Nanoscale imaging of pT217‐tau in aged rhesus macaque: Trans‐synaptic propagation and seeding of tau pathology in entorhinal cortex

Tau pathology in Alzheimer’s Disease (AD) targets higher cortical circuits, propagating from the entorhinal cortex (ERC) to “seed” pathology throughout the network. Recent discoveries indicate that tau phosphorylated at threonine-217 (pT217-tau) is captured in CSF and plasma as an early biomarker of AD. However, the role of pT217-tau in brain tau pathology is unknown, especially as soluble tau species are dephosphorylated postmortem in humans. We examined the ultrastructural localization of pT217-tau in layer II ERC of the rhesus macaque model of sporadic AD, focusing on evidence of propagation between neurons.