APP mediates tau uptake and its overexpression leads to the exacerbated tau pathology.

Alzheimer's disease (AD), as the most common type of dementia, has two pathological hallmarks, extracellular senile plaques composed of β-amyloid peptides and intracellular neurofibrillary tangles containing phosphorylated-tau protein. Amyloid precursor protein (APP) and tau each play central roles in AD, although how APP and tau interact and synergize in the disease process is largely unknown. Here, we showed that soluble tau interacts with the N-terminal of APP in vitro in cell-free and cell culture systems, which can be further confirmed in vivo in the brain of 3XTg-AD mouse. In addition, APP is involved in the cellular uptake of tau through endocytosis. APP knockdown or N-terminal APP-specific antagonist 6KApoEp can prevent tau uptake in vitro, resulting in an extracellular tau accumulation in cultured neuronal cells. Interestingly, in APP/PS1 transgenic mouse brain, the overexpression of APP exacerbated tau propagation. Moreover, in the human tau transgenic mouse brain, overexpression of APP promotes tau phosphorylation, which is significantly remediated by 6KapoEp. All these results demonstrate the important role of APP in the tauopathy of AD. Targeting the pathological interaction of N-terminal APP with tau may provide an important therapeutic strategy for AD.