Parinejad Neda, Peco Emilie, Ferreira Tiago, Stacey Stephanie M, van Meyel Donald J
McGill Centre for Research in Neuroscience, Montreal, Quebec H3G 1A4, Canada, BRaIN Program, Research Institute of the McGill University Health Centre, Montreal, Quebec H3G 1A4, Canada, Integrated Program in Neuroscience, McGill University, Montreal, Quebec H3A 2B4, Canada, and.
McGill Centre for Research in Neuroscience, Montreal, Quebec H3G 1A4, Canada, BRaIN Program, Research Institute of the McGill University Health Centre, Montreal, Quebec H3G 1A4, Canada.
J Neurosci. 2016 Jul 20;36(29):7640-7. doi: 10.1523/JNEUROSCI.0197-16.2016.
Patients with Type 6 episodic ataxia (EA6) have mutations of the excitatory amino acid transporter EAAT1 (also known as GLAST), but the underlying pathophysiological mechanism for EA6 is not known. EAAT1 is a glutamate transporter expressed by astrocytes and other glia, and it serves dual function as an anion channel. One EA6-associated mutation is a P>R substitution (EAAT1(P>R)) that in transfected cells has a reduced rate of glutamate transport and an abnormal anion conductance. We expressed this EAAT1(P>R) mutation in glial cells of Drosophila larvae and found that these larvae exhibit episodic paralysis, and their astrocytes poorly infiltrate the CNS neuropil. These defects are not seen in Eaat1-null mutants, and so they cannot be explained by loss of glutamate transport. We instead explored the role of the abnormal anion conductance of the EAAT1(P>R) mutation, and to do this we expressed chloride cotransporters in astrocytes. Like the EAAT1(P>R) mutation, the chloride-extruding K(+)-Cl(-) cotransporter KccB also caused astroglial malformation and paralysis, supporting the idea that the EAAT1(P>R) mutation causes abnormal chloride flow from CNS glia. In contrast, the Na(+)-K(+)-Cl(-) cotransporter Ncc69, which normally allows chloride into cells, rescued the effects of the EAAT1(P>R) mutation. Together, our results indicate that the cytopathology and episodic paralysis in our Drosophila EA6 model stem from a gain-of-function chloride channelopathy of glial cells.
We studied a mutation found in episodic ataxia of the dual-function glutamate transporter/anion channel EAAT1, and discovered it caused malformation of astrocytes and episodes of paralysis in a Drosophila model. These effects were mimicked by a chloride-extruding cotransporter and were rescued by restoring chloride homeostasis to glial cells with a Na(+)-K(+)-2Cl(-) cotransporter. Our findings reveal a new pathophysiological mechanism in which astrocyte cytopathology and neural circuit dysfunction arise via disruption of the ancillary function of EAAT1 as a chloride channel. In some cases, this mechanism might also be important for neurological diseases related to episodic ataxia, such as hemiplegia, migraine, and epilepsy.
6型发作性共济失调（EA6）患者存在兴奋性氨基酸转运体EAAT1（也称为GLAST）的突变，但EA6潜在的病理生理机制尚不清楚。EAAT1是一种由星形胶质细胞和其他神经胶质细胞表达的谷氨酸转运体，它具有阴离子通道的双重功能。一种与EA6相关的突变是P>R替代（EAAT1(P>R)），在转染细胞中，其谷氨酸转运速率降低且阴离子电导异常。我们在果蝇幼虫的神经胶质细胞中表达了这种EAAT1(P>R)突变，发现这些幼虫表现出发作性麻痹，并且它们的星形胶质细胞对中枢神经系统神经纤维网的浸润较差。在Eaat1基因敲除突变体中未观察到这些缺陷，因此不能用谷氨酸转运功能丧失来解释。相反，我们探讨了EAAT1(P>R)突变异常阴离子电导的作用，为此我们在星形胶质细胞中表达了氯共转运体。与EAAT1(P>R)突变一样，向外转运氯离子的钾氯共转运体KccB也导致星形胶质细胞畸形和麻痹，这支持了EAAT1(P>R)突变导致中枢神经系统神经胶质细胞中氯离子异常流动的观点。相比之下，通常允许氯离子进入细胞的钠钾氯共转运体Ncc69挽救了EAAT1(P>R)突变的影响。总之，我们的结果表明，我们的果蝇EA6模型中的细胞病理学和发作性麻痹源于神经胶质细胞功能获得性氯通道病。
我们研究了在具有双重功能的谷氨酸转运体/阴离子通道EAAT1的发作性共济失调中发现的一种突变，并发现它在果蝇模型中导致星形胶质细胞畸形和发作性麻痹。这些效应被一种向外转运氯离子的共转运体模拟，并通过用钠钾2氯共转运体恢复神经胶质细胞的氯稳态而得到挽救。我们的发现揭示了一种新的病理生理机制，其中星形胶质细胞的细胞病理学和神经回路功能障碍是通过EAAT1作为氯通道的辅助功能受到破坏而产生的。在某些情况下，这种机制对于与发作性共济失调相关的神经系统疾病，如偏瘫、偏头痛和癫痫，可能也很重要。
