Imaging of Tau and Microtubules to Study Mechanisms of Tau Pathologies and Neurodegeneration

The nervous system undergoes constant remodeling and adapting of its structural organization to fulfill its function, the propagation and processing of information. The structural backbone of neurons are arrays of microtubules (MTs) maintaining their specialized morphologies and serving as railway system for the transport of cargoes and information. The functional regulation of this complex system is based on many different factors, while microtubule-associated proteins (MAPs) like tau being one of them. The tau protein is of particular interest as it plays a central role in numerous neurodegenerative diseases, called tauopathies, where Alzheimer’s Disease (AD) is the most common and prominent example. Hallmark of tauopathies such as AD is the aggregation and increased phosphorylation of tau, while also many other post-translational modifications (PTMs) of the protein are described and linked to neurodegeneration. Scope of this thesis are investigations on how the neuronal MTs, MT-dynamics and MT-dependent transport are affected by post-translational changes of the tau protein. A new type of toxic gain of function of tau is described, as it impairs axonal transport when cleaved at a diseases relevant site and microtubule-targeting drugs are introduced as pharmacological modifiers of MAP-microtubule interaction. The effect of MT-stabilization by Epothilone D on the MT-cytoskeleton as well as the effect of a tau knockout is further investigated by cutting-edge microscopy (DNA-PAINT SMLM) and algorithm-based quantification of the MT array. Changes of the MT organization and structure on the level of individual MTs upon stabilization and tau knockout are described. Accumulating evidence suggests that pathologically modified monomeric and soluble oligomeric forms of tau should be considered as harmful tau species. Hence, a cell-based model allowing investigations of disease-like modified tau, its oligomerization, and MT-interaction is implemented enabling the screening for modulators of early-stage aggregation and phosphorylation of tau. Potential drug candidates with polypharmacological activity are presented