Venue: centre Broca
English-language defence
Nathan Bénac
IINS
Thesis supervisor: Laurent Groc 
Title
Résumé
Understanding how neurons develop to form the organized pattern of synaptic connections remains a central question in neuroscience. The vast majority of excitatory synapses are formed early in development during a synaptogenesis window. N-methyl-D-aspartate receptors (NMDAR) have long been a strong candidate to drive synaptogenesis as both in vivo and in vitro data show a key role for NMDAR during that phase. Furthermore, the facts that NMDAR are found in the developmentally immature “silent” synapses and among the first receptors to accumulate at the site of nascent synapses together lead to the assumption that NMDAR’s clustering is a nucleation point. Yet, the mechanisms underpinning the early clustering of NMDAR into synaptogenic assemblies remain enigmatic. Evidences that NMDAR can directly interact with other surface proteins, including receptors, has promoted the possibility that surface protein-protein interaction (PPI) represents a potent way to cluster receptors. Using a combination of live imaging and super-resolution microscopy, we observed that the interaction between D1R-GluN1-NMDAR were promoted in immature neurons, during the synaptogenesis phase. We showed that the D1R-GluN1-NMDAR interaction directly shapes the organization of NMDAR, allowing their functional clustering and synaptogenesis. Indeed, preventing the interaction in immature neurons, and not in mature neurons, altered the formation of excitatory post-synapses. We then focused on the intracellular and extracellular regulatory mechanisms of the interaction. We demonstrated a role of metabotropic glutamate receptors (mGluR) and casein kinase 1 (CK1) in promoting the interaction between D1R and GluN1-NMDAR. On the other hand, the facts that the hyaluronic acid (HA), one of the main components of the extracellular matrix (ECM), is enriched early in the immature brain and it regulates the surface diffusion of macromolecules opens the hypothesis that the ECM regulates the ability of NMDAR to interact with other surface macromolecules, including D1R. Yet, classical approaches have mainly focused on degrading the ECM. Herein, we aimed at increasing the ECM content in HA by over-expressing both the wild-type form of the rat hyaluronan synthase 2 (HAS2) or one bearing the two point-mutations present in the naked mole rat (NMR; N178S and N301S) which produces very high molecular weight HA (vHMW-HA). Weobserved that increasing the matrix impaired the development of the neuron and modified both the surface organization and trafficking of NMDAR. These findings validate our strategy, and open new paths for investigating the role of the ECM on neuronal development.
Keywords: NMDA receptor, protein-protein interaction, dopamine type I receptor, synaptogenesis, super-resolution microscopy, brain extracellular matrix, hyaluronic acid, naked mole rat
Publications
Bénac, N., Ezequiel Saraceno, G., Butler, C., Kuga, N., Nishimura, Y., Yokoi, T., Su, P., Sasaki, T., Petit-Pedrol, M., Galland, R., Studer, V., Liu, F., Ikegaya, Y., Sibarita, J.-B., Groc, L. Non-canonical interplay between glutamatergic NMDA and dopamine receptors shapes synaptogenesis. Nat. Commun. 15, 27. (2024) doi: 10.1038/s41467-023-44301-z.
Butler, C., Saraceno, G.E., Kechkar, A., Bénac, N., Studer, V., Dupuis, J.P., Groc, L., Galland, R., Sibarita, J.-B. Multi-Dimensional Spectral Single Molecule Localization Microscopy. Front. Bioinforma. 2, 813494. (2022) doi: 10.3389/fbinf.2022.813494.
Hunter, D., Petit-Pedrol, M., Fernandes, D., Bénac, N., Rodrigues, C., Kreye, J., Ceanga, M., Prüss, H., Geis, C., Groc, L. Converging synaptic and network dysfunctions in distinct autoimmune encephalitis. EMBO Rep. 25, 1623–1649. (2024) doi: 10.1038/s44319-024-00056-2.
Villéga, F., Fernandes, A., Jézéquel, J., Uyttersprot, F., Bénac, N., Zenagui, S., Bastardo, L., Gréa, H., Bouchet, D., Villetelle, L., Nicole, O., Rogemond, V., Honnorat, J., Dupuis, J.P., Groc, L. Ketamine alleviates NMDA receptor hypofunction through synaptic trapping. Neuron S0896627324004902 (2024) doi: 10.1016/j.neuron.2024.06.028.
Jury
Cyril Herry (president)
Sabine Levi (reporter)
Cécile Charrier (reporter)
Alexander Dityatev (examiner)
Laurent Groc (thesis supervisor)