Unveiling the role of the endolysosomal system 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 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 endolysosomal system remain elusive. 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 endolysosomal system, LBs and PD pathogenesis.

METHODS

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 endolysosomal system, we decided to use the super-resolution microscopy STED in combination with transmission electron microscopy (TEM) to cross-confirm the results observed.

RESULTS

The combination of immunocytochemistry and the super-resolution microscopy STED offered us a better understanding of the interactions between LBs and trafficking vesicles while showing several different. Our LIPA aggregates showed ultrastructural features of authentic LBs, showing interactions with vesicles such as the early/late endosomes (EEA-1/Rab7), exosomes (CD9) but also the degradation vesicles (LAMP1/2A) caracterized by multiple co-localization with those markers. Those results where confirmed using TEM on our LBs, showing that they are composed of multiple vesicles and also shown distorted organelles such as mitochondria, Golgi apparatus or reticulum endoplasmic.

CONCLUSION

Those results allowed us to observe and to better understand how alpha-synuclein aggregates impact the trafficking of the vesicles inside the cell and how those aggregates where managed in the cell overtime.