Elucidating the role of autophagy in the clearance of phosphorylated tau protein in human neurons

More than 40 million people world-wide suffer from tauopathies–neurodegenerative diseases in which the aggregation of microtubule-associated protein tau into intracellular inclusions is a core pathology. Recent studies have shown that the ubiquitin-proteasome system (UPS) and the autophagy pathway are responsible for the normal turnover of tau in neurons. Autophagy is a conserved cellular mechanism that is essential for neuronal homeostasis and impaired as a result of aging, which is the primary risk factor for most tauopathies. Thus, we hypothesized that dysfunctions in the autophagy pathway impair turnover of tau, and thus facilitate pathogenic aggregation. To test this hypothesis, we first treated human induced pluripotent stem cell (hiPSC)-derived neurons with two compounds that have been shown to promote autophagy, and found that these compounds decreased levels of phosphorylated tau protein, suggesting that autophagy may mediate homeostatic clearance of phospho-tau in human neurons. We also found that inhibition of the UPS induces autophagy and promotes the clearance of both phospho-tau and total tau non-selectively.In order to identify whether autophagy truly regulates the clearance of phosphorylated tau, we set out to establish a CRISPR/Cas9-based system that would allow us to disrupt autophagy in an efficient and inducible fashion. We have characterized two inducible systems, gathering a foundational understanding of how the system can be applied to genetic screens in hiPSC-derived cell types. Thus, this study both expands on the current knowledge regarding degradation of tau in human neurons and lays the groundwork for further genetic studies using an inducible-Cas9 system