Homer1a-Dependent Crosstalk Between NMDA and Metabotropic Glutamate Receptors in Mouse Neurons

Federica Bertaso,Joël Bockaert,Gautier Roussignol,Laurent Fagni,Fabrice Ango,Paul Worley,Lin Mei

doi:10.1371/journal.pone.0009755

Abstract

BackgroundA large number of evidences suggest that group-I metabotropic glutamate receptors (mGluR1a, 1b, 1c, 5a, 5b) can modulate NMDA receptor activity. Interestingly, a physical link exists between these receptors through a Homer-Shank multi-protein scaffold that can be disrupted by the immediate early gene, Homer1a. Whether such a versatile link supports functional crosstalk between the receptors is unknown.Methodology/Principal FindingsHere we used biochemical, electrophysiological and molecular biological approaches in cultured mouse cerebellar neurons to investigate this issue. We found that Homer1a or dominant negative Shank3 mutants that disrupt the physical link between the receptors allow inhibition of NMDA current by group-I mGluR agonist. This effect is antagonized by pertussis toxin, but not thapsigargin, suggesting the involvement of a G protein, but not intracellular calcium stores. Also, this effect is voltage-sensitive, being present at negative, but not positive membrane potentials. In the presence of DHPG, an apparent NMDA “tail current” was evoked by large pulse depolarization, only in neurons transfected with Homer1a. Co-immunoprecipitation experiments showed interaction between G-protein βγ subunits and NMDA receptor in the presence of Homer1a and group-I mGluR agonist.Conclusions/SignificanceAltogether these results suggest a direct inhibition of NMDA receptor-channel by Gbetagamma subunits, following disruption of the Homer-Shank3 complex by the immediate early gene Homer1a. This study provides a new molecular mechanism by which group-I mGluRs could dynamically regulate NMDA receptor function.

Highlights

The neurotransmitter glutamate activates both ionotropic (AMPA, kainate and NMDA subtypes) and metabotropic receptors at mammalian central synapses
In the present study we examined whether this versatile multiprotein complex could underlie a functional crosstalk between mGluR1a and NMDA receptors (NMDA-Rs) when these receptors are strictly co-activated, in cultured neurons
In the present study we examined whether the physical link established between group-I mGluRs and NMDA-R by the Shank3 multiprotein complex could be responsible for a functional crosstalk between these two receptors

Summary

Introduction

The neurotransmitter glutamate activates both ionotropic (AMPA, kainate and NMDA subtypes) and metabotropic (mGluR1-8 subtypes) receptors at mammalian central synapses. Among the eight mGluR subtypes, mGluR1 and mGluR5 (group-I mGluRs) are localized in an annulus that circumscribes the postsynaptic density (PSD) [1] As they display low affinity for glutamate, optimal activation of these receptors would be achieved only upon large synaptic release of the neurotransmitter glutamate. Crosstalk between group-I mGluRs and NMDA-Rs has long been investigated by examining the effect of prestimulation of the mGluRs on subsequent evoked NMDA currents. A physical link exists between these receptors through a Homer-Shank multi-protein scaffold that can be disrupted by the immediate early gene, Homer1a. Whether such a versatile link supports functional crosstalk between the receptors is unknown

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Results

Conclusion