Oligodendrocytes are susceptible to Zika virus infection in a mouse model of perinatal exposure: Implications for CNS complications

Translocator protein (TSPO) is a biomarker of Zika virus (ZIKV) infection-associated neuroinflammation

Zika is a systemic inflammatory disease caused by infection with Zika virus (ZIKV). ZIKV infection in adults is associated with encephalitis marked by elevated expression of pro-inflammatory cytokines and chemokines, as well as increased brain infiltration of immune cells. In this study, we demonstrate that ZIKV encephalitis in a mouse infection model exhibits increased brain TSPO expression. TSPO expression on brain-resident and infiltrating immune cells in ZIKV infection correlates with disease and inflammation status in the brain. Brain TSPO expression can also be sensitively detected ex vivo and in vitro using radioactive small molecule probes that specifically bind to TSPO, such as [3H]PK11195. TSPO expression on brain-resident and infiltrating immune cells is a biomarker of ZIKV neuroinflammation, which can also be a general biomarker of acute viral neuroinflammatory disease.

Human Brain In Vitro Model for Pathogen Infection-Related Neurodegeneration Study

Recent advancements in stem cell biology and tissue engineering have revolutionized the field of neurodegeneration research by enabling the development of sophisticated in vitro human brain models. These models, including 2D monolayer cultures, 3D organoids, organ-on-chips, and bioengineered 3D tissue models, aim to recapitulate the cellular diversity, structural organization, and functional properties of the native human brain. This review highlights how these in vitro brain models have been used to investigate the effects of various pathogens, including viruses, bacteria, fungi, and parasites infection, particularly in the human brain cand their subsequent impacts on neurodegenerative diseases. Traditional studies have demonstrated the susceptibility of different 2D brain cell types to infection, elucidated the mechanisms underlying pathogen-induced neuroinflammation, and identified potential therapeutic targets. Therefore, current methodological improvement brought the technology of 3D models to overcome the challenges of 2D cells, such as the limited cellular diversity, incomplete microenvironment, and lack of morphological structures by highlighting the need for further technological advancements. This review underscored the significance of in vitro human brain cell from 2D monolayer to bioengineered 3D tissue model for elucidating the intricate dynamics for pathogen infection modeling. These in vitro human brain cell enabled researchers to unravel human specific mechanisms underlying various pathogen infections such as SARS-CoV-2 to alter blood-brain-barrier function and Toxoplasma gondii impacting neural cell morphology and its function. Ultimately, these in vitro human brain models hold promise as personalized platforms for development of drug compound, gene therapy, and vaccine. Overall, we discussed the recent progress in in vitro human brain models, their applications in studying pathogen infection-related neurodegeneration, and future directions.

Oligodendrocyte-derived IL-33 functions as a microglial survival factor during neuroinvasive flavivirus infection

In order to recover from infection, organisms must balance robust immune responses to pathogens with the tolerance of immune-mediated pathology. This balance is particularly critical within the central nervous system, whose complex architecture, essential function, and limited capacity for self-renewal render it susceptible to both pathogen- and immune-mediated pathology. Here, we identify the alarmin IL-33 and its receptor ST2 as critical for host survival to neuroinvasive flavivirus infection. We identify oligodendrocytes as the critical source of IL-33, and microglia as the key cellular responders. Notably, we find that the IL-33/ST2 axis does not impact viral control or adaptive immune responses; rather, it is required to promote the activation and survival of microglia. In the absence of intact IL-33/ST2 signaling in the brain, neuroinvasive flavivirus infection triggered aberrant recruitment of monocyte-derived peripheral immune cells, increased neuronal stress, and neuronal cell death, effects that compromised organismal survival. These findings identify IL-33 as a critical mediator of CNS tolerance to pathogen-initiated immunity and inflammation.

Molecular and Cellular Mechanisms Underlying Neurologic Manifestations of Mosquito-Borne Flavivirus Infections

Flaviviruses are a family of enveloped viruses with a positive-sense RNA genome, transmitted by arthropod vectors. These viruses are known for their broad cellular tropism leading to infection of multiple body systems, which can include the central nervous system. Neurologic effects of flavivirus infection can arise during both acute and post-acute infectious periods; however, the molecular and cellular mechanisms underlying post-acute sequelae are not fully understood. Here, we review recent studies that have examined molecular and cellular mechanisms that may contribute to neurologic sequelae following infection with the West Nile virus, Japanese encephalitis virus, Zika virus, dengue virus, and St. Louis encephalitis virus. Neuronal death, either from direct infection or due to the resultant inflammatory response, is a common mechanism by which flavivirus infection can lead to neurologic impairment. Other types of cellular damage, such as oxidative stress and DNA damage, appear to be more specific to certain viruses. This article aims to highlight mechanisms of cellular damage that are common across several flavivirus members and mechanisms that are more unique to specific members. Our goal is to inspire further research to improve understanding of this area in the hope of identifying treatment options for flavivirus-associated neurologic changes.

Exploring New Mechanism of Depression from the Effects of Virus on Nerve Cells

Depression is a common neuropsychiatric disorder with long-term recurrent depressed mood, pain and despair, pessimism and anxiety, and even suicidal tendencies as the main symptoms. Depression usually induces or aggravates the development of other related diseases, such as sleep disorders and endocrine disorders. In today's society, the incidence of depression is increasing worldwide, and its pathogenesis is complex and generally believed to be related to genetic, psychological, environmental, and biological factors. Current studies have shown the key role of glial cells in the development of depression, and it is noteworthy that some recent evidence suggests that the development of depression may be closely related to viral infections, such as SARS-CoV-2, BoDV-1, ZIKV, HIV, and HHV6, which infect the organism and cause some degree of glial cells, such as astrocytes, oligodendrocytes, and microglia. This can affect the transmission of related proteins, neurotransmitters, and cytokines, which in turn leads to neuroinflammation and depression. Based on the close relationship between viruses and depression, this paper provides an in-depth analysis of the new mechanism of virus-induced depression, which is expected to provide a new perspective on the mechanism of depression and a new idea for the diagnosis of depression in the future.

Organotypic hippocampal culture model reveals differential responses to highly similar Zika virus isolates

INTRODUCTION

Zika virus (ZIKV) caused an outbreak in Brazil, in 2015, being associated to microcephaly. ZIKV has a strong neurotropism leading to death of infected cells in different brain regions, including the hippocampus, a major site for neurogenesis. The neuronal populations of the brain are affected differently by ZIKV from Asian and African ancestral lineages. However, it remains to be investigated whether subtle variations in the ZIKV genome can impact hippocampus infection dynamics and host response.

OBJECTIVE

This study evaluated how two Brazilian ZIKV isolates, PE243 and SPH2015, that differ in two specific missense amino acid substitutions, one in the NS1 protein and the other in the NS4A protein, affect the hippocampal phenotype and transcriptome.

METHODS

Organotypic hippocampal cultures (OHC) from infant Wistar rats were infected with PE243 or SPH2015 and analyzed in time series using immunofluorescence, confocal microscopy, RNA-Seq and RT-qPCR.

RESULTS

Unique patterns of infection and changes in neuronal density in the OHC were observed for PE243 and SPH2015 between 8 and 48 h post infection (p.i.). Phenotypic analysis of microglia indicated that SPH2015 has a greater capacity for immune evasion. Transcriptome analysis of OHC at 16 h p.i. disclosed 32 and 113 differentially expressed genes (DEGs) in response to infection with PE243 and SPH2015, respectively. Functional enrichment analysis suggested that infection with SPH2015 activates mostly astrocytes rather than microglia. PE243 downregulated biological process of proliferation of brain cells and upregulated those associated with neuron death, while SPH2015 downregulated processes related to neuronal development. Both isolates downregulated cognitive and behavioral development processes. Ten genes were similarly regulated by both isolates. They are putative biomarkers of early hippocampus response to ZIKV infection. At 5, 7, and 10 days p.i., neuronal density of infected OHC remained below controls, and mature neurons of infected OHC showed an increase in the epigenetic mark H3K4me3, which is associated to a transcriptionally active state. This feature is more prominent in response to SPH2015.

CONCLUSION

Subtle genetic diversity of the ZIKV affects the dynamics of viral dissemination in the hippocampus and host response in the early stages of infection, which may lead to different long-term effects in neuronal population.

Oligodendrocyte-derived IL-33 functions as a microglial survival factor during neuroinvasive flavivirus infection

In order to recover from infection, organisms must balance robust immune responses to pathogens with the tolerance of immune-mediated pathology. This balance is particularly critical within the central nervous system, whose complex architecture, essential function, and limited capacity for self-renewal render it susceptible to both pathogen- and immune-mediated pathology. Here, we identify the alarmin IL-33 and its receptor ST2 as critical for host survival to neuroinvasive flavivirus infection. We identify oligodendrocytes as the critical source of IL-33, and microglia as the key cellular responders. Notably, we find that the IL-33/ST2 axis does not impact viral control or adaptive immune responses; rather, it is required to promote the activation and survival of microglia. In the absence of intact IL-33/ST2 signaling in the brain, neuroinvasive flavivirus infection triggered aberrant recruitment of monocyte-derived peripheral immune cells, increased neuronal stress, and neuronal cell death, effects that compromised organismal survival. These findings identify IL-33 as a critical mediator of CNS tolerance to pathogen-initiated immunity and inflammation.

The multitaskers of the brain: Glial responses to viral infections and associated post-infectious neurologic sequelae

Many viral infections cause acute and chronic neurologic diseases which can lead to degeneration of cortical functions. While neurotropic viruses that gain access to the central nervous system (CNS) may induce brain injury directly via infection of neurons or their supporting cells, they also alter brain function via indirect neuroimmune mechanisms that may disrupt the blood-brain barrier (BBB), eliminate synapses, and generate neurotoxic astrocytes and microglia that prevent recovery of neuronal circuits. Non-neuroinvasive, neurovirulent viruses may also trigger aberrant responses in glial cells, including those that interfere with motor and sensory behaviors, encoding of memories and executive function. Increasing evidence from human and animal studies indicate that neuroprotective antiviral responses that amplify levels of innate immune molecules dysregulate normal neuroimmune processes, even in the absence of neuroinvasion, which may persist after virus is cleared. In this review, we discuss how select emerging and re-emerging RNA viruses induce neuroimmunologic responses that lead to dysfunction of higher order processes including visuospatial recognition, learning and memory, and motor control. Identifying therapeutic targets that return the neuroimmune system to homeostasis is critical for preventing virus-induced neurodegenerative disorders.

Mechanisms of Zika astrocyte infection and neuronal toxicity

Objectives

Zika virus (ZIKV) has become an epidemic in several countries and was declared a major public health issue by the WHO. Although ZIKV infection is asymptomatic or shows mild fever-related symptoms in most people, the virus can be transmitted from a pregnant mother to the fetus, resulting in severe brain developmental abnormalities, including microcephaly. Multiple groups have identified developmental neuronal and neuronal progenitor compromise during ZIKV infection within the fetal brain, but little is known about whether ZIKV could infect human astrocytes and its effect on the developing brain. Thus, our objective was to determine astrocyte ZiKV infection in a developmental-dependent manner.

Methods

We analyze infection of pure cultures of astrocytes and mixed cultures of neurons and astrocytes in response to ZIKV using plaque assays, confocal, and electron microscopy to identify infectivity, ZIKV accumulation and intracellular distribution as well as apoptosis and interorganelle dysfunction.

Results

Here, we demonstrated that ZIKV enters, infects, replicates, and accumulates in large quantities in human fetal astrocytes in a developmental-dependent manner. Astrocyte infection and intracellular viral accumulation resulted in neuronal apoptosis, and we propose astrocytes are a ZIKV reservoir during brain development.

Conclusions

Our data identify astrocytes in different stages of development as major contributors to the devastating effects of ZIKV in the developing brain.

The role of glial cells in Zika virus-induced neurodegeneration

Zika virus (ZIKV) is a strongly neurotropic flavivirus whose infection has been associated with microcephaly in neonates. However, clinical and experimental evidence indicate that ZIKV also affects the adult nervous system. In this regard, in vitro and in vivo studies have shown the ability of ZIKV to infect glial cells. In the central nervous system (CNS), glial cells are represented by astrocytes, microglia, and oligodendrocytes. In contrast, the peripheral nervous system (PNS) constitutes a highly heterogeneous group of cells (Schwann cells, satellite glial cells, and enteric glial cells) spread through the body. These cells are critical in both physiological and pathological conditions; as such, ZIKV-induced glial dysfunctions can be associated with the development and progression of neurological complications, including those related to the adult and aging brain. This review will address the effects of ZIKV infection on CNS and PNS glial cells, focusing on cellular and molecular mechanisms, including changes in the inflammatory response, oxidative stress, mitochondrial dysfunction, Ca²⁺ and glutamate homeostasis, neural metabolism, and neuron-glia communication. Of note, preventive and therapeutic strategies that focus on glial cells may emerge to delay and/or prevent the development of ZIKV-induced neurodegeneration and its consequences.

Differential proteomics of Zika virus (ZIKV) infection reveals molecular changes potentially involved in immune system evasion by a Brazilian strain of ZIKV

Zika virus (ZIKV) is an arbovirus that was responsible for multiple outbreaks from 2007 to 2015. It has been linked to cases of microcephaly in Brazil in 2015, among other neurological disorders. Differences among strains might be the reason for different clinical outcomes of infection. To evaluate this hypothesis, we performed a comparative proteomic analysis of Vero cells infected with the African strain MR766 (ZIKVAFR) and the Brazilian strain 17 SM (ZIKVBR). A total of 550 proteins were identified as differentially expressed in ZIKVAFR- or ZIKVBR-infected cells compared to the control. The main findings included upregulation of immune system pathways (neutrophil degranulation and adaptive/innate immune system) and potential activation of immune-system-related pathways by ZIKVAFR (mTOR, JAK-STAT, NF-κB, and others) compared with the ZIKVBR/control. In addition, phagocytosis by macrophages and engulfment of leukocytes were activated in ZIKVAFR infection. An in vivo analysis using an immunocompetent C57BL/6N mouse model identified interstitial pneumonia with neutrophil infiltration in the lungs only in mice infected with ZIKVBR at 48 hours postinfection, with a significant amount of virus detected. Likewise, only animals infected with ZIKVBR had viral material in the cytoplasm of lung macrophages. These results suggest that activation of the immune system by ZIKVAFR infection may lead to faster viral clearance by immune cells.

Modeling infectious diseases of the central nervous system with human brain organoids

Bacteria, fungi, viruses, and protozoa are known to infect and induce diseases in the human central nervous system (CNS). Modeling the mechanisms of interaction between pathogens and the CNS microenvironment is essential to understand their pathophysiology and develop new treatments. Recent advancements in stem cell technologies have allowed for the creation of human brain organoids, which more closely resembles the human CNS microenvironment when compared to classical 2-dimensional (2D) cultures. Now researchers can utilize these systems to investigate and reinvestigate questions related to CNS infection in a human-derived brain organoid system. Here in this review, we highlight several infectious diseases which have been tested in human brain organoids and compare similarities in response to these pathogens across different investigations. We also provide a brief overview of some recent advancements which can further enrich this model to develop new and better therapies to treat brain infections.

Apoptosis during ZIKA Virus Infection: Too Soon or Too Late?

Cell death by apoptosis is a major cellular response in the control of tissue homeostasis and as a defense mechanism in the case of cellular aggression such as an infection. Cell self-destruction is part of antiviral responses, aimed at limiting the spread of a virus. Although it may contribute to the deleterious effects in infectious pathology, apoptosis remains a key mechanism for viral clearance and the resolution of infection. The control mechanisms of cell death processes by viruses have been extensively studied. Apoptosis can be triggered by different viral determinants through different pathways as a result of virally induced cell stresses and innate immune responses. Zika virus (ZIKV) induces Zika disease in humans, which has caused severe neurological forms, birth defects, and microcephaly in newborns during the last epidemics. ZIKV also surprised by revealing an ability to persist in the genital tract and in semen, thus being sexually transmitted. Mechanisms of diverting antiviral responses such as the interferon response, the role of cytopathic effects and apoptosis in the etiology of the disease have been widely studied and debated. In this review, we examined the interplay between ZIKV infection of different cell types and apoptosis and how the virus deals with this cellular response. We illustrate a duality in the effects of ZIKV-controlled apoptosis, depending on whether it occurs too early or too late, respectively, in neuropathogenesis, or in long-term viral persistence. We further discuss a prospective role for apoptosis in ZIKV-related therapies, and the use of ZIKV as an oncolytic agent.

Acute neurologic emerging flaviviruses

The COVID-19 pandemic has shed light on the challenges we face as a global society in preventing and containing emerging and re-emerging pathogens. Multiple intersecting factors, including environmental changes, host immunological factors, and pathogen dynamics, are intimately connected to the emergence and re-emergence of communicable diseases. There is a large and expanding list of communicable diseases that can cause neurological damage, either through direct or indirect routes. Novel pathogens of neurotropic potential have been identified through advanced diagnostic techniques, including metagenomic next-generation sequencing, but there are also known pathogens which have expanded their geographic distribution to infect non-immune individuals. Factors including population growth, climate change, the increase in animal and human interface, and an increase in international travel and trade are contributing to the expansion of emerging and re-emerging pathogens. Challenges exist around antimicrobial misuse giving rise to antimicrobial-resistant infectious neurotropic organisms and increased susceptibility to infection related to the expanded use of immunomodulatory treatments. In this article, we will review key concepts around emerging and re-emerging pathogens and discuss factors associated with neurotropism and neuroinvasion. We highlight several neurotropic pathogens of interest, including West Nile virus (WNV), Zika Virus, Japanese Encephalitis Virus (JEV), and Tick-Borne Encephalitis Virus (TBEV). We emphasize neuroinfectious diseases which impact the central nervous system (CNS) and focus on flaviviruses, a group of vector-borne pathogens that have expanded globally in recent years and have proven capable of widespread outbreak.

Inflammation Unleashed in Viral-Induced Epileptogenesis

Viral infection of the central nervous system increasingly places people at risk of developing life-threatening and treatment-resistant acute and chronic seizures (epilepsy). The emergence of new human viruses due to ongoing social, political, and ecological changes places people at risk more than ever before. The development of new preventative or curative strategies is critical to address this burden. However, our understanding of the complex relationship between viruses and the brain has been hindered by the lack of animal models that survive the initial infection and are amenable for long-term mechanistic, behavioral, and pharmacological studies in the process of viral-induced epileptogenesis. In this review, we focus on the Theiler’s murine encephalomyelitis virus (TMEV) mouse model of viral infection–induced epilepsy. The TMEV model has a number of important advantages to address the quintessential processes underlying the development of epilepsy following a viral infection, as well as fuel new therapeutic development. In this review, we highlight the contributions of the TMEV model to our current understanding of the relationship between viral infection, inflammation, and seizures.

The legacy of ZikaPLAN: a transnational research consortium addressing Zika

Global health research partnerships with institutions from high-income countries and low- and middle-income countries are one of the European Commission's flagship programmes. Here, we report on the ZikaPLAN research consortium funded by the European Commission with the primary goal of addressing the urgent knowledge gaps related to the Zika epidemic and the secondary goal of building up research capacity and establishing a Latin American-European research network for emerging vector-borne diseases. Five years of collaborative research effort have led to a better understanding of the full clinical spectrum of congenital Zika syndrome in children and the neurological complications of Zika virus infections in adults and helped explore the origins and trajectory of Zika virus transmission. Individual-level data from ZikaPLAN`s cohort studies were shared for joint analyses as part of the Zika Brazilian Cohorts Consortium, the European Commission-funded Zika Cohorts Vertical Transmission Study Group, and the World Health Organization-led Zika Virus Individual Participant Data Consortium. Furthermore, the legacy of ZikaPLAN includes new tools for birth defect surveillance and a Latin American birth defect surveillance network, an enhanced Guillain-Barre Syndrome research collaboration, a de-centralized evaluation platform for diagnostic assays, a global vector control hub, and the REDe network with freely available training resources to enhance global research capacity in vector-borne diseases.