Detection and conformational characterization of misfolded proteins in neurodegenerative diseases

Abstract

Fibrils composed of tau protein are a pathological hallmark of several neurodegenerative disorders collectively termed “tauopathies”, including Alzheimer’s disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Pick’s disease (PiD). We show that when recombinant tau protein is seeded with fibrils isolated from tauopathy brains, the amyloid formed shares many of the structural features of tauopathy fibrils. Our results suggest that brain-isolated fibrils act as a conformational template for the formation of recombinant tau fibrils. ☐ The critical concentration for this seeded tau structural propagation reaction is within the range of tau concentration found in neurons and is significantly higher than the standard tau fibrillization reaction that relies on a polyanion inducer to spontaneously induce tau misfolding. We characterize this dynamic equilibrium and show that it is consistent with the fast clearance of tau fibrils from cell models. Brain-derived seeds propagate recombinant tau fibers that closely resemble tauopathy pathology, suggesting a biochemical model of tau misfolding that is of improved utility for structural studies and drug screening. ☐ The elevated tau concentration in AD cerebrospinal fluid (CSF) is a biomarker of the disease, but the tau conformation has not been assessed. We developed a tau seeding assay that detects <1 pg of pathogenic tau conformation. Amyloidogenic tau was found in CSF from individuals with AD, CBD, PiD, and PSP, but not in CSF from age-matched controls. This amyloidogenic tau from tauopathy CSF propagated distinct conformations of recombinant tau fibrils. These findings suggest a possible biomarker directly linked to tau pathology and support the possibility of prion-like propagation of tau deposits between neurons in tauopathies. ☐ Many other neurodegenerative diseases are also associated with aggregated. The molecular pathways of protein misfolding to form amyloids often include diverse oligomeric species, only some of which progress to the amyloid state. We show that prefibrillar huntingtin oligomers, isolated from Huntington’s disease (HD) brain and from the R6/2 and YAC128 mouse models of HD, stimulate polyglutamine amyloid formation. These prefibrillar huntingtin oligomers are stable and potent seeds of amyloid formation.