Japanese encephalitis virus invasion of cell: allies and alleys

RAB4B and Japanese encephalitis virus E protein interaction is essential for viral entry in early endosomes

RAB4B (Ras-Related GTP-Binding Protein 4b) is essential for intracellular trafficking and endosomal recycling processes. Our previous study, we demonstrated that RAB4B promotes Japanese encephalitis virus (JEV) replication in PK15 cells. However, the exact mechanisms underlying the role of RAB4B in JEV internalization remain unclear. Here, a genome-wide CRISPR/Cas9 library screen was performed, which identified RAB4B, along with other significant hits like ST8SIA4 and ELAVL1, as essential mediators of JEV replication. In vitro validation using RAB4B knockout in U251 and BV2 cells showed a significant reduction in JEV genome copies and viral titers, which were restored upon reintroducing RAB4B, confirming its pivotal role in viral propagation. Further mechanistic investigation revealed that RAB4B is required for JEV internalization into early endosomes. Co-immunoprecipitation and in vitro binding assays demonstrated a direct interaction between RAB4B and the JEV E protein, highlighting the functional importance of this interaction. In vivo experiments with RAB4B knockout mice showed a reduction in viral load in the brain and improved survival rates compared to wild-type mice. Taken together, these findings provide compelling evidence that RAB4B is indispensable for JEV entry and replication.

Rosmarinic acid-mediated downregulation of RIG-I and p62 in microglia confers resistance to Japanese encephalitis virus-induced inflammation

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic pathogen that causes encephalitis in humans and reproductive failure in pigs. The transmission of JEV between humans and animals poses a significant public health threat and results in substantial economic losses. Excessive inflammation in the central nervous system of JEV-infected patients is a major cause of mortality and disability. Rosmarinic acid (RA), a polyhydroxyphenolic compound isolated from medicinal herbs, has been preliminarily shown to possess anti-inflammatory properties and significantly inhibit JEV-induced neuroinflammation in mice.

RESULTS

This study investigated the antiviral capacity and potential mechanisms of RA in JEV-infected cells. The results demonstrated that RA could inhibit JEV replication in vitro. Furthermore, the expression levels of inflammatory cytokines (including IL-6, IL-1β, CCL-2, and TNF-α), membrane receptors (including RIG-I, TLR3, TLR4, TLR7, and TLR8), NF-κB complex and p62/SQSTM1 were assessed using qPCR, ELISA, and Western blot, respectively. The findings indicated that RA significantly suppressed the expression of IL-6, IL-1α, TNF-α, and CCL-2 in JEV-infected BV-2 cells in a dose-dependent manner. Additionally, RA treatment downregulated the expression levels of RIG-I and p62, while p62 silencing inhibited the upregulation of inflammatory cytokines in JEV-infected BV-2 cells.

CONCLUSION

Our present study highlights the important role of RA-mediated reduction of RIG-I and p62 in microglia, conferring resistance to Japanese encephalitis virus-induced inflammation.

Insights into mosquito-borne arbovirus receptors

The increasing global prevalence of mosquito-borne viruses has emerged as a significant threat to human health and life. Identifying receptors for these viruses is crucial for improving our knowledge of viral pathogenesis and developing effective antiviral strategies. The widespread application of CRISPR-Cas9 screening have led to the discovery of many mosquito-borne virus receptors. The revealed structures of virus-receptor complexes also provide important information for understanding their interaction mechanisms. This review provides a comprehensive summary of both conventional and novel approaches for identifying new viral receptors and the putative entry factors of the most prevalent mosquito-borne viruses within the Flaviviridae, Togaviridae, and Bunyavirales. At the same time, we emphasize the common receptors utilized by these viruses for entry into both vertebrate hosts and mosquito vectors. We discuss promising avenues for developing anti-mosquito-borne viral strategies that target these receptors. Notably, targeting universal receptors of specific mosquito-borne viruses in both vertebrates and mosquitoes offers dual benefits for disease prevention. Additionally, the widespread use of AI-based machine learning and protein structure prediction will accelerate the identification of new viral receptors and provide new avenues for antiviral drug discovery.

Analyzing the factors affecting virus invasion by quantitative single-particle analysis

Viral diseases are among the main threats to public health. Understanding the factors affecting viral invasion is important for antiviral research. Until now, it was known that most viruses have very low plaque-forming unit (PFU)-to-particle ratios. However, further investigation is required to determine the underlying factors. Here, using quantitative single-particle analysis methods, the invasion of Semliki Forest virus (SFV), Japanese encephalitis virus (JEV), and influenza A virus (IAV) containing attachment to the cell surface, entry into the cell, transport towards the cell interior, and fusion with endosomes to release nucleocapsids were quantitatively analysed in parallel. It was found that for SFV with an PFU-to-particle ratio of approximately 1:2, an entry efficiency of approximately 31% limited infection. For JEV, whose PFU-to-particle ratio was approximately 1:310, an attachment efficiency of approximately 27% and an entry efficiency of 10% were the main factors limiting its infection. Meanwhile, for IAV with PFU-to-particle ratios of 1:8100, 5% attachment efficiency, 9% entry efficiency, and 53% fusion efficiency significantly limited its infection. These results suggest that viruses with different infectivities have different limited steps in the invasion process. Moreover, there are significant differences in attachment efficiencies among viruses, emphasizing the pivotal role of attachment in viral invasion. The influence of the virus purification method on virus invasion was also investigated. This study, for the first time, reports the efficiencies of different stages of virus invasion, leading to a better understanding of virus invasion and providing a protocol to quantitatively analyse the virus invasion efficiency.

Host Factor Rab4b Promotes Japanese Encephalitis Virus Replication

Although the Japanese encephalitis virus (JEV) infects various cell types, its receptor molecules are still not clearly understood. In our laboratory's prior research, Rab4b was identified as a potential host factor that facilitates JEV infection in PK15 cells, utilizing a genome-wide CRISPR/Cas9 knockout library (PK-15-GeCKO). To further explore the effect of Rab4b on JEV replication, we used the Rab4b knockout PK15 cell line using the CRISPR/Cas9 technology and overexpressing the Rab4b PK15 cell line, with IFA, RT-qPCR, and Western blot to study the effect of Rab4b on viral replication in the whole life cycle of the JEV. The results show that the knockout of Rab4b inhibited the replication of the JEV in PK15 cells, and the overexpression of Rab4b promoted the replication of the JEV in PK15 cell lines. Furthermore, we demonstrated for the first time that host factor Rab4b facilitates the adsorption, internalization, assembly, and release of the JEV, thereby promoting JEV replication. This study enriches the regulatory network between the JEV and host factors and lays the experimental foundation for further understanding of the function of the Rab4b protein.

Regulation of Protein Conformation Enables Cell-Selective Targeting of Virus-Mimicking Nanoparticles for siRNA Therapy of Glioblastoma

Orthotopic glioblastoma (GBM) has an aggressive growth pattern and complex pathogenesis, becoming one of the most common and deadly tumors of the central nervous system (CNS). The emergence of RNA therapies offers promise for the treatment of GBM. However, the efficient and precise delivery of RNA drugs to specific tumor cells in the brain with high cellular heterogeneity remains ongoing. Here, a strategy is proposed to regulate protein conformation through lipid nanoenvironments to custom-design virus-mimicking nanoparticles (VMNs) with excellent selective cell targeting capabilities, leading to efficient and precise delivery of small interfering RNA for effective treatment of GBM. The optimized VMNs not only retain the ability to cross the blood-brain barrier and release the RNA by lysosomal escape like natural viruses but also ensure precise enrichment in the GBM area. This study lays the conceptual foundation for the custom design of VMNs with superior cell-selective targeting capabilities and opens up the possibility of RNA therapies for the efficient treatment of GBM and CNS tumors.

The mutation of Japanese encephalitis virus envelope protein residue 389 attenuates viral neuroinvasiveness

The envelope (E) protein of the Japanese encephalitis virus (JEV) is a key protein for virus infection and adsorption of host cells, which determines the virulence of the virus and regulates the intensity of inflammatory response. The mutation of multiple aa residues in the E protein plays a critical role in the attenuated strain of JEV. This study demonstrated that the Asp to Gly, Ser, and His mutation of the E389 site, respectively, the replication ability of the viruses in cells was significantly reduced, and the viral neuroinvasiveness was attenuated to different degrees. Among them, the mutation at E389 site enhanced the E protein flexibility contributed to the attenuation of neuroinvasiveness. In contrast, less flexibility of E protein enhanced the neuroinvasiveness of the strain. Our results indicate that the mechanism of attenuation of E389 aa mutation attenuates neuroinvasiveness is related to increased flexibility of the E protein. In addition, the increased flexibility of E protein enhanced the viral sensitivity to heparin inhibition in vitro, which may lead to a decrease in the viral load entering brain. These results suggest that E389 residue is a potential site affecting JEV virulence, and the flexibility of the E protein of aa at this site plays an important role in the determination of neuroinvasiveness.

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.

One-Step Dual-Color Labeling of Viral Envelope and Intraviral Genome with Quantum Dots Harnessing Virus Infection

Labeling the genome and envelope of a virus with multicolor quantum dots (QDs) simultaneously enables real-time monitoring of viral uncoating and genome release, contributing to our understanding of virus infection mechanisms. However, current labeling techniques require genetic modification, which alters the virus's composition and infectivity. To address this, we utilized the CRISPR/Cas13 system and a bioorthogonal metabolic method to label the Japanese encephalitis virus (JEV) genome and envelopes with different-colored QDs in situ. This technique allows one-step two-color labeling of the viral envelope and intraviral genome with QDs harnessing virus infection. In combination with single-virus tracking, we visualized JEV uncoating and genome release in real time near the endoplasmic reticulum of live cells. This labeling strategy allows for real-time visualization of uncoating and genome release at the single-virus level, and it is expected to advance the study of other viral infection mechanisms.

CRISPR/Cas9-Mediated Knockout of the HuR Gene in U251 Cell Inhibits Japanese Encephalitis Virus Replication

Human antigen R (HuR) is an RNA-binding protein that regulates the post-transcriptional reaction of its target mRNAs. HuR is a critical factor in cancer development and has been identified as a potential target in many cancer models. It participates in the viral life cycle by binding to viral RNAs. In prior work, we used CRISPR/Cas9 screening to identify HuR as a prospective host factor facilitating Japanese encephalitis virus (JEV) infection. The HuR gene was successfully knocked out in U251 cell lines using the CRISPR/Cas9 gene-editing system, with no significant difference in cell growth between U251-WT and U251-HuR-KO2 cells. Here, we experimentally demonstrate for the first time that the knockout of the HuR gene inhibits the replication ability of JEV in U251 cell lines. These results play an essential role in regulating the replication level of JEV and providing new insights into virus-host interactions and potential antiviral strategies. It also offers a platform for investigating the function of HuR in the life cycle of flaviviruses.

Antiviral activity of prion protein against Japanese encephalitis virus infection in vitro and in vivo

Flaviviruses are a major cause of viral diseases worldwide, for which effective treatments have yet to be discovered. The prion protein (PrPc) is abundantly expressed in brain cells and has been shown to play a variety of roles, including neuroprotection, cell homeostasis, and regulation of cellular signaling. However, it is still unclear whether PrPc can protect against flaviviruses. In this study, we investigated the role of PrPc in regulating autophagy flux and its potential antiviral activity during Japanese encephalitis virus (JEV) infection. Our in vivo experiment showed that JEV was more lethal to the PrPc knocked out mice which was further supported by histological analysis, western blot and rtPCR results from infected mice brain samples. Role of PrPc against viral propagation in vitro was verified through cell survival study, protein expression and RNA replication analysis, and adenoviral vector assay by overexpressing PrPc. Further analysis indicated that after virus entry, PrPc inhibited autophagic flux that prevented JEV replication inside the host cell. Our results from in vivo and in vitro investigations demonstrate that prion protein effectively inhibited JEV propagation by regulating autophagy flux which is used by JEV to release its genetic material and replication after entering the host cell, suggesting that prion protein may be a promising therapeutic target for flavivirus infection.

Shift in dominant genotypes of Japanese encephalitis virus and its impact on current vaccination strategies

Japanese encephalitis (JE) is a zoonotic ailment from the Japanese encephalitis virus (JEV). JEV belongs to the flavivirus genus and is categorized into a solitary serotype consisting of five genetically diverse genotypes (I, II, III, IV, and V). The JEV genotype III (GIII) was the prevailing strain responsible for multiple outbreaks in countries endemic to JEV until 1990. In recent years, significant improvements have occurred in the epidemiology of JE, encompassing the geographical expansion of the epidemic zone and the displacement of prevailing genotypes. The dominant genotype of the JEV has undergone a progressive shift from GIII to GI due to variations in its adaptability within avian populations. From 2021 to 2022, Australia encountered an epidemic of viral encephalitis resulting from infection with the GIV JEV pathogen. The current human viral encephalitis caused by GIV JEV is the initial outbreak since its initial discovery in Indonesia during the late 1970s. Furthermore, following a time frame of 50 years, the detection and isolation of GV JEV have been reported in Culex mosquitoes across China and South Korea. Evidence suggests that the prevalence of GIV and GV JEV epidemic regions may be on the rise, posing a significant threat to public safety and the sustainable growth of animal husbandry. The global approach to preventing and managing JE predominantly revolves around utilizing the GIII strain vaccine for vaccination purposes. Nevertheless, research has demonstrated that the antibodies generated by the GIII strain vaccine exhibit limited capacity to neutralize the GI and GV strains. Consequently, these antibodies cannot protect against JEV challenge caused by animal GI and GV strains. The limited cross-protective and neutralizing effects observed between various genotypes may be attributed to the low homology of the E protein with other genotypes. In addition, due to the GIV JEV outbreak in Australia, further experiments are needed to evaluate the protective efficiency of the current GIII based JE vaccine against GIV JEV. The alteration of the prevailing genotype of JEV and the subsequent enlargement of the geographical extent of the epidemic have presented novel obstacles in JE prevention and control. This paper examines the emerging features of the JE epidemic in recent years and the associated problems concerning prevention and control.

PARP1 inhibition protects mice against Japanese encephalitis virus infection

Japanese encephalitis (JE) is a vector-borne viral disease that causes acute encephalitis in children. Although vaccines have been developed against the JE virus (JEV), no effective antiviral therapy exists. Our study shows that inhibition of poly(ADP-ribose) polymerase 1 (PARP1), an NAD+-dependent (poly-ADP) ribosyl transferase, protects against JEV infection. Interestingly, PARP1 is critical for JEV pathogenesis in Neuro-2a cells and mice. Small molecular inhibitors of PARP1, olaparib, and 3-aminobenzamide (3-AB) significantly reduce clinical signs and viral load in the serum and brains of mice and improve survival. PARP1 inhibition confers protection against JEV infection by inhibiting autophagy. Mechanistically, upon JEV infection, PARP1 PARylates AKT and negatively affects its phosphorylation. In addition, PARP1 transcriptionally upregulates PTEN, the PIP3 phosphatase, negatively regulating AKT. PARP1-mediated AKT inactivation promotes autophagy and JEV pathogenesis by increasing the FoxO activity. Thus, our findings demonstrate PARP1 as a potential mediator of JEV pathogenesis that can be effectively targeted for treating JE.

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.

Virulence and Cross-Protection Conferred by an Attenuated Genotype I-Based Chimeric Japanese Encephalitis Virus Strain Harboring the E Protein of Genotype V in Mice

Japanese encephalitis virus (JEV) genotype V (GV) emerged in China in 2009, then South Korea, and has since spread to other regions in Asia and beyond, raising concern about its pathogenicity and the cross-protection offered by JEV vaccines against different genotypes. In this study, we replaced the structural proteins (C-prM-E) of an attenuated genotype I (GI) SD12-F120 strain with those of a virulent GV XZ0934 strain to construct a recombinant chimeric GI-GV JEV (JEV-GI/V) strain to determine the role of the structural proteins in virulence and cross-protection. The recombinant chimeric virus was highly neurovirulent and neuroinvasive in mice. This demonstrated the determinant role of the structural proteins in the virulence of the GV strain. Intracerebral or intraperitoneal inoculation of mice with JEV-GI/V-E5 harboring a combination of substitutions (N47K, L107F, E138K, H123R, and I176R) in E protein, but not mutants containing single substitution of these residues, resulted in decreased or disappeared mortality, suggesting that these residues synergistically, but not individually, played a role in determining the neurovirulence and neuroinvasiveness of the GV strain. Immunization of mice with attenuated strain JEV-GI/V-E5 provided complete protection and induced high neutralizing antibody titers against parental strain JEV-GI/V, but partial cross-protection and low cross-neutralizing antibodies titers against the heterologous GI and GIII strains in mice, suggesting the reduced cross-protection of JEV vaccines among different genotypes. Overall, these findings suggested the essential role of the structural proteins in determination of the virulence of GV strain, and highlighted the need for a novel vaccine against this newly emerged strain. IMPORTANCE The GV JEV showed an increase in epidemic areas, which exhibited higher pathogenicity in mice than the prevalent GI and GIII strains. We replaced a recombinant chimeric GI-GV JEV (JEV-GI/V) strain to determine the role of the structural proteins in virulence and cross-protection. It was found that the essential role of the structural proteins is to determinethe virulence of the GV strain. It is also suggested that there is reduced cross-protection of JEV vaccines among different genotypes, which provides basic data for subsequent JEV prevention, control, and new vaccine development.

The Japanese Encephalitis Antigenic Complex Viruses: From Structure to Immunity

In the last three decades, several flaviviruses of concern that belong to different antigenic groups have expanded geographically. This has resulted in the presence of often more than one virus from a single antigenic group in some areas, while in Europe, Africa and Australia, additionally, multiple viruses belonging to the Japanese encephalitis (JE) serogroup co-circulate. Morphological heterogeneity of flaviviruses dictates antibody recognition and affects virus neutralization, which influences infection control. The latter is further impacted by sequential infections involving diverse flaviviruses co-circulating within a region and their cross-reactivity. The ensuing complex molecular virus-host interplay leads to either cross-protection or disease enhancement; however, the molecular determinants and mechanisms driving these outcomes are unclear. In this review, we provide an overview of the epidemiology of four JE serocomplex viruses, parameters affecting flaviviral heterogeneity and antibody recognition, host immune responses and the current knowledge of the cross-reactivity involving JE serocomplex flaviviruses that leads to differential clinical outcomes, which may inform future preventative and therapeutic interventions.

P34L Mutation of swine TIM-1 enhances its ability to mediate Japanese encephalitis virus infection

Japanese encephalitis virus (JEV) is a major causative agent of neurological infection affecting humans and pigs. Human T Cell Immunoglobulin and Mucin Domain 1 (hTIM-1) enhances the infection of JEV through virion-associated phosphatidylserine (PS) binding. Here, five swine TIM-1 (sTIM-1) gene variants were cloned from pig lung tissues by reverse-transcriptase polymerase chain reaction (RT-PCR). Sequence alignment analysis revealed that the gene homology between the sTIM-1 and hTIM-1 was 42.3-43.8%. Furthermore, ectopic expression of all five sTIM-1 variants in 293 T cells can promote JEV entry and infection. However, sTIM-1 V3 exhibited significantly less potent at promoting virus entry compared to the other four variants. Further studies revealed that the 34th amino acid of sTIM-1is critical for the entry of JEV, which is Pro34 in sTIM-1V3 while Leu34 in other four sTIM-1 variants. Mechanically, leucine at locus 34 was associated with the membrane distribution of sTIM-1, thereby affecting viral entry and infection. In total, our findings provide evidence that the PS receptor sTIM-1 promotes the infection of JEV and that the 34th amino acid position is critical for sTIM-1 to mediate viral infection.

Genomic Characteristics and E Protein Bioinformatics Analysis of JEV Isolates from South China from 2011 to 2018

Japanese encephalitis is a mosquito-borne zoonotic epidemic caused by the Japanese encephalitis virus (JEV). JEV is not only the leading cause of Asian viral encephalitis, but also one of the leading causes of viral encephalitis worldwide. To understand the genetic evolution and E protein characteristics of JEV, 263 suspected porcine JE samples collected from South China from 2011 to 2018 were inspected. It was found that 78 aborted porcine fetuses were JEV-nucleic-acid-positive, with a positive rate of 29.7%. Furthermore, four JEV variants were isolated from JEV-nucleic-acid-positive materials, namely, CH/GD2011/2011, CH/GD2014/2014, CH/GD2015/2015, and CH/GD2018/2018. The cell culture and virus titer determination of four JEV isolates showed that four JEV isolates could proliferate stably in Vero cells, and the virus titer was as high as 108.5 TCID 50/mL. The whole-genome sequences of four JEV isolates were sequenced. Based on the phylogenetic analysis of the JEV E gene and whole genome, it was found that CH/GD2011/2011 and CH/GD2015/2015 belonged to the GIII type, while CH/GD2014/2014 and CH/GD2018/2018 belonged to the GI type, which was significantly different from that of the JEV classical strain CH/BJ-1/1995. Bioinformatics tools were used to analyze the E protein phosphorylation site, glycosylation site, B cell antigen epitope, and modeled 3D structures of E protein in four JEV isolates. The analysis of the prevalence of JEV and the biological function of E protein can provide a theoretical basis for the prevention and control of JEV and the design of antiviral drugs.

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.

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

A comprehensive understanding of the human immune response to virus infection is imperative for developing effective therapies, antivirals, and vaccines. Dendritic cells (DCs) are among the first cells to encounter the virus and are also key antigen-presenting cells that link the innate and adaptive immune system. In this study, we focus on the human immune response to the mosquito-borne Japanese encephalitis virus (JEV), which is the leading cause of virus-induced encephalitis in south-east Asia and has the potential to become a global pathogen. We describe the gene regulatory circuit of JEV infection in human monocyte-derived DCs (moDCs) along with its functional validation. We observe that JEV can productively infect human moDCs leading to robust transcriptional activation of the interferon and NF-κB-mediated antiviral and inflammatory pathways. This is accompanied with DC maturation and release of pro-inflammatory cytokines and chemokines TNFα, IL-6, IL-8, IL-12, MCP-1. and RANTES. JEV-infected moDCs activated T-regulatory cells (Tregs) in allogenic mixed lymphocyte reactions (MLR) as seen by upregulated FOXP3 mRNA expression, suggestive of a host response to reduce virus-induced immunopathology. The virus also downregulated transcripts involved in Peroxisome Proliferator Activated Receptor (PPAR) signalling and fatty acid metabolism pathways suggesting that changes in cellular metabolism play a crucial role in driving the DC maturation and antiviral responses. Collectively, our data describe and corroborate the human DC transcriptional network that is engaged upon JEV sensing.

CRISPR screening of porcine sgRNA library identifies host factors associated with Japanese encephalitis virus replication

Japanese encephalitis virus (JEV) is a mosquito-borne zoonotic flavivirus that causes encephalitis and reproductive disorders in mammalian species. However, the host factors critical for its entry, replication, and assembly are poorly understood. Here, we design a porcine genome-scale CRISPR/Cas9 knockout (PigGeCKO) library containing 85,674 single guide RNAs targeting 17,743 protein-coding genes, 11,053 long ncRNAs, and 551 microRNAs. Subsequently, we use the PigGeCKO library to identify key host factors facilitating JEV infection in porcine cells. Several previously unreported genes required for JEV infection are highly enriched post-JEV selection. We conduct follow-up studies to verify the dependency of JEV on these genes, and identify functional contributions for six of the many candidate JEV-related host genes, including EMC3 and CALR. Additionally, we identify that four genes associated with heparan sulfate proteoglycans (HSPGs) metabolism, specifically those responsible for HSPGs sulfurylation, facilitate JEV entry into porcine cells. Thus, beyond our development of the largest CRISPR-based functional genomic screening platform for pig research to date, this study identifies multiple potentially vulnerable targets for the development of medical and breeding technologies to treat and prevent diseases caused by JEV.

Avian Flavivirus Enters BHK-21 Cells by a Low pH-Dependent Endosomal Pathway

Duck Tembusu virus (DTMUV), a pathogenic member of the Flavivirus family, was first discovered in the coastal provinces of South-Eastern China in 2010. Many previous reports have clearly shown that some Flaviviruses utilize several endocytic pathways to enter the host cells, however, the detailed mechanism of DTMUV entry into BHK-21 cells, which is usually employed to produce commercial veterinary vaccines for DTMUV, as well as of other Flaviviruses by serial passages, is still unknown. In this study, DTMUV entry into BHK-21 cells was found to be inhibited by noncytotoxic concentrations of the agents chloroquine, NH₄Cl, and Bafilomycin A1, which blocked the acidification of the endosomes. Inactivation of virions by acid pretreatment is a hallmark of viruses that utilize a low-pH-mediated entry pathway. Exposure of DTMUV virions to pH 5.0 in the absence of host cell membranes decreased entry into cells by 65%. Furthermore, DTMUV infection was significantly decreased by chlorpromazine treatment, or by knockdown of the clathrin heavy chain (CHC) through RNA interference, which suggested that DTMUV entry depends on clathrin. Taken together, these findings highlight that a low endosomal pH is an important route of entry for DTMUV.

Hsp40 Protein DNAJB6 Interacts with Viral NS3 and Inhibits the Replication of the Japanese Encephalitis Virus

The Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus prevalent in east and southeast Asia, the Western Pacific, and northern Australia. Since viruses are obligatory intracellular pathogens, the dynamic processes of viral entry, replication, and assembly are dependent on numerous host-pathogen interactions. Efforts to identify JEV-interacting host factors are ongoing because their identification and characterization remain incomplete. Three enzymatic activities of flavivirus non-structural protein 3 (NS3), including serine protease, RNA helicase, and triphosphatase, play major roles in the flaviviruses lifecycle. To identify cellular factors that interact with NS3, we screened a human brain cDNA library using a yeast two-hybrid assay, and identified eight proteins that putatively interact with NS3: COPS5, FBLN5, PPP2CB, CRBN, DNAJB6, UBE2N, ZNF350, and GPR137B. We demonstrated that the DnaJ heat shock protein family (Hsp40) member B6 (DNAJB6) colocalizes and interacts with NS3, and has a negative regulatory function in JEV replication. We also show that loss of DNAJB6 function results in significantly increased viral replication, but does not affect viral binding or internalization. Moreover, the time-course of DNAJB6 disruption during JEV infection varies in a viral load-dependent manner, suggesting that JEV targets this host chaperone protein for viral benefit. Deciphering the modes of NS3-interacting host proteins functions in virion production will shed light on JEV pathogenic mechanisms and may also reveal new avenues for antiviral therapeutics.

Recent advances in understanding Japanese encephalitis

Japanese encephalitis (JE) is a clinical manifestation of the brain inflammation caused by JE virus (JEV). This virus imparts permanent neurological damage, thus imposing a heavy burden on public health and society. Neuro-inflammation is the hallmark of JEV infection. The prolonged pro-inflammatory response is due primarily to microglial activation, which eventually leads to severe encephalitis. A continual effort is going on in the scientific community toward an understanding of cellular and molecular factors that are involved in JEV neuro-invasion and inflammatory processes. This review not only gives a comprehensive update on the recent advances on understanding virus structure and mechanisms of pathogenesis but also briefly discusses crucial unresolved issues. We also highlight challenging areas of research that might open new avenues for controlling virus-induced neuro-inflammation.

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.

The Multifaceted Roles of Autophagy in Flavivirus-Host Interactions

Autophagy is an evolutionarily conserved cellular process in which intracellular components are eliminated via lysosomal degradation to supply nutrients for organelle biogenesis and metabolic homeostasis. Flavivirus infections underlie multiple human diseases and thus exert an immense burden on public health worldwide. Mounting evidence indicates that host autophagy is subverted to modulate the life cycles of flaviviruses, such as hepatitis C virus, dengue virus, Japanese encephalitis virus, West Nile virus and Zika virus. The diverse interplay between autophagy and flavivirus infection not only regulates viral growth in host cells but also counteracts host stress responses induced by viral infection. In this review, we summarize the current knowledge on the role of autophagy in the flavivirus life cycle. We also discuss the impacts of virus-induced autophagy on the pathogeneses of flavivirus-associated diseases and the potential use of autophagy as a therapeutic target for curing flavivirus infections and related human diseases.

Acidity/Alkalinity of Japanese Encephalitis Virus E Protein Residue 138 Alters Neurovirulence in Mice

The Japanese encephalitis virus (JEV) envelope (E) protein, as one of mediators of virus entry into host cells, plays a critical role in determining virulence. The Glu-to-Lys mutation of residue 138 in E protein (E138) plays an important role in attenuating JEV vaccine strain SA14-14-2. However, it is not clear how E138 attenuates JEV. Here, we demonstrate that the Glu-to-Arg mutation of E138 also determines the attenuation of JEV strain 10S3. Likewise, for its parent strain (HEN0701), a virulence strain, the mutations of E138 are responsible for virulence alteration. Furthermore, we demonstrated that mutations of alkaline residues in E138 contributed to the attenuation of neurovirulence; in contrast, mutations of acidic residues enhanced the neurovirulence of the strains. Moreover, acidity in residue E47 had a similar effect on neurovirulence. Furthermore, the alkaline E138 residue enhanced susceptibility to heparin inhibition in vitro and limited JEV diffusion in mouse brain. These results suggest that the acidity/alkalinity of the E138 residue plays an important role in neurovirulence determination.IMPORTANCE The E protein is the only glycoprotein in mature JEV, and it plays an important role in viral neurovirulence. E protein mutations attenuate JEV neurovirulence through unclear mechanisms. Here, we discovered that E138 is a predominant determinant of JEV neurovirulence. We demonstrated that the alkalinity/acidity of E138 determines JEV neurovirulence. These data contribute to the characterization of the E protein and the rational development of novel JEV vaccines.

Flavivirus Receptors: Diversity, Identity, and Cell Entry

Flaviviruses are emerging and re-emerging arthropod-borne pathogens responsible for significant mortality and morbidity worldwide. The genus comprises more than seventy small, positive-sense, single-stranded RNA viruses, which are responsible for a spectrum of human and animal diseases ranging in symptoms from mild, influenza-like infection to fatal encephalitis and haemorrhagic fever. Despite genomic and structural similarities across the genus, infections by different flaviviruses result in disparate clinical presentations. This review focusses on two haemorrhagic flaviviruses, dengue virus and yellow fever virus, and two neurotropic flaviviruses, Japanese encephalitis virus and Zika virus. We review current knowledge on host-pathogen interactions, virus entry strategies and tropism.

Porcine sapovirus Cowden strain enters LLC-PK cells via clathrin- and cholesterol-dependent endocytosis with the requirement of dynamin II

Caliciviruses in the genus Sapovirus are a significant cause of viral gastroenteritis in humans and animals. However, the mechanism of their entry into cells is not well characterized. Here, we determined the entry mechanism of porcine sapovirus (PSaV) strain Cowden into permissive LLC-PK cells. The inhibition of clathrin-mediated endocytosis using chlorpromazine, siRNAs, and a dominant negative (DN) mutant blocked entry and infection of PSaV Cowden strain, confirming a role for clathrin-mediated internalization. Entry and infection were also inhibited by the cholesterol-sequestering drug methyl-β-cyclodextrin and was restored by the addition of soluble cholesterol, indicating that cholesterol also contributes to entry and infection of this strain. Furthermore, the inhibition of dynamin GTPase activity by dynasore, siRNA depletion of dynamin II, or overexpression of a DN mutant of dynamin II reduced the entry and infection, suggesting that dynamin mediates the fission and detachment of clathrin- and cholesterol-pits for entry of this strain. In contrast, the inhibition of caveolae-mediated endocytosis using nystatin, siRNAs, or a DN mutant had no inhibitory effect on entry and infection of this strain. It was further determined that cell entry of PSaV Cowden strain required actin rearrangements for vesicle internalization, endosomal trafficking from early to late endosomes through microtubules, and late endosomal acidification for uncoating. We conclude that PSaV strain Cowden is internalized into LLC-PK cells by clathrin- and cholesterol-mediated endocytosis that requires dynamin II and actin rearrangement, and that the uncoating occurs in the acidified late endosomes after trafficking from the early endosomes through microtubules.

Early Events in Japanese Encephalitis Virus Infection: Viral Entry

Japanese encephalitis virus (JEV), a mosquito-borne zoonotic flavivirus, is an enveloped positive-strand RNA virus that can cause a spectrum of clinical manifestations, ranging from mild febrile illness to severe neuroinvasive disease. Today, several killed and live vaccines are available in different parts of the globe for use in humans to prevent JEV-induced diseases, yet no antivirals are available to treat JEV-associated diseases. Despite the progress made in vaccine research and development, JEV is still a major public health problem in southern, eastern, and southeastern Asia, as well as northern Oceania, with the potential to become an emerging global pathogen. In viral replication, the entry of JEV into the cell is the first step in a cascade of complex interactions between the virus and target cells that is required for the initiation, dissemination, and maintenance of infection. Because this step determines cell/tissue tropism and pathogenesis, it is a promising target for antiviral therapy. JEV entry is mediated by the viral glycoprotein E, which binds virions to the cell surface (attachment), delivers them to endosomes (endocytosis), and catalyzes the fusion between the viral and endosomal membranes (membrane fusion), followed by the release of the viral genome into the cytoplasm (uncoating). In this multistep process, a collection of host factors are involved. In this review, we summarize the current knowledge on the viral and cellular components involved in JEV entry into host cells, with an emphasis on the initial virus-host cell interactions on the cell surface.

PLVAP and GKN3 Are Two Critical Host Cell Receptors Which Facilitate Japanese Encephalitis Virus Entry Into Neurons

Japanese Encephalitis Virus (JEV), a globally important pathogen, belongs to the family Flaviviridae, is transmitted between vertebrate hosts by mosquitoes, principally by Culex tritaeniorhynchus. The E-glycoprotein of the virus mediates its attachment to the host cell receptors. In this study, we cloned and purified JEV E-glycoprotein in pET28a vector using E. coli BL21 (DE3) cells. A pull down assay was performed using plasma membrane fraction of BALB/c mouse brain and E-glycoprotein as a bait protein. 2-Dimensional Gel Electrophoresis based separation of the interacting proteins was analyzed by mass spectrometry. Among all the identified partners of E-glycoprotein, PLVAP (Plasmalemma vesicle associated protein) and GKN3 (Gastrokine3) showed significant up-regulation in both JEV infected mouse brain and neuro2a cells. In-silico studies also predicted significant interaction of these receptors with E-glycoprotein. Additionally, overexperssion and silencing of these receptors resulted in increase and reduction in viral load respectively, suggesting them as two critical cellular receptors governing JEV entry and propagation in neurons. In support, we observed significant expression of PLVAP but not GKN3 in post-mortem autopsied human brain tissue. Our results establish two novel receptor proteins in neurons in case of JEV infection, thus providing potential targets for antiviral research.

Rab5, Rab7, and Rab11 Are Required for Caveola-Dependent Endocytosis of Classical Swine Fever Virus in Porcine Alveolar Macrophages

The members of Flaviviridae utilize several endocytic pathways to enter a variety of host cells. Our previous work showed that classical swine fever virus (CSFV) enters porcine kidney (PK-15) cells through a clathrin-dependent pathway that requires Rab5 and Rab7. The entry mechanism for CSFV into other cell lines remains unclear, for instance, porcine alveolar macrophages (3D4/21 cells). More importantly, the trafficking of CSFV within endosomes controlled by Rab GTPases is unknown in 3D4/21 cells. In this study, entry and postinternalization of CSFV were analyzed using chemical inhibitors, RNA interference, and dominant-negative (DN) mutants. Our data demonstrated that CSFV entry into 3D4/21 cells depends on caveolae, dynamin, and cholesterol but not clathrin or macropinocytosis. The effects of DN mutants and knockdown of four Rab proteins that regulate endosomal trafficking were examined on CSFV infection, respectively. The results showed that Rab5, Rab7, and Rab11, but not Rab9, regulate CSFV endocytosis. Confocal microscopy showed that virus particles colocalize with Rab5, Rab7, or Rab11 within 30 min after virus entry and further with lysosomes, suggesting that after internalization CSFV moves to early, late, and recycling endosomes and then into lysosomes before the release of the viral genome. Our findings provide insights into the life cycle of pestiviruses in macrophages.IMPORTANCE Classical swine fever, is caused by classical swine fever virus (CSFV). The disease is notifiable to World Organisation for Animal Health (OIE) in most countries and causes significant financial losses to the pig industry globally. Understanding the processes of CSFV endocytosis and postinternalization will advance our knowledge of the disease and provide potential novel drug targets against CSFV. With this objective, we used systematic approaches to dissect these processes in CSFV-infected 3D4/21 cells. The data presented here demonstrate for the first time to our knowledge that CSFV is able to enter cells via caveola-mediated endocytosis that requires Rab5, Rab7 and Rab11, in addition to the previously described classical clathrin-dependent pathway that requires Rab5 and Rab7. The characterization of CSFV entry will further promote our current understanding of Pestivirus cellular entry pathways and provide novel targets for antiviral drug development.

Identification of Glucose-Regulated Protein 78 (GRP78) as a Receptor in BHK-21 Cells for Duck Tembusu Virus Infection

Since 2010, outbreak and spread of tembusu virus (TMUV) caused huge losses to the breeding industry of waterfowl in several provinces of China. In this study, we identify the glucose-regulated protein 78 (GRP78) as a receptor in BHK-21 cells for duck TMUV infection. Using cell membrane from BHK-21 cells, a TMUV-binding protein of approximately 70 kDa was observed by viral overlay protein binding assay (VOPBA). LC-MS/MS analysis and co-immunoprecipitation identified GRP78 as a protein interacting with TMUV. Antibody against GRP78 inhibited the binding of TMUV to the cell surface of BHK-21 cells. Indirect immunofluorescence studies showed the colocalization of GRP78 with TMUV in virus-infected BHK-21 cells. We found that GRP78 over-expression increased TMUV infection, whereas GRP78 knockdown by using a specific small interfering RNA inhibited TMUV infection in BHK-21 cells. Taken together, our results indicate that GRP78 is a novel host factor involved in TMUV entry.

Rab5 and Rab11 Are Required for Clathrin-Dependent Endocytosis of Japanese Encephalitis Virus in BHK-21 Cells

During infection Japanese encephalitis virus (JEV) generally enters host cells via receptor-mediated clathrin-dependent endocytosis. The trafficking of JEV within endosomes is controlled by Rab GTPases, but which Rab proteins are involved in JEV entry into BHK-21 cells is unknown. In this study, entry and postinternalization of JEV were analyzed using biochemical inhibitors, RNA interference, and dominant negative (DN) mutants. Our data demonstrate that JEV entry into BHK-21 cells depends on clathrin, dynamin, and cholesterol but not on caveolae or macropinocytosis. The effect on JEV infection of dominant negative (DN) mutants of four Rab proteins that regulate endosomal trafficking was examined. Expression of DN Rab5 and DN Rab11, but not DN Rab7 and DN Rab9, significantly inhibited JEV replication. These results were further tested by silencing Rab5 or Rab11 expression before viral infection. Confocal microscopy showed that virus particles colocalized with Rab5 or Rab11 within 15 min after virus entry, suggesting that after internalization JEV moves to early and recycling endosomes before the release of the viral genome. Our findings demonstrate the roles of Rab5 and Rab11 on JEV infection of BHK-21 cells through the endocytic pathway, providing new insights into the life cycle of flaviviruses.IMPORTANCE Although Japanese encephalitis virus (JEV) utilizes different endocytic pathways depending on the cell type being infected, the detailed mechanism of its entry into BHK-21 cells is unknown. Understanding the process of JEV endocytosis and postinternalization will advance our knowledge of JEV infection and pathogenesis as well as provide potential novel drug targets for antiviral intervention. With this objective, we used systematic approaches to dissect this process. The results show that entry of JEV into BHK-21 cells requires a low-pH environment and that the process occurs through dynamin-, actin-, and cholesterol-dependent clathrin-mediated endocytosis that requires Rab5 and Rab11. Our work provides a detailed picture of the entry of JEV into BHK-21 cells and the cellular events that follow.

GRP78 Is an Important Host Factor for Japanese Encephalitis Virus Entry and Replication in Mammalian Cells

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is the leading cause of viral encephalitis in Southeast Asia with potential to become a global pathogen. Here, we identify glucose-regulated protein 78 (GRP78) as an important host protein for virus entry and replication. Using the plasma membrane fractions from mouse neuronal (Neuro2a) cells, mass spectroscopy analysis identified GRP78 as a protein interacting with recombinant JEV envelope protein domain III. GRP78 was found to be expressed on the plasma membranes of Neuro2a cells, mouse primary neurons, and human epithelial Huh-7 cells. Antibodies against GRP78 significantly inhibited JEV entry in all three cell types, suggesting an important role of the protein in virus entry. Depletion of GRP78 by small interfering RNA (siRNA) significantly blocked JEV entry into Neuro2a cells, further supporting its role in virus uptake. Immunofluorescence studies showed extensive colocalization of GRP78 with JEV envelope protein in virus-infected cells. This interaction was also confirmed by immunoprecipitation studies. Additionally, GRP78 was shown to have an important role in JEV replication, as treatment of cells post-virus entry with subtilase cytotoxin that specifically cleaved GRP78 led to a substantial reduction in viral RNA replication and protein synthesis, resulting in significantly reduced extracellular virus titers. Our results indicate that GRP78, an endoplasmic reticulum chaperon of the HSP70 family, is a novel host factor involved at multiple steps of the JEV life cycle and could be a potential therapeutic target.IMPORTANCE Recent years have seen a rapid spread of mosquito-borne diseases caused by flaviviruses. The flavivirus family includes West Nile, dengue, Japanese encephalitis, and Zika viruses, which are major threats to public health with potential to become global pathogens. JEV is the major cause of viral encephalitis in several parts of Southeast Asia, affecting a predominantly pediatric population with a high mortality rate. This study is focused on identification of crucial host factors that could be targeted to cripple virus infection and ultimately lead to development of effective antivirals. We have identified a cellular protein, GRP78, that plays a dual role in virus entry and virus replication, two crucial steps of the virus life cycle, and thus is a novel host factor that could be a potential therapeutic target.

Sulfated Glycans and Related Digestive Enzymes in the Zika Virus Infectivity: Potential Mechanisms of Virus-Host Interaction and Perspectives in Drug Discovery

As broadly reported, there is an ongoing Zika virus (ZIKV) outbreak in countries of Latin America. Recent findings have demonstrated that ZIKV causes severe defects on the neural development in fetuses in utero and newborns. Very little is known about the molecular mechanisms involved in the ZIKV infectivity. Potential therapeutic agents are also under investigation. In this report, the possible mechanisms of action played by glycosaminoglycans (GAGs) displayed at the surface proteoglycans of host cells, and likely in charge of interactions with surface proteins of the ZIKV, are highlighted. As is common for the most viruses, these sulfated glycans serve as receptors for virus attachment onto the host cells and consequential entry during infection. The applications of (1) exogenous sulfated glycans of different origins and chemical structures capable of competing with the virus attachment receptors (supposedly GAGs) and (2) GAG-degrading enzymes able to digest the virus attachment receptors on the cells may be therapeutically beneficial as anti-ZIKV. This communication attempts, therefore, to offer some guidance for the future research programs aimed to unveil the molecular mechanisms underlying the ZIKV infectivity and to develop therapeutics capable of decreasing the devastating consequences caused by ZIKV outbreak in the Americas.

Zika virus: An emergent neuropathological agent

The emergence of Zika virus in the Americas has followed a pattern that is familiar from earlier epidemics of other viruses, where a new disease is introduced into a human population and then spreads rapidly with important public health consequences. In the case of Zika virus, an accumulating body of recent evidence implicates the virus in the etiology of serious pathologies of the human nervous system, that is, the occurrence of microcephaly in neonates and Guillain-Barré syndrome in adults. Zika virus is an arbovirus (arthropod-borne virus) and a member of the family Flaviviridae, genus Flavivirus. Zika virions are enveloped and icosahedral, and contain a nonsegmented, single-stranded, positive-sense RNA genome, which encodes 3 structural and 7 nonstructural proteins that are expressed as a single polyprotein that undergoes cleavage. Zika genomic RNA replicates in the cytoplasm of infected host cells. Zika virus was first detected in 1947 in the blood of a febrile monkey in Uganda's Zika Forest and in crushed suspensions of the Aedes mosquito, which is one of the vectors for Zika virus. The virus remained obscure, with a few human cases confined to Africa and Asia. There are two lineages of the Zika virus, African and Asian, with the Asian strain causing outbreaks in Micronesia in 2007 and French Polynesia in 2013-2014. From here, the virus spread to Brazil with the first report of autochthonous Zika transmission in the Americas in March 2015. The rapid advance of the virus in the Americas and its likely association with microcephaly and Guillain-Barré syndrome make Zika an urgent public health concern. Ann Neurol 2016;80:479-489.