New roles for astrocytes: redefining the functional architecture of the brain

Bi-directionally protective communication between neurons and astrocytes under ischemia

The extensive existing knowledge on bi-directional communication between astrocytes and neurons led us to hypothesize that not only ischemia-preconditioned (IP) astrocytes can protect neurons but also IP neurons protect astrocytes from lethal ischemic injury. Here, we demonstrated for the first time that neurons have a significant role in protecting astrocytes from ischemic injury. The cultured medium from IP neurons (IPcNCM) induced a remarkable reduction in LDH and an increase in cell viability in ischemic astrocytes in vitro. Selective neuronal loss by kainic acid injection induced a significant increase in apoptotic astrocyte numbers in the brain of ischemic rats in vivo. Furthermore, TUNEL analysis, DNA ladder assay, and the measurements of ROS, GSH, pro- and anti-apoptotic factors, anti-oxidant enzymes and signal molecules in vitro and/or in vivo demonstrated that IP neurons protect astrocytes by an EPO-mediated inhibition of pro-apoptotic signals, activation of anti-apoptotic proteins via the P13K/ERK/STAT5 pathways and activation of anti-oxidant proteins via up-regulation of anti-oxidant enzymes. We demonstrated the existence of astro-protection by IP neurons under ischemia and proposed that the bi-directionally protective communications between cells might be a common activity in the brain or peripheral organs under most if not all pathological conditions.

Streptozotocin alters glucose transport, connexin expression and endoplasmic reticulum functions in neurons and astrocytes

The study was undertaken to explore the cell-specific streptozotocin (STZ)-induced mechanistic alterations. STZ-induced rodent model is a well-established experimental model of Alzheimer's disease (AD) and in our previous studies we have established it as an in vitro screening model of AD by employing N2A neuronal cells. Therefore, STZ was selected in the present study to understand the STZ-induced cell-specific alterations by utilizing neuronal N2A and astrocytes C6 cells. Both neuronal and astrocyte cells were treated with STZ at 10, 50, 100 and 1000μM concentrations for 48h. STZ exposure caused significant decline in cellular viability and augmented cytotoxicity of cells involving astrocytes activation. STZ treatment also disrupted the energy metabolism by altered glucose uptake and its transport in both cells as reflected with decreased expression of glucose transporters (GLUT) 1/3. The consequent decrease in ATP level and decreased mitochondrial membrane potential was also observed in both the cells. STZ caused increased intracellular calcium which could cause the initiation of endoplasmic reticulum (ER) stress. Significant upregulation of ER stress-related markers were observed in both cells after STZ treatment. The cellular communication of astrocytes and neurons was altered as reflected by increased expression of connexin 43 along with DNA fragmentation. STZ-induced apoptotic death was evaluated by elevated expression of caspase-3 and PI/Hoechst staining of cells. In conclusion, study showed that STZ exert alike biochemical alterations, ER stress and cellular apoptosis in both neuronal and astrocyte cells.

Post-Translational Tubulin Modifications in Human Astrocyte Cultures

The cytoskeletal protein tubulin plays an integral role in the functional specialization of many cell types. In the central nervous system, post-translational modifications and the expression of specific tubulin isotypes in neurons have been analyzed in greater detail than in their astrocytic counterparts. In this study, we characterized post-translational specifications of tubulin in human astrocytes using the normal human astrocyte (NHA; Lonza) commercial cell line of fetal origin. Immunocytochemical techniques were implemented in conjunction with confocal microscopy to image class III β-tubulin (βIII-tubulin), acetylated tubulin, and polyglutamylated tubulin using fluorescent antibody probes. Fluorescent probe intensity differences and colocalization were quantitatively assessed with the 'EBImage' package for the statistical programming language R. Colocalization analysis revealed that, although both acetylated tubulin and polyglutamylated tubulin showed a high degree of correlation with βIII-tubulin, the correlation with acetylated tubulin was stronger. Quantification and statistical analysis of fluorescence intensity demonstrated that the fluorescence probe intensity ratio for acetylated tubulin/βIII-tubulin was greater than the ratio for polyglutamylated tubulin/βIII-tubulin. The open source GEODATA set GSE819950, comprising RNA sequencing data for the NHA cell line, was mined for the expression of enzymes responsible for tubulin modifications. Our analysis uncovered greater expression at the mRNA level for enzymes reported to function in acetylation and deacetylation as compared to enzymes implicated in glutamylation and deglutamylation. Taken together, the results represent a step toward unraveling the tubulin isotypic expression profile and post-translational modification patterns in astrocytes during human brain development.

Astrocytic Process Plasticity and IKKβ/NF-κB in Central Control of Blood Glucose, Blood Pressure, and Body Weight

Central regulation of metabolic physiology is mediated critically through neuronal functions; however, whether astrocytes are also essential remains unclear. Here we show that the high-order processes of astrocytes in the mediobasal hypothalamus displayed shortening in fasting and elongation in fed status. Chronic overnutrition and astrocytic IKKβ/NF-κB upregulation similarly impaired astrocytic plasticity, leading to sustained shortening of high-order processes. In physiology, astrocytic IKKβ/NF-κB upregulation resulted in early-onset effects, including glucose intolerance and blood pressure rise, and late-onset effects, including body weight and fat gain. Appropriate inhibition in astrocytic IKKβ/NF-κB protected against chronic overnutrition impairing astrocytic plasticity and these physiological functions. Mechanistically, astrocytic regulation of hypothalamic extracellular GABA level and therefore BDNF expression were found partly accountable. Hence, astrocytic process plasticity and IKKβ/NF-κB play significant roles in central control of blood glucose, blood pressure, and body weight as well as the central induction of these physiological disorders leading to disease.

Mathematical investigation of IP3-dependent calcium dynamics in astrocytes

We study evoked calcium dynamics in astrocytes, a major cell type in the mammalian brain. Experimental evidence has shown that such dynamics are highly variable between different trials, cells, and cell subcompartments. Here we present a qualitative analysis of a recent mathematical model of astrocyte calcium responses. We show how the major response types are generated in the model as a result of the underlying bifurcation structure. By varying key channel parameters, mimicking blockers used by experimentalists, we manipulate this underlying bifurcation structure and predict how the distributions of responses can change. We find that store-operated calcium channels, plasma membrane bound channels with little activity during calcium transients, have a surprisingly strong effect, underscoring the importance of considering these channels in both experiments and mathematical settings. Variation in the maximum flow in different calcium channels is also shown to determine the range of stable oscillations, as well as set the range of frequencies of the oscillations. Further, by conducting a randomized search through the parameter space and recording the resulting calcium responses, we create a database that can be used by experimentalists to help estimate the underlying channel distribution of their cells.

SOX9 Is an Astrocyte-Specific Nuclear Marker in the Adult Brain Outside the Neurogenic Regions

Astrocytes have in recent years become the focus of intense experimental interest, yet markers for their definitive identification remain both scarce and imperfect. Astrocytes may be recognized as such by their expression of glial fibrillary acidic protein, glutamine synthetase, glutamate transporter 1 (GLT1), aquaporin-4, aldehyde dehydrogenase 1 family member L1, and other proteins. However, these proteins may all be regulated both developmentally and functionally, restricting their utility. To identify a nuclear marker pathognomonic of astrocytic phenotype, we assessed differential RNA expression by FACS-purified adult astrocytes and, on that basis, evaluated the expression of the transcription factor SOX9 in both mouse and human brain. We found that SOX9 is almost exclusively expressed by astrocytes in the adult brain except for ependymal cells and in the neurogenic regions, where SOX9 is also expressed by neural progenitor cells. Transcriptome comparisons of SOX9+ cells with GLT1+ cells showed that the two populations of cells exhibit largely overlapping gene expression. Expression of SOX9 did not decrease during aging and was instead upregulated by reactive astrocytes in a number of settings, including a murine model of amyotrophic lateral sclerosis (SOD1G93A), middle cerebral artery occlusion, and multiple mini-strokes. We quantified the relative number of astrocytes using the isotropic fractionator technique in combination with SOX9 immunolabeling. The analysis showed that SOX9+ astrocytes constitute ∼10-20% of the total cell number in most CNS regions, a smaller fraction of total cell number than previously estimated in the normal adult brain.SIGNIFICANCE STATEMENT Astrocytes are traditionally identified immunohistochemically by antibodies that target cell-specific antigens in the cytosol or plasma membrane. We show here that SOX9 is an astrocyte-specific nuclear marker in all major areas of the CNS outside of the neurogenic regions. Based on SOX9 immunolabeling, we document that astrocytes constitute a smaller fraction of total cell number than previously estimated in the normal adult mouse brain.

Non-Neuronal Cells in the Hypothalamic Adaptation to Metabolic Signals

Although the brain is composed of numerous cell types, neurons have received the vast majority of attention in the attempt to understand how this organ functions. Neurons are indeed fundamental but, in order for them to function correctly, they rely on the surrounding "non-neuronal" cells. These different cell types, which include glia, epithelial cells, pericytes, and endothelia, supply essential substances to neurons, in addition to protecting them from dangerous substances and situations. Moreover, it is now clear that non-neuronal cells can also actively participate in determining neuronal signaling outcomes. Due to the increasing problem of obesity in industrialized countries, investigation of the central control of energy balance has greatly increased in attempts to identify new therapeutic targets. This has led to interesting advances in our understanding of how appetite and systemic metabolism are modulated by non-neuronal cells. For example, not only are nutrients and hormones transported into the brain by non-neuronal cells, but these cells can also metabolize these metabolic factors, thus modifying the signals reaching the neurons. The hypothalamus is the main integrating center of incoming metabolic and hormonal signals and interprets this information in order to control appetite and systemic metabolism. Hence, the factors transported and released from surrounding non-neuronal cells will undoubtedly influence metabolic homeostasis. This review focuses on what is known to date regarding the involvement of different cell types in the transport and metabolism of nutrients and hormones in the hypothalamus. The possible involvement of non-neuronal cells, in particular glial cells, in physiopathological outcomes of poor dietary habits and excess weight gain are also discussed.

Astroglial Ca2+ signaling is generated by the coordination of IP3R and store-operated Ca2+ channels

Astrocytes play key roles in the central nervous system and regulate local blood flow and synaptic transmission via intracellular calcium (Ca²⁺) signaling. Astrocytic Ca²⁺ signals are generated by multiple pathways: Ca²⁺ release from the endoplasmic reticulum (ER) via the inositol 1, 4, 5-trisphosphate receptor (IP₃R) and Ca²⁺ influx through various Ca²⁺ channels on the plasma membrane. However, the Ca²⁺ channels involved in astrocytic Ca²⁺ homeostasis or signaling have not been fully characterized. Here, we demonstrate that spontaneous astrocytic Ca²⁺ transients in cultured hippocampal astrocytes were induced by cooperation between the Ca²⁺ release from the ER and the Ca²⁺ influx through store-operated calcium channels (SOCCs) on the plasma membrane. Ca²⁺ imaging with plasma membrane targeted GCaMP6f revealed that spontaneous astroglial Ca²⁺ transients were impaired by pharmacological blockade of not only Ca²⁺ release through IP₃Rs, but also Ca²⁺ influx through SOCCs. Loss of SOCC activity resulted in the depletion of ER Ca²⁺, suggesting that SOCCs are activated without store depletion in hippocampal astrocytes. Our findings indicate that sustained SOCC activity, together with that of the sarco-endoplasmic reticulum Ca²⁺-ATPase, contribute to the maintenance of astrocytic Ca²⁺ store levels, ultimately enabling astrocytic Ca²⁺ signaling.

The antidiabetic drug metformin decreases mitochondrial respiration and tricarboxylic acid cycle activity in cultured primary rat astrocytes

Metformin is an antidiabetic drug that is used daily by millions of patients worldwide. Metformin is able to cross the blood-brain barrier and has recently been shown to increase glucose consumption and lactate release in cultured astrocytes. However, potential effects of metformin on mitochondrial tricarboxylic acid (TCA) cycle metabolism in astrocytes are unknown. We investigated this by mapping ¹³ C labeling in TCA cycle intermediates and corresponding amino acids after incubation of primary rat astrocytes with [U-¹³ C]glucose. The presence of metformin did not compromise the viability of cultured astrocytes during 4 hr of incubation, but almost doubled cellular glucose consumption and lactate release. Compared with control cells, the presence of metformin dramatically lowered the molecular ¹³ C carbon labeling (MCL) of the cellular TCA cycle intermediates citrate, α-ketoglutarate, succinate, fumarate, and malate, as well as the MCL of the TCA cycle intermediate-derived amino acids glutamate, glutamine, and aspartate. In addition to the total molecular ¹³ C labeling, analysis of the individual isotopomers of TCA cycle intermediates confirmed a severe decline in labeling and a significant lowering in TCA cycling ratio in metformin-treated astrocytes. Finally, the oxygen consumption of mitochondria isolated from metformin-treated astrocytes was drastically reduced in the presence of complex I substrates, but not of complex II substrates. These data demonstrate that exposure to metformin strongly impairs complex I-mediated mitochondrial respiration in astrocytes, which is likely to cause the observed decrease in labeling of mitochondrial TCA cycle intermediates and the stimulation of glycolytic lactate production. © 2017 Wiley Periodicals, Inc.

Astrocyte heme oxygenase-1 reduces mortality and improves outcome after collagenase-induced intracerebral hemorrhage

Pharmacotherapies that increase CNS expression of heme oxygenase-1 (HO-1) and other antioxidant proteins have improved outcome in experimental models of spontaneous intracerebral hemorrhage (ICH). In order to more specifically investigate the relationship between HO-1 and ICH outcome, mice expressing human HO-1 driven by the glial fibrillary acidic protein (GFAP) promoter (GFAP·HMOX1 mice) were tested in a model of in situ parenchymal hemorrhage. Injection of collagenase into the striata of wild-type (WT) mice resulted in a 26.3% mortality rate, with deaths equally distributed between males and females. Mortality was reduced to 4.48% in GFAP·HMOX1 mice. Cell viability in the injected striata of surviving WT mice was reduced by about half at one week and was significantly increased in transgenics; this benefit persisted over a 22day observation period. Cell counts guided by design-based stereology indicated loss of ~40% of neurons in WT hemorrhagic striata at one week, which was decreased by half in transgenics; no significant differences in microglia or astrocyte numbers were observed. Blood-brain barrier disruption and short-term neurological deficits were also mitigated in GFAP·HMOX1 mice, but long-term outcome did not differ from that of WT survivors. These results suggest that astrocyte HO-1 overexpression provides robust neuroprotection after acute intracerebral hemorrhage. Further investigation of drug or genetic therapies that selectively increase astrocyte HO-1 is warranted.

The Triangle of Death in Alzheimer's Disease Brain: The Aberrant Cross-Talk Among Energy Metabolism, Mammalian Target of Rapamycin Signaling, and Protein Homeostasis Revealed by Redox Proteomics

SIGNIFICANCE

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder and represents one of the most disabling conditions. AD shares many features in common with systemic insulin resistance diseases, suggesting that it can be considered as a metabolic disease, characterized by reduced insulin-stimulated growth and survival signaling, increased oxidative stress (OS), proinflammatory cytokine activation, mitochondrial dysfunction, impaired energy metabolism, and altered protein homeostasis. Recent Advances: Reduced glucose utilization and energy metabolism in AD have been associated with the buildup of amyloid-β peptide and hyperphosphorylated tau, increased OS, and the accumulation of unfolded/misfolded proteins. Mammalian target of rapamycin (mTOR), which is aberrantly activated in AD since early stages, plays a key role during AD neurodegeneration by, on one side, inhibiting insulin signaling as a negative feedback mechanism and, on the other side, regulating protein homeostasis (synthesis/clearance).

CRITICAL ISSUES

It is likely that the concomitant and mutual alterations of energy metabolism-mTOR signaling-protein homeostasis might represent a self-sustaining triangle of harmful events that trigger the degeneration and death of neurons and the development and progression of AD. Intriguingly, the altered cross-talk between the components of such a triangle of death, beyond altering the redox homeostasis of the neuron, is further exacerbated by increased levels of OS that target and impair key components of the pathways involved. Redox proteomic studies in human samples and animal models of AD-like dementia led to identification of oxidatively modified components of the pathways composing the triangle of death, therefore revealing the crucial role of OS in fueling this aberrant vicious cycle.

FUTURE DIRECTIONS

The identification of compounds able to restore the function of the pathways targeted by oxidative damage might represent a valuable therapeutic approach to slow or delay AD. Antioxid. Redox Signal. 26, 364-387.

Astrocytic modulation of neuronal excitability through K+ spatial buffering

The human brain contains two major cell populations, neurons and glia. While neurons are electrically excitable and capable of discharging short voltage pulses known as action potentials, glial cells are not. However, astrocytes, the prevailing subtype of glia in the cortex, are highly connected and can modulate the excitability of neurons by changing the concentration of potassium ions in the extracellular environment, a process called K⁺ clearance. During the past decade, astrocytes have been the focus of much research, mainly due to their close association with synapses and their modulatory impact on neuronal activity. It has been shown that astrocytes play an essential role in normal brain function including: nitrosative regulation of synaptic release in the neocortex, synaptogenesis, synaptic transmission and plasticity. Here, we discuss the role of astrocytes in network modulation through their K⁺ clearance capabilities, a theory that was first raised 50 years ago by Orkand and Kuffler. We will discuss the functional alterations in astrocytic activity that leads to aberrant modulation of network oscillations and synchronous activity.

Neuropathophysiology of Brain Injury

Every year in the United States, millions of individuals incur ischemic brain injury from stroke, cardiac arrest, or traumatic brain injury. These acquired brain injuries can lead to death or long-term neurologic and neuropsychological impairments. The mechanisms of ischemic and traumatic brain injury that lead to these deficiencies result from a complex interplay of interdependent molecular pathways, including excitotoxicity, acidotoxicity, ionic imbalance, oxidative stress, inflammation, and apoptosis. This article reviews several mechanisms of brain injury and discusses recent developments. Although much is known from animal models of injury, it has been difficult to translate these effects to humans.

Involvement of Normalized Glial Fibrillary Acidic Protein Expression in the Hippocampi in Antidepressant-Like Effects of Xiaoyaosan on Chronically Stressed Mice

The research has only yielded a partial comprehension of MDD and the mechanisms underlying the antidepressant-like effects of XYS. Therefore, in this study, we aimed to explore the effects of XYS on chronic unpredictable mild stress- (CUMS-) induced changes in the neuronal and the astrocytic markers in the mouse hippocampus. The physical states and depressive-like behaviors in mice with CUMS were recorded. The serum contents of brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) were measured. The protein and mRNA expressions and the immunoreactivities of glial fibrillary acidic protein (GFAP) and neuronal nuclei (NeuN) in mouse hippocampus were detected using a Western blot, qRT-PCR, and immunohistochemical staining, respectively. XYS treatment markedly improved the physical state and depressive-like behaviors in mice subjected to CUMS compared with the model group, and the serum contents of BDNF and GDNF were significantly upregulated. XYS treatment also elevated the protein and mRNA levels, as well as the immunoreactivity of GFAP in the hippocampus. However, CUMS did not influence NeuN expression. In conclusion, these results reveal that chronic administration of XYS elicits antidepressant-like effects in a mouse model of depression and may normalize glial fibrillary acidic protein expression in the hippocampi of mice with CUMS.

Vulnerability of primary neurons derived from Tg2576 Alzheimer mice to oxygen and glucose deprivation: role of intraneuronal amyloid-β accumulation and astrocytes

Microvascular dysfunction is considered an integral part of Alzheimer disease (AD) pathogenesis, but the possible relationship between amyloid pathology, microvascular dysfunction and cell death is still unclear. In order to investigate the influence of intraneuronal amyloid-β (Aβ) accumulation on vulnerability to hypoxia, we isolated primary cortical neurons from Tg2576 (carrying the amyloid precursor protein APPSwe mutation) and wild-type fetal mice. We first demonstrated that neurons isolated from Tg2576 newborn mice show an increase in VEGFa mRNA expression and a decrease in the expression of the two VEGF receptors, Flt1 and Kdr, compared with wild-type cells. Moreover, APPSwe primary neurons displayed higher spontaneous and glutamate-induced cell death. We then deprived the cultures of oxygen and glucose (OGD) as an in vitro model of hypoxia. After OGD, APPSwe neurons display higher levels of cell death in terms of percentage of pyknotic/fragmented nuclei and mitochondrial depolarization, accompanied by an increase in the intraneuronal Aβ content. To explore the influence of intraneuronal Aβ peptide accumulation, we used the γ-secretase inhibitor LY450139, which showed that the reduction of the intracellular amyloid fully protects APPSwe neurons from OGD-induced degeneration. Conditioned medium from OGD-exposed APPSwe or wild-type astrocytes protected APPswe neurons but not wild-type neurons, during OGD. In conclusion, the presence of the mutated human APP gene, leading to the intracellular accumulation of APP and Aβ fragments, worsens OGD toxicity. Protection of APPSwe neurons can be obtained either using a γ-secretase inhibitor or astrocyte conditioned medium.

Summary:In vitro systems derived from AD mice can be used to investigate the vulnerability of AD neurons to different neurotoxic challenges, including oxygen glucose deprivation.

Astrocytic Orosomucoid-2 Modulates Microglial Activation and Neuroinflammation

Orosomucoid (ORM) is an acute-phase protein that belongs to the immunocalin subfamily, a group of small-molecule-binding proteins with immunomodulatory functions. Little is known about the role of ORM proteins in the CNS. The aim of the present study was to investigate the brain expression of ORM and its role in neuroinflammation. Expression of Orm2, but not Orm1 or Orm3, was highly induced in the mouse brain after systemic injection of lipopolysaccharide (LPS). Plasma levels of ORM2 were also significantly higher in patients with cognitive impairment than in normal subjects. RT-PCR, Western blot, and immunofluorescence analyses revealed that astrocytes are the major cellular sources of ORM2 in the inflamed mouse brain. Recombinant ORM2 protein treatment decreased microglial production of proinflammatory mediators and reduced microglia-mediated neurotoxicity in vitro LPS-induced microglial activation, proinflammatory cytokines in hippocampus, and neuroinflammation-associated cognitive deficits also decreased as a result of intracerebroventricular injection of recombinant ORM2 protein in vivo Moreover, lentiviral shRNA-mediated Orm2 knockdown enhanced LPS-induced proinflammatory cytokine gene expression and microglial activation in the hippocampus. Mechanistically, ORM2 inhibited C-C chemokine ligand 4 (CCL4)-induced microglial migration and activation by blocking the interaction of CCL4 with C-C chemokine receptor type 5. Together, the results from our cultured glial cells, mouse neuroinflammation model, and patient studies suggest that ORM2 is a novel mediator of astrocyte-microglial interaction. We also report that ORM2 exerts anti-inflammatory effects by modulating microglial activation and migration during brain inflammation. ORM2 can be exploited therapeutically for the treatment of neuroinflammatory diseases.SIGNIFICANCE STATEMENT Neural cell interactions are important for brain physiology and pathology. Particularly, the interaction between non-neuronal cells plays a central role in regulating brain inflammation, which is closely linked to many brain disorders. Here, we newly identified orosomucoid-2 (ORM2) as an endogenous protein that mediates such non-neuronal glial cell interactions. Based on the critical role of astrocyte-derived ORM2 in modulating microglia-mediated neuroinflammation, ORM2 can be exploited for the diagnosis, prevention, or treatment of devastating brain disorders that have a strong neuroinflammatory component, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis.

Nutrition, Health, and Regulatory Aspects of Digestible Maltodextrins

Digestible maltodextrins are low-sweet saccharide polymers consisting of D-glucose units linked primarily linearly with alpha-1,4 bonds, but can also have a branched structure through alpha-1,6 bonds. Often, maltodextrins are classified by the amount of reducing sugars present relative to the total carbohydrate content; between 3 and 20 percent in the case of digestible maltodextrins. These relatively small polymers are used as food ingredients derived by hydrolysis from crops naturally rich in starch. Through advances in production technology, the application possibilities in food products have improved during the last 20 years. However, since glucose from digested maltodextrins is rapidly absorbed in the small intestine, the increased use has raised questions about potential effects on metabolism and health. Therefore, up-to-date knowledge concerning production, digestion, absorption, and metabolism of maltodextrins, including potential effects on health, were reviewed. Exchanging unprocessed starch with maltodextrins may lead to an increased glycemic load and therefore post meal glycaemia, which are viewed as less desirable for health. Apart from beneficial food technological properties, its use should accordingly also be viewed in light of this. Finally, this review reflects on regulatory aspects, which differ significantly in Europe and the United States, and, therefore, have implications for communication and marketing.

Astrocyte-neuron interaction in diphenyl ditelluride toxicity directed to the cytoskeleton

Diphenylditelluride (PhTe)₂ is a neurotoxin that disrupts cytoskeletal homeostasis. We are showing that different concentrations of (PhTe)₂ caused hypophosphorylation of glial fibrillary acidic protein (GFAP), vimentin and neurofilament subunits (NFL, NFM and NFH) and altered actin organization in co-cultured astrocytes and neurons from cerebral cortex of rats. These mechanisms were mediated by N-methyl-d-aspartate (NMDA) receptors without participation of either L-type voltage-dependent calcium channels (L-VDCC) or metabotropic glutamate receptors. Upregulated Ca²⁺ influx downstream of NMDA receptors activated Ca²⁺-dependent protein phosphatase 2B (PP2B) causing hypophosphorylation of astrocyte and neuron IFs. Immunocytochemistry showed that hypophosphorylated intermediate filaments (IF) failed to disrupt their organization into the cytoskeleton. However, phalloidin-actin-FITC stained cytoskeleton evidenced misregulation of actin distribution, cell spreading and increased stress fibers in astrocytes. βIII tubulin staining showed that neurite meshworks are not altered by (PhTe)₂, suggesting greater susceptibility of astrocytes than neurons to (PheTe)₂ toxicity. These findings indicate that signals leading to IF hypophosphorylation fail to disrupt the cytoskeletal IF meshwork of interacting astrocytes and neurons in vitro however astrocyte actin network seems more susceptible. Our findings support that intracellular Ca²⁺ is one of the crucial signals that modulate the action of (PhTe)₂ in co-cultured astrocytes and neurons and highlights the cytoskeleton as an end-point of the neurotoxicity of this compound. Cytoskeletal misregulation is associated with cell dysfunction, therefore, the understanding of the molecular mechanisms mediating the neurotoxicity of this compound is a matter of increasing interest since tellurium compounds are increasingly released in the environment.

An improved method for growing neurons: Comparison with standard protocols

BACKGROUND

Since different culturing parameters - such as media composition or cell density - lead to different experimental results, it is important to define the protocol used for neuronal cultures. The vital role of astrocytes in maintaining homeostasis of neurons - both in vivo and in vitro - is well established: the majority of improved culturing conditions for primary dissociated neuronal cultures rely on astrocytes.

NEW METHOD

Our culturing protocol is based on a novel serum-free preparation of astrocyte - conditioned medium (ACM). We compared the proposed ACM culturing method with other two commonly used methods Neurobasal/B27- and FBS- based media. We performed morphometric characterization by immunocytochemistry and functional analysis by calcium imaging for all three culture methods at 1, 7, 14 and 60days in vitro (DIV).

RESULTS

ACM-based cultures gave the best results for all tested criteria, i.e. growth cone's size and shape, neuronal outgrowth and branching, network activity and synchronization, maturation and long-term survival. The differences were more pronounced when compared with FBS-based medium. Neurobasal/B27 cultures were comparable to ACM for young cultures (DIV1), but not for culturing times longer than DIV7.

COMPARISON WITH EXISTING METHOD(S)

ACM-based cultures showed more robust neuronal outgrowth at DIV1. At DIV7 and 60, the activity of neuronal network grown in ACM had a more vigorous spontaneous electrical activity and a higher degree of synchronization.

CONCLUSIONS

We propose our ACM-based culture protocol as an improved and more suitable method for both short- and long-term neuronal cultures.

Differential hypothalamic leptin sensitivity in obese rat offspring exposed to maternal and postnatal intake of chocolate and soft drink

Background/objective:

Intake of high-energy foods and maternal nutrient overload increases the risk of metabolic diseases in the progeny such as obesity and diabetes. We hypothesized that maternal and postnatal intake of chocolate and soft drink will affect leptin sensitivity and hypothalamic astrocyte morphology in adult rat offspring.

Methods:

Pregnant Sprague-Dawley rats were fed ad libitum chow diet only (C) or with chocolate and high sucrose soft drink supplement (S). At birth, litter size was adjusted into 10 male offspring per mother. After weaning, offspring from both dietary groups were assigned to either S or C diet, giving four groups until the end of the experiment at 26 weeks of age.

Results:

As expected, adult offspring fed the S diet post weaning became obese (body weight: P<0.01, %body fat per kg: P<0.001) and this was due to the reduced energy expenditure (P<0.05) and hypothalamic astrogliosis (P<0.001) irrespective of maternal diet. Interesting, offspring born to S-diet-fed mothers and fed the S diet throughout postnatal life became obese despite lower energy intake than controls (P<0.05). These SS offspring showed increased feed efficiency (P<0.001) and reduced fasting pSTAT3 activity (P<0.05) in arcuate nucleus (ARC) compared with other groups. The findings indicated that the combination of the maternal and postnatal S-diet exposure induced persistent changes in leptin signalling, hence affecting energy balance. Thus, appetite regulation was more sensitive to the effect of leptin than energy expenditure, suggesting differential programming of leptin sensitivity in ARC in SS offspring. Effects of the maternal S diet were normalized when offspring were fed a chow diet after weaning.

Conclusions:

Maternal intake of chocolate and soft drink had long-term consequences for the metabolic phenotype in the offspring if they continued on the S diet in postnatal life. These offspring displayed obesity despite lowered energy intake associated with alterations in hypothalamic leptin signalling.

Interactions with Astroglia Influence the Shape of the Developing Dendritic Arbor and Restrict Dendrite Growth Independent of Promoting Synaptic Contacts

Astroglia play key roles in the development of neurons, ranging from regulating neuron survival to promoting synapse formation, yet basic questions remain about whether astrocytes might be involved in forming the dendritic arbor. Here, we used cultured hippocampal neurons as a simple in vitro model that allowed dendritic growth and geometry to be analyzed quantitatively under conditions where the extent of interactions between neurons and astrocytes varied. When astroglia were proximal to neurons, dendrites and dendritic filopodia oriented toward them, but the general presence of astroglia significantly reduced overall dendrite growth. Further, dendritic arbors in partial physical contact with astroglia developed a pronounced pattern of asymmetrical growth, because the dendrites in direct contact were significantly smaller than the portion of the arbor not in contact. Notably, thrombospondin, the astroglial factor shown previously to promote synapse formation, did not inhibit dendritic growth. Thus, while astroglia promoted the formation of presynaptic contacts onto dendrites, dendritic growth was constrained locally within a developing arbor at sites where dendrites contacted astroglia. Taken together, these observations reveal influences on spatial orientation of growth as well as influences on morphogenesis of the dendritic arbor that have not been previously identified.

Environmental cues determine the fate of astrocytes after spinal cord injury

Reactive astrogliosis occurs after central nervous system (CNS) injuries whereby resident astrocytes form rapid responses along a graded continuum. Following CNS lesions, naïve astrocytes are converted into reactive astrocytes and eventually into scar-forming astrocytes that block axon regeneration and neural repair. It has been known for decades that scarring development and its related extracellular matrix molecules interfere with regeneration of injured axons after CNS injury, but the cellular and molecular mechanisms for controlling astrocytic scar formation and maintenance are not well known. Recent use of various genetic tools has made tremendous progress in better understanding genesis of reactive astrogliosis. Especially, the latest experiments demonstrate environment-dependent plasticity of reactive astrogliosis because reactive astrocytes isolated from injured spinal cord form scarring astrocytes when transplanted into injured spinal cord, but revert in retrograde to naive astrocytes when transplanted into naive spinal cord. The interactions between upregulated type I collagen and its receptor integrin β1 and the N-cadherin-mediated cell adhesion appear to play major roles for local astrogliosis around the lesion. This review centers on the environment-dependent plasticity of reactive astrogliosis after spinal cord injury and its potential as a therapeutic target.

Glial cells and energy balance

The search for new strategies and drugs to abate the current obesity epidemic has led to the intensification of research aimed at understanding the neuroendocrine control of appetite and energy expenditure. This intensified investigation of metabolic control has also included the study of how glial cells participate in this process. Glia, the most abundant cell type in the central nervous system, perform a wide spectrum of functions and are vital for the correct functioning of neurons and neuronal circuits. Current evidence indicates that hypothalamic glia, in particular astrocytes, tanycytes and microglia, are involved in both physiological and pathophysiological mechanisms of appetite and metabolic control, at least in part by regulating the signals reaching metabolic neuronal circuits. Glia transport nutrients, hormones and neurotransmitters; they secrete growth factors, hormones, cytokines and gliotransmitters and are a source of neuroprogenitor cells. These functions are regulated, as glia also respond to numerous hormones and nutrients, with the lack of specific hormonal signaling in hypothalamic astrocytes disrupting metabolic homeostasis. Here, we review some of the more recent advances in the role of glial cells in metabolic control, with a special emphasis on the differences between glial cell responses in males and females.

Role and Therapeutic Potential of Astrocytes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. The molecular mechanism underlying the progressive degeneration of motor neuron remains uncertain but involves a non-cell autonomous process. In acute injury or degenerative diseases astrocytes adopt a reactive phenotype known as astrogliosis. Astrogliosis is a complex remodeling of astrocyte biology and most likely represents a continuum of potential phenotypes that affect neuronal function and survival in an injury-specific manner. In ALS patients, reactive astrocytes surround both upper and lower degenerating motor neurons and play a key role in the pathology. It has become clear that astrocytes play a major role in ALS pathology. Through loss of normal function or acquired new characteristics, astrocytes are able to influence motor neuron fate and the progression of the disease. The use of different cell culture models indicates that ALS-astrocytes are able to induce motor neuron death by secreting a soluble factor(s). Here, we discuss several pathogenic mechanisms that have been proposed to explain astrocyte-mediated motor neuron death in ALS. In addition, examples of strategies that revert astrocyte-mediated motor neuron toxicity are reviewed to illustrate the therapeutic potential of astrocytes in ALS. Due to the central role played by astrocytes in ALS pathology, therapies aimed at modulating astrocyte biology may contribute to the development of integral therapeutic approaches to halt ALS progression.

Emerging mechanisms underlying astrogenesis in the developing mammalian brain

In the developing brain, the three major cell types, i.e., neurons, astrocytes and oligodendrocytes, are generated from common multipotent neural stem cells (NSCs). In particular, astrocytes eventually occupy a great fraction of the brain and play pivotal roles in the brain development and functions. However, NSCs cannot produce the three major cell types simultaneously from the beginning; e.g., it is known that neurogenesis precedes astrogenesis during brain development. How is this fate switching achieved? Many studies have revealed that extracellular cues and intracellular programs are involved in the transition of NSC fate specification. The former include growth factor- and cytokine-signaling, and the latter involve epigenetic machinery, including DNA methylation, histone modifications, and non-coding RNAs. Accumulating evidence has identified a complex array of epigenetic modifications that control the timing of astrocytic differentiation of NSCs. In this review, we introduce recent progress in identifying the molecular mechanisms of astrogenesis underlying the tight regulation of neuronal-astrocytic fate switching of NSCs.

Cardiolipin in Central Nervous System Physiology and Pathology

Cardiolipin, an anionic phospholipid found primarily in the inner mitochondrial membrane, has many well-defined roles within the peripheral tissues, including the maintenance of mitochondrial membrane fluidity and the regulation of mitochondrial functions. Within the central nervous system (CNS), cardiolipin is found within both neuronal and non-neuronal glial cells, where it regulates metabolic processes, supports mitochondrial functions, and promotes brain cell viability. Furthermore, cardiolipin has been shown to act as an elimination signal and participate in programmed cell death by apoptosis of both neurons and glia. Since cardiolipin is associated with regulating brain homeostasis, the modification of its structure, or even a decrease in the overall levels of cardiolipin, can result in mitochondrial dysfunction, which is a characteristic feature of many diseases. In this review, we outline the various functions of cardiolipin within the cells of the CNS, including neurons, astrocytes, microglia, and oligodendrocytes. In addition, we discuss the role cardiolipin may play in the pathogenesis of the neurodegenerative disorders Alzheimer's disease and Parkinson's disease, as well as traumatic brain injury.

Hyperglycemia and high nitric oxide level induced oxidative stress in the brain and molecular alteration in the neurons and glial cells of laboratory mouse, Mus musculus

Chronic hyperglycemia (glucotoxicity) is reported to have detrimental effects on various brain functions leading to neurodegenerative changes. However, the effect of hyperglycemia in combination with high nitric oxide (NO) level (reported to be increased during glucotoxicity), on brain functions is not clear yet. The present study was designed to investigate the effects of hyperglycemic drug Streptozotocin (STZ) and NO donor Sodium nitroprusside (SNP) on the brain of laboratory mouse, Mus musculus. Effects of these conditions were studied on the markers of oxidative stress, NF-κB signalling and the markers of neuronal and glial cell activation/inflammation. Results indicate increased level of MDA and altered antioxidant enzymes activity in both the treated groups compared to control but high levels of AGEs, AOPP and AR activity (markers of diabetic complications) were observed in STZ group only. On the other hand, while STZ group showed decreased IL-6 level, it was increased in SNP group but IFN-ϒ level increased in both the treated groups compared to control. Further, in addition to alterations in the expressions of iNOS, IKKβ, IKBα and NF-κB subunits (RelA-p65/RelB-p50) observed in the neurons and glial cells of different brain regions (hypothalamus, basolateral amygdala and cerebral cortex), enhanced expression of microglial CD11b and astrocytic GFAP was also found in both the treated groups compared to control. Present findings led us to conclude that both hyperglycemia and high NO level causes oxidative stress in addition to molecular alteration in the neurons and glial cells. It is suggested that high blood glucose and NO level induced oxidative stress may lead to neuroinflammation possibly via NF-κB signalling.

Neuroprotective and Ameliorating Impacts of Omega-3 Against Aspartame-induced Neuronal and Astrocytic Degeneration

Aspartame (ASP) is one of the commonest artificial sweetener used all over the world and considered as an extremely risky compound and raises a lot of controversy. Therefore, this study was designed to investigate cellular damage of the anterior horn cells in the spinal cord of albino male rats and the possibility of hindering these changes by using omega-3 (OM3).Thirty seven adult male albino rats were divided into three groups: Control, ASP-treated and ASP + OM3-treated groups. Spinal cord sections were prepared and stained with Hx&E, caspase-3 and GFAP immunostaining. All data were morphometrically and statistically analyzed. In ASP-treated group, the cell body of some degenerated neurons was swollen and its cytoplasm was vacuolated. Their nuclei were eccentric and pyknotic. Moreover, other neurons were of a heterogeneous pattern in the form of cell body shrinkage, loss of Nissl substance, intensely stained eosinophilic cytoplasm and a small darkly stained nucleus that may eventually fragment. However, the cells were apparently normal in ASP+ OM3-treated group. Strong +ve caspase-3 stained neurons were detected in ASP-treated group. Furthermore, the immunoreaction was faint on treating the rats with both ASP and OM3. Few number of +ve GFAP- stained astrocytes were observed in ASP-treated rats. On the other hand, the immunoreactivity for GFAP was found to be intense in the ASP + OM3-treated group. Additionally, there was a significant decrease in the surface area percentage of the +ve GFAP-stained astrocytes of the ASP-treated group compared to the control and the ASP + OM3-treated groups. Anat Rec, 300:1290-1298, 2017. © 2017 Wiley Periodicals, Inc.

The search for true numbers of neurons and glial cells in the human brain: A review of 150 years of cell counting

For half a century, the human brain was believed to contain about 100 billion neurons and one trillion glial cells, with a glia:neuron ratio of 10:1. A new counting method, the isotropic fractionator, has challenged the notion that glia outnumber neurons and revived a question that was widely thought to have been resolved. The recently validated isotropic fractionator demonstrates a glia:neuron ratio of less than 1:1 and a total number of less than 100 billion glial cells in the human brain. A survey of original evidence shows that histological data always supported a 1:1 ratio of glia to neurons in the entire human brain, and a range of 40-130 billion glial cells. We review how the claim of one trillion glial cells originated, was perpetuated, and eventually refuted. We compile how numbers of neurons and glial cells in the adult human brain were reported and we examine the reasons for an erroneous consensus about the relative abundance of glial cells in human brains that persisted for half a century. Our review includes a brief history of cell counting in human brains, types of counting methods that were and are employed, ranges of previous estimates, and the current status of knowledge about the number of cells. We also discuss implications and consequences of the new insights into true numbers of glial cells in the human brain, and the promise and potential impact of the newly validated isotropic fractionator for reliable quantification of glia and neurons in neurological and psychiatric diseases. J. Comp. Neurol. 524:3865-3895, 2016. © 2016 Wiley Periodicals, Inc.

Astrocytic Insulin Signaling Couples Brain Glucose Uptake with Nutrient Availability

We report that astrocytic insulin signaling co-regulates hypothalamic glucose sensing and systemic glucose metabolism. Postnatal ablation of insulin receptors (IRs) in glial fibrillary acidic protein (GFAP)-expressing cells affects hypothalamic astrocyte morphology, mitochondrial function, and circuit connectivity. Accordingly, astrocytic IR ablation reduces glucose-induced activation of hypothalamic pro-opio-melanocortin (POMC) neurons and impairs physiological responses to changes in glucose availability. Hypothalamus-specific knockout of astrocytic IRs, as well as postnatal ablation by targeting glutamate aspartate transporter (GLAST)-expressing cells, replicates such alterations. A normal response to altering directly CNS glucose levels in mice lacking astrocytic IRs indicates a role in glucose transport across the blood-brain barrier (BBB). This was confirmed in vivo in GFAP-IR KO mice by using positron emission tomography and glucose monitoring in cerebral spinal fluid. We conclude that insulin signaling in hypothalamic astrocytes co-controls CNS glucose sensing and systemic glucose metabolism via regulation of glucose uptake across the BBB.

Follistatin-like protein 1 suppressed pro-inflammatory cytokines expression during neuroinflammation induced by lipopolysaccharide

Follistain-like protein 1 (FSTL1), has been recently demonstrated to be involved in the embryo development of nervous system and glioblastoma. However, the role of FSTL1 in neuroinflammation remains unexplored. In this study, the expression of FSTL1 in astrocytes was verified and its role was studied in neuroinflammation induced by in vivo intracerebroventricular (ICV) injection of lipopolysaccharide (LPS) or LPS treatment to astrocytes in vitro. FSTL1 was significantly induced after ICV LPS injection or LPS treatment. FSTL1 suppressed upregulation of pro-inflammatory cytokines in astrocytes after LPS treatment. Moreover, FSTL1 downregulated expression of pro-inflammatory cytokines through suppressing MAPK/p-ERK1/2 pathway in astrocytes. Our results suggest that FSTL1 may play an anti-inflammatory role in neuroinflammation mediated by astrocytes.

Construction of the human forebrain

The adult human brain is arguably the most complex of biological systems. It contains 86 billion neurons (the information processing cells of the brain) and many more support cells. The neurons, with the assistance of the support cells, form trillions of connections creating complex, interconnected neural networks that support all human thought, feeling, and action. A challenge for modern neuroscience is to provide a model that accounts for this exquisitely complex and dynamic system. One fundamental part of this model is an account of how the human brain develops. This essay describes two important aspects of this developmental story. The first part of the story focuses on the remarkable and dynamic set of events that unfold during the prenatal period to give rise to cell lineage that form the essential substance of the brain, particularly the structures of the cerebral hemispheres. The second part of the story focuses on the formation of the major brain pathways of the cerebrum, the intricate fiber bundles that connect different populations of neurons to form the information processing systems that support all human thought and action. These two aspects of early brain development provide an essential foundation for understanding how the structure, organization, and functioning of the human brain emerge. WIREs Cogn Sci 2017, 8:e1409. doi: 10.1002/wcs.1409 For further resources related to this article, please visit the WIREs website.

Castanea sativa Mill. Bark Extract Protects U-373 MG Cells and Rat Brain Slices Against Ischemia and Reperfusion Injury

Ischemic brain injury is one of the most important causes of death worldwide. The use of one-drug-multi-target agents based on natural compounds is a promising therapeutic option for cerebral ischemia due to their pleiotropic properties. This study assessed the neuroprotective properties of Castanea sativa Mill. bark extract (ENC) in human astrocytoma U-373 MG cells subjected to oxygen-glucose deprivation and reperfusion and rat cortical slices subjected to ischemia-like conditions or treated with glutamate or hydrogen peroxide. Neuroprotective effects were determined by assessing cells or slices viability (MTT assay), ROS formation (DCFH-DA assay), apoptosis (sub G0/G1 peak), nuclear fragmentation and chromatin condensation (DAPI staining) as well as changes in lysosomes and mitochondria morphology (Acridine Orange and Rhodamine123 staining, respectively). ENC treatment before injury on U-373 MG cells (5-50 μg/ml) and cortical slices (50-100 μg/ml) provided neuroprotection, while lower or higher concentrations (100 μg/ml U-373 MG cells, 200 μg/ml brain slices) were ineffective. ENC addition during reperfusion or after the injury was not found to be effective. The results suggest that ENC might hold potential as preventive neuroprotective agent, and indicate the importance of further studies exploring its mechanism of action. J. Cell. Biochem. 118: 839-850, 2017. © 2016 Wiley Periodicals, Inc.

The Indispensable Roles of Microglia and Astrocytes during Brain Development

Glia are essential for brain functioning during development and in the adult brain. Here, we discuss the various roles of both microglia and astrocytes, and their interactions during brain development. Although both cells are fundamentally different in origin and function, they often affect the same developmental processes such as neuro-/gliogenesis, angiogenesis, axonal outgrowth, synaptogenesis and synaptic pruning. Due to their important instructive roles in these processes, dysfunction of microglia or astrocytes during brain development could contribute to neurodevelopmental disorders and potentially even late-onset neuropathology. A better understanding of the origin, differentiation process and developmental functions of microglia and astrocytes will help to fully appreciate their role both in the developing as well as in the adult brain, in health and disease.

Novel insights into role of miR-320a-VDAC1 axis in astrocyte-mediated neuronal damage in neuroAIDS

Astroglia are indispensable component of the tripartite synapse ensheathing innumerous soma and synapses. Its proximity to neurons aids the regulation of neuronal functions, health and survival through dynamic neuroglia crosstalk. Susceptibility of astrocyte to HIV-1 infection and subsequent latency culminates in compromised neuronal health. The viral protein HIV-1 transactivator of transcription (Tat) is neurotoxic. HIV-1 Tat is detected in brain of AIDS patients even in cases where viral load is non-detectable due to successful HAART therapy. Recently, we demonstrated that HIV-1 Tat triggers excess ATP release from astrocytes that causes neuronal death by activating purinergic receptor system. Using well-characterized model system of human primary astrocytes and neurons, we probed into the molecular mechanism for enhanced ATP release in HIV-1 Tat affected astrocytes. HIV-1 Tat modulated the miRNA machinery in astrocytes and perturbed the levels of voltage dependent anion channel 1 (VDAC1), a channel present in the outer mitochondrial membrane and plasma membrane that regulates extracellular ATP release. Our studies with autopsy tissue sections also showed concordantly dysregulated VDAC1 and miR-320a levels in HIV-1 patients suffering from mild cognitive impairment (MCI). We report a novel molecular cascade of miRNA-mediated ATP release through regulation of VDAC1. Downregulation of VDAC1 either with miR-320a mimic or VDAC1 siRNA in HIV-1 Tat-affected astroglia could rescue the neurons from glia-mediated indirect death. Our findings reveal a novel upstream therapeutic target that could be employed to thwart the astroglia-mediated neurotoxicity in HIV-1 neuropathogenesis. GLIA 2017;65:250-263.

Nigella sativa Oil Reduces Extrapyramidal Symptoms (EPS)-Like Behavior in Haloperidol-Treated Rats

The symptoms of Parkinsonism and oral dyskinesia have been showing to be induced by neuroleptics that significantly affect its clinical use. In this study, we investigate whether Nigella sativa-oil (NS) (black cumin seeds)-a traditional medicine used for the seizure treatment in eastern country-may reduce the haloperidol (HAL)-induced extrapyramidal symptoms (EPS)-like behavior in rats. After combine treatment with HAL (1 mg/kg) on NS (0.2 ml/rat), rats displayed a significant decreased EPS-like behavior including movement disorders and oral dyskinesia as compared to controls. Immunohistochemical analysis indicates that NS reduced astrogliosis in caudate and accumbens nuclei. These results suggest that NS may consider as an adjunct to antipsychotics to reduce the EPS-like side effect.

Direct modulation of GFAP-expressing glia in the arcuate nucleus bi-directionally regulates feeding

Multiple hypothalamic neuronal populations that regulate energy balance have been identified. Although hypothalamic glia exist in abundance and form intimate structural connections with neurons, their roles in energy homeostasis are less known. Here we show that selective Ca²⁺ activation of glia in the mouse arcuate nucleus (ARC) reversibly induces increased food intake while disruption of Ca²⁺ signaling pathway in ARC glia reduces food intake. The specific activation of ARC glia enhances the activity of agouti-related protein/neuropeptide Y (AgRP/NPY)-expressing neurons but induces no net response in pro-opiomelanocortin (POMC)-expressing neurons. ARC glial activation non-specifically depolarizes both AgRP/NPY and POMC neurons but a strong inhibitory input to POMC neurons balances the excitation. When AgRP/NPY neurons are inactivated, ARC glial activation fails to evoke any significant changes in food intake. Collectively, these results reveal an important role of ARC glia in the regulation of energy homeostasis through its interaction with distinct neuronal subtype-specific pathways.

Multivariate Meta-Analysis of Brain-Mass Correlations in Eutherian Mammals

The general assumption that brain size differences are an adequate proxy for subtler differences in brain organization turned neurobiologists toward the question why some groups of mammals such as primates, elephants, and whales have such remarkably large brains. In this meta-analysis, an extensive sample of eutherian mammals (115 species distributed in 14 orders) provided data about several different biological traits and measures of brain size such as absolute brain mass (AB), relative brain mass (RB; quotient from AB and body mass), and encephalization quotient (EQ). These data were analyzed by established multivariate statistics without taking specific phylogenetic information into account. Species with high AB tend to (1) feed on protein-rich nutrition, (2) have a long lifespan, (3) delayed sexual maturity, and (4) long and rare pregnancies with small litter sizes. Animals with high RB usually have (1) a short life span, (2) reach sexual maturity early, and (3) have short and frequent gestations. Moreover, males of species with high RB also have few potential sexual partners. In contrast, animals with high EQs have (1) a high number of potential sexual partners, (2) delayed sexual maturity, and (3) rare gestations with small litter sizes. Based on these correlations, we conclude that Eutheria with either high AB or high EQ occupy positions at the top of the network of food chains (high trophic levels). Eutheria of low trophic levels can develop a high RB only if they have small body masses.

Astrocyte Differentiation of Human Pluripotent Stem Cells: New Tools for Neurological Disorder Research

Astrocytes have a central role in brain development and function, and so have gained increasing attention over the past two decades. Consequently, our knowledge about their origin, differentiation and function has increased significantly, with new research showing that astrocytes cultured alone or co-cultured with neurons have the potential to improve our understanding of various central nervous system diseases, such as amyotrophic lateral sclerosis, Alzheimer’s disease, or Alexander disease. The generation of astrocytes derived from pluripotent stem cells (PSCs) opens up a new area for studying neurologic diseases in vitro; these models could be exploited to identify and validate potential drugs by detecting adverse effects in the early stages of drug development. However, as it is now known that a range of astrocyte populations exist in the brain, it will be important in vitro to develop standardized protocols for the in vitro generation of astrocyte subsets with defined maturity status and phenotypic properties. This will then open new possibilities for co-cultures with neurons and the generation of neural organoids for research purposes. The aim of this review article is to compare and summarize the currently available protocols and their strategies to generate human astrocytes from PSCs. Furthermore, we discuss the potential role of human-induced PSCs derived astrocytes in disease modeling.

Quinolinic acid neurotoxicity: Differential roles of astrocytes and microglia via FGF-2-mediated signaling in redox-linked cytoskeletal changes

QUIN is a glutamate agonist playing a role in the misregulation of the cytoskeleton, which is associated with neurodegeneration in rats. In this study, we focused on microglial activation, FGF2/Erk signaling, gap junctions (GJs), inflammatory parameters and redox imbalance acting on cytoskeletal dynamics of the in QUIN-treated neural cells of rat striatum. FGF-2/Erk signaling was not altered in QUIN-treated primary astrocytes or neurons, however cytoskeleton was disrupted. In co-cultured astrocytes and neurons, QUIN-activated FGF2/Erk signaling prevented the cytoskeleton from remodeling. In mixed cultures (astrocyte, neuron, microglia), QUIN-induced FGF-2 increased level failed to activate Erk and promoted cytoskeletal destabilization. The effects of QUIN in mixed cultures involved redox imbalance upstream of Erk activation. Decreased connexin 43 (Cx43) immunocontent and functional GJs, was also coincident with disruption of the cytoskeleton in primary astrocytes and mixed cultures. We postulate that in interacting astrocytes and neurons the cytoskeleton is preserved against the insult of QUIN by activation of FGF-2/Erk signaling and proper cell-cell interaction through GJs. In mixed cultures, the FGF-2/Erk signaling is blocked by the redox imbalance associated with microglial activation and disturbed cell communication, disrupting the cytoskeleton. Thus, QUIN signal activates differential mechanisms that could stabilize or destabilize the cytoskeleton of striatal astrocytes and neurons in culture, and glial cells play a pivotal role in these responses preserving or disrupting a combination of signaling pathways and cell-cell interactions. Taken together, our findings shed light into the complex role of the active interaction of astrocytes, neurons and microglia in the neurotoxicity of QUIN.

Protection by Neuroglobin Expression in Brain Pathologies

Astrocytes play an important role in physiological, metabolic, and structural functions, and when impaired, they can be involved in various pathologies including Alzheimer, focal ischemic stroke, and traumatic brain injury. These disorders involve an imbalance in the blood flow and nutrients such as glucose and lactate, leading to biochemical and molecular changes that cause neuronal damage, which is followed by loss of cognitive and motor functions. Previous studies have shown that astrocytes are more resilient than neurons during brain insults as a consequence of their more effective antioxidant systems, transporters, and enzymes, which made them less susceptible to excitotoxicity. In addition, astrocytes synthesize and release different protective molecules for neurons, including neuroglobin, a member of the globin family of proteins. After brain injury, neuroglobin expression is induced in astrocytes. Since neuroglobin promotes neuronal survival, its increased expression in astrocytes after brain injury may represent an endogenous neuroprotective mechanism. Here, we review the role of neuroglobin in the central nervous system, its relationship with different pathologies, and the role of different factors that regulate its expression in astrocytes.

Blood-brain barrier breakdown and neovascularization processes after stroke and traumatic brain injury

PURPOSE OF REVIEW

Angiogenesis or vascular reorganization plays a role in recovery after stroke and traumatic brain injury (TBI). In this review, we have focused on two major events that occur during stroke and TBI from a vascular perspective - what is the process and time course of blood-brain barrier (BBB) breakdown? and how does the surrounding vasculature recover and facilitate repair?

RECENT FINDINGS

Despite differences in the primary injury, the BBB changes overlap between stroke and TBI. Disruption of BBB involves a series of events: formation of caveolae, trans and paracellular disruption, tight junction breakdown and vascular disruption. Confounding factors that need careful assessment and standardization are the severity, duration and extent of the stroke and TBI that influences BBB disruption. Vascular repair proceeds through long-term neovascularization processes: angiogenesis, arteriogenesis and vasculogenesis. Enhancing each of these processes may impart beneficial effects in endogenous recovery.

SUMMARY

Our understanding of BBB breakdown acutely after the cerebrovascular injury has come a long way; however, we lack a clear understanding of the course of BBB disruption and BBB recovery and the evolution of individual cellular events associated with BBB change. Neovascularization responses have been widely studied in stroke for their role in functional recovery but the role of vascular reorganization after TBI in recovery is much less defined.

Translational potential of astrocytes in brain disorders

Fundamentally, all brain disorders can be broadly defined as the homeostatic failure of this organ. As the brain is composed of many different cells types, including but not limited to neurons and glia, it is only logical that all the cell types/constituents could play a role in health and disease. Yet, for a long time the sole conceptualization of brain pathology was focused on the well-being of neurons. Here, we challenge this neuron-centric view and present neuroglia as a key element in neuropathology, a process that has a toll on astrocytes, which undergo complex morpho-functional changes that can in turn affect the course of the disorder. Such changes can be grossly identified as reactivity, atrophy with loss of function and pathological remodeling. We outline the pathogenic potential of astrocytes in variety of disorders, ranging from neurotrauma, infection, toxic damage, stroke, epilepsy, neurodevelopmental, neurodegenerative and psychiatric disorders, Alexander disease to neoplastic changes seen in gliomas. We hope that in near future we would witness glial-based translational medicine with generation of deliverables for the containment and cure of disorders. We point out that such as a task will require a holistic and multi-disciplinary approach that will take in consideration the concerted operation of all the cell types in the brain.

Cell-specific modulation of plasticity and cortical state by cholinergic inputs to the visual cortex

Acetylcholine (ACh) modulates diverse vital brain functions. Cholinergic neurons from the basal forebrain innervate a wide range of cortical areas, including the primary visual cortex (V1), and multiple cortical cell types have been found to be responsive to ACh. Here we review how different cell types contribute to different cortical functions modulated by ACh. We specifically focus on two major cortical functions: plasticity and cortical state. In layer II/III of V1, ACh acting on astrocytes and somatostatin-expressing inhibitory neurons plays critical roles in these functions. Cell type specificity of cholinergic modulation points towards the growing understanding that even diffuse neurotransmitter systems can mediate specific functions through specific cell classes and receptors.

Time-dependent uptake and trafficking of vesicles capturing extracellular S100B in cultured rat astrocytes

Astrocytes, the most heterogeneous glial cells in the central nervous system, contribute to brain homeostasis, by regulating a myriad of functions, including the clearance of extracellular debris. When cells are damaged, cytoplasmic proteins may exit into the extracellular space. One such protein is S100B, which may exert toxic effects on neighboring cells unless it is removed from the extracellular space, but the mechanisms of this clearance are poorly understood. By using time-lapse confocal microscopy and fluorescently labeled S100B (S100B-Alexa⁴⁸⁸ ) and fluorescent dextran (Dextran⁵⁴⁶ ), a fluid phase uptake marker, we examined the uptake of fluorescently labeled S100B-Alexa⁴⁸⁸ from extracellular space and monitored trafficking of vesicles that internalized S100B-Alexa⁴⁸⁸ . Initially, S100B-Alexa⁴⁸⁸ and Dextran⁵⁴⁶ internalized with distinct rates into different endocytotic vesicles; S100B-Alexa⁴⁸⁸ internalized into smaller vesicles than Dextran⁵⁴⁶ . At a later stage, S100B-Alexa⁴⁸⁸ -positive vesicles substantially co-localized with Dextran⁵⁴⁶ -positive endolysosomes and with acidic LysoTracker-positive vesicles. Cell treatment with anti-receptor for advanced glycation end products (RAGE) antibody, which binds to RAGE, a 'scavenger receptor', partially inhibited uptake of S100B-Alexa⁴⁸⁸ , but not of Dextran⁵⁴⁶ . The dynamin inhibitor dynole 34-2 inhibited internalization of both fluorescent probes. Directional mobility of S100B-Alexa⁴⁸⁸ -positive vesicles increased over time and was inhibited by ATP stimulation, an agent that increases cytosolic free calcium concentration ([Ca²⁺ ]_i ). We conclude that astrocytes exhibit RAGE- and dynamin-dependent vesicular mechanism to efficiently remove S100B from the extracellular space. If a similar process occurs in vivo, astroglia may mitigate the toxic effects of extracellular S100B by this process under pathophysiologic conditions. This study reveals the vesicular clearance mechanism of extracellular S100B in astrocytes. Initially, fluorescent S100B internalizes into smaller endocytotic vesicles than dextran molecules. At a later stage, both probes co-localize within endolysosomes. S100B internalization is both dynamin- and RAGE-dependent, whereas dextran internalization is dependent on dynamin. Vesicle internalization likely mitigates the toxic effects of extracellular S100B and other waste products.

Localization of nectin-2δ at perivascular astrocytic endfoot processes and degeneration of astrocytes and neurons in nectin-2 knockout mouse brain

Nectins are Ca²⁺-independent immunoglobulin-like cell-cell adhesion molecules. In the nervous system, among four members (nectin-1, -2, -3, and -4), nectin-1 and -3 are asymmetrically localized at puncta adherentia junctions formed between the mossy fiber terminals and the dendrites of CA3 pyramidal neurons in the mouse hippocampus and heterophilic trans-interactions between nectin-1 and nectin-3 are involved in the selective interaction of axons and dendrites of cultured neurons. By contrast, nectin-2, which has two splicing variants, nectin-2α and -2δ, has not been well characterized in the brain. We showed here that nectin-2α was expressed in both cultured mouse neurons and astrocytes whereas nectin-2δ was selectively expressed in the astrocytes. Nectin-2δ was localized at the adhesion sites between adjacent cultured astrocytes, but in the brain it was localized on the plasma membranes of astrocytic perivascular endfoot processes facing the basement membrane of blood vessels. Genetic ablation of nectin-2 caused degeneration of astrocytic perivascular endfoot processes and neurons in the cerebral cortex. These results uncovered for the first time the localization and critical functions of nectin-2 in the brain.

On the role of the extracellular space on the holistic behavior of the brain

Multiple players are involved in the brain integrative action besides the classical neuronal and astrocyte networks. In the past, the concept of complex cellular networks has been introduced to indicate that all the cell types in the brain can play roles in its integrative action. Intercellular communication in the complex cellular networks depends not only on well-delimited communication channels (wiring transmission) but also on diffusion of signals in physically poorly delimited extracellular space pathways (volume transmission). Thus, the extracellular space and the extracellular matrix are the main players in the intercellular communication modes in the brain. Hence, the extracellular matrix is an 'intelligent glue' that fills the brain and, together with the extracellular space, contributes to the building-up of the complex cellular networks. In addition, the extracellular matrix is part of what has been defined as the global molecular network enmeshing the entire central nervous system, and plays important roles in synaptic contact homeostasis and plasticity. From these premises, a concept is introduced that the global molecular network, by enmeshing the central nervous system, contributes to the brain holistic behavior. Furthermore, it is suggested that plastic 'brain compartments' can be detected in the central nervous system based on the astrocyte three-dimensional tiling of the brain volume and on the existence of local differences in cell types and extracellular space fluid and extracellular matrix composition. The relevance of the present view for neuropsychiatry is discussed. A glossary box with terms and definitions is provided.