Soluble form of the APP fragment, sAPPβ, positively regulates tau secretion.

Extracellular tau has been highlighted in the pathogenesis of Alzheimer disease (AD), which is the most common neurodegenerative disease. Pathological analyses as well as model animal studies suggest that amyloid-β peptide (Aβ) deposition facilitates the spreading of tau aggregation pathology via extracellular tau. However, the precise mechanism of tau secretion remains unknown. Here, we show that the overexpression of amyloid precursor protein (APP) enhances the secretion of tau phosphorylated at threonine 181 in mouse neuroblastoma Neuro2a cells. Moreover, we found that soluble amyloid precursor protein β (sAPPβ), which is generated by β-site APP cleaving enzyme 1 (BACE1), mediates tau secretion. Our results demonstrate that BACE1-mediated cleavage of APP plays pathological roles in AD pathogenesis by not only Aβ production, but by the spreading of tau aggregation pathology via sAPPβ in AD patients.