Christine Sato

Nicastrin modulates presenilin-mediated notch/glp-1 signal transduction and βAPP processing

Nicastrin, a transmembrane glycoprotein, forms high molecular weight complexes with presenilin 1 and presenilin 2. Suppression of nicastrin expression in Caenorhabditis elegans embryos induces a subset of notch/glp-1 phenotypes similar to those induced by simultaneous null mutations in both presenilin homologues of C. elegans (sel-12 and hop-1). Nicastrin also binds carboxy-terminal derivatives of β-amyloid precursor protein (βAPP), and modulates the production of the amyloid β-peptide (Aβ) from these derivatives. Missense mutations in a conserved hydrophilic domain of nicastrin increase Aβ42 and Aβ40 peptide secretion. Deletions in this domain inhibit Aβ production. Nicastrin and presenilins are therefore likely to be functional components of a multimeric complex necessary for the intramembranous proteolysis of proteins such as Notch/GLP-1 and βAPP.

Screening for PS1 mutations in a referral-based series of AD cases: 21 novel mutations

Background: Mutations in the presenilin-1 gene (PS1) account for a majority of patients with early-onset familial AD. However, the clinical indications and algorithms for genetic testing in dementia are still evolving. Methods: The entire open reading frame of the PS1 gene was sequenced in a series of 414 consecutive patients referred for diagnostic testing, including 372 patients with AD and 42 asymptomatic persons with a strong family history of AD. Results: Forty-eight independent patients screened had a PS1 mutation including 21 novel mutations. In addition, 3% of subjects (11/413) had a known polymorphism, the Glu318Gly substitution. The majority of the mutations were missense substitutions but there were three insertions and Δexon 10 mutation. With six exceptions (codons 35, 178, 352, 354, 358, and 365) most of the mutations occurred at residues conserved in the homologous PS2 gene or in PS1 of other species. Conclusions: Eleven percent of a referral-based series of patients with AD can be explained by coding sequence mutations in the PS1 gene. The high frequency of PS1 mutations in this study indicates that screening for PS1 mutations in AD is likely to be successful, especially when directed at patients with a positive family history with onset before 60 years (90% of those with PS1 mutations were affected by age 60 years). This will also have significance for the secondary identification of at-risk relatives who might be candidates for future prophylactic therapies for AD.

Nicastrin binds to membrane-tethered Notch

The presenilins and nicastrin, a type 1 transmembrane glycoprotein, form high molecular weight complexes that are involved in cleaving the β-amyloid precursor protein (βAPP) and Notch in their transmembrane domains. The former process (termed γ-secretase cleavage) generates amyloid β-peptide (Aβ), which is involved in the pathogenesis of Alzheimers disease. The latter process (termed S3-site cleavage) generates Notch intracellular domain (NICD), which is involved in intercellular signalling. Nicastrin binds both full-length βAPP and the substrates of γ-secretase (C99- and C83-βAPP fragments), and modulates the activity of γ-secretase. Although absence of the Caenorhabditis elegans nicastrin homologue (aph-2) is known to cause an embryonic-lethal glp-1 phenotype, the role of nicastrin in this process has not been explored. Here we report that nicastrin binds to membrane-tethered forms of Notch (substrates for S3-site cleavage of Notch), and that, although mutations in the conserved 312–369 domain of nicastrin strongly modulate γ-secretase, they only weakly modulate the S3-site cleavage of Notch. Thus, nicastrin has a similar role in processing Notch and βAPP, but the 312–369 domain may have differential effects on these activities. In addition, we report that the Notch and βAPP pathways do not significantly compete with each other.

Analysis of the glucocerebrosidase gene in Parkinson's disease

Parkinsons disease (PD) is a common progressive neurodegenerative disorder characterized clinically by a combination of motor symptoms. Identifying novel PD genetic risk factors is important for understanding its pathogenesis. A recent study suggested that up to 21% of subjects with PD may have mutations in the glucocerebrosidase (GBA) gene. We investigated the GBA gene for mutations in 88 PD cases and 122 normal controls and detected the presence of heterozygous GBA mutations in 5 PD cases and in 1 control. Sequencing of the entire open reading frame of the GBA gene in a subset of 25 cases with early‐onset PD (<50 years of age) uncovered no additional mutations. Our results demonstrate a marginally significant association of GBA mutations with PD and suggest that variations in the GBA gene may constitute a rare susceptibility factor for PD (P = 0.048).

Brain levels of CDK5 activator p25 are not increased in Alzheimer's or other neurodegenerative diseases with neurofibrillary tangles

Elevated levels of p25 and constitutive activation of CDK5 have been observed in AD brains. This has led to the hypothesis that increased p25 levels could promote neurofibrillary tangles (NFT) through CDK5‐mediated hyperphosphorylation of tau, the principal component of NFTs. We examined p25 immunoreactivity in brains from sporadic and familial AD cases, as well as other neurologic diseases that exhibit NFT, such as Downs syndrome (DS), Picks disease (Pick), corticobasal degeneration (CBD), progressive supranuclear palsy (PSP), frontotemporal dementia (FTD). Neither the p25 immunoreactivity nor the p25/p35 ratio was elevated in the AD brains or in the other tauopathies (n = 34) compared with controls (n = 11). Although Aβ peptides have been suggested to activate calpain‐mediated cleavage of p35 to p25 in cultured neurons, p25 levels in brains of TgCRND8 mice, which express high levels of brain Aβ peptides, were similar to those of non‐Tg littermates. Our data suggest that high Aβ levels in brain do not activate p35 proteolysis, and p25 is unlikely to be a causative agent for NFT formation in AD or other tauopathies.

Investigation of C9orf72 in 4 Neurodegenerative Disorders

OBJECTIVE To estimate the allele frequency of C9orf72 (G4C2) repeats in amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), Alzheimer disease (AD), and Parkinson disease (PD). DESIGN The number of repeats was estimated by a 2-step genotyping strategy. For expansion carriers, we sequenced the repeat flanking regions and obtained APOE genotypes and MAPT H1/H2 haplotypes. SETTING Hospitals specializing in neurodegenerative disorders. SUBJECTS We analyzed 520 patients with FTLD, 389 patients with ALS, 424 patients with AD, 289 patients with PD, 602 controls, 18 families, and 29 patients with PD with the LRRK2 G2019S mutation. MAIN OUTCOME MEASURE The expansion frequency. RESULTS Based on a prior cutoff (>30 repeats), the expansion was detected in 9.3% of patients with ALS, 5.2% of patients with FTLD, and 0.7% of patients with PD but not in controls or patients with AD. It was significantly associated with family history of ALS or FTLD and age at onset of FTLD. Phenotype variation (ALS vs FTLD) was not associated with MAPT, APOE, or variability in the repeat flanking regions. Two patients with PD were carriers of 39 and 32 repeats with questionable pathological significance, since the 39-repeat allele does not segregate with PD. No expansion or intermediate alleles (20-29 repeats) were found among the G2019S carriers and AD cases with TAR DNA-binding protein 43-positive inclusions. Surprisingly, the frequency of the 10-repeat allele was marginally increased in all 4 neurodegenerative diseases compared with controls, indicating the presence of an unknown risk variation in the C9orf72 locus. CONCLUSIONS The C9orf72 expansion is a common cause of ALS and FTLD, but not of AD or PD. Our study raises concern about a reliable cutoff for the pathological repeat number, which is important in the utility of genetic screening.

Rare coding mutations identified by sequencing of Alzheimer disease genome-wide association studies loci

To detect rare coding variants underlying loci detected by genome‐wide association studies (GWAS) of late onset Alzheimer disease (LOAD).

Heterogeneity within a large kindred with frontotemporal dementia: a novel progranulin mutation.

Background: Frontotemporal dementia (FTD) in several 17q21-linked families was recently explained by truncating mutations in the progranulin gene (GRN). Objective: To determine the frequency of GRN mutations in a cohort of Caucasian patients with FTD without mutations in known FTD genes. Methods: GRN was sequenced in a series of 78 independent FTD patients including 23 familial subjects. A different Calabrian dataset (109 normal control subjects and 96 FTD patients) was used to establish the frequency of the GRN mutation. Results: A novel truncating GRN mutation (c.1145insA) was detected in a proband of an extended consanguineous Calabrian kindred. Segregation analysis of 70 family members revealed 19 heterozygous mutation carriers including 9 patients affected by FTD. The absence of homozygous carriers in a highly consanguineous kindred may indicate that the loss of both GRN alleles might lead to embryonic lethality. An extremely variable age at onset in the mutation carriers (more than five decades apart) is not explained by APOE genotypes or the H1/H2 MAPT haplotypes. Intriguingly, the mutation was excluded in four FTD patients belonging to branches with an autosomal dominant mode of inheritance of FTD, suggesting that another novel FTD gene accounts for the disease in the phenocopies. It is difficult to clinically distinguish phenocopies from GRN mutation carriers, except that language in mutation carriers was more severely compromised. Conclusion: The current results imply further genetic heterogeneity of frontotemporal dementia, as we detected only one GRN-linked family (about 1%). The value of discovering large kindred includes the possibility of a longitudinal study of GRN mutation carriers.

Benign hereditary chorea: clinical, genetic, and pathological findings.

Benign hereditary chorea is an autosomal dominant disorder presenting with childhood‐onset chorea, no dementia, and little or no progression. We present a family with typical clinical features of benign hereditary chorea. Pathological investigation of the brain of an affected family member who died of an unrelated condition showed no significant gross or histological abnormalities. Genetic evaluation showed a novel single nucleotide substitution of intron 2 of the TITF‐1 gene (also referred to as TTF, NKX2.1, and T/ebp) on chromosome 14 which is predicted to have drastic consequences on the maturation processes of TITF‐1. Ann Neurol 2003

Rare coding mutations identified by sequencing of Alzheimer's disease GWAS loci

To detect rare coding variants underlying loci detected by genome‐wide association studies (GWAS) of late onset Alzheimer disease (LOAD).