Epileptiform stimulus increases Homer 1a expression to modulate synapse number and activity in hippocampal cultures

Yan Li, Jonathan Popko, Kelly A. Krogh, Stanley A. Thayer

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Neurons adapt to seizure activity structurally and functionally to attenuate hyperactive neural circuits. Homer proteins provide a scaffold in the postsynaptic density (PSD) by binding to ligands through an EVH1 domain and to other Homer proteins by a coiled-coil domain. The short Homer isoform 1a (H1a) has a ligand-binding domain but lacks a coiled-coil domain and thus acts in a dominant-negative manner to uncouple Homer scaffolds. Here, we show that treating rat hippocampal cultures with bicuculline and 4-aminopyridine (Bic+4-AP) evoked epileptiform activity and synchronized Ca2+ spiking, measured with whole cell current-clamp and fura-2-based digital imaging; Bic+4-AP increased H1a mRNA through the activation of metabotropic glutamate receptor 5 (mGluR5). Treatment with Bic+4-AP for 4 h attenuated burst firing and induced synapse loss. Synaptic changes were measured using a confocal imaging-based assay that quantified clusters of PSD-95 fused to green fluorescent protein. Treatment with an mGluR5 antagonist blocked H1a expression, synapse loss, and burst attenuation. Overexpression of H1a inhibited burst firing similar to Bic+4-AP treatment. Furthermore, knockdown of H1a using a short hairpin RNA (shRNA) strategy reduced synapse loss and burst attenuation induced by Bic+4-AP treatment. Thus an epileptiform stimulus applied to hippocampal neurons in culture induced burst firing and H1a expression through the activation of mGluR5; a 4-h exposure to this stimulus resulted in synapse loss and burst attenuation. These results suggest that H1a expression functions in a negative-feedback manner to reduce network excitability by regulating the number of synapses.

Original languageEnglish (US)
Pages (from-to)1494-1504
Number of pages11
JournalJournal of neurophysiology
Volume109
Issue number6
DOIs
StatePublished - 2013

Keywords

  • Epilepsy
  • Homer proteins
  • Metabotropic glutamate receptors
  • PSD-95
  • Synapse loss

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