Yan Liang

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.

The Presenilin 1 Protein Is a Component of a High Molecular Weight Intracellular Complex That Contains β-Catenin

The presenilin (PS) genes associated with Alzheimer disease encode polytopic transmembrane proteins which undergo physiologic endoproteolytic cleavage to generate stable NH2- and COOH-terminal fragments (NTF or CTF) which co-localize in intracellular membranes, but are tightly regulated in their stoichiometry and abundance. We have used linear glycerol velocity and discontinuous sucrose gradient analysis to investigate the distribution and native conformation of PS1 and PS2 during this regulated processing in cultured cells and in brain. The PS1 NTF and CTF co-localize in the endoplasmic reticulum (ER) and in the Golgi apparatus, where they are components of a ∼250-kDa complex. This complex also contains β-catenin but not β-amyloid precursor protein (APP). In contrast, the PS1 holoprotein precursor is predominantly localized to the rough ER and smooth ER, where it is a component of a ∼180-kDa native complex. PS2 forms similar but independent complexes. Restricted incorporation of the presenilin NTF and CTF along with a potentially functional ligand (β-catenin) into a multimeric complex in the ER and Golgi apparatus may provide an explanation for the regulated accumulation of the NTF and CTF.

In vivo reduction of amyloid-β by a mutant copper transporter

Cu ions have been suggested to enhance the assembly and pathogenic potential of the Alzheimers disease amyloid-β (Aβ) peptide. To explore this relationship in vivo, toxic-milk (txJ) mice with a mutant ATPase7b transporter favoring elevated Cu levels were analyzed in combination with the transgenic (Tg) CRND8 amyloid precursor protein mice exhibiting robust Aβ deposition. Unexpectedly, TgCRND8 mice homozygous for the recessive txJ mutation examined at 6 months of age exhibited a reduced number of amyloid plaques and diminished plasma Aβ levels. In addition, homozygosity for txJ increased survival of young TgCRND8 mice and lowered endogenous CNS Aβ at times before detectable increases in Cu in the CNS. These data suggest that the beneficial effect of the txJ mutation on CNS Aβ burden may proceed by a previously undescribed mechanism, likely involving increased clearance of peripheral pools of Aβ peptide.

Mutations of PKD1 in ADPKD2 cysts suggest a pathogenic effect of trans- heterozygous mutations

Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in PKD1 and PKD2. The products of these genes associate to form heteromeric complexes. Several models have been proposed to explain the mechanism of cyst formation. Here we find somatic mutations of PKD2 in 71% of ADPKD2 cysts analysed. Clonal somatic mutations of PKD1 were identified in a subset of cysts that lacked PKD2 mutations.

Frontotemporal dementia with novel tau pathology and a Glu342Val tau mutation

It is unclear how tau gene mutations cause frontotemporal dementia (FTD) with parkinsonism linked to chromosome 17 (FTDP‐17), but those in exon 10 (E10) or the following intron may be pathogenic by altering E10 splicing, perturbing the normal 1:1 ratio of four versus three microtubule‐binding repeat tau (4R:3R tau ratio) and forming tau inclusions. We report on a 55‐year old woman with frontotemporal dementia and a family history of FTDP‐17 in whom we found a novel E12 (Glu342Val) tau gene mutation, prominent frontotemporal neuron loss, intracytoplasmic tau aggregates, paired helical tau filaments, increased 4R tau messenger RNA, increased 4R tau without E2 or E3 inserts, decreased 4R tau with these inserts, and a 4R:3R tau ratio greater than 1 in gray and white matter. Thus, this novel Glu342Val mutation may cause FTDP‐17 by unprecedented mechanisms that alter splicing of E2, E3, and E10 to preferentially increase 4R tau without amino terminal inserts and promote aggregation of tau filaments into cytopathic inclusions. Ann Neurol 2000;48:850–858

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.

Cloning and characterization of the Drosophila presenilin homologue

MUTATIONS in two genes, PS1 and PS2, coding for the presenilins, have been linked to the early onset form of familial Alzheimers disease (AD). Here we report the identification of a Drosophila melanogaster homologue of human PS genes, Dps, which maps to band 77B-C on chromosome 3 and is expressed at multiple developmental stages. The predicted amino acid sequence of the Dps product is 53% identical to human presenilins, with the greatest similarity in the putative transmembrane domains, the hydrophobic domains at the beginning and the end of the cytoplasmic TM6-TM7 loop and the C-terminus. Analysis of Dps in a genetically tractable model system such as Drosophila may provide insight into the mechanisms of Alzheimers disease (AD) necessary for the development of rational therapeutic approaches.

Association studies of cholesterol metabolism genes (CH25H, ABCA1 and CH24H) in Alzheimer's disease

Recent studies have demonstrated that cholesterol metabolism has an important role in Alzheimers disease (AD) pathogenesis, suggesting that cholesterol-related genes may be significant genetic risk factors for AD. Based on the results of genome-wide screens, along with biological studies, we selected three genes as candidates for AD risk factors: ATP-binding cassette transporter A1 (ABCA1), cholesterol 25-hydroxylase (CH25H) and cholesterol 24-hydroxylase (CH24H). Case-control of North American Caucasians and AD families of Caribbean Hispanic origin were examined. Although excellent biological candidates, the case-control dataset did not support the hypothesis that these three genes were associated with susceptibility to AD. Similarly, no association was found in the Caribbean Hispanic families for CH25H. However, we did observe a possible interaction between ABCA1 and APOE in the Hispanics.

Mutation analysis of CHCHD10 in different neurodegenerative diseases

Sir, A recent study by Bannwarth et al. (2014) implicated CHCHD10 as a novel gene for amyotrophic lateral sclerosis/frontotemporal lobar degeneration (ALS/FTLD), reporting a p.S59L substitution (c.176C > T; NM_213720.2) in a large French kindred. Affected family members were presented with a complex phenotype that included symptoms of amyotrophic lateral sclerosis (ALS), frontotemporal lobar degeneration (FTLD), cerebellar ataxia, Parkinson’s disease and a mitochondrial myopathy associated with multiple mitochondrial DNA deletions. So far, seven missense CHCHD10 mutations have been reported in patients with a broad phenotypic range, including ALS/FTLD (p.S59L and p.P34S) (Bannwarth et al. , 2014; Chaussenot et al. , 2014), ALS (p.R15L and p.G66V) (Johnson et al. , 2014; Muller et al. , 2014), myopathy (p.R15S and p.G58R) (Ajroud-Driss et al. , 2015) and late-onset spinal motor neuronopathy (p.G66V) (Penttila et al. , 2015). All of them affect exon 2 (a mutational hotspot of CHCHD10 ). Notably, mitochondrial dysfunction has been implicated in several neurodegenerative diseases (Lin and Beal, 2006; Cozzolino et al. , 2013); however, there are no studies evaluating the contribution of CHCHD10 to pure FTLD, Parkinson’s disease or Alzheimer’s disease. Hence, we sequenced CHCHD10 exon 2 in 204 ALS, 153 Parkinson’s disease and 141 Alzheimer’s disease patients from Canada and 158 FTLD patients from Italy in addition to 497 control subjects from USA/UK, Canada and Italy. The cases of ALS and FTLD were free from mutations in SOD1 , GRN , FUS , TARDBP and MATR3 or a repeat expansion in C9orf72 . We identified a known CHCHD10 pathogenic p.R15L mutation (Johnson et al. , 2014; Muller et al. , 2014) in a patient with sporadic ALS (Patient 8807) (Fig. 1A), who developed symptoms involving his upper limb at 54 years of age and remains alive 12 years later. The p.R15L …

Mutations in the open reading frame of the β-site APP cleaving enzyme (BACE) locus are not a common cause of Alzheimer's disease

Abstract Amyloid β-peptide (Aβ) plays a central role in the pathogenesis of Alzheimers disease (AD). The gene encoding the β-site APP cleaving enzyme (BACE), one of two enzymes that sequentially cleave the β-amyloid precursor protein to generate Aβ, has recently been cloned. We tested the hypothesis that BACE might be genetically associated with AD by linkage analysis (56 pedigrees), by direct nucleotide sequencing of the entire open reading frame (20 subjects with familial AD, and 10 subjects with sporadic AD) and by allelic association analysis (155 AD cases and 173 non-demented controls). Our results revealed no evidence for either genetic linkage or allelic association between BACE and AD, and no coding sequence mutations were detected in the open reading frame of the BACE gene. These data suggest that while BACE protein plays an important role in the pathogenesis of AD, and may be a robust therapeutic target, it is unlikely to be a major AD susceptibility locus.