Dept of Biology, Program in Neuroscience, Syracuse University, Syracuse, NY, 13210, USA.
Dept of Biology, Program in Neuroscience, Syracuse University, Syracuse, NY, 13210, USA.
Neurochem Int. 2020 Dec;141:104888. doi: 10.1016/j.neuint.2020.104888. Epub 2020 Oct 22.
System x is a heterodimeric amino acid antiporter that, in the central nervous system, is best known for linking the import of L-cystine (CySS) with the export of L-glutamate for the production and maintenance of cellular glutathione (GSH) and extracellular glutamate levels, respectively. Yet, mice that are null for system x are healthy, fertile, and, morphologically, their brains are grossly normal. This suggests other glutamate and/or cyst(e)ine transport mechanisms may be upregulated in compensation. To test this, we measured the plasma membrane expression of Excitatory Amino Acid Transporters (EAATs) 1-3, the Alanine-Serine-Cysteine-Transporter (ASCT) 1, the sodium-coupled neutral amino acid transporter (SNAT) 3 and the L Amino Acid Transporter (LAT) 2 in striatum, hippocampus and cortex of male and female mice using Western Blot analysis. Present results demonstrate brain region and transporter-specific changes occurs in female system x null mice with increased expression of EAAT1 and ASCT1 occurring in the striatum and cortex, respectively, and decreased SNAT 3 expression in cortex. In male system x null brain, only SNAT3 was altered significantly - increasing in the cortex, but decreasing in the striatum. Total levels of GSH and CyS were similar to that found in age and sex-matched littermate control mice, however, reductions in the ratio of reduced to oxidized GSH (GSH/GSSG) - a hallmark of oxidative stress - were found in all three brain regions in female system x null mice, whereas this occurred exclusively in the striatum of males. Protein levels of Superoxide dismutase (SOD) 1 were reduced, whereas SOD2 was enhanced in the hippocampus of male x null mice only. Finally, striatal vulnerability to 3-nitropropionic acid (3-NP)-mediated oxidative stress in either sex showed no genotype difference, although 3-NP was more toxic to female mice of either genotype, as evidenced by an increase in moribundity as compared to males.
系统 x 是一种异二聚体氨基酸协同转运蛋白，在中枢神经系统中，它最为人所知的是将 L-胱氨酸（CySS）的摄取与 L-谷氨酸的输出联系起来，分别用于细胞谷胱甘肽（GSH）和细胞外谷氨酸水平的产生和维持。然而，系统 x 缺失的小鼠是健康的、有生育能力的，而且从形态上看，它们的大脑大体上是正常的。这表明其他谷氨酸和/或半胱氨酸转运机制可能上调以代偿。为了验证这一点，我们使用 Western Blot 分析测量了雄性和雌性小鼠纹状体、海马体和皮质中兴奋性氨基酸转运体（EAAT）1-3、丙氨酸-丝氨酸-半胱氨酸转运体（ASCT）1、钠偶联中性氨基酸转运体（SNAT）3 和 L 氨基酸转运体（LAT）2 的质膜表达。目前的结果表明，在雌性系统 x 缺失的小鼠中，脑区和转运体特异性变化发生，纹状体和皮质中 EAAT1 和 ASCT1 的表达增加，皮质中 SNAT 3 的表达减少。在雄性系统 x 缺失的大脑中，只有 SNAT3 显著改变——在皮质中增加，而在纹状体中减少。GSH 和 CyS 的总水平与年龄和性别匹配的同窝对照小鼠相似，但发现雌性系统 x 缺失小鼠的所有三个脑区的 GSH/氧化型 GSH（GSH/GSSG）比值（氧化应激的标志）降低，而这种情况仅发生在雄性的纹状体中。雄性 x 缺失小鼠海马体的超氧化物歧化酶（SOD）1 蛋白水平降低，而 SOD2 水平升高。最后，无论性别如何，3-硝基丙酸（3-NP）介导的氧化应激对纹状体的易感性没有基因型差异，尽管 3-NP 对两种基因型的雌性小鼠毒性更大，这表现为与雄性相比，濒死率增加。
