Novel human neuronal tau model exhibiting neurofibrillary tangles and transcellular propagation

Abstract

Tauopathies are a class of neurodegenerative diseases, including Alzheimer’s disease, frontotemporal dementia and progressive supranuclear palsy, that are associated with the pathological aggregation of tau protein in neurofibrillary tangles (NFT). Studies have characterized tau as a “prion-like” protein given its ability to form distinct, stable amyloid conformations capable of transcellular and multigenerational propagation in clonal fashion. It has been proposed that progression of tauopathy could be due to the prion-like propagation of tau, suggesting the possibility that end-stage pathologies like NFT formation may require an instigating event such as tau seeding. To investigate this, we applied a novel human induced pluripotent stem cell (hiPSC) system we have developed to serve as a human neuronal model. We introduced the tau repeat domain (tau-RD) with P301L and V337M (tau-RD-LM) mutations into hiPSC-derived neurons and observed expression of tau-RD at levels similar to total tau in postmortem AD brains. Tau aggregation occurred without the addition of recombinant tau fibrils. The conditioned media from tau-RD cultures contained tau-RD seeds, which were capable of inducing aggregate formation in homotypic mode in non-transduced recipient neuronal cultures. The resultant NFTs were thioflavin-positive, silver stain-positive, and assumed fibrillary appearance on transmission electron microscopy (TEM) with immunogold, which revealed paired helical filament 1 (PHF1)-positive NFTs, representing possible recruitment of endogenous tau in the aggregates. Functionally, expression of tau-RD caused neurotoxicity that manifested as axon retraction, synaptic density reduction, and enlargement of lysosomes. The results of our hiPSC study were reinforced by the observation that Tau-RD-LM is excreted in exosomes, which mediated the transfer of human tau to wild-type mouse neurons in vivo. Our hiPSC human neuronal system provides a model for further studies of tau aggregation and pathology, as well as a means to study transcellular propagation and related neurodegenerative mechanisms.

Protein Biomarkers and Neuroproteomics Characterization of Microvesicles/Exosomes from Human Cerebrospinal Fluid Following Traumatic Brain Injury

“…In terms of potentials of MV/E containing brain proteins versus freely soluble biomarkers in biofluids, there are several emerging studies showing the exosome- containing Tau could be a form of circulating biomarker for Alzheimer’s disease [44,45] and well as for post-TBI chronic traumatic encephalopathy [46]. The potential advantages of MVE-embedded protein markers are that since these proteins are shielded by the lipid bilayer membrane of MVE, (i) these proteins might be more preserved in their initial state; and (ii) they are protected from proteolytic degradation.…”

A Novel Tau Antibody Detecting the First Amino-Terminal Insert Reveals Conformational Differences Among Tau Isoforms

“…Besides the high variety of conformations adopted by monomeric Tau, there is also the diversity of pathological representation among the different Tauopathies. This diversity is thought to be attributed to unique Tau strains formed by the cross-talk between post-translational modifications and leading to the distinct Tau conformations that specify the structural differences of the deposited Tau filaments (Clavaguera et al, 2013;Guo and Lee, 2014;Boluda et al, 2015;Brettschneider et al, 2015;Goedert and Spillantini, 2017;Reilly et al, 2017). This heterogeneity of the deposits is evidenced by their different sensitivity when treated with proteases (Taniguchi-Watanabe et al, 2016).…”

“…In AD, all six isoforms are integrated into the neuronal inclusions, while in progressive supranuclear palsy and corticobasal degenerations the inclusions primarily contain 4R Tau and in Pick's disease the Pick bodies consist only of 3R Tau (Buee and Delacourte, 1999). Different Tau inclusions also vary in size and morphology, leading to the hypothesis that Tauopathies are characterized by unique Tau strains formed by a specific combination of post-translational modifications on the Tausplicing isoforms (Clavaguera et al, 2013;Guo and Lee, 2014;Boluda et al, 2015;Brettschneider et al, 2015;Goedert and Spillantini, 2017;Reilly et al, 2017). However, the underlying mechanism is still poorly understood.…”

From the prion-like propagation hypothesis to therapeutic strategies of anti-tau immunotherapy

“…In vitro, even if a few studies showed that extracellular tau may bind to neuronal receptors (muscarinic [83], Na + / K + ATPase (NKA) [161]…) and have toxic effects, most have shown that incubated aggregates/seeds are internalized by endocytosis and promote aggregation of overexpressed tau in cell lines [66,75,86,93,94,134,135,148,156,[170][171][172]. Nevertheless, most seeding assays use transfection reagents and thus bypass receptor-mediated endocytosis, which may be a critical step in prion-like propagation.…”