Functional Characterization of Tau Mutation and Post-translational Modifications

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PROJECT SUMMARY/ ABSTRACT Protein aggregation is a hallmark of neurodegenerative diseases, including Alzheimer's Disease, and these diseases lack effective therapeutics. We currently lack an understanding of the molecular and cellular mechanisms controlling protein aggregation in the human brain, which would enable new therapeutic strategies. The protein tau aggregates in the brain in a number of neurodegenerative diseases called tauopathies, including Alzheimer's Disease. In early stages of disease, tau aggregates only in specific neurons despite being expressed in every neuron in the brain, implying that specific factors in the cellular environment predispose tau to aggregation. Similarly, tau mutations are associated with the onset of only specific tauopathies. Together, these disease features imply that tau is exquisitely sensitive to both its sequence properties and its cellular environment. Post-translational modifications (PTM) are a mechanism by which the cellular environment can act on a protein similarly to mutation. Tau is heavily post-translationally modified and changes to tau PTMs are correlated with progression of disease. Indeed, tau phosphorylation and proteolysis have been proposed to be central events in the onset and progression of tauopathies. Similarly, mutations are correlated with early disease onset and are known to hasten in vitro tau aggregation. Mutations can also cause changes in PTMs by changing tau interaction partners. The function and causality of these changes to tau sequence, however, is unknown. I hypothesize that PTMs and mutations license tau to access specific conformations to form aggregates. The goal of this proposal is to comprehensively identify (1) the biological basis of tau PTM changes and (2) how tau mutation and PTMs cause aggregation. I have shown that mitochondrial electron transport chain dysfunction causes a remodeling of tau PTMs, including the accumulation of a tau proteolytic fragment. In Aim 1, I will acquire new training in mass spectrometry (MS)-based proteomics to determine the tau PTM changes that occur due to ETC dysfunction and how those control tau aggregation. In Aim 2, I will use deep mutational scanning (DMS) to comprehensively probe tau's sequence-structure relationship. As part of Aim 2, I will use cross-link MS to directly compare in vitro and in vivo tau states to will reveal the structural mechanisms for the identified PTM and sequence changes. I am ideally positioned to complete the proposed research, as this proposal complements my training in protein biophysics and functional genomics in iPSC-derived neurons with novel MS-based techniques. Completion of this proposal will identify which PTMs and mutations control tau aggregation, as well as the development of new technologies to probe tau structure in vitro and in vivo. Completion of this proposal will provide me with essential skills and training to be a successful independent investigator.