Impairment of Neuronal Glutamate Uptake and Modulation of the Glutamate Transporter GLT-1 Induced by Retinal Ischemia

Glutamatergic pathways mediate transmission of pain. Strategies to reduce glutamatergic neurotransmission may have beneficial effects to mitigate nociception. Recent work revealed that overexpression of the astrocytic glutamate transporter (GLT-1) by transgenic or pharmacologic approaches produced a diminished visceral nociceptive response to colonic distension. The purpose of this study was to determine the effect of GLT-1 overexpression on the visceromotor response to bladder distension. Increased glutamate uptake activity produced by 1-wk ceftriaxone (CTX) treatment attenuated 60–64% the visceromotor response to graded bladder distension compared with vehicle-treated mice. One-hour pretreatment with selective GLT-1 antagonist dihydrokainate reversed the blunted visceromotor response to bladder distension produced by 1-wk CTX, suggesting that GLT-1 overexpression mediated the analgesic effect of CTX. Moreover, sensitization of the visceromotor response to bladder distension produced by local bladder irritation (acrolein) was also attenuated by 1-wk CTX treatment. A model of cross-organ sensitization of bladder visceromotor response to distension was next studied to determine whether increased expression of GLT-1 can mitigate colon to bladder sensitization. Intracolonic trinitrobenzene sulfonic acid (TNBS) administered 1 h before eliciting the visceromotor response to graded bladder distension produced a 75–138% increase in visceromotor response compared with animals receiving intracolonic vehicle. In marked contrast, animals treated with 1-wk CTX + intracolonic TNBS showed no enhanced visceromotor response compared with the 1-wk vehicle + intracolonic vehicle group. The study suggests that GLT-1 overexpression attenuates the visceromotor response to bladder distension and both local irritant-induced and cross-organ-sensitized visceromotor response to bladder distension.

Download Full-text

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.

Download Full-text

Effect of Acute Exposure to Ammonia on Glutamate Transport in Glial Cells Isolated From the Salamander Retina

Journal of Neurophysiology ◽

10.1152/jn.2001.86.2.836 ◽

2001 ◽

Vol 86 (2) ◽

pp. 836-844 ◽

Cited By ~ 15

Author(s):

Dominic Mort ◽

Païkan Marcaggi ◽

James Grant ◽

David Attwell

Keyword(s):

Glial Cells ◽

Glutamate Uptake ◽

Ph Dependence ◽

Glutamate Transporter ◽

Ammonia Concentration ◽

Ammonia Level ◽

Glutamate Transport ◽

Acute Exposure ◽

Ph Change ◽

Glutamine Synthesis

A rise of brain ammonia level, as occurs in liver failure, initially increases glutamate accumulation in neurons and glial cells. We investigated the effect of acute exposure to ammonia on glutamate transporter currents in whole cell clamped glial cells from the salamander retina. Ammonia potentiated the current evoked by a saturating concentration ofl-glutamate, and decreased the apparent affinity of the transporter for glutamate. The potentiation had a Michaelis-Menten dependence on ammonia concentration, with a K m of 1.4 mM and a maximum potentiation of 31%. Ammonia also potentiated the transporter current produced by d-aspartate. Potentiation of the glutamate transport current was seen even with glutamine synthetase inhibited, so ammonia does not act by speeding glutamine synthesis, contrary to a suggestion in the literature. The potentiation was unchanged in the absence of Cl− ions, showing that it is not an effect on the anion current gated by the glutamate transporter. Ammonium ions were unable to substitute for Na+in driving glutamate transport. Although they can partially substitute for K+ at the cation counter-transport site of the transporter, their occupancy of these sites would produce a potentiation of <1%. Ammonium, and the weak bases methylamine and trimethylamine, increased the intracellular pH by similar amounts, and intracellular alkalinization is known to increase glutamate uptake. Methylamine and trimethylamine potentiated the uptake current by the amount expected from the known pH dependence of uptake, but ammonia gave a potentiation that was larger than could be explained by the pH change, and some potentiation of uptake by ammonia was still seen when the internal pH was 8.8, at which pH further alkalinization does not increase uptake. These data suggest that ammonia speeds glutamate uptake both by increasing cytoplasmic pH and by a separate effect on the glutamate transporter. Approximately two-thirds of the speeding is due to the pH change.

Download Full-text

The Meningococcal ABC-Type l-Glutamate Transporter GltT Is Necessary for the Development of Experimental Meningitis in Mice

Infection and Immunity ◽

10.1128/iai.01424-08 ◽

2009 ◽

Vol 77 (9) ◽

pp. 3578-3587 ◽

Cited By ~ 17

Author(s):

Roberta Colicchio ◽

Susanna Ricci ◽

Florentia Lamberti ◽

Caterina Pagliarulo ◽

Chiara Pagliuca ◽

...

Keyword(s):

Histological Analysis ◽

Glutamate Uptake ◽

Glutamate Transporter ◽

Systemic Infection ◽

Fold Increase ◽

Wild Type ◽

Nutrient Source ◽

Infectious Dose ◽

Life Threatening ◽

The Brain

ABSTRACT Experimental animal models of bacterial meningitis are useful to study the host-pathogen interactions occurring at the cerebral level and to analyze the pathogenetic mechanisms behind this life-threatening disease. In this study, we have developed a mouse model of meningococcal meningitis based on the intracisternal inoculation of bacteria. Experiments were performed with mouse-passaged serogroup C Neisseria meningitidis. Survival and clinical parameters of infected mice and microbiological and histological analysis of the brain demonstrated the establishment of meningitis with features comparable to those of the disease in humans. When using low bacterial inocula, meningococcal replication in the brain was very efficient, with a 1,000-fold increase of viable counts in 18 h. Meningococci were also found in the blood, spleens, and livers of infected mice, and bacterial loads in different organs were dependent on the infectious dose. As glutamate uptake from the host has been implicated in meningococcal virulence, mice were infected intracisternally with an isogenic strain deficient in the ABC-type l-glutamate transporter GltT. Noticeably, the mutant was attenuated in virulence in mixed infections, indicating that wild-type bacteria outcompeted the GltT-deficient meningococci. The data show that the GltT transporter plays a role in meningitis and concomitant systemic infection, suggesting that meningococci may use l-glutamate as a nutrient source and as a precursor to synthesize the antioxidant glutathione.

Download Full-text

Prenatal exposure to the cannabinoid receptor agonist WIN 55,212-2 increases glutamate uptake through overexpression of GLT1 and EAAC1 glutamate transporter subtypes in rat frontal cerebral cortex

Neuropharmacology ◽

10.1016/j.neuropharm.2007.05.019 ◽

2007 ◽

Vol 53 (3) ◽

pp. 369-378 ◽

Cited By ~ 28

Author(s):

Pasqualina Castaldo ◽

Simona Magi ◽

Silvana Gaetani ◽

Tommaso Cassano ◽

Luca Ferraro ◽

...

Keyword(s):

Cerebral Cortex ◽

Prenatal Exposure ◽

Receptor Agonist ◽

Cannabinoid Receptor ◽

Glutamate Uptake ◽

Glutamate Transporter ◽

Frontal Cerebral Cortex

Download Full-text

Effects of glutamate transporter and receptor ligands on neuronal glutamate uptake

Neuroscience Research ◽

10.1016/j.neures.2005.06.003 ◽

2005 ◽

Vol 53 (1) ◽

pp. 77-83 ◽

Cited By ~ 4

Author(s):

Carina R. Boeck ◽

Eduardo H. Kroth ◽

Mauro J. Bronzatto ◽

Fluvia M. Jardim ◽

Diogo O. Souza ◽

...

Keyword(s):

Glutamate Uptake ◽

Glutamate Transporter ◽

Receptor Ligands

Download Full-text

T117 THE ROLE OF SPINAL GLUTAMATE UPTAKE VIA GLUTAMATE TRANSPORTER FOR INCISION-INDUCED PAIN BEHAVIORS IN RATS

European Journal of Pain Supplements ◽

10.1016/s1754-3207(11)70062-1 ◽

2011 ◽

Vol 5 (S1) ◽

pp. 19-20

Author(s):

S. Reichl ◽

A. Boecker ◽

V. Keller ◽

P.K. Zahn ◽

E.M. Pogatzki-Zahn

Keyword(s):

Glutamate Uptake ◽

Glutamate Transporter ◽

Pain Behaviors

Download Full-text

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

ISRN Neurology ◽

10.1155/2013/893605 ◽

2013 ◽

Vol 2013 ◽

pp. 1-16 ◽

Cited By ~ 11

Author(s):

Alexandra E. Schreiner ◽

Eric Berlinger ◽

Julia Langer ◽

Karl W. Kafitz ◽

Christine R. Rose

Keyword(s):

Cell Damage ◽

Glutamate Uptake ◽

Hippocampal Slices ◽

Glutamate Transporter ◽

Reactive Astrocytes ◽

Extracellular Glutamate ◽

Sodium Imaging ◽

Ca1 Area ◽

And Function ◽

Transporter Expression

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.

Download Full-text