Autophagy of amyloid beta-protein in differentiated neuroblastoma cells exposed to oxidative stress

Oxidative stress is considered important for the pathogenesis of Alzheimer disease (AD), which is characterized by the formation of senile plaques rich in amyloid beta-protein (A beta). A beta cytotoxicity has been found dependent on lysosomes, which are abundant in AD neurons and are shown to partially co-localize with A beta. To determine whether oxidative stress has any influence on the relationship between lysosomes and A beta(1-42) (the most toxic form of A beta), we studied the effect of hyperoxia (40% versus 8% ambient oxygen) on the intracellular localization of A beta(1-42) (assessed by immunocytochemistry) in retinoic acid differentiated SH-SY5Y neuroblastoma cells maintained in serum-free OptiMEM medium. In control cells, A beta(1-42) was mainly localized to small non-lysosomal cytoplasmic granules. Only occasionally A beta(1-42) was found in large (over I mu m) lysosomal-associated. membrane protein 2 positive vacuoles, devoid of the early endosomal marker rab5. These large A beta(1-42) -containing lysosomes were not detectable in the presence of serum (known to suppress autophagy), while their number increased dramatically (up to 24-fold) after exposure of cells to hyperoxia during 5 days. Activation of autophagy by hyperoxia was confirmed by transmission electron microscopy. Furthermore, an inhibitor of autophagic sequestration 3-methyladenine prevented the accumulation of A beta(1-42)-positive lysosomes due to hyperoxia. In parallel experiments, intralysosomal accumulation of A beta(1-40) following oxidative stress has been found as well. The results suggest that A beta can be autophagocytosed and its accumulation within neuronal lysosomes is enhanced by oxidative stress. (c) 2005 Elsevier Ireland Ltd. All rights reserved.