CSFN, Center for Structural and Functional Neuroscience, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, Montana 59812, USA.
Glia. 2011 Oct;59(10):1387-401. doi: 10.1002/glia.21176. Epub 2011 May 17.
The system x(C)- (Sx(C)-) transporter functions to mediate the exchange of extracellular cystine (L-Cys(2)) and intracellular glutamate (L-Glu). Internalized L-Cys(2) serves as a rate-limiting precursor for the biosynthesis of glutathione (GSH), while the externalized L-Glu can contribute to either excitatory signaling or excitotoxicity. In the present study the influence of culture conditions (with and without dibutyryl-cAMP) and GSH levels on the expression of Sx(C)- were investigated in primary rat astrocyte cultures. Sx(C)- activity in dbcAMP-treated cells was nearly sevenfold greater than in untreated astrocytes and increased further (∼threefold) following the depletion of intracellular GSH with buthionine sulfoximine. This increase in Sx(C)- triggered by GSH depletion was only observed in the dbcAMP-treated phenotype and was distinct from the Nrf2-mediated response initiated by exposure to electrophiles. Changes in Sx(C)- activity correlated with increases in both protein and mRNA levels of the xCT subunit of the Sx(C)- heterodimer, an increase in the V(max) for L-Glu uptake and was linked temporally to GSH levels. This induction of Sx(C)- was not mimicked by hydrogen peroxide nor attenuated by nonspecific antioxidants but was partially prevented by the co-administration of the cell-permeant thiols GSH-ethyl ester and N-acetylcysteine. These findings demonstrate that the expression of Sx(C)- on astrocytes is dynamically regulated by intracellular GSH levels in a cell- and phenotype-dependent manner. The presence of this pathway likely reflects the inherent vulnerability of the CNS to oxidative damage and raises interesting questions as to the functional consequences of changes in Sx(C)- activity in CNS injury and disease.
系统 x(C)-(Sx(C)-)转运蛋白的功能是介导细胞外胱氨酸 (L-Cys(2)) 和细胞内谷氨酸 (L-Glu) 的交换。内吞的 L-Cys(2) 作为谷胱甘肽 (GSH) 生物合成的限速前体，而外排的 L-Glu 可以促进兴奋性信号或兴奋性毒性。在本研究中，研究了培养条件（有和没有二丁酰环腺苷酸）和 GSH 水平对原代大鼠星形胶质细胞培养物中 Sx(C)-表达的影响。dbcAMP 处理的细胞中的 Sx(C)-活性几乎是未处理星形胶质细胞的七倍，并且在用丁硫氨酸亚砜亚胺耗尽细胞内 GSH 后进一步增加（约三倍）。这种由 GSH 耗竭引发的 Sx(C)-增加仅在 dbcAMP 处理的表型中观察到，与暴露于亲电子物质引发的 Nrf2 介导的反应不同。Sx(C)-活性的变化与 Sx(C)-异二聚体的 xCT 亚基的蛋白和 mRNA 水平的增加相关，L-Glu 摄取的 V(max)增加，并与 GSH 水平具有时间相关性。过氧化氢不能模拟这种 Sx(C)-的诱导，非特异性抗氧化剂也不能减弱这种诱导，但细胞通透性硫醇 GSH-乙酯和 N-乙酰半胱氨酸的共同给药部分阻止了这种诱导。这些发现表明，星形胶质细胞中 Sx(C)-的表达受到细胞内 GSH 水平的动态调节，这种调节方式依赖于细胞和表型。这种途径的存在可能反映了中枢神经系统对氧化损伤的固有脆弱性，并提出了在中枢神经系统损伤和疾病中 Sx(C)-活性变化的功能后果方面的有趣问题。
