Sensitive detection and propagation of brain-derived tau assemblies in HEK293 based wild-type tau seeding assays

The assembly of tau into filaments defines the tauopathies, a group of neurodegenerative diseases including Alzheimer’s disease (AD), Pick’s disease (PiD), corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP). The seeded aggregation of tau has been modelled in cell culture using pro-aggregant modifications such as truncation of the N- and C-termini and point-mutations within the tau microtubule-binding repeat domain. While providing experimental convenience, this limits the applicability of research findings to sporadic disease, where filaments contain wild-type, full-length tau isoforms. We therefore aimed to develop a sensitive and specific biosensor assay for the seeded aggregation of brain-derived tau species utilizing full-length, wild-type tau stably expressed in HEK293 cells. We show that addition of brain-derived tau extracted from cases of AD, PiD, CBD, or PSP induces the formation of HA- or GFP-tagged 0N3R or 0N4R tau aggregates. By isolating and expanding a single cell containing AD-seeded aggregates, we generated a cell line that propagates insoluble tau. We demonstrate that HEK293-propagated tau is hyperphosphorylated at disease relevant sites and retains a seeding profile similar to AD brain-derived material. We propose that these cell lines will aid pre-clinical, high-throughput screening for modifiers of seeded aggregation with greater conformational and strain specificity than existing cell-based biosensor assays.