Astrocytic alteration induced by Japanese encephalitis virus infection

A Review of miRNA Regulation in Japanese Encephalitis (JEV) Virus Infection

Japanese encephalitis (JE) is a mosquito-borne disease that causes neuronal damage and inflammation of microglia, and in severe cases, it can be fatal. JE infection can resist cellular immune responses and survive in host cells. Japanese encephalitis virus (JEV) infects macrophages and peripheral blood lymphocytes. In addition to regulating biological signaling pathways, microRNAs in cells also influence virus-host interactions. Under certain circumstances, viruses can change microRNA production. These changes affect the replication and spread of the virus. Host miRNAs can contain viral pathogenicity by downregulating the antiviral immune response pathways. Simultaneous profiling of miRNA and messenger RNA (mRNA) could help us detect pathogenic factors, and dual RNA detection is possible. This work highlights important miRNAs involved in human JE infection. In this study, we have shown the important miRNAs that play significant roles in JEV infection. We found that during JEV infection, miRNA-155, miRNA-29b, miRNA-15b, miRNA-146a, miRNA-125b-5p, miRNA-30la, miRNA-19b-3p, and miRNA-124, cause upregulation of human genes whereas miRNA-432, miRNA-370, miRNA- 33a-5p, and miRNA-466d-3p are responsible for downregulation of human genes respectively. Further, these miRNAs are also responsible for the inflammatory effects. Although several other miRNAs critical to the JEV life cycle are yet unknown, there is currently no evidence for the role of miRNAs in persistence.

Fundamental neurochemistry review: Glutamatergic dysfunction as a central mechanism underlying flavivirus-induced neurological damage

The Flaviviridae family comprises positive-sense single-strand RNA viruses mainly transmitted by arthropods. Many of these pathogens are especially deleterious to the nervous system, and a myriad of neurological symptoms have been associated with infections by Zika virus (ZIKV), West Nile virus (WNV), and Japanese encephalitis virus (JEV) in humans. Studies suggest that viral replication in neural cells and the massive release of pro-inflammatory mediators lead to morphological alterations of synaptic spine structure and changes in the balance of excitatory/inhibitory neurotransmitters and receptors. Glutamate is the predominant excitatory neurotransmitter in the brain, and studies propose that either enhanced release or impaired uptake of this amino acid contributes to brain damage in several conditions. Here, we review existing evidence suggesting that glutamatergic dysfunction-induced by flaviviruses is a central mechanism for neurological damage and clinical outcomes of infection. We also discuss current data suggesting that pharmacological approaches that counteract glutamatergic dysfunction show benefits in animal models of such viral diseases.

Japanese encephalitis viral infection modulates proinflammatory cyto/chemokine profile in primary astrocyte and cell line of astrocytic origin

Japanese Encephalitis Virus (JEV) is a neurotropic virus that invades Central Nervous System (CNS) and causes severe neuroinflammation. Given the abundance and the position of astrocytes in the CNS, we speculate that they might play a critical role in the process of neuroinflammation. Unfortunately, the role of astrocytes in JEV-mediated neuroinflammation has long been understated. In this study, we have attempted to assess the role of astrocyte-mediated neuroinflammation upon JEV infection. Mouse model of JEV infection, generated by intraperitoneal injection, showed severe reactive astrogliosis. To further address our hypothesis, we employed immortalized astrocytic cell line (in vitro) and primary astrocyte-enriched culture (ex vivo) as experimental models. JEV infection in the astrocytes induces proinflammatory cytokines like MCP1/CCL2 and IL6 in both ex vivo and in vitro cultures as observed from the cytometric bead array analysis. A significantly altered cytokine profile was observed using PCR analysis in in vitro and ex vivo models upon infection, with respect to control, validating our previous results. We also show that there exists a major inconsistency in the viral replication kinetics, wherein the cell line showed a robust rate of replication whereas the primary astrocyte-enriched culture showed negligibly low number of plaques, underlining the importance of the selection of appropriate experimental model system. In conclusion, we claim that astrocytes significantly contribute to JEV-mediated neuroinflammation, despite not being a CNS immune cell.

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.

Cryptic etiopathological conditions of equine nervous system with special emphasis on viral diseases

The importance of horse (Equus caballus) to equine practitioners and researchers cannot be ignored. An unevenly distributed population of equids harbors numerous diseases, which can affect horses of any age and breed. Among these, the affections of nervous system are potent reason for death and euthanasia in equids. Many episodes associated with the emergence of equine encephalitic conditions have also pose a threat to human population as well, which signifies their pathogenic zoonotic potential. Intensification of most of the arboviruses is associated with sophisticated interaction between vectors and hosts, which supports their transmission. The alphaviruses, bunyaviruses, and flaviviruses are the major implicated groups of viruses involved with equines/humans epizootic/epidemic. In recent years, many outbreaks of deadly zoonotic diseases such as Nipah virus, Hendra virus, and Japanese encephalitis in many parts of the globe addresses their alarming significance. The equine encephalitic viruses differ in their global distribution, transmission and main vector species involved, as discussed in this article. The current review summarizes the status, pathogenesis, pathology, and impact of equine neuro-invasive conditions of viral origin. A greater understanding of these aspects might be able to provide development of advances in neuro-protective strategies in equine population.

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.

Encephalitic Arboviruses: Emergence, Clinical Presentation, and Neuropathogenesis

Arboviruses are arthropod-borne viruses that exhibit worldwide distribution, contributing to systemic and neurologic infections in a variety of geographical locations. Arboviruses are transmitted to vertebral hosts during blood feedings by mosquitoes, ticks, biting flies, mites, and nits. While the majority of arboviral infections do not lead to neuroinvasive forms of disease, they are among the most severe infectious risks to the health of the human central nervous system. The neurologic diseases caused by arboviruses include meningitis, encephalitis, myelitis, encephalomyelitis, neuritis, and myositis in which virus- and immune-mediated injury may lead to severe, persisting neurologic deficits or death. Here we will review the major families of emerging arboviruses that cause neurologic infections, their neuropathogenesis and host neuroimmunologic responses, and current strategies for treatment and prevention of neurologic infections they cause.

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.

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 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.

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.

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.

Japanese encephalitis virus induces matrix metalloproteinase-9 in rat brain astrocytes via NF-κB signalling dependent on MAPKs and reactive oxygen species

BACKGROUND AND PURPOSE

Japanese encephalitis virus (JEV) is a member of the family Flaviviridae and JEV infection is a major cause of acute encephalopathy in children, which destroys cells in the CNS, including astrocytes and neurons. However, the detailed mechanisms underlying the inflammatory action of JEV are largely unclear.

EXPERIMENTAL APPROACH

The effect of JEV on the expression of matrix metalloproteinase (MMP)-9 was determined by gelatin zymography, Western blot analysis, real-time PCR and promoter assay. The involvement of the NADPH oxidase and reactive oxygen species (ROS), MAPKs, and the transcription factor NF-κB in these responses was investigated by using selective pharmacological inhibitors and transfection with appropriate siRNAs.

KEY RESULTS

JEV induced the expression of the pro-form of MMP-9 in rat brain astrocytes (RBA-1 cells). In RBA-1 cells, JEV induced MMP-9 expression and promoter activity, which was inhibited by pretreatment with inhibitors of NADPH oxidase (diphenylene iodonium chloride or apocynin), MAPKs (U0126, SB203580 or SP600125) and a ROS scavenger (N-acetylcysteine), or transfection with siRNAs of p47(phox) , ERK1, JNK2 and p38. In addition, JEV-induced MMP-9 expression was reduced by pretreatment with an inhibitor of NF-κB (helenalin) or transfection with p65 siRNA. Moreover, JEV-stimulated NF-κB activation was inhibited by pretreatment with the inhibitors of NADPH oxidase and MAPKs.

CONCLUSIONS AND IMPLICATIONS

MMP-9 expression induced by JEV infection of RBA-1 cells was mediated through the generation of ROS and activation of p42/p44 MAPK, p38 MAPK and JNK1/2, leading to NF-κB activation.

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.

Comparative analysis of immune responses to Russian spring-summer encephalitis and Omsk hemorrhagic fever viruses in mouse models

Omsk hemorrhagic fever virus (OHFV) and Russian spring-summer encephalitis virus (RSSEV) are tick-borne flaviviruses that have close homology but different pathology and disease outcomes. Previously, we reported that C57BL/6 and BALB/c mice were excellent models to study the pathology and clinical signs of human RSSEV and OHFV infection. In the study described here, we found that RSSEV infection induced robust release of proinflammatory cytokines (IL-1α, IL-1β, IL-6 and TNF-α) and chemokines (MCP-1, MIP-1β, RANTES and KC) in the brain at 9 and 11dpi, together with moderate to low Th1 and Th2 cytokines. In contrast, OHFV infection stimulated an early and prominent induction of IL-1α, TNF-α, IL-12p70, MCP-1, MIP-1α and MIP-1β in the spleen of infected mice. Collectively our data suggest that a differential host response to infection may lead to the alternate disease outcomes seen following OHFV or RSSEV infection.

Morphological changes in human neural cells following tick-borne encephalitis virus infection

Tick-borne encephalitis (TBE) is one of the leading and most dangerous human viral neuroinfections in Europe and north-eastern Asia. The clinical manifestations include asymptomatic infections, fevers and debilitating encephalitis that might progress into chronic disease or fatal infection. To understand TBE pathology further in host nervous systems, three human neural cell lines, neuroblastoma, medulloblastoma and glioblastoma, were infected with TBE virus (TBEV). The susceptibility and virus-mediated cytopathic effect, including ultrastructural and apoptotic changes of the cells, were examined. All the neural cell lines tested were susceptible to TBEV infection. Interestingly, the neural cells produced about 100- to 10 000-fold higher virus titres than the conventional cell lines of extraneural origin, indicating the highly susceptible nature of neural cells to TBEV infection. The infection of medulloblastoma and glioblastoma cells was associated with a number of major morphological changes, including proliferation of membranes of the rough endoplasmic reticulum and extensive rearrangement of cytoskeletal structures. The TBEV-infected cells exhibited either necrotic or apoptotic morphological features. We observed ultrastructural apoptotic signs (condensation, margination and fragmentation of chromatin) and other alterations, such as vacuolation of the cytoplasm, dilatation of the endoplasmic reticulum cisternae and shrinkage of cells, accompanied by a high density of the cytoplasm. On the other hand, infected neuroblastoma cells did not exhibit proliferation of membranous structures. The virions were present in both the endoplasmic reticulum and the cytoplasm. Cells were dying preferentially by necrotic mechanisms rather than apoptosis. The neuropathological significance of these observations is discussed.

Japanese encephalitis virus infection activates caspase-8 and -9 in a FADD-independent and mitochondrion-dependent manner

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, replicates primarily at the endoplasmic reticulum and thereby triggers apoptosis of infected cells. This study investigated the hierarchical activation of the caspase network induced by JEV infection. It was found that JEV activated the initiators caspase-8 and -9, as well as effector caspase-3, in infected baby hamster kidney and mouse neuroblastoma (N18) cells. In neuronal N18 cells, JEV infection triggered cytochrome c release from mitochondria, which in turn activated caspase-9 and -3. Treatment of JEV-infected N18 cells with cyclosporin A or ruthenium red, which attenuate mitochondrial injuries, blocked activation of caspase-9 or -3, typifying that, in neuronal cells, this apoptosis involves the mitochondrial pathway. Alternatively, in caspase-3-deficient MCF-7 cells, JEV persisted and readily triggered a typical apoptotic response, including cytochrome c release and full activation of caspase-9 and -8 along with caspase-6, indicating that JEV did not require caspase-3 to manifest caspase-8 activation and apoptosis. Interestingly, a Fas-associated death-domain-containing protein (FADD) dominant-negative mutant, which interfered with transmission of the extracellular death signals into cells through the Fas/tumour necrosis factor (TNF) receptor, failed to block JEV-induced apoptosis and caspase-8 activation, implying that receptor oligomerization of the Fas/TNF pathway might not participate in JEV-induced apoptosis. Taken together, these results illustrate that JEV infection triggers caspase cascades involving the initiators caspase-8 and -9, probably through FADD-independent but mitochondrion-dependent pathways.

Canine distemper virus infection of primary hippocampal cells induces increase in extracellular glutamate and neurodegeneration

The canine distemper virus (CDV) belongs to the Morbillivirus genus which includes important human pathogens like the closely related measles virus. CDV infection can reach the nervous system where it causes serious malfunctions. Although this pathology is well described, the molecular events in brain infection are still poorly understood. Here we studied infection in vitro by CDV using a model of dissociated cell cultures from newborn rat hippocampus. We used a recombinant CDV closely related to the neurovirulent A75/17 which also expresses the enhanced green fluorescent protein. We found that infected neurons and astrocytes could be clearly detected, and that infection spreads only slowly to neighboring cells. Interestingly, this infection causes a massive cell death of neurons, which includes also non-infected neurons. Antagonists of NMDA-type or alpha-amino-3-hydroxy-5-methylisoxazole-4-propinate (AMPA)-type glutamate receptors could slow down this neuron loss, indicating an involvement of the glutamatergic system in the induction of cell death in infected and non-infected cells. Finally, we show that, following CDV infection, there is a steady increase in extracellular glutamate in infected cultures. These results indicate that CDV infection induces excitotoxic insults on neurons via glutamatergic signaling.

DNAzyme-mediated inhibition of Japanese encephalitis virus replication in mouse brain

Japanese encephalitis virus (JEV) is an arthropod-borne flavivirus with a single-stranded RNA genome containing non-coding regions (NCRs) at its 5' and 3'-ends. The NCRs have flavivirus-conserved sequences that are important for virus replication. Here we describe DNAzymes (Dzs) that cleave the RNA sequence of the 3'-NCR of JEV genome in vitro. The nuclease-resistant Dzs, containing phosphorothioate linkages, were efficiently taken up by mouse neuronal and glial cells, and addition of a continuous stretch of 10 guanosine residues (poly-(G)(10)) to the 3'-end of a Dz led to its enhanced delivery to cells containing scavenger receptors (ScRs). These novel Dzs inhibited JEV replication in cultured mouse cells of neuronal and macrophage origin. JEV is a neurotropic virus that actively replicates in mouse brain. Here we show that intra-cerebral (i.c.) administration of a poly-(G)(10)-tethered, phosphorothioated Dz in JEV-infected mice led to more than 99.99% inhibition of virus replication in brain, resulting in a dose-dependent extended lifespan or complete recovery of the infected animals. This is the first report of in vivo application of a Dz to control a virus infection in an animal model.

Neuroprotection conferred by astrocytes is insufficient to protect animals from succumbing to Japanese encephalitis

Astrocytes play a key role in regulating aspects of inflammation and in the homeostatic maintenance of the central nervous system (CNS). However, the role of astrocytes in viral encephalitis mediated inflammation is not well documented. As Japanese encephalitis virus (JEV) infection is localized to neurons and considering the importance of astrocytes in supporting neuronal survival and function, we have exploited an experimental model of Japanese encephalitis (JE) to better understand the role of astrocytes in JE. Suckling mice pups were inoculated with the virus and 2 and 4 days later we analyzed a panel of molecules characteristic of reactive astrogliosis. We show that JEV infection increases the expression of astrocyte-specific glial fibrillary acidic protein (GFAP), the glutamate aspartate transporter (GLAST), glutamate transporter-1 (GLT-1) and ceruloplasmin (CP). The transcript levels of growth factors produced predominantly by activated astrocytes such as nerve growth factor (NGF) and ciliary neurotrophin factor (CNTF) were elevated following JEV infection. The transcript level of brain-derived neurotrophic factor (BDNF) was also elevated following JEV infection. Both NGF and CNTF were capable of preventing ROS mediated neuronal death following in vitro JEV infection to a certain extent. Taken altogether, these data indicate that increased astrogliosis following JEV infection is accompanied by the enhanced ability of astrocytes to detoxify glutamate, inactivate free radical and produce neurotrophic factors that are involved in neuronal protection. However, this elevated physiological state of astrocyte is insufficient in conferring neuroprotection, as infected animals eventually succumb to infection. The response of astrocytes to JE can be amplified to modulate the adaptive response of brain to induce neuroprotection.

Proinflammatory mediators released by activated microglia induces neuronal death in Japanese encephalitis

While a number of studies have documented the importance of microglia in central nervous system (CNS) response to injury, infection and disease, little is known regarding its role in viral encephalitis. We therefore, exploited an experimental model of Japanese Encephalitis, to better understand the role played by microglia in Japanese Encephalitis Virus (JEV) infection. Lectin staining performed to assess microglial activation indicated a robust increase in reactive microglia following infection. A difference in the topographic distribution of activated, resting, and phagocytic microglia was also observed. The levels of various proinflammatory mediators, such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (Cox-2), IL-6, IL-1beta, TNF-alpha, and MCP-1 that have been implicated in microglial response to an activational state was significantly elevated following infection. These cytokines exhibited region selective expression in the brains of infected animals, with the highest expression observed in the hippocampus. Moreover, the expression of neuronal specific nuclear protein NeuN was markedly downregulated during progressive infection indicating neuronal loss. In vitro studies further confirmed that microglial activation and subsequent release of various proinflammatory mediators induces neuronal death following JEV infection. Although initiation of immune responses by microglial cells is an important protective mechanism in the CNS, unrestrained inflammatory responses may result in irreparable brain damage. Our findings suggest that the increased microglial activation following JEV infection influences the outcome of viral pathogenesis. It is likely that the increased microglial activation triggers bystander damage, as the animals eventually succumb to infection.

Retinoic acid-inducible gene-I mediates RANTES/CCL5 expression in U373MG human astrocytoma cells stimulated with double-stranded RNA

Retinoic acid-inducible gene-I (RIG-I) mediates part of the cell signaling in response to viral infection. Polyinosinic-polycytidilic acid (poly IC) is a synthetic double-stranded RNA (dsRNA) and mimics viral infection when applied to cell cultures. The CC chemokine, RANTES (regulated on activation, normal T-cell expressed and secreted), is a potent attractant for inflammatory cells such as memory T-lymphocytes, monocytes and eosinophils. In the present study, we demonstrated that poly IC enhances the expression of RIG-I in U373MG human astrocytoma cells. The RNA interference of RIG-I resulted in the suppression of the poly IC-induced RANTES expression. Pretreatment of the cells with SB203580, an inhibitor of p38 mitogen-activated protein kinase, and dexamethasone inhibited the poly IC-induced expression of RIG-I. Furthermore, poly IC upregulated RIG-I in normal human astrocytes in culture and the in vivo injection of poly IC into the striatum of the mouse brain induced the expression of RIG-I in astrocytes. We conclude that RIG-I may be involved in immune reactions against viral infection, at least in part, through the regulation of RANTES expression in astrocytes.

Immunopathology of flavivirus infections

With the recent emergence of the flavivirus, West Nile virus (WNV), in particular, the New York strain of Lineage I WNV in North America in 1999, there has been a significant increase in activity in neurotropic flavivirus research. These viruses cause encephalitis that can result in permanent neurological sequelae or death. Attempts to develop vaccines have made progress, but have been variably successful, despite considerable commercial underwriting. Thus, the discovery of ways and means to combat disease is no less urgent. As such, most recent work has been directed towards dissecting and understanding the pathogenesis of disease, as a way of informing possible approaches to abrogation or amelioration of illness. Whether inherent to flaviviruses or because humans are incidental, dead-end hosts, it is clear that these viruses interact with their human hosts in extremely complex ways. This occurs from the cellular level, at which infection must be established to produce disease, to its interaction with the adaptive immune response, which may result in its eradication, with or without immunopathological and consequent neurological sequelae. As human proximity to and contact with flavivirus insect vectors and amplifying hosts cannot practically be eliminated, our understanding of the pathogenesis of flavivirus-induced diseases, especially with regard to possible targets for treatment, is imperative.

Double-stranded RNA induces production of RANTES and IL-8 by human nasal fibroblasts

Double-stranded RNA (dsRNA) and the viral RNA mimic, polyinosine-polycytidylic acid (poly(I:C)), are recognized by toll-like receptor 3 (TLR3) that mediates the innate immune response to viral infections. In this study, we investigated the effects of poly(I:C) on the production of chemokines (IL-8, RANTES, and eotaxin), Type I IFNs (IFNalpha and IFNbeta), Th1-cytokines (IL-12 and IFNgamma), and pro-inflammatory cytokines (TNF-alpha and IL-1beta) by human nasal mucosa-derived fibroblasts. Human nasal fibroblasts were treated with poly(I:C), and levels of cytokines and chemokines were measured by ELISA. Incubation with poly(I:C) significantly enhanced the secretion of RANTES and IL-8. However, eotaxin, IL-1beta, TNF-alpha, IFNalpha, IFNgamma, and IL-12 were not secreted from nasal fibroblasts stimulated with poly(I:C). The JNK inhibitor SP600125 and the PI3-kinase inhibitor LY294002 significantly blocked the poly(I:C)-induced release of RANTES and IL-8, whereas the p38 MAP kinase inhibitor SB203580 suppressed poly(I:C)-induced secretion of IL-8, but not RANTES. Nasal fibroblasts play an important role in initiating antiviral responses and inflammation of the nasal cavity by producing chemokines leading to enhanced inflammatory cell recruitment.

Neuronal CXCL10 directs CD8+ T-cell recruitment and control of West Nile virus encephalitis

The activation and entry of antigen-specific CD8(+) T cells into the central nervous system is an essential step towards clearance of West Nile virus (WNV) from infected neurons. The molecular signals responsible for the directed migration of virus-specific T cells and their cellular sources are presently unknown. Here we demonstrate that in response to WNV infection, neurons secrete the chemokine CXCL10, which recruits effector T cells via the chemokine receptor CXCR3. Neutralization or a genetic deficiency of CXCL10 leads to a decrease in CXCR3(+) CD8(+) T-cell trafficking, an increase in viral burden in the brain, and enhanced morbidity and mortality. These data support a new paradigm in chemokine neurobiology, as neurons are not generally considered to generate antiviral immune responses, and CXCL10 may represent a novel neuroprotective agent in response to WNV infection in the central nervous system.

Antiviral effect of dehydroepiandrosterone on Japanese encephalitis virus infection

Japanese encephalitis virus (JEV), which causes neurological disorders, completes its life cycle and triggers apoptotic cell death in infected cells. Dehydroepiandrosterone (DHEA), an adrenal-derived steroid, has been implicated in protection against neurotoxicity and protection of animals from viral-induced encephalitis, resulting in an increased survival rate of the animals. Currently, the mechanisms underlying the beneficial effects of DHEA against the virus are largely unknown. In this study, DHEA suppression of JEV replication and virus-induced apoptosis in murine neuroblastoma (N18) cells was investigated. It was found that DHEA suppressed JEV-induced cytopathic effects, JEV-induced apoptotic cell death and JEV propagation in a concentration-dependent manner. Antiviral activity was more efficient in cultures treated with DHEA immediately after viral adsorption compared with that in cultures receiving delayed administration after adsorption or transient exposure before adsorption. JEV-induced cytotoxicity was accompanied by the inactivation of extracellular signal-regulated protein kinase (ERK). Inactivation of ERK by JEV infection was reversed by DHEA. When cells were treated with the ERK inhibitor U0126, DHEA lost its antiviral effect. Activation of ERK by anisomycin mimicked the action of DHEA in suppressing JEV-induced cytotoxicity. DHEA-related compounds, such as its sulfate ester (DHEAS) and pregnenolone, were unable to suppress JEV-induced cytotoxicity and ERK inactivation. The hormone-receptor antagonists ICI 182780 and flutamide failed to abrogate the antiviral effect of DHEA. These findings suggest that the antiviral effect of DHEA is not linked directly to the genomic steroid-receptor pathways and suggest that the signalling pathways of ERK play a role in the antiviral action of DHEA.

Structure and dynamics of a predicted ferredoxin-like selenoprotein in Japanese encephalitis virus

Homologues of the selenoprotein glutathione peroxidase (GPx) have been previously identified in poxviruses and in RNA viruses including HIV-1 and hepatitis C virus (HCV). Sequence analysis of the NS4 region of Japanese encephalitis virus (JEV) suggests it may encode a structurally related but functionally distinct selenoprotein gene, more closely related to the iron-binding protein ferredoxin than to GPx, with three highly conserved UGA codons that align with essential Cys residues of ferredoxin. Comparison of the probe JEV sequence to an aligned family of ferredoxin sequences gave an overall 30.3% identity and 45.8% similarity, and was statistically significant at 4.9 S.D. (P < 10(-6)) above the average score computed for randomly shuffled sequences. A 3-dimensional model of the hypothetical JEV protein (JEV model) was constructed by homology modeling using SYBYL, based upon a high resolution X-ray structure of ferredoxin (PDB code: 1awd). The JEV model and the model from 1awd were subsequently subjected to molecular dynamics simulations in aqueous medium using AMBER 6. The solution structure of the JEV model indicates that it could fold into a tertiary structure globally similar to ferredoxin 1awd, with RMSD between the averaged structures of 1.8 A for the aligned regions. The modeling and MD simulations data also indicate that this structure for the JEV protein is energetically favorable, and that it could be quite stable at room temperature. This protein might play a role in JEV infection and replication via TNF and other cellular stimuli mediated via redox mechanisms.

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

Infection with Japanese encephalitis virus (JEV) causes cerebral inflammation and stimulates inflammatory cytokine expression. Glial cells orchestrate immunocyte recruitment to focal sites of viral infection within the central nervous system (CNS) and synchronize immune cell functions through a regulated network of cytokines and chemokines. Since immune cell infiltration is prominent, we investigated the production of a responding chemoattractant, RANTES (regulated upon activation, normal T-cell expressed and secreted), in response to JEV infection of glial cells. Infection with JEV was found to elicit the production of RANTES from primary neurons/glia, mixed glia, microglia, and astrocytes but not from neuron cultures. The production of RANTES did not seem to be directly responsible for JEV-induced neuronal death but instead contributed to the recruitment of immune cells. RANTES expression required viral replication and the activation of extracellular signal-regulated kinase (ERK) as well as transcription factors, including nuclear factor kappa B (NF-kappaB) and nuclear factor IL-6 (NF-IL-6). The induction of RANTES expression by JEV infection in glial cells needed the coordinate activation of NF-kappaB and NF-IL-6. Using enzymatic inhibitors, we demonstrated a strong correlation between the ERK signaling pathway and RANTES expression. However, JEV replication was not dependent on the activation of ERK, NF-kappaB, and NF-IL-6. Altogether, these results demonstrated that infection of glial cells by JEV provided the early ERK-, NF-kappaB-, and NF-IL-6-mediated signals that directly activated RANTES expression, which might be involved in the initiation and amplification of inflammatory responses in the CNS.

Manipulation of cell surface macromolecules by flaviviruses

Cell surface macromolecules play a crucial role in the biology and pathobiology of flaviviruses, both as receptors for virus entry and as signaling molecules for cell–cell interactions in the processes of vascular permeability and inflammation. This review examines the cell tropism and pathogenesis of flaviviruses from the standpoint of cell surface molecules, which have been implicated as receptors in both virus–cell as well as cell–cell interactions. The emerging picture is one that encompasses extensive regulation and interplay among the invading virus, viral immune complexes, Fc receptors, major histocompatibility complex antigens, and adhesion molecules.

Neuronal apoptosis pathways in Sindbis virus encephalitis

Sindbis virus infects neurons of the brain and spinal cord leading to neuronal apoptosis and encephalitis in mice. During postnatal development, neurons of mice remain susceptible to infection but become refractory to SV-induced programmed cell death. Failure to undergo programmed cell death results in a persistent infection. However, some neurovirulent strains of Sindbis virus overcome the age-dependent protective function in neurons, leading to enhanced apoptotic cell death in the central nervous system and higher mortality rates. Sindbis virus infections can also cause hind-limb paralysis due to the death of infected spinal cord motor neurons. However, spinal cord neuron death in older mice appears to occur by mechanisms that differ from classical apoptosis observed in newborn mice based on the morphology of dying neurons at these two sites. Sindbis virus infections of mosquitoes and some mosquito cell lines, on the other hand, do not induce cell death but persistent infections, a phenomenon also observed occasionally in cultured mammalian cells as well as in brains of infected mice surviving lethal infections. Thus, both viral and cellular factors contribute to the varied outcomes of infection. The molecular mechanisms that govern the susceptibility or resistance of particular cell types to SV-induced cell death are not well understood. Furthermore, the cellular execution machinery that produces the characteristic morphological distinctions between brain and spinal cord (i.e. apoptotic versus non-apoptotic) remain to be discovered.

Neurotrophic and neurotoxic effects of zinc on neonatal cortical neurons

Although zinc exerts direct neurotoxic action, this metal is also essential for the activity of numerous biological systems and zinc deficiency has been associated with various pathologies. We investigated the cellular responses and neuronal viability following exposure to different concentrations of zinc in primary cultures of neonatal rat cortical neurons. Higher concentrations of zinc (0.15 and 0.2 mM) triggered excessive zinc influx, glutathione depletion and ATP loss leading to necrotic neuronal death. In contrast, lower concentrations of zinc (0.05 and 0.1 mM) attenuated serum-deprivation induced apoptotic neuronal death. The antiapoptotic action of low amounts of zinc was found both in mixed cultures and neuron-enriched cultures indicating the independence of glial mediator. Neurotrophic action was not accompanied by significant alteration in those cellular responses but required chelatable zinc. The N-methyl-D-aspartate (NMDA) antagonist, MK-801, mimicked the beneficial effect of zinc in protecting neuronal death. Moreover, both MK-801 and zinc eliminated NMDA-induced neuronal injury. The results suggest that zinc is an intrinsic factor for neuron survival and exogenous zinc, in low amounts, is an active neuroprotectant against serum deprivation in part through the antagonism of NMDA receptor activation.

Zinc toxicity on neonatal cortical neurons: involvement of glutathione chelation

Several mechanisms have been implicated in pathological neuronal death including zinc neurotoxicity, calcium excitotoxicity and oxidative injury. Glutathione (GSH) serves to provide reducing equivalents for the maintenance of oxidant homeostasis, and also plays roles in intracellular and intercellular signaling in the brain. We investigated the role of GSH homeostasis in the neurotoxic action of zinc using both mixed cortical cultures containing neurons and glia, and cortical neurons prepared from 1-day-old rats. Zinc caused neuronal cell death in a concentration-dependent manner. In parallel, a high concentration of zinc depleted GSH, in a time-dependent manner, preceding the onset of neuronal damage. Depletion of GSH by diethylmaleate injured neurons and exacerbated zinc-induced death. In contrast, replenishment of GSH attenuated zinc neurotoxicity. The thiol-containing compounds N-acetylcysteine and GSH chemically chelated zinc leading to decreases in the influx of zinc, the fall in GSH level and neuronal death. Interestingly, the glycolytic substrate pyruvate, but not lactate, chelated zinc concentration dependently and prevented its toxicity. On the other hand, pyrrolidine dithiocarbamate, serving as a zinc chaperon, enhanced its entry and toxicity. The results suggest that zinc non-enzymatically depleted GSH, an intrinsic factor for neuron survival, leading to activation of the cellular death signal and eventually neuronal death.

Pathogenesis of flavivirus encephalitis

Within the flavivirus family, viruses that cause natural infections of the central nervous system (CNS) principally include members of the Japanese encephalitis virus (JEV) serogroup and the tick-borne encephalitis virus (TBEV) serocomplex. The pathogenesis of diseases involves complex interactions of viruses, which differ in neurovirulence potential, and a number of host factors, which govern susceptibility to infection and the capacity to mount effective antiviral immune responses both in the periphery and within the CNS. This chapter summarizes progress in the field of flavivirus neuropathogenesis. Mosquito-borne and tickborne viruses are considered together. Flavivirus neuropathogenesis involves both neuroinvasiveness (capacity to enter the CNS) and neurovirulence (replication within the CNS), both of which can be manipulated experimentally. Neuronal injury as a result of bystander effects may be a factor during flavivirus neuropathogenesis given that microglial activation and elaboration of inflammatory mediators, including IL-1β and TNF-α, occur in the CNS during these infections and may accompany the production of nitric oxide and peroxynitrite, which can cause neurotoxicity.

Expression of a full-length hepatitis C virus cDNA up-regulates the expression of CC chemokines MCP-1 and RANTES

We had previously reported the cloning of the complete genome of an isolate of hepatitis C virus (HCV), HCV-S1, of genotype 1b. We have constructed a full-length complementary DNA (cDNA) clone of HCV-S1 using nine overlapping cDNA clones that encompassed its entire genome. HCV core, E1, E2, NS-3, -4B, -5A, and -5B proteins were detected in 293T cells by immunoblot analyses when expression of the full-length HCV-S1 was driven under a CMV promoter. Expression of full-length HCV-S1 led to induction of the CC chemokines RANTES and MCP-1 at both the mRNA and the protein levels in HeLa, Huh7, and HepG2 cells. Reporter gene assays showed that a minimal MCP-1 promoter construct containing 128 nucleotides upstream of its translational start site was sufficient for optimal HCV-mediated activation. HCV induced AP-1 binding activities to this region, as determined from electrophoretic mobility shift assays and supershifts with anti-AP-1 antibodies. Transfection of full-length HCV-S1 up-regulated both AP-1 binding activities as well as c-jun transcripts. A minimal promoter construct containing 181 nucleotides upstream of the RANTES translational start site was sufficient for maximal HCV-mediated induction. Gel mobility shift and supershift assays showed that HCV induced NF-kappaB and other unknown binding activities to the A/B-site within this region. In HeLa cells, HCV core and NS5A could separately augment promoter activities of both MCP-1 and RANTES. In Huh7 cells, only NS5A produced a similar effect, while rather surprisingly, HCV core induced a dramatic reduction in promoter activities of these two genes. This study provides the first direct evidence for the induction of CC chemokines in HCV infection and draws attention to their roles in affecting the progress and outcome of HCV-associated liver diseases.

Estrogen attenuates tumor necrosis factor-alpha expression to provide ischemic neuroprotection in female rats

Proinflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) plays an important role in the pathogenesis of neurodegenerative diseases including ischemia. Circulating estrogen is positively associated with neuroprotection against ischemia in female rats. In the present study, we examined whether endogenous estrogen levels affect ischemia-induced TNF-alpha expression in normal cycling female rats. An elevated concentration of TNF-alpha was toxic to neurons. A high level of expression of TNF-alpha accompanied the decline in circulating estrogen levels in normal cycling female rats. Estrogen administration attenuated endotoxin-induced TNF-alpha expression and neuronal injury, indicating that the down-regulation of TNF-alpha expression plays a role in ischemic neuroprotection by estrogen. Therefore, we propose that one mechanism by which estrogen protects females from ischemic damage is through the regulation of TNF-alpha production.

Japanese encephalitis virus stimulates superoxide dismutase activity in rat glial cultures

Japanese encephalitis virus (JEV) infection is commonly associated with inflammatory reaction and neurological disease that occurs in the infected animals. Reactive oxygen species have been implicated as a critical mediator for inflammation and diseases. The present study investigated the change of redox potential in glial cells following JEV infection. JEV infection induced the generation of superoxide anion and nitric oxide in rat cortical glial cells. Manganese superoxide dismutase, but not copper/zinc superoxide dismutase was activated by JEV infection, and this activation was blocked by pyrrolidine dithiocarbamate. In addition, the increased superoxide dismutase activity was also apparent in JEV acutely, or persistently infected continuous cell lines. These results suggest that cellular factors regulating oxidative pathway might play roles in responding to JEV infection.

Role of reactive oxygen intermediates in Japanese encephalitis virus infection in murine neuroblastoma cells

Infection with Japanese encephalitis virus (JEV), a mosquito-borne, neurotropic flavivirus, may cause acute encephalitis in humans and induce severe cytopathic effects in various types of cultured cells. This study attempted to determine whether JEV infection induces free radical generation and whether oxidative stress contributes to virus-induced cell death in neuroblastoma cells. A rise in the intracellular level of free radicals indicated by the 2',7'-dichlorofluorescein fluorescence was observed in N18 cells following JEV infection. Cellular flavon-containing enzymes were involved in JEV-induced fluorescent change. Cells were moderately protected from JEV-induced death by diphenyleneiodonium, a flavon-containing enzyme inhibitor, whereas common antioxidants such as N-acetylcysteine, pyrrolidine dithiocarbamate, Tiron, and Trolox turned out to be ineffective. These results suggest that the direct antioxidant action is not helpful in prevention of JEV-induced neuronal cell death.

Tyrosine kinase signaling involved in glutamate-induced astrocyte proliferation

Proliferation of astrocytes is a common response of the CNS to injury and disease. The mechanisms controlling the proliferation of astrocytes are of great interest. In this paper, the signaling pathways underlying glutamate-induced astrocyte proliferation are investigated. Glutamate stimulates the proliferation of non-synchronized, subconfluent cultures of rat cortical astrocytes. Glutamate-induced cell proliferation is not prevented by inhibitors of G protein, protein kinase A, protein kinase C, phosphatidylinositol 3 kinase, extracellular signal-regulated kinase, or phospholipase A2. However, the tyrosine kinase inhibitors Genistein and Herbimycin A inhibit the glutamate-induced proliferation. Moreover, this proliferation is mediated by the activation of glutamate metabotropic receptors. These results suggest that glutamate induces astrocyte proliferation through a tyrosine kinase pathway.

Identification of genes involved in the host response to neurovirulent alphavirus infection

Single-amino-acid mutations in Sindbis virus proteins can convert clinically silent encephalitis into uniformly lethal disease. However, little is known about the host gene response during avirulent and virulent central nervous system (CNS) infections. To identify candidate host genes that modulate alphavirus neurovirulence, we utilized GeneChip Expression analysis to compare CNS gene expression in mice infected with two strains of Sindbis virus that differ by one amino acid in the E2 envelope glycoprotein. Infection with Sindbis virus, dsTE12H (E2-55 HIS), resulted in 100% mortality in 10-day-old mice, whereas no disease was observed in mice infected with dsTE12Q (E2-55 GLN). dsTE12H, compared with dsTE12Q, replicated to higher titers in mouse brain and induced more CNS apoptosis. Infection with the neurovirulent dsTE12H strain was associated with both a greater number of host genes with increased expression and greater changes in levels of host gene expression than was infection with the nonvirulent dsTE12Q strain. In particular, dsTE12H infection resulted in greater increases in the levels of mRNAs encoding chemokines, proteins involved in antigen presentation and protein degradation, complement proteins, interferon-regulated proteins, and mitochondrial proteins. At least some of these increases may be beneficial for the host, as evidenced by the demonstration that enforced expression of the antiapoptotic mitochondrial protein peripheral benzodiazepine receptor (PBR) protects neonatal mice against lethal Sindbis virus infection. Thus, our findings identify specific host genes that may play a role in the host protective or pathologic response to neurovirulent Sindbis virus infection.