PS1/gamma-secretase acts as rogue chaperone of glutamate transporter EAAT2/GLT-1 in Alzheimer's disease

The recently discovered interaction between presenilin 1 (PS1), a catalytic subunit of γ-secretase responsible for the generation of amyloid-β(Aβ) peptides, and GLT-1, the major glutamate transporter in the brain (EAAT2 in the human) may provide a mechanistic link between two important pathological aspects of Alzheimer's disease (AD): abnormal Aβoccurrence and neuronal network hyperactivity. In the current study, we employed a FRET-based approach, fluorescence lifetime imaging microscopy (FLIM), to characterize the PS1/GLT-1 interaction in its native environment in the brain tissue of sporadic AD (sAD) patients. There was significantly less interaction between PS1 and GLT-1 in sAD brains, compared to tissue from patients with frontotemporal lobar degeneration (FTLD), or non-demented age-matched controls. Since PS1 has been shown to adopt pathogenic "closed" conformation in sAD but not in FTLD, we assessed the impact of changes in PS1 conformation on the interaction. Familial AD (fAD) PS1 mutations which induce a "closed" PS1 conformation similar to that in sAD brain and gamma-secretase modulators (GSMs) which induce a "relaxed" conformation, reduced and increased the interaction, respectively. This indicates that PS1 conformation seems to have a direct effect on the interaction with GLT-1. Furthermore, using biotinylation/streptavidin pull-down, western blotting, and cycloheximide chase assays, we determined that the presence of PS1 increased GLT-1 cell surface expression and GLT-1 homomultimer formation, but did not impact GLT-1 protein stability. Together, the current findings suggest that the newly described PS1/GLT-1 interaction endows PS1 with chaperone activity, modulating GLT-1 transport to the cell surface and stabilizing the dimeric-trimeric states of the protein. The diminished PS1/GLT-1 interaction suggests that these functions of the interaction may not work properly in AD.

Ketone Body Rescued Seizure Behavior of LRP1 Deficiency in Drosophila by Modulating Glutamate Transport

LRP1, the low-density lipoprotein receptor 1, would be a novel candidate gene of epilepsy according to our bioinformatic results and the animal study. In this study, we explored the role of LRP1 in epilepsy and whether beta-hydroxybutyrate, the principal ketone body of the ketogenic diet, can treat epilepsy caused by LRP1 deficiency in drosophila. UAS/GAL4 system was used to establish different genotype models. Flies were given standard, high-sucrose, and ketone body food randomly. The bang-sensitive test was performed on flies and seizure-like behavior was assessed. In morphologic experiments, we found that LRP1 deficiency caused partial loss of the ellipsoidal body and partial destruction of the fan-shaped body. Whole-body and glia LRP1 defect flies had a higher seizure rate compared to the control group. Ketone body decreased the seizure rate in behavior test in all LRP1 defect flies, compared to standard and high sucrose diet. Overexpression of glutamate transporter gene Eaat1 could mimic the ketone body effect on LRP1 deficiency flies. This study demonstrated that LRP1 defect globally or in glial cells or neurons could induce epilepsy in drosophila. The ketone body efficaciously rescued epilepsy caused by LRP1 knockdown. The results support screening for LRP1 mutations as discriminating conduct for individuals who require clinical attention and further clarify the mechanism of the ketogenic diet in epilepsy, which could help epilepsy patients make a precise treatment case by case.

Rapid Regulation of Glutamate Transport: Where Do We Go from Here?

Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na⁺-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.

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

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

In vivo glutamate clearance defects in a mouse model of Lafora disease

Lafora disease (LD) is a fatal rare neurodegenerative disorder characterized by epilepsy, neurodegeneration and insoluble polyglucosan accumulation in brain and other peripheral tissues. Although in the last two decades we have increased our knowledge on the molecular basis underlying the pathophysiology of LD, only a small part of the research in LD has paid attention to the mechanisms triggering one of the most lethal features of the disease: epilepsy. Recent studies in our laboratory suggested that a dysfunction in the activity of the mouse astrocytic glutamate transporter 1 (GLT-1) could contribute to epilepsy in LD. In this work, we present new in vivo evidence of a GLT-1 dysfunction, contributing to increased levels of extracellular glutamate in the hippocampus of a mouse model of Lafora disease (Epm2b-/-, lacking the E3-ubiquitin ligase malin). According to our results, Epm2b-/- mice showed an increased neuronal activity, as assessed by c-fos expression, in the hippocampus, an area directly correlated to epileptogenesis. This brain area presented lesser ability to remove synaptic glutamate after local GLT-1 blockade with dihydrokainate (DHK), in comparison to Epm2b+/+ animals, suggesting that these animals have a compromised glutamate clearance when a challenging condition was presented. These results correlate with a hippocampal upregulation of the minor isoform of the Glt-1 gene, named Glt-1b, which has been associated with compensatory mechanisms activated in response to neuronal stress. In conclusion, the hippocampus of Epm2b-/- mice presents an in vivo impairment in glutamate uptake which could contribute to epileptogenesis.

GLAST (GLutamate and ASpartate Transporter) in human prefrontal cortex; interactome in healthy brains and the expression of GLAST in brains of chronic alcoholics

We have analysed post-mortem samples of prefrontal cortex from control and alcoholic human brains by the technique of Western blotting to estimate and compare the expressions of glutamate transporter GLAST (Excitatory Amino Acid Transporter One; EAAT1). Furthermore, using the non-alcoholic prefrontal cortex and custom-made GLAST (EAAT1) antibody we determined GLAST (EAAT1) "interactome" i.e. the set of proteins selectively bound by GLAST (EAAT1). We found that GLAST (EAAT1) was significantly more abundant (about 1.6-fold) in the cortical tissue from alcoholic brains compared to that from non-alcoholic controls. The greatest increase in the level of GLAST (EAAT1) was found in plasma membrane fraction (2.2-fold). Additionally, using the prefrontal cortical tissue from control brains, we identified 38 proteins specifically interacting with GLAST (EAAT1). These can be classified as contributing to the cell structure (6 proteins; 16%), energy and general metabolism (18 proteins; 47%), neurotransmitter metabolism (three proteins; 8%), signalling (6 proteins: 16%), neurotransmitter storage/release at synapses (three proteins; 8%) and calcium buffering (two proteins; 5%). We discuss possible consequences of the increased expression of GLAST (EAAT1) in alcoholic brain tissue and whether or how this could disturb the function of the proteins potentially interacting with GLAST (EAAT1) in vivo. The data represent an extension of our previous proteomic and metabolomic studies of human alcoholism revealing another aspect of the complexity of changes imposed on brain by chronic long-term consumption of ethanol.

growing beef steers, concomitant with increased GTRAP3-18 content

Hepatic glutamate uptake and conversion to glutamine is critical for whole-body N metabolism, but how this process is regulated during growth is poorly described. The hepatic glutamate uptake activities, protein content of system [Formula: see text] transporters (EAAC1, GLT-1) and regulatory proteins (GTRAP3-18, ARL6IP1), glutamine synthetase (GS) activity and content, and glutathione (GSH) content, were compared in liver tissue of weaned Angus steers randomly assigned (n = 8) to predominantly lean (growing) or predominantly lipid (finished) growth regimens. Steers were fed a cotton seed hull-based diet to achieve final body weights of 301 or 576 kg, respectively, at a constant rate of growth. Liver tissue was collected at slaughter and hepatic membranes fractionated. Total (75%), Na+-dependent (90%), system [Formula: see text]-dependent (abolished) glutamate uptake activity, and EAAC1 content (36%) in canalicular membrane-enriched vesicles decreased as steers developed from growing (n = 6) to finished (n = 4) stages, whereas Na+-independent uptake did not change. In basolateral membrane-enriched vesicles, total (60%), Na+-dependent (60%), and Na+-independent (56%) activities decreased, whereas neither system [Formula: see text]-dependent uptake nor protein content changed. EAAC1 protein content in liver homogenates (n = 8) decreased in finished vs. growing steers, whereas GTRAP3-18 and ARL6IP1 content increased and GLT-1 content did not change. Concomitantly, hepatic GS activity decreased (32%) as steers fattened, whereas GS and GSH contents did not differ. We conclude that hepatic glutamate uptake and GS synthesis capacities are reduced in livers of finished versus growing beef steers, and that hepatic system [Formula: see text] transporter activity/EAAC1 content is inversely proportional to GTRAP3-18 content.

Astrocyte membrane properties are altered in a rat model of developmental cortical malformation but single-cell astrocytic glutamate uptake is robust

Developmental cortical malformations (DCMs) are linked with severe epilepsy and are caused by both genetic and environmental insults. DCMs include several neurological diseases, such as focal cortical dysplasia, polymicrogyria, schizencephaly, and others. Human studies have implicated astrocyte reactivity and dysfunction in the pathophysiology of DCMs, but their specific role is unknown. As astrocytes powerfully regulate glutamate neurotransmission, and glutamate levels are known to be increased in human epileptic foci, understanding the role of astrocytes in the pathological sequelae of DCMs is extremely important. Additionally, recent studies examining astrocyte glutamate uptake in DCMs have reported conflicting results, adding confusion to the field. In this study we utilized the freeze lesion (FL) model of DCM, which is known to induce reactive astrocytosis and cause significant changes in astrocyte morphology, proliferation, and distribution. Using whole-cell patch clamp recording from astrocytes, we recorded both UV-uncaging and synaptically evoked glutamate transporter currents (TCs), widely accepted assays of functional glutamate transport by astrocytes. With this approach, we set out to test the hypothesis that astrocyte membrane properties and glutamate transport were disrupted in this model of DCM. Though we found that the developmental maturation of astrocyte membrane resistance was disrupted by FL, glutamate uptake by individual astrocytes was robust throughout FL development. Interestingly, using an immunolabeling approach, we observed spatial and developmental differences in excitatory amino acid transporter (EAAT) expression in FL cortex. Spatially specific differences in EAAT2 (GLT-1) and EAAT1 (GLAST) expression suggest that the relative contribution of each EAAT to astrocytic glutamate uptake may be altered in FL cortex. Lastly, we carefully analyzed the amplitudes and onset times of both synaptically- and UV uncaging-evoked TCs. We found that in the FL cortex, synaptically-evoked, but not UV uncaging-evoked TCs, were larger in amplitude. Additionally, we found that the amount of electrical stimulation required to evoke a synaptic TC was significantly reduced in the FL cortex. Both of these findings are consistent with increased excitatory input to the FL cortex, but not with changes in how individual astrocytes remove glutamate. Taken together, our results demonstrate that the maturation of astrocyte membrane resistance, local distribution of glutamate transporters, and glutamatergic input to the cortex are altered in the FL model, but that single-cell astrocytic glutamate uptake is robust.

Astroglial glutamate transporters coordinate excitatory signaling and brain energetics

In the mammalian brain, a family of sodium-dependent transporters maintains low extracellular glutamate and shapes excitatory signaling. The bulk of this activity is mediated by the astroglial glutamate transporters GLT-1 and GLAST (also called EAAT2 and EAAT1). In this review, we will discuss evidence that these transporters co-localize with, form physical (co-immunoprecipitable) interactions with, and functionally couple to various 'energy-generating' systems, including the Na(+)/K(+)-ATPase, the Na(+)/Ca(2+) exchanger, glycogen metabolizing enzymes, glycolytic enzymes, and mitochondria/mitochondrial proteins. This functional coupling is bi-directional with many of these systems both being regulated by glutamate transport and providing the 'fuel' to support glutamate uptake. Given the importance of glutamate uptake to maintaining synaptic signaling and preventing excitotoxicity, it should not be surprising that some of these systems appear to 'redundantly' support the energetic costs of glutamate uptake. Although the glutamate-glutamine cycle contributes to recycling of neurotransmitter pools of glutamate, this is an over-simplification. The ramifications of co-compartmentalization of glutamate transporters with mitochondria for glutamate metabolism are discussed. Energy consumption in the brain accounts for ∼20% of the basal metabolic rate and relies almost exclusively on glucose for the production of ATP. However, the brain does not possess substantial reserves of glucose or other fuels. To ensure adequate energetic supply, increases in neuronal activity are matched by increases in cerebral blood flow via a process known as 'neurovascular coupling'. While the mechanisms for this coupling are not completely resolved, it is generally agreed that astrocytes, with processes that extend to synapses and endfeet that surround blood vessels, mediate at least some of the signal that causes vasodilation. Several studies have shown that either genetic deletion or pharmacologic inhibition of glutamate transport impairs neurovascular coupling. Together these studies strongly suggest that glutamate transport not only coordinates excitatory signaling, but also plays a pivotal role in regulating brain energetics.

Homeostasis of the astrocytic glutamate transporter GLT-1 is altered in mouse models of Lafora disease

Lafora disease (LD, OMIM 254780) is a fatal rare disorder characterized by epilepsy and neurodegeneration. Although in recent years a lot of information has been gained on the molecular basis of the neurodegeneration that accompanies LD, the molecular basis of epilepsy is poorly understood. Here, we present evidence indicating that the homeostasis of glutamate transporter GLT-1 (EAAT2) is compromised in mouse models of LD. Our results indicate that primary astrocytes from LD mice have reduced capacity of glutamate transport, probably because they present a reduction in the levels of the glutamate transporter at the plasma membrane. On the other hand, the overexpression in cellular models of laforin and malin, the two proteins related to LD, results in an accumulation of GLT-1 (EAAT2) at the plasma membrane and in a severe reduction of the ubiquitination of the transporter. All these results suggest that the laforin/malin complex slows down the endocytic recycling of the GLT-1 (EAAT2) transporter. Since, defects in the function of this transporter lead to excitotoxicity and epilepsy, we suggest that the epilepsy that accompanies LD could be due, at least in part, to deficiencies in the function of the GLT-1 (EAAT2) transporter.

Molecular physiology of EAAT anion channels

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. After release from presynaptic nerve terminals, glutamate is quickly removed from the synaptic cleft by a family of five glutamate transporters, the so-called excitatory amino acid transporters (EAAT1-5). EAATs are prototypic members of the growing number of dual-function transport proteins: they are not only glutamate transporters, but also anion channels. Whereas the mechanisms underlying secondary active glutamate transport are well understood at the functional and at the structural level, mechanisms and cellular roles of EAAT anion conduction have remained elusive for many years. Recently, molecular dynamics simulations combined with simulation-guided mutagenesis and experimental analysis identified a novel anion-conducting conformation, which accounts for all experimental data on EAAT anion currents reported so far. We here review recent findings on how EAATs accommodate a transporter and a channel in one single protein.

GLAST But Not Least--Distribution, Function, Genetics and Epigenetics of L-Glutamate Transport in Brain--Focus on GLAST/EAAT1

Synaptically released L-glutamate, the most important excitatory neurotransmitter in the CNS, is removed from extracellular space by fast and efficient transport mediated by several transporters; the most abundant ones are EAAT1/GLAST and EAAT2/GLT1. The review first summarizes their location, functions and basic characteristics. We then look at genetics and epigenetics of EAAT1/GLAST and EAAT2/GLT1 and perform in silico analyses of their promoter regions. There is one CpG island in SLC1A2 (EAAT2/GLT1) gene and none in SLC1A3 (EAAT1/GLAST) suggesting that DNA methylation is not the most important epigenetic mechanism regulating EAAT1/GLAST levels in brain. There are targets for specific miRNA in SLC1A2 (EAAT2/GLT1) gene. We also note that while defects in EAAT2/GLT1 have been associated with various pathological states including chronic neurodegenerative diseases, very little is known on possible contributions of defective or dysfunctional EAAT1/GLAST to any specific brain disease. Finally, we review evidence of EAAT1/GLAST involvement in mechanisms of brain response to alcoholism and present some preliminary data showing that ethanol, at concentrations which may be reached following heavy drinking, can have an effect on the distribution of EAAT1/GLAST in cultured astrocytes; the effect is blocked by baclofen, a GABA-B receptor agonist and a drug potentially useful in the treatment of alcoholism. We argue that more research effort should be focused on EAAT1/GLAST, particularly in relation to alcoholism and drug addiction.

Glutamate transporter control of ambient glutamate levels

Accurate knowledge of the ambient extracellular glutamate concentration in brain is required for understanding its potential impacts on tonic and phasic receptor signaling. Estimates of ambient glutamate based on microdialysis measurements are generally in the range of ∼2-10μM, approximately 100-fold higher than estimates based on electrophysiological measurements of tonic NMDA receptor activity (∼25-90nM). The latter estimates are closer to the low nanomolar estimated thermodynamic limit of glutamate transporters. The reasons for this discrepancy are not known, but it has been suggested that microdialysis measurements could overestimate ambient extracellular glutamate because of reduced glutamate transporter activity in a region of metabolically impaired neuropil adjacent to the dialysis probe. We explored this issue by measuring diffusion gradients created by varying membrane densities of glutamate transporters expressed in Xenopus oocytes. With free diffusion from a pseudo-infinite 10μM glutamate source, the surface concentration of glutamate depended on transporter density and was reduced over 2 orders of magnitude by transporters expressed at membrane densities similar to those previously reported in hippocampus. We created a diffusion model to simulate the effect of transport impairment on microdialysis measurements with boundary conditions corresponding to a 100μm radius probe. A gradient of metabolic disruption in a thin (∼100μm) region of neuropil adjacent to the probe increased predicted [Glu] in the dialysate over 100-fold. The results provide support for electrophysiological estimates of submicromolar ambient extracellular [Glu] in brain and provide a possible explanation for the higher values reported using microdialysis approaches.

Regulation of hepatic EAAT-2 glutamate transporter expression in human liver cholestasis

AIM: To investigate the activity and expression of EAAT2 glutamate transporter in both in vitro and in vivo models of cholestasis.

METHODS: This study was conducted on human hepatoblastoma HepG2 cell cultures, the liver of bile duct ligated rats and human specimens from cholestatic patients. EAAT2 glutamate transporter activity and expression were analyzed using a substrate uptake assay, immunofluorescence, reverse transcription-polymerase chain reaction, and immunohistochemistry, respectively.

RESULTS: In HepG2 cells, cholestasis was mimicked by treating cells with the protein kinase C activator, phorbol 12-myristate 13-acetate. Under such conditions, EAAT2 transporter activity was decreased both at the level of substrate affinity and maximal transport velocity. The decreased uptake was correlated with intracellular translocation of EAAT2 molecules as demonstrated using immunofluorescence. In the liver of bile duct ligated rats, an increase in EAAT2 transporter protein expression in hepatocytes was demonstrated using immunohistochemistry. The same findings were observed in human liver specimens of cholestasis in which high levels of γ-glutamyl transpeptidase were documented in patients with biliary atresia and progressive familial intrahepatic cholestasis type 3.

CONCLUSION: This study demonstrates the alteration in glutamate handling by hepatocytes in liver cholestasis and suggests a potential cross-talk between glutamatergic and bile systems.

Genetic deletion of the neuronal glutamate transporter, EAAC1, results in decreased neuronal death after pilocarpine-induced status epilepticus

Excitatory amino acid carrier 1 (EAAC1 also called EAAT3) is a Na(+)-dependent glutamate transporter expressed by both glutamatergic and GABAergic neurons. It provides precursors for the syntheses of glutathione and GABA and contributes to the clearance of synaptically released glutamate. Mice deleted of EAAC1 are more susceptible to neurodegeneration in models of ischemia, Parkinson's disease, and aging. Antisense knock-down of EAAC1 causes an absence seizure-like phenotype. Additionally, EAAC1 expression increases after chemonvulsant-induced seizures in rodent models and in tissue specimens from patients with refractory epilepsy. The goal of the present study was to determine if the absence of EAAC1 affects the sensitivity of mice to seizure-induced cell death. A chemoconvulsant dose of pilocarpine was administered to EAAC1(-/-) mice and to wild-type controls. Although EAAC1(-/-) mice experienced increased latency to seizure onset, no significant differences in behavioral seizure severity or mortality were observed. We examined EAAC1 immunofluorescence 24h after pilocarpine administration and confirmed that pilocarpine causes an increase in EAAC1 protein. Forty-eight hours after induction of seizures, cell death was measured in hippocampus and in cortex using Fluoro-Jade C. Surprisingly, there was ∼2-fold more cell death in area CA1 of wild-type mice than in the corresponding regions of the EAAC1(-/-) mice. Together, these studies indicate that absence of EAAC1 results in either a decrease in pilocarpine-induced seizures that is not detectable by behavioral criteria (surprising, since EAAC1 provides glutamate for GABA synthesis), or that the absence of EAAC1 results in less pilocarpine/seizure-induced cell death, possible explanations as discussed.

Enhanced GLT-1 mediated glutamate uptake and migration of primary astrocytes directed by fibronectin-coated electrospun poly-L-lactic acid fibers

Bioengineered fiber substrates are increasingly studied as a means to promote regeneration and remodeling in the injured central nervous system (CNS). Previous reports largely focused on the ability of oriented scaffolds to bridge injured regions and direct outgrowth of axonal projections. In the present work, we explored the effects of electrospun microfibers on the migration and physiological properties of brain astroglial cells. Primary rat astrocytes were cultured on either fibronectin-coated poly-L-lactic acid (PLLA) films, fibronectin-coated randomly oriented PLLA electrospun fibers, or fibronectin-coated aligned PLLA electrospun fibers. Aligned PLLA fibers strongly altered astrocytic morphology, orienting cell processes, actin microfilaments, and microtubules along the length of the fibers. On aligned fibers, astrocytes also significantly increased their migration rates in the direction of fiber orientation. We further investigated if fiber topography modifies astrocytic neuroprotective properties, namely glutamate and glutamine transport and metabolism. This was done by quantifying changes in mRNA expression (qRT-PCR) and protein levels (Western blotting) for a battery of relevant biomolecules. Interestingly, we found that cells grown on random and/or aligned fibers increased the expression levels of two glutamate transporters, GLAST and GLT-1, and an important metabolic enzyme, glutamine synthetase, as compared to the fibronectin-coated films. Functional assays revealed increases in glutamate transport rates due to GLT-1 mediated uptake, which was largely determined by the dihydrokainate-sensitive GLT-1. Overall, this study suggests that aligned PLLA fibers can promote directed astrocytic migration, and, of most importance, our in vitro results indicate for the first time that electrospun PLLA fibers can positively modify neuroprotective properties of glial cells by increasing rates of glutamate uptake.