Amplification of seeding-competent tau aggregates by PMCA in human and experimental tauopathies

Tau assemblies, associated with tauopathies, are believed to self-propagate through prion-like mechanisms in the central nervous system, driving neurodegeneration. Recently, protein seed amplification assays have emerged as highly sensitive methods for detecting trace amounts of misfolded protein assemblies across various neurodegenerative diseases. In this study, we utilized protein misfolding cyclic amplification (PMCA) to demonstrate that tau assemblies from the brains of transgenic mice or human patients with tauopathies can be efficiently amplified. Amplification was achieved using complex matrix substrates, such as brain homogenates or cell lysates expressing aggregation-prone mutant tau proteins, with heparin as a cofactor. This assay enabled the highly sensitive detection of tau assemblies, even at 1-million-fold dilutions of brain homogenate from aged and symptomatic THY-Tau30 transgenic mice (a model of tauopathy) and human cases of frontotemporal lobar degeneration (FTLD-P301L). Tau assemblies from Alzheimer's disease (AD) patients were also successfully amplified, albeit with lower sensitivity compared to other tauopathies. Critically, the PMCA-generated tau assemblies retained seeding competence, inducing further tau aggregation in reporter tau "biosensor" cells and in young THY-Tau30 mice following intracerebral injection. Together, our findings establish PMCA as an in vitro model for studying the seeded aggregation of tau assemblies, providing a powerful tool to advance research into tau aggregation mechanisms and the development of therapeutic interventions.