Abstract
SLC1A3 encodes the glial glutamate transporter hEAAT1, which removes glutamate from the synaptic cleft via stoichiometrically coupled Na+-K+-H+-glutamate transport. In a young man with migraine with aura including hemiplegia, we identified a novel SLC1A3 mutation that predicts the substitution of a conserved threonine by proline at position 387 (T387P) in hEAAT1. To evaluate the functional effects of the novel variant, we expressed the wildtype or mutant hEAAT1 in mammalian cells and performed whole-cell patch clamp, fast substrate application, and biochemical analyses. T387P diminishes hEAAT1 glutamate uptake rates and reduces the number of hEAAT1 in the surface membrane. Whereas hEAAT1 anion currents display normal ligand and voltage dependence in cells internally dialyzed with Na+-based solution, no anion currents were observed with internal K+. Fast substrate application demonstrated that T387P abolishes K+-bound retranslocation. Our finding expands the phenotypic spectrum of genetic variation in SLC1A3 and highlights impaired K+ binding to hEAAT1 as a novel mechanism of glutamate transport dysfunction in human disease.
Highlights
Glutamate is the major excitatory neurotransmitter in the central nervous system, and altered brain excitability caused by disturbed glutamate homeostasis plays a role in various paroxysmal neurological disorders[1,2,3]
Glutamate is a potent trigger of cortical spreading depression (CSD), the electrophysiological correlate of migraine aura[4], and imbalance of glutamate release and clearance has been shown to underlie hemiplegic migraine (HM), a severe monogenic subtype of migraine with transient hemiparesis and other aura symptoms[5,6]
Genetic variation in SLC1A3 – the gene encoding EAAT1 - has been linked to several neurological disorders with partially overlapping clinical features[8,9,10,11]
Summary
Glutamate is the major excitatory neurotransmitter in the central nervous system, and altered brain excitability caused by disturbed glutamate homeostasis plays a role in various paroxysmal neurological disorders[1,2,3]. Glutamate is a potent trigger of cortical spreading depression (CSD), the electrophysiological correlate of migraine aura[4], and imbalance of glutamate release and clearance has been shown to underlie hemiplegic migraine (HM), a severe monogenic subtype of migraine with transient hemiparesis and other aura symptoms[5,6]. Genetic variation in SLC1A3 – the gene encoding EAAT1 - has been linked to several neurological disorders with partially overlapping clinical features[8,9,10,11]. We searched for and identified a novel heterozygous SLC1A3 mutation in a young man with a similar but less severe clinical phenotype with recurrent episodes of migrainous headache accompanied by transient hemiparesis. To characterize the functional effects of the newly identified mutation on transporter function and compare them with results on other SLC1A3 mutations, we used both electrophysiology and biochemistry
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