Investigating the Effect of Phosphorylated Tau 217 on Exocytosis of Synaptic Vesicles in Hippocampal Neurons

Abstract

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, characterized by neurofibrillary tangles containing hyperphosphorylated tau protein, with phosphorylation at threonine 217 (p-tau217) serving as a biomarker for AD pathogenesis. The functional impact of p-tau217 on synaptic transmission remains elusive. This study investigated the effects of p-tau217 on synaptic vesicle exocytosis in primary hippocampal neurons by infecting cultured neurons with adeno-associated virus constructs including wild-type tau, tau T217E (phosphorylation-mimicking mutant), and tau T217A (nonphosphorylation-mimicking mutant). Synaptic vesicle exocytosis was assessed using FM 4-64 destaining assays, and synaptic density was evaluated through immunofluorescence staining using antibodies against VGlut1 and PSD95, and inhibitory synaptic vesicle exocytosis was examined using VGAT-CypHer5E imaging. I found that the release amount of FM 4-64 during 1200 electrical stimuli significantly decreased in neurons infected with tau T217E compared with neurons with tau WT and increased decay time constants for FM 4-64, indicating that phosphorylated tau at 217 alters synaptic exocytosis and kinetics of exocytosis. Immunofluorescence analysis revealed a reduction in colocalized synaptic puncta density in T217E-expressing neurons, with presynaptic density being particularly affected while postsynaptic density remained largely unchanged. These findings indicate that phosphorylated tau217 alters synapses and particularly, presynaptic terminals in hippocampal neurons, which play an important roles in learning and memory. Based on these observations, I conclude that phosphorylated tau at 217 alters synaptic functions and synapse organization in hippocampal neurons, aggravating AD pathogenesis. My findings advance understanding synaptic dysfunction in tauopathies and support phosphorylated tau at 217 as a potential therapeutic target for AD intervention.

Date of Award	2025
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Hyo Keun PARK (Supervisor)