title: Disruption of an EAAT-Mediated Chloride Channel in a Drosophila Model of Ataxia.
abstract: 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.
authors.affiliation: 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.
authors.forename: Neda
authors.initials: N
authors.lastname: Parinejad
authors.affiliation: 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.
authors.forename: Emilie
authors.identifier: 0000-0003-4852-1983
authors.initials: E
authors.lastname: Peco
authors.affiliation: 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.
authors.forename: Tiago
authors.identifier: 0000-0001-6866-1540
authors.initials: T
authors.lastname: Ferreira
authors.affiliation: McGill Centre for Research in Neuroscience, Montreal, Quebec H3G 1A4, Canada, Integrated Program in Neuroscience, McGill University, Montreal, Quebec H3A 2B4, Canada, and.
authors.forename: Stephanie M
authors.identifier: 0000-0003-3356-2619
authors.initials: SM
authors.lastname: Stacey
authors.affiliation: 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 Department of Neurology and Neurosurgery, McGill University, Montreal, Quebec H3A 2B4, Canada don.vanmeyel@mcgill.ca.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: van Meyel
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D002524:Cerebellar Ataxia / Q000235:genetics* / Q000473:pathology* / Q000503:physiopathology; D018118:Chloride Channels / Q000378:metabolism; D004195:Disease Models, Animal; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D027341:Excitatory Amino Acid Transporter 1 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007814:Larva; D008124:Locomotion / Q000235:genetics; D008297:Male; D009154:Mutation / Q000235:genetics; D009457:Neuroglia / Q000378:metabolism; D018709:Statistics, Nonparametric; D027981:Symporters / Q000235:genetics / Q000378:metabolism; D000096922:K Cl- Cotransporters
chemical_list: D018118:Chloride Channels; D029721:Drosophila Proteins; D027341:Excitatory Amino Acid Transporter 1; D049452:Green Fluorescent Proteins; D027981:Symporters; D000096922:K Cl- Cotransporters; C493394:SLC1A3 protein, human
keywords: Drosophila; EAAT; astrocyte; channelopathy; episodic ataxia