Intraneuronal amyloid-beta1-42 production triggered by sustained increase of cytosolic calcium concentration induces neuronal death.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence in the brain of senile plaques which contain an amyloid core made of beta-amyloid peptide (Abeta). Abeta is produced by the cleavage of the amyloid precursor protein (APP). Since impairment of neuronal calcium signalling has been causally implicated in ageing and AD, we have investigated the influence of an influx of extracellular calcium on the metabolism of human APP in rat cortical neurones. We report that a high cytosolic calcium concentration, induced by neuronal depolarization, inhibits the alpha-secretase cleavage of APP and triggers the accumulation of intraneuronal C-terminal fragments produced by the beta-cleavage of the protein (CTFbeta). Increase in cytosolic calcium concentration specifically induces the production of large amounts of intraneuronal Abeta1-42, which is inhibited by nimodipine, a specific antagonist of l-type calcium channels. Moreover, calcium release from endoplasmic reticulum is not sufficient to induce the production of intraneuronal Abeta, which requires influx of extracellular calcium mediated by the capacitative calcium entry mechanism. Therefore, a sustained high concentration of cytosolic calcium is needed to induce the production of intraneuronal Abeta1-42 from human APP. Our results show that this accumulation of intraneuronal Abeta1-42 induces neuronal death, which is prevented by a functional gamma-secretase inhibitor.