ED Sciences de la Vie et de la Santé
Alpha-synucléin cerebral amyloids in synucleinopathies: quantification, bioactivity and strain properties.
by Ludivine SABATIER (Institut des Maladies Neurodégénératives)
The defense will take place at 14h00 - Salle de conférence Site Carreire de l'Université de Bordeaux Bâtiment CARF 146, rue Léo Saignat 33076 Bordeaux cedex.
in front of the jury composed of
- Joan TORRENT - Chargé de recherche - Université de Montpellier - Rapporteur
- Human REZAEI - Directeur de recherche - Université Paris-Saclay - Rapporteur
- Sophie LECOMTE - Directrice de recherche - Université de Bordeaux - Examinateur
- Nadia EL MAMMERI - Chargée de recherche - Université de Bordeaux - Examinateur
The presence of proteinaceous inclusions primarily composed of alpha-synuclein (a-syn), a protein naturally present in the brain, is the hallmark of synucleinopathies, a group of neurodegenerative diseases. These include multiple system atrophy (MSA), Parkinson's disease (PD), and dementia with Lewy bodies. Within inclusion bodies, a-syn is found in the form of amyloid fibrils. By analogy with prion diseases, it is now generally accepted that synucleinopathies represent distinct a-syn strains. The molecular basis of their divergent phenotypes lies in the structure of the protein's amyloid assemblies, which differs across these pathologies. The bioactivity of an amyloid – its ability to recruit normal a-syn, induce its aggregation and propagate the pathology – constitutes, alongside structure, a strain property. However, the precise links between structure and bioactivity remain to be established. Numerous studies have shown that fibrils derived from MSA samples are more bioactive than those from PD samples. Although these studies attempted to normalize or quantify amyloids, we identified several biases related to their identification and quantification, such that these bioactivity measurements may reflect differences in dose rather than in specific bioactivity – i.e. relative to the amount of amyloids. Furthermore, a structural heterogeneity of fibrils exists within MSA itself, but the functional consequences of this heterogeneity remain to be determined. To this end, our study first focused on the identification of methodological biases, before developing procedures enabling unbiased measurement of the amount of amyloid a-syn in biological samples. We established native blotting methods (drop-blot and filter-blot), which allow evaluation of the relative amyloid load in samples through immunolabelling with specific antibody pairs that we identified. Moreover, as some commercial ELISAs do not allow accurate measurement of a-syn amyloids, due to the use of inappropriate antibodies, we developed two in-house ELISA assays: one detecting all a-syn species, and a second specifically and absolutely quantifying amyloid assemblies. Thanks to the development of these tools, we were able to accurately quantify amyloid a-syn present in brain samples from synucleinopathy patients, in order to determine their specific bioactivity. We chose to use a HEK-hSyn-YFP reporter cell line as a model. These in vitro studies showed that fibrils contained in MSA brains are more bioactive than PD fibrils, both when using crude brain homogenates or amyloid-enriched samples obtained by biochemical fractionation from the same brain tissues. Remarkably, by extending these measurements to different brain regions across different patients, we were able to demonstrate that the bioactivity of MSA fibrils was distinct depending on the patient from whom they were derived, while this property was conserved across brain regions within a given patient. These data document the existence of amyloid sub-strain populations within a single strain. This corroborates studies that revealed structural diversity among MSA filaments from different patients. Our work further indicates the absence of notable structural evolution during the course of cerebral disease progression. Biochemical and functional characterization of the in vitro-generated aggregates will determine whether the strain properties of the brain-derived amyloids are conserved upon replication.
ED Sociétés, Politique, Santé Publique
Vestibular integration in modified gravity and motion sickness
by Tess BONNARD (Institut de neurosciences cognitives et intégratives d'Aquitaine)
The defense will take place at 9h30 - Amphithéâtre BBS (RDC) 2 rue Docteur Hoffmann Martinot, Bâtiment Biologie Santé (BBS), 33076, Bordeaux Cedex
in front of the jury composed of
- Etienne GUILLAUD - Ingénieur de recherche - CNRS - Directeur de these
- Gaëlle QUARCK - Professeure des universités - Université de Caen - Rapporteur
- Lionel BRINGOUX - Professeur des universités - Aix Marseille Université - Rapporteur
- Guillemette GAUQUELIN KOCH - Professeure des universités - Centre National d'Études Spatiales (CNES) - Examinateur
- Jordan NAVARRO - Professeur des universités - Université Lumière Lyon 2 - Examinateur
- Valérie FRANCO-VIDAL - Professeure des universités - praticienne hospitalière - Centre hospitalier universitaire de Bordeaux (CHU) - Examinateur
Motion sickness is a common phenomenon characterized by distressing symptoms and a temporary decline in performance. It occurs in a variety of sensory contexts and varies among individuals depending on demographic, genetic, and experience-related factors. Despite extensive research, its mechanisms, manifestations, and predictorsremainonly partially understood. Space motion sickness, experienced by astronauts during the first days of weightlessness,representsa specific case whose underlying causesremainpoorly understood. Motionsicknessisgenerallyexplainedbysensoryconflictsandmultisensoryreweightingmechanismsinvolving primarily the vestibular system.However, fewstudieshavedirectlyinvestigatedthesensorychangesinducedbytheseconflictsorcompareddifferentsensorycontexts. Abetterunderstandingofthesemechanismscouldcontributeto thedevelopmentof non-pharmacologicalpreventionstrategies, ascurrenttreatmentsoftenproducesideeffectsthatare notwellsuitedtooperationalconstraints. Thisthesisaimsto identify the sensory conflicts involved intwoformsof motionsicknessand theassociatedsensory reweighting strategies. Space motionsickness,presumedto have avestibularorigin,wasreproducedusingparabolicflights,whereascybersickness,presumedto have avisualorigin,wasinvestigatedin alaboratorysetting.Vestibular,visual, andmultisensoryassessmentswereconductedbeforeandafterexposureto examine themechanismsofsensoryreweighting.Vestibulartestswerealsoperformedduringthedifferentgravitationalphases of the flight toinvestigatetheeffectsofgravityonvestibularfunction. The results show an impairment of canal-related functions (angular accelerations) bothimmediatelyduring weightlessness and after parabolic flights and virtual reality exposure,whereasotolithic functions (linear accelerations) remain stable. Visuo-oculomotor reflexes decrease after parabolic flights but remain unchanged following virtual reality exposure. Postural imbalance alsoemergesafter virtual reality exposure. These findings suggest a resilience of otolithic inputs and highlight a marked sensitivity of the semicircular canals to changes in gravity, despite their theoretical independence from gravitational forces. They support a vestibular origin in the development of space motion sickness. Sensory reweighting strategies differ depending on the experimental paradigm. These observations suggest that the sensory input detectinga movementgains increased weighting during multisensory integration. Onanotherhand, several physiological markers as well as sleep were investigated toidentifysymptomatic differences and susceptibility factors. The resultsindicatethat symptomatology depends primarily on the experimental context rather than on the type of sensory conflict. Facial colorimetryemergesas a relevant objective indicator of motion sickness severity. No baseline physiological marker robustly predicts susceptibility, although greater visual sensitivity in virtual reality and increased canal sensitivity during parabolicflightappear to constitute risk factors. Sleep qualityemergesas the strongest predictoridentified, with participantsexhibitingpoorer sleep habits being more vulnerable to space motion sickness. Taken together, these findings advance our understanding of both terrestrial and space motion sickness. They highlight thecentral roleof sensory integration strategies, propose a novel objective indicator of motion sickness, andidentifya potential susceptibility factor for space motion sickness.