Alzheimer's disease linked Aß42 exerts product feedback inhibition on γ-secretase impairing downstream cell signaling.

ABSTRACT

Amyloid ß (Aß) peptides accumulating in the brain are proposed to trigger Alzheimer's disease (AD). However, molecular cascades underlying their toxicity are poorly defined. Here, we explored a novel hypothesis for Aß42 toxicity that arises from its proven affinity for γ-secretases. We hypothesized that the reported increases in Aß42, particularly in the endolysosomal compartment, promote the establishment of a product feedback inhibitory mechanism on γ-secretases, and thereby impair downstream signaling events. We conducted kinetic analyses of γ-secretase activity in cell-free systems in the presence of Aß, as well as cell-based and ex vivo assays in neuronal cell lines, neurons, and brain synaptosomes to assess the impact of Aß on γ-secretases. We show that human Aß42 peptides, but neither murine Aß42 nor human Aß17-42 (p3), inhibit γ-secretases and trigger accumulation of unprocessed substrates in neurons, including C-terminal fragments (CTFs) of APP, p75, and pan-cadherin. Moreover, Aß42 treatment dysregulated cellular homeostasis, as shown by the induction of p75-dependent neuronal death in two distinct cellular systems. Our findings raise the possibility that pathological elevations in Aß42 contribute to cellular toxicity via the γ-secretase inhibition, and provide a novel conceptual framework to address Aß toxicity in the context of γ-secretase-dependent homeostatic signaling.