Genetic Variations in ABCA7 Can Increase Secreted Levels of Amyloid-β40 and Amyloid-β42 Peptides and ABCA7 Transcription in Cell Culture Models.
Alzheimer's disease (AD) is characterized by extracellular deposits of amyloid-β (Aβ) in the brain. ABCA7 is highly expressed in the brain and a susceptibility gene for late-onset AD (LOAD). The minor alleles at two ABCA7 single-nucleotide polymorphisms (SNPs), rs3764650 (T>G; intron13) and rs3752246 at a predicted myristoylation site (C>G; exon33; p.Gly1527Ala), are significantly associated with LOAD risk; however, the mechanism of this association is unknown. Functional consequences of both SNPs were examined in HEK293 and CHO cells stably expressing AβPPSwe. Luciferase reporter assays in HEK293 cells suggested that intron13 carrying rs3764650 major T-allele (int13-T) possessed promoter-enhancing capabilities. Co-transfection experiments with hABCA7 and int13-T resulted in significantly increased ABCA7 protein level relative to that with int13-G. Expression of hABCA7 carrying rs3752246 risk allele led to increases in secreted Aβ40 and Aβ42 and β-secretase activity in CHO- and HEK-AβPPSwe cells. Hydroxymyristic acid treatment of cells expressing hABCA7 carrying the rs3752246 major G allele resulted in increased β-secretase activity and levels of Aβ, suggesting that lack of myristoylation contributes to the observed cell-phenotypes. Molecular weight determination, by gel-electrophoresis and mass spectrometry, of hABCA7 peptides spanning position 1527 showed loss of post-translational modification in the risk-allele peptide. These results suggest that decreased expression, or impaired function, of ABCA7 may contribute to AD pathology.
Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.|Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Michelle
M
Bamji-Mirza
Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.|Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Yan
Y
Li
Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.|Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Dema
D
Najem
Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Qing Yan
QY
Liu
Banner Sun Health Research Institute, Sun City, AZ, USA.
Douglas
D
Walker
Banner Sun Health Research Institute, Sun City, AZ, USA.
Lih-Fen
LF
Lue
Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Jacek
J
Stupak
Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Kenneth
K
Chan
Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Jianjun
J
Li
Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada.
Mahdi
M
Ghani
The Key Laboratory of Geriatrics, Beijing Hospital & Beijing Institute of Geriatrics, Chinese Ministry of Health, Beijing, China.
Ze
Z
Yang
Tanz Centre for Research in Neurodegenerative Diseases, University of Toronto, Toronto, ON, Canada.
Ekaterina
E
Rogaeva
Department of Pathology and Laboratory Medicine, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada.|Human Health Therapeutics Portfolio, Life Sciences Division, National Research Council Canada, Ottawa, ON, Canada.
Wandong
W
Zhang
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D016229:Amyloid beta-Peptides / Q000378:metabolism*; D016564:Amyloid beta-Protein Precursor / Q000378:metabolism*; D000704:Analysis of Variance; D000818:Animals; D016466:CHO Cells; D003412:Cricetulus; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D014644:Genetic Variation / Q000235:genetics*; D057809:HEK293 Cells; D006801:Humans; D007438:Introns / Q000235:genetics; D019814:Myristic Acid / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism*; D020641:Polymorphism, Single Nucleotide; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics*; D014162:Transfection
C411895:ABCA7 protein, human; D018528:ATP-Binding Cassette Transporters; D016229:Amyloid beta-Peptides; D016564:Amyloid beta-Protein Precursor; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42); D019814:Myristic Acid
ABC transporters; ABCA7 protein; Alzheimer’s disease; BACE1 protein; SNPs; amyloid beta-peptides; genome-wide association study; myristoylation