title: Enzymatic characteristics of I213T mutant presenilin-1/gamma-secretase in cell models and knock-in mouse brains: familial Alzheimer disease-linked mutation impairs gamma-site cleavage of amyloid precursor protein C-terminal fragment beta.
abstract: Presenilin (PS)/gamma-secretase-mediated intramembranous proteolysis of amyloid precursor protein produces amyloid beta (Abeta) peptides in which Abeta species of different lengths are generated through multiple cleavages at the gamma-, zeta-, and epsilon-sites. An increased Abeta42/Abeta40 ratio is a common characteristic of most cases of familial Alzheimer disease (FAD)-linked PS mutations. However, the molecular mechanisms underlying amyloid precursor protein proteolysis leading to increased Abeta42/Abeta40 ratios still remain unclear. Here, we report our findings on the enzymatic analysis of gamma-secretase derived from I213T mutant PS1-expressing PS1/PS2-deficient (PS(-/-)) cells and from the brains of I213T mutant PS1 knock-in mice. Kinetics analyses revealed that the FAD mutation reduced de novo Abeta generation, suggesting that mutation impairs the total catalytic rate of gamma-secretase. Analysis of each Abeta species revealed that the FAD mutation specifically reduced Abeta40 levels more drastically than Abeta42 levels, leading to an increased Abeta42/Abeta40 ratio. By contrast, the FAD mutation increased the generation of longer Abeta species such as Abeta43, Abeta45, and >Abeta46. These results were confirmed by analyses of gamma-secretase derived from I213T knock-in mouse brains, in which the reduction of de novo Abeta generation was mutant allele dose-dependent. Our findings clearly indicate that the mechanism underlying the increased Abeta42/Abeta40 ratio observed in cases of FAD mutations is related to the differential inhibition of gamma-site cleavage reactions, in which the reaction producing Abeta40 is subject to more inhibition than that producing Abeta42. Our results also provide novel insight into how enhancing the generation of longer Abetas may contribute to Alzheimer disease onset.
authors.affiliation: Laboratory for Alzheimer's Disease, RIKEN Brain Science Institute, Wako-shi, Saitama 351-0198, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Shimojo
authors.forename: Naruhiko
authors.initials: N
authors.lastname: Sahara
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Mizoroki
authors.forename: Satoru
authors.initials: S
authors.lastname: Funamoto
authors.forename: Maho
authors.initials: M
authors.lastname: Morishima-Kawashima
authors.forename: Takashi
authors.initials: T
authors.lastname: Kudo
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Takeda
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Ihara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ichinose
authors.forename: Akihiko
authors.initials: A
authors.lastname: Takashima
mesh_terms: D000544:Alzheimer Disease / Q000235:genetics* / Q000473:pathology*; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000235:genetics*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D006720:Homozygote; D006801:Humans; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D009154:Mutation; D053764:Presenilin-1 / Q000235:genetics* / Q000502:physiology*; D017434:Protein Structure, Tertiary
chemical_list: D016564:Amyloid beta-Protein Precursor; D053764:Presenilin-1