Tau is a microtubule-associated protein well known for its stabilization of microtubules in axons. Recently, it has emerged that tau participates in synaptic function as part of the molecular pathway leading to amyloid-beta (A␤)-driven synaptotoxicity in the context of Alzheimer's disease. Here, we report the implication of tau in the profound functional synaptic modification associated with synaptic plasticity. By exposing murine cultured cortical neurons to a pharmacological synaptic activation, we induced translocation of endogenous tau from the dendritic to the postsynaptic compartment. We observed similar tau translocation to the postsynaptic fraction in acute hippocampal slices subjected to long-term potentiation. When we performed live confocal microscopy on cortical neurons transfected with human-tau-GFP, we visualized an activity-dependent accumulation of tau in the postsynaptic density. Coprecipitation using phalloidin revealed that tau interacts with the most predominant cytoskeletal component present, filamentous actin. Finally, when we exposed cortical cultures to 100 nM human synthetic A␤ oligomers (A␤o's) for 15 min, we induced mislocalization of tau into the spines under resting conditions and abrogated subsequent activity-dependent synaptic tau translocation. These changes in synaptic tau dynamics may rely on a difference between physiological and pathological phosphorylation of tau. Together, these results suggest that intense synaptic activity drives tau to the postsynaptic density of excitatory synapses and that A␤o-driven tau translocation to the spine deserves further investigation as a key event toward synaptotoxicity in neurodegenerative diseases.

Highlights d Autophagy induction in hippocampal neurons is required to promote memory formation d Hippocampal autophagy induction enhances activitydependent synaptic plasticity d Inducing autophagy in old hippocampi is sufficient to reverse age-impaired memory d Autophagy integrates the effects of youthful systemic factors in the aged brain