title: APP overexpression in the absence of NPC1 exacerbates metabolism of amyloidogenic proteins of Alzheimer's disease.
abstract: 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.
authors.affiliation: Centre for Prions and Protein Folding Diseases, Centre for Neuroscience, Department of Medicine, and.
authors.forename: Mahua
authors.initials: M
authors.lastname: Maulik
authors.affiliation: Department of Medicine, and.
authors.forename: Kyle
authors.initials: K
authors.lastname: Peake
authors.affiliation: Centre for Prions and Protein Folding Diseases, Department of Psychiatry, University of Alberta, Edmonton, AB T6G 2M8, Canada.
authors.forename: JiYun
authors.initials: J
authors.lastname: Chung
authors.affiliation: Centre for Prions and Protein Folding Diseases, Department of Psychiatry, University of Alberta, Edmonton, AB T6G 2M8, Canada.
authors.forename: Yanlin
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Medicine, and.
authors.forename: Jean E
authors.initials: JE
authors.lastname: Vance
authors.affiliation: Centre for Prions and Protein Folding Diseases, Centre for Neuroscience, Department of Medicine, and Department of Psychiatry, University of Alberta, Edmonton, AB T6G 2M8, Canada skar@ualberta.ca.
authors.forename: Satyabrata
authors.initials: S
authors.lastname: Kar
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000235:genetics / Q000378:metabolism*; D058227:Amyloidogenic Proteins / Q000378:metabolism*; D000818:Animals; D001343:Autophagy; D045744:Cell Line, Tumor; D002470:Cell Survival; D002784:Cholesterol / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008247:Lysosomes / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D000077296:Niemann-Pick C1 Protein; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*
chemical_list: D016564:Amyloid beta-Protein Precursor; D058227:Amyloidogenic Proteins; D047908:Intracellular Signaling Peptides and Proteins; D000077296:Niemann-Pick C1 Protein; C106831:Npc1 protein, mouse; D011506:Proteins; D002784:Cholesterol; D046988:Proteasome Endopeptidase Complex