Japanese Encephalitis Virus Infected Human Monocyte-Derived Dendritic Cells Activate a Transcriptional Network Leading to an Antiviral Inflammatory Response

HSV-1 alters lipid metabolism and induces lipid droplet accumulation in functionally impaired mouse dendritic cells

Herpes simplex virus type 1 (HSV-1) significantly impairs dendritic cell (DC) function, ultimately eliciting the death of these cells. Here, we sought to assess whether HSV-1 modulates lipid metabolism in mouse DCs as a mechanism of immune evasion. For this, we performed RT-qPCR gene arrays with ingenuity pathway analysis (IPA), RNA sequencing (RNA-seq) and gene set enrichment analysis (GSEA), confocal microscopy, transmission electron microscopy, ultra-high-performance liquid chromatography-quadrupole time-of-flight (UHPLC-QTOF) analysis, pharmacological inhibition of eight lipid-metabolism-related enzymes in HSV-1-infected DCs, co-cultures between virus-specific transgenic CD4+ and CD8+ T cells and HSV-1-infected DCs, and in vivo assays with mice. We found that HSV-1 significantly alters lipid metabolism in DCs and induces lipid droplet (LD) accumulation in these cells. Pharmacological inhibition of two particular lipid metabolism enzymes was found to partially restore DC function. Overall, these results suggest that lipid metabolism plays an important role in the impairment of DC function by HSV-1.

Key virulence factors responsible for differences in pathogenicity between clinically proven live-attenuated Japanese encephalitis vaccine SA14-14-2 and its pre-attenuated highly virulent parent SA14

Japanese encephalitis virus (JEV), a neuroinvasive and neurovirulent orthoflavivirus, can be prevented in humans with the SA14-14-2 vaccine, a live-attenuated version derived from the wild-type SA14 strain. To determine the viral factors responsible for the differences in pathogenicity between SA14 and SA14-14-2, we initially established a reverse genetics system that includes a pair of full-length infectious cDNAs for both strains. Using this cDNA pair, we then systematically exchanged genomic regions between SA14 and SA14-14-2 to generate 20 chimeric viruses and evaluated their replication capability in cell culture and their pathogenic potential in mice. Our findings revealed the following: (i) The single envelope (E) protein of SA14-14-2, which contains nine mutations (eight in the ectodomain and one in the stem region), is both necessary and sufficient to render SA14 non-neuroinvasive and non-neurovirulent. (ii) Conversely, the E protein of SA14 alone is necessary for SA14-14-2 to become highly neurovirulent, but it is not sufficient to make it highly neuroinvasive. (iii) The limited neuroinvasiveness of an SA14-14-2 derivative that contains the E gene of SA14 significantly increases (approaching that of the wild-type strain) when two viral nonstructural proteins are replaced by their counterparts from SA14: (a) NS1/1', which has four mutations on the external surface of the core β-ladder domain; and (b) NS2A, which has two mutations in the N-terminal region, including two non-transmembrane α-helices. In line with their roles in viral pathogenicity, the E, NS1/1', and NS2A genes all contribute to the enhanced spread of the virus in cell culture. Collectively, our data reveal for the first time that the E protein of JEV has a dual function: It is the master regulator of viral neurovirulence and also the primary initiator of viral neuroinvasion. After the initial E-mediated neuroinvasion, the NS1/1' and NS2A proteins act as secondary promoters, further amplifying viral neuroinvasiveness.

Proteome modulation triggers potent antiviral response in Japanese Encephalitis Virus infected human macrophages

Japanese encephalitis virus (JEV) is a mosquito-borne neurotropic virus that claims thousands of children's lives globally every year, causing neuropsychiatric sequelae. While neuronal cell pathogenesis is a terminal consequence of JEV infection, the virus hijacks macrophages during initial replication and propagation, making macrophages critical cells of host immune defense that dictate the outcomes of infection. Though a plethora of studies have been reported using various neuronal and immune cells, a global response of human macrophages to JEV infection is yet to be explored. In this study, we assessed the kinetics of global proteome dysregulation employing an in vitro JEV infection model using human monocyte-derived macrophages (THP-1). A comparative assessment of the proteome of the infected THP-1 cells revealed differential regulation of 428 proteins at 24 h post-infection (hpi), which was later increased to 443 by 48 h post-infection. Global gene ontology analysis of the differentially expressed proteins highlighted several critical pathways related to immune and metabolic processes that are known to play either proviral or antiviral effects during infection. Notably, several antiviral proteins, including STAT2, OAS1, MX1, MX2, RIG-I, ISG15, and ISG20, were significantly upregulated at both time points post-infection. In contrast, a considerable downregulation of BCL-2, an anti-apoptotic protein at 48hpi indicates the activation of cell death pathways. Further, gene set enrichment analysis identified the type I interferon signaling pathway as one of the top upregulated pathways following JEV infection in human macrophages. Altogether, this study demonstrates human macrophage responses to JEV infection at the proteome level for the first time, highlighting several critical and novel antiviral proteins and pathways that not only advance our understanding of anti-JEV immunity but also aid in developing strategies to control this acute global public health menace.

Allosteric Activator-Regulated CRISPR/Cas12a System Enables Biosensing and Imaging of Intracellular Endogenous and Exogenous Targets

Sensors designed based on the trans-cleavage activity of CRISPR/Cas12a systems have opened up a new era in the field of biosensing. The current design of CRISPR/Cas12-based sensors in the "on-off-on" mode mainly focuses on programming the activator strand (AS) to indirectly switch the trans-cleavage activity of Cas12a in response to target information. However, this design usually requires the help of additional auxiliary probes to keep the activator strand in an initially "blocked" state. The length design and dosage of the auxiliary probe need to be strictly optimized to ensure the lowest background and the best signal-to-noise ratio. This will inevitably increase the experiment complexity. To solve this problem, we propose using AS after the "RESET" effect to directly regulate the Cas12a enzymatic activity. Initially, the activator strand was rationally designed to be embedded in a hairpin structure to deprive its ability to activate the CRISPR/Cas12a system. When the target is present, target-mediated strand displacement causes the conformation change in the AS, the hairpin structure is opened, and the CRISPR/Cas12a system is reactivated; the switchable structure of AS can be used to regulate the degree of activation of Cas12a according to the target concentration. Due to the advantages of low background and stability, the CRISPR/Cas12a-based strategy can not only image endogenous biomarkers (miR-21) in living cells but also enable long-term and accurate imaging analysis of the process of exogenous virus invasion of cells. Release and replication of virus genome in host cells are indispensable hallmark events of cell infection by virus; sensitive monitoring of them is of great significance to revealing virus infection mechanism and defending against viral diseases.

Methotrimeprazine is a neuroprotective antiviral in JEV infection via adaptive ER stress and autophagy

Japanese encephalitis virus (JEV) pathogenesis is driven by a combination of neuronal death and neuroinflammation. We tested 42 FDA-approved drugs that were shown to induce autophagy for antiviral effects. Four drugs were tested in the JE mouse model based on in vitro protective effects on neuronal cell death, inhibition of viral replication, and anti-inflammatory effects. The antipsychotic phenothiazines Methotrimeprazine (MTP) & Trifluoperazine showed a significant survival benefit with reduced virus titers in the brain, prevention of BBB breach, and inhibition of neuroinflammation. Both drugs were potent mTOR-independent autophagy flux inducers. MTP inhibited SERCA channel functioning, and induced an adaptive ER stress response in diverse cell types. Pharmacological rescue of ER stress blocked autophagy and antiviral effect. MTP did not alter translation of viral RNA, but exerted autophagy-dependent antiviral effect by inhibiting JEV replication complexes. Drug-induced autophagy resulted in reduced NLRP3 protein levels, and attenuation of inflammatory cytokine/chemokine release from infected microglial cells. Our study suggests that MTP exerts a combined antiviral and anti-inflammatory effect in JEV infection, and has therapeutic potential for JE treatment.

Secreted NS1 proteins of tick-borne encephalitis virus and West Nile virus block dendritic cell activation and effector functions

The flavivirus non-structural protein 1 (NS1) is secreted from infected cells into the circulation and the serum levels correlate with disease severity. The effect of secreted NS1 (sNS1) on non-infected mammalian immune cells is largely unknown. Here, we expressed recombinant sNS1 proteins of tick-borne encephalitis virus (TBEV) and West Nile virus (WNV) and investigated their effects on dendritic cell (DC) effector functions. Murine bone marrow-derived DCs (BMDCs) showed reduced surface expression of co-stimulatory molecules and decreased release of pro-inflammatory cytokines when treated with sNS1 of TBEV or WNV prior to poly(I:C) stimulation. Transcriptional profiles of BMDCs that were sNS1-exposed prior to poly(I:C) stimulation showed two gene clusters that were downregulated by TBEV or WNV sNS1 and that were associated with innate and adaptive immune responses. Functionally, both sNS1 proteins modulated the capacity for BMDCs to induce specific T-cell responses as indicated by reduced IFN-γ levels in both CD4+ and CD8+ T cells after BMDC co-cultivation. In human monocyte-derived DCs, poly(I:C)-induced upregulation of co-stimulatory molecules and cytokine responses were even more strongly impaired by TBEV sNS1 or WNV sNS1 pretreatment than in the murine system. Our findings indicate that exogenous flaviviral sNS1 proteins interfere with DC-mediated stimulation of T cells, which is crucial for the initiation of cell-mediated adaptive immune responses in human flavivirus infections. Collectively, our data determine soluble flaviviral NS1 as a virulence factor responsible for a dampened immune response to flavivirus infections. IMPORTANCE The effective initiation of protective host immune responses controls the outcome of infection, and dysfunctional T-cell responses have previously been associated with symptomatic human flavivirus infections. We demonstrate that secreted flavivirus NS1 proteins modulate innate immune responses of uninfected bystander cells. In particular, sNS1 markedly reduced the capacity of dendritic cells to stimulate T-cell responses upon activation. Hence, by modulating cellular host responses that are required for effective antigen presentation and initiation of adaptive immunity, sNS1 proteins may contribute to severe outcomes of flavivirus disease.

High-throughput sequencing-based Detection of Japanese encephalitis virus and its effect on micro ribonucleic acid

it was to explore the mechanism of Japanese encephalitis virus (JEV) and micro ribonucleic acid (miRNA) under high-throughput sequencing. 20 experimental mice, with good growth status and no disease infection, were selected. The cells used in the experiment included mouse microglial cell line (BV2), mouse neuroblastoma cell line (NA), and mouse brain endothelial cell line (bEnd.3). JEV titration was performed with JEV-infected cells, ribonucleic acid (RNA) in the cells was extracted, and finally the miRNA high-throughput sequencing data was analyzed. Agarose gel electrophoresis showed that the 28S and 18S electrophoresis bands were bright. Among the miRNAs detected in mouse brain tissues, 2986 were down-regulated and 1251 were up-regulated. Among miRNAs detected in NA cells, 4238 the decreasing expression and 2356 were expressed increasingly. In reducing miRNA expression, 1 multiplicity of infection (MOI) of P3 strain infection was more significant than 0.1 MOI. 10 miRNAs with significantly decreasing expression were miR-466d-3p, miR-381-3p, miR-540-3p, miR-466a-3p, miR-467a-3p, miR-574-5p, miR-199a-5p, miR-467a-5p, miR-674-5p, and miR-376b-3p. These were all obviously down-regulated in JEV-infected BV2, NA, and bEnd.3 neurons. High-throughput sequencing of JEV-infected mouse brain tissues and mouse neuronal cells found that JEV infection led to down-regulation of overall miRNA expression in host cells.

Mosquito CYP4C21 knockout reduces dengue virus and Zika virus replication in Aedes aegypti cells

Aedes aegypti (Ae. aegypti) is a major vector of dengue virus (DENV) and Zika virus (ZIKV). Understanding the complex interaction mechanisms between mosquito vectors and arboviruses is essential to interrupt virus transmission. This study constructed CYP4C21 knockout (KO) Aag2 cells (Ae. aegypti cells) and confirmed that CYP4C21 KO reduced DENV2 and ZIKV copies in Aag2 cells, which suggests that CYP4C21 may play an important role in mosquito infection with arboviruses. Furthermore, it is the first report of the CYP4 family related to viral infection, which lays the foundation for exploring the role of the CYP4C21 in the interaction of Ae. aegypti and arbovirus and provides novel insights into the function of cytochrome family proteins.

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.

Japanese Encephalitis Virus: An Update on the Potential Antivirals and Vaccines

Japanese encephalitis virus (JEV) is the causal agent behind Japanese encephalitis (JE), a potentially severe brain infection that spreads through mosquito bites. JE is predominant over the Asia-Pacific Region and has the potential to spread globally with a higher rate of morbidity and mortality. Efforts have been made to identify and select various target molecules essential in JEV’s progression, but until now, no licensed anti-JEV drug has been available. From a prophylactic point of view, a few licensed JE vaccines are available, but various factors, viz., the high cost and different side effects imposed by them, has narrowed their global use. With an average occurrence of >67,000 cases of JE annually, there is an urgent need to find a suitable antiviral drug to treat patients at the acute phase, as presently only supportive care is available to mitigate infection. This systematic review highlights the current status of efforts put in to develop antivirals against JE and the available vaccines, along with their effectiveness. It also summarizes epidemiology, structure, pathogenesis, and potential drug targets that can be explored to develop a new range of anti-JEV drugs to combat JEV infection globally.

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.

Lipid balance remodelling by human positive-strand RNA viruses and the contribution of lysosomes

A marked reorganization of internal membranes occurs in the cytoplasm of cells infected by single stranded positive-sense RNA viruses. Most cell compartments change their asset to provide lipids for membrane rearrangement into replication organelles, where to concentrate viral proteins and enzymes while hiding from pathogen pattern recognition molecules. Because the endoplasmic reticulum is a central hub for lipid metabolism, when viruses hijack the organelle to form their replication organelles, a cascade of events change the intracellular environment. This results in a marked increase in lipid consumption, both by lipolysis and lipophagy of lipid droplets. In addition, lipids are used to produce energy for viral replication. At the same time, inflammation is started by signalling lipids, where lysosomal processing plays a relevant role. This review is aimed at providing an overview on what takes place after human class IV viruses have released their genome into the host cell and the consequences on lipid metabolism, including lysosomes.

QKI deficiency in macrophages protects mice against JEV infection by regulating cell migration and antiviral response

Japanese encephalitis (JE) is a major reason to cause viral encephalitis, with 50% patients suffering from severe neuro-inflammation and permanent neural injury. Effective anti-viral treatment is urgently needed. Here, we found RNA binding protein quaking (QKI) was involved in the progression of JE by regulating migration and anti-viral response of macrophages. After JE virus (JEV) infection, QKI-deficient mice had lower viral loads in the brain and fewer neurological symptoms. In comparison with control mice, proinflammatory cytokines in the brain of QKI-deficient animals revealed distinct patterns, with lower levels of IL-6 (interleukin-6) and IFN-β (interferon-β) at the early stage but higher levels at the end of JE. Then we found infiltration of CCR2 positive ((C-C motif) receptor 2) peripheral macrophages and CCR2 expression on macrophages were inhibited in QKI-deficient mice, while the expression of CCR2 ligands was not changed. Bioinformatical analysis showed that a QRE (quaking response element) located on 3'UTR (untranslated region) of Ccr2. We further verified that QKI was able to interact with Ccr2 mRNA and regulate its degradation in vitro. Additionally, since the IFN-β production was increased in QKI-ablation mice after JEV infection, the anti-viral response was analyzed. Results in QKI-silenced N9 cells showed that the expression of RIG-I (retinoic acid-inducible gene-I) and TBK1 (TANK binding kinase 1) was increased, thus further inducing IRF3 (interferon regulatory factor 3) phosphorylation and interferon activation. Overall, these results revealed QKI mediated the anti-viral process via interfering migration of macrophages to CNS (central nervous system) and enhancing RIG-I/IRF3/IFN-β pathway to restrict virus dissemination.

Human Guanylate-Binding Protein 1 Positively Regulates Japanese Encephalitis Virus Replication in an Interferon Gamma Primed Environment

RNA virus infection triggers interferon (IFN) receptor signaling, leading to the activation of hundreds of interferon-stimulated genes (ISGs). Guanylate-binding proteins (GBPs) belong to one such IFN inducible subfamily of guanosine triphosphatases (GTPases) that have been reported to exert broad anti-microbial activity and regulate host defenses against several intracellular pathogens. Here, we investigated the role of human GBP1 (hGBP1) in Japanese encephalitis virus (JEV) infection of HeLa cells in both an IFNγ unprimed and primed environment. We observed enhanced expression of GBP1 both at transcript and protein levels upon JEV infection, and GBP1 association with the virus replication membranes. Depletion of hGBP1 through siRNA had no effect on JEV replication or virus induced cell death in the IFNγ unprimed environment. IFNγ stimulation provided robust protection against JEV infection. Knockdown of GBP1 in the primed environment upregulated expression and phosphorylation of signal transducer and activator of transcription 1 (STAT1) and significantly reduced JEV replication. Depletion of GBP1 in an IFNγ primed environment also inhibited virus replication in human neuroblastoma SH-SH5Y cells. Our data suggests that in the presence of IFNγ, GBP1 displays a proviral role by inhibiting innate immune responses to JEV infection.

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.