Transient Oxygen/Glucose Deprivation Causes a Delayed Loss of Mitochondria and Increases Spontaneous Calcium Signaling in Astrocytic Processes

Enhancing CNS mitophagy: drug development and disease-relevant models

Mitophagy, the selective degradation of mitochondria, is impaired in many neurodegenerative diseases (NDs), resulting in an accumulation of dysfunctional mitochondria and neuronal damage. Although enhancing mitophagy shows promise as a therapeutic strategy, the clinical significance of mitophagy activators remains uncertain due to limited understanding and poor representation of mitophagy in the central nervous system (CNS). This review explores recent insights into which mitophagy pathways to target and the extent of modulation necessary to be therapeutic towards NDs. We also highlight the complexities of mitophagy in the CNS, highlighting the need for disease-relevant models. Last, we outline crucial aspects of in vitro models to consider during drug discovery, aiming to bridge the gap between preclinical research and clinical applications in treating NDs through mitophagy modulation.

Transplantation of astrocyte-derived mitochondria into injured astrocytes has a protective effect following stretch injury

Traumatic brain injury (TBI) is a global public-health problem. Astrocytes, and their mitochondria, are important factors in the pathogenesis of TBI-induced secondary injury. Mitochondria extracted from healthy tissues and then transplanted have shown promise in models of a variety of diseases. However, the effect on recipient astrocytes is unclear. Here, we isolated primary astrocytes from newborn C57BL/6 mice, one portion of which was used to isolate mitochondria, and another was subjected to stretch injury (SI) followed by transplantation of the isolated mitochondria. After incubation for 12 h, cell viability, mitochondrial dysfunction, calcium overload, redox stress, inflammatory response, and apoptosis were improved. Live-cell imaging showed that the transplanted mitochondria were incorporated into injured astrocytes and fused with their mitochondrial networks, which was in accordance with the changes in the expression levels of markers of mitochondrial dynamics. The astrocytic IKK/NF-κB pathway was decelerated whereas the AMPK/PGC-1α pathway was accelerated by transplantation. Together, these results indicate that exogenous mitochondria from untreated astrocytes can be incorporated into injured astrocytes and fuse with their mitochondrial networks, improving cell viability by ameliorating mitochondrial dysfunction, redox stress, calcium overload, and inflammation.

Neuronal and astrocyte NCX isoform/splice variants: How do they participate in Na+ and Ca2+ signalling?

NCX1, NCX2, and NCX3 gene isoforms and their splice variants are characteristically expressed in different regions of the brain. The tissue-specific splice variants of NCX1-3 isoforms show specific expression profiles in neurons and astrocytes, whereas the relevant NCX isoform/splice variants exhibit diverse allosteric modes of Na+- and Ca2+-dependent regulation. In general, overexpression of NCX1-3 genes leads to neuroprotective effects, whereas their ablation gains the opposite results. At this end, the partial contributions of NCX isoform/splice variants to neuroprotective effects remain unresolved. The glutamate-dependent Na+ entry generates Na+ transients (in response to neuronal cell activities), whereas the Na+-driven Ca2+ entry (through the reverse NCX mode) raises Ca2+ transients. This special mode of signal coupling translates Na+ transients into the Ca2+ signals while being a part of synaptic neurotransmission. This mechanism is of general interest since disease-related conditions (ischemia, metabolic stress, and stroke among many others) trigger Na+ and Ca2+ overload with deadly outcomes of downstream apoptosis and excitotoxicity. The recently discovered mechanisms of NCX allosteric regulation indicate that some NCX variants might play a critical role in the dynamic coupling of Na+-driven Ca2+ entry. In contrast, the others are less important or even could be dangerous under altered conditions (e.g., metabolic stress). This working hypothesis can be tested by applying advanced experimental approaches and highly focused computational simulations. This may allow the development of structure-based blockers/activators that can selectively modulate predefined NCX variants to lessen the life-threatening outcomes of excitotoxicity, ischemia, apoptosis, metabolic deprivation, brain injury, and stroke.

Porcine Astrocytes and Their Relevance for Translational Neurotrauma Research

Astrocytes are essential to virtually all brain processes, from ion homeostasis to neurovascular coupling to metabolism, and even play an active role in signaling and plasticity. Astrocytic dysfunction can be devastating to neighboring neurons made inherently vulnerable by their polarized, excitable membranes. Therefore, correcting astrocyte dysfunction is an attractive therapeutic target to enhance neuroprotection and recovery following acquired brain injury. However, the translation of such therapeutic strategies is hindered by a knowledge base dependent almost entirely on rodent data. To facilitate additional astrocytic research in the translatable pig model, we present a review of astrocyte findings from pig studies of health and disease. We hope that this review can serve as a road map for intrepid pig researchers interested in studying astrocyte biology.

Activation of Glutamate Transport Increases Arteriole Diameter in v ivo: Implications for Neurovascular Coupling

In order to meet the energetic demands of cell-to-cell signaling, increases in local neuronal signaling are matched by a coordinated increase in local blood flow, termed neurovascular coupling. Multiple different signals from neurons, astrocytes, and pericytes contribute to this control of blood flow. Previously, several groups demonstrated that inhibition/ablation of glutamate transporters attenuates the neurovascular response. However, it was not determined if glutamate transporter activation was sufficient to increase blood flow. Here, we used multiphoton imaging to monitor the diameter of fluorescently labeled cortical arterioles in anesthetized C57/B6J mice. We delivered vehicle, glutamate transporter substrates, or a combination of a glutamate transporter substrate with various pharmacologic agents via a glass micropipette while simultaneously visualizing changes in arteriole diameter. We developed a novel image analysis method to automate the measurement of arteriole diameter in these time-lapse analyses. Using this workflow, we first conducted pilot experiments in which we focally applied L-glutamate, D-aspartate, or L-threo-hydroxyaspartate (L-THA) and measured arteriole responses as proof of concept. We subsequently applied the selective glutamate transport substrate L-THA (applied at concentrations that do not activate glutamate receptors). We found that L-THA evoked a significantly larger dilation than that observed with focal saline application. This response was blocked by co-application of the potent glutamate transport inhibitor, L-(2S,3S)-3-[3-[4-(trifluoromethyl)-benzoylamino]benzyloxy]-aspartate (TFB-TBOA). Conversely, we were unable to demonstrate a reduction of this effect through co-application of a cocktail of glutamate and GABA receptor antagonists. These studies provide the first direct evidence that activation of glutamate transport is sufficient to increase arteriole diameter. We explored potential downstream mechanisms mediating this transporter-mediated dilation by using a Ca2+ chelator or inhibitors of reversed-mode Na+/Ca2+ exchange, nitric oxide synthetase, or cyclo-oxygenase. The estimated effects and confidence intervals suggested some form of inhibition for a number of these inhibitors. Limitations to our study design prevented definitive conclusions with respect to these downstream inhibitors; these limitations are discussed along with possible next steps. Understanding the mechanisms that control blood flow are important because changes in blood flow/energy supply are implicated in several neurodegenerative disorders and are used as a surrogate measure of neuronal activity in widely used techniques such as functional magnetic resonance imaging (fMRI).

Glioblastoma Microenvironment and Cellular Interactions

Simple Summary

This paper summarizes the crosstalk between tumor/non-tumor cells and other elements of the glioblastoma (GB) microenvironment. In tumor pathology, glial cells result in the highest number of cancers, and GB is considered the most lethal tumor of the central nervous system (CNS). The tumor microenvironment (TME) is a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be a key factor for the ineffective treatment since the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. A deeper understanding of cell–cell interactions in the TME and with the tumor cells could be the basis for a more efficient therapy.

Abstract

The central nervous system (CNS) represents a complex network of different cells, such as neurons, glial cells, and blood vessels. In tumor pathology, glial cells result in the highest number of cancers, and glioblastoma (GB) is considered the most lethal tumor in this region. The development of GB leads to the infiltration of healthy tissue through the interaction between all the elements of the brain network. This results in a GB microenvironment, a complex peritumoral hallo composed of tumor cells and several non-tumor cells (e.g., nervous cells, stem cells, fibroblasts, vascular and immune cells), which might be the principal factor for the ineffective treatment due to the fact that the microenvironment modulates the biologic status of the tumor with the increase in its evasion capacity. Crosstalk between glioma cells and the brain microenvironment finally inhibits the beneficial action of molecular pathways, favoring the development and invasion of the tumor and its increasing resistance to treatment. A deeper understanding of cell–cell interactions in the tumor microenvironment (TME) and with the tumor cells could be the basis for a more efficient therapy.

Astrocyte Bioenergetics and Major Psychiatric Disorders

Ongoing research continues to add new elements to the emerging picture of involvement of astrocyte energy metabolism in the pathophysiology of major psychiatric disorders, including schizophrenia, mood disorders, and addictions. This review outlines what is known about the energy metabolism in astrocytes, the most numerous cell type in the brain, and summarizes the recent work on how specific perturbations of astrocyte bioenergetics may contribute to the neuropsychiatric conditions. The role of astrocyte energy metabolism in mental health and disease is reviewed on the organism, organ, and cell level. Data arising from genomic, metabolomic, in vitro, and neurobehavioral studies is critically analyzed to suggest future directions in research and possible metabolism-focused therapeutic interventions.

Astrocyte Mitochondria in White-Matter Injury

This review summarizes the diverse structure and function of astrocytes to describe the bioenergetic versatility required of astrocytes that are situated at different locations. The intercellular domain of astrocyte mitochondria defines their roles in supporting and regulating astrocyte-neuron coupling and survival against ischemia. The heterogeneity of astrocyte mitochondria, and how subpopulations of astrocyte mitochondria adapt to interact with other glia and regulate axon function, require further investigation. It has become clear that mitochondrial permeability transition pores play a key role in a wide variety of human diseases, whose common pathology may be based on mitochondrial dysfunction triggered by Ca2+ and potentiated by oxidative stress. Reactive oxygen species cause axonal degeneration and a reduction in axonal transport, leading to axonal dystrophies and neurodegeneration including Alzheimer's disease, amyotrophic lateral sclerosis, Parkinson's disease, and Huntington's disease. Developing new tools to allow better investigation of mitochondrial structure and function in astrocytes, and techniques to specifically target astrocyte mitochondria, can help to unravel the role of mitochondrial health and dysfunction in a more inclusive context outside of neuronal cells. Overall, this review will assess the value of astrocyte mitochondria as a therapeutic target to mitigate acute and chronic injury in the CNS.

Mitochondrial Dynamics: A Potential Therapeutic Target for Ischemic Stroke

Stroke is one of the leading causes of death and disability worldwide. Brain injury after ischemic stroke involves multiple pathophysiological mechanisms, such as oxidative stress, mitochondrial dysfunction, excitotoxicity, calcium overload, neuroinflammation, neuronal apoptosis, and blood-brain barrier (BBB) disruption. All of these factors are associated with dysfunctional energy metabolism after stroke. Mitochondria are organelles that provide adenosine triphosphate (ATP) to the cell through oxidative phosphorylation. Mitochondrial dynamics means that the mitochondria are constantly changing and that they maintain the normal physiological functions of the cell through continuous division and fusion. Mitochondrial dynamics are closely associated with various pathophysiological mechanisms of post-stroke brain injury. In this review, we will discuss the role of the molecular mechanisms of mitochondrial dynamics in energy metabolism after ischemic stroke, as well as new strategies to restore energy homeostasis and neural function. Through this, we hope to uncover new therapeutic targets for the treatment of ischemic stroke.

Impaired Mitophagy in Neurons and Glial Cells during Aging and Age-Related Disorders

Aging is associated with a decline in cognitive function, which can partly be explained by the accumulation of damage to the brain cells over time. Neurons and glia undergo morphological and ultrastructure changes during aging. Over the past several years, it has become evident that at the cellular level, various hallmarks of an aging brain are closely related to mitophagy. The importance of mitochondria quality and quantity control through mitophagy is highlighted by the contribution that defects in mitochondria-autophagy crosstalk make to aging and age-related diseases. In this review, we analyze some of the more recent findings regarding the study of brain aging and neurodegeneration in the context of mitophagy. We discuss the data on the dynamics of selective autophagy in neurons and glial cells during aging and in the course of neurodegeneration, focusing on three mechanisms of mitophagy: non-receptor-mediated mitophagy, receptor-mediated mitophagy, and transcellular mitophagy. We review the role of mitophagy in neuronal/glial homeostasis and in the molecular pathogenesis of neurodegenerative disorders, such as Parkinson's disease, Alzheimer's disease, and other disorders. Common mechanisms of aging and neurodegeneration that are related to different mitophagy pathways provide a number of promising targets for potential therapeutic agents.

Astroglial Hemichannels and Pannexons: The Hidden Link between Maternal Inflammation and Neurological Disorders

Maternal inflammation during pregnancy causes later-in-life alterations of the offspring’s brain structure and function. These abnormalities increase the risk of developing several psychiatric and neurological disorders, including schizophrenia, intellectual disability, bipolar disorder, autism spectrum disorder, microcephaly, and cerebral palsy. Here, we discuss how astrocytes might contribute to postnatal brain dysfunction following maternal inflammation, focusing on the signaling mediated by two families of plasma membrane channels: hemi-channels and pannexons. [Ca²⁺]_i imbalance linked to the opening of astrocytic hemichannels and pannexons could disturb essential functions that sustain astrocytic survival and astrocyte-to-neuron support, including energy and redox homeostasis, uptake of K⁺ and glutamate, and the delivery of neurotrophic factors and energy-rich metabolites. Both phenomena could make neurons more susceptible to the harmful effect of prenatal inflammation and the experience of a second immune challenge during adulthood. On the other hand, maternal inflammation could cause excitotoxicity by producing the release of high amounts of gliotransmitters via astrocytic hemichannels/pannexons, eliciting further neuronal damage. Understanding how hemichannels and pannexons participate in maternal inflammation-induced brain abnormalities could be critical for developing pharmacological therapies against neurological disorders observed in the offspring.

Repair Mechanisms of the Neurovascular Unit after Ischemic Stroke with a Focus on VEGF

The functional neural circuits are partially repaired after an ischemic stroke in the central nervous system (CNS). In the CNS, neurovascular units, including neurons, endothelial cells, astrocytes, pericytes, microglia, and oligodendrocytes maintain homeostasis; however, these cellular networks are damaged after an ischemic stroke. The present review discusses the repair potential of stem cells (i.e., mesenchymal stem cells, endothelial precursor cells, and neural stem cells) and gaseous molecules (i.e., nitric oxide and carbon monoxide) with respect to neuroprotection in the acute phase and regeneration in the late phase after an ischemic stroke. Commonly shared molecular mechanisms in the neurovascular unit are associated with the vascular endothelial growth factor (VEGF) and its related factors. Stem cells and gaseous molecules may exert therapeutic effects by diminishing VEGF-mediated vascular leakage and facilitating VEGF-mediated regenerative capacity. This review presents an in-depth discussion of the regeneration ability by which endogenous neural stem cells and endothelial cells produce neurons and vessels capable of replacing injured neurons and vessels in the CNS.

Neuromodulation and neuroprotective effects of chlorogenic acids in excitatory synapses of mouse hippocampal slices

The increased healthspan afforded by coffee intake provides novel opportunities to identify new therapeutic strategies. Caffeine has been proposed to afford benefits through adenosine A2A receptors, which can control synaptic dysfunction underlying some brain disease. However, decaffeinated coffee and other main components of coffee such as chlorogenic acids, also attenuate brain dysfunction, although it is unknown if they control synaptic function. We now used electrophysiological recordings in mouse hippocampal slices to test if realistic concentrations of chlorogenic acids directly affect synaptic transmission and plasticity. 3-(3,4-dihydroxycinnamoyl)quinic acid (CA, 1-10 μM) and 5-O-(trans-3,4-dihydroxycinnamoyl)-D-quinic acid (NCA, 1-10 μM) were devoid of effect on synaptic transmission, paired-pulse facilitation or long-term potentiation (LTP) and long-term depression (LTD) in Schaffer collaterals-CA1 pyramidal synapses. However, CA and NCA increased the recovery of synaptic transmission upon re-oxygenation following 7 min of oxygen/glucose deprivation, an in vitro ischemia model. Also, CA and NCA attenuated the shift of LTD into LTP observed in hippocampal slices from animals with hippocampal-dependent memory deterioration after exposure to β-amyloid 1-42 (2 nmol, icv), in the context of Alzheimer's disease. These findings show that chlorogenic acids do not directly affect synaptic transmission and plasticity but can indirectly affect other cellular targets to correct synaptic dysfunction. Unraveling the molecular mechanisms of action of chlorogenic acids will allow the design of hitherto unrecognized novel neuroprotective strategies.

The Glioblastoma Microenvironment: Morphology, Metabolism, and Molecular Signature of Glial Dynamics to Discover Metabolic Rewiring Sequence

Different functional states determine glioblastoma (GBM) heterogeneity. Brain cancer cells coexist with the glial cells in a functional syncytium based on a continuous metabolic rewiring. However, standard glioma therapies do not account for the effects of the glial cells within the tumor microenvironment. This may be a possible reason for the lack of improvements in patients with high-grade gliomas therapies. Cell metabolism and bioenergetic fitness depend on the availability of nutrients and interactions in the microenvironment. It is strictly related to the cell location in the tumor mass, proximity to blood vessels, biochemical gradients, and tumor evolution, underlying the influence of the context and the timeline in anti-tumor therapeutic approaches. Besides the cancer metabolic strategies, here we review the modifications found in the GBM-associated glia, focusing on morphological, molecular, and metabolic features. We propose to analyze the GBM metabolic rewiring processes from a systems biology perspective. We aim at defining the crosstalk between GBM and the glial cells as modules. The complex networking may be expressed by metabolic modules corresponding to the GBM growth and spreading phases. Variation in the oxidative phosphorylation (OXPHOS) rate and regulation appears to be the most important part of the metabolic and functional heterogeneity, correlating with glycolysis and response to hypoxia. Integrated metabolic modules along with molecular and morphological features could allow the identification of key factors for controlling the GBM-stroma metabolism in multi-targeted, time-dependent therapies.

MK801 regulates the expression of key osteoarthritis factors in osteoarthritis synovial fibroblasts through complement C5

BACKGROUND

Osteoarthritis is currently one of the most common chronic diseases. As life expectancy increases, its prevalence and incidence are expected to rise. At present, more and more evidences prove the correlation between the complement system and osteoarthritis (OA). This study aims to investigate complement C5's influence on the effect of MK801 on osteoarthritis synovial fibroblasts (OA-SFs).

METHODS

We used IL-1b to induce OA-SFs derived from mice to obtain OA-SFs. And we performed RT-PCR and Western Blot assays to evaluate the expression levels of associated mRNA and protein. The alteration of MAC expression on OA-SFs cell membrane was evaluated by immunofluorescence assay. The expression of related inflammatory factors of OA-SFs was evaluated by ELISA experiment.

RESULTS

MK801 could significantly inhibit the expression of osteoarthritis (OA) marker factors, such as: membrane attack complex (MAC), tumor necrosis factor-α (TNF-α) and matrix metalloproteinase-13 (MMP13). Meanwhile, MK801 can significantly inhibit the expression of complement C5 (C5) in OA-SFs. Immunofluorescence assay showed that MAC expression on OA-SFs cell membrane was significantly inhibited by MK801. The nucleo-plasmic separation experiment demonstrated that MK801 could significantly inhibit the activation of Nuclear factor-κB (NF-κB) signaling pathway in OA-SFs. Futhermore, koncking down the expression of C5 reversed the inhibition MK801 on the expression of OA-SFs inflammatory factors.

CONCLUSIONS

These results illustrated two points: first, MK801 inhibited the generation of MAC and the release of inflammation factors in OA-SFs through C5; second: MK801 inhibited the activation of NF-κB signaling pathway in OA-SFs.

Tissue Engineered Bands of Büngner for Accelerated Motor and Sensory Axonal Outgrowth

Following peripheral nerve injury comprising a segmental defect, the extent of axon regeneration decreases precipitously with increasing gap length. Schwann cells play a key role in driving axon re-growth by forming aligned tubular guidance structures called bands of Büngner, which readily occurs in distal nerve segments as well as within autografts - currently the most reliable clinically-available bridging strategy. However, host Schwann cells generally fail to infiltrate large-gap acellular scaffolds, resulting in markedly inferior outcomes and motivating the development of next-generation bridging strategies capable of fully exploiting the inherent pro-regenerative capability of Schwann cells. We sought to create preformed, implantable Schwann cell-laden microtissue that emulates the anisotropic structure and function of naturally-occurring bands of Büngner. Accordingly, we developed a biofabrication scheme leveraging biomaterial-induced self-assembly of dissociated rat primary Schwann cells into dense, fiber-like three-dimensional bundles of Schwann cells and extracellular matrix within hydrogel micro-columns. This engineered microtissue was found to be biomimetic of morphological and phenotypic features of endogenous bands of Büngner, and also demonstrated 8 and 2× faster rates of axonal extension in vitro from primary rat spinal motor neurons and dorsal root ganglion sensory neurons, respectively, compared to 3D matrix-only controls or planar Schwann cells. To our knowledge, this is the first report of accelerated motor axon outgrowth using aligned Schwann cell constructs. For translational considerations, this microtissue was also fabricated using human gingiva-derived Schwann cells as an easily accessible autologous cell source. These results demonstrate the first tissue engineered bands of Büngner (TE-BoBs) comprised of dense three-dimensional bundles of longitudinally aligned Schwann cells that are readily scalable as implantable grafts to accelerate axon regeneration across long segmental nerve defects.

TRP Channels Regulation of Rho GTPases in Brain Context and Diseases

Neurological and neuropsychiatric disorders are mediated by several pathophysiological mechanisms, including developmental and degenerative abnormalities caused primarily by disturbances in cell migration, structural plasticity of the synapse, and blood-vessel barrier function. In this context, critical pathways involved in the pathogenesis of these diseases are related to structural, scaffolding, and enzymatic activity-bearing proteins, which participate in Ca²⁺- and Ras Homologs (Rho) GTPases-mediated signaling. Rho GTPases are GDP/GTP binding proteins that regulate the cytoskeletal structure, cellular protrusion, and migration. These proteins cycle between GTP-bound (active) and GDP-bound (inactive) states due to their intrinsic GTPase activity and their dynamic regulation by GEFs, GAPs, and GDIs. One of the most important upstream inputs that modulate Rho GTPases activity is Ca²⁺ signaling, positioning ion channels as pivotal molecular entities for Rho GTPases regulation. Multiple non-selective cationic channels belonging to the Transient Receptor Potential (TRP) family participate in cytoskeletal-dependent processes through Ca²⁺-mediated modulation of Rho GTPases. Moreover, these ion channels have a role in several neuropathological events such as neuronal cell death, brain tumor progression and strokes. Although Rho GTPases-dependent pathways have been extensively studied, how they converge with TRP channels in the development or progression of neuropathologies is poorly understood. Herein, we review recent evidence and insights that link TRP channels activity to downstream Rho GTPase signaling or modulation. Moreover, using the TRIP database, we establish associations between possible mediators of Rho GTPase signaling with TRP ion channels. As such, we propose mechanisms that might explain the TRP-dependent modulation of Rho GTPases as possible pathways participating in the emergence or maintenance of neuropathological conditions.

I2 imidazoline receptor modulation protects aged SAMP8 mice against cognitive decline by suppressing the calcineurin pathway

Brain aging and dementia are current problems that must be solved. The levels of imidazoline 2 receptors (I₂-IRs) are increased in the brain in Alzheimer's disease (AD) and other neurodegenerative diseases. We tested the action of the specific and selective I₂-IR ligand B06 in a mouse model of accelerated aging and AD, the senescence-accelerated mouse prone 8 (SAMP8) model. Oral administration of B06 for 4 weeks improved SAMP8 mouse behavior and cognition and reduced AD hallmarks, oxidative stress, and apoptotic and neuroinflammation markers. Likewise, B06 regulated glial excitatory amino acid transporter 2 and N-methyl-D aspartate 2A and 2B receptor subunit protein levels. Calcineurin (CaN) is a phosphatase that controls the phosphorylation levels of cAMP response element-binding (CREB), apoptotic mediator BCL-2-associated agonist of cell death (BAD) and GSK3β, among other molecules. Interestingly, B06 was able to reduce the levels of the CaN active form (CaN A). Likewise, CREB phosphorylation, BAD gene expression, and other factors were modified after B06 treatment. Moreover, phosphorylation of a target of CaN, nuclear factor of activated T-cells, cytoplasmic 1 (NFAT_C1), was increased in B06-treated mice, impeding the transcription of genes related to neuroinflammation and neural plasticity. In summary, this I₂ imidazoline ligand can exert its beneficial effects on age-related conditions by modulating CaN pathway action and affecting several molecular pathways, playing a neuroprotective role in SAMP8 mice.

Drug development in targeting ion channels for brain edema

Cerebral edema is a pathological hallmark of various central nervous system (CNS) insults, including traumatic brain injury (TBI) and excitotoxic injury such as stroke. Due to the rigidity of the skull, edema-induced increase of intracranial fluid significantly complicates severe CNS injuries by raising intracranial pressure and compromising perfusion. Mortality due to cerebral edema is high. With mortality rates up to 80% in severe cases of stroke, it is the leading cause of death within the first week. Similarly, cerebral edema is devastating for patients of TBI, accounting for up to 50% mortality. Currently, the available treatments for cerebral edema include hypothermia, osmotherapy, and surgery. However, these treatments only address the symptoms and often elicit adverse side effects, potentially in part due to non-specificity. There is an urgent need to identify effective pharmacological treatments for cerebral edema. Currently, ion channels represent the third-largest target class for drug development, but their roles in cerebral edema remain ill-defined. The present review aims to provide an overview of the proposed roles of ion channels and transporters (including aquaporins, SUR1-TRPM4, chloride channels, glucose transporters, and proton-sensitive channels) in mediating cerebral edema in acute ischemic stroke and TBI. We also focus on the pharmacological inhibitors for each target and potential therapeutic strategies that may be further pursued for the treatment of cerebral edema.

Genetically Encoded Tools for Research of Cell Signaling and Metabolism under Brain Hypoxia

Hypoxia is characterized by low oxygen content in the tissues. The central nervous system (CNS) is highly vulnerable to a lack of oxygen. Prolonged hypoxia leads to the death of brain cells, which underlies the development of many pathological conditions. Despite the relevance of the topic, different approaches used to study the molecular mechanisms of hypoxia have many limitations. One promising lead is the use of various genetically encoded tools that allow for the observation of intracellular parameters in living systems. In the first part of this review, we provide the classification of oxygen/hypoxia reporters as well as describe other genetically encoded reporters for various metabolic and redox parameters that could be implemented in hypoxia studies. In the second part, we discuss the advantages and disadvantages of the primary hypoxia model systems and highlight inspiring examples of research in which these experimental settings were combined with genetically encoded reporters.

Ex Vivo Imaging of Mitochondrial Dynamics and Trafficking in Astrocytes

Mitochondria are essential organelles involved in energy supply and calcium homeostasis. The regulated distribution of mitochondria in polarized cells, particularly neurons, is thought to be essential to these roles. Altered mitochondrial function and impairment of mitochondrial distribution and dynamics is implicated in a number of neurologic disorders. Several recent reports have described mechanisms regulating the activity-dependent distribution of mitochondria within astrocyte processes and the functional consequences of altered mitochondrial transport. Here we provide an ex vivo method for monitoring the transport of mitochondria within the processes of astrocytes using organotypic "slice" cultures. These methods can be easily adapted to investigate a wide range of mitochondrial behaviors, including fission and fusion dynamics, mitophagy, and calcium signaling in astrocytes and other cell types of the central nervous system. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Preparation of brain slices Basic Protocol 2: Preparation of gene gun bullets Basic Protocol 3: Gene gun transfection of slices Basic Protocol 4: Visualization and tracking of mitochondrial movement Alternate Protocol: Transduction of EGFP-mito via viral injection of the neonatal mouse brain.

Glutamate Transporters and Mitochondria: Signaling, Co-compartmentalization, Functional Coupling, and Future Directions

In addition to being an amino acid that is incorporated into proteins, glutamate is the most abundant neurotransmitter in the mammalian CNS, the precursor for the inhibitory neurotransmitter γ-aminobutyric acid, and one metabolic step from the tricarboxylic acid cycle intermediate α-ketoglutarate. Extracellular glutamate is cleared by a family of Na⁺-dependent transporters. These transporters are variably expressed by all cell types in the nervous system, but the bulk of clearance is into astrocytes. GLT-1 and GLAST (also called EAAT2 and EAAT1) mediate this activity and are extremely abundant proteins with their expression enriched in fine astrocyte processes. In this review, we will focus on three topics related to these astrocytic glutamate transporters. First, these transporters co-transport three Na⁺ ions and a H⁺ with each molecule of glutamate and counter-transport one K⁺; they are also coupled to a Cl^- conductance. The movement of Na⁺ is sufficient to cause profound astrocytic depolarization, and the movement of H⁺ is linked to astrocytic acidification. In addition, the movement of Na⁺ can trigger the activation of Na⁺ co-transporters (e.g. Na⁺-Ca²⁺ exchangers). We will describe the ways in which these ionic movements have been linked as signals to brain function and/or metabolism. Second, these transporters co-compartmentalize with mitochondria, potentially providing a mechanism to supply glutamate to mitochondria as a source of fuel for the brain. We will provide an overview of the proteins involved, discuss the evidence that glutamate is oxidized, and then highlight some of the un-resolved issues related to glutamate oxidation. Finally, we will review evidence that ischemic insults (stroke or oxygen/glucose deprivation) cause changes in these astrocytic mitochondria and discuss the ways in which these changes have been linked to glutamate transport, glutamate transport-dependent signaling, and altered glutamate metabolism. We conclude with a broader summary of some of the unresolved issues.

On the special role of NCX in astrocytes: Translating Na+-transients into intracellular Ca2+ signals

As a solute carrier electrogenic transporter, the sodium/calcium exchanger (NCX1-3/SLC8A1-A3) links the trans-plasmalemmal gradients of sodium and calcium ions (Na⁺, Ca²⁺) to the membrane potential of astrocytes. Classically, NCX is considered to serve the export of Ca²⁺ at the expense of the Na⁺ gradient, defined as a "forward mode" operation. Forward mode NCX activity contributes to Ca²⁺ extrusion and thus to the recovery from intracellular Ca²⁺ signals in astrocytes. The reversal potential of the NCX, owing to its transport stoichiometry of 3 Na⁺ to 1 Ca²⁺, is, however, close to the astrocytes' membrane potential and hence even small elevations in the astrocytic Na⁺ concentration or minor depolarisations switch it into the "reverse mode" (Ca²⁺ import/Na⁺ export). Notably, transient Na⁺ elevations in the millimolar range are induced by uptake of glutamate or GABA into astrocytes and/or by the opening of Na⁺-permeable ion channels in response to neuronal activity. Activity-related Na⁺ transients result in NCX reversal, which mediates Ca²⁺ influx from the extracellular space, thereby generating astrocyte Ca²⁺ signalling independent from InsP₃-mediated release from intracellular stores. Under pathological conditions, reverse NCX promotes cytosolic Ca²⁺ overload, while dampening Na⁺ elevations of astrocytes. This review provides an overview on our current knowledge about this fascinating transporter and its special functional role in astrocytes. We shall delineate that Na⁺-driven, reverse NCX-mediated astrocyte Ca²⁺ signals are involved neurone-glia interaction. Na⁺ transients, translated by the NCX into Ca²⁺ elevations, thereby emerge as a new signalling pathway in astrocytes.

Intracellular Neuroprotective Mechanisms in Neuron-Glial Networks Mediated by Glial Cell Line-Derived Neurotrophic Factor

Glial cell line-derived neurotrophic factor (GDNF) has a pronounced neuroprotective effect in various nervous system pathologies, including ischaemic brain damage and neurodegenerative diseases. In this work, we studied the effect of GDNF on the ultrastructure and functional activity of neuron-glial networks during acute hypoxic exposure, a key damaging factor in numerous brain pathologies. We analysed the molecular mechanisms most likely involved in the positive effects of GDNF. Hypoxia modelling was performed on day 14 of culturing primary hippocampal cells obtained from mouse embryos (E18). GDNF (1 ng/ml) was added to the culture medium 20 min before oxygen deprivation. Acute hypoxia-induced irreversible changes in the ultrastructure of neurons and astrocytes led to the loss of functional Сa²⁺ activity and neural network disruption. Destructive changes in the mitochondrial apparatus and its functional activity characterized by an increase in the basal oxygen consumption rate and respiratory chain complex II activity during decreased stimulated respiration intensity were observed 24 hours after hypoxic injury. At a concentration of 1 ng/ml, GDNF maintained the functional metabolic network activity in primary hippocampal cultures and preserved the structure of the synaptic apparatus and number of mature chemical synapses, confirming its neuroprotective effect. GDNF maintained the normal structure of mitochondria in neuronal outgrowth but not in the soma. Analysis of the possible GDNF mechanism revealed that RET kinase, a component of the receptor complex, and the PI3K/Akt pathway are crucial for the neuroprotective effect of GDNF. The current study also revealed the role of GDNF in the regulation of HIF-1α transcription factor expression under hypoxic conditions.

Reverse NCX Attenuates Cellular Sodium Loading in Metabolically Compromised Cortex

In core regions of ischemic stroke, disruption of blood flow causes breakdown of ionic gradients and, ultimately, calcium overload and cell death. In the surrounding penumbra, cells may recover upon reperfusion, but recovery is hampered by additional metabolic demands imposed by peri-infarct depolarizations (PIDs). There is evidence that sodium influx drives PIDs, but no data exist on PID-related sodium accumulations in vivo. Here, we found that PIDs in mouse neocortex are associated with propagating sodium elevations in neurons and astrocytes. Similar transient sodium elevations were induced in acute tissue slices by brief chemical ischemia. Blocking NMDA-receptors dampened sodium and accompanying calcium loads of neurons in tissue slices, while inhibiting glutamate transport diminished sodium influx into astrocytes, but amplified neuronal sodium loads. In both cell types, inhibition of sodium/calcium exchange (NCX) increased sodium transients. Blocking NCX also significantly reduced calcium transients, a result confirmed in vivo. Our study provides the first quantitative data on sodium elevations in peri-infarct regions in vivo. They suggest that sodium influx drives reversal of NCX, triggering a massive secondary calcium elevation while promoting export of sodium. Reported neuroprotective effects of NCX activity in stroke models might thus be related to its dampening of ischemia-induced sodium loading.

Hypoxia-reoxygenation of primary astrocytes results in a redistribution of mitochondrial size and mitophagy

Astrocytes serve to maintain proper neuronal function and support neuronal viability, but remain largely understudied in research of cerebral ischemia. Astrocytic mitochondria are core participants in the metabolic activity of astrocytes. The objective of this study is to assess astrocyte mitochondrial competence during hypoxia and post-hypoxia reoxygenation and to determine cellular adaptive and pathological changes in the mitochondrial network. We hypothesize that during metabolic distress in astrocytes; mitochondrial networks undergo a shift in fission-fusion dynamics that results in a change in the morphometric state of the entire mitochondrial network. This mitochondrial network shift may be protective during metabolic distress by priming mitochondrial size and facilitating mitophagy. We demonstrated that hypoxia and post-hypoxia reoxygenation of rat primary astrocytes results in a redistribution of mitochondria to smaller sizes evoked by increased mitochondrial fission. Excessive mitochondrial fission corresponded to Drp-1 dephosphorylation at Ser 637, which preceded mitophagy of relatively small mitochondria. Reoxygenation of astrocytes marked the initiation of elevated mitophagic activity primarily reserved to the perinuclear region where a large number of the smallest mitochondria occurred. Although, during hypoxia astrocytic ATP content was severely reduced, after reoxygenation ATP content returned to near normoxic values and these changes mirrored mitochondrial superoxide production. Concomitant with these changes in astrocytic mitochondria, the number of astrocytic extensions declined only after 10-hours post-hypoxic reoxygenation. Overall, we posit a drastic mitochondrial network change that is triggered by a metabolic crisis during hypoxia; these changes are followed by mitochondrial degradation and retraction of astrocytic extensions during reoxygenation.

The Role of Astrocytes in the Central Nervous System Focused on BK Channel and Heme Oxygenase Metabolites: A Review

Astrocytes outnumber neurons in the human brain, and they play a key role in numerous functions within the central nervous system (CNS), including glutamate, ion (i.e., Ca²⁺, K⁺) and water homeostasis, defense against oxidative/nitrosative stress, energy storage, mitochondria biogenesis, scar formation, tissue repair via angiogenesis and neurogenesis, and synapse modulation. After CNS injury, astrocytes communicate with surrounding neuronal and vascular systems, leading to the clearance of disease-specific protein aggregates, such as β-amyloid, and α-synuclein. The astrocytic big conductance K⁺ (BK) channel plays a role in these processes. Recently, potential therapeutic agents that target astrocytes have been tested for their potential to repair the brain. In this review, we discuss the role of the BK channel and antioxidant agents such as heme oxygenase metabolites following CNS injury. A better understanding of the cellular and molecular mechanisms of astrocytes’ functions in the healthy and diseased brains will greatly contribute to the development of therapeutic approaches following CNS injury, such as Alzheimer’s disease, Parkinson’s disease, and stroke.

Role of Astrocytic Mitochondria in Limiting Ischemic Brain Injury?

Until recently, astrocyte processes were thought to be too small to contain mitochondria. However, it is now clear that mitochondria are found throughout fine astrocyte processes and are mobile with neuronal activity resulting in positioning near synapses. In this review, we discuss evidence that astrocytic mitochondria confer selective resiliency to astrocytes during ischemic insults and the functional significance of these mitochondria for normal brain function.

Neutrophil-mediated and low density lipoprotein receptor-mediated dual-targeting nanoformulation enhances brain accumulation of scutellarin and exerts neuroprotective effects against ischemic stroke

Delivery of poorly permeable drugs across the blood-brain barrier (BBB) is a great challenge in the treatment of ischemic stroke.

Neurointegrity and neurophysiology: astrocyte, glutamate, and carbon monoxide interactions

Astrocyte contributions to brain function and prevention of neuropathologies are as extensive as that of neurons. Astroglial regulation of glutamate, a primary neurotransmitter, is through uptake, release through vesicular and non-vesicular pathways, and catabolism to intermediates. Homeostasis by astrocytes is considered to be of primary importance in determining normal central nervous system health and central nervous system physiology - glutamate is central to dynamic physiologic changes and central nervous system stability. Gasotransmitters may affect diverse glutamate interactions positively or negatively. The effect of carbon monoxide, an intrinsic central nervous system gasotransmitter, in the complex astrocyte homeostasis of glutamate may offer insights to normal brain development, protection, and its use as a neuromodulator and neurotherapeutic. In this article, we will review the effects of carbon monoxide on astrocyte homeostasis of glutamate.

Neurovascular dysfunction in vascular dementia, Alzheimer's and atherosclerosis

Efficient blood supply to the brain is of paramount importance to its normal functioning and improper blood flow can result in potentially devastating neurological consequences. Cerebral blood flow in response to neural activity is intrinsically regulated by a complex interplay between various cell types within the brain in a relationship termed neurovascular coupling. The breakdown of neurovascular coupling is evident across a wide variety of both neurological and psychiatric disorders including Alzheimer’s disease. Atherosclerosis is a chronic syndrome affecting the integrity and function of major blood vessels including those that supply the brain, and it is therefore hypothesised that atherosclerosis impairs cerebral blood flow and neurovascular coupling leading to cerebrovascular dysfunction. This review will discuss the mechanisms of neurovascular coupling in health and disease and how atherosclerosis can potentially cause cerebrovascular dysfunction that may lead to cognitive decline as well as stroke. Understanding the mechanisms of neurovascular coupling in health and disease may enable us to develop potential therapies to prevent the breakdown of neurovascular coupling in the treatment of vascular brain diseases including vascular dementia, Alzheimer’s disease and stroke.

Ca2+, Astrocyte Activation and Calcineurin/NFAT Signaling in Age-Related Neurodegenerative Diseases

Mounting evidence supports a fundamental role for Ca²⁺ dysregulation in astrocyte activation. Though the activated astrocyte phenotype is complex, cell-type targeting approaches have revealed a number of detrimental roles of activated astrocytes involving neuroinflammation, release of synaptotoxic factors and loss of glutamate regulation. Work from our lab and others has suggested that the Ca²⁺/calmodulin dependent protein phosphatase, calcineurin (CN), provides a critical link between Ca²⁺ dysregulation and the activated astrocyte phenotype. A proteolyzed, hyperactivated form of CN appears at high levels in activated astrocytes in both human tissue and rodent tissue around regions of amyloid and vascular pathology. Similar upregulation of the CN-dependent transcription factor nuclear factor of activated T cells (NFAT4) also appears in activated astrocytes in mouse models of Alzheimer's disease (ADs) and traumatic brain injury (TBI). Major consequences of hyperactivated CN/NFAT4 signaling in astrocytes are neuroinflammation, synapse dysfunction and glutamate dysregulation/excitotoxicity, which will be covered in this review article.

Assessment of cytosolic free calcium changes during ceramide-induced cell death in MDA-MB-231 breast cancer cells expressing the calcium sensor GCaMP6m

Alterations in Ca²⁺ signaling can regulate key cancer hallmarks such as proliferation, invasiveness and resistance to cell death. Changes in the regulation of intracellular Ca²⁺ and specific components of Ca²⁺ influx are a feature of several cancers and/or cancer subtypes, including the basal-like breast cancer subtype, which has a poor prognosis. The development of genetically encoded calcium indicators, such as GCaMP6, represents an opportunity to measure changes in intracellular free Ca²⁺ during processes relevant to breast cancer progression that occur over long periods (e.g. hours), such as cell death. This study describes the development of a MDA-MB-231 breast cancer cell line stably expressing GCaMP6m. The cell line retained the key features of this aggressive basal-like breast cancer cell line. Using this model, we defined alterations in relative cytosolic free Ca²⁺ ([Ca²⁺]_CYT) when the cells were treated with C2-ceramide. Cell death was measured simultaneously via assessment of propidium iodide permeability. Treatment with ceramide produced delayed and heterogeneous sustained increases in [Ca²⁺]_CYT. Where cell death occurred, [Ca²⁺]_CYT increases preceded cell death. The sustained increases in [Ca²⁺]_CYT were not related to the rapid morphological changes induced by ceramide. Silencing of the plasma membrane Ca²⁺ ATPase isoform 1 (PMCA1) was associated with an augmentation in ceramide-induced increases in [Ca²⁺]_CYT and also cell death. This work demonstrates the utility of GCaMP6 Ca²⁺ indicators for investigating [Ca²⁺]_CYT changes in breast cancer cells during events relevant to tumor progression, which occur over hours rather than minutes.

An Angiopep-2 functionalized nanoformulation enhances brain accumulation of tanshinone IIA and exerts neuroprotective effects against ischemic stroke

Effective intervention against ischemic stroke requires delivery of potent neuroprotective drugs to the brain.

Neutrophil affinity for PGP and HAIYPRH (T7) peptide dual-ligand functionalized nanoformulation enhances the brain delivery of tanshinone IIA and exerts neuroprotective effects against ischemic stroke by inhibiting proinflammatory signaling pathways

A great challenge to the therapy of ischemic stroke is the poor physicochemical properties and inability of the drug to cross the blood–brain barrier (BBB).

Regulation of mitochondrial dynamics in astrocytes: Mechanisms, consequences, and unknowns

Astrocytes are the major glial cell in the central nervous system. These polarized cells possess numerous processes that ensheath the vasculature and contact synapses. Astrocytes play important roles in synaptic signaling, neurotransmitter synthesis and recycling, control of nutrient uptake, and control of local blood flow. Many of these processes depend on local metabolism and/or energy utilization. While astrocytes respond to increases in neuronal activity and metabolic demand by upregulating glycolysis and glycogenolysis, astrocytes also possess significant capacity for oxidative (mitochondrial) metabolism. Mitochondria mediate energy supply and metabolism, cellular survival, ionic homeostasis, and proliferation. These organelles are dynamic structures undergoing extensive fission and fusion, directed movement along cytoskeletal tracts, and degradation. While many of the mechanisms underlying the dynamics of these organelles and their physiologic roles have been characterized in neurons and other cells, the roles that mitochondrial dynamics play in glial physiology is less well understood. Recent work from several laboratories has demonstrated that mitochondria are present within the fine processes of astrocytes, that their movement is regulated, and that they contribute to local Ca²⁺ signaling within the astrocyte. They likely play a role in local ATP production and metabolism, particularly that of glutamate. Here we will review these and other findings describing the mechanism by which mitochondrial dynamics are regulated in astrocytes, how mitochondrial dynamics might influence astrocyte and brain metabolism, and draw parallels to mitochondrial dynamics in neurons. Additionally, we present new analyses of the size, distribution, and dynamics of mitochondria in astrocytes performed using in vivo using 2-photon microscopy.

MEK/ERK- and calcineurin/NFAT-mediated mechanism of cerebral hyperemia and brain injury following NMDA receptor activation

N-methyl-d-aspartate (NMDA) receptor activation increases regional cerebral blood flow (rCBF) and induces neuronal injury, but similarities between these processes are poorly understood. In this study, by measuring rCBF in vivo, we identified a clear correlation between cerebral hyperemia and brain injury. NMDA receptor activation induced brain injury as a result of rCBF increase, which was attenuated by an inhibitor of mitogen-activated protein kinase or calcineurin. Moreover, NMDA induced phosphorylation of extracellular signal-regulated kinase (ERK) and nuclear translocation of nuclear factor of activated T-cell (NFAT) in neurons. Therefore, a MEK/ERK- and calcineurin/NFAT-mediated mechanism of neurovascular coupling underlies the pathophysiology of neurovascular disorders.

Local energy on demand: Are 'spontaneous' astrocytic Ca2+-microdomains the regulatory unit for astrocyte-neuron metabolic cooperation?

Astrocytes are a neural cell type critically involved in maintaining brain energy homeostasis as well as signaling. Like neurons, astrocytes are a heterogeneous cell population. Cortical astrocytes show a complex morphology with a highly branched aborization and numerous fine processes ensheathing the synapses of neighboring neurons, and typically extend one process connecting to blood vessels. Recent studies employing genetically encoded fluorescent calcium (Ca²⁺) indicators have described 'spontaneous' localized Ca²⁺-transients in the astrocyte periphery that occur asynchronously, independently of signals in other parts of the cells, and that do not involve somatic Ca²⁺ transients; however, neither it is known whether these Ca²⁺-microdomains occur at or near neuronal synapses nor have their molecular basis nor downstream effector(s) been identified. In addition to Ca²⁺ microdomains, sodium (Na⁺) transients occur in astrocyte subdomains, too, most likely as a consequence of Na⁺ co-transport with the neurotransmitter glutamate, which also regulates mitochondrial movements locally - as do cytoplasmic Ca²⁺ levels. In this review, we cover various aspects of these local signaling events and discuss how structural and biophysical properties of astrocytes might foster such compartmentation. Astrocytes metabolically interact with neurons by providing energy substrates to active neurons. As a single astrocyte branch covers hundreds to thousands of synapses, it is tempting to speculate that these metabolic interactions could occur localized to specific subdomains of astrocytes, perhaps even at the level of small groups of synapses. We discuss how astrocytic metabolism might be regulated at this scale and which signals might contribute to its regulation. We speculate that the astrocytic structures that light up transiently as Ca²⁺-microdomains might be the functional units of astrocytes linking signaling and metabolic processes to adapt astrocytic function to local energy demands. The understanding of these local regulatory and metabolic interactions will be fundamental to fully appreciate the complexity of brain energy homeostasis as well as its failure in disease and may shed new light on the controversy about neuron-glia bi-directional signaling at the tripartite synapse.

Genetically Encoded Calcium Indicators as Probes to Assess the Role of Calcium Channels in Disease and for High-Throughput Drug Discovery

The calcium ion (Ca²⁺) is an important signaling molecule implicated in many cellular processes, and the remodeling of Ca²⁺ homeostasis is a feature of a variety of pathologies. Typical methods to assess Ca²⁺ signaling in cells often employ small molecule fluorescent dyes, which are sometimes poorly suited to certain applications such as assessment of cellular processes, which occur over long periods (hours or days) or in vivo experiments. Genetically encoded calcium indicators are a set of tools available for the measurement of Ca²⁺ changes in the cytosol and subcellular compartments, which circumvent some of the inherent limitations of small molecule Ca²⁺ probes. Recent advances in genetically encoded calcium sensors have greatly increased their ability to provide reliable monitoring of Ca²⁺ changes in mammalian cells. New genetically encoded calcium indicators have diverse options in terms of targeting, Ca²⁺ affinity and fluorescence spectra, and this will further enhance their potential use in high-throughput drug discovery and other assays. This review will outline the methods available for Ca²⁺ measurement in cells, with a focus on genetically encoded calcium sensors. How these sensors will improve our understanding of the deregulation of Ca²⁺ handling in disease and their application to high-throughput identification of drug leads will also be discussed.