Cloning of a gene bearing missense mutations in early-onset familial Alzheimer's disease

Alzheimer's disease and apolipoprotein E-4 allele in an Amish population

Alzheimer's Disease (AD) is a complex genetic disorder with four loci already identified. Mutations in three of these, the amyloid precursor protein, presenilin I, and presenilin II, cause early-onset AD. The apolipoprotein E (APOE) gene contributes primarily to late-onset AD. The APOE-4 allele acts in a dose-related fashion to increase risk and decrease the age-of-onset distribution in AD. We examined the effect of APOE on AD in a previously unstudied Amish population that has a lower prevalence of dementia compared with other populations. We sampled a large inbred family with 6 late-onset AD members. We also genotyped 53 individuals from the general Amish population as controls for the APOE allele frequency estimates. The frequency of the APOE-4 allele in the Amish controls was 0.037 +/- 0.02. This differed significantly compared with three independent sets of non-Amish white controls (p < 2 x 10(-4), p < 6 x 10(-5), and p < 2 x 10(-6)). In addition, all Amish AD-affected individuals had APOE 3/3 genotypes; no APOE X/4 or 4/4 individuals were observed. We suggest that the lower frequency of dementia in the Amish may be partially explained by the decreased frequency of the APOE-4 allele in this population, and that the inbred nature of this pedigree, with its strong clustering of cases contrasted against the lower frequency of dementia, indicates that additional genetic factors influence late-onset AD.

Genetic analysis of mechanisms of aging

A wide range of genetic models with postponed aging are now available, from selected mice and Drosophilia to mutant Caenorhabditis elegans and Saccharomyces cerevisiae. These systems allow efficient testing of alternative mechanistic hypotheses for aging. Genetic analysis is forging stronger connections between particular alleles and susceptibility to particular 'diseases of aging'; for example, two different genes for Alzheimer disease have been identified.

Amyloid beta-peptide and oxidative cellular injury in Alzheimer's disease

Alzheimer's disease is a progressive neurodegenerative disorder that affects primarily learning and memory functions. There is significant neuronal loss and impairment of metabolic functioning in the temporal lobe, an area believed to be crucial for learning and memory tasks. Aggregated deposits of amyloid beta-peptide may have a causative role in the development and progression of AD. We review the cellular actions of A beta and how they can contribute to the cytotoxicity observed in AD. A beta causes plasma membrane lipid peroxidation, impairment of ion-motive ATPases, glutamate uptake, uncoupling of a G-protein linked receptor, and generation of reactive oxygen species. These effects contribute to the loss of intracellular calcium homeostasis reported in cultured neurons. Many cell types other than neurons show alterations in the Alzheimer's brain. The effects of A beta on these cell types is also reviewed.

Embryonic genes expressed in Alzheimer's disease brains

Alzheimer's disease (AD)-specific or characteristic gene expression was explored by the identification of cDNA clones by means of differential screening for embryonic brain cDNA library with 32P-labeled cDNA probes prepared from mRNA of AD and normal human brains. To isolate neuronal genes in degenerating neurons, we used rat embryonic cDNA library at stage day 15 when glial cells developed poorly in the brain. Seventeen embryonic genes were identified as embryonic alpha-tubulin, embryonic beta-tubulin, hnRNP, protein L-isoaspartyl methyltransferase (PIMT), ferritin heavy chain, type IV collagen, actin-binding protein cofilin, profilin and nine novel sequences designated as A1-9. We characterized these genes by Northern blot analysis, RNase protection assay and immunohistochemical studies, showing that PIMT and a novel gene designated as A5 showed the transcriptional up-regulation in AD brains. In addition, the immunohistochemical studies showed PIMT, type IV collagen, and cofilin were associated with neurofibrillary tangles in degenerating neurons, brain vessels in affected regions, and synaptosomal structures in AD brains, respectively. The catalogue presented here also showed the involvement of cytoskeletal proteins, cytoskeleton-associated proteins, and an iron-storage protein, suggesting the presence of regenerating activity and the abnormal metabolisms in affected neurons of AD brains.

Fluorescent light-induced chromatid breaks distinguish Alzheimer disease cells from normal cells in tissue culture

The neurodegeneration and amyloid deposition of sporadic Alzheimer disease (AD) also occur in familial AD and in all trisomy-21 Down syndrome (DS) patients, suggesting a common pathogenetic mechanism. We investigated whether defective processing of damaged DNA might be that mechanism, as postulated for the neurodegeneration in xeroderma pigmentosum, a disease with defective repair not only of UV radiation-induced, but also of some oxygen free radical-induced, DNA lesions. We irradiated AD and DS skin fibroblasts or blood lymphocytes with fluorescent light, which is known to cause free radical-induced DNA damage. The cells were then treated with either beta-cytosine arabinoside (araC) or caffeine, and chromatid breaks were quantified. At least 28 of 31 normal donors and 10 of 11 donors with nonamyloid neurodegenerations gave normal test results. All 12 DS, 11 sporadic AD, and 16 familial AD patients tested had abnormal araC and caffeine tests, as did XP-A cells. In one of our four AD families, an abnormal caffeine test was found in all 10 afflicted individuals (including 3 asymptomatic when their skin biopsies were obtained) and in 8 of 11 offspring at a 50% risk for AD. Our tests could prove useful in predicting inheritance of familial AD and in supporting, or rendering unlikely, the diagnosis of sporadic AD in patients suspected of having the disease.

APOE alleles in Alzheimer's disease and vascular dementia in a population aged 85+

Apolipoprotein E genotyping was carried out in a stratified random sample of 52 patients with Alzheimer's disease, 48 patients with vascular or mixed dementia, and 49 nondemented controls in a population-based study of people aged 85 and older (the Vantaa 85+ Study). Our results indicate that the apolipoprotein E epsilon 4 allele is associated with approximately a twofold increase in clinically diagnosed Alzheimer's disease in this very old general population aged 85+. When combined with previous studies, our data also suggest that the association is decreasing with age. In contrast, there appears to be no relation between apolipoprotein E alleles and clinically diagnosed vascular dementia.

The heat shock/oxidative stress connection. Relevance to Alzheimer disease

Involvement of free-radical oxidations in the aging process has been a topic of interest since Harman's original contribution. Because of the close association between aging and Alzheimer disease (AD) and the qualitative similarity in the neuropathology of both conditions, it has been proposed by many investigators that oxidative stress may be important in Ad. If such modality of injury was indeed involved, one should expect to find markers of oxidation and heat shock (since free radicals are key mediators of heat-shock induction) in brains of patients with AD. In fact, several studies documented abnormal expression of antioxidant enzymes and heat-shock proteins (HSP) along with other markers of oxidation in AD brains. We showed that abnormally expressed antioxidant enzymes are topographically associated with senile plaques and neurofibrillary tangles, and that the activity of these enzymes is (contrary to what one would expect) markedly reduced. These findings have recently been confirmed by other investigators. Despite a large amount of evidence that suggests an association between oxidative stress and the pathogenesis of AD, it is not yet known whether oxidative stress is a cause or consequence of the disorder. Future research efforts regarding the oxidative stress hypothesis of AD should include attempts at generating AD pathology by oxidative means in laboratory animals, determining the role and integrity of the heat-shock response in AD, as well as that of various antioxidant systems, growth factors, and hormones with antioxidant and neuroprotective properties.

Three different mutations of presenilin 1 gene in early-onset Alzheimer's disease families

Presenilin-1 (PS-1) gene of three Japanese pedigrees with early-onset familial Alzheimer's disease (FAD) disclosed two novel missense mutations resulting in Val96Phe and Ile213Thr, and one mutation resulting in His163Arg. The mean age at onset in a family with His163Arg mutation was similar to those reported in other families with His163Arg. Our results suggested the existence of a variety of PS-1 mutations, and that early-onset FAD with PS-1 mutations is highly penetrant and is only rarely subject to modulation by genetic or environmental modifying factors.

The effect of tetraethylammonium on intracellular calcium concentration in Alzheimer's disease fibroblasts with APP, S182 and E5-1 missense mutations

It has been proposed that the lack of intracellular calcium concentration ([Ca2+]i) increase induced by the potassium channel blocker tetraethylammonium (TEA) in skin fibroblast cell lines identifies patients with both sporadic and familial Alzheimer's disease (AD). In order to verify this hypothesis, the effect of TEA on [Ca2+]i was studied in single fura-2-loaded skin fibroblast cell lines available in the Tissue Bank of the Italian Research Council. Four out of eight familial AD patients (one patient with S182 mutation, one patient with E5-1 mutation and two patients with 717 Val-->Ile APP mutation) and two out of five sporadic AD patients showed a positive response to TEA, whereas five out of 11 control lines were unresponsive. Our data suggest that the absence of the TEA-induced increase in [Ca2+]i in skin fibroblast cell lines does not identify all AD patients.

Recent advances. Medical genetics

Images

A beta A4 amyloid precursor protein gene and Alzheimer's disease

Alzheimer's disease is a senile dementia caused by progressive neurodegeneration of the central nervous system. One of the most prominent pathological characteristics is beta A4 amyloid deposition in senile plaques in the brain parenchyma and in cerebral blood vessels. beta A4 amyloid is processed from a larger integral membrane protein, the beta A4 amyloid precursor protein. Different pathogenic mutations in this protein have been detected in a small number of Alzheimer's disease families. Here functional implications of these mutations on the processing of the precursor protein and the beta A4 amyloid deposition will be discussed with respect to the pathogenesis of Alzheimer's disease and related disorders.

Genetic mapping using haplotype, association and linkage methods suggests a locus for severe bipolar disorder (BPI) at 18q22-q23

Manic depressive illness, or bipolar disorder (BP), is characterized by episodes of elevated mood (mania) and depression. We designed a multistage study in the genetically isolated population of the Central Valley of Costa Rica to identify genes that promote susceptibility to severe BP (termed BPI), and screened the genome ot two Costa Rican BPI pedigrees (McInnes et al., submitted). We considered only individuals who fulfilled very stringent diagnostic criteria for BPI to be affected. The strongest evidence for a BPI locus was observed in 18q22-q23. We tested 16 additional markers in this region and seven yielded peak lod scores over 1.0. These suggestive lod scores were obtained over a far greater chromosomal length (about 40 cM) than in any other genome region. This localization is supported by marker haplotypes shared by 23 of 26 BPI affected individuals studied. Additionally, marker allele frequencies over portions of this region are significantly different in the patient sample from those of the general Costa Rican population. Finally, we performed an analysis which made use of both the evidence for linkage and for association in 18q23, and we observed significant lod scores for two markers in this region.

Immunohistochemical analysis of presenilin-1 expression in the mouse brain

At least 22 different mutations associated with early-onset familial Alzheimer's disease (AD) in various kindreds have been reported to occur in a recently identified gene on chromosome 14, presenilin 1 (PS-1) (Sherrington et al. (1995) Nature 375, 754-760 [1] and reviewed by Van Broeckhoven (1995) Nat. Genet. 11, 230-231 [2]). In order to study the localization of PS-1 in the brain, we raised a polyclonal antiserum specific to a fragment of the predicted protein sequence of PS-1. PS-1 immunostaining was found intracellularly, in the perikaria of discrete cells, mostly neurons, appearing as thick granules, resembling large-size vesicles. These granules were located in the periphery of cell bodies and extended into dendrites and neurites. PS-1 expression was found to be broadly distributed throughout the mouse brain, not only in structures involved in AD pathology, but also in structures unaltered by this disease.

Molecular genetics of Alzheimer's disease

Four genes have thus far been implicated in the etiology of Alzheimer's disease (AD). A series of mutations in the amyloid precursor protein (APP) gene on chromosome 21, which cause disease with a typical onset of 55 years of age, have been described. These include mutations at APP670/671, APP692, and APP717. The epsilon 4 allele of the apolipoprotein E (ApoE) gene on chromosome 19 is positively associated with disease, whereas the epsilon 2 allele is usually negatively associated with disease. Mutations in the S182 gene on chromosome 14 seem to cause disease with an onset age of < 50 years and mutations in a gene on chromosome 1 (S182 Like Protein: S182LP) cause disease with variable onset. These genetic findings are reviewed within the framework of the amyloid cascade hypothesis of AD etiology and pathogenesis. The occurrence and effects of the mutations in APP and the fact that the epsilon 4 allele of ApoE are genetic risk factors point to the hypothesis that the extracellular deposition of beta-amyloid is the key initiating event in the pathogenesis of AD.

Clinical subgroups of the Alzheimer syndrome

During the last decade, senile dementia and the presenile disease that was named after Alois Alzheimer have been considered a single entity called Alzheimer's disease (AD). This same decade has witnessed the development of many diagnostic tools, such as CT, MRI, and SPECT imaging, that have made possible the systematic analysis of symptoms of brain disorders. With the aid of these sophisticated techniques, it is possible to divide the disorder into clinically relevant subgroups, one of which corresponds to the disease first described by Alzheimer. The disease exists in sporadic and familial forms, and in subgroups of these two basic types. Because the heterogeneity of AD is incontestable, it is time to reconsider the current use of the term "Alzheimer's disease." Because it labels different subgroups whose characteristics are often markedly different, the term "Alzheimer syndrome" appears to be more appropriate.

Gene expression of ND4, a subunit of complex I of oxidative phosphorylation in mitochondria, is decreased in temporal cortex of brains of Alzheimer's disease patients

Gene expression of mitochondrial DNA-encoded ND4 in brains of Alzheimer's disease (AD) patients and age-matched controls was measured using Northern blot. The level of ND4 message in temporal cortex of control subjects was higher than in motor cortex, whereas the level of ND4 gene expression in temporal cortex of AD brains was decreased compared with that in temporal cortex of controls. A control probe showed no difference in expression between the two areas of AD and control brains. These and previous data suggest that neurons vulnerable to AD express higher levels of enzymes of oxidative phosphorylation than do spared neurons, and that this difference may promote selective neuronal vulnerability of AD.

Molecular cloning and expression of the rat homologue of presenilin-1

The rat homologue of the presenilin-1 (PS-1) gene, which is responsible for early-onset familial Alzheimer's disease linked to chromosome 14, was cloned and sequenced. The predicted amino acid sequence showed quite high homology among rat, mouse, and human PS-1. Especially, the amino acid sequences of the putative transmembrane domains were highly conserved among the three species. The expression ĺevel of the PS-1 gene increased during brain development and the number of transcripts of the PS-1 gene changed during brain development. We found one transcript of the PS-1 gene in embryonic day 12 (E12)-E15 rat brain and two transcripts in E18-adult rat brain. Therefore, PS-1 may play a role in neurogenesis.

The amyloid precursor protein of Alzheimer's disease in the reduction of copper(II) to copper(I)

The transition metal ion copper(II) has a critical role in chronic neurologic diseases. The amyloid precursor protein (APP) of Alzheimer's disease or a synthetic peptide representing its copper-binding site reduced bound copper(II) to copper(I). This copper ion-mediated redox reaction led to disulfide bond formation in APP, which indicated that free sulfhydryl groups of APP were involved. Neither superoxide nor hydrogen peroxide had an effect on the kinetics of copper(II) reduction. The reduction of copper(II) to copper(I) by APP involves an electron-transfer reaction and could enhance the production of hydroxyl radicals, which could then attack nearby sites. Thus, copper-mediated toxicity may contribute to neurodegeneration in Alzheimer's disease.

Rational design of an animal model for Alzheimer's disease: introduction of multiple human genomic transgenes to reproduce AD pathology in a rodent

A major obstacle to understanding the pathogenesis of Alzheimer's disease is the lack of easily studied animal models. Our approach is to apply transgenic methods to humanize mice and rats, employing methods that introduce large genomic transgenes, because this improves the level of transgene protein expression and the tissue specificity of expression. Our plan is to reproduce AD pathology in rodents by making them transgenic for several human proteins involved in AD. This report describes transgenic animal lines that we have produced, and summarizes our current approach and future plans. Two human genes known to be involved in AD pathology are the amyloid precursor protein (APP) and the E4 isoform of apolipoprotein E (apoE4). So far, we have produced and analyzed a transgenic line carrying the entire human APP gene cloned in a yeast artificial chromosome. We have also produced but not yet analyzed a mouse carrying the human apoE4 gene. Work is in progress to produce a transgenic line carrying a disease-causing mutation in the human APP gene. As we produce these animals, we are breeding them together, and also breeding them with a mouse line that lacks endogenous apoE, to produce an animal model carrying several human proteins whose interaction is believed to be instrumental in development of AD pathology. These transgenic animals will be useful for dissecting the biochemical and physiological steps leading to AD, and for development of therapies for disease intervention.

Inclusion body myositis

Images

Neurological stamp. Valeriana officinalis (garden heliotrope)

Images

Identification and characterization of presenilin I-467, I-463 and I-374

We cloned a novel isoform of presenilin I (presenilin I-374) besides previously published presenilin I-467 and I-463 in human lymphocytes. Presenilin I-463 was identical to presenilin I-467 except a 12 bp nucleotides deletion in its amino terminal region. Another isoform, presenilin I-374 was produced by an alternative splicing with an additional exon consisting of 92 bp nucleotides (exon 11), which resulted in the frame shift with a stop codon to generate a truncated presenilin consisting of 374 amino acids. The transcripts for presenilin I-467/463 was ubiquitously detected while that for presenilin I-374 was selectively detected in liver, spleen, kidney. Abnormal behavior of presenilin I on gel electrophoresis was found with affinity-purified antibodies against presenilin I.

Genetic association between intronic polymorphism in presenilin-1 gene and late-onset Alzheimer's disease. Alzheimer's Disease Collaborative Group

BACKGROUND

Mutations in the presenilin-1 (PS-1) gene are associated with early-onset Alzheimer's disease. 40-50% of the risk for late-onset disease has been attributed to alleles at the apolipoprotein E (ApoE) locus. We have looked for an association between PS-1 and late- onset disease.

METHODS

We collected blood samples from 208 white cases of dementia of the Alzheimer type and from 185 age-matched controls (mean ages 76.9 and 76.2 years, respectively; 58% female in each series). Clinical diagnostic accuracy for Alzheimer's disease in our patients is 96%. We also studied 29 African-American patients with dementia of the Alzheimer type and 50 age-matched controls (cases vs controls, 77.2 vs 72.0 years; 72 vs 77% female). We used PCR to test for an association between Alzheimer's disease and a polymorphism within the intron 3' to exon 8 of the PS-1 gene. The ApoE genotype of most of the cases and controls was known from previous investigations.

FINDINGS

Homozygosity of the 1 allele in the PS-1 gene was associated with a doubling of the risk for late-onset Alzheimer's disease compared with the [12]/[22] genotype (odds ratio 1.97, 95% Cl 1.29-3.00). The proportion of Alzheimer's disease cases in the white population that could be attributed to homozygosity at this locus, as estimated by the attributable fraction, was 0.22. This compares with 0.35 for a single copy of ApoE4 and 0.15 for two copies. The smaller African-American series showed similar distribution of PS-1 genotype between cases and controls.

INTERPRETATION

In our white series of cases, PS-1 accounted for about half as much of the risk for late-onset Alzheimer's disease as did ApoE4.

Conservation of synteny between the genome of the pufferfish (Fugu rubripes) and the region on human chromosome 14 (14q24.3) associated with familial Alzheimer disease (AD3 locus)

The genome of the pufferfish (Fugu rubripes) (400 Mb) is approximately 7.5 times smaller than the human genome, but it has a similar gene repertoire to that of man. If regions of the two genomes exhibited conservation of gene order (i.e., were syntenic), it should be possible to reduce dramatically the effort required for identification of candidate genes in human disease loci by sequencing syntenic regions of the compact Fugu genome. We have demonstrated that three genes (dihydrolipoamide succinyltransferase, S31iii125, and S20i15), which are linked to FOS in the familial Alzheimer disease focus (AD3) on human chromosome 14, have homologues in the Fugu genome adjacent to Fugu cFOS. The relative gene order of cFOS, S31iii125, and S20i15 was the same in both genomes, but in Fugu these three genes lay within a 12.4-kb region, compared to >600 kb in the human AD3 locus. These results demonstrate the conservation of synteny between the genomes of Fugu and man and highlight the utility of this approach for sequence-based identification of genes in human disease loci.

The geneticist's approach to complex disease

Many studies are in progress worldwide to elucidate the genetics of complex diseases. Nevertheless, few articles are available that provide the scientific rationale and give guidelines for such ambitious endeavours. We describe the methodology and background necessary to study the genetics of complex disease and discuss how to analyze the data. We also provide a table of some ongoing studies. In particular, we wish to emphasize the analysis of intermediate, heritable, quantitative traits as a means of dissecting the genetic basis of a complex trait.

Apolipoprotein E alleles as risk factors in Alzheimer's disease

Alzheimer's disease (AD) is unique in medicine in that millions of people suffer from what appears to be the same form of disease, and unlike most other late-onset diseases, the genetic etiologies have been well identified. Three early onset forms of AD inherited as autosomal dominant traits account for less than 2% of prevalent AD. A major susceptibility locus, apolipoprotein E (APOE, gene; apoE, protein) is associated with risk and age of onset distributions for the common familial and sporadic late-onset AD. The identification of additional genetic susceptibility genes in the etiology of AD and the metabolic mechanisms leading to differences in age of onset and disease pathogenesis are active areas of current research.

Alzheimer-associated presenilins 1 and 2: neuronal expression in brain and localization to intracellular membranes in mammalian cells

Mutations in two recently identified genes appear to cause the majority of early-onset familial Alzheimer's disease (FAD). These two novel genes, presenilin 1 (PS1) and presenilin 2 (PS2) are members of an evolutionarily conserved gene family. The normal biological role(s) of the presenilins and the mechanism(s) by which the FAD-associated mutations exert their effect remain unknown. Employing in situ hybridization, we demonstrate that the expression patterns of PS1 and PS2 in the brain are extremely similar to each other and that messages for both are primarily detectable in neuronal populations. Immunochemical analyses indicate that PS1 and PS2 are similar in size and localized to similar intracellular compartments (endoplasmic reticulum and Golgi complex). FAD-associated mutations in PS1 and PS2 do not significantly modify either their migration patterns on SDS-polyacrylamide gel electrophoresis or their overall subcellular localization, although subtle differences in perinuclear staining were noted for mutant PS1.

Neurogenetic diseases: molecular diagnosis and therapeutic approaches

A neurogenetic disorder is defined as a clinical disease caused by a defect in one or more genes which affect the differentiation and function of the neuroectoderm and its derivatives. Genetic findings in various neurogenetic disorders are discussed. Huntington disease, spinobulbar muscular atrophy, and the autosomal dominant cerebellar ataxias are examples of autosomal dominant disorders caused by the expansion of trinucleotides (CAG) within disease genes. The CAG expansions appear to result in a gain of gene function. Prenatal, presymptomatic, and differential diagnostic tests are based on the detection of the repeat expansions. Point mutations within disease genes result in many additional neurogenetic disorders. An autosomal dominant form of amyotrophic lateral sclerosis and various types of craniosynostotic syndromes are described. The mutations in the disease genes also appear to result in a gain of gene function. Molecular diagnosis in these disorders is based on the direct examination of the mutated gene by methods such as single-strand conformation polymorphism analysis, denaturing gradient gel electrophoresis, and direct DNA sequencing. In many neurogenetic disorders the disease gene has not yet been identified. Here molecular diagnosis relies on indirect approaches based on methods such as the analysis of linkage and of allelic association. Hereditary forms of dystonia are presented as examples. Common sporadic neurological disorders such as Alzheimer and Parkinson diseases frequently have multifactorial causes. Investigations into the molecular basis and the development of diagnostic tests in these two important diseases are discussed. At present no curative therapies exist in neurogenetic disorders. Gene therapeutic approaches, however, provide promise for a cure in at least some of these diseases. Basic principles of gene therapy are explained and attempts at gene therapy in Alzheimer and Parkinson diseases are described. Finally, some of the many obstacles are summarized that must be overcome before gene therapy becomes feasible in most monogenic neurological diseases.

Review. David Oppenheimer Memorial Lecture 1995: Some neuropathological aspects of Alzheimer's disease and its relevance to other disciplines

Recent studies of diffuse A beta plaques point to the neurons as a source of A beta in diffuse plaques. The neuritic (primitive and classical) plaques appear to be the product of microglia and the myocytes are the source of amyloid deposits in the meningeal and cortical vessels. Dyshoric angiopathy is associated with deposits of amyloid by perivascular cells. Fibrillization of the neuron-derived diffuse, thioflavine-negative or benign plaques is poor or undetectable by current morphological methods including ultrastructural immunocytochemistry. It appears that fibrillization depends on the length of the A beta peptides and on the presence of amyloid-associated proteins. Four genes are now tightly linked with Alzheimer's disease (AD) and they are located on chromosomes 21, 19, 14 and 1. Therefore, AD should be considered a polyaetiological disease or syndrome. There are currently five transgenic mouse models overexpressing beta-APP. There is also a myocyte tissue culture model in which both soluble and fibrillized A beta are found. The relationship between A beta and neurofibrillary pathology is not clear and the current cascade hypothesis proposing that A beta pathology drives the formulation of neurofibrillary tangles is being questioned. There is growing evidence that it is not the A beta hypothesis, but the co-existing A beta neurofibrillary tangle pathology hypothesis which will be the basis for AD neuropathology.

Regulation of amyloid protein precursor (APP) binding to collagen and mapping of the binding sites on APP and collagen type I

The specific binding of the amyloid precursor protein (APP) to extracellular matrix molecules suggests that APP regulates cell interactions and has a function as a cell adhesion molecule and/or substrate adhesion molecule. On the molecular level APP has binding sites for collagen, laminin, and glycosaminoglycans which is a characteristic feature of cell adhesion molecules. We have examined the interactions between the APP and collagen types I and IV and identified the corresponding binding sites on APP and collagen type I. We show that APP bound most efficiently to collagen type I in a concentration-dependent and specific manner in the native and heat-denatured states, suggesting an involvement of a contiguous binding site on collagen. This binding site was identified on the cyanogen bromide fragment alpha 1(I)CB6 of collagen type I, which also binds heparin. APP did not bind to collagen type I-heparin complexes, which suggests that there are overlapping binding sites for heparin and APP on collagen. We localized the site of APP that mediates collagen binding within residues 448-465 of APP695, which are encoded by the ubiquitously expressed APP exon 12, whereas the high affinity heparin binding site of APP is located in exon 9. Since a peptide encompassing this region binds to collagen type I and inhibits APP-collagen type I binding in nanomolar concentrations, this region may comprise the major part of the collagen type I binding site of APP. Moreover, our data also indicate that the collagen binding site is involved in APP-APP interaction that can be modulated by Zn(II) and heparin. Taken together, the data suggest that the regulation of APP binding to collagen type I by heparin occurs through the competitive binding of heparin and APP to collagen.

Regulation of APP processing. Potential for the therapeutical reduction of brain amyloid burden

The role of brain amyloid in the pathogenesis of Alzheimer's disease (AD) is discussed controversially, but combined genetic and biochemical evidence points to a central role of the gene encoding the amyloid precursor APP in at least some forms of AD. This article proposes that preventing brain amyloid formation is a rational concept for drug treatment of AD. We suggest that pharmacologically active ligands for specific cell surface receptor subtypes--normally stimulated by neurotransmitters, growth factors, and cytokines--constitute a class of chemicals that might be useful to accelerate processing of APP into non-amyloidogenic, and biologically active, derivatives. This class of agents includes muscarinic m1 and m3 agonists, serotoninergic 5-HT2a and 5-HT2c agonists, glutamatergic mGluR1 agonists, as well as agonists for bradykinin and vasopressin receptors.

Morphological, biochemical, and genetic support for an apolipoprotein E effect on microtubular metabolism

There are two distinct viewpoints on the association of the inheritance of apolipoprotein E (APOE) alleles and the age of onset distribution of Alzheimer's disease (AD): genetic and phenotypic expression. There have been multiple corroborations of the APOE-epsilon 4 association with Alzheimer's disease in populations around the world in clinic based studies as well as emerging epidemiological studies. The genetic data do not imply mechanism of pathogenesis. The phenotypic expression of AD has been based in theories based on amyloid plaques or neurofibrillary tangles. ApoE protein interacts with both beta-amyloid and tau in an isoform-specific manner. The interaction with tau had been thought to be an in vitro artifact, since apoE had not been previously localized to the neuronal cytoplasm. Immuno-EM studies have localized apoE in neuronal cytoplasm. ApoE3 interacts with both tau and MAP2c at the microtubule binding repeat domain under conditions in which apoE4 is less tightly bound. These data further support a hypothesis that apoE3 (and apoE2) protect the microtubule binding domain of tau from binding to itself to form paired helical filaments and neurofibrillary tangles, while protecting the site for microtubule stabilizing interactions with beta-tubulin. These data are supported by recent data from APOE knock-out mice demonstrating dendritic alterations leading to synaptic simplification similar to that observed in AD.

Evolution of senescence: Alzheimer's disease and evolution

The genetic basis of Alzheimer's disease is becoming clear; it appears to fit the postulates of the two main theories of the evolution of senescence, with both polymorphic alleles and rare mutations involved.

The molecular significance of amyloid beta-peptide for Alzheimer's disease

Alzheimer's disease is the most common form of dementia. Although the majority of the cases occur sporadically, in some rare cases Alzheimer's disease is genetically inherited. Pathologically, Alzheimer's disease is characterized by the accumulation of senile plaques with-in the extracellular space of brain regions known to be important for intellectual functions. In addition to senile plaques, deposits of identical biochemical composition are found in the walls of meningeal and cerebral blood vessels. Senile plaques are surrounded by degenerating neurons indicating a toxic interference of amyloid plaques with neurons. The major component of senile plaques is the 4kDa amyloid beta-peptide. This peptide has been shown to exhibit neurotoxic properties when added to cultured neurons, or injected into rat brains. Amyloid beta-peptide is derived from a high molecular weight precursor, the beta-amyloid precursor protein, by proteolytic processing. Mutations responsible for the early onset of Alzheimer's disease in some families are found within the gene coding for the beta-amyloid precursor protein. These mutations strongly influence the generation of amyloid beta-peptide resulting in a significant overproduction of the peptide or the generation of elongated forms which are known to aggregate and precipitate much faster. Moreover, mutations found in other genes known to cause early onset of Alzheimer's disease have been shown to interfere directly with the production or precipitation of amyloid beta-peptide.