Brain microvascular endothelial-astrocyte cell responses following Japanese encephalitis virus infection in an in vitro human blood-brain barrier model

Harnessing the Potential of Exosomes in Therapeutic Interventions for Brain Disorders

Exosomes, which are nano-sized natural vesicles secreted by cells, are crucial for intercellular communication and interactions, playing a significant role in various physiological and pathological processes. Their characteristics, such as low toxicity and immunogenicity, high biocompatibility, and remarkable drug delivery capabilities-particularly their capacity to traverse the blood-brain barrier-make exosomes highly promising vehicles for drug administration in the treatment of brain disorders. This review provides a comprehensive overview of exosome biogenesis and isolation techniques, strategies for the drug loading and functionalization of exosomes, and exosome-mediated blood-brain barrier penetration mechanisms, with a particular emphasis on recent advances in exosome-based drug delivery for brain disorders. Finally, we address the opportunities and challenges associated with utilizing exosomes as a drug delivery system for the brain, summarizing the barriers to clinical translation and proposing future research directions.

Viruses and the Brain-A Relationship Prone to Trouble

Neurological disorders, some of which are associated with viral infections, are growing due to the aging and expanding population. Despite strong defenses of the central nervous system, some viruses have evolved ways to breach them, which often result in dire consequences. In this review, we recount the various ways by which different viruses can enter the CNS, and we describe the consequences of such invasions. Consequences may manifest as acute disease, such as encephalitis, meningitis, or result in long-term effects, such as neuromuscular dysfunction, as occurs in poliomyelitis. We discuss evidence for viral involvement in the causation of well-known chronic neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, as well as vascular dementia in the elderly. We also describe the approaches currently available to control a few of the neural viral infections. These include antivirals that are effective against human immunodeficiency virus and herpes simplex virus, as well as vaccines valuable for controlling rabies virus, poliomyelitis virus, and some flavivirus infections. There is an urgent need to better understand, at a molecular level, how viruses contribute to acute and, especially, chronic neurological diseases and to develop more precise and effective vaccines and therapies.

Key virulence factors responsible for differences in pathogenicity between clinically proven live-attenuated Japanese encephalitis vaccine SA14-14-2 and its pre-attenuated highly virulent parent SA14

Japanese encephalitis virus (JEV), a neuroinvasive and neurovirulent orthoflavivirus, can be prevented in humans with the SA14-14-2 vaccine, a live-attenuated version derived from the wild-type SA14 strain. To determine the viral factors responsible for the differences in pathogenicity between SA14 and SA14-14-2, we initially established a reverse genetics system that includes a pair of full-length infectious cDNAs for both strains. Using this cDNA pair, we then systematically exchanged genomic regions between SA14 and SA14-14-2 to generate 20 chimeric viruses and evaluated their replication capability in cell culture and their pathogenic potential in mice. Our findings revealed the following: (i) The single envelope (E) protein of SA14-14-2, which contains nine mutations (eight in the ectodomain and one in the stem region), is both necessary and sufficient to render SA14 non-neuroinvasive and non-neurovirulent. (ii) Conversely, the E protein of SA14 alone is necessary for SA14-14-2 to become highly neurovirulent, but it is not sufficient to make it highly neuroinvasive. (iii) The limited neuroinvasiveness of an SA14-14-2 derivative that contains the E gene of SA14 significantly increases (approaching that of the wild-type strain) when two viral nonstructural proteins are replaced by their counterparts from SA14: (a) NS1/1', which has four mutations on the external surface of the core β-ladder domain; and (b) NS2A, which has two mutations in the N-terminal region, including two non-transmembrane α-helices. In line with their roles in viral pathogenicity, the E, NS1/1', and NS2A genes all contribute to the enhanced spread of the virus in cell culture. Collectively, our data reveal for the first time that the E protein of JEV has a dual function: It is the master regulator of viral neurovirulence and also the primary initiator of viral neuroinvasion. After the initial E-mediated neuroinvasion, the NS1/1' and NS2A proteins act as secondary promoters, further amplifying viral neuroinvasiveness.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Trends in temporal and spatial changes of Japanese encephalitis in Chinese mainland, 2004-2019: A population-based surveillance study

BACKGROUND

Japanese encephalitis (JE) is a serious health concern in China, with approximately 80 % of global infections occurring in China. To develop effective prevention and control strategies, this study explored the epidemiological characteristics of JE in China based on spatiotemporal data, to understand the patterns and trends of JE incidence in different regions and time periods.

METHOD

The incidence and mortality rates of JE were extracted from the Public Health Data Center, the official website of the National Health Commission of the People's Republic of China, and the National Notifiable Infectious Disease Surveillance System from 2004 to 2019. Joinpoint regression was applied to examine the spatiotemporal patterns and annual percentage change in incidence and mortality of the JE.

RESULTS

From 2004 to 2019, a total of 43,569 cases of JE were diagnosed, including 2081 deaths. The annual incidence rate of JE decreased from 0.4171/100,000 in 2004 to 0.0298/100,000 in 2019, with an annual percentage change (APC) of -13.5 % (P < 0.001). The annual mortality rate of JE showed three stages of change, with inflection points in 2006 and 2014. The incidence and mortality rates of JE have declined in all provinces of China, and more cases were reported in 0-14 years of age, accounting for nearly 80 % of all patients.

CONCLUSIONS

The morbidity and mortality rates of JE in China are generally on a downward trend, and emphasis should be placed on strengthening disease surveillance in special areas and populations, popularizing vaccination, and increasing publicity.

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

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

Promising Strategies to Reduce the SARS-CoV-2 Amyloid Deposition in the Brain and Prevent COVID-19-Exacerbated Dementia and Alzheimer's Disease

The COVID-19 pandemic, caused by infection with the SARS-CoV-2 virus, is associated with cognitive impairment and Alzheimer's disease (AD) progression. Once it enters the brain, the SARS-CoV-2 virus stimulates accumulation of amyloids in the brain that are highly toxic to neural cells. These amyloids may trigger neurological symptoms in COVID-19. The meningeal lymphatic vessels (MLVs) play an important role in removal of toxins and mediate viral drainage from the brain. MLVs are considered a promising target to prevent COVID-19-exacerbated dementia. However, there are limited methods for augmentation of MLV function. This review highlights new discoveries in the field of COVID-19-mediated amyloid accumulation in the brain associated with the neurological symptoms and the development of promising strategies to stimulate clearance of amyloids from the brain through lymphatic and other pathways. These strategies are based on innovative methods of treating brain dysfunction induced by COVID-19 infection, including the use of photobiomodulation, plasmalogens, and medicinal herbs, which offer hope for addressing the challenges posed by the SARS-CoV-2 virus.

In Vitro Blood-Brain Barrier Models for Neuroinfectious Diseases: A Narrative Review

The blood-brain barrier (BBB) is a complex, dynamic, and adaptable barrier between the peripheral blood system and the central nervous system. While this barrier protects the brain and spinal cord from inflammation and infection, it prevents most drugs from reaching the brain tissue. With the expanding interest in the pathophysiology of BBB, the development of in vitro BBB models has dramatically evolved. However, due to the lack of a standard model, a range of experimental protocols, BBB-phenotype markers, and permeability flux markers was utilized to construct in vitro BBB models. Several neuroinfectious diseases are associated with BBB dysfunction. To conduct neuroinfectious disease research effectively, there stems a need to design representative in vitro human BBB models that mimic the BBB's functional and molecular properties. The highest necessity is for an in vitro standardised BBB model that accurately represents all the complexities of an intact brain barrier. Thus, this in-depth review aims to describe the optimization and validation parameters for building BBB models and to discuss previous research on neuroinfectious diseases that have utilized in vitro BBB models. The findings in this review may serve as a basis for more efficient optimisation, validation, and maintenance of a structurally- and functionally intact BBB model, particularly for future studies on neuroinfectious diseases.

Immunopathology of herpes simplex virus-associated neuroinflammation: Unveiling the mysteries

The immunopathology of herpes simplex virus (HSV)-associated neuroinflammation is a captivating and intricate field of study within the scientific community. HSV, renowned for its latent infection capability, gives rise to a spectrum of neurological expressions, ranging from mild symptoms to severe encephalitis. The enigmatic interplay between the virus and the host's immune responses profoundly shapes the outcome of these infections. This review delves into the multifaceted immune reactions triggered by HSV within neural tissues, intricately encompassing the interplay between innate and adaptive immunity. Furthermore, this analysis delves into the delicate equilibrium between immune defence and the potential for immunopathology-induced neural damage. It meticulously dissects the roles of diverse immune cells, cytokines, and chemokines, unravelling the intricacies of neuroinflammation modulation and its subsequent effects. By exploring HSV's immune manipulation and exploitation mechanisms, this review endeavours to unveil the enigmas surrounding the immunopathology of HSV-associated neuroinflammation. This comprehensive understanding enhances our grasp of viral pathogenesis and holds promise for pioneering therapeutic strategies designed to mitigate the neurological ramifications of HSV infections.

The spatiotemporal distribution and prognostic factors of Japanese encephalitis in Shanxi Province, China, 2005-2022

Japanese encephalitis (JE) is a naturally occurring localized disease caused by the Japanese encephalitis virus, which is spread by the Culex tritaeniorhynchus. China has a high rate of JE. Shanxi, located in North China, has a high prevalence of adult JE. Adult JE has more severe complications, mortality, and a higher disease burden, making it a public health issue. This retrospective study examined the dynamic epidemic changes, high-risk areas of JE, and clinical characteristics and prognostic factors of adult JE in Shanxi Province. The findings revealed that July to September was the primary epidemic season of JE and that JE cases were mainly in individuals over the age of 40. The incidence of JE from 2005 to 2022 demonstrated a positive spatial correlation with significant clustering characteristics, with high-incidence clusters in the south and southeast. Multivariate logistic regression analysis revealed that higher cerebrospinal fluid pressure, higher white blood cell counts, higher neutrophil percentage, deep coma, and lower albumin were independent factors for poor prognosis of adult JE. The developed risk prediction model holds great promise in early prognosis assessment of patients, providing a basis for clinical decision-making and early clinical intervention.

Japanese Encephalitis virus infection in astrocytes modulate microglial function: Correlation with inflammation and oxidative stress

BACKGROUND

Japanese Encephalitis Virus (JEV) is a neurotropic virus which has the propensity to infect neuronal and glial cells of the brain. Astrocyte-microglia crosstalk leading to the secretion of various factors plays a major role in controlling encephalitis in brain. This study focused on understanding the role of astrocytic mediators that further shaped the microglial response towards JEV infection.

METHODS

After establishing JEV infection in C8D1A (mouse astrocyte cell line) and primary astrocyte enriched cultures (PAEC), astrocyte supernatant was used for preparation of conditioned media. Astrocyte supernatant was treated with UV to inactivate JEV and the supernatant was added to N9 culture media in ratio 1:1 for preparation of conditioned media. N9 microglial cells post treatment with astrocyte conditioned media and JEV infection were checked for expression of various inflammatory genes by qRT-PCR, levels of secreted cytokines in N9 cell supernatant were checked by cytometric bead array. N9 cell lysates were checked for expression of proteins - pNF-κβ, IBA-1, NS3 and RIG-I by western blotting. Viral titers were measured in N9 supernatant by plaque assays. Immunocytochemistry experiments were done to quantify the number of infected microglial cells after astrocyte conditioned medium treatment. Expression of different antioxidant enzymes was checked in N9 cells by western blotting, levels of reactive oxygen species (ROS) was detected by fluorimetry using DCFDA dye.

RESULTS

N9 microglial cells post treatment with JEV-infected astrocyte conditioned media and JEV infection were activated, showed an upsurge in expression of inflammatory genes and cytokines both at the transcript and protein levels. These N9 cells showed a decrease in quantity of viral titers and associated viral proteins in comparison to control cells (not treated with conditioned media but infected with JEV). Also, N9 cells upon conditioned media treatment and JEV infection were more prone to undergo oxidative stress as observed by the decreased expression of antioxidant enzymes SOD-1, TRX-1 and increased secretion of reactive oxygen species (ROS).

CONCLUSION

Astrocytic mediators like TNF-α, MCP-1 and IL-6 influence microglial response towards JEV infection by promoting inflammation and oxidative stress in them. As a result of increased microglial inflammation and secretion of ROS, viral replication is lessened in conditioned media treated and JEV infected microglial cells as compared to control cells with no conditioned media treatment but only JEV infection.

Type I/type III IFN and related factors regulate JEV infection and BBB endothelial integrity

BACKGROUND

Japanese encephalitis virus (JEV) remains a predominant cause of Japanese encephalitis (JE) globally. Its infection is usually accompanied by disrupted blood‒brain barrier (BBB) integrity and central nervous system (CNS) inflammation in a poorly understood pathogenesis. Productive JEV infection in brain microvascular endothelial cells (BMECs) is considered the initial event of the virus in penetrating the BBB. Type I/III IFN and related factors have been described as negative regulators in CNS inflammation, whereas their role in JE remains ambiguous.

METHODS

RNA-sequencing profiling (RNA-seq), real-time quantitative PCR, enzyme-linked immunosorbent assay, and Western blotting analysis were performed to analyze the gene and protein expression changes between mock- and JEV-infected hBMECs. Bioinformatic tools were used to cluster altered signaling pathway members during JEV infection. The shRNA-mediated immune factor-knockdown hBMECs and the in vitro transwell BBB model were utilized to explore the interrelation between immune factors, as well as between immune factors and BBB endothelial integrity.

RESULTS

RNA-Seq data of JEV-infected hBMECs identified 417, 1256, and 2748 differentially expressed genes (DEGs) at 12, 36, and 72 h post-infection (hpi), respectively. The altered genes clustered into distinct pathways in gene ontology (GO) terms and KEGG pathway enrichment analysis, including host antiviral immune defense and endothelial cell leakage. Further investigation revealed that pattern-recognition receptors (PRRs, including TLR3, RIG-I, and MDA5) sensed JEV and initiated IRF/IFN signaling. IFNs triggered the expression of interferon-induced proteins with tetratricopeptide repeats (IFITs) via the JAK/STAT pathway. Distinct PRRs exert different functions in barrier homeostasis, while treatment with IFN (IFN-β and IFN-λ1) in hBMECs stabilizes the endothelial barrier by alleviating exogenous destruction. Despite the complex interrelationship, IFITs are considered nonessential in the IFN-mediated maintenance of hBMEC barrier integrity.

CONCLUSIONS

This research provided the first comprehensive description of the molecular mechanisms of host‒pathogen interplay in hBMECs responding to JEV invasion, in which type I/III IFN and related factors strongly correlated with regulating the hBMEC barrier and restricting JEV infection. This might help with developing an attractive therapeutic strategy in JE.

Mice as an Animal Model for Japanese Encephalitis Virus Research: Mouse Susceptibility, Infection Route, and Viral Pathogenesis

Japanese encephalitis virus (JEV), a zoonotic flavivirus, is principally transmitted by hematophagous mosquitoes, continually between susceptible animals and incidentally from those animals to humans. For almost a century since its discovery, JEV was geographically confined to the Asia-Pacific region with recurrent sizable outbreaks involving wildlife, livestock, and people. However, over the past decade, it has been detected for the first time in Europe (Italy) and Africa (Angola) but has yet to cause any recognizable outbreaks in humans. JEV infection leads to a broad spectrum of clinical outcomes, ranging from asymptomatic conditions to self-limiting febrile illnesses to life-threatening neurological complications, particularly Japanese encephalitis (JE). No clinically proven antiviral drugs are available to treat the development and progression of JE. There are, however, several live and killed vaccines that have been commercialized to prevent the infection and transmission of JEV, yet this virus remains the main cause of acute encephalitis syndrome with high morbidity and mortality among children in the endemic regions. Therefore, significant research efforts have been directed toward understanding the neuropathogenesis of JE to facilitate the development of effective treatments for the disease. Thus far, multiple laboratory animal models have been established for the study of JEV infection. In this review, we focus on mice, the most extensively used animal model for JEV research, and summarize the major findings on mouse susceptibility, infection route, and viral pathogenesis reported in the past and present, and discuss some unanswered key questions for future studies.

Steroids for the treatment of viral encephalitis: a systematic literature review and meta-analysis

BACKGROUND

Specific antiviral treatment is only available for a small subset of viral encephalitis (VE). Adjunctive steroids are used, but there is scant evidence evaluating its utility. We present a systematic review and meta-analysis on the outcome of steroid use in VE.

METHODS

We conducted a systematic literature review and reported it according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) standards. Two observational studies from unpublished or partially published data were added. For the meta-analysis, we employed the metaphor package of the statistical software R-4.3.1.

RESULTS

We screened 378 studies and included 50. 155 patients were added from the Houston and Linz cohorts. Individual data were available for 281 persons, 120 (43%) of whom received steroids. The most common pathogens were herpes simplex virus 1, West Nile virus, and measles. Study designs and patient outcomes were heterogeneous. Only three of the trials report an advantage of steroid therapy. Steroid-induced side effects were scarce. Ten cohorts were included into the meta-analysis. For the pooled data, the null hypothesis could not be rejected (p = 0.245) using a random effects model, i.e., a benefit of steroid treatment on survival in VE could not be shown.

CONCLUSIONS

Steroids as potent anti-inflammatory agents may act through a reduction of secondary inflammation-mediated damage. Our data do not support the use of steroids in VE. However, multiple shortcomings apply. Standardized controlled trials are needed to investigate optimal dosing and timing of steroid administration and to explore potential subgroups that could benefit.

The role of the blood-brain barrier during neurological disease and infection

A healthy brain is protected by the blood-brain barrier (BBB), which is formed by the endothelial cells that line brain capillaries. The BBB plays an extremely important role in supporting normal neuronal function by maintaining the homeostasis of the brain microenvironment and restricting pathogen and toxin entry to the brain. Dysfunction of this highly complex and regulated structure can be life threatening. BBB dysfunction is implicated in many neurological diseases such as stroke, Alzheimer's disease, multiple sclerosis, and brain infections. Among other mechanisms, inflammation and/or flow disturbances are major causes of BBB dysfunction in neurological infections and diseases. In particular, in ischaemic stroke, both inflammation and flow disturbances contribute to BBB disruption, leading to devastating consequences. While a transient or minor disruption to the barrier function could be tolerated, chronic or a total breach of the barrier can result in irreversible brain damage. It is worth noting that timing and extent of BBB disruption play an important role in the process of any repair of brain damage and treatment strategies. This review evaluates and summarises some of the latest research on the role of the BBB during neurological disease and infection with a focus on the effects of inflammation and flow disturbances on the BBB. The BBB's crucial role in protecting the brain is also the bottleneck in central nervous system drug development. Therefore, innovative strategies to carry therapeutics across the BBB and novel models to screen drugs, and to study the complex, overlapping mechanisms of BBB disruption are urgently needed.

Immune Functions of Astrocytes in Viral Neuroinfections

Neuroinfections of the central nervous system (CNS) can be triggered by various pathogens. Viruses are the most widespread and have the potential to induce long-term neurologic symptoms with potentially lethal outcomes. In addition to directly affecting their host cells and inducing immediate changes in a plethora of cellular processes, viral infections of the CNS also trigger an intense immune response. Regulation of the innate immune response in the CNS depends not only on microglia, which are fundamental immune cells of the CNS, but also on astrocytes. These cells align blood vessels and ventricle cavities, and consequently, they are one of the first cell types to become infected after the virus breaches the CNS. Moreover, astrocytes are increasingly recognized as a potential viral reservoir in the CNS; therefore, the immune response initiated by the presence of intracellular virus particles may have a profound effect on cellular and tissue physiology and morphology. These changes should be addressed in terms of persisting infections because they may contribute to recurring neurologic sequelae. To date, infections of astrocytes with different viruses originating from genetically distinct families, including Flaviviridae, Coronaviridae, Retroviridae, Togaviridae, Paramyxoviridae, Picomaviridae, Rhabdoviridae, and Herpesviridae, have been confirmed. Astrocytes express a plethora of receptors that detect viral particles and trigger signaling cascades, leading to an innate immune response. In this review, we summarize the current knowledge on virus receptors that initiate the release of inflammatory cytokines from astrocytes and depict the involvement of astrocytes in immune functions of the CNS.

Mechanisms of Neuroinvasion and Neuropathogenesis by Pathologic Flaviviruses

Flaviviruses are present on every continent and cause significant morbidity and mortality. In many instances, severe cases of infection with flaviviruses involve the invasion of and damage to the central nervous system (CNS). Currently, there are several mechanisms by which it has been hypothesized flaviviruses reach the brain, including the disruption of the blood-brain barrier (BBB) which acts as a first line of defense by blocking the entry of many pathogens into the brain, passing through the BBB without disruption, as well as travelling into the CNS through axonal transport from peripheral nerves. After flaviviruses have entered the CNS, they cause different neurological symptoms, leading to years of neurological sequelae or even death. Similar to neuroinvasion, there are several identified mechanisms of neuropathology, including direct cell lysis, blockage of the cell cycle, indication of apoptosis, as well as immune induced pathologies. In this review, we aim to summarize the current knowledge in the field of mechanisms of both neuroinvasion and neuropathogenesis during infection with a variety of flaviviruses and examine the potential contributions and timing of each discussed pathway.

Japanese Encephalitis Virus-Infected Cells

RNA virus infections have been a leading cause of pandemics. Aided by global warming and increased connectivity, their threat is likely to increase over time. The flaviviruses are one such RNA virus family, and its prototypes such as the Japanese encephalitis virus (JEV), Dengue virus, Zika virus, West Nile virus, etc., pose a significant health burden on several endemic countries. All viruses start off their life cycle with an infected cell, wherein a series of events are set in motion as the virus and host battle for autonomy. With their remarkable capacity to hijack cellular systems and, subvert/escape defence pathways, viruses are able to establish infection and disseminate in the body, causing disease. Using this strategy, JEV replicates and spreads through several cell types such as epithelial cells, fibroblasts, monocytes and macrophages, and ultimately breaches the blood-brain barrier to infect neurons and microglia. The neurotropic nature of JEV, its high burden on the paediatric population, and its lack of any specific antivirals/treatment strategies emphasise the need for biomedical research-driven solutions. Here, we highlight the latest research developments on Japanese encephalitis virus-infected cells and discuss how these can aid in the development of future therapies.

Recent advances to overcome the burden of Japanese encephalitis: A zoonotic infection with problematic early detection

Japanese encephalitis (JE) is a vector-borne neurotropic disease caused by Japanese encephalitis virus (JEV) associated with high mortality rate distributed from Eastern and Southern Asia to Northern Queensland (Australia). The challenges in early detection and lack of point-of-care biomarkers make it the most important Flavivirus causing encephalitis. There is no specific treatment for the disease, although vaccines are licenced. In this review, we focussed on point-of-care biomarkers as early detection tools and developing the effective therapeutic agents that could halt JE. We have also provided molecular details of JEV, disease progression, and its pathogenesis with recent findings which might bring insights to overcome the disease burden.

RIG-I contributes to dsDNA-induced innate immune activation in human brain microvascular endothelial cells

Human brain microvascular epithelial cells (HBMECs) play a pivotal role in maintaining the stability of the blood-brain barrier (BBB), a potent physiological barrier to prevent the invasion of exotic pathogens. Our previous study indicated that polyI:C, an analog of double-stranded RNA (dsRNA), could initiate the TLR3/IFNs antiviral signaling pathway in HBMECs. However, the response of HBMECs to dsDNA remains unclear. In this study, we demonstrated that a dsDNA mimic, poly(dA:dT), could induce the production of a series of antiviral factors, including IFN-β, IFN-λ1, and ISGs. Furthermore, the poly(dA:dT)-activated HBMECs could effectively restrain HSV-1 replication. In addition, we found that RIG-I rather than cGAS and IFI16 had a more crucial role in sensing poly(dA:dT). These observations indicate that HBMECs possess a dsDNA sensing system, and RIG-I may partly contribute to the dsDNA-induced antiviral innate immunity.

Novel Antiviral Efficacy of Hedyotis diffusa and Artemisia capillaris Extracts against Dengue Virus, Japanese Encephalitis Virus, and Zika Virus Infection and Immunoregulatory Cytokine Signatures

Currently, there are no specific therapeutics for flavivirus infections, including dengue virus (DENV) and Zika virus (ZIKV). In this study, we evaluated extracts from the plants Hedyotis diffusa (HD) and Artemisia capillaris (AC) to determine the antiviral activity against DENV, ZIKV, and Japanese encephalitis virus (JEV). HD and AC demonstrated inhibitory activity against JEV, ZIKV, and DENV replication and reduced viral RNA levels in a dose-responsive manner, with non-cytotoxic concentration ranging from 0.1 to 10 mg/mL. HD and AC had low cytotoxicity to Vero cells, with CC₅₀ values of 33.7 ± 1.6 and 30.3 ± 1.7 mg/mL (mean ± SD), respectively. The anti-flavivirus activity of HD and AC was also consistent in human cell lines, including human glioblastoma (T98G), human chronic myeloid leukemia (K562), and human embryonic kidney (HEK-293T) cells. Viral-infected, HD-treated cells demonstrated downregulation of cytokines including CCR1, CCL26, CCL15, CCL5, IL21, and IL17C. In contrast, CCR1, CCL26, and AIMP1 were elevated following AC treatment in viral-infected cells. Overall, HD and AC plant extracts demonstrated flavivirus replication inhibitory activity, and together with immunoregulatory cytokine signatures, these results suggest that HD and AC possess bioactive compounds that may further be refined as promising candidates for clinical applications.

A Journey to the Central Nervous System: Routes of Flaviviral Neuroinvasion in Human Disease

Many arboviruses, including viruses of the Flavivirus genera, are known to cause severe neurological disease in humans, often with long-lasting, debilitating sequalae in surviving patients. These emerging pathogens impact millions of people worldwide, yet still relatively little is known about the exact mechanisms by which they gain access to the human central nervous system. This review focusses on potential haematogenous and transneural routes of neuroinvasion employed by flaviviruses and identifies numerous gaps in knowledge, especially regarding lesser-studied interfaces of possible invasion such as the blood-cerebrospinal fluid barrier, and novel routes such as the gut-brain axis. The complex balance of pro-inflammatory and antiviral immune responses to viral neuroinvasion and pathology is also discussed, especially in the context of the hypothesised Trojan horse mechanism of neuroinvasion. A greater understanding of the routes and mechanisms of arboviral neuroinvasion, and how they differ between viruses, will aid in predictive assessments of the neuroinvasive potential of new and emerging arboviruses, and may provide opportunity for attenuation, development of novel intervention strategies and rational vaccine design for highly neurovirulent arboviruses.

The role of glutathione conjugation on the transcellular transport process of PEGylated liposomes across the blood brain barrier

Notwithstanding the growing evidence of improved drug delivery efficiency to the brain by ligand modification of PEGylated liposomes, the comprehensive knowledge of their transport processes and payload across the BBB is yet to be revealed. Herein, this study sought to understand the glutathione (GSH) ligand effect on transcellular transport mechanisms of liposomes through the blood-brain barrier (BBB) by comparing PEGylated liposomes (PEG-L) and GSH PEGylated liposomes (GSH-PEG-L). Endocytosis and exocytosis of liposomes including the role of secreted extracellular vesicles (EVs) of brain endothelial cells (BECs) were assessed. Further pharmacokinetics and brain distribution analysis of gemcitabine loaded liposomes were carried in healthy rats to ascertain the in vivo applicability. Our findings suggested that the presence of GSH increased the cellular uptake of liposomes by up to 3-fold in human brain microvascular endothelial cells depending on the dose but not in astrocytes. The cell exposure to liposomes particularly GSH-PEG-L dramatically increased the cell secretion of small and microvesicles with liposomal components, though different liposomes preferred different vesicles for exocytosis. This correlated with GSH-PEG-L transport efficiency of 4% across the in vitro BBB model in 24 h, 1.7-fold higher than that of PEG-L (p < 0.05). In rats, while PEG-L and GSH-PEG-L showed similar pharmacokinetic profiles and prolonged circulation properties, 3.8% of the total injected dose (ID) of gemcitabine was found in the brain of the GSH-PEG-L group at 8 h post-injection, compared with 2.8% ID in the PEG-L group. A brain: blood concentration ratio of 1.27 ± 0.12 indicated that an active transport mechanism to cross the BBB for GSH-PEG-L. Overall, this study revealed that GSH augmented the transcellular transport efficiency of liposomes through BBB to improve targeted brain delivery by enhancing cellular uptake and vesicular exocytosis route of BECs.

Japanese encephalitis viral infection modulates proinflammatory cyto/chemokine profile in primary astrocyte and cell line of astrocytic origin

Japanese Encephalitis Virus (JEV) is a neurotropic virus that invades Central Nervous System (CNS) and causes severe neuroinflammation. Given the abundance and the position of astrocytes in the CNS, we speculate that they might play a critical role in the process of neuroinflammation. Unfortunately, the role of astrocytes in JEV-mediated neuroinflammation has long been understated. In this study, we have attempted to assess the role of astrocyte-mediated neuroinflammation upon JEV infection. Mouse model of JEV infection, generated by intraperitoneal injection, showed severe reactive astrogliosis. To further address our hypothesis, we employed immortalized astrocytic cell line (in vitro) and primary astrocyte-enriched culture (ex vivo) as experimental models. JEV infection in the astrocytes induces proinflammatory cytokines like MCP1/CCL2 and IL6 in both ex vivo and in vitro cultures as observed from the cytometric bead array analysis. A significantly altered cytokine profile was observed using PCR analysis in in vitro and ex vivo models upon infection, with respect to control, validating our previous results. We also show that there exists a major inconsistency in the viral replication kinetics, wherein the cell line showed a robust rate of replication whereas the primary astrocyte-enriched culture showed negligibly low number of plaques, underlining the importance of the selection of appropriate experimental model system. In conclusion, we claim that astrocytes significantly contribute to JEV-mediated neuroinflammation, despite not being a CNS immune cell.

Meningeal lymphatic vessels mediate neurotropic viral drainage from the central nervous system

Recent studies have demonstrated that brain meningeal lymphatic vessels (MLVs) act as a drainage path directly into the cervical lymph nodes (CLNs) for macromolecules contained in the cerebrospinal fluid (CSF). However, the role of MLVs during CNS viral infection remains unexplored. Here, we found that infection with several neurotropic viruses in mice promotes MLV expansion but also causes impaired MLV-mediated drainage of macromolecules. Notably, MLVs could drain virus from the CNS to CLNs. Surgical ligation of the lymph vessels or photodynamic ablation of dorsal MLVs increased neurological damage and mortality of virus-infected mice. By contrast, pretreatment with vascular endothelial growth factor C promoted expansion of functional MLVs and alleviated the effects of viral infection. Together, these data indicate that functional MLVs facilitate virus clearance, and MLVs represent a critical path for virus spreading from the CNS to the CLNs. MLV-based therapeutic strategies may thus be useful for alleviating infection-induced neurological damage.

Microglia in antiviral immunity of the brain and spinal cord

Viral infections of the central nervous system (CNS) are a significant cause of neurological impairment and mortality worldwide. As tissue resident macrophages, microglia are critical initial responders to CNS viral infection. Microglia seem to coordinate brain-wide antiviral responses of both brain resident cells and infiltrating immune cells. This review discusses how microglia may promote this antiviral response at a molecular level, from potential mechanisms of virus recognition to downstream cytokine responses and interaction with antiviral T cells. Recent advancements in genetic tools to specifically target microglia in vivo promise to further our understanding about the precise mechanistic role of microglia in CNS infection.

Detection of Japanese Encephalitis by Metagenomic Next-Generation Sequencing of Cerebrospinal Fluid: A Case Report and Literature Review

Japanese encephalitis (JE) is an acute viral central nervous system disease, although less than 1% of patients infected with Japanese encephalitis virus (JEV) result in JE, which has an extremely poor prognosis. The Routine detection methods for JEV are time-consuming or limited by hospital conditions, therefore, need the quicker and sensitive techniques to detect JEV. Here, we reported a 14-year-old female who was admitted to our hospital with a severe fever, progressively headache and unconsciousness. Based on the clinical presentation, Preliminary diagnosis on admission indicated central nervous system infection of suspected viral meningoencephalitis or autoimmune encephalitis. The patient's symptoms were unrelieved after being treated with empiric antiviral therapy. Magnetic resonance imaging (MRI) showed that the lesions were located in the bilateral thalamus, head of caudate nucleus, and right lenticular nucleus, so we had to consider the possibility of Flaviviruses infection. We sent the cerebrospinal fluid (CSF) for metagenomic next-generation sequencing (mNGS) immediately, subsequent result suggested the infection caused by JEV. Two days later the results of the serum agglutination test confirmed that virus immunoglobulin M antibody positive. After a week treatment with intravenous immunoglobulin (IVIG), meanwhile, the lumbar puncture was used to check the pressure and various indicators of the CSF again to evaluate the treatment effect, An decrease in the number of WBC indicates, protein and unique RNA reads that the previous experimental treatment was effective, accompany by temperature and consciousness of the patient was normalized. Two weeks after admission, the patient was transferred to the rehabilitation hospital, MR showed the lesions had disappeared completely after 2 months of follow-up. We believed that mNGS may be an effective method for rapid identification of JE.

Vectorial Release of Human RNA Viruses from Epithelial Cells

Epithelial cells are apico-basolateral polarized cells that line all tubular organs and are often targets for infectious agents. This review focuses on the release of human RNA virus particles from both sides of polarized human cells grown on transwells. Most viruses that infect the mucosa leave their host cells mainly via the apical side while basolateral release is linked to virus propagation within the host. Viruses do this by hijacking the cellular factors involved in polarization and trafficking. Thus, understanding epithelial polarization is essential for a clear understanding of virus pathophysiology.

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.

In human astrocytes neurotropic flaviviruses increase autophagy, yet their replication is autophagy-independent

Astrocytes, an abundant type of glial cells, are the key cells providing homeostasis in the central nervous system. Due to their susceptibility to infection, combined with high resilience to virus-induced cell death, astrocytes are now considered one of the principal types of cells, responsible for virus retention and dissemination within the brain. Autophagy plays an important role in elimination of intracellular components and in maintaining cellular homeostasis and is also intertwined with the life cycle of viruses. The physiological significance of autophagy in astrocytes, in connection with the life cycle and transmission of viruses, remains poorly investigated. In the present study, we investigated flavivirus-induced modulation of autophagy in human astrocytes by monitoring a tandem fluorescent-tagged LC3 probe (mRFP-EGFP-LC3) with confocal and super-resolution fluorescence microscopy. Astrocytes were infected with tick-borne encephalitis virus (TBEV) or West Nile virus (WNV), both pathogenic flaviviruses, and with mosquito-only flavivirus (MOF), which is considered non-pathogenic. The results revealed that human astrocytes are susceptible to infection with TBEV, WNV and to a much lower extent also to MOF. Infection and replication rates of TBEV and WNV are paralleled by increased rate of autophagy, whereas autophagosome maturation and the size of autophagic compartments are not affected. Modulation of autophagy by rapamycin and wortmannin does not influence TBEV and WNV replication rate, whereas bafilomycin A1 attenuates their replication and infectivity. In human astrocytes infected with MOF, the low infectivity and the lack of efficient replication of this flavivirus are mirrored by the absence of an autophagic response.

Pathogenicity and virulence of Japanese encephalitis virus: Neuroinflammation and neuronal cell damage

Thousands of human deaths occur annually due to Japanese encephalitis (JE), caused by Japanese encephalitis virus. During the virus infection of the central nervous system, reactive gliosis, uncontrolled inflammatory response, and neuronal cell death are considered as the characteristic features of JE. To date, no specific treatment has been approved to overcome JE, indicating a need for the development of novel therapies. In this article, we focused on basic biological mechanisms in glial (microglia and astrocytes) and neuronal cells that contribute to the onset of neuroinflammation and neuronal cell damage during Japanese encephalitis virus infection. We also provided comprehensive knowledge about anti-JE therapies tested in clinical or pre-clinical settings, and discussed recent therapeutic strategies that could be employed for JE treatment. The improved understanding of JE pathogenesis might lay a foundation for the development of novel therapies to halt JE.Abbreviations AKT: a serine/threonine-specific protein kinase; AP1: activator protein 1; ASC: apoptosis-associated speck-like protein containing a CARD; ASK1: apoptosis signal-regulated kinase 1; ATF3/4/6: activating transcription factor 3/4/6; ATG5/7: autophagy-related 5/7; BBB: blood-brain barrier; Bcl-3/6: B-cell lymphoma 3/6 protein; CCL: C-C motif chemokine ligand; CCR2: C-C motif chemokine receptor 2; CHOP: C/EBP homologous protein; circRNA: circular RNA; CNS: central nervous system; CXCL: C-X-C motif chemokine ligand; dsRNA: double-stranded RNA; EDEM1: endoplasmic reticulum degradation enhancer mannosidase alpha-like 1; eIF2-ɑ: eukaryotic initiation factor 2 alpha; ER: endoplasmic reticulum; ERK: extracellular signal-regulated kinase; GRP78: 78-kDa glucose-regulated protein; ICAM: intercellular adhesion molecule; IFN: interferon; IL: interleukin; iNOS: inducible nitric oxide synthase; IRAK1/2: interleukin-1 receptor-associated kinase 1/2; IRE-1: inositol-requiring enzyme 1; IRF: interferon regulatory factor; ISG15: interferon-stimulated gene 15; JE: Japanese encephalitis; JEV: Japanese encephalitis virus; JNK: c-Jun N-terminal kinase; LAMP2: lysosome-associated membrane protein type 2; LC3-I/II: microtubule-associated protein 1 light chain 3-I/II; lncRNA: long non-coding RNA; MAPK: mitogen-activated protein kinase; miR/miRNA: microRNA; MK2: mitogen-activated protein kinase-activated protein kinase 2; MKK4: mitogen-activated protein kinase kinase 4; MLKL: mixed-linage kinase domain-like protein; MMP: matrix metalloproteinase; MyD88: myeloid differentiation factor 88; Nedd4: neural precursor cell-expressed developmentally downregulated 4; NF-κB: nuclear factor kappa B; NKRF: nuclear factor kappa B repressing factor; NLRP3: NLR family pyrin domain containing 3; NMDAR: N-methyl-D-aspartate receptor; NO: nitric oxide; NS2B/3/4: JEV non-structural protein 2B/3/4; P: phosphorylation. p38: mitogen-activated protein kinase p38; PKA: protein kinase A; PAK4: p21-activated kinase 4; PDFGR: platelet-derived growth factor receptor; PERK: protein kinase R-like endoplasmic reticulum kinase; PI3K: phosphoinositide 3-kinase; PTEN: phosphatase and tensin homolog; Rab7: Ras-related GTPase 7; Raf: proto-oncogene tyrosine-protein kinase Raf; Ras: a GTPase; RIDD: regulated IRE-1-dependent decay; RIG-I: retinoic acid-inducible gene I; RIPK1/3: receptor-interacting protein kinase 1/3; RNF11/125: RING finger protein 11/125; ROS: reactive oxygen species; SHIP1: SH2-containing inositol 5' phosphatase 1; SOCS5: suppressor of cytokine signaling 5; Src: proto-oncogene tyrosine-protein kinase Src; ssRNA = single-stranded RNA; STAT: signal transducer and activator of transcription; TLR: toll-like receptor; TNFAIP3: tumor necrosis factor alpha-induced protein 3; TNFAR: tumor necrosis factor alpha receptor; TNF-α: tumor necrosis factor-alpha; TRAF6: tumor necrosis factor receptor-associated factor 6; TRIF: TIR-domain-containing adapter-inducing interferon-β; TRIM25: tripartite motif-containing 25; VCAM: vascular cell adhesion molecule; ZO-1: zonula occludens-1.

The Effect of a Combined Ganciclovir, Methylprednisolone, and Immunoglobulin Regimen on Survival and Functional Outcomes in Patients With Japanese Encephalitis

Objective: There is currently no effective treatment for Japanese encephalitis, which has a high rate of morbidity and mortality. This study assessed the effectiveness of a ganciclovir, methylprednisolone, and immunoglobulin combination (TAGMIC) therapy in decreasing cognitive impairment and mortality among patients with Japanese encephalitis.

Methods: We retrospectively assessed the clinical data of 31 patients diagnosed with Japanese encephalitis, who were admitted to an intensive care unit. Patients were divided into the TAGMIC and non-TAGMIC group according to their treatment regime. We compared the 60-day, 6-month, and overall mortality and survival curves between groups. We also compared Barthel Index scores, Montreal Cognitive Assessment (MoCA) scores, and diffusion tensor imaging (DTI) results.

Results: There was no significant difference in the 30-day mortality rate or Kaplan–Meier survival curve between groups. The 60-day, 6-month, and overall mortality rates in the TAGMIC group were significantly reduced (P = 0.043, P = 0.018, and P = 0.018, respectively) compared with the non-TAGMIC group (0, 0, 0 vs. 31.25, 37.5, 37.5%, respectively). The 60-day, 6-month, and overall Kaplan–Meier survival curves were significantly different between groups (P = 0.020, P = 0.009, P = 0.009, respectively). There was no significant difference in the Barthel Index scores of surviving patients. Among the five patients who underwent MoCA and DTI, four had a score of 0/5 for delayed recall (no cue), while the remaining patient had a score of 2/5. All five patients were able to achieve a score of 5/5 with classification and multiple-choice prompts, and had sparse or broken corpus callosum (or other) fibre bundles.

Conclusion: TAGMIC treatment can reduce mortality due to severe Japanese encephalitis. The memory loss of surviving patients is mainly due to a disorder of the memory retrieval process, which may be related to the breakage of related fibre bundles.

Proteomic landscape of Japanese encephalitis virus-infected fibroblasts

Advances in proteomics have enabled a comprehensive understanding of host-pathogen interactions. Here we have characterized Japanese encephalitis virus (JEV) infection-driven changes in the mouse embryonic fibroblast (MEF) proteome. Through tandem mass tagging (TMT)-based mass spectrometry, we describe changes in 7.85 % of the identified proteome due to JEV infection. Pathway enrichment analysis showed that proteins involved in innate immune sensing, interferon responses and inflammation were the major upregulated group, along with the immunoproteasome and poly ADP-ribosylation proteins. Functional validation of several upregulated anti-viral innate immune proteins, including an active cGAS-STING axis, was performed. Through siRNA depletion, we describe a crucial role of the DNA sensor cGAS in restricting JEV replication. Further, many interferon-stimulated genes (ISGs) were observed to be induced in infected cells. We also observed activation of TLR2 and inhibition of TLR2 signalling using TLR1/2 inhibitor CU-CPT22-blocked production of inflammatory cytokines IL6 and TNF-α from virus-infected N9 microglial cells. The major proteins that were downregulated by infection were involved in cell adhesion (collagens), transport (solute carrier and ATP-binding cassette transporters), sterol and lipid biosynthesis. Several collagens were found to be transcriptionally downregulated in infected MEFs and mouse brain. Collectively, our data provide a bird's-eye view into how fibroblast protein composition is rewired following JEV infection.

Pathobiology of Japanese encephalitis virus infection

Japanese encephalitis virus (JEV) is a flavivirus, spread by the bite of carrier Culex mosquitoes. The subsequent disease caused is Japanese encephalitis (JE), which is the leading global cause of virus-induced encephalitis. The disease is predominant in the entire Asia-Pacific region with the potential of global spread. JEV is highly neuroinvasive with symptoms ranging from mild fever to severe encephalitis and death. One-third of JE infections are fatal, and half of the survivors develop permanent neurological sequelae. Disease prognosis is determined by a series of complex and intertwined signaling events dictated both by the virus and the host. All flaviviruses, including JEV replicate in close association with ER derived membranes by channelizing the protein and lipid components of the ER. This leads to activation of acute stress responses in the infected cell-oxidative stress, ER stress, and autophagy. The host innate immune and inflammatory responses also enter the fray, the components of which are inextricably linked to the cellular stress responses. These are especially crucial in the periphery for dendritic cell maturation and establishment of adaptive immunity. The pathogenesis of JEV is a combination of direct virus induced neuronal cell death and an uncontrolled neuroinflammatory response. Here we provide a comprehensive review of the JEV life cycle and how the cellular stress responses dictate the pathobiology and resulting immune response. We also deliberate on how modulation of these stress pathways could be a potential strategy to develop therapeutic interventions, and define the persisting challenges.

In vivo oxygen measurement in cerebrospinal fluid of pigs to determine physiologic and pathophysiologic oxygen values during CNS infections

During infection and inflammation, a reduced oxygen level clearly affects cellular functions. Oxygen levels during CNS infections are unknown. Here we established and evaluated an in vivo measurement system to characterize the oxygen level in parallel with bacterial numbers (CFU/mL), the cell number and pH level inside the CSF of healthy compared to Streptococcus suis-infected pigs. The animals were anesthetized over a seven-hour period with isoflurane in air/oxygen at physiologic arterial partial pressure of oxygen. Oxygen levels in CSF of anesthetized pigs were compared to euthanized pigs. The detected partial pressure of oxygen in the CSF remained constant in a range of 47-63 mmHg, independent of the infection status (bacterial or cell number). In contrast, the pH value showed a slight drop during infection, which correlated with cell and bacterial number in CSF. We present physiologic oxygen and pH values in CSF during the onset of bacterial meningitis.

Blood-brain barrier disruption in atrial fibrillation: a potential contributor to the increased risk of dementia and worsening of stroke outcomes?

Atrial fibrillation (AF) has become one of the most significant health problems worldwide, warranting urgent answers to currently pending questions on the effects of AF on brain function. Recent evidence has emerged to show an association between AF and an increased risk of developing dementia and worsening of stroke outcomes. A healthy brain is protected by the blood–brain barrier (BBB), which is formed by the endothelial cells that line cerebral capillaries. These endothelial cells are continuously exposed to shear stress (the frictional force generated by blood flow), which affects endothelial cell structure and function. Flow disturbances as experienced during AF can disrupt the BBB and leave the brain vulnerable to damage. Investigating the plausible mechanisms in detail, linking AF to cerebrovascular damage is difficult in humans, leading to paucity of available clinical data. Here, we discuss the available evidence for BBB disruption during AF due to altered cerebral blood flow, and how this may contribute to an increased risk of dementia and worsening of stroke outcomes.

Cryopreservation of human cerebral microvascular endothelial cells and astrocytes in suspension and monolayers

The blood-brain barrier (BBB) keeps pathogens and toxins out of the brain but also impedes the entry of pharmaceuticals. Human cerebral microvascular endothelial cells (hCMECs) and astrocytes are the main functional cell components of the BBB. Although available commercially as cryopreserved cells in suspension, improvements in their cryopreservation and distribution as cryopreserved monolayers could enhance BBB in vitro studies. Here, we examined the response to slow cooling and storage in liquid nitrogen of immortalized hCMEC/D3 cells and human primary astrocytes in suspension and in monolayers. HCMEC/D3 cells in suspension cryopreserved in 5% dimethyl sulfoxide (DMSO) and 95% fetal bovine serum or in 5% DMSO and 6% hydroxyethyl starch (HES) showed post-thaw membrane integrities above 90%, similar to unfrozen control. Cryopreservation did not affect the time-dependent ability of hCMEC/D3 cells to form tubes on Matrigel. Primary astrocytes in suspension cryopreserved in the presence of 5% DMSO and 6% HES had improved viability over those cryopreserved in 10% DMSO. Monolayers of single cultures or co-cultures of hCMEC/D3 cells and astrocytes on fibronectin-coated Rinzl coverslips retained membrane integrities and metabolic function, after freezing in 5% DMSO, 6% HES, and 2% chondroitin sulfate, that were comparable to those of unfrozen controls even after overnight incubation. Rinzl is better than glass or Thermanox as an underlying solid substrate for cryopreserving hCMEC/D3 monolayers. Cryopreserved hCMEC/D3 monolayers expressed the junction proteins ZO-1 and claudin-5 similar to their unfrozen counterparts. Hence, we describe improved cryopreservation protocols for hCMEC/D3 cells and astrocytes in suspension, and a novel protocol for the cryopreservation of monolayers of hCMEC/D3 cells and astrocytes as single cultures or co-cultures that could expand their distribution for research on disease modeling, drug screening, and targeted therapy pertaining to the BBB.

Neurotropic Viruses, Astrocytes, and COVID-19

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

Tembusu Virus entering the central nervous system caused nonsuppurative encephalitis without disrupting the blood-brain barrier

Tembusu Virus (TMUV) is an emerging and re-emerging zoonotic pathogen that adversely affects poultry industry in recent years. TMUV disease is characterized by nonsuppurative encephalitis in ducklings. The duckling infection model was established to study the mechanism of TMUV crossing the blood-brain barrier (BBB) into the central nervous system (CNS). Here, we showed that no obvious clinical symptoms and enhancement of BBB permeability occurred at the early stage of infection (3∼5 dpi). While simultaneously virus particles were observed by transmission electron microscopy in the brain, inducing the accumulation of inflammatory cytokines. Neurological symptoms and disruption of BBB appeared at the intermediate stage of infection (7∼9 dpi). It was confirmed that TMUV could survive and propagate in brain microvascular endothelial cells (BMECs), but did not affect the permeability of BBB in vivo and in vitro at an early date. In conclusion, TMUV enters the CNS then causes encephalitis, and finally destruct the BBB, which may be due to the direct effect of TMUV on BMECs and the subsequent response of "inflammatory storm".IMPORTANCE The TMUV disease has caused huge losses to the poultry industry in Asia, which is potentially harmful to public health. Neurological symptoms and their sequelae are the main characters of this disease. However, the mechanism of how this virus enters the brain and causes encephalitis is unclear. In this study, we confirmed that the virus entered the CNS and then massively destroyed BBB and the BBB damage was closely associated with the subsequent outbreak of inflammation. TMUV may enter the CNS through the transcellular and "Trojan horse" pathways. These findings can fill the knowledge gap in the pathogenesis of TMUV-infected poultry and be benefit for the treatment of TMUV disease. What's more, TMUV is a representative to study the infection of avian flavivirus. Therefore, our studies have significances both for understanding of the full scope of mechanisms of TMUV and other flavivirus infection, and conceivably, for therapeutics.

Ezrin is essential for the entry of Japanese encephalitis virus into the human brain microvascular endothelial cells

Japanese encephalitis virus (JEV) remains the predominant cause of viral encephalitis worldwide. It reaches the central nervous system upon crossing the blood-brain barrier through pathogenic mechanisms that are not completely understood. Here, using a high-throughput siRNA screening assay combined with verification experiments, we found that JEV enters the primary human brain microvascular endothelial cells (HBMEC) through a caveolae-mediated endocytic pathway. The role of ezrin, an essential host factor for JEV entry based on our screening, in caveolae-mediated JEV internalization was investigated. We observed that JEV internalization in HBMEC is largely dependent on ezrin-mediated actin cytoskeleton polymerization. Moreover, Src, a protein predicted by a STRING database search, was found to be required in JEV entry. By a variety of pharmacological inhibition and immunoprecipitation assays, we found that Src, ezrin, and caveolin-1 were sequentially activated and formed a complex during JEV infection. A combination of in vitro kinase assay and subcellular analysis demonstrated that ezrin is essential for Src-caveolin-1 interactions. In vivo, both Src and ezrin inhibitors protected ICR suckling mice against JEV-induced mortality and diminished mouse brain viral load. Therefore, JEV entry into HBMEC requires the activation of the Src-ezrin-caveolin-1 signalling axis, which provides potential targets for restricting JEV infection.

Immune response and blood-brain barrier dysfunction during viral neuroinvasion

The blood-brain barrier (BBB), which protects the CNS from pathogens, is composed of specialized brain microvascular endothelial cells (BMECs) joined by tight junctions and ensheathed by pericytes and astrocyte endfeet. The stability of the BBB structure and function is of great significance for the maintenance of brain homeostasis. When a neurotropic virus invades the CNS via a hematogenous or non-hematogenous route, it may cause structural and functional disorders of the BBB, and also activate the BBB anti-inflammatory or pro-inflammatory innate immune response. This article focuses on the structural and functional changes that occur in the three main components of the BBB (endothelial cells, astrocytes, and pericytes) in response to infection with neurotropic viruses transmitted by hematogenous routes, and also briefly describes the supportive effect of three cells on the BBB under normal physiological conditions. For example, all three types of cells express several PRRs, which can quickly sense the virus and make corresponding immune responses. The pro-inflammatory immune response will exacerbate the destruction of the BBB, while the anti-inflammatory immune response, based on type I IFN, consolidates the stability of the BBB. Exploring the details of the interaction between the host and the pathogen at the BBB during neurotropic virus infection will help to propose new treatments for viral encephalitis. Enhancing the defense function of the BBB, maintaining the integrity of the BBB, and suppressing the pro-inflammatory immune response of the BBB provide more ideas for limiting the neuroinvasion of neurotropic viruses. In the future, these new treatments are expected to cooperate with traditional antiviral methods to improve the therapeutic effect of viral encephalitis.

Zika Virus Infection Promotes Local Inflammation, Cell Adhesion Molecule Upregulation, and Leukocyte Recruitment at the Blood-Brain Barrier

The blood-brain barrier (BBB) largely prevents toxins and pathogens from accessing the brain. Some viruses have the ability to cross this barrier and replicate in the central nervous system (CNS). Zika virus (ZIKV) was responsible in 2015 to 2016 for a major epidemic in South America and was associated in some cases with neurological impairments. Here, we characterized some of the mechanisms behind its neuroinvasion using an innovative in vitro human BBB model. ZIKV efficiently replicated, was released on the BBB parenchyma side, and triggered subtle modulation of BBB integrity as well as an upregulation of inflammatory and cell adhesion molecules (CAMs), which in turn favored leukocyte recruitment. Finally, we showed that ZIKV-infected mouse models displayed similar CAM upregulation and that soluble CAMs were increased in plasma samples from ZIKV-infected patients. Our observations suggest a complex interplay between ZIKV and the BBB, which may trigger local inflammation, leukocyte recruitment, and possible cerebral vasculature impairment.IMPORTANCE Zika virus (ZIKV) can be associated with neurological impairment in children and adults. To reach the central nervous system, viruses have to cross the blood-brain barrier (BBB), a multicellular system allowing a tight separation between the bloodstream and the brain. Here, we show that ZIKV infects cells of the BBB and triggers a subtle change in its permeability. Moreover, ZIKV infection leads to the production of inflammatory molecules known to modulate BBB integrity and participate in immune cell attraction. The virus also led to the upregulation of cellular adhesion molecules (CAMs), which in turn favored immune cell binding to the BBB and potentially increased infiltration into the brain. These results were also observed in a mouse model of ZIKV infection. Furthermore, plasma samples from ZIKV-infected patients displayed an increase in CAMs, suggesting that this mechanism could be involved in neuroinflammation triggered by ZIKV.

Update on T cells in the virally infected brain: friends and foes

PURPOSE OF REVIEW

The present review will outline neuroprotective and neurotoxic effects of central nervous system (CNS) infiltrating T cells during viral infections. Evidence demonstrating differential roles for antiviral effector and resident memory T-cell subsets in virologic control and immunopathology in the CNS will be discussed. Potential therapeutic targets emanating from a growing understanding of T-cell-initiated neuropathology that impacts learning and memory will also be delineated.

RECENT FINDINGS

The critical role for T cells in preventing and clearing CNS infections became incontrovertible during the era of acquired immunodeficiency syndrome. Recent studies have further defined differential roles of T-cell subsets, including resident memory T cells (Trm), in antiviral immunity and, unexpectedly, in postinfectious cognitive dysfunction. Mechanisms of T-cell-mediated effects include differential innate immune signaling within neural cells that are virus-specific.

SUMMARY

T-cell cytokines that are essential for cell-mediated virologic control during neurotropic viral infections have recently been identified as potential targets to prevent post-infection memory disorders. Further identification of T-cell subsets, their antigen specificity, and postinfection localization of Trm will enhance the efficacy of immunotherapies through minimization of immunopathology.

Engagement of people with multiple sclerosis to enhance research into the physiological effect of hyperbaric oxygen therapy

BACKGROUND

Thousands of people with multiple sclerosis (MS) have used self-administered oxygen therapy in the UK. Clinical trials have been performed, with scant evidence that people with MS have been consulted to explore how they benefit from or how to optimize this treatment. The conventional MS disease disability scores used in trials seldom reflect the effects individuals report when using oxygen therapy to treat their symptoms.

METHODS

Three people with MS and the manager of an MS Centre formed a public involvement group and collaborated with clinicians and scientists to inform a lab-based study to investigate the physiological effects of oxygen therapy on microvascular brain endothelial cells.

RESULTS

People with MS often use oxygen therapy at a later stage when their symptoms worsen and only after using other treatments. The frequency of oxygen therapy sessions and hyperbaric pressure is individualized and varies for people with MS. Despite direct comparisons of efficacy proving difficult, most individuals are exposed to 100% O₂ at 1.5 atmosphere absolute (ATA; 1140 mmHg absolute) for 60 min. In a laboratory-based study human brain endothelial cells were exposed in vitro to 152 mmHg O₂ for 60 min with and without pressure, as this equates to 20% O₂ achievable via hyperbarics, which was then replicated at atmospheric pressure. A significant reduction in endothelial cells ICAM-1 (CD54) implicated in inflammatory cell margination across the blood brain barrier was observed under oxygen treatment.

CONCLUSIONS

By collaborating with people living with MS, we were able to design laboratory-based experimental protocols that replicate their treatment regimens to advance our understanding of the physiological effects of hyperbaric oxygen treatment on brain cells and their role in neuroinflammation.

Transcriptional and Functional Changes of the Human Microvasculature during Physiological Aging and Alzheimer Disease

Aging of the circulatory system correlates with the pathogenesis of a large spectrum of diseases. However, it is largely unknown which factors drive the age-dependent or pathological decline of the vasculature and how vascular defects relate to tissue aging. The goal of the study is to design a multianalytical approach to identify how the cellular microenvironment (i.e., fibroblasts) and serum from healthy donors of different ages or Alzheimer disease (AD) patients can modulate the functionality of organ-specific vascular endothelial cells (VECs). Long-living human microvascular networks embedding VECs and fibroblasts from skin biopsies are generated. RNA-seq, secretome analyses, and microfluidic assays demonstrate that fibroblasts from young donors restore the functionality of aged endothelial cells, an effect also achieved by serum from young donors. New biomarkers of vascular aging are validated in human biopsies and it is shown that young serum induces angiopoietin-like-4, which can restore compromised vascular barriers. This strategy is then employed to characterize transcriptional/functional changes induced on the blood-brain barrier by AD serum, demonstrating the importance of PTP4A3 in the regulation of permeability. Features of vascular degeneration during aging and AD are recapitulated, and a tool to identify novel biomarkers that can be exploited to develop future therapeutics modulating vascular function is established.

Recent advances in understanding Japanese encephalitis

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