M. Ikeda

Presenilins Interact with Armadillo Proteins Including Neural‐Specific Plakophilin‐Related Protein and β‐Catenin

Abstract : Missense substitutions in the presenilin 1 (PS1) and presenilin 2 (PS2) proteins are associated with early‐onset familial Alzheimers disease. We have used yeast‐two‐hybrid and coimmunoprecipitation methods to show that the large cytoplasmic loop domains of PS1 and PS2 interact specifically with three members of the armadillo protein family, including β‐catenin, p0071, and a novel neuronal‐specific armadillo protein—neural plakophilin‐related armadillo protein (NPRAP). The PS1 : NPRAP interaction occurs between the arm repeats of NPRAP and residues 372‐399 at the C‐terminal end of the large cytoplasmic loop of PS1. The latter residues contain a single arm‐like domain and are highly conserved in the presenilins, suggesting that they form a functional armadillo protein binding site for the presenilins.

Normal brain development in PS1 hypomorphic mice with markedly reduced γ-secretase cleavage of βAPP

Abstract Presenilin 1-null mice die at birth from brain and skeletal developmental deformities due to disrupted Notch signaling. Presenilin 1-null mice also have severely reduced γ-secretase cleavage of βAPP. The assumption has been that facilitation of Notch signaling and βAPP processing by presenilin 1 are analogous functions. Here we describe a presenilin 1-targetted mouse model that expresses extremely low levels (∼1% of normal) of mutant PS1-M146L. Homozygous mice have significantly reduced viability due to a Notch-like phenotype. The animals that survive have severe axial skeletal deformities and markedly diminished γ-secretase activity and accumulation of βAPP-C100, but no obvious abnormalities in brain development. These results suggest that, in mice, a marked reduction of PS1-facilitated γ-secretase activity is not detrimental to normal brain development.

Absence of association between Alzheimer disease and the −491 regulatory region polymorphism of APOE

A novel polymorphism (-491 A/T) within the regulatory region on the apolipoprotein E gene has recently been reported to be associated with risk for Alzheimer disease (AD). To test this association in an independent data set, we have examined this polymorphism in a sample of 88 well-characterized AD cases and compared the allele frequency and genotype frequencies for this polymorphism with those observed in 112 cognitively normal subjects drawn from the same ethnic group. These results suggest that in the current data set at least, the -491 A/T polymorphism is not associated with risk for AD, but may be in partial linkage disequilibrium with the APOE epsilon2/epsilon3/epsilon4 polymorphism.

Proteolytic processing of presenilin-1 (PS-1) is not associated with Alzheimer's disease with or without PS-1 mutations.

Cerebral presenilin‐1 protein (PS‐1) is normally composed of the amino‐terminal fragment (NTF) with M r 28 kDa and the carboxy‐terminal fragment (CTF) with 18 kDa. We analyzed human PS‐1 in brains with early‐onset familial Alzheimers disease (FAD) with and without PS‐1 mutations to study whether mutated PS‐1 was abnormally metabolized. Cerebral PS‐1 were found to be cleaved into two fragments of NTF and CTF independently of the occurrence of PS‐1 mutation in human brains. A small portion of PS‐1 was recently found to suffer another processing by caspase‐3, an apoptosis‐related cysteine protease. In contrast to the recent finding that the Volga‐German mutation on presenilin‐2 (PS‐2) affects the increasing caspase‐3 PS‐2 fragment, the PS‐1 mutation did not cause a significant change in PS‐1 fragmentation. We conclude that PS‐1 fragmentation and other (probably caspase‐3‐mediated) digestion following apoptosis occur independently of PS‐1 mutations.

Amyloid-β-protein isoforms in brain of subjects with PS1-linked, βAPP-linked and sporadic alzheimer disease

To determine whether similar abnormalities of various soluble full-length and N-terminal truncated Abeta peptides occur in postmortem cerebral cortex of affected PS1 mutation carriers, we examined the amounts of two amyloid species ending at residue 40 or at residues 42(43) using sandwich ELISA systems. Our results indicate that PS1 mutations effect a dramatic accumulation in brain of the highly insoluble potentially neurotoxic long-tailed isoforms of the Abeta peptide such as Abeta1-42(43) and Abetax-42(43). This enhancing effect of PS1 mutation on Abetax-42(43) deposition was highly similar to that of a betaAPP mutation (Val717Ile) but the effects on Abetax-40 production were significantly different between these two causal genes. In contrast to previous studies of soluble Abeta in plasma and in supernatants from cultured fibroblasts of subjects with PS1 mutations, our studies also show that there is an increase in insoluble Abetax-40 peptides in brain of subjects with PS1 mutations.

A presenilin‐1 mutation in a Japanese family with Alzheimer's disease and distinctive abnormalities on cranial MRI

Some patients with familial Alzheimers disease (FAD) have mutations in the presenilin-1 (PS-1) gene on chromosome 14. We report a Japanese family with AD and an Ala285Val substitution in exon 8 of the PS-1 gene. FAD in this family was characterized by relatively late onset (mean age, 50 years) and absence of myoclonus, seizures, or paratonia. Levels of tau were markedly elevated in CSF whereas CSF levels of amyloid P protein were normal. MRI of the cranium showed marked linear signal abnormalities within white matter in the parieto-occipital lobes, consistent with cortical amyloid angiopathy of the type encountered in patients with the PS-1 gene mutation.

Failure to detect missense mutations in the S182 gene in a series of late-onset Alzheimer's disease cases

The possibility of an interaction of multiple genes has been speculated in pathogenesis of Alzheimers disease (AD). Because we have recently cloned a novel gene S182 bearing five different missense mutations which segregate with early-onset familial AD, we sought the frequency of these mutations in familial and sporadic late-onset AD to clarify the incidence of these mutations in the disease. The current study showed lack of these mutations in 118 independent subjects affected with late-onset Alzheimers disease.