Evidence suggests that interactions between distinct tau polymorphs, monomeric tau, and the cellular environment cause different patterns of prion-like spatiotemporal propagation of pathology that dictate unique phenotypes and drive disease progression. Misfolded tau polymorphs are both ‘seed’ and ‘structure’ for templated amplification producing tau ‘strains’ with distinct conformations and activities. Existing cellular biosensors measuring tau aggregation sensitively detect seed presence or monitor monomer oligomerization, but do not inform dynamic aspects of tau monomer recruitment to disease-associated polymorphs.

We engineered human embryonic kidney cells with inducible full-length tau-green fluorescent protein (GFP) expression to carry disease-associated, detergent-insoluble tau fibrils derived from AD and CTE post-mortem brain. We then use biochemical and microscopy approaches to monitor tau seed amplification and degradation under certain conditions or with the influence of specific risk or resilience factors.

Tau seeds trigger pathological conversion of soluble tau-GFP monomer into a detergent-insoluble form, remaining stable for multiple weeks in culture. Suppressing soluble tau-GFP monomer expression causes a gradual degradation process which can be recovered when tau monomer expression is resumed. Levels of insoluble tau-GFP are dynamically responsive to cellular conditions, showing a robust increase with autophagy inhibition. Comparing biosensor cells bearing distinct tau aggregates underscores conformation-dependent functional differences. Lastly, we identified cellular proteomic factors which delay tau seed amplification using this platform.

We developed a novel cellular biosensor for monitoring the aggregation dynamics of AD and CTE brain-derived tau, expanding our understanding of disease-specific interactions between diverse protein aggregates and the cellular environment and allowing identification of disease risk and resilience mechanisms.