Amyotrophic Lateral Sclerosis-linked Glutamate Transporter Mutant Has Impaired Glutamate Clearance Capacity

Abstract

We have investigated the functional impact of a naturally occurring mutation of the human glutamate transporter GLT1 (EAAT2), which had been detected in a patient with sporadic amyotrophic lateral sclerosis. The mutation involves a substitution of the putative N-linked glycosylation site asparagine 206 by a serine residue (N206S) and results in reduced glycosylation of the transporter and decreased uptake activity. Electrophysiological analysis of N206S revealed a pronounced reduction in transport rate compared with wild-type, but there was no alteration in the apparent affinities for glutamate and sodium. In addition, no change in the sensitivity for the specific transport inhibitor dihydrokainate was observed. However, the decreased rate of transport was associated with a reduction of the N206S transporter in the plasma membrane. Under ionic conditions, which favor the reverse operation mode of the transporter, N206S exhibited an increased reverse transport capacity. Furthermore, if coexpressed in the same cell, N206S manifested a dominant negative effect on the wild-type GLT1 activity, whereas it did not affect wild-type EAAC1. These findings provide evidence for a role of the N-linked glycosylation in both cellular trafficking and transport function. The resulting alteration in glutamate clearance capacity likely contributes to excitotoxicity that participates in motor neuron degeneration in amyotrophic lateral sclerosis.

Altered Expression and Uptake Activity of Spinal Glutamate Transporters after Nerve Injury Contribute to the Pathogenesis of Neuropathic Pain in Rats

“…Regulation of regional glutamate uptake has been linked critically to the prevention of glutamate neurotoxicity as well as the pathogenesis of neurological disorders, including brain ischemia, epilepsy, amyotrophic lateral sclerosis, spinal cord injury, and Alzheimer's disease (Mennerick et al, 1999;Lievens et al, 2000;Vorwerk et al, 2000;Bigini et al, 2001;Trotti et al, 2001;VeraPortocarrero et al, 2002). The present findings suggest a new strategy for treating neuropathic pain by reducing regional glutamate availability and preventing glutamate overexcitation via an enhanced GT system.…”

“…GLAST and GLT-1 are expressed primarily in glial cells, whereas EAAC1 is the predominant neuronal GT (Robinson and Dowd, 1997;Danbolt, 2001). Both neuronal and glial GTs actively participate in a number of fundamental physiological functions, including synaptic plasticity, by regulating extracellular glutamate concentration (Mennerick et al, 1999;Lievens et al, 2000;Vorwerk et al, 2000;Trotti et al, 2001). Importantly, GTs regulate the duration and intensity of glutamate receptor activation during signal transduction.…”

“…Importantly, GTs regulate the duration and intensity of glutamate receptor activation during signal transduction. As such, GTs play a critical role in preventing overstimulation of glutamate receptors, a process that could trigger both neuroplastic changes and excitotoxic cascades under a variety of pathological conditions, including spinal cord and peripheral nerve injury (Mennerick et al, 1999;Lievens et al, 2000;Vorwerk et al, 2000;Trotti et al, 2001).…”

The Hydroxyl Side Chain of a Highly Conserved Serine Residue Is Required for Cation Selectivity and Substrate Transport in the Glial Glutamate Transporter GLT-1/SLC1A2

“…SLC1A2 (GLT-1, EAAT2), which is located on the perisynaptic side of astrocytes, is responsible for 90% of glutamate clearance in the mammalian central nervous system (4). Because high extracellular glutamate concentration causes excitotoxicity, SLC1A2 dysfunction has been associated with numerous neurological diseases such as amyotrophic lateral sclerosis, epilepsy, or Alzheimer disease (1,(5)(6)(7). Each transport cycle of glutamate transporters consists of the cotransport of glutamate, three sodium ions, and one proton followed by the countertransport of one potassium ion (8 -10).…”

Buyang Huanwu decoction increases the expression of glutamate transporter-1 and glutamate synthetase in association with PACAP-38 following focal ischemia

“…These findings not only answer how BYHWD decreased glutamate concentration, but also provide direct evidence that astrocytes closely participated in the protective role of BYHWD following focal ischemia, which may be a new point for the study of traditional medicine. In addition, impaired glutamate transport is known to induce neurotoxicity associated with numerous neurological processes, such as Alzheimer's disease, Huntington's disease and amyotrophic lateral sclerosis (29,30). This highlights the importance of the BYHWD treatment not only in stroke outcome, the main focus of the present study, but also in other neuropathologies, which deserve further study.…”