Date of Award
12-24-2025
Date Published
January 2026
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Biology
Advisor(s)
Sandra Hewett
Keywords
Astrocytes;E/I balance;Epileptogenesis;Seizure;System xc-;xCT
Subject Categories
Medical Sciences | Medicine and Health Sciences | Neurosciences
Abstract
Astrocytes play a central role in maintaining excitatory/inhibitory (E/I) balance in the central nervous system by supporting intracellular glutathione (GSH) synthesis and regulating extracellular glutamate. System xc– (Sxc–), an obligate cystine/glutamate antiporter encoded by SLC7a11, couples the import of L-cystine with the export of L-glutamate. It is highly expressed throughout the cortex, hippocampus, striatum, and cerebellum, where its activity provides cystine—the rate-limiting substrate for cysteine-dependent GSH production—and contributes to ambient glutamatergic tone. Although global loss of Sxc– alters seizure threshold and redox homeostasis, whether these effects arise specifically from the loss of astrocytic Sxc– has remained unresolved. This thesis examined whether selective deletion of Sxc– from astrocytes affects redox maintenance, acute seizure susceptibility, and epileptogenic progression. To address this, an astrocyte-specific conditional Sxc– knockout (Sxc– AcKO; mGFAP-Cre-SLC7A11fl/fl) was compared to Cre-positive wild-type littermates (WT; mGFAP-Cre-SLC7A11+/+). Immunohistochemistry confirmed efficient deletion of xCT in cortex and hippocampus. Redox status was evaluated under basal conditions and three hours after PTZ-induced seizures by quantifying reduced and oxidized glutathione (GSH and GSSG) and cyst(e)ine (CyS and CySS) in both brain regions via HPLC. Basal glutathione and cyst(e)ine levels did not differ between genotypes in cortex [WT vs Sxc– AcKO: Combined GSH (p = 0.3471), GSSG (p = 0.5971); Female GSH (p = 0.1680), GSSG (p = 0.5540); Male GSH (p = 0.1071), GSSG (p = 0.0698)] or hippocampus [Combined GSH (p = 0.3540), GSSG (p = 0.5467); Female GSH (p = 0.5722), GSSG (p = 0.9490); Male GSH (p = 0.3760), GSSG (p = 0.4005)], with no sex-dependent differences. Following PTZ-induced seizures, GSH increased significantly in both genotypes (p-values < 0.0001 for all comparisons), demonstrating preserved antioxidant buffering. In contrast, cyst(e)ine regulation diverged by sex and genotype after PTZ-induced seizures: WT females displayed post-seizure increases in hippocampal CyS and CySS, whereas female Sxc– AcKO mice showed significant reductions in cortical and hippocampal CyS and/or CySS (p < 0.05). Male Sxc– AcKO mice maintained CyS/CySS across conditions, indicating a female-specific vulnerability in sustaining cyst(e)ine pools during oxidative stress. Acute seizure susceptibility was assessed using PTZ doses from 25–58 mg/kg. Sxc– AcKO mice exhibited a significant rightward shift in the convulsive seizure dose-response curve when sexes were combined [ED50: WT = 42.12 (1.59–1.66) mg/kg vs. Sxc– AcKO = 45.30 (1.64–1.67) mg/kg, p = 0.032], an effect driven by females [WT = 40.99 (1.60–1.63) mg/kg vs. Sxc– AcKO = 44.04 (1.62–1.66) mg/kg, p = 0.013]. Latency to convulsion was significantly prolonged in Sxc– AcKO mice at 58 mg/kg [WT = 175.5 ± 24.0s vs Sxc– AcKO = 325.6 ± 66.2s, p = 0.044]. During chronic PTZ kindling (39 mg/kg/day), Sxc– AcKO mice showed reduced kindling acquisition [28% (8/29) vs. WT 54% (14/26), p = 0.043] and delayed progression to the kindled state (combined latency: 14.3 ± 1.8 vs. 10.9 ± 0.78 days, p = 0.062). Male Sxc– AcKO mice demonstrated a significant delay in day of kindling onset [13.8 ± 1.7 vs. 10.0 ± 0.7 days, p = 0.039]. Together, these findings show that astrocyte Sxc– is dispensable for basal redox maintenance but essential for maintaining cyst(e)ine availability during oxidative stress in females. Its loss elevates seizure threshold, prolongs seizure onset, and slows epileptogenesis, identifying astrocyte Sxc– as a key modulator of redox metabolism and neuronal excitability.
Access
Open Access
Recommended Citation
Sutton, Samantha Olivia, "Exploring the Role of Astrocyte System xc– in Excitatory/Inhibitory Balance" (2025). Theses - ALL. 997.
https://surface.syr.edu/thesis/997
