Department of Biomedical Sciences and Public Health, School of Medicine, University "Politecnica delle Marche", Via Tronto 10/A, 60126, Ancona, Italy.
Cell Death Dis. 2018 Jun 28;9(7):731. doi: 10.1038/s41419-018-0784-6.
In brain ischemia, reduction in oxygen and substrates affects mitochondrial respiratory chain and aerobic metabolism, culminating in ATP production impairment, ionic imbalance, and cell death. The restoration of blood flow and reoxygenation are frequently associated with exacerbation of tissue injury, giving rise to ischemia/reperfusion (I/R) injury. In this setting, the imbalance of brain bioenergetics induces important metabolic adaptations, including utilization of alternative energy sources, such as glutamate. Although glutamate has long been considered as a neurotoxin, it can also be used as intermediary metabolite for ATP synthesis, and both the Na/Ca exchanger (NCX) and the Na-dependent excitatory amino-acid transporters (EAATs) are essential in this pathway. Here we analyzed the role of NCX in the potential of glutamate to improve metabolism and survival of neuronal cells subjected to hypoxia/reoxygenation (H/R). In SH-SY5Y neuroblastoma cells differentiated into a neuron-like state, H/R produced a significant cell damage, a decrease in ATP cellular content, and intracellular Ca alterations. Exposure to glutamate at the onset of the reoxygenation phase attenuated H/R-induced cell damage and evoked a significant raise in intracellular ATP levels. Furthermore, we found that in H/R cells NCX reverse-mode activity was reduced, and that glutamate limited such reduction. All the effects induced by glutamate supplementation were lost when cells were transfected with small interfering RNA against NCX1 and EAAT3, suggesting the need of a specific functional interplay between these proteins for glutamate-induced protection. Collectively, our results revealed the potential beneficial effect of glutamate in an in vitro model of H/R injury and focused on the essential role exerted by NCX1. Although preliminary, these findings could be a starting point to further investigate in in vivo systems such protective effect in ischemic settings, shedding a new light on the classical view of glutamate as detrimental factor.
在脑缺血中，氧气和底物的减少会影响线粒体呼吸链和有氧代谢，最终导致 ATP 产生受损、离子失衡和细胞死亡。血流的恢复和再氧合常常与组织损伤的加剧有关，导致缺血/再灌注 (I/R) 损伤。在这种情况下，大脑生物能量的失衡会引起重要的代谢适应，包括利用替代能源，如谷氨酸。尽管谷氨酸长期以来一直被认为是一种神经毒素，但它也可以作为 ATP 合成的中间代谢物，而 Na/Ca 交换器 (NCX) 和 Na 依赖性兴奋性氨基酸转运体 (EAATs) 在这一途径中是必不可少的。在这里，我们分析了 NCX 在谷氨酸改善缺氧/复氧 (H/R) 后神经元细胞代谢和存活能力中的作用。在分化为神经元样状态的 SH-SY5Y 神经母细胞瘤细胞中，H/R 导致细胞损伤显著、ATP 细胞含量减少和细胞内 Ca 改变。在复氧阶段开始时暴露于谷氨酸可减轻 H/R 诱导的细胞损伤，并引起细胞内 ATP 水平的显著升高。此外，我们发现 H/R 细胞中 NCX 反向模式活性降低，而谷氨酸限制了这种降低。当用针对 NCX1 和 EAAT3 的小干扰 RNA 转染细胞时，谷氨酸补充引起的所有作用都消失了，这表明这些蛋白之间需要特定的功能相互作用才能引起谷氨酸诱导的保护。总之，我们的结果揭示了谷氨酸在体外 H/R 损伤模型中的潜在有益作用，并强调了 NCX1 所发挥的重要作用。尽管这些发现是初步的，但它们可能为进一步在缺血性环境中研究这种保护作用提供了一个起点，为谷氨酸作为有害因素的经典观点提供了新的视角。
