RESUMO
Oxidative stress is an early event in the pathogenesis of Alzheimer's disease (AD). We previously reported that, in SK-N-MC cells, the xanthine/xanthine oxidase (X-XOD) free radical generating system regulates the metabolism/processing of the amyloid-ß protein precursor (AßPP). Oxidative stress alters the two main cellular proteolytic machineries, the ubiquitin/proteasome (UPS) and the autophagy/lysosome systems, and recent studies have established connections between the malfunctioning of these and the pathogenesis of AD. The aim of the present work was to examine the involvement of these proteolytic systems in the regulation of AßPP metabolism by X-XOD. The proteasome inhibitor MG132 was found to accelerate the metabolism/processing of AßPP promoted by X-XOD because it significantly enhances the secretion of α-secretase-cleaved soluble AßPP and also the levels of both carboxy-terminal fragments (CTFs) produced by α- and ß-secretase. Further, MG132 modulated the intracellular accumulation of holo-AßPP and/or AßPP CTFs. This indicates that the X-XOD modulation of AßPP metabolism/processing involves the UPS pathway. With respect to the autophagy/lysosome pathway, the AßPP processing and intracellular location patterns induced by X-XOD treatment closely resembled those produced by the lysosome inhibitor ammonium chloride. The present results suggest that the regulation of AßPP metabolism/processing by mild oxidative stress requires UPS activity with a simultaneous reduction in that of the autophagy/lysosome system.
