Thesis defense – Ana Moreira de Sá

Venue: Centre Broca

Defense in english

Ana Moreira de Sá
IINS
Team: Synapses and neural circuits in behaviour
Thesis supervisor: Christophe Mulle

Title

Abstract

The full-length amyloid precursor protein (APP), a key player in Alzheimer’s disease (AD), is ubiquitously expressed throughout the brain. APP is abundantly expressed in presynaptic compartments where it interacts with proteins of the presynaptic release machinery. However, the physiological functions of APP at synapses remain in great part elusive. In this work, we study the physiological role of APP in short-term synaptic plasticity and information transfer within the hippocampus circuitry. Our work focuses on the CA3 region of the hippocampus and on mossy fiber (MF) synapses between the axons of the dentate gyrus (DG) and CA3 pyramidal cells (CA3 PCs).

We deleted APP and the related protein APLP2 in DG granular cells (DG-GCs) using a viral gene transfer strategy in APP/APLP2 double floxed mice. By combining optogenetics and ex vivo electrophysiology, we found that the selective deletion of APP in DG-GCs strongly impairs presynaptic short‑term plasticity at MF-CA3 PC synapses, expressed as a high level of synaptic facilitation in response to repeated presynaptic stimulation, without altering nor basal synaptic properties nor intrinsic excitability of DG-GCs. Additionally, the lack of APP altered the time course of post-tetanic potentiation, a form of presynaptic plasticity lasting several minutes following a high frequency train of stimulation. We then investigated the molecular mechanisms by which APP controls presynaptic short-term plasticity by isolating GFP-labelled MF-CA3 synaptosomes, and by performing a comparative proteomic screening to identify presynaptic proteins dysregulated in the absence of APP. We identified prospectively interesting targets that are dysregulated, including ZnT3, complexins I and II, and CSPa. We discuss the potential causative role of these proteins in the observed functional deficits, as well as the possible mechanisms by which APP controls presynaptic plasticity.

Concurrently, we virally deleted APP and APLP2 in postsynaptic CA3 PCs and performed ex vivo electrophysiology. We discovered that the lack of APP in CA3 pyramidal cells leads to a selective downregulation of MF-CA3 EPSCs mediated by kainate receptors (KARs), but not by AMPA or NMDA receptors. This was also observed in the APP/PS1 mouse model of AD and in conditional presenilin KO mice. We report that the GluK2 subunit of KARs interacts with APP and its biologically active fragments, and this interaction is likely responsible for regulating synaptic KARs levels. We interpret these results by a previously unknown transsynaptic role for APP.

Altogether, our data supports a pivotal role of APP in synaptic transmission and plasticity mechanisms at the MF-CA3 synapse. We propose that shedding light on the physiological contribution of full-length APP in the activity of hippocampal circuits will enhance our understanding of how disruption of APP functions contributes to the pathophysiology of AD.

Keywords: APP, synaptic plasticity, hippocampus, Alzheimer’s disease, presynaptic mechanisms

Publications

 Marneffe C, Moreira-de-Sá A, Lecomte S, Erhardt A, Mulle C. Short term plasticity at hipocampal mossy fiber synapses. Accepted for publication at Neuroscience on the 26^th of August 2024.

Lopes CR, Silva JS, Santos J, Rodrigues MS, Madeira D, Oliveira A, Moreira-de-Sá A, Lourenço VS, (…), Ferreira SG. Downregulation of Sirtuin 1 does not account for the impaired long-term potentiation in the prefrontal cortex of female APPswe/PS1dE9 modelling Alzheimer’s disease. J. Mol. Sci. 2023 April 9; 24(8)6968. doi: 10.3390/ijms24086968

Barthet G^†, Moreira-de-Sá A^†, Zhang P, Deforges S, Castenheira J, Gorlewicz A, Mulle C. Presenilin and APP regulate synaptic kainate receptors. J Neurosci. 2022 Oct 26;42(49):9253-62. doi: 10.1523/jneurosci.0297-22.2022
^†These authors have contributed equally to this work and share first authorship

Moreira-de-Sá A, Lourenço VS, Canas PM, Cunha RA. Adenosine A_2AReceptors as Biomarkers of Brain Diseases. Front Neuros 2021 Jul 16;15:702581. doi:10.3389/fnins.2021.702581.

Moreira-de-Sá A, Gonçalves FQ, Lopes JP, Silva HB, Tomé ÂR, Cunha RA, Canas PM. Motor Deficits Coupled to Cerebellar and Striatal Alterations in Ube3a^m-/p+Mice Modelling Angelman Syndrome Are Attenuated by Adenosine A_2A Receptor Blockade. Mol Neurobiol. 2021 Jun;58(6):2543-2557. doi:10.1007/s12035-020-02275-9.

Moreira-de-Sá A, Gonçalves FQ, Lopes JP, Silva HB, Tomé ÂR, Cunha RA, Canas PM. Adenosine A_2A receptors format long-term depression and memory strategies in a mouse model of Angelman syndrome. Neurobiol Dis. 2020 Dec;146:105137. doi:10.1016/j.nbd.2020.105137.

Jury

Dr. Nathalie Sans (présidente)
Dr. Nelson Rebola (rapporteur)
Dr. Joris de Wit (rapporteur)
Dr. Marie-Claude Potier (examinatrice)
Dr. Noa Lipstein (examinatrice)