Role of methionine 35 in the intracellular Ca 2+ homeostasis dysregulation and Ca 2+ ‐dependent apoptosis induced by amyloid β‐peptide in human neuroblastoma IMR32 cells

Amyloid β‐peptide (Aβ) plays a fundamental role in the pathogenesis of Alzheimer’s disease. We recently reported that the redox state of the methionine residue in position 35 of amyloid β‐peptide (Aβ) 1–42 (Met35) strongly affects the peptide’s ability to trigger apoptosis and is thus a major determinant of its neurotoxicity. Dysregulation of intracellular Ca 2+ homeostasis resulting in the activation of pro‐apoptotic pathways has been proposed as a mechanism underlying Aβ toxicity. Therefore, we investigated correlations between the Met35 redox state, Aβ toxicity, and altered intracellular Ca 2+ signaling in human neuroblastoma IMR32 cells. Cells incubated for 6–24 h with 10 μM Aβ1–42 exhibited significantly increased KCl‐induced Ca 2+ transient amplitudes and resting free Ca 2+ concentrations. Nifedipine‐sensitive Ca 2+ current densities and Ca v 1 channel expression were markedly enhanced by Aβ1–42. None of these effects were observed when cells were exposed to Aβ containing oxidized Met35 (Aβ1–42 Met35‐Ox ). Cell pre‐treatment with the intracellular Ca 2+ chelator 1,2‐bis(2‐aminophenoxy)ethane‐ N,N,N’,N’ ‐tetraacetic acid acetoxymethyl ester (1 μM) or the Ca v 1 channel blocker nifedipine (5 μM) significantly attenuated Aβ1–42‐induced apoptosis but had no effect on Aβ1–42 Met35‐Ox toxicity. Collectively, these data suggest that reduced Met35 plays a critical role in Aβ1–42 toxicity by rendering the peptide capable of disrupting intracellular Ca 2+ homeostasis and thereby provoking apoptotic cell death.