Lesion-Induced Alterations in Astrocyte Glutamate Transporter Expression and Function in the Hippocampus

Astrocytes express the sodium-dependent glutamate transporters GLAST and GLT-1, which are critical to maintain low extracellular glutamate concentrations. Here, we analyzed changes in their expression and function following a mechanical lesion in the CA1 area of organotypic hippocampal slices. 6-7 days after lesion, a glial scar had formed along the injury site, containing strongly activated astrocytes with increased GFAP and S100β immunoreactivity, enlarged somata, and reduced capability for uptake of SR101. Astrocytes in the scar’s periphery were swollen as well, but showed only moderate upregulation of GFAP and S100β and efficiently took up SR101. In the scar, clusters of GLT-1 and GLAST immunoreactivity colocalized with GFAP-positive fibers. Apart from these, GLT-1 immunoreactivity declined with increasing distance from the scar, whereas GLAST expression appeared largely uniform. Sodium imaging in reactive astrocytes indicated that glutamate uptake was strongly reduced in the scar but maintained in the periphery. Our results thus show that moderately reactive astrocytes in the lesion periphery maintain overall glutamate transporter expression and function. Strongly reactive astrocytes in the scar, however, display clusters of GLAST and GLT-1 immunoreactivity together with reduced glutamate transport activity. This reduction might contribute to increased extracellular glutamate concentrations and promote excitotoxic cell damage at the lesion site.

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Differential Promotion of Glutamate Transporter Expression and Function by Glucocorticoids in Astrocytes from Various Brain Regions

Journal of Biological Chemistry ◽

10.1074/jbc.m502581200 ◽

2005 ◽

Vol 280 (41) ◽

pp. 34924-34932 ◽

Cited By ~ 90

Author(s):

Jürgen Zschocke ◽

Nadhim Bayatti ◽

Albrecht M. Clement ◽

Heidrun Witan ◽

Maciej Figiel ◽

...

Keyword(s):

Glutamate Transporter ◽

Brain Regions ◽

And Function ◽

Transporter Expression

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Ischemic Preconditioning Reveals that GLT1/EAAT2 Glutamate Transporter is a Novel PPARγ Target Gene Involved in Neuroprotection

Journal of Cerebral Blood Flow & Metabolism ◽

10.1038/sj.jcbfm.9600438 ◽

2007 ◽

Vol 27 (7) ◽

pp. 1327-1338 ◽

Cited By ~ 103

Author(s):

Cristina Romera ◽

Olivia Hurtado ◽

Judith Mallolas ◽

Marta P Pereira ◽

Jesús R Morales ◽

...

Keyword(s):

Nervous System ◽

Ischemic Preconditioning ◽

Transcriptional Activity ◽

Target Gene ◽

Glutamate Uptake ◽

Glutamate Release ◽

Glutamate Transporter ◽

Glutamate Transport ◽

Extracellular Glutamate ◽

Pparγ Agonist

Excessive levels of extracellular glutamate in the nervous system are excitotoxic and lead to neuronal death. Glutamate transport, mainly by glutamate transporter GLT1/EAAT2, is the only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels in the central nervous system. We recently showed that neuroprotection after experimental ischemic preconditioning (IPC) involves, at least partly, the upregulation of the GLT1/EAAT2 glutamate transporter in astrocytes, but the mechanisms were unknown. Thus, we decided to explore whether activation of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ, known for its antidiabetic and antiinflammatory properties, is involved in glutamate transport. First, we found that the PPARγ antagonist T0070907 inhibits both IPC-induced tolerance and reduction of glutamate release after lethal oxygen-glucose deprivation (OGD) (70.1% ± 3.4% versus 97.7% ± 5.2% of OGD-induced lactate dehydrogenase (LDH) release and 61.8% ± 5.9% versus 85.9% ± 7.9% of OGD-induced glutamate release in IPC and IPC + T0070907 1 μmol/L, respectively, n = 6 to 12, P < 0.05), as well as IPC-induced astrocytic GLT-1 overexpression. IPC also caused an increase in nuclear PPARγ transcriptional activity in neurons and astrocytes (122.1% ± 8.1% and 158.6% ± 22.6% of control PPARγ transcriptional activity, n = 6, P < 0.05). Second, the PPARγ agonist rosiglitazone increased both GLT-1/EAAT2 mRNA and protein expression and [3H]glutamate uptake, and reduced OGD-induced cell death and glutamate release (76.3% ± 7.9% and 65.5% ± 15.1% of OGD-induced LDH and glutamate release in rosiglitazone 1 μmol/l, respectively, n = 6 to 12, P < 0.05). Finally, we have identified six putative PPAR response elements (PPREs) in the GLT1/EAAT2 promoter and, consistently, rosiglitazone increased fourfold GLT1/EAAT2 promoter activity. All these data show that the GLT1/EAAT2 glutamate transporter is a target gene of PPARγ leading to neuroprotection by increasing glutamate uptake.

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Glutamate transporter expression and function in human glial progenitors

Glia ◽

10.1002/glia.10310 ◽

2004 ◽

Vol 45 (2) ◽

pp. 133-143 ◽

Cited By ~ 51

Author(s):

Nicholas J. Maragakis ◽

Joerg Dietrich ◽

Victor Wong ◽

Haipeng Xue ◽

Margot Mayer-Proschel ◽

...

Keyword(s):

Glutamate Transporter ◽

Glial Progenitors ◽

And Function ◽

Transporter Expression

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Atorvastatin prevents cell damage via modulation of oxidative stress, glutamate uptake and glutamine synthetase activity in hippocampal slices subjected to oxygen/glucose deprivation

Neurochemistry International ◽

10.1016/j.neuint.2013.03.002 ◽

2013 ◽

Vol 62 (7) ◽

pp. 948-955 ◽

Cited By ~ 22

Author(s):

Samuel Vandresen-Filho ◽

Wagner C. Martins ◽

Daniela B. Bertoldo ◽

Gianni Mancini ◽

Bruno A. Herculano ◽

...

Keyword(s):

Oxidative Stress ◽

Glutamine Synthetase ◽

Cell Damage ◽

Glutamate Uptake ◽

Hippocampal Slices ◽

Glucose Deprivation ◽

Oxygen Glucose Deprivation ◽

Synthetase Activity ◽

Glutamine Synthetase Activity

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Astrocytic group I mGluR-dependent potentiation of astrocytic glutamate and potassium uptake

Journal of Neurophysiology ◽

10.1152/jn.00517.2012 ◽

2013 ◽

Vol 109 (9) ◽

pp. 2404-2414 ◽

Cited By ~ 33

Author(s):

Prakash Devaraju ◽

Min-Yu Sun ◽

Timothy L. Myers ◽

Kelli Lauderdale ◽

Todd A. Fiacco

Keyword(s):

Charge Transfer ◽

Metabotropic Glutamate Receptors ◽

Glutamate Uptake ◽

Hippocampal Slices ◽

Glutamate Transporter ◽

Metabotropic Glutamate ◽

Group I ◽

Group I Mglurs ◽

G Protein Coupled

One of the most important functions of astrocytes is removal of glutamate released during synaptic transmission. Surprisingly, the mechanisms by which astrocyte glutamate uptake is acutely modulated remain to be clarified. Astrocytes express metabotropic glutamate receptors (mGluRs) and other G protein-coupled receptors (GPCRs), which are activated during neuronal activity. Here, we test the hypothesis that astrocytic group I mGluRs acutely regulate glutamate uptake by astrocytes in situ. This hypothesis was tested in acute mouse hippocampal slices. Activation of astrocytic mGluRs, using a tetanic high-frequency stimulus (HFS) applied to Schaffer collaterals, led to potentiation of the amplitude of the synaptically evoked glutamate transporter currents (STCs) and associated charge transfer without changes in kinetics. Similar potentiation of STCs was not observed in the presence of group I mGluR antagonists or the PKC inhibitor, PKC 19–36, suggesting that HFS-induced potentiation of astrocyte glutamate uptake is astrocytic group I mGluR and PKC dependent. Pharmacological stimulation of a transgenic GPCR (MrgA1R), expressed exclusively in astrocytes, also potentiated STC amplitude and charge transfer, albeit quicker and shorter lasting compared with HFS-induced potentiation. The amplitude of the slow, inward astrocytic current due to potassium (K+) influx was also enhanced following activation of the endogenous mGluRs or the astrocyte-specific MrgA1 Gq GPCRs. Taken together, these findings suggest that astrocytic group I mGluR activation has a synergistic, modulatory effect on the uptake of glutamate and K+.

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Yokukansan, a Traditional Japanese Medicine, Enhances the Glutamate Transporter GLT-1 Function in Cultured Rat Cortical Astrocytes

Evidence-based Complementary and Alternative Medicine ◽

10.1155/2018/6804017 ◽

2018 ◽

Vol 2018 ◽

pp. 1-9 ◽

Cited By ~ 2

Author(s):

Toshiyuki Ueki ◽

Zenji Kawakami ◽

Hitomi Kanno ◽

Yuji Omiya ◽

Kazushige Mizoguchi ◽

...

Keyword(s):

Glutamate Uptake ◽

Glutamate Transporter ◽

Culture Conditions ◽

Mrna Levels ◽

Extracellular Glutamate ◽

Cultured Astrocytes ◽

Traditional Japanese Medicine ◽

Uptake Activity ◽

The Brain ◽

Necrosis Factor

Astrocytes carry two glutamate transporters—GLAST and GLT-1—the latter of which is responsible for >90% of glutamate uptake activity in the brain; however, under culture conditions, the GLT-1 expression in astrocytes is exceedingly low, as is the glutamate uptake activity mediated by GLT-1. This study aimed to elucidate the effects of yokukansan (YKS) in relation to the GLT-1-mediated regulation of extracellular glutamate concentrations. Thus, we treated cultured astrocytes with tumor necrosis factor-α (TNF-α) and dibutyryl-cAMP (dBcAMP) (hereinafter, referred to as “TA”) to increase GLT-1 expression and then functionally examined how YKS would affect glutamate uptake ability derived from GLT-1. Contrary to expectations, although the TA treatments did not affect the uptake activity, YKS significantly augmented it. Conversely, GLAST-derived glutamate uptake was significantly reduced by TA treatments but was unaffected by YKS. Subsequently, we analyzed the GLT-1 protein and mRNA levels and found that TA treatments had significantly increased them, which were then further augmented by YKS. These findings suggest that YKS enhances GLT-1-derived glutamate transport functions in TA-treated cultured astrocytes and that this process entails increased GLT-1 protein and mRNA levels. This type of mechanism may contribute to the YKS-mediated regulation of extracellular glutamate concentrations.

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The non-adrenergic imidazoline-1 receptor protein Nischarin is a key regulator of astrocyte glutamate uptake

10.1101/2020.11.28.402222 ◽

2020 ◽

Author(s):

Swati Gupta ◽

Narges Bazargani ◽

James Drew ◽

Souvik Modi ◽

Hélène Marie ◽

...

Keyword(s):

Drug Targets ◽

Glutamate Uptake ◽

Glutamate Transporter ◽

Super Resolution ◽

Surface Expression ◽

Glutamate Excitotoxicity ◽

Receptor Protein ◽

List Type ◽

And Function ◽

Novel Drug

SummaryAstrocytic GLT-1 is the main glutamate transporter involved in glutamate buffering in the brain, pivotal for glutamate removal at excitatory synapses to terminate neurotransmission and for preventing excitotoxicity. We show here that the surface expression and function of GLT-1 can be rapidly modulated through the interaction of its N-terminus with the nonadrenergic imidazoline-1 receptor protein, Nischarin. The phox domain of Nischarin is critical for interaction and internalization of surface GLT-1. Using live super-resolution imaging, we found that glutamate accelerated Nischarin-GLT-1 internalization into endosomal structures. The surface GLT-1 level increased in Nischarin knockout astrocytes, and this correlated with a significant increase in transporter uptake current. Furthermore, Nischarin knockout in astrocytes is neuroprotective against glutamate excitotoxicity. These data provide new molecular insights into regulation of GLT-1 surface level and function and suggest novel drug targets for the treatment of neurological disorders.HighlightsThe phox domain of Nischarin interacts with the N-terminal tail of the main astrocyte glutamate transporter, GLT-1.Nischarin promotes internalization of GLT-1 to endosomes.Glutamate modulates GLT-1 surface levels via regulation of the Nischarin-GLT-1 interaction.Genetic loss of Nischarin significantly increases GLT-1 surface expression, resulting in increased glutamate transport currents and enhanced neuroprotection.

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Astrocytic glutamate uptake coordinates experience-dependent, eye-specific refinement in developing visual cortex

10.1101/2020.05.25.113613 ◽

2020 ◽

Author(s):

Grayson Sipe ◽

Jeremy Petravicz ◽

Rajeev Rikhye ◽

Rodrigo Garcia ◽

Nikolaos Mellios ◽

...

Keyword(s):

Visual Cortex ◽

Glutamate Uptake ◽

Ocular Dominance ◽

Glutamate Transporter ◽

Monocular Deprivation ◽

Spine Density ◽

Ocular Dominance Plasticity ◽

Contralateral Eye ◽

Cortical Inputs ◽

And Function

ABSTRACTThe uptake of glutamate by astrocytes actively shapes synaptic transmission, however its role in the development and plasticity of neuronal circuits remains poorly understood. The astrocytic glutamate transporter, GLT1 is the predominant source of glutamate clearance in the adult mouse cortex. Here, we examined the structural and functional development of the visual cortex in GLT1 heterozygous (HET) mice using two-photon microscopy, immunohistochemistry and slice electrophysiology. We find that though eye-specific thalamic axonal segregation is intact, binocular refinement in the primary visual cortex is disrupted. Eye-specific responses to visual stimuli in GLT1 HET mice show altered binocular matching, with abnormally high responses to ipsilateral compared to contralateral eye stimulation and a greater mismatch between preferred orientation selectivity of ipsilateral and contralateral eye responses. Furthermore, the balance of excitation and inhibition in cortical circuits is dysregulated with an increase in somatostatin positive interneurons, decrease in parvalbumin positive interneurons, and increase in dendritic spine density in the basal dendrites of layer 2/3 excitatory neurons. Monocular deprivation induces atypical ocular dominance plasticity in GLT1 HET mice, with an unusual depression of ipsilateral open eye responses; however, this change in ipsilateral responses correlates well with an upregulation of GLT1 protein following monocular deprivation. These results demonstrate that a key function of astrocytic GLT1 function during development is the experience-dependent refinement of ipsilateral eye inputs relative to contralateral eye inputs in visual cortex.SIGNIFICANCEWe show that astrocytic glutamate uptake via the transporter GLT1 is necessary for activity-dependent regulation of cortical inputs. Dysregulation of GLT1 expression and function leads to a disruption of binocular refinement and matching in visual cortex. Inputs from the ipsilateral eye are stronger, and monocular deprivation, which upregulates GLT1 expression in a homeostatic fashion, causes a paradoxical reduction of ipsilateral, non-deprived eye, responses. These results provide new evidence for the importance of glutamate transport in cortical development, function, and plasticity.

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