Characterization of the structural and molecular properties of propagating tau in vitro and in vivo

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Project summary/abstract. Tau protein accumulates into pathogenic deposits in many neurodegenerative diseases, including Alzheimer disease (AD) and some forms of Gerstmann-Sträussler-Scheinker disease (GSS). Using cryo-electron microscopy (cryo-EM) recent groundbreaking studies have determined the existence of multiple tau conformers, which may differ between tau diseases. The tau aggregates in AD and GSS contain all 6 isoforms of tau, and both have been ultrastructurally determined to contain paired helical filaments (PHFs). However in AD, there exists an ultrastructural polymorph to PHFs, comprised of the same amino acid sequence but a differing interface, named straight filaments (SFs). These SFs are not found in GSS, nor is it known why tau would fold into PHFs versus SFs in AD. This means that therapeutics designed to target specific tau conformers may not be suitable for all tau polymorphs within a disease. Numerous studies have demonstrated that tau acts in a ‘prion-like’ manner, templating the misfolding from pathogenic ‘donor’ to naïve ‘receiver’ tau, in both in vitro and in vivo models of tau diseases. However, how donor tau acts as a template to receiver tau is not yet known; the mechanism(s) of which would provide a myriad of targets to reduce tau propagation and thus disease dissemination throughout the brain. Our study aims to answer the following questions: is the structure of tau conferred from donor to receiver tau in vivo, and therefore are our in vivo models of neurodegeneration valid for investigating tau propagation (aim 1)? How are the numerous post-translational modifications (PTMs) on tau relevant to tau polymorph formation (aim 2b), and are these PTMs recapitulated from donor to receiver tau both in vivo (aim 2a) and in vitro (aim 3)? What are the gene changes that are occurring in a circuit of diseased brain cells, and are these changes spreading to both anterogradely and retrogradely connected cells (aim 3)? Using novel in vivo and in vitro systems including custom microfluidic cell culture devices, cryo-EM imaging and analysis, mass spectrometry and RNAseq, we aim to answer these vital questions and thus identify future targets for preventing tau propagation.