Extracellular tau oligomers exert neurocytotoxicity by triggering mitochondrial dysfunction

Background Abnormal tau aggregation is implicated in the development of neurodegenerative diseases such as Alzheimer's disease (AD). The presence of tau in the extracellular space and the spread of tau between nerve cells is associated with its toxicity. At present, researchers are trying to treat AD by limiting, blocking or removing extracellular tau. Objective To investigate the molecular mechanism underlying the cytotoxicity of extracellular tau oligomers. Methods The morphology of tau oligomers was observed by transmission electron microscopy. The neurocytotoxicity of tau oligomers was examined using CCK-8 assay. The localization of tau oligomers in cells was observed by laser confocal microscopy. The influence of tau oligomers on apoptosis was detected by Hoechst 33342/PI double-staining, Annexin V/PI double-staining and flow cytometry. JC-1 staining, DCFH-DA staining and Fluo-4 AM staining were used to evaluate the effect of tau oligomers on mitochondria. Western blot analysis was used to investigate the mechanism underlying the effects of tau oligomers on apoptosis and autophagy. Results After treatment with tau oligomers, the viability of SH-SY5Y cells decreased, and a typical apoptotic morphology was observed. Tau oligomers can enter cells, decrease the mitochondrial membrane potential, increase reactive oxygen species levels and drive calcium levels up to disrupt calcium homeostasis. The cytotoxicity of tau oligomers is closely related to the induction of mitochondrial apoptosis and blockade of mitophagy. Conclusions This study provides a molecular mechanism for understanding the cytotoxicity of extracellular tau oligomers and provides a therapeutic target for the development of effective treatment strategies for tau-related diseases.