A novel <i>C. elegans</i> model for MAPT/Tau spreading reveals genes critical for endolysosomal integrity and seeded MAPT/Tau aggregation

The spreading of MAPT/Tau pathology is closely associated with the progression of neurodegeneration and cognitive decline in Alzheimer disease and other tauopathies. A key event in this process is the rupture of endolysosomal vesicles following the intercellular transfer of MAPT/Tau aggregates, releasing the transferred MAPT/Tau species into the cytosol where they can promote the aggregation of endogenous MAPT/Tau. However, understanding of the cellular pathways involved in this process remains limited. In this study, we investigated cellular pathways that prevent endolysosomal vesicle rupture. We established a new <i>C. elegans</i> model of MAPT/Tau spreading by introducing an mCherry-labeled, disease-associated aggregation-prone fragment of human MAPT/Tau (F3ΔK281::mCh) into the six touch receptor neurons. F3ΔK281::mCh transgenic animals exhibited significant neurotoxicity and mechanosensory deficits due to the accumulation of this MAPT/Tau fragment. In addition, its intercellular transmission compromised the endolysosomal system in receiving hypodermal cells. Using this model, we conducted an unbiased genome-wide RNAi screen and identified 59 genes critical for maintaining endolysosomal integrity. GO-term analysis revealed an enrichment of genes related to the ESCRT complex, the ubiquitin-proteasome system, mRNA splicing, and fatty acid metabolism. Silencing of selected conserved genes exacerbated seeded MAPT/Tau aggregation in a human induced pluripotent stem cell (hiPSC)-derived cortical neuron model and triggered endolysosomal rupture in HEK293T cells, confirming the crucial role of endolysosomal damage in seeded MAPT/Tau aggregation. Overall, this study discovered novel cellular pathways that safeguard endolysosomal integrity. These findings may guide the development of therapeutics that improve endolysosomal integrity to halt the progression of MAPT/Tau pathology.<b>Abbreviations</b>: AD: Alzheimer disease; ALM: anterior lateral microtubule cell; AVM: anterior ventral microtubule cell; BWM: body wall muscle; <i>C. elegans</i>: <i>Caenorhabditis elegans</i>; DA: dopaminergic; hiPSC: human induced pluripotent stem cell; LGALS3: galectin 3; MAPT/Tau: microtubule associated protein tau; mCh: monomeric Cherry; PD: Parkinson disease; PLM: posterior lateral microtubule cell; PVM: posterior ventral microtubule cell; sfGFP: superfolder green flourescent protein; SNCA: synuclein alpha; nt-cntrl: non-targeting siRNA; rPHFs: recombinant paired helical filaments.