Nakajima Kazuyuki, Yamamoto Shinichi, Kohsaka Shinichi, Kurihara Tadashi
Department of Bioinformatics, Faculty of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan.
Neurosci Lett. 2008 May 16;436(3):331-4. doi: 10.1016/j.neulet.2008.03.058. Epub 2008 Mar 26.
As previously reported, activated microglia facilitate the expression of a glial cell-type glutamate transporter, glutamate transporter-1 (GLT-1; EAAT2), around injured motoneurons in axotomized rat facial nucleus. This phenomenon suggests that the motoneurons stimulate microglia to enhance the levels of GLT-1. In the present study, we investigated the effects of neuronal stimulus on the uptake of glutamate (Glu) by microglia and on the expression of GLT-1 protein in microglia in vitro. A 14C-Glu uptake experiment revealed that microglia enhance uptake of Glu by stimulation with neuronal conditioned medium (NCM). The NCM-stimulated uptake was significantly suppressed in the presence of dihydrokinate (a specific GLT-1 inhibitor), suggesting that GLT-1 is a major glutamate transporter for the uptake. Furthermore, immunoblotting analysis revealed that the amounts of GLT-1, but not another glial cell-type glutamate transporter glutamate-aspartate transporter (GLAST: EAAT1), increased significantly in microglia by treatment with NCM. Altogether, neuronal stimulus was found to promote the uptake of Glu in microglia, probably due to the increased levels of GLT-1.
如先前报道，活化的小胶质细胞可促进胶质细胞型谷氨酸转运体——谷氨酸转运体-1（GLT-1；EAAT2）在切断轴突的大鼠面神经核中受损运动神经元周围的表达。这一现象表明，运动神经元刺激小胶质细胞以提高GLT-1的水平。在本研究中，我们在体外研究了神经元刺激对小胶质细胞摄取谷氨酸（Glu）以及对小胶质细胞中GLT-1蛋白表达的影响。一项¹⁴C-Glu摄取实验表明，小胶质细胞通过用神经元条件培养基（NCM）刺激来增强对Glu的摄取。在存在二氢激酶（一种特异性GLT-1抑制剂）的情况下，NCM刺激的摄取被显著抑制，这表明GLT-1是摄取的主要谷氨酸转运体。此外，免疫印迹分析显示，通过用NCM处理，小胶质细胞中GLT-1的量显著增加，而另一种胶质细胞型谷氨酸转运体——谷氨酸-天冬氨酸转运体（GLAST；EAAT1）的量则没有增加。总之，发现神经元刺激可促进小胶质细胞对Glu的摄取，这可能是由于GLT-1水平的升高。
