Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Ataxia-linked SLC1A3 mutations alter EAAT1 chloride channel activity and glial regulation of CNS function (#349)

Qianyi Wu 1 , Azman Akhter 2 , Shashank Pant 3 , Eunjoo Cho 4 , Jin Xin Zhu 4 , Alastair Garner 5 , Tomoko Ohyama 5 , Emad Tajkhorshid 3 , Donald van Meyel 2 4 5 , Renae Ryan 6
  1. Weill Cornell Medicine, New York, NY, United States
  2. Department of Neurology and Neurosurgery and Integrated Program in Neuroscience, McGill University, Montreal, Quebec, Canada
  3. Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL , USA
  4. Research Institute of the McGill University Health Centre, Montreal, Quebec, Canada
  5. Department of Biology, McGill University, Montreal, QC, Canada
  6. School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Sydney, New South Wales, Australia

Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). Excitatory Amino Acid Transporters (EAATs) regulate extracellular glutamate by transporting it into cells, mostly glia, to terminate neurotransmission and to avoid neurotoxicity. EAATs are also chloride (Cl-) channels, but the physiological role of Cl-conductance through EAATs is poorly understood. Mutations of human EAAT1 (hEAAT1) have been identified in patients with episodic ataxia type 6 (EA6). One mutation showed increased Cl- channel activity and decreased glutamate transport, but the relative contributions of each function of hEAAT1 to mechanisms underlying the pathology of EA6 remain unclear. Here we investigated the effects of five additional EA6-related mutations on hEAAT1 function in Xenopus laevis oocytes, and on CNS function in a Drosophila melanogaster model of locomotor behaviour. Our results indicate that mutations with decreased hEAAT1 Cl- channel activity and functional glutamate transport can also contribute to the pathology of EA6, highlighting the importance of Cl- homeostasis in glial cells for proper CNS function. We also identified a novel mechanism involving an ectopic sodium (Na+) leak conductance in glial cells, due to protein-lipid interactions between the EA6-related mutant and lipids in the membrane bilayer. Together, these results reveal how these mutant transporters contributes to the pathology of EA6 and strongly support the idea that EA6 is primarily an ion channelopathy of CNS glia.