LySyT · Understanding the role of lysosomes in the intercellular TNT-mediated spreading of α-synuclein and the impact of lysosomal dysfunction

Understanding the role of lysosomes in the intercellular TNT-mediated spreading of α-synuclein and the impact of lysosomal dysfunction

Although neurodegenerative diseases (NDs) are one of the top 10 global causes of death, our knowledge about the basic molecular mechanisms underlying their pathogenesis is still lacking. The accumulation of misfolded protein aggregates in affected brain regions is a common hallmark shared by several NDs. In Parkinson’s disease (PD), misfolded alpha-synuclein (α-syn) proteins accumulate within neurons in the so-called Lewy bodies. Substantial findings support the capability of misfolded α-syn proteins to propagate in cellular and in animal models by transferring between cells and by inducing the aggregation of endogenous proteins (seeding activity). Lysosomes are responsible for the degradation of misfolded aggregates and their dysfunction is a common trait of NDs; however, the mechanisms leading to lysosomal damage and how this damage contributes to neurodegeneration is not clear. In this project we applied the state-of-the-art imaging approaches both in live and fixed conditions (e.g., confocal live-cell imaging microscopy, super resolution microscopy, and correlative electron microscopy) together with biochemistry and molecular biology to test our ground-breaking hypothesis that dysfunctional lysosomes are transferred through Tunneling nanotubes (TNTs), membranous bridges connecting distant cells, and contribute to the propagation of the pathology. It has been previously shown that α-syn fibrils are transferred through TNTs between neurons while inside lysosomes, and that the fibrils induced the misfolding and aggregation of the normal soluble protein after their transfer. Here, the LySyT project focused on outstanding questions: i) how lysosomes enter and move inside TNS; ii) how α-syn fibrils, while inside lysosomes, could seed the misfolding of soluble α-syn in recipient cells; iii) where seeding occurs inside the cell and the role of lysosomes in this event; and iv) the fate of α-syn-loaded lysosomes. This project had high translational application, as it aimed at understanding of the mechanisms of propagation of the α-syn pathology and the effects on neurons, which are essential step to identify suitable therapeutic targets for PD. Lysosomal dysfunction is also a common feature of Lysosomal Storage Diseases (LSDs), a group of about 50 rare, inherited metabolic disorders caused by the defective function of a specific lysosomal enzyme. Classically, LSDs are classified in diverse forms encompassing a wide spectrum of clinical phenotypes and the most severe forms of LSDs affect the nervous system. With the aim to better elucidate the pathogenesis of LSDs and to highlight possible similarities with NDs, the LySyT project also studied the possible role of TNTs in the lysosomal pathology of LSDs. *Image name: The lysosome: an ally in spreading Parkinson’s disease. Image description: 3D rendering of a lysosome (grey) facilitating the formation of new α-syn aggregates (green) induced by the pre-existing α-syn aggregates (red).

Data: CORDIS, © European Union