Amyloid-β (Aβ)
peptides originating from β-
amyloid precursor
protein (APP) are critical in
Alzheimer's disease (AD). Cellular
cholesterol levels/distribution can regulate production and clearance of Aβ
peptides, albeit with contradictory outcomes. To better understand the relationship between
cholesterol homeostasis and APP/Aβ metabolism, we have recently generated a bigenic ANPC mouse line overexpressing mutant human APP in the absence of Niemann-Pick type C-1
protein required for intracellular
cholesterol transport. Using this unique bigenic ANPC mice and complementary stable N2a cells, we have examined the functional consequences of cellular
cholesterol sequestration in the endosomal-lysosomal system, a major site of Aβ production, on APP/Aβ metabolism and its relation to neuronal viability. Levels of APP C-terminal fragments (α-CTF/β-CTF) and Aβ
peptides, but not APP
mRNA/
protein or soluble APPα/APPβ, were increased in ANPC mouse brains and N2a-ANPC cells. These changes were accompanied by reduced clearance of
peptides and an increased level/activity of γ-
secretase, suggesting that accumulation of APP-CTFs is due to decreased turnover, whereas increased Aβ levels may result from a combination of increased production and decreased turnover. APP-CTFs and Aβ
peptides were localized primarily in early-/late-endosomes and to some extent in lysosomes/autophagosomes.
Cholesterol sequestration impaired endocytic-autophagic-lysosomal, but not proteasomal, clearance of APP-CTFs/Aβ
peptides. Moreover, markers of oxidative stress were increased in vulnerable brain regions of ANPC mice and enhanced β-CTF/Aβ levels increased susceptibility of N2a-ANPC cells to H2O2-induced toxicity. Collectively, our results show that cellular
cholesterol sequestration plays a key role in APP/Aβ metabolism and increasing neuronal vulnerability to oxidative stress in AD-related pathology.