Date of Award

Spring 2016

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Lobner, Doug

Second Advisor

Baker, David A.

Third Advisor

Mynlieff, Michelle


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.