Divergent pathways account for two distinct effects of amyloid β peptides on exocytosis and Ca2+ currents:: involvement of ROS and NF-κB

Amyloid peptides (AbetaPs) are implicated in neuronal death associated with Alzheimer's disease. Their toxicity involves disruption cellular Ca2+ homeostasis, leading to activation of caspases and cell death. Antioxidants can prevent such cell death and show beneficial clinical effects in Alzheimer's disease patients. Using the model neurosecretory cell line, PC12, we have shown that AbetaPs cause enhancement of evoked exocytosis via formation of a Cd2+-resistant Ca2+ influx pathway, and also cause selective, functional up-regulation of current through L-type Ca2+ channels. The involvement of reactive oxygen species (ROS) in these effects were investigated by examining the ability of various antioxidants to interfere with these responses. Both melatonin and ascorbic acid fully blocked the enhancement of catecholamine secretion caused by application of AbetaP((1-40)), as monitored in real time amperometrically, but inhibition of the transcriptional regulator NF-kappaB with SN-50 did not affect secretion. Enhanced immunofluorescence, observed in AbetaP-treated cells using a monoclonal antibody raised against the N-terminus of AbetaP, was also suppressed by melatonin. Ascorbic acid, melatonin and ebselen also fully prevented augmentation of whole-cell Ca2+ currents caused by application of AbetaP((1-40)). By contrast, inhibitors of NF-kappaB (sulfasalazine and SN-50) were able to prevent AbetaP induced Ca2+ channel current enhancement, whilst inhibitors of mitogen-activated protein kinase and protein kinase C could not. Our results indicate that augmentation or induction by AbetaPs of two important, distinct factors regulating Ca2+ homeostasis is mediated by increased ROS production, but only one of these (up-regulation of native Ca2+ channels) requires activation of NF-kappaB.