Distinct α-Synuclein Strains Differentially Promote Tau Inclusions in Neurons

Many neurodegenerative diseases are characterized by the accumulation of insoluble protein aggregates, including neurofibrillary tangles comprised of tau in Alzheimer's disease and Lewy bodies composed of alpha-synuclein in Parkinson's disease. Moreover, different pathological proteins frequently codeposit in disease brains. To test whether aggregated alpha-synuclein can directly cross-seed tau fibrillization, we administered preformed alpha-synuclein fibrils assembled from recombinant protein to primary neurons and transgenic mice. Remarkably, we discovered two distinct strains of synthetic alpha-synuclein fibrils that demonstrated striking differences in the efficiency of cross-seeding tau aggregation, both in neuron cultures and in vivo. Proteinase K digestion revealed conformational differences between the two synthetic alpha-synuclein strains and also between sarkosyl-insoluble alpha-synuclein extracted from two subgroups of Parkinson's disease brains. We speculate that distinct strains of pathological alpha-synuclein likely exist in neurodegenerative disease brains and may underlie the tremendous heterogeneity of synucleinopathies.