Fig. 5.

3R/4R tau seeds include hyperphosphorylated and sarkosyl-insoluble forms, with those that occur at early and late stages of AD neuropathology being largely protease resistant. a Brain homogenates from cases with absent/low Braak scores (0–II) or those designated AD (Braak V–VI) were treated with proteinase K (PK) prior to RT-QuIC analysis. Protease treated and mock-treated brain homogenates were used to seed the RT-QuIC assay. Endpoint-dilution analysis indicated quantitative seeding doses are comparable even after PK digestion. b SDS-PAGE analysis of treated (+ PK, pink) and untreated (−PK, black) brain homogenates confirmed efficiency of PK digestion. c Seeding doses (log SD₅₀ per mg tissue) for (+ PK, pink) and untreated (−PK, black) brain homogenates are shown per case as indicated. d Immunoprecipitation using phospho-tau antibodies deplete up to 1 log of seeding activity. Log reduction of seeding activity is shown for phospho-tau antibodies, and when compared to seeding activities in brain homogenate supernatants subjected to isotype depletion. Each data point represents the log reduction detected in an individual AD case (Braak VI, n = 4). e Braak I cases contain sarkosyl-insoluble tau, albeit at much lower levels than that found in Braak VI cases. Lane 1, 1:2 dilution of 10% w/v Braak I brain homogenate. Lane 2, 1:4 dilution of 10% w/v Braak I brain homogenate. Lane 3, assuming 100% recovery of sarkosyl-insoluble product, ~ 8.2X 10% brain homogenate equivalent. Lane 4, assuming 100% recovery of sarkosyl-insoluble product, ~ 2.7X 10% brain homogenate equivalent. Lane 5, 1:2 dilution of 10% w/v Braak VI brain homogenate. Lane 6, assuming 100% recovery of sarkosyl-insoluble product, ~ 8.2X 10% brain homogenate equivalent. f Sarkosyl insoluble tau filaments have seeding activities that approach those detected in the total brain homogenate from which they were extracted. Seeding doses are shown for sarkosyl-insoluble extract equivalents, assuming 100% tau recovery from the brain tissue homogenates from which they were derived. Numbers in parentheses indicate case numbers as shown through panels (a–f)