Probing Molecular Insights into Zika Virus⁻Host Interactions

Multi-omics analysis of antiviral interactions of Elizabethkingia anophelis and Zika virus

The microbial communities residing in the mosquito midgut play a key role in determining the outcome of mosquito pathogen infection. Elizabethkingia anophelis, originally isolated from the midgut of Anopheles gambiae possess a broad-spectrum antiviral phenotype, yet a gap in knowledge regarding the mechanistic basis of its interaction with viruses exists. The current study aims to identify pathways and genetic factors linked to E. anophelis antiviral activity. The understanding of E. anophelis antiviral mechanism could lead to novel transmission barrier tools to prevent arboviral outbreaks. We utilized a non-targeted multi-omics approach, analyzing extracellular lipids, proteins, metabolites of culture supernatants coinfected with ZIKV and E. anophelis. We observed a significant decrease in arginine and phenylalanine levels, metabolites that are essential for viral replication and progression of viral infection. This study provides insights into the molecular basis of E. anophelis antiviral phenotype. The findings lay a foundation for in-depth mechanistic studies.

LINC08148 promotes the caveola-mediated endocytosis of Zika virus through upregulating transcription of Src

Long non-coding RNAs (lncRNAs) represent a new group of host factors involved in viral infection. Current study identified an intergenic lncRNA, LINC08148, as a proviral factor of Zika virus (ZIKV) and Dengue virus 2 (DENV2). Knockout (KO) or silencing of LINC08148 decreases the replication of ZIKV and DENV2. LINC08148 mainly acts at the endocytosis step of ZIKV but at a later stage of DENV2. RNA-seq analysis reveals that LINC08148 knockout downregulates the transcription levels of five endocytosis-related genes including AP2B1, CHMP4C, DNM1, FCHO1, and Src. Among them, loss of Src significantly decreases the uptake of ZIKV. Trans-complementation of Src in the LINC08148KO cells largely restores the caveola-mediated endocytosis of ZIKV, indicating that the proviral effect of LINC08148 is exerted through Src. Finally, LINC08148 upregulates the Src transcription through associating with its transcription factor SP1. This work establishes an essential role of LINC08148 in the ZIKV entry, underscoring a significance of lncRNAs in the viral infection.

IMPORTANCE

Long non-coding RNAs (lncRNAs), like proteins, participate in viral infection. However, functions of most lncRNAs remain unknown. In this study, we performed a functional screen based on microarray data and identified a new proviral lncRNA, LINC08148. Then, we uncovered that LINC08148 is involved in the caveola-mediated endocytosis of ZIKV, rather than the classical clathrin-mediated endocytosis. Mechanistically, LINC08148 upregulates the transcription of Src, an initiator of caveola-mediated endocytosis, through binding to its transcription factor SP1. This study identifies a new lncRNA involved in the ZIKV infection, suggesting lncRNAs and cellular proteins are closely linked and cooperate to regulate viral infection.

Insights into the structure, functional perspective, and pathogenesis of ZIKV: an updated review

Zika virus (ZIKV) poses a serious threat to the entire world. The rapid spread of ZIKV and recent outbreaks since 2007 have caused worldwide concern about the virus. Diagnosis is complicated because of the cross-reactivity of the virus with other viral antibodies. Currently, the virus is diagnosed by molecular techniques such as RT-PCR and IgM-linked enzyme immunoassays (MAC-ELISA). Recently, outbreaks and epidemics have been caused by ZIKV, and severe clinical symptoms and congenital malformations have also been associated with the virus. Although most ZIKV infections present with a subclinical or moderate flu-like course of illness, severe symptoms such as Guillain-Barre syndrome in adults and microcephaly in children of infected mothers have also been reported. Because there is no reliable cure for ZIKV and no vaccine is available, the public health response has focused primarily on preventing infection, particularly in pregnant women. A comprehensive approach is urgently needed to combat this infection and stop its spread and imminent threat. In view of this, this review aims to present the current structural and functional viewpoints, structure, etiology, clinical prognosis, and measures to prevent this transmission based on the literature and current knowledge. Moreover, we provide thorough description of the current understanding about ZIKV interaction with receptors, and a comparative examination of its similarities and differences with other viruses.

Developing brain under renewed attack: viral infection during pregnancy

Living in a globalized world, viral infections such as CHIKV, SARS-COV-2, and ZIKV have become inevitable to also infect the most vulnerable groups in our society. That poses a danger to these populations including pregnant women since the developing brain is sensitive to maternal stressors including viral infections. Upon maternal infection, the viruses can gain access to the fetus via the maternofetal barrier and even to the fetal brain during which factors such as viral receptor expression, time of infection, and the balance between antiviral immune responses and pro-viral mechanisms contribute to mother-to-fetus transmission and fetal infection. Both the direct pro-viral mechanisms and the resulting dysregulated immune response can cause multi-level impairment in the maternofetal and brain barriers and the developing brain itself leading to dysfunction or even loss of several cell populations. Thus, maternal viral infections can disturb brain development and even predispose to neurodevelopmental disorders. In this review, we discuss the potential contribution of maternal viral infections of three relevant relative recent players in the field: Zika, Chikungunya, and Severe Acute Respiratory Syndrome Coronavirus-2, to the impairment of brain development throughout the entire route.

Zika virus as an emerging arbovirus of international public health concern

Zika virus (ZIKV) was identified in 1947 in a rhesus monkey during an investigation of the yellow fever virus in the Zika Forest of Uganda; it was also isolated later from humans in Nigeria. The main distribution areas of ZIKV were the African mainland and South-East Asia in the 1980s, Micronesia in 2007, and more recently the Americas in 2014. ZIKV belongs to the Flaviviridae family and Flavivirus genus. ZIKV infection, which is transmitted by Aedes mosquitoes, is an emerging arbovirus disease. The clinical symptoms of ZIKV infection are fever, headache, rashes, arthralgia, and conjunctivitis, which clinically resemble dengue fever syndrome. Sometimes, ZIKV infection has been associated with Guillain-Barré syndrome and microcephaly. At the end of 2015, following an increase in cases of ZIKV infection associated with Guillain-Barré syndrome and microcephaly in newborns in Brazil, the World Health Organization declared a global emergency. Therefore, considering the global distribution and pathogenic nature of this virus, the current study aimed at reviewing the virologic features, transmission patterns, clinical manifestations, diagnosis, treatment, and prevention of ZIKV infection.

Clinical Management of Herpes Simplex Virus Keratitis

Herpes simplex virus (HSV) keratitis is one of the leading causes of blindness worldwide. Additionally, up to 90% of the population in some countries is seropositive for HSV. HSV can cause a wide spectrum of ocular disease ranging from blepharitis to retinitis. Although the initial clinical expressions of HSV-1 and HSV-2 are similar, HSV-2 has been reported more frequently in association with recurrent HSV disease. Besides irreversible vision loss from keratitis, HSV also causes encephalitis and genital forms of the disease. Despite these statistics, there remains no vaccine against HSV. Current treatment therapies for related ocular diseases include the use of oral and topical antivirals and topical corticosteroids. While effective in many cases, they fail to address the latency and elimination of the virus, making it ineffective in addressing recurrences, a factor which increases the risk of vision loss. As such, there is a need for continued research of other potential therapeutic targets. This review utilized several published articles regarding the manifestations of HSV keratitis, antiviral immune responses to HSV infection, and clinical management of HSV keratitis. This review will summarize the current knowledge on the host–virus interaction in HSV infections, as well as highlighting the current and potential antiviral therapeutics.

TGF-β1 Promotes Zika Virus Infection in Immortalized Human First-Trimester Trophoblasts via the Smad Pathway

The Zika virus (ZIKV) is well known for causing congenital Zika syndrome if the infection occurs during pregnancy; however, the mechanism by which the virus infects and crosses the placenta barrier has not been completely understood. In pregnancy, TGF-β1 is abundant at the maternal–fetal interface. TGF-β1 has been reported to enhance rubella virus binding and infection in human lung epithelial cells. Therefore, in this study, we investigate the role of TGF-β1 in ZIKV infection in the immortalized human first-trimester trophoblasts, i.e., Swan.71. The cells were treated with TGF-β1 (10 ng/mL) for two days before being inoculated with the virus (American strain PRVABC59) at a multiplicity of infection of five. The results showed an enhancement of ZIKV infection, as demonstrated by the immunofluorescent assay and flow cytometry analysis. Such enhanced infection effects were abolished using SB431542 or SB525334, inhibitors of the TGF-β/Smad signaling pathway. An approximately 2-fold increase in the virus binding to the studied trophoblasts was found. In the presence of the Smad inhibitors, virus replication was significantly suppressed. An enhancement in Tyro3 and AXL (receptors for ZIKV) expression induced by TGF-β1 was also noted. The results suggest that TGF-β1 promotes the virus infection via the Smad pathway. Further studies should be carried out to clarify the underlying mechanisms of these findings.

Pathogenesis and Manifestations of Zika Virus-Associated Ocular Diseases

Zika virus (ZIKV) is mosquito-borne flavivirus that caused a significant public health concern in French Polynesia and South America. The two major complications that gained the most media attention during the ZIKV outbreak were Guillain-Barré syndrome (GBS) and microcephaly in newborn infants. The two modes of ZIKV transmission are the vector-borne and non-vector borne modes of transmission. Aedes aegypti and Aedes albopictus are the most important vectors of ZIKV. ZIKV binds to surface receptors on permissive cells that support infection and replication, such as neural progenitor cells, dendritic cells, dermal fibroblasts, retinal pigment epithelial cells, endothelial cells, macrophages, epidermal keratinocytes, and trophoblasts to cause infection. The innate immune response to ZIKV infection is mediated by interferons and natural killer cells, whereas the adaptive immune response is mediated by CD8⁺T cells, Th1 cells, and neutralizing antibodies. The non-structural proteins of ZIKV, such as non-structural protein 5, are involved in the evasion of the host's immune defense mechanisms. Ocular manifestations of ZIKV arise from the virus' ability to cross both the blood-brain barrier and blood-retinal barrier, as well as the blood-aqueous barrier. Most notably, this results in the development of GBS, a rare neurological complication in acute ZIKV infection. This can yield ocular symptoms and signs. Additionally, infants to whom ZIKV is transmitted congenitally develop congenital Zika syndrome (CZS). The ocular manifestations are widely variable, and include nonpurulent conjunctivitis, anterior uveitis, keratitis, trabeculitis, congenital glaucoma, microphthalmia, hypoplastic optic disc, and optic nerve pallor. There are currently no FDA approved therapeutic agents for treating ZIKV infections and, as such, a meticulous ocular examination is an important aspect of the diagnosis. This review utilized several published articles regarding the ocular findings of ZIKV, antiviral immune responses to ZIKV infection, and the pathogenesis of ocular manifestations in individuals with ZIKV infection. This review summarizes the current knowledge on the viral immunology of ZIKV, interactions between ZIKV and the host's immune defense mechanism, pathological mechanisms, as well as anterior and posterior segment findings associated with ZIKV infection.

Cellular Nanosponges for Biological Neutralization

Biological neutralization represents a general strategy that deploys therapeutic agents to bind with harmful molecules or infectious pathogens, block their bioactivity, and thus prevent them from causing the diseases. Here, a comprehensive review of using cell-membrane-coated nanoparticles, namely "cellular nanosponges," as host decoys for a wide range of biological neutralization applications is provided. Compared to traditional neutralization strategies, the cellular nanosponges stand out by mimicking susceptible host cells rather than accommodating the structures of the causative agents for the design of therapeutics. As all pathological agents must interact with host cells for bioactivity, nanosponges bypass the diversity of these agents and create function-driven and broad-spectrum neutralization solutions. The review focuses on the recent progress of using this new nanomedicine platform for neutralization against five primary pathological agents, including bacterial toxins, chemical toxicants, inflammatory cytokines, pathological antibodies, and viruses. Existing studies have established cellular nanosponges as versatile tools for biological neutralization. A thorough review of the cellular nanosponge technology is expected to inspire more refined cellular nanosponge designs and unique neutralization applications to address unsolved medical problems.

Host Molecules Regulating Neural Invasion of Zika Virus and Drug Repurposing Strategy

Zika virus (ZIKV) is a mosquito-borne, single-stranded RNA virus belonging to the genus Flavivirus. Although ZIKV infection is usually known to exhibit mild clinical symptoms, intrauterine ZIKV infections have been associated with severe neurological manifestations, including microcephaly and Guillain Barre syndrome (GBS). Therefore, it is imperative to understand the mechanisms of ZIKV entry into the central nervous system (CNS) and its effect on brain cells. Several routes of neuro-invasion have been identified, among which blood–brain barrier (BBB) disruption is the commonest mode of access. The molecular receptors involved in viral entry remain unknown; with various proposed molecular ZIKV-host interactions including potential non-receptor mediated cellular entry. As ZIKV invade neuronal cells, they trigger neurotoxic mechanisms via cell-autonomous and non-cell autonomous pathways, resulting in neurogenesis dysfunction, viral replication, and cell death, all of which eventually lead to microcephaly. Together, our understanding of the biological mechanisms of ZIKV exposure would aid in the development of anti-ZIKV therapies targeting host cellular and/or viral components to combat ZIKV infection and its neurological manifestations. In this present work, we review the current understanding of ZIKV entry mechanisms into the CNS and its implications on the brain. We also highlight the status of the drug repurposing approach for the development of potential antiviral drugs against ZIKV.

Host cytoskeletal vimentin serves as a structural organizer and an RNA-binding protein regulator to facilitate Zika viral replication

We discovered a dual role of vimentin underlying Zika virus (ZIKV) replication. The vimentin network reorganizes to surround the replication complex. Depletion of vimentin resulted in drastic segregation of viral proteins and subsequent defective infection, indicating its function as an “organizer” that ensures the concentration of all necessary factors for high replication efficacy. With omics analysis, we prove that vimentin also functions as a “regulator” that dominates RNA-binding proteins during infection. These two roles complement one another to make an integrated view of vimentin in regulating ZIKV infection. Collectively, our study fills the long-term gap in our knowledge of the cellular function of intermediate filaments in addition to structural support and provides a potential target for ZIKV therapy.

Emerging microbe infections, such as Zika virus (ZIKV), pose an increasing threat to human health. Investigations on ZIKV replication have revealed the construction of replication complexes (RCs), but the role of cytoskeleton in this process is largely unknown. Here, we investigated the function of cytoskeletal intermediate filament protein vimentin in the life cycle of ZIKV infection. Using advanced imaging techniques, we uncovered that vimentin filaments undergo drastic reorganization upon viral protein synthesis to form a perinuclear cage-like structure that embraces and concentrates RCs. Genetic removal of vimentin markedly disrupted the integrity of RCs and resulted in fragmented subcellular dispersion of viral proteins. This led to reduced viral genome replication, viral protein production, and release of infectious virions, without interrupting viral binding and entry. Furthermore, mass spectrometry and RNA-sequencing screens identified interactions and interplay between vimentin and hundreds of endoplasmic reticulum (ER)-resident RNA-binding proteins. Among them, the cytoplasmic-region of ribosome receptor binding protein 1, an ER transmembrane protein that directly binds viral RNA, interacted with and was regulated by vimentin, resulting in modulation of ZIKV replication. Together, the data in our work reveal a dual role for vimentin as a structural element for RC integrity and as an RNA-binding-regulating hub during ZIKV infection, thus unveiling a layer of interplay between Zika virus and host cell.

Murine Trophoblast Stem Cells and Their Differentiated Cells Attenuate Zika Virus In Vitro by Reducing Glycosylation of the Viral Envelope Protein

Zika virus (ZIKV) infection during pregnancy can cause devastating fetal neuropathological abnormalities, including microcephaly. Most studies of ZIKV infection in pregnancy have focused on post-implantation stage embryos. Currently, we have limited knowledge about how a pre-implantation stage embryo deals with a viral infection. This study investigates ZIKV infection on mouse trophoblast stem cells (TSCs) and their in vitro differentiated TSCs (DTSCs), which resemble the cellular components of the trophectoderm layer of the blastocyst that later develops into the placenta. We demonstrate that TSCs and DTSCs are permissive to ZIKV infection; however, ZIKV propagated in TSCs and DTSCs exhibit substantially lower infectivity, as shown in vitro and in a mouse model compared to ZIKV that was generated in Vero cells or mouse embryonic fibroblasts (MEFs). We further show that the low infectivity of ZIKV propagated in TSCs and DTSCs is associated with a reduced level of glycosylation on the viral envelope (E) proteins, which are essential for ZIKV to establish initial attachment by binding to cell surface glycosaminoglycans (GAGs). The decreased level of glycosylation on ZIKV E is, at least, partially due to the low-level expression of a glycosylation-related gene, Hexa, in TSCs and DTSCs. Furthermore, this finding is not limited to ZIKV since similar observations have been made as to the chikungunya virus (CHIKV) and West Nile virus (WNV) propagated in TSCs and DTSCs. In conclusion, our results reveal a novel phenomenon suggesting that murine TSCs and their differentiated cells may have adapted a cellular glycosylation system that can limit viral infectivity by altering the glycosylation of viral envelope proteins, therefore serving as a unique, innate anti-viral mechanism in the pre-implantation stage embryo.

Cell membrane skeletal protein 4.1R participates in entry of Zika virus into cells

Zika virus (ZIKV) is a typical mosquito-borne flavivirus known to cause severe fetal microcephaly and adult Guillain-Barré syndrome. Currently, there are no specific drugs or licensed vaccines available for ZIKV infection, and further research is required to identify host cell proteins involved in the virus's life cycle. Viruses are known to use host cell membrane skeletal proteins, such as actin and spectrin, to complete cell entry, transportation, and release. Here, based on immunoprecipitation, the Axl and ZIKV envelope (E) protein were shown to interact with the cell membrane skeleton protein 4.1R. Furthermore, deletion of 4.1R significantly reduced virus titer and viral protein synthesis. Our study showed that 4.1R is an important host cell protein during ZIKV infection and may be involved in the process of viral entry into host cells.

Zika Virus: A New Therapeutic Candidate for Glioblastoma Treatment

Glioblastoma (GBM) is the most aggressive among the neurological tumors. At present, no chemotherapy or radiotherapy regimen is associated with a positive long-term outcome. In the majority of cases, the tumor recurs within 32-36 weeks of initial treatment. The recent discovery that Zika virus (ZIKV) has an oncolytic action against GBM has brought hope for the development of new therapeutic approaches. ZIKV is an arbovirus of the Flaviviridae family, and its infection during development has been associated with central nervous system (CNS) malformations, including microcephaly, through the targeting of neural stem/progenitor cells (NSCs/NPCs). This finding has led various groups to evaluate ZIKV's effects against glioblastoma stem cells (GSCs), supposedly responsible for GBM onset, progression, and therapy resistance. While preliminary data support ZIKV tropism toward GSCs, a more accurate study of ZIKV mechanisms of action is fundamental in order to launch ZIKV-based clinical trials for GBM patients.

Nanomedicine based approaches for combating viral infections

Millions of people die each year from viral infections across the globe. There is an urgent need to overcome the existing gap and pitfalls of the current antiviral therapy which include increased dose and dosing frequency, bioavailability challenges, non-specificity, incidences of resistance and so on. These stumbling blocks could be effectively managed by the advent of nanomedicine. Current review emphasizes over an enhanced understanding of how different lipid, polymer and elemental based nanoformulations could be potentially and precisely used to bridle the said drawbacks in antiviral therapy. The dawn of nanotechnology meeting vaccine delivery, role of RNAi therapeutics in antiviral treatment regimen, various regulatory concerns towards clinical translation of nanomedicine along with current trends and implications including unexplored research avenues for advancing the current drug delivery have been discussed in detail.

Gist of Zika Virus pathogenesis

Zika virus (ZIKV) is a mosquito-borne neurotropic flavivirus. ZIKV infection may lead to microcephaly in developing fetus and Guillain-Barré Syndrome (GBS) like symptoms in adults. ZIKV was first reported in humans in 1952 from Uganda and the United Republic of Tanzania. Later, ZIKV outbreak was reported in 2007 from the Yap Island. ZIKV re-emerged as major outbreak in the year 2013 from French Polynesia followed by second outbreak in the year 2015 from Brazil. ZIKV crosses the blood-tissue barriers to enter immune-privileged organs. Clinical manifestations in ZIKV disease includes rash, fever, conjunctivitis, muscle and joint pain, headache, transverse myelitis, meningoencephalitis, Acute Disseminated Encephalomyelitis (ADEM). The understanding of the molecular mechanism of ZIKV pathogenesis is very important to develop potential diagnostic and therapeutic interventions for ZIKV infected patients.

Neurotropic Viruses, Astrocytes, and COVID-19

At the end of 2019, the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was discovered in China, causing a new coronavirus disease, termed COVID-19 by the WHO on February 11, 2020. At the time of this paper (January 31, 2021), more than 100 million cases have been recorded, which have claimed over 2 million lives worldwide. The most important clinical presentation of COVID-19 is severe pneumonia; however, many patients present various neurological symptoms, ranging from loss of olfaction, nausea, dizziness, and headache to encephalopathy and stroke, with a high prevalence of inflammatory central nervous system (CNS) syndromes. SARS-CoV-2 may also target the respiratory center in the brainstem and cause silent hypoxemia. However, the neurotropic mechanism(s) by which SARS-CoV-2 affects the CNS remain(s) unclear. In this paper, we first address the involvement of astrocytes in COVID-19 and then elucidate the present knowledge on SARS-CoV-2 as a neurotropic virus as well as several other neurotropic flaviviruses (with a particular emphasis on the West Nile virus, tick-borne encephalitis virus, and Zika virus) to highlight the neurotropic mechanisms that target astroglial cells in the CNS. These key homeostasis-providing cells in the CNS exhibit many functions that act as a favorable milieu for virus replication and possibly a favorable environment for SARS-CoV-2 as well. The role of astrocytes in COVID-19 pathology, related to aging and neurodegenerative disorders, and environmental factors, is discussed. Understanding these mechanisms is key to better understanding the pathophysiology of COVID-19 and for developing new strategies to mitigate the neurotropic manifestations of COVID-19.

Nanotechnology advances in pathogen- and host-targeted antiviral delivery: multipronged therapeutic intervention for pandemic control

The COVID-19 pandemic's high mortality rate and severe socioeconomic impact serve as a reminder of the urgent need for effective countermeasures against viral pandemic threats. In particular, effective antiviral therapeutics capable of stopping infections in its tracks is critical to reducing infection fatality rate and healthcare burden. With the field of drug delivery witnessing tremendous advancement in the last two decades owing to a panoply of nanotechnology advances, the present review summarizes and expounds on the research and development of therapeutic nanoformulations against various infectious viral pathogens, including HIV, influenza, and coronaviruses. Specifically, nanotechnology advances towards improving pathogen- and host-targeted antiviral drug delivery are reviewed, and the prospect of achieving effective viral eradication, broad-spectrum antiviral effect, and resisting viral mutations are discussed. As several COVID-19 antiviral clinical trials are met with lackluster treatment efficacy, nanocarrier strategies aimed at improving drug pharmacokinetics, biodistributions, and synergism are expected to not only contribute to the current disease treatment efforts but also expand the antiviral arsenal against other emerging viral diseases.

Positive Feedback Loop of Long Noncoding RNA OASL-IT1 and Innate Immune Response Restricts the Replication of Zika Virus in Epithelial A549 Cells

Expression of host noncoding RNAs and coding mRNAs is significantly altered by viral infection. In the current study, we screened the transcriptional profile of human lung epithelial A549 cells infected with Zika virus (ZIKV) by microarray assay. Seventy-nine long noncoding RNAs (lncRNAs) and 140 mRNAs were differentially expressed (DE). The bioinformatics analysis revealed that the mRNAs adjacent to the DE lncRNAs were closely related to the host responses to viral infection. We selected 7 lncRNAs from the top 50 hits for validation. The quantitative real-time PCR data confirmed that expression of selected lncRNAs was induced by ZIKV infection. Moreover, the expression of 7 lncRNAs was induced by infection of dengue virus, Japanese encephalitis virus, or vesicular stomatitis virus, or by treatment of poly(I:C) and IFN-β. Furthermore, loss of innate immune adaptor IPS-1 or receptor IFNAR1 resulted in lower induction levels of several lncRNAs by ZIKV. Overexpression of 3 lncRNAs (RPL27-OT1, OASL-IT1, and REC8-OT3) reduced the virus yields of ZIKV. Knockout of OASL-IT1 significantly enhanced ZIKV replication. In OASL-IT1 knockout cells, the levels of interferons (IFNs) and the activation of 3 innate immune signaling pathways triggered by ZIKV were dramatically reduced. Collectively, our work found a positive feedback loop in the IFN system, in which IFNs and OASL-IT1 regulate each other, thereby promoting establishment of antiviral defense.

The activation of antiviral RNA interference not only exists in neural progenitor cells but also in somatic cells in mammals

The RNA interference (RNAi) pathway directs an important antiviral immunity mechanism in plants and invertebrates. Recently, we and others have demonstrated that the antiviral RNAi response is also conserved in mammals, at least to five distinct RNA viruses, including Zika virus (ZIKV). ZIKV may preferentially infect neuronal progenitor cells (NPCs) in the developing foetal brain. Ex vivo ZIKV infection induces RNAi-mediated antiviral response in human NPCs, but not in the more differentiated NPCs or somatic cells. However, litter is known about the in vivo property or function of the virus-derived small-interfering RNAs (vsiRNAs) targeting ZIKV. Here we report a surprising observation: different from ex vivo observations, viral small RNAs (vsRNAs) targeting ZIKV were produced in vivo upon infection in both central neuron system (CNS) and muscle tissues. In addition, our findings demonstrate the production of canonical vsiRNAs in murine CNS upon antiviral RNAi activation by Sindbis virus (SINV), suggesting the possibility of antiviral immune strategy applied by mammals in the CNS.

Inositol-Requiring Enzyme 1α Promotes Zika Virus Infection through Regulation of Stearoyl Coenzyme A Desaturase 1-Mediated Lipid Metabolism

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus which has become a global epidemic threat due to its rapid spread and association with serious consequences of infection, including neonatal microcephaly. Inositol-requiring enzyme 1α (IRE1α) is an endoplasmic reticulum (ER)-related transmembrane protein that mediates unfolded protein response (UPR) pathway and has been indicated to play an important role in flavivirus replication. However, the mechanism of how IRE1α affects ZIKV replication remains unknown. In this study, we explored the role of IRE1α in ZIKV infection in vitro and in vivo by using CRISPR/Cas9-based gene knockout and RNA interference-based gene knockdown techniques. Both knockout and knockdown of IRE1α dramatically reduced ZIKV replication levels, including viral RNA levels, protein expression, and titers in different human cell lines. Trans-complementation with IRE1α restored viral replication levels decreased by IRE1α depletion. Furthermore, the proviral effect of IRE1α was dependent on its kinase and RNase activities. Importantly, we found that IRE1α promoted the replication of ZIKV through upregulating the accumulation of monounsaturated fatty acid (MUFA) rate-limiting enzyme stearoyl coenzyme A (stearoyl-CoA) desaturase 1 (SCD1), which further affected the production of oleic acid (OA) and lipid droplet. Finally, our data demonstrated that in the brain tissues of ZIKV-infected mice, the replication levels of ZIKV and virus-related lesions were significantly suppressed by both the kinase and RNase inhibitors of IRE1α. Taken together, our results identified IRE1α as a ZIKV dependency factor which promotes viral replication through affecting SCD1-mediated lipid metabolism, potentially providing a novel molecular target for the development of anti-ZIKV agents.IMPORTANCE Zika virus (ZIKV) has been linked to serious neurologic disorders and causes widespread concern in the field of global public health. Inositol requiring enzyme 1α (IRE1α) is an ER-related transmembrane protein that mediates unfolded protein response (UPR) pathway. Here, we revealed that IRE1α is a proviral factor for ZIKV replication both in culture cells and mice model, which relies on its kinase and RNase activities. Importantly, we further provided evidence that upon ZIKV infection, IRE1α is activated and splices XBP1 mRNA which enhances the expression of monounsaturated fatty acids rate-limiting enzyme stearoyl coenzyme A (stearoyl-CoA) desaturase 1 (SCD1) and subsequent lipid droplet production. Our data uncover a novel mechanism of IRE1α proviral effect by modulating lipid metabolism, providing the first evidence of a close relationship between IRE1α-mediated UPR, lipid metabolism, and ZIKV replication and indicating IRE1α inhibitors as potentially effective anti-ZIKV agents.

Immune Reactivity of a 20-mer Peptide Representing the Zika E Glycan Loop Involves the Antigenic Determinants E-152/156/158

Mosquito-borne Zika virus (ZIKV) causes a severe congenital syndrome and neurological disorders in humans. With the aim to develop a live-attenuated ZIKV strain, we generated a chimeric viral clone ZIKALIVax with African MR766-NIID strain as backbone and the envelope E protein of epidemic Brazilian BeH810915 strain. The MR766-NIID residues E-T152/I156/Y158 were introduced into BeH810915 E protein leading to a nonglycosylated ZIKALIVax. Recently, we reported that the residues E-152/156/158 that are part of ZIKV glycan loop (GL) region might have an impact on the availability of neutralizing antibody epitopes on ZIKV surface. In the present study, we evaluated the antigenic reactivity of a synthetic 20-mer peptide representing the ZIKALIVax GL region. The GL-related peptide was effective for the detection of GL-reactive antibody in mouse anti-ZIKALIVax immune serum. We showed that the residue E-158 influences the antigenic reactivity of GL-related peptide. The ZIKALIVax peptide was effective in generating mouse antibodies with reactivity against a recombinant E domain I that encompasses the GL region. The GL peptide-reactive antibodies revealed that antigenic reactivity of E-domain I may be impacted by both residues E-152 and E-156. In conclusion, we proposed a role for the residues E-152/156/158 as key antigenic determinants of ZIKV glycan loop region.

Placental Alkaline Phosphatase Promotes Zika Virus Replication by Stabilizing Viral Proteins through BIP

Zika virus (ZIKV) infection during pregnancy causes intrauterine growth defects and microcephaly, but knowledge of the mechanism through which ZIKV infects and replicates in the placenta remains elusive. Here, we found that ALPP, an alkaline phosphatase expressed primarily in placental tissue, promoted ZIKV infection in both human placental trophoblasts and astrocytoma cells. ALPP bound to ZIKV structural and nonstructural proteins and thereby prevented their proteasome-mediated degradation and enhanced viral RNA replication and virion biogenesis. In addition, the function of ALPP in ZIKV infection depends on its phosphatase activity. Furthermore, we demonstrated that ALPP was stabilized through interactions with BIP, which is the endoplasmic reticulum (ER)-resident heat shock protein 70 chaperone. The chaperone activity of BIP promoted ZIKV infection and mediated the interaction between ALPP and ZIKV proteins. Collectively, our findings reveal a previously unrecognized mechanism through which ALPP facilitates ZIKV replication by coordinating with the BIP protein.IMPORTANCE ZIKV is a recently emerged mosquito-borne flavivirus that can cause devastating congenital Zika syndrome in pregnant women and Guillain-Barré syndrome in adults, but how ZIKV specifically targets the placenta is not well understood. Here, we identified an alkaline phosphatase (ALPP) that is expressed primarily in placental tissue and promotes ZIKV infection by colocalizing with ZIKV proteins and preventing their proteasome-mediated degradation. The phosphatase activity of ALPP could be required for optimal ZIKV infection, and ALPP is stabilized by BIP via its chaperone activity. This report provides novel insights into host factors required for ZIKV infection, which potentially has implications for ZIKV infection of the placenta.

Modulation of the Innate Immune Response by Targeting Toll-like Receptors: A Perspective on Their Agonists and Antagonists

Toll-like receptors (TLRs) are a class of proteins that recognize pathogen-associated molecular patterns (PAMPs) and damaged-associated molecular patterns (DAMPs), and they are involved in the regulation of innate immune system. These transmembrane receptors, localized at the cellular or endosomal membrane, trigger inflammatory processes through either myeloid differentiation primary response 88 (MyD88) or TIR-domain-containing adapter-inducing interferon-β (TRIF) signaling pathways. In the last decades, extensive research has been performed on TLR modulators and their therapeutic implication under several pathological conditions, spanning from infections to cancer, from metabolic disorders to neurodegeneration and autoimmune diseases. This Perspective will highlight the recent discoveries in this field, emphasizing the role of TLRs in different diseases and the therapeutic effect of their natural and synthetic modulators, and it will discuss insights for the future exploitation of TLR modulators in human health.

Differential gene expression elicited by ZIKV infection in trophoblasts from congenital Zika syndrome discordant twins

Zika virus (ZIKV) causes congenital Zika syndrome (CZS), which is characterized by fetal demise, microcephaly and other abnormalities. ZIKV in the pregnant woman circulation must cross the placental barrier that includes fetal endothelial cells and trophoblasts, in order to reach the fetus. CZS occurs in ~1-40% of cases of pregnant women infected by ZIKV, suggesting that mothers' infection by ZIKV during pregnancy is not deterministic for CZS phenotype in the fetus. Therefore, other susceptibility factors might be involved, including the host genetic background. We have previously shown that in three pairs of dizygotic twins discordant for CZS, neural progenitor cells (NPCs) from the CZS-affected twins presented differential in vitro ZIKV susceptibility compared with NPCs from the non-affected. Here, we analyzed human-induced-pluripotent-stem-cell-derived (hiPSC-derived) trophoblasts from these twins and compared by RNA-Seq the trophoblasts from CZS-affected and non-affected twins. Following in vitro exposure to a Brazilian ZIKV strain (ZIKVBR), trophoblasts from CZS-affected twins were significantly more susceptible to ZIKVBR infection when compared with trophoblasts from the non-affected. Transcriptome profiling revealed no differences in gene expression levels of ZIKV candidate attachment factors, IFN receptors and IFN in the trophoblasts, either before or after ZIKVBR infection. Most importantly, ZIKVBR infection caused, only in the trophoblasts from CZS-affected twins, the downregulation of genes related to extracellular matrix organization and to leukocyte activation, which are important for trophoblast adhesion and immune response activation. In addition, only trophoblasts from non-affected twins secreted significantly increased amounts of chemokines RANTES/CCL5 and IP10 after infection with ZIKVBR. Overall, our results showed that trophoblasts from non-affected twins have the ability to more efficiently activate genes that are known to play important roles in cell adhesion and in triggering the immune response to ZIKV infection in the placenta, and this may contribute to predict protection from ZIKV dissemination into fetuses' tissues.

A complex between the Zika virion and the Fab of a broadly cross-reactive neutralizing monoclonal antibody revealed by cryo-EM and single particle analysis at 4.1 Å resolution

Zika virus (ZIKV) recently emerged as a major public health concern because it can cause fetal microcephaly and neurological disease such as the Guillain-Barré syndrome. A particularly potent class of broadly neutralizing antibodies (nAbs) targets a quaternary epitope located at the interface of two envelope proteins monomers, exposed at the surface of the mature virion. This “E-dimer-dependent epitope” (EDE), comprises the fusion loop of one monomer at the tip of domain II of E and a portion of the domains I and III of the adjacent monomer. Since this epitope largely overlaps with the binding site of the precursor membrane protein (prM) during Zika virion maturation, its molecular surface is evolutionary conserved in flaviviruses such as Dengue and Zika viruses, and can elicit antibodies that broadly neutralize various ZIKV strains. Here, we present a cryo-EM reconstruction at 4.1 Å resolution of the virion bound to the antigen binding fragment (Fab) of an antibody that targets this mutationally-constrained quaternary epitope. The Fab incompletely covers the surface of the virion as it does not bind next to its 5-fold icosahedral axes. The structure reveals details of the binding mode of this potent neutralizing class of antibodies and can inform the design of immunogens and vaccines targeting this conserved epitope.

Glucose-Regulated Protein 78 Interacts with Zika Virus Envelope Protein and Contributes to a Productive Infection

Zika virus (ZIKV; Flaviviridae) is a mosquito-borne flavivirus shown to cause fetal abnormalities collectively known as congenital Zika syndrome and Guillain-Barré syndrome in recent outbreaks. Currently, there is no specific treatment or vaccine available, and more effort is needed to identify cellular factors in the viral life cycle. Here, we investigated interactors of ZIKV envelope (E) protein by combining protein pull-down with mass spectrometry. We found that E interacts with the endoplasmic reticulum (ER) resident chaperone, glucose regulated protein 78 (GRP78). Although other flaviviruses are known to co-opt ER resident proteins, including GRP78, to enhance viral infectivity, the role ER proteins play during the ZIKV life cycle is yet to be elucidated. We showed that GRP78 levels increased during ZIKV infection and localised to sites coincident with ZIKV E staining. Depletion of GRP78 using specific siRNAs significantly reduced reporter-virus luciferase readings, viral protein synthesis, and viral titres. Additionally, GRP78 depletion reduced the ability of ZIKV to disrupt host cell translation and altered the localisation of viral replication factories, though there was no effect on viral RNA synthesis. In summary, we showed GRP78 is a vital host-factor during ZIKV infection, which may be involved in the coordination of viral replication factories.

Current Efforts in the Development of Vaccines for the Prevention of Zika and Chikungunya Virus Infections

Arboviruses represent major challenges to public health, particularly in tropical, and subtropical regions, and a substantial risk to other parts of the world as respective vectors extend their habitats. In recent years, two viruses transmitted by Aedes mosquitoes, Chikungunya and Zika virus, have gathered increased interest. After decades of regionally constrained outbreaks, both viruses have recently caused explosive outbreaks on an unprecedented scale, causing immense suffering and massive economic burdens in affected regions. Chikungunya virus causes an acute febrile illness that often transitions into a chronic manifestation characterized by debilitating arthralgia and/or arthritis in a substantial subset of infected individuals. Zika infection frequently presents as a mild influenza-like illness, often subclinical, but can cause severe complications such as congenital malformations in pregnancy and neurological disorders, including Guillain-Barré syndrome. With no specific treatments or vaccines available, vector control remains the most effective measure to manage spread of these diseases. Given that both viruses cause antibody responses that confer long-term, possibly lifelong protection and that such responses are cross-protective against the various circulating genetic lineages, the development of Zika and Chikungunya vaccines represents a promising route for disease control. In this review we provide a brief overview on Zika and Chikungunya viruses, the etiology and epidemiology of the illnesses they cause and the host immune response against them, before summarizing past and current efforts to develop vaccines to alleviate the burden caused by these emerging diseases. The development of the urgently needed vaccines is hampered by several factors including the unpredictable epidemiology, feasibility of rapid clinical trial implementation during outbreaks and regulatory pathways. We will give an overview of the current developments.

Investigation of the immunogenicity of Zika glycan loop

Background

Zika virus (ZIKV) is a major human pathogen and member of the Flavivirus genus. Previous studies have identified neutralizing antibodies from Zika patients that bind to quaternary epitopes across neighboring envelope (E) proteins, called E dimer epitopes (EDE). An asparagine-linked glycan on the “glycan loop” (GL) of the ZIKV envelope protein protects the functionally important “fusion loop” on the opposite E subunit in the dimer, and EDE antibodies have been shown to bind to both of these loops. Human EDE antibodies have been divided into two subclasses based on how they bind to the glycan loop region: EDE1 antibodies do not require glycosylation for binding, while EDE2 antibodies strongly rely on the glycan for binding.

Methods

ZIKV GL was expressed on tobacco mosaic virus nanoparticles. Mice were immunized with GL or full-length monomeric E and the immune response was analyzed by testing the ability of sera and monoclonal antibodies to bind to GL and to neutralize ZIKV in in vitro cellular assay.

Results

We report here the existence of ZIKV moderately neutralizing antibodies that bind to E monomers through epitopes that include the glycan loop. We show that sera from human Zika patients contain antibodies capable of binding to the unglycosylated glycan loop in the absence of the rest of the envelope protein. Furthermore, mice were inoculated with recombinant E monomers and produced neutralizing antibodies that either recognize unglycosylated glycan loop or require glycan for their binding to monomeric E. We demonstrate that both types of antibodies neutralize ZIKV to some extent in a cellular virus neutralization assay.

Conclusions

Analogous to the existing EDE antibody nomenclature, we propose a new classification for antibodies that bind to E monomer epitopes (EME): EME1 and EME2 for those that do not require and those that do require glycan for binding to E, respectively.

Topology, Antiviral Functional Residues and Mechanism of IFITM1

Interferon-inducible transmembrane proteins (IFITM1/2/3) have been reported to suppress the entry of a wide range of viruses. However, their antiviral functional residues and specific mechanisms are still unclear. Here, we firstly resolved the topology of IFITM1 on the plasma membrane where N-terminus points into the cytoplasm and C-terminus resides extracellularly. Further, KRRK basic residues of IFITM1 locating at 62–67 of the conserved intracellular loop (CIL) were found to play a key role in the restriction on the Zika virus (ZIKV) and dengue virus (DENV). Similarly, KRRK basic residues of IFITM2/3 also contributed to suppressing ZIKV replication. Finally, IFITM1 was revealed to be capable of restricting the release of ZIKV particles from endosome to cytosol so as to impede the entry of ZIKV into host cells, which was tightly related with the inhibition of IFITM1 on the acidification of organelles. Overall, our study provided topology, antiviral functional residues and the mechanism of interferon-inducible transmembrane proteins.

Crosstalk between RNA Metabolism and Cellular Stress Responses during Zika Virus Replication

Zika virus (ZIKV) is a mosquito-borne virus associated with neurological disorders such as Guillain-Barré syndrome and microcephaly. In humans, ZIKV is able to replicate in cell types from different tissues including placental cells, neurons, and microglia. This intricate virus-cell interaction is accompanied by virally induced changes in the infected cell aimed to promote viral replication as well as cellular responses aimed to counteract or tolerate the virus. Early in the infection, the 11-kb positive-sense RNA genome recruit ribosomes in the cytoplasm and the complex is translocated to the endoplasmic reticulum (ER) for viral protein synthesis. In this process, ZIKV replication is known to induce cellular stress, which triggers both the expression of innate immune genes and the phosphorylation of eukaryotic translation initiation factor 2 (eIF2α), shutting-off host protein synthesis. Remodeling of the ER during ZIKV replication also triggers the unfolded protein response (UPR), which induces changes in the cellular transcriptional landscapes aimed to tolerate infection or trigger apoptosis. Alternatively, ZIKV replication induces changes in the adenosine methylation patterns of specific host mRNAs, which have different consequences in viral replication and cellular fate. In addition, the ZIKV RNA genome undergoes adenosine methylation by the host machinery, which results in the inhibition of viral replication. However, despite these relevant findings, the full scope of these processes to the outcome of infection remains poorly elucidated. This review summarizes relevant aspects of the complex crosstalk between RNA metabolism and cellular stress responses against ZIKV and discusses their possible impact on viral pathogenesis.

NS5 Conservative Site Is Required for Zika Virus to Restrict the RIG-I Signaling

During host-virus co-evolution, cells develop innate immune systems to inhibit virus invasion, while viruses employ strategies to suppress immune responses and maintain infection. Here, we reveal that Zika virus (ZIKV), a re-emerging arbovirus causing public concerns and devastating complications, restricts host immune responses through a distinct mechanism. ZIKV nonstructural protein 5 (NS5) interacts with the host retinoic acid-inducible gene I (RIG-I), an essential signaling molecule for defending pathogen infections. NS5 subsequently represses K63-linked polyubiquitination of RIG-I, attenuates the phosphorylation and nuclear translocation of interferon regulatory factor 3 (IRF3), and inhibits the expression and production of interferon-β (IFN-β), thereby restricting the RIG-I signaling pathway. Interestingly, we demonstrate that the methyltransferase (MTase) domain of NS5 is required for the repression of RIG-I ubiquitination, IRF3 activation, and IFN-β production. Detailed studies further reveal that the conservative active site D146 of NS5 is critical for the suppression of the RIG-I signaling. Therefore, we uncover an essential role of NS5 conservative site D146 in ZIKV-mediated repression of innate immune system, illustrate a distinct mechanism by which ZIKV evades host immune responses, and discover a potential target for anti-viral infection.

Hydroxycarboxylic Acid Receptor 2 Is a Zika Virus Restriction Factor That Can Be Induced by Zika Virus Infection Through the IRE1-XBP1 Pathway

Zika virus (ZIKV) is an emerging arthropod-borne virus and belongs to the Flaviviridae family. The infection of ZIKV has become the global health crisis because of its rapid spread and association with severe neurological disorders, including congenital microcephaly and Guillain-Barre Syndrome. To identify host factors contributing to ZIKV pathogenesis, transcriptomic landscape in ZIKV-infected cells was examined with mRNA microarray analysis and we observed that the expression of hydroxycarboxylic acid receptor 2 (HCAR2) could be significantly induced by ZIKV infection. By utilizing two IRE1 inhibitors and XBP1-specific shRNAs, we revealed that the up-regulation of HCAR2 expression induced by ZIKV was dependent on the IRE1-XBP1 pathway. Through the CRISPR/Cas9 system, we generated HCAR2-deficient cell clones in two cell types (human lung carcinoma epithelial A549 cell and human hepatoma Huh7.5 cell). We found that the depletion of HCAR2 significantly increased the replication level of ZIKV, including RNA levels, protein expression levels, and viral titers. In addition, our data demonstrated that the antiviral effect of HCAR2 was not involved in viral entry process and was not dependent on its antilipolytic effect on nicotinic acid/HCAR2-mediated signaling pathway. Taken together, our results indicated that HCAR2 could function as a restriction factor in control of ZIKV replication, potentially providing a novel molecular target for anti-ZIKV therapeutics.

The Envelope Residues E152/156/158 of Zika Virus Influence the Early Stages of Virus Infection in Human Cells

Emerging infections of mosquito-borne Zika virus (ZIKV) pose an increasing threat to human health, as documented over the recent years in South Pacific islands and the Americas in recent years. To better understand molecular mechanisms underlying the increase in human cases with severe pathologies, we recently demonstrated the functional roles of structural proteins capsid (C), pre-membrane (prM), and envelop (E) of ZIKV epidemic strains with the initiation of viral infection in human cells. Specifically, we found that the C-prM region contributes to permissiveness of human host cells to ZIKV infection and ZIKV-induced cytopathic effects, whereas the E protein is associated with viral attachment and early infection. In the present study, we further characterize ZIKV E proteins by investigating the roles of residues isoleucine 152 (Ile152), threonine 156 (Thr156), and histidine 158 (His158) (i.e., the E-152/156/158 residues), which surround a unique N-glycosylation site (E-154), in permissiveness of human host cells to epidemic ZIKV infection. For comparison purpose, we generated mutant molecular clones of epidemic BeH819015 (BR15) and historical MR766-NIID (MR766) strains that carry each other's E-152/156/158 residues, respectively. We observed that the BR15 mutant containing the E-152/156/158 residues from MR766 was less infectious in A549-Dual™ cells than parental virus. In contrast, the MR766 mutant containing E-152/156/158 residues from BR15 displayed increased infectivity. The observed differences in infectivity were, however, not correlated with changes in viral binding onto host-cells or cellular responses to viral infection. Instead, the E-152/156/158 residues from BR15 were associated with an increased efficiency of viral membrane fusion inside infected cells due to conformational changes of E protein that enhance exposure of the fusion loop. Our data highlight an important contribution of E-152/156/158 residues to the early steps of ZIKV infection in human cells.

Atlastin Endoplasmic Reticulum-Shaping Proteins Facilitate Zika Virus Replication

The endoplasmic reticulum (ER) is the site for Zika virus (ZIKV) replication and is central to the cytopathic effects observed in infected cells. ZIKV induces the formation of ER-derived large cytoplasmic vacuoles followed by "implosive" cell death. Little is known about the nature of the ER factors that regulate flavivirus replication. Atlastins (ATL1, -2, and -3) are dynamin-related GTPases that control the structure and the dynamics of the ER membrane. We show here that ZIKV replication is significantly decreased in the absence of ATL proteins. The appearance of infected cells is delayed, the levels of intracellular viral proteins and released virus are reduced, and the cytopathic effects are strongly impaired. We further show that ATL3 is recruited to viral replication sites and interacts with the nonstructural viral proteins NS2A and NS2B3. Thus, proteins that shape and maintain the ER tubular network ensure efficient ZIKV replication.IMPORTANCE Zika virus (ZIKV) is an emerging virus associated with Guillain-Barré syndrome, and fetal microcephaly as well as other neurological complications. There is no vaccine or specific antiviral treatment against ZIKV. We found that endoplasmic reticulum (ER)-shaping atlastin proteins (ATL1, -2, and -3), which induce ER membrane fusion, facilitate ZIKV replication. We show that ATL3 is recruited to the viral replication site and colocalize with the viral proteins NS2A and NS2B3. The results provide insights into host factors used by ZIKV to enhance its replication.

Molecular signatures associated with prostate cancer cell line (PC-3) exposure to inactivated Zika virus

The recent outbreak of Zika virus (ZIKV) infection associated with microcephaly cases has elicited much research on the mechanisms involved in ZIKV-host cell interactions. It has been described that Zika virus impairs cell growth, raising a hypothesis about its oncolytic potential against cancer cells. ZIKV tumor cell growth inhibition was later confirmed for glioblastoma. It was also demonstrated that an inactivated ZIKV prototype (ZVp) based on bacterial outer membrane vesicles has antiproliferative activity upon other cancer cell lines, such as PC-3 prostate cancer cell. This study aims at understanding the pathways that might be involved with the antiproliferative effect of Zika virus against prostate cancer cells. A metabolomic approach based on high-resolution mass spectrometry analysis led to the identification of 21 statistically relevant markers of PC-3 cells treated with ZVp. The markers were associated with metabolic alterations that trigger lipid remodeling, endoplasmic reticulum stress, inflammatory mediators, as well as disrupted porphyrin and folate metabolism. These findings highlight molecular signatures of ZVp-induced response that may be involved on cellular pathways triggered by its antiproliferative effect. To our knowledge, this is the first reported metabolomic assessment of ZIKV effect on prostate cancer cells, a promising topic for further research.

Dissecting the Toxic Effects of Zika Virus Proteins on Neural Progenitor Cells

The mechanisms by which Zika virus (ZIKV) disrupts neurogenesis and causes microcephaly are poorly understood. In this issue of Neuron, Li et al. (2019) demonstrate that ZIKV protease NS2B-NS3 heterodimers cleave Septin-2 and lead to cytokinesis defects.

Cross-Reaction, Enhancement, and Neutralization Activity of Dengue Virus Antibodies against Zika Virus: A Study in the Mexican Population

Zika virus (ZIKV), an emerging mosquito-borne flavivirus, has quickly spread in many regions around the world where dengue virus (DENV) is endemic. This represents a major health concern, given the high homology between these two viruses, which can result in cross-reactivity. The aim of this study was to determine the cross-reacting antibody response of the IgM and IgG classes against the recombinant envelope protein of ZIKV (rE-ZIKV) in sera from patients with acute-phase infection of different clinical forms of dengue, i.e., dengue fever (DF) and dengue hemorrhagic fever (DHF) (before the arrival of ZIKV in Mexico 2010), as well as acute-phase sera of ZIKV patients, together with the implications in neutralization and antibody-dependent enhancement. Differences in IgM responses were observed in a number of DF and DHF patients whose sera cross-reacted with the rE-ZIK antigen, with 42% recognition between acute-phase DHF and ZIKV but 27% recognition between DF and ZIKV. Regarding IgG antibodies, 71.5% from the DF group showed cross-reactivity to rE-ZIKV in contrast with 50% and only 25% of DHF and ZIKV serum samples, respectively, which specifically recognized the homologous antigen. The DHF group showed more enhancement of ZIKV infection of FCRγ-expressing cells compared to the DF group. Furthermore, the DHF group also showed a higher cross-neutralizing ability than that of DF. This is the first report where DF and DHF serum samples were evaluated for cross-reactivity against Zika protein and ZIKV. Furthermore, DENV serum samples cross-protect against ZIKV through neutralizing antibodies but at the same time mediate antibody-dependent enhancement in the sequential ZIKV infection.

Therapeutic Advances Against ZIKV: A Quick Response, a Long Way to Go

Zika virus (ZIKV) is a mosquito-borne flavivirus that spread throughout the American continent in 2015 causing considerable worldwide social and health alarm due to its association with ocular lesions and microcephaly in newborns, and Guillain-Barré syndrome (GBS) cases in adults. Nowadays, no licensed vaccines or antivirals are available against ZIKV, and thus, in this very short time, the scientific community has conducted enormous efforts to develop vaccines and antivirals. So that, different platforms (purified inactivated and live attenuated viruses, DNA and RNA nucleic acid based candidates, virus-like particles, subunit elements, and recombinant viruses) have been evaluated as vaccine candidates. Overall, these vaccines have shown the induction of vigorous humoral and cellular responses, the decrease of viremia and viral RNA levels in natural target organs, the prevention of vertical and sexual transmission, as well as that of ZIKV-associated malformations, and the protection of experimental animal models. Some of these vaccine candidates have already been assayed in clinical trials. Likewise, the search for antivirals have also been the focus of recent investigations, with dozens of compounds tested in cell culture and a few in animal models. Both direct acting antivirals (DAAs), directed to viral structural proteins and enzymes, and host acting antivirals (HAAs), directed to cellular factors affecting all steps of the viral life cycle (binding, entry, fusion, transcription, translation, replication, maturation, and egress), have been evaluated. It is expected that this huge collaborative effort will produce affordable and effective therapeutic and prophylactic tools to combat ZIKV and other related still unknown or nowadays neglected flaviviruses. Here, a comprehensive overview of the advances made in the development of therapeutic measures against ZIKV and the questions that still have to be faced are summarized.

Infectivity of Zika virus on primary cells support tree shrew as animal model

Zika virus (ZIKV) is a mosquito-borne flavivirus that caused the public health emergency. Recently, we have proved a novel small animal tree shrew was susceptive to ZIKV infection and presented the most common rash symptoms as ZIKV patients. Here we further cultured the primary cells from different tissues of this animal to determine the tissue tropism of ZIKV infection in vitro. The results showed that the primary cells from tree shrew kidney, lung, liver, skin and aorta were permissive to ZIKV infection and could support viral replication by the detection of viral specific RNA intra- and extra-cells. In comparing, the skin fibroblast and vascular endothelial cells were highly permissive to ZIKV infection with high releasing of active virus particles in supernatants proved by its infectivity in established neonatal mouse model. The expressions of ZIKV envelop and nonstructural protein-1, and the effects and strong immune response of primary tree shrew cells were also detected followed by ZIKV infection. These findings provide powerful in vitro cell-level evidence to support tree shrew as animal model of ZIKV infection and may help to explain the rash manifestations in vivo.

The E3 ligase TRIM56 is a host restriction factor of Zika virus and depends on its RNA-binding activity but not miRNA regulation, for antiviral function

Infection by Zika virus (ZIKV) is linked to microcephaly and other neurological disorders, posing a significant health threat. Innate immunity is the first line of defense against invading pathogens, but relatively little is understood regarding host intrinsic mechanisms that guard against ZIKV. Here, we show that host tripartite motif-containing protein 56 (TRIM56) poses a barrier to ZIKV infection in cells of neural, epithelial and fibroblast origins. Overexpression of TRIM56, but not an E3 ligase-dead mutant or one lacking a short C-terminal portion, inhibited ZIKV RNA replication. Conversely, depletion of TRIM56 increased viral RNA levels. Although the C-terminal region of TRIM56 bears sequence homology to NHL repeat of TRIM-NHL proteins that regulate miRNA activity, knockout of Dicer, which abolishes production of miRNAs, had no demonstrable effect on ZIKV restriction imposed by TRIM56. Rather, we found that TRIM56 is an RNA-binding protein that associates with ZIKV RNA in infected cells. Moreover, a recombinant TRIM56 fragment comprising the C-terminal 392 residues captured ZIKV RNA in cell-free reactions, indicative of direct interaction. Remarkably, deletion of a short C-terminal tail portion abrogated the TRIM56-ZIKV RNA interaction, concomitant with a loss in antiviral activity. Altogether, our study reveals TRIM56 is an RNA binding protein that acts as a ZIKV restriction factor and provides new insights into the antiviral mechanism by which this E3 ligase tackles flavivirus infections.

A Chimeric Zika Virus between Viral Strains MR766 and BeH819015 Highlights a Role for E-glycan Loop in Antibody-mediated Virus Neutralization

Zika virus (ZIKV) is an emerging mosquito-borne flavivirus which is of major public health concern. ZIKV infection is recognized as the cause of congenital Zika disease and other neurological defects, with no specific prophylactic or therapeutic treatments. As the humoral immune response is an essential component of protective immunity, there is an urgent need for effective vaccines that confer protection against ZIKV infection. In the present study, we evaluate the immunogenicity of chimeric viral clone ZIKBeHMR-2, in which the region encoding the structural proteins of the African strain MR766 backbone was replaced with its counterpart from the epidemic strain BeH819015. Three amino-acid substitutions I152T, T156I, and H158Y were introduced in the glycan loop of the E protein (E-GL) making ZIKBeHMR-2 a non-glycosylated virus. Adult BALB/c mice inoculated intraperitoneally with ZIKBeHMR-2 developed anti-ZIKV antibodies directed against viral proteins E and NS1 and a booster dose increased antibody titers. Immunization with ZIKBeHMR-2 resulted in a rapid production of neutralizing anti-ZIKV antibodies. Antibody-mediated ZIKV neutralization was effective against viral strain MR766, whereas epidemic ZIKV strains were poorly sensitive to neutralization by anti-ZIKBeHMR-2 immune sera. From our data, we propose that the three E-GL residues at positions E-152, E-156, and E-158 greatly influence the accessibility of neutralizing antibody epitopes on ZIKV.

Expression and purification of domain III proteins from Dengue and Zika viruses

The envelope (E) protein from Dengue and Zika viruses comprises three functional and structural domains (DI, DII, and DIII). Domain III induces most of the neutralizing antibodies and, as such, is considered as having the highest antigenic potential for the evaluation of population-level surveillance and for detecting past infections in both Dengue and Zika patients. The present study aimed to clone and express recombinant proteins of domain III from Dengue virus serotype 2 and from Zika virus in a prokaryotic system, as well as evaluate their immunogenicity and cross-reactivity. Both antigens were successfully purified and their antigenicity was assessed in mice. The antibodies elicited by domain III of Zika and Dengue virus antigens recognized specifically the native proteins in infected cells. Furthermore, the antigens showed a more specific immunogenic response than that of domain III proteins from Dengue virus. The generated recombinant proteins can be potentially used in subunit vaccines or for surveillance studies.

Autophagy in Zika Virus Infection: A Possible Therapeutic Target to Counteract Viral Replication

Zika virus (ZIKV) still constitutes a public health concern, however, no vaccines or therapies are currently approved for treatment. A fundamental process involved in ZIKV infection is autophagy, a cellular catabolic pathway delivering cytoplasmic cargo to the lysosome for degradation—considered as a primordial form of innate immunity against invading microorganisms. ZIKV is thought to inhibit the Akt-mTOR signaling pathway, which causes aberrant activation of autophagy promoting viral replication and propagation. It is therefore appealing to study the role of autophagic molecular effectors during viral infection to identify potential targets for anti-ZIKV therapeutic intervention.

The Roles of prM-E Proteins in Historical and Epidemic Zika Virus-mediated Infection and Neurocytotoxicity

The Zika virus (ZIKV) was first isolated in Africa in 1947. It was shown to be a mild virus that had limited threat to humans. However, the resurgence of the ZIKV in the most recent Brazil outbreak surprised us because it causes severe human congenital and neurologic disorders including microcephaly in newborns and Guillain-Barré syndrome in adults. Studies showed that the epidemic ZIKV strains are phenotypically different from the historic strains, suggesting that the epidemic ZIKV has acquired mutations associated with the altered viral pathogenicity. However, what genetic changes are responsible for the changed viral pathogenicity remains largely unknown. One of our early studies suggested that the ZIKV structural proteins contribute in part to the observed virologic differences. The objectives of this study were to compare the historic African MR766 ZIKV strain with two epidemic Brazilian strains (BR15 and ICD) for their abilities to initiate viral infection and to confer neurocytopathic effects in the human brain’s SNB-19 glial cells, and further to determine which part of the ZIKV structural proteins are responsible for the observed differences. Our results show that the historic African (MR766) and epidemic Brazilian (BR15 and ICD) ZIKV strains are different in viral attachment to host neuronal cells, viral permissiveness and replication, as well as in the induction of cytopathic effects. The analysis of chimeric viruses, generated between the MR766 and BR15 molecular clones, suggests that the ZIKV E protein correlates with the viral attachment, and the C-prM region contributes to the permissiveness and ZIKV-induced cytopathic effects. The expression of adenoviruses, expressing prM and its processed protein products, shows that the prM protein and its cleaved Pr product, but not the mature M protein, induces apoptotic cell death in the SNB-19 cells. We found that the Pr region, which resides on the N-terminal side of prM protein, is responsible for prM-induced apoptotic cell death. Mutational analysis further identified four amino-acid residues that have an impact on the ability of prM to induce apoptosis. Together, the results of this study show that the difference of ZIKV-mediated viral pathogenicity, between the historic and epidemic strains, contributed in part the functions of the structural prM-E proteins.

Investigational drugs for the treatment of Zika virus infection: a preclinical and clinical update

INTRODUCTION

The Zika virus (ZIKV) infection results in severe neurological complications and has emerged as a threat to public health worldwide. No drugs or vaccines are available for use in the clinic and the need for novel and effective therapeutic agents is urgent.

AREAS COVERED

This review describes the latest progress of antiviral development for the treatment of ZIKV infection; it primarily focuses on the literature describing 20 potential anti-ZIKV drugs/agents currently being tested in vivo or in clinical trials. The paper also discusses the need for novel ZIKV inhibitors and the critical issues for successful antiviral drug development.

EXPERT OPINION

So far, 20 compounds have been tested in vivo and three in the clinical trials; progressing these compounds to the clinic is a challenge. Novel ZIKV inhibitors that target virus or host factors are urgently needed. Knowledge-driven drug repurposing, structure-based discovery, RNA interference, long noncoding RNAs, miRNAs, and peptide inhibitors may pave the way for the discovery of such novel agents.

Research Models and Tools for the Identification of Antivirals and Therapeutics against Zika Virus Infection

Zika virus recently re-emerged and caused global outbreaks mainly in Central Africa, Southeast Asia, the Pacific Islands and in Central and South America. Even though there is a declining trend, the virus continues to spread throughout different geographical regions of the world. Since its re-emergence in 2015, massive advances have been made regarding our understanding of clinical manifestations, epidemiology, genetic diversity, genomic structure and potential therapeutic intervention strategies. Nevertheless, treatment remains a challenge as there is no licensed effective therapy available. This review focuses on the recent advances regarding research models, as well as available experimental tools that can be used for the identification and characterization of potential antiviral targets and therapeutic intervention strategies.