Rare bioactive tau oligomers from Alzheimer brain support both templated misfolding and fibril formation

Abstract In Alzheimer’s disease, both classical neurofibrillary tangles, and diffusible, aqueous soluble (High Molecular Weight, or HMW) species are able to support templated misfolding. How these tau proteoforms relate is uncertain. Using sequential size exclusion and anion exchange chromatography, we fractionated the HMW tau population and found both seed competent, and seed not competent proteoforms. Super resolution, atomic force, and immunogold electron microscopy confirmed that the size and conformation of both bioactive and non-bioactive tau proteoforms are similar, with dimers, trimers, and tetramers predominating. The presence of surface phosphorylation correlates with seeding capacity. Bioactive tau at fMol concentrations can induce seeding in a reporter cell. The soluble bioactive species support aggregation of a truncated repeat domain tau construct into thioflavin T positive fibrils and retain seeding activity over serial amplification in vitro and in cellulo, whereas non-bioactive oligomeric species do not. Together, these findings indicate that oligomeric assembly is required but not sufficient for seeding; instead, specific biochemical attributes of a rare oligomeric tau subset confer self-propagating, prion-like templated misfolding. Competing Interest Statement Dr Hyman owns stock in Novartis; he serves on the SAB of Dewpoint and has an option for stock. He serves on a scientific advisory board or is a consultant for AbbVie, Alexion, Ambagon, Aprinoia Therapeutics, Arvinas, Avrobio, AstraZenica, Biogen, Bioinsights, BMS, Cell Signaling, Cure Alz Fund, CurieBio, Dewpoint, Etiome, Latus, Merck, Novartis, Paragon, Pfizer, Sanofi, Sofinnova, SV Health, Takeda, TD Cowen, Vigil, Violet, Voyager, WaveBreak. His laboratory is supported by research grants from the National Institutes of Health, Cure Alzheimer's Fund, Tau Consortium, and the JPB Foundation - and sponsored research agreement from Abbvie and Sanofi. He has a collaborative project with Biogen and Neurimmune. Footnotes This revised version includes the following changes: 1. Statistical analyses for dot blot quantification have been added to Figures 1C and 4C,D. 2. The dot blot quantification values from Figure 4C, D have been added to Supplementary Figures S7 and S8. 3. A supplementary table showing fold changes in phospho-epitope signal between bioactive and non-bioactive species has been added. 4. RT-QuIC assays with non-bioactive species and the AD core fragment have been moved from the Supplementary Information to main Figure 6. 5. RT-QuIC assays with bioactive species and full-length 0N4R/0N3R have been moved from main Figure 6 to Supplementary Figure S9.