ER Stress-Mediated Apoptotic Pathway Induced by Aβ Peptide Requires the Presence of Functional Mitochondria

Abstract

Amyloid-β (Aβ) peptide plays a significant role in the pathogenesis of Alzheimer's disease (AD). Previously we found that Aβ induces both mitochondrial and endoplasmic reticulum (ER) dysfunction leading to apoptosis, and now we address the relevance of ER-mitochondria crosstalk in apoptotic cell death triggered by Aβ peptide. Using mitochondrial DNA-depleted ρ0 cells derived from the human NT2 teratocarcinoma cell line, characterized by the absence of functional mitochondria, and the parental ρ+ cells, we report here that treatment with the synthetic Aβ_1-40 peptide, or the classical ER stressors thapsigargin or brefeldin A, increases GRP78 expression levels and caspase activity, two ER stress markers, and also depletes ER calcium stores. Significantly, we show that the presence of functional mitochondria is required for ER stress-mediated apoptotic cell death triggered by toxic insults such as Aβ. We found that the increase in the levels of the pro-apoptotic transcription factor GADD153/CHOP, which mediates ER stress-induced cell death, as well as caspase-9 and -3 activation and increased number of TUNEL-positive cells, occurs in treated parental ρ+ cells but is abolished in ρ0 cells. Our results strongly support the close communication between ER and mitochondria during apoptotic cell death induced by the Aβ peptide and provide insights into the molecular cascade of cell death in AD.