Department of Neurobiology, Centre for Glial Biology in Medicine, University of Alabama at Birmingham, 1719 6th Ave. S., CIRC 425, Birmingham, AL 35294, USA.
Brain. 2010 Apr;133(Pt 4):1013-25. doi: 10.1093/brain/awq049.
During neuronal activity astrocytes function to remove extracellular increases in potassium, which are largely mediated by the inwardly-rectifying potassium channel Kir4.1, and to take up excess glutamate via glutamate transporter 1, a glial-specific glutamate transporter. Here we demonstrate that expression of both of these proteins is reduced by nearly 80% following a crush spinal cord injury in adult male rats, 7 days post-injury. This loss extended to spinal segments several millimetres rostral and caudal to the lesion epicentre, and persisted at 4 weeks post-injury. Importantly, we demonstrate that loss of these two proteins is not a direct result of astrocyte loss, as immunohistochemistry at 7 days and western blots at 4 weeks demonstrate a marked up-regulation in glial fibrillary acidic protein expression. Kir4.1 and glutamate transporter 1 expression were partially rescued by post-spinal cord injury administration of physiological levels of 17beta-oestradiol (0.08 mg/kg/day) in vivo. Utilizing an in vitro culture system we demonstrate that 17beta-oestradiol treatment (50 nM) is sufficient to increase glutamate transporter 1 protein expression in spinal cord astrocytes. This increase in glutamate transporter 1 protein expression was reversed and Kir4.1 expression reduced in the presence of an oestrogen receptor antagonist, Fulvestrant 182,780 suggesting a direct translational regulation of Kir4.1 and glutamate transporter 1 via genomic oestrogen receptors. Using whole-cell patch-clamp recordings in cultured spinal cord astrocytes, we show that changes in protein expression following oestrogen application led to functional changes in Kir4.1 mediated currents. These findings suggest that the neuroprotective benefits previously seen with 17beta-oestradiol after spinal cord injury may be in part due to increased Kir4.1 and glutamate transporter 1 expression in astrocytes leading to improved potassium and glutamate homeostasis.
在神经元活动期间,星形胶质细胞的功能是去除细胞外钾的增加,这主要是通过内向整流钾通道 Kir4.1 来实现的,并通过谷氨酸转运体 1(一种胶质特异性谷氨酸转运体)摄取过量的谷氨酸。在这里,我们证明在成年雄性大鼠脊髓损伤后 7 天,这两种蛋白质的表达几乎减少了 80%。这种损失延伸到损伤中心几个毫米的脊髓节段,并且在损伤后 4 周持续存在。重要的是,我们证明这两种蛋白质的丢失不是星形胶质细胞丢失的直接结果,因为在 7 天的免疫组织化学和 4 周的 Western blot 显示胶质纤维酸性蛋白表达明显上调。在脊髓损伤后,体内给予生理水平的 17β-雌二醇(0.08mg/kg/天)可部分挽救 Kir4.1 和谷氨酸转运体 1 的表达。利用体外培养系统,我们证明 17β-雌二醇(50nM)处理足以增加脊髓星形胶质细胞中谷氨酸转运体 1 的蛋白表达。在雌激素受体拮抗剂 Fulvestrant 182,780 的存在下,这种谷氨酸转运体 1 蛋白表达的增加被逆转,Kir4.1 表达减少,表明通过基因组雌激素受体对 Kir4.1 和谷氨酸转运体 1 进行直接翻译调节。使用体外培养的脊髓星形胶质细胞全细胞膜片钳记录,我们表明雌激素应用后蛋白表达的变化导致 Kir4.1 介导的电流的功能变化。这些发现表明,先前在脊髓损伤后观察到的 17β-雌二醇的神经保护益处可能部分归因于星形胶质细胞中 Kir4.1 和谷氨酸转运体 1 的表达增加,从而改善钾和谷氨酸的稳态。