Inhibition of Intracellular Cholesterol Transport Alters Presenilin Localization and Amyloid Precursor Protein Processing in Neuronal Cells

Abstract

Generation of amyloid-beta (Abeta) from the amyloid precursor protein (APP) requires proteolytic cleavage by two proteases, beta- and gamma-secretase. Several lines of evidence suggest a role for cholesterol on secretase activities, although the responsible cellular mechanisms remain unclear. Here we show that alterations in cholesterol transport from late endocytic organelles to the endoplasmic reticulum have important consequences for both APP processing and the localization of gamma-secretase-associated presenilins (PS). Exposure of neuronal cells to cholesterol transport-inhibiting agents resulted in a marked decrease in beta-cleavage of full-length APP. In contrast, gamma-secretase activity on APP C-terminal fragments was enhanced, increasing the production of both Abeta40 and Abeta42. Remarkably, retention of cholesterol in endosomal/lysosomal compartments induced PS1 and PS2 to accumulate in Rab7-positive vesicular organelles implicated in cholesterol sorting. Accumulation of PS in vesicular compartments was prominent in both Chinese hamster ovary cells deficient in Niemann-Pick C1 protein as well as in neuronal cells exposed to the cholesterol transport-inhibiting agent U18666A. Because Abeta42 also localized to PS1-containing vesicular compartments, organelles involved in cholesterol transport might represent an important site for gamma-secretase activity. Our results suggest that the subcellular distribution of cholesterol may be an important factor in how cholesterol alters Abeta production and the risk of Alzheimer's disease.

Association of γ-Secretase with Lipid Rafts in Post-Golgi and Endosome Membranes

“…However, cholesterol accumulates in late endosome-like storage organelles when intracellular cholesterol transport is inhibited. Interestingly, PS1 and PS2 also redistribute to these organelles and consequently result in enhanced ␥-secretase processing of APP (35). In agreement with these data, we show that components of the ␥-secretase complex reside in cholesterol-rich domains of TGN and TGN-derived vesicles (containing syntaxin 6 and VAMP4), and recycling endosomes (containing syntaxin 13) and are not readily detectable in plasma membrane rafts (containing SNAP-23).…”

“…First, DIMs were found to be the principal compartment containing monomeric and oligomeric A␤ in brain (30,31). Second, experimental manipulations that result in cholesterol loading and depletion, or affect intracellular cholesterol transport, modulate A␤ production in cultured cells and animal models (26,(32)(33)(34)(35). Third, BACE1 is localized and cleaves APP in lipid rafts (33,36).…”

Involvement of oxidative stress-induced abnormalities in ceramide and cholesterol metabolism in brain aging and Alzheimer's disease

“…The average age of patients was 79.8 Ϯ 2.0 (range 54-94). Average postmortem interval for all AD patients was 5.6 Ϯ 0.6 h (range [2][3][4][5][6][7][8][9][10][11][12][13][14]. No clinical stage-associated difference in average postmortem interval was present.…”

“…Two factors that are believed to contribute to neuronal dysfunction and degeneration in AD are increased oxidative stress and increased production of neurotoxic forms of A␤ (2). Alterations in lipid metabolism may also play roles in AD because the risk of AD is affected by inheritance of different isoforms of apolipoprotein E (3), changes in cholesterol metabolism can affect A␤ production in cell culture and in vivo (4)(5)(6), and drugs that lower cholesterol levels may reduce the risk of AD (7,8). However, a direct link between alterations in the metabolism of cholesterol and other membrane lipids in AD has not been established, and it is not known whether and how such lipid alterations might lead to neuronal dysfunction and death.…”

Lipid rafts, cholesterol, and the brain

“…The analysis of temporal cortex from AD subjects showed loss of lipid rafts (MolanderMelin et al 2005), while hippocampi showed reduced cholesterol content in the rafts (Ledesma et al 2003). In addition the inhibition of cholesterol transport alters PS1 localization and APP processing in neuronal cells (Runz et al 2002).…”