Neurotropic Viruses, Astrocytes, and COVID-19

The fate of neuronal synapse homeostasis in aging, infection, and inflammation

Neuroplasticity is the brain's ability to reorganize and modify its neuronal connections in response to environmental stimuli, experiences, learning, and disease processes. This encompasses a variety of mechanisms, including changes in synaptic strength and connectivity, the formation of new synapses, alterations in neuronal structure and function, and the generation of new neurons. Proper functioning of synapses, which facilitate neuron-to-neuron communication, is crucial for brain activity. Neuronal synapse homeostasis, which involves regulating and maintaining synaptic strength and function in the central nervous system (CNS), is vital for this process. Disruptions in synaptic balance, due to factors like inflammation, aging, or infection, can lead to impaired brain function. This review highlights the main aspects and mechanisms underlying synaptic homeostasis, particularly in the context of aging, infection, and inflammation.

The Development of Epilepsy Following CNS Viral Infections: Mechanisms

PURPOSE OF REVIEW

This review examines the role of different viral infections in epileptogenesis, with a focus on Herpesviruses such as Human Herpesvirus 6 (HHV-6) and Epstein Barr Virus (EBV), Flaviviruses, Picornaviruses, Human Immunodeficiency Virus (HIV), Influenzavirus and Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS-CoV-2).

RECENT FINDINGS

A growing literature on animal models, such as the paradigmatic Theiler's murine encephalomyelitis virus (TMEV) model, and clinical investigations in patients with epilepsy have started to elucidate cellular mechanisms implicated in seizure initiation and development of epilepsy following viral infections. A central role of neuroinflammation has emerged, with evidence of activation of the innate and adaptive immunity, dysregulation of microglial and astrocytic activity and production of multiple cytokines and other inflammatory mediators. Several chronic downstream effects result in increased blood-brain barrier permeability, direct neuronal damage, and modifications of ion channels ultimately leading to altered neuronal excitability and seizure generation. Key findings underscore the complex interplay between initial viral infection, neuroinflammation, and later development of epilepsy. Further research is needed to elucidate these mechanisms and develop targeted interventions.

Maternal COVID-19 infection associated with offspring neurodevelopmental disorders

Maternal COVID-19 infection increases the incidence of neurodevelopmental disorders (NDDs) in offspring, although the underlying mechanisms have not been elucidated. This study demonstrated that COVID-19 infection during pregnancy disrupted the balance of maternal and fetal immune environments, driving alterations in astrocytes, endothelial cells, and excitatory neurons. A risk score was established using 47 unique genes in the single-cell transcriptome of gestational mothers. The high risk score in CD4 proliferating T cell level served as an indicator for increased risk of offspring NDDs. Summary-based Mendelian randomization and phenome-wide association study analyses were conducted to identify the causal association of the transcriptional changes with the increased risk of offspring NDDs. Additionally, 10 drugs were identified as potential therapeutic candidates. Our findings support a model where the maternal COVID-19 infection changed the levels of CD4 proliferating T cells, leading to the alterations of astrocytes, endothelial cells, and excitatory neurons in offspring, contributing to the increased risk of NDDs in these individuals.

[Interaction of somatic findings and psychiatric symptoms in COVID-19. A scoping review]

An infection with SARS-CoV‑2 can affect the central nervous system, leading to neurological as well as psychiatric symptoms. In this respect, mechanisms of inflammation seem to be of much greater importance than the virus itself. This paper deals with the possible contributions of organic changes to psychiatric symptomatology and deals especially with delirium, cognitive symptoms, depression, anxiety, posttraumatic stress disorder and psychosis. Processes of neuroinflammation with infection of capillary endothelial cells and activation of microglia and astrocytes releasing high amounts of cytokines seem to be of key importance in all kinds of disturbances. They can lead to damage in grey and white matter, impairment of cerebral metabolism and loss of connectivity. Such neuroimmunological processes have been described as a organic basis for many psychiatric disorders, as affective disorders, psychoses and dementia. As the activation of the glia cells can persist for a long time after the offending agent has been cleared, this can contribute to long term sequalae of the infection.

Role of the SARS-CoV-2 Virus in Brain Cells

COVID-19, caused by the SARS-CoV-2 virus, can have neurological effects, including cognitive symptoms like brain fog and memory problems. Research on the neurological effects of COVID-19 is ongoing, and factors such as inflammation, disrupted blood flow, and damage to blood vessels may contribute to cognitive symptoms. Notably, some authors and existing evidence suggest that the SARS-CoV-2 virus can enter the central nervous system through different routes, including the olfactory nerve and the bloodstream. COVID-19 infection has been associated with neurological symptoms such as altered consciousness, headaches, dizziness, and mental disorders. The exact mechanisms and impact on memory formation and brain shrinkage are still being studied. This review will focus on pathways such as the olfactory nerve and blood-brain barrier disruption, and it will then highlight the interactions of the virus with different cell types in the brain, namely neurons, astrocytes, oligodendrocytes, and microglia.

Astrocytes Are a Key Target for Neurotropic Viral Infection

Astrocytes are increasingly recognized as important viral host cells in the central nervous system. These cells can produce relatively high quantities of new virions. In part, this can be attributed to the characteristics of astrocyte metabolism and its abundant and dynamic cytoskeleton network. Astrocytes are anatomically localized adjacent to interfaces between blood capillaries and brain parenchyma and between blood capillaries and brain ventricles. Moreover, astrocytes exhibit a larger membrane interface with the extracellular space than neurons. These properties, together with the expression of various and numerous viral entry receptors, a relatively high rate of endocytosis, and morphological plasticity of intracellular organelles, render astrocytes important target cells in neurotropic infections. In this review, we describe factors that mediate the high susceptibility of astrocytes to viral infection and replication, including the anatomic localization of astrocytes, morphology, expression of viral entry receptors, and various forms of autophagy.

COVID-19 Induces Neuroinflammation and Suppresses Peroxisomes in the Brain

OBJECTIVE

Peroxisome injury occurs in the central nervous system (CNS) during multiple virus infections that result in neurological disabilities. We investigated host neuroimmune responses and peroxisome biogenesis factors during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection using a multiplatform strategy.

METHODS

Brain tissues from coronavirus disease 2019 (COVID-19) (n = 12) and other disease control (ODC) (n = 12) patients, as well as primary human neural cells and Syrian hamsters, infected with a clinical variant of SARS-CoV-2, were investigated by droplet digital polymerase chain reaction (ddPCR), quantitative reverse transcriptase PCR (RT-qPCR), and immunodetection methods.

RESULTS

SARS-CoV-2 RNA was detected in the CNS of 4 patients with COVID-19 with viral protein (NSP3 and spike) immunodetection in the brainstem. Olfactory bulb, brainstem, and cerebrum from patients with COVID-19 showed induction of pro-inflammatory transcripts (IL8, IL18, CXCL10, NOD2) and cytokines (GM-CSF and IL-18) compared to CNS tissues from ODC patients (p < 0.05). Peroxisome biogenesis factor transcripts (PEX3, PEX5L, PEX11β, and PEX14) and proteins (PEX3, PEX14, PMP70) were suppressed in the CNS of COVID-19 compared to ODC patients (p < 0.05). SARS-CoV-2 infection of hamsters revealed viral RNA detection in the olfactory bulb at days 4 and 7 post-infection while inflammatory gene expression was upregulated in the cerebrum of infected animals by day 14 post-infection (p < 0.05). Pex3 transcript levels together with catalase and PMP70 immunoreactivity were suppressed in the cerebrum of SARS-CoV-2 infected animals (p < 0.05).

INTERPRETATION

COVID-19 induced sustained neuroinflammatory responses with peroxisome biogenesis factor suppression despite limited brainstem SARS-CoV-2 neurotropism in humans. These observations offer insights into developing biomarkers and therapies, while also implicating persistent peroxisome dysfunction as a contributor to the neurological post-acute sequelae of COVID-19. ANN NEUROL 2023;94:531-546.

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.

Astrocytes - friends or foes in neurodegenerative disorders

Astrocytes (AS) are the most abundant glial cells in the central nervous system (CNS). They have various morphologies and numerous (50-60) branching prolongations, with roles in the maintenance of the CNS function and homeostasis. AS in the optic nerve head (ONH) have specific distribution and function and are involved in the pathogenesis of glaucoma and other neural diseases, modify their morphologies, location, immune phenotype, and ultrastructure, thus being the key players in the active remodeling processes of the ONH.

Astrocytes and the Psychiatric Sequelae of COVID-19: What We Learned from the Pandemic

COVID-19, initially regarded as specific lung disease, exhibits an extremely broad spectrum of symptoms. Extrapulmonary manifestations of the disease also include important neuropsychiatric symptoms with atypical characteristics. Are these disturbances linked to stress accompanying every systemic infection, or are due to specific neurobiological changes associated with COVID-19? Evidence accumulated so far indicates that the pathophysiology of COVID-19 is characterized by systemic inflammation, hypoxia resulting from respiratory failure, and neuroinflammation (either due to viral neurotropism or in response to cytokine storm), all affecting the brain. It is reasonable to hypothesize that all these events may initiate or worsen psychiatric and cognitive disorders. Damage to the brain triggers a specific type of reactive response mounted by neuroglia cells, in particular by astrocytes which are the homeostatic cell par excellence. Astrocytes undergo complex morphological, biochemical, and functional remodeling aimed at mobilizing the regenerative potential of the central nervous system. If the brain is not directly damaged, resolution of systemic pathology usually results in restoration of the physiological homeostatic status of neuroglial cells. The completeness and dynamics of this process in pathological conditions remain largely unknown. In a subset of patients, glial cells could fail to recover after infection thus promoting the onset and progression of COVID-19-related neuropsychiatric diseases. There is evidence from post-mortem examinations of the brains of COVID-19 patients of alterations in both astrocytes and microglia. In conclusion, COVID-19 activates a huge reactive response of glial cells, that physiologically act as the main controller of the inflammatory, protective and regenerative events. However, in some patients the restoration of glial physiological state does not occur, thus compromising glial function and ultimately resulting in homeostatic failure underlying a set of specific neuropsychiatric symptoms related to COVID-19.

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.

RVG Peptide-Functionalized Favipiravir Nanoparticle Delivery System Facilitates Antiviral Therapy of Neurotropic Virus Infection in a Mouse Model

Neurotropic viruses severely damage the central nervous system (CNS) and human health. Common neurotropic viruses include rabies virus (RABV), Zika virus, and poliovirus. When treating neurotropic virus infection, obstruction of the blood-brain barrier (BBB) reduces the efficiency of drug delivery to the CNS. An efficient intracerebral delivery system can significantly increase intracerebral delivery efficiency and facilitate antiviral therapy. In this study, a rabies virus glycopeptide (RVG) functionalized mesoporous silica nanoparticle (MSN) packaging favipiravir (T-705) was developed to generate T-705@MSN-RVG. It was further evaluated for drug delivery and antiviral treatment in a VSV-infected mouse model. The RVG, a polypeptide consisting of 29 amino acids, was conjugated on the nanoparticle to enhance CNS delivery. The T-705@MSN-RVG caused a significant decrease in virus titers and virus proliferation without inducing substantial cell damage in vitro. By releasing T-705, the nanoparticle promoted viral inhibition in the brain during infection. At 21 days post-infection (dpi), a significantly enhanced survival ratio (77%) was observed in the group inoculated with nanoparticle compared with the non-treated group (23%). The viral RNA levels were also decreased in the therapy group at 4 and 6 dpi compared with that of the control group. The T-705@MSN-RVG could be considered a promising system for CNS delivery for treating neurotropic virus infection.

Astrocytes in the pathophysiology of neuroinfection

Key homeostasis providing cells in the central nervous system (CNS) are astrocytes, which belong to the class of cells known as atroglia, a highly heterogeneous type of neuroglia and a prominent element of the brain defence. Diseases evolve due to altered homeostatic state, associated with pathology-induced astroglia remodelling represented by reactive astrocytes, astroglial atrophy and astrodegeneration. These features are hallmarks of most infectious insults, mediated by bacteria, protozoa and viruses; they are also prominent in the systemic infection. The COVID-19 pandemic revived the focus into neurotropic viruses such as SARS-CoV2 (Coronaviridae) but also the Flaviviridae viruses including tick-borne encephalitis (TBEV) and Zika virus (ZIKV) causing the epidemic in South America prior to COVID-19. Astrocytes provide a key response to neurotropic infections in the CNS. Astrocytes form a parenchymal part of the blood-brain barrier, the site of virus entry into the CNS. Astrocytes exhibit aerobic glycolysis, a form of metabolism characteristic of highly morphologically plastic cells, like cancer cells, hence a suitable milieu for multiplication of infectious agent, including viral particles. However, why the protection afforded by astrocytes fails in some circumstances is an open question to be studied in the future.

How viral infections cause neuronal dysfunction: a focus on the role of microglia and astrocytes

In recent decades, a number of infectious viruses have emerged from wildlife or reemerged that pose a serious threat to global health and economies worldwide. Although many of these viruses have a specific target tissue, neurotropic viruses have evolved mechanisms to exploit weaknesses in immune defenses that eventually allow them to reach and infect cells of the central nervous system (CNS). Once in the CNS, these viruses can cause severe neuronal damage, sometimes with long-lasting, life-threatening consequences. Remarkably, the ability to enter the CNS and cause neuronal infection does not appear to determine whether a viral strain causes neurological complications. The cellular mechanisms underlying the neurological consequences of viral infection are not fully understood, but they involve neuroimmune interactions that have so far focused mainly on microglia. As the major immune cells in the brain, reactive microglia play a central role in neuroinflammation by responding directly or indirectly to viruses. Chronic reactivity of microglia leads to functions that are distinct from their beneficial roles under physiological conditions and may result in neuronal damage that contributes to the pathogenesis of various neurological diseases. However, there is increasing evidence that reactive astrocytes also play an important role in the response to viruses. In this review article, we summarize the recent contributions of microglia and astrocytes to the neurological impairments caused by viral infections. By expanding knowledge in this area, therapeutic approaches targeting immunological pathways may reduce the incidence of neurological and neurodegenerative disorders and increase the therapeutic window for neural protection.

Nanosystems for gene therapy targeting brain damage caused by viral infections

Several human pathogens can cause long-lasting neurological damage. Despite the increasing clinical knowledge about these conditions, most still lack efficient therapeutic interventions. Gene therapy (GT) approaches comprise strategies to modify or adjust the expression or function of a gene, thus providing therapy for human diseases. Since recombinant nucleic acids used in GT have physicochemical limitations and can fail to reach the desired tissue, viral and non-viral vectors are applied to mediate gene delivery. Although viral vectors are associated to high levels of transfection, non-viral vectors are safer and have been further explored. Different types of nanosystems consisting of lipids, polymeric and inorganic materials are applied as non-viral vectors. In this review, we discuss potential targets for GT intervention in order to prevent neurological damage associated to infectious diseases as well as the role of nanosized non-viral vectors as agents to help the selective delivery of these gene-modifying molecules. Application of non-viral vectors for delivery of GT effectors comprise a promising alternative to treat brain inflammation induced by viral infections.

Effective strategies against COVID-19 and the importance of infection sequelae

COVID-19 is a serious threat to human health and development. The acute burden of the pandemic includes more than 18.2 million deaths worldwide, and is unprecedented in modern times. This represents only a fraction of the total burden, as it excludes infection sequelae. An effective global strategic paradigm has been missing throughout the pandemic. The 'flattening the curve' approach neglected the importance of infection sequelae, and being centered on healthcare capacity was conceptually contrary to a people-centered health system. In March 2022, the World Health Organization revised its pandemic approach, importantly shifting emphasis away from managing transmission and towards prevention. Despite limitations, this now recognizes the role of infection sequelae, whose impact is becoming clearer in both variety and scale. Drawing on the foundational concepts of Sun Tzu and Carl von Clausewitz, most country approaches do not qualify as strategies, but rather as operational plans. They are also largely ineffective, neglecting infection sequelae, viral evolution dangers and other parameters. The purpose of this article is to summarize the evidence on COVID-19 infection sequelae, and alongside other contextual parameters use this to motivate that infection should be prevented. This is then used to answer the question: What is an effective strategy against COVID-19?

An improved Fuzzy based GWO algorithm for predicting the potential host receptor of COVID-19 infection

Coronavirus disease (COVID-19) is caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and has infected millions worldwide. SARS-CoV-2 spike protein uses Angiotensin-converting enzyme 2 (ACE2) and Transmembrane serine protease 2 (TMPRSS2) for entering and fusing the host cell membrane. However, interaction with spike protein receptors and protease processing are not the only factors determining coronaviruses' entry. Several proteases mediate the entry of SARS-CoV-2 virus into the host cell. Identifying receptor factors helps understand tropism, transmission, and pathogenesis of COVID-19 infection in humans. The paper aims to identify novel viral receptor or membrane proteins that are transcriptionally and biologically similar to ACE2 and TMPRSS2 through a fuzzy clustering technique that employs the Grey wolf optimizer (GWO) algorithm for finding the optimal cluster center. The exploratory and exploitation capability of GWO algorithm is improved by hybridizing mutation and crossover operators of the evolutionary algorithm. Also, the genetic diversity of the grey wolf population is enhanced by eliminating weak individuals from the population. The proposed clustering algorithm's effectiveness is shown by detecting novel viral receptors and membrane proteins associated with the pathogenesis of SARS-CoV-2 infection. The expression profiles of ACE2 protein and its co-receptor factor are analyzed and compared with single-cell transcriptomics profiling using the Seurat R toolkit, mass spectrometry (MS), and immunohistochemistry (IHC). Our advanced clustering method infers that cell that expresses high ACE2 level are more affected by SARS-CoV-infection. So, SARS-CoV-2 virus affects lung, intestine, testis, heart, kidney, and liver more severely than brain, bone marrow, skin, spleen, etc. We have identified 58 novel viral receptors and 816 membrane proteins, and their role in the pathogenicity mechanism of SARS-CoV-2 infection has been studied. Besides, our study confirmed that Neuropilins (NRP1), G protein-coupled receptor 78 (GPR78), C-type lectin domain family 4 member M (CLEC4M), Kringle containing transmembrane protein 1 (KREMEN1), Asialoglycoprotein receptor 1 (ASGR1), A Disintegrin and metalloprotease 17 (ADAM17), Furin, Neuregulin-1,(NRG1), Basigin or CD147 and Poliovirus receptor (PVR) are the potential co-receptors of SARS-CoV-2 virus. A significant finding is that heparin derivative glycosaminoglycans could block the replication of SARS-CoV-2 virus inside the host cytoplasm. The membrane protein N-Deacetylase/N-Sulfotransferase-2 (NDST2), Extostosin protein (EXT1, EXT2, and EXT3), Glucuronic acid epimerase (GLCE), and Xylosyltransferase I, II (XYLT1, XYLT2) could act as the therapeutic target for inhibiting the spread of SARS-CoV-2 infection. Drugs such as carboplatin and gemcitabine are effective in such situations.

Role of neuroinflammation mediated potential alterations in adult neurogenesis as a factor for neuropsychiatric symptoms in Post-Acute COVID-19 syndrome-A narrative review

Persistence of symptoms beyond the initial 3 to 4 weeks after infection is defined as post-acute COVID-19 syndrome (PACS). A wide range of neuropsychiatric symptoms like anxiety, depression, post-traumatic stress disorder, sleep disorders and cognitive disturbances have been observed in PACS. The review was conducted based on PRISMA-S guidelines for literature search strategy for systematic reviews. A cytokine storm in COVID-19 may cause a breach in the blood brain barrier leading to cytokine and SARS-CoV-2 entry into the brain. This triggers an immune response in the brain by activating microglia, astrocytes, and other immune cells leading to neuroinflammation. Various inflammatory biomarkers like inflammatory cytokines, chemokines, acute phase proteins and adhesion molecules have been implicated in psychiatric disorders and play a major role in the precipitation of neuropsychiatric symptoms. Impaired adult neurogenesis has been linked with a variety of disorders like depression, anxiety, cognitive decline, and dementia. Persistence of neuroinflammation was observed in COVID-19 survivors 3 months after recovery. Chronic neuroinflammation alters adult neurogenesis with pro-inflammatory cytokines supressing anti-inflammatory cytokines and chemokines favouring adult neurogenesis. Based on the prevalence of neuropsychiatric symptoms/disorders in PACS, there is more possibility for a potential impairment in adult neurogenesis in COVID-19 survivors. This narrative review aims to discuss the various neuroinflammatory processes during PACS and its effect on adult neurogenesis.

Silent Hypoxemia in the Emergency Department: A Retrospective Cohort of Two Clinical Phenotypes in Critical COVID-19

Introduction: Understanding hypoxemia, with and without the clinical signs of acute respiratory failure (ARF) in COVID-19, is key for management. Hence, from a population of critical patients admitted to the emergency department (ED), we aimed to study silent hypoxemia (Phenotype I) in comparison to symptomatic hypoxemia with clinical signs of ARF (Phenotype II). Methods: This multicenter study was conducted between 1 March and 30 April 2020. Adult patients who were presented to the EDs of nine Great-Eastern French hospitals for confirmed severe or critical COVID-19, who were then directly admitted to the intensive care unit (ICU), were retrospectively included. Results: A total of 423 critical COVID-19 patients were included, out of whom 56.1% presented symptomatic hypoxemia with clinical signs of ARF, whereas 43.9% presented silent hypoxemia. Patients with clinical phenotype II were primarily intubated, initially, in the ED (46%, p < 0.001), whereas those with silent hypoxemia (56.5%, p < 0.001) were primarily intubated in the ICU. Initial univariate analysis revealed higher ICU mortality (29.2% versus 18.8%, p < 0.014) and in-hospital mortality (32.5% versus 18.8%, p < 0.002) in phenotype II. However, multivariate analysis showed no significant differences between the two phenotypes regarding mortality and hospital or ICU length of stay. Conclusions: Silent hypoxemia is explained by various mechanisms, most physiological and unspecific to COVID-19. Survival was found to be comparable in both phenotypes, with decreased survival in favor of Phenotype II. However, the spectrum of silent to symptomatic hypoxemia appears to include a continuum of disease progression, which can brutally evolve into fatal ARF.

3D Bioprinted Neural-Like Tissue as a Platform to Study Neurotropism of Mouse-Adapted SARS-CoV-2

The effects of neuroinvasion by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) become clinically relevant due to the numerous neurological symptoms observed in Corona Virus Disease 2019 (COVID-19) patients during infection and post-COVID syndrome or long COVID. This study reports the biofabrication of a 3D bioprinted neural-like tissue as a proof-of-concept platform for a more representative study of SARS-CoV-2 brain infection. Bioink is optimized regarding its biophysical properties and is mixed with murine neural cells to construct a 3D model of COVID-19 infection. Aiming to increase the specificity to murine cells, SARS-CoV-2 is mouse-adapted (MA-SARS-CoV-2) in vitro, in a protocol first reported here. MA-SARS-CoV-2 reveals mutations located at the Orf1a and Orf3a domains and is evolutionarily closer to the original Wuhan SARS-CoV-2 strain than SARS-CoV-2 used for adaptation. Remarkably, MA-SARS-CoV-2 shows high specificity to murine cells, which present distinct responses when cultured in 2D and 3D systems, regarding cell morphology, neuroinflammation, and virus titration. MA-SARS-CoV-2 represents a valuable tool in studies using animal models, and the 3D neural-like tissue serves as a powerful in vitro platform for modeling brain infection, contributing to the development of antivirals and new treatments for COVID-19.

Neurological effects of COVID-19 in infants and children

Neurological manifestations of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in children are becoming increasingly apparent as the coronavirus disease (COVID-19) pandemic continues. While children manifest relatively milder features of the disease, accumulating evidence warrants concern that COVID-19 exacts both acute- and long-term effects on the developing central and peripheral nervous systems. This review focuses on the relatively underinvestigated topic of the effects of SARS-CoV-2 on the brain in infancy and childhood, concluding that clinicians should be attentive to both the acute effects and long-term consequences of COVID-19 from a neurological perspective.

Potential role of astrocyte angiotensin converting enzyme 2 in the neural transmission of COVID-19 and a neuroinflammatory state induced by smoking and vaping

BACKGROUND

Knowledge of the entry receptors responsible for SARS-CoV-2 is key to understand the neural transmission and pathogenesis of COVID-19 characterized by a neuroinflammatory scenario. Understanding the brain distribution of angiotensin converting enzyme 2 (ACE2), the primary entry receptor for SARS-CoV-2, remains mixed. Smoking has been shown as a risk factor for COVID-19 severity and it is not clear how smoking exacerbates the neural pathogenesis in smokers.

METHODS

Immunohistochemistry, real-time PCR and western blot assays were used to systemically examine the spatial-, cell type- and isoform-specific expression of ACE2 in mouse brain and primary cultured brain cells. Experimental smoking exposure was conducted to evaluate the effect of smoking on brain expression.

RESULTS

We observed ubiquitous expression of ACE2 but uneven brain distribution, with high expression in the cerebral microvasculature, medulla oblongata, hypothalamus, subventricular zones, and meninges around medulla oblongata and hypothalamus. Co-staining with cell type-specific markers demonstrates ACE2 is primarily expressed in astrocytes around the microvasculature, medulla oblongata, hypothalamus, ventricular and subventricular zones of cerebral ventricles, and subependymal zones in rhinoceles and rostral migratory streams, radial glial cells in the lateral ventricular zones, tanycytes in the third ventricle, epithelial cells and stroma in the cerebral choroid plexus, as well as cerebral pericytes, but rarely detected in neurons and cerebral endothelial cells. ACE2 expression in astrocytes is further confirmed in primary cultured cells. Furthermore, isoform-specific analysis shows astrocyte ACE2 has the peptidase domain responsible for SARS-CoV-2 entry, indicating astrocytes are indeed vulnerable to SARS-CoV-2 infection. Finally, our data show experimental tobacco smoking and electronic nicotine vaping exposure increase proinflammatory and/or immunomodulatory cytokine IL-1a, IL-6 and IL-5 without significantly affecting ACE2 expression in the brain, suggesting smoking may pre-condition a neuroinflammatory state in the brain.

CONCLUSIONS

The present study demonstrates a spatial- and cell type-specific expression of ACE2 in the brain, which might help to understand the acute and lasting post-infection neuropsychological manifestations in COVID-19 patients. Our data highlights a potential role of astrocyte ACE2 in the neural transmission and pathogenesis of COVID-19. This also suggests a pre-conditioned neuroinflammatory and immunocompromised scenario might attribute to exacerbated COVID-19 severity in the smokers.

Molecular Mechanisms in the Genesis of Seizures and Epilepsy Associated With Viral Infection

Seizures are a common presenting symptom during viral infections of the central nervous system (CNS) and can occur during the initial phase of infection ("early" or acute symptomatic seizures), after recovery ("late" or spontaneous seizures, indicating the development of acquired epilepsy), or both. The development of acute and delayed seizures may have shared as well as unique pathogenic mechanisms and prognostic implications. Based on an extensive review of the literature, we present an overview of viruses that are associated with early and late seizures in humans. We then describe potential pathophysiologic mechanisms underlying ictogenesis and epileptogenesis, including routes of neuroinvasion, viral control and clearance, systemic inflammation, alterations of the blood-brain barrier, neuroinflammation, and inflammation-induced molecular reorganization of synapses and neural circuits. We provide clinical and animal model findings to highlight commonalities and differences in these processes across various neurotropic or neuropathogenic viruses, including herpesviruses, SARS-CoV-2, flaviviruses, and picornaviruses. In addition, we extensively review the literature regarding Theiler's murine encephalomyelitis virus (TMEV). This picornavirus, although not pathogenic for humans, is possibly the best-characterized model for understanding the molecular mechanisms that drive seizures, epilepsy, and hippocampal damage during viral infection. An enhanced understanding of these mechanisms derived from the TMEV model may lead to novel therapeutic interventions that interfere with ictogenesis and epileptogenesis, even within non-infectious contexts.

Neurological manifestations in patients with COVID-19: A systematic review and meta-analysis

INTRODUCTION

The intensification of coronavirus disease 2019 (COVID-19) complications, severe symptoms, and high mortality rate has led researchers to focus on this significant issue. While respiratory and cardiac complications have been described as high-risk manifestations in patients with COVID-19, neurological complications can also enhance mortality. This study aimed to evaluate the prevalence of neurological complications arises from SARS-CoV-2 and assess the mortality rate from neurological complications.

MATERIAL AND METHODS

Literature review was conducted by searching in PubMed/Medline, Web of Sciences, and Embase. After performing search strategies with relevant terms, a number of articles were excluded, including review articles, systematic review or meta-analysis, duplicate publication of same researchers, congress abstracts, animal studies, case reports, case series, and articles reporting a history of neurological features prior to COVID-19 infection. After retrieving the data, statistical analysis was performed using the STATA Version 14 software.

RESULTS

From 4455 retrieved publications, 20 articles were selected for further analysis. Among 18,258 included patients, 2791 showed neurological symptoms, which were classified into different groups. Headache, confusion, and fatigue were reported as the most non-specific neurological features in confirmed COVID-19 patients. Psychiatric symptoms, CNS disorders, cerebrovascular disorders, CNS inflammatory disorders, PNS disorders, neuromuscular disorders, etc., were defined as specific neurological manifestations. The pooled prevalence of neurological manifestations and mortality rate of COVID-19 patients with neurological features were estimated to be 23.0% (95% CI: 17.8-29.2) and 29.1% (95% CI: 20.3-39.8), respectively.

CONCLUSION

Neurological manifestations may commonly happen in patients with COVID-19. This study reported a high prevalence of neurological complications and mortality rates in COVID-19 patients. Therefore, patients with COVID-19 who indicated neurological symptoms should be taken seriously and should receive early treatment to prevent undesirable events.

Multimodal Benefits of Exercise in Patients With Multiple Sclerosis and COVID-19

Multiple sclerosis (MS) is a demyelinating disease characterized by plaque formation and neuroinflammation. The plaques can present in various locations, causing a variety of clinical symptoms in patients with MS. Coronavirus disease-2019 (COVID-19) is also associated with systemic inflammation and a cytokine storm which can cause plaque formation in several areas of the brain. These concurring events could exacerbate the disease burden of MS. We review the neuro-invasive properties of SARS-CoV-2 and the possible pathways for the entry of the virus into the central nervous system (CNS). Complications due to this viral infection are similar to those occurring in patients with MS. Conditions related to MS which make patients more susceptible to viral infection include inflammatory status, blood-brain barrier (BBB) permeability, function of CNS cells, and plaque formation. There are also psychoneurological and mood disorders associated with both MS and COVID-19 infections. Finally, we discuss the effects of exercise on peripheral and central inflammation, BBB integrity, glia and neural cells, and remyelination. We conclude that moderate exercise training prior or after infection with SARS-CoV-2 can produce health benefits in patients with MS patients, including reduced mortality and improved physical and mental health of patients with MS.

Dissecting the Molecular Mechanisms Surrounding Post-COVID-19 Syndrome and Neurological Features

Many of the survivors of the novel coronavirus disease (COVID-19) are suffering from persistent symptoms, causing significant morbidity and decreasing their quality of life, termed "post-COVID-19 syndrome" or "long COVID". Understanding the mechanisms surrounding PCS is vital to developing the diagnosis, biomarkers, and possible treatments. Here, we describe the prevalence and manifestations of PCS, and similarities with previous SARS epidemics. Furthermore, we look at the molecular mechanisms behind the neurological features of PCS, where we highlight important neural mechanisms that may potentially be involved and pharmacologically targeted, such as glutamate reuptake in astrocytes, the role of NMDA receptors and transporters (EAAT2), ROS signaling, astrogliosis triggered by NF-κB signaling, KNDy neurons, and hypothalamic networks involving Kiss1 (a ligand for the G-protein-coupled receptor 54 (GPR54)), among others. We highlight the possible role of reactive gliosis following SARS-CoV-2 CNS injury, as well as the potential role of the hypothalamus network in PCS manifestations.

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.

HIV, HSV, SARS-CoV-2 and Ebola Share Long-Term Neuropsychiatric Sequelae

Long COVID, in which disease-related symptoms persist for months after recovery, has led to a revival of the discussion of whether neuropsychiatric long-term symptoms after viral infections indeed result from virulent activity or are purely psychological phenomena. In this review, we demonstrate that, despite showing differences in structure and targeting, many viruses have highly similar neuropsychiatric effects on the host. Herein, we compare severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), human immunodeficiency virus 1 (HIV-1), Ebola virus disease (EVD), and herpes simplex virus 1 (HSV-1). We provide evidence that the mutual symptoms of acute and long-term anxiety, depression and post-traumatic stress among these viral infections are likely to result from primary viral activity, thus suggesting that these viruses share neuroinvasive strategies in common. Moreover, it appears that secondary induced environmental stress can lead to the emergence of psychopathologies and increased susceptibility to viral (re)infection in infected individuals. We hypothesize that a positive feedback loop of virus-environment-reinforced systemic responses exists. It is surmised that this cycle of primary virulent activity and secondary stress-induced reactivation, may be detrimental to infected individuals by maintaining and reinforcing the host's immunocompromised state of chronic inflammation, immunological strain, and maladaptive central-nervous-system activity. We propose that this state can lead to perturbed cognitive processing and promote aversive learning, which may manifest as acute, long-term neuropsychiatric illness.

Can SARS-CoV-2 Infection Lead to Neurodegeneration and Parkinson's Disease?

The SARS-CoV-2 pandemic has affected the daily life of the worldwide population since 2020. Links between the newly discovered viral infection and the pathogenesis of neurodegenerative diseases have been investigated in different studies. This review aims to summarize the literature concerning COVID-19 and Parkinson's disease (PD) to give an overview on the interface between viral infection and neurodegeneration with regard to this current topic. We will highlight SARS-CoV-2 neurotropism, neuropathology and the suspected pathophysiological links between the infection and neurodegeneration as well as the psychosocial impact of the pandemic on patients with PD. Some evidence discussed in this review suggests that the SARS-CoV-2 pandemic might be followed by a higher incidence of neurodegenerative diseases in the future. However, the data generated so far are not sufficient to confirm that COVID-19 can trigger or accelerate neurodegenerative diseases.

Dysautonomia following COVID-19 is not associated with subjective limitations or symptoms but is associated with objective functional limitations

Background

Individuals who contract coronavirus disease 2019 (COVID-19) can suffer with persistent and debilitating symptoms long after the initial acute illness. Heart rate (HR) profiles determined during cardiopulmonary exercise testing (CPET) and delivered as part of a post-COVID recovery service may provide insight into the presence and impact of dysautonomia on functional ability.

Objective

Using an active, working-age, post–COVID-19 population, the purpose of this study was to (1) determine and characterize any association between subjective symptoms and dysautonomia; and (2) identify objective exercise capacity differences between patients classified “with” and those “without” dysautonomia.

Methods

Patients referred to a post–COVID-19 service underwent comprehensive clinical assessment, including self-reported symptoms, CPET, and secondary care investigations when indicated. Resting HR >75 bpm, HR increase with exercise <89 bpm, and HR recovery <25 bpm 1 minute after exercise were used to define dysautonomia. Anonymized data were analyzed and associations with symptoms, and CPET outcomes were determined.

Results

Fifty-one of the 205 patients (25%) reviewed as part of this service evaluation had dysautonomia. There were no associations between symptoms or perceived functional limitation and dysautonomia (P >.05). Patients with dysautonomia demonstrated objective functional limitations with significantly reduced work rate (219 ± 37 W vs 253 ± 52 W; P <.001) and peak oxygen consumption (V̇o₂: 30.6 ± 5.5 mL/kg/min vs 35.8 ± 7.6 mL/kg/min; P <.001); and a steeper (less efficient) V̇e/V̇co₂ slope (29.9 ± 4.9 vs 27.7 ± 4.7; P = .005).

Conclusion

Dysautonomia is associated with objective functional limitations but is not associated with subjective symptoms or limitation.

Methodologies for Generating Brain Organoids to Model Viral Pathogenesis in the CNS

(1) Background: The human brain is of interest in viral research because it is often the target of viruses. Neurological infections can result in consequences in the CNS, which can result in death or lifelong sequelae. Organoids modeling the CNS are notable because they are derived from stem cells that differentiate into specific brain cells such as neural progenitors, neurons, astrocytes, and glial cells. Numerous protocols have been developed for the generation of CNS organoids, and our goal was to describe the various CNS organoid models available for viral pathogenesis research to serve as a guide to determine which protocol might be appropriate based on research goal, timeframe, and budget. (2) Methods: Articles for this review were found in Pubmed, Scopus and EMBASE. The search terms used were "brain + organoid" and "CNS + organoid" (3) Results: There are two main methods for organoid generation, and the length of time for organoid generation varied from 28 days to over 2 months. The costs for generating a population of organoids ranged from USD 1000 to 5000. (4) Conclusions: There are numerous methods for generating organoids representing multiple regions of the brain, with several types of modifications for fine-tuning the model to a researcher's specifications. Organoid models of the CNS can serve as a platform for characterization and mechanistic studies that can reduce or eliminate the use of animals, especially for viruses that only cause disease in the human CNS.

Functionalized Nanoparticles in Prevention and Targeted Therapy of Viral Diseases With Neurotropism Properties, Special Insight on COVID-19

Neurotropic viruses have neural-invasive and neurovirulent properties to damage the central nervous system (CNS), leading to humans' fatal symptoms. Neurotropic viruses comprise a lot of viruses, such as Zika virus (ZIKV), herpes simplex virus (HSV), rabies virus (RABV), and severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2). Effective therapy is needed to prevent infection by these viruses in vivo and in vitro. However, the blood-brain barrier (BBB) usually prevents macromolecules from entering the CNS, which challenges the usage of the traditional probes, antiviral drugs, or neutralizing antibodies in the CNS. Functionalized nanoparticles (NPs) have been increasingly reported in the targeted therapy of neurotropic viruses due to their sensitivity and targeting characteristics. Therefore, the present review outlines efficient functionalized NPs to further understand the recent trends, challenges, and prospects of these materials.

Molecular Mechanisms of SARS-CoV-2/COVID-19 Pathogenicity on the Central Nervous System: Bridging Experimental Probes to Clinical Evidence and Therapeutic Interventions

The coronavirus disease 2019 (COVID-19) pandemic, induced by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has dramatically impacted the global healthcare systems, constantly challenging both research and clinical practice. Although it was initially believed that the SARS-CoV-2 infection is limited merely to the respiratory system, emerging evidence indicates that COVID-19 affects multiple other systems including the central nervous system (CNS). Furthermore, most of the published clinical studies indicate that the confirmed CNS inflammatory manifestations in COVID-19 patients are meningitis, encephalitis, acute necrotizing encephalopathy, acute transverse myelitis, and acute disseminated encephalomyelitis. In addition, the neuroinflammation along with accelerated neurosenescence and susceptible genetic signatures in COVID-19 patients might prime the CNS to neurodegeneration and precipitate the occurrence of neurodegenerative diseases, including Alzheimer's and Parkinson's diseases. Thus, this review provides a critical evaluation and interpretive analysis of existing published preclinical as well as clinical studies on the key molecular mechanisms modulating neuroinflammation and neurodegeneration induced by the SARS-CoV-2. In addition, the essential age- and gender-dependent impacts of SARS-CoV-2 on the CNS of COVID-19 patients are also discussed.

PTSD as an Endothelial Disease: Insights From COVID-19

SARS-CoV-2 virus, the etiologic agent of COVID-19, has affected almost every aspect of human life, precipitating stress-related pathology in vulnerable individuals. As the prevalence rate of posttraumatic stress disorder in pandemic survivors exceeds that of the general and special populations, the virus may predispose to this disorder by directly interfering with the stress-processing pathways. The SARS-CoV-2 interactome has identified several antigens that may disrupt the blood-brain-barrier by inducing premature senescence in many cell types, including the cerebral endothelial cells. This enables the stress molecules, including angiotensin II, endothelin-1 and plasminogen activator inhibitor 1, to aberrantly activate the amygdala, hippocampus, and medial prefrontal cortex, increasing the vulnerability to stress related disorders. This is supported by observing the beneficial effects of angiotensin receptor blockers and angiotensin converting enzyme inhibitors in both posttraumatic stress disorder and SARS-CoV-2 critical illness. In this narrative review, we take a closer look at the virus-host dialog and its impact on the renin-angiotensin system, mitochondrial fitness, and brain-derived neurotrophic factor. We discuss the role of furin cleaving site, the fibrinolytic system, and Sigma-1 receptor in the pathogenesis of psychological trauma. In other words, learning from the virus, clarify the molecular underpinnings of stress related disorders, and design better therapies for these conditions. In this context, we emphasize new potential treatments, including furin and bromodomains inhibitors.

Challenges and Opportunities of Targeting Astrocytes to Halt Neurodegenerative Disorders

Neurodegenerative diseases are a heterogeneous group of disorders whose incidence is likely to duplicate in the next 30 years along with the progressive aging of the western population. Non-cell-specific therapeutics or therapeutics designed to tackle aberrant pathways within neurons failed to slow down or halt neurodegeneration. Yet, in the last few years, our knowledge of the importance of glial cells to maintain the central nervous system homeostasis in health conditions has increased exponentially, along with our awareness of their fundamental and multifaced role in pathological conditions. Among glial cells, astrocytes emerge as promising therapeutic targets in various neurodegenerative disorders. In this review, we present the latest evidence showing the astonishing level of specialization that astrocytes display to fulfill the demands of their neuronal partners as well as their plasticity upon injury. Then, we discuss the controversies that fuel the current debate on these cells. We tackle evidence of a potential beneficial effect of cell therapy, achieved by transplanting astrocytes or their precursors. Afterwards, we introduce the different strategies proposed to modulate astrocyte functions in neurodegeneration, ranging from lifestyle changes to environmental cues. Finally, we discuss the challenges and the recent advancements to develop astrocyte-specific delivery systems.

Silent hypoxia in COVID-19: a gut microbiota connection

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has triggered the COVID-19 pandemic. Several factors induce hypoxia in COVID-19. Despite being hypoxic, some SARS-CoV-2-infected individuals do not experience any respiratory distress, a phenomenon termed ‘silent (or happy) hypoxia’. Prolonged undetected hypoxia could be dangerous, sometimes leading to death. A few studies attempted to unravel what causes silent hypoxia, however, the exact mechanisms are still elusive. Here, we aim to understand how SARS-CoV-2 causes silent hypoxia.