Gegelashvili G, Danbolt N C, Schousboe A
PharmaBiotec Research Center, Department of Biological Sciences, Royal Danish School of Pharmacy, Copenhagen.
J Neurochem. 1997 Dec;69(6):2612-5. doi: 10.1046/j.1471-4159.1997.69062612.x.
The glutamate transporters in the plasma membranes of neural cells secure termination of the glutamatergic synaptic transmission and keep the glutamate levels below toxic concentrations. Astrocytes express two types of glutamate transporters, GLAST (EAAT1) and GLT1 (EAAT2). GLT1 predominates quantitatively and is responsible for most of the glutamate uptake activity in the juvenile and adult brain. However, GLT1 is severely down-regulated in amyotrophic lateral sclerosis, a progressive neurodegenerative disease. Furthermore, selective loss of this transporter occurs in cultured astroglia. Expression of GLAST, but not of GLT1, seems to be regulated via the glutamate receptor signalling. The present study was undertaken to examine whether neuronal factors, other than glutamate, influence the expression of astroglial glutamate transporters. The expression of GLT1 and GLAST was examined in primary cultures of cerebellar granule neurons, cortical neurons, and astrocytes under different experimental conditions, including those that mimic neuron-astrocyte interactions. Pure astroglial cultures expressed only GLAST, whereas astrocytes grown in the presence of neurons expressed both GLAST (at increased levels) and GLT1. The induction of GLT1 protein and its mRNA was reproduced in pure cortical astroglial cultures supplemented with conditioned media from cortical neuronal cultures or from mixed neuron-glia cultures. This treatment did not change the levels of GLAST. These results suggest that soluble neuronal factors differentially regulate the expression of GLT1 and GLAST in cultured astroglia. Further elucidation of the molecular nature of the secreted neuronal factors and corresponding signalling pathways regulating the expression of the astroglial glutamate transporters in vitro may reveal mechanisms important for the understanding and treatment of neurological diseases.
神经细胞质膜中的谷氨酸转运体确保了谷氨酸能突触传递的终止，并使谷氨酸水平保持在毒性浓度以下。星形胶质细胞表达两种类型的谷氨酸转运体，即GLAST（EAAT1）和GLT1（EAAT2）。GLT1在数量上占主导地位，负责幼年和成年大脑中大部分的谷氨酸摄取活性。然而，在肌萎缩侧索硬化症（一种进行性神经退行性疾病）中，GLT1会严重下调。此外，在培养的星形胶质细胞中会出现这种转运体的选择性缺失。GLAST的表达似乎通过谷氨酸受体信号传导进行调节，而GLT1则不然。本研究旨在检验除谷氨酸外的神经元因子是否会影响星形胶质细胞谷氨酸转运体的表达。在不同实验条件下，包括模拟神经元 - 星形胶质细胞相互作用的条件下，检测了小脑颗粒神经元、皮质神经元和星形胶质细胞原代培养物中GLT1和GLAST的表达。纯星形胶质细胞培养物仅表达GLAST，而在有神经元存在的情况下生长的星形胶质细胞同时表达GLAST（水平升高）和GLT1。在补充了来自皮质神经元培养物或混合神经元 - 胶质细胞培养物的条件培养基的纯皮质星形胶质细胞培养物中，再现了GLT1蛋白及其mRNA的诱导。这种处理并未改变GLAST的水平。这些结果表明，可溶性神经元因子在培养的星形胶质细胞中对GLT1和GLAST的表达有不同的调节作用。进一步阐明体外调节星形胶质细胞谷氨酸转运体表达的分泌性神经元因子的分子性质和相应信号通路，可能会揭示对理解和治疗神经疾病很重要的机制。
