tissue. Microglial activation, proinflammatory cytokine release and leukocytes trafficking are associated following JEV infection in central nervous system (CNS). How the pattern recognition receptors sense the viral nucleic acid and how the microglial and neuronal cells behaves following JEV infection is still unelucidated. There is scarcity of data on the expression levels of toll like receptors (TLRs), cytokines and chemokines in JEV infection in invitro model. To explore the molecular mechanisms of JEV infection of microglial cells and neuronal cells, we studied the expression profile of TLRs, cytokines and chemokines in JEV infected microglial cell line BV2 and Neuronal cell line Neuro 2A. For the present study, we developed the mouse model of encephalitis by intracerebral (IC) injection of JE virus for virus propagation, disease progression and damage study. Our results demonstrate the exaggerated release of some specific TLRs, cytokines and chemokines in invitro cell culture of microglial and Neuro 2A cell line, which are associated with bad outcome in invivo study.

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.

Viruses, parkinsonism and Parkinson's disease: the past, present and future

Parkinsonism secondary to viral infections is not an uncommon occurrence and has been brought under the spotlight with the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. A variety of viruses have been described with a potential of inducing or contributing to the occurrence of parkinsonism and Parkinson's disease (PD), although the relationship between the two remains a matter of debate originating with the description of encephalitis lethargica in the aftermath of the Spanish flu in 1918. While some viral infections have been linked to an increased risk for the development of PD, others seem to have a causal link with the occurrence of parkinsonism. Here, we review the currently available evidence on viral-induced parkinsonism with a focus on potential pathophysiological mechanisms and clinical features. We also review the evidence on viral infections as a risk factor for developing PD and the link between SARS-CoV-2 and parkinsonism, which might have important implications for future research and treatments.

Neurological Complications of Dengue Fever

PURPOSE OF REVIEW

To discuss the neurological complications of dengue virus (DENV) infection and their pathogenesis.

RECENT FINDINGS

Include recognition of the four different serotypes of DENV and their epidemiology as well as recognition of the expanded dengue syndrome encompassing multisystem involvement in the severe form of the disease including involvement of the central nervous system (CNS). DENV is a neurotropic virus with the ability to infect the supporting cells of the CNS. Neural injury during the acute stage of the infection results from direct neuro-invasion and/or the phenomenon of antibody-dependent enhancement, resulting in plasma leakage and coagulopathy. Immune mechanisms have been implicated in the development of the delayed neurological sequelae through molecular mimicry. A myriad of neurological syndromes has been described as a result of the involvement of the CNS, the peripheral nervous system (PNS), or both. Neurological manifestations in DENV infection are increasingly being recognized, some of which are potentially fatal if not treated promptly. DENV encephalopathy and encephalitis should be considered in the differential diagnosis of other acute febrile encephalopathies, autoimmune encephalitides, and in cases of encephalopathy/encephalitis related to SARS-CoV2 infection, especially in dengue-endemic areas. Acute disseminated encephalomyelitis (ADEM) may be occasionally encountered. Clinicians should be knowledgeable of the expanded dengue syndrome characterized by the concurrent compromise of cardiac, neurological, gastrointestinal, renal, and hematopopoietic systems. Isolated cranial nerve palsies occur rather uncommonly and are often steroid responsive. These neuropathies may result from the direct involvement of cranial nerve nuclei or nerve involvement or may be immune-mediated. Even if the diagnosis of dengue is confirmed, it is absolutely imperative to exclude other well-known causes of isolated cranial nerve palsies. Ischemic and hemorrhagic strokes may occur following dengue fever. The pathogenesis may be beyond the commonly observed thrombocytopenia and include cerebral vasculitis. Involvement of ocular blood vessels may cause maculopathy or retinal hemorrhages. Posterior reversible encephalopathy syndrome (PRES) is uncommon and possibly related to dysregulated cytokine release phenomena. Lastly, any patient developing acute neuromuscular weakness during the course or within a fortnight of remission from dengue fever must be screened for acute inflammatory demyelinating polyneuropathy (AIDP), hypokalemic paralysis, or acute myositis. Rarely, a Miller-Fisher-like syndrome with negative anti-GQ1b antibody may develop.

Innate Immune Signaling and Role of Glial Cells in Herpes Simplex Virus- and Rabies Virus-Induced Encephalitis

The environment of the central nervous system (CNS) represents a double-edged sword in the context of viral infections. On the one hand, the infectious route for viral pathogens is restricted via neuroprotective barriers; on the other hand, viruses benefit from the immunologically quiescent neural environment after CNS entry. Both the herpes simplex virus (HSV) and the rabies virus (RABV) bypass the neuroprotective blood-brain barrier (BBB) and successfully enter the CNS parenchyma via nerve endings. Despite the differences in the molecular nature of both viruses, each virus uses retrograde transport along peripheral nerves to reach the human CNS. Once inside the CNS parenchyma, HSV infection results in severe acute inflammation, necrosis, and hemorrhaging, while RABV preserves the intact neuronal network by inhibiting apoptosis and limiting inflammation. During RABV neuroinvasion, surveilling glial cells fail to generate a sufficient type I interferon (IFN) response, enabling RABV to replicate undetected, ultimately leading to its fatal outcome. To date, we do not fully understand the molecular mechanisms underlying the activation or suppression of the host inflammatory responses of surveilling glial cells, which present important pathways shaping viral pathogenesis and clinical outcome in viral encephalitis. Here, we compare the innate immune responses of glial cells in RABV- and HSV-infected CNS, highlighting different viral strategies of neuroprotection or Neuroinflamm. in the context of viral encephalitis.

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.

Inhibition of Japanese encephalitis virus proliferation by long non-coding RNA SUSAJ1 in PK-15 cells

BACKGROUND

Japanese encephalitis virus is a mosquito-borne neurotropic flavivirus that causes acute viral encephalitis in humans. Pigs are crucial amplifier host of JEV. Recently, increasing evidence has shown that long non-coding RNAs (lncRNAs) play important roles in virus infection.

METHODS

JEV proliferation was evaluated after overexpression or knockdown of lncRNA-SUSAJ1 using western blotting and reverse-transcription polymerase chain reaction (RT-PCR). C-C chemokine receptor type 1 (CCR1) was found to regulate the expression of lncRNA-SUSAJ1 by inhibitors screen. The expression of lncRNA-SUSAJ1 was detected using RT-PCR after overexpression or knockdown of transcription factor SP1. In addition, the enrichments of transcription factor SP1 on the promoter of lncRNA-SUSAJ1 were analyzed by chromatin immunoprecipitation.

RESULTS

In this study, we demonstrated that swine lncRNA-SUSAJ1 could suppress JEV proliferation in PK-15 cells. We also found that CCR1 inhibited the expression of lncRNA-SUSAJ1 via the transcription factor SP1. In addition, knockdown of CCR1 could upregulated the expression of SP1 and lncRNA-SUSAJ1, resulting in resistance to JEV proliferation.

CONCLUSIONS

These findings illustrate the importance of lncRNAs in virus proliferation, and reveal how this virus regulates lncRNAs in host cells to promote its proliferation.

Efficient control of Japanese encephalitis virus in the central nervous system of infected pigs occurs in the absence of a pronounced inflammatory immune response

Background

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia. JEV infection of mice and humans can lead to an uncontrolled inflammatory response in the central nervous system (CNS), resulting in a detrimental outcome. Pigs act as important amplification and reservoir hosts, and JEV infection of pigs is mostly subclinical. Information on virus spread in the CNS and immune responses controlling JEV infection in the CNS of pigs, however remains scarce.

Methods

Nine-week-old pigs were inoculated intranasal or intradermal with a relevant dose of 10⁵ TCID₅₀ of JEV genotype 3 Nakayama strain. Clinical signs were assessed daily, and viral spread was followed by RT-qPCR. mRNA expression profiles were determined to study immune responses in the CNS.

Results

Besides a delay of 2 days to reach the peak viremia upon intranasal compared to intradermal inoculation, the overall virus spread via both inoculation routes was highly similar. JEV appearance in lymphoid and visceral organs was in line with a blood-borne JEV dissemination. JEV showed a particular tropism to the CNS but without the induction of neurological signs. JEV entry in the CNS probably occurred via different hematogenous and neuronal pathways, but replication in the brain was mostly efficiently suppressed and associated with a type I IFN-independent activation of OAS1 expression. In the olfactory bulb and thalamus, where JEV replication was not completely controlled by this mechanism, a short but strong induction of chemokine gene expression was detected. An increased IFNy expression was simultaneously observed, probably originating from infiltrating T cells, correlating with a fast suppression of JEV replication. The chemokine response was however not associated with the induction of a strong inflammatory response, nor was an induction of the NLRP3 inflammasome observed.

Conclusions

These findings indicate that an adequate antiviral response and an attenuated inflammatory response contribute to a favorable outcome of JEV infection in pigs and help to explain the limited neurological disease compared to other hosts. We show that the NLRP3 inflammasome, a key mediator of neurologic disease in mice, is not upregulated in pigs, further supporting its important role in JEV infections.

Degradation of MicroRNA miR-466d-3p by Japanese Encephalitis Virus NS3 Facilitates Viral Replication and Interleukin-1β Expression

Japanese encephalitis virus (JEV) infection alters microRNA (miRNA) expression in the central nervous system (CNS). However, the mechanism contributing to miRNA regulation in the CNS is not known. We discovered global degradation of mature miRNA in mouse brains and neuroblastoma (NA) cells after JEV infection. Integrative analysis of miRNAs and mRNAs suggested that several significantly downregulated miRNAs and their targeted mRNAs were clustered into an inflammation pathway. Transfection with miRNA 466d-3p (miR-466d-3p) decreased interleukin-1β (IL-1β) expression and inhibited JEV replication in NA cells. However, miR-466d-3p expression increased after JEV infection in the presence of cycloheximide, indicating that viral protein expression reduced miR-466d-3p expression. We generated all the JEV coding proteins and demonstrated NS3 helicase protein to be a potent miRNA suppressor. The NS3 proteins of Zika virus, West Nile virus, and dengue virus serotype 1 (DENV-1) and DENV-2 also decreased miR-466d-3p expression. Results from helicase-blocking assays and in vitro unwinding assays demonstrated that NS3 could unwind pre-miR-466d and induce miRNA dysfunction. Computational models and an RNA immunoprecipitation assay revealed arginine-rich domains of NS3 to be crucial for pre-miRNA binding and degradation of host miRNAs. Importantly, site-directed mutagenesis of conserved residues in NS3 revealed that R226G and R202W reduced the binding affinity and degradation of pre-miR-466d. These results expand the function of flavivirus helicases beyond unwinding duplex RNA to degrade pre-miRNAs. Hence, we revealed a new mechanism for NS3 in regulating miRNA pathways and promoting neuroinflammation.IMPORTANCE Host miRNAs have been reported to regulate JEV-induced inflammation in the CNS. We found that JEV infection could reduce expression of host miRNA. The helicase region of the NS3 protein bound specifically to miRNA precursors and could lead to incorrect unwinding of miRNA precursors, thereby reducing the expression of mature miRNAs. This observation led to two major findings. First, our results suggested that JEV NS3 protein induced miR-466d-3p degradation, which promoted IL-1β expression and JEV replication. Second, arginine molecules on NS3 were the main miRNA-binding sites, because we demonstrated that miRNA degradation was abolished if arginines at R226 and R202 were mutated. Our study provides new insights into the molecular mechanism of JEV and reveals several amino acid sites that could be mutated for a JEV vaccine.

Genome-wide profiling of host-encoded circular RNAs highlights their potential role during the Japanese encephalitis virus-induced neuroinflammatory response

BACKGROUND

Japanese encephalitis virus (JEV) is one of the common causes of acute encephalitis in humans. Japanese encephalitis is characterized by the uncontrolled release of inflammatory cytokines, which ultimately results in neuronal cell damage. In recent years, with the advancement of high-throughput sequencing technology, studies have shown that circRNAs, by competing with endogenous miRNAs, play a vital role in the pathology of CNS diseases. However, it is unknown whether circRNAs participate in JEV-induced neuroinflammation.

RESULTS

By employing Illumina RNA-sequencing, we identified 180 circRNAs and 58 miRNAs that showed significant differential expression in JEV-infected mice brain tissues. The functional enrichment analyses revealed that these differentially regulated circRNAs were predominantly related to neurotransmission, histone modifications, transcription misregulation, and inflammation-associated calcium signaling pathway. Our established competing endogenous RNA (ceRNA) interaction network suggested the correlation of several circRNAs, miRNAs, and mRNAs in regulating the inflammatory response during JEV infection. Among the predicted interactions, the correlation between circ_0000220, miR-326-3p, and BCL3/MK2/TRIM25 mRNAs was experimentally validated by knockdown or overexpression of the non-coding RNA entities in cultured mouse microglia. The knockdown of circ_0000220 or overexpression of miR-326-3p caused a lower production of JEV-induced inflammatory cytokines.

CONCLUSIONS

Conclusively, our study provides new insights into the host response to JEV infection and proposes the circRNA-targeting therapeutic interventions to rein in Japanese encephalitis.

Inflammation During Virus Infection: Swings and Roundabouts

Inflammation constitutes a concerted series of cellular and molecular responses that follow disturbance of systemic homeostasis, by either toxins or infectious organisms. Leukocytes modulate inflammation through production of secretory mediators, like cytokines and chemokines, which work in an autocrine and/or paracrine manner. These mediators can either promote or attenuate the inflammatory response and depending on differential temporal and spatial expression play a crucial role in the outcome of infection. Even though the objective is clearance of the pathogen with minimum damage to host, the pathogenesis of multiple human pathogenic viruses has been suggested to emanate from a dysregulation of the inflammatory response, sometimes with fatal consequences. This review discusses the nature and the outcome of inflammatory response, which is triggered in the human host subsequent to infection by single-sense plus-strand RNA viruses. In view of such harmful effects of a dysregulated inflammatory response, an exogenous regulation of these reactions by either interference or supplementation of critical regulators has been suggested. Currently multiple such factors are being tested for their beneficial and adverse effects. A successful use of such an approach in diseases of viral etiology can potentially protect the affected individual without directly affecting the virus life cycle. Further, such approaches whenever applicable would be useful in mitigating death and/or debility that is caused by the infection of those viruses which have proven particularly difficult to control by either prophylactic vaccines and/or therapeutic strategies using specific antiviral drugs.

miR-301a Regulates Inflammatory Response to Japanese Encephalitis Virus Infection via Suppression of NKRF Activity

Microglia being the resident macrophage of brain provides neuroprotection following diverse microbial infections. Japanese encephalitis virus (JEV) invades the CNS, resulting in neuroinflammation, which turns the neuroprotective role of microglia detrimental as characterized by increased microglial activation and neuronal death. Several host factors, including microRNAs, play vital roles in regulating virus-induced inflammation. In the current study, we demonstrate that the expression of miR-301a is increased in JEV-infected microglial cells and human brain. Overexpression of miR-301a augments the JEV-induced inflammatory response, whereas inhibition of miR-301a completely reverses the effects. Mechanistically, NF-κB-repressing factor (NKRF) functioning as inhibitor of NF-κB activation is identified as a potential target of miR-301a in JEV infection. Consequently, miR-301a-mediated inhibition of NKRF enhances nuclear translocation of NF-κB, which, in turn, resulted in amplified inflammatory response. Conversely, NKRF overexpression in miR-301a-inhibited condition restores nuclear accumulation of NF-κB to a basal level. We also observed that JEV infection induces classical activation (M1) of microglia that drives the production of proinflammatory cytokines while suppressing alternative activation (M2) that could serve to dampen the inflammatory response. Furthermore, in vivo neutralization of miR-301a in mouse brain restores NKRF expression, thereby reducing inflammatory response, microglial activation, and neuronal apoptosis. Thus, our study suggests that the JEV-induced expression of miR-301a positively regulates inflammatory response by suppressing NKRF production, which might be targeted to manage viral-induced neuroinflammation.

Dengue Virus Infection of Blood-Brain Barrier Cells: Consequences of Severe Disease

More than 500 million people worldwide are infected each year by any of the four-dengue virus (DENV) serotypes. The clinical spectrum caused during these infections is wide and some patients may develop neurological alterations during or after the infection, which could be explained by the cryptic neurotropic and neurovirulent features of flaviviruses like DENV. Using in vivo and in vitro models, researchers have demonstrated that DENV can affect the cells from the blood-brain barrier (BBB) in several ways, which could result in brain tissue damage, neuronal loss, glial activation, tissue inflammation and hemorrhages. The latter suggests that BBB may be compromised during infection; however, it is not clear whether the damage is due to the infection per se or to the local and/or systemic inflammatory response established or activated by the BBB cells. Similarly, the kinetics and cascade of events that trigger tissue damage, and the cells that initiate it, are unknown. This review presents evidence of the BBB cell infection with DENV and the response established toward it by these cells; it also describes the consequences of this response on the nervous tissue, compares these evidence with the one reported with neurotropic viruses of the Flaviviridae family, and shows the complexity and unpredictability of dengue and the neurological alterations induced by it. Clinical evidence and in vitro and in vivo models suggest that this virus uses the bloodstream to enter nerve tissue where it infects the different cells of the neurovascular unit. Each of the cell populations respond individually and collectively and control infection and inflammation, in other cases this response exacerbates the damage leaving irreversible sequelae or causing death. This information will allow us to understand more about the complex disease known as dengue, and its impact on a specialized and delicate tissue like is the nervous tissue.

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.

Research advancements in the neurological presentation of flaviviruses

Owing to the large-scale epidemic of Zika virus disease and its association with microcephaly, properties that allow flaviviruses to cause nervous system diseases are an important area of investigation. At present, although potential pathogenic mechanisms of flaviviruses in the nervous system have been examined, they have not been completely elucidated. In this paper, we review the possible mechanisms of blood-brain barrier penetration, the pathological effects on neurons, and the association between virus mutations and neurotoxicity. A hypothesis on neurotoxicity caused by the Zika virus is presented. Clarifying the mechanisms of virulence of flaviviruses will be helpful in finding better antiviral drugs and optimizing the treatment of symptoms.

Differential Expression Levels of Inflammatory Chemokines and TLRs in Patients Suffering from Mild and Severe Japanese Encephalitis

Japanese encephalitis (JE) is a vector-borne viral disease with clinical manifestations ranging from asymptomatic to severe neurological symptoms and even leading to death. The exact pathophysiology for diverse clinical spectrum of the disease is complex and has not yet been defined. Studies have postulated that during JE infection, inflammatory cytokines and chemokines are produced after the initial recognition of viral antigens through the engagement of toll-like receptors (TLR) pathways. However, there is paucity of knowledge on the expression levels of chemokines and TLRs among mild and severely affected JE patients. Hence, to better understand disease pathogenesis, we examined the mRNA expression of chemokines, CCL2 and CCL5, and their respective receptors CCR2 and CCR5 along with TLRs viz. TLR3, TLR7, TLR8, and TLR9 in context of mild and severely Japanese encephalitis virus (JEV)-infected (n = 19) and healthy (n = 19) individuals. Our study showed significant downregulation of CCL2, CCL5, CCR2, CCR5, and TLR3 by log 0.87, 1.02, 0.82, 0.68, and 0.37-fold respectively, among mild cases compared with controls. Significant difference of gene expression among mild and severe JE cases for CCL2 (p < 0.001), CCL5 (p < 0.01), and TLR7 (p < 0.05) was observed. In conclusion, our results proposes that chemokines viz. CCL2 and CCL5 along with TLR7 may be associated with degree of pathogenesis of JE and could be putative therapeutic targets for preventing severe inflammation during viral encephalitis.

Palm Fruit Bioactives modulate human astrocyte activity in vitro altering the cytokine secretome reducing levels of TNFα, RANTES and IP-10

Neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease, are becoming more prevalent and an increasing burden on society. Neurodegenerative diseases often arise in the milieu of neuro-inflammation of the brain. Reactive astrocytes are key regulators in the development of neuro-inflammation. This study describes the effects of Palm Fruit Bioactives (PFB) on the behavior of human astrocytes which have been activated by IL-1β. When activated, the astrocytes proliferate, release numerous cytokines/chemokines including TNFα, RANTES (CCL5), IP-10 (CXCL10), generate reactive oxygen species (ROS), and express specific cell surface biomarkers such as the Intercellular Adhesion Molecule (ICAM), Vascular Cellular Adhesion Molecule (VCAM) and the Neuronal Cellular Adhesion Molecule (NCAM). Interleukin 1-beta (IL-1β) causes activation of human astrocytes with marked upregulation of pro-inflammatory genes. We show significant inhibition of these pro-inflammatory processes when IL-1β-activated astrocytes are exposed to PFB. PFB causes a dose-dependent and time-dependent reduction in specific cytokines: TNFα, RANTES, and IP-10. We also show that PFB significantly reduces ROS production by IL-1β-activated astrocytes. Furthermore, PFB also reduces the expression of ICAM and VCAM, both in activated and naïve human astrocytes in vitro. Since reactive astrocytes play an essential role in the neuroinflammatory state preceding neurodegenerative diseases, this study suggests that PFB may have a potential role in their prevention and/or treatment.

Japanese encephalitis virus induces apoptosis by inhibiting Foxo signaling pathway

Japanese encephalitis virus (JEV) infection induces brain tissue disease characterized by neuron death. however, little is known about the underlying mechanism. Using RNA sequencing, we profiled global mRNA expression changes in response to in vitro and in vivo JEV infection. Integration analysis of in vitro and in vivo mRNA transcriptome revealed that JEV infection regulated apoptosis-related Foxo signaling pathway. Foxo expression was reduced by JEV infection in vitro and in vivo. Knockdown of Foxo promoted apoptosis, while its overexpression reduced apoptosis in JEV-infected Neuro-2a cells. JEV infection in Neuro-2a cells decreased the expression of Foxo downstream genes including pro-apoptotic protein Bim, anti-apoptotic protein Bcl-6 and p21. Overexpression of anti-apoptotic proteins Bcl-6 and p21 repressed JEV-induced apoptosis. These findings suggest that Foxo primarily exerts an anti-apoptotic function via Bcl-6 and p21 in JEV-infected Neuro-2a cells. A STAT3 binding site was identified in the promoter region of Foxo by TFBIND software and confirmed by ChIP and reporter assays. JEV infection reduced STAT3 expression as well as its binding at the Foxo promoter compared to mock infection in Neuro-2a cells. Moreover, STAT3 knockdown reduced Foxo promoter activity and Foxo expression. Therefore, JEV reduced Foxo expression, at least in part, by downregulating STAT3. Taken together, we found that JEV induced cell apoptosis by inhibiting STAT3-Foxo-Bcl-6/p21 pathway, which provides a novel insight into JEV-caused encephalitis.

Interplay of inflammatory gene expression in pericytes following Japanese encephalitis virus infection

Neuroinflammation is a pathological hallmark and has been implicated in the pathogenesis of Japanese encephalitis. Although brain pericytes show regulatory effects on neuroinflammation, their involvement in Japanese encephalitis-associated neuroinflammation is not understood. Here, we demonstrated that brain microvascular pericytes could be an alternative cellular source for the induction and/or amplification of neuroinflammation caused by Japanese encephalitis virus (JEV) infection. Infection of cultured pericytes with JEV caused profound production of IL-6, RANTES, and prostaglandin E2 (PGE2). Mechanistic studies revealed that JEV infection elicited an elevation of the toll-like receptor 7 (TLR7)/MyD88 signaling axis, leading to the activation of NF-κB through IKK signaling and p65 phosphorylation as well as cAMP response element-binding protein (CREB) via phosphorylation. We further demonstrated that extracellular signal-regulated kinase (ERK) could be an alternative regulator in transducing signals to NF-κB, CREB, and cytosolic phospholipase A2 (cPLA2) through the phosphorylation mechanism. Released IL-6 and RANTES played an active role in the disruption of endothelial barrier integrity and leukocyte chemotaxis, respectively. cPLA2/PGE2 had a role in activating NF-κB and CREB DNA-binding activities and inflammatory cytokine transcription via the EP2/cAMP/PKA mechanism in an autocrine loop. These inflammatory responses and biochemical events were also detected in the brain of JEV-infected mice. The current findings suggest that pericytes might have pathological relevance in Japanese encephalitis-associated neuroinflammation through a TLR7-related mechanism. The consequences of pericyte activation are their ability to initiate and/or amplify inflammatory cytokine expression by which cellular function of endothelial cells and leukocytes are regulated in favor of CNS infiltration by leukocytes.

Neurological Manifestations of Dengue Infection

Dengue counts among the most commonly encountered arboviral diseases, representing the fastest spreading tropical illness in the world. It is prevalent in 128 countries, and each year >2.5 billion people are at risk of dengue virus infection worldwide. Neurological signs of dengue infection are increasingly reported. In this review, the main neurological complications of dengue virus infection, such as central nervous system (CNS), peripheral nervous system, and ophthalmic complications were discussed according to clinical features, treatment and possible pathogenesis. In addition, neurological complications in children were assessed due to their atypical clinical features. Finally, dengue infection and Japanese encephalitis were compared for pathogenesis and main clinical manifestations.

Significance of CCL2, CCL5 and CCR2 polymorphisms for adverse prognosis of Japanese encephalitis from an endemic population of India

Japanese encephalitis (JE) is a major contributor for viral encephalitis in Asia. Vaccination programme has limited success for largely populated JE endemic countries like India and disease exposure is unavoidable. Involvement of chemokines and its co-receptors for adverse prognosis of JE have been documented both in vitro and in vivo. Identification of the genetic predisposing factor for JE infection in humans is crucial but not yet established. Therefore, we investigated the association of single nucleotide polymorphisms (SNPs) in chemokines (CCL2 and CCL5) and its co-receptors (CCR2 and CCR5) with their protein level for JE. The study enrolled 87 symptomatic JE cases (mild: severe = 24:63) and 94 asymptomatic controls. Our study demonstrated that CCL2 (rs1024611G), CCL5 (rs2280788G) and CCR2 (rs1799864A) significantly associated with JE (Odds ratio = 1.63, 2.95 and 2.62, respectively and P = 0.045, P = 0.05 and P = 0.0006, respectively). The study revealed that rs1024611G allele was associated with elevated level of CCL2. CCL5 elevation associated with JE mortality having a Cox proportional hazard of 1.004 (P = 0.033). In conclusion, SNPs of chemokine viz. CCL2 (rs1024611G) and its receptor CCR2 (rs1799864A) significantly associated with JE which may serve as possible genetic predisposing factor and CCL5 protein level may act as marker for disease survival.

Microarray Analysis Identifies the Potential Role of Long Non-Coding RNA in Regulating Neuroinflammation during Japanese Encephalitis Virus Infection

Japanese encephalitis virus (JEV) is the leading cause of epidemic encephalitis worldwide. JEV-induced neuroinflammation is characterized by profound neuronal cells damage accompanied by activation of glial cells. Albeit long non-coding RNAs (lncRNAs) have been emerged as important regulatory RNAs with profound effects on various biological processes, it is unknown how lncRNAs regulate JEV-induced inflammation. Here, using microarray approach, we identified 618 lncRNAs and 1,007 mRNAs differentially expressed in JEV-infected mice brain. The functional annotation analysis revealed that differentially regulated transcripts were predominantly involved in various signaling pathways related to host immune and inflammatory responses. The lncRNAs with their potential to regulate JEV-induced inflammatory response were identified by constructing the lncRNA-mRNA coexpression network. Furthermore, silencing of the two selected lncRNAs (E52329 and N54010) resulted in reducing the phosphorylation of JNK and MKK4, which are known to be involved during inflammatory response. Collectively, we first demonstrated the transcriptomic landscape of lncRNAs in mice brain infected with JEV and analyzed the coexpression network of differentially regulated lncRNAs and mRNAs during JEV infection. Our results provide a better understanding of the host response to JEV infection and suggest that the identified lncRNAs may be used as potential therapeutic targets for the management of Japanese encephalitis.

Regulation of inflammation in Japanese encephalitis

Background

Uncontrolled inflammatory response of the central nervous system is a hallmark of severe Japanese encephalitis (JE). Although inflammation is necessary to mount an efficient immune response against virus infections, exacerbated inflammatory response is often detrimental. In this context, cells of the monocytic lineage appear to be important forces driving JE pathogenesis.

Main body

Brain-infiltrating monocytes, macrophages and microglia play a major role in central nervous system (CNS) inflammation during JE. Moreover, the role of inflammatory monocytes in viral neuroinvasion during JE and mechanisms of cell entry into the CNS remains unclear. The identification of cellular and molecular actors in JE inflammatory responses may help to understand the mechanisms behind excessive inflammation and to develop therapeutics to treat JE patients. This review addresses the current knowledge about mechanisms of virus neuroinvasion, neuroinflammation and therapeutics critical for JE outcome.

Conclusion

Understanding the regulation of inflammation in JE is challenging. Elucidation of the remaining open questions will help to the development of therapeutic approaches avoiding detrimental inflammatory responses in JE.

Zika virus tropism and interactions in myelinating neural cell cultures: CNS cells and myelin are preferentially affected

The recent global outbreak of Zika virus (ZIKV) infection has been linked to severe neurological disorders affecting the peripheral and central nervous systems (PNS and CNS, respectively). The pathobiology underlying these diverse clinical phenotypes are the subject of intense research; however, even the principal neural cell types vulnerable to productive Zika infection remain poorly characterised. Here we used CNS and PNS myelinating cultures from wild type and Ifnar1 knockout mice to examine neuronal and glial tropism and short-term consequences of direct infection with a Brazilian variant of ZIKV. Cell cultures were infected pre- or post-myelination for various intervals, then stained with cell-type and ZIKV-specific antibodies. In bypassing systemic immunity using ex vivo culture, and the type I interferon response in Ifnar1 deficient cells, we were able to evaluate the intrinsic infectivity of neural cells. Through systematic quantification of ZIKV infected cells in myelinating cultures, we found that ZIKV infection is enhanced in the absence of the type I interferon responses and that CNS cells are considerably more susceptible to infection than PNS cells. In particular, we demonstrate that CNS axons and myelinating oligodendrocytes are especially vulnerable to injury. These results have implications for understanding the pathobiology of neurological symptoms associated with ZIKV infection. Furthermore, we provide a quantifiable ex vivo infection model that can be used for fundamental and therapeutic studies on viral neuroinvasion and its consequences.

p21-Activated Kinase 4 Signaling Promotes Japanese Encephalitis Virus-Mediated Inflammation in Astrocytes

Japanese encephalitis virus (JEV) targets central nervous system, resulting in neuroinflammation with typical features of neuronal death along with hyper activation of glial cells. Exploring the mechanisms responsible for the JEV-caused inflammatory response remains a pivotal area of research. In the present study, we have explored the function of p21-activated kinase 4 (PAK4) in JEV-mediated inflammatory response in human astrocytes. The results showed that JEV infection enhances the phosphorylation of PAK4 in U251 cells and mouse brain. Knockdown of PAK4 resulted in decreased expression of inflammatory cytokines that include tumor necrosis factor alpha, interleukin-6, interleukin-1β, and chemokine (C-C motif) ligand 5 and interferon β upon JEV infection, suggesting that PAK4 signaling promotes JEV-mediated inflammation. In addition, we found that knockdown of PAK4 led to the inhibition of MAPK signaling including ERK, p38 MAPK and JNK, and also resulted in the reduced nuclear translocation of NF-κB and phosphorylation of AP-1. These results demonstrate that PAK4 signaling actively promotes JEV-mediated inflammation in human astrocytes via MAPK-NF-κB/AP-1 pathway, which will provide a new insight into the molecular mechanism of the JEV-induced inflammatory response.

Interleukin-1β secreted from betanodavirus-infected microglia caused the death of neurons in giant grouper brains

High interleukin (IL)-1β gene expression was observed in dead giant grouper brains after nervous necrosis virus (NNV) infection. To investigate the neuronal death caused by NNV infection, primary tissue culture of giant grouper brains (pGB) was performed. In NNV-infected pGB cells, the viral capsid protein was detected in both neurons and microglia; furthermore, microglial proliferation and neuronal death were observed. The culture supernatant (CS) of NNV-infected pGB cells contained IL-1β and tumor necrosis factor-α, which were mainly released from the microglia. A new batch of pGB cells was treated with CS, resulting in neuronal death, which could be prevented by blocking the IL-1β in the CS by using anti-IL-1β polyclonal antibodies. Moreover, pGB cells treated with recombinant IL-1β showed microglial proliferation and neuronal death. Thus, NNV infection may activate microglial proliferation and stimulate microglial secretion of IL-1β, which is a critical cytokine responsible for neuronal death in NNV-infected grouper brains.

A study of glutamate levels, NR1, NR2A, NR2B receptors and oxidative stress in rat model of Japanese encephalitis

There is paucity of studies on the role of glutamate excitotoxicity in cell damage in Japanese encephalitis. In this study the glutamate levels and its NMDA receptors, and oxidative stress markers in different brain regions have been evaluated and correlated with neurobehavioral changes at different time points. Twelve day old Wistar rats were inoculated with 3×10⁶pfu/ml intracerebrally. The neurobehavioral effects were evaluated by spontaneous locomotor activity (SLA), grip strength and rota rod test on 10, 33 and 48days post inoculation (dpi). Glutamate level was evaluated by enzyme linked immunosorbent assay, mRNA gene expression of ionotropic glutamate receptors N-methyl d-aspartate (NMDA) receptor 1, 2A and 2B (NR1, NR2A and NR2B) were evaluated by real time PCR. Malondialdehyde (MDA), glutathione (GSH) and glutathione peroxidase (GPx) levels were measured by spectrophotometer in different brain regions of JEV infected rats on 10, 33 and 48dpi. There was significant increase in motor deficit, grip strength and decreased locomotor activity on 10 and 33dpi. Glutamate levels were increased in thalamus, midbrain, frontal cortex, striatum and cerebellum on 10 and 33dpi and were followed by a recovery on 48dpi. Glutamate NMDR receptors NR1, NR2A and NR2B were reduced in thalamus, midbrain, frontal cortex, striatum and cerebellum on 10dpi which was followed by recovery after 33dpi. A significant increase in MDA level in thalamus, midbrain, frontal cortex, striatum and cerebellum was noted on 10 and 33dpi. The antioxidant GSH and GPx were significantly reduced in these brain regions on 10 and 33dpi. Glutamate, MDA, GSH and GPx correlated in different brain regions as the disease progress. Increased Glutamate level may be related to oxidative stress and may be responsible for behavioral alterations in rat model of Japanese encephalitis.

Tick-borne encephalitis virus induces chemokine RANTES expression via activation of IRF-3 pathway

Background

Tick-borne encephalitis virus (TBEV) is one of the most important flaviviruses that targets the central nervous system (CNS) and causes encephalitides in humans. Although neuroinflammatory mechanisms may contribute to brain tissue destruction, the induction pathways and potential roles of specific chemokines in TBEV-mediated neurological disease are poorly understood.

Methods

BALB/c mice were intracerebrally injected with TBEV, followed by evaluation of chemokine and cytokine profiles using protein array analysis. The virus-infected mice were treated with the CC chemokine antagonist Met-RANTES or anti-RANTES mAb to determine the role of RANTES in affecting TBEV-induced neurological disease. The underlying signaling mechanisms were delineated using RANTES promoter luciferase reporter assay, siRNA-mediated knockdown, and pharmacological inhibitors in human brain-derived cell culture models.

Results

In a mouse model, pathological features including marked inflammatory cell infiltrates were observed in brain sections, which correlated with a robust up-regulation of RANTES within the brain but not in peripheral tissues and sera. Antagonizing RANTES within CNS extended the survival of mice and reduced accumulation of infiltrating cells in the brain after TBEV infection. Through in vitro studies, we show that virus infection up-regulated RANTES production at both mRNA and protein levels in human brain-derived cell lines and primary progenitor-derived astrocytes. Furthermore, IRF-3 pathway appeared to be essential for TBEV-induced RANTES production. Site mutation of an IRF-3-binding motif abrogated the RANTES promoter activity in virus-infected brain cells. Moreover, IRF-3 was activated upon TBEV infection as evidenced by phosphorylation of TBK1 and IRF-3, while blockade of IRF-3 activation drastically reduced virus-induced RANTES expression.

Conclusions

Our findings together provide insights into the molecular mechanism underlying RANTES production induced by TBEV, highlighting its potential importance in the process of neuroinflammatory responses to TBEV infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-016-0665-9) contains supplementary material, which is available to authorized users.

MicroRNA-19b-3p Modulates Japanese Encephalitis Virus-Mediated Inflammation via Targeting RNF11

Japanese encephalitis virus (JEV) can invade the central nervous system and consequently induce neuroinflammation, which is characterized by profound neuronal cell damage accompanied by astrogliosis and microgliosis. Albeit microRNAs (miRNAs) have emerged as major regulatory noncoding RNAs with profound effects on inflammatory response, it is unknown how astrocytic miRNAs regulate JEV-induced inflammation. Here, we found the involvement of miR-19b-3p in regulating the JEV-induced inflammatory responsein vitroandin vivo The data demonstrated that miR-19b-3p is upregulated in cultured cells and mouse brain tissues during JEV infection. Overexpression of miR-19b-3p led to increased production of inflammatory cytokines, including tumor necrosis factor alpha, interleukin-6, interleukin-1β, and chemokine (C-C motif) ligand 5, after JEV infection, whereas knockdown of miR-19b-3p had completely opposite effects. Mechanistically, miR-19b-3p modulated the JEV-induced inflammatory response via targeting ring finger protein 11, a negative regulator of nuclear factor kappa B signaling. We also found that inhibition of ring finger protein 11 by miR-19b-3p resulted in accumulation of nuclear factor kappa B in the nucleus, which in turn led to higher production of inflammatory cytokines.In vivosilencing of miR-19b-3p by a specific antagomir reinvigorates the expression level of RNF11, which in turn reduces the production of inflammatory cytokines, abrogates gliosis and neuronal cell death, and eventually improves the survival rate in the mouse model. Collectively, our results demonstrate that miR-19b-3p positively regulates the JEV-induced inflammatory response. Thus, miR-19b-3p targeting may constitute a thought-provoking approach to rein in JEV-induced inflammation.

IMPORTANCE

Japanese encephalitis virus (JEV) is one of the major causes of acute encephalitis in humans worldwide. The pathological features of JEV-induced encephalitis are inflammatory reactions and neurological diseases resulting from glia activation. MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression posttranscriptionally. Accumulating data indicate that miRNAs regulate a variety of cellular processes, including the host inflammatory response under pathological conditions. Recently, a few studies demonstrated the role of miRNAs in a JEV-induced inflammatory response in microglia; however, their role in an astrocyte-derived inflammatory response is largely unknown. The present study reveals that miR-19b-3p targets ring finger protein 11 in glia and promotes inflammatory cytokine production by enhancing nuclear factor kappa B activity in these cells. Moreover, administration of an miR-19b-3p-specific antagomir in JEV-infected mice reduces neuroinflammation and lethality. These findings suggest a new insight into the molecular mechanism of the JEV-induced inflammatory response and provide a possible therapeutic entry point for treating viral encephalitis.

Transcriptional regulation of miR-15b by c-Rel and CREB in Japanese encephalitis virus infection

MicroRNAs (miRNAs) have been well known to play diverse roles in viral infection at the level of posttranscriptional repression. However, much less is understood about the mechanism by which miRNAs are regulated during viral infection. It is likely that both host and virus contain factors to modulate miRNA expression. Here we report the up-regulation of microRNA-15b (miR-15b) in vitro upon infection with Japanese encephalitis virus (JEV). Analysis of miR-15b precursor, pri-miR-15b and pre-miR-15b, suggest that the regulation occurs transcriptionally. Further, we identified the transcriptional regulatory region of miR-15b that contains consensus binding motif for NF-κB subunit c-Rel and cAMP-response element binding protein (CREB), which are known as transcription factor to regulate gene expression. By promoter fusion and mutational analyses, we demonstrated that c-Rel and CREB bind directly to the promoter elements of miR-15b, which are responsible for miR-15b transcription in response to JEV infection. Finally, we showed that pharmacological inhibition of ERK and NF-κB signaling pathway blocked induction of miR-15b in JEV infection, suggesting important roles of ERK and NF-κB pathway in the regulation of miR-15b gene. Therefore, our observations indicate that induced expression of miR-15b is modulated by c-Rel and CREB in response to JEV infection.

LincRNA-Cox2 Promotes Late Inflammatory Gene Transcription in Macrophages through Modulating SWI/SNF-Mediated Chromatin Remodeling

Long intergenic noncoding RNAs (lincRNAs) are long noncoding transcripts (>200 nt) from the intergenic regions of annotated protein-coding genes. One of the most highly induced lincRNAs in macrophages upon TLR ligation is lincRNA-Cox2, which was recently shown to mediate the activation and repression of distinct classes of immune genes in innate immune cells. We report that lincRNA-Cox2, located at chromosome 1 proximal to the PG-endoperoxide synthase 2 (Ptgs2/Cox2) gene, is an early-primary inflammatory gene controlled by NF-κB signaling in murine macrophages. Functionally, lincRNA-Cox2 is required for the transcription of NF-κB-regulated late-primary inflammatory response genes stimulated by bacterial LPS. Specifically, lincRNA-Cox2 is assembled into the switch/sucrose nonfermentable (SWI/SNF) complex in cells after LPS stimulation. This resulting lincRNA-Cox2/SWI/SNF complex can modulate the assembly of NF-κB subunits to the SWI/SNF complex, and ultimately, SWI/SNF-associated chromatin remodeling and transactivation of the late-primary inflammatory-response genes in macrophages in response to microbial challenge. Therefore, our data indicate a new regulatory role for NF-κB-induced lincRNA-Cox2 as a coactivator of NF-κB for the transcription of late-primary response genes in innate immune cells through modulation of epigenetic chromatin remodeling.

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

Japanese encephalitis virus (JEV) can target CNS and cause neuroinflammation that is characterized by profound neuronal damage and concomitant microgliosis/astrogliosis. Although microRNAs (miRNAs) have emerged as a major regulatory network with profound effects on inflammatory response, it is less clear how they regulate JEV-induced inflammation. In this study, we found that miR-15b is involved in modulating the JEV-induced inflammatory response. The data demonstrate that miR-15b is upregulated during JEV infection of glial cells and mouse brains. In vitro overexpression of miR-15b enhances the JEV-induced inflammatory response, whereas inhibition of miR-15b decreases it. Mechanistically, ring finger protein 125 (RNF125), a negative regulator of RIG-I signaling, is identified as a direct target of miR-15b in the context of JEV infection. Furthermore, inhibition of RNF125 by miR-15b results in an elevation in RIG-I levels, which, in turn, leads to a higher production of proinflammatory cytokines and type I IFN. In vivo knockdown of virus-induced miR-15b by antagomir-15b restores the expression of RNF125, reduces the production of inflammatory cytokines, attenuates glial activation and neuronal damage, decreases viral burden in the brain, and improves survival in the mouse model. Taken together, our results indicate that miR-15b modulates the inflammatory response during JEV infection by negative regulation of RNF125 expression. Therefore, miR-15b targeting may constitute an interesting and promising approach to control viral-induced neuroinflammation.

A preliminary randomized double blind placebo-controlled trial of intravenous immunoglobulin for Japanese encephalitis in Nepal

Background

Japanese encephalitis (JE) virus (JEV) is a mosquito-borne flavivirus found across Asia that is closely related to West Nile virus. There is no known antiviral treatment for any flavivirus. Results from in vitro studies and animal models suggest intravenous immunoglobulin (IVIG) containing virus-specific neutralizing antibody may be effective in improving outcome in viral encephalitis. IVIG’s anti-inflammatory properties may also be beneficial.

Methodology/Principal Findings

We performed a pilot feasibility randomized double-blind placebo-controlled trial of IVIG containing anti-JEV neutralizing antibody (ImmunoRel, 400mg/kg/day for 5 days) in children with suspected JE at two sites in Nepal; we also examined the effect on serum neutralizing antibody titre and cytokine profiles. 22 children were recruited, 13 of whom had confirmed JE; 11 received IVIG and 11 placebo, with no protocol violations. One child (IVIG group) died during treatment and two (placebo) subsequently following hospital discharge. Overall, there was no difference in outcome between treatment groups at discharge or follow up. Passive transfer of anti-JEV antibody was seen in JEV negative children. JEV positive children treated with IVIG had JEV-specific neutralizing antibody titres approximately 16 times higher than those treated with placebo (p=0.2), which was more than could be explained by passive transfer alone. IL-4 and IL-6 were higher in the IVIG group.

Conclusions/Significance

A trial of IVIG for JE in Nepal is feasible. IVIG may augment the development of neutralizing antibodies in JEV positive patients. IVIG appears an appealing option for JE treatment that warrants further study.

Trial Registration

ClinicalTrials.gov NCT01856205

A tick-borne encephalitis model in infant rats infected with langat virus

Tick-borne encephalitis virus (TBEV) is the causative agent of human TBE, a severe infection that can cause long-lasting neurologic sequelae. Langat virus (LGTV), which is closely related to TBEV, has a low virulence for human hosts and has been used as a live vaccine against TBEV. Tick-borne encephalitis by natural infection of LGTV in humans has not been described, but one of 18,500 LGTV vaccinees developed encephalitis. The pathogenetic mechanisms of TBEV are poorly understood and, currently, no effective therapy is available. We developed an infant rat model of TBE using LGTV as infective agent. Infant Wistar rats were inoculated intracisternally with 10 focus-forming units of LGTV and assessed for clinical disease and neuropathologic findings at Days 2, 4, 7, and 9 after infection. Infection with LGTV led to gait disturbance, hypokinesia, and reduced weight gain or weight loss. Cerebrospinal fluid concentrations of RANTES, interferon-γ, interferon-β, interleukin-6, and monocyte chemotactic protein-1 were increased in infected animals. The brains of animals with LGTV encephalitis exhibited characteristic perivascular inflammatory cuffs and glial nodules; immunohistochemistry documented the presence of LGTV in the thalamus, hippocampus, midbrain, frontal pole, and cerebellum. Thus, LGTV meningoencephalitis in infant rats mimics important clinical and histopathologic features of human TBE. This new model provides a tool to investigate disease mechanisms and to evaluate new therapeutic strategies against encephalitogenic flaviviruses.

Flaviviruses, an expanding threat in public health: focus on dengue, West Nile, and Japanese encephalitis virus

The flaviviruses dengue, West Nile, and Japanese encephalitis represent three major mosquito-borne viruses worldwide. These pathogens impact the lives of millions of individuals and potentially could affect non-endemic areas already colonized by mosquito vectors. Unintentional transport of infected vectors (Aedes and Culex spp.), traveling within endemic areas, rapid adaptation of the insects into new geographic locations, climate change, and lack of medical surveillance have greatly contributed to the increase in flaviviral infections worldwide. The mechanisms by which flaviviruses alter the immune and the central nervous system have only recently been examined despite the alarming number of infections, related deaths, and increasing global distribution. In this review, we will discuss the expansion of the geographic areas affected by flaviviruses, the potential threats to previously unaffected countries, the mechanisms of pathogenesis, and the potential therapeutic interventions to limit the devastating consequences of these viruses.

The Potential Role of Chemokines in Alzheimer's Disease Pathogenesis

Alzheimer's disease (AD) is a neurodegenerative disorder and leading cause of dementia, which begins with impaired memory. The neuropathological hallmarks of AD include destructive alterations of neurons by neurofibrillary tangles, neuritic amyloid plaques, and neuroinflammatory process in the brain. Chemokines have a major role in inflammatory cell attraction and glial cell activation and/or modulation in the central nervous system. Moreover, the clinical and immunopathological evidence could show dual key role of chemokines in their pro- and anti-inflammatory properties in AD. However, their effects in neurodegeneration and/or neuroprotection remain an area of investigation. This review article provides an overview of characteristic, cellular source and activity of chemokines, and their roles in neuronal glial cell interaction in AD.

Infection and injury of human astrocytes by tick-borne encephalitis virus

Tick-borne encephalitis (TBE), a disease caused by tick-borne encephalitis virus (TBEV), represents the most important flaviviral neural infection in Europe and north-eastern Asia. In the central nervous system (CNS), neurons are the primary target for TBEV infection; however, infection of non-neuronal CNS cells, such as astrocytes, is not well understood. In this study, we investigated the interaction between TBEV and primary human astrocytes. We report for the first time, to the best of our knowledge, that primary human astrocytes are sensitive to TBEV infection, although the infection did not affect their viability. The infection induced a marked increase in the expression of glial fibrillary acidic protein, a marker of astrocyte activation. In addition, expression of matrix metalloproteinase 9 and several key pro-inflammatory cytokines/chemokines (e.g. tumour necrosis factor α, interferon α, interleukin (IL)-1β, IL-6, IL-8, interferon γ-induced protein 10, macrophage inflammatory protein, but not monocyte chemotactic protein 1) was upregulated. Moreover, we present a detailed description of morphological changes in TBEV-infected cells, as investigated using three-dimensional electron tomography. Several novel ultrastructural changes were observed, including the formation of unique tubule-like structures of 17.9 ±0.15 nm diameter with associated viral particles and/or virus-induced vesicles and located in the rough endoplasmic reticulum of the TBEV-infected cells. This is the first demonstration that TBEV infection activates primary human astrocytes. The infected astrocytes might be a potential source of pro-inflammatory cytokines in the TBEV-infected brain, and might contribute to the TBEV-induced neurotoxicity and blood-brain barrier breakdown that occurs during TBE. The neuropathological significance of our observations is also discussed.

Flaviviruses are neurotropic, but how do they invade the CNS?

Flaviruses (FV) are RNA viruses carried by mosquitoes. Neurological signs including acute encephalitis, meningitis and acute flaccid paralysis develop in a small percentage of infected individuals; long term sequlae are, Parkinsonism, dystonias and cognitive changes. FV neuroinfection is neurotropic involving subcortical nuclei (substantia nigra and thalamus) anterior horn neurons and neocortex. Glycosylation of the FV E envelope protein is one determinant of neuroinvasion, increasing both axonal and trans-epithelial transportation. Neutralizing antibodies against the E and NS proteins prevents FV uptake into several cell types, including axons. CD8+ T cells are vital for clearance of WNF infected cells from the CNS, whereas TLR-3 and TLR-7 mediated anti-virus response through increased serum inflammatory cytokines to disrupt the BBB providing infected leucocytes and free virus access to the CNS (so called Trojan horse) Cellular virus attachment factors, promoting FV cell entry are widely distributed and include DC-SIGN (that detects complex carbohydrate molecules); Glycosamino glycans (GAG), Heparan sulphate(HSPG) Semaphorin 7A, Low Density Lipid receptors (LDLR); these are not FV specific virus entry receptors. The FV also crosses epithelial and endothelial barriers by disrupting Tight Junction complexes to increase BBB permeability. This review describes the multiple pathways responsible for the neuroinvasive properties of the Flaviviruses.

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.

Inflammatory markers in the patients of Japanese encephalitis

OBJECTIVES

Japanese encephalitis (JE) is one of the commonest viral encephalitis especially prevalent in Southeast Asia. Estimated mortality rate of JE is approximately 30%, with survivors undergoing severe and irreversible neurological sequelae. Although central nervous system (CNS) inflammation is imminent upon JE infection, the pathways underlying the same have not yet been clearly elucidated. However, cytokines-tumor necrosis factor-alpha (TNF-alpha) and interlukin-2 (IL-2), are small secreted proteins, which mediate and regulate immunity. Therefore, we wanted to evaluate the role, if any, of these cytokines in the pathogenesis of JE.

METHODS

We measured the levels of TNF-alpha and IL-2 in the serum and cerebrospinal fluid (CSF) of patients suffering JE, using enzyme-linked immunosorbent assay (ELISA).

RESULTS

JE infection caused a remarkable increase (p<0.0001) in the levels of TNF-alpha in the serum and CSF, while IL-2 levels were unaffected.

DISCUSSION

These results show that TNF-alpha pathway is involved in JE infection-triggered neuroinflammation.