Structural and pharmacological studies on the abnormal aggregation and normal function of tau

Tau is a microtubule-associated protein predominantly expressed in neuronal cells. In Alzheimer\u27s disease (AD), tau forms filamentous inclusions named neurofibrillary tangles. In addition, tau fibrillar lesions are also found in other neurodegenerative diseases. Accumulating data suggest the misfolding and amyloidogenesis of tau directly contributes to the onset and progression of tauopathies. Identification of tau genetic mutations in families afflicted by frontotemporal dementia and parksinsonism linked to chromosome-17 (FTDP-17) has unequivocally established the pathogenic role of tau aggregates in neurodegeneration. Therefore, tau has become a target of novel therapies for neurodegenerative diseases. However, our knowledge about the structural requirements for tau to form fibrillary tangles and associate with microtubules remains incomplete. We compared the function of two important VQIXXK motifs in the microtubule-binding domain, PHF6 and PHF6*, in tau fibrillization. Tau deletion and mutation constructs were generated and characterized for filament formation. The shared VQI sequence in both motifs is not absolutely required for tau assembly. However, K280 in PHF6* is inhibitory while K311 is essential for tau fibrillization. This is the first report that manipulation of a single residue in tau leads to complete elimination of tau fibrillization. The second part of my thesis was aimed at clarifying the largely unknown structural requirements for tau to productively bind to microtubules. PHF6, PHF6* and A6 motifs are all indispensable for tau to promote microtubule assembly. However, 7R4 does not have much influence on this. Further characterization indicates the lysines are important factors in tau-microtubule interactions, which was also demonstrated to be true for tau FTDP-17 mutations. This affords us new insights in understanding the pathogenic mechanism of tau mutations in neurodegenerative tauopathies. Lastly, we found that oleocanthal, a natural aldehydic compound in olive oil, is a potent inhibitor of tau aggregation. The action mode of oleocanthal in inhibiting tau aggregation was therefore investigated. We postulated that the aldehyde groups of oleocanthal probably react with the amino side chain of lysines in tau, which was verified in our studies using mass spectrometry. This has increased our understanding of tau aggregation inhibition and offered new thoughts in future drug design