Proteomic analysis links truncated tau to lysosome motility, autophagy, and endo‐lysosomal dysfunction

Abstract INTRODUCTION Tauopathies involve progressive accumulation of abnormal tau species that disrupt the autophagy‐lysosomal pathway (ALP), critical for degrading intracellular macromolecules and aggregates, leading to toxicity and cell death. This study examines how overexpression of the N‐terminally truncated Tau35 protein affects proteolytic pathways, including autophagy and endo‐lysosomal processes. METHODS Using the Tau35 mouse model and SH‐SY5Y human neuroblastoma cells stably expressing Tau35 or full‐length tau, we assessed protein degradation and lysosomal function via Western blotting, proteomics of lysosome‐enriched brain fractions, cathepsin activity assays, endocytosis/proteolysis assays, and live‐cell imaging using LysoTracker. RESULTS We identified early endo‐lysosomal alterations associated with Tau35 expression, including increased endocytosis, disrupted autophagic flux, proteolytic impairment, and lysosomal motility defects. DISCUSSION These findings extend previous research by elucidating Tau35‐induced dysfunction in intracellular degradation systems and offer mechanistic insight into tauopathy progression. This work provides a foundation for developing targeted therapies to restore acidification, proteostasis, and lysosomal function in tauopathies. Highlights Tau35, an N‐terminally truncated tau fragment, disrupts proteolytic pathways : We show that Tau35 overexpression leads to significant alterations in autophagy and endo‐lysosomal function. Endo‐lysosomal dysfunction is an early pathological event : Our findings demonstrate early‐stage increases in endocytosis, impaired proteolytic activity, altered autophagic flux, and disrupted lysosomal motility in Tau35‐expressing models. In vivo and in vitro models confirm consistent pathogenic signatures : Parallel studies in a Tau35 mouse model and SH‐SY5Y cells reveal converging cellular and molecular dysfunctions. Lysosome‐enriched proteomics reveals novel pathway alterations : Proteomic profiling of lysosomal fractions identifies Tau35‐specific protein dysregulation contributing to disease pathology. Mechanistic insights into tauopathy progression : These results provide a mechanistic understanding of how truncated tau species contribute to neuronal dysfunction, offering a rationale for targeting endo‐lysosomal pathways in therapeutic development.