ACE-2, TMPRSS2, and Neuropilin-1 Receptor Expression on Human Brain Astrocytes and Pericytes and SARS-CoV-2 Infection Kinetics.

Angiotensin Converting Enzyme 2 (ACE-2), Transmembrane Serine Protease 2 (TMPRSS-2) and Neuropilin-1 cellular receptors support the entry of SARS-CoV-2 into susceptible human target cells and are characterized at the molecular level. Some evidence on the expression of entry receptors at mRNA and protein levels in brain cells is available, but co-expression of these receptors and confirmatory evidence on brain cells is lacking. SARS-CoV-2 infects some brain cell types, but infection susceptibility, multiple entry receptor density, and infection kinetics are rarely reported in specific brain cell types. Highly sensitive Taqman ddPCR, flow-cytometry and immunocytochemistry assays were used to quantitate the expression of ACE-2, TMPRSS-2 and Neuropilin-1 at mRNA and protein levels on human brain-extracted pericytes and astrocytes, which are an integral part of the Blood-Brain-Barrier (BBB). Astrocytes showed moderate ACE-2 (15.9 ± 1.3%, Mean ± SD, n = 2) and TMPRSS-2 (17.6%) positive cells, and in contrast show high Neuropilin-1 (56.4 ± 39.8%, n = 4) protein expression. Whereas pericytes showed variable ACE-2 (23.1 ± 20.7%, n = 2), Neuropilin-1 (30.3 ± 7.5%, n = 4) protein expression and higher TMPRSS-2 mRNA (667.2 ± 232.3, n = 3) expression. Co-expression of multiple entry receptors on astrocytes and pericytes allows entry of SARS-CoV-2 and progression of infection. Astrocytes showed roughly four-fold more virus in culture supernatants than pericytes. SARS-CoV-2 cellular entry receptor expression and "in vitro" viral kinetics in astrocytes and pericytes may improve our understanding of viral infection "in vivo". In addition, this study may facilitate the development of novel strategies to counter the effects of SARS-CoV-2 and inhibit viral infection in brain tissues to prevent the spread and interference in neuronal functions.

Assessment of SARS-CoV-2 infection in astrocytes

Discovered in late 2019 in a market in the city of Wuhan, Hubei Province, China, SARS-CoV-2 is an important member of the Coronaviridae family, responsible for bringing the whole world into a state of alert causing a global pandemic. The virus has been identified as causing a characteristic clinical condition known as "Corona-virus disease 2019" (COVID-19), causing an Acute Respiratory Syndrome. Being a respiratory virus, transmitted by direct contact with an infected person and by touching contaminated surfaces, SARS-CoV-2 quickly spread throughout the world, causing a pandemic, having today more than 535 million people infected and causing more than million deaths. In addition to the respiratory system, the virus is present in other cells in the body. Findings show the presence of SARS-CoV-2 in cerebrospinal fluid associated with changes in the expression of neuronal inflammation markers, as well as an increased expression of cytokines released by astrocytes, indicating an alteration in the Central Nervous System (CNS). In this project, we analyzed the effects of SARS-CoV-2 infection directly on astrocytes, glial cells that are extremely important for the maintenance of homeostasis and CNS defense. Therefore, we produced astrocytes from three human iPSC strains to verify aspects of cell morphology and physiology, as well as gene and protein expression, after infection with the virus. We found that SARS-CoV-2 is capable of infecting astrocytes, but some studies are still needed to better elucidate its role in the interaction with this cell type in the CNS.

Regulatory role of endoplasmic reticulum resident chaperone protein ERp29 in anti-murine ß-coronavirus host cell response.

Gap junctional intercellular communication (GJIC) involving astrocytes is important for proper CNS homeostasis. As determined in our previous studies, trafficking of the predominant astrocyte GJ protein, Connexin43 (Cx43), is disrupted in response to infection with a neurotropic murine ß-coronavirus (MHV-A59). However, how host factors are involved in Cx43 trafficking and the infection response is not clear. Here, we show that Cx43 retention due to MHV-A59 infection was associated with increased ER stress and reduced expression of chaperone protein ERp29. Treatment of MHV-A59-infected astrocytes with the chemical chaperone 4-sodium phenylbutyrate increased ERp29 expression, rescued Cx43 transport to the cell surface, increased GJIC, and reduced ER stress. We obtained similar results using an astrocytoma cell line (delayed brain tumor) upon MHV-A59 infection. Critically, delayed brain tumor cells transfected to express exogenous ERp29 were less susceptible to MHV-A59 infection and showed increased Cx43-mediated GJIC. Treatment with Cx43 mimetic peptides inhibited GJIC and increased viral susceptibility, demonstrating a role for intercellular communication in reducing MHV-A59 infectivity. Taken together, these results support a therapeutically targetable ERp29-dependent mechanism where ß-coronavirus infectivity is modulated by reducing ER stress and rescuing Cx43 trafficking and function.

Young COVID-19 Patients Show a Higher Degree of Microglial Activation When Compared to Controls.

The severe acute respiratory syndrome-corona virus type 2 (SARS-CoV-2) is the cause of human coronavirus disease 2019 (COVID-19). Since its identification in late 2019 SARS-CoV-2 has spread rapidly around the world creating a global pandemic. Although considered mainly a respiratory disease, COVID-19 also encompasses a variety of neuropsychiatric symptoms. How infection with SARS-CoV-2 leads to brain damage has remained largely elusive so far. In particular, it has remained unclear, whether signs of immune cell and / or innate immune and reactive astrogliosis are due to direct effects of the virus or may be an expression of a non-specific reaction of the brain to a severe life-threatening disease with a considerable proportion of patients requiring intensive care and invasive ventilation activation. Therefore, we designed a case-control-study of ten patients who died of COVID-19 and ten age-matched non-COVID-19-controls to quantitatively assess microglial and astroglial response. To minimize possible effects of severe systemic inflammation and / or invasive therapeutic measures we included only patients without any clinical or pathomorphological indication of sepsis and who had not been subjected to invasive intensive care treatment. Our results show a significantly higher degree of microglia activation in younger COVID-19 patients, while the difference was less and not significant for older COVID-19 patients. The difference in the degree of reactive gliosis increased with age but was not influenced by COVID-19. These preliminary data warrants further investigation of larger patient cohorts using additional immunohistochemical markers for different microglial phenotypes.

Do SARS-CoV-2 Variants Differ in Their Neuropathogenicity?

Neurological complications associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections are a huge societal problem. Although the neuropathogenicity of SARS-CoV-2 is not yet fully understood, there is evidence that SARS-CoV-2 can invade and infect cells of the central nervous system. Kong et al. (https://doi.org/10.1128/mbio.02308-22) shows that the mechanism of virus entry into astrocytes in brain organoids and primary astrocytes differs from entry into respiratory epithelial cells. However, how SARS-CoV-2 enters susceptible CNS cells and whether there are differences among SARS-CoV-2 variants is still unclear. In vivo and in vitro models are useful to study these important questions and may reveal important differences among SARS-CoV-2 variants in their neuroinvasive, neurotropic, and neurovirulent potential. In this commentary we address how this study contributes to the understanding of the neuropathology of SARS-CoV-2 and its variants.

Emerging Roles of Type-I Interferons in Neuroinflammation, Neurological Diseases, and Long-Haul COVID.

Interferons (IFNs) are pleiotropic cytokines originally identified for their antiviral activity. IFN-α and IFN-ß are both type I IFNs that have been used to treat neurological diseases such as multiple sclerosis. Microglia, astrocytes, as well as neurons in the central and peripheral nervous systems, including spinal cord neurons and dorsal root ganglion neurons, express type I IFN receptors (IFNARs). Type I IFNs play an active role in regulating cognition, aging, depression, and neurodegenerative diseases. Notably, by suppressing neuronal activity and synaptic transmission, IFN-α and IFN-ß produced potent analgesia. In this article, we discuss the role of type I IFNs in cognition, neurodegenerative diseases, and pain with a focus on neuroinflammation and neuro-glial interactions and their effects on cognition, neurodegenerative diseases, and pain. The role of type I IFNs in long-haul COVID-associated neurological disorders is also discussed. Insights into type I IFN signaling in neurons and non-neuronal cells will improve our treatments of neurological disorders in various disease conditions.

SARS-CoV-2 infects neurons and induces neuroinflammation in a non-human primate model of COVID-19.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the etiologic agent of coronavirus disease 2019 (COVID-19), can induce a plethora of neurological complications in some patients. However, it is still under debate whether SARS-CoV-2 directly infects the brain or whether CNS sequelae result from systemic inflammatory responses triggered in the periphery. By using high-resolution microscopy, we investigated whether SARS-CoV-2 reaches the brain and how viral neurotropism can be modulated by aging in a non-human primate model of COVID-19. Seven days after infection, SARS-CoV-2 was detected in the olfactory cortex and interconnected regions and was accompanied by robust neuroinflammation and neuronal damage exacerbated in aged, diabetic animals. Our study provides an initial framework for identifying the molecular and cellular mechanisms underlying SARS-CoV-2 neurological complications, which will be essential to reducing both the short- and long-term burden of COVID-19.

Neuropilin-1 Mediates SARS-CoV-2 Infection of Astrocytes in Brain Organoids, Inducing Inflammation Leading to Dysfunction and Death of Neurons.

Coronavirus disease 2019 (COVID-19) is frequently associated with neurological deficits, but how severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) induces these effects remains unclear. Here, we show that astrocytes are readily infected by SARS-CoV-2, but surprisingly, neuropilin-1, not angiotensin-converting enzyme 2 (ACE2), serves as the principal receptor mediating cell entry. Infection is further positively modulated by the two-pore segment channel 2 (TPC2) protein that regulates membrane trafficking and endocytosis. Astrocyte infection produces a pathological response closely resembling reactive astrogliosis characterized by elevated type I interferon (IFN) production, increased inflammation, and the decreased expression of transporters of water, ions, choline, and neurotransmitters. These combined events initiated within astrocytes produce a hostile microenvironment that promotes the dysfunction and death of uninfected bystander neurons. IMPORTANCE SARS-CoV-2 infection primarily targets the lung but may also damage other organs, including the brain, heart, kidney, and intestine. Central nervous system (CNS) pathologies include loss of smell and taste, headache, delirium, acute psychosis, seizures, and stroke. Pathological loss of gray matter occurs in SARS-CoV-2 infection, but it is unclear whether this is due to direct viral infection, indirect effects associated with systemic inflammation, or both. Here, we used induced pluripotent stem cell (iPSC)-derived brain organoids and primary human astrocytes from the cerebral cortex to study direct SARS-CoV-2 infection. Our findings support a model where SARS-CoV-2 infection of astrocytes produces a panoply of changes in the expression of genes regulating innate immune signaling and inflammatory responses. The deregulation of these genes in astrocytes produces a microenvironment within the CNS that ultimately disrupts normal neuron function, promoting neuronal cell death and CNS deficits.

The neurobiology of long COVID.

Persistent neurological and neuropsychiatric symptoms affect a substantial fraction of people after COVID-19 and represent a major component of the post-acute COVID-19 syndrome, also known as long COVID. Here, we review what is understood about the pathobiology of post-acute COVID-19 impact on the CNS and discuss possible neurobiological underpinnings of the cognitive symptoms affecting COVID-19 survivors. We propose the chief mechanisms that may contribute to this emerging neurological health crisis.

Morphological, cellular, and molecular basis of brain infection in COVID-19 patients.

Although increasing evidence confirms neuropsychiatric manifestations associated mainly with severe COVID-19 infection, long-term neuropsychiatric dysfunction (recently characterized as part of "long COVID-19" syndrome) has been frequently observed after mild infection. We show the spectrum of cerebral impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, ranging from long-term alterations in mildly infected individuals (orbitofrontal cortical atrophy, neurocognitive impairment, excessive fatigue and anxiety symptoms) to severe acute damage confirmed in brain tissue samples extracted from the orbitofrontal region (via endonasal transethmoidal access) from individuals who died of COVID-19. In an independent cohort of 26 individuals who died of COVID-19, we used histopathological signs of brain damage as a guide for possible SARS-CoV-2 brain infection and found that among the 5 individuals who exhibited those signs, all of them had genetic material of the virus in the brain. Brain tissue samples from these five patients also exhibited foci of SARS-CoV-2 infection and replication, particularly in astrocytes. Supporting the hypothesis of astrocyte infection, neural stem cell-derived human astrocytes in vitro are susceptible to SARS-CoV-2 infection through a noncanonical mechanism that involves spike-NRP1 interaction. SARS-CoV-2-infected astrocytes manifested changes in energy metabolism and in key proteins and metabolites used to fuel neurons, as well as in the biogenesis of neurotransmitters. Moreover, human astrocyte infection elicits a secretory phenotype that reduces neuronal viability. Our data support the model in which SARS-CoV-2 reaches the brain, infects astrocytes, and consequently, leads to neuronal death or dysfunction. These deregulated processes could contribute to the structural and functional alterations seen in the brains of COVID-19 patients.

Non-Productive Infection of Glial Cells with SARS-CoV-2 in Hamster Organotypic Cerebellar Slice Cultures.

The numerous neurological syndromes associated with COVID-19 implicate an effect of viral pathogenesis on neuronal function, yet reports of direct SARS-CoV-2 infection in the brain are conflicting. We used a well-established organotypic brain slice culture to determine the permissivity of hamster brain tissues to SARS-CoV-2 infection. We found levels of live virus waned after inoculation and observed no evidence of cell-to-cell spread, indicating that SARS-CoV-2 infection was non-productive. Nonetheless, we identified a small number of infected cells with glial phenotypes; however, no evidence of viral infection or replication was observed in neurons. Our data corroborate several clinical studies that have assessed patients with COVID-19 and their association with neurological involvement.

The Effects of Royal Jelly Acid, 10-Hydroxy-trans-2-decenoic Acid, on Neuroinflammation and Oxidative Stress in Astrocytes Stimulated with Lipopolysaccharide and Hydrogen Peroxide

The increased prevalence of neurodegenerative diseases, especially during the COVID-19 outbreak, necessitates the search for natural immune- and cognitive-enhancing agents. 10-Hydroxy-trans-2-decenoic acid (10-H2DA), the main fatty acid of royal jelly, has several pharmacological activities. Given the fundamental role of astrocytes in regulating immune responses of the central nervous system, we used cortical astrocytes to examine the effect of 10-H2DA on the expression of genes associated with neuroinflammation and the production of neurotrophins, as well as cellular resistance to H2O2-induced cytotoxicity. Astrocytes, pretreated with a range of concentrations of 10-H2DA for 24 h, were exposed to lipopolysaccharide (LPS) for 3 h, after which the expression of proinflammatory cytokines (IL-1β, IL-6, and tumor necrosis factor-α (TNF-α)) and neurotrophic factors (BDNF, GDNF, and IGF-1) was evaluated. In the absence of LPS, 10-H2DA had no significant effect on the mRNA expression of neurotrophins or cytokines except for IL-1β, which significantly increased with low doses of 10-H2DA (3 µM). 10-H2DA (10 µM) pretreatment of LPS-stimulated cells did not significantly inhibit the expression of cytokine encoding genes;however, it significantly lowered the mRNA expression of GDNF and tended to decrease BDNF and IGF-1 expression compared with LPS alone. Additionally, 10-H2DA did not protect astrocytes against H2O2-induced oxidative stress. Our data indicate no anti-inflammatory, antioxidant, or neurotrophic effect of 10-H2DA in astrocytes undergoing inflammation or oxidative stress. The effect of IGF-1 inhibition by 10-H2DA on neuronal ketogenesis needs investigation.

The Pathobiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: The Case for Neuroglial Failure.

Although myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) has a specific and distinctive profile of clinical features, the disease remains an enigma because causal explanation of the pathobiological matrix is lacking. Several potential disease mechanisms have been identified, including immune abnormalities, inflammatory activation, mitochondrial alterations, endothelial and muscular disturbances, cardiovascular anomalies, and dysfunction of the peripheral and central nervous systems. Yet, it remains unclear whether and how these pathways may be related and orchestrated. Here we explore the hypothesis that a common denominator of the pathobiological processes in ME/CFS may be central nervous system dysfunction due to impaired or pathologically reactive neuroglia (astrocytes, microglia and oligodendrocytes). We will test this hypothesis by reviewing, in reference to the current literature, the two most salient and widely accepted features of ME/CFS, and by investigating how these might be linked to dysfunctional neuroglia. From this review we conclude that the multifaceted pathobiology of ME/CFS may be attributable in a unifying manner to neuroglial dysfunction. Because the two key features - post exertional malaise and decreased cerebral blood flow - are also recognized in a subset of patients with post-acute sequelae COVID, we suggest that our findings may also be pertinent to this entity.

Shared Inflammatory Pathology of Stroke and COVID-19.

Though COVID-19 is primarily characterized by symptoms in the periphery, it can also affect the central nervous system (CNS). This has been established by the association between stroke and COVID-19. However, the molecular mechanisms that cause stroke related to a COVID-19 infection have not been fully explored. More specifically, stroke and COVID-19 exhibit an overlap of molecular mechanisms. These similarities provide a way to better understand COVID-19 related stroke. We propose here that peripheral macrophages upregulate inflammatory proteins such as matrix metalloproteinases (MMPs) in response to SARS-CoV-2 infection. These inflammatory molecules and the SARS-CoV-2 virus have multiple negative effects related to endothelial dysfunction that results in the disruption of the blood-brain barrier (BBB). Finally, we discuss how the endothelial blood-brain barrier injury alters central nervous system function by leading to astrocyte dysfunction and inflammasome activation. Our goal is to elucidate such inflammatory pathways, which could provide insight into therapies to combat the negative neurological effects of COVID-19.

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.

Characterizing Concussion Using Brain Derived Exosomes

Traumatic brain injury (TBI) currently afflicts 357,000 enlisted military men and women in the US Armed Services. For the most common form of TBI, Mild Traumatic Brain Injury (mTBI) most patients recover within a year following the incident, but 10-20 of mild cases result in a long-term disability including seizures and emotional and behavioral issues. Although much has been learned about molecular changes in the brain following injury, access to these biomarkers following mTBI is lacking. The accurate diagnosis and precise individual clinical management of traumatic brain injury (TBI) is limited by the lack of accessible molecular biomarkers that are informative regarding the unique mixture of injury mechanisms in each TBI patient.

Glutamate Receptor and Kynurenine Pathway Functioning in the Pathobiology of Gulf War Illness

This project has 2 aims: (i) examine the involvement in veterans with Gulf War Illness of a neural excitatory state as a consequence of impaired brain immune, neuron and glia functioning using biomarkers obtained from cerebrospinal fluid (CSF) in 1990-1991 Gulf War veterans with (n=46) and without (n=23) GWI, and (ii) examine involvement in veterans with GWI of a neural excitatory state defined as increased glutamatergic receptor functioning by testing the effect of a single infusion of 0.5 mg/kg of N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine on gamma band EEG (for NMDAR target engagement), other EEG markers, and on symptoms of Gulf War Illness in 19 cases. Outcomes will provide evidence of an expected neural excitatory and pro-inflammatory state in cases that could predispose to neuronal damage via NMDAR hyperactivation through kynurenine pathway activation, and will provide evidence in humans of possible effects of temporarily blocking NMDARs with a subanesthetic dose (0.5 mg/kg) of ketamine.

Microglia activation and cone disruption are the main alterations in the retina of human donors with COVID‐19

PurposeThe presence of SARS‐CoV‐2 in the eye and different alterations in the ocular tissues have been described. However, the health state of the retinal cells in these patients is unknown. The aim was to analyze the morphology of the retinal cells and glial activation in human donor deceased by COVID‐19.MethodsRetinas from human donors with COVID‐19 (n = 9) and from a group control (n = 5) were analyzed. Samples were obtained from the General University Hospital Consortium of Valencia. Photoreceptors, Müller cells, astrocytes, microglia and retinal blood vessels and the location of ACE2 protein were studied through immunohistochemistry staining in cross‐sections and wholemount retinas (using calbindin, recoverin, GFAP, CRALBP and Collagen Type IV, Iba‐1 and ACE2). Confocal microscopy and a quantitative analysis of Iba‐1 positive cells were performed.ResultsThe mean age of COVID‐19 and control group was 77 ± 11 and 68 ± 7 years, respectively. Müller cells, retinal pigment epithelium and outer segment of photoreceptors showed ACE2 immunostaining. The staining of ACE2 protein in the outer segment of photoreceptors was weaker in some COVID‐19 patients. Several patients presented a swelling of the axon terminal of cone photoreceptors and disruptions in the structure of Müller cells. The ramified resident microglial cells changed to an ameboid shape and most of these cells migrated to the retinal vessels. Moreover, the microglia activation in the retina of COVID‐19 patients was confirmed by a reduction of the total area occupied by these cells.ConclusionsMorphological alterations in the cone photoreceptors and Müller cells, variations in the staining of ACE2 protein and microglia activation was found in human donor retinas with COVID‐19. Support: FEDER‐PID2019‐106230RB‐I00. FPU16/04114, FPU18/02964. RETICS‐FEDER RD16/0008/0016. Retina Asturias/Cantabria. FARPE‐FUNDALUCE. IDIFEDER/2017/064.