Iron-Export Ferroxidase Activity of β-Amyloid Precursor Protein Is Inhibited by Zinc in Alzheimer's Disease

Alzheimer's Disease (AD) is complicated by pro-oxidant intraneuronal Fe2+ elevation as well as extracellular Zn2+ accumulation within amyloid plaque. We found that the AD beta-amyloid protein precursor (APP) possesses ferroxidase activity mediated by a conserved H-ferritin-like active site, which is inhibited specifically by Zn2+. Like ceruloplasmin, APP catalytically oxidizes Fe2+, loads Fe3+ into transferrin, and has a major interaction with ferroportin in HEK293T cells (that lack ceruloplasmin) and in human cortical tissue. Ablation of APP in HEK293T cells and primary neurons induces marked iron retention, whereas increasing APP695 promotes iron export. Unlike normal mice, APP(-/-) mice are vulnerable to dietary iron exposure, which causes Fe2+ accumulation and oxidative stress in cortical neurons. Paralleling iron accumulation, APP ferroxidase activity in AD postmortem neocortex is inhibited by endogenous Zn2+, which we demonstrate can originate from Zn2+-laden amyloid aggregates and correlates with A beta burden. Abnormal exchange of cortical zinc may link amyloid pathology with neuronal iron accumulation in AD.