O-GlcNAcylation promotes non-amyloidogenic processing of amyloid-β protein precursor via inhibition of endocytosis from the plasma membrane.

Amyloid-beta protein precursor (A beta PP) is transported to the plasma membrane, where it is sequentially cleaved by alpha-secretase and gamma-secretase. This is called non-amyloidogenic pathway since it precludes the production of amyloid-beta (A beta), the main culprit of Alzheimer's disease (AD). Alternatively, onceA beta PP undergoes clathrin-dependent endocytosis, it can be sequentially cleaved by beta-secretase and gamma-secretase at endosomes, producing A alpha(amyloidogenic pathway). beta -N-acetylglucosamine (GlcNAc) can be attached to serine/threonine residues of the target proteins. This novel type of O-linked glycosylation is called O-GlcNAcylation mediated by O-GlcNAc transferase (OGT). The removal of GlcNAc is mediated by O-GlcNAcase (OGN). Recently, it is shown that O-GlcNAcylation of A beta PP increases the non-amyloidogenic pathway. To investigate the regulatory role for O-GlcNAcylation in A beta PP processing, we first tested the effects of inhibitor for OGN, PUGNAc, on A beta PP metabolism in HeLa cells stably transfected with Swedish mutant form of A beta PP. Increasing O-GlcNAcylated A beta PP level increased beta-secretase product while decreased beta-secretase products. We found that PUGNAc increased the trafficking rate of A beta PP from the trans-Golgi network to the plasma membrane, and selectively decreased the endocytosis rate of A beta PP. These events may contribute to the increased A beta PP level in the plasma membrane by PUGNAc. Inhibiting clathrin-dependent endocytosis prevented the effect of PUGNAc on A beta, suggesting that the effect of PUGNAc was mainly mediated by decreasing A beta PP endocytosis. These results strongly indicate that O-GlcNAcylation promotes the plasma membrane localization of A beta PP, which enhances the non-amyloidogenic processing of A beta PP. Thus, O-GlcNAcylation of A beta PP can be a potential therapeutic strategy for AD.