Glutamate transporter-dependent mTOR phosphorylation in Müller glia cells.
Glutamate transporter-dependent mTOR phosphorylation in Müller glia cells.
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DOI：
10.1042/an20120022
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发表时间：
2012-08-16
期刊：
影响因子：
4.7
通讯作者：
Ortega A
中科院分区：
文献类型：
--
作者：
María López-Colomé A;Martínez-Lozada Z;Guillem AM;López E;Ortega A
谷氨酸(Glu)是视网膜中主要信号通路上的兴奋性递质，通过激活信号级联在转录和翻译水平上调节蛋白质合成，参与蛋白质谱的变化。谷氨酸活性依赖的差异基因表达与离子型和代谢型谷氨酸受体的激活有关；然而，最近的研究表明，钠离子依赖的谷氨酸转运体参与了这一过程。在视网膜内，摄取Glu的目的是补充可释放池，防止兴奋性毒性，主要由位于Müler径向胶质细胞的GLAST/EAAT-1(钠依赖的谷氨酸/天冬氨酸转运体/兴奋性氨基酸转运体-1)携带。在前人研究谷氨酸诱导的GLAST表达变化的基础上，本研究探讨了GLAST信号转导途径在Müller细胞蛋白质合成调控中的作用。为此，我们探讨了D-天冬氨酸(D-Asp)对原代培养的鸡Müler胶质细胞Ser-2448 mTOR(雷帕霉素的哺乳动物靶标)磷酸化的影响。结果表明，D-天冬氨酸转运诱导mTOR的磷酸化，并具有时间和剂量依赖性，类似于可转运的GLAST抑制剂THA(苏氨酸-β-羟基天冬氨酸)。导致mTOR磷酸化的信号转导途径包括钙离子内流、p60src、磷脂酰肌醇3-激酶、蛋白激酶B、mTOR和p70S6K。有趣的是，GLAST的活性促进了AP-1(激活蛋白-1)与DNA的结合，支持了视网膜长期反应中的转运蛋白信号传递功能。这些结果为Müller胶质细胞中的Glu信号传递增加了一条新的受体非依赖的途径，并进一步加强了这些细胞在视网膜谷氨酸能传递调节中的关键参与。
Glu (glutamate), the excitatory transmitter at the main signalling pathway in the retina, is critically involved in changes in the protein repertoire through the activation of signalling cascades, which regulate protein synthesis at transcriptional and translational levels. Activity-dependent differential gene expression by Glu is related to the activation of ionotropic and metabotropic Glu receptors; however, recent findings suggest the involvement of Na+-dependent Glu transporters in this process. Within the retina, Glu uptake is aimed at the replenishment of the releasable pool, and for the prevention of excitotoxicity and is carried mainly by the GLAST/EAAT-1 (Na+-dependent glutamate/aspartate transporter/excitatory amino acids transporter-1) located in Müller radial glia. Based on the previous work showing the alteration of GLAST expression induced by Glu, the present work investigates the involvement of GLAST signalling in the regulation of protein synthesis in Müller cells. To this end, we explored the effect of D-Asp (D-aspartate) on Ser-2448 mTOR (mammalian target of rapamycin) phosphorylation in primary cultures of chick Müller glia. The results showed that D-Asp transport induces the time- and dose-dependent phosphorylation of mTOR, mimicked by the transportable GLAST inhibitor THA (threo-β-hydroxyaspartate). Signalling leading to mTOR phosphorylation includes Ca2+ influx, the activation of p60src, phosphatidylinositol 3-kinase, protein kinase B, mTOR and p70S6K. Interestingly, GLAST activity promoted AP-1 (activator protein-1) binding to DNA, supporting a function for transporter signalling in retinal long-term responses. These results add a novel receptor-independent pathway for Glu signalling in Müller glia, and further strengthen the critical involvement of these cells in the regulation of glutamatergic transmission in the retina.