Relations entre les agrégats de Tau ou d'alpha-synucléine et le dysfonctionnement de l'autophagie

Relationships between Tau/alpha-synuclein aggregates and autophagy dysfunction

• Auteur / Autrice : Valentine Thomas
• Direction : Christel Brou
• Type : Projet de thèse
• Discipline(s) : Biologie moléculaire et cellulaire
• Date : Inscription en doctorat le 30/09/2023
• Etablissement(s) : Sorbonne université
• Ecole(s) doctorale(s) : École doctorale Physiologie, Physiopathologie et Thérapeutique (Paris ; 2000-....)
• Partenaire(s) de recherche : Laboratoire : Trafic membranaire et Pathogénèse

Mots clés

Mots clés libres

Protéines amyloides

Alzheimer

Autophagie

Parkinson

Maladie Neurodegénérative

Amyloid proteins

Neurodegenerative disease

Autophagy

Alzheimer

Parkinson

Résumé

Non relevant

Alzheimer's disease (AD) and Parkinson's disease (PD) are characterized by the appearance of protein aggregates in brain neurons. These misfolded proteins (Tau and alpha-synuclein for AD and PD respectively) spread gradually to neighboring regions of the brain following predictable patterns in correlation with the progressive emergence of neurological symptoms. Once transferred between cells the misfolded proteins work as proteopathic seeds to template misfolding of endogenous native proteins, thus propagating the pathology, according to the Prion hypothesis, as well as inducing alterations of neurons functions, eventually resulting in neurodegeneration (ND)(1). Another hallmark of these neurodegenerative diseases is the dysfunction of the autophagy-lysosomal pathway, which plays a key role in clearance of aggregated proteins in healthy cells (2,3). However, how the presence of amyloid aggregates and abnormal autophagy are linked, and whether one is cause or consequence of the other, is not well understood yet and constitute the main questions of this project. This project will rely on the parallel study of Tau and alpha-synuclein fibrils in neuronal cells by focusing on their formation, their stability and degradation, and their effect on cellular machineries. Our data indicated that alpha-syn fibrils affect both lysosomal morphology and function and could suggest that α-syn-loaded lysosomes are not correctly repaired and their degradation by autophagy is blocked, entailing an accumulation of damaged lysosomes (4). This could explain why α-syn aggregates accumulate and propagate in Parkinson patient's brains. On the other hand, we have developed a cellular model where fluorescent RD-Tau aggregates (containing a fragment of Tau accounting for aggregation) are endogenously formed and spread over the culture5. We observed that Tau aggregates could be recognized as autophagy cargo but were not delivered to lysosomes. Altogether, our data suggest that autophagy fails in degrading both α-syn aggregates (stored in damaged lysosomes), and FL-Tau aggregates (outside lysosomes). However, the specific mechanisms and the consequences for the cells were not addressed yet. Specifically, using cell biology, biochemistry, super resolution imaging and mass spectrometry (MS) approaches, the project will consist in: 1. showing that endogenously formed FL-Tau aggregates, or synuclein fibrils are stable and understanding what are the precise molecular mechanisms through which they escape autophagy. 2. assessing whether the presence of the aggregates affects the general autophagy mechanisms of the cells. 3. uncovering the mechanisms and subcellular localization of aggregate seeding. 4. assessing the impact of Tau and/or synuclein aggregates on lysosomal morphology and activity, by lysosome purification followed by mass spectrometry analysis. Together, this project will allow to understand if common or different pathways give rise to lysosomal failure and accumulation of misfolded proteins characteristic of both diseases.