The effects of extracellular glutamate within the nervous system are controlled by 4 groups of membrane proteins. These include ionotropic and metabotropic (mGluR) glutamate receptors, glutamate uptake transporters, and the cystine/glutamate antiporter system called x. Although the glutamate receptor families and uptake transporters have been studied extensively, there has been much less interest in the xc antiporter, which may play a critical role in many CNS pathologies. The glutamate/cystine antiporter couples the import of cystine to the export of glutamate. Concentrations of extracellular glutamate as low as 30uM reverse this process, inhibiting the uptake of cystine. Cystine is required for the synthesis of the potent intracellular reducing agent glutathione (GSH). When GSH is depleted by the presence of extracellular glutamate, cells suffer from oxidative stress and die. This form of glutamate toxicity, called oxidative glutamate toxicity, induces a form of programmed cell death which is distinct from classical apoptosis, but shares some characteristics of apoptosis such as the requirement for de novo macromolecular synthesis and caspase activation. In CNS pathologies such as localized cerebral infarction some neurons die rapidly by necrosis while others die more slowly by a programmed cell death pathway sharing features of oxidative glutamate toxicity. We have therefore developed a model system to study oxidative glutamate toxicity, which is also an excellent model for studying the effects of oxidative stress on nerve cells. The work in this proposal will extend our ongoing studies on the molecular mechanisms of oxidative stress induced nerve cell death, with emphasis on examining the function of the recently cloned xc antiporter, the role of caspases in the cell death program, and the identification genes which regulate oxidative stress in the nervous system. These are aspects of the oxidative glutamate toxicity programmed cell death pathway which have not been examined in detail up to this time, but are critical to our understanding of what may be a major pathway leading to nerve cell injury and death pathway in the CNS. This work is directly relevant to CNS trauma and stroke as well as to all chronic degenerative diseases where oxidative stress is a pathological hallmark.
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