Long-term depression links amyloid-β to the pathological hyperphosphorylation of tau

In Alzheimer's disease, soluble oligomers of the amyloid-β peptide (Aβ_o) trigger a cascade of events that includes abnormal hyperphosphorylation of the protein tau, which is essential for pathogenesis. However, the mechanistic link between these two key pathological proteins remains unclear. Using hippocampal slices, we show here that an Aβ_o-mediated increase in glutamate release probability causes enhancement of synaptically evoked N-methyl-d-aspartate subtype glutamate receptor (NMDAR)-dependent long-term depression (LTD). We also find that elevated glutamate release probability is required for Aβ_o-induced pathological hyperphosphorylation of tau, which is likewise NMDAR dependent. Finally, we show that chronic, repeated chemical or optogenetic induction of NMDAR-dependent LTD alone is sufficient to cause tau hyperphosphorylation without Aβ_o. Together, these results support a possible causal chain in which Aβ_o increases glutamate release probability, thus leading to enhanced LTD induction, which in turn drives hyperphosphorylation of tau. Our data identify a mechanistic pathway linking the two critical pathogenic proteins of AD.