Aim: Hyperphosphorylated tau plays a crucial role in the pathogenesis of Alzheimer's disease (AD). Whether mammalian target of rapamycin (mTOR) directly interacts with the Tau protein at Ser214, Ser356 and Thr231 is not clear. This study aimed to investigate whether mTOR-regulated tau phosphorylation disrupts mitochondrial dynamics and function and whether rapamycin, an mTOR inhibitor, can modulate tau phosphorylation levels and attenuate AD-related alterations. Methods: Adeno-associated virus (AAV) vectors were used to intracranially deliver the TauS214E/T231E/S356E (Tau3E) variant into 2-month-old C57BL/6 mice. The mice were intraperitoneally administered the mTOR inhibitor rapamycin for one week, followed by assessment via the Morris water maze test. Western blot analysis, immunofluorescence staining, and flow cytometry were employed to measure the expression levels of mTOR, p70S6K, and tau; mitochondrial dynamics; and reactive oxygen species (ROS) in HT22 cells and a mouse model overexpressing Tau3E, as well as in postmortem brain tissues from AD patients. Results: p-mTORS2448 colocalized with p-TauSer214, p-TauSer356, and p-TauThr231 in the hippocampal CA3 region of AD patients. HT22 cells and C57BL/6 mice overexpressing Tau3E presented elevated levels of p-mTOR, downstream target p-p70S6K, and ROS production; mitochondrial fragmentation; and p-TauSer214, p-TauSer356, and p-TauThr231. Rapamycin treatment partially mitigated the cognitive and molecular alterations in Tau3E mice. Conclusion: This study revealed a causal link between Tau phosphorylation at Ser214, Ser356, and p-Thr231 and mTOR upregulation and downstream impairments in ROS, mitochondrial dysfunction and cognitive function. Treatment using mTOR inhibitor rapamycin (i.p.) can alleviate impairment, reduce p-Tau and restore mitochondrial homeostasis, neuronal loss and cognitive impairment in mice.
