Astrocyte and Oligodendrocyte Cross-Talk in the Central Nervous System

Glia-glia crosstalk via semaphorins: Emerging implications in neurodegeneration

The central nervous system (CNS) is wired by a complex network of integrated glial and neuronal signals, which is critical for its development and homeostasis. In this context, glia-glia communication is a complex and dynamic process that is essential for ensuring optimal CNS function. Semaphorins, which include secreted and transmembrane molecules, and their receptors, mainly found in the plexin and neuropilin families, are expressed in a wide range of cell types, including glia. In the CNS, semaphorin signalling is involved in a spectrum of processes, including neurogenesis, neuronal migration and wiring, and glial cell recruitment. Recently, semaphorins and plexins have attracted intense research aimed at elucidating their roles in instructing glial cell behavior during development or in response to inflammatory stimuli. In this review, we provide an overview of the multifaceted role of semaphorins in glia-glia communication, highlighting recent discoveries about semaphoring-dependent regulation of glia functions in healthy conditions. We also discuss the mechanisms of gliaglia crosstalk mediated by semaphorins under pathological conditions, and how these interactions may provide potential avenues for therapeutic intervention in neuroinflammation-mediated neurodegeneration.

Oligodendrocytes, the Forgotten Target of Gene Therapy

If the billions of oligodendrocytes (OLs) populating the central nervous system (CNS) of patients could express their feelings, they would undoubtedly tell gene therapists about their frustration with the other neural cell populations, neurons, microglia, or astrocytes, which have been the favorite targets of gene transfer experiments. This review questions why OLs have been left out of most gene therapy attempts. The first explanation is that the pathogenic role of OLs is still discussed in most CNS diseases. Another reason is that the so-called ubiquitous CAG, CBA, CBh, or CMV promoters-widely used in gene therapy studies-are unable or poorly able to activate the transcription of episomal transgene copies brought by adeno-associated virus (AAV) vectors in OLs. Accordingly, transgene expression in OLs has either not been found or not been evaluated in most gene therapy studies in rodents or non-human primates. The aims of the current review are to give OLs their rightful place among the neural cells that future gene therapy could target and to encourage researchers to test the effect of OL transduction in various CNS diseases.

ALS-linked mutant TDP-43 in oligodendrocytes induces oligodendrocyte damage and exacerbates motor dysfunction in mice

Nuclear clearance and cytoplasmic aggregation of TAR DNA-binding protein of 43 kDa (TDP-43) are pathological hallmarks of amyotrophic lateral sclerosis (ALS) and its pathogenic mechanism is mediated by both loss-of-function and gain-of-toxicity of TDP-43. However, the role of TDP-43 gain-of-toxicity in oligodendrocytes remains unclear. To investigate the impact of excess TDP-43 on oligodendrocytes, we established transgenic mice overexpressing the ALS-linked mutant TDP-43M337V in oligodendrocytes through crossbreeding with Mbp-Cre mice. Two-step crossbreeding of floxed TDP-43M337V and Mbp-Cre mice resulted in the heterozygous low-level systemic expression of TDP-43M337V with (Cre-positive) or without (Cre-negative) oligodendrocyte-specific overexpression of TDP-43M337V. Although Cre-negative mice also exhibit subtle motor dysfunction, TDP-43M337V overexpression in oligodendrocytes aggravated clasping signs and gait disturbance accompanied by myelin pallor in the corpus callosum and white matter of the lumbar spinal cord in Cre-positive mice. RNA sequencing analysis of oligodendrocyte lineage cells isolated from whole brains of 12-month-old transgenic mice revealed downregulation of myelinating oligodendrocyte marker genes and cholesterol-related genes crucial for myelination, along with marked upregulation of apoptotic pathway genes. Immunofluorescence staining showed cleaved caspase 3-positive apoptotic oligodendrocytes surrounded by activated microglia and astrocytes in aged transgenic mice. Collectively, our findings demonstrate that an excess amount of ALS-linked mutant TDP-43 expression in oligodendrocytes exacerbates motor dysfunction in mice, likely through oligodendrocyte dysfunction and neuroinflammation. Therefore, targeting oligodendrocyte protection, particularly through ameliorating TDP-43 pathology, could represent a potential therapeutic approach for ALS.

Terra incognita of glial cell dynamics in the etiology of leukodystrophies: Broadening disease and therapeutic perspectives

Neuroglial cells, also known as glia, are primarily characterized as auxiliary cells within the central nervous system (CNS). The recent findings have shed light on their significance in numerous physiological processes and their involvement in various neurological disorders. Leukodystrophies encompass an array of rare and hereditary neurodegenerative conditions that were initially characterized by the deficiency, aberration, or degradation of myelin sheath within CNS. The primary cellular populations that experience significant alterations are astrocytes, oligodendrocytes and microglia. These glial cells are either structurally or metabolically impaired due to inherent cellular dysfunction. Alternatively, they may fall victim to the accumulation of harmful by-products resulting from metabolic disturbances. In either situation, the possible replacement of glial cells through the utilization of implanted tissue or stem cell-derived human neural or glial progenitor cells hold great promise as a therapeutic strategy for both the restoration of structural integrity through remyelination and the amelioration of metabolic deficiencies. Various emerging treatment strategies like stem cell therapy, ex-vivo gene therapy, infusion of adeno-associated virus vectors, emerging RNA-based therapies as well as long-term therapies have demonstrated success in pre-clinical studies and show promise for rapid clinical translation. Here, we addressed various leukodystrophies in a comprehensive and detailed manner as well as provide prospective therapeutic interventions that are being considered for clinical trials. Further, we aim to emphasize the crucial role of different glial cells in the pathogenesis of leukodystrophies. By doing so, we hope to advance our understanding of the disease, elucidate underlying mechanisms, and facilitate the development of potential treatment interventions.

Modulation of αv integrins by lebecetin, a viper venom-derived molecule, in experimental neuroinflammation and demyelination models

Several neurodegenerative diseases, such as multiple sclerosis and Parkinson's disease, are linked to alterations in myelin content or structure. Transmembrane receptors such as integrins could be involved in these alterations. In the present study, we investigated the role of αv-integrins in experimental models of neuroinflammation and demyelination with the use of lebecetin (LCT), a C-lectin protein purified from Macrovipera lebetina viper venom, as an αv-integrin modulator. In a model of neuroinflammation, LCT inhibited the upregulation of αv, β3, β5, α5, and β1 integrins, as well as the associated release of pro-inflammatory factor IL-6 and chemokine CXCL-10, and decreased the expression of phosphorylated NfκB. The subsequent "indirect culture" between reactive astrocytes and oligodendrocytes showed a down-regulation of αv and β3 integrins versus upregulation of β1 one, accompanied by a reduced expression of myelin basic protein (MBP). Treatment of oligodendrocytes with LCT rectified the changes in integrin and MBP expression. Through Western blot quantification, LCT was shown to upregulate the expression levels of PI3K and p-mTOR while downregulating expression levels of p-AKT in oligodendrocytes, suggesting the neuroprotective and pro-myelinating effects of LCT may be related to the PI3K/mTor/AKT pathway. Concomitantly, we found that LCT promoted remyelination by tracking the increased expression of MBP in the brains of cuprizone-intoxicated mice. These results point to an involvement of integrins in not only neuroinflammation but demyelination as well. Thus, targeting αv integrins could offer potential therapeutic avenues for the treatment of demyelinating diseases.

Astrocyte-Mediated Neuroinflammation in Neurological Conditions

Astrocytes are one of the key glial types of the central nervous system (CNS), accounting for over 20% of total glial cells in the brain. Extensive evidence has established their indispensable functions in the maintenance of CNS homeostasis, as well as their broad involvement in neurological conditions. In particular, astrocytes can participate in various neuroinflammatory processes, e.g., releasing a repertoire of cytokines and chemokines or specific neurotrophic factors, which result in both beneficial and detrimental effects. It has become increasingly clear that such astrocyte-mediated neuroinflammation, together with its complex crosstalk with other glial cells or immune cells, designates neuronal survival and the functional integrity of neurocircuits, thus critically contributing to disease onset and progression. In this review, we focus on the current knowledge of the neuroinflammatory responses of astrocytes, summarizing their common features in neurological conditions. Moreover, we highlight several vital questions for future research that promise novel insights into diagnostic or therapeutic strategies against those debilitating CNS diseases.

Small Scale, Big Impact: Nanotechnology-Enhanced Drug Delivery for Brain Diseases

Central nervous system (CNS) diseases, ranging from brain cancers to neurodegenerative disorders like dementia and acute conditions such as strokes, have been heavily burdening healthcare and have a direct impact on patient quality of life. A significant hurdle in developing effective treatments is the presence of the blood-brain barrier (BBB), a highly selective barrier that prevents most drugs from reaching the brain. The tight junctions and adherens junctions between the endothelial cells and various receptors expressed on the cells make the BBB form a nonfenestrated and highly selective structure that is crucial for brain homeostasis but complicates drug delivery. Nanotechnology offers a novel pathway to circumvent this barrier, with nanoparticles engineered to ferry drugs across the BBB, protect drugs from degradation, and deliver medications to the designated area. After years of development, nanoparticle optimization, including sizes, shapes, surface modifications, and targeting ligands, can enable nanomaterials tailored to specific brain drug delivery settings. Moreover, smart nano drug delivery systems can respond to endogenous and exogenous stimuli that control subsequent drug release. Here, we address the importance of the BBB in brain disease treatment, summarize different delivery routes for brain drug delivery, discuss the cutting-edge nanotechnology-based strategies for brain drug delivery, and further offer valuable insights into how these innovations in nanoparticle technology could revolutionize the treatment of CNS diseases, presenting a promising avenue for noninvasive, targeted therapeutic interventions.

Isolation methods and characterization of primary rat neurovascular cells

BACKGROUND

There is significant interest in isolating cells of the blood-brain barrier (BBB) for use in in vitro screening of therapeutics and analyzing cell specific roles in neurovascular pathology. Primary brain cells play an advantageous role in BBB models; however, isolation procedures often do not produce cells at high enough yields for experiments. In addition, although numerous reports provide primary cell isolation methods, the field is lacking in documentation and detail of expected morphological changes that occur throughout culturing and there are minimal troubleshooting resources. Here, we present simplified, robust, and reproducible methodology for isolating astrocytes, pericytes, and endothelial cells, and demonstrate several morphological benchmarks for each cell type throughout the process and culture timeframe. We also analyze common considerations for developing neurovascular cell isolation procedures and recommend solutions for troubleshooting.

RESULTS

The presented methodology isolated astrocytes, pericytes, and endothelial cells and enabled cell attachment, maturation, and cell viability. We characterized milestones in cell maturation over 12 days in culture, a common timeline for applications of these cell types in BBB models. Phase contrast microscopy was used to show initial cell plating, attachment, and daily growth of isolated cells. Confocal microscopy images were analyzed to determine the identity of cell types and changes to cell morphology. Nuclear staining was also used to show the viability and proliferation of glial cells at four time points. Astrocyte branches became numerous and complex with increased culture time. Microglia, oligodendrocytes, and neurons were present in mixed glial cultures for 12 days, though the percentage of microglia and neurons expectedly decreased after passaging, with microglia demonstrating a less branched morphology.

CONCLUSIONS

Neurovascular cells can be isolated through our optimized protocols that minimize cell loss and encourage the adhesion and proliferation of isolated cells. By identifying timepoints of viable glia and neurons within an astrocyte-dominant mixed culture, these cells can be used to evaluate drug targeting, uptake studies, and response to pathological stimulus in the neurovascular unit.

Advancing understanding of the role of IL-22 in myelination: insights from the Cuprizone mouse model

Despite significant advancements in the field, the pathophysiology of multiple sclerosis (MS) remains partially understood, with limited therapeutic options available for this debilitating condition. The precise impact of Interleukin-22 (IL-22) in the context of MS is still incompletely elucidated with some evidence suggesting its protective role. To provide a more comprehensive understanding of the role of IL-22, we investigated its effect on remyelination in a mouse model of demyelination induced by Cuprizone. Mice underwent a 6 week regimen of Cuprizone or vehicle, followed or not by intraperitoneal administration of IL-22. Behavioral assessments including tail suspension and inverted screen tests were conducted, alongside histological, histochemical, and quantitative PCR analyses. In Cuprizone-treated mice, IL-22 significantly improved motor and behavioral performance and robustly promoted remyelination in the corpus callosum. Additionally, IL-22 administration led to a significant elevation in MBP transcription in brain biopsies of treated mice. These findings collectively suggest a crucial role for IL-22 in the pathophysiology of MS, particularly in supporting the process of remyelination. These results offer potential avenues for expanding therapeutic strategies for MS treatment. Ongoing experiments aim to further unravel the underlying mechanisms of IL-22 action.

Cerebral White Matter Alterations Associated With Oligodendrocyte Vulnerability in Organic Acidurias: Insights in Glutaric Aciduria Type I

The white matter is an important constituent of the central nervous system, containing axons, oligodendrocytes, and its progenitor cells, astrocytes, and microglial cells. Oligodendrocytes are central for myelin synthesis, the insulating envelope that protects axons and allows normal neural conduction. Both, oligodendrocytes and myelin, are highly vulnerable to toxic factors in many neurodevelopmental and neurodegenerative disorders associated with disturbances of myelination. Here we review the main alterations in oligodendrocytes and myelin observed in some organic acidurias/acidemias, which correspond to inherited neurometabolic disorders biochemically characterized by accumulation of potentially neurotoxic organic acids and their derivatives. The yet incompletely understood mechanisms underlying the high vulnerability of OLs and/or myelin in glutaric acidemia type I, the most prototypical cerebral organic aciduria, are particularly discussed.

Citrullinated isomer of myelin basic protein can induce inflammatory responses in astrocytes

Purpose

During the course of demyelinating inflammatory diseases, myelin-derived proteins, including myelin basic protein(MBP), are secreted into extracellular space. MBP shows extensive post-translational modifications, including deimination/citrullination. Deiminated MBP is structurally less ordered, susceptible to proteolytic attack, and more immunogenic than unmodified MBP. This study investigated the effect of the deiminated/citrullinated isomer of MBP(C8) and the unmodified isomer of MBP(C1) on cultured primary astrocytes.

Methods

MBP charge isomers were isolated/purified from bovine brain. Primary astrocyte cultures were prepared from the 2-day-old Wistar rats. For evaluation of glutamate release/uptake a Fluorimetric glutamate assay was used. Expression of peroxisome proliferator-activated receptor-gamma(PPAR-γ), excitatory amino acid transporter 2(EAAT2), the inhibitor of the nuclear factor kappa-B(ikB) and high mobility group-B1(HMGB1) protein were assayed by Western blot analysis. IL-17A expression was determined in cell medium by ELISA.

Results

We found that MBP(C8) and MBP(C1) acted differently on the uptake/release of glutamate in astrocytes: C1 increased glutamate uptake and did not change its release, whereas C8 decreased glutamate release but did not change its uptake. Both isomers increased the expression of PPAR-γ and EAAT2 to the same degree. Western blots of cell lysates revealed decreased expression of ikB and increased expression of HMGB1 proteins after treatment of astrocytes by C8. Moreover, C8-treated cells released more nitric oxide and proinflammatory IL-17A than C1-treated cells.

Conclusions

These data suggest that the most immunogenic deiminated isomer C8, in parallel to the decreases in glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B(NF-kB).

Summary statement

The most modified-citrullinated myelin basic protein charge isomer decreases glutamate release, elicits an inflammatory response and enhances the secretion of proinflammatory molecules via activation of nuclear factor kappa B in astrocytes.

The role of glial cells in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has traditionally been considered a neuron-centric disease. This view is now outdated, with increasing recognition of cell autonomous and non-cell autonomous contributions of central and peripheral nervous system glia to ALS pathomechanisms. With glial research rapidly accelerating, we comprehensively interrogate the roles of astrocytes, microglia, oligodendrocytes, ependymal cells, Schwann cells and satellite glia in nervous system physiology and ALS-associated pathology. Moreover, we highlight the inter-glial, glial-neuronal and inter-system polylogue which constitutes the healthy nervous system and destabilises in disease. We also propose classification based on function for complex glial reactive phenotypes and discuss the pre-requisite for integrative modelling to advance translation. Given the paucity of life-enhancing therapies currently available for ALS patients, we discuss the promising potential of harnessing glia in driving ALS therapeutic discovery.

NetREm: Network Regression Embeddings reveal cell-type transcription factor coordination for gene regulation

Transcription factor (TF) coordination plays a key role in target gene (TG) regulation via protein-protein interactions (PPIs) and DNA co-binding to regulatory elements. Single-cell technologies facilitate gene expression measurement for individual cells and cell-type identification, yet the connection between TF coordination and TG regulation of various cell types remains unclear. To address this, we have developed a novel computational approach, Network Regression Embeddings (NetREm), to reveal cell-type TF-TF coordination activities for TG regulation. NetREm leverages network-constrained regularization using prior knowledge of direct and/or indirect PPIs among TFs to analyze single-cell gene expression data. We test NetREm by simulation data and benchmark its performance in 4 real-world applications that have gold standard TF-TG networks available: mouse (mESCs) and simulated human (hESCs) embryonic stem (ESCs), human hematopoietic stem (HSCs), and mouse dendritic (mDCs) cells. Further, we use NetREm to prioritize valid novel TF-TF coordination links in human Peripheral Blood Mononuclear cell (PBMC) sub-types. We apply NetREm to analyze various cell types in both central (CNS) and peripheral (PNS) nerve system (NS) (e.g. neuronal, glial, Schwann cells (SCs)) as well as in Alzheimers disease (AD). Our findings uncover cell-type coordinating TFs and identify new TF-TG candidate links. We validate our top predictions using Cut&Run and knockout loss-of-function expression data in rat/mouse models and compare results with additional functional genomic data, including expression quantitative trait loci (eQTL) and Genome-Wide Association Studies (GWAS) to link genetic variants (single nucleotide polymorphisms (SNPs)) to TF coordination.

Ion transporter cascade, reactive astrogliosis and cerebrovascular diseases

Cerebrovascular diseases and their sequalae, such as ischemic stroke, chronic cerebral hypoperfusion, and vascular dementia are significant contributors to adult disability and cognitive impairment in the modern world. Astrocytes are an integral part of the neurovascular unit in the CNS and play a pivotal role in CNS homeostasis, including ionic and pH balance, neurotransmission, cerebral blood flow, and metabolism. Astrocytes respond to cerebral insults, inflammation, and diseases through unique molecular, morphological, and functional changes, collectively known as reactive astrogliosis. The function of reactive astrocytes has been a subject of debate. Initially, astrocytes were thought to primarily play a supportive role in maintaining the structure and function of the nervous system. However, recent studies suggest that reactive astrocytes may have both beneficial and detrimental effects. For example, in chronic cerebral hypoperfusion, reactive astrocytes can cause oligodendrocyte death and demyelination. In this review, we will summarize the (1) roles of ion transporter cascade in reactive astrogliosis, (2) role of reactive astrocytes in vascular dementia and related dementias, and (3) potential therapeutic approaches for dementing disorders targeting reactive astrocytes. Understanding the relationship between ion transporter cascade, reactive astrogliosis, and cerebrovascular diseases may reveal mechanisms and targets for the development of therapies for brain diseases associated with reactive astrogliosis.

Iron deficiency in astrocytes alters cellular status and impacts on oligodendrocyte differentiation

Iron deficiency (ID) has been shown to affect central nervous system (CNS) development and induce hypomyelination. Previous work from our laboratory in a gestational ID model showed that both oligodendrocyte (OLG) and astrocyte (AST) maturation was impaired. To explore the contribution of AST iron to the myelination process, we generated an in vitro ID model by silencing divalent metal transporter 1 (DMT1) in AST (siDMT1 AST) or treating AST with Fe3+ chelator deferoxamine (DFX; DFX AST). siDMT1 AST showed no changes in proliferation but remained immature. Co-cultures of oligodendrocyte precursors cells (OPC) with siDMT1 AST and OPC cultures incubated with siDMT1 AST-conditioned media (ACM) rendered a reduction in OPC maturation. These findings correlated with a decrease in the expression of AST-secreted factors IGF-1, NRG-1, and LIF, known to promote OPC differentiation. siDMT1 AST also displayed increased mitochondrial number and reduced mitochondrial size as compared to control cells. DFX AST also remained immature and DFX AST-conditioned media also hampered OPC maturation in culture, in keeping with a decrease in the expression of AST-secreted growth factors IGF-1, NRG-1, LIF, and CNTF. DFX AST mitochondrial morphology and number showed results similar to those observed in siDMT1 AST. In sum, our results show that ID, induced through two different methods, impacts AST maturation and mitochondrial functioning, which in turn hampers OPC differentiation.

Norepinephrine-Activated p38 MAPK Pathway Mediates Stress-Induced Cytotoxic Edema of Basolateral Amygdala Astrocytes

The amygdala is a core region in the limbic system that is highly sensitive to stress. Astrocytes are key players in stress disorders such as anxiety and depression. However, the effects of stress on the morphology and function of amygdala astrocytes and its potential mechanisms remain largely unknown. Hence, we performed in vivo and in vitro experiments using a restraint stress (RS) rat model and stress-induced astrocyte culture, respectively. Our data show that norepinephrine (NE) content increased, cytotoxic edema occurred, and aquaporin-4 (AQP4) expression was up-regulated in the basolateral amygdala (BLA) obtained from RS rats. Additionally, the p38 mitogen-activated protein kinase (MAPK) pathway was also observed to be significantly activated in the BLA of rats subjected to RS. The administration of NE to in vitro astrocytes increased the AQP4 level and induced cell edema. Furthermore, p38 MAPK signaling was activated. The NE inhibitor alpha-methyl-p-tyrosine (AMPT) alleviated cytotoxic edema in astrocytes, inhibited AQP4 expression, and inactivated the p38 MAPK pathway in RS rats. Meanwhile, in the in vitro experiment, the p38 MAPK signaling inhibitor SB203580 reversed NE-induced cytotoxic edema and down-regulated the expression of AQP4 in astrocytes. Briefly, NE-induced activation of the p38 MAPK pathway mediated cytotoxic edema in BLA astrocytes from RS rats. Thus, our data provide novel evidence that NE-induced p38 MAPK pathway activation may be one of the mechanisms leading to cytotoxic edema in BLA under stress conditions, which also could enable the development of an effective therapeutic strategy against cytotoxic edema in BLA under stress and provide new ideas for the treatment of neuropsychiatric diseases.

Astrocyte signaling and interactions in Multiple Sclerosis

Multiple Sclerosis (MS) is a common cause of impairment in working-aged adults. MS is characterized by neuroinflammation and infiltration of peripheral immune cells to the brain, which cause myelin loss and death of oligodendrocytes and neurons. Many studies on MS have focused on the peripheral immune sources of demyelination and repair. However, recent studies revealed that a glial cell type, the astrocytes, undergo robust morphological and transcriptomic changes that contribute significantly to demyelination and myelin repair. Here, we discuss recent findings elucidating signaling modalities that astrocytes acquire or lose in MS and how these changes alter the interactions of astrocytes with other nervous system cell types.

The Vestibular Nuclei: A Cerebral Reservoir of Stem Cells Involved in Balance Function in Normal and Pathological Conditions

In this review, we explore the intriguing realm of neurogenesis in the vestibular nuclei-a critical brainstem region governing balance and spatial orientation. We retrace almost 20 years of research into vestibular neurogenesis, from its discovery in the feline model in 2007 to the recent discovery of a vestibular neural stem cell niche. We explore the reasons why neurogenesis is important in the vestibular nuclei and the triggers for activating the vestibular neurogenic niche. We develop the symbiotic relationship between neurogenesis and gliogenesis to promote vestibular compensation. Finally, we examine the potential impact of reactive neurogenesis on vestibular compensation, highlighting its role in restoring balance through various mechanisms.

Reactive Gliosis in Neonatal Disorders: Friend or Foe for Neuroregeneration?

A developing nervous system is particularly vulnerable to the influence of pathophysiological clues and injuries in the perinatal period. Astrocytes are among the first cells that react to insults against the nervous tissue, the presence of pathogens, misbalance of local tissue homeostasis, and a lack of oxygen and trophic support. Under this background, it remains uncertain if induced astrocyte activation, recognized as astrogliosis, is a friend or foe for progressing neonatal neurodevelopment. Likewise, the state of astrocyte reactivity is considered one of the key factors discriminating between either the initiation of endogenous reparative mechanisms compensating for aberrations in the structures and functions of nervous tissue or the triggering of neurodegeneration. The responses of activated cells are modulated by neighboring neural cells, which exhibit broad immunomodulatory and pro-regenerative properties by secreting a plethora of active compounds (including interleukins and chemokines, neurotrophins, reactive oxygen species, nitric oxide synthase and complement components), which are engaged in cell crosstalk in a paracrine manner. As the developing nervous system is extremely sensitive to the influence of signaling molecules, even subtle changes in the composition or concentration of the cellular secretome can have significant effects on the developing neonatal brain. Thus, modulating the activity of other types of cells and their interactions with overreactive astrocytes might be a promising strategy for controlling neonatal astrogliosis.

Inflammation, Autoimmunity and Neurodegenerative Diseases, Therapeutics and Beyond

Neurodegenerative disease (ND) incidence has recently increased due to improved life expectancy. Alzheimer's (AD) or Parkinson's disease (PD) are the most prevalent NDs. Both diseases are poly genetic, multifactorial and heterogenous. Preventive medicine, a healthy diet, exercise, and controlling comorbidities may delay the onset. After the diseases are diagnosed, therapy is needed to slow progression. Recent studies show that local, peripheral and age-related inflammation accelerates NDs' onset and progression. Patients with autoimmune disorders like inflammatory bowel disease (IBD) could be at higher risk of developing AD or PD. However, no increase in ND incidence has been reported if the patients are adequately diagnosed and treated. Autoantibodies against abnormal tau, β amyloid and α- synuclein have been encountered in AD and PD and may be protective. This discovery led to the proposal of immune-based therapies for AD and PD involving monoclonal antibodies, immunization/ vaccines, pro-inflammatory cytokine inhibition and anti-inflammatory cytokine addition. All the different approaches have been analysed here. Future perspectives on new therapeutic strategies for both disorders are concisely examined.

Inflammatory processes in the prefrontal cortex induced by systemic immune challenge: Focusing on neurons

Peripheral immune challenge induces neurobiological alterations in the brain and related neuropsychiatric symptoms both in humans and other mammals. One of the best known physiological effects of systemic inflammation is sickness behavior. However, in addition to this depression-like state, there are other cognitive outcomes of peripherally induced neuroinflammation that can be linked to the dysfunction of higher-order cortical areas, such as the prefrontal cortex (PFC). As the physiological activity of the PFC is largely based on the balanced interplay of excitatory pyramidal cells and inhibitory interneurons, it may be hypothesized that neuroinflammatory processes result in a shift of excitatory/inhibitory balance, which is a common hallmark of several neuropsychiatric conditions. Indeed, many data suggest that peripherally induced neuroinflammation is strongly associated with molecular and functional changes in PFC neurons leading to disturbances in their synaptic networks. Different experimental approaches may cause some incongruence in the reviewed data. However, it is commonly agreed that acute systemic inflammation leads to changes in the excitatory/inhibitory balance in the PFC by proinflammatory signaling at the brain borders and in the brain parenchyma. These cellular changes result in altered local and brain-wide network activity inducing disturbances in the top-down control of goal-directed behavior and cognition regulated by the PFC. Lipopolysaccharide (LPS)-treated rodents are the most widely used experimental models of peripherally induced neuroinflammation, so the majority of the reviewed data come from studies utilizing the LPS model. This may limit their general interpretation regarding the neuronal effects of peripheral immune activation. In addition, several biological variables (e.g., sex, age) can influence the PFC effects of systemic immune challenge, not only the nature and severity of immune activation. Therefore, it would be desirable to investigate inflammation-related neuronal changes in the PFC using other models of systemic inflammation as well, and to focus on the targeted fine-tuning of the affected cell types via common molecular mechanisms of the immune and nervous systems.

The role of glial autophagy in Alzheimer's disease

Although Alzheimer's disease is the most pervasive neurodegenerative disorder, the mechanism underlying its development is still not precisely understood. Available data indicate that pathophysiology of this disease may involve impaired autophagy in glial cells. The dysfunction is manifested as reduced ability of astrocytes and microglia to clear abnormal protein aggregates. Consequently, excessive accumulation of amyloid beta plaques and neurofibrillary tangles activates microglia and astrocytes leading to decreased number of mature myelinated oligodendrocytes and death of neurons. These pathologic effects of autophagy dysfunction can be rescued by pharmacological activation of autophagy. Therefore, a deeper understanding of the molecular mechanisms involved in autophagy dysfunction in glial cells in Alzheimer's disease may lead to the development of new therapeutic strategies. However, such strategies need to take into consideration differences in regulation of autophagy in different types of neuroglia.

Pro-myelinating clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over the chronic implantation period. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

TGN020 application against aquaporin 4 improved multiple sclerosis by inhibiting astrocytes, microglia, and NLRP3 inflammasome in a cuprizone mouse model

In multiple sclerosis (MS), activation of the astrocytes and microglia induces a cascading inflammatory response. Overexpression of the aquaporin 4 (AQP4) in the glia is a trigger for this reaction. This study aimed to block AQP4 by injecting TGN020 to alleviate the symptoms of MS. Total of 30 male mice were randomly divided into control (intact), cuprizone model of MS (fed with 0.2% cuprizone for 35 days), and TGN020-treated (received daily intraperitoneal injections of 200 mg/kg TGN020 with cuprizone intake) groups. Astrogliosis, M1-M2 microglia polarization, NLRP3 inflammasome activation, and demyelination were investigated in the corpus callosum by immunohistochemistry, real-time PCR, western blot, and luxol fast blue staining. The Rotarod test was performed for a behavior assessment. AQP4 inhibition caused a significant decrease in the expression of the astrocyte-specific marker, GFAP. It also changed the microglia polarization from M1 to M2 indicated by a significant downregulation of iNOS, CD86, MHC-ІІ, and upregulation of arginase1, CD206, and TREM-2. In addition, western blot data showed a significant decrease in the NLRP3, caspase1, and IL-1b proteins in the treatment group, which indicated inflammasome inactivation. The molecular changes following the TGN020 injection resulted in remyelination and motor recovery enhancement in the treatment group. In conclusion, the results draw the attention to the role of AQP4 in the cuprizone model of MS.

Elevated SIRT2 of serum exosomes is positively correlated with diagnosis of acute ischemic stroke patients

BACKGROUND

Silent Information Regulator 2 (SIRT2) protein inhibition has been shown to play a neuroprotective role in acute ischemic stroke (AIS) in mice. However, its role in AIS patients has not been fully understood. In this study, we aimed to analyze SIRT2 protein expression in serum exosomes of AIS and non-AIS patients, and evaluate its potential role in diagnosis and prognosis of AIS.

METHODS

Serum exosomes from 75 non-AIS subjects and 75 AIS patients were isolated. The SIRT2 protein levels in exosomes were analyzed using enzyme linked immunosorbent assay (ELISA). The National Institutes of Health Stroke Scale (NIHSS) was used to evaluate the severity of the disease. The modified Rankin Scale (mRS) was employed to assess the functional outcomes of the patients at 3-months following stroke onset.

RESULTS

The SIRT2 protein concentration of serum exosomes were higher in AIS patients than non-AIS patients (p < 0.001). Furthermore, the receiver operative characteristic curve (ROC) demonstrated that higher serum exosome SIRT2 could differentiate AIS patients from non-AIS patients with a sensitivity of 81.3% and a specificity of 75.3%. The area under the curve was 0.838 (95% CI: 0.775, 0.902). Additionally, higher SIRT2 concentration of serum exosomes were associated with NIHSS ≥ 4 (p < 0.001) and mRS ≥ 3 (p = 0.025) in AIS patients. The ROC analysis showed SIRT2 could discriminate stroke with NIHSS ≥ 4 from mild stroke (NIHSS < 4) with a sensitivity of 75.0% and a specificity of 69.6%. The area under the curve was 0.771 (95% CI: 0.661,0.881). Similarly, the test showed SIRT2 could differentiate between AIS patients with mRS ≥ 3 from those with mRS < 3 with a sensitivity of 78.3% and a specificity of 51.9%. The area under the curve was 0.663 (95% CI: 0.531,0.796). The logistic regression analysis revealed that SIRT2 concentration in serum exosomes can independently predict the diagnosis of AIS (odd ratio = 1.394, 95%CI 1.231-1.577, p < 0.001) and higher NIHSS scores (≥ 4) (odd ratio = 1.258, 95%CI 1.084-1.460, p = 0.002). However, it could not independently predict the prognosis of AIS (odd ratio = 1.065, 95%CI 0.983-1.154, p = 0.125).

CONCLUSION

The elevation of SIRT2 in serum exosomes may be a valuable biomarker of AIS, which may be a potential diagnostic tool to facilitate decision making for AIS patients.

The role and potential therapeutic targets of astrocytes in central nervous system demyelinating diseases

Astrocytes play vital roles in the central nervous system, contributing significantly to both its normal functioning and pathological conditions. While their involvement in various diseases is increasingly recognized, their exact role in demyelinating lesions remains uncertain. Astrocytes have the potential to influence demyelination positively or negatively. They can produce and release inflammatory molecules that modulate the activation and movement of other immune cells. Moreover, they can aid in the clearance of myelin debris through phagocytosis and facilitate the recruitment and differentiation of oligodendrocyte precursor cells, thereby promoting axonal remyelination. However, excessive or prolonged astrocyte phagocytosis can exacerbate demyelination and lead to neurological impairments. This review provides an overview of the involvement of astrocytes in various demyelinating diseases, emphasizing the underlying mechanisms that contribute to demyelination. Additionally, we discuss the interactions between oligodendrocytes, oligodendrocyte precursor cells and astrocytes as therapeutic options to support myelin regeneration. Furthermore, we explore the role of astrocytes in repairing synaptic dysfunction, which is also a crucial pathological process in these disorders.

Current advances in stem cell therapy in the treatment of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory disease related to the central nervous system (CNS) with a significant global burden. In this illness, the immune system plays an essential role in its pathophysiology and progression. The currently available treatments are not recognized as curable options and, at best, might slow the progression of MS injuries to the CNS. However, stem cell treatment has provided a new avenue for treating MS. Stem cells may enhance CNS healing and regulate immunological responses. Likewise, stem cells can come from various sources, including adipose, neuronal, bone marrow, and embryonic tissues. Choosing the optimal cell source for stem cell therapy is still a difficult verdict. A type of stem cell known as mesenchymal stem cells (MSCs) is obtainable from different sources and has a strong immunomodulatory impact on the immune system. According to mounting data, the umbilical cord and adipose tissue may serve as appropriate sources for the isolation of MSCs. Human amniotic epithelial cells (hAECs), as novel stem cell sources with immune-regulatory effects, regenerative properties, and decreased antigenicity, can also be thought of as a new upcoming contender for MS treatment. Overall, the administration of stem cells in different sets of animal and clinical trials has shown immunomodulatory and neuroprotective results. Therefore, this review aims to discuss the different types of stem cells by focusing on MSCs and their mechanisms, which can be used to treat and improve the outcomes of MS disease.

Manganese-induced apoptosis through the ROS-activated JNK/FOXO3a signaling pathway in CTX cells, a model of rat astrocytes

Manganese (Mn) is an essential trace element that maintains many normal physiological functions. However, multi-system disorders would occur once overexposure to Mn, especially neurotoxicity. Despite evidence demonstrating the critical role of ROS-activated JNK/FOXO3a signaling pathway in neuronal survival, the specific mechanisms by which it contributes to Mn-induced neurotoxicity are still unclear. The objectives of this study was to examine the modulation of the JNK/FOXO3a signaling pathway, which is activated by ROS, in Mn-induced apoptosis, using a rat brain astrocyte cell line (CTX cells). This study found that a dose-dependent decrease in cell viability of CTX cells was observed with 150, 200, 250, 300 μmol/L Mn. The results of apoptosis-related protein assay showed that Mn decreased the expression of anti-apoptotic protein Bcl-2 and enhanced the expression of apoptosis-related proteins like Bax and Cleaved-Caspase3. In addition, treatment with Mn resulted in elevated ROS levels and increased phosphorylation levels of JNK. Conversely, phosphorylation of nuclear transcription factors FOXO3a, which regulates expression of transcription factors including Bim and PUMA, was decreased. Depletion of ROS by N-acetyl-L-cysteine (NAC) and inhibition of the JNK pathway by SP600125 prevented Mn-induced JNK/FOXO3a pathway activation and, more importantly, the level of apoptosis was also significantly reduced. Confirmation of Mn-induced apoptosis in CTX cells through ROS generation and activation of the JNK/FOXO3a signaling pathway was the outcome of this study. These findings offer fresh insights into the neurotoxic mechanisms of Mn and therapeutic targets following Mn exposure.

Vitamin B complex suppresses neuroinflammation in activated microglia: in vitro and in silico approach combined with dynamical modeling

Activated microglia is critically involved in the regulation of neuroinflammation/neurodegradation. Hereby, the anti-inflammatory effects of the vitamin B complex (VBC - B₁, B₂, B₃, B₅, B₆, and B₁₂) on the function and phenotype of lipopolysaccharide (LPS)-stimulated BV2 microglial cells were examined in vitro. Additionally, VBC-treated microglia supernatants were evaluated on SH-SY5Y cells to investigate the effects on neurons' viability. Further, anti-inflammatory mechanisms of VBC were examined by molecular dockingstudies to determine the binding affinity of each VBC component to Toll-like receptor 4 (TLR4) signalling pathway proteins and inducible nitric oxide synthase. In addition, the dynamical model which simulates VBC inhibition of TLR4 signalling pathway proteins activated by LPS has been constructed and excellent agreement with experimental data has been observed (adjR² = 0.9715 and 0.9909 for TNF-α and IL-6, respectively). The obtained data demonstrated that VBC treatment reduced the inflammatory mediators secreted by LPS-stimulated microglia, diminished their neurotoxic effects against neurons, and induced changes in phenotype profile toward M2 microglia type. Finally, the constructed dynamical model provides deeper insight into the involvement of each VBC component on the VBC inhibitory potential toward the TLR4 signalling pathway and enables optimization of novel VBC formulations as well as inhibitory potential of new putative inhibitors.

lThyroid hormone transporter Mct8/Oatp1c1 deficiency compromises proper oligodendrocyte maturation in the mouse CNS

Proper CNS myelination depends on the timed availability of thyroid hormone (TH) that induces differentiation of oligodendrocyte precursor cells (OPCs) to mature, myelinating oligodendrocytes. Abnormal myelination is frequently observed in Allan-Herndon-Dudley syndrome caused by inactivating mutations in the TH transporter MCT8. Likewise, persistent hypomyelination is a key CNS feature of the Mct8/Oatp1c1 double knockout (Dko) mouse model, a well-established mouse model for human MCT8 deficiency that exhibits diminished TH transport across brain barriers and thus a TH deficient CNS. Here, we explored whether decreased myelin content is caused by an impairment in oligodendrocyte maturation. To that end, we studied OPC and oligodendrocyte populations in Dko mice versus wild-type and single TH transporter knockout animals at different developmental time points (at postnatal days P12, P30, and P120) using multi-marker immunostaining and confocal microscopy. Only in Dko mice we observed a reduction in cells expressing the oligodendroglia marker Olig2, encompassing all stages between OPCs and mature oligodendrocytes. Moreover, Dko mice exhibited at all analysed time points an increased portion of OPCs and a reduced number of mature oligodendrocytes both in white and grey matter regions indicating a differentiation blockage in the absence of Mct8/Oatp1c1. We also assessed cortical oligodendrocyte structural parameters by visualizing and counting the number of mature myelin sheaths formed per oligodendrocyte. Again, only Dko mice displayed a reduced number of myelin sheaths that in turn exhibited an increase in length indicating a compensatory response to the reduced number of mature oligodendrocyte. Altogether, our studies underscore an oligodendrocyte differentiation impairment and altered oligodendrocyte structural parameters in the global absence of Mct8 and Oatp1c1. Both mechanisms most likely do not only cause the abnormal myelination state but also contribute to compromised neuronal functionality in Mct8/Oatp1c1 deficient animals.

Glial Cell Metabolic Profile Upon Iron Deficiency: Oligodendroglial and Astroglial Casualties of Bioenergetic Adjustments

Iron deficiency (ID) represents one of the most prevalent nutritional deficits, affecting almost two billion people worldwide. Gestational iron deprivation induces hypomyelination due to oligodendroglial maturation deficiencies and is thus a useful experimental model to analyze oligodendrocyte (OLG) requirements to progress to a mature myelinating state. A previous proteomic study in the adult ID brain by our group demonstrated a pattern of dysregulated proteins involved in the tricarboxylic acid cycle and mitochondrial dysfunction. The aim of the present report was to assess bioenergetics metabolism in primary cultures of OLGs and astrocytes (ASTs) from control and ID newborns, on the hypothesis that the regulation of cell metabolism correlates with cell maturation. Oxygen consumption and extracellular acidification rates were measured using a Seahorse extracellular flux analyzer. ID OLGs and ASTs both exhibited decreased spare respiratory capacity, which indicates that ID effectively induces mitochondrial dysfunction. A decrease in glycogen granules was observed in ID ASTs, and an increase in ROS production was detected in ID OLGs. Immunolabeling of structural proteins showed that mitochondrial number and size were increased in ID OLGs, while an increased number of smaller mitochondria was observed in ID ASTs. These results reflect an unfavorable bioenergetic scenario in which ID OLGs fail to progress to a myelinating state, and indicate that the regulation of cell metabolism may impact cell fate decisions and maturation.

Neuronal Prosurvival Role of Ceramide Synthase 2 by Olidogendrocyte-to-Neuron Extracellular Vesicle Transfer

Ageing is associated with notorious alterations in neurons, i.e., in gene expression, mitochondrial function, membrane degradation or intercellular communication. However, neurons live for the entire lifespan of the individual. One of the reasons why neurons remain functional in elderly people is survival mechanisms prevail over death mechanisms. While many signals are either pro-survival or pro-death, others can play both roles. Extracellular vesicles (EVs) can signal both pro-toxicity and survival. We used young and old animals, primary neuronal and oligodendrocyte cultures and neuroblastoma and oligodendrocytic lines. We analysed our samples using a combination of proteomics and artificial neural networks, biochemistry and immunofluorescence approaches. We found an age-dependent increase in ceramide synthase 2 (CerS2) in cortical EVs, expressed by oligodendrocytes. In addition, we show that CerS2 is present in neurons via the uptake of oligodendrocyte-derived EVs. Finally, we show that age-associated inflammation and metabolic stress favour CerS2 expression and that oligodendrocyte-derived EVs loaded with CerS2 lead to the expression of the antiapoptotic factor Bcl2 in inflammatory conditions. Our study shows that intercellular communication is altered in the ageing brain, which favours neuronal survival through the transfer of oligodendrocyte-derived EVs containing CerS2.

Fundamental Neurochemistry Review: Incorporating a greater diversity of cell types, including microglia, in brain organoid cultures improves clinical translation

Brain organoids have the potential to improve clinical translation, with the added benefit of reducing any extraneous use of experimental animals. As brain organoids are three-dimensional in vitro constructs that emulate the human brain, they bridge in vitro and in vivo studies more appropriately than monocultures. Although many factors contribute to the failure of extrapolating monoculture-based information to animal-based experiments and clinical trials, for the purpose of this review, we will focus on glia (non-neuronal brain cells), whose functions and transcriptome are particularly abnormal in monocultures. As discussed herein, glia require signals from-and contact with-other cell types to exist in their homeostatic state, which likely contributes to some of the differences between data derived from monocultures and data derived from brain organoids and even two-dimensional co-cultures. Furthermore, we highlight transcriptomic differences between humans and mice in regard to aging and Alzheimer's disease, emphasizing need for a model using the human genome-again, a benefit of brain organoids-to complement data derived from animals. We also identify an urgency for guidelines to improve the reporting and transparency of research using organoids. The lack of reporting standards creates challenges for the comparison and discussion of data from different articles. Importantly, brain organoids mark the first human model enabling the study of brain cytoarchitecture and development.

The Memory Orchestra: Contribution of Astrocytes

For decades, memory research has centered on the role of neurons, which do not function in isolation. However, astrocytes play important roles in regulating neuronal recruitment and function at the local and network levels, forming the basis for information processing as well as memory formation and storage. In this review, we discuss the role of astrocytes in memory functions and their cellular underpinnings at multiple time points. We summarize important breakthroughs and controversies in the field as well as potential avenues to further illuminate the role of astrocytes in memory processes.

Pro-myelinating Clemastine administration improves recording performance of chronically implanted microelectrodes and nearby neuronal health

Intracortical microelectrodes have become a useful tool in neuroprosthetic applications in the clinic and to understand neurological disorders in basic neurosciences. Many of these brain-machine interface technology applications require successful long-term implantation with high stability and sensitivity. However, the intrinsic tissue reaction caused by implantation remains a major failure mechanism causing loss of recorded signal quality over time. Oligodendrocytes remain an underappreciated intervention target to improve chronic recording performance. These cells can accelerate action potential propagation and provides direct metabolic support for neuronal health and functionality. However, implantation injury causes oligodendrocyte degeneration and leads to progressive demyelination in surrounding brain tissue. Previous work highlighted that healthy oligodendrocytes are necessary for greater electrophysiological recording performance and the prevention of neuronal silencing around implanted microelectrodes over chronic implantation. Thus, we hypothesize that enhancing oligodendrocyte activity with a pharmaceutical drug, Clemastine, will prevent the chronic decline of microelectrode recording performance. Electrophysiological evaluation showed that the promyelination Clemastine treatment significantly elevated the signal detectability and quality, rescued the loss of multi-unit activity, and increased functional interlaminar connectivity over 16-weeks of implantation. Additionally, post-mortem immunohistochemistry showed that increased oligodendrocyte density and myelination coincided with increased survival of both excitatory and inhibitory neurons near the implant. Overall, we showed a positive relationship between enhanced oligodendrocyte activity and neuronal health and functionality near the chronically implanted microelectrode. This study shows that therapeutic strategy that enhance oligodendrocyte activity is effective for integrating the functional device interface with brain tissue over chronic implantation period.

Abstract Figure

Astrocyte endfoot formation controls the termination of oligodendrocyte precursor cell perivascular migration during development

Oligodendrocyte precursor cells (OPCs) undergo an extensive and coordinated migration in the developing CNS, using the pre-formed scaffold of developed blood vessels as their physical substrate for migration. While OPC association with vasculature is critical for dispersal, equally important for permitting differentiation and proper myelination of target axons is their appropriate and timely detachment, but regulation of this process remains unclear. Here we demonstrate a correlation between the developmental formation of astrocytic endfeet on vessels and the termination of OPC perivascular migration. Ex vivo and in vivo live imaging shows that astrocyte endfeet physically displace OPCs from vasculature, and genetic abrogation of endfoot formation hinders both OPC detachment from vessels and subsequent differentiation. Astrocyte-derived semaphorins 3a and 6a act to repel OPCs from blood vessels at the cessation of their perivascular migration and, in so doing, permit subsequent OPC differentiation by insulating them from a maturation inhibitory endothelial niche.

Role of stress-related glucocorticoid changes in astrocyte-oligodendrocyte interactions that regulate myelin production and maintenance

Repeated activation of stress responses and elevated corticosteroids result in alterations of neuronal physiology and metabolism, and lead to disturbances of normal connectivity between neurons in various brain regions. In addition, stress responses are also associated with anomalies in the function of glial cells, particularly astrocytes and oligodendrocytes, which in turn may further contribute to the mechanisms of neuronal dysfunction. The actions of corticosteroids on astrocytes are very likely mediated by the presence of intracellular and cell membrane-bound CORT receptors. Although apparently less abundant than in astrocytes, activation of CORT receptors in oligodendrocytes also leads to structural changes that are reflected in myelin maintenance and plasticity. The close interactions between astrocytes and oligodendrocytes through extracellular matrix molecules, soluble factors and astrocyte-oligodendrocyte gap junctions very likely mediate part of the disturbances in myelin structure, leading to plastic myelin adaptations or pathological myelin disruptions that may significantly influence brain connectivity. Likewise, the intimate association of the tips of some astrocytes processes with a majority of nodes of Ranvier in the white matter suggest that stress and overexposure to corticosteroids may lead to remodeling of node of Ranvier and their specific extracellular milieu.

Nanomedicine-based immunotherapy for Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease caused by the deposition of amyloid β (Aβ) fibrils forming extracellular plaques and the development of neurofibrillary tangles (NFT) of intracellular hyperphosphorylated tau protein. Currently, the AD treatments focus on improving cognitive and behavioral symptoms and have limited success. It is imperative to develop novel treatment approaches that can control/inhibit AD progression, especially in the elderly population. Immunotherapy provides a promising and safe treatment option for AD by boosting the patient's immune system. The minimum immune surveillance in the immune-privileged brain, however, makes immunotherapy for AD a challenging endeavor. Therefore, the success of AD immunotherapy depends mainly on the strategy by which therapeutics is delivered to the brain rather than its efficacy. The blood-brain barrier (BBB) is a major obstacle to therapeutic delivery into the brain microenvironment. Various nano-formulations have been exploited to improve the efficacy of AD immunotherapy. In this review, the applications of different types of nano-formulations in augmenting AD immunotherapy have been discussed.

Implications of fractalkine on glial function, ablation and glial proteins/receptors/markers—understanding its therapeutic usefulness in neurological settings: a narrative review

Background

Fractalkine (CX3CL1) is a chemokine predominantly released by neurons. As a signaling molecule, CX3CL1 facilitates talk between neurons and glia. CX3CL1 is considered as a potential target which could alleviate neuroinflammation. However, certain controversial results and ambiguous role of CX3CL1 make it inexorable to decipher the overall effects of CX3CL1 on the physiopathology of glial cells.

Main body of the abstract

Implications of cross-talk between CX3CL1 and different glial proteins/receptors/markers will give a bird eye view of the therapeutic significance of CX3CL1. Keeping with the need, this review identifies the effects of CX3CL1 on glial physiopathology, glial ablation, and gives a wide coverage on the effects of CX3CL1 on certain glial proteins/receptors/markers.

Short conclusion

Pinpoint prediction of the therapeutic effect of CX3CL1 on neuroinflammation needs further research. This is owing to certain obscure roles and implications of CX3CL1 on different glial proteins/receptors/markers, which are crucial under neurological settings. Further challenges are imposed due to the dichotomous roles played by CX3CL1. The age-old chemokine shows many newer scopes of research in near future. Thus, overall assessment of the effect of CX3CL1 becomes crucial prior to its administration in neuroinflammation.

Advantages of Rho-associated kinases and their inhibitor fasudil for the treatment of neurodegenerative diseases

Ras homolog (Rho)-associated kinases (ROCKs) belong to the serine-threonine kinase family, which plays a pivotal role in regulating the damage, survival, axon guidance, and regeneration of neurons. ROCKs are also involved in the biological effects of immune cells and glial cells, as well as the development of neurodegenerative disorders such as Alzheimer's disease, Parkinson's disease, and multiple sclerosis. Previous studies by us and others confirmed that ROCKs inhibitors attenuated the symptoms and progression of experimental models of the abovementioned neurodegenerative diseases by inhibiting neuroinflammation, regulating immune imbalance, repairing the blood-brain barrier, and promoting nerve repair and myelin regeneration. Fasudil, the first ROCKs inhibitor to be used clinically, has a good therapeutic effect on neurodegenerative diseases. Fasudil increases the activity of neural stem cells and mesenchymal stem cells, thus optimizing cell therapy. This review will systematically describe, for the first time, the effects of abnormal activation of ROCKs on T cells, B cells, microglia, astrocytes, oligodendrocytes, and pericytes in neurodegenerative diseases of the central nervous system, summarize the therapeutic potential of fasudil in several experimental models of neurodegenerative diseases, and clarify the possible cellular and molecular mechanisms of ROCKs inhibition. This review also proposes that fasudil is a novel potential treatment, especially in combination with cell-based therapy. Findings from this review add support for further investigation of ROCKs and its inhibitor fasudil for the treatment of neurodegenerative diseases.

Interactions Between Astrocytes and Oligodendroglia in Myelin Development and Related Brain Diseases

Astrocytes (ASTs) and oligodendroglial lineage cells (OLGs) are major macroglial cells in the central nervous system. ASTs communicate with each other through connexin (Cx) and Cx-based network structures, both of which allow for quick transport of nutrients and signals. Moreover, ASTs interact with OLGs through connexin (Cx)-mediated networks to modulate various physiological processes in the brain. In this article, following a brief description of the infrastructural basis of the glial networks and exocrine factors by which ASTs and OLGs may crosstalk, we focus on recapitulating how the interactions between these two types of glial cells modulate myelination, and how the AST-OLG interactions are involved in protecting the integrity of the blood-brain barrier (BBB) and regulating synaptogenesis and neural activity. Recent studies further suggest that AST-OLG interactions are associated with myelin-related diseases, such as multiple sclerosis. A better understanding of the regulatory mechanisms underlying AST-OLG interactions may inspire the development of novel therapeutic strategies for related brain diseases.

Dysfunction of the neurovascular unit in brain aging

An emerging concept termed the neurovascular unit (NVU) underlines neurovascular coupling. It has been reported that NVU impairment can result in neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Aging is a complex and irreversible process caused by programmed and damage-related factors. Loss of biological functions and increased susceptibility to additional neurodegenerative diseases are major characteristics of aging. In this review, we describe the basics of the NVU and discuss the effect of aging on NVU basics. Furthermore, we summarize the mechanisms that increase NVU susceptibility to neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease. Finally, we discuss new treatments for neurodegenerative diseases and methods of maintaining an intact NVU that may delay or diminish aging.

CCPLS reveals cell-type-specific spatial dependence of transcriptomes in single cells

MOTIVATION

Cell-cell communications regulate internal cellular states, e.g. gene expression and cell functions, and play pivotal roles in normal development and disease states. Furthermore, single-cell RNA sequencing methods have revealed cell-to-cell expression variability of highly variable genes (HVGs), which is also crucial. Nevertheless, the regulation of cell-to-cell expression variability of HVGs via cell-cell communications is still largely unexplored. The recent advent of spatial transcriptome methods has linked gene expression profiles to the spatial context of single cells, which has provided opportunities to reveal those regulations. The existing computational methods extract genes with expression levels influenced by neighboring cell types. However, limitations remain in the quantitativeness and interpretability: they neither focus on HVGs nor consider the effects of multiple neighboring cell types.

RESULTS

Here, we propose CCPLS (Cell-Cell communications analysis by Partial Least Square regression modeling), which is a statistical framework for identifying cell-cell communications as the effects of multiple neighboring cell types on cell-to-cell expression variability of HVGs, based on the spatial transcriptome data. For each cell type, CCPLS performs PLS regression modeling and reports coefficients as the quantitative index of the cell-cell communications. Evaluation using simulated data showed our method accurately estimated the effects of multiple neighboring cell types on HVGs. Furthermore, applications to the two real datasets demonstrate that CCPLS can extract biologically interpretable insights from the inferred cell-cell communications.

AVAILABILITY AND IMPLEMENTATION

The R package is available at https://github.com/bioinfo-tsukuba/CCPLS. The data are available at https://github.com/bioinfo-tsukuba/CCPLS_paper.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

An Integrative Analysis of Identified Schizophrenia-Associated Brain Cell Types and Gene Expression Changes

Schizophrenia (SCZ) is a severe mental disorder that may result in hallucinations, delusions, and extremely disordered thinking. How each cell type in the brain contributes to SCZ occurrence is still unclear. Here, we leveraged the human dorsolateral prefrontal cortex bulk RNA-seq data, then used the RNA-seq deconvolution algorithm CIBERSORTx to generate SCZ brain single-cell RNA-seq data for a comprehensive analysis to understand SCZ-associated brain cell types and gene expression changes. Firstly, we observed that the proportions of brain cell types in SCZ differed from normal samples. Among these cell types, astrocyte, pericyte, and PAX6 cells were found to have a higher proportion in SCZ patients (astrocyte: SCZ = 0.163, control = 0.145, P.adj = 4.9 × 10^-4, effect size = 0.478; pericyte: SCZ = 0.057, control = 0.066, P.adj = 1.1 × 10^-4, effect size = 0.519; PAX6: SCZ = 0.014, control = 0.011, P.adj = 0.014, effect size = 0.377), while the L5/6_IT_CAR3 cells and LAMP5 cells are the exact opposite (L5/6_IT_Car3: SCZ = 0.102, control = 0.108, P.adj = 0.016, effect size = 0.369; LAMP5: SCZ = 0.057, control = 0.066, P.adj = 2.2 × 10^-6, effect size = 0.617). Next, we investigated gene expression in cell types and functional pathways in SCZ. We observed chemical synaptic transmission dysregulation in two types of GABAergic neurons (PVALB and LAMP5), and immune reaction involvement in GABAergic neurons (SST) and non-neuronal cell types (endothelial and oligodendrocyte). Furthermore, we observed that some differential expression genes from bulk RNA-seq displayed cell-type-specific abnormalities in the expression of molecules in SCZ. Finally, the cell types with the SCZ-related transcriptomic changes could be considered to belong to the same module since we observed two major similar coordinated transcriptomic changes across these cell types. Together, our results offer novel insights into cellular heterogeneity and the molecular mechanisms underlying SCZ.

Palmitoylethanolamide and White Matter Lesions: Evidence for Therapeutic Implications

Palmitoylethanolamide (PEA), the naturally occurring amide of ethanolamine and palmitic acid, is an endogenous lipid compound endowed with a plethora of pharmacological functions, including analgesic, neuroprotective, immune-modulating, and anti-inflammatory effects. Although the properties of PEA were first characterized nearly 65 years ago, the identity of the receptor mediating these actions has long remained elusive, causing a period of research stasis. In the last two decades, a renewal of interest in PEA occurred, and a series of interesting studies have demonstrated the pharmacological properties of PEA and clarified its mechanisms of action. Recent findings showed the ability of formulations containing PEA in promoting oligodendrocyte differentiation, which represents the first step for the proper formation of myelin. This evidence opens new and promising research opportunities. White matter defects have been detected in a vast and heterogeneous group of diseases, including age-related neurodegenerative disorders. Here, we summarize the history and pharmacology of PEA and discuss its therapeutic potential in restoring white matter defects.

Impact of chronic exposure to legacy environmental contaminants on the corpus callosum microstructure: A diffusion MRI study of Inuit adolescents

Exposure to environmental contaminants is an important public health concern for the Inuit population of northern Québec, who have been exposed to mercury (Hg), polychlorinated biphenyls (PCBs) and lead (Pb). During the last 25 years, the Nunavik Child Development Study (NCDS) birth cohort has reported adverse associations between these exposures and brain function outcomes. In the current study, we aimed to determine whether contaminant exposure is associated with alterations of the corpus callosum (CC), which plays an important role in various cognitive, motor and sensory function processes. Magnetic resonance imaging (MRI) was administered to 89 NCDS participants (mean age ± SD = 18.4 ± 1.2). Diffusion-weighted imaging was assessed to characterize the microstructure of the CC white matter in 7 structurally and functionally distinct regions of interest (ROIs) using a tractography-based segmentation approach. The following metrics were computed: fiber tract density, fractional anisotropy (FA), axial diffusivity (AD) and radial diffusivity (RD). Multiple linear regression models adjusted for sex, age, current alcohol/drug use and fish nutrients (omega-3 fatty acids and selenium) were conducted to assess the association between diffusion-weighted imaging metrics and Hg, PCB 153 and Pb concentrations obtained at birth in the cord blood and postnatally (mean values from blood samples at 11 and 18 years of age). Exposures were not associated with fiber tract density. Nor were significant associations found with cord and postnatal blood Pb concentrations for FA. However, pre- and postnatal Hg and PCB concentrations were significantly associated with higher FA of several regions of the CC, namely anterior midbody, posterior midbody, isthmus, and splenium, with the most pronounced effects observed in the splenium. FA results were mainly associated with lower RD. This study shows that exposure to Hg and PCB 153 alters the posterior microstructure of the CC, providing neuroimaging evidence of how developmental exposure to environmental chemicals can impair brain function and behavior in late adolescence.

A perspective on astrocyte regulation of neural circuit function and animal behavior

Studies over the past two decades have demonstrated that astrocytes are tightly associated with neurons and play pivotal roles in neural circuit development, operation, and adaptation in health and disease. Nevertheless, precisely how astrocytes integrate diverse neuronal signals, modulate neural circuit structure and function at multiple temporal and spatial scales, and influence animal behavior or disease through aberrant excitation and molecular output remains unclear. This Perspective discusses how new and state-of-the-art approaches, including fluorescence indicators, opto- and chemogenetic actuators, genetic targeting tools, quantitative behavioral assays, and computational methods, might help resolve these longstanding questions. It also addresses complicating factors in interpreting astrocytes' role in neural circuit regulation and animal behavior, such as their heterogeneity, metabolism, and inter-glial communication. Research on these questions should provide a deeper mechanistic understanding of astrocyte-neuron assemblies' role in neural circuit function, complex behaviors, and disease.

Crosstalk of Astrocytes and Other Cells during Ischemic Stroke

Stroke is a leading cause of death and long-term disability worldwide. Astrocytes structurally compose tripartite synapses, blood–brain barrier, and the neurovascular unit and perform multiple functions through cell-to-cell signaling of neurons, glial cells, and vasculature. The crosstalk of astrocytes and other cells is complicated and incompletely understood. Here we review the role of astrocytes in response to ischemic stroke, both beneficial and detrimental, from a cell–cell interaction perspective. Reactive astrocytes provide neuroprotection through antioxidation and antiexcitatory effects and metabolic support; they also contribute to neurorestoration involving neurogenesis, synaptogenesis, angiogenesis, and oligodendrogenesis by crosstalk with stem cells and cell lineage. In the meantime, reactive astrocytes also play a vital role in neuroinflammation and brain edema. Glial scar formation in the chronic phase hinders functional recovery. We further discuss astrocyte enriched microRNAs and exosomes in the regulation of ischemic stroke. In addition, the latest notion of reactive astrocyte subsets and astrocytic activity revealed by optogenetics is mentioned. This review discusses the current understanding of the intimate molecular conversation between astrocytes and other cells and outlines its potential implications after ischemic stroke. “Neurocentric” strategies may not be sufficient for neurological protection and recovery; future therapeutic strategies could target reactive astrocytes.

Co-Ultramicronized Palmitoylethanolamide/Luteolin Restores Oligodendrocyte Homeostasis via Peroxisome Proliferator-Activated Receptor-α in an In Vitro Model of Alzheimer's Disease

Oligodendrocytes are cells fundamental for brain functions as they form the myelin sheath and feed axons. They perform these critical functions thanks to the cooperation with other glial cells, mainly astrocytes. The astrocyte/oligodendrocyte crosstalk needs numerous mediators and receptors, such as peroxisome proliferator-activated receptors (PPARs). PPAR agonists promote oligodendrocyte precursor cells (OPCs) maturation in myelinating oligodendrocytes. In the Alzheimer's disease brain, deposition of beta-amyloid (Aβ) has been linked to several alterations, including astrogliosis and changes in OPCs maturation. However, very little is known about the molecular mechanisms. Here, we investigated for the first time the maturation of OPCs co-cultured with astrocytes in an in vitro model of Aβ1-42 toxicity. We also tested the potential beneficial effect of the anti-inflammatory and neuroprotective composite palmitoylethanolamide and luteolin (co-ultra PEALut), which is known to engage the isoform alfa of the PPARs. Our results show that Aβ1-42 triggers astrocyte reactivity and inflammation and reduces the levels of growth factors important for OPCs maturation. Oligodendrocytes indeed show low cell surface area and few arborizations. Co-ultra PEALut counteracts the Aβ1-42-induced inflammation and astrocyte reactivity preserving the morphology of co-cultured oligodendrocytes through a mechanism that in some cases involves PPAR-α. This is the first evidence of the negative effects exerted by Aβ1-42 on astrocyte/oligodendrocyte crosstalk and discloses a never-explored co-ultra PEALut ability in restoring oligodendrocyte homeostasis.

Astrocytes promote the proliferation of oligodendrocyte precursor cells through connexin 47-mediated LAMB2 secretion in exosomes

BACKGROUND

Oligodendrocyte precursor cells (OPCs) can proliferate and differentiate into oligodendrocytes, the only myelin-forming cells in the central nervous system. Proliferating OPCs promotes remyelination in neurodegenerative diseases. Astrocytes (ASTs) are the most widespread cells in the brain and play a beneficial role in the proliferation of OPCs. Connexin 47 (Cx47) is the main component of AST-OPC gap junctions to regulate OPC proliferation. Nonetheless, the specific mechanism remains unclear.

METHODS AND RESULTS

This study investigates the proliferation mechanism of OPCs connected to ASTs via Cx47. Cx47 siRNA significantly inhibited OPCs from entering the proliferation cycle. Transcriptome sequencing of OPCs and gene ontology enrichment analysis revealed that ASTs enhanced the exosome secretion by OPCs via Cx47. Transmission electron microscopy, Western blot, and nanoparticle tracking analysis indicated that the OPC proliferation was related to extracellular exosomes. Cx47 siRNA decreased the OPC proliferation and exosome secretion in AST-OPC cocultures. Exogenous exosome supplementation alleviated the inhibitory effect of Cx47 siRNA and significantly improved OPC proliferation. Mass spectrometry revealed that LAMB2 was abundant in exosomes. The administration of exogenous LAMB2 induced DNA replication in the S phase in OPCs by activating cyclin D1.

CONCLUSIONS

Collectively, ASTs induce the secretion of exosomes that carry LAMB2 by OPCs via Cx47 to upregulate cyclin D1 thereby accelerating OPC proliferation.