* 600300

SOLUTE CARRIER FAMILY 1 (GLIAL HIGH AFFINITY GLUTAMATE TRANSPORTER), MEMBER 2; SLC1A2


Alternative titles; symbols

EXCITATORY AMINO ACID TRANSPORTER 2; EAAT2
GLUTAMATE TRANSPORTER 1; GLT1


Other entities represented in this entry:

EAAT2b, INCLUDED
GLT1A, INCLUDED
GLT1B, INCLUDED

HGNC Approved Gene Symbol: SLC1A2

Cytogenetic location: 11p13     Genomic coordinates (GRCh38): 11:35,251,205-35,420,507 (from NCBI)


Gene-Phenotype Relationships
Location Phenotype Phenotype
MIM number
Inheritance Phenotype
mapping key
11p13 Developmental and epileptic encephalopathy 41 617105 AD 3

TEXT

Description

Glutamate transporters are membrane-bound proteins localized in glial cells and/or presynaptic glutamatergic nerve endings. They are essential for the removal and termination of action of the excitatory neurotransmitter glutamate from the synapse (Shashidharan et al., 1994).

Several subtypes of glutamate transporters have been defined by differences in sequence, pharmacology, tissue distribution, and channel-like properties, including SLC1A2 (EAAT2), SLC1A3 (EAAT1 or GLAST; 600111), SLC1A1 (EAAC1 or EAAT3; 133550), and SLC1A6 (EAAT4; 600637). SLC1A2 is selectively localized to astroglia; SLC1A1 and SLC1A6 are selectively localized in neurons; and SLC1A3 is found in both neurons and astroglia (Rothstein et al., 1994; Maragakis et al., 2004).


Cloning and Expression

By screening a human brainstem and cerebellum cDNA library, Shashidharan et al. (1994) isolated a cDNA corresponding to the SLC1A2 gene. The predicted 565-amino acid protein is homologous to a rat brain sodium-dependent glutamate/aspartate transporter. (See also Krishnan et al., 1993).

Su et al. (2003) described the cloning and characterization of the human EAAT2 promoter, demonstrating elevated expression in astrocytes. Regulators of EAAT2 transport, both positive and negative, altered EAAT2 transcription, promoter activity, mRNA, and protein, implying that transcriptional processes can regulate EAAT2 expression. The authors also raised the possibility that the EAAT2 promoter may be useful for targeting gene expression in the brain and for identifying molecules capable of modulating glutamate transport that could potentially inhibit, ameliorate, or prevent various neurodegenerative diseases.

Kirschner et al. (1994) isolated the cDNA for mouse Eaat2. The mouse Eaat2 amino acid sequence shares 99% and 97% identity with its rat and human homologs, respectively. It is expressed predominantly in the brain, where it may function as a glia-specific transporter.

Utsunomiya-Tate et al. (1997) isolated several tissue-specific GLT1 variants from mouse brain and liver. They determined that brain and liver GLT1 cDNA clones have different 5-prime ends, corresponding to replacement of 6 N-terminal amino acids in brain GLT1 by 3 N-terminal amino acids in liver GLT1. In addition, the authors found 2 alternative 3-prime ends in both brain and liver cDNAs, corresponding to replacement of 22 C-terminus amino acids (the 'a' end) by 11 C-terminal amino acids (the 'b' end). The authors designated the 2 liver GLT1 mRNAs as mGLT1A and mGLT1B, which have the same N termini and different C termini. In vitro expression studies showed that the channel properties were not changed by the alteration of N or C termini.

From rat brain, Schmitt et al. (2002) cloned a cDNA corresponding to a GLT1 variant, rat GLT1B or human EAAT2b, which is generated by alternative splicing at the 3-prime end of the GLT1 cDNA. Northern blot analysis showed that the 11-kb GLT1 mRNA predominates in the brain, while the 12.5-kb GLT1 variant mRNA predominates in the retina. The GLT1 variant was preferentially expressed in neurons of the central and peripheral nervous systems, but only occasionally in astrocytes. EAAT2b has a truncated intracellular C-terminal domain with a unique terminal sequence of 11 amino acids. In vitro, the EAAT2b protein showed functional glutamate transport activity (see also Maragakis et al., 2004).


Mapping

Using somatic cell hybrids and fluorescence in situ hybridization (FISH), Li and Francke (1995) assigned the human SLC1A2 gene to chromosome 11p13-p12. By FISH, Takai et al. (1996) mapped the gene, which they called glutamate transporter-1 (GLT1), to 11p13-p11.2.

Using an interspecific backcross analysis, Kirschner et al. (1994) mapped the mouse Eaat2 gene to the central region of chromosome 2, where it is located near quantitative trait loci that modulate neuroexcitability and seizure frequency in mouse models of alcohol withdrawal and epilepsy. The authors noted that mouse chromosome 2 shows syntenic homology to a region on human 11p.


Gene Function

GLT1 is a transporter that actively removes the excitatory neurotransmitter glutamate from the extracellular space. The extracellular concentration of glutamate must be kept low to ensure a high signal-to-noise ratio during synaptic activation, and to prevent neuronal damage from excessive activation of the glutamate receptors. Excess glutamate causes neurotoxicity and may contribute to cellular damage in neurologic disorders such as stroke, trauma, Alzheimer disease (AD; see 104300), amyotrophic lateral sclerosis (ALS; see 105400), and Huntington disease (143100) (Choi, 1988; Kanai et al., 1993).

In mice in which the Glt1 gene was disrupted in embryonic stem cells by homologous recombination, Tanaka et al. (1997) observed lethal spontaneous seizures and increased susceptibility to acute cortical injury. The authors attributed the effects to elevated levels of residual glutamate in the brains of these mice, and concluded that GLT1 contributes to the maintenance of low levels of extracellular glutamate concentrations.

In the retina, the glutamate transporter GLAST is expressed in Muller cells, whereas the glutamate transporter GLT1 is found only in cones and various types of bipolar cells. To investigate the functional role of this differential distribution of glutamate transporters, Harada et al. (1998) analyzed Glast and Glt1 mutant mice. In Glast-deficient mice, the electroretinogram b-wave and oscillatory potentials were reduced and retinal damage after ischemia was exacerbated, whereas Glt1-deficient mice showed almost normal electroretinograms and mildly increased retinal damage after ischemia. These results demonstrated that Glast is required for normal signal transmission between photoreceptors and bipolar cells and that both Glast and Glt1 play a neuroprotective role during ischemia in the retina.

For a discussion of a possible role of the SLC1A2 gene in nicotine dependence, see 188890.

EAAT2 Findings in Amyotrophic Lateral Sclerosis

In patients with amyotrophic lateral sclerosis, Rothstein et al. (1992) found a marked decrease in the maximal velocity of transport for high-affinity glutamate uptake in synaptosomes from spinal cord, motor cortex, and somatosensory cortex. The affinity of the transporter for glutamate was not altered. The authors suggested that defects in the clearance of extracellular glutamate due to a faulty transporter could lead to neurotoxic levels of extracellular glutamate and be pathogenic in ALS. By immunohistochemical analysis, Rothstein et al. (1995) found that GLT1 was severely decreased in ALS brain tissue, both in the motor cortex (71 to 90% decrease from control) and in the spinal cord. As there was no loss of astroglia, the authors hypothesized a primary defect in the GLT1 protein, secondary loss due to down-regulation, or other toxic processes.

Lin et al. (1998) reported that 60 to 70% of sporadic ALS patients have a 30 to 95% loss of the astroglial glutamate transporter EAAT2 protein in motor cortex and spinal cord. In neuropathologically affected areas of the nervous system of 65% of their group of ALS patients, but not in other brain regions, Lin et al. (1998) identified multiple aberrant mRNAs. They were also detectable in the cerebrospinal fluid of living ALS patients early in the disease, suggesting diagnostic utility. The aberrant mRNAs were not found in nonneurologic disease or other disease controls. In vitro expression studies suggested that proteins translated from these aberrant mRNAs may undergo rapid degradation and/or produce a dominant-negative effect on normal EAAT2, resulting in loss of protein and activity. These findings suggested that loss of EAAT2 in ALS is due to aberrant mRNA resulting from RNA processing errors.

Honig et al. (2000) analyzed postmortem brain specimens from 6 patients with ALS, 9 patients with AD, 6 patients with Lewy body disease (127750), and 6 normal controls to ascertain the specificity of alternatively spliced mRNA variants of EAAT2 for ALS. Honig et al. (2000) identified splice variants lacking exons 7, 9, or both 7 and 9, in all brain regions studied in normal controls, as well as in all brain regions of the diseased brains. Quantitative analysis, using RT-PCR, showed that the 2 alternatively spliced isoforms were present as minor species (2-15%) in all specimens, but did show a statistically significant increase of exon 7-skipping isoforms in ALS brains. The authors noted the discrepancy between their findings and those of Lin et al. (1998), and suggested that quantitative differences in the isoforms may be relevant to the pathogenesis of ALS.

Also in contrast to the findings reported by Lin et al. (1998), Flowers et al. (2001) demonstrated that the 2 EAAT2 mRNA transcript variants, specifically one that retains intron 7 and one that skips exon 9, were present in all CNS areas studied in 17 sporadic ALS patients, 7 AD patients, and 19 control subjects. In addition, the ratios of these variants to normal transcripts were not altered in patients as compared to normal controls. The variant mRNAs were not detected in the CSF of 17 ALS and 8 control samples. Flowers et al. (2001) suggested that the exon 9-skipping variant is a physiologic form and that the intron 7-retaining variant may be rapidly degraded via mRNA surveillance mechanisms. They concluded that these EAAT2 variants are not linked to ALS.

Guo et al. (2003) generated transgenic mice overexpressing EAAT2 and crossed these with mice bearing the ALS-associated SOD1 mutant G93A (147450.0008). The amount of EAAT2 protein and the associated Na(+)-dependent glutamate uptake was increased about 2-fold in EAAT2 transgenic mice. The transgenic EAAT2 protein was properly localized to the cell surface on the plasma membrane. Increased EAAT2 expression protected neurons from L-glutamate-induced cytotoxicity and cell death in vitro. The EAAT2/G93A double transgenic mice showed a statistically significant delay in grip strength decline but not in the onset of paralysis, body weight decline, or life span when compared with G93A littermates. A delay in the loss of motor neurons and their axonal morphologies, as well as other events including caspase-3 (CASP3; 600636) activation and SOD1 aggregation, were also observed. The authors hypothesized that loss of EAAT2 may contribute to, but does not cause, motor neuron degeneration in ALS.

In 10 ALS patients, Maragakis et al. (2004) found an average 2-fold increase in EAAT2b in the motor cortex, whereas EAAT2 levels were decreased by up to 94% compared to controls. Immunostaining showed that EAAT2b expression in ALS brains was located in neuropil and neurons. Functional transporter studies demonstrated a large loss of EAAT2 activity.

Using a blinded screen of 1,040 FDA-approved drugs and nutritionals, Rothstein et al. (2005) discovered that many beta-lactam antibiotics are potent stimulators of GLT1 expression. Furthermore, this action appeared to be mediated through increased transcription of the GLT1 gene. Beta-lactams and various semisynthetic derivatives are potent antibiotics that act to inhibit bacterial synthetic pathways. When delivered to animals, the beta-lactam ceftriaxone increased both brain expression of GLT1 and its biochemical and functional activity. Rothstein et al. (2005) found that ceftriaxone was neuroprotective in vitro when used in models of ischemic injury and motor neuron degeneration, both based in part on glutamate toxicity. When used in an animal model of the fatal disease ALS, the drug delayed loss of neurons and muscle strength, and increased mouse survival.

Hoye et al. (2018) searched RNA sequence data generated from different purified CNS cell types and identified EAAT2 as a candidate glial target of miR218 (616770). Luciferase assays showed that miR218 directly binds to the 3-prime UTR of EAAT2, which was sufficient to repress its translation in astrocytes. However, miR218 is expressed only at low levels in both wildtype and ALS astrocytes, indicating that miR218 is not an endogenous regulator of protein expression in adult astrocytes. Further investigation showed that neighboring astrocytes take up the extracellular miR218 released from dying motor neurons in ALS. Examination of the extracellular state of miR218 revealed that miR218 is protein-bound and not encapsulated in vesicles, and also capable of binding oligonucleotides. Mice with whole spinal cord depletion of miR218 showed characteristics of ALS, and miR218 derived from dying motor neurons was taken up by neighboring astrocytes in vivo and mediated changes in astrocytic expression such as loss of EAAT2. Hoye et al. (2018) found that translated mRNAs downregulated in ALS astrocytes contain miR218 binding sites and are derepressed upon miR218 inhibition, indicating that the effects of motor neuron-derived miR218 on astrocytes extend beyond EAAT2 and functionally regulate the expression of other astrocytic proteins and cellular states in neurodegeneration, Inhibition of motor neuron-derived miR218 in ALS model mice further corroborated that miR218 released from dying motor neurons can lead to loss of homeostatic protein expression, such as EAAT2, and astrogliosis.


Molecular Genetics

Developmental and Epileptic Encephalopathy 41

In 2 unrelated patients with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified 2 different de novo heterozygous missense mutations in the SLC1A2 gene (600300.0001-600300.0002). The mutations were found by targeted sequencing of 27 candidate genes in 531 patients with a similar disorder. Functional studies of the variants and studies of patient cells were not performed.

In 2 unrelated patients with DEE41, Guella et al. (2017) identified de novo heterozygous missense mutations in the SLC1A2 gene (600300.0003 and 600300.0004). The first patient was identified from a cohort of 42 individuals with epileptic encephalopathy who underwent sequencing of candidate genes; the second patient was identified through collaboration with clinical and research databases. In vitro functional studies of the variants and studies of patient cells were not performed, but Guella et al. (2017) postulated a toxic gain-of-function effect, perhaps related to glutamate toxicity.

Functional Studies of SLC1A2 Mutations

Based on the channel conformation of the prokaryotic sodium-aspartate symporter from Pyrococcus horikoshii, Kovermann et al. (2022) determined that 3 epileptic encephalopathy-associated mutations in human EAAT2, gly82 to arg (G82R; 600300.0001), leu85 to pro (L85P; 600300.0002), and pro289 to arg (P289R; 600300.0004), are located in proximity to the EAAT anion channel. Ectopic expression in mammalian cells revealed that G82R and P289R, but not L85P, impaired endoplasmic reticulum exit and surface membrane expression of EAAT2. However, all 3 mutants virtually abolished L-glutamate uptake through EAAT2, and all 3 mutants enhanced EAAT2 anion channel anion currents. In particular, G82R and L85P enlarged the pore diameter and made the anion channel significantly permeable for L-gluconate and L-glutamate. In contrast, P289R modified opening of the EAAT2 anion channel, but not its selectivity.

Associations Pending Confirmation

In 55 patients with ALS, Meyer et al. (1998) found no sequence alterations in the EAAT2 gene. In 2 of 7 affected members of a family with autosomal dominant hereditary spastic paraplegia (see, e.g., 182600), Meyer et al. (1998) found heterozygosity for a 269C-G transition, resulting in an ala79-to-gly (A79G) amino acid substitution in the EAAT2 protein. The mutation was present in father and his son, but the authors concluded that the mutation was a rare polymorphism since it did not cosegregate with the disorder.

Using SSCP analysis, Aoki et al. (1998) identified an asn206-to-ser mutation (N206S), a potential N-linked glycosylation site, in the EAAT2 gene in a heterozygous sporadic ALS patient. By Western blot analysis, Trotti et al. (2001) determined that wildtype GLT1 is expressed as a 70-kD protein, whereas N206S is a 60- to 65-kD protein. The size of both proteins is equivalent after glycosidase treatment, presumably by deglycosylating the N216 site as well. Functional analysis and immunofluorescence microscopy demonstrated that cells expressing N206S have reduced transport activity and plasma membrane expression and increased cytoplasmic expression compared to wildtype. The mutant protein also exhibited increased reverse transport activity. Coexpression of mutant and wildtype GLT1 resulted in a dominant-negative effect on wildtype activity, suggesting an impairment of glutamate clearance at synapses in vivo.

Mallolas et al. (2006) hypothesized that some individuals are susceptible to excitotoxicity after stroke (see 601367) due to impaired glutamate uptake mediated by glutamate transporters, such as EAAT2, the primary transporter in adults. By examining 101 stroke patients and 106 controls, they identified an A-to-C polymorphism at position -181 from the transcriptional start site of EAAT2 that abolished an activator protein-2 (AP2; 107580) recognition sequence and created a novel consensus binding site for the repressor transcription factor GCF2 (LRRFIP1; 603256). The prevalence of the polymorphism in stroke patients was comparable to that in healthy subjects. However, stroke patients with the -181C allele showed higher plasma glutamate concentrations and earlier neurologic deterioration than those with the -181A allele, in spite of having similar baseline characteristics. Following transfection into rat astrocytes, the -181C human promoter was not activated by AP2 and was repressed with GCF2, and its activity in the presence of GCF2 was reduced when compared with the AP2-cotransfected -181A promoter. Rats with middle cerebral artery occlusion expressed Gcf2. Mallolas et al. (2006) concluded that a functional polymorphism in the EAAT2 promoter alters the regulation pattern and decreases promoter activity, resulting in higher plasma glutamate levels and possibly explaining the failure of glutamate antagonists in some stroke victims.


Animal Model

Matsugami et al. (2006) found that the brains of mice lacking Glast or Glt1 developed normally but that Glast/Glt1 double-knockout mice died around embryonic days 17 to 18 and exhibited cortical, hippocampal, and olfactory bulb disorganization. Several essential aspects of neuronal development, such as stem cell proliferation, radial migration, neuronal differentiation, and survival of subplate neurons, were impaired. Matsugami et al. (2006) concluded that the regulation of extracellular glutamate concentration and the maintenance of glutamate-mediated synaptic transmission is necessary for normal brain development.


ALLELIC VARIANTS ( 4 Selected Examples):

.0001 DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, GLY82ARG, 244G-C
  
RCV000240886

In a 6-year-old girl (patient EG1291) with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified a de novo heterozygous c.244G-C transversion (c.244G-C, NM_004171.3) in the SLC1A2 gene, resulting in a gly82-to-arg (G82R) substitution in the first extracellular domain. The mutation was not found in the Exome Sequencing Project, 1000 Genomes Project, or ExAC databases. Functional studies of the variant and studies of patient cells were not performed. The patient had onset of infantile spasms in the first days of life. The same de novo heterozygous G82R mutation had been previously identified in another patient with early-onset epilepsy in the study of the Epi4K Consortium and Epilepsy Phenome/Genome Project (2013), which included 264 probands with epileptic encephalopathy who underwent exome sequencing.


.0002 DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, LEU85PRO
  
RCV000240924...

In a 17-year-old girl (patient T23159) with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified a de novo heterozygous c.254T-C transition (c.254T-C, NM_004171.3) the SLC1A2 gene, resulting in a leu85-to-pro (L85P) substitution. The mutation was not found in the Exome Sequencing Project, 1000 Genomes Project, or ExAC databases. Functional studies of the variant and studies of patient cells were not performed. The patient had onset of myoclonic seizures in the first days of life.


.0003 DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, GLY82ARG, 244G-A
  
RCV000505595...

In a 6.5-year-old boy (subject A) with developmental and epileptic encephalopathy-41 (DEE41; 617105), Guella et al. (2017) identified a de novo heterozygous c.244G-A transition (c.244G-A, NM_004171.3) in the SLC1A2 gene, resulting in a gly82-to-arg (G82R) substitution in a residue joining the first pair of transmembrane domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the gnomAD browser database. In vitro functional studies of the variant and studies of patient cells were not performed. The patient had onset of refractory seizures in the first weeks of life. A c.244G-C transversion in the SLC1A2 gene, resulting in the same G82R substitution, had been reported in another patient with DEE41 (600300.0001).


.0004 DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, PRO289ARG
  
RCV000505637...

In a 10-year-old boy (subject C) with developmental and epileptic encephalopathy-41 (DEE41; 617105), Guella et al. (2017) reported a de novo heterozygous c.866C-G transversion (c.866C-G, NM_004171.3) in the SLC1A2 gene, resulting in a pro289-to-arg (P289R) substitution at a highly conserved residue in the middle of the fifth transmembrane domain. In vitro functional studies of the variant and studies of patient cells were not performed. The patient had onset of refractory spasms in the first days of life.


REFERENCES

  1. Aoki, M., Lin, C. L., Rothstein, J. D., Geller, B. A., Hosler, B. A., Munsat, T. L., Horvitz, H. R., Brown, R. H. Mutations in the glutamate transporter EAAT2 gene do not cause abnormal EAAT2 transcripts in amyotrophic lateral sclerosis. Ann. Neurol. 43: 645-653, 1998. [PubMed: 9585360, related citations] [Full Text]

  2. Choi, D. W. Glutamate neurotoxicity and diseases of the nervous system. Neuron 1: 623-634, 1988. [PubMed: 2908446, related citations] [Full Text]

  3. Epi4K Consortium and Epilepsy Phenome/Genome Project. De novo mutations in epileptic encephalopathies. Nature 501: 217-221, 2013. [PubMed: 23934111, images, related citations] [Full Text]

  4. Epi4K Consortium. De novo mutations in SLC1A2 and CACNA1A are important causes of epileptic encephalopathies. Am. J. Hum. Genet. 99: 287-298, 2016. [PubMed: 27476654, related citations] [Full Text]

  5. Flowers, J. M., Powell, J. F., Leigh, P. N., Andersen, P., Shaw, C. E. Intron 7 retention and exon 9 skipping EAAT2 mRNA variants are not associated with amyotrophic lateral sclerosis. Ann. Neurol. 49: 643-649, 2001. [PubMed: 11357955, related citations]

  6. Guella, I., McKenzie, M. B., Evans, D. M., Buerki, S. E., Toyota, E. B., Van Allen, M. I., Epilepsy Genomics Study, Suri, M., Elmslie, F., Deciphering Developmental Disorders Study, Simon, M. E. H., van Gassen, K. L. I., Heron, D., Keren, B., Nava, C., Connolly, M. B., Demos, M., Farrer, M. J. De novo mutations in YWHAG cause early-onset epilepsy. Am. J. Hum. Genet. 101: 300-310, 2017. [PubMed: 28777935, images, related citations] [Full Text]

  7. Guo, H., Lai, L., Butchbach, M. E. R., Stockinger, M. P., Shan, X., Bishop, G. A., Lin, C. G. Increased expression of the glial glutamate transporter EAAT2 modulates excitotoxicity and delays the onset but not the outcome of ALS in mice. Hum. Molec. Genet. 12: 2519-2532, 2003. [PubMed: 12915461, related citations] [Full Text]

  8. Harada, T., Harada, C., Watanabe, M., Inoue, Y., Sakagawa, T., Nakayama, N., Sasaki, S., Okuyama, S., Watase, K., Wada, K., Tanaka, K. Functions of the two glutamate transporters GLAST and GLT-1 in the retina. Proc. Nat. Acad. Sci. 95: 4663-4666, 1998. [PubMed: 9539795, images, related citations] [Full Text]

  9. Honig, L. S., Chambliss, D. D., Bigio, E. H., Carroll, S. L., Elliott, J. L. Glutamate transporter EAAT2 splice variants occur not only in ALS, but also in AD and controls. Neurology 55: 1082-1088, 2000. [PubMed: 11071482, related citations] [Full Text]

  10. Hoye, M. L., Regan, M. R., Jensen, L. A., Lake, A. M., Reddy, L. V., Vidensky, S., Richard, J.-P., Maragakis, N. J., Rothstein, J. D., Dougherty, J. D., Miller, T. M. Motor neuron-derived microRNAs cause astrocyte dysfunction in amyotrophic lateral sclerosis. Brain 141: 2561-2575, 2018. [PubMed: 30007309, images, related citations] [Full Text]

  11. Kanai, Y., Smith, C. P., Hediger, M. A. The elusive transporters with a high affinity for glutamate. Trends Neurosci. 16: 365-730, 1993. [PubMed: 7694407, related citations] [Full Text]

  12. Kirschner, M. A., Copeland, N. G., Gilbert, D. J., Jenkins, N. A., Amara, S. G. Mouse excitatory amino acid transporter EAAT2: isolation, characterization, and proximity to neuroexcitability loci on mouse chromosome 2. Genomics 24: 218-224, 1994. [PubMed: 7698742, related citations] [Full Text]

  13. Kovermann, P., Kolobkova, Y., Franzen, A., Fahlke, C. Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function. Epilepsia 63: 388-401, 2022. [PubMed: 34961934, related citations] [Full Text]

  14. Krishnan, S. N., Desai, T., Wyman, R. J., Haddad, G. G. Cloning of a glutamate transporter from human brain. Soc. Neurosci. Abstr. 19: 219 only, 1993.

  15. Li, X., Francke, U. Assignment of the gene SLC1A2 coding for the human glutamate transporter EAAT2 to human chromosome 11 bands p13-p12. Cytogenet. Cell Genet. 71: 212-213, 1995. [PubMed: 7587378, related citations] [Full Text]

  16. Lin, C.-L. G., Bristol, L. A., Jin, L., Dykes-Hoberg, M., Crawford, T., Clawson, L., Rothstein, J. D. Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis. Neuron 20: 589-602, 1998. [PubMed: 9539131, related citations] [Full Text]

  17. Mallolas, J., Hurtado, O., Castellanos, M., Blanco, M., Sobrino, T., Serena, J., Vivancos, J., Castillo, J., Lizasoain, I., Moro, M. A., Davalos, A. A polymorphism in the EAAT2 promoter is associated with higher glutamate concentrations and higher frequency of progressing stroke. J. Exp. Med. 203: 711-717, 2006. [PubMed: 16520390, images, related citations] [Full Text]

  18. Maragakis, N. J., Dykes-Hoberg, M., Rothstein, J. D. Altered expression of the glutamate transporter EAAT2b in neurological disease. Ann. Neurol. 55: 469-477, 2004. [PubMed: 15048885, related citations] [Full Text]

  19. Matsugami, T. R., Tanemura, K., Mieda, M., Nakatomi, R., Yamada, K., Kondo, T., Ogawa, M., Obata, K., Watanabe, M., Hashikawa, T., Tanaka, K. Indispensability of the glutamate transporters GLAST and GLT1 to brain development. Proc. Nat. Acad. Sci. 103: 12161-12166, 2006. [PubMed: 16880397, images, related citations] [Full Text]

  20. Meyer, T., Munch, C., Volkel, H., Booms, P., Ludolph, A. C. The EAAT2 (GLT-1) gene in motor neuron disease: absence of mutations in amyotrophic lateral sclerosis and a point mutation in patients with hereditary spastic paraplegia. J. Neurol. Neurosurg. Psychiat. 65: 594-596, 1998. [PubMed: 9771796, related citations] [Full Text]

  21. Rothstein, J. D., Martin, L. J., Kuncl, R. W. Decreased glutamate transport by the brain and spinal cord in amyotrophic lateral sclerosis. New Eng. J. Med. 326: 1464-1468, 1992. [PubMed: 1349424, related citations] [Full Text]

  22. Rothstein, J. D., Martin, L., Levey, A. I., Dykes-Hoberg, M., Jin, L., Wu, D., Nash, N., Kuncl, R. W. Localization of neuronal and glial glutamate transporters. Neuron 13: 713-725, 1994. [PubMed: 7917301, related citations] [Full Text]

  23. Rothstein, J. D., Patel, S., Regan, M. R., Haenggeli, C., Huang, Y. H., Bergles, D. E., Jin, L., Dykes Hoberg, M., Vidensky, S., Chung, D. S., Toan, S. V., Bruijn, L. I., Su, Z., Gupta, P., Fisher, P. B. Beta-lactam antibiotics offer neuroprotection by increasing glutamate transporter expression. Nature 433: 73-77, 2005. [PubMed: 15635412, related citations] [Full Text]

  24. Rothstein, J. D., Van Kammen, M., Levey, A. I., Martin, L. J., Kuncl, R. W. Selective loss of glial glutamate transporter GLT-1 in amyotrophic lateral sclerosis. Ann. Neurol. 38: 73-84, 1995. [PubMed: 7611729, related citations] [Full Text]

  25. Schmitt, A., Asan, E., Lesch, K.-P., Kugler, P. A splice variant of glutamate transporter GLT1/EAAT2 expressed in neurons: cloning and localization in rat nervous system. Neuroscience 109: 45-61, 2002. [PubMed: 11784699, related citations] [Full Text]

  26. Shashidharan, P., Wittenberg, I., Plaitakis, A. Molecular cloning of human brain glutamate/aspartate transporter II. Biochim. Biophys. Acta 1191: 393-396, 1994. [PubMed: 8172925, related citations] [Full Text]

  27. Su, Z., Leszczyniecka, M., Kang, D., Sarkar, D., Chao, W., Volsky, D. J., Fisher, P. B. Insights into glutamate transport regulation in human astrocytes: cloning of the promoter for excitatory amino acid transporter 2 (EAAT2). Proc. Nat. Acad. Sci. 100: 1955-1960, 2003. [PubMed: 12578975, images, related citations] [Full Text]

  28. Takai, S., Kawakami, H., Nakayama, T., Yamada, K., Nakamura, S. Localization of the gene encoding the human L-glutamate transporter (GLT-1) to 11p11.2-p13 by fluorescence in situ hybridization. Hum. Genet. 97: 387-389, 1996. [PubMed: 8786089, related citations] [Full Text]

  29. Tanaka, K., Watase, K., Manabe, T., Yamada, K., Watanabe, M., Takahashi, K., Iwama, H., Nishikawa, T., Ichihara, N., Kikuchi, T., Okuyama, S., Kawashima, N., Hori, S., Takimoto, M., Wada, K. Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1. Science 276: 1699-1702, 1997. [PubMed: 9180080, related citations] [Full Text]

  30. Trotti, D., Aoki, M., Pasinelli, P., Berger, U. V., Danbolt, N. C., Brown, R. H., Jr., Hediger, M. A. Amyotrophic lateral sclerosis-linked glutamate transporter mutant has impaired glutamate clearance capacity. J. Biol. Chem. 276: 576-582, 2001. [PubMed: 11031254, related citations] [Full Text]

  31. Utsunomiya-Tate, N., Endou, H., Kanai, Y. Tissue specific variants of glutamate transporter GLT-1. FEBS Lett. 416: 312-316, 1997. [PubMed: 9373176, related citations] [Full Text]


Bao Lige - updated : 02/02/2023
Bao Lige - updated : 12/04/2018
Cassandra L. Kniffin - updated : 09/13/2017
Cassandra L. Kniffin - updated : 09/19/2016
Paul J. Converse - updated : 1/11/2007
Patricia A. Hartz - updated : 9/15/2006
George E. Tiller - updated : 9/12/2005
Ada Hamosh - updated : 1/21/2005
Cassandra L. Kniffin - updated : 6/15/2004
Cassandra L. Kniffin - reorganized : 6/11/2004
Cassandra L. Kniffin - updated : 6/3/2004
Victor A. McKusick - updated : 3/27/2003
Cassandra L. Kniffin - updated : 7/9/2002
Victor A. McKusick - updated : 4/12/1999
Victor A. McKusick - updated : 2/15/1999
Victor A. McKusick - updated : 5/21/1998
Victor A. McKusick - updated : 6/12/1997
Creation Date:
Victor A. McKusick : 1/9/1995
mgross : 02/02/2023
mgross : 02/02/2023
alopez : 11/19/2020
alopez : 11/10/2020
joanna : 10/18/2020
alopez : 12/04/2018
carol : 09/18/2017
ckniffin : 09/13/2017
alopez : 09/20/2016
ckniffin : 09/19/2016
wwang : 10/06/2009
ckniffin : 9/14/2009
wwang : 6/19/2008
mgross : 1/11/2007
wwang : 9/22/2006
terry : 9/15/2006
alopez : 10/20/2005
terry : 9/12/2005
terry : 3/3/2005
terry : 2/14/2005
tkritzer : 1/21/2005
terry : 1/21/2005
carol : 6/15/2004
ckniffin : 6/15/2004
carol : 6/11/2004
ckniffin : 6/3/2004
cwells : 4/2/2003
terry : 3/27/2003
tkritzer : 8/9/2002
ckniffin : 7/9/2002
carol : 7/8/2002
cwells : 2/27/2001
carol : 4/12/1999
carol : 2/16/1999
terry : 2/15/1999
terry : 6/16/1998
terry : 5/21/1998
mark : 6/12/1997
jamie : 2/4/1997
terry : 3/29/1996
terry : 3/29/1996
mark : 2/22/1996
mark : 1/28/1996
terry : 1/23/1996
carol : 1/27/1995
terry : 1/9/1995

* 600300

SOLUTE CARRIER FAMILY 1 (GLIAL HIGH AFFINITY GLUTAMATE TRANSPORTER), MEMBER 2; SLC1A2


Alternative titles; symbols

EXCITATORY AMINO ACID TRANSPORTER 2; EAAT2
GLUTAMATE TRANSPORTER 1; GLT1


Other entities represented in this entry:

EAAT2b, INCLUDED
GLT1A, INCLUDED
GLT1B, INCLUDED

HGNC Approved Gene Symbol: SLC1A2

Cytogenetic location: 11p13     Genomic coordinates (GRCh38): 11:35,251,205-35,420,507 (from NCBI)


Gene-Phenotype Relationships

Location Phenotype Phenotype
MIM number
Inheritance Phenotype
mapping key
11p13 Developmental and epileptic encephalopathy 41 617105 Autosomal dominant 3

TEXT

Description

Glutamate transporters are membrane-bound proteins localized in glial cells and/or presynaptic glutamatergic nerve endings. They are essential for the removal and termination of action of the excitatory neurotransmitter glutamate from the synapse (Shashidharan et al., 1994).

Several subtypes of glutamate transporters have been defined by differences in sequence, pharmacology, tissue distribution, and channel-like properties, including SLC1A2 (EAAT2), SLC1A3 (EAAT1 or GLAST; 600111), SLC1A1 (EAAC1 or EAAT3; 133550), and SLC1A6 (EAAT4; 600637). SLC1A2 is selectively localized to astroglia; SLC1A1 and SLC1A6 are selectively localized in neurons; and SLC1A3 is found in both neurons and astroglia (Rothstein et al., 1994; Maragakis et al., 2004).


Cloning and Expression

By screening a human brainstem and cerebellum cDNA library, Shashidharan et al. (1994) isolated a cDNA corresponding to the SLC1A2 gene. The predicted 565-amino acid protein is homologous to a rat brain sodium-dependent glutamate/aspartate transporter. (See also Krishnan et al., 1993).

Su et al. (2003) described the cloning and characterization of the human EAAT2 promoter, demonstrating elevated expression in astrocytes. Regulators of EAAT2 transport, both positive and negative, altered EAAT2 transcription, promoter activity, mRNA, and protein, implying that transcriptional processes can regulate EAAT2 expression. The authors also raised the possibility that the EAAT2 promoter may be useful for targeting gene expression in the brain and for identifying molecules capable of modulating glutamate transport that could potentially inhibit, ameliorate, or prevent various neurodegenerative diseases.

Kirschner et al. (1994) isolated the cDNA for mouse Eaat2. The mouse Eaat2 amino acid sequence shares 99% and 97% identity with its rat and human homologs, respectively. It is expressed predominantly in the brain, where it may function as a glia-specific transporter.

Utsunomiya-Tate et al. (1997) isolated several tissue-specific GLT1 variants from mouse brain and liver. They determined that brain and liver GLT1 cDNA clones have different 5-prime ends, corresponding to replacement of 6 N-terminal amino acids in brain GLT1 by 3 N-terminal amino acids in liver GLT1. In addition, the authors found 2 alternative 3-prime ends in both brain and liver cDNAs, corresponding to replacement of 22 C-terminus amino acids (the 'a' end) by 11 C-terminal amino acids (the 'b' end). The authors designated the 2 liver GLT1 mRNAs as mGLT1A and mGLT1B, which have the same N termini and different C termini. In vitro expression studies showed that the channel properties were not changed by the alteration of N or C termini.

From rat brain, Schmitt et al. (2002) cloned a cDNA corresponding to a GLT1 variant, rat GLT1B or human EAAT2b, which is generated by alternative splicing at the 3-prime end of the GLT1 cDNA. Northern blot analysis showed that the 11-kb GLT1 mRNA predominates in the brain, while the 12.5-kb GLT1 variant mRNA predominates in the retina. The GLT1 variant was preferentially expressed in neurons of the central and peripheral nervous systems, but only occasionally in astrocytes. EAAT2b has a truncated intracellular C-terminal domain with a unique terminal sequence of 11 amino acids. In vitro, the EAAT2b protein showed functional glutamate transport activity (see also Maragakis et al., 2004).


Mapping

Using somatic cell hybrids and fluorescence in situ hybridization (FISH), Li and Francke (1995) assigned the human SLC1A2 gene to chromosome 11p13-p12. By FISH, Takai et al. (1996) mapped the gene, which they called glutamate transporter-1 (GLT1), to 11p13-p11.2.

Using an interspecific backcross analysis, Kirschner et al. (1994) mapped the mouse Eaat2 gene to the central region of chromosome 2, where it is located near quantitative trait loci that modulate neuroexcitability and seizure frequency in mouse models of alcohol withdrawal and epilepsy. The authors noted that mouse chromosome 2 shows syntenic homology to a region on human 11p.


Gene Function

GLT1 is a transporter that actively removes the excitatory neurotransmitter glutamate from the extracellular space. The extracellular concentration of glutamate must be kept low to ensure a high signal-to-noise ratio during synaptic activation, and to prevent neuronal damage from excessive activation of the glutamate receptors. Excess glutamate causes neurotoxicity and may contribute to cellular damage in neurologic disorders such as stroke, trauma, Alzheimer disease (AD; see 104300), amyotrophic lateral sclerosis (ALS; see 105400), and Huntington disease (143100) (Choi, 1988; Kanai et al., 1993).

In mice in which the Glt1 gene was disrupted in embryonic stem cells by homologous recombination, Tanaka et al. (1997) observed lethal spontaneous seizures and increased susceptibility to acute cortical injury. The authors attributed the effects to elevated levels of residual glutamate in the brains of these mice, and concluded that GLT1 contributes to the maintenance of low levels of extracellular glutamate concentrations.

In the retina, the glutamate transporter GLAST is expressed in Muller cells, whereas the glutamate transporter GLT1 is found only in cones and various types of bipolar cells. To investigate the functional role of this differential distribution of glutamate transporters, Harada et al. (1998) analyzed Glast and Glt1 mutant mice. In Glast-deficient mice, the electroretinogram b-wave and oscillatory potentials were reduced and retinal damage after ischemia was exacerbated, whereas Glt1-deficient mice showed almost normal electroretinograms and mildly increased retinal damage after ischemia. These results demonstrated that Glast is required for normal signal transmission between photoreceptors and bipolar cells and that both Glast and Glt1 play a neuroprotective role during ischemia in the retina.

For a discussion of a possible role of the SLC1A2 gene in nicotine dependence, see 188890.

EAAT2 Findings in Amyotrophic Lateral Sclerosis

In patients with amyotrophic lateral sclerosis, Rothstein et al. (1992) found a marked decrease in the maximal velocity of transport for high-affinity glutamate uptake in synaptosomes from spinal cord, motor cortex, and somatosensory cortex. The affinity of the transporter for glutamate was not altered. The authors suggested that defects in the clearance of extracellular glutamate due to a faulty transporter could lead to neurotoxic levels of extracellular glutamate and be pathogenic in ALS. By immunohistochemical analysis, Rothstein et al. (1995) found that GLT1 was severely decreased in ALS brain tissue, both in the motor cortex (71 to 90% decrease from control) and in the spinal cord. As there was no loss of astroglia, the authors hypothesized a primary defect in the GLT1 protein, secondary loss due to down-regulation, or other toxic processes.

Lin et al. (1998) reported that 60 to 70% of sporadic ALS patients have a 30 to 95% loss of the astroglial glutamate transporter EAAT2 protein in motor cortex and spinal cord. In neuropathologically affected areas of the nervous system of 65% of their group of ALS patients, but not in other brain regions, Lin et al. (1998) identified multiple aberrant mRNAs. They were also detectable in the cerebrospinal fluid of living ALS patients early in the disease, suggesting diagnostic utility. The aberrant mRNAs were not found in nonneurologic disease or other disease controls. In vitro expression studies suggested that proteins translated from these aberrant mRNAs may undergo rapid degradation and/or produce a dominant-negative effect on normal EAAT2, resulting in loss of protein and activity. These findings suggested that loss of EAAT2 in ALS is due to aberrant mRNA resulting from RNA processing errors.

Honig et al. (2000) analyzed postmortem brain specimens from 6 patients with ALS, 9 patients with AD, 6 patients with Lewy body disease (127750), and 6 normal controls to ascertain the specificity of alternatively spliced mRNA variants of EAAT2 for ALS. Honig et al. (2000) identified splice variants lacking exons 7, 9, or both 7 and 9, in all brain regions studied in normal controls, as well as in all brain regions of the diseased brains. Quantitative analysis, using RT-PCR, showed that the 2 alternatively spliced isoforms were present as minor species (2-15%) in all specimens, but did show a statistically significant increase of exon 7-skipping isoforms in ALS brains. The authors noted the discrepancy between their findings and those of Lin et al. (1998), and suggested that quantitative differences in the isoforms may be relevant to the pathogenesis of ALS.

Also in contrast to the findings reported by Lin et al. (1998), Flowers et al. (2001) demonstrated that the 2 EAAT2 mRNA transcript variants, specifically one that retains intron 7 and one that skips exon 9, were present in all CNS areas studied in 17 sporadic ALS patients, 7 AD patients, and 19 control subjects. In addition, the ratios of these variants to normal transcripts were not altered in patients as compared to normal controls. The variant mRNAs were not detected in the CSF of 17 ALS and 8 control samples. Flowers et al. (2001) suggested that the exon 9-skipping variant is a physiologic form and that the intron 7-retaining variant may be rapidly degraded via mRNA surveillance mechanisms. They concluded that these EAAT2 variants are not linked to ALS.

Guo et al. (2003) generated transgenic mice overexpressing EAAT2 and crossed these with mice bearing the ALS-associated SOD1 mutant G93A (147450.0008). The amount of EAAT2 protein and the associated Na(+)-dependent glutamate uptake was increased about 2-fold in EAAT2 transgenic mice. The transgenic EAAT2 protein was properly localized to the cell surface on the plasma membrane. Increased EAAT2 expression protected neurons from L-glutamate-induced cytotoxicity and cell death in vitro. The EAAT2/G93A double transgenic mice showed a statistically significant delay in grip strength decline but not in the onset of paralysis, body weight decline, or life span when compared with G93A littermates. A delay in the loss of motor neurons and their axonal morphologies, as well as other events including caspase-3 (CASP3; 600636) activation and SOD1 aggregation, were also observed. The authors hypothesized that loss of EAAT2 may contribute to, but does not cause, motor neuron degeneration in ALS.

In 10 ALS patients, Maragakis et al. (2004) found an average 2-fold increase in EAAT2b in the motor cortex, whereas EAAT2 levels were decreased by up to 94% compared to controls. Immunostaining showed that EAAT2b expression in ALS brains was located in neuropil and neurons. Functional transporter studies demonstrated a large loss of EAAT2 activity.

Using a blinded screen of 1,040 FDA-approved drugs and nutritionals, Rothstein et al. (2005) discovered that many beta-lactam antibiotics are potent stimulators of GLT1 expression. Furthermore, this action appeared to be mediated through increased transcription of the GLT1 gene. Beta-lactams and various semisynthetic derivatives are potent antibiotics that act to inhibit bacterial synthetic pathways. When delivered to animals, the beta-lactam ceftriaxone increased both brain expression of GLT1 and its biochemical and functional activity. Rothstein et al. (2005) found that ceftriaxone was neuroprotective in vitro when used in models of ischemic injury and motor neuron degeneration, both based in part on glutamate toxicity. When used in an animal model of the fatal disease ALS, the drug delayed loss of neurons and muscle strength, and increased mouse survival.

Hoye et al. (2018) searched RNA sequence data generated from different purified CNS cell types and identified EAAT2 as a candidate glial target of miR218 (616770). Luciferase assays showed that miR218 directly binds to the 3-prime UTR of EAAT2, which was sufficient to repress its translation in astrocytes. However, miR218 is expressed only at low levels in both wildtype and ALS astrocytes, indicating that miR218 is not an endogenous regulator of protein expression in adult astrocytes. Further investigation showed that neighboring astrocytes take up the extracellular miR218 released from dying motor neurons in ALS. Examination of the extracellular state of miR218 revealed that miR218 is protein-bound and not encapsulated in vesicles, and also capable of binding oligonucleotides. Mice with whole spinal cord depletion of miR218 showed characteristics of ALS, and miR218 derived from dying motor neurons was taken up by neighboring astrocytes in vivo and mediated changes in astrocytic expression such as loss of EAAT2. Hoye et al. (2018) found that translated mRNAs downregulated in ALS astrocytes contain miR218 binding sites and are derepressed upon miR218 inhibition, indicating that the effects of motor neuron-derived miR218 on astrocytes extend beyond EAAT2 and functionally regulate the expression of other astrocytic proteins and cellular states in neurodegeneration, Inhibition of motor neuron-derived miR218 in ALS model mice further corroborated that miR218 released from dying motor neurons can lead to loss of homeostatic protein expression, such as EAAT2, and astrogliosis.


Molecular Genetics

Developmental and Epileptic Encephalopathy 41

In 2 unrelated patients with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified 2 different de novo heterozygous missense mutations in the SLC1A2 gene (600300.0001-600300.0002). The mutations were found by targeted sequencing of 27 candidate genes in 531 patients with a similar disorder. Functional studies of the variants and studies of patient cells were not performed.

In 2 unrelated patients with DEE41, Guella et al. (2017) identified de novo heterozygous missense mutations in the SLC1A2 gene (600300.0003 and 600300.0004). The first patient was identified from a cohort of 42 individuals with epileptic encephalopathy who underwent sequencing of candidate genes; the second patient was identified through collaboration with clinical and research databases. In vitro functional studies of the variants and studies of patient cells were not performed, but Guella et al. (2017) postulated a toxic gain-of-function effect, perhaps related to glutamate toxicity.

Functional Studies of SLC1A2 Mutations

Based on the channel conformation of the prokaryotic sodium-aspartate symporter from Pyrococcus horikoshii, Kovermann et al. (2022) determined that 3 epileptic encephalopathy-associated mutations in human EAAT2, gly82 to arg (G82R; 600300.0001), leu85 to pro (L85P; 600300.0002), and pro289 to arg (P289R; 600300.0004), are located in proximity to the EAAT anion channel. Ectopic expression in mammalian cells revealed that G82R and P289R, but not L85P, impaired endoplasmic reticulum exit and surface membrane expression of EAAT2. However, all 3 mutants virtually abolished L-glutamate uptake through EAAT2, and all 3 mutants enhanced EAAT2 anion channel anion currents. In particular, G82R and L85P enlarged the pore diameter and made the anion channel significantly permeable for L-gluconate and L-glutamate. In contrast, P289R modified opening of the EAAT2 anion channel, but not its selectivity.

Associations Pending Confirmation

In 55 patients with ALS, Meyer et al. (1998) found no sequence alterations in the EAAT2 gene. In 2 of 7 affected members of a family with autosomal dominant hereditary spastic paraplegia (see, e.g., 182600), Meyer et al. (1998) found heterozygosity for a 269C-G transition, resulting in an ala79-to-gly (A79G) amino acid substitution in the EAAT2 protein. The mutation was present in father and his son, but the authors concluded that the mutation was a rare polymorphism since it did not cosegregate with the disorder.

Using SSCP analysis, Aoki et al. (1998) identified an asn206-to-ser mutation (N206S), a potential N-linked glycosylation site, in the EAAT2 gene in a heterozygous sporadic ALS patient. By Western blot analysis, Trotti et al. (2001) determined that wildtype GLT1 is expressed as a 70-kD protein, whereas N206S is a 60- to 65-kD protein. The size of both proteins is equivalent after glycosidase treatment, presumably by deglycosylating the N216 site as well. Functional analysis and immunofluorescence microscopy demonstrated that cells expressing N206S have reduced transport activity and plasma membrane expression and increased cytoplasmic expression compared to wildtype. The mutant protein also exhibited increased reverse transport activity. Coexpression of mutant and wildtype GLT1 resulted in a dominant-negative effect on wildtype activity, suggesting an impairment of glutamate clearance at synapses in vivo.

Mallolas et al. (2006) hypothesized that some individuals are susceptible to excitotoxicity after stroke (see 601367) due to impaired glutamate uptake mediated by glutamate transporters, such as EAAT2, the primary transporter in adults. By examining 101 stroke patients and 106 controls, they identified an A-to-C polymorphism at position -181 from the transcriptional start site of EAAT2 that abolished an activator protein-2 (AP2; 107580) recognition sequence and created a novel consensus binding site for the repressor transcription factor GCF2 (LRRFIP1; 603256). The prevalence of the polymorphism in stroke patients was comparable to that in healthy subjects. However, stroke patients with the -181C allele showed higher plasma glutamate concentrations and earlier neurologic deterioration than those with the -181A allele, in spite of having similar baseline characteristics. Following transfection into rat astrocytes, the -181C human promoter was not activated by AP2 and was repressed with GCF2, and its activity in the presence of GCF2 was reduced when compared with the AP2-cotransfected -181A promoter. Rats with middle cerebral artery occlusion expressed Gcf2. Mallolas et al. (2006) concluded that a functional polymorphism in the EAAT2 promoter alters the regulation pattern and decreases promoter activity, resulting in higher plasma glutamate levels and possibly explaining the failure of glutamate antagonists in some stroke victims.


Animal Model

Matsugami et al. (2006) found that the brains of mice lacking Glast or Glt1 developed normally but that Glast/Glt1 double-knockout mice died around embryonic days 17 to 18 and exhibited cortical, hippocampal, and olfactory bulb disorganization. Several essential aspects of neuronal development, such as stem cell proliferation, radial migration, neuronal differentiation, and survival of subplate neurons, were impaired. Matsugami et al. (2006) concluded that the regulation of extracellular glutamate concentration and the maintenance of glutamate-mediated synaptic transmission is necessary for normal brain development.


ALLELIC VARIANTS 4 Selected Examples):

.0001   DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, GLY82ARG, 244G-C
SNP: rs886037942, ClinVar: RCV000240886

In a 6-year-old girl (patient EG1291) with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified a de novo heterozygous c.244G-C transversion (c.244G-C, NM_004171.3) in the SLC1A2 gene, resulting in a gly82-to-arg (G82R) substitution in the first extracellular domain. The mutation was not found in the Exome Sequencing Project, 1000 Genomes Project, or ExAC databases. Functional studies of the variant and studies of patient cells were not performed. The patient had onset of infantile spasms in the first days of life. The same de novo heterozygous G82R mutation had been previously identified in another patient with early-onset epilepsy in the study of the Epi4K Consortium and Epilepsy Phenome/Genome Project (2013), which included 264 probands with epileptic encephalopathy who underwent exome sequencing.


.0002   DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, LEU85PRO
SNP: rs886037943, ClinVar: RCV000240924, RCV003362736, RCV003556299

In a 17-year-old girl (patient T23159) with developmental and epileptic encephalopathy-41 (DEE41; 617105), the Epi4K Consortium (2016) identified a de novo heterozygous c.254T-C transition (c.254T-C, NM_004171.3) the SLC1A2 gene, resulting in a leu85-to-pro (L85P) substitution. The mutation was not found in the Exome Sequencing Project, 1000 Genomes Project, or ExAC databases. Functional studies of the variant and studies of patient cells were not performed. The patient had onset of myoclonic seizures in the first days of life.


.0003   DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, GLY82ARG, 244G-A
SNP: rs886037942, ClinVar: RCV000505595, RCV001857241

In a 6.5-year-old boy (subject A) with developmental and epileptic encephalopathy-41 (DEE41; 617105), Guella et al. (2017) identified a de novo heterozygous c.244G-A transition (c.244G-A, NM_004171.3) in the SLC1A2 gene, resulting in a gly82-to-arg (G82R) substitution in a residue joining the first pair of transmembrane domain. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in the gnomAD browser database. In vitro functional studies of the variant and studies of patient cells were not performed. The patient had onset of refractory seizures in the first weeks of life. A c.244G-C transversion in the SLC1A2 gene, resulting in the same G82R substitution, had been reported in another patient with DEE41 (600300.0001).


.0004   DEVELOPMENTAL AND EPILEPTIC ENCEPHALOPATHY 41

SLC1A2, PRO289ARG
SNP: rs781379291, gnomAD: rs781379291, ClinVar: RCV000505637, RCV003558430

In a 10-year-old boy (subject C) with developmental and epileptic encephalopathy-41 (DEE41; 617105), Guella et al. (2017) reported a de novo heterozygous c.866C-G transversion (c.866C-G, NM_004171.3) in the SLC1A2 gene, resulting in a pro289-to-arg (P289R) substitution at a highly conserved residue in the middle of the fifth transmembrane domain. In vitro functional studies of the variant and studies of patient cells were not performed. The patient had onset of refractory spasms in the first days of life.


REFERENCES

  1. Aoki, M., Lin, C. L., Rothstein, J. D., Geller, B. A., Hosler, B. A., Munsat, T. L., Horvitz, H. R., Brown, R. H. Mutations in the glutamate transporter EAAT2 gene do not cause abnormal EAAT2 transcripts in amyotrophic lateral sclerosis. Ann. Neurol. 43: 645-653, 1998. [PubMed: 9585360] [Full Text: https://doi.org/10.1002/ana.410430514]

  2. Choi, D. W. Glutamate neurotoxicity and diseases of the nervous system. Neuron 1: 623-634, 1988. [PubMed: 2908446] [Full Text: https://doi.org/10.1016/0896-6273(88)90162-6]

  3. Epi4K Consortium and Epilepsy Phenome/Genome Project. De novo mutations in epileptic encephalopathies. Nature 501: 217-221, 2013. [PubMed: 23934111] [Full Text: https://doi.org/10.1038/nature12439]

  4. Epi4K Consortium. De novo mutations in SLC1A2 and CACNA1A are important causes of epileptic encephalopathies. Am. J. Hum. Genet. 99: 287-298, 2016. [PubMed: 27476654] [Full Text: https://doi.org/10.1016/j.ajhg.2016.06.003]

  5. Flowers, J. M., Powell, J. F., Leigh, P. N., Andersen, P., Shaw, C. E. Intron 7 retention and exon 9 skipping EAAT2 mRNA variants are not associated with amyotrophic lateral sclerosis. Ann. Neurol. 49: 643-649, 2001. [PubMed: 11357955]

  6. Guella, I., McKenzie, M. B., Evans, D. M., Buerki, S. E., Toyota, E. B., Van Allen, M. I., Epilepsy Genomics Study, Suri, M., Elmslie, F., Deciphering Developmental Disorders Study, Simon, M. E. H., van Gassen, K. L. I., Heron, D., Keren, B., Nava, C., Connolly, M. B., Demos, M., Farrer, M. J. De novo mutations in YWHAG cause early-onset epilepsy. Am. J. Hum. Genet. 101: 300-310, 2017. [PubMed: 28777935] [Full Text: https://doi.org/10.1016/j.ajhg.2017.07.004]

  7. Guo, H., Lai, L., Butchbach, M. E. R., Stockinger, M. P., Shan, X., Bishop, G. A., Lin, C. G. Increased expression of the glial glutamate transporter EAAT2 modulates excitotoxicity and delays the onset but not the outcome of ALS in mice. Hum. Molec. Genet. 12: 2519-2532, 2003. [PubMed: 12915461] [Full Text: https://doi.org/10.1093/hmg/ddg267]

  8. Harada, T., Harada, C., Watanabe, M., Inoue, Y., Sakagawa, T., Nakayama, N., Sasaki, S., Okuyama, S., Watase, K., Wada, K., Tanaka, K. Functions of the two glutamate transporters GLAST and GLT-1 in the retina. Proc. Nat. Acad. Sci. 95: 4663-4666, 1998. [PubMed: 9539795] [Full Text: https://doi.org/10.1073/pnas.95.8.4663]

  9. Honig, L. S., Chambliss, D. D., Bigio, E. H., Carroll, S. L., Elliott, J. L. Glutamate transporter EAAT2 splice variants occur not only in ALS, but also in AD and controls. Neurology 55: 1082-1088, 2000. [PubMed: 11071482] [Full Text: https://doi.org/10.1212/wnl.55.8.1082]

  10. Hoye, M. L., Regan, M. R., Jensen, L. A., Lake, A. M., Reddy, L. V., Vidensky, S., Richard, J.-P., Maragakis, N. J., Rothstein, J. D., Dougherty, J. D., Miller, T. M. Motor neuron-derived microRNAs cause astrocyte dysfunction in amyotrophic lateral sclerosis. Brain 141: 2561-2575, 2018. [PubMed: 30007309] [Full Text: https://doi.org/10.1093/brain/awy182]

  11. Kanai, Y., Smith, C. P., Hediger, M. A. The elusive transporters with a high affinity for glutamate. Trends Neurosci. 16: 365-730, 1993. [PubMed: 7694407] [Full Text: https://doi.org/10.1016/0166-2236(93)90094-3]

  12. Kirschner, M. A., Copeland, N. G., Gilbert, D. J., Jenkins, N. A., Amara, S. G. Mouse excitatory amino acid transporter EAAT2: isolation, characterization, and proximity to neuroexcitability loci on mouse chromosome 2. Genomics 24: 218-224, 1994. [PubMed: 7698742] [Full Text: https://doi.org/10.1006/geno.1994.1609]

  13. Kovermann, P., Kolobkova, Y., Franzen, A., Fahlke, C. Mutations associated with epileptic encephalopathy modify EAAT2 anion channel function. Epilepsia 63: 388-401, 2022. [PubMed: 34961934] [Full Text: https://doi.org/10.1111/epi.17154]

  14. Krishnan, S. N., Desai, T., Wyman, R. J., Haddad, G. G. Cloning of a glutamate transporter from human brain. Soc. Neurosci. Abstr. 19: 219 only, 1993.

  15. Li, X., Francke, U. Assignment of the gene SLC1A2 coding for the human glutamate transporter EAAT2 to human chromosome 11 bands p13-p12. Cytogenet. Cell Genet. 71: 212-213, 1995. [PubMed: 7587378] [Full Text: https://doi.org/10.1159/000134111]

  16. Lin, C.-L. G., Bristol, L. A., Jin, L., Dykes-Hoberg, M., Crawford, T., Clawson, L., Rothstein, J. D. Aberrant RNA processing in a neurodegenerative disease: the cause for absent EAAT2, a glutamate transporter, in amyotrophic lateral sclerosis. Neuron 20: 589-602, 1998. [PubMed: 9539131] [Full Text: https://doi.org/10.1016/s0896-6273(00)80997-6]

  17. Mallolas, J., Hurtado, O., Castellanos, M., Blanco, M., Sobrino, T., Serena, J., Vivancos, J., Castillo, J., Lizasoain, I., Moro, M. A., Davalos, A. A polymorphism in the EAAT2 promoter is associated with higher glutamate concentrations and higher frequency of progressing stroke. J. Exp. Med. 203: 711-717, 2006. [PubMed: 16520390] [Full Text: https://doi.org/10.1084/jem.20051979]

  18. Maragakis, N. J., Dykes-Hoberg, M., Rothstein, J. D. Altered expression of the glutamate transporter EAAT2b in neurological disease. Ann. Neurol. 55: 469-477, 2004. [PubMed: 15048885] [Full Text: https://doi.org/10.1002/ana.20003]

  19. Matsugami, T. R., Tanemura, K., Mieda, M., Nakatomi, R., Yamada, K., Kondo, T., Ogawa, M., Obata, K., Watanabe, M., Hashikawa, T., Tanaka, K. Indispensability of the glutamate transporters GLAST and GLT1 to brain development. Proc. Nat. Acad. Sci. 103: 12161-12166, 2006. [PubMed: 16880397] [Full Text: https://doi.org/10.1073/pnas.0509144103]

  20. Meyer, T., Munch, C., Volkel, H., Booms, P., Ludolph, A. C. The EAAT2 (GLT-1) gene in motor neuron disease: absence of mutations in amyotrophic lateral sclerosis and a point mutation in patients with hereditary spastic paraplegia. J. Neurol. Neurosurg. Psychiat. 65: 594-596, 1998. [PubMed: 9771796] [Full Text: https://doi.org/10.1136/jnnp.65.4.594]

  21. Rothstein, J. D., Martin, L. J., Kuncl, R. W. Decreased glutamate transport by the brain and spinal cord in amyotrophic lateral sclerosis. New Eng. J. Med. 326: 1464-1468, 1992. [PubMed: 1349424] [Full Text: https://doi.org/10.1056/NEJM199205283262204]

  22. Rothstein, J. D., Martin, L., Levey, A. I., Dykes-Hoberg, M., Jin, L., Wu, D., Nash, N., Kuncl, R. W. Localization of neuronal and glial glutamate transporters. Neuron 13: 713-725, 1994. [PubMed: 7917301] [Full Text: https://doi.org/10.1016/0896-6273(94)90038-8]

  23. Rothstein, J. D., Patel, S., Regan, M. R., Haenggeli, C., Huang, Y. H., Bergles, D. E., Jin, L., Dykes Hoberg, M., Vidensky, S., Chung, D. S., Toan, S. V., Bruijn, L. I., Su, Z., Gupta, P., Fisher, P. B. Beta-lactam antibiotics offer neuroprotection by increasing glutamate transporter expression. Nature 433: 73-77, 2005. [PubMed: 15635412] [Full Text: https://doi.org/10.1038/nature03180]

  24. Rothstein, J. D., Van Kammen, M., Levey, A. I., Martin, L. J., Kuncl, R. W. Selective loss of glial glutamate transporter GLT-1 in amyotrophic lateral sclerosis. Ann. Neurol. 38: 73-84, 1995. [PubMed: 7611729] [Full Text: https://doi.org/10.1002/ana.410380114]

  25. Schmitt, A., Asan, E., Lesch, K.-P., Kugler, P. A splice variant of glutamate transporter GLT1/EAAT2 expressed in neurons: cloning and localization in rat nervous system. Neuroscience 109: 45-61, 2002. [PubMed: 11784699] [Full Text: https://doi.org/10.1016/s0306-4522(01)00451-1]

  26. Shashidharan, P., Wittenberg, I., Plaitakis, A. Molecular cloning of human brain glutamate/aspartate transporter II. Biochim. Biophys. Acta 1191: 393-396, 1994. [PubMed: 8172925] [Full Text: https://doi.org/10.1016/0005-2736(94)90192-9]

  27. Su, Z., Leszczyniecka, M., Kang, D., Sarkar, D., Chao, W., Volsky, D. J., Fisher, P. B. Insights into glutamate transport regulation in human astrocytes: cloning of the promoter for excitatory amino acid transporter 2 (EAAT2). Proc. Nat. Acad. Sci. 100: 1955-1960, 2003. [PubMed: 12578975] [Full Text: https://doi.org/10.1073/pnas.0136555100]

  28. Takai, S., Kawakami, H., Nakayama, T., Yamada, K., Nakamura, S. Localization of the gene encoding the human L-glutamate transporter (GLT-1) to 11p11.2-p13 by fluorescence in situ hybridization. Hum. Genet. 97: 387-389, 1996. [PubMed: 8786089] [Full Text: https://doi.org/10.1007/BF02185779]

  29. Tanaka, K., Watase, K., Manabe, T., Yamada, K., Watanabe, M., Takahashi, K., Iwama, H., Nishikawa, T., Ichihara, N., Kikuchi, T., Okuyama, S., Kawashima, N., Hori, S., Takimoto, M., Wada, K. Epilepsy and exacerbation of brain injury in mice lacking the glutamate transporter GLT-1. Science 276: 1699-1702, 1997. [PubMed: 9180080] [Full Text: https://doi.org/10.1126/science.276.5319.1699]

  30. Trotti, D., Aoki, M., Pasinelli, P., Berger, U. V., Danbolt, N. C., Brown, R. H., Jr., Hediger, M. A. Amyotrophic lateral sclerosis-linked glutamate transporter mutant has impaired glutamate clearance capacity. J. Biol. Chem. 276: 576-582, 2001. [PubMed: 11031254] [Full Text: https://doi.org/10.1074/jbc.M003779200]

  31. Utsunomiya-Tate, N., Endou, H., Kanai, Y. Tissue specific variants of glutamate transporter GLT-1. FEBS Lett. 416: 312-316, 1997. [PubMed: 9373176] [Full Text: https://doi.org/10.1016/s0014-5793(97)01232-5]


Contributors:
Bao Lige - updated : 02/02/2023
Bao Lige - updated : 12/04/2018
Cassandra L. Kniffin - updated : 09/13/2017
Cassandra L. Kniffin - updated : 09/19/2016
Paul J. Converse - updated : 1/11/2007
Patricia A. Hartz - updated : 9/15/2006
George E. Tiller - updated : 9/12/2005
Ada Hamosh - updated : 1/21/2005
Cassandra L. Kniffin - updated : 6/15/2004
Cassandra L. Kniffin - reorganized : 6/11/2004
Cassandra L. Kniffin - updated : 6/3/2004
Victor A. McKusick - updated : 3/27/2003
Cassandra L. Kniffin - updated : 7/9/2002
Victor A. McKusick - updated : 4/12/1999
Victor A. McKusick - updated : 2/15/1999
Victor A. McKusick - updated : 5/21/1998
Victor A. McKusick - updated : 6/12/1997

Creation Date:
Victor A. McKusick : 1/9/1995

Edit History:
mgross : 02/02/2023
mgross : 02/02/2023
alopez : 11/19/2020
alopez : 11/10/2020
joanna : 10/18/2020
alopez : 12/04/2018
carol : 09/18/2017
ckniffin : 09/13/2017
alopez : 09/20/2016
ckniffin : 09/19/2016
wwang : 10/06/2009
ckniffin : 9/14/2009
wwang : 6/19/2008
mgross : 1/11/2007
wwang : 9/22/2006
terry : 9/15/2006
alopez : 10/20/2005
terry : 9/12/2005
terry : 3/3/2005
terry : 2/14/2005
tkritzer : 1/21/2005
terry : 1/21/2005
carol : 6/15/2004
ckniffin : 6/15/2004
carol : 6/11/2004
ckniffin : 6/3/2004
cwells : 4/2/2003
terry : 3/27/2003
tkritzer : 8/9/2002
ckniffin : 7/9/2002
carol : 7/8/2002
cwells : 2/27/2001
carol : 4/12/1999
carol : 2/16/1999
terry : 2/15/1999
terry : 6/16/1998
terry : 5/21/1998
mark : 6/12/1997
jamie : 2/4/1997
terry : 3/29/1996
terry : 3/29/1996
mark : 2/22/1996
mark : 1/28/1996
terry : 1/23/1996
carol : 1/27/1995
terry : 1/9/1995