Seeding variability of different alpha synuclein strains in synucleinopathies

Objectives: Currently, the exact reasons why different ?-synucleinopathies exhibit variable pathologies and phenotypes are still unknown. A potential explanation may be the existence of distinctive ?-synuclein conformers or strains. Here, we intend to analyze the seeding activity of dementia with Lewy bodies (DLB) and Parkinson's disease (PD) brain-derived ?-synuclein seeds by real-time quaking-induced conversion (RT-QuIC) and to investigate the structure and morphology of the ?-synuclein aggregates generated by RT-QuIC. Methods: A misfolded ?-synuclein-enriched brain fraction from frontal cortex and substantia nigra pars compacta tissue, isolated by several filtration and centrifugation steps, was subjected to ?-synuclein/RT-QuIC analysis. Our study included neuropathologically well-characterized cases with DLB, PD, and controls (Ctrl). Biochemical and morphological analyses of RT-QuIC products were conducted by western blot, dot blot analysis, Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. Results: Independently from the brain region, we observed different seeding kinetics of ?-synuclein in the RT-QuIC in patients with DLB compared to PD and Ctrl. Biochemical characterization of the RT-QuIC product indicated the generation of a proteinase K-resistant and fibrillary ?-synuclein species in DLB-seeded reactions, whereas PD and control seeds failed in the conversion of wild-type ?-synuclein substrate. Interpretation: Structural variances of ?-synuclein seeding kinetics and products in DLB and PD indicated, for the first time, the existence of different ?-synuclein strains in these groups. Therefore, our study contributes to a better understanding of the clinical heterogeneity among ?-synucleinopathies, offers an opportunity for a specific diagnosis, and opens new avenues for the future development of strain-specific therapies. Ann Neurol 2019;85:691-703.