Glial Cell Function Research Articles

Anti-Semaphorin 4D Rescues Motor, Cognitive, and Respiratory Phenotypes in a Rett Syndrome Mouse Model.

Rett syndrome is a neurodevelopmental disorder caused by mutations of the methyl-CpG binding protein 2 gene. Abnormal physiological functions of glial cells contribute to pathogenesis of Rett syndrome. Semaphorin 4D (SEMA4D) regulates processes central to neuroinflammation and neurodegeneration including cytoskeletal structures required for process extension, communication, and migration of glial cells. Blocking SEMA4D-induced gliosis may preserve normal glial and neuronal function and rescue neurological dysfunction in Rett syndrome. We evaluated the pre-clinical therapeutic efficacy of an anti-SEMA4D monoclonal antibody in the Rett syndrome Mecp2T158A transgenic mouse model and investigated the contribution of glial cells as a proposed mechanism of action in treated mice and in primary glial cultures isolated from Mecp2T158A/y mutant mice. SEMA4D is upregulated in neurons while glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1-positive cells are upregulated in Mecp2T158A/y mice. Anti-SEMA4D treatment ameliorates Rett syndrome-specific symptoms and improves behavioural functions in both pre-symptomatic and symptomatic cohorts of hemizygous Mecp2T158A/y male mice. Anti-SEMA4D also reduces astrocyte and microglia activation in vivo. In vitro experiments demonstrate an abnormal cytoskeletal structure in mutant astrocytes in the presence of SEMA4D, while anti-SEMA4D antibody treatment blocks SEMA4D–Plexin B1 signaling and mitigates these abnormalities. These results suggest that anti-SEMA4D immunotherapy may be an effective treatment option to alleviate symptoms and improve cognitive and motor function in Rett syndrome.

Alcohol Dependence in Rats Is Associated with Global Changes in Gene Expression in the Central Amygdala.

Alcohol dependence is associated with adverse consequences of alcohol (ethanol) use and is evident in most severe cases of alcohol use disorder (AUD). The central nucleus of the amygdala (CeA) plays a critical role in the development of alcohol dependence and escalation of alcohol consumption in dependent subjects. Molecular mechanisms underlying the CeA-driven behavioral changes are not well understood. Here, we examined the effects of alcohol on global gene expression in the CeA using a chronic intermittent ethanol (CIE) vapor model in rats and RNA sequencing (RNA-Seq). The CIE procedure resulted in robust changes in CeA gene expression during intoxication, as the number of differentially expressed genes (DEGs) was significantly greater than those expected by chance. Over-representation analysis of cell types, functional groups and molecular pathways revealed biological categories potentially important for the development of alcohol dependence in our model. Genes specific for astrocytes, myelinating oligodendrocytes, and endothelial cells were over-represented in the DEG category, suggesting that these cell types were particularly affected by the CIE procedure. The majority of the over-represented functional groups and molecular pathways were directly related to the functions of glial and endothelial cells, including extracellular matrix (ECM) organization, myelination, and the regulation of innate immune response. A coordinated regulation of several ECM metalloproteinases (e.g., Mmp2; Mmp14), their substrates (e.g., multiple collagen genes and myelin basic protein; Mbp), and a metalloproteinase inhibitor, Reck, suggests a specific mechanism for ECM re-organization in response to chronic alcohol, which may modulate neuronal activity and result in behavioral changes, such as an escalation of alcohol drinking. Our results highlight the importance of glial and endothelial cells in the effects of chronic alcohol exposure on the CeA, and demonstrate further insight into the molecular mechanisms of alcohol dependence in rats. These molecular targets may be used in future studies to develop therapeutics to treat AUD.

Ceruloplasmin deletion in myelinating glial cells induces myelin disruption and oxidative stress in the central and peripheral nervous systems

Ceruloplasmin (Cp) is a ferroxidase enzyme that is essential for cell iron efflux and has been postulated to have a neuroprotective role. During the myelination process, oligodendrocytes (OLs) and Schwann cells (SCs) express high levels of Cp, but the role of this enzyme in glial cell development and function is completely unknown. To define the function of Cp in the myelination of the central and peripheral nervous systems, we have conditionally knocked-out Cp specifically in OLs and SCs during early postnatal development as well as in aged mice. Cp ablation in early OLs (postnatal day 2, P2) significantly affects the differentiation of these cells and the synthesis of myelin through the first four postnatal weeks. The total number of mature myelinating OLs was reduced, and the density of apoptotic OLs was increased. These changes were accompanied with reductions in the percentage of myelinated axons and increases in the g-ratio of myelinated fibers. Cp ablation in young myelinating OLs (P30 or P60) did not affect myelin synthesis and/or OL numbers, however, Cp loss in aged OLs (8 months) induced cell iron overload, apoptotic cell death, brain oxidative stress, neurodegeneration and myelin disruption. Furthermore, Cp deletion in SCs affected postnatal SC development and myelination and produced motor coordination deficits as well as oxidative stress in young and aged peripheral nerves. Together, our data indicate that Cp ferroxidase activity is essential for OLs and SCs maturation during early postnatal development and iron homeostasis in matured myelinating cells. Additionally, our results suggest that Cp expression in myelinating glial cells is crucial to prevent oxidative stress and neurodegeneration in the central and peripheral nervous systems.

Receptor-Receptor Interactions and Glial Cell Functions with a Special Focus on G Protein-Coupled Receptors.

The discovery that receptors from all families can establish allosteric receptor–receptor interactions and variably associate to form receptor complexes operating as integrative input units endowed with a high functional and structural plasticity has expanded our understanding of intercellular communication. Regarding the nervous system, most research in the field has focused on neuronal populations and has led to the identification of many receptor complexes representing an important mechanism to fine-tune synaptic efficiency. Receptor–receptor interactions, however, also modulate glia–neuron and glia–glia intercellular communication, with significant consequences on synaptic activity and brain network plasticity. The research on this topic is probably still at the beginning and, here, available evidence will be reviewed and discussed. It may also be of potential interest from a pharmacological standpoint, opening the possibility to explore, inter alia, glia-based neuroprotective therapeutic strategies.

Gambogic Acid Relieves Neuropathic Pain in Rats by Regulating CXCR4-TXNIP/NLRP3 Pathway

Neuropathic pain is caused by abnormal sensory processing in the central nervous system (CNS). The immune response of the CNS is related to the function of glial cells and is critical in neuropathic pain. Agents based on cytokines and glial cells in the CNS have potential for the treatment of neuropathic pain. Gambogic acid (GA) is one of the main components of Garcinia cambogia, which has anti-inflammatory, antitumor, and analgesic effects. However, the effect of GA on neuropathic pain and related mechanisms are still unclear. Previous studies indicated that GA could reduce CXCR4 expression in neuropathic pain. In this study, we found that GA could alleviate nerve pain behavior in rats by measuring the incubation period of heat shrinkage and mechanical pain threshold. Also, GA reduced inflammation in chronic constriction injury rats. We further found GA reduced the apoptosis of spinal cord nerve cells in chronic constriction injury rats. Mechanically, we noticed GA relieved neuropathic pain in rats via regulating CXCR4-TXNIP/NLRP3 pathway. Our data confirmed that GA could serve as a promising drug for the treatment of neuropathic pain.

Stem Cells: Innovative Therapeutic Options for Neurodegenerative Diseases?

Neurodegenerative diseases are characterized by the progressive loss of structure and/or function of both neurons and glial cells, leading to different degrees of pathology and loss of cognition. The hypothesis of circuit reconstruction in the damaged brain via direct cell replacement has been pursued extensively so far. In this context, stem cells represent a useful option since they provide tissue restoration through the substitution of damaged neuronal cells with exogenous stem cells and create a neuro-protective environment through the release of bioactive molecules for healthy neurons, as well. These peculiar properties of stem cells are opening to potential therapeutic strategies for the treatment of severe neurodegenerative disorders, for which the absence of effective treatment options leads to an increasingly socio-economic burden. Currently, the introduction of new technologies in the field of stem cells and the implementation of alternative cell tissues sources are pointing to exciting frontiers in this area of research. Here, we provide an update of the current knowledge about source and administration routes of stem cells, and review light and shadows of cells replacement therapy for the treatment of the three main neurodegenerative disorders (Amyotrophic lateral sclerosis, Parkinson’s, and Alzheimer’s disease).

Oligodendrocytes and Microglia: Key Players in Myelin Development, Damage and Repair.

Oligodendrocytes, the myelin-making cells of the CNS, regulate the complex process of myelination under physiological and pathological conditions, significantly aided by other glial cell types such as microglia, the brain-resident, macrophage-like innate immune cells. In this review, we summarize how oligodendrocytes orchestrate myelination, and especially myelin repair after damage, and present novel aspects of oligodendroglial functions. We emphasize the contribution of microglia in the generation and regeneration of myelin by discussing their beneficial and detrimental roles, especially in remyelination, underlining the cellular and molecular components involved. Finally, we present recent findings towards human stem cell-derived preclinical models for the study of microglia in human pathologies and on the role of microbiome on glial cell functions.

Astrocytes in the Ventromedial Hypothalamus Involve Chronic Stress-Induced Anxiety and Bone Loss in Mice.

Chronic stress is one of the main risk factors of bone loss. While the neurons and neural circuits of the ventromedial hypothalamus (VMH) mediate bone loss induced by chronic stress, the detailed intrinsic mechanisms within the VMH nucleus still need to be explored. Astrocytes in brain regions play important roles in the regulation of metabolism and anxiety-like behavior through interactions with surrounding neurons. However, whether astrocytes in the VMH affect neuronal activity and therefore regulate chronic stress-induced anxiety and bone loss remain elusive. In this study, we found that VMH astrocytes were activated during chronic stress-induced anxiety and bone loss. Pharmacogenetic activation of the Gi and Gq pathways in VMH astrocytes reduced and increased the levels of anxiety and bone loss, respectively. Furthermore, activation of VMH astrocytes by optogenetics induced depolarization in neighboring steroidogenic factor-1 (SF-1) neurons, which was diminished by administration of N-methyl-D-aspartic acid (NMDA) receptor blocker but not by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor blocker. These results suggest that there may be a functional “glial-neuron microcircuit” in VMH nuclei that mediates anxiety and bone loss induced by chronic stress. This study not only advances our understanding of glial cell function but also provides a potential intervention target for chronic stress-induced anxiety and bone loss therapy.

Genetically Predicted Brain C4A Expression Is Associated With TSPO and Hippocampal Morphology

BackgroundAlterations in the immune system, particularly C4A, have been implicated in the pathophysiology of schizophrenia. C4A promotes synapse elimination by microglia in preclinical models; however, it is unknown whether this process is also present in living humans and how it affects brain morphology. MethodsParticipants (N = 111; 33 patients with psychosis, 37 individuals at clinical high risk, and 41 healthy control subjects) underwent a TSPO [18F]FEPPA positron emission tomography scan and a magnetic resonance imaging scan. Brain C4A expression was genetically predicted as a function of the dosage of each of 4 structural elements (C4AL, C4BL, C4AS, C4BS). ResultsHigher genetically predicted brain C4A expression was associated with higher brain microglial marker (TSPO) and altered hippocampal morphology, including reduced surface area and medial displacement in the CA1 area. This study is the first to quantify genetically predicted brain C4A expression in individuals at clinical high risk, showing significantly lower C4A in individuals at clinical high risk compared with healthy control subjects. We also showed a robust effect of sex on genetically predicted brain C4A expression and effects of both sex and cannabis use on brain TSPO. ConclusionsThis study shows for the first time complement system (C4A) coupling with a microglial marker (TSPO) and hippocampal morphology in living human brain. These findings pave the way for future research on the interaction between C4A and glial cell function, which has the potential to inform the disease mechanism underlying psychosis and schizophrenia.

Histamine triggers microglial responses indirectly via astrocytes and purinergic signaling.

Histamine is a monoaminergic neurotransmitter which is released within the entire brain from ascending axons originating in the tuberomammillary nucleus in a sleep state-dependent fashion. Besides the modulation of neuronal firing patterns, brain histamine levels are also thought to modulate functions of glial cells. Microglia are the innate immune cells and professional phagocytes of the central nervous system, and histamine was previously shown to have multiple effects on microglial functions in health and disease. Isolated microglia respond only to agonists of the Hrh2 subtype of histamine receptors (Hrh), and the expression of that isoform is confirmed by a metadata analysis of microglia transcriptomes. When we studied the effect of the histamine receptor isoforms in cortical and thalamic microglia by in situ live cell Ca2+ imaging using a novel, microglia-specific indicator mouse line, microglial cells respond to external histamine application mainly in a Hrh1-, and to a lower extent also in a Hrh2-dependent manner. The Hrh1 response was sensitive to blockers of purinergic P2ry12 receptors, and since Hrh1 expression was predominantly found in astrocytes, we suggest that the Hrh1 response in microglia is mediated by astrocyte ATP release and activation of P2ry12 receptors in microglia. Histamine also stimulates microglial phagocytic activity via Hrh1- and P2ry12-mediated signaling. Taken together, we provide evidence that histamine acts indirectly on microglial Ca2+ levels and phagocytic activity via astrocyte histamine receptor-controlled purinergic signaling.

Amyloid-β oligomers block lysosomal targeting of miRNPs to prevent miRNP recycling and target repression in glial cells.

Upon exposure to amyloid-β oligomers (Aβ1-42), glial cells start expressing proinflammatory cytokines, despite an increase in levels of repressive microRNAs (miRNAs). Exploring the mechanism of this potential immunity of target cytokine mRNAs against repressive miRNAs in amyloid-β-exposed glial cells, we have identified differential compartmentalization of repressive miRNAs in glial cells that explains this aberrant miRNA function. In Aβ1-42-treated cells, whereas target mRNAs were found to be associated with polysomes attached to endoplasmic reticulum (ER), the miRNA ribonucleoprotein complexes (miRNPs) were found to be present predominantly with endosomes that failed to recycle to ER-attached polysomes, preventing repression of mRNA targets. Aβ1-42 oligomers, by masking Rab7a proteins on endosomal surfaces, affected Rab7a interaction with Rab-interacting lysosomal protein (RILP), restricting the lysosomal targeting and recycling of miRNPs. RNA-processing body (P-body) localization of the miRNPs was found to be enhanced in amyloid-β-treated cells as a consequence of enhanced endosomal retention of miRNPs. Interestingly, depletion of P-body components partly rescued the miRNA function in glial cells exposed to amyloid-β and restricted the excess cytokine expression. This article has an associated First Person interview with the first author of the paper.

Expression of Urea Transporter B in Normal and Injured Brain

Urea transporter B (UT-B) is a membrane channel protein widely distributed in mammals, and plays a significant physiological role by regulating urea and water transportation in different tissues. More and more studies have found that UT-B is related to neurological diseases, including myelinopathy and depression. When urea accumulates in the brains of UT-B knockout mice, the synaptic plasticity of neurons is reduced, and the morphology and function of glial cells are also changed. However, the distribution and expression change of UT-B remain unclear. The purpose of this study is to determine the expression characteristics of UT-B in the brain. Through single-cell RNA sequencing, UT-B was found to express universally and substantially throughout the various cells in the central nervous system except for endothelial and smooth muscle cells. UT-B was detected in the third cerebral ventricular wall, granule cell layer of the dentate gyrus, and other parts of the hippocampal, cerebral cortex, substantia nigra, habenular, and lateral hypothalamic nucleus by immunohistochemistry. Compared with the membrane expression of UT-B in glial cells, the subcellular localization of UT-B is in the Golgi apparatus of neurons. Further, the expression of UT-B was regulated by osmotic pressure in vitro. In the experimental traumatic brain injury model (TBI), the number of UT-B positive neurons near the ipsilateral cerebral cortex increased first and then decreased over time, peaking at the 24 h. We inferred that change in UT-B expression after the TBI was an adaptation to changed urea levels. The experimental data suggest that the UT-B may be a potential target for the treatment of TBI and white matter edema.

MiR-146a Dysregulates Energy Metabolism During Neuroinflammation.

Alzheimer's disease (AD) and other neurodegenerative diseases are characterized by chronic neuroinflammation and a reduction in brain energy metabolism. An important role has emerged for small, non-coding RNA molecules known as microRNAs (miRNAs) in the pathophysiology of many neurodegenerative disorders. As epigenetic regulators, miRNAs possess the capacity to regulate and fine tune protein production by inhibiting translation. Several miRNAs, which include miR-146a, are elevated in the brain, CSF, and plasma of AD patients. miR-146a participates in pathways that regulate immune activation and has several mRNA targets which encode for proteins involved in cellular energy metabolism. An additional role for extracellular vesicles (EVs) has also emerged in the progression AD, as EVs can transfer functionally active proteins and RNAs from diseased to healthy cells. In the current study, we exposed various cell types present within the CNS to immunomodulatory molecules and observed significant upregulation of miR-146a expression, both within cells and within their secreted EVs. Further, we assessed the effects of miR-146a overexpression on bioenergetic function in primary rat glial cells and found significant reductions in oxidative phosphorylation and glycolysis. Lastly, we correlated miR-146a expression levels within various regions of the AD brain to disease staging and found significant, positive correlations. These novel results demonstrate that the modulation of miR-146a in response to neuroinflammatory stimuli may mediate the loss of mitochondrial integrity and function in cells, thereby contributing to the progression of beta-amyloid and tau pathology in the AD brain. Multiple inflammatory stimuli can upregulate miRNA-146a expression within neurons, mixed glial cells, and brain endothelial cells, which is either retained within these cells or released from them as extracellular vesicle cargo. The upregulation of miR-146a disrupts cellular bioenergetics in mixed glial cells. This mechanism may play a critical role in the neuroinflammatory response observed during Alzheimer's disease.

Glial Purinergic Signaling in Neurodegeneration

Purinergic signaling regulates neuronal and glial cell functions in the healthy CNS. In neurodegenerative diseases, purinergic signaling becomes dysregulated and can affect disease-associated phenotypes of glial cells. In this review, we discuss how cell-specific expression patterns of purinergic signaling components change in neurodegeneration and how dysregulated glial purinergic signaling and crosstalk may contribute to disease pathophysiology, thus bearing promising potential for the development of new therapeutical options for neurodegenerative diseases.

Cholinergic Modulation of Neuroinflammation: Focus on α7 Nicotinic Receptor.

All nervous system pathologies (e.g., neurodegenerative/demyelinating diseases and brain tumours) develop neuroinflammation, a beneficial process during pathological events, aimed at removing damaged cells, toxic agents, and/or pathogens. Unfortunately, excessive inflammation frequently occurs during nervous system disorders, becoming a detrimental event capable of enhancing neurons and myelinating glial cell impairment, rather than improving their survival and activity. Consequently, targeting the neuroinflammation could be relevant for reducing brain injury and rescuing neuronal and glial cell functions. Several studies have highlighted the role of acetylcholine and its receptors in the regulation of central and peripheral inflammation. In particular, α7 nicotinic receptor has been described as one of the main regulators of the “brain cholinergic anti-inflammatory pathway”. Its expression in astrocytes and microglial cells and the ability to modulate anti-inflammatory cytokines make this receptor a new interesting therapeutic target for neuroinflammation regulation. In this review, we summarize the distribution and physiological functions of the α7 nicotinic receptor in glial cells (astrocytes and microglia) and its role in the modulation of neuroinflammation. Moreover, we explore how its altered expression and function contribute to the development of different neurological pathologies and exacerbate neuroinflammatory processes.

Expression Analysis of Zinc Transporters in Nervous Tissue Cells Reveals Neuronal and Synaptic Localization of ZIP4.

In the last years, research has shown that zinc ions play an essential role in the physiology of brain function. Zinc acts as a potent neuromodulatory agent and signaling ions, regulating healthy brain development and the function of both neurons and glial cells. Therefore, the concentration of zinc within the brain and its cells is tightly controlled. Zinc transporters are key regulators of (extra-) cellular zinc levels, and deregulation of zinc homeostasis and zinc transporters has been associated with neurodegenerative and neuropsychiatric disorders. However, to date, the presence of specific family members and their subcellular localization within brain cells have not been investigated in detail. Here, we analyzed the expression of all zinc transporters (ZnTs) and Irt-like proteins (ZIPs) in the rat brain. We further used primary rat neurons and rat astrocyte cell lines to differentiate between the expression found in neurons or astrocytes or both. We identified ZIP4 expressed in astrocytes but significantly more so in neurons, a finding that has not been reported previously. In neurons, ZIP4 is localized to synapses and found in a complex with major postsynaptic scaffold proteins of excitatory synapses. Synaptic ZIP4 reacts to short-term fluctuations in local zinc levels. We conclude that ZIP4 may have a so-far undescribed functional role at excitatory postsynapses.

Early life exposure to air pollution impacts neuronal and glial cell function leading to impaired neurodevelopment

AbstractThe World Health Organisation recently listed air pollution as the most significant threat to human health. Air pollution comprises particulate matter (PM), metals, black carbon and gases such as ozone (O3), nitrogen dioxide (NO2) and carbon monoxide (CO). In addition to respiratory and cardiovascular disease, PM exposure is linked with increased risk of neurodegeneration as well as neurodevelopmental impairments. Critically, studies suggest that PM crosses the placenta, making direct in utero exposure a reality. Rodent models reveal that neuroinflammation, neurotransmitter imbalance and oxidative stress are triggered following gestational/early life exposure to PM, and may be exacerbated by concomitant mitochondrial dysfunction. Gestational PM exposure (potentiated by mitochondrial impairment in the metabolically active neonatal brain) not only impacts neurodevelopment but may sensitise the brain to subsequent cognitive impairment. Having reviewed this field, we conclude that strategies are urgently required to reduce exposure to PM during this sensitive developmental period.

Glial cell type-specific gene expression in the mouse cerebrum using the piggyBac system and in utero electroporation

Glial cells such as astrocytes and oligodendrocytes play crucial roles in the central nervous system. To investigate the molecular mechanisms underlying the development and the biological functions of glial cells, simple and rapid techniques for glial cell-specific genetic manipulation in the mouse cerebrum would be valuable. Here we uncovered that the Gfa2 promoter is suitable for selective gene expression in astrocytes when used with the piggyBac system and in utero electroporation. In contrast, the Blbp promoter, which has been used to induce astrocyte-specific gene expression in transgenic mice, did not result in astrocyte-specific gene expression. We also identified the Plp1 and Mbp promoters could be used with the piggyBac system and in utero electroporation to induce selective gene expression in oligodendrocytes. Furthermore, using our technique, neuron-astrocyte or neuron-oligodendrocyte interactions can be visualized by labeling neurons, astrocytes and oligodendrocytes differentially. Our study provides a fundamental basis for specific transgene expression in astrocytes and/or oligodendrocytes in the mouse cerebrum.

M6A Modifications Play Crucial Roles in Glial Cell Development and Brain Tumorigenesis.

RNA methylation is a reversible post-transcriptional modification to RNA and has a significant impact on numerous biological processes. N 6-methyladenosine (m6A) is known as one of the most common types of eukaryotic mRNA methylation modifications, and exists in a wide variety of organisms, including viruses, yeast, plants, mice, and humans. Widespread and dynamic m6A methylation is identified in distinct developmental stages in the brain, and controls development of neural stem cells and their differentiation into neurons, glial cells such as oligodendrocytes and astrocytes. Here we summarize recent advances in our understanding of RNA methylation regulation in brain development, neurogenesis, gliogenesis, and its dysregulation in brain tumors. This review will highlight biological roles of RNA methylation in development and function of neurons and glial cells, and provide insights into brain tumor formation, and diagnostic and treatment strategies.

Amphioxus neuroglia: Molecular characterization and evidence for early compartmentalization of the developing nerve cord.

Glial cells play important roles in the development and homeostasis of metazoan nervous systems. However, while their involvement in the development and function in the central nervous system (CNS) of vertebrates is increasingly well understood, much less is known about invertebrate glia and the evolutionary history of glial cells more generally. An investigation into amphioxus glia is therefore timely, as this organism is the best living proxy for the last common ancestor of all chordates, and hence provides a window into the role of glial cell development and function at the transition of invertebrates and vertebrates. We report here our findings on amphioxus glia as characterized by molecular probes correlated with anatomical data at the transmission electron microscopy (TEM) level. The results show that amphioxus glial lineages express genes typical of vertebrate astroglia and radial glia, and that they segregate early in development, forming what appears to be a spatially separate cell proliferation zone positioned laterally, between the dorsal and ventral zones of neural cell proliferation. Our study provides strong evidence for the presence of vertebrate-type glial cells in amphioxus, while highlighting the role played by segregated progenitor cell pools in CNS development. There are implications also for our understanding of glial cells in a broader evolutionary context, and insights into patterns of precursor cell deployment in the chordate nerve cord.