Oligomeric ß-Amyloid Suppresses Hippocampal γ-Oscillations through Activation of the mTOR/S6K1 Pathway.

Neuronal synchronization at gamma frequency (30-100 Hz: γ) is impaired in early-stage Alzheimer's disease (AD) patients and AD models. Oligomeric Aß1-42 caused a concentration-dependent reduction of γ-oscillation strength and regularity while increasing its frequency. The mTOR1 inhibitor rapamycin prevented the Aß1-42-induced suppression of γ-oscillations, whereas the mTOR activator leucine mimicked the Aß1-42-induced suppression. Activation of the downstream kinase S6K1, but not inhibition of eIF4E, was required for the Aß1-42-induced suppression. The involvement of the mTOR/S6K1 signaling in the Aß1-42-induced suppression was confirmed in Aß-overexpressing APP/PS1 mice, where inhibiting mTOR or S6K1 restored degraded γ-oscillations. To assess the network changes that may underlie the mTOR/S6K1 mediated γ-oscillation impairment in AD, we tested the effect of Aß1-42 on IPSCs and EPSCs recorded in pyramidal neurons. Aß1-42 reduced EPSC amplitude and frequency and IPSC frequency, which could be prevented by inhibiting mTOR or S6K1. These experiments indicate that in early AD, oligomer Aß1-42 impairs γ-oscillations by reducing inhibitory interneuron activity by activating the mTOR/S6K1 signaling pathway, which may contribute to early cognitive decline and provides new therapeutic targets.