AP-1 mediates β-amyloid-induced iNOS expression in PC12 cells via the ERK2 and p38 MAPK signaling pathways

Nitrosative stress with subsequent inflammatory cell death has been implicated in some neurodegenerative disorders such as Alzheimer's disease (AD). Expression of inducible nitric oxide synthase (iNOS) and production of nitric oxide (NO) have been frequently elevated in AD. In this study, we have investigated the molecular mechanisms underlying nitrosative stress induced by β-amyloid (Aβ), a neurotoxic peptide associated with senile plaques formed in the brains of patients with AD. Exposure of rat pheochromocytoma (PC12) cells to the Aβ resulted in increased mRNA and protein expression of iNOS and generation of NO. NO can rapidly interact with superoxide anion, forming more reactive peroxynitrite. Treatment of PC12 cells with Aβ led to increased peroxynitrite production and nitrotyrosine formation. Aβ induced activation of redox sensitive transcription factor activator protein-1 (AP-1), and AP-1 antisense oligonucleotide abolished the Aβ-induced iNOS expression. Moreover, Aβ transiently activated extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) via phosphorylation. Pharmacologic inhibition of both enzymes or dominant-negative mutation of ERK2 or p38 MAPK effectively down-regulated DNA binding as well as transcriptional activity of AP-1 and subsequent iNOS expression and NO production. The above findings suggest that Aβ induces iNOS expression in PC12 cells through activation of AP-1 which is regulated by upstream kinases, such as ERK and p38 MAPK.