Upregulation of Glutamate Transporter GLT-1 by mTOR-Akt-NF-κB Cascade in Astrocytic Oxygen-Glucose Deprivation
Upregulation of Glutamate Transporter GLT-1 by mTOR-Akt-NF-κB Cascade in Astrocytic Oxygen-Glucose Deprivation
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DOI：
10.1002/glia.22566
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发表时间：
2013-12-01
期刊：
影响因子：
6.2
通讯作者：
Shen, Ying
中科院分区：
文献类型：
--
作者：
Ji, Yi-Fei;Zhou, Liang;Shen, Ying
过量的细胞外谷氨酸导致中枢神经系统神经元死亡。兴奋性谷氨酸转运体亚型2（GLT-1）在脑缺血中携带大量谷氨酸重摄取。虽然GLT-1的表达在缺血期间波动，但对其调节机制知之甚少。在此，我们显示了在氧葡萄糖剥夺（OGD）中通过哺乳动物雷帕霉素靶蛋白（mTOR）-Akt-核因子-kB（NF-kB）信号级联上调GLT-1。我们发现，短暂的雷帕霉素治疗显着增加GLT-1在培养的星形胶质细胞的表达。雷帕霉素增加了raptor在Ser 792的磷酸化，减少了rictor在Thr 1135的磷酸化，表明mTOR复合物1（mTORC 1）和mTOR复合物2（mTORC 2）都参与了GLT-1的表达。raptor和rictor破坏实验进一步证实了这一结论。Akt被mTORC 1抑制激活，并且是GLT-1表达所必需的，因为Akt的特异性抑制剂triciribine阻断了GLT-1表达的增加。mTOR-Akt级联反应激活NF-κ B，增加NF-κ B基序结合磷蛋白（KBBP）表达和GLT-1转录。我们接下来证明了mTOR-Akt-NF-kB级联在OGD中被激活，随后引起GLT-1的上调。支持性证据包括：（1）Akt或NF-kB的抑制阻断了OGD诱导的GLT-1上调;（2）Raptor敲除加OGD不增加GLT-1表达的增加;（3）完整的mTORC 2是GLT-1增强所必需的。总之，我们的数据首次表明mTOR-Akt-NF-kB级联在OGD中上调GLT-1中起关键作用。这种信号级联可能在脑缺血和神经退行性疾病中促进谷氨酸摄取。
Excessive extracellular glutamate leads to neuronal death in central nervous system. Excitatory glutamate transporter subtype 2 (GLT-1) carries bulk of glutamate reuptake in cerebral ischemia. Although GLT-1 expression fluctuates during the period of ischemia, little is known about its regulatory mechanism. Here we show an up-regulation of GLT-1 via mammalian target of rapamycin (mTOR)-Akt-nuclear factor-kB (NF-kB) signaling cascade in oxygen glucose deprivation (OGD). We found that brief rapamycin treatment significantly increased GLT-1 expression in cultured astrocytes. Rapamycin increased phosphorylation of raptor at Ser792 and decreased phosphorylation of rictor at Thr1135, suggesting that both mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2) are involved in GLT-1 expression. This conclusion was further confirmed by raptor and rictor disruption experiments. Akt was activated by mTORC1 inhibition and required for GLT-1 expression because triciribine, a specific inhibitor of Akt, blocked the increase of GLT-1 expression. mTOR-Akt cascade then activated NF-kB and increased kB-motif-binding phosphoprotein (KBBP) expression and GLT-1 transcription. We next demonstrated that mTOR-Akt-NF-kB cascade was activated in OGD and subsequently caused the upregulation of GLT-1. Supporting evidence included: (1) inhibition of Akt or NF-kB occluded OGD-induced GLT-1 upregulation; (2) Raptor knock-down plus OGD did not add to the increase of GLT-1 expression; (3) Intact mTORC2 was required for GLT-1 enhancement. In summary, our data first showed that mTOR-Akt-NF-kB cascade played critical roles to up-regulate GLT-1 in OGD. This signaling cascade may work to promote glutamate uptake in brain ischemia and neurodegenerative diseases.