Enterovirus 71 infection caused neuronal cell death and cytokine expression in cultured rat neural cells

GRP78 recognizes EV-F 3D protein and activates NF-κB to repress virus replication by interacting with CHUK/IKBKB

Enteroviruses are the causative agents associated with several human and animal diseases, posing a significant threat to human and animal health. As one of the host immune defense strategies, innate immunity plays a crucial role in defending against invading pathogens, where the host utilizes a variety of mechanisms to inhibit or eliminate the pathogen. Here, we report a new strategy for the host to repress enterovirus replication by the 78 kDa glucose-regulated protein (GRP78), also known as heat shock protein family A member 5 (HSPA5). The GRP78 recognizes the EV-encoded RNA-dependent RNA polymerases (RdRPs) 3D protein and interacts with the nuclear factor kappa B kinase complex (CHUK) and subunit beta gene (IKBKB) to facilitate the phosphorylation and nuclear translocation of NF-κB, which induces the production of inflammatory factors and leads to a broad inhibition of enterovirus replication. These findings demonstrate a new role of GRP78 in regulating host innate immunity in response to viral infection and provide new insights into the mechanism underlying enterovirus replication and NF-κB activation.IMPORTANCEGRP78 is known as a molecular chaperone for protein folding and plays a critical role in maintaining protein folding and participating in cell proliferation, cell survival, apoptosis, and metabolism. However, the functions of GRP78 to participate in enterovirus genome replication and innate immune responses are rarely documented. In this study, we explored the functions of the EV-3D-interacting protein GRP78 and found that GRP78 inhibits enterovirus replication by activating NF-κB through binding to EV-F 3D and interacting with the NF-κB signaling molecules CHUK/IKBKB. This is the first report that GRP78 interacts with CHUK/IKBKB to activate the NF-κB signaling pathway, which leads to the expression of the proinflammatory cytokines and inhibition of enterovirus replication. These results demonstrate a unique mechanism of virus replication regulation by GRP78 and provide insights into the prevention and treatment of viral infections.

Chemoproteomics enables identification of coatomer subunit zeta-1 targeted by a small molecule for enterovirus A71 inhibition

Human enterovirus A71 (EV-A71) is a significant etiological agent responsible for epidemics of hand, foot, and mouth disease (HFMD) in Asia-Pacific regions. There are presently no licensed antivirals against EV-A71, and the druggable target for EV-A71 remains very limited. The phenotypic hit 10,10'-bis(trifluoromethyl) marinopyrrole A derivative, herein termed MPA-CF3, is a novel potent small-molecule inhibitor against EV-A71, but its pharmacological target(s) and antiviral mechanisms are not defined. Here, quantitative chemoproteomics deciphered the antiviral target of MAP-CF3 as host factor coatomer subunit zeta-1 (COPZ1). Mechanistically, MPA-CF3 disrupts the interaction of COPZ1 with the EV-A71 nonstructural protein 2C by destabilizing COPZ1 upon binding. The destruction of this interaction blocks the coatomer-mediated transport of 2C to endoplasmic reticulum, and ultimately inhibits EV-A71 replication. Taken together, our study disclosed that MPA-CF3 can be a structurally novel host-targeting anti-EV-A71 agent, providing a structural basis for developing the COPZ1-targeting broad-spectrum antivirals against enteroviruses. The mechanistic elucidation of MPA-CF3 against EV-A71 may offer an alternative COPZ1-involved therapeutic pathway for enterovirus infection.

Molecular Mechanisms Associated with Neurodegeneration of Neurotropic Viral Infection

Viral infections of the central nervous system (CNS) cause variable outcomes from acute to severe neurological sequelae with increased morbidity and mortality. Viral neuroinvasion directly or indirectly induces encephalitis via dysregulation of the immune response and contributes to the alteration of neuronal function and the degeneration of neuronal cells. This review provides an overview of the cellular and molecular mechanisms of virus-induced neurodegeneration. Neurotropic viral infections influence many aspects of neuronal dysfunction, including promoting chronic inflammation, inducing cellular oxidative stress, impairing mitophagy, encountering mitochondrial dynamics, enhancing metabolic rewiring, altering neurotransmitter systems, and inducing misfolded and aggregated pathological proteins associated with neurodegenerative diseases. These pathogenetic mechanisms create a multidimensional injury of the brain that leads to specific neuronal and brain dysfunction. The understanding of the molecular mechanisms underlying the neurophathogenesis associated with neurodegeneration of viral infection may emphasize the strategies for prevention, protection, and treatment of virus infection of the CNS.

Modulation of plasmacytoid dendritic cell and CD4+ T cell differentiation accompanied by upregulation of the cholinergic anti-inflammatory pathway induced by enterovirus 71

Enterovirus 71 (EV71) is a neurotropic enterovirus associated with hand, foot, and mouth disease (HFMD) fatalities. In this study, we investigated the impact of EV71 on plasmacytoid dendritic cells (pDCs) and CD4+ T cells. The results showed that pDCs were promptly activated, secreting interferon (IFN)-α and inducing CD4+ T cell proliferation and differentiation during early EV71 infection. This initiated adaptive immune responses and promoted proinflammatory cytokine production by CD4+ T cells. Over time, viral nucleic acids and proteins were synthesized in pDCs and CD4+ T cells. Concurrently, the cholinergic anti-inflammatory pathway (CAP) was activated, exhibiting an anti-inflammatory role. With constant viral stimulation, pDCs and CD4+ T cells showed reduced differentiation and cytokine secretion. Defects in pDCs were identified as a key factor in CD4+ T cell tolerance. CAP had a more significant regulatory effect on CD4+ T cells than on pDCs and was capable of inhibiting inflammation in these cells.

Frequency and Focus of in Vitro Studies of Microglia-Expressed Cytokines in Response to Viral Infection: A Systematic Review

It is well known that as part of their response to infectious agents such as viruses, microglia transition from a quiescent state to an activated state that includes proinflammatory and anti-inflammatory phases; this behavior has been described through in vitro studies. However, recent in vivo studies on the function of microglia have questioned the two-phase paradigm; therefore, a change in the frequency of in vitro studies is expected. A systematic review was carried out to identify the microglial cytokine profile against viral infection that has been further evaluated through in vitro studies (pro-inflammatory or anti-inflammatory), along with analysis of its publication frequency over the years. For this review, 531 articles published in the English language were collected from PubMed, Web of Science, EBSCO and ResearchGate. Only 27 papers met the inclusion criteria for this systematic review. In total, 19 cytokines were evaluated in these studies, most of which are proinflammatory; the most common are IL-6, followed by TNF-α and IL-1β. It should be pointed out that half of the studies were published between 2015 and 2022 (raw data available in https://github.com/dadriba05/SystematicReview.git ). In this review, we identified that evaluation of pro-inflammatory cytokines released by microglia against viral infections has been performed more frequently than that of anti-inflammatory cytokines; additionally, a higher frequency of evaluation of the response of microglia cells to viral infection through in vitro studies from 2015 and beyond was noted.

Understanding the Neurotrophic Virus Mechanisms and Their Potential Effect on Systemic Lupus Erythematosus Development

Central nervous system (CNS) pathologies are a public health concern, with viral infections one of their principal causes. These viruses are known as neurotropic pathogens, characterized by their ability to infiltrate the CNS and thus interact with various cell populations, inducing several diseases. The immune response elicited by neurotropic viruses in the CNS is commanded mainly by microglia, which, together with other local cells, can secrete inflammatory cytokines to fight the infection. The most relevant neurotropic viruses are adenovirus (AdV), cytomegalovirus (CMV), enterovirus (EV), Epstein-Barr Virus (EBV), herpes simplex virus type 1 (HSV-1), and herpes simplex virus type 2 (HSV-2), lymphocytic choriomeningitis virus (LCMV), and the newly discovered SARS-CoV-2. Several studies have associated a viral infection with systemic lupus erythematosus (SLE) and neuropsychiatric lupus (NPSLE) manifestations. This article will review the knowledge about viral infections, CNS pathologies, and the immune response against them. Also, it allows us to understand the relevance of the different viral proteins in developing neuronal pathologies, SLE and NPSLE.

Human brain organoids to explore SARS-CoV-2-induced effects on the central nervous system

Severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). In less than three years, an estimated 600 million infections with SARS-CoV-2 occurred worldwide, resulting in a pandemic with tremendous impact especially on economic and health sectors. Initially considered a respiratory disease, COVID-19, along with its long-term sequelae (long-COVID) rather is a systemic disease. Neurological symptoms like dementia or encephalopathy were reported early during the pandemic as concomitants of the acute phase and as characteristics of long-COVID. An excessive inflammatory immune response is hypothesized to play a major role in this context. However, direct infection of neural cells may also contribute to the neurological aspects of (long)-COVID-19. To mainly explore such direct effects of SARS-CoV-2 on the central nervous system, human brain organoids provide a useful platform. Infecting these three-dimensional tissue cultures allows the study of viral neurotropism as well as of virus-induced effects on single cells or even the complex cellular network within the organoid. In this review, we summarize the experimental studies that used SARS-CoV-2-infected human brain organoids to unravel the complex nature of (long)-COVID-19-related neurological manifestations.

The internal ribosome entry site determines the neurotropic potential of enterovirus A71

The mechanisms underlying tissue-specific replication of enteroviruses are currently unclear. Although enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16) are both common pathogens that cause hand-foot-mouth disease, they display quite different neurotropic properties. Herein, we characterized the role of the internal ribosomal entry site (IRES) in determining neurovirulence using an oral inoculation model of EV-A71. The receptor transgenic (hSCARB2-Tg) mice developed neurological symptoms after being infected with a mouse-adapted EV-A71 strain (MP4) via different administrative routes. Intragastric administration of the MP4 strain caused pathological changes such as neuronal loss and neuropil vacuolation, whereas replacing EV-A71 IRES with CV-A16 abolished the neuropathological phenotypes. The attenuated neurotropic potential of IRES-swapped EV-A71 was observed even in mice that received intraperitoneal and intracerebral inoculations. Fewer chimeric MP4 viral RNAs and proteins were detected in the mouse tissues, regardless of the inoculation route. Tissue-specific replication can be reflected in cell-based characterization. While chimeric MP4 virus replicated poorly in human intestinal C2BBe1 and neuroblastoma SH-SY5Y cells, its replication in susceptible rhabdomyosarcoma cells was not affected. Overall, our results demonstrated that the IRES determined the neurotropic potential of EV-A71 and CV-A16, emphasizing the importance of the IRES in tissue tropism, along with the host receptors.

The Influence of Virus Infection on Microglia and Accelerated Brain Aging

Microglia are the resident immune cells of the central nervous system contributing substantially to health and disease. There is increasing evidence that inflammatory microglia may induce or accelerate brain aging, by interfering with physiological repair and remodeling processes. Many viral infections affect the brain and interfere with microglia functions, including human immune deficiency virus, flaviviruses, SARS-CoV-2, influenza, and human herpes viruses. Especially chronic viral infections causing low-grade neuroinflammation may contribute to brain aging. This review elucidates the potential role of various neurotropic viruses in microglia-driven neurocognitive deficiencies and possibly accelerated brain aging.

Antiviral activity of sophoridine against enterovirus 71 in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Enterovirus 71 (EV71) has a propensity to cause hand-foot-and-mouth disease (HFMD) epidemics associated with neurological sequelae. Unfortunately, no drugs are currently available for the clinical treatment of EV71 infections. Sophoridine (SRI) is one of the most abundant alkaloids in Sophora flavescens Aiton (Leguminosae), which has been used to treat fever, throat inflammation, cancer, and other diseases.

MATERIALS AND METHODS

In this study, we found that SRI inhibits EV71 infection in Vero cells. To study the antiviral activity of SRI, Vero cells were divided into 3 treatment groups based on the timing of SRI dosing: prior to viral adsorption (Group A), during viral adsorption (Group B), and after viral adsorption (Group C). We further revealed the antiviral activity of SRI with the attachment assay and the penetration assay. For Group A, 50% viability of Vero cells was observed at a SRI concentration of 61.39 μg/mL, whereas for Groups B, 50% viability was observed at SRI concentrations of 196.86 μg/mL. Furthermore, 29.7% cell viability was observed even at a SRI concentration of 1000 μg/mL in Groups C. The results show that SRI was highly effective against EV71 when Vero cells were pretreated with SRI for 2 h (Group A). Further researches indicate SRI was highly effective at inhibiting EV71 attachment when the SRI concentrations over 250 μg/mL (P < 0.001).

CONCLUSIONS

We have shown that Vero cell viability increases when SRI is administered prior to viral adsorption. This suggests that SRI has the considerable potential as an antiviral for EV71 disease prevention.

The untranslated regions of EV-A71 contribute to its pathogenicity and virulence

Enterovirus A71 (EV-A71) is known for its manifestation as hand foot and mouth disease (HFMD), which has caused countless large-scale epidemic outbreaks throughout the world. However, the molecular pathogenesis of EV-A71 infection is still elusive. Previous studies found that the biological characteristics of a mild EV-A71 strain (SDLY1) and a severe EV-A71 strain (SDLY107) are significantly different, and sequence analysis showed that there are several differences in nucleotide sites of UTRs (88 nt, 123 nt, 143 nt, 154 nt, 187 nt, 241 nt, 243 nt, 253 nt, 291 nt, 438 nt, 440 nt, 571 nt, 579 nt, 602 nt, 658 nt, 664 nt, 690 nt, 696 nt, 7328 nt, 7335 nt, 7367 nt, and 7395 nt). The aim of this study was to determine whether these amino sites in UTRs are associated with the pathogenesis of EV-A71 and are responsible for different clinical manifestations. Based on the reverse genetics technology, we rescued two chimeric viruses SDLY107(1-5'UTR) and SDLY107(1-3'UTR) by replacing 5'UTR/3'UTR gene fragments of an infectious cDNA clone. Replication kinetics and cytotoxicity assays showed that the virulence of the two chimeric strains significantly changed in vitro. The viral loads of the two chimeric strains in infected ICR mice were reduced and pathological damage in the brains, lungs, intestinal tissues, and muscles were lightened. Our findings suggest that some nucleotide sites in UTRs may have a function in the pathogenicity and virulence of EV-A71.

Pyroptosis induced by enterovirus A71 infection in cultured human neuroblastoma cells

Enterovirus A71 (EV-A71) infection can cause hand, foot and mouth disease (HFMD), and even fatal meningoencephalitis. Unfortunately, there is currently no effective treatment for EV-A71 infection due to the lack of understanding of the mechanism of neurological diseases. In this study, we employed SH-SY5Y human neuroblastoma cells to explore the roles of caspase-1 in neuropathogenesis. The expression and activity of caspase-1 were analyzed. The potential immuneconsequences mediated by caspase-1 including cell death, lysis, DNA degradation, and secretion of pro-inflammatory were also examined. We found the gene expression levels of caspase-1, IL-1β, IL-18 and active caspase-1 were markedly increased in the SH-SY5Y cells at 48 h post EV-A71 infection. The cell death, lysis, and DNA degradation were also increased during infection, which could be significantly alleviated by caspase-1 inhibition. These observations provided additional experimental evidence supporting caspase-1-mediated pyroptosis as a novel pathway of inflammatory programmed cell death.

Antiviral and Inflammatory Cellular Signaling Associated with Enterovirus 71 Infection

Enterovirus 71 (EV71) infection has become a major threat to global public health, especially in infants and young children. Epidemiological studies have indicated that EV71 infection is responsible for severe and even fatal cases of hand, foot, and mouth disease (HFMD). Accumulated evidence indicates that EV71 infection triggers a plethora of interactive signaling pathways, resulting in host immune evasion and inflammatory response. This review mainly covers the effects of EV71 infection on major antiviral and inflammatory cellular signal pathways. EV71 can activate cellular signaling networks including multiple cell surface and intracellular receptors, intracellular kinases, calcium flux, and transcription factors that regulate antiviral innate immunity and inflammatory response. Cellular signaling plays a critical role in the regulation of host innate immune and inflammatory pathogenesis. Elucidation of antiviral and inflammatory cellular signaling pathways initiated by EV71 will not only help uncover the potential mechanisms of EV71 infection-induced pathogenesis, but will also provide clues for the design of therapeutic strategies against EV71 infection.

Pyroptosis induced by enterovirus 71 and coxsackievirus B3 infection affects viral replication and host response

Enterovirus 71 (EV71) is the primary causative pathogen of hand, foot, and mouth disease (HFMD), affecting children with severe neurological complications. Pyroptosis is a programmed cell death characterized by cell lysis and inflammatory response. Although proinflammatory response has been implicated to play important roles in EV71-caused diseases, the involvement of pyroptosis in the pathogenesis of EV71 is poorly defined. We show that EV71 infection induced caspase-1 activation. Responding to the activation of caspase-1, the expression and secretion of both IL-1β and IL-18 were increased in EV71-infected cells. The treatment of caspase-1 inhibitor markedly improved the systemic response of the EV71-infected mice. Importantly, caspase-1 inhibitor suppressed EV71 replication in mouse brains. Similarly, pyroptosis was activated by the infection of coxsackievirus B3 (CVB3), an important member of the Enterovirus genus. Caspase-1 activation and the increased expression of IL-18 and NLRP3 were demonstrated in HeLa cells infected with CVB3. Caspase-1 inhibitor also alleviated the overall conditions of virus-infected mice with markedly decreased replication of CVB3 and reduced expression of caspase-1. These results indicate that pyroptosis is involved in the pathogenesis of both EV71 and CVB3 infections, and the treatment of caspase-1 inhibitor is beneficial to the host response during enterovirus infection.

Immunopathogenesis and Virus-Host Interactions of Enterovirus 71 in Patients with Hand, Foot and Mouth Disease

Enterovirus 71 (EV71) is a global infectious disease that affects millions of people. The virus is the main etiological agent for hand, foot, and mouth disease with outbreaks and epidemics being reported globally. Infection can cause severe neurological, cardiac, and respiratory problems in children under the age of 5. Despite on-going efforts, little is known about the pathogenesis of EV71, how the host immune system responds to the virus and the molecular mechanisms behind these responses. Moreover, current animal models remain limited, because they do not recapitulate similar disease patterns and symptoms observed in humans. In this review the role of the host-viral interactions of EV71 are discussed together with the various models available to examine: how EV71 utilizes its proteins to cleave host factors and proteins, aiding virus replication; how EV71 uses its own viral proteins to disrupt host immune responses and aid in its immune evasion. These discoveries along with others, such as the EV71 crystal structure, have provided possible targets for treatment and drug interventions.

Involvement of inducible nitric oxide synthase and mitochondrial dysfunction in the pathogenesis of enterovirus 71 infection

Enterovirus71 (EV71) is recognized as the main causative agent of severe hand, foot and mouth disease (HFMD). However, the pathogenesis of EV71 infection has not been well characterized. Clinical evidence indicated that inducible nitric oxide synthase (iNOS) induction in the lung of HFMD patients contributes to the severe symptoms of pulmonary edema. In the present study, we recruited 142 subjects including HFMD patients and controls, and serum level of nitric oxide (NO) was determined. Next, cellular and animal model were used to further investigate the roles of iNOS and mitochondria damage during EV71 infection. Serum NO level in HFMD patients with mild or severe symptoms was higher than that in controls, and there was a trend towards an increase in the serum NO level of severe cases relative to mild cases. EV71 infection caused apoptosis and increased levels of NO, iNOS, superoxide dismutase (SOD) activity and malondialdehyde (MDA), and degraded mitochondrial membrane potential (ΔΨm) in vitro. Pathological alterations of mitochondrial morphology were observed in vitro and in vivo. Furthermore, the expression of iNOS levels in target organs including brain, spinal cord, skeletal muscle, lung and heart were increased with the progression of the pathogenesis of EV71 infection in mice. Taken together, iNOS and mitochondrial damage participate in the pathogenesis of EV71 infection.

Susceptibility of naïve and differentiated PC12 cells to Japanese encephalitis virus infection

Japanese encephalitis is a mosquito-borne disease caused by Japanese encephalitis virus (JEV) infection. Although JEV infects and replicates in cells with multiple tissue origins, neurons are the preferential cells for JEV infection. Currently, the identities of JEV cell tropism are largely unclear. To gain better insight into the underlying identities of JEV cell tropism, this study was designed to compare the JEV cell tropism with naïve or differentiated PC12 cells. Through nerve growth factor-differentiated PC12 cells, we discovered that JEV efficiently replicated in differentiated PC12 cells rather than naïve cells. Mechanistic studies revealed that viral adsorption/attachment seemed not to be a crucial factor. Supporting data showed that antagonizing postreceptor intracellular signaling of interferons, along with the activation of suppressor of cytokine signaling-3 (SOCS3) expression and protein tyrosine phosphatase activity, were apparent in differentiated PC12 cells after JEV infection. Independent of differentiating inducing agents, the upregulation of SOCS3 expression and protein tyrosine phosphatase activity, as well as preferential JEV tropism, were common in JEV-infected differentiated PC12 cells. Using cultured primary neurons, JEV efficiently replicated in embryonic neurons rather than adult neurons, and the preference was accompanied by higher SOCS3 expression and protein tyrosine phosphatase activity. Given that both SOCS3 and protein tyrosine phosphatases have been implicated in the process of neuronal differentiation, JEV infection seems to not only create an antagonizing strategy to escape host's interferon antiviral response but also takes advantage of cellular machinery to favor its replication. Taken together, current findings imply that dynamic changes within cellular regulators of antiviral machinery could be accompanied by events of neuronal differentiation, thus concurrently playing roles in the control of JEV cell tropism and replication. © 2017 IUBMB Life, 69(2):79-87, 2017.