title: Chronic exposure to sub-lethal beta-amyloid (Abeta) inhibits the import of nuclear-encoded proteins to mitochondria in differentiated PC12 cells.
abstract: Studies on amyloid beta (Abeta|), the peptide thought to play a crucial role in the pathogenesis of Alzheimer's disease, have implicated mitochondria in Abeta-mediated neurotoxicity. We used differentiated PC12 cells stably transfected with an inducible green fluorescent protein (GFP) fusion protein containing an N'-terminal mitochondrial targeting sequence (mtGFP), to examine the effects of sub-lethal Abeta on the import of nuclear-encoded proteins to mitochondria. Exposure to sub-lethal Abeta(25-35) (10 mumol/L) for 48 h inhibited mtGFP import to mitochondria; average rates decreased by 20 +/- 4%. Concomitant with the decline in mtGFP, cytoplasmic mtGFP increased significantly while mtGFP expression and intramitochondrial mtGFP turnover were unchanged. Sub-lethal Abeta(1-42) inhibited mtGFP import and increased cytoplasmic mtGFP but only after 96 h. The import of two endogenous nuclear-encoded mitochondrial proteins, mortalin/mtHsp70 and Tom20 also declined. Prior to the decline in import, mitochondrial membrane potential (mmp), and reactive oxygen species levels were unchanged in Abeta-treated cells versus reverse phase controls. Sustained periods of decreased import were associated with decreased mmp, increased reactive oxygen species, increased vulnerability to oxygen-glucose deprivation and altered mitochondrial morphology. These findings suggest that an Abeta-mediated inhibition of mitochondrial protein import, and the consequent mitochondrial impairment, may contribute to Alzheimer's disease.
authors.affiliation: Genetics and Development Division, Toronto Western Research Institute, University Health Network Toronto, Ontario, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sirk
authors.forename: Ziping
authors.initials: Z
authors.lastname: Zhu
authors.forename: Jehangir S
authors.initials: JS
authors.lastname: Wadia
authors.forename: Natalya
authors.initials: N
authors.lastname: Shulyakova
authors.forename: Nam
authors.initials: N
authors.lastname: Phan
authors.forename: Jamie
authors.initials: J
authors.lastname: Fong
authors.forename: Linda R
authors.initials: LR
authors.lastname: Mills
mesh_terms: D016229:Amyloid beta-Peptides / Q000494:pharmacology*; D000704:Analysis of Variance; D000818:Animals; D001345:Autoradiography; D002454:Cell Differentiation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry / Q000379:methods; D005947:Glucose / Q000172:deficiency; D049452:Green Fluorescent Proteins / Q000378:metabolism; D000860:Hypoxia / Q000503:physiopathology; D047468:Immunoprecipitation / Q000379:methods; D008928:Mitochondria / Q000187:drug effects / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism / Q000382:microbiology; D009687:Nuclear Proteins / Q000378:metabolism*; D016716:PC12 Cells / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017382:Reactive Oxygen Species; D013997:Time Factors; D014162:Transfection / Q000379:methods
chemical_list: D016229:Amyloid beta-Peptides; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments; D017382:Reactive Oxygen Species; C075222:amyloid beta-protein (1-42); C074636:amyloid beta-protein (25-35); D049452:Green Fluorescent Proteins; D005947:Glucose