Astrocytic dysfunction: Insights on the role in neurodegeneration

The role of miRNAs in multiple sclerosis pathogenesis, diagnosis, and therapeutic resistance

In recent years, microRNAs (miRNAs) have gained increased attention from researchers around the globe. Although it is twenty nucleotides long, it can modulate several gene targets simultaneously. Their mal expression is a signature of various pathologies, and they provide the foundation to elucidate the molecular mechanisms of each pathology. Among the debilitating central nervous system (CNS) disorders with a growing prevalence globally is the multiple sclerosis (MS). Moreover, the diagnosis of MS is challenging due to the lack of disease-specific biomarkers, and the diagnosis mainly depends on ruling out other disabilities. MS could adversely affect patients' lives through its progression, and only symptomatic treatments are available as therapeutic options, but an exact cure is yet unavailable. Consequently, this review hopes to further the study of the biological features of miRNAs in MS and explore their potential as a therapeutic target.

Electroacupuncture exerts prolonged analgesic and neuroprotective effects in a persistent dental pain model induced by multiple dental pulp injuries: GABAergic interneurons-astrocytes interaction

Pain within the trigeminal system, particularly dental pain, is poorly understood. This study aimed to determine whether single or multiple dental pulp injuries induce persistent pain, its association with trigeminal central nociceptive pathways and whether electroacupuncture (EA) provides prolonged analgesic and neuroprotective effects in a persistent dental pain model. Models of single dental pulp injury (SDPI) and multiple dental pulp injuries (MDPI) were used to induce trigeminal neuropathic pain. The signs of dental pain-related behavior were assessed using the mechanical head withdrawal threshold (HWT). Immunofluorescence and western blot protocols were used to monitor astrocyte activation, changes in apoptosis-related proteins, and GABAergic interneuron plasticity. SDPI mice exhibited an initial marked decrease in HWT from days one to 14, followed by progressive recovery from days 21 to 42. From days 49 to 70, the HWT increased and returned to the control values. In contrast, MDPI mice showed a persistent decrease in HWT from days one to 70. MDPI increased glial fibrillary acidic protein (GFAP) and decreased glutamine synthetase (GS) and glutamate transporter-1 (GLT1) expression in the Vi/Vc transition zone of the brainstem on day 70, whereas no changes in astrocytic markers were observed on day 70 after SDPI. Increased expression of cleaved cysteine-aspartic protease-3 (cleaved caspase-3) and Bcl-2-associated X protein (Bax), along with decreased B-cell lymphoma/leukemia 2 (Bcl-2), were observed at day 70 after MDPI but not after SDPI. The downregulation of glutamic acid decarboxylase (GAD65) expression was observed on day 70 only after MDPI. The effects of MDPI-induced lower HWT from days one to 70 were attenuated by 12 sessions of EA treatment (days one to 21 after MDPI). Changes in astrocytic GFAP, GS, and GLT-1, along with cleaved caspase-3, Bax, Bcl-2, and GAD65 expression observed 70 days after MDPI, were reversed by EA treatment. The results suggest that persistent dental pain in mice was induced by MDPI but not by SDPI. This effect was associated with trigeminal GABAergic interneuron plasticity along with morphological and functional changes in astrocytes. EA exerts prolonged analgesic and neuroprotective effects that might be associated with the modulation of neuron-glia crosstalk mechanisms.

Exposure to metam sodium-based pesticide impaired cognitive performances in adult mice: Involvement of oxidative damage and glial activation

Cognitive integrity is a critical aspect of neurological function, and a decline in cognitive function is a hallmark of neurotoxicity. Oxidative stress is a significant pathological feature contributing to cognitive deficits that can arise from exposure to environmental pollutants such as pesticides. Among these, Metam sodium-based pesticides (MS-BP) are an emergent type of pesticide widely used in the agriculture and public health sectors for controlling pests and diseases. Our prior research has shown that animals exposed to MS-BP during the early stages of brain development caused cognitive impairments. In the present study, we tested whether exposure to this compound in a fully matured brain would affect cognitive performance and induce oxidative damage to the central nervous system. In this context, adult mice received chronic treatment with increasing doses of MS-BP and subjected to a set of behavioral paradigms. Following behavioral assessment, oxidative stress and glial activation were evaluated. Our main findings showed that MS-BP chronic exposure impaired recognition and short- and long-term memory. These alterations were accompanied by increased superoxide dismutase activity and malondialdehyde level and a marked decrease in catalase activity in specific brain areas. Moreover, exposure to MS-BP is associated with a significant rise in the density of astrocytic and microglial markers, indicating a possible glial cell response within the prefrontal cortex and hippocampus. The present work demonstrated that MS-BP altered cognitive performance likely through oxidative damage to the brain.

Expression of Cytoskeletal Proteins (GFAP, Vimentin), Proapoptotic Protein (Caspase-3) and Protective Protein (S100) in the Epileptic Focus in Adults and Children with Drug-Resistant Temporal Lobe Epilepsy Associated with Focal Cortical Dysplasia

The European Commission of the International League Against Epilepsy (ILAE) has identified glial mechanisms of seizures and epileptogenesis as top research priorities. The aim of our study was to conduct a comparative analysis of the expression levels of cytoskeletal proteins (glial fibrillar acidic protein (GFAP) and vimentin), protective protein S100, and proapoptotic caspase-3 protein in patients with drug-resistant epilepsy (DRE) associated with focal cortical dysplasia (FCD). We aimed to investigate how the expression levels of these proteins depend on age (both in children and adults), gender, and disease duration, using immunohistochemistry. Nonparametric statistical methods were employed for data analysis. In the epileptic focus area of the cortex and white matter in patients with FCD-associated temporal lobe DRE, a higher level of expression of these proteins was observed. Age and gender differences were found for vimentin and S100. In the early stages of disease development, there was a compensatory sequential increase in the expression of cytoskeletal and protective proteins. In patients with DRE, depending on the disease duration, patterns of development of neurodegeneration were noted, which is accompanied by apoptosis of gliocytes. These results provide insights into epilepsy mechanisms and may contribute to improving diagnostic and treatment approaches.

Riluzole treatment modulates KCC2 and EAAT-2 receptor expression and Ca2+ accumulation following ventral root avulsion injury

Avulsion injury results in motoneuron death due to the increased excitotoxicity developing in the affected spinal segments. This study focused on possible short and long term molecular and receptor expression alterations which are thought to be linked to the excitotoxic events in the ventral horn with or without the anti-excitotoxic riluzole treatment. In our experimental model the left lumbar 4 and 5 (L4, 5) ventral roots of the spinal cord were avulsed. Treated animals received riluzole for 2 weeks. Riluzole is a compound that acts to block voltage-activated Na⁺ and Ca²⁺ channels. In control animals the L4, 5 ventral roots were avulsed without riluzole treatment. Expression of astrocytic EAAT-2 and that of KCC2 in motoneurons on the affected side of the L4 spinal segment were detected after the injury by confocal and dSTORM imaging, intracellular Ca²⁺ levels in motoneurons were quantified by electron microscopy. The KCC2 labeling in the lateral and ventrolateral parts of the L4 ventral horn was weaker compared with the medial part of L4 ventral horn in both groups. Riluzole treatment dramatically enhanced motoneuron survival but was not able to prevent the down-regulation of KCC2 expression in injured motoneurons. In contrast, riluzole successfully obviated the increase of intracellular calcium level and the decrease of EAAT-2 expression in astrocytes compared with untreated injured animals. We conclude that KCC2 may not be an essential component for survival of injured motoneurons and riluzole is able to modulate the intracellular level of calcium and expression of EAAT-2.

Glia Signaling and Brain Microenvironment in Migraine

Migraine is a complicated neurological disorder affecting 6% of men and 18% of women worldwide. Various mechanisms, including neuroinflammation, oxidative stress, altered mitochondrial function, neurotransmitter disturbances, cortical hyperexcitability, genetic factors, and endocrine system problems, are responsible for migraine. However, these mechanisms have not completely delineated the pathophysiology behind migraine, and they should be further studied. The brain microenvironment comprises neurons, glial cells, and vascular structures with complex interactions. Disruption of the brain microenvironment is the main culprit behind various neurological disorders. Neuron-glia crosstalk contributes to hyperalgesia in migraine. In the brain, microenvironment and related peripheral regulatory circuits, microglia, astrocytes, and satellite cells are necessary for proper function. These are the most important cells that could induce migraine headaches by disturbing the balance of the neurotransmitters in the nervous system. Neuroinflammation and oxidative stress are the prominent reactions glial cells drive during migraine. Understanding the role of cellular and molecular components of the brain microenvironment on the major neurotransmitters engaged in migraine pathophysiology facilitates the development of new therapeutic approaches with higher effectiveness for migraine headaches. Investigating the role of the brain microenvironment and neuroinflammation in migraine may help decipher its pathophysiology and provide an opportunity to develop novel therapeutic approaches for its management. This review aims to discuss the neuron-glia interactions in the brain microenvironment during migraine and their potential role as a therapeutic target for the treatment of migraine.

Cortical Astrocyte Progenitors and Astrocytes from Human Pluripotent Stem Cells

Astrocytes coordinate several homeostatic processes of the central nervous system and play essential roles for normal brain development and response to disease conditions. Protocols for the conversion of human induced pluripotent stem cells (hiPSCs) into mature astrocytes have opened to the generation of in vitro systems to explore astrocytes’ functions in living human cell contexts and patient-specific settings. In this study, we present an optimized monolayer procedure to commit hiPSC-derived cortical progenitors into enriched populations of cortical astrocyte progenitor cells (CX APCs) that can be further amplified and efficiently differentiated into mature astrocytes. Our optimized system provides a valid tool to explore the role of these cells in neurodevelopmental and neuropsychiatric diseases, opening it up to applications in drug development and biomarkers discovery/validation.

Astrocytes-Derived Small Extracellular Vesicles Hinder Glioma Growth

All cells are capable of secreting extracellular vesicles (EVs), which are not a means to eliminate unneeded cellular compounds but represent a process to exchange material (nucleic acids, lipids and proteins) between different cells. This also happens in the brain, where EVs permit the crosstalk between neuronal and non-neuronal cells, functional to homeostatic processes or cellular responses to pathological stimuli. In brain tumors, EVs are responsible for the bidirectional crosstalk between glioblastoma cells and healthy cells, and among them, astrocytes, that assume a pro-tumoral or antitumoral role depending on the stage of the tumor progression. In this work, we show that astrocyte-derived small EVs (sEVs) exert a defensive mechanism against tumor cell growth and invasion. The effect is mediated by astrocyte-derived EVs (ADEVs) through the transfer to tumor cells of factors that hinder glioma growth. We identified one of these factors, enriched in ADEVs, that is miR124. It reduced both the expression and function of the volume-regulated anion channel (VRAC), that, in turn, decreased the cell migration and invasion of murine glioma GL261 cells.

Host immune responses in the central nervous system during fungal infections

Fungal infections in the central nervous system (CNS) cause high morbidity and mortality. The frequency of CNS mycosis has increased over the last two decades as more individuals go through immunocompromised conditions for various reasons. Nevertheless, options for clinical interventions for CNS mycoses are still limited. Thus, there is an urgent need to understand the host-pathogen interaction mechanisms in CNS mycoses for developing novel treatments. Although the CNS has been regarded as an immune-privileged site, recent studies demonstrate the critical involvement of immune responses elicited by CNS-resident and CNS-infiltrated cells during fungal infections. In this review, we discuss mechanisms of fungal invasion in the CNS, fungal pathogen detection by CNS-resident cells (microglia, astrocytes, oligodendrocytes, neurons), roles of CNS-infiltrated leukocytes, and host immune responses. We consider that understanding host immune responses in the CNS is crucial for endeavors to develop treatments for CNS mycosis.

[Morphological characteristics of the brain nervous tissue during aging]

OBJECTIVE

Identification of morphological manifestations and evaluation of morphometric parameters of the nervous tissue in various structures of the human brain during aging.

MATERIAL AND METHODS

Autopsy material was obtained from patients whose causes of death were not associated with neurological diseases. Three age groups were studied: young (35-45 years old) (n=10); eldery (75-89 years old) (n=20); centenarians (over 90 years old) (n=10). Quantitative analysis of large neurons in the compact part of the substantia nigra, basal ganglia, layer V of the cortex, and the pyramidal layer of the hippocampus was carried out. In addition, the brain mass, the thickness of the cortex of the precentral gyrus were measured, the glial index was calculated, and the morphological signs of age-related involution of the brain tissue and intracerebral vessels were assessed.

RESULTS

In senile and centenarians, compared with young people, there was a progressive reduction in large neurons of layer V of the cortex, basal ganglia, the pyramidal layer of the hippocampus and substantia nigra, a decrease in brain mass and thickness of the cortex of the precentral gyrus, as well as an increase in the glial index. Changes in blood vessels characteristic of aging are described. Also, during aging, signs characteristic of neurodegeneration were found.

CONCLUSION

The results of the study confirm that such brain structures as the cortex of the precentral gyrus, the hippocampus, the basal ganglia, and the substantia nigra lose large neurons with age, followed by the development of gliosis. The identified morphological changes characteristic of aging are phenomenologically similar to a certain set of morphological changes in neurodegenerative diseases of late age.

High-Throughput Analysis of Astrocyte Cultures Shows Prevention of Reactive Astrogliosis by the Multi-Nutrient Combination Fortasyn Connect

Astrocytes are specialized glial cells that tile the central nervous system (CNS) and perform numerous essential functions. Astrocytes react to various forms of CNS insults by altering their morphology and molecular profile, through a process known as reactive astrogliosis. Accordingly, astrocyte reactivity is apparent in many neurodegenerative diseases, among which one is Alzheimer’s disease (AD). Recent clinical trials on early-stage AD have demonstrated that Fortasyn Connect (FC), a multi-nutrient combination providing specific precursors and cofactors for phospholipid synthesis, helps to maintain neuronal functional connectivity and cognitive performance of patients. Several studies have shown that FC may act through its effects on neuronal survival and synaptogenesis, leading to reduced astrocyte reactivity, but whether FC can directly counteract astrocyte reactivity remains to be elucidated. Hence, we developed an in vitro model of reactive astrogliosis using the pro-inflammatory cytokines TNF-α and IFN-γ together with an automated high-throughput assay (AstroScan) to quantify molecular and morphological changes that accompany reactive astrogliosis. Next, we showed that FC is potent in preventing cytokine-induced reactive astrogliosis, a finding that might be of high relevance to understand the beneficial effects of FC-based interventions in the context of neurodegenerative diseases.

Metaball skinning of synthetic astroglial morphologies into realistic mesh models for visual analytics and in silico simulations

Motivation

Astrocytes, the most abundant glial cells in the mammalian brain, have an instrumental role in developing neuronal circuits. They contribute to the physical structuring of the brain, modulating synaptic activity and maintaining the blood–brain barrier in addition to other significant aspects that impact brain function. Biophysically, detailed astrocytic models are key to unraveling their functional mechanisms via molecular simulations at microscopic scales. Detailed, and complete, biological reconstructions of astrocytic cells are sparse. Nonetheless, data-driven digital reconstruction of astroglial morphologies that are statistically identical to biological counterparts are becoming available. We use those synthetic morphologies to generate astrocytic meshes with realistic geometries, making it possible to perform these simulations.

Results

We present an unconditionally robust method capable of reconstructing high fidelity polygonal meshes of astroglial cells from algorithmically-synthesized morphologies. Our method uses implicit surfaces, or metaballs, to skin the different structural components of astrocytes and then blend them in a seamless fashion. We also provide an end-to-end pipeline to produce optimized two- and three-dimensional meshes for visual analytics and simulations, respectively. The performance of our pipeline has been assessed with a group of 5000 astroglial morphologies and the geometric metrics of the resulting meshes are evaluated. The usability of the meshes is then demonstrated with different use cases.

Availability and implementation

Our metaball skinning algorithm is implemented in Blender 2.82 relying on its Python API (Application Programming Interface). To make it accessible to computational biologists and neuroscientists, the implementation has been integrated into NeuroMorphoVis, an open source and domain specific package that is primarily designed for neuronal morphology visualization and meshing.

Supplementary information

Supplementary data are available at Bioinformatics online.

Neuroprotective and Immunomodulatory Action of the Endocannabinoid System under Neuroinflammation

Endocannabinoids (eCBs) are lipid-based retrograde messengers with a relatively short half-life that are produced endogenously and, upon binding to the primary cannabinoid receptors CB_1/2, mediate multiple mechanisms of intercellular communication within the body. Endocannabinoid signaling is implicated in brain development, memory formation, learning, mood, anxiety, depression, feeding behavior, analgesia, and drug addiction. It is now recognized that the endocannabinoid system mediates not only neuronal communications but also governs the crosstalk between neurons, glia, and immune cells, and thus represents an important player within the neuroimmune interface. Generation of primary endocannabinoids is accompanied by the production of their congeners, the N-acylethanolamines (NAEs), which together with N-acylneurotransmitters, lipoamino acids and primary fatty acid amides comprise expanded endocannabinoid/endovanilloid signaling systems. Most of these compounds do not bind CB_1/2, but signal via several other pathways involving the transient receptor potential cation channel subfamily V member 1 (TRPV1), peroxisome proliferator-activated receptor (PPAR)-α and non-cannabinoid G-protein coupled receptors (GPRs) to mediate anti-inflammatory, immunomodulatory and neuroprotective activities. In vivo generation of the cannabinoid compounds is triggered by physiological and pathological stimuli and, specifically in the brain, mediates fine regulation of synaptic strength, neuroprotection, and resolution of neuroinflammation. Here, we review the role of the endocannabinoid system in intrinsic neuroprotective mechanisms and its therapeutic potential for the treatment of neuroinflammation and associated synaptopathy.

Disarranged neuroplastin environment upon aging and chronic stress recovery in female Sprague Dawley rats

Chronic stress produces long-term metabolic changes throughout the superfamily of nuclear receptors, potentially causing various pathologies. Sex hormones modulate the stress response and generate a sex-specific age-dependent metabolic imprint, especially distinct in the reproductive senescence of females. We monitored chronic stress recovery in two age groups of female Sprague Dawley rats to determine whether stress and/or aging structurally changed the glycolipid microenvironment, a milieu playing an important role in cognitive functions. Old females experienced memory impairment even at basal conditions, which was additionally amplified by stress. On the other hand, the memory of young females was not disrupted. Stress recovery was followed by a microglial decrease and an increase in astrocyte count in the hippocampal immune system. Since dysfunction of the brain immune system could contribute to disturbed synaptogenesis, we analyzed neuroplastin expression and the lipid environment. Neuroplastin microenvironments were explored by analyzing immunofluorescent stainings using a newly developed Python script method. Stress reorganized glycolipid microenvironment in the Cornu Ammonis 1 (CA1) and dentate gyrus (DG) hippocampal regions of old females but in a very different fashion, thus affecting neuroplasticity. The postulation of four possible neuroplastin environments pointed to the GD1a ganglioside enrichment during reproductive senescence of stressed females, as well as its high dispersion in both regions and to GD1a and GM1 loss in the CA1 region. A specific lipid environment might influence neuroplastin functionality and underlie synaptic dysfunction triggered by a combination of aging and chronic stress.

Rutin improves glutamate uptake and inhibits glutamate excitotoxicity in rat brain slices

Rutin is an important flavonoid consumed in the daily diet. It is also known as vitamin P and has been extensively investigated due to its pharmacological properties. On the other hand, neuronal death induced by glutamate excitotoxicity is present in several diseases including neurodegenerative diseases. The neuroprotective properties of rutin have been under investigation, although its mechanism of action is still poorly understood. We hypothesized that the mechanisms of neuroprotection of rutin are associated with the increase in glutamate metabolism in astrocytes. This study aimed to evaluate the protective effects of rutin with a focus on the modulation of glutamate detoxification. We used brain organotypic cultures from post-natal Wistar rats (P7-P9) treated with rutin to evaluate neural cell protection and levels of proteins involved in the glutamate metabolism. Moreover, we used cerebral cortex slices from adult Wistar rats to evaluate glutamate uptake. We showed that rutin inhibited the cell death and loss of glutamine synthetase (GS) induced by glutamate that was associated with an increase in glutamate-aspartate transporter (GLAST) in brain organotypic cultures from post-natal Wistar rats. Additionally, it was observed that rutin increased the glutamate uptake in cerebral cortex slices from adult Wistar rats. We conclude that rutin is a neuroprotective agent that prevents glutamate excitotoxicity and thereof suggest that this effect involves the regulation of astrocytic metabolism.

Astrocytes as Guardians of Neuronal Excitability: Mechanisms Underlying Epileptogenesis

Astrocytes are key homeostatic regulators in the central nervous system and play important roles in physiology. After brain damage caused by e.g., status epilepticus, traumatic brain injury, or stroke, astrocytes may adopt a reactive phenotype. This process of reactive astrogliosis is important to restore brain homeostasis. However, persistent reactive astrogliosis can be detrimental for the brain and contributes to the development of epilepsy. In this review, we will focus on physiological functions of astrocytes in the normal brain as well as pathophysiological functions in the epileptogenic brain, with a focus on acquired epilepsy. We will discuss the role of astrocyte-related processes in epileptogenesis, including reactive astrogliosis, disturbances in energy supply and metabolism, gliotransmission, and extracellular ion concentrations, as well as blood-brain barrier dysfunction and dysregulation of blood flow. Since dysfunction of astrocytes can contribute to epilepsy, we will also discuss their role as potential targets for new therapeutic strategies.

Ketotherapeutics for neurodegenerative diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are, respectively, the most prevalent and fastest growing neurodegenerative diseases worldwide. The former is primarily characterized by memory loss and the latter by the motor symptoms of tremor and bradykinesia. Both AD and PD are progressive diseases that share several key underlying mitochondrial, inflammatory, and other metabolic pathologies. This review will detail how these pathologies intersect with ketone body metabolism and signaling, and how ketone bodies, particularly d-β-hydroxybutyrate (βHB), may serve as a potential adjunctive nutritional therapy for two of the world's most devastating conditions.

Potential Astrocytic Receptors and Transporters in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is the most common cause of dementia and is characterized by the progressive loss of memory and cognition in the aging population. However, the etiology of and therapies for AD remain far from understood. Astrocytes, the most abundant neuroglia in the brain, have recently aroused substantial concern due to their involvement in synaptotoxicity, amyloidosis, neuroinflammation, and oxidative stress. In this review, we summarize the candidate molecules of astrocytes, especially receptors and transporters, that may be involved in AD pathogenesis. These molecules include excitatory amino acid transporters (EAATs), metabotropic glutamate receptor 5 (mGluR5), the adenosine 2A receptor (A2AR), the α7-nicotinic acetylcholine receptor (α7-nAChR), the calcium-sensing receptor (CaSR), S100β, and cannabinoid receptors. We describe the characteristics of these molecules and the neurological and pharmacological underpinnings of these molecules in AD. Among these molecules, EAATs, A2AR, and mGluR5 are strongly related to glutamate-mediated synaptotoxicity and are involved in glutamate transmission or the clearance of extrasynaptic glutamate in the AD brain. The α7-nAChR, CaSR, and mGluR5 are receptors of Aβ and can induce a plethora of toxic effects, such as the production of excess Aβ, synaptotoxicity, and NO production triggered by changes in intracellular calcium signaling. Antagonists or positive allosteric modulators of these receptors can repair cognitive ability and modify neurobiological changes. Moreover, blocking S100β or activating cannabinoid receptors reduces neuroinflammation, oxidative stress, and reactive astrogliosis. Thus, targeting these molecules might provide alternative approaches for treating AD.

Neuroprotective effects of ranolazine versus pioglitazone in experimental diabetic neuropathy: Targeting Nav1.7 channels and PPAR-γ

Diabetic neuropathy (DN) is a common complication of diabetes mellitus (DM). Pathophysiology of DN includes inflammation and changes in expression and function of voltage-gated sodium channels (Nav) in peripheral nerves; and central reduction of Peroxisome Proliferator Activated Receptor-Gamma (PPAR-γ) expression.

AIM

This study explored the effect of ranolazine (RN) versus pioglitazone (PIO) in DN induced in rats. The role of sciatic interleukin (IL)-1β, tumor necrosis factor-alpha (TNF)-α, Nav1.7, and spinal PPAR-γ expressions were determined.

MATERIALS AND METHODS

For induction of Type-2 DM, 40 high fat diet-fed rats were challenged by a single dose of intraperitoneal streptozotocin (30 mg/kg). One week later, oral PIO (10 mg/kg; once daily) or RN (20, 50 and 100 mg/kg; twice daily) were administered for six weeks. Weekly body weight and fasting blood sugar (FBS) were measured. Rats were tested for thermal hyperalgesia and mechanical allodynia. At the end of the experiment, sciatic nerves homogenates were examined for TNF-α and IL-1B levels, and Nav1.7 channel expression. Segments of spinal cords were investigated for the PPAR-γ gene expression. Evaluation of histopathology of sciatic nerves and spinal cords were done.

KEY FINDINGS

In diabetic rats, PIO and RN individually improved evoked-pain behaviors, reduced sciatic TNF-α and 1L-1B levels; downregulated expressional levels of Nav1.7 channels; and increased the spinal PPAR-γ gene expression. RN in the dose of 100 mg/kg/day showed the most advantageous effects.

SIGNIFICANCE

RN has neuroprotective effects in Type-2 diabetes-induced DN. Further studies of combined RN-PIO treatment are recommended, especially in diabetic patients with cardiovascular co-morbidity.

Spatio-temporal expression profile of NGF and the two-receptor system, TrkA and p75NTR, in experimental autoimmune encephalomyelitis

BACKGROUND

Nerve growth factor (NGF) and its receptors, tropomyosin receptor kinase A (TrkA) and pan-neurotrophin receptor p75 (p75NTR), are known to play bidirectional roles between the immune and nervous system. There are only few studies with inconclusive results concerning the expression pattern and role of NGF, TrkA, and p75NTR (NGF system) under the neuroinflammatory conditions in multiple sclerosis (MS) and its mouse model, the experimental autoimmune encephalomyelitis (EAE). The aim of this study is to investigate the temporal expression in different cell types of NGF system in the central nervous system (CNS) during the EAE course.

METHODS

EAE was induced in C57BL/6 mice 6-8 weeks old. CNS tissue samples were collected on specific time points: day 10 (D10), days 20-22 (acute phase), and day 50 (chronic phase), compared to controls. Real-time PCR, Western Blot, histochemistry, and immunofluorescence were performed throughout the disease course for the detection of the spatio-temporal expression of the NGF system.

RESULTS

Our findings suggest that both NGF and its receptors, TrkA and p75NTR, are upregulated during acute and chronic phase of the EAE model in the inflammatory lesions in the spinal cord. NGF and its receptors were co-localized with NeuN+ cells, GAP-43+ axons, GFAP+ cells, Arginase1+ cells, and Mac3+ cells. Furthermore, TrkA and p75NTR were sparsely detected on CNPase+ cells within the inflammatory lesion. Of high importance is our observation that despite EAE being a T-mediated disease, only NGF and p75NTR were shown to be expressed by B lymphocytes (B220+ cells) and no expression on T lymphocytes was noticed.

CONCLUSION

Our results indicate that the components of the NGF system are subjected to differential regulation during the EAE disease course. The expression pattern of NGF, TrkA, and p75NTR is described in detail, suggesting possible functional roles in neuroprotection, neuroregeneration, and remyelination by direct and indirect effects on the components of the immune system.

A neuroglia-based interpretation of glaucomatous neuroretinal rim thinning in the optic nerve head

Neuroretinal rim thinning (NRR) is a characteristic glaucomatous optic disc change. However, the precise mechanism of the rim thinning has not been completely elucidated. This review focuses on the structural role of the glioarchitecture in the formation of the glaucomatous NRR thinning. The NRR is a glia-framed structure, with honeycomb geometry and mechanically reinforced astrocyte processes along the transverse plane. When neural damage selectively involves the neuron and spares the glia, the gross structure of the tissue is preserved. The disorganization and loss of the glioarchitecture are the two hallmarks of optic nerve head (ONH) remodeling in glaucoma that leads to the thinning of NRR tissue upon axonal loss. This is in contrast to most non-glaucomatous optic neuropathies with optic disc pallor where hypertrophy of the glioarchitecture is associated with the seemingly absent optic disc cupping. Arteritic anterior ischemic optic neuropathy is an exception where pan-necrosis of ONH tissue leads to NRR thinning. Milder ischemia indicates selective neuronal loss that spares glia in non-arteritic anterior ischemic optic neuropathy. The biological reason is the heterogeneous glial response determined by the site, type, and severity of the injury. The neuroglial interpretation explains how the cellular changes underlie the clinical findings. Updated understandings on glial responses illustrate the mechanical, microenvironmental, and microglial modulation of activated astrocytes in glaucoma. Findings relevant to the possible mechanism of the astrocyte death in advanced glaucoma are also emerging. Ultimately, a better understanding of glaucomatous glial response may lead to glia-targeting neuroprotection in the future.

The Opening of Connexin 43 Hemichannels Alters Hippocampal Astrocyte Function and Neuronal Survival in Prenatally LPS-Exposed Adult Offspring

Clinical evidence has revealed that children born from mothers exposed to viral and bacterial pathogens during pregnancy are more likely to suffer various neurological disorders including schizophrenia, autism bipolar disorder, major depression, epilepsy, and cerebral palsy. Despite that most research has centered on the impact of prenatal inflammation in neurons and microglia, the potential modifications of astrocytes and neuron-astrocyte communication have received less scrutiny. Here, we evaluated whether prenatally LPS-exposed offspring display alterations in the opening of astrocyte hemichannels and pannexons in the hippocampus, together with changes in neuroinflammation, intracellular Ca²⁺ and nitric oxide (NO) signaling, gliotransmitter release, cell arborization, and neuronal survival. Ethidium uptake recordings revealed that prenatal LPS exposure enhances the opening of astrocyte Cx43 hemichannels and Panx1 channels in the hippocampus of adult offspring mice. This enhanced channel activity occurred by a mechanism involving a microglia-dependent production of IL-1β/TNF-α and the stimulation of p38 MAP kinase/iNOS/[Ca²⁺]_i-mediated signaling and purinergic/glutamatergic pathways. Noteworthy, the activity of Cx43 hemichannels affected the release of glutamate, [Ca²⁺]_i handling, and morphology of astrocytes, whereas also disturbed neuronal function, including the dendritic arbor and spine density, as well as survival. We speculate that excitotoxic levels of glutamate triggered by the activation of Cx43 hemichannels may contribute to hippocampal neurotoxicity and damage in prenatally LPS-exposed offspring. Therefore, the understanding of how astrocyte-neuron crosstalk is an auspicious avenue toward the development of broad treatments for several neurological disorders observed in children born to women who had a severe infection during gestation.

Astrocytes: Role and Functions in Brain Pathologies

Astrocytes are a population of cells with distinctive morphological and functional characteristics that differ within specific areas of the brain. Postnatally, astrocyte progenitors migrate to reach their brain area and related properties. They have a regulatory role of brain functions that are implicated in neurogenesis and synaptogenesis, controlling blood-brain barrier permeability and maintaining extracellular homeostasis. Mature astrocytes also express some genes enriched in cell progenitors, suggesting they can retain proliferative potential. Considering heterogeneity of cell population, it is not surprising that their disorders are related to a wide range of different neuro-pathologies. Brain diseases are characterized by the active inflammatory state of the astrocytes, which is usually described as up-regulation of glial fibrillary acidic protein (GFAP). In particular, the loss of astrocytes function as a result of cellular senescence could have implications for the neurodegenerative disorders, such as Alzheimer disease and Huntington disease, and for the aging brain. Astrocytes can also drive the induction and the progression of the inflammatory state due to their Ca²⁺ signals and that it is strongly related to the disease severity/state. Moreover, they contribute to the altered neuronal activity in several frontal cortex pathologies such as ischemic stroke and epilepsy. There, we describe the current knowledge pertaining to astrocytes' role in brain pathologies and discuss the possibilities to target them as approach toward pharmacological therapies for neuro-pathologies.

Reactive Astrocytes in Neurodegenerative Diseases

Astrocytes, the largest and most numerous glial cells in the central nervous system (CNS), play a variety of important roles in regulating homeostasis, increasing synaptic plasticity and providing neuroprotection, thus helping to maintain normal brain function. At the same time, astrocytes can participate in the inflammatory response and play a key role in the progression of neurodegenerative diseases. Reactive astrocytes are strongly induced by numerous pathological conditions in the CNS. Astrocyte reactivity is initially characterized by hypertrophy of soma and processes, triggered by different molecules. Recent studies have demonstrated that neuroinflammation and ischemia can elicit two different types of reactive astrocytes, termed A1s and A2s. However, in the case of astrocyte reactivity in different neurodegenerative diseases, the recently published research issues remain a high level of conflict and controversy. So far, we still know very little about whether and how the function or reactivity of astrocytes changes in the progression of different neurodegenerative diseases. In this review, we aimed to briefly discuss recent studies highlighting the complex contribution of astrocytes in the process of various neurodegenerative diseases, which may provide us with new prospects for the development of an excellent therapeutic target for neurodegenerative diseases.

Preserved Cerebral Oxygen Metabolism in Astrocytic Dysfunction: A Combination Study of 15O-Gas PET with 14C-Acetate Autoradiography

Fluorocitrate (FC) is a specific metabolic inhibitor of the tricarboxylic acid (TCA) cycle in astrocytes. The purpose of this study was to evaluate whether inhibition of the astrocyte TCA cycle by FC would affect the oxygen metabolism in the rat brain. At 4 h after the intracranial FC injection, the rats (n = 9) were investigated by ¹⁵O-labeled gas PET to measure the cerebral blood flow (CBF), the cerebral metabolic rate of oxygen (CMRO₂), oxygen extraction fraction (OEF), and cerebral blood volume (CBV). After the ¹⁵O-gas PET, the rats were given an intravenous injection of ¹⁴C-acetate for autoradiography. ¹⁵O-gas PET showed no significant differences in any of the measured parameters between the ipsilateral and contralateral striatum (high dose group: CBF (54.4 ± 8.8 and 55.3 ± 11.6 mL/100mL/min), CMRO₂ (7.0 ± 0.9 and 7.1 ± 1.2 mL/100mL/min), OEF (72.0 ± 8.9 and 70.8 ± 8.2%), and CBV (4.1 ± 0.8 and 4.2 ± 0.9 mL/100mL), respectively). In contrast, the ¹⁴C-acetate autoradiography revealed a significant inhibition of the astrocyte metabolism in the ipsilateral striatum. The regional cerebral oxygen consumption as well as the hemodynamic parameters were maintained even in the face of inhibition of the astrocyte TCA cycle metabolism in the rat brain.

Evidence for Sexual Dimorphism in the Response to TLR3 Activation in the Developing Neonatal Mouse Brain: A Pilot Study

Toll-like receptor (TLR)3 activation during the neonatal period produces responses linked to the origins of neuropsychiatric disorders. Although there is sexual dimorphism in neuropsychiatric disorders, it is unknown if brain responses to TLR3 activation are sex-specific. We hypothesized that poly I:C in a post-natal day (P)8 model induces a sexually dimorphic inflammatory responses. C57BL6 mice received intraperitoneal injection of poly I:C (10 mg/kg) or vehicle [normal saline (NS)] at P8. Pups were killed at 6 or 14 h for caspase 3 and 8 activity assays, NFkB ELISA, IRF3, AP1, and GFAP western blotting and cytokines/chemokines gene expression real time qRT-PCR (4–6/group). A second group of pups were killed at 24 h (P9) or 7 days (P15) after poly I:C to assess astrocytic (GFAP) and microglia (Iba1) activation in the hippocampus, thalamus and cortex using immunohistochemistry, and gene and protein expression of cytokines/chemokines using real time RT-PCR and MSD, respectively (4–6/group). Non-parametric analysis was applied. Six hours after poly I:C, caspase-3 and -8 activities in cytosolic fractions were 1.6 and 2.8-fold higher in poly I:C-treated than in NS-treated female mice, respectively, while gene expressions of pro-inflammatory cytokines were upregulated in both sexes. After poly I:C, IRF3 nuclear translocation occurred earlier (6 h) in female mice and later (14 h) in male mice. At 14 h after poly I:C, only male mice also had increased nuclear NFκB levels (88%, p < 0.001) and GFAP expression coinciding with persistent IL-6 and FAS gene upregulation (110 and 77%, respectively; p < 0.001) and IL-10 gene downregulation (-42%, p < 0.05). At 24 h after poly I:C, IL-1β, CXCL-10, TNF-α, and MCP-1 were similarly increased in both sexes but at 7 days after exposure, CXCL-10 and INFγ were increased and IL-10 was decreased only in female mice. Accordingly, microglial activation persisted at 7 days after poly I:C in the hippocampus, thalamus and cortex of female mice. This preliminary study suggests that TLR3 activation may produce in the developing neonatal mouse brain a sexually dimorphic response with early activation of caspase-dependent pathways in female mice, activation of inflammatory cascades in both sexes, which then persists in female mice. Further well-powered studies are essential to confirm these sex-specific findings.

The Role of Connexin and Pannexin Channels in Perinatal Brain Injury and Inflammation

Perinatal brain injury remains a major cause of death and life-long disability. Perinatal brain injury is typically associated with hypoxia-ischemia and/or infection/inflammation. Both hypoxia-ischemia and infection trigger an inflammatory response in the brain. The inflammatory response can contribute to brain cell loss and chronic neuroinflammation leading to neurological impairments. It is now well-established that brain injury evolves over time, and shows a striking spread from injured to previously uninjured regions of the brain. There is increasing evidence that this spread is related to opening of connexin hemichannels and pannexin channels, both of which are large conductance membrane channels found in almost all cell types in the brain. Blocking connexin hemichannels within the first 3 h after hypoxia-ischemia has been shown to improve outcomes in term equivalent fetal sheep but it is important to also understand the downstream pathways linking membrane channel opening with the development of injury in order to identify new therapeutic targets. Open membrane channels release adenosine triphosphate (ATP), and other neuroactive molecules, into the extracellular space. ATP has an important physiological role, but has also been reported to act as a damage-associated molecular pattern (DAMP) signal mediated through specific purinergic receptors and so act as a primary signal 1 in the innate immune system inflammasome pathway. More crucially, extracellular ATP is a key inflammasome signal 2 activator, with purinergic receptor binding triggering the assembly of the multi-protein inflammasome complex. The inflammasome pathway and complex formation contribute to activation of inflammatory caspases, and the release of inflammatory cytokines, including interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-18, and vascular endothelial growth factor (VEGF). We propose that the NOD-like receptor protein-3 (NLRP3) inflammasome, which has been linked to inflammatory responses in models of ischemic stroke and various inflammatory diseases, may be one mechanism by which connexin hemichannel opening especially mediates perinatal brain injury.

Aberrant Calcium Signals in Reactive Astrocytes: A Key Process in Neurological Disorders

Astrocytes are abundant cells in the brain that regulate multiple aspects of neural tissue homeostasis by providing structural and metabolic support to neurons, maintaining synaptic environments and regulating blood flow. Recent evidence indicates that astrocytes also actively participate in brain functions and play a key role in brain disease by responding to neuronal activities and brain insults. Astrocytes become reactive in response to injury and inflammation, which is typically described as hypertrophy with increased expression of glial fibrillary acidic protein (GFAP). Reactive astrocytes are frequently found in many neurological disorders and are a hallmark of brain disease. Furthermore, reactive astrocytes may drive the initiation and progression of disease processes. Recent improvements in the methods to visualize the activity of reactive astrocytes in situ and in vivo have helped elucidate their functions. Ca²⁺ signals in reactive astrocytes are closely related to multiple aspects of disease and can be a good indicator of disease severity/state. In this review, we summarize recent findings concerning reactive astrocyte Ca²⁺ signals. We discuss the molecular mechanisms underlying aberrant Ca²⁺ signals in reactive astrocytes and the functional significance of aberrant Ca²⁺ signals in neurological disorders.

Genotoxic effects of neurotoxin ß-N-methylamino-l-alanine in human peripheral blood cells

The non-proteinogenic amino acid ß-N-methylamino-l-alanine (BMAA) is associated with the development of neurodegenerative diseases such as Alzheimer's disease, amyotrophic lateral sclerosis/parkinsonism-dementia complex (ALS-PDC) and amyotrophic lateral sclerosis. BMAA is known to induce neurotoxic effects leading to neurodegeneration via multiple mechanisms including misfolded protein accumulation, glutamate induced excitotoxicity, calcium dyshomeostasis, endoplasmic reticulum stress and oxidative stress. In the present study, for the first time, genotoxic activity of BMAA (2.5, 5, 10 and 20 μg/mL) was studied in human peripheral blood cells (HPBCs) using the comet and cytokinesis-block micronucleus cytome assays. In addition, the influence of BMAA on the oxidative stress was assessed. At non-cytotoxic concentrations BMAA did not induce formation of DNA strand breaks in HPBCs after 4 and 24 h exposure; however, it significantly increased the number of micronuclei after 24 and 48 h at 20 μg/mL and nucleoplasmic bridges after 48 h at 20 μg/mL. The frequency of nuclear buds was slightly though non-significantly increased after 48 h. Altogether, this indicates that in HPBCs BMAA is clastogenic and induces complex genomic alterations including structural chromosomal rearrangements and gene amplification. No influence on oxidative stress markers was noticed. These findings provide new evidence that environmental neurotoxin BMAA, in addition to targeting common pathways involved in neurodegeneration, can also induce genomic instability in non-target HPBCs suggesting that it might be involved in cancer development. Therefore, these data are important in advancing our current knowledge and opening new questions in the understanding of the mechanisms of BMAA toxicity, particularly in the context of genotoxicity.

Astroglia in Alzheimer's Disease

Alzheimer's disease is the most common cause of dementia. Cellular changes in the brains of the patients suffering from Alzheimer's disease occur well in advance of the clinical symptoms. At the cellular level, the most dramatic is a demise of neurones. As astroglial cells carry out homeostatic functions of the brain, it is certain that these cells are at least in part a cause of Alzheimer's disease. Historically, Alois Alzheimer himself has recognised this at the dawn of the disease description. However, the role of astroglia in this disease has been understudied. In this chapter, we summarise the various aspects of glial contribution to this disease and outline the potential of using these cells in prevention (exercise and environmental enrichment) and intervention of this devastating disease.

Astrocyte-Mediated Neuromodulatory Regulation in Preclinical ALS: A Metadata Analysis

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease characterized by progressive degradation of motoneurons in the central nervous system (CNS). Astrocytes are key regulators for inflammation and neuromodulatory signaling, both of which contribute to ALS. The study goal was to ascertain potential temporal changes in astrocyte-mediated neuromodulatory regulation with transgenic ALS model progression: glutamate, GTL-1, GluR1, GluR2, GABA, ChAT activity, VGF, TNFα, aspartate, and IGF-1. We examine neuromodulatory changes in data aggregates from 42 peer-reviewed studies derived from transgenic ALS mixed cell cultures (neurons + astrocytes). For each corresponding experimental time point, the ratio of transgenic to wild type (WT) was found for each compound. ANOVA and a student's t-test were performed to compare disease stages (early, post-onset, and end stage). Glutamate in transgenic SOD1-G93A mixed cell cultures does not change over time (p > 0.05). GLT-1 levels were found to be decreased 23% over WT but only at end-stage (p < 0.05). Glutamate receptors (GluR1, GluR2) in SOD1-G93A were not substantially different from WT, although SOD1-G93A GluR1 decreased by 21% from post-onset to end-stage (p < 0.05). ChAT activity was insignificantly decreased. VGF is decreased throughout ALS (p < 0.05). Aspartate is elevated by 25% in SOD1-G93A but only during end-stage (p < 0.05). TNFα is increased by a dramatic 362% (p < 0.05). Furthermore, principal component analysis identified TNFα as contributing to 55% of the data variance in the first component. Thus, TNFα, which modulates astrocyte regulation via multiple pathways, could be a strategic treatment target. Overall results suggest changes in neuromodulator levels are subtle in SOD1-G93A ALS mixed cell cultures. If excitotoxicity is present as is often presumed, it could be due to ALS cells being more sensitive to small changes in neuromodulation. Hence, seemingly unsubstantial or oscillatory changes in neuromodulators could wreak havoc in ALS cells, resulting in failed microenvironment homeostasis whereby both hyperexcitability and hypoexcitability can coexist. Future work is needed to examine local, spatiotemporal neuromodulatory homeostasis and assess its functional impact in ALS.

Heavy Alcohol Exposure Activates Astroglial Hemichannels and Pannexons in the Hippocampus of Adolescent Rats: Effects on Neuroinflammation and Astrocyte Arborization

A mounting body of evidence indicates that adolescents are specially more susceptible to alcohol influence than adults. However, the mechanisms underlying this phenomenon remain poorly understood. Astrocyte-mediated gliotransmission is crucial for hippocampal plasticity and recently, the opening of hemichannels and pannexons has been found to participate in both processes. Here, we evaluated whether adolescent rats exposed to ethanol exhibit changes in the activity of astrocyte hemichannels and pannexons in the hippocampus, as well as alterations in astrocyte arborization and cytokine levels. Adolescent rats were subjected to ethanol (3.0 g/kg) for two successive days at 48-h periods over 14 days. The opening of hemichannels and pannexons was examined in hippocampal slices by dye uptake, whereas hippocampal cytokine levels and astroglial arborization were determined by ELISA and Sholl analysis, respectively. We found that adolescent ethanol exposure increased the opening of connexin 43 (Cx43) hemichannels and pannexin-1 (Panx1) channels in astrocytes. Blockade of p38 mitogen-activated protein kinase (MAPK), inducible nitric oxide synthase (iNOS) and cyclooxygenases (COXs), as well as chelation of intracellular Ca²⁺, drastically reduced the ethanol-induced channel opening in astrocytes. Importantly, ethanol-induced Cx43 hemichannel and Panx1 channel activity was correlated with increased levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), IL-6 in the hippocampus, as well as with profound alterations in astrocyte arbor complexity. Thus, we propose that uncontrolled opening of astrocyte hemichannels and pannexons may contribute not only to the glial dysfunction and neurotoxicity caused by adolescent alcohol consumption, but also to the pathogenesis of alcohol use disorders in the adulthood.

Neuronal Activity-Dependent Activation of Astroglial Calcineurin in Mouse Primary Hippocampal Cultures

Astrocytes respond to neuronal activity by generating calcium signals which are implicated in the regulation of astroglial housekeeping functions and/or in modulation of synaptic transmission. We hypothesized that activity-induced calcium signals in astrocytes may activate calcineurin (CaN), a calcium/calmodulin-regulated protein phosphatase, implicated in neuropathology, but whose role in astroglial physiology remains unclear. We used a lentiviral vector expressing NFAT-EYFP (NY) fluorescent calcineurin sensor and a chemical protocol of LTP induction (cLTP) to show that, in mixed neuron-astrocytic hippocampal cultures, cLTP induced robust NY translocation into astrocyte nuclei and, hence, CaN activation. NY translocation was abolished by the CaN inhibitor FK506, and was not observed in pure astroglial cultures. Using Fura-2 single cell calcium imaging, we found sustained Ca²⁺ elevations in juxtaneuronal, but not distal, astrocytes. Pharmacological analysis revealed that both the Ca²⁺ signals and the nuclear NY translocation in astrocytes required NMDA and mGluR5 receptors and depended on extracellular Ca²⁺ entry via a store-operated mechanism. Our results provide a proof of principle that calcineurin in astrocytes may be activated in response to neuronal activity, thereby delineating a framework for investigating the role of astroglial CaN in the physiology of central nervous system.

Compromised astrocyte function and survival negatively impact neurons in infantile neuronal ceroid lipofuscinosis

The neuronal ceroid lipofuscinoses (NCLs) are the most common cause of childhood dementia and are invariably fatal. Early localized glial activation occurs in these disorders, and accurately predicts where neuronal loss is most pronounced. Recent evidence suggests that glial dysfunction may contribute to neuron loss, and we have now explored this possibility in infantile NCL (INCL, CLN1 disease). We grew primary cultures of astrocytes, microglia, and neurons derived from Ppt1 deficient mice (Ppt1^−/−) and assessed their properties compared to wildtype (WT) cultures, before co-culturing them in different combinations (astrocytes with microglia, astrocytes or microglia with neurons, all three cell types together). These studies revealed that both Ppt1^−/− astrocytes and microglia exhibit a more activated phenotype under basal unstimulated conditions, as well as alterations to their protein expression profile following pharmacological stimulation. Ppt1^{- /−} astrocytes also displayed abnormal calcium signalling and an elevated cytoplasmic Ca²⁺ level, and a profound defect in their survival. Ppt1^−/− neurons displayed decreased neurite outgrowth, altered complexity, a reduction in cell body size, and impaired neuron survival with prolonged time in culture. In co-cultures, the presence of both astrocytes and microglia from Ppt1^−/− mice further impaired the morphology of both wild type and Ppt1^−/− neurons. This negative influence was more pronounced for Ppt1^−/− microglia, which appeared to trigger increased Ppt1^−/− neuronal death. In contrast, wild type glial cells, especially astrocytes, ameliorated some of the morphological defects observed in Ppt1^−/− neurons. These findings suggest that both Ppt1^−/− microglia and astrocytes are dysfunctional and may contribute to the neurodegeneration observed in CLN1 disease. However, the dysfunctional phenotypes of Ppt1^−/− glia are different from those present in CLN3 disease, suggesting that the pathogenic role of glia may differ between NCLs.

Astrocytic Atrophy Following Status Epilepticus Parallels Reduced Ca2+ Activity and Impaired Synaptic Plasticity in the Rat Hippocampus

Epilepsy is a group of neurological disorders commonly associated with the neuronal malfunction leading to generation of seizures. Recent reports point to a possible contribution of astrocytes into this pathology. We used the lithium-pilocarpine model of status epilepticus (SE) in rats to monitor changes in astrocytes. Experiments were performed in acute hippocampal slices 2-4 weeks after SE induction. Nissl staining revealed significant neurodegeneration in the pyramidal cell layers of hippocampal CA1, CA3 areas, and the hilus, but not in the granular cell layer of the dentate gyrus. A significant increase in the density of astrocytes stained with an astrocyte-specific marker, sulforhodamine 101, was observed in CA1 stratum (str.) radiatum. Astrocytes in this area were also whole-cell loaded with a morphological tracer, Alexa Fluor 594, for two-photon excitation imaging. Sholl analyses showed no changes in the size of the astrocytic domain or in the number of primary astrocytic branches, but a significant reduction in the number of distal branches that are resolved with diffraction-limited light microscopy (and are thought to contain Ca2+ stores, such as mitochondria and endoplasmic reticulum). The atrophy of astrocytic branches correlated with the reduced size, but not overall frequency of Ca2+ events. The volume tissue fraction of nanoscopic (beyond the diffraction limit) astrocytic leaflets showed no difference between control and SE animals. The results of spatial entropy-complexity spectrum analysis were also consistent with changes in ratio of astrocytic branches vs. leaflets. In addition, we observed uncoupling of astrocytes through the gap-junctions, which was suggested as a mechanism for reduced K+ buffering. However, no significant difference in time-course of synaptically induced K+ currents in patch-clamped astrocytes argued against possible alterations in K+ clearance by astrocytes. The magnitude of long-term-potentiation (LTP) was reduced after SE. Exogenous D-serine, a co-agonist of NMDA receptors, has rescued the initial phase of LTP. This suggests that the reduced Ca2+-dependent release of D-serine by astrocytes impairs initiation of synaptic plasticity. However, it does not explain the failure of LTP maintenance which may be responsible for cognitive decline associated with epilepsy.

Detrimental Effects of Paraquat on Astrocytes-Regulating Synaptic Functions

Paraquat (PQ) exposure is known as a risk factor for developing neurodegenerative diseases. Astrocytes are implicated and affected in neurodegenerative diseases and brain injuries, so it is suspected that PQ may impose detrimental effects on astrocytes function. Here, we present a study of the effects of PQ on synaptic function of astrocytes. Human astrocytes (HA1800) were separately treated with PQ at 200, 400, and 800 µmol/L for 12, 24, and 48 hours, respectively. The concentrations of membrane cholesterol, intracellular glutamate, and adenosine triphosphate (ATP) were assessed by measuring changes with Kits after PQ treatment. Expression levels of glial fibrillary acidic protein (GFAP) and apolipoprotein E (ApoE) were detected using Western blot method. The results indicated that astrocytes were highly susceptible to PQ showing astrogliosis characterized by enhanced GFAP expression (P < .05). The decreased cholesterol level and ApoE expression were observed in PQ-treated astrocytes and so were the decreased levels of glutamates and ATP in PQ-treated astrocytes. These results suggested that PQ exerted the detrimental effects on synaptic function of astrocytes, which may be involved in the progressive process of neurodegenerative disorders.

DISC1 regulates lactate metabolism in astrocytes: implications for psychiatric disorders

Our knowledge of how genetic risk variants contribute to psychiatric disease is mainly limited to neurons. However, the mechanisms whereby the same genetic risk factors could affect the physiology of glial cells remain poorly understood. We studied the role of a psychiatric genetic risk factor, Disrupted-In-Schizophrenia-1 (DISC1), in metabolic functions of astrocytes. We evaluated the effects of knockdown of mouse endogenous DISC1 (DISC1-KD) and expression of a dominant-negative, C-terminus truncated human DISC1 (DN-DISC1) on the markers of energy metabolism, including glucose uptake and lactate production, in primary astrocytes and in mice with selective expression of DN-DISC1 in astrocytes. We also assessed the effects of lactate treatment on altered affective behaviors and impaired spatial memory in DN-DISC1 mice. Both DISC1-KD and DN-DISC1 comparably decreased mRNA and protein levels of glucose transporter 4 and glucose uptake by primary astrocytes. Decreased glucose uptake was associated with reduced oxidative phosphorylation and glycolysis as well as diminished lactate production in vitro and in vivo. No significant effects of DISC1 manipulations in astrocytes were observed on expression of the subunits of the electron transport chain complexes or mitofilin, a neuronal DISC1 partner. Lactate treatment rescued the abnormal behaviors in DN-DISC1 male and female mice. Our results suggest that DISC1 may be involved in the regulation of lactate production in astrocytes to support neuronal activity and associated behaviors. Abnormal expression of DISC1 in astrocytes and resulting abnormalities in energy supply may be responsible for aspects of mood and cognitive disorders observed in patients with major psychiatric illnesses.

The Role of Microglia and Peripheral Monocytes in Retinal Damage after Corneal Chemical Injury

Eyes that have experienced alkali burn to the surface are excessively susceptible to subsequent severe glaucoma and retinal ganglion cell loss, despite maximal efforts to prevent or slow down the disease. Recently, we have shown, in mice and rabbits, that such retinal damage is neither mediated by the alkali itself reaching the retina nor by intraocular pressure elevation. Rather, it is caused by the up-regulation of tumor necrosis factor-α (TNF-α), which rapidly diffuses posteriorly, causing retinal ganglion cell apoptosis and CD45⁺ cell activation. Herein, we investigated the involvement of peripheral blood monocytes and microglia in retinal damage. Using CX3CR1^+/EGFP::CCR2^+/RFP reporter mice and bone marrow chimeras, we show that peripheral CX3CR1⁺CD45^hiCD11b⁺MHC-II⁺ monocytes infiltrate into the retina from the optic nerve at 24 hours after the burn and release further TNF-α. A secondary source of peripheral monocyte response originates from a rare population of patrolling myeloid CCR2⁺ cells of the retina that differentiate into CX3CR1⁺ macrophages within hours after the injury. As a result, CX3CR1⁺CD45^loCD11b⁺ microglia become reactive at 7 days, causing further TNF-α release. Prompt TNF-α inhibition after corneal burn suppresses monocyte infiltration and microglia activation, and protects the retina. This study may prove relevant to other injuries of the central nervous system.

Glial cells are functionally impaired in juvenile neuronal ceroid lipofuscinosis and detrimental to neurons

The neuronal ceroid lipofuscinoses (NCLs or Batten disease) are a group of inherited, fatal neurodegenerative disorders of childhood. In these disorders, glial (microglial and astrocyte) activation typically occurs early in disease progression and predicts where neuron loss subsequently occurs. We have found that in the most common juvenile form of NCL (CLN3 disease or JNCL) this glial response is less pronounced in both mouse models and human autopsy material, with the morphological transformation of both astrocytes and microglia severely attenuated or delayed. To investigate their properties, we isolated glia and neurons from Cln3-deficient mice and studied their basic biology in culture. Upon stimulation, both Cln3-deficient astrocytes and microglia also showed an attenuated ability to transform morphologically, and an altered protein secretion profile. These defects were more pronounced in astrocytes, including the reduced secretion of a range of neuroprotective factors, mitogens, chemokines and cytokines, in addition to impaired calcium signalling and glutamate clearance. Cln3-deficient neurons also displayed an abnormal organization of their neurites. Most importantly, using a co-culture system, Cln3-deficient astrocytes and microglia had a negative impact on the survival and morphology of both Cln3-deficient and wildtype neurons, but these effects were largely reversed by growing mutant neurons with healthy glia. These data provide evidence that CLN3 disease astrocytes are functionally compromised. Together with microglia, they may play an active role in neuron loss in this disorder and can be considered as potential targets for therapeutic interventions.

Potassium 2-(1-hydroxypentyl)-benzoate attenuates neuronal apoptosis in neuron-astrocyte co-culture system through neurotrophy and neuroinflammation pathway

Potassium 2-(1-hydroxypentyl)-benzoate (d,l-PHPB), a new drug candidate for ischemic stroke at the phase II clinic trial, has been shown to protect neurons by inhibiting oxidative injury and reducing neuron apoptosis in previous studies. But the mechanisms of d,l-PHPB remain to be studied. In this study, a neuron–astrocytes co-culture system was used to elucidate the roles of astrocytes in neuroprotection of d,l-PHPB under oxygen-glucose deprivation/reoxygenation (OGD/R) condition. Our data showed that d,l-PHPB reduced neuronal apoptosis in mono-culture system and this effect was enhanced in neuron–astrocyte co-culture system under the OGD/R condition. Meanwhile, d,l-PHPB obviously increased the levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), which were mainly secreted from astrocytes, in the co-culture system after OGD/R. The PI3K/AKT and ERK signaling pathways as well as the p-TRKA/B receptors were involved in the process. In addition, the levels of TNF-α and IL-1β secreted from astrocytes after OGD/R were markedly reduced after d,l-PHPB treatment, which was mainly due to the suppression of phosphorylated p38. In conclusion, the present study demonstrates that the neuroprotective effects of d,l-PHPB were improved by astrocytes, mainly mediated by increasing the release of BDNF/NGF and attenuating inflammatory cytokines.

Neurotoxicity of the Cyanotoxin BMAA Through Axonal Degeneration and Intercellular Spreading

β-Methylamino-L-alanine (BMAA) is implicated in neurodegeneration and neurotoxicity, particularly in ALS-Parkinson Dementia Complex. Neurotoxic properties of BMAA have been partly elucidated, while its transcellular spreading capacity has not been examined. Using reconstructed neuronal networks in microfluidic chips, separating neuronal cells into two subcompartments-(1) the proximal, containing first-order neuronal soma and dendrites, and (2) a distal compartment, containing either only axons originating from first-order neurons or second-order striatal neurons-creates a cortico-striatal network. Using this system, we investigated the toxicity and spreading of BMAA in murine primary neurons. We used a newly developed antibody to detect BMAA in cells. After treatment with 10 μM BMAA, the cyanotoxin was incorporated in first-degree neurons. We also observed a rapid trans-neuronal spread of BMAA to unexposed second-degree neurons in 48 h, followed by axonal degeneration, with limited somatic death. This in vitro study demonstrates BMAA axonal toxicity at sublethal concentrations and, for the first time, the transcellular spreading abilities of BMAA. This neuronal dying forward spread that could possibly be associated with progression of some neurodegenerative diseases especially amyotrophic lateral sclerosis.

Astroglia as a cellular target for neuroprotection and treatment of neuro-psychiatric disorders

Astrocytes are key homeostatic cells of the central nervous system. They cooperate with neurons at several levels, including ion and water homeostasis, chemical signal transmission, blood flow regulation, immune and oxidative stress defense, supply of metabolites and neurogenesis. Astroglia is also important for viability and maturation of stem-cell derived neurons. Neurons critically depend on intrinsic protective and supportive properties of astrocytes. Conversely, all forms of pathogenic stimuli which disturb astrocytic functions compromise neuronal functionality and viability. Support of neuroprotective functions of astrocytes is thus an important strategy for enhancing neuronal survival and improving outcomes in disease states. In this review, we first briefly examine how astrocytic dysfunction contributes to major neurological disorders, which are traditionally associated with malfunctioning of processes residing in neurons. Possible molecular entities within astrocytes that could underpin the cause, initiation and/or progression of various disorders are outlined. In the second section, we explore opportunities enhancing neuroprotective function of astroglia. We consider targeting astrocyte-specific molecular pathways which are involved in neuroprotection or could be expected to have a therapeutic value. Examples of those are oxidative stress defense mechanisms, glutamate uptake, purinergic signaling, water and ion homeostasis, connexin gap junctions, neurotrophic factors and the Nrf2-ARE pathway. We propose that enhancing the neuroprotective capacity of astrocytes is a viable strategy for improving brain resilience and developing new therapeutic approaches.

Prolonged Dysfunction of Astrocytes and Activation of Microglia Accelerate Degeneration of Dopaminergic Neurons in the Rat Substantia Nigra and Block Compensation of Early Motor Dysfunction Induced by 6-OHDA

Progressive degeneration of dopaminergic neurons in the substantia nigra (SN) is the underlying cause of Parkinson’s disease (PD). The disease in early stages is difficult to diagnose, because behavioral deficits are masked by compensatory processes. Astrocytic and microglial pathology precedes motor symptoms. Besides supportive functions of astrocytes in the brain, their role in PD is unrecognized. Prolonged dysfunction of astrocytes could increase the vulnerability of dopaminergic neurons and advance their degeneration during aging. The aim of our studies was to find out whether prolonged dysfunction of astrocytes in the SN is deleterious for neuronal functioning and if it influences their survival after toxic insult or changes the compensatory potential of the remaining neurons. In Wistar rat model, we induced activation, prolonged dysfunction, and death of astrocytes by chronic infusion of fluorocitrate (FC) into the SN, without causing dopaminergic neuron degeneration. Strongly enhanced dopamine turnover in the SN after 7 days of FC infusion was induced probably by microglia activated in response to astrocyte stress. The FC effect was reversible, and astrocyte pool was replenished 3 weeks after the end of infusion. Importantly, the prolonged astrocyte dysfunction and microglia activation accelerated degeneration of dopaminergic neurons induced by 6-hydroxydopamine and blocked the behavioral compensation normally observed after moderate neurodegeneration. Impaired astrocyte functioning, activation of microglia, diminishing compensatory capability of the dopaminergic system, and increasing neuronal vulnerability to external insults could be the underlying causes of PD. This animal model of prolonged astrocyte dysfunction can be useful for in vivo studies of glia–microglia–neuron interaction.

Post-spinal cord injury astrocyte-mediated functional recovery in rats after intraspinal injection of the recombinant adenoviral vectors Ad5-VEGF and Ad5-ANG

OBJECTIVE The most actively explored therapeutic strategy for overcoming spinal cord injury (SCI) is the delivery of genes encoding molecules that stimulate regeneration. In a mouse model of amyotrophic lateral sclerosis and in preliminary clinical trials in patients with amyotrophic lateral sclerosis, the combined administration of recombinant adenoviral vectors (Ad5-VEGF+Ad5-ANG) encoding the neurotrophic/angiogenic factors vascular endothelial growth factor ( VEGF) and angiogenin ( ANG) was found to slow the development of neurological deficits. These results suggest that there may be positive effects of this combination of genes in posttraumatic spinal cord regeneration. The objective of the present study was to determine the effects of Ad5-VEGF+Ad5-ANG combination therapy on motor function recovery and reactivity of astrocytes in a rat model of SCI. METHODS Spinal cord injury was induced in adult Wistar rats by the weight-drop method. Rats (n = 51) were divided into 2 groups: the experimental group (Ad5-VEGF+Ad5-ANG) and the control group (Ad5-GFP [green fluorescent protein]). Recovery of motor function was assessed using the Basso, Beattie, and Bresnahan scale. The duration and intensity of infectivity and gene expression from the injected vectors were assessed by immunofluorescent detection of GFP. Reactivity of glial cells was assessed by changes in the number of immunopositive cells expressing glial fibrillary acidic protein (GFAP), S100β, aquaporin 4 (AQP4), oligodendrocyte transcription factor 2, and chondroitin sulfate proteoglycan 4. The level of S100β mRNA expression in the spinal cord was estimated by real-time polymerase chain reaction. RESULTS Partial recovery of motor function was observed 30 days after surgery in both groups. However, Basso, Beattie, and Bresnahan scores were 35.9% higher in the Ad5-VEGF+Ad5-ANG group compared with the control group. Specific GFP signal was observed at distances of up to 5 mm in the rostral and caudal directions from the points of injection. A 1.5 to 2.0-fold increase in the number of GFAP⁺, S100β⁺, and AQP4⁺ cells was observed in the white and gray matter at a distance of up to 5 mm from the center of the lesion site in the caudal and rostral directions. At 30 days after injury, a 2-fold increase in S100β transcripts was observed in the Ad5-VEGF+Ad5-ANG group compared with the control group. CONCLUSIONS Intraspinal injection of recombinant adenoviral vectors encoding VEGF and ANG stimulates functional recovery after traumatic SCI. The increased number of S100β⁺ astrocytes induced by this approach may be a beneficial factor for maintaining the survival and function of neurons. Therefore, gene therapy with Ad5-VEGF+Ad5-ANG vectors is an effective therapeutic method for SCI treatment.

Suppression of SNARE-dependent exocytosis in retinal glial cells and its effect on ischemia-induced neurodegeneration

Nervous tissue is characterized by a tight structural association between glial cells and neurons. It is well known that glial cells support neuronal functions, but their role under pathologic conditions is less well understood. Here, we addressed this question in vivo using an experimental model of retinal ischemia and transgenic mice for glia‐specific inhibition of soluble N‐ethylmaleimide‐sensitive factor attachment protein receptor (SNARE)‐dependent exocytosis. Transgene expression reduced glutamate, but not ATP release from single Müller cells, impaired glial volume regulation under normal conditions and reduced neuronal dysfunction and death in the inner retina during the early stages of ischemia. Our study reveals that the SNARE‐dependent exocytosis in glial cells contributes to neurotoxicity during ischemia in vivo and suggests glial exocytosis as a target for therapeutic approaches.