Oxidative stress up-regulates presenilin 1 in lipid rafts in neuronal cells

Abstract

Oxidative stress is associated with β‐amyloid peptide (Aβ) accumulation in the brains of Alzheimer's disease patients. Aβ is generated upon the sequential proteolytic cleavage of transmembrane amyloid precursor protein (APP) by two membrane‐bound proteases, β‐secretase (BACE1) and the γ‐secretase complex comprising presenilin 1 (PS1), nicastrin, APH‐1 and PEN‐2. Recent evidence suggests that significant amounts of BACE1 and γ‐secretase components localize in the cholesterol‐rich region of membranes known as lipid rafts, where Aβ production occurs preferentially. In this study, we investigated the effects of oxidative stress on the BACE1 and γ‐secretase components in lipid rafts using human neuroblastoma SH‐SY5Y cells exposed to ethacrynic acid (EA), a compound that induces cellular glutathione depletion. Following exposure of cells to EA, heme oxygenase‐1, a marker protein of oxidative stress, was strongly induced. Moreover, treatment with EA resulted in a significant increase in PS1 protein levels, but not those of nicastrin, APH‐1, PEN‐2 or BACE1, in both cell lysates and the lipid raft fraction. This increase in PS1 protein expression was prevented by co‐treatment with an antioxidant, N‐acetylcysteine (NAC). EA additionally induced a significant increase in PS1 mRNA expression, which was inhibited by NAC. Finally, EA treatment was found to promote Aβ secretion from cells expressing Swedish mutant APP. It appears that in our cell culture model, oxidative stress enhances PS1 protein levels in lipid rafts via up‐regulation of PS1 transcription, which may constitute the mechanism underlying the oxidative stress‐associated promotion of Aβ production. © 2009 Wiley‐Liss, Inc.