Aggregation of the microtubule-associated protein tau into amyloid fibrils with distinct conformations is hallmark to several neurodegenerative diseases termed tauopathies. Mechanisms underlying structural polymorphism observed across these diseases remain largely unclear. However, the persistence of distinct fibril conformations in specific tauopathies suggests that disease-specific environments influence both the pathological progression and aggregation of tau.
Chronic traumatic encephalopathy (CTE) is characterised by the accumulation of hyperphosphorylated tau (p-tau) amyloid within neuronal cell bodies and processes, concentrated around small blood vessels at the depths of cortical sulci. CTE is a primary tauopathy, in which tau aggregation is the sole defining feature of the disease, and it lacks any other validated biomarkers, creating substantial diagnostic challenges. Postmortem neuropathological examination of p-tau lesions remains the only reliable means of CTE diagnosis. Unlike other common tauopathies such as Alzheimer’s disease, which are associated with ageing and genetic risk factors, the only established risk factor for CTE is prolonged exposure to repetitive head impacts (RHI).
We aim to develop novel fluorescent probes which identify and discriminate CTE pathology through structural differences between p-tau amyloid polymorphs. We report an in vitro system for recombinantly producing tau amyloid filaments with polymorphic diversity, including the use of cryo electron microscopy (cryo-EM) to identify potential polymorphs associated with CTE and other tauopathies. Produced filaments are utilised to develop a multivariate fluorescence array, leveraging advances in protein adaptive differential scanning fluorometry (paDSF) and excitation multiplexed bright emission recordings (EMBER) to identify candidate molecules with desirable properties. In parallel, pathological labelling by candidate probes are tested using a unique repository of human CTE lesions that are under the custodianship of the Australian Sports Brain Bank (ASBB). Immunohistochemistry (IHC) and immunofluorescence (IF) approaches are used to reveal tau deposition patterns and other histological features in both CTE and other tauopathies within formalin-fixed paraffin-embedded human cortex tissue. Establishment of these workflows is critical, for both the validation of candidate probes in situ and as an entry point for the potential discrimination and accurate diagnosis of CTE in living patients.