Characterization of adult rat astrocyte cultures

Effects of methylphenidate on mitochondrial dynamics and bioenergetics in the prefrontal cortex of juvenile rats are sex-dependent

Methylphenidate (MPH) is a central nervous system stimulant drug and a first order prescription in the treatment of Attention Deficit Hyperactivity Disorder (ADHD). Although MPH biochemistry in neurodevelopment is not completely understood, studies showed it alters energy metabolism in rat brains. ADHD prevalence during neurodevelopment is related to males and the investigation has been mainly done in these subjects, therefore, little is known about MPH action in females and, consequently, about sexual dimorphism. In the present study we evaluated markers of mitochondrial dynamics (DRP1 and MFN2, fission and fusion, respectively), biogenesis (mtTFA) and bioenergetics (respiratory chain complexes) in prefrontal cortex of male and female juvenile rats submitted to exposure to MPH to better understand MPH effect during postnatal neurodevelopment. ATP and oxidative stress levels were also evaluated. Wistar rats received intraperitoneal injection of MPH (2.0 mg/kg) or control (saline), once a day, from 15th to 45th day of age. Results showed that MPH increased DRP1 and decreased MFN2, as well as increased mtTFA in prefrontal cortex of male rats. In female, MPH decreased NRF1 and increased Parkin, which are mitochondrial regulatory proteins. Respiratory chain complexes (complex I, SDH, complexes III and IV), ATP production and oxidative stress parameters were altered and shown to be sex-dependent. Taken together, results suggest that chronic MPH exposure at an early age in healthy animals changes mitochondrial dynamics, biogenesis and bioenergetics differently depending on the sex of the subjects.

Targeting senescent cells with NKG2D-CAR T cells

This study investigates the efficacy of NKG2D chimeric antigen receptor (CAR) engineered T cells in targeting and eliminating stress-induced senescent cells in vitro. Cellular senescence contributes to age-related tissue decline and is characterized by permanent cell cycle arrest and the senescence-associated secretory phenotype (SASP). Immunotherapy, particularly CAR-T cell therapy, emerges as a promising approach to selectively eliminate senescent cells. Our focus is on the NKG2D receptor, which binds to ligands (NKG2DLs) upregulated in senescent cells, offering a target for CAR-T cells. Using mouse embryonic fibroblasts (MEFs) and astrocytes (AST) as senescence models, we demonstrate the elevated expression of NKG2DLs in response to genotoxic and oxidative stress. NKG2D-CAR T cells displayed potent cytotoxicity against these senescent cells, with minimal effects on non-senescent cells, suggesting their potential as targeted senolytics. In conclusion, our research presents the first evidence of NKG2D-CAR T cells' ability to target senescent brain cells, offering a novel approach to manage senescence-associated diseases. The findings pave the way for future investigations into the therapeutic applicability of NKG2D-targeting CAR-T cells in naturally aged organisms and models of aging-associated brain diseases in vivo.

Differences between cultured astrocytes from neonatal and adult Wistar rats: focus on in vitro aging experimental models

Astrocytes play key roles regulating brain homeostasis and accumulating evidence has suggested that glia are the first cells that undergo functional changes with aging, which can lead to a decline in brain function. In this context, in vitro models are relevant tools for studying aged astrocytes and, here, we investigated functional and molecular changes in cultured astrocytes obtained from neonatal or adult animals submitted to an in vitro model of aging by an additional period of cultivation of cells after confluence. In vitro aging induced different metabolic effects regarding glucose and glutamate uptake, as well as glutamine synthetase activity, in astrocytes obtained from adult animals compared to those obtained from neonatal animals. In vitro aging also modulated glutathione-related antioxidant defenses and increased reactive oxygen species and cytokine release especially in astrocytes from adult animals. Interestingly, in vitro aged astrocytes from adult animals exposed to pro-oxidant, inflammatory, and antioxidant stimuli showed enhanced oxidative and inflammatory responses. Moreover, these functional changes were correlated with the expression of the senescence marker p21, cytoskeleton markers, glutamate transporters, inflammatory mediators, and signaling pathways such as nuclear factor κB (NFκB)/nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase 1 (HO-1). Alterations in these genes are remarkably associated with a potential neurotoxic astrocyte phenotype. Therefore, considering the experimental limitations due to the need for long-term maintenance of the animals for studying aging, astrocyte cultures obtained from adult animals further aged in vitro can provide an improved experimental model for understanding the mechanisms associated with aging-related astrocyte dysfunction.

HIV-1 mRNA knockdown with CRISPR/CAS9 enhances neurocognitive function

Mixed glia are infiltrated with HIV-1 virus early in the course of infection leading to the development of a persistent viral reservoir in the central nervous system. Modification of the HIV-1 genome using gene editing techniques, including CRISPR/Cas9, has shown great promise towards eliminating HIV-1 viral reservoirs; whether these techniques are capable of removing HIV-1 viral proteins from mixed glia, however, has not been systematically evaluated. Herein, the efficacy of adeno-associated virus 9 (AAV9)-CRISPR/Cas9 gene editing for eliminating HIV-1 messenger RNA (mRNA) from cortical mixed glia was evaluated in vitro and in vivo. In vitro, a within-subjects experimental design was utilized to treat mixed glia isolated from neonatal HIV-1 transgenic (Tg) rats with varying doses (0, 0.9, 1.8, 2.7, 3.6, 4.5, or 5.4 µL corresponding to a physical titer of 0, 4.23 × 109, 8.46 × 109, 1.269 × 1010, 1.692 × 1010, 2.115 × 1010, and 2.538 × 1010 gc/µL) of CRISPR/Cas9 for 72 h. Dose-dependent decreases in the number of HIV-1 mRNA, quantified using an innovative in situ hybridization technique, were observed in a subset (i.e., n = 5 out of 8) of primary mixed glia. In vivo, HIV-1 Tg rats were retro-orbitally inoculated with CRISPR/Cas9 for two weeks, whereby treatment resulted in profound excision (i.e., approximately 53.2%) of HIV-1 mRNA from the medial prefrontal cortex. Given incomplete excision of the HIV-1 viral genome, the clinical relevance of HIV-1 mRNA knockdown for eliminating neurocognitive impairments was evaluated via examination of temporal processing, a putative neurobehavioral mechanism underlying HIV-1-associated neurocognitive disorders (HAND). Indeed, treatment with CRISPR/Cas9 protractedly, albeit not permanently, restored the developmental trajectory of temporal processing. Proof-of-concept studies, therefore, support the susceptibility of mixed glia to gene editing and the potential of CRISPR/Cas9 to serve as a novel therapeutic strategy for HAND, even in the absence of full viral eradication.

The Diversity of Astrocyte Activation during Multiple Sclerosis: Potential Cellular Targets for Novel Disease Modifying Therapeutics

Neuroglial cells, and especially astrocytes, constitute the most varied group of central nervous system (CNS) cells, displaying substantial diversity and plasticity during development and in disease states. The morphological changes exhibited by astrocytes during the acute and chronic stages following CNS injury can be characterized more precisely as a dynamic continuum of astrocytic reactivity. Different subpopulations of reactive astrocytes may be ascribed to stages of degenerative progression through their direct pathogenic influence upon neurons, neuroglia, the blood-brain barrier, and infiltrating immune cells. Multiple sclerosis (MS) constitutes an autoimmune demyelinating disease of the CNS. Despite the previously held notion that reactive astrocytes purely form the structured glial scar in MS plaques, their continued multifaceted participation in neuroinflammatory outcomes and oligodendrocyte and neuronal function during chronicity, suggest that they may be an integral cell type that can govern the pathophysiology of MS. From a therapeutic-oriented perspective, astrocytes could serve as key players to limit MS progression, once the integral astrocyte-MS relationship is accurately identified. This review aims toward delineating the current knowledge, which is mainly focused on immunomodulatory therapies of the relapsing-remitting form, while shedding light on uncharted approaches of astrocyte-specific therapies that could constitute novel, innovative applications once the role of specific subgroups in disease pathogenesis is clarified.

Astrocytes in the central nervous system and their functions in health and disease: A review

Astrocytes are key cells in the central nervous system. They are involved in many important functions under physiological and pathological conditions. As part of neuroglia, they have been recognised as cellular elements in their own right. The name astrocyte was first proposed by Mihaly von Lenhossek in 1895 because of the finely branched processes and star-like appearance of these particular cells. As early as the late 19^th and early 20^th centuries, Ramon y Cajal and Camillo Golgi had noted that although astrocytes have stellate features, their morphology is extremely diverse. Modern research has confirmed the morphological diversity of astrocytes both in vitro and in vivo and their complex, specific, and important roles in the central nervous system. In this review, the functions of astrocytes and their roles are described.

Age-dependent effects of resveratrol in hypothalamic astrocyte cultures

OBJECTIVES

The hypothalamus plays critical roles in maintaining brain homeostasis and increasing evidence has highlighted astrocytes orchestrating several of hypothalamic functions. However, it remains unclear how hypothalamic astrocytes participate in neurochemical mechanisms associated with aging process, as well as whether these cells can be a target for antiaging strategies. In this sense, the aim of this study is to evaluate the age-dependent effects of resveratrol, a well-characterized neuroprotective compound, in primary astrocyte cultures derived from the hypothalamus of newborn, adult, and aged rats.

METHODS

Male Wistar rats (2, 90, 180, and 365 days old) were used in this study. Cultured astrocytes from different ages were treated with 10 and 100 μM resveratrol and cellular viability, metabolic activity, astrocyte morphology, release of glial cell line-derived neurotrophic factor (GDNF), transforming growth factor β (TGF-β), tumor necrosis factor α (TNF-α), interleukins (IL-1β, IL-6, and IL-10), as well as the protein levels of Nrf2 and HO-1 were evaluated.

RESULTS

In vitro astrocytes derived from neonatal, adults, and aged animals changed metabolic activity and the release of trophic factors (GDNF and TGF-β), as well as the inflammatory mediators (TNF-α, IL-1β, IL-6, and IL-10). Resveratrol prevented these alterations. In addition, resveratrol changed the immunocontent of Nrf2 and HO-1. The results indicated that the effects of resveratrol seem to have a dose- and age-associated glioprotective role.

CONCLUSION

These findings demonstrate for the first time that resveratrol prevents the age-dependent underlying functional reprogramming of in vitro hypothalamic astrocytes, reinforcing its antiaging activity, and consequently, its glioprotective role.

Are cytoskeleton changes observed in astrocytes functionally linked to aging?

Astrocytes are active participants in the performance of the Central Nervous System (CNS) in both health and disease. During aging, astrocytes are susceptible to reactive astrogliosis, a molecular state characterized by functional changes in response to pathological situations, and cellular senescence, characterized by loss of cell division, apoptosis resistance, and gain of proinflammatory functions. This results in two different states of astrocytes, which can produce proinflammatory phenotypes with harmful consequences in chronic conditions. Reactive astrocytes and senescent astrocytes share morpho-functional features that are dependent on the organization of the cytoskeleton. However, such changes in the cytoskeleton have yet to receive the necessary attention to explain their role in the alterations of astrocytes that are associated with aging and pathologies. In this review, we summarize all the available findings that connect changes in the cytoskeleton of the astrocytes with aging. In addition, we discuss future avenues that we believe will guide such a novel topic.

Mapping the functional expression of auxiliary subunits of KCa1.1 in glioblastoma

Glioblastoma (GBM) is the most aggressive glial tumor, where ion channels, including K_Ca1.1, are candidates for new therapeutic options. Since the auxiliary subunits linked to K_Ca1.1 in GBM are largely unknown we used electrophysiology combined with pharmacology and gene silencing to address the functional expression of K_Ca1.1/β subunits complexes in both primary tumor cells and in the glioblastoma cell line U-87 MG. The pattern of the sensitivity (activation/inhibition) of the whole-cell currents to paxilline, lithocholic acid, arachidonic acid, and iberiotoxin; the presence of inactivation of the whole-cell current along with the loss of the outward rectification upon exposure to the reducing agent DTT collectively argue that K_Ca1.1/β3 complex is expressed in U-87 MG. Similar results were found using human primary glioblastoma cells isolated from patient samples. Silencing the β3 subunit expression inhibited carbachol-induced Ca²⁺ transients in U-87 MG thereby indicating the role of the K_Ca1.1/β3 in the Ca²⁺ signaling of glioblastoma cells. Functional expression of the K_Ca1.1/β3 complex, on the other hand, lacks cell cycle dependence. We suggest that the K_Ca1.1/β3 complex may have diagnostic and therapeutic potential in glioblastoma in the future.

Lipopolysaccharide Induces Gliotoxicity in Hippocampal Astrocytes from Aged Rats: Insights About the Glioprotective Roles of Resveratrol

Astrocytes may undergo a functional remodeling with aging, acquiring a pro-inflammatory state. In line with this, resveratrol represents an interesting strategy for a healthier brain aging since it can improve glial functions. In the present study, we investigated the glioprotective role of resveratrol against lipopolysaccharide (LPS)-induced gliotoxicity in hippocampal aged astrocytes. Astrocyte cultures were obtained from aged rats (365 days old) and challenged in vitro with LPS in the presence of resveratrol. Cultured astrocytes from newborn rats were used as an age comparative for evaluating LPS gliotoxicity. In addition, aged rats were submitted to an acute systemic inflammation with LPS. Hippocampal astrocyte cultures were also obtained from these LPS-stimulated aged animals to further investigate the glioprotective effects of resveratrol in vitro. Overall, our results show that LPS induced a higher inflammatory response in aged astrocytes, compared to newborn astrocytes. Several inflammatory and gene expression alterations promoted by LPS in aged astrocyte cultures were similar in hippocampal tissue from aged animals submitted to in vivo LPS injection, corroborating our in vitro findings. Resveratrol, in turn, presented anti-inflammatory effects in aged astrocyte cultures, which were associated with downregulation of p21 and pro-inflammatory cytokines, Toll-like receptors (TLRs), and nuclear factor κB (NFκB). Resveratrol also improved astroglial functions. Upregulation of sirtuin 1 (SIRT1), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase 1 (HO-1) represent potential molecular mechanisms associated with resveratrol-mediated glioprotection. In summary, our data show that resveratrol can prime aged astrocytes against gliotoxic stimuli, contributing to a healthier brain aging.

Neuron-specific mitochondrial oxidative stress results in epilepsy, glucose dysregulation and a striking astrocyte response

Mitochondrial superoxide (O₂^-) production is implicated in aging, neurodegenerative disease, and most recently epilepsy. Yet the specific contribution of neuronal O₂^- to these phenomena is unclear. Here, we selectively deleted superoxide dismutase-2 (SOD2) in neuronal basic helix-loop-helix transcription factor (NEX)-expressing cells restricting deletion to a subset of excitatory principle neurons primarily in the forebrain (cortex and hippocampus). This resulted in nSOD2 KO mice that lived into adulthood (2-3 months) with epilepsy, selective loss of neurons, metabolic rewiring and a marked mitohormetic gene response. Surprisingly, expression of an astrocytic gene, glial fibrillary acidic protein (GFAP) was significantly increased relative to WT. Further studies in rat primary neuron-glial cultures showed that increased mitochondrial O₂^-, specifically in neurons, was sufficient to upregulate GFAP. These results suggest that neuron-specific mitochondrial O₂^- is sufficient to drive a complex and catastrophic epileptic phenotype and highlights the ability of SOD2 to act in a cell-nonautonomous manner to influence an astrocytic response.

Negative Feedback Role of Astrocytes in Shaping Excitation in Brain Cell Co-cultures

Glial cells play an important role in maintaining neuronal homeostasis and may thus influence excitability in epileptogenesis. These cells in the brain have glutamate (Glu) transporters, which remove this neurotransmitter from the extracellular space. Lack of negative (-) feedback makes local neuronal circuits more excitable and potentially contributing to epileptogenic phenomena. In this study, the role of glial cells in providing (-) feedback is shown through different models of brain cells in culture imaged for intracellular calcium concentration [(Ca²⁺)_i]. Moreover, here we study the individual cells by putting them in categories. Neuronal networks with high and low (-) feedback were established by using anti-mitotics to deplete glial cells. Separate stimuli with very low subthreshold concentrations of Glu (250-750 nM) were added to cultures to test if the order of stimulations matter in regard to calcium dynamics outcomes. Additionally, KCl and ATP were used to stimulate glial cells. We found that for cultures high in (-) feedback, order of the stimulus was not important in predicting cellular responses and because of the complexity of networks in low (-) feedback cultures the order of stimulus matters. As an additional method for analysis, comparison of high (-) feedback cultures, and pure astrocytes was also considered. Glial cells in pure astrocyte cultures tend to be larger in size than glial cells in high (-) feedback cultures. The potential effect of (-) feedback at the blood brain barrier (BBB) was also considered for the inflammatory responses of nitric oxide (NO) production and [Ca²⁺]_i regulation using brain microvascular endothelial cells (BMVECs). The inflammatory and calcium signaling pathways both indicate the negative feedback role of astrocytes, poised between the BBB and structures deeper within the brain, where neuronal synapses are homeostatically maintained by glial uptake of neurotransmitters.

Sigma 1 Receptor Modulates Optic Nerve Head Astrocyte Reactivity

Purpose

Stimulation of Sigma 1 Receptor (S1R) is neuroprotective in retina and optic nerve. S1R is expressed in both neurons and glia. The purpose of this work is to evaluate the ability of S1R to modulate reactivity responses of optic nerve head astrocytes (ONHAs) by investigating the extent to which S1R activation alters ONHA reactivity under conditions of ischemic cellular stress.

Methods

Wild type (WT) and S1R knockout (KO) ONHAs were derived and treated with vehicle or S1R agonist, (+)-pentazocine ((+)-PTZ). Cells were subjected to six hours of oxygen glucose deprivation (OGD) followed by 18 hours of re-oxygenation (OGD/R). Astrocyte reactivity responses were measured. Molecules that regulate ONHA reactivity, signal transducer and activator of transcription 3 (STAT3) and nuclear factor kappa B (NF-kB), were evaluated.

Results

Baseline glial fibrillary acidic protein (GFAP) levels were increased in nonstressed KO ONHAs compared with WT cultures. Baseline cellular migration was also increased in nonstressed KO ONHAs compared with WT. Treatment with (+)-PTZ increased cellular migration in nonstressed WT ONHAs but not in KO ONHAs. Exposure of both WT and KO ONHAs to ischemia (OGD/R), increased GFAP levels and cellular proliferation. However, (+)-PTZ treatment of OGD/R-exposed ONHAs enhanced GFAP levels, cellular proliferation, and cellular migration in WT but not KO cultures. The (+)-PTZ treatment of WT ONHAs also enhanced the OGD/R-induced increase in cellular pSTAT3 levels. However, treatment of WT ONHAs with (+)-PTZ abrogated the OGD/R-induced rise in NF-kB(p65) activation.

Conclusions

Under ischemic stress conditions, S1R activation enhanced ONHA reactivity characteristics. Future studies should address effects of these responses on RGC survival.

Aging is associated with glial senescence in the brainstem - implications for age-related sympathetic overactivity

Accumulating evidence suggests that the sympathetic nervous system (SNS) overactivity plays a crucial role in age-related increase in the risk for cardiovascular diseases such as hypertension, myocardial infarction, stroke and heart diseases. Previous studies indicate that neuroinflammation in key brainstem regions that regulate sympathetic outflow plays a pathogenic role in aging-mediated sympathoexcitation. However, the molecular mechanisms underlying this phenomenon are not clear. While senescent cells and their secretory phenotype (SASP) have been implicated in the pathogenesis of several age-related diseases, their role in age-related neuroinflammation in the brainstem and SNS overactivity has not been investigated. To test this, we isolated brainstems from young (2-4 months) and aged (24 months) male C57BL/6J mice and assessed senescence using a combination of RNA-in situ hybridization, PCR analysis, multiplex assay and SA-β gal staining. Our results show significant increases in p16Ink4a expression, increased activity of SA-β gal and increases in SASP levels in the aged brainstem, suggesting age-induced senescence in the brainstem. Further, analysis of senescence markers in glial cells enriched fraction from fresh brainstem samples demonstrated that glial cells are more susceptible to senesce with age in the brainstem. In conclusion, our study suggests that aging induces glial senescence in the brainstem which likely causes inflammation and SNS overactivity.

Transcriptional heterogeneity between primary adult grey and white matter astrocytes underlie differences in modulation of in vitro myelination

Background

Multiple sclerosis (MS) is an inflammation-mediated demyelinating disease of the central nervous system that eventually results in secondary axonal degeneration due to remyelination failure. Successful remyelination is orchestrated by astrocytes (ASTRs) and requires sequential activation, recruitment, and maturation of oligodendrocyte progenitor cells (OPCs). In both MS and experimental models, remyelination is more robust in grey matter (GM) than white matter (WM), which is likely related to local differences between GM and WM lesions. Here, we investigated whether adult gmASTRs and wmASTRs per se and in response to MS relevant Toll-like receptor (TLR) activation differently modulate myelination.

Methods

Differences in modulation of myelination between adult gmASTRs and wmASTRs were examined using an in vitro myelinating system that relies on a feeding layer of ASTRs. Transcriptional profiling and weighted gene co-expression network analysis were used to analyze differentially expressed genes and gene networks. Potential differential modulation of OPC proliferation and maturation by untreated adult gmASTRs and wmASTRs and in response to TLR3 and TLR4 agonists were assessed.

Results

Our data reveal that adult wmASTRs are less supportive to in vitro myelination than gmASTRs. WmASTRs more abundantly express reactive ASTR genes and genes of a neurotoxic subtype of ASTRs, while gmASTRs have more neuro-reparative transcripts. We identified a gene network module containing cholesterol biosynthesis enzyme genes that positively correlated with gmASTRs, and a network module containing extracellular matrix-related genes that positively correlated with wmASTRs. Adult wmASTRs and gmASTRs responding to TLR3 agonist Poly(I:C) distinctly modulate OPC behavior, while exposure to TLR4 agonist LPS of both gmASTRs and wmASTRs results in a prominent decrease in myelin membrane formation.

Conclusions

Primary adult gmASTRs and wmASTRs are heterogeneous at the transcriptional level, differed in their support of in vitro myelination, and their pre-existing phenotype determined TLR3 agonist responses. These findings point to a role of ASTR heterogeneity in regional differences in remyelination efficiency between GM and WM lesions.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-020-02045-3.

Astroglial asthenia and loss of function, rather than reactivity, contribute to the ageing of the brain

Astroglia represent a class of heterogeneous, in form and function, cells known as astrocytes, which provide for homoeostasis and defence of the central nervous system (CNS). Ageing is associated with morphological and functional remodelling of astrocytes with a prevalence of morphological atrophy and loss of function. In particular, ageing is associated with (i) decrease in astroglial synaptic coverage, (ii) deficits in glutamate and potassium clearance, (iii) reduced astroglial synthesis of synaptogenic factors such as cholesterol, (iv) decrease in aquaporin 4 channels in astroglial endfeet with subsequent decline in the glymphatic clearance, (v) decrease in astroglial metabolic support through the lactate shuttle, (vi) dwindling adult neurogenesis resulting from diminished proliferative capacity of radial stem astrocytes, (vii) decline in the astroglial-vascular coupling and deficient blood-brain barrier and (viii) decrease in astroglial ability to mount reactive astrogliosis. Decrease in reactive capabilities of astroglia are associated with rise of age-dependent neurodegenerative diseases. Astroglial morphology and function can be influenced and improved by lifestyle interventions such as intellectual engagement, social interactions, physical exercise, caloric restriction and healthy diet. These modifications of lifestyle are paramount for cognitive longevity.

Antioxidant and neuroprotective effects of mGlu3 receptor activation on astrocytes aged in vitro

Astrocytes play a key role by providing antioxidant support to nearby neurons under oxidative stress. We have previously demonstrated that in vitro astroglial subtype 3 metabotropic glutamate receptor (mGlu3R) is neuroprotective. However, its role during aging has been poorly explored. Our study aimed to determine whether LY379268, an mGlu3R agonist, exerts an antioxidant effect on aged cultured rat astrocytes. Aged cultured astrocytes obtained after 9-weeks (9w) in vitro were positive for β-galactosidase stain, showed decreased mGlu3R and glutathione (GSH) levels and superoxide dismutase (SOD) activity, while nuclear erythroid factor 2 (Nrf2) protein levels, reactive oxygen species (ROS) production and apoptosis were increased. Treatment of 9w astrocytes with LY379268 resulted in an increase in mGlu3R and Nrf2 protein levels and SOD activity, and decreased mitochondrial ROS levels and apoptosis. mGlu3R activation in aged astrocytes also prevented hippocampal neuronal death induced by Aβ_1-42 in co-culture assays. We conclude that activation of mGlu3R in aged astrocytes had an anti-oxidant effect and protected hippocampal neurons against Aβ-induced neurotoxicity. The present study suggests mGlu3R activation in aging astrocytes as a therapeutic strategy to slow down age-associated neurodegeneration.

Edaravone protects rat astrocytes from oxidative or neurotoxic inflammatory insults by restoring Akt/Bcl-2/Caspase-3 signaling axis

Astrocytes are the major glia cells in the central nervous system (CNS). Increasing evidence indicates that more than to be safe-guard and supporting cells for neurons, astrocytes play a broad spectrum of neuroprotective and pathological functions. Thus, they are compelling models to decipher mechanistic insights of glia cells to CNS insults and for the development of drugs. Edaravone is a free radical scavenger with the capacity to eliminate hydroxyl radicals and lipid peroxides. In this study, we examined the neuroprotective effects of edaravone in rat astrocytes challenged by hydrogen peroxide (H₂O₂) or bacterial lipopolysaccharides (LPS), respectively. We discovered that edaravone attenuated H₂O₂-induced oxidative stress by reactivating the Akt signaling axis and antagonistically restoring the expression of apoptosis associated regulators such as Bcl-2 and Caspase-3. Consistently, inhibition of Akt signaling by LY294002 attenuated the anti-oxidative activity of edaravone. In addition, edaravone mitigated LPS-induced morphological changes in astrocytes and alleviated the inflammatory activation and expression of TNF-α, IL-1β, IL-6 and NOS2. In summary, our data suggested that edavarone effectively protects astrocytes from oxidative stress or infectious insults, which may pave a new avenue for its application in preclinical research and human disease therapeutics.

Additive Effect of Resveratrol on Astrocyte Swelling Post-exposure to Ammonia, Ischemia and Trauma In Vitro

Swelling of astrocytes represents a major component of the brain edema associated with many neurological conditions, including acute hepatic encephalopathy (AHE), traumatic brain injury (TBI) and ischemia. It has previously been reported that exposure of cultured astrocytes to ammonia (a factor strongly implicated in the pathogenesis of AHE), oxygen/glucose deprivation, or to direct mechanical trauma results in an increase in cell swelling. Since dietary polyphenols have been shown to exert a protective effect against cell injury, we examined whether resveratrol (RSV, 3,5,4'-trihydroxy-trans-stilbene, a stilbenoid phenol), has a protective effect on astrocyte swelling following its exposure to ammonia, oxygen-glucose deprivation (OGD), or trauma in vitro. Ammonia increased astrocyte swelling, and pre- or post-treatment of astrocytes with 10 and 25 µM RSV displayed an additive effect, while 5 µM did not prevent the effect of ammonia. However, pre-treatment of astrocytes with 25 µM RSV slightly, but significantly, reduced the trauma-induced astrocyte swelling at earlier time points (3 h), while post-treatment had no significant effect on the trauma-induced cell swelling at the 3 h time point. Instead, pre- or post-treatment of astrocytes with 25 µM RSV had an additive effect on trauma-induced astrocyte swelling. Further, pre- or post-treatment of astrocytes with 5 or 10 µM RSV had no significant effect on trauma-induced astrocyte swelling. When 5 or 10 µM RSV were added prior to, or during the process of OGD, as well as post-OGD, it caused a slight, but not statistically significant decline in cell swelling. However, when 25 µM RSV was added during the process of OGD, as well as after the cells were returned to normal condition (90 min period), such treatment showed an additive effect on the OGD-induced astrocyte swelling. Noteworthy, a higher concentration of RSV (25 µM) exhibited an additive effect on levels of phosphorylated forms of ERK1/2, and p38^MAPK, as well as an increased activity of the Na⁺-K⁺-Cl^- co-transporter-1 (NKCC1), factors known to induce astrocytes swelling, when the cells were treated with ammonia or after trauma or ischemia. Further, inhibition of ERK1/2, and p38^MAPK diminished the RSV-induced exacerbation of cell swelling post-ammonia, trauma and OGD treatment. These findings strongly suggest that treatment of cultured astrocytes with RSV enhanced the ammonia, ischemia and trauma-induced cell swelling, likely through the exacerbation of intercellular signaling kinases and ion transporters. Accordingly, caution should be exercised when using RSV for the treatment of these neurological conditions, especially when brain edema is also suspected.

Titanium dioxide nanoparticles promote oxidative stress, autophagy and reduce NLRP3 in primary rat astrocytes

Titanium dioxide nanoparticles (TiO₂-NPs) are widely used in the food industry, cosmetics, personal care and paints among others. Through occupational exposure and daily consumption, and because of their small size, TiO₂-NPs can enter the body through different routes such as oral, dermal and inhalation, and accumulate in multiple organs including the brain. TiO₂-NPs cause severe damage to many cell types, however their effects in the central nervous system remain largely unexplored. Therefore, in the present study we determined the cytotoxic effect of TiO₂-NPs on rat astrocytes. We tested the oxidant properties of TiO₂-NPs through DTT depletion, and measured oxidative stress-induced damage in mitochondria, through oxidation of 2,7-dichlorodihydrofluorescein diacetate (H₂DCFDA) and loss of mitochondrial membrane potential (ΔΨm) with Mitotracker Green FM. We further examined oxidative stress-derived responses such as IκB-α degradation by Western Blot, NF-κB translocation by EMSA, autophagy induction by LC3-II levels, and expression of the inflammasome protein NLRP3. TiO₂-NPs showed high oxidant properties and induced strong oxidative stress in astrocytes following their internalization, causing mitochondrial damage detected by ΔΨm loss. Responses against oxidative damage such as NF-κB translocation and autophagy were induced and NLRP3 protein expression was downregulated, indicating lower inflammasome-mediated responses in astrocytes. These results support TiO₂-NPs cytotoxicity in astrocytes, cells that play key roles in neuronal homeostasis and their dysfunction can lead to neurological disorders including cognitive impairment and memory loss.

Isolation of endothelial cells, pericytes and astrocytes from mouse brain

Primary cell isolation from the central nervous system (CNS) has allowed fundamental understanding of blood-brain barrier (BBB) properties. However, poorly described isolation techniques or suboptimal cellular purity has been a weak point of some published scientific articles. Here, we describe in detail how to isolate and enrich, using a common approach, endothelial cells (ECs) from adult mouse brains, as well as pericytes (PCs) and astrocytes (ACs) from newborn mouse brains. Our approach allowed the isolation of these three brain cell types with purities of around 90%. Furthermore, using our protocols, around 3 times more PCs and 2 times more ACs could be grown in culture, as compared to previously published protocols. The cells were identified and characterized using flow cytometry and confocal microscopy. The ability of ECs to form a tight monolayer was assessed for passages 0 to 3. The expression of claudin-5, occludin, zonula occludens-1, P-glycoprotein-1 and breast cancer resistance protein by ECs, as well as the ability of the cells to respond to cytokine stimuli (TNF-α, IFN-γ) was also investigated by q-PCR. The transcellular permeability of ECs was evaluated in the presence of pericytes or astrocytes in a Transwell® model by measuring the transendothelial electrical resistance (TEER), dextran-FITC and sodium fluorescein permeability. Overall, ECs at passages 0 and 1 featured the best properties valued in a BBB model. Furthermore, pericytes did not increase tightness of EC monolayers, whereas astrocytes did regardless of their seeding location. Finally, ECs resuspended in fetal bovine serum (FBS) and dimethyl sulfoxide (DMSO) could be cryopreserved in liquid nitrogen without affecting their phenotype nor their capacity to form a tight monolayer, thus allowing these primary cells to be used for various longitudinal in vitro studies of the blood-brain barrier.

Mechanism of the neuroprotective effect of injecting brain cells on ST36 in an animal model of Parkinson's disease

In Parkinson's disease, the dopaminergic neurons of the brain are destroyed. Dopamine is an important neurotransmitter that acts on the basal ganglia of the brain, allowing precise body movement. In the early stages of Parkinson's disease, levodopa appears to alleviate clinical symptoms; however, during long-term use, motor complications occur. There is no clear treatment or remedy for Parkinson's disease; therefore, the development of novel therapies is urgently required. In the present study, mouse choroid plexus cells were transplanted into ST36 in a mouse model of Parkinson's disease to determine whether the motor function could be restored. Pole tests showed changes in motor dysfunction in the mice. The athletic ability of the mice was significantly lowered after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) injection and significantly increased after choroidal neuron cell treatment. Injection of di-alkyl indocarbocyanine (DiI) (as a trace substance) confirmed that the choroid plexus cells injected into acupuncture point ST36 were transferred to the brain. In the Parkinson's disease model, choroid plexus cell injection into ST36 inhibited the decrease in tyrosine hydroxylase (TH) expression and decreased the activation of inflammatory factors mitochondrial cytochrome C oxidase (COX2) and inducible NO synthase (iNOS). Apoptosis factors Cytochrome C and BCL2 associated X, apoptosis regulator (BAX) levels were decreased and B-Cell CLL/Lymphoma 2 (BCL2) levels were increased. Taken together, these results suggest that the injection of choroid plexus cell at ST36 had neuroprotective effects in the Parkinson's disease mouse model. The results suggest new possibilities for the treatment of Parkinson's disease.

Changes in Inflammatory Response, Redox Status and Na+, K+-ATPase Activity in Primary Astrocyte Cultures from Female Wistar Rats Subject to Ovariectomy

Astrocytes are dynamic glial cells that maintain brain homeostasis, particularly metabolic functions, inflammatory response, and antioxidant defense. Since menopause may be associated with brain dysfunction, in the present study, we evaluated anti- and proinflammatory cytokine release in cortical and hippocampal astrocyte cultures obtained from adult female Wistar rats subjected to ovariectomy, a known experimental model of menopause. We also tested some parameters of metabolic functionality (Na⁺, K⁺-ATPase activity) and cellular redox status, such as antioxidant enzyme defenses (superoxide dismutase and catalase) and the intracellular production of reactive oxygen species in this experimental model. Female adult Wistar rats (180 days-age) were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomy (submitted to surgery to removal of the ovaries). Thirty days after ovariectomy or sham surgery, we prepared astrocyte cultures from control and ovariectomy surgery animals. Ovariectomized rats presented an increase in pro-inflammatory cytokines (tumor necrosis factor α, interleukins 1β, 6, and 18) and a decrease in interleukin 10 release, an anti-inflammatory cytokine, in cortical and hippocampal astrocytes, when compared to those obtained from sham group (control). In addition, Na⁺,K⁺-ATPase activity decreased in hippocampal astrocytes, but not in cortical astrocyte cultures. In contrast, antioxidant enzymes did not alter in cortical astrocyte cultures, but increased in hippocampal astrocytes. In summary, our findings suggest that ovariectomy is able to induce an inflammatory response in vivo, which could be detected in in vitro astrocytes after approximately 4 weeks.

Astrocyte culture models: Molecular and function characterization of primary culture, immortalized astrocytes and C6 glioma cells

The understanding of the physiology of astrocytes and their role in brain function progresses continuously. Primary astrocyte culture is an alternative method to study these cells in an isolated system: in their physiologic and pathologic states. Cell lines are often used as an astrocyte model, since they are easier and faster to manipulate and cost less. However, there are a few studies evaluating the different features of these cells which may put into question the validity of using them as astrocyte models. The aim of this study was to compare primary cultures (PC) with two cell lines - immortalized astrocytes and C6 cells, in terms of protein characterization, morphology and metabolic functional activity. Our results showed, under the same culture condition, that immortalized astrocytes and C6 are positive for differentiated astrocytic markers (eg. GFAP, S100B, AQP4 and ALDH1L1), although expressing them in less quantities then primary astrocyte cultures. Glutamate metabolism and cell communication are reduced in proliferative cells. However, glucose uptake is elevated in C6 lineage cells in comparison with primary astrocytes, probably due to their tumorigenic origin and high proliferation rate. Immortalized astrocytes presented a lower growth rate than C6 cells, and a similar basal morphology as primary astrocytes. However, they did not prove to be as good reproductive models of some of the classic astrocytic functions, such as S100B secretion and GFAP content, especially while under stimulation. In contrast, C6 cells presented similar results in comparison to primary astrocytes in response to stimuli. Here we provide a functional comparison of three astrocytic models, in an attempt to select the most suitable model for the study of astrocytes, optimizing the research in this area of knowledge.

Activated peripheral blood mononuclear cell mediators trigger astrocyte reactivity

Sepsis is characterized by a severe and disseminated inflammation. In the central nervous system, sepsis promotes synaptic dysfunction and permanent cognitive impairment. Besides sepsis-induced neuronal dysfunction, glial cell response has been gaining considerable attention with microglial activation as a key player. By contrast, astrocytes' role during acute sepsis is still underexplored. Astrocytes are specialized immunocompetent cells involved in brain surveillance. In this context, the potential communication between the peripheral immune system and astrocytes during acute sepsis still remains unclear. We hypothesized that peripheral blood mononuclear cell (PBMC) mediators are able to affect the brain during an episode of acute sepsis. With this in mind, we first performed a data-driven transcriptome analysis of blood from septic patients to identify common features among independent clinical studies. Our findings evidenced pronounced impairment in energy-related signaling pathways in the blood of septic patients. Since astrocytes are key for brain energy homeostasis, we decided to investigate the communication between PBMC mediators and astrocytes in a rat model of acute sepsis, induced by cecal ligation and perforation (CLP). In the CLP animals, we identified widespread in vivo brain glucose hypometabolism. Ex vivo analyses demonstrated astrocyte reactivity along with reduced glutamate uptake capacity during sepsis. Also, by exposing cultured astrocytes to mediators released by PBMCs from CLP animals, we reproduced the energetic failure observed in vivo. Finally, by pharmacologically inhibiting phosphoinositide 3-kinase (PI3K), a central metabolic pathway downregulated in the blood of septic patients and reduced in the CLP rat brain, we mimicked the PBMC mediators effect on glutamate uptake but not on glucose metabolism. These results suggest that PBMC mediators are capable of directly mediating astrocyte reactivity and contribute to the brain energetic failure observed in acute sepsis. Moreover, the evidence of PI3K participation in this process indicates a potential target for therapeutic modulation.

High-glucose medium induces cellular differentiation and changes in metabolic functionality of oligodendroglia

Oligodendrocyte precursor cells (OPC) are a uniformly distributed population of glial cells that are well known for proliferating and differentiating into mature oligodendrocytes to form the myelin sheet in the central nervous system (CNS). Since monocarboxylate transporter 1 (MCT1) has shown to be expressed by oligodendroglia, the involvement of these cells with the metabolic support to axons has emerged as an important role in the maintenance of neuronal functionality. Hyperglycemia is a metabolic dysfunction highly associated with oxidative stress, a classical feature linked to many disorders such as diabetes mellitus. Despite of being widely investigated in several different cell cultures, including astrocytes and neurons, such condition has been poorly investigated in OPC culture. Thus, the aim of this study was to explore the possible effects of high-glucose exposure in acute and chronic conditions on oligodendroglial development and functionality in vitro. In this sense, we have demonstrated that under high-glucose exposure OPC improved its differentiation rate without affecting its membrane integrity and its morphology. Besides, chronic high-glucose condition also increased glucose uptake and lactate release. On the other hand, our findings also showed that, unlike what happens in other glial cells and neurons, high-glucose exposure did not seem to induce oxidative stress in OPC culture. Therefore, as far as we have investigated in this present study, we suggest that OPC may be able to support neurons and other glial cells during hyperglycemia events.

Astrocyte senescence: Evidence and significance

Astrocytes participate in numerous aspects of central nervous system (CNS) physiology ranging from ion balance to metabolism, and disruption of their physiological roles can therefore be a contributor to CNS dysfunction and pathology. Cellular senescence, one of the mechanisms of aging, has been proposed as a central component of the age dependency of neurodegenerative disorders. Cumulative evidence supports an integral role of astrocytes in the initiation and progression of neurodegenerative disease and cognitive decline with aging. The loss of astrocyte function or the gain of neuroinflammatory function as a result of cellular senescence could have profound implications for the aging brain and neurodegenerative disorders, and we propose the term “astrosenescence” to describe this phenotype. This review summarizes the current evidence pertaining to astrocyte senescence from early evidence, in vitro characterization and relationship to age‐related neurodegenerative disease. We discuss the significance of targeting senescent astrocytes as a novel approach toward therapies for age‐associated neurodegenerative disease.

The protection effect and mechanism of hyperbaric oxygen therapy in rat brain with traumatic injury

PURPOSE

To investigate the effect of hyperbaric oxygen therapy (HBOT) on traumatic brain injury (TBI) outcome.

METHODS

The modified Marmarou's weight drop device was used to generate non-lethal moderate TBI rat model, and further developed in vitro astrocytes culturing system. Then, we analyzed the expression changes of interested genes and protein by quantitative PCR and western blot.

RESULTS

Multiple HBO treatments significantly reduced the expression of apoptosis promoting genes, such as c-fos, c-jun, Bax and weakened the activation of Caspase-3 in model rats. On the contrary, HBOT alleviated the decrease of anti-apoptosis gene Bcl-2 and promoted the expression of neurotrophic factors (NTFs), such as NGF, BDNF, GDNF and NT-3 in vivo. As a consequent, the neuropathogenesis was remarkably relied with HBOT. Astrocytes from TBI brain or those cultured with 21% O2 density expressed higher NTFs than that of corresponding controls, from sham brain and cultured with 7% O2, respectively. The NTFs expression was the highest in astrocytes form TBI brain and cultured with 21% O2, suggesting a synergistic effect existed between TBI and the following HBO treatment in astrocytes.

CONCLUSION

Our findings provided evidence for the clinical usage of HBO treating brain damages.

The imidazoline I2 receptor agonist 2-BFI attenuates hypersensitivity and spinal neuroinflammation in a rat model of neuropathic pain

Chronic pain is a large, unmet public health problem. Recent studies have demonstrated the importance of neuroinflammation in the establishment and maintenance of chronic pain. However, pharmacotherapies that reduce neuroinflammation have not been successfully developed to treat chronic pain thus far. Several preclinical studies have established imidazoline I₂ receptor (I₂R) agonists as novel candidates for chronic pain therapies, and while some I₂R ligands appear to modulate neuroinflammation in certain scenarios, whether they exert anti-neuroinflammatory effects in models of chronic pain is unknown. This study examined the effects of the prototypical I₂R agonist 2-(2-benzofuranyl)-2-imidazoline hydrochloride (2-BFI) on hypersensitivity and neuroinflammation induced by chronic constriction injury (CCI), a neuropathic pain model in rats. In CCI rats, twice-daily treatment with 10 mg/kg 2-BFI for seven days consistently increased mechanical and thermal nociception thresholds, reduced GFAP and Iba-1 levels in the dorsal horn of the spinal cord, and reduced levels of TNF-α relative to saline treatment. These results were recapitulated in primary mouse cortical astrocyte cultures. Incubation with 2-BFI attenuated GFAP expression and supernatant TNF-α levels in LPS-stimulated cultures. These results suggest that I₂R agonists such as 2-BFI may reduce neuroinflammation which may partially account for their antinociceptive effects.

Monitoring Astrocyte Reactivity and Proliferation in Vitro Under Ischemic-Like Conditions

Ischemic stroke is a complex brain injury caused by a thrombus or embolus obstructing blood flow to parts of the brain. This leads to deprivation of oxygen and glucose, which causes energy failure and neuronal death. After an ischemic stroke insult, astrocytes become reactive and proliferate around the injury site as it develops. Under this scenario, it is difficult to study the specific contribution of astrocytes to the brain region exposed to ischemia. Therefore, this article introduces a methodology to study primary astrocyte reactivity and proliferation under an in vitro model of an ischemia-like environment, called oxygen glucose deprivation (OGD). Astrocytes were isolated from 1-4 day-old neonatal rats and the number of non-specific astrocytic cells was assessed using astrocyte selective marker Glial Fibrillary Acidic Protein (GFAP) and nuclear staining. The period in which astrocytes are subjected to the OGD condition can be customized, as well as the percentage of oxygen they are exposed to. This flexibility allows scientists to characterize the duration of the ischemic-like condition in different groups of cells in vitro. This article discusses the timeframes of OGD that induce astrocyte reactivity, hypertrophic morphology, and proliferation as measured by immunofluorescence using Proliferating Cell Nuclear Antigen (PCNA). Besides proliferation, astrocytes undergo energy and oxidative stress, and respond to OGD by releasing soluble factors into the cell medium. This medium can be collected and used to analyze the effects of molecules released by astrocytes in primary neuronal cultures without cell-to-cell interaction. In summary, this primary cell culture model can be efficiently used to understand the role of isolated astrocytes upon injury.

Age-Dependent Neurochemical Remodeling of Hypothalamic Astrocytes

The hypothalamus is a crucial integrative center in the central nervous system, responsible for the regulation of homeostatic activities, including systemic energy balance. Increasing evidence has highlighted a critical role of astrocytes in orchestrating hypothalamic functions; they participate in the modulation of synaptic transmission, metabolic and trophic support to neurons, immune defense, and nutrient sensing. In this context, disturbance of systemic energy homeostasis, which is a common feature of obesity and the aging process, involves inflammatory responses. This may be related to dysfunction of hypothalamic astrocytes. In this regard, the aim of this study was to evaluate the neurochemical properties of hypothalamic astrocyte cultures from newborn, adult, and aged Wistar rats. Age-dependent changes in the regulation of glutamatergic homeostasis, glutathione biosynthesis, amino acid profile, glucose metabolism, trophic support, and inflammatory response were observed. Additionally, signaling pathways including nuclear factor erythroid-derived 2-like 2/heme oxygenase-1 p38 mitogen-activated protein kinase, nuclear factor kappa B, phosphatidylinositide 3-kinase/Akt, and leptin receptor expression may represent putative mechanisms associated with the cellular alterations. In summary, our findings indicate that as age increases, hypothalamic astrocytes remodel and exhibit changes in their neurochemical properties. This process may play a role in the onset and/or progression of metabolic disorders.

Phosphorylation of astrocytic connexin43 by ERK1/2 impairs blood-brain barrier in acute cerebral ischemia

Background

Connexins are a family of transmembrane proteins that form gap junctions, which are important for diffusion of cytosolic factors such as ions and second messenger signaling molecules. Our previous study has shown that Connexin40 (Cx40), one dominant connexin expressed in brain, was involved in brain injury. In this study, Cx43, another dominant connexin in brain, was investigated. Using bilateral common carotid artery occlusion-induced ischemia rat model, we tested the expression and phosphorylation level of Cx43 as well as heteromeric Cx40/Cx43 complex formation in brain after ischemia induction. We screened total 16 kinase inhibitors to identify the kinase for Cx43 phosphorylation and confirmed the result using siRNA targeting the specific kinase. Finally, we explored the role of the identified kinase in brain damage using in vivo rat model.

Results

We discovered that phosphorylation of Cx43 increased after ischemia. The formation of Cx40/Cx43 heteromeric complex on membrane also increased. Inhibition of ERK activity resulted in inhibition of Cx43 phosphorylation on astrocytes. In in vivo model, application of ERK inhibitor and siRNA prevented brain damage and protected blood–brain barrier integrity in rat.

Conclusion

Our study provides evidence that Cx43 phosphorylation by ERK is implicated in ischemia induced brain damage.

Bidirectional apical-basal traffic of the cation-independent mannose-6-phosphate receptor in brain endothelial cells

Brain capillary endothelium mediates the exchange of nutrients between blood and brain parenchyma. This barrier function of the brain capillaries also limits passage of pharmaceuticals from blood to brain, which hinders treatment of several neurological disorders. Receptor-mediated transport has been suggested as a potential pharmaceutical delivery route across the brain endothelium, e.g. reports have shown that the transferrin receptor (TfR) facilitates transcytosis of TfR antibodies, but it is not known whether this recycling receptor itself traffics from apical to basal membrane in the process. Here, we elucidate the endosomal trafficking of the retrograde transported cation-independent mannose-6-phosphate receptor (MPR300) in primary cultures of brain endothelial cells (BECs) of porcine and bovine origin. Receptor expression and localisation of MPR300 in the endo-lysosomal system and trafficking of internalised receptor are analysed. We also demonstrate that MPR300 can undergo bidirectional apical-basal trafficking in primary BECs in co-culture with astrocytes. This is, to our knowledge, the first detailed study of retrograde transported receptor trafficking in BECs, and the study demonstrates that MPR300 can be transported from the luminal to abluminal membrane and reverse. Such trafficking of MPR300 suggests that retrograde transported receptors in general may provide a mechanism for transport of pharmaceuticals into the brain.

Hippocampal Astrocyte Cultures from Adult and Aged Rats Reproduce Changes in Glial Functionality Observed in the Aging Brain

Astrocytes are dynamic cells that maintain brain homeostasis, regulate neurotransmitter systems, and process synaptic information, energy metabolism, antioxidant defenses, and inflammatory response. Aging is a biological process that is closely associated with hippocampal astrocyte dysfunction. In this sense, we demonstrated that hippocampal astrocytes from adult and aged Wistar rats reproduce the glial functionality alterations observed in aging by evaluating several senescence, glutamatergic, oxidative and inflammatory parameters commonly associated with the aging process. Here, we show that the p21 senescence-associated gene and classical astrocyte markers, such as glial fibrillary acidic protein (GFAP), vimentin, and actin, changed their expressions in adult and aged astrocytes. Age-dependent changes were also observed in glutamate transporters (glutamate aspartate transporter (GLAST) and glutamate transporter-1 (GLT-1)) and glutamine synthetase immunolabeling and activity. Additionally, according to in vivo aging, astrocytes from adult and aged rats showed an increase in oxidative/nitrosative stress with mitochondrial dysfunction, an increase in RNA oxidation, NADPH oxidase (NOX) activity, superoxide levels, and inducible nitric oxide synthase (iNOS) expression levels. Changes in antioxidant defenses were also observed. Hippocampal astrocytes also displayed age-dependent inflammatory response with augmentation of proinflammatory cytokine levels, such as TNF-α, IL-1β, IL-6, IL-18, and messenger RNA (mRNA) levels of cyclo-oxygenase 2 (COX-2). Furthermore, these cells secrete neurotrophic factors, including glia-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), S100 calcium-binding protein B (S100B) protein, and transforming growth factor-β (TGF-β), which changed in an age-dependent manner. Classical signaling pathways associated with aging, such as nuclear factor erythroid-derived 2-like 2 (Nrf2), nuclear factor kappa B (NFκB), heme oxygenase-1 (HO-1), and p38 mitogen-activated protein kinase (MAPK), were also changed in adult and aged astrocytes and are probably related to the changes observed in senescence marker, glutamatergic metabolism, mitochondrial dysfunction, oxidative/nitrosative stress, antioxidant defenses, inflammatory response, and trophic factors release. Together, our results reinforce the role of hippocampal astrocytes as a target for understanding the mechanisms involved in aging and provide an innovative tool for studies of astrocyte roles in physiological and pathological aging brain.

Glioprotective Effect of Resveratrol: an Emerging Therapeutic Role for Oligodendroglial Cells

Resveratrol is a natural polyphenol compound highly found in red wine that displays several beneficial effects on the central nervous system (CNS), preventing or slowing the progression of a wide variety of neurological diseases. Its neuroprotective role is particularly associated to modulation of antioxidant and anti-inflammatory responses in glial cells in a mechanism dependent of heme oxygenase 1 (HO-1) signaling pathway. Oligodendrocyte progenitor cells (OPC), primarily known for giving rise to mature oligodendrocytes, have emerged as dynamic cells that are also important to maintain the CNS homeostasis. In this sense, we have demonstrated that resveratrol has a protective effect on oligodendroglial functionality against lipopolysaccharide (LPS)-mediated cytotoxicity and that its glioprotective mechanism involves the nuclear factor erythroid 2-related factor 2 (Nrf2) and HO-1 pathways. LPS, through toll-like receptor 4 (TLR4), affected the release of trophic factors by OPC, including transforming growth factor beta (TGF-β), brain-derived neurotrophic factor (BDNF), and glial cell-derived neurotrophic factor (GDNF), and resveratrol reestablished the trophic factor release to control levels. Additionally, resveratrol prevented the LPS-induced increase in the intracellular reactive oxygen species (ROS) as well as the decrease in glutathione (GSH) levels and in glutamate cysteine ligase (GCL) activity, through Nrf2/HO-1 signaling pathways. Resveratrol also prevented the increase of the transcriptional activities of nuclear factor κB (NFκB) and hypoxia-inducible factor 1 alpha (HIF-1α) after LPS challenge. In summary, this is the first study showing the glioprotective effect of resveratrol on oligodendroglial cells.

Systemic Inflammation as a Driver of Brain Injury: the Astrocyte as an Emerging Player

Severe systemic inflammation has strong effects on brain functions, promoting permanent neurocognitive dysfunction and high mortality rates. Additionally, hippocampal damage seems to be directly involved in this process and astrocytes play an important role in neuroinflammation and in the neuroimmune response. However, the contribution of the astrocytes to the pathology of acute brain dysfunction is not well understood. Recently, our group established a protocol for obtaining astrocyte cultures from mature brain to allow the characterization of these cells and their functions under pathologic conditions. The present study was designed to characterize astrocyte function after acute systemic inflammation induced by cecal ligation and perforation (CLP). Hippocampal astrocyte cultures from CLP animals presented increased levels of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, IL-18, and cyclooxygenase-2 and decreased levels of IL-10. This proinflammatory profile was accompanied by an increase in Toll-like receptor (TLR)2 mRNA expression levels and no change either in TLR4 or in vascular endothelial growth factor (VEGF) gene expression. These alterations were associated with increased expressions of p21, nuclear factor kappa B (NFκB), and inducible nitric oxide synthase (iNOS) in astrocytes from CLP animals. The same parameters were also evaluated in whole hippocampal tissue, but differences in this profile were found compared to hippocampal astrocyte cultures from CLP, reflecting an interaction between other central nervous system cell types, which may mask specific astrocytic changes. These results improve our understanding of the mechanisms by which astrocytes react against systemic inflammation, and suggest these cells to be potential targets for therapeutic modulation.

Astrocyte-mediated inflammation in cortical spreading depression

Background Cortical spreading depression (CSD) related diseases such as migraine, cerebrovascular diseases, and epilepsy have been associated with reactive astrocytosis, yet the mechanisms of these tissue changes remain unclear. CSD-induced inflammatory response has been proposed to play a role in some neurological disorders and thus may also contribute to reactive astrocytosis. Methods Using ex vivo brain slices and in vitro astrocytic cultures, we aimed to characterize CSD related changes in astrocytes and markers of inflammation by immunocyto- and immunohistochemistry. CSD was induced by application of KCl (3 mol/l) on neocortical tissues. The application of KCl was repeated weekly over the course of four weeks. Results CSD induced an increase in the mean number and volume of astrocytes in rat brain tissue when compared to controls, whereas no changes in neuronal numbers and volumes were seen. These cell-type specific changes, suggestive of reactive astrocytosis, were paralleled by an increased expression of protein markers indicative of astrocytes and neuroinflammation in ex vivo brain slices of animals undergoing CSD when compared to sham-treated controls. Cultured astrocytes showed an increased expression of the immune modulatory enzyme indoleamine 2,3-dioxygenase and an elevated expression of the pro-inflammatory markers, IL-6, IL-1β, and TNFα in addition to increased levels of toll like receptors (TLR3 and TLR4) and astrocytic markers after induction of CSD. Conclusion These findings indicate that CSD related reactive astrocytosis is linked to an upregulation of inflammatory markers. Targeting inflammation with already approved and available immunomodulatory treatments may thus represent a strategy to combat or ameliorate CSD-related disease.

Homocysteine Induces Glial Reactivity in Adult Rat Astrocyte Cultures

Astrocytes are dynamic glial cells associated to neurotransmitter systems, metabolic functions, antioxidant defense, and inflammatory response, maintaining the brain homeostasis. Elevated concentrations of homocysteine (Hcy) are involved in the pathogenesis of age-related neurodegenerative disorders, such as Parkinson and Alzheimer diseases. In line with this, our hypothesis was that Hcy could promote glial reactivity in a model of cortical primary astrocyte cultures from adult Wistar rats. Thus, cortical astrocytes were incubated with different concentrations of Hcy (10, 30, and 100 μM) during 24 h. After the treatment, we analyzed cell viability, morphological parameters, antioxidant defenses, and inflammatory response. Hcy did not induce any alteration in cell viability; however, it was able to induce cytoskeleton rearrangement. The treatment with Hcy also promoted a significant decrease in the activities of Na⁺, K⁺ ATPase, superoxide dismutase (SOD), and glutathione peroxidase (GPx), as well as in the glutathione (GSH) content. Additionally, Hcy induced an increase in the pro-inflammatory cytokine release. In an attempt to elucidate the putative mechanisms involved in the Hcy-induced glial reactivity, we measured the nuclear factor kappa B (NFκB) transcriptional activity and heme oxygenase 1 (HO-1) expression, which were activated and inhibited by Hcy, respectively. In summary, our findings provide important evidences that Hcy modulates critical astrocyte parameters from adult rats, which might be associated to the aging process.

[18F]FDG PET signal is driven by astroglial glutamate transport

Contributions of glial cells to neuroenergetics have been the focus of extensive debate. Here we provide the first positron emission tomography (PET) evidence that activation of the astrocytic glutamate transport via GLT-1 triggers widespread but graded glucose uptake in the rodent brain. Our results highlight the need for a reevaluation of the interpretation of [¹⁸F]FDG PET data, whereby astrocytes would be recognized to contribute significantly to the [¹⁸F]FDG signal.

Sex Differences in Mouse Hippocampal Astrocytes after In-Vitro Ischemia

Astrogliosis following hypoxia/ischemia (HI)-related brain injury plays a role in increased morbidity and mortality in neonates. Recent clinical studies indicate that the severity of brain injury appear to be sex dependent, and that the male neonates are more susceptible to the effects of HI-related brain injury, resulting in more severe neurological outcomes as compared to females with comparable brain injuries. The development of reliable methods to isolate and maintain highly enriched populations of sexed hippocampal astrocytes is essential to understand the cellular basis of sex differences in the pathological consequences of neonatal HI. In this study, we describe a method for creating sex specific hippocampal astrocyte cultures that are subjected to a model of in-vitro ischemia, oxygen-glucose deprivation, followed by reoxygenation. Subsequent reactive astrogliosis was examined by immunostaining for the Glial Fibrillary Acidic Protein (GFAP) and S100B. This method provides a useful tool to study the role of male and female hippocampal astrocytes following neonatal HI, separately.

Fluctuations in glucose levels induce glial toxicity with glutamatergic, oxidative and inflammatory implications

Astrocytes are dynamic cells that maintain brain homeostasis by regulating neurotransmitter systems, antioxidant defenses, inflammatory responses and energy metabolism. Astroglial cells are also primarily responsible for the uptake and metabolism of glucose in the brain. Diabetes mellitus (DM) is a pathological condition characterized by hyperglycemia and is associated with several changes in the central nervous system (CNS), including alterations in glial function. Classically, excessive glucose concentrations are used to induce experimental models of astrocyte dysfunction; however, hypoglycemic episodes may also cause several brain injuries. The main focus of the present study was to evaluate how fluctuations in glucose levels induce cytotoxicity. The culture medium of astroglial cells was replaced twice as follows: (1) from 6mM (control) to 12mM (high glucose), and (2) from 12mM to 0mM (glucose deprivation). Cell viability, mitochondrial function, oxidative/nitrosative stress, glutamate metabolism, inflammatory responses, nuclear factor κB (NFκB) transcriptional activity and p38 mitogen-activated protein kinase (p38 MAPK) levels were assessed. Our in vitro experimental model showed that up and down fluctuations in glucose levels decreased cell proliferation, induced mitochondrial dysfunction, increased oxidative/nitrosative stress with consequent cellular biomolecular damage, impaired glutamate metabolism and increased pro-inflammatory cytokine release. Additionally, activation of the NFκB and p38 signaling pathways were putative mechanisms of the effects of glucose fluctuations on astroglial cells. In summary, for the first time, we show that changes in glucose concentrations, from high-glucose levels to glucose deprivation, exacerbate glial injury.

Anti-aging effects of guanosine in glial cells

Guanosine, a guanine-based purine, has been shown to exert beneficial roles in in vitro and in vivo injury models of neural cells. Guanosine is released from astrocytes and modulates important astroglial functions, including glutamatergic metabolism, antioxidant, and anti-inflammatory activities. Astrocytes are crucial for regulating the neurotransmitter system and synaptic information processes, ionic homeostasis, energy metabolism, antioxidant defenses, and the inflammatory response. Aging is a natural process that induces numerous changes in the astrocyte functionality. Thus, the search for molecules able to reduce the glial dysfunction associated with aging may represent an approach for avoiding the onset of age-related neurological diseases. Hence, the aim of this study was to evaluate the anti-aging effects of guanosine, using primary astrocyte cultures from newborn, adult, and aged Wistar rats. Concomitantly, we evaluated the role of heme oxygenase 1 (HO-1) in guanosine-mediated glioprotection. We observed age-dependent changes in glutamate uptake, glutamine synthetase (GS) activity, the glutathione (GSH) system, pro-inflammatory cytokine (tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β)) release, and the transcriptional activity of nuclear factor kB (NFkB), which were prevented by guanosine in an HO-1-dependent manner. Our findings suggest guanosine to be a promising therapeutic agent able to provide glioprotection during the aging process. Thus, this study contributes to the understanding of the cellular and molecular mechanisms of guanosine in the aging process.

Higher Vulnerability of Menadione-Exposed Cortical Astrocytes of Glutaryl-CoA Dehydrogenase Deficient Mice to Oxidative Stress, Mitochondrial Dysfunction, and Cell Death: Implications for the Neurodegeneration in Glutaric Aciduria Type I

Patients affected by glutaric aciduria type I (GA-I) show progressive cortical leukoencephalopathy whose pathogenesis is poorly known. In the present work, we exposed cortical astrocytes of wild-type (Gcdh ^+/+ ) and glutaryl-CoA dehydrogenase knockout (Gcdh ^-/- ) mice to the oxidative stress inducer menadione and measured mitochondrial bioenergetics, redox homeostasis, and cell viability. Mitochondrial function (MTT and JC1-mitochondrial membrane potential assays), redox homeostasis (DCFH oxidation, nitrate and nitrite production, GSH concentrations and activities of the antioxidant enzymes SOD and GPx), and cell death (propidium iodide incorporation) were evaluated in primary cortical astrocyte cultures of Gcdh ^+/+ and Gcdh ^-/- mice unstimulated and stimulated by menadione. We also measured the pro-inflammatory response (TNFα levels, IL1-β and NF-ƙB) in unstimulated astrocytes obtained from these mice. Gcdh ^-/- mice astrocytes were more vulnerable to menadione-induced oxidative stress (decreased GSH concentrations and altered activities of the antioxidant enzymes), mitochondrial dysfunction (decrease of MTT reduction and JC1 values), and cell death as compared with Gcdh ^+/+ astrocytes. A higher inflammatory response (TNFα, IL1-β and NF-ƙB) was also observed in Gcdh ^-/- mice astrocytes. These data indicate a higher susceptibility of Gcdh ^-/- cortical astrocytes to oxidative stress and mitochondrial dysfunction, probably leading to cell death. It is presumed that these pathomechanisms may contribute to the cortical leukodystrophy observed in GA-I patients.