Department of Molecular Biosciences, School of Veterinary Medicine, University ofCalifornia, Davis, California 95616, USA.
J Biol Chem. 2013 May 10;288(19):13831-41. doi: 10.1074/jbc.M112.441055. Epub 2013 Apr 3.
FMR1 CGG expansion repeats in the premutation range have not been linked to astrocyte pathophysiology.
Premutation cortical astrocytes display decreased Glu transporter expression/activity and enhanced asynchronous Ca(2+) oscillations.
Glu transport and Ca(2+) signaling defects in premutation astrocytes could contribute to FXTAS neuropathology.
Premutation astrocytes may have an etiological role in FXTAS neuropathology. Premutation CGG repeat expansions (55-200 CGG repeats; preCGG) within the fragile X mental retardation 1 (FMR1) gene can cause fragile X-associated tremor/ataxia syndrome. Defects in early neuronal migration and morphology, electrophysiological activity, and mitochondria trafficking have been described in a premutation mouse model, but whether preCGG mutations also affect astrocyte function remains unknown. PreCGG cortical astrocytes (∼170 CGG repeats) displayed 3-fold higher Fmr1 mRNA and 30% lower FMR1 protein (FMRP) when compared with WT. PreCGG astrocytes showed modest reductions in expression of glutamate (Glu) transporters GLT-1 and GLAST and attenuated Glu uptake (p < 0.01). Consistent with astrocyte cultures in vitro, aged preCGG mice cerebral cortex also displayed reduced GLAST and GLT-1 expression. Approximately 65% of the WT and preCGG cortical astrocytes displayed spontaneous asynchronous Ca(2+) oscillations. PreCGG astrocytes exhibited nearly 50% higher frequency of asynchronous Ca(2+) oscillations (p < 0.01) than WT, a difference mimicked by chronic exposure of WT astrocytes to l-trans-pyrrolidine-2,4-dicarboxylic acid (l-trans-PDC) or by partial suppression of GLAST using siRNA interference. Acute challenge with Glu augmented the frequency of Ca(2+) oscillations in both genotypes. Additionally, 10 μm Glu elicited a sustained intracellular Ca(2+) rise in a higher portion of preCGG astrocytes when compared with WT. Pharmacological studies showed that mGluR5, but not NMDA receptor, contributed to Glu hypersensitivity in preCGG astrocytes. These functional defects in preCGG astrocytes, especially in Glu signaling, may contribute to fragile X-associated tremor/ataxia syndrome neuropathology.
脆性 X 智力低下 1 基因（FMR1）的前突变 CGG 扩展重复序列并未与星形胶质细胞病理生理学相关联。
前突变皮质星形胶质细胞显示谷氨酸转运体表达/活性降低和增强的异步 Ca(2+)振荡。
前突变星形胶质细胞中的 Glu 转运和 Ca(2+)信号缺陷可能导致 FXTAS 神经病理学。
前突变星形胶质细胞可能在前突变型 FXTAS 神经病理学中具有病因作用。脆性 X 智力低下 1 基因（FMR1）中的脆性 X 相关震颤/共济失调综合征（FXTAS）前突变 CGG 重复扩展（55-200 CGG 重复；前 CGG）可引起脆性 X 相关震颤/共济失调综合征。在一个前突变小鼠模型中，已经描述了早期神经元迁移和形态、电生理活性和线粒体运输的缺陷，但前 CGG 突变是否也影响星形胶质细胞功能尚不清楚。与 WT 相比，前 CGG 皮质星形胶质细胞（约 170 CGG 重复）显示出 3 倍的 Fmr1 mRNA 和 30%的 FMR1 蛋白（FMRP）降低。前 CGG 星形胶质细胞的谷氨酸（Glu）转运体 GLT-1 和 GLAST 表达减少，Glu 摄取减少（p<0.01）。与体外星形胶质细胞培养一致，老年前 CGG 小鼠大脑皮层也显示出 GLAST 和 GLT-1 表达减少。大约 65%的 WT 和前 CGG 皮质星形胶质细胞显示自发的异步 Ca(2+)振荡。前 CGG 星形胶质细胞的异步 Ca(2+)振荡频率几乎高出 WT 50%（p<0.01），WT 星形胶质细胞慢性暴露于 l-反式-吡咯烷-2,4-二羧酸（l-反式-PDC）或使用 siRNA 干扰部分抑制 GLAST 可模拟该差异。急性 Glu 刺激会增加两种基因型中 Ca(2+)振荡的频率。此外，与 WT 相比，10 μm Glu 刺激前 CGG 星形胶质细胞中更高比例的细胞内 Ca(2+)持续升高。药理学研究表明，代谢型谷氨酸受体 5（mGluR5），而不是 NMDA 受体，在前 CGG 星形胶质细胞的 Glu 超敏反应中起作用。前 CGG 星形胶质细胞中的这些功能缺陷，尤其是在 Glu 信号转导中，可能导致脆性 X 相关震颤/共济失调综合征神经病理学。
