Expression, Distribution, and Trafficking of Pore-Forming and Auxiliary Subunits of Kainate Receptors

Abstract

Kainate receptors (KARs), a subgroup of ionotropic glutamate receptors (iGluRs), are modulators of neuronal excitability. When co-assembled with their auxiliary subunits Neto2 and Neto1, KARs display slow activation and deactivation. This allows temporal summation of the excitatory postsynaptic currents, which may be involved in epilepsy. While Neto2 and Neto1 regulate KARs’ functions, their developmental expression profiles are unknown. KARs are also regulated by post-translational modifications (PTMs) that affect their surface expression and involvement in neuronal excitability/hyperexcitability. Palmitoylation of the GluK2 promotes KAR surface expression. However, it is unknown if changes to this PTM would lead to receptor internalisation.
Using in situ blotting, we identified developmental changes in Neto2 and Neto1 regional expression in the rat brain. We have also investigated epilepsy-related changes in iGluR expression using a lithium-low dose pilocarpine model (RISE).
Our results established different spatio-temporal changes for individual KAR proteins during development. In the hippocampus, Neto2 was mainly expressed in the hilus of the dentate gyrus, whereas Neto1 expression was prominent in the stratum lucidum of CA3. While in the cerebellum Neto1 and GluK5 immunolabellings were weak, Neto2 and GluK2/3 were clearly identified in the granular cell layer. Neto2 and Neto1 showed prominent expression in the inner cortical layers, which matched with other KAR subunits expression profiles. This co-expression suggests a regulatory role of Neto proteins and region-specific changes in subunit compositions and functional properties of KARs throughout development. Apart from a decrease in GluN2B NMDA receptor subunit, no detectable changes in other iGluR proteins were detected in the RISE model of epilepsy. We found that non-palmitoylation of the GluK2 increased its SUMOylation and reduced surface expression. This mimickes kainate-induced long-term depression (LTD), which reduces neuronal excitability. Taken together, we revealed aspects of KAR-Neto2 and Neto1 interplay and generated solid basis for the identification of the involvement of PTMs in downstream mechanisms of kainate-induced LTD.

Date of Award	28 Nov 2019
Original language	English
Awarding Institution	The University of Bristol
Supervisor	Elek Molnar (Supervisor) & Jeremy M Henley (Supervisor)