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

Characterization of VPS41, a gene required for vacuolar trafficking and high-affinity iron transport in yeast

Mutations in the yeast gene VPS41 give rise to poor growth on low iron medium, severe alterations in vacuolar morphology, and cause the missorting of membranous and soluble vacuolar proteins. Our studies predict that VPS41 encodes a hydrophilic protein of 992 amino acids that contains no obvious signal sequence or hydrophobic domains. The deduced Vps41p sequence contains a domain rich in glutamic and aspartic residues, as well as a domain with resemblance to a region of clathrin heavy chain. We have also identified and sequenced putative VPS41 homologues from Caenorhabditis elegans, plants, and humans. The VPS41 homologues (but not the yeast VPS41 itself) contain a conserved cysteine-rich RING-H2 zinc finger at their COOH termini. Biochemical experiments suggest that VPS41 functions in post-Golgi protein processing: the deletion mutant exhibits defective high affinity transport due to impaired Fet3p activity and also exhibits defects in the processing and sorting of multiple vacuolar hydrolases.

beta-Amyloid (A beta) deposition in the medial temporal lobe of patients with dementia with Lewy bodies

The distribution and density of diffuse, primitive and classic beta-amyloid (A beta) deposits in the medial temporal lobe (MTL) was studied in cases of dementia with Lewy bodies (DLB) with and without associated Alzheimer's disease (AD) and 15 cases of sporadic AD. In the 'pure' DLB cases, virtually no A beta deposits were observed in the CA regions of the hippocampus or dentate gyrus whereas deposits were distributed throughout the MTL in DLB/AD and AD cases. Densities of diffuse and primitive A beta deposits were similar in AD and DLB/AD cases but density was significantly reduced in the 'pure' DLB cases. The density of the classic deposits was significantly reduced in DLB cases with or without associated AD compared with AD cases. These results suggest that A beta deposition in the MTL in 'pure' DLB cases is similar to that of elderly non-demented patients while, with the exception of the classic deposits, A beta deposition in DLB/AD cases is similar to that in cases of AD alone.

The genotype 2/2 of the presenilin-1 polymorphism is decreased in Spanish early-onset Alzheimer's disease

We have found a significantly lower frequency of the presenilin-1 (PS-1) intronic polymorphism 2/2 genotype in early-onset Alzheimer's disease (AD) patients without APOE epsilon4 alleles (2/2 = 0.054; P = 0.009) as compared to age matched non-epsilon4 controls (2/2 = 0.227). Moreover the average age of onset in AD patients with the PS-1 2/2 genotype is older than that in AD patients with a 1/2 genotype or with a 1/1 genotype. This data suggest a protective effect of the 2/2 genotype which would delay the age of onset in AD. Our results do not support an association between the 1/1 genotype and AD. However, a non-significant increase of the 1/1 genotype is found in non-epsilon4 AD patients (P = 0.20).

T/G polymorphism at intron 9 of presenilin 1 gene is associated with, but not responsible for sporadic late-onset Alzheimer's disease in Japanese population

To investigate whether presenilin 1 (PS1) gene, a major causative gene of familial early-onset Alzheimer's disease (AD), also contributes to the etiology of sporadic AD, we evaluated associations between Japanese AD and polymorphisms located at 14q24.3. While the D14S43 and FOS loci showed no association with either early- or late-onset AD, late-onset AD carrying no APOE-epsilon4 allele was associated with the G allele of the T/G polymorphism located at intron 9 of the PS1 gene (P = 0.016). Considering another study showing a positive association between AD and the T allele, this polymorphism is associated with, but not responsible for sporadic late-onset Alzheimer's disease.

Skeletal and CNS defects in Presenilin-1-deficient mice

Presenilin-1 (PS1) is the major gene responsible for early-onset familial Alzheimer's disease (FAD). To understand the normal function of PS1, we have generated a targeted null mutation in the murine homolog of PS1. We report that PS1-/- mice die shortly after natural birth or Caesarean section. The skeleton of homozygous mutants is grossly deformed. Hemorrhages occur in the CNS of PS1 null mutants with varying location, severity, and time of onset. The ventricular zone of PS1-/- brains is markedly thinner by embryonic day 14.5, indicating an impairment in neurogenesis. Bilateral cerebral cavitation caused by massive neuronal loss in specific subregions of the mutant brain is prominent after embryonic day 16.5. These results show that PS1 is required for proper formation of the axial skeleton, normal neurogenesis, and neuronal survival.

Immunoreactivity of presenilin-1 in human, rat and mouse brain

Monoclonal antibodies (mAbs) D3G6 and C8A5, specific for amino acid residues 160-168 of S182 protein, immunolabeled neurons, ependymal and choroid plexus cells, and myocytes in brain sections from normal subjects and people with Alzheimer disease or Down syndrome and in rats and mice. Oligodendroglia, microglia, and the majority of astrocytes were negative. S182 protein or a fragment of the protein detected with these mAbs is not a constituent of amyloid-beta deposits or tangles.

Presenilin 1 is required for Notch1 and DII1 expression in the paraxial mesoderm

Approximately 10% of cases of Alzheimer's disease are familial and associated with autosomal dominant inheritance of mutations in genes encoding the amyloid precursor protein, presenilin 1 (PS1) and presenilin 2 (PS2). Mutations in PS1 are linked to about 25% of cases of early-onset familial Alzheimer's disease. PS1, which is endoproteolytically processed in vivo, is a multipass transmembrane protein and is a functional homologue of SEL-12, a Caenorhabditis elegans protein that facilitates signalling mediated by the Notch/LIN-12 family of receptors. To examine potential roles for PS1 in facilitating Notch-mediated signalling during mammalian embryogenesis, we generated mice with targeted disruptions of PS1 alleles (PS1-/- mice). PS1-/- embryos exhibited abnormal patterning of the axial skeleton and spinal ganglia, phenotypes traced to defects in somite segmentation and differentiation. Moreover, expression of mRNA encoding Notch1 and Dll1 (delta-like gene 1), a vertebrate Notch ligand, is markedly reduced in the presomitic mesoderm of PS1-/- embryos compared to controls. Hence, PS1 is required for the spatiotemporal expression of Notch1 and Dll1, which are essential for somite segmentation and maintenance of somite borders.

Proteolytic processing of the Alzheimer disease-associated presenilin-1 generates an in vivo substrate for protein kinase C

The majority of familial Alzheimer disease mutations are linked to the recently cloned presenilin (PS) genes, which encode two highly homologous proteins (PS-1 and PS-2). It was shown that the full-length PS-2 protein is phosphorylated constitutively within its N-terminal domain by casein kinases, whereas the PS-1 protein is not. Full-length PS proteins undergo endoproteolytic cleavage within their hydrophilic loop domain resulting in the formation of approximately 20-kDa C-terminal fragments (CTF) and approximately 30-kDa N-terminal fragments [Thinakaran, G., et al. (1996) Neuron 17, 181-190]. Here we describe the surprising finding that the CTF of PS-1 is phosphorylated by protein kinase C (PKC). Stimulation of PKC causes a 4- to 5-fold increase of the phosphorylation of the approximately 20-kDa CTF of PS-1 resulting in reduced mobility in SDS gels. PKC-stimulated phosphorylation occurs predominantly on serine residues and can be induced either by direct stimulation of PKC with phorbol-12,13-dibutyrate or by activation of the m1 acetylcholine receptor-signaling pathway with the muscarinic agonist carbachol. However, phosphorylation of full-length PS-1 and PS-2 is not altered upon PKC stimulation. In addition, a mutant form of PS-1 lacking exon 10, which does not undergo endoproteolytic cleavage [Thinakaran, G., et al. (1996) Neuron 17, 181-190] is not phosphorylated by PKC, although it still contains all PKC phosphorylation sites conserved between different species. These results show that PKC phosphorylates the PS-1 CTF. Therefore, endoproteolytic cleavage of full-length PS-1 results in the generation of an in vivo substrate for PKC. The selective phosphorylation of the PS-1 CTF indicates that the physiological and/or pathological properties of the CTF are regulated by PKC activity.

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.

Controlling amyloid beta-peptide fibril formation with protease-stable ligands

We have previously shown that short peptides incorporating the sequence KLVFF can bind to the approximately 40amino acid residue Alzheimer amyloid beta-peptide (Abeta) and disrupt amyloid fibril formation (Tjernberg, L. O., Näslund, J., Lindqvist, F., Johansson, J., Karlström, A. R., Thyberg, J., Terenius, L., and Nordstedt, C. (1996) J. Biol. Chem. 271, 8545-8548). Here, it is shown that KLVFF binds stereospecifically to the homologous sequence in Abeta (i.e. Abeta16-20). Molecular modeling suggests that association of the two homologous sequences leads to the formation of an atypical anti-parallel beta-sheet structure stabilized primarily by interaction between the Lys, Leu, and COOH-terminal Phe. By screening combinatorial pentapeptide libraries exclusively composed of D-amino acids, several ligands with a general motif containing phenylalanine in the second position and leucine in the third position were identified. Ligands composed of D-amino acids were not only capable of binding Abeta but also prevented formation of amyloid-like fibrils. These ligands are protease-resistant and may thus be useful as experimental agents against amyloid fibril formation in vivo.

Evidence for a six-transmembrane domain structure of presenilin 1

Mutations in genes encoding presenilin 1 and presenilin 2 account for the majority of cases of early-onset familial Alzheimer's disease. The presenilins have been localized to the endoplasmic reticulum and Golgi, but which of the multiple hydrophobic segments of the polypeptide chain span the lipid bilayer is unclear. To address this question, we have constructed a series of chimeric molecules in which a topologically neutral reporter protein (a C-terminal fragment of prolactin) containing three artificial glycosylation sites is fused to presenilin 1 following each of the 10 potential transmembrane domains identified in hydrophobicity plots. We have expressed these chimeras by translation in reticulocyte lysate containing canine pancreatic microsomes and by synthesis in transfected COS cells. Based on utilization of the glycosylation sites and sensitivity of the reporter to protease digestion, we provide evidence that presenilin 1 has six transmembrane segments with the N and C termini in the cytoplasm. This model provides important clues to the potential functions of different parts of the presenilin molecule and how these might relate to the pathogenesis of Alzheimer's disease.

A 1.1-Mb transcript map of the hereditary hemochromatosis locus

In the process of positionally cloning a candidate gene responsible for hereditary hemochromatosis (HH), we constructed a 1.1-Mb transcript map of the region of human chromosome 6p that lies 4.5 Mb telomeric to HLA-A. A combination of three gene-finding techniques, direct cDNA selection, exon trapping, and sample sequencing, were used initially for a saturation screening of the 1.1-Mb region for expressed sequence fragments. As genetic analysis further narrowed the HH candidate locus, we sequenced completely 0.25 Mb of genomic DNA as a final measure to identify all genes. Besides the novel MHC class 1-like HH candidate gene HLA-H, we identified a family of five butyrophilin-related sequences, two genes with structural similarity to a type 1 sodium phosphate transporter, 12 novel histone genes, and a gene we named RoRet based on its strong similarity to the 52-kD Ro/SSA lupus and Sjogren's syndrome auto-antigen and the RET finger protein. Several members of the butyrophilin family and the RoRet gene share an exon of common evolutionary origin called B30-2. The B30-2 exon was originally isolated from the HLA class 1 region, yet has apparently "shuffled" into several genes along the chromosome telomeric to the MHC. The conservation of the B30-2 exon in several novel genes and the previously described amino acid homology of HLA-H to MHC class 1 molecules provide further support that this gene-rich region of 6p21.3 is related to the MHC. Finally, we performed an analysis of the four approaches for gene finding and conclude that direct selection provides the most effective probes for cDNA screening, and that as much as 30% of ESTs in this 1.1-Mb region may be derived from noncoding genomic DNA.

Mutations in mitochondrial cytochrome c oxidase genes segregate with late-onset Alzheimer disease

Mounting evidence suggests that defects in energy metabolism contribute to the pathogenesis of Alzheimer disease (AD). Cytochrome c oxidase (CO) is kinetically abnormal, and its activity is decreased in brain and peripheral tissue in late-onset AD. CO is encoded by both the mitochondrial and the nuclear genomes. Its catalytic centers, however, are encoded exclusively by two mitochondrial genes, CO1 and CO2 (encoding CO subunits I and II, respectively). We searched these genes, as well as other mitochondrial genes, for mutations that might alter CO activity and cosegregate with AD. In the present study, specific missense mutations in the mitochondrial CO1 and CO2 genes but not the CO3 gene were found to segregate at a higher frequency with AD compared with other neurodegenerative or metabolic diseases. These mutations appear together in the same mitochondrial DNA molecule and define a unique mutant mitochondrial genome. Asymptomatic offspring of AD mothers had higher levels of these mutations than offspring of AD fathers, suggesting that these mutations can be maternally inherited. Cell lines expressing these mutant mitochondrial DNA molecules exhibited a specific decrease in CO activity and increased production of reactive oxygen species. We suggest that specific point mutations in the CO1 and CO2 genes cause the CO defect in AD. A CO defect may represent a primary etiologic event, directly participating in a cascade of events that results in AD.

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.

A twin study of late-onset depression and apolipoprotein E epsilon 4 as risk factors for Alzheimer's disease

A prior history of depression and the epsilon 4 allele of apolipoprotein E (APOE) have each been associated with development of Alzheimer's disease (AD). In a sample of 142 elderly twins from a large study of dementia, we examined the relation of major depression, APOE genotype and AD using time-dependent proportional hazards models. Compared against the risk for AD with no history of depression and no epsilon 4 allele, the risk ratio for AD with two epsilon 4 alleles was 2.87 (C.I. = 1.56-5.28), with one epsilon 4 allele, 1.82 (C.I. = 1.09-3.04) and with late-onset depression and no epsilon 4 allele, 2.95 (C.I. = 1.55-5.62). There was no suggestion of an interaction between prior depression and APOE genotype in their effects on AD risk. Results were similar when the sample was stratified by twin pair, so that a single genetic marker is unlikely to explain the relation among depression, APOE, and dementia. Risk ratios declined substantially with increasing intervals between the onset of depression and AD. Thus, for many individuals, the association of depression and AD may reflect the occurrence of prodromal depressive symptoms rather than a true risk relationship.

Abnormal distribution of neurofilament L in neurons with Alzheimer's disease

Abnormality of cytoskeletal proteins is closely related to the pathology of Alzheimer's disease. As neurofilament proteins are major cytoskeletal components of neurons, abnormality of neurofilaments is proposed in brain with Alzheimer's disease. Free-floating sections of the hippocampus with Alzheimer's disease were studied immunohistochemically, using a polyclonal antibody specifically bound to the tail region of neurofilament L (NF-L). In brains with early onset type of Alzheimer's disease, many neurons and dystrophic neurites were labeled by the antibody, while these observations were not seen in either brains with late onset type or control brains. Double immunohistochemical staining of NF-L and tau protein demonstrated that abnormal deposition of NF-L was not always accompanied with that of tau protein, indicating that the abnormal deposition of NF-L might not occur in parallel with that of tau protein. These observations suggest the involvement of neurofilament proteins on the pathology of Alzheimer's disease in a different way than tau protein.

Light and electron microscopic localization of presenilin-1 in primate brain

Several genes have been implicated in the pathogenesis of early-onset familial Alzheimer's disease. A majority of the autosomal dominant cases are linked to recently identified mutations in the presenilin-1 gene on chromosome 14. The native presenilin-1 protein in primates has not been well characterized, and its precise localization is unknown. We have studied the native presenilin-1 protein in monkey brain and peripheral tissues by using a monoclonal antibody specific for the N-terminal domain of human presenilin-1. Western blots detect polypeptide species of approximately 49 and approximately 32 kDa from COS-7 and PC12 cells transfected with full-length human presenilin-1 cDNA and from in vitro translations of the normal human presenilin-1 mRNA. A 32 kDa polypeptide is detected in monkey peripheral tissues, with the highest expression in testis and lung. In all brain regions the 32 kDa band is the predominant form of presenilin-1, and it is found in particulate subfractions. Light microscopic immunocytochemistry reveals presenilin-1 staining in all brain regions, with the strongest labeling in neurons and neuropil. In addition, weaker immunoreactivity is also present in glia and blood vessels. Neuronal staining shows significant variability, with particularly intense labeling of certain cell types, including large neocortical and hippocampal pyramidal neurons, magnocellular basal forebrain neurons, brainstem motoneurons, and some populations of interneurons. By electron microscopic immunocytochemistry, highly selective presenilin-1 staining is seen on the cytoplasmic surfaces of membranous organelles, which suggest localization to the endoplasmic reticulum-Golgi intermediate compartment, a subdomain of the endoplasmic reticulum, and some coated transport vesicles.

Reduced levels of antioxidants in brains of apolipoprotein E-deficient mice following closed head injury

Recent animal model studies using apolipoprotein E (apoE)-deficient (knockout) mice revealed that these mice have memory deficits and neurochemical derangements and that they recover from closed head injury less adequately than control mice. In the present study, we examined the possibility that the diminished recovery of apoE-deficient mice from head injury is related to a reduction in their ability to counteract oxidative damage. Measurements of reducing agents by cyclic voltammetry revealed that cortical homogenates of apoE-deficient and control mice contain similar levels of these compounds whose oxidation potentials for the two groups of mice are at 400 +/- 40 mV and 900 +/- 50 mV. The responses of the apoE-deficient and control groups to closed head injury were both biphasic and were composed of initial reductions followed by subsequent increases in the levels of reducing antioxidant equivalents. However, the two groups differed markedly in the magnitude of their response. This difference was most pronounced with the 400-mV reducing compounds, such that at 4 h after injury their levels in injured control mice increased over twofold relative to the noninjured control mice, whereas the corresponding anodic current of the apoE-deficient mice recovered only to its original level and did not increase further even by 24 h after injury. In vitro studies using recombinant apoE allele E3 and beta very low density lipoprotein revealed that this lipoprotein can delay Cu(2+)-induced lipid peroxidation. This suggests that the inability of the apoE-deficient mice to respond to brain injury by a surge in brain reducing compounds may be related, at least in part to direct antioxidant activity of apoE.

Clinical and molecular analysis of neurodegenerative diseases

Clinical and molecular analyses of neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and spinocerebellar ataxia type 1 (SCA1) were performed. In the present study, a Japanese family of AD with an Ala285Val substitution in exon 8 of the presenilin-1 (PS-1) gene was found. This family was characterized by relatively late onset (mean age at 50 years) in familial AD with PS-1 gene mutation and by absence of myoclonus, seizure or paratonia. Magnetic resonance image (MRI) study showed marked linear signal abnormalities in white matter of parietoocctipital lobes, suggesting a presence of cortical amyloid angiopathy of the patient with PS-1 gene mutation. Clinical characteristics of familial amyotrophic lateral sclerosis (FALS) with four different missense point mutations in exons 2, 4, and 5 of the Cu/Zn superoxide dismutase (SOD) gene were reported. Although features of progressive neurogenic muscular atrophy was common in patients of these families, patients of each family showed characteristic clinical features. Although lower motor sign was evident in all cases, hyperreflexia varied from 0 to 100% among patients with the different mutations, and Babinski sign was not observed in any cases. Bulbar palsy was frequent with a mutation, but not present with another mutation. SOD activity of red blood cells was generally reduced with minor variations. CAG trinucleotide repeat expansion was analyzed in 25 families with hereditary ataxia of Menzel type in the northeast of Japan. Twenty of 38 patients in 12 families had expanded allele for spinocerebellar ataxia type 1 (SCA1). Study of the number of CAG repeats in various tissues showed no differences in the repeat length in lymphocytes, muscle or brain; sperm, however, showed an obvious expansion. This may be a clue to a possible mechanism for the molecular basis of paternal anticipation of the disease. These results suggest that clinical features of some familial cases of neurodegenerative diseases such as AD, ALS, and SCA1 are well correlated with their genetic mutations.

Cellular and molecular neurosurgery: pathways from concept to reality--part I: target disorders and concept approaches to gene therapy of the central nervous system

Recent advances in cellular and molecular biology and better understanding of genetic and biochemical bases of different central nervous system (CNS) disorders have made gene therapy of the CNS a realistic goal. Concept approaches for gene therapy of CNS disorders are reviewed and include the following: 1) gene replacement with a single normal allele to correct the inherited global neurodegenerative disorders, such as enzyme deficiencies; 2) brain repair to restore the function of a particular subset of cells that were lost because of a neurodegenerative process; 3) gene therapy of brain tumors; and 4) gene therapy of stroke. Techniques of viral vector-mediated CNS transfer of a therapeutic gene, transplantation of genetically modified cells, fetal embryonic implantation and/or implantation of genetically engineered neural progenitor cells, and production of a specific enzyme, neurotransmitter, and/or growth factor are discussed with respect to the therapeutic potential for global and localized CNS neurodegenerative disorders and stroke. Transfection of the CNS tumor cells with the drug susceptibility ("suicide") gene and/or "toxic" gene and antisense strategies and a concept of adoptive immunotherapy of brain tumors are also discussed. Other approaches, such as transfer of drug-resistant genes and monoclonal antibody gene transfer, are briefly discussed. In addition to summarizing current principles of gene therapy for several groups of CNS disorders, the issues that remain to be resolved in clinical reality, such as delivery of the genetic material and regulation of the cellular expression of the transgene, and the negatives associated with the concepts of gene therapy, such as transient gene expression, toxicity of viral proteins, drawbacks of antisense therapy, and the problem of immune response to the transfected protein, have been also identified.

Murine models of brain aging and age-related neurodegenerative diseases

In the past, structural changes in the brain with aging have been studied using a variety of animal models, with rats and nonhuman primates being the most popular. With the rapid evolution of mouse genetics, murine models have gained increased attention in the neurobiology of aging. The genetic contribution of age-related traits as well as specific mechanistic hypotheses underlying brain aging and age-related neurodegenerative diseases can now be assessed by using genetically-selected and genetically-manipulated mice. Against this background of increased demand for aging research in mouse models, relatively few studies have examined structural alterations with aging in the normal mouse brain, and the data available are almost exclusively restricted to the C57BL/6 strain. Moreover, many older studies have used quantitative techniques which today can be questioned regarding their accuracy. Here we review the state of knowledge about structural changes with aging in outbred, inbred, genetically-selected, and genetically-engineered murine models. Moreover, we suggest several new opportunities that are emerging to study brain aging and age-related neurodegenerative diseases using genetically-defined mouse models. By reviewing the literature, it has become clear to us that in light of the rapid progress in genetically-engineered and selected mouse models for brain aging and age-related neurodegenerative diseases, there is a great and urgent need to study and define morphological changes in the aging brain of normal inbred mice and to analyze the structural changes in genetically-engineered mice more carefully and completely than accomplished to date. Such investigations will broaden knowledge in the neurobiology of aging, particularly regarding the genetics of aging, and possibly identify the most useful murine models.

Enhanced production and oligomerization of the 42-residue amyloid beta-protein by Chinese hamster ovary cells stably expressing mutant presenilins

Mutations in the presenilin 1 (PS1) and presenilin 2 (PS2) genes cause the most common and aggressive form of early onset familial Alzheimer's disease. To elucidate their pathogenic mechanism, wild-type (wt) or mutant (M146L, C410Y) PS1 and wt or mutant (M239V) PS2 genes were stably transfected into Chinese hamster ovary cells that overexpress the beta-amyloid precursor protein (APP). The identity of the 43-45-kDa PS1 holoproteins was confirmed by N-terminal radiosequencing. PS1 was rapidly processed (t1/2 = 40 min) in the endoplasmic reticulum into stable fragments. Wild-type and mutant PS2 holoproteins exhibited similar half lives (1.5 h); however, their endoproteolytic fragments showed both mutation-specific and cell type-specific differences. Mutant PS1 or PS2 consistently induced a 1.4-2.5-fold increase (p < 0.001) in the relative production of the highly amyloidogenic 42-residue form of amyloid beta-protein (Abeta42) as determined by quantitative immunoprecipitation and by enzyme-linked immunosorbent assay. In mutant PS1 and PS2 cell lines with high increases in Abeta42/Abetatotal ratios, spontaneous formation of low molecular weight oligomers of Abeta42 was observed in media, suggesting enhanced Abeta aggregation from the elevation of Abeta42. We conclude that mutant PS1 and PS2 proteins enhance the proteolysis of beta-amyloid precursor protein by the gamma-secretase cleaving at Abeta residue 42, thereby promoting amyloidogenesis.

Autosomal dominant early onset dementia and leukoencephalopathy in a Japanese family: clinical, neuroimaging and genetic studies

We report here the results of clinical, neuroimaging and genetic studies of autosomal dominant dementia and leukoencephalopathy in a Japanese family. Twenty-two individuals in this family were examined clinically (17 living, 5 deceased), neuroradiologically and genetically (16 of 17 living members). Ten (5 deceased) of 22 individuals had early onset dementia (age of onset: 45.2 +/- 12.1 years on average) and four of them had multiple white matter lesions and brain atrophy on brain MRI without history of brain ischemic attack. Another four individuals had abnormal white matter lesions on brain MRI without dementia. Linkage studies for chromosome 1q31-42, 14q24.3 and 21q21 responsible for Alzheimer's disease, chromosome 19p13.1-13.2 for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) and chromosome 3 for familial non-specific dementia suggested no specific haplotypes cosegregated with the disease. Apo E genotypes were E2/2 and E2/3 in this family. Clinical, neuroimaging and genetic studies revealed that the disease in this family was distinguished from known familial dementia. This is the first report of a large Japanese family with autosomal dominant early onset dementia and leukoencephalopathy.

Analysis of the 5' sequence, genomic structure, and alternative splicing of the presenilin-1 gene (PSEN1) associated with early onset Alzheimer disease

Mutations in the human presenilin genes (PSEN1 and PSEN2) are associated with early onset familial Alzheimer disease. The presenilin genes encode integral membrane proteins with similar structures, which suggests that they may have closely related, but as yet unknown functions. Analysis of the 5' upstream sequence and the structure of the PSEN1 gene reveals that the 5' sequence contains multiple putative transcription regulatory elements including clusters of STAT elements involved in transcriptional activation in response to signal transduction. The first four exons contain untranslated sequences, with Exons 1 and 2 representing alternate initial transcription sites. The function of these alternate initial exons is unclear. Exon 4 bears the first ATG sequence. The last 12 bp of Exon 4 is used as an alternative splice donor site. Exon 9 is alternately spliced in leukocytes, but not in most other tissues. Splicing of Exon 9 is predicted to cause significant structural changes to the protein. The majority of transcripts expressed in most tissues are polyadenylated 1127 bp from the TAG stop codon in Exon 13. A small proportion of transcripts contain the same 5'UTR and ORF but are polyadenylated 4435 bp from the stop codon. The longer polyadenylated transcripts contain three additional palindromes and at least one additional stem-loop structure with stabilities greater than -16 kcal/mol.

Degradation of amyloid beta-protein by a metalloprotease secreted by microglia and other neural and non-neural cells

Amyloid beta-protein (Abeta) is the major component of neuritic (amyloid) plaques in Alzheimer's disease, and its deposition is an early and constant event in the complex pathogenetic cascade of the disease. Although many studies have focused on the biosynthetic processing of the beta-amyloid precursor protein and on the production and polymerization of Abeta, understanding the degradation and clearance of Abeta has received very little attention. By incubating the conditioned medium of metabolically labeled Abeta-secreting cells with media of various cultured cell lines, we observed a time-dependent decrease in the amount of Abeta in the mixed media. The factor principally responsible for this decrease was a secreted metalloprotease released by both neural and non-neural cells. Among the cells examined, the microglial cell line, BV-2, produced the most Abeta-degrading activity. The protease was completely blocked by the metalloprotease inhibitor, 1,10-phenanthroline, and partially inhibited by EDTA, whereas inhibitors of other protease classes produced little or no inhibition. Substrate analysis suggests that the enzyme was a non-matrix metalloprotease. The protease cleaved both Abeta1-40 and Abeta1-42 peptides secreted by beta-amyloid precursor protein-transfected cells but failed to degrade low molecular weight oligomers of Abeta that form in the culture medium. Lipopolysaccharide, a stimulator of macrophages/microglia, activated BV-2 cells to increase their Abeta-degrading metalloprotease activity. We conclude that secreted Abeta1-40 and Abeta1-42 peptides are constitutively degraded by a metalloprotease released by microglia and other neural cells, providing a potential mechanism for the clearance of Abeta in brain tissue.

The presenilin 2 mutation (N141I) linked to familial Alzheimer disease (Volga German families) increases the secretion of amyloid beta protein ending at the 42nd (or 43rd) residue

To gain insights into the significance of presenilins (PS) in the pathogenetic mechanisms of early-onset familial Alzheimer disease (FAD), we expressed cDNAs for wild-type PS2 and PS2 with the Volga German (N141I) mutation in cultured cells and then examined the metabolism of the transfected proteins and their effect on the C-terminal properties of secreted amyloid beta protein (A beta). PS2 was identified as a 50- to 55-kDa protein, which was cleaved to produce N-terminal fragments of 35-40 kDa and C-terminal fragments of 19-23 kDa. The Volga German (N141I) mutation did not cause any significant change in the metabolism of PS2. COS-1 cells doubly transfected with cDNAs for N141I mutant PS2 and human beta-amyloid precursor protein (betaAPP) or a C-terminal fragment thereof, as well as mouse Neuro2a neuroblastoma cells stably transfected with N141I mutant PS2 alone, secreted 1.5- to 10-fold more A beta ending at residues 42 (or 43) [A beta42(43)] compared with those expressing the wild-type PS2. These results strongly suggest that the PS2 mutation (N141I) linked to FAD alters the metabolism of A beta/betaAPP to foster the production of the form of A beta that most readily deposits in amyloid plaques. Thus, mutant PS2 may lead to AD by altering the metabolism of A beta/betaAPP.

Current advances in Alzheimer's disease. A medical model paradigm for psychiatric education

Psychiatrists have the expertise to play a major leadership role in the diagnosis and treatment of Alzheimer's disease. Psychiatry residents should be trained to recognize both the cognitive and noncognitive symptoms of this disease. Psychiatrists are in an excellent position to keep up with the rapidly expanding pharmacologic armamentarium to treat this devastating illness. Although such potentials are exciting, they undoubtedly will be complicated. Residency directors and departmental chairs should instill enthusiasm toward basic science advances and their clinical implications. Understanding the mechanisms underlying specific central nervous system illnesses should increase the likelihood of discovering the pathophysiology of others. The more psychiatrists and psychiatric residents become interested in these discoveries and the science underlying such progress in Alzheimer's disease, the better they will be able to keep up to date with progress in understanding other psychiatric disorders.

Clinical rationale of genetic testing in dementia

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The genetics of dementia in late life

Recent advances in the genetics of AD and other late-life dementias have provided new insights but also have raised new queries and ethical issues. This review reflects the current state of knowledge in a rapidly evolving field. The complex relation of genes and environment to AD, VaD, and other late-life dementias suggests that the answers to these many issues will evolve through time. New issues undoubtedly will arise as additional genes are discovered and new data accrue that relate APOE and other genes to the mechanism and expression of dementing illness. The clinical relevance and applicability of such research findings will increase when effective treatments become available. Given this potential, we encourage readers to monitor new developments as they arise.

Increased incidence of anti-beta-amyloid autoantibodies secreted by Epstein-Barr virus transformed B cell lines from patients with Alzheimer's disease

During the past several years, evidence has been accumulated to support the thesis that immunological factors may play some role in Alzheimer's disease (AD). We have characterized the reactive antigens detected by certain monoclonal antibodies secreted by Epstein-Barr virus (EBV)-transformed B cell lines from the peripheral blood of AD patients and controls. Autoantibodies against beta-amyloid protein beta-amyloid protein (beta-A) in amyloid plaques and blood vessels and in enzyme-linked immunosorbent assays (ELISA) have been reported in four cell lines derived from an AD patient. In this study, over 3300 EBV-transformed B cell lines from thirteen individuals were tested in ELISAs for antibodies against beta-A peptides. Significantly more autoantibodies against beta-A (1-40) were found in the AD group, 2.26 +/- 0.62% (39/1794 cell lines) than in the control group, 0.28 +/- 0.36% (5/1552 cell lines) with P < 0.005. These new antibodies did not react with plaques or amyloid deposits in blood vessels. In contrast to the four plaque-reactive autoantibodies which reacted better with beta-A (1-40) than with beta-A (1-28), 70% of these anti-beta-A (1-40) antibodies reacted as well or better with beta-A (1-28). Many of them were also reactive with beta-A (1-16). Tested against a panel of cytoskeletal proteins and Hela cells, many of these anti-beta-A (1-40) antibodies appear to be polyreactive. The higher incidence of anti-beta-A antibody secreting B cells in AD patients provides further evidence that autoimmunity may play a role in AD.

Apolipoprotein E4 and Alzheimer's disease in São Paulo-Brazil

Several recently published studies showed the existence of an association between the allele epsilon 4 of the apolipoprotein E and Alzheimer's disease (AD) in developed countries. We examined this association in 55 patients with possible or probable AD and 56 elderly controls referred to outpatient clinics at the "Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo" and "Centro de Saúde Escola da Faculdade de Saúde Pública da Universidade de São Paulo". The allele epsilon 4 was significantly more frequent among patients than controls (20.9% vs 8.9%, p = 0.038). Thirty-six percent of the cases presented with at least one allele epsilon 4 compared with only 17.9% of the controls (p = 0.027). The presence of at least one epsilon 4 allele increased by 2.63 times the risk of subjects being diagnosed as suffering from AD. All three epsilon 4 epsilon 4 patients were male and had a pre-senile onset of the disease. There was no significant difference between senile and pre-senile cases (41.9% vs 29.2%, p = 0.326) nor between men and women (36.0% vs 36.7%, p = 0.959) regarding their risk of being epsilon 4. The age at onset of symptoms did not differ among the different genotype groups, although epsilon 4 epsilon 4 cases showed a consistent trend for earlier onset. When only patients with the diagnosis of "probable AD" were included in the analysis (n = 43), we observed that 22.1% of the alleles were epsilon 4, a rate that was significantly higher than the 8.9% of controls (p = 0.024). This study supports the association between the presence of the epsilon 4 allele and AD and extend this finding to Brazilian patients. Nonetheless, the presence of this allele is not necessary nor sufficient for the development of the disease and it is possible that its contribution to the pathogenesis of the disorder depends on the subject's ethnic group.

Formation of stable complexes between two Alzheimer's disease gene products: presenilin-2 and beta-amyloid precursor protein

Mutations in the presenilin genes are associated with early onset familial Alzheimer's disease and lead to increased accumulation of beta A4 peptide, the proteolytic product of the amyloid precursor protein (APP). To test whether presenilins interfere with APP metabolism, presenilin-2 (PS2) was coexpressed with APP in mammalian cells. Analysis of PS2 immunoprecipitates revealed that a fraction of APP was associated with the PS2 immunocomplexes. This non-covalent association was specific for the APP family of proteins and restricted to immature forms, occurring probably during transit through the endoplasmic reticulum. Additionally, coexpression with PS2 resulted in a decrease of APP secretion, suggesting a direct participation of presenilins in the intracellular sorting, trafficking and processing of APP molecules.

Distinct processing of endogenous and overexpressed recombinant presenilin 1

The presenilin 1 (PS1) gene has been identified by positional cloning. More than 30 mutations were detected in this gene which cosegregate with Alzheimer's disease (AD). Understanding their role in disease pathogenesis requires a characterization of the PS1 protein. We have generated a set of antibodies against the three major hydrophilic domains of the deduced amino acid sequence. Analyzing cultured cells and brain samples, we identified the endogenous PS1 polypeptide as well as amino- and carboxy-terminal fragments. These metabolites were much more abundant than the full-length molecule, indicating substantial processing. Overexpression of human PS1 markedly increased the full-length polypeptide but hardly altered the amount of the metabolites. Instead, additional proteolytic fragments appeared suggesting a different metabolism of the excess PS1, which may impede studies in transfected cells. Our results indicate a tight regulation of the endogenous PS1 metabolites. PS1 and its fragments are shown to be integral membrane proteins of the endoplasmic reticulum. The mechanisms regulating the generation of the metabolites, their potential function, and role in AD remain to be studied.

Cloning of the cDNA encoding rat Presenilin-1

We isolated rat presenilin-1 (PS-1; also called S182 previously) cDNA from total brain RNA by using a reverse transcription-polymerase chain reaction (RT-PCR) technique with primers homologous to the conserved sequences of human and mouse PS-1. Rat PS-1 cDNA encoded 468 amino acids (aa) and the deduced aa sequence was highly homologous to those of the human (88.4%) and mouse (92.7%). Northern blot analysis of the rat PS-1 cDNA revealed two mRNA species in rat neurotypic pheochromocytoma and glioma cell lines (PC-12 and C6, respectively) that migrated at rates corresponding to approximately 3.0 and 7.5 kb.

Expression of presenilin-1 and -2 mRNAs in rat and Alzheimer's disease brains

Recently, new genetic linkages have been identified for early-onset familial Alzheimer's disease (AD). Mutations have been found in the presenilin (PS)-1 (S182) gene on chromosome 14 and the PS-2 (STM2/E5-a) gene on chromosome 1. We have investigated the distribution of gene expression of both presenilins in normal rat brain, and in human control and AD cases using in situ hybridization histochemistry. In normal rat brain, intense PS-1 mRNA expression was observed predominantly in neurons, particularly hippocampal pyramidal and dentate granular neurons and cerebellar Purkinje and granular neurons. The distribution of intensely expressing PS-2 mRNA cells was similar to that of PS-1, but additional groups in the brain stem and cortex were identified. Faint but significant mRNA expression of both PS genes was detected in white matter. In control human cases, the same neuronal cell types as seen in rat brain expressed both PS mRNAs in the hippocampus and cerebellum. In AD cases, the expression of both mRNAs was markedly decreased in the hippocampus but not in the cerebellum. In addition, PS-2 hybridization showed increased mRNA expression in astrocyte-like cells in affected areas of AD cases. The present data indicate that the PS genes may play important roles in specific neurons in normal brain, and that the decreased expression in neurons in sporadic AD brain may bear some relationship to the pathogenesis.

Increased plasma apolipoprotein E (apoE) levels in Alzheimer's disease

We measured the concentration of apolipoprotein E (apoE) in plasma from 184 non-fasted subjects in order to determine whether important variations might exist linking plasma apoE levels to clinical phenotypes among early and late onset sporadic Alzheimer's disease (AD) and Down's syndrome (DS). A significant increase in the level of plasma apoE was observed in non-fasted late-onset AD patients (with a mean level of 3.26 +/- 0.08 microgram apoE/mg total protein for n = 84 patients) when compared with the plasma apoE levels of control individuals (mean of 2.32 +/- 0.10 microgram apoE/mg total protein, n = 51 patients; P < 0.001). A similar increase was found for non-fasted early-onset AD patients (mean of 3.69 +/- 0.17 microgram apoE/mg total protein, n = 20) when compared with the plasma apoE levels of control individuals (P < 0.001). Plasma apoE levels for DS patients did not differ significantly from those of controls (P > 0.05). The association of elevated plasma apoE levels in AD may be relevant to clarifying the mechanism(s) whereby apoE isoforms specify differential risk for development of AD.

Abeta1-40 but not Abeta1-42 levels in cortex correlate with apolipoprotein E epsilon4 allele dosage in sporadic Alzheimer's disease

Apolipoprotein E (ApoE) epsilon4 allele is established to be a risk factor for the development of late-onset Alzheimer's disease (AD) which is associated with increased frequency of senile plaques and extent of amyloid angiopathy. In a recent report, we demonstrated that ApoE epsilon4 dosage correlates with an increase in A beta1-40 but not A beta1-42/43-immunoreactive plaques. In the present study, we sought to confirm this relationship at a biochemical level by using a sensitive ELISA to measure the amounts of A beta1-42/43 and A beta1-40 in cerebral cortex in 36 cases of sporadic AD. We found that dosage of ApoE epsilon4 allele correlated significantly with cortical A beta1-40 levels, while levels of A beta1-42 showed no significant association with genotype. These results parallel our immunohistochemical findings and suggest that A beta1-40 may play a key role in the pathogenesis of late-onset sporadic AD.

Cloning of Xenopus presenilin-alpha and -beta cDNAs and their differential expression in oogenesis and embryogenesis

Human presenilin (ps)-1 and -2 genes have recently been shown to be involved in genesis of early-onset familial Alzheimer's disease. By probing with human (H-) ps-1 cDNA, we isolated two types of cDNA clones, named X-ps-alpha and -beta, from a Xenopus brain cDNA library. The encoded proteins, X-PS-alpha and -beta, may correspond to H-PS-1 and -2 with 89.4 and 85.9% similarity, respectively. The strongest expression of these genes was observed in ovaries and in the early stages of oogenesis, although weak or moderate expression was detected ubiquitously for both X-ps-alpha and -beta genes in multiple tissues. Upon oocyte maturation, the X-ps-beta mRNA level was constant even after fertilization until the midblastula transition. Zygotic expression of these genes became evident only at the tailbud stage. We propose that presenilins may function in preventing cells from undergoing apoptotic degeneration particularly prior to embryonic development and in developmentally matured tissues.

Cloning of human and mouse cDNAs encoding novel zinc finger proteins expressed in cerebellum and hippocampus

We identified a novel gene, kf-1, highly expressed in the normal cerebellum but not in the cerebral cortex, the expression of which could have been augmented in the cerebral cortex of a sporadic Alzheimer's disease patient. We cloned human and mouse entire kf-1 cDNAs encoding conserved 79 kDa proteins containing a zinc-binding RING-H2 finger motif at the carboxy-terminus as found in acetylcholine receptor-associated protein (RAPsyn). The 3'-untranslated regions are highly conserved between human and mouse as to constitute a common mRNA secondary structure. In situ hybridization analysis of mouse brain sections revealed strong kf-1 expression in the cerebellum and hippocampus. We propose that KF-1 is involved in membranous protein-sorting apparatus similarly to RAPsyn. We mapped the human kf-1 gene to 2p11.2.

Isolation and characterization of Drosophila presenilin homolog

Presenilin-1 (PS1) and presenilin-2 (PS2) are associated with a majority of early onset familial Alzheimer's disease (FAD). Sequence analysis of PS1/2 has revealed integral transmembrane proteins which are highly homologous to the protein coded by sel-12, a Caenorhabditis elegans gene involved in the lin-12/Notch signaling pathway. The normal function of PS1/2, as well as the pathogenesis caused by mutations of these genes in FAD, are unknown however. We have identified a Drosophila presenilin homolog (DPS) and mapped the chromosomal location of this gene. DPS shows 53% amino acid identity to PS1/2 and 45% to the sel-12 product. Strong amino acid conservations appear at the position associated with FAD. In embryonic stages, DPS is expressed primarily in the CNS.

Phosphorylation, subcellular localization, and membrane orientation of the Alzheimer's disease-associated presenilins

Presenilins 1 and 2 are unglycosylated proteins with apparent molecular mass of 45 and 50 kDa, respectively, in transfected COS-1 and Chinese hamster ovary cells. They colocalize with proteins from the endoplasmic reticulum and the Golgi apparatus in transfected and untransfected cells. In COS-1 cells low amounts of intact endogeneous presenilin 1 migrating at 45 kDa are detected together with relative larger amounts of presenilin 1 fragments migrating between 18 and 30 kDa. The presenilins have a strong tendency to form aggregates (mass of 100-250 kDa) in SDS-polyacrylamide gel electrophoresis, which can be partially resolved when denatured by SDS at 37 degrees C instead of 95 degrees C. Sulfation, glycosaminoglycan modification, or acylation of the presenilins was not observed, but both proteins are posttranslationally phosphorylated on serine residues. The mutations Ala-246 --> Glu or Cys-410 --> Tyr that cause Alzheimer's disease do not interfere with the biosynthesis or phosphorylation of presenilin 1. Finally, using low concentrations of digitonin to selectively permeabilize the cell membrane but not the endoplasmic reticulum membrane, it is demonstrated that the two major hydrophilic domains of presenilin 1 are oriented to the cytoplasm. The current investigation documents the posttranslational modifications and subcellular localization of the presenilins and indicates that postulated interactions with amyloid precursor protein metabolism should occur in the early compartments of the biosynthetic pathway.

Metallothioneins in brain--the role in physiology and pathology

A symposium on the role of brain metallothioneins (MTs) in physiology and pathology was held at the 1996 Annual Society of Toxicology Meeting in Anaheim, California. The objectives of this symposium were to: (1) review the physiologic function of MTs, (2) examine the distribution of brain MTs with particular emphasis on cell-specific localization (neurons vs neuroglia), (3) discuss MT gene responsiveness upon toxic insult with metals, and (4) discuss the potential role of MTs in the etiology of neurodegenerative disorders. Dr. Cherian discussed the biochemical properties of the MTs, emphasizing structural similarities and differences between the MTs. Dr. Klaassen addressed the expression and distribution of the MTs in brains with special reference to the cell-specific localization of MTs. Dr. Aschner provided data illustrating a potential role for MTs in attenuating the cytotoxicity caused by methylmercury (MeHg) in cultured neonatal astrocytes. Dr. Palmiter discussed the properties of MT-III and the increased sensitivity of MT-III knockout mice to kainate-induced seizures. Cerebral zinc metabolism, its relationship to MT homeostasis, and its pathogenic potential in Alzheimer's disease was addressed by Dr. Bush.

Presenilin-1 gene intronic polymorphism in sporadic and familial Alzheimer's disease

A recent observation has shown a genetic association between an intronic polymorphism in the Presenilin-1 (PS-1) gene and late onset Alzheimer's disease (AD). The homozygosity of the 1 allele in the PS-1 gene was associated with a doubling of the risk for late onset AD. However, contrasting results have been published. We analyzed the distribution of the PS-1 intronic polymorphism in patients with sporadic AD and in seven familial AD (FAD) families carrying pathogenetic mutations in the amyloid precursor protein (APP) and Presenilin (PS-1 and PS-2) genes. Significant differences in PS-1 allele frequencies were observed in the Presenilin genes mutated families but not in late onset AD patients and in APP mutated families.

Alzheimer's disease: genotypes, phenotypes, and treatments

What causes Alzheimer's disease? Selkoe's Perspective reviews recent research identifying four different genetic causes of Alzheimer's disease and suggests that all four point toward the deposition of amyloid beta in the brain as the initial trigger for the disease.