Understanding alpha-synuclein strain-dependent pathology in Parkinson's disease

Abstract

Parkinson’s disease (PD) is defined by α-synuclein (α-syn) aggregation. Distinct polymorphs—flat "ribbons" and cylindrical "fibrils"—are associated with different disease phenotypes, but how cells process these strains and how mutations affect their structural fidelity remains poorly understood. This thesis utilized a novel seed amplification assay (SAA), Attobright, to investigate these dynamics. Optimized Attobright SAA (using K23Q monomers) demonstrated that fibrils grow via secondary nucleation, increasing in complexity, whereas ribbons do not. Both polymorphs retained their structural signatures even after cross-seeding. In SH-SY5Y cells, fibrils induced higher inclusion intensity than ribbons. Though both were gradually cleared by cells, only fibril-treated conditioned medium (CM) induced inclusions in naïve cells, confirming superior cell-to-cell propagation. Using iPSC-derived neurons, the study found that PD mutations (GBA1, A53T, and idiopathic) generally increased α-syn intensity post-treatment, with GBA1 mutations significantly impairing aggregate clearance. Crucially, while strain fidelity was generally preserved during cellular processing, the A53T mutation disrupted this stability; ribbons released from A53T neurons shifted to a fibril-like amplification pattern. These results highlight distinct pathological profiles for α-syn strains and reveal that the A53T mutation can fundamentally alter strain fidelity. This work also establishes Attobright as a powerful tool for high-sensitivity detection of protein aggregates in diverse experimental models.