Why study the aggregation pathway of Tau?

Despite decades of research and discovery efforts, clinically robust diagnostic and therapeutic tools are lacking for patients afflicted with neurodegenerative diseases associated with neurofibrillary tangles made of the tau protein in the brain, also known as tauopathies that include Alzheimer’s disease (AD), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), and Chronic Traumatic Encephalopathy (CTE). Among the most significant findings of the past decade is that the intrinsically disordered tau protein, when unbound, forms amyloid fibrils with unique structures for each tauopathy across patients with the same disease. Hence, generating tauopathy specific fibrils are prime targets for biomedical studies. The specific unmet challenge that this team is targeting is the reliable generation of rationally designed, synthetic, tauopathy protein fibrils that adopt disease-specific structures found in AD, CBD, PSP or CTE and display shape-selective templated seeding of naïve tau in vitro and in cells.

The controlled assembly pathway of Tau into these exact pathological structures are the core tools needed for the screening of tauopathy-specific antibodies, medicinal compounds and other therapeutics.

Knowledge Gap?

Shape-controlled assembly of tau into well-defined fibril phenotypes along a predicted aggregation pathway has never been achieved to date, despite the critical importance of replicating pathological tau fibril phenotypes. Reliably replicating aggregation pathways that reproduce pathological hallmarks is a necessary starting point for screening medicinal compounds and developing tauopathy therapeutics.

Han Lab Strategy?

The Han lab engages in serious collaboration with neuroscientists and clinical researchers to help advance the development of therapeutic strategies for tauopathies. The role of the Han lab is to generate out of the box solutions because the “obvious” approaches have been tried and failed or are being tested by thousands of researchers. The Han lab is uniquely focusing on establishing the “molecular grammar” of Tau protein assembly. That includes identifying a peptide motif that forms strand-loop-strand (SLS) structures in 4R Tauopathy fibrils and can in and of itself form fibrils that display “infectious prion” properties, as well as uncovering the molecular signatures that guide Tau into forming in register aggregation to neat fibrils with active ends that display templating property as found in prions. This property of seeding-active fibrils is well known but its molecular basis is not, which means that this property cannot be easily replicated in the laboratory until the design principle of tau prions are uncovered. Furthermore, the Han lab discovered the critical role of structured water at specific residues in pinning tau molecules at hotspot residues to achieve robust in register stacking of tau into fibrils that are  fundamental to the prion-like properties of tauopathy mimicking fibrils.

Unique Han Lab Tools and Concepts:

Our Focus on visualizing the entire dynamic assembly process from the ensemble structure of tau in its IDP state to the folded structure of the assembled tau fibrils relies on pulsed dipolar electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR) and Cryogenic Electron Microscopy (CRYO-EM) to reach Angstrom to 10 nm scale distances. Double Electron Electron Resonance (DEER) yields a probability distribution of intra-tau distances, P(r), and is the first go-to-step to gain first insight to the complete conformational ensemble of Tau in IDP and/or fibril state. Furthermore, Overhauser Dynamic Nuclear Polarization (ODNP) spectroscopy of spin labeled tau is used to determine the local hydration water dynamics and 17O NMR chemical shift signatures to characterize the local structuring of water, both applied in solution state under ambient conditions.