Venue : Neurocentre Magendie conference room
Thesis supervisor : Mathieu Letellier ; team “Cell adhesion molecules in synapse assembly”
Synaptic scaling is a form of homeostatic plasticity where synapses adjust their own efficacy to compensate for normal or pathological variations in neuronal activity such as neurodegenerative disorders or sensory deprivation after a lesion. In a well-established paradigm, the chronic application of tetrodotoxin (TTX) in primary neurons, to block presynaptic action potential propagation, induces a significant upscaling of miniature excitatory postsynaptic currents mediated-AMPA receptors. Numerous regulators of this plasticity have been identified including microRNAs (miRs), which are small endogenous non-coding RNAs, inhibiting protein translation by binding to mRNA targets. This led us to hypothesize that the most highly expressed microRNA in the brain, miR-124, could be an important regulator of homeostatic scaling by controlling the expression of synaptopodin, a structural protein of dendritic spines playing a crucial role in homeostatic plasticity.
By combining qRT-PCR, immunocytochemistry and in vitro electrophysiology approaches, first we showed that a global 48 hrs TTX treatment in hippocampal primary neurons led to a decrease in miR-124 level and an increase in the expression of synaptopodin and synaptic AMPA receptors containing the GluA2 subunit which is another miR-124 target. Moreover, we observed that the synaptic accumulation of AMPA receptors and synaptopodin could be synapse-specific by expressing the tetanus toxin to block the activity of individual presynapses, which suggested a local homeostatic regulation. Importantly, we found that overexpressing miR-124 or inhibiting its interaction with synaptopodin or GluA2 mRNAs blocked the synaptic homeostatic response. In addition, FRAP experiments suggested that synaptopodin controlled AMPA receptor trafficking at the membrane by probably retaining them in dendritic spines, which could explain its role during homeostatic plasticity.
Key words : homeostatic plasticity, synaptic scaling, miR-124, synaptopodin, AMPA receptors
- Nathalie Sans – Présidente du jury
- Cyril Hanus – Rapporteur
- Jean-Christophe Poncer – Rapporteur
- Isabelle Caillé – Examinatrice
- Mathieu Letellier – Directeur de thèse
- Olivier Thoumine – Invité