Ogura Masato, Nakamichi Noritaka, Takano Katsura, Oikawa Hirotaka, Kambe Yuki, Ohno Yu, Taniura Hideo, Yoneda Yukio
Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kanazawa, Japan.
J Neurosci Res. 2006 Jun;83(8):1447-60. doi: 10.1002/jnr.20855.
The prevailing view is that the glutamine (Gln) transporter (GlnT/ATA1/SAT1/SNAT1) is a member of the system A transporter superfamily with the ability to fuel the glutamate/Gln cycle at nerve terminals in glutamatergic neurons. Semiquantitative reverse transcription-polymerase chain reaction revealed similarly high expression of mRNA for GlnT by rat brain neocortical astrocytes as well as neurons, with progressively lower expression by cerebellar astrocytes, hippocampal astrocytes, and whole-brain microglia in culture. [(3)H]Gln was accumulated in a temperature-dependent manner with a saturable profile in both cultured neocortical neurons and astrocytes, whereas biochemical and pharmacological analyses on [(3)H]Gln accumulation revealed the expression of both system A and system L transporters by cultured neocortical neurons and astrocytes. Exposure to lipopolysaccharide (LPS) for 24 hr resulted in a significant decrease in both GlnT mRNA expression and [(3)H]Gln accumulation, with a concomitant drastic increase in nitrite formation in cultured neocortical astrocytes. Moreover, LPS significantly inhibited the promoter activity of GlnT in the astrocytic cell line C6 glioma cells as well as primary rat neocortical astrocytes in culture. These results suggest that activation by LPS would lead to down-regulation of the expression of GlnT responsible for the incorporation of extracellular Gln into intracellular spaces across plasma membranes through the inhibition of its promoter activity in cultured rat neocortical astrocytes.
普遍观点认为，谷氨酰胺（Gln）转运体（GlnT/ATA1/SAT1/SNAT1）是系统A转运体超家族的成员，能够在谷氨酸能神经元的神经末梢为谷氨酸/Gln循环提供燃料。半定量逆转录-聚合酶链反应显示，大鼠脑新皮质星形胶质细胞和神经元中GlnT的mRNA表达同样高，而培养的小脑星形胶质细胞、海马星形胶质细胞和全脑小胶质细胞的表达则逐渐降低。[³H]Gln在培养的新皮质神经元和星形胶质细胞中以温度依赖的方式积累，具有饱和曲线，而对[³H]Gln积累的生化和药理学分析显示，培养的新皮质神经元和星形胶质细胞中同时表达系统A和系统L转运体。暴露于脂多糖（LPS）24小时导致培养的新皮质星形胶质细胞中GlnT mRNA表达和[³H]Gln积累显著降低，同时亚硝酸盐形成急剧增加。此外，LPS显著抑制星形胶质细胞系C6胶质瘤细胞以及培养的原代大鼠新皮质星形胶质细胞中GlnT的启动子活性。这些结果表明，LPS激活会导致负责将细胞外Gln通过质膜转运到细胞内空间的GlnT表达下调，这是通过抑制其在培养的大鼠新皮质星形胶质细胞中的启动子活性实现的。
