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GluRdelta orphan receptors are gated by group I metabotropic glutamate receptors: unraveling new mechanisms of glutamate receptors functions – DELTAplane

GluRdelta orphan receptors: synaptic functions and mechanisms

Glutamate is the main excitatory neurotransmitter in the vertebrate central nervous system. It exerts its effects via ionotropic receptors (iGluRs) that form ion channels and metabotropic receptors (mGluRs) that activate intracellular secondary pathways. Glutamate receptor subunits GluRdelta1 and GluRdelta2 are orphan homologs of iGluRs. Despite 20 years of research, no ligand has been identified that triggers opening of their channel.

Functional coupling of GluRdelta orphan receptors with glutamate metabotropic receptors

The aims of this project are to:<br />1) assess that group I mGluRs gate recombinant and native cerebellar and cortical GluRdelta channels<br />2) identify signaling and scaffolding partners involved in mGluR-GluRdelta crosstalks and provide insights into the dynamics of their interactions.<br />3) establish the relevance of mGluR-gated GluRdelta currents to the functions of cerebellar and cortical circuits.<br />

The experimental program relies on a combination of physiological and molecular approaches. In addition to patch-clamp and molecular engineering techniques, approaches include viral transfer of mutant GluRdelta subunits and KO mice lines. A combination of pharmacological, molecular and BRET imaging of protein-protein interactions will allow the identification of signaling and scaffolding partners involved in mGluR-GluRdelta coupling.

- mGluR1 gates recombinant and native GluRdelta2 channels (manuscript in revision involving the 3 partners, see illustration)
- GluRdelta1 is widely expressed in the adult brain (manuscript in preparation, partner 1).
- Methods for the study of dynamic interactions within glutamate receptor scaffolding complexes (2 articles et 2 comments published by partner 2).

“De-orphanization” of GluR-delta receptors by mGluRs is likely to have a strong impact. Indeed, the ionotropic functions of the GluRdelta family have remained elusive and an mGluR-GluRdelta crosstalk would have far-reaching implications on synaptic transmission and receptor signaling. Finally, recent evidence of GluRdelta1 and -2 implications in schizophrenia and autism provides the functional coupling of GluRdelta channels and mGluRs with important biomedical perspectives.

- GKAP-DLC2 interaction organizes the postsynaptic scaffold complex to enhance synaptic NMDA receptor activity - Moutin E et al. (2012) J Cell Sci 125: 2030-2040
- Dynamic remodeling of scaffold interactions in dendritic spines controls synaptic excitability. Moutin E et al. (2012) J Cell Biol 198: 251-263.
- Scaffold remodeling in space and time controls synaptic transmission. Perroy J and Moutin E. (2012) BioArchitecture 2: 29-32.

Glutamate is the main excitatory neurotransmitter in the vertebrate central nervous system. It exerts its effects via ionotropic receptors (iGluRs) that form ion channels and metabotropic receptors (mGluRs) that activate intracellular secondary pathways. Glutamate receptor subunits GluRdelta1 and GluRdelta2 are orphan homologs of iGluRs. Despite 20 years of research, no ligand has been identified that triggers opening of their channel.

The consortium of three partners gathered in the present proposal has obtained strong unpublished evidence that GluRdelta channels are nonetheless functional. Our results indicate that the channel of both GluRdelta subunits opens through a crosstalk with group I mGluRs in a heterologous expression system, in cerebellar Purkinje neurons and at a cerebellar synapse. We also found that the adult expression of both GluRdelta subunits across structures and cell types, hence their implications in brain functions and diseases, is broader than originally reported.

The aims of this project are to:
1) assess that group I mGluRs gate recombinant and native cerebellar and cortical GluRdelta channels
2) identify signaling and scaffolding partners involved in mGluR-GluRdelta crosstalks and provide insights into the dynamics of their interactions.
3) establish the relevance of mGluR-gated GluRdelta currents to the functions of cerebellar and cortical circuits.

The experimental program relies on a combination of physiological and molecular approaches that are already established in our laboratories. In addition to standard patch-clamp and molecular engineering techniques, approaches notably include viral transfer of existing dominant negative GluRdelta subunits to demonstrate the contribution of the GluRdelta channel pore to mGluR-gated currents in neurons. A combination of pharmacological, molecular and BRET imaging of protein-protein interactions will allow the identification of signaling and scaffolding partners involved in mGluR-GluRdelta coupling.

The feasibility of this project is assessed by our unpublished results and by the consortium expertise in iGluRs and cortical networks (partner 1), in mGluRs and their signaling and scaffolding interactions (partner 2) and in cerebellar synaptic transmission and plasticity (partner 3). On a technical ground, molecular engineering, viral transfer, and BRET imaging of protein-protein interactions are routinely used within the consortium. A solid foundation for the proposed work is also provided by the shared expertise in receptor/channel and synaptic electrophysiology. The largest part of the equipment, facilities, biological tools and cellular/animal models necessary to achieve each partner’s contribution to this project is already available in each relevant laboratory.

“De-orphanization” of GluR-delta receptors by mGluRs is likely to have a strong impact on a broad audience. Indeed, the ionotropic functions of the GluRdelta family have remained elusive for two decades and an mGluR-GluRdelta crosstalk would represent an original mechanism with far-reaching implications on synaptic transmission and receptor signaling. Finally, recent evidence of GluRdelta1 and -2 implications in schizophrenia and autism provides the functional coupling of GluRdelta channels and mGluRs with important biomedical perspectives.

Project coordination

Bertrand Lambolez (CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B) – bertrand.lambolez@snv.jussieu.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

UMR5203 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE LANGUEDOC-ROUSSILLON
UMR7102 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS B
UMR8119 CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - DELEGATION REGIONALE ILE-DE-FRANCE SECTEUR PARIS A

Help of the ANR 516,641 euros
Beginning and duration of the scientific project: December 2011 - 36 Months

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