The aim of this thesis is to better understand the regulation of the cystine/glutamate antiporter (system xc-) and its role in regulating neuronal survival and death. Expressed primarily on astrocytes, system xc- takes up cystine and releases glutamate in a 1:1 ratio. Cystine uptake is the rate-limiting step in glutathione synthesis, the brain’s main antioxidant. Glutamate released into the extrasynaptic space can regulate neuronal function; however excessive glutamate release can cause excitotoxicity. The dual actions of system xc- make it of interest in many neurodegenerative diseases where oxidative stress and excitotoxicity are involved. We investigated the regulation of system xc- in SOD1-G93A transgenic mouse model of ALS. We observed an increase in cystine uptake and glutamate release through system xc- in spinal cord slices of SOD1-G93A transgenic mice. We did not observe a change in the function of the main glutamate clearance transporter, excitatory amino acid transporter (EAAT). This study was the first to show that system xc- activity is dysregulated in an ALS model and suggests that the excitotoxicity in the SOD1-G93A transgenic mouse may be due to increased system xc- activity. Using primary mixed cortical cultures we assessed how different compounds that deplete intracellular glutathione (GSH), L-buthionine-sulfoximine (BSO) and diethyl maleate (DEM), affect system xc- function. Both compounds caused significant decreases in intracellular GSH levels; however, DEM caused an increase in cystine uptake through system xc-, while unexpectedly BSO caused a decrease in uptake. Also, DEM caused a decrease in intracellular cysteine, while BSO increased cysteine levels. The results suggest that negative feedback by intracellular cysteine is a more important regulator of system xc- than intracellular GSH. Transforming growth factor-β1 (TGF-β1) is a cytokine involved in regulating many cellular processes, including neuronal survival and death. We found that TGF-β1 increased cystine uptake through system xc- in astrocyte-enriched glial cultures via the MAPK/ERK pathway. TGF-β1 increased the export of GSH from astrocytes, which suggests a neuroprotective role; however, in mixed cortical cultures TGF-β1 enhanced rotenone-induced neurotoxicity through AMPA receptors. The data suggests that the increase in system xc- activity by TGF-β1 may have antioxidant defenses, but also exacerbates excitotoxicity
