Résumés / Abstracts 2021

Interplay between the endolysosomal system and protein aggregation in the pathogenesis of Parkinson’s disease

OBJECTIVE
While progress has been made in understanding the neurodegenerative mechanisms that lead to cell death in Parkinson’s disease (PD), early causal pathogenic events are not clear. Converging findings point at endolysosomal system (ELS) dysfunction as the early mechanism and key pathway affected in PD. However, the exact mechanism by which alpha-synuclein aggregates, also called Lewy Bodies (LBs), disrupt the ELS remain elusive.

METHODS
To answer this question, our group created a new optogenetic-based model of PD that allows for the real-time induction of α-syn aggregates under the blue light control, that mimics all cardinal LBs features. This system is referred to as Light-Inducible Protein Aggregation (LIPA) and allows us to explore unsolved questions related to early interactions between the ELS, LBs and PD pathogenesis. Using the LIPA system inside living cells, we were able to study the direct impact of our aggregates on vesicle homeostasis. To specifically investigate the interactions between our LIPA aggregates and the ELS, we decided to use the super-resolution microscopy STED in combination with transmission electron microscopy (TEM) overtime. Then, we used live-cell confocal microscopy to decipher how alpha-synuclein quickly interacts with the ELS at the very first steps of aggregation.

RESULTS
The STED microscopy overtime offered us a better understanding of the interactions between alpha-synuclein aggregation and trafficking vesicles (EEA-1/Rab5, Lamp1/Lamp2A) showing a quick and robust colocalization between those markers and our aggregates. Interestingly, those vesicles (early endosomes and lysosomes) were specifically interacting with alpha-synuclein and were not colocalizing with our LIPA-empty control aggregates. Those results were confirmed using TEM, showing that they are composed of multiple vesicles and distorted organelles. Our live-cell confocal microscopy data revealed that the alpha-synuclein, few seconds after aggregation, quickly bind to the membrane of Rab5-positive endosomes forming a dynamic complex that will further bind to other Rab5/alpha-synuclein complex leading to the formation of bigger aggregates.

CONCLUSION
Those results allowed us to observe and to better understand how alpha-synuclein aggregates impact the trafficking of the vesicles inside the cell overtime, suggesting that the ELS play a key role in alpha-synuclein aggregation, especially the early endosomes.