title: {gamma}-Secretase Substrate Concentration Modulates the Abeta42/Abeta40 Ratio: IMPLICATIONS FOR ALZHEIMER DISEASE.
abstract: Mutation of the amyloid precursor protein (APP), presenilin-1, or presenilin-2 results in the development of early onset autosomal dominant forms of Alzheimer disease (AD). These mutations lead to an increased Abeta42/Abeta40 ratio that correlates with the onset of disease. However, it remains unknown how these mutations affect gamma-secretase, a protease that generates the termini of Abeta40 and Abeta42. Here we have determined the reaction mechanism of gamma-secretase with wild type and three mutated APP substrates. Our findings indicate that despite the overall outcome of an increased Abeta42/Abeta40 ratio, these mutations each display rather distinct reactivity to gamma-secretase. Intriguingly, we found that the ratio of Abeta42/Abeta40 is variable with substrate concentration; increased substrate concentrations result in higher ratios of Abeta42/Abeta40. Moreover, we demonstrated that reduction of gamma-secretase substrate concentration by BACE1 inhibition in cells decreased the Abeta42/Abeta40 ratio. This study indicates that biological factors affecting targets such as BACE1 and APP, which ultimately cause an increased concentration of gamma-secretase substrate, can augment the Abeta42/Abeta40 ratio and may play a causative role in sporadic AD. Therefore, strategies lowering the Abeta42/Abeta40 ratio through partial reduction of gamma-secretase substrate production may introduce a practical therapeutic modality for treatment of AD.
authors.affiliation: Molecular Pharmacology and Chemistry Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021 and Department of Biology, Rensselaer Polytechnic Institute, Troy, New York 12180.
authors.forename: Ye Ingrid
authors.initials: YI
authors.lastname: Yin
authors.forename: Bhramdeo
authors.initials: B
authors.lastname: Bassit
authors.forename: Lei
authors.initials: L
authors.lastname: Zhu
authors.forename: Xia
authors.initials: X
authors.lastname: Yang
authors.forename: Chunyu
authors.initials: C
authors.lastname: Wang
authors.forename: Yue-Ming
authors.initials: YM
authors.lastname: Li
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases / Q000737:chemistry / Q000378:metabolism*; D016229:Amyloid beta-Peptides / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D001665:Binding Sites; D051379:Mice; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010446:Peptide Fragments / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D016229:Amyloid beta-Peptides; D010446:Peptide Fragments; C078592:amyloid beta-protein (1-40); C075222:amyloid beta-protein (1-42); D053829:Amyloid Precursor Protein Secretases; D016282:Aspartic Acid Endopeptidases; C509282:Bace1 protein, mouse