Neuronal intranuclear inclusions in polyglutamine diseases: nuclear weapons or nuclear fallout?
Explore the source record for details and available documents.
Apoptosis↗
Biomedical subjects
R E Tanzi
Publications and source records attributed to R E Tanzi.
Alpha-2 macroglobulin is genetically associated with Alzheimer disease.
Alpha-2-macroglobulin (alpha-2M; encoded by the gene A2M) is a serum pan-protease inhibitor that has been implicated in Alzheimer disease (AD) based on its ability to mediate the clearance and degradation of A beta, the major component of beta-amyloid deposits. Analysis of a deletion in the A2M gene at the 5' splice site of 'exon II' of the bait region (exon 18) revealed that inheritance of the deletion (A2M-2) confers increased risk for AD (Mantel-Haenzel odds ratio=3.56, P=0.001). The sibship disequilibrium test (SDT) also revealed a significant association between A2M and AD (P=0.00009). These values were comparable to those obtained for the APOE-epsilon4 allele in the same sample, but in contrast to APOE-epsilon4, A2M-2 did not affect age of onset. The observed association of A2M with AD did not appear to account for the previously published linkage of AD to chromosome 12, which we were unable to confirm in this sample. A2M, LRP1 (encoding the alpha-2M receptor) and the genes for two other LRP ligands, APOE and APP (encoding the amyloid beta-protein precursor), have now all been genetically linked to AD, suggesting that these proteins may participate in a common neuropathogenic pathway leading to AD.
Age of Onset↗
Of calcium, caspases, and cognitive decline.
Explore the source record for details and available documents.
Alzheimer Disease↗
Genetic association of an alpha2-macroglobulin (Val1000lle) polymorphism and Alzheimer's disease.
alpha2-Macroglobulin (A2M) is a proteinase inhibitor found in association with senile plaques (SP) in Alzheimer's disease (AD). A2M has been implicated biochemically in binding and degradation of the amyloid beta (Abeta) protein which accumulates in SP. We studied the relationship between Alzheimer's disease and a common A2M polymorphism, Val1000 (GTC)/Ile1000 (ATC), which occurs near the thiolester active site of the molecule. In an initial exploratory data set (90 controls and 171 Alzheimer's disease) we noted an increased frequency of the G/G genotype from 0.07 to 0.12. We therefore tested the hypothesis that the G/G genotype is over-represented in Alzheimer's disease in an additional independent data set: a group of 359 controls and 566 Alzheimer's disease patients. In the hypothesis testing cohort, the G/G genotype increased from 0.07 in controls to 0.12 in Alzheimer's disease (P < 0.05, Fisher's exact test). The odds ratio for Alzheimer's disease associated with the G/G genotype was 1.77 (1.16-2.70, P < 0.01) and in combination with APOE4 was 9.68 (95% CI 3.91-24.0, P < 0.001). The presence of the G allele was associated with an increase in Abeta burden in a small series. The A2M receptor, A2M-r/LRP, is a multifunctional receptor whose ligands include apolipoprotein E and the amyloid precursor protein. These four proteins have each been genetically linked to Alzheimer's disease, suggesting that they may participate in a common disease pathway.
Alleles↗
Alzheimer's disease: genetic studies and transgenic models.
Recent advances in a variety of areas of research, particularly in genetics and in transgenic (Tg)/gene targeting approaches, have had a substantial impact on our understanding of Alzheimer's disease (AD) and related disorders. After briefly reviewing the progress that has been made in diagnostic assessments of patients with senile dementia and in investigations of the neuropathology of AD, we discuss some of the genes/proteins that are causative or risk factors for this disease, including those encoding amyloid precursor protein, presenilin 1 and 2, and apolipoprotein E. In addition, we comment on several potential new candidate loci/genes. Subsequently, we review selected recent reports of analyses of a variety of lines of Tg mice that show several neuropathological features of AD, including A beta-amyloid deposits and dystrophic neurites. Finally, we discuss the several important issues in future investigations of Tg mice, with particular emphasis on the influences of genetic strains on phenotype, especially behavior, and strategies for making new models of neurodegenerative disorders. We believe that investigations of these Tg models will (a) enhance understanding of the relationships between impaired performance on memory tasks and the pathological/biochemical abnormalities in brain, (b) help to clarify pathogenic mechanisms in vivo, (c) lead to identification of new therapeutic targets, and (d) allow testing of new treatment strategies first in mice and then, if successful, in humans with AD.
Alzheimer Disease↗
Cerebrospinal fluid levels of amyloid precursor protein and amyloid beta-peptide in Alzheimer's disease and major depression - inverse correlation with dementia severity.
Alzheimer's disease (AD) is the most common neurodegenerative disorder characterized by progressive dementia that ultimately leads to death. Histopathological hallmarks of AD include brain amyloid deposits and neurofibrillary tangles. Major depression is a frequent diagnosis in every gerontopsychiatric clinic that sees patients with both cognitive and affective disorders. Many depressed patients, in fact, are clinically characterized by cognitive impairments. Thus, an assay that excludes - or confirms - probable AD in cognitively impaired patients is desirable. Such assays may use protein markers that are derived from such histopathologically relevant molecules as the amyloid precursor protein (APP) and its derivatives including the amyloid beta-peptides (Abeta). To evaluate the differential diagnostic properties of cerebrospinal fluid (CSF) Abeta and secreted soluble ectodomain (APPs), we quantitated CSF levels of these measures in AD patients and compared them to age-matched control patients with major depression. CSF levels of APPs and Abeta were similar in patients with AD or major depression, and the apolipoprotein E genotype had no influence on CSF levels of Abeta in AD patients. Measurement of Abeta peptide using a novel zinc/copper capture ELISA that detects aggregated Abeta peptides as well demonstrated similar levels in AD and major depression. In AD patients, CSF levels of total Abeta (Abeta1-40 plus Abeta1-42) were inversely correlated with a functional measure of dementia severity (NOSGER), suggesting that CSF levels of Abeta decrease with advancing severity of AD. Thus, CSF levels of Abeta are not useful for the differentiation of AD from major depression. However, CSF levels of Abeta reflect the severity of dementia and may be useful as biological markers of the stage of the disease.
Aged↗
Zinc-induced Alzheimer's Abeta1-40 aggregation is mediated by conformational factors.
The heterogeneous precipitates of Abeta that accumulate in the brain cortex in Alzheimer's disease possess varying degrees of resistance to resolubilization. We previously found that Abeta1-40 is rapidly precipitated in vitro by physiological concentrations of zinc, a neurochemical that is highly abundant in brain compartments where Abeta is most likely to precipitate. We now present evidence that the zinc-induced precipitation of Abeta is mediated by a peptide dimer and favored by conditions that promote alpha-helical and diminish beta-sheet conformations. The manner in which the synthetic peptide is solubilized was critical to its behavior in vitro. Zinc-induced Abeta aggregation was dependent upon the presence of NaCl, was enhanced by alpha-helical-promoting solvents, but was abolished when the peptide stock solution was stored frozen. The Abeta aggregates induced by zinc were reversible by chelation, but could then be reprecipitated by zinc for several cycles, indicating that the peptide's conformation is probably preserved in the zinc-mediated assembly. In contrast, Abeta aggregates induced by low pH (5.5) were not resolubilized by returning the pH milieu to 7.4. The zinc-Abeta interaction exhibits features resembling the gelation process of zinc-mediated fibrin assembly, suggesting that, in events such as clot formation or injury, reversible Abeta assembly could be physiologically purposive. Such a mechanism is contemplated in the early evolution of diffuse plaques in Alzheimer's disease and suggests a possible therapeutic strategy for the resolubilization of some forms of Abeta deposit in the disease.
Alzheimer Disease↗
Genetics of aging.
The role of genetics in determining life-span is complex and paradoxical. Although the heritability of life-span is relatively minor, some genetic variants significantly modify senescence of mammals and invertebrates, with both positive and negative impacts on age-related disorders and life-spans. In certain examples, the gene variants alter metabolic pathways, which could thereby mediate interactions with nutritional and other environmental factors that influence life-span. Given the relatively minor effect and variable penetrance of genetic risk factors that appear to affect survival and health at advanced ages, life-style and other environmental influences may profoundly modify outcomes of aging.
Aging↗
Alternative cleavage of Alzheimer-associated presenilins during apoptosis by a caspase-3 family protease.
Most cases of early-onset familial Alzheimer's disease (FAD) are caused by mutations in the genes encoding the presenilin 1 (PS1) and PS2 proteins, both of which undergo regulated endoproteolytic processing. During apoptosis, PS1 and PS2 were shown to be cleaved at sites distal to their normal cleavage sites by a caspase-3 family protease. In cells expressing PS2 containing the asparagine-141 FAD mutant, the ratio of alternative to normal PS2 cleavage fragments was increased relative to wild-type PS2-expressing cells, suggesting a potential role for apoptosis-associated cleavage of presenilins in the pathogenesis of Alzheimer's disease.
Alzheimer Disease↗
Evidence for phosphorylation and oligomeric assembly of presenilin 1.
Pathogenic mutations in presenilin 1 (PS1) are associated with approximately 50% of early-onset familial Alzheimer disease. PS1 is endoproteolytically cleaved to yield a 30-kDa N-terminal fragment (NTF) and an 18-kDa C-terminal fragment (CTF). Using COS7 cells transfected with human PS1, we have found that phorbol 12, 13-dibutyrate and forskolin increase the state of phosphorylation of serine residues of the human CTF. Phosphorylation of the human CTF resulted in a shift in electrophoretic mobility from a single major species of 18 kDa to a doublet of 20-23 kDa. This mobility shift was also observed with human PS1 that had been transfected into mouse neuroblastoma (N2a) cells. Treatment of the phosphorylated CTF doublet with phage lambda protein phosphatase eliminated the 20- to 23-kDa doublet while enhancing the 18-kDa species, consistent with the interpretation that the electrophoretic mobility shift was due to the addition of phosphate to the 18-kDa species. The NTF and CTF eluted from a gel filtration column at an estimated mass of over 100 kDa, suggesting that these fragments exist as an oligomerized species. Upon phosphorylation of the PS1 CTF, the apparent mass of the NTF- or CTF-containing oligomers was unchanged. Thus, the association of PS1 fragments may be maintained during cycles of phosphorylation/dephosphorylation of the PS1 CTF.
Animals↗
Endoproteolytic cleavage and proteasomal degradation of presenilin 2 in transfected cells.
Mutations in the presenilin genes, PS1 and PS2, cause a major portion of early onset familial Alzheimer's disease (FAD). The biological roles of the presenilins and how their pathological mutations confer FAD are unknown. In this study, we set out to examine the processing and degradation pathways of PS2. For regulated expression of PS2, we have established inducible cell lines expressing PS2 under the tight control of the tetracycline-responsive transactivator. Western blot analysis revealed that PS2 was detected as an approximately 53-55-kDa polypeptide (54-kDa PS2) as well as a high molecular mass form (HMW-PS2). Using a stably transfected, inducible cell system, we have found that PS2 is proteolytically cleaved into two stable cellular polypeptides including an approximately 20-kDa C-terminal fragment and an approximately 34-kDa N-terminal fragment. PS2 is polyubiquitinated in vivo, and the degradation of PS2 is inhibited by proteasome inhibitors, N-acetyl-L-leucinal-L-norleucinal and lactacystin. Our studies suggest that PS2 normally undergoes endoproteolytic cleavage and is degraded via the proteasome pathway.
Alzheimer Disease↗
Phosphorylation of Alzheimer beta-amyloid precursor-like proteins.
Amyloid precursor-like proteins (APLPs), APLP1 and APLP2, are members of a gene family which include the Alzheimer beta-amyloid precursor protein (APP). APLP1, APLP2, and APP contain highly homologous amino acid sequences, especially in their cytoplasmic domains, although APLPs lack the beta-amyloid domain derived by proteolytic processing from APP. APP is phosphorylated at three sites in the cytoplasmic domain in cultured cells and adult rat brain [Suzuki et al. (1994) EMBO J. 13, 1114-1122; Oishi, et al. (1997) Mol. Med. 3, 109-121] and at sites in the extracellular domain in cultured cells [Knops et al. (1993) Biochem. Biophys. Res. Commun. 197, 380-385; Hung & Selkoe (1994) EMBO J. 13, 534-542; Walter et al. (1997) J. Biol. Chem. 272, 1896-1903]. We report here that a cytoplasmic domain peptide from APLP1 is phosphorylated in vitro by protein kinase C and that a cytoplasmic domain peptide from APLP2 is phosphorylated in vitro by protein kinase C and cdc2 kinase. APLP2 is phosphorylated by cdc2 kinase at a site homologous to the cdc2 kinase site phosphorylated in APP. Furthermore, phosphorylation of this site occurs in a cell cycle-dependent manner in cultured cells. These findings indicate that in intact cells the phosphorylation of APLP2 appears to be regulated in a similar fashion to that of APP.
Alzheimer Disease↗
A novel presenilin-1 mutation: increased beta-amyloid and neurofibrillary changes.
The prevalence of known mutations in presenilin genes (PS1 and PS2) causing early-onset familial Alzheimer's disease (FAD) was assessed in a population of 98 singleton early-onset AD cases, 29 early-onset FAD cases, and 15 late-onset FAD cases. None of the cases tested positive for the eight mutations initially reported, and none of these mutations were observed in 60 age-matched controls. A novel mutation (R269H) in PS1 was found in a single case of early-onset AD but not in any other AD or control case. Thus, the PS mutations tested are quite rare in early-onset AD. Amyloid beta protein (A beta) deposition was investigated in the temporal cortex of the R269H mutation case using end-specific monoclonal antibodies to detect the presence of A beta x-40 and A beta x-42 subspecies. Stereologically unbiased tangle and neuropil thread counts were obtained from the same region. R269H PS1 mutation was associated with early age of dementia onset, higher amounts of total A beta and A beta x-42, and increased neuronal cytoskeletal changes. Thus, if the changes observed on this case prove to be typical of PS1 mutations, PS1 mutations may impact both amyloid deposition and neurofibrillary pathology.
Age of Onset↗
Presenilins and Alzheimer's disease.
Mutations in the genes encoding the presenilins cause the majority of early-onset cases of Alzheimer's disease (AD). The identification of the presenilin genes has provided new opportunities for elucidating the molecular mechanisms underlying the etiology and pathogenesis of AD. Recent progress has been made in attempts to understand the normal and pathological functions of the presenilins, emphasizing the effects of presenilin familial AD mutations on the amyloid beta-protein precursor, the presenilins themselves, and apoptotic cell death.
Alzheimer Disease↗
Developmental regulation of presenilin mRNA expression parallels notch expression.
Mutations in the presenilin (PS) 1 and 2 genes are associated with autosomal dominant Alzheimer disease. PS1 shares striking homology with sel-12, a C. elegans gene implicated in the function of lin-12/Notch, a protein important in neurogenesis. We studied mRNA expression using RT-PCR and in situ hybridization techniques during neural development in mouse and rat. Strong expression of PSs and Notch1 was observed in embryos, especially in the ventricular zone, which decreased gradually as embryos developed. Very low levels of PSs and Notch were present in adulthood, their signals present primarily in the hippocampus and cerebellum. These observations show that, like Notch, PS1 and PS2 are strongly developmentally regulated, and support the plausibility of an interaction between PSs and Notch.
Animals↗
In situ hybridization analysis of presenilin 1 mRNA in Alzheimer disease and in lesioned rat brain.
Presenilin-1 (PS-1) gene mutations are responsible for the majority of the early onset familial forms of Alzheimer disease (AD). Neither PS-1's anatomic distribution in brain nor expression in AD have been reported. Using in situ hybridization in the rat forebrain, we show that PS-1 mRNA expression is primarily in cortical and hippocampal neurons, with less expression in subcortical structures, in a regional pattern similar to APP695. Excitotoxic lesions lead to loss of PS-1 signal. A neuronal pattern of expression of PS-1 mRNA was also observed in the human hippocampal formation. AD and control levels did not differ. PS-1 is expressed in brain areas vulnerable to AD changes more so than in areas spared in AD; however, PS-1 expression is not sufficient to mark vulnerable regions. Collectively, these data suggest that the neuropathogenic process consequent to PS-1 mutations begins in neuronal cell populations.
Aged↗
Association of a novel human FE65-like protein with the cytoplasmic domain of the beta-amyloid precursor protein.
We identified a novel human homologue of the rat FE65 gene, hFE65L, by screening the cytoplasmic domain of beta-amyloid precursor protein (beta PP) with the "interaction trap." The cytoplasmic domains of the beta PP homologues, APLP1 and APLP2 (amyloid precursor-like proteins), were also tested for interaction with hFE65L. APLP2, but not APLP1, was found to interact with hFE65L. We confirmed these interactions in vivo by successfully coimmunoprecipatating endogenous beta PP and APLP2 from mammalian cells overexpressing a hemagglutinin-tagged fusion of the C-terminal region of hFE65L. We report the existence of a human FE65 gene family and evidence supporting specific interactions between members of the beta PP and FE65 protein families. Sequence analysis of the FE65 human gene family reveals the presence of two phosphotyrosine interaction (PI) domains. Our data show that a single PI domain is sufficient for binding of hFE65L to the cytoplasmic domain of beta PP and APLP2. The PI domain of the protein, Shc, is known to interact with the NPXYp motif found in the cytoplasmic domain of a number of different growth factor receptors. Thus, it is likely that the PI domains present in the C-terminal moiety of the hFE65L protein bind the NPXY motif located in the cytoplasmic domain of beta PP and APLP2.
Amino Acid Sequence↗
Expression and analysis of presenilin 1 in a human neuronal system: localization in cell bodies and dendrites.
Mutations in the recently identified presenilin 1 gene on chromosome 14 cause early onset familial Alzheimer disease (FAD). Herein we describe the expression and analysis of the protein coded by presenilin 1 (PS1) in NT2N neurons, a human neuronal model system. PS1 was expressed using recombinant Semliki Forest virions and detected by introduced antigenic tags or antisera to PS1-derived peptides. Immunoprecipitation revealed two major PS1 bands of approximately 43 and 50 kDa, neither of which were N-glycosylated or O-glycosylated. Immunoreactive PS1 was detected in cell bodies and dendrites of NT2N neurons but not in axons or on the cell surface. PS1 was also detected in BHK cells, where it was also intracellular and colocalized with calnexin, a marker for the rough endoplasmic reticulum. A mutant form of PS1 linked to FAD did not differ from the wild-type protein at the light microscopic level. The model system described here will enable studies of the function of PS1 in human neurons and the role of mutant PS1 in FAD.
Alzheimer Disease↗