(544f) Detection and Structural Analysis of Misfolded Tau Protein in Neurodegenerative Disease

Paired helical filaments (PHFs) of tau protein are a pathological hallmark of several neurodegenerative disorders including Alzheimer’s disease (AD). We have developed a technique for sensitive detection of PHFs and faithful amplification of their distinct conformation. We show that when recombinant tau protein is incubated with PHFs isolated from humans with AD, the nucleation-associated lag phase is shortened. We find that as little as 100 pg of misfolded tau protein accelerates the conversion of recombinant tau into fibrils, and that misfolded tau may be detected by this method in both AD brain samples (N=3/3 positive, 0/3 negative) and AD cerebrospinal fluid samples (N=13/14 positive, 0/8 negative). Additionally, we found that the recombinant tau amyloid formed in the presence of AD PHFs shares many of the structural features of the AD brain-derived seed. In comparison, tau amyloids formed with heparin as an inducing agent—a common biochemical model of tau misfolding—are structurally distinct from AD PHFs. Ultrastructural analysis by electron microscopy, circular dichroism, and GdnHCl denaturation showed that AD PHF seeded recombinant tau fibrils are similar in structure and stability to tau fibrils isolated from AD brain tissue, while heparin-induced recombinant tau fibrils have a significantly different morphology, secondary structure, and stability. Our results show that AD brain PHF seeds act as a conformational template for the formation of recombinant tau fibrils, while heparin induces a distinct recombinant tau fiber conformation. Such an in vitro biochemical model may be of improved utility for structural studies specific to different tauopathies and for drug screening approaches that use recombinant tau. The combined detection and structural analysis of misfolded tau by amyloid seeding also suggests possible new specific biomarkers for diagnosing and monitoring different tauopathies.