RESUMEN
The amino acid sequence of amyloid precursor protein (APP) is highly conserved, and age-related A beta aggregates have been described in a variety of vertebrate animals, with the notable exception of mice and rats. Three amino acid substitutions distinguish mouse and human A beta that might contribute to their differing properties in vivo. To examine the amyloidogenic potential of mouse A beta, we studied several lines of transgenic mice overexpressing wild-type mouse amyloid precursor protein (moAPP) either alone or in conjunction with mutant PS1 (PS1dE9). Neither overexpression of moAPP alone nor co-expression with PS1dE9 caused mice to develop Alzheimer-type amyloid pathology by 24 months of age. We further tested whether mouse A beta could accelerate the deposition of human A beta by crossing the moAPP transgenic mice to a bigenic line expressing human APPswe with PS1dE9. The triple transgenic animals (moAPP x APPswe/PS1dE9) produced 20% more A beta but formed amyloid deposits no faster and to no greater extent than APPswe/PS1dE9 siblings. Instead, the additional mouse A beta increased the detergent solubility of accumulated amyloid and exacerbated amyloid deposition in the vasculature. These findings suggest that, although mouse A beta does not influence the rate of amyloid formation, the incorporation of A beta peptides with differing sequences alters the solubility and localization of the resulting aggregates.
Asunto(s)
Péptidos beta-Amiloides/química , Amiloide/química , Secuencia de Aminoácidos , Animales , Humanos , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Datos de Secuencia Molecular , Péptidos/química , Presenilina-1/metabolismo , Estructura Terciaria de Proteína , Homología de Secuencia de Aminoácido , Solubilidad , TransgenesRESUMEN
Epidemiological studies suggest that individuals with greater education or more cognitively demanding occupations have diminished risk of developing dementia. We wanted to test whether this effect could be recapitulated in rodents using environmental enrichment, a paradigm well documented to attenuate behavioral deficits induced by various pathological insults. Here, we demonstrate that learning and memory deficits observed in a transgenic mouse model of Alzheimer's disease can be ameliorated by enrichment. Female transgenic mice overexpressing amyloid precursor protein and/or presenilin-1 and nontransgenic controls were placed into enriched or standard cages at 2 months of age and tested for cognitive behavior after 6 months of differential housing. Enrichment significantly improved performance of all genotypes in the radial water maze and in the classic and repeated-reversal versions of the Morris water maze. However, enrichment did not benefit all genotypes equally. Mice overproducing amyloid-beta (Abeta), particularly those with amyloid deposits, showed weaker memory for the platform location in the classic Morris water maze and learned new platform positions in the repeated-reversals task less quickly than their nontransgenic cagemates. Nonetheless, enrichment normalized the performance of Abeta-overproducing mice to the level of standard-housed nontransgenic mice. Moreover, this functional preservation occurred despite increased neuritic plaque burden in the hippocampus of double-transgenic animals and elevated steady-state Abeta levels, because both endogenous and transgene-derived Abeta are increased in enriched animals. These results demonstrate that the generation of Abeta in vivo and its impact on the function of the nervous system can be strongly modulated by environmental factors.
Asunto(s)
Enfermedad de Alzheimer/complicaciones , Trastornos del Conocimiento/etiología , Ambiente , Factores de Edad , Péptidos beta-Amiloides/genética , Precursor de Proteína beta-Amiloide/genética , Precursor de Proteína beta-Amiloide/metabolismo , Análisis de Varianza , Animales , Conducta Animal , Modelos Animales de Enfermedad , Ensayo de Inmunoadsorción Enzimática/métodos , Femenino , Hipocampo/metabolismo , Humanos , Inmunohistoquímica/métodos , Aprendizaje por Laberinto/fisiología , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Presenilina-1 , Factores de TiempoRESUMEN
Risk for late onset Alzheimer disease (LOAD) and plasma amyloid beta levels (Abeta42; encoded by APP), an intermediate phenotype for LOAD, show linkage to chromosome 10q. Several strong candidate genes (VR22, PLAU, IDE) lie within the 1-lod support interval for linkage. Others have independently identified haplotypes in the chromosome 10q region harboring IDE that show highly significant association with intermediate AD phenotypes and with risk for AD. To pursue these associations, we analyzed the same haplotypes for association with plasma Abeta42 in 24 extended LOAD families and for association with LOAD in two independent case-control series. One series (MCR, 188 age-matched case-control pairs) did not show association (p=0.64) with the six haplotypes in the 276-kb region spanning three genes (IDE, KNSL1, and HHEX) previously shown to associate with LOAD. The other series (MCJ, 109 age-matched case-control pairs) showed significant (p=0.003) association with these haplotypes. In the MCJ series, the H4 (odds ratio [OR]=5.1, p=0.003) and H2(H7) haplotypes (OR=0.60, p=0.04) had the same effects previously reported. In this series, the H8 haplotype (OR=2.7, p=0.098) also had an effect similar as in one previous case control series but not in others. In the extended families, the H8 haplotype was associated with significantly elevated plasma Abeta42 (p=0.02). In addition, the H5(H10) haplotype, which is associated with reduced risk for AD in the other study is associated with reduced plasma Abeta42 (p=0.007) in our family series. These results provide strong evidence for pathogenic variant(s) in the 276-kb region harboring IDE that influence intermediate AD phenotypes and risk for AD.
Asunto(s)
Enfermedad de Alzheimer/genética , Péptidos beta-Amiloides/sangre , Predisposición Genética a la Enfermedad , Variación Genética , Insulisina/genética , Fragmentos de Péptidos/sangre , Adulto , Anciano , Enfermedad de Alzheimer/sangre , Estudios de Casos y Controles , Cromosomas Humanos Par 10 , Haplotipos , Humanos , Desequilibrio de Ligamiento , Persona de Mediana Edad , Datos de Secuencia Molecular , Polimorfismo de Nucleótido SimpleRESUMEN
Amyloid precursor protein (APP) is endoproteolytically processed by BACE1 and gamma-secretase to release amyloid peptides (Abeta40 and 42) that aggregate to form senile plaques in the brains of patients with Alzheimer's disease (AD). The C-terminus of Abeta40/42 is generated by gamma-secretase, whose activity is dependent upon presenilin (PS 1 or 2). Missense mutations in PS1 (and PS2) occur in patients with early-onset familial AD (FAD), and previous studies in transgenic mice and cultured cell models demonstrated that FAD-PS1 variants shift the ratio of Abeta40 : 42 to favor Abeta42. One hypothesis to explain this outcome is that mutant PS alters the specificity of gamma-secretase to favor production of Abeta42 at the expense of Abeta40. To test this hypothesis in vivo, we studied Abeta40 and 42 levels in a series of transgenic mice that co-express the Swedish mutation of APP (APPswe) with two FAD-PS1 variants that differentially accelerate amyloid pathology in the brain. We demonstrate a direct correlation between the concentration of Abeta42 and the rate of amyloid deposition. We further show that the shift in Abeta42 : 40 ratios associated with the expression of FAD-PS1 variants is due to a specific elevation in the steady-state levels of Abeta42, while maintaining a constant level of Abeta40. These data suggest that PS1 variants do not simply alter the preferred cleavage site for gamma-secretase, but rather that they have more complex effects on the regulation of gamma-secretase and its access to substrates.
Asunto(s)
Endopeptidasas/metabolismo , Proteínas de la Membrana/genética , Mutación Missense , Edad de Inicio , Enfermedad de Alzheimer/genética , Enfermedad de Alzheimer/patología , Secretasas de la Proteína Precursora del Amiloide , Péptidos beta-Amiloides/genética , Péptidos beta-Amiloides/metabolismo , Animales , Ácido Aspártico Endopeptidasas , Encéfalo/metabolismo , Encéfalo/patología , Células Cultivadas , Endopeptidasas/genética , Humanos , Proteínas de la Membrana/metabolismo , Ratones , Ratones Transgénicos , Fragmentos de Péptidos/genética , Fragmentos de Péptidos/metabolismo , Presenilina-1RESUMEN
Using plasma amyloid beta protein (Abeta42) levels as an intermediate, quantitative phenotype for late onset Alzheimer's disease (LOAD), we previously obtained significant linkage at approximately 80 cM on chromosome 10. Linkage to the same region was obtained independently in a study of affected LOAD sib-pairs. Together, these two studies provide strong evidence for a novel LOAD locus on chromosome 10 that acts to increase Abeta42. VR22 is a large (1.7 Mb) gene located at 80 cM that encodes alpha-T catenin, which is a binding partner of beta catenin. This makes VR22 an attractive candidate gene because beta catenin interacts with presenilin 1, which has many mutations that elevate Abeta42 and cause early onset familial AD. We identified two intronic VR22 SNPs (4360 and 4783) in strong linkage disequilibrium (LD) that showed highly significant association (P=0.0001 and 0.0006) with plasma Abeta42 in 10 extended LOAD families. This association clearly contributed to the linkage at approximately 80 cM because the lod scores decreased when linkage analysis was performed conditional upon the VR22 association. This association replicated in another independent set of 12 LOAD families (P=0.04 for 4783 and P=0.08 for 4360). Bounding of the association region using multiple SNPs showed VR22 to be the only confirmed gene within the region of association. These findings indicate that VR22 has variant(s) which influence Abeta42 and contribute to the previously reported linkage for plasma Abeta42 in LOAD families.