The pathogenesis of Parkinson's disease (PD) and Multiple system atrophy (MSA) involves the accumulation of aggregated forms of α-Synuclein in the brain. Progressive staging of α-Synuclein pathology in patient brains correlates with disease symptoms, and disease heterogeneity may be caused by distinct α-Synuclein strains. α-Synuclein pathology can spread in the brain of rodents following intracerebral injection of pathological α-Synuclein seeds. In the current studies, we investigated the ability of recombinant α-Synuclein assemblies with different conformations, i.e. fibrils and ribbons, as well as PD and MSA derived assemblies, i.e. Protein Misfolding Cyclic amplification (PMCA) assemblies and sarkosyl-insoluble fractions, to induce α-Synuclein pathology in primary neurons and mouse brains in vivo.
We showed that recombinant α-Synuclein assemblies induced seeding, with higher potency of fibrils compared to ribbons. PD and MSA PMCA assemblies were potent seeders, although distinct regional and morphological patterns of α-Synuclein pathology were observed in vivo. Sarkosyl-insoluble samples from MSA, but not from PD, were potent seeders in primary neurons.
Ubiquitin colocalization with α-Synuclein aggregates is a robust neuropathological hallmark in patient brains and a better understanding of the regulation of ubiquitinylation may provide important knowledge about the cellular response to α-Synuclein accumulation. We used the primary neuron seeding model to identify specific deubiquitinase enzymes which upon silencing reduced α-Synuclein seeding. These enzymes are under further investigation.
Taken together, our findings support that distinct α-Synuclein strains may define different synucleinopathies and that in vitro and in particular in vivo seeding models might be useful for validating new potential treatment principles.