Ataxia-linked SLC1A3 mutations alter EAAT1 chloride channel activity and glial regulation of CNS function
Qianyi Wu, Azman Akhter, Shashank Pant, Eunjoo Cho, Jin Xin Zhu, Alastair Garner, Tomoko Ohyama, Emad Tajkhorshid, Donald J. van Meyel, Renae M. Ryan
Qianyi Wu, Azman Akhter, Shashank Pant, Eunjoo Cho, Jin Xin Zhu, Alastair Garner, Tomoko Ohyama, Emad Tajkhorshid, Donald J. van Meyel, Renae M. Ryan
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Research Article Neuroscience

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

Abstract

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 5 additional EA6-related mutations on hEAAT1 function in Xenopus laevis oocytes, and on CNS function in a Drosophila melanogaster model of locomotor behavior. Our results indicate that mutations resulting in decreased hEAAT1 Cl– channel activity but with 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 what we believe is a novel mechanism involving an ectopic sodium (Na+) leak conductance in glial cells. Together, these results strongly support the idea that EA6 is primarily an ion channelopathy of CNS glia.

Authors

Qianyi Wu, Azman Akhter, Shashank Pant, Eunjoo Cho, Jin Xin Zhu, Alastair Garner, Tomoko Ohyama, Emad Tajkhorshid, Donald J. van Meyel, Renae M. Ryan

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Figure 1

Stoichiometry of transport and locations of EA6 mutations in the hEAAT1 structure.

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Stoichiometry of transport and locations of EA6 mutations in the hEAAT1 ...
(A) The transport of each substrate molecule (glutamate or aspartate) is coupled to the cotransport of 3 sodium ions (Na+) and 1 proton (H+), and the countertransport of a potassium ion (K+); the transport process also activates a thermodynamically uncoupled chloride channel. (B and C) Locations of EA6-related mutations in the structure of hEAAT1 (PDB: 5LLU) (B) and on a topology schematic (C) are shown. Cartoon representation of transmembrane domains (TMDs) 1 and 2 from the scaffold domain are omitted for clarity, while the whole scaffold domain is shown in transparent white surface representation. TMDs in B are coloured as per C. Figure was made using ChimeraX (84).