Faculty of Medicine, Department of Medical Biology, Adnan Menderes University, Aydin, Turkey.
Hum Exp Toxicol. 2020 Jul;39(7):938-947. doi: 10.1177/0960327120907142. Epub 2020 Feb 21.
Excitotoxicity is the presence of excessive glutamate, which is normally taken up by glutamate transporters on astrocytes. Glutamate transporter 1 (GLT-1) is the major transporter on glia cells clearing more than 90% of the glutamate. Sirtuin 4 (SIRT4) is a mitochondrial sirtuin which is expressed in the brain. Previously, it was shown that loss of SIRT4 leads to a more severe reaction to kainic acid, an excitotoxic agent, and also decreased GLT-1 expression in the brain. In this study, we aimed to investigate whether overexpression of SIRT4 is protective against excitotoxicity in glia cells. We overexpressed SIRT4 in A172 glioma cell line and treated with kainic acid in order to induce excitotoxicity. We observed that SIRT4 overexpression increased the cell viability after kainic acid treatment. In addition, reduced glutamate was detected in glutamate assay with overexpression of SIRT4 after kainic acid treatment since SIRT4 decreased cell death by preventing excitotoxicity. Our results show that overexpression of SIRT4 increased the protein levels of GLT-1 and glutamate dehydrogenase (GDH) after kainic acid (KA) treatment so that excess glutamate can be absorbed. However, overexpression of SIRT4 decreased glutamine synthetase (GS) levels. These results demonstrate that, by inhibiting GS, SIRT4 prevents glutamine formation, which will be converted to glutamate in neurons. SIRT4 prevents excitotoxicity via upregulating glutamate metabolism. Finally, our results may show that SIRT4 might prevent excitotoxicity and related cell death via reducing GS expression and upregulating GLT-1 and GDH levels. Therefore, it is important to develop therapeutics against excitotoxicity through SIRT4-related pathways in the cell.
兴奋性毒性是指谷氨酸的含量过高，而谷氨酸通常被星形胶质细胞上的谷氨酸转运体摄取。谷氨酸转运体 1 (GLT-1) 是胶质细胞上的主要转运体，可清除超过 90%的谷氨酸。Sirtuin 4 (SIRT4) 是一种存在于大脑中的线粒体 Sirtuin。先前的研究表明，SIRT4 的缺失会导致对红藻氨酸（一种兴奋性毒素）的反应更严重，并且大脑中的 GLT-1 表达也会减少。在这项研究中，我们旨在研究 SIRT4 的过表达是否对胶质细胞的兴奋性毒性有保护作用。我们在 A172 神经胶质瘤细胞系中过表达 SIRT4，并用红藻氨酸处理以诱导兴奋性毒性。我们观察到，SIRT4 的过表达增加了红藻氨酸处理后的细胞活力。此外，在用红藻氨酸处理后，通过 SIRT4 过表达进行谷氨酸检测时，检测到谷氨酸减少，因为 SIRT4 通过防止兴奋性毒性来减少细胞死亡。我们的结果表明，SIRT4 的过表达增加了红藻氨酸（KA）处理后 GLT-1 和谷氨酸脱氢酶（GDH）的蛋白水平，从而可以吸收过量的谷氨酸。然而，SIRT4 的过表达降低了谷氨酰胺合成酶（GS）的水平。这些结果表明，通过抑制 GS，SIRT4 防止了谷氨酰胺的形成，而谷氨酰胺将在神经元中转化为谷氨酸。SIRT4 通过调节谷氨酸代谢来防止兴奋性毒性。最后，我们的结果可能表明，SIRT4 通过降低 GS 表达和上调 GLT-1 和 GDH 水平，可防止兴奋性毒性和相关的细胞死亡。因此，通过 SIRT4 相关途径开发针对兴奋性毒性的治疗方法非常重要。
