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

Tau phosphorylation in cells transfected with wild-type or an Alzheimer's disease mutant Presenilin 1

We have studied the effect of overexpressing either wild-type or an Alzheimer's disease mutant Presenilin 1 (PS1) on tau phosphorylation in transfected Chinese hamster ovary (CHO) and COS cells. Tau transfected into these cells is predominantly non-phosphorylated at many PHF-tau sites but co-transfection with the tau kinase glycogen synthase kinase-3 beta (GSK-3 beta) induces phosphorylation that generates epitopes for several phosphorylation-dependent antibodies. Co-transfection of tau with either wild-type or mutant PS1 did not alter tau phosphorylation as detected by five different antibodies. Likewise, co-transfection of the PS1s did not influence GSK-3 beta-mediated tau phosphorylation. The implications of these results for the pathogenesis of Alzheimer's disease are discussed.

Nontoxic amyloid beta peptide 1-42 suppresses acetylcholine synthesis. Possible role in cholinergic dysfunction in Alzheimer's disease

We show here that amyloid beta peptide1-42 (Abeta1-42) may play a key role in the pathogenesis of the cholinergic dysfunction seen in Alzheimer's disease (AD), in addition to its putative role in amyloid plaque formation. Abeta1-42 freshly solubilized in water (non-aged Abeta1-42), which was not neurotoxic without preaggregation, suppressed acetylcholine (ACh) synthesis in cholinergic neurons at very low concentrations (10-100 nM), although non-aged Abeta1-40 was ineffective. Non-aged Abeta1-42 impaired pyruvate dehydrogenase (PDH) activity by activating mitochondrial tau protein kinase I/glycogen synthase kinase-3beta, as we have already shown in hippocampal neurons (Hoshi, M., Takashima, A., Noguchi, K., Murayama, M., Sato, M., Kondo, S., Saitoh, Y., Ishiguro, K., Hoshino, T., and Imahori, K. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 2719-2723). Neither choline acetyltransferase activity nor choline metabolism was affected. Therefore, the major cause of reduced ACh synthesis was considered to be an inadequate supply of acetyl-CoA owing to PDH impairment. Soluble Abeta1-42 increases specifically in AD brain (Kuo, Y.-M., Emmerling, M. R., Vigo-Pelfrey, C., Kasunic, T. C., Kirkpatrick, J. B., Murdoch, G. H., Ball, M. J., and Roher, A. E. (1996) J. Biol. Chem. 271, 4077-4081). This increase in soluble Abeta1-42 may disturb cholinergic function, leading to the deterioration of memory and cognitive function that is characteristic of AD.

An intronic polymorphism in the presenilin-1 gene does not influence the amount or molecular form of the amyloid beta protein deposited in Alzheimer's disease

The frequency of the allele-1 polymorphism in intron 8 of the presenilin-1 (PS-1) gene, and the proportion of individuals homozygous in this respect, was investigated in 57 patients with autopsy verified Alzheimer's disease (AD). In 33 of these patients the amount of amyloid beta protein (A beta) was compared across the three PS-1 genotype groups (1/1, 1/2, 2/2). No excess of the allele-1 was detected in these patients with confirmed AD and no variations in the extent of A beta deposition, as either A beta 40 or A beta 42, in terms of plaque number or percentage area of tissue occupied, were found. We conclude that this intronic PS-1 polymorphism does not influence the pathological phenotype of AD, at least as far as A beta deposition is concerned.

Assignment of Alzheimer's presenilin-2 (PS-2) gene to 1q42.1 by fluorescence in situ hybridization

Presenilin-2 (PS-2) was suggested to be localized on 1q31-42 based on linkage analysis and cDNA cloning. The final identification of PS-2 as the causal gene for early-onset familial Alzheimer's disease in Voga-German pedigrees was concluded based on the point mutation found in the candidate cDNA isolated from this familial AD. We present evidence of its physical genome mapping of PS-2 on chromosome 1q42.1 by fluorescence in situ hybridization method.

Expression of presenilin 1 and 2 (PS1 and PS2) in human and murine tissues

Mutations in genes encoding related proteins, termed presenilin 1 (PS1) and presenilin 2 (PS2), are linked to the majority of cases with early-onset familial Alzheimer's disease (FAD). To clarify potential function(s) of presenilins and relationships of presenilin expression to pathogenesis of AD, we examined the expression of PS1 and PS2 mRNA and PS1 protein in human and mouse. Semi-quantitative PCR of reverse-transcribed RNA (RT-PCR) analysis revealed that PS1 and PS2 mRNA are expressed ubiquitously and at comparable levels in most human and mouse tissues, including adult brain. However, PS1 mRNA is expressed at significantly higher levels in developing brain. In situ hybridization studies of mouse embryos revealed widespread expression of PS1 mRNA with a neural expression pattern that, in part, overlaps that reported for mRNA encoding specific Notch homologs. In situ hybridization analysis in adult mouse brain revealed that PS1 and PS2 mRNAs are enriched in neurons of the hippocampal formation and entorhinal cortex. Although PS1 and PS2 mRNA are expressed most prominently in neurons, lower but significant levels of PS1 and PS2 transcripts are also detected in white matter glial cells. Moreover, cultured neurons and astrocytes express PS1 and PS2 mRNAs. Using PS1-specific antibodies in immunoblot analysis, we demonstrate that PS1 accumulates as approximately 28 kDa N-terminal and approximately 18 kDa C-terminal fragments in brain. Immunocytochemical studies of mouse brain reveal that PS1 protein accumulates in a variety of neuronal populations with enrichment in somatodendritic and neuropil compartments.

Amyloid beta peptide of Alzheimer's disease downregulates Bcl-2 and upregulates bax expression in human neurons

Neuronal apoptosis is a suspected cause of neurodegeneration in Alzheimer's disease (AD). Increased levels of amyloid beta peptide (Abeta) induce neuronal apoptosis in vitro and in vivo. The underlying molecular mechanism of Abeta neurotoxicity is not clear. The normal concentration of Abeta in cerebrospinal fluid is 4 nM. We treated human neuron primary cultures with 100 nM amyloid beta peptides Abeta(1-40) and Abeta(1-42) and the control reverse peptide Abeta(40-1). We find that although little neuronal apoptosis is induced by either peptide after 3 d of treatment, Abeta(1-42) provokes a rapid and sustained downregulation of a key anti-apoptotic protein, bcl-2, whereas it increases levels of bax, a protein known to promote cell death. In contrast, the Abeta(1-40) downregulation of bcl-2 is gradual, although the levels are equivalent to those of Abeta(1-42)-treated neurons by 72 hr of treatment. Abeta(1-40) does not upregulate bax levels. The control, reverse peptide Abeta(40-1), does not affect either bcl-2 or bax protein levels. In addition, we found that the Abeta(1-40)- and Abeta(1-42)- but not Abeta(40-1)-treated neurons had increased vulnerability to low levels of oxidative stress. Therefore, we propose that although high physiological amounts of Abeta are not sufficient to induce apoptosis, Abeta depletes the neurons of one of its anti-apoptotic mechanisms. We hypothesize that increased Abeta in individuals renders the neurons vulnerable to age-dependent stress and neurodegeneration.

The apolipoprotein E epsilon4 allele causes a faster decline of cognitive performances in Down's syndrome subjects

The apolipoprotein E gene (APOE), located on human chromosome 19, has three common alleles (epsilon2, epsilon3, epsilon4) which encode for the three main isoforms indicated as E2, E3 and E4 respectively. Several findings indicate epsilon4 allele as an important risk factor in both sporadic and familial late-onset Alzheimer's disease (AD). Pathological changes similar to AD are seen in almost all patients with Down's syndrome (DS) aged over 35 (senile plaques, neurofibrillary tangles and neuronal loss); a proportion of these may subsequently develop dementia. Aim of this study is to evaluate the possible pathological role of epsilon4 allele as risk factor for developing AD in a DS population. ApoE epsilon4 allele frequency is not significantly different in DS cases and controls. We found a statistically significant inverse correlation between full scale IQ values and age of patients in the subgroup of DS subjects selected for the presence of at least one epsilon4 allele, while no correlation was observed in DS subjects with other ApoE genotypes. A longitudinal analysis of cognitive performances (available in 38 patients) showed a faster rate of decline in intellectual ability in those subjects carrying at least one epsilon4 allele. Our data support the hypothesis that ApoE epsilon4 allele has a contributory role in accelerating the mental deterioration of AD-type in DS patients.

Mutant presenilins of Alzheimer's disease increase production of 42-residue amyloid beta-protein in both transfected cells and transgenic mice

The mechanism by which mutations in the presenilin (PS) genes cause the most aggressive form of early-onset Alzheimer's disease (AD) is unknown, but fibroblasts from mutation carriers secrete increased levels of the amyloidogenic A beta 42 peptide, the main component of AD plaques. We established transfected cell and transgenic mouse models that coexpress human PS and amyloid beta-protein precursor (APP) genes and analyzed quantitatively the effects of PS expression on APP processing. In both models, expression of wild-type PS genes did not alter APP levels, alpha- and beta-secretase activity and A beta production. In the transfected cells, PS1 and PS2 mutations caused a highly significant increase in A beta 42 secretion in all mutant clones. Likewise, mutant but not wildtype PS1 transgenic mice showed significant overproduction of A beta 42 in the brain, and this effect was detectable as early as 2-4 months of age. Different PS mutations had differential effects on A beta generation. The extent of A beta 42 increase did not correlate with presenilin expression levels. Our data demonstrate that the presenilin mutations cause a dominant gain of function and may induce AD by enhancing A beta 42 production, thus promoting cerebral beta-amyloidosis.

Amyloid precursor protein, copper and Alzheimer's disease

Although a consensus that Alzheimer's disease (AD) is a single disease has not yet been reached, the involvement of the amyloid precursor protein (APP) and beta A4 (A beta) in the pathologic changes advances our understanding of the underlying molecular alterations. Increasing evidence implicates oxidative stress in the neurodegenerative process of AD. This hypothesis is based on the toxicity of beta A4 in cell cultures, and the findings that aggregation of beta A4 can be induced by metal-catalyzed oxidation and that free oxygen radicals might be involved in APP metabolism. Another neurological disorder, familial amyotrophic lateral sclerosis (FALS), supports our view that AD and FALS might be linked through a common mechanism. In FALS, SOD-Cu(I) complexes are affected by hydrogen peroxide and free radicals are produced. In AD, the reduction of Cu(II) to Cu(I) by APP involves an electron-transfer reaction and could also lead to a production of hydroxyl radicals. Thus, copper-mediated toxicity of APP-Cu(II)/(I) complexes may contribute to neurodegeneration in AD.

Oxidative stress hypothesis in Alzheimer's disease

The major hurdle in understanding Alzheimer's disease (AD) is a lack of knowledge about the etiology and pathogenesis of selective neuron death. In recent years, considerable data have accrued indicating that the brain in AD is under increased oxidative stress and this may have a role in the pathogenesis of neuron degeneration and death in this disorder. The direct evidence supporting increased oxidative stress in AD is: (1) increased brain Fe, Al, and Hg in AD, capable of stimulating free radical generation; (2) increased lipid peroxidation and decreased polyunsaturated fatty acids in the AD brain, and increased 4-hydroxynonenal, an aldehyde product of lipid peroxidation in AD ventricular fluid; (3) increased protein and DNA oxidation in the AD brain; (4) diminished energy metabolism and decreased cytochrome c oxidase in the brain in AD; (5) advanced glycation end products (AGE), malondialdehyde, carbonyls, peroxynitrite, heme oxygenase-1 and SOD-1 in neurofibrillary tangles and AGE, heme oxygenase-1, SOD-1 in senile plaques; and (6) studies showing that amyloid beta peptide is capable of generating free radicals. Supporting indirect evidence comes from a variety of in vitro studies showing that free radicals are capable of mediating neuron degeneration and death. Overall, these studies indicate that free radicals are possibly involved in the pathogenesis of neuron death in AD. Because tissue injury itself can induce reactive oxygen species (ROS) generation, it is not known whether this is a primary or secondary event. Even if free radical generation is secondary to other initiating causes, they are deleterious and part of a cascade of events that can lead to neuron death, suggesting that therapeutic efforts aimed at removal of ROS or prevention of their formation may be beneficial in AD.

Presenilin proteins undergo heterogeneous endoproteolysis between Thr291 and Ala299 and occur as stable N- and C-terminal fragments in normal and Alzheimer brain tissue

Humans inheriting missense mutations in the presenilin (PS)1 and -2 genes undergo progressive cerebral deposition of the amyloid beta-protein at an early age and develop a clinically and pathologically severe form of familial Alzheimer's disease (FAD). Because PS1 mutations cause the most aggressive known form of AD, it is important to elucidate the structure and function of this multitransmembrane protein in the brain. Using a panel of region-specific PS antibodies, we characterized the presenilin polypeptides in mammalian tissues, including brains of normal, AD, and PS1-linked FAD subjects, and in transfected and nontransfected cell lines. Very little full-length PS1 or -2 was detected in brain and untransfected cells; instead the protein occurred as a heterogeneous array of stable N- and C-terminal proteolytic fragments that differed subtly among cell types and mammalian tissues. Sequencing of the major C-terminal fragment from PS1-transfected human 293 cells showed that the principal endoproteolytic cleavage occurs at and near Met298 in the proximal portion of the large hydrophilic loop. Full-length PS1 in these cells is quickly turned over (T1/2 approximately 60 min), in part to the two major fragments. The sizes and amounts of the PS fragments were not significantly altered in four FAD brains with the Cys410Tyr PS1 missense mutation. Our results indicate that presenilins are rapidly processed to N- and C-terminal fragments in both neural and nonneural cells and that interference with this processing is not an obligatory feature of FAD-causing mutations.

Amyloid (Abeta) deposition in chromosome 1-linked Alzheimer's disease: the Volga German families

Amyloid beta protein (Abeta) deposition was investigated in the frontal cortex of 6 cases of (genetically confirmed) chromosome 1-linked Alzheimer's disease (AD) (PS-2 gene mutation) among the Volga German families using the end-specific monoclonal antibodies BA27 and BC05 to detect the presence of Abeta40 and Abeta42(43), respectively. In all patients, Abeta42(43) was the predominant peptide species present, although the total amount of Abeta40 and Abeta42(43) deposited in plaques did not differ from that seen in sporadic AD and was significantly lower than that occurring in AD due to PS-1 gene mutations. Therefore, mutations in the PS-2 gene, like those in the presenilin-1 (PS-1) and amyloid precursor protein (APP) genes, are associated with an initial and preferential deposition of Abeta42(43) within the brain. Although the mechanism(s) whereby the PS-1 and PS-2 gene mutations operate remains unclear, it seems from the present study that the effect of the PS-2 gene mutation on the brain is much less severe, at least as far as Abeta deposition is concerned, than that of the PS-1 mutation, which seems to confer a much earlier and a much more aggressive development of AD.

Preparing for presymptomatic DNA testing for early onset Alzheimer's disease/cerebral haemorrhage and hereditary Pick disease

The acceptability of presymptomatic testing in 21 people at 50% risk for the APP-692 mutation causing presenile Alzheimer's disease or cerebral haemorrhage resulting from cerebral amyloid angiopathy (FAD-CH), and in 43 people at 50% risk for hereditary Pick disease (HPD) was assessed. Neither group differed in demographic variables. Thirty-nine people (64%) in the whole group would request presymptomatic testing if it were clinically available, although two-thirds did not yet feel ready to take it. The most important reasons in the HPD and FAD-CH group for taking the test were: to further basic research (42% and 47%, respectively), informing children (47% and 50%, respectively), future planning (29% and 47%, respectively), and relieving uncertainty (46% and 27%, respectively). The most commonly cited effect of an unfavourable test result concerned increasing problems for spouses (75% and 76%, respectively) and children (61% and 57%, respectively). Most respondents denied that an unfavourable result would have adverse effects on personal mood or relationship. One-third of all respondents favoured prenatal testing where one of the parents had an increased risk for HPD or FAD-CH. Participants would encourage their offspring to have the test before starting a relationship (35%) and before family planning (44%). Thirty-seven percent of the respondents would encourage their children to opt for prenatal diagnosis. People at risk for HPD were significantly more preoccupied with the occurrence of potential symptoms in themselves, compared with those at risk for FAD-CH, reflecting the devastating impact that disinhibition in the affected patient has on the family. Our findings underline the need for adequate counselling and the availability of professional and community resources to deal with the impact of test results in subjects and their relatives.

Lymphocyte content of amyloid precursor protein is increased in Down's syndrome and aging

We quantified cellular amyloid precursor protein (APP) in ethanol-permeabilized peripheral lymphocytes from 13 subjects with Alzheimer's disease (AD), 11 subjects with Down's syndrome (DS), and 13 healthy elderly and 31 healthy young controls. APP content was analyzed by indirect immunofluorescence and flow cytometry, using the 22C11 monoclonal antibody (mAb) directed against an N-terminal domain of APP. Authenticity of 22C11 APP signal was confirmed by immunoblotting and flow cytometry studies with the mAb 6E10, directed against the A beta domain of APP. Consistent with gene dosage, patients with DS had 1.51-fold higher lymphocyte APP signal than age-matched normal young subjects (corrected p < 0.05). Both AD patients and elderly control groups had significantly increased lymphocyte APP signal compared to young controls (either comparison corrected p < 0.01). Indeed, increasing age in non-DS subjects was significantly correlated with lymphocyte APP (r = 0.508, p < 0.0001), such that APP immunoreactivity more than doubled from 20 to 80 years. Lymphocyte APP was nonsignificantly higher in AD vs. aged controls in this small sample. Increased cellular APP content in DS and aging may correspond to generalized alterations in expression or processing of this molecule, and suggests a novel determinant for the timing of AD onset.

Diagnosis of Alzheimer's disease. Report of an International Psychogeriatric Association Special Meeting Work Group under the cosponsorship of Alzheimer's Disease International, the European Federation of Neurological Societies, the World Health Organization, and the World Psychiatric Association

Current knowledge with respect to the diagnosis of Alzheimer's disease (AD) is reviewed. There is agreement that AD is a characteristic clinicopathologic entity that is amenable to diagnosis. The diagnosis of AD should no longer be considered one of exclusion. Rather, the diagnostic process is one of recognition of the characteristic features of AD and of conditions that can have an impact on presentation or mimic aspects of the clinicopathologic picture. The present availability of improved prognosis, management, and treatment strategies makes the proper, and state-of-the-art, diagnosis of AD a clinical imperative in all medical settings. Concurrently, information regarding the relevance and applicability of current diagnostic procedures in diverse cultural settings must continue to accrue.

Enhanced aggregation of beta-amyloid-containing peptides by extracellular matrix and their degradation by the 68 kDa serine protease prepared from human brain

To explore whether extracellular matrix components in human brain affect the deposition and aggregation of beta-amyloid containing peptides, human brain samples from patients with sporadic Alzheimer's disease and normal aged were analyzed by Western blot analysis. All major beta-amyloid-containing peptides contained epitope(s) which is recognized by anti heparan sulfate antibody. Incubation of brain beta-amyloid-containing peptides with human collagen type IV in neutral pH efficiently generated a high molecular weight aggregated band, approximately 5-fold that of the control sample. We have previously found a serine protease which is capable of cleaving an oligopeptide at the N-terminus of beta-amyloid. In this study, the protease, which also contains heparan sulfate glycoconjugates, degraded the above brain peptides as natural substrates, although with different efficiency. These findings suggest that extra-cellular matrix components affect the processing and aggregation of beta-amyloid-containing peptides in human brain.

Early detection of Alzheimer's disease by combining apolipoprotein E and neuroimaging

New treatments for Alzheimer's disease (AD) are more likely to slow or halt disease progression rather than to reverse existing neuronal damage. Identifying persons with mild cognitive complaints who are at risk for AD will allow investigators to apply anti-dementia treatments before extensive brain damage develops. The discovery of the apolipoprotein E epsilon 4 allele (APOE epsilon 4) as a major risk factor for AD offers promise of assisting in early detection and prediction of Alzheimer's disease, particularly when genetic assessments are combined with other biomarkers such as neuroimaging. Studies of relatives at risk for familial AD using neuroimaging (positron emission tomography [PET]) and genetic assessments of APOE suggest that at-risk relatives with APOE epsilon 4 have lower parietal metabolism than those without APOE epsilon 4. Additional techniques that might increase sensitivity and specificity include longitudinal assessment of clinical and brain functional change, pharmacological challenges of short-acting anticholinergic agents, and memory activation paradigms during functional scanning. Such strategies should eventually assist in early detection of AD and in vivo therapeutic monitoring of brain function during experimental anti-dementia treatment trials.

Brain beta-spectrin is a component of senile plaques in Alzheimer's disease

Spectrin is a multifunctional cortical membrane skeleton protein. We report here that the beta-subunit of spectrin is an integral component of beta-amyloid plaques in Alzheimer's disease (AD). We prepared anti-beta-spectrin antibodies by using synthetic peptides corresponding to the N-terminal and C-terminal domains of beta-spectrin variants. When tissues from post-mortem AD brains were immunostained with these domain-specific affinity purified beta-spectrin antibodies, beta-amyloid plaques were specifically stained in the cortical parenchyma in approximately one third of the cases. The staining was unaffected by preadsorption of beta-spectrin antibodies with A4/beta 1-40 peptide. The sodium dodecyl sulfate-insoluble amyloids were also stained by the beta-spectrin antibodies. The anti-alpha-spectrin antibody stained neuronal processes, but not amyloid plaques. The presence of beta-spectrin in the amyloid plaques in a subset of sporadic AD cases suggests that distinct biochemical pathways are involved in the formation or deposition of beta-amyloid plaques, and that an abnormality of beta-spectrin structure or function may be involved in the formation or deposition of beta-amyloid plaques in this subset of AD cases.

No association between alpha 1-antichymotrypsin and familial Alzheimer's disease

Alzheimer's disease (AD) is the most common mid to late age-of-onset neurodegenerative disorder. AD has a strong and complex genetic etiology, and multiple genes, acting independently and/or interacting, likely affect the risk of developing AD. Several genes involved with AD already have been described, but only the APOE gene on chromosome 19q has been shown to affect the risk of the most common form of AD, occurring with onset over the age of 65. Because a substantial portion of late-onset AD is not explained by APOE, other genes affecting late-onset AD likely occur. These could act either independently or perhaps interact with APOE. alpha 1-Antichymotrypsin (ACT) is a major component of the amyloid plaques found in the brains of AD patients and may play a role in the pathophysiology of AD. It has been proposed that a specific polymorphism within the ACT gene interacts with APOE to increase the risk of developing AD. Our results do not confirm this finding.

The length of amyloid-beta in hereditary cerebral hemorrhage with amyloidosis, Dutch type. Implications for the role of amyloid-beta 1-42 in Alzheimer's disease

In hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), a genetic variant (E22Q) of amyloid beta (Abeta) accumulates predominantly in the small vessels of leptomeninges and cerebral cortex, leading to fatal strokes in the fifth or sixth decade of life. Abeta deposition in the neuropil occurs mainly in the form of preamyloid, Congo red negative deposits, while mature neuritic plaques and neurofibrillary tangles, hallmark lesions in Alzheimer's disease (AD), are characteristically absent. A recent hypothesis regarding the pathogenesis of AD states that Abeta extending to residues 42-43 (as opposed to shorter species) can seed amyloid formation and trigger the development of neuritic plaques followed by neuronal damage in AD. We characterized biochemically and immunohistochemically Abeta from three cases of HCHWA-D to determine its length in vascular and parenchymal deposits. Mass spectrometry of formic acid-soluble amyloid, purified by size-exclusion gel chromatography, showed that Abeta 1-40 and its carboxyl-terminal truncated derivatives were the predominant forms in leptomeningeal and cortical vessels. Abeta 1-42 was a minor component in these amyloid extracts. Immunohistochemistry with antibodies S40 and S42, specific for Abeta ending at Val-40 or Ala-42, respectively, were consistent with the biochemical data from vascular amyloid. In addition, parenchymal preamyloid lesions were specifically stained with S42 and were not labeled by S40, in agreement with the pattern reported for AD, Down's syndrome, and aged dogs. Our results suggest that in HCHWA-D the carboxyl-terminal Abeta heterogeneity is due to limited proteolysis in vivo. Moreover, they suggest that Abeta species ending at Ala-42 may not be critical for the seeding of amyloid formation and the development of AD-like neuritic changes.

Assessment of normal and mutant human presenilin function in Caenorhabditis elegans

We provide evidence that normal human presenilins can substitute for Caenorhabditis elegans SEL-12 protein in functional assays in vivo. In addition, six familial Alzheimer disease-linked mutant human presenilins were tested and found to have reduced ability to rescue the sel-12 mutant phenotype, suggesting that they have lower than normal presenilin activity. A human presenilin 1 deletion variant that fails to be proteolytically processed and a mutant SEL-12 protein that lacks the C terminus display considerable activity in this assay, suggesting that neither presenilin proteolysis nor the C terminus is absolutely required for normal presenilin function. We also show that sel-12 is expressed in most neural and nonneural cell types in all developmental stages. The reduced activity of mutant presenilins and as yet unknown gain-of-function properties may be a contributing factor in the development of Alzheimer disease.

Requirement of the familial Alzheimer's disease gene PS2 for apoptosis. Opposing effect of ALG-3

ALG-3, a truncated mouse homologue of the chromosome 1 familial Alzheimer's disease gene PS2, rescues T hybridoma 3DO cells from T-cell receptor-induced apoptosis by inhibiting Fas ligand induction and Fas signaling. Here we show that ALG-3 transfected 3DO cells express a COOH-terminal PS2 polypeptide. Overexpression of PS2 in ALG-3 transfected 3DO cells reconstitutes sensitivity to receptor-induced cell death, suggesting that the artificial PS2 polypeptide functions as a dominant negative mutant of PS2. ALG-3 and antisense PS2 protect PC12 cells from glutamate-induced apoptosis but not from death induced by hydrogen peroxide or the free radical MPP+. Thus, the PS2 gene is required for some forms of cell death in diverse cell types, and its function is opposed by ALG-3.

The neurochemistry of Alzheimer's disease

The last 15-20 years have seen a wealth of studies to characterize the neurochemical abnormalities of Alzheimer's disease, in particular those involving the beta-amyloid and tau proteins, as well as more recently, apolipoprotein E4. This article provides a summary of the evidence for the involvement of these proteins in Alzheimer's disease pathogenesis based on postmortem brain and CSF studies.

The tRNA(Gln) 4336 mitochondrial DNA variant is not a high penetrance mutation which predisposes to dementia before the age of 75 years

The genetic factors that predispose to Alzheimer's disease (AD) are heterogeneous. Two recent reports have suggested that a mitochondrial DNA mutation within the tRNAGln gene, located at position 4336, may be a risk factor for AD, as it was found in 10/256 (3.9%) cases with AD confirmed by necropsy. Although low prevalences of this mutation were detected in non-demented subjects in both of these studies, the controls were not carefully matched with the AD cases. We have investigated the frequency of this mutation in two community based elderly cohorts in Cambridgeshire, who have participated in longitudinal studies of cognitive function. The 4336 mitochondrial mutation was detected in 8/ 443 people examined. These people were found to be non-demented at ages 74, 81, 84, 86, 89, 90, 91, and 102 years, in contrast to the previously described cases whose onset of dementia occurred between 60 and 76 years (mean 68). Accordingly, we believe that this mitochondrial variant is not a high penetrance mutation which predisposes to dementia before the age of 76 years.

Genetics of Alzheimer's disease

Alzheimer's disease (AD) is characterised neuropathologically by the accumulation of neuritic plaques and neurofibrillary tangles as well as by cerebrovascular amyloid deposition and neuronal cell loss. The major component of neuritic plaques and cerebrovascular amyloid is a 40-42 amino acid peptide termed beta-amyloid, derived as a proteolytic fragment from the large amyloid precursor protein (APP), a membrane-bound protein expressed in most tissues. The last few years have seen considerable advances in understanding the pathogenesis of Alzheimer's disease through genetic studies. The importance of the beta-amyloid peptide in the pathogenesis of AD has been strengthened by the identification of pathogenic mutations in the APP gene on chromosome 21.

Wide range in age of onset for chromosome 1--related familial Alzheimer's disease

Mutations in three different genes on chromosomes 1, 14, and 21 cause autosomal dominant forms of familial Alzheimer's disease (FAD). Most result in an early-onset phenotype. However, several kindreds of Volga German ancestry have the same chromosome 1 gene mutation and demonstrate a relatively older mean age of onset and include individuals with late age of onset. In these families, the mean age of onset is 54.9 +/- 8.4 years (range, 40-75 years), mean age at death is 65.9 +/- 10.2 years (range, 43-88 years), and mean disease duration is 11.3 +/- 4.6 years (range, 5-23 years). This contrasts with a group of 7 families with chromosome 14 mutations in which the mean age of onset is 44.8 +/- 4.8 years (range, 30-55 years), mean age at death is 52.6 +/- 5.7 years (range, 39-65 years), and mean disease duration is 7.6 +/- 3.2 years (range, 2-17 years). (All means are significantly different in the 2 groups of families, p < 0.005.) In the chromosome 1 families, 7 persons (16%) had an age of onset at or older than 65 years and 22 (54%) survived to age 65 or older versus none in the chromosome 14 families. An example of probable nonpenetrance of disease at age 89 was also found in a chromosome 1 kindred. It is concluded that, unlike the chromosome 14 gene, mutations in the chromosome 1 FAD gene may result in individuals with a late age of onset overlapping with the more common sporadic form of the disease occurring in the general population. In light of the great variability in age of onset in persons with identical mutations, study of the genetic and environmental factors contributing to delayed onset of disease in chromosomal 1 FAD kindreds will be an important area for further investigation. Apolipoprotein E genotype may be one such factor that plays a partial role in this variability.

The clinical phenotype of two missense mutations in the presenilin I gene in Japanese patients

We report the clinical and neuropathologic phenotypes associated with two different missense mutations in the presenilin 1 (PS-1) gene in Japanese patients with early-onset familial Alzheimer's disease (FAD). In the AM/JPN1 pedigree a missense mutation (C-->T) was found at nucleotide 1102, which is predicted to cause an alanine-to-valine missense substitution at codon 260. In this family, the disease had a mean age of onset of 40.3 years and an indolent course (range, 8-19 years). Neuropathologic studies in 3 members of this pedigree showed widespread senile plaques, neurofibrillary tangles, and neuronal loss, as well as abundant perivascular subpial amyloid deposits in the Virchow-Robin spaces and the presence of Pick-like intraneuronal inclusions in the dentate gyrus. In the second pedigree, transmitting a C-->T nucleotide substitution at position 1027, leading to the missense mutation of alanine to valine at codon 285, the disease had a later onset (mean, 51 years) but a more rapid course. Comparison of the disease phenotypes associated with other missense mutations in exon 9 of PS-1 reveals no clinical or pathological phenotype, which uniquely distinguishes Alzheimer's disease associated with PS-1 mutations from other forms of early-onset FAD, implying that direct mutation screening is required to identify these cases.

A vector for expressing foreign genes in the brains and hearts of transgenic mice

An expression plasmid (MoPrP.Xho), for use in transgenic mice, was developed from the promoter, 5' intronic, and 3' untranslated sequences of the murine prion protein gene. Analyses of mice harboring the MoPrP.Xho construct with cDNA genes encoding the amyloid precursor protein (APP) and human presenilin 1 demonstrated that this vector provides relatively high levels of transgene-encoded polypeptides in brains and hearts of transgenic mice. The MoPrP.Xho vector should be very useful in strategies designed to overexpress a variety of wild-type and disease related mutant transgenes in the heart and brain.

Application of PET in dementia disorders

Positron emission tomography (PET) is a valuable tool for understanding of functional correlates of biological and structural changes in brain of patients with various dementia diseases. As such it can provide valuable physiological correlates important for diagnosis, management and research of dementia disorders. A crucial question is whether PET is capable of early or preclinical detection of dementia. Longitudinal PET studies in Alzheimer families with chromosomal aberrations will be important for. Impairment of cerebral blood flow and glucose metabolism is a common feature in patients with Alzheimer's disease. The pattern of changes is distinct from other forms of dementia and correlates with neuropsychological impairments. Neuroreceptor studies have to be further applied as well as monitoring of drug treatment effects.

Damage, repair, and mutagenesis in nuclear genes after mouse forebrain ischemia-reperfusion

To determine whether oxidative stress after cerebral ischemia-reperfusion affects genetic stability in the brain, we studied mutagenesis after forebrain ischemia-reperfusion in Big Blue transgenic mice (male C57BL/6 strain) containing a reporter lacI gene, which allows detection of mutation frequency. The frequency of mutation in this reporter lacI gene increased from 1.5 to 7.7 (per 100,000) in cortical DNA after 30 min of forebrain ischemia and 8 hr of reperfusion and remained elevated at 24 hr reperfusion. Eight DNA lesions that are characteristic of DNA damage mediated by free radicals were detected. Four mutagenic lesions (2,6-diamino-4-hydroxy-5-formamidopyrimidine, 8-hydroxyadenine, 5-hydroxycytosine, and 8-hydroxyguanine) examined by gas chromatography/mass spectrometry and one corresponding 8-hydroxy-2'-deoxyguanosine by a method of HPLC with electrochemical detection increased in cortical DNA two- to fourfold (p < 0.05) during 10-20 min of reperfusion. The damage to gamma-actin and DNA polymerase-beta genes was detected within 20 min of reperfusion based on the presence of formamidopyrimidine DNA N-glycosylase-sensitive sites. These genes became resistant to the glycosylase within 4-6 hr of reperfusion, suggesting a reduction in DNA damage and presence of DNA repair in nuclear genes. These results suggest that nuclear genes could be targets of free radicals.

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.

Cognitive and neurobiologic markers of early Alzheimer disease

Recent studies indicate that impairments in two cognitive domains characterize the cognitive abnormalities that appear earliest in the course of Alzheimer disease (AD). These cognitive domains pertain to memory and executive function ability; in particular, memory test scores reflecting the difference between immediate and delayed recall and tasks that assess cognitive flexibility (e.g., set-shifting). Preliminary data indicate that tasks of this nature, along with specific genetic information (i.e., APOE-4 status), are important in identifying which individuals with recent cognitive changes (considered to have "questionable" disease) will progress to the point where they meet criteria for AD over time. When this cognitive and genetic information is combined with neuroimaging measures targeted at the brain regions demonstrating pathology early in AD, it may serve as specific and accurate prognostic markers of AD.

Effect of aluminium on expression and processing of amyloid precursor protein

The environmental agent aluminium has been extensively investigated for a potential role in the aetiology of Alzheimer's disease. Despite many investigations there is at present no definite proof for any involvement. If aluminium is involved it is possible that its action is mediated through interaction with the synthesis or processing of amyloid precursor protein (APP). The present study compared aluminium loaded IMR-32 neuroblastoma cells and rat brains with control cells and brains to determine if aluminium affected APP expression and/or processing. In the IMR-32 model system aluminium had no effect on steady-state APP mRNA levels or on the ratio of individual isoforms. It also had no quantitative or qualitative effect on APP-immunoreactive bands detected in protein extracts from conditioned medium of these cells. In total cell extracts, aluminium reduced the intensity of APP-immunoreactive bands between 120-105 kDa but had no effect on a 9 kDa band. In rat brains, aluminium had no effect on APP-immunoreactive bands from soluble or insoluble-membranous extracts. The results, in general, provide no evidence for any effect of aluminium on APP expression or processing.

Alzheimer-associated presenilin-2 confers increased sensitivity to apoptosis in PC12 cells

Presenilin-2 is a gene of unknown function recently identified based upon linkage with some forms of familial Alzheimer's disease. To investigate potential effects of PS-2 on cell viability, rat pheochromocytoma (PC12) cells were stably transfected with cDNA constructs encoding either full-length human PS-2 or, for comparison, mouse Bcl-X(L). Overexpression of PS-2 conferred increased sensitivity to the apoptotic stimuli staurosporine and hydrogen peroxide. In contrast, Bcl-X(L) overexpression significantly reduced cell death induced by these stimuli. These results suggest that one function of PS-2 may involve modulation of cell viability.

Membrane topology of the C. elegans SEL-12 presenilin

Mutant presenilins cause Alzheimer's disease. Presenilins have multiple hydrophobic regions that could theoretically span a membrane, and a knowledge of the membrane topology is crucial for deducing the mechanism of presenilin function. By analyzing the activity of beta-galactosidase hybrid proteins expressed in C. elegans, we show that the C. elegans SEL-12 presenilin has eight transmembrane domains and that there is a cleavage site after the sixth transmembrane domain. We examine the presenilin sequence in view of the predicted topology and discuss possible mechanisms for presenilin function.

Familial Alzheimer's disease-linked presenilin 1 variants elevate Abeta1-42/1-40 ratio in vitro and in vivo

Mutations in the presenilin 1 (PS1) and presenilin 2 genes cosegregate with the majority of early-onset familial Alzheimer's disease (FAD) pedigrees. We now document that the Abeta1-42(43)/Abeta1-40 ratio in the conditioned media of independent N2a cell lines expressing three FAD-linked PS1 variants is uniformly elevated relative to cells expressing similar levels of wild-type PS1. Similarly, the Abeta1-42(43)/Abeta1-40 ratio is elevated in the brains of young transgenic animals coexpressing a chimeric amyloid precursor protein (APP) and an FAD-linked PS1 variant compared with brains of transgenic mice expressing APP alone or transgenic mice coexpressing wild-type human PS1 and APP. These studies provide compelling support for the view that one mechanism by which these mutant PS1 cause AD is by increasing the extracellular concentration of Abeta peptides terminating at 42(43), species that foster Abeta deposition.

Presenilin-1 polymorphism in patients with Alzheimer's disease, vascular dementia and alcohol-associated dementia in Japanese population

We investigated the genetic association between intronic polymorphism in Presenilin-1 (PS-1) gene and patients with various types of dementia such as Alzheimer's disease (AD), vascular dementia (VD) and alcohol associated dementia (ALD), in Japanese population. Homozygosity for allele 1 of the PS-1 polymorphism was significantly increased in late-onset sporadic AD, but not in early-onset sporadic AD, familial AD, VD and ALD. When late-onset sporadic AD patients were divided on the basis of apolipoprotein E (APOE) genotype, homozygosity for the allele 1 of the PS-1 polymorphism was significantly increased in patients with late-onset sporadic AD without APOE epsilon 4 allele, but not in those with APOE epsilon 4 allele. Intronic mutation in PS-1 gene may be specific and one of the genetic risk factor for late-onset sporadic AD.

Serum levels of the iron binding protein p97 are elevated in Alzheimer's disease

Alzheimer's disease is a progressive and incurable disease whose prevalence increases dramatically with age. A biochemical marker for monitoring the onset and progression of the disease would be a valuable tool for disease management. In addition, such a marker might be used as an end point in clinical intervention protocols. Here we provide evidence that the soluble form of the iron binding protein p97 is found in elevated amounts in the serum of Alzheimer's patients compared with healthy controls. This biochemical marker has the potential for identifying subjects afflicted with the disease and possibly for monitoring the onset and longitudinal progression of the disease.

Sequence analysis of presenilin-1 gene mutation in Japanese Alzheimer's disease patients

The mutations of presenilins (PSs) gene and their clinicopathological correlations to Alzheimer's disease (AD) have lately attracted considerable attention. In this report we analyzed fifteen Japanese familial Alzheimer's disease (FAD) including 12 early-onset FAD and 13 sporadic AD patients for the mutation of PS-1 gene by direct sequence analysis. We found the mutations, G384A, E280A in two FAD and H163R in one sporadic AD patient, and no N1411 or M239V mutation in PS-2 gene, and no mutation in exons 16 and 17 in amyloid precursor protein (APP) gene. Families in which we failed to find the mutation by this screening may have mutations elsewhere in PSs or in APP gene, or yet unidentified other AD loci may exist. This is the first report to find a sporadic AD patient having PS-1 mutation.

Issues in genetic testing for susceptibility to alcoholism: lessons from Alzheimer's disease and Huntington's disease

Evidence from family, twin, and adoption studies suggest a heritable basis for alcoholism. However, alcoholism is likely to be genetically heterogeneous, and any genetic connection is likely to be in the form of genes conferring an increased risk or susceptibility. In this study, we present the evidence for a genetic component for alcoholism, and examine the precedent for genetic testing and screening for genetic susceptibility using Huntington's disease and Alzheimer's disease as examples. Finally, we discuss the preparations that need to be made before taking any findings about the genetics of alcoholism from the research laboratory into the clinic.

Protein topology of presenilin 1

Mutations in a gene encoding a multitransmembrane protein, termed presenilin 1 (PS1), are causative in the majority of early-onset cases of AD. To determine the topology of PS1, we utilized two strategies: first, we tested whether putative transmembranes are sufficient to export a protease-sensitive substrate across a lipid bilayer; and second, we examined the binding of antibodies to specific PS1 epitopes in cultured cells selectively permeabilized with the pore-forming toxin, streptolysin-O. We document that the "loop," N-terminal, and C-terminal domains of PS1 are oriented toward the cytoplasm.