Transgenic Dendra2::tau expression allows in vivo monitoring of tau proteostasis in Caenorhabditis elegans

Protein homeostasis is perturbed in aging-related neurodegenerative diseases called tauopathies, which are pathologically characterized by aggregation of the microtubule-associated protein tau (encoded by the human MAPT gene). Transgenic Caenorhabditis elegans serve as a powerful model organism to study tauopathy disease mechanisms, but moderating transgenic expression level has proven problematic. To study neuronal tau proteostasis, we generated a suite of transgenic strains expressing low, medium or high levels of Dendra2::tau fusion proteins by comparing integrated multicopy transgene arrays with single-copy safe-harbor locus strains generated by recombinase-mediated cassette exchange. Multicopy Dendra2::tau strains exhibited expression level-dependent neuronal dysfunction that was modifiable by known genetic suppressors or an enhancer of tauopathy. Single-copy Dendra2::tau strains lacked distinguishable phenotypes on their own but enabled detection of enhancer-driven neuronal dysfunction. We used multicopy Dendra2::tau strains in optical pulse-chase experiments measuring tau turnover in vivo and found that Dendra2::tau turned over faster than the relatively stable Dendra2. Furthermore, Dendra2::tau turnover was dependent on the protein expression level and independent of co-expression with human TDP-43 (officially known as TARDBP), an aggregating protein interacting with pathological tau. We present Dendra2::tau transgenic C. elegans as a novel tool for investigating molecular mechanisms of tau proteostasis.