Shih Andy Y, Erb Heidi, Sun Xiaojian, Toda Shigenobu, Kalivas Peter W, Murphy Timothy H
Kinsmen Laboratory of Neurological Research and Brain Research Center, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3.
J Neurosci. 2006 Oct 11;26(41):10514-23. doi: 10.1523/JNEUROSCI.3178-06.2006.
The cystine/glutamate exchanger (xCT) provides intracellular cyst(e)ine for production of glutathione, a major cellular antioxidant. Using xCT overexpression and underexpression, we present evidence that xCT-dependent glutathione production modulates both neuroprotection from oxidative stress and cell proliferation. In embryonic and adult rat brain, xCT protein was enriched at the CSF-brain barrier (i.e., meninges) and also expressed in the cortex, hippocampus, striatum, and cerebellum. To examine the neuroprotective role of xCT, various non-neuronal cell types (astrocytes, meningeal cells, and peripheral fibroblasts) were cocultured with immature cortical neurons and exposed to oxidative glutamate toxicity, a model involving glutathione depletion. Cultured meningeal cells, which naturally maintain high xCT expression, were more neuroprotective than astrocytes. Selective xCT overexpression in astrocytes was sufficient to enhance glutathione synthesis/release and confer potent glutathione-dependent neuroprotection from oxidative stress. Moreover, normally nonprotective fibroblasts could be re-engineered to be neuroprotective with ectopic xCT overexpression indicating that xCT is a key step in the pathway to glutathione synthesis. Conversely, astrocytes and meningeal cells derived from sut/sut mice (xCT loss-of-function mutants) showed greatly reduced proliferation in culture attributable to increased oxidative stress and thiol deficiency, because growth could be rescued by the thiol-donor beta-mercaptoethanol. Strikingly, sut/sut mice developed brain atrophy by early adulthood, exhibiting ventricular enlargement, thinning of the cortex, and shrinkage of the striatum. Our results indicate that xCT can provide neuroprotection by enhancing glutathione export from non-neuronal cells such as astrocytes and meningeal cells. Furthermore, xCT is critical for cell proliferation during development in vitro and possibly in vivo.
胱氨酸/谷氨酸交换体（xCT）为细胞内谷胱甘肽的生成提供胞内胱氨酸（半胱氨酸），谷胱甘肽是一种主要的细胞抗氧化剂。通过xCT的过表达和低表达，我们提供了证据表明xCT依赖的谷胱甘肽生成可调节氧化应激诱导的神经保护作用和细胞增殖。在胚胎和成年大鼠脑中，xCT蛋白在脑脊液-脑屏障（即脑膜）处富集，也在皮质、海马、纹状体和小脑中表达。为了研究xCT的神经保护作用，将各种非神经元细胞类型（星形胶质细胞、脑膜细胞和外周成纤维细胞）与未成熟皮质神经元共培养，并使其暴露于氧化型谷氨酸毒性下，这是一种涉及谷胱甘肽耗竭的模型。天然维持高xCT表达的培养脑膜细胞比星形胶质细胞具有更强的神经保护作用。星形胶质细胞中选择性的xCT过表达足以增强谷胱甘肽的合成/释放，并赋予强大的谷胱甘肽依赖性氧化应激神经保护作用。此外，正常情况下无保护作用的成纤维细胞通过异位xCT过表达可被改造为具有神经保护作用，这表明xCT是谷胱甘肽合成途径中的关键步骤。相反，来自sut/sut小鼠（xCT功能缺失突变体）的星形胶质细胞和脑膜细胞在培养中增殖显著减少，这归因于氧化应激增加和硫醇缺乏，因为生长可通过硫醇供体β-巯基乙醇挽救。令人惊讶的是，sut/sut小鼠在成年早期出现脑萎缩，表现为脑室扩大、皮质变薄和纹状体萎缩。我们的结果表明，xCT可通过增强星形胶质细胞和脑膜细胞等非神经元细胞的谷胱甘肽输出提供神经保护作用。此外，xCT对于体外发育过程中以及可能在体内的细胞增殖至关重要。
