Neural stem cell depletion and CNS developmental defects after enteroviral infection

The knowns and unknowns of cardiac autoimmunity in viral myocarditis

Myocarditis can result from various infectious and non-infectious causes that can lead to dilated cardiomyopathy (DCM) and heart failure. Among the infectious causes, viruses are commonly suspected. But the challenge is our inability to demonstrate infectious viral particles during clinical presentations, partly because by that point, the viruses would have damaged the tissues and be cleared by the immune system. Therefore, viral signatures such as viral nucleic acids and virus-reactive antibodies may be the only readouts pointing to viruses as potential primary triggers of DCM. Thus, it becomes hard to explain persistent inflammatory infiltrates that might occur in individuals affected with chronic myocarditis/DCM manifesting myocardial dysfunctions. In these circumstances, autoimmunity is suspected, and antibodies to various autoantigens have been demonstrated, suggesting that immune therapies to suppress the autoimmune responses may be necessary. From this perspective, we endeavoured to determine whether or not the known viral causes are associated with development of autoimmune responses to cardiac antigens that include both cardiotropic and non-cardiotropic viruses. If so, what their nature and significance are in developing chronic myocarditis resulting from viruses as primary triggers.

Transcriptome sequencing analysis of echovirus 30 infection reveals its potential pathogenesis

Echovirus 30 (E30) causes various diseases, such as viral encephalitis; aseptic meningitis; hand, foot, and mouth diseases; and acute flaccid paralysis. Related neurological infections are most concerning. However, the molecular mechanisms of E30 pathogenesis are not fully understood. There is a growing research interest in E30 as a cause of neurological disease. The aim of this study was to describe E30 infection, especially the changes in differential factor expressions after infection, in human glioma (U251) cells and mice brains using transcriptome sequencing analysis. Clear changes in the gene expression of factors associated with the defense response to viruses, inflammation-related signaling pathways, and neurological complication-related pathways were observed. Our results suggest that after E30 infection, the genes related to immune response were induced in the human glioma cells and mice brains, whereas genes functioning in the development and function of neural tissue were inhibited. Overall, this study successfully established E30 infection of U251 and mouse brain tissue, profiled the infection-induced changes in cellular and organizational transcriptomes, and revealed the molecular level changes during E30 infection.

Harmine and 7,8-dihydroxyflavone synergistically suitable for amyotrophic lateral sclerosis management: An in silico study

Introduction: Amyotrophic lateral sclerosis (ALS) is a fatal neurological disease characterized by progressive degeneration of both upper and lower motor neurons, resulting in paralysis and eventually leads to death from respiratory failure typically within 3 to 5 years of symptom onset. The aim of this work was to predict the pharmacokinetics and identify unique protein targets that are associated with potential anti-ALS phytochemicals and FDA-approved drugs, by in silico approaches.

Materials and methods: Standard computational tools (webserver and software) were used, and the methods used are clustering analysis, pharmacokinetics and molecular target predictions, and molecular docking simulation.

Results and discussion: The results show that riluzole, β-asarone, cryptotanshinone, harmine and 7,8-dihydroxyflavone have similar pharmacokinetics properties. Riluzole and harmine show 95% probability of target on norepinephrine transporter. Huperzine-A and cryptotanshinone show 100% probability of target on acetylcholinesterase. 7,8-dihydroxyflavone shows 35% probability of target on several carbonic anhydrases, 40% probability of target on CYP19A1, and 100% probability of target on inhibitor of nuclear factor kappa B kinase beta subunit and neurotrophic tyrosine kinase receptor type 2, respectively. Harmine also shows 95% probability of target on dual specificity tyrosine-phosphorylation-regulated kinases, threonine-protein kinases (haspin and PIM3), adrenergic receptors, cyclin-dependent kinases (CDK5 and CDK9), monoamine oxidase A, casein kinase I delta, serotonin receptors, dual specificity protein kinases (CLK1, CLK2, and CLK4), and nischarin, respectively. Also, the results of gene expression network show possible involvement of CDK1, CDK2, CDK4, ERK1, ERK2 and MAPK14 signaling pathways. This study shows that riluzole and harmine have closely similar physicochemical and pharmacokinetics properties as well as molecular targets, such as norepinephrine transporter (SLC6A2). Harmine, huperzine-A and cryptotanshinone could modulate acetylcholinesterase (AChE), which is involved in ALS-pathogenesis. The impact of 7,8-dihydroxyflavone on several carbonic anhydrases (CA) I, II, VII, IX, XII, and XIV, as well as CYP19A1, could help in remediating the respiratory failure associated with ALS.

Conclusion: Overall, harmine is found to be superior to riluzole, and the combination of harmine with 7,8-dihydroxyflavone can provide more effective treatment for ALS than the current regime. Further work is needed to validate the predicted therapeutic targets of harmine identified in this study on ALS model or clinical trials, using in silico, in vitro and in vivo techniques.

Graphical abstract:

Sublethal enteroviral infection exacerbates disease progression in an ALS mouse model

Background

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of the motor neuron system associated with both genetic and environmental risk factors. Infection with enteroviruses, including poliovirus and coxsackievirus, such as coxsackievirus B3 (CVB3), has been proposed as a possible causal/risk factor for ALS due to the evidence that enteroviruses can target motor neurons and establish a persistent infection in the central nervous system (CNS), and recent findings that enteroviral infection-induced molecular and pathological phenotypes closely resemble ALS. However, a causal relationship has not yet been affirmed.

Methods

Wild-type C57BL/6J and G85R mutant superoxide dismutase 1 (SOD1^G85R) ALS mice were intracerebroventricularly infected with a sublethal dose of CVB3 or sham-infected. For a subset of mice, ribavirin (a broad-spectrum anti-RNA viral drug) was given subcutaneously during the acute or chronic stage of infection. Following viral infection, general activity and survival were monitored daily for up to week 60. Starting at week 20 post-infection (PI), motor functions were measured weekly. Mouse brains and/or spinal cords were harvested at day 10, week 20 and week 60 PI for histopathological evaluation of neurotoxicity, immunohistochemical staining of viral protein, neuroinflammatory/immune and ALS pathology markers, and NanoString and RT-qPCR analysis of inflammatory gene expression.

Results

We found that sublethal infection (mimicking chronic infection) of SOD1^G85R ALS mice with CVB3 resulted in early onset and progressive motor dysfunction, and shortened lifespan, while similar viral infection in C57BL/6J, the background strain of SOD1^G85R mice, did not significantly affect motor function and mortality as compared to mock infection within the timeframe of the current study (60 weeks PI). Furthermore, we showed that CVB3 infection led to a significant increase in proinflammatory gene expression and immune cell infiltration and induced ALS-related pathologies (i.e., TAR DNA-binding protein 43 (TDP-43) pathology and neuronal damage) in the CNS of both SOD1^G85R and C57BL/6J mice. Finally, we discovered that early (day 1) but not late (day 15) administration of ribavirin could rescue ALS-like neuropathology and symptoms induced by CVB3 infection.

Conclusions

Our study identifies a new risk factor that contributes to early onset and accelerated progression of ALS and offers opportunities for the development of novel targeted therapies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02380-7.

Neural Stem Cells: What Happens When They Go Viral?

Viruses that infect the central nervous system (CNS) are associated with developmental abnormalities as well as neuropsychiatric and degenerative conditions. Many of these viruses such as Zika virus (ZIKV), cytomegalovirus (CMV), and herpes simplex virus (HSV) demonstrate tropism for neural stem cells (NSCs). NSCs are the multipotent progenitor cells of the brain that have the ability to form neurons, astrocytes, and oligodendrocytes. Viral infections often alter the function of NSCs, with profound impacts on the growth and repair of the brain. There are a wide spectrum of effects on NSCs, which differ by the type of virus, the model system, the cell types studied, and the age of the host. Thus, it is a challenge to predict and define the consequences of interactions between viruses and NSCs. The purpose of this review is to dissect the mechanisms by which viruses can affect survival, proliferation, and differentiation of NSCs. This review also sheds light on the contribution of key antiviral cytokines in the impairment of NSC activity during a viral infection, revealing a complex interplay between NSCs, viruses, and the immune system.

CVB3-Mediated Mitophagy Plays an Important Role in Viral Replication via Abrogation of Interferon Pathways

Coxsackievirus B3 (CVB3) is a common enterovirus that causes systemic inflammatory diseases, such as myocarditis, meningitis, and encephalitis. CVB3 has been demonstrated to subvert host cellular responses via autophagy to support viral replication in neural stem cells. Mitophagy, a specialized form of autophagy, contributes to mitochondrial quality control via degrading damaged mitochondria. Here, we show that CVB3 infection induces mitophagy in human neural progenitor cells, HeLa and H9C2 cardiomyocytes. In particular, CVB3 infection triggers mitochondrial fragmentation, loss of mitochondrial membrane potential, and Parkin/LC3 translocation to the mitochondria. Rapamycin or carbonyl cyanide m-chlorophenyl hydrazone (CCCP) treatment led to increased CVB3 RNA copy number in a dose-dependent manner, suggesting enhanced viral replication via autophagy/mitophagy activation, whereas knockdown of PTEN-induced putative kinase protein 1(PINK1) led to impaired mitophagy and subsequent reduction in viral replication. Furthermore, CCCP treatment inhibits the interaction between mitochondrial antiviral signaling protein (MAVS) and TANK-binding kinase 1(TBK1), thus contributing to the abrogation of type I and III interferon (IFN) production, suggesting that mitophagy is essential for the inhibition of interferon signaling. Our findings suggest that CVB3-mediated mitophagy suppresses IFN pathways by promoting fragmentation and subsequent sequestration of mitochondria by autophagosomes.

Human Neural Stem Cell Systems to Explore Pathogen-Related Neurodevelopmental and Neurodegenerative Disorders

Building and functioning of the human brain requires the precise orchestration and execution of myriad molecular and cellular processes, across a multitude of cell types and over an extended period of time. Dysregulation of these processes affects structure and function of the brain and can lead to neurodevelopmental, neurological, or psychiatric disorders. Multiple environmental stimuli affect neural stem cells (NSCs) at several levels, thus impairing the normal human neurodevelopmental program. In this review article, we will delineate the main mechanisms of infection adopted by several neurotropic pathogens, and the selective NSC vulnerability. In particular, TORCH agents, i.e., Toxoplasma gondii, others (including Zika virus and Coxsackie virus), Rubella virus, Cytomegalovirus, and Herpes simplex virus, will be considered for their devastating effects on NSC self-renewal with the consequent neural progenitor depletion, the cellular substrate of microcephaly. Moreover, new evidence suggests that some of these agents may also affect the NSC progeny, producing long-term effects in the neuronal lineage. This is evident in the paradigmatic example of the neurodegeneration occurring in Alzheimer's disease.

Neuropathology in Neonatal Mice After Experimental Coxsackievirus B2 Infection Using a Prototype Strain, Ohio-1

Coxsackievirus B (CVB) causes severe morbidity and mortality in neonates and is sometimes associated with severe brain damage resulting from acute severe viral encephalomyelitis. However, the neuropathology of CVB infection remains unclear. A prototype strain of coxsackievirus B2 (Ohio-1) induces brain lesions in neonatal mice, resulting in dome-shaped heads, ventriculomegaly, and loss of the cerebral cortex. Here, we characterized the glial pathology in this mouse model. Magnetic resonance imaging revealed an absence of the cerebral cortex within 2 weeks after inoculation. Histopathology showed that virus replication triggered activation of microglia and astrocytes, and induced apoptosis in the cortex, with severe necrosis and lateral ventricular dilation. In contrast, the brainstem and cerebellum remained morphologically intact. Immunohistochemistry revealed high expression of the coxsackievirus and adenovirus receptor (a primary receptor for CVB) in mature neurons of the cortex, hippocampus, thalamus, and midbrain, demonstrating CVB2 infection of mature neurons in these areas. However, apoptosis and neuroinflammation from activated microglia and astrocytes differed in thalamic and cortical areas. Viral antigens were retained in the brains of animals in the convalescence phase with seroconversion. This animal model will contribute to a better understanding of the neuropathology of CVB infection.

Coxsackievirus B3 Infection of Human Neural Progenitor Cells Results in Distinct Expression Patterns of Innate Immune Genes

Coxsackievirus B3 (CVB3), a member of Picornaviridae family, is an important human pathogen that causes a wide range of diseases, including myocarditis, pancreatitis, and meningitis. Although CVB3 has been well demonstrated to target murine neural progenitor cells (NPCs), gene expression profiles of CVB3-infected human NPCs (hNPCs) has not been fully explored. To characterize the molecular signatures and complexity of CVB3-mediated host cellular responses in hNPCs, we performed QuantSeq 3′ mRNA sequencing. Increased expression levels of viral RNA sensors (RIG-I, MDA5) and interferon-stimulated genes, such as IFN-β, IP-10, ISG15, OAS1, OAS2, Mx2, were detected in response to CVB3 infection, while IFN-γ expression level was significantly downregulated in hNPCs. Consistent with the gene expression profile, CVB3 infection led to enhanced secretion of inflammatory cytokines and chemokines, such as interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1). Furthermore, we show that type I interferon (IFN) treatment in hNPCs leads to significant attenuation of CVB3 RNA copy numbers, whereas, type II IFN (IFN-γ) treatment enhances CVB3 replication and upregulates suppressor of cytokine signaling 1/3 (SOCS) expression levels. Taken together, our results demonstrate the distinct molecular patterns of cellular responses to CVB3 infection in hNPCs and the pro-viral function of IFN-γ via the modulation of SOCS expression.

Enterovirus and Encephalitis

Enterovirus-induced infection of the central nervous system (CNS) results in acute inflammation of the brain (encephalitis) and constitutes a significant global burden to human health. These viruses are thought to be highly cytolytic, therefore normal brain function could be greatly compromised following enteroviral infection of the CNS. A further layer of complexity is added by evidence showing that some enteroviruses may establish a persistent infection within the CNS and eventually lead to pathogenesis of certain neurodegenerative disorders. Interestingly, enterovirus encephalitis is particularly common among young children, suggesting a potential causal link between the development of the neuroimmune system and enteroviral neuroinvasion. Although the CNS involvement in enterovirus infections is a relatively rare complication, it represents a serious underlying cause of mortality. Here we review a selection of enteroviruses that infect the CNS and discuss recent advances in the characterization of these enteroviruses with regard to their routes of CNS infection, tropism, virulence, and immune responses.

Understanding the Role of Antiviral Cytokines and Chemokines on Neural Stem/Progenitor Cell Activity and Survival

Viral infections of the central nervous system are accompanied by the expression of cytokines and chemokines that can be critical for the control of viral replication in the brain. The outcomes of cytokine/chemokine signaling in neural cells vary widely, with cell-specific effects on cellular activity, proliferation, and survival. Neural stem/progenitor cells (NSPCs) are often altered during viral infections, through direct infection by the virus or by the influence of immune cell activity or cytokine/chemokine signaling. However, it has been challenging to dissect the contribution of the virus and specific inflammatory mediators during an infection. In addition to initiating an antiviral program in infected NSPCs, cytokines/chemokines can induce multiple changes in NSPC behavior that can perturb NSPC numbers, differentiation into other neural cells, and migration to sites of injury, and ultimately brain development and repair. The focus of this review was to dissect the effects of common antiviral cytokines and chemokines on NSPC activity, and to consider the subsequent pathological consequences for the host from changes in NSPC function.

Promoting remyelination through cell transplantation therapies in a model of viral-induced neurodegenerative disease

Multiple sclerosis (MS) is a central nervous system (CNS) disease characterized by chronic neuroinflammation, demyelination, and axonal damage. Infiltration of activated lymphocytes and myeloid cells are thought to be primarily responsible for white matter damage and axonopathy. Several United States Food and Drug Administration-approved therapies exist that impede activated lymphocytes from entering the CNS thereby limiting new lesion formation in patients with relapse-remitting forms of MS. However, a significant challenge within the field of MS research is to develop effective and sustained therapies that allow for axonal protection and remyelination. In recent years, there has been increasing evidence that some kinds of stem cells and their derivatives seem to be able to mute neuroinflammation as well as promote remyelination and axonal integrity. Intracranial infection of mice with the neurotropic JHM strain of mouse hepatitis virus (JHMV) results in immune-mediated demyelination and axonopathy, making this an excellent model to interrogate the therapeutic potential of stem cell derivatives in evoking remyelination. This review provides a succinct overview of our recent findings using intraspinal injection of mouse CNS neural progenitor cells and human neural precursors into JHMV-infected mice. JHMV-infected mice receiving these cells display extensive remyelination associated with axonal sparing. In addition, we discuss possible mechanisms associated with sustained clinical recovery. Developmental Dynamics 248:43-52, 2019. © 2018 Wiley Periodicals, Inc.

Enteroviral Infection: The Forgotten Link to Amyotrophic Lateral Sclerosis?

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that primarily attacks motor neurons in the brain and spinal cord, leading to progressive paralysis and ultimately death. Currently there is no effective therapy. The majority of ALS cases are sporadic, with no known family history; unfortunately the etiology remains largely unknown. Contribution of Enteroviruses (EVs), a family of positive-stranded RNA viruses including poliovirus, coxsackievirus, echovirus, enterovirus-A71 and enterovirus-D68, to the development of ALS has been suspected as they can target motor neurons, and patients with prior poliomyelitis show a higher risk of motor neuron disease. Multiple efforts have been made to detect enteroviral genome in ALS patient tissues over the past two decades; however the clinical data are controversial and a causal relationship has not yet been established. Recent evidence from in vitro and animal studies suggests that enterovirus-induced pathology remarkably resembles the cellular and molecular phenotype of ALS, indicating a possible link between enteroviral infection and ALS pathogenesis. In this review, we summarize the nature of enteroviral infection, including route of infection, cells targeted, and viral persistence within the central nervous system (CNS). We review the molecular mechanisms underlying viral infection and highlight the similarity between viral pathogenesis and the molecular and pathological features of ALS, and finally, discuss the potential role of enteroviral infection in frontotemporal dementia (FTD), a disease that shares common clinical, genetic, and pathological features with ALS, and the significance of anti-viral therapy as an option for the treatment of ALS.

Neural precursor cells derived from induced pluripotent stem cells exhibit reduced susceptibility to infection with a neurotropic coronavirus

The present study examines the susceptibility of mouse induced pluripotent stem cell-derived neural precursor cells (iPSC-NPCs) to infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV). Similar to NPCs derived from striatum of day 1 postnatal GFP-transgenic mice (GFP-NPCs), iPSC-derived NPCs (iPSC-NPCs) are able to differentiate into terminal neural cell types and express MHC class I and II in response to IFN-γ treatment. However, in contrast to postnatally-derived NPCs, iPSC-NPCs express low levels of carcinoembryonic antigen-cell adhesion molecule 1a (CEACAM1a), the surface receptor for JHMV, and are less susceptible to infection and virus-induced cytopathic effects. The relevance of this in terms of therapeutic application of NPCs resistant to viral infection is discussed.

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The neurotropic virus JHMV infects and kills mouse post-natal neural progenitor cells (NPCs).

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This study examines if JHMV infects mouse inducible pluripotent stem cell-derived NPCs.

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iPSC-NPCs are less susceptible to infection with JHMV and subsequent lytic effects.

The antiviral cytokine interferon-gamma restricts neural stem/progenitor cell proliferation through activation of STAT1 and modulation of retinoblastoma protein phosphorylation

Neural stem/progenitor cells (NPSCs) express receptors for many inflammatory cytokines, with varying effects on differentiation and proliferation depending on the stage of development and the milieu of inflammatory mediators. In primary neurons and astrocytes, we recently showed that interferon gamma (IFNγ), a potent antiviral cytokine that is required for the control and clearance of many central nervous system (CNS) infections, could differentially affect cell survival and cell cycle progression depending upon the cell type and the profile of activated intracellular signaling molecules. Here, we show that IFNγ inhibits proliferation of primary NSPCs through dephosphorylation of the tumor suppressor Retinoblastoma protein (pRb), which is dependent on activation of signal transducers and activators of transcription‐1 (STAT1) signaling pathways. Our results show i) IFNγ inhibits neurosphere growth and proliferation rate in a dose‐dependent manner; ii) IFNγ blocks cell cycle progression through a late‐stage G1/S phase restriction; iii) IFNγ induces phosphorylation and expression of STAT1 and STAT3; iv) IFNγ decreases cyclin E/cdk2 expression and reduces phosphorylation of cyclin D1 and pRb on serine residue 795; and v) the effects of IFNγ on NSPC proliferation, cell cycle protein expression, and pRb phosphorylation are STAT1‐dependent. These data define a mechanism by which IFNγ could contribute to a reduction in NSPC proliferation in inflammatory conditions. Further delineation of the effects of inflammatory cytokines on NSPC growth could improve our understanding of how CNS infections and other inflammatory events disrupt brain development and NSPC function. © 2016 The Authors. Journal of Neuroscience Research Published by Wiley Periodicals, Inc.

Interferon gamma protects neonatal neural stem/progenitor cells during measles virus infection of the brain

BACKGROUND

In the developing brain, self-renewing neural stem/progenitor cells (NSPC) give rise to neuronal and glial lineages. NSPC survival and differentiation can be altered by neurotropic viruses and by the anti-viral immune response. Several neurotropic viruses specifically target and infect NSPCs, in addition to inducing neuronal loss, which makes it difficult to distinguish between effects on NSPCs that are due to direct viral infection or due to the anti-viral immune response.

METHODS

We have investigated the impact of anti-viral immunity on NSPCs in measles virus (MV)-infected neonates. A neuron-restricted viral infection model was used, where NSPCs remain uninfected. Thus, an anti-viral immune response was induced without the confounding issue of NSPC infection. Two-transgenic mouse lines were used: CD46+ mice express the human isoform of CD46, the MV entry receptor, under the control of the neuron-specific enolase promoter; CD46+/IFNγ-KO mice lack the key anti-viral cytokine IFNγ. Multi-color flow cytometry and Western Blot analysis were used to quantify effects on NSPC, neuronal, and glial cell number, and quantify effects on IFNγ-mediated signaling and cell markers, respectively.

RESULTS

Flow cytometric analysis revealed that NSPCs were reduced in CD46+/IFNγ-KO mice at 3, 7, and 10 days post-infection (dpi), but were unaffected in CD46+ mice. Early neurons showed the greatest cell loss at 7 dpi in both genotypes, with no effect on mature neurons and glial cells. Thus, IFNγ protected against NSPC loss, but did not protect young neurons. Western Blot analyses on hippocampal explants showed reduced nestin expression in the absence of IFNγ, and reduced doublecortin and βIII-tubulin in both genotypes. Phosphorylation of STAT1 and STAT2 occurred independently of IFNγ in the hippocampus, albeit with distinct regulation of activation.

CONCLUSIONS

This is the first study to demonstrate bystander effects of anti-viral immunity on NSPC function. Our results show IFNγ protects the NSPC population during a neonatal viral CNS infection. Significant loss of NSPCs in CD46+/IFNγ-KO neonates suggests that the adaptive immune response is detrimental to NSPCs in the absence of IFNγ. These results reveal the importance and contribution of the anti-viral immune response to neuropathology and may be relevant to other neuroinflammatory conditions.

Neurotropic Enterovirus Infections in the Central Nervous System

Enteroviruses are a group of positive-sense single stranded viruses that belong to the Picornaviridae family. Most enteroviruses infect humans from the gastrointestinal tract and cause mild symptoms. However, several enteroviruses can invade the central nervous system (CNS) and result in various neurological symptoms that are correlated to mortality associated with enteroviral infections. In recent years, large outbreaks of enteroviruses occurred worldwide. Therefore, these neurotropic enteroviruses have been deemed as re-emerging pathogens. Although these viruses are becoming large threats to public health, our understanding of these viruses, especially for non-polio enteroviruses, is limited. In this article, we review recent advances in the trafficking of these pathogens from the peripheral to the central nervous system, compare their cell tropism, and discuss the effects of viral infections in their host neuronal cells.

In vitro interaction between coxsackievirus B3 VP1 protein and human pleckstrin homology domain retinal protein (PHR1)

Coxsackievirus B3 (CVB3) infection causes central nervous system diseases including aseptic meningitis and encephalitis. To understand the mechanism of this virus, a yeast two-hybrid system was used to screen cellular proteins from a human heart cDNA library. The results revealed that the human Pleckstrin Homology Domain Retinal protein (PHR1), a PH domain-containing protein with low expression in the heart and high expression in the brain, interacts with CVB3 VP1, a major structural protein of CVB3. Yeast mating assays and in vitro coimmunoprecipitation verified the interaction between CVB3 VP1 and PHR1. An α-galactosidase assay indicated that of α-galactosidase activity was higher in positive clones than in controls suggesting a strong interaction. Furthermore, assay of deletion mutants defined the minimal region of PHR1 required for its interaction with VP1 as amino acids 95-172 and two regions of VP1 required for its interaction with PHR1 as amino acids 729-767 and 811-859. The results revealed multiple binding sites between PHR1 and CVB3 VP1 and suggested that the strong interaction between these two proteins might play an important role in central nervous system disease in the human brain.

Recent progress in understanding coxsackievirus replication, dissemination, and pathogenesis

Coxsackieviruses (CVs) are relatively common viruses associated with a number of serious human diseases, including myocarditis and meningo-encephalitis. These viruses are considered cytolytic yet can persist for extended periods of time within certain host tissues requiring evasion from the host immune response and a greatly reduced rate of replication. A member of Picornaviridae family, CVs have been historically considered non-enveloped viruses - although recent evidence suggest that CV and other picornaviruses hijack host membranes and acquire an envelope. Acquisition of an envelope might provide distinct benefits to CV virions, such as resistance to neutralizing antibodies and efficient nonlytic viral spread. CV exhibits a unique tropism for progenitor cells in the host which may help to explain the susceptibility of the young host to infection and the establishment of chronic disease in adults. CVs have also been shown to exploit autophagy to maximize viral replication and assist in unconventional release from target cells. In this article, we review recent progress in clarifying virus replication and dissemination within the host cell, identifying determinants of tropism, and defining strategies utilized by the virus to evade the host immune response. Also, we will highlight unanswered questions and provide future perspectives regarding the potential mechanisms of CV pathogenesis.

Mutant murine hepatitis virus-induced apoptosis in the hippocampus

The mutant virus Mu-3 was isolated from the soluble receptor-resistant mutant 7 virus (srr7), which is a neuropathogenic strain of the mouse hepatitis virus JHMV, and cloned as a soluble receptor-resistant mutant from the highly neuropathogenic JHMV strain cl-2 virus (cl-2). In order to identify specific characteristics of Mu-3, the pathology of Mu-3-infected mice was compared with that of srr7- and cl-2-infected mice. The neuropathology after Mu-3 infection exhibited a mixed pattern comparable to that induced by srr7 and cl-2 infections. In addition, Mu-3 infection caused marked apoptotic lesions in the hippocampal region, particularly in the CA2 and CA3 subregions, in the brains of all infected mice. In contrast, in cl-2 infection, 10-20% of the infected mice exhibited apoptosis in the hippocampus, which was primarily observed in the CA1 subregion. Apoptosis also occurred in the pyramidal neurons and CD11b-bearing cells. The apoptotic cells, indicated by caspase 3-activation, were a mixed population of infected and a higher number of uninfected cells. These data indicated that apoptosis observed in Mu-3 infection could be induced by the indirect effects of infection in addition to direct effects of the infected cells occurring in a cell-autonomous manner.

Death waits for no man--does it wait for a virus? How enteroviruses induce and control cell death

Enteroviruses (EVs) are the most common human viral pathogens. They cause a variety of pathologies, including myocarditis and meningoencephalopathies, and have been linked to the onset of type I diabetes. These pathologies result from the death of cells in the myocardium, central nervous system, and pancreas, respectively. Understanding the role of EVs in inducing cell death is crucial to understanding the etiologies of these diverse pathologies. EVs both induce and delay host cell death, and their exquisite control of this balance is crucial for their success as human viral pathogens. Thus, EVs are tightly involved with cell death signaling pathways and interact with host cell signaling at multiple points. Here, we review the literature detailing the mechanisms of EV-induced cell death. We discuss the mechanisms by which EVs induce cell death, the signaling pathways involved in these pathways, and the strategies by which EVs antagonize cell death pathways. We also discuss the role of cell death in both the resulting pathology in the host and in the facilitation of viral spread.

The impact of juvenile coxsackievirus infection on cardiac progenitor cells and postnatal heart development

Coxsackievirus B (CVB) is an enterovirus that most commonly causes a self-limited febrile illness in infants, but cases of severe infection can manifest in acute myocarditis. Chronic consequences of mild CVB infection are unknown, though there is an epidemiologic association between early subclinical infections and late heart failure, raising the possibility of subtle damage leading to late-onset dysfunction, or chronic ongoing injury due to inflammatory reactions during latent infection. Here we describe a mouse model of juvenile infection with a subclinical dose of coxsackievirus B3 (CVB3) which showed no evident symptoms, either immediately following infection or in adult mice. However following physiological or pharmacologically-induced cardiac stress, juvenile-infected adult mice underwent cardiac hypertrophy and dilation indicative of progression to heart failure. Evaluation of the vasculature in the hearts of adult mice subjected to cardiac stress showed a compensatory increase in CD31⁺ blood vessel formation, although this effect was suppressed in juvenile-infected mice. Moreover, CVB3 efficiently infected juvenile c-kit⁺ cells, and cardiac progenitor cell numbers were reduced in the hearts of juvenile-infected adult mice. These results suggest that the exhausted cardiac progenitor cell pool following juvenile CVB3 infection may impair the heart's ability to increase capillary density to adapt to increased load.

Coxsackievirus B (CVB) is a significant human pathogen, causing myocarditis, aseptic meningitis and encephalitis. The lasting consequences of juvenile CVB infection on the developing host have yet to be adequately inspected. Here, we show that CVB efficiently infected juvenile cardiac progenitor cells both in culture and the young heart. Furthermore, we describe a mouse model of juvenile infection with a subclinical dose of CVB which showed no symptoms of disease into adulthood. However following physiological or pharmacologically-induced cardiac stress, juvenile-infected mice underwent cardiac hypertrophy and dilation indicative of progression to heart failure. These results suggest that mild CVB infection in the young host may impair the ability of the heart to adapt to increased load leading to pathological remodeling later in adult life.

Coxsackievirus B exits the host cell in shed microvesicles displaying autophagosomal markers

Coxsackievirus B3 (CVB3), a member of the picornavirus family and enterovirus genus, causes viral myocarditis, aseptic meningitis, and pancreatitis in humans. We genetically engineered a unique molecular marker, “fluorescent timer” protein, within our infectious CVB3 clone and isolated a high-titer recombinant viral stock (Timer-CVB3) following transfection in HeLa cells. “Fluorescent timer” protein undergoes slow conversion of fluorescence from green to red over time, and Timer-CVB3 can be utilized to track virus infection and dissemination in real time. Upon infection with Timer-CVB3, HeLa cells, neural progenitor and stem cells (NPSCs), and C2C12 myoblast cells slowly changed fluorescence from green to red over 72 hours as determined by fluorescence microscopy or flow cytometric analysis. The conversion of “fluorescent timer” protein in HeLa cells infected with Timer-CVB3 could be interrupted by fixation, suggesting that the fluorophore was stabilized by formaldehyde cross-linking reactions. Induction of a type I interferon response or ribavirin treatment reduced the progression of cell-to-cell virus spread in HeLa cells or NPSCs infected with Timer-CVB3. Time lapse photography of partially differentiated NPSCs infected with Timer-CVB3 revealed substantial intracellular membrane remodeling and the assembly of discrete virus replication organelles which changed fluorescence color in an asynchronous fashion within the cell. “Fluorescent timer” protein colocalized closely with viral 3A protein within virus replication organelles. Intriguingly, infection of partially differentiated NPSCs or C2C12 myoblast cells induced the release of abundant extracellular microvesicles (EMVs) containing matured “fluorescent timer” protein and infectious virus representing a novel route of virus dissemination. CVB3 virions were readily observed within purified EMVs by transmission electron microscopy, and infectious virus was identified within low-density isopycnic iodixanol gradient fractions consistent with membrane association. The preferential detection of the lipidated form of LC3 protein (LC3 II) in released EMVs harboring infectious virus suggests that the autophagy pathway plays a crucial role in microvesicle shedding and virus release, similar to a process previously described as autophagosome-mediated exit without lysis (AWOL) observed during poliovirus replication. Through the use of this novel recombinant virus which provides more dynamic information from static fluorescent images, we hope to gain a better understanding of CVB3 tropism, intracellular membrane reorganization, and virus-associated microvesicle dissemination within the host.

Enteroviruses are significant human pathogens, causing myocarditis, aseptic meningitis and encephalitis. The mechanisms of enterovirus dissemination in the host and cell-to-cell spread may be critical factors influencing viral pathogenesis. Here, we have generated a recombinant coxsackievirus expressing “fluorescence timer” protein (Timer-CVB3) which assists in following the progression of infection within the host. Unexpectedly, we observed the shedding of microvesicles containing virus in partially-differentiated progenitor cells infected with Timer-CVB3. These extracellular microvesicles (EMVs) were released in high levels following cellular differentiation, and may play a role in virus dissemination. Timer-CVB3 will be a valuable tool in monitoring virus spread in the infected host.

Epidemiology of enteroviral meningoencephalitis in neonates and young infants

AIM

To describe the epidemiology of enteroviral meningoencephalitis in northern New South Wales, Australia, with a specific focus on neonatal and young infant cases.

METHODS

A retrospective review of PCR-confirmed enteroviral meningoencephalitis cases in the Hunter New England Local Health District of northern NSW was conducted for the period 2008-2012.

RESULTS

One hundred nine patients met the case definition. There was summer seasonality, with 50% (55/109) of cases occurring between December and February. Neonates and young infants (<3 months of age) accounted for 42% (46/109) of cases, with 20% (9/46) being premature births. Fever (83%) was the most common presentation in this age group, followed by irritability (40%), feeding difficulties (40%) and rash (17%). All received at least one antibiotic during their admission, with 26% (12/46) also treated empirically with acyclovir. There was one death. Where testing was undertaken, cerebrospinal fluid (CSF) protein levels were high in 90% (28/31) of neonates and young infants, but the CSF white cell count was variable, with 57% <10/mm(3) and 21% >100/mm(3) .

CONCLUSION

Early diagnosis of enteroviral meningoencephalitis could alter management, potentially reducing the period of treatment with empirical antimicrobials and permitting earlier discharge.

Distinct neural stem cell tropism, early immune activation, and choroid plexus pathology following coxsackievirus infection in the neonatal central nervous system

Coxsackievirus B3 (CVB3) and lymphocytic choriomeningitis virus (LCMV) are both neurotropic RNA viruses, which can establish a persistent infection and cause meningitis and encephalitis in the neonatal host. Utilizing our neonatal mouse model of infection, we evaluated the consequences of early viral infection upon the host central nervous system (CNS) by comparing CVB3 and LCMV infection. Both viruses expressed high levels of viral protein in the choroid plexus and subventricular zone (SVZ), a region of neurogenesis. LCMV infected a greater number of cells in the SVZ and targeted both nestin(+) (neural progenitor cell marker) and olig2(+) (glial progenitor marker) cells at a relatively equal proportion. In contrast, CVB3 preferentially infected nestin(+) cells within the SVZ. Microarray analysis revealed differential kinetics and unique host gene expression changes for each infection. MHC class I gene expression, several developmental-related Hox genes, and transthyretin (TTR), a protein secreted in the cerebrospinal fluid by the choroid plexus, were specifically downregulated following CVB3 infection. Also, we identified severe pathology in the choroid plexus of CVB3-infected animals at 48 h post infection accompanied by a decrease in the level of TTR and carbonic anhydrase II. These results demonstrate broader neural progenitor and stem cell (NPSC) tropism for LCMV in the neonatal CNS, whereas CVB3 targeted a more specific subset of NPSCs, stimulated a distinct early immune response, and induced significant acute damage in the choroid plexus.

T cell mediated suppression of neurotropic coronavirus replication in neural precursor cells

Neural precursor cells (NPCs) are the subject of intense investigation for their potential to treat neurodegenerative disorders, yet the consequences of neuroinvasive virus infection of NPCs remain unclear. This study demonstrates that NPCs support replication following infection by the neurotropic JHM strain of mouse hepatitis virus (JHMV). JHMV infection leads to increased cell death and dampens IFN-γ-induced MHC class II expression. Importantly, cytokines secreted by CD4+ T cells inhibit JHMV replication in NPCs, and CD8+ T cells specifically target viral peptide-pulsed NPCs for lysis. Furthermore, treatment with IFN-γ inhibits JHMV replication in a dose-dependent manner. Together, these findings suggest that T cells play a critical role in controlling replication of a neurotropic virus in NPCs, a finding which has important implications when considering immune modulation for NPC-based therapies for treatment of human neurologic diseases.

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Murine neural precursor cells are infected by JHMV in a CEACAM1a-dependent manner.

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Peptide-pulsed NPCs are targeted for lysis by virus-specific CD8+ T cells.

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JHMV replication in NPCs is suppressed by CD4+ T cells through IFN-γ secretion.

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IFN-γ dampens CEACAM1a expression and JHMV protein production in NPCs.

Coxsackievirus B3 infects the bone marrow and diminishes the restorative capacity of erythroid and lymphoid progenitors

Coxsackievirus B3 (CVB3) is known to infect stem cells in the neonatal central nervous system. Here, we evaluated the effects of CVB3 infection on the major source and repository of stem cells, the bone marrow (BM). Viral genome was detectable in BM within 24 h of infection, and productive infection of BM cells was evident, peaking at 48 h postinfection (p.i.), when ∼1 to 2% of BM cells produced infectious virus particles. Beginning at 2 to 3 days p.i., a dramatic and persistent loss of immature erythroid cells, B and T lymphocytes, and neutrophils was observed in BM and, by day 3 to 4 p.i., the femoral BM stroma was largely destroyed. Analysis of peripheral blood revealed a modest neutrophilia, a loss of reticulocytes, and a massive lymphopenia. The abundance of multipotent progenitor cells (Lin(-)/c-kit(+)/Flt3(+)) in BM declined ∼10-fold during CVB3 infection and, consistent with a deficiency of primitive hematopoietic progenitors, serum levels of the hematopoietic growth factor Flt3 ligand were dramatically elevated. Therefore, we analyzed the regenerative capacity of BM from CVB3-infected mice. Granulocyte/macrophage progenitors displayed a relatively normal proliferative ability, consistent with the fact that the peripheral blood level of neutrophils-which are very short-lived cells-remained high throughout infection. However, erythroid and lymphoid hematopoietic progenitors in BM from CVB3-infected mice showed a markedly reduced colony-forming capacity, consonant with the observed loss of both lymphocytes and immature erythroid cells/reticulocytes from the BM and peripheral blood. In summary, CVB3 infects the BM and exerts differential effects on the various hematopoietic progenitor populations.