L-Glutamate (Glu) is the major excitatory neurotransmitter in the mammalian CNS and five types of high-affinity Glu transporters (EAAT1-5) have been identified. The transporters EAAT1 and EAAT2 in glial cells are responsible for the majority of Glu uptake while neuronal EAATs appear to have specialized roles at particular types of synapses. Dysfunction of EAATs is specifically implicated in the pathology of neurodegenerative conditions such as amyotrophic lateral sclerosis, epilepsy, Huntington's disease, Alzheimer's disease and ischemic stroke injury, and thus treatments that can modulate EAAT function may prove beneficial in these conditions. Recent advances have been made in our understanding of the regulation of EAATs, including their trafficking, splicing and post-translational modification. This article summarises some recent developments that improve our understanding of the roles and regulation of EAATs.

Glutathione peroxidases have been thought to function in cellular antioxidant defense. However, some recent studies on Gpx1 knockout (؊/؊) mice have failed to show a role for Gpx1 under conditions of oxidative stress such as hyperbaric oxygen and the exposure of eye lenses to high levels of H 2 O 2 . These findings have, unexpectedly, raised the issue of the role of Gpx1, especially under conditions of oxidative stress. Here we demonstrate a role for Gpx1 in protection against oxidative stress by showing that Gpx1 (؊/؊) mice are highly sensitive to the oxidant paraquat. Lethality was already detected within 24 h in mice exposed to paraquat at 10 mg⅐kg ؊1 (approximately 1 ⁄7 the LD 50 of wild-type controls). The effects of paraquat were dose-related. In the 30 mg⅐kg ؊1 -treated group, 100% of mice died within 5 h, whereas the controls showed no evidence of toxicity. We further demonstrate that paraquat transcriptionally upregulates Gpx1 in normal cells, reinforcing a role for Gpx1 in protection against paraquat toxicity. Finally, we show that cortical neurons from Gpx1 (؊/؊) mice are more susceptible to H 2 O 2 ; 30% of neurons from Gpx1 (؊/؊) mice were killed when exposed to 65 M H 2 O 2 , whereas the wild-type controls were unaffected. These data establish a function for Gpx1 in protection against some oxidative stressors and in protection of neurons against H 2 O 2 . Further, they emphasize the need to elucidate the role of Gpx1 in protection against different oxidative stressors and in different disease states and suggest that Gpx1 (؊/؊) mice may be valuable for studying the role of H 2 O 2 in neurodegenerative disorders.

Mutations in Cu/Zn superoxide dismutase (SOD1) are linked to motor neuron death in familial amyotrophic lateral sclerosis (ALS) by an unclear mechanism, although misfolded SOD1 aggregates are commonly associated with disease. Proteomic analysis of the transgenic SOD1 G93A ALS rat model revealed significant up-regulation of endoplasmic reticulum (ER)-resident protein-disulfide isomerase (PDI) family members in lumbar spinal cords. Expression of SOD1 mutants (mSOD1) led to an up-regulation of PDI in motor neuron-like NSC-34 cells but not other cell lines. Inhibition of PDI using bacitracin increased aggregate production, even in wild type SOD1 transfectants that do not readily form inclusions, suggesting PDI may protect SOD1 from aggregation. Moreover, PDI co-localized with intracellular aggregates of mSOD1 and bound to both wild type and mSOD1. SOD1 was also found in the microsomal fraction of cells despite being a predominantly cytosolic enzyme, confirming ER-Golgi-dependent secretion. In SOD1 G93A mice, a significant up-regulation of unfolded protein response entities was also observed during disease, including caspase-12, -9, and -3 cleavage. Our findings therefore implicate unfolded protein response and ER stress-induced apoptosis in the pathophysiologyoffamilialALS.ThepossibilitythatPDImaybeatherapeutic target to prevent SOD1 aggregation is also raised by this study.Mutations in the Cu/Zn-superoxide dismutase (SOD1) 2 gene are associated with 20% of familial amyotrophic lateral sclerosis (FALS) cases (1), and when these mutations are overexpressed in transgenic rodents (2, 3), motor neuron degeneration reminiscent of ALS results. Although SOD1 is thermally very stable (4), abnormal mutant SOD1 (mSOD1) aggregates are present in spinal cords of FALS patients and transgenic mice (5). The mechanism of mSOD1-mediated toxicity is unclear but is non-cell autonomous and involves apoptotic signaling (reviewed in Ref. 6). The selective toxicity for motor neurons also remains unresolved.SOD1 is an intracellular homodimeric metalloprotein that forms an unusually stable intrasubunit disulfide bond between two highly conserved cysteines, Cys 57 and Cys 146 . Recent evidence implicates the disulfide-reduced monomer as the aggregation-prone and common neurotoxic intermediate for over 100 mSOD1 proteins (7-11). Hence, modulation of disulfide bond formation may be important in mSOD1-linked toxicity.The disulfide status of proteins is largely regulated by ER stress-inducible enzymes. ER stress is triggered when misfolded proteins accumulate within the lumen, inducing the unfolded protein response (UPR) (12). The 78-kDa chaperone immunoglobulin-binding protein (BiP) controls activity of the three major UPR sensors: the kinase and endonuclease IRE1, the basic leucine-zipper transcription factor ATF6, and the PERK kinase (13). The combined effect of the activation of these three molecules is the up-regulation of genes encoding ER-resident chaperones and down-regulation of protein synthesis. Proteindisulfide isomerase (PDI) and en...