title: Tau Trimers Are the Minimal Propagation Unit Spontaneously Internalized to Seed Intracellular Aggregation.
abstract: Tau amyloid assemblies propagate aggregation from the outside to the inside of a cell, which may mediate progression of the tauopathies. The critical size of Tau assemblies, or "seeds," responsible for this activity is currently unknown, but this could be important for the design of effective therapies. We studied recombinant Tau repeat domain (RD) and Tau assemblies purified from Alzheimer disease (AD) brain composed largely of full-length Tau. Large RD fibrils were first sonicated to create a range of assembly sizes. We confirmed our ability to resolve stable assemblies ranging from n = 1 to >100 units of Tau using size exclusion chromatography, fluorescence correlation spectroscopy, cross-linking followed by Western blot, and mass spectrometry. All recombinant Tau assemblies bound heparan sulfate proteoglycans on the cell surface, which are required for Tau uptake and seeding, because they were equivalently sensitive to inhibition by heparin and chlorate. However, cells only internalized RD assemblies of n ≥ 3 units. We next analyzed Tau assemblies from AD or control brains. AD brains contained aggregated species, whereas normal brains had predominantly monomer, and no evidence of large assemblies. HEK293 cells and primary neurons spontaneously internalized Tau of n ≥ 3 units from AD brain in a heparin- and chlorate-sensitive manner. Only n ≥ 3-unit assemblies from AD brain spontaneously seeded intracellular Tau aggregation in HEK293 cells. These results indicate that a clear minimum size (n = 3) of Tau seed exists for spontaneous propagation of Tau aggregation from the outside to the inside of a cell, whereas many larger sizes of soluble aggregates trigger uptake and seeding.
authors.affiliation: From the Center for Alzheimer's and Neurodegenerative Diseases, University of Texas Southwestern Medical Center, Dallas, Texas 75390 and.
authors.forename: Hilda
authors.initials: H
authors.lastname: Mirbaha
authors.affiliation: From the Center for Alzheimer's and Neurodegenerative Diseases, University of Texas Southwestern Medical Center, Dallas, Texas 75390 and.
authors.forename: Brandon B
authors.initials: BB
authors.lastname: Holmes
authors.affiliation: From the Center for Alzheimer's and Neurodegenerative Diseases, University of Texas Southwestern Medical Center, Dallas, Texas 75390 and.
authors.forename: David W
authors.initials: DW
authors.lastname: Sanders
authors.affiliation: the Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130.
authors.forename: Jan
authors.initials: J
authors.lastname: Bieschke
authors.affiliation: From the Center for Alzheimer's and Neurodegenerative Diseases, University of Texas Southwestern Medical Center, Dallas, Texas 75390 and Marc.Diamond@UTSouthwestern.edu.
authors.forename: Marc I
authors.initials: MI
authors.lastname: Diamond
mesh_terms: D001704:Biopolymers / Q000378:metabolism*; D002850:Chromatography, Gel; D057809:HEK293 Cells; D006801:Humans; D013050:Spectrometry, Fluorescence; D016875:tau Proteins / Q000378:metabolism*
chemical_list: D001704:Biopolymers; C054369:MAPT protein, human; D016875:tau Proteins
keywords: Tau protein; amyloid; endocytosis; neurodegenerative disease; prion; structure