The presence of disease‐associated tau leads to adverse effects on the autophagy and endolysosomal pathway in a cell model of tauopathy

Abstract Background Dysfunctions in the autophagy and endolysosomal pathways have been reported in Alzheimer’s Disease and related tauopathies. The presence of disease‐associated tau itself may play a role in damaging these pathways leading to its altered clearance. Minimal expression of a disease‐associated truncated tau species (Tau35) in mice results in a progressive tauopathy phenotype, including increased tau phosphorylation, cognitive and behavioural abnormalities and impaired protein clearance. In this study, we sought to explore the effects of Tau35 on the autophagy and endolysosomal pathway in cultured cells expressing Tau35 and from Tau35 mice. Method Chinese hamster ovary (CHO) cells stably expressing Tau35 (CHO‐Tau35) or full‐length human 2N4R tau (CHO‐FL) were generated. Primary cortical neurons from Tau35 transgenic and wild‐type mice were isolated and cultured for 14 days in vitro (DIV). Cells were fixed for immunocytochemistry or lysed to isolate protein/RNA for western blotting and RT‐qPCR to detect the effect of Tau35 expression on autophagy and lysosomal‐related proteins and genes. Result CHO‐Tau35 cells exhibited a marked reduction in several autophagy and lysosomal‐related markers, including LC3‐II, LAMP2 and cathepsin D. CHO‐Tau35 cells also accumulated lipid droplets and showed disruptions in mammalian target of rapamycin complex 1 (mTORC1) activity and autophagic flux. Moreover, Tau35 expression also resulted in alterations in early endocytic markers, including EEA1. Similar reductions in autophagic and endosomal markers were observed in primary cortical neurons cultured from Tau35 mice. Notably, the nuclear translocation of transcription factor EB (TFEB), a key mediator of lysosomal biogenesis, as well as the transcription of several TFEB‐target genes, was significantly reduced in both CHO‐FL and CHO‐Tau35 cells. Conclusion Our findings suggest that disease‐associated truncated tau damages the clearance of cellular proteins and reduces TFEB‐mediated lysosomal biogenesis. Investigating whether autophagy is disrupted due to tau‐induced lysosomal dysfunction may lead to the identification of novel therapeutic targets for dementia.