The E280A presenilin 1 Alzheimer mutation produces increased A beta 42 deposition and severe cerebellar pathology

Changes in gamma-secretase activity and specificity caused by the introduction of consensus aspartyl protease active motif in Presenilin 1

Presenilin (PS1 or PS2) is an essential component of the active γ-secretase complex that liberates the Aβ peptides from amyloid precursor protein (APP). PS1 is regarded as an atypical aspartyl protease harboring two essential aspartic acids in the context of the sequence D257LV and D385FI, respectively, rather than the typical DTG...DTG catalytic motif of classical aspartyl proteases. In the present studies, we introduced the sequence DTG in PS1 at and around the catalytic D257 and D385 residues to generate three PS1 mutants: D257TG, D385TG, and the double-mutant D257TG/D385TG. The effects of these changes on the γ-secretase activity in the presence or absence of γ-secretase inhibitors and modulators were investigated. The results showed that PS1 mutants having D385TG robustly enhanced Aβ₄₂ production compared to the wild type (wt), and were more sensitive than wt to inhibition by a classical aspartyl protease transition state mimic, and fenchylamine, a sulfonamide derivative. Unlike wt PS1 and some of its clinical mutants, all three PS1 artificial mutants decreased cleavage of Notch S3-site, suggesting that these artificial mutations may trigger conformational changes at the substrate docking and catalytic site that cause alteration of substrate specificity and inhibition pattern. Consistent with this notion, we have found that NSAID enzymatic inhibitors of COX, known modulators of the γ-secretase activity, cause PS1 mutants containing D385TG to produce higher levels of both Aβ₃₈ and Aβ₄₂, but to reduce levels of Aβ₃₉, showing a pattern of Aβ formation different from that observed with wild type PS1 and its clinical mutants. This study provides an important structural clue for the rational design of drugs to inhibit processing of APP at the γ-site without interfering with Notch processing.

Novel role of presenilins in maturation and transport of integrin beta 1

Presenilins (PSs) play important roles in modulating the trafficking and maturation of several membrane proteins. However, the target membrane proteins whose trafficking and maturation are regulated by PS are largely unknown. By characterizing PS-deficient fibroblasts, we found that integrin beta1 maturation is promoted markedly in PS1 and PS2 double-deficient fibroblasts and moderately in PS1- or PS2-deficient fibroblasts; in contrast, nicastrin maturation is completely inhibited in PS1 and PS2 double-deficient fibroblasts. Subcellular fractionation analysis demonstrated that integrin beta1 maturation is promoted in the Golgi apparatus. The mature integrin beta1 with an increased expression level was delivered to the cell surface, which resulted in an increased cell surface expression level of mature integrin beta1 in PS1 and PS2 double-deficient fibroblasts. PS1 and PS2 double-deficient fibroblasts exhibited an enhanced ability to adhere to culture dishes coated with integrin beta1 ligands, namely, fibronectin and laminin. The inhibition of gamma-secretase activity enhances neither integrin beta1 maturation nor the adhesion of wild-type cells. Moreover, PS deficiency also promoted the maturation of integrins alpha3 and alpha5 and the cell surface expression of integrin alpha3. Integrins alpha3 and alpha5 were coimmunoprecipitated with integrin beta1, suggesting the formation of the functional heterodimers integrins alpha3beta1 and alpha5beta1. Note that integrin beta1 exhibited features opposite those of nicastrin in terms of maturation and trafficking from the endoplasmic reticulum (ER) to the Golgi apparatus in PS1 and PS2 double-deficient fibroblasts. Our results therefore suggest that PS regulates the maturation of membrane proteins in opposite directions and cell adhesion by modulating integrin maturation.

Altered neuronal gene expression in brain regions differentially affected by Alzheimer's disease: a reference data set

Alzheimer's Disease (AD) is the most widespread form of dementia during the later stages of life. If improved therapeutics are not developed, the prevalence of AD will drastically increase in the coming years as the world's population ages. By identifying differences in neuronal gene expression profiles between healthy elderly persons and individuals diagnosed with AD, we may be able to better understand the molecular mechanisms that drive AD pathogenesis, including the formation of amyloid plaques and neurofibrillary tangles. In this study, we expression profiled histopathologically normal cortical neurons collected with laser capture microdissection (LCM) from six anatomically and functionally discrete postmortem brain regions in 34 AD-afflicted individuals, using Affymetrix Human Genome U133 Plus 2.0 microarrays. These regions include the entorhinal cortex, hippocampus, middle temporal gyrus, posterior cingulate cortex, superior frontal gyrus, and primary visual cortex. This study is predicated on previous parallel research on the postmortem brains of the same six regions in 14 healthy elderly individuals, for which LCM neurons were similarly processed for expression analysis. We identified significant regional differential expression in AD brains compared with control brains including expression changes of genes previously implicated in AD pathogenesis, particularly with regard to tangle and plaque formation. Pinpointing the expression of factors that may play a role in AD pathogenesis provides a foundation for future identification of new targets for improved AD therapeutics. We provide this carefully phenotyped, laser capture microdissected intraindividual brain region expression data set to the community as a public resource.

Molecular genetics of Alzheimer's disease: an update

Alzheimer's disease (AD) is a complex disorder of the central nervous system (CNS). Molecular genetic research has provided a wealth of information regarding the genetic etiology of this devastating disease. Identification and functional characterization of autosomal dominant mutations in the amyloid precursor protein gene (APP) and the presenilin genes 1 and 2 (PSEN1 and PSEN2) have contributed substantially to our understanding of the biological mechanisms leading towards CNS neurodegeneration in AD. Nonetheless, a large part of the genetic etiology remains unresolved, especially that of more common, sporadic forms of AD. While substantial efforts were invested in the identification of genetic risk factors underlying sporadic AD, using carefully designed genetic association studies in large patient-control groups, the only firmly established risk factor remains the epsilon4 allele of the apolipoprotein E gene (APOE). Nevertheless, one can expect that with the current availability of high-throughput genotyping platforms and dense maps of single-nucleotide polymorphisms (SNPs), large-scale genetic studies will eventually generate additional knowledge about the genetic risk profile for AD. This review provides an overview of the current understanding in the field of AD genetics, covering both the rare monogenic forms as well as recent developments in the search for novel AD susceptibility genes.

Neurodegenerative diseases: new concepts of pathogenesis and their therapeutic implications

Abstract Neurodegenerative diseases as diverse as Alzheimer's, Parkinson's, and Creutzfeldt-Jakob disease share a common pathogenetic mechanism involving aggregation and deposition of misfolded proteins, which leads to progressive central nervous system disease. Although the type of aggregated protein and the regional and cellular distribution of deposition vary from disease to disease, these disorders may all be linked by similar pathways of protein aggregation with fibril formation and amyloid deposition. This perspective on pathogenesis suggests that a wide variety of neurodegenerative diseases can be grouped mechanistically as brain amyloidoses, an outlook that yields novel insights into potential therapeutic approaches that may be applicable across the broad spectrum of neurodegenerative disease.

Oxidative stress activates a positive feedback between the gamma- and beta-secretase cleavages of the beta-amyloid precursor protein

Sequential cleavages of the beta-amyloid precursor protein cleaving enzyme 1 (BACE1) by beta-secretase and gamma-secretase generate the amyloid beta-peptides, believed to be responsible of synaptic dysfunction and neuronal cell death in Alzheimer's disease (AD). Levels of BACE1 are increased in vulnerable regions of the AD brain, but the underlying mechanism is unknown. Here we show that oxidative stress (OS) stimulates BACE1 expression by a mechanism requiring gamma-secretase activity involving the c-jun N-terminal kinase (JNK)/c-jun pathway. BACE1 levels are increased in response to OS in normal cells, but not in cells lacking presenilins or amyloid precursor protein. Moreover, BACE1 is induced in association with OS in the brains of mice subjected to cerebral ischaemia/reperfusion. The OS-induced BACE1 expression correlates with an activation of JNK and c-jun, but is absent in cultured cells or mice lacking JNK. Our findings suggest a mechanism by which OS induces BACE1 transcription, thereby promoting production of pathological levels of amyloid beta in AD.

The road to LOAD: late-onset Alzheimer's disease and a possible way to block it

The ageing brain becomes increasingly less able to destroy or eject toxic amyloid (A) beta42 peptide byproducts of normal neuronal activity that consequently accumulate to induce Alzheimer's disease (AD). Therefore, the various components of the Abeta-clearing machinery are prime targets for AD therapeutics. In this connection, there are reports that taking statins to lower circulating cholesterol to prevent cardiovascular disease can also prevent late-onset AD (LOAD) the most common form of the disease. However, it seems unlikely that statins would prevent LOAD by lowering the very long-lived brain cholesterol that is controlled independently from the very much shorter-lived circulating cholesterol. In fact, reducing the ability of the brain astrocytes to make cholesterol for their closely associated neuron clients' synaptogenesis could damage the brain rather than protect it. However, a plausible way statins might prevent LOAD is to target a main component of the clearance machinery, low-density lipoprotein receptor-related protein 1 (LRP1), the brain's powerful Abeta-efflux driver. This is indicated by a reported ability of micromolar concentrations of lovastatin and simvastatin to strongly stimulate brain vascular endothelial cells to make this Abeta ejector. Therefore, if this holds up, taking a statin over the years would prevent the normal decline of LRP1 in the ageing brain and a LOAD-driving accumulation of Abeta.

The role of presenilin and its interacting proteins in the biogenesis of Alzheimer's beta amyloid

The biogenesis and accumulation of the beta amyloid protein (Abeta) is a key event in the cascade of oxidative and inflammatory processes that characterises Alzheimer's disease. The presenilins and its interacting proteins play a pivotal role in the generation of Abeta from the amyloid precursor protein (APP). In particular, three proteins (nicastrin, aph-1 and pen-2) interact with presenilins to form a large multi-subunit enzymatic complex (gamma-secretase) that cleaves APP to generate Abeta. Reconstitution studies in yeast and insect cells have provided strong evidence that these four proteins are the major components of the gamma-secretase enzyme. Current research is directed at elucidating the roles that each of these protein play in the function of this enzyme. In addition, a number of presenilin interacting proteins that are not components of gamma-secretase play important roles in modulating Abeta production. This review will discuss the components of the gamma-secretase complex and the role of presenilin interacting proteins on gamma-secretase activity.

The topography of grey matter involvement in early and late onset Alzheimer's disease

Clinical observations have suggested that the neuropsychological profile of early and late onset forms of Alzheimer's disease (EOAD and LOAD) differ in that neocortical functions are more affected in the former and learning in the latter, suggesting that they might be different diseases. The aim of this study is to assess the brain structural basis of these observations, and test whether neocortical areas are more heavily affected in EOAD and medial temporal areas in LOAD. Fifteen patients with EOAD and 15 with LOAD (onset before and after age 65; Mini Mental State Examination 19.8, SD 4.0 and 20.7, SD 4.2) were assessed with a neuropsychological battery and high-resolution MRI together with 1:1 age- and sex-matched controls. Cortical atrophy was assessed with cortical pattern matching, and hippocampal atrophy with region-of-interest-based analysis. EOAD patients performed more poorly than LOAD on visuospatial, frontal-executive and learning tests. EOAD patients had the largest atrophy in the occipital [25% grey matter (GM) loss in the left and 24% in the right hemisphere] and parietal lobes (23% loss on both sides), while LOAD patients were remarkably atrophic in the hippocampus (21 and 22% loss). Hippocampal GM loss of EOAD (9 and 16% to the left and right) and occipital (12 and 14%) and parietal (13 and 12%) loss of LOAD patients were less marked. In EOAD, GM loss of 25% or more was mapped to large neocortical areas and affected all lobes, with relative sparing of primary sensory, motor, and visual cortex, and anterior cingulate and orbital cortex. In LOAD, GM loss was diffusely milder (below 15%); losses of 15-20% were confined to temporoparietal and retrosplenial cortex, and reached 25% in restricted areas of the medial temporal lobe and right superior temporal gyrus. These findings indicate that EOAD and LOAD differ in their typical topographic patterns of brain atrophy, suggesting different predisposing or aetiological factors.

Depressive symptoms associated with hereditary Alzheimer's disease: a case description

The authors describe a family group studied by the Centro de Biología Molecular y Biotecnología, and the Clínica de la Memoria, las Demencias y el Envejecimiento (Universidad Tecnológica de Pereira, Colombia), and evaluate the association of depressive symptoms with Alzheimer's disease (AD). This family presented a hereditary pattern for AD characterized by an early onset of dementia symptoms, a long preclinical depressive course, and, once the first symptoms of dementia appeared, a rapid progression to severe cognitive function impairment. The authors found a high prevalence of depressive symptoms in this family and propose that the symptoms could be an important risk factor for developing AD in the presence of other risk factors such as the APOE E4 allele.

Canine cognitive dysfunction and the cerebellum: acetylcholinesterase reduction, neuronal and glial changes

The specific functional and pathological alterations observed in Alzheimer's disease are less severe in the cerebellum than in other brain areas, particularly the entorhinal cortex and hippocampus. Since dense core amyloid-beta plaque formation has been associated with an acetylcholinesterase heterogeneous nucleator action, we examined if an acetylcholinesterase imbalance was involved in cerebellum plaque deposition. By using the canine counterpart of senile dementia of the Alzheimer's type, a promising model of human brain aging and early phases of Alzheimer's disease, we investigated how cerebellar pathology and acetylcholinesterase density could be related with cognitive dysfunction. As in Alzheimer's disease, the late affectation of the cerebellum was evidenced by its lack of amyloid-beta plaque and the presence of diffuse deposition throughout all cortical grey matter layers. The highest acetylcholinesterase optic density corresponded to cerebellar islands of the granular layer and was predominantly associated with synaptic glomeruli and the somata of Golgi cells. Its reduction correlated with aging and loss of granule cells, whereas cognitive deficit only correlated with loss of Purkinje cells. The observed Bergmann glia alterations may correspond to a reactive response to the loss and damage of the Purkinje cells, their specific neuronal partner. Regarding the role of acetylcholinesterase mediation in amyloid-beta deposition, our data argue against an interaction between these two proteins because acetylcholinesterase reduction correlates with aging but not with cognitive deficit. Finally, our data support the use of companion dogs of all breeds to study aging and early phases of Alzheimer's disease.

Alzheimer's presenilin 1 causes chromosome missegregation and aneuploidy

Mutations in the presenilin 1 gene cause most early onset familial Alzheimer's disease (FAD). Here, we report that a defect in the cell cycle - improper chromosome segregation - can be caused by abnormal presenilin function and therefore may contribute to AD pathogenesis. Specifically we find that either over-expression or FAD mutation in presenilin 1 (M146L and M146V) leads to chromosome missegregation and aneuploidy in vivo and in vitro: (1) Up to 20% of lymphocytes and neurons of FAD-PS-1 transgenic and knocking mice are aneuploid by metaphase chromosome analysis and in situ hybridization. (2) Transiently transfected human cells over-expressing normal or mutant PS-1 develop similar aneuploidy within 48 h, including trisomy 21. (3) Mitotic spindles in the PS-1 transfected cells contain abnormal microtubule arrays and lagging chromosomes. Several mechanisms by which chromosome missegregation induced by presenilin may contribute to Alzheimer's disease are discussed.

Enhanced brain activity may precede the diagnosis of Alzheimer's disease by 30 years

Presenilin 1 (PSEN1) mutations cause autosomal dominant familial Alzheimer's disease (FAD). PSEN1 mutation carriers undergo the course of cognitive deterioration, which is typical for sporadic Alzheimer's disease but disease onset is earlier and disease progression is faster. Here, we sought to detect signs of FAD in presymptomatic carriers of the PSEN1 mutation (C410Y) by use of a neuropsychological examination, functional MRI during learning and memory tasks and MRI volumetry. We examined five non-demented members of a FAD family and 21 non-related controls. Two of the five family members were carrying the mutation; one was 20 years old and the other 45 years old. The age of clinical manifestation of FAD in the family studied here is approximately 48 years. Neuropsychological assessments suggested subtle problems with episodic memory in the 20-year-old mutation carrier. The middle-aged mutation carrier fulfilled criteria for amnestic mild cognitive impairment. The 20-year-old mutation carrier exhibited increased, while the middle-aged mutation carrier exhibited decreased brain activity compared to controls within memory-related neural networks during episodic learning and retrieval, but not during a working-memory task. The increased memory-related brain activity in the young mutation carrier might reflect a compensatory effort to overcome preclinical neural dysfunction caused by first pathological changes. The activity reductions in the middle-aged mutation carrier might reflect gross neural dysfunction in a more advanced stage of neuropathology. These data suggest that functional neuroimaging along with tasks that challenge specifically those brain areas which are initial targets of Alzheimer's disease pathology may reveal activity alterations on a single-subject level decades before the clinical manifestation of Alzheimer's disease.

Chinese Presenilin-1 V97L mutation enhanced Abeta42 levels in SH-SY5Y neuroblastoma cells

Presenilin-1 gene mutations have been proven to be associated with the majority of early-onset familial Alzheimer's disease (FAD). There have been, however, no systematic studies of Presenilin-1 gene mutation in FAD in China so far. We found a novel Val-->Leu missense mutation at codon 97 (Val97Leu) of the Presenilin-1 gene in a Chinese FAD pedigree. To verify whether this mutation is pathologically functional, we established mutation type and wild type Presenilin-1 gene stably transfected cell lines (human neuroblastoma SH-SY5Y cells) to detect beta-amyloid (Abeta) concentrations using ELISA and radioimmunity methods. We also examined levels of beta-amyloid precursor protein cleaving enzyme (BACE) and amyloid precursor protein (APP) to explore their impact upon beta-amyloid production. Our results showed that Abeta42 concentration was significantly enhanced at 48h when compared to that at 24h in the mutant type cells. At 48h Abeta42 levels in the V97L mutants was also found to be elevated significantly, both intracellularly and extracellularly when compared to wild and mock transfected cells. The total Abeta in either group did not alter, consistent with unchanged BACE and APP expression levels. Our data reveal that the Presenilin-1 V97L variant can elevate Abeta42 levels both intracellularly and extracellularly, and was a potentially pathogenic mutation for this Chinese FAD pedigree. It also suggests that there are common mechanisms in the pathogenesis of FAD between Chinese and other ethnic populations, although their gene mutation sites are different.

Ex situ atomic force microscopy analysis of beta-amyloid self-assembly and deposition on a synthetic template

The beta-amyloid (Abeta) deposition, which is the conversion of soluble Abeta peptides to insoluble plaques on a surface, is an essential pathological process in Alzheimer's disease (AD). The identification and characterization of possible environmental factors that may influence amyloid deposition in vivo are important to unveil the underlying etiology of AD. According to the amyloid cascade hypothesis, diffuse plaques are initial and visual deposits in the early event of AD, leading to amyloid plaques. To study amyloid deposition and growth in vitro, we prepared a synthetic template by immobilizing Abeta seeds on an N-hydroxysuccinimide ester-activated solid surface. According to our analysis with an ex situ atomic force microscope, the formation of amyloid plaque-like aggregates was mediated by the interaction between Abeta in a solution and on a synthetic template, suggesting that Abeta oligomers function well as seeds for amyloid deposition. It was observed that insoluble amyloid aggregates formed on the template surface serve as a sink of soluble Abeta in a solution as well as mediate the formation of intermediates in the pathway of amyloid fibrillization in a solution. Relative seeding efficiencies of fresh monomers, oligomers, and fully grown fibrils were analyzed by measuring the deposited plaque volume and its height distribution through atomic force microscopy. The result revealed that oligomeric forms of Abeta act more efficiently as seeds than monomers or fibrils do. Fluorescence spectroscopy with thioflavin T confirmed that amyloid aggregate formation proceeds in a concentration-dependent manner. Analysis with Fourier transform infrared spectroscopy indicated a progressive transition of soluble Abeta42 monomer to amyloid fibrils having antiparallel beta-sheet structure on the template. Furthermore, studies on the interaction between Abeta40 and 42, two major variants of Abeta derived from the amyloid precursor protein, showed that amyloid aggregate formation on the surface was accelerated further by the homogeneous association of soluble Abeta42 onto Abeta42 seeds than by other combinations. A slightly acidic condition was found to be unfavorable for amyloid formation. This study gives insight into understanding the effects of environmental factors on amyloid formation via the use of a synthetic template system.

Aging sensitizes toward ROS formation and lipid peroxidation in PS1M146L transgenic mice

Mutations in the presenilins (PS) account for the majority of familial Alzheimer disease (FAD) cases. To test the hypothesis that oxidative stress can underlie the deleterious effects of presenilin mutations, we analyzed lipid peroxidation products (4-hydroxynonenal (HNE) and malondialdehyde) and antioxidant defenses in brain tissue and levels of reactive oxygen species (ROS) in splenic lymphocytes from transgenic mice bearing human PS1 with the M146L mutation (PS1M146L) compared to those from mice transgenic for wild-type human PS1 (PS1wt) and nontransgenic littermate control mice. In brain tissue, HNE levels were increased only in aged (19-22 months) PS1M146L transgenic animals compared to PS1wt mice and not in young (3-4 months) or middle-aged mice (13-15 months). Similarly, in splenic lymphocytes expressing the transgenic PS1 proteins, mitochondrial and cytosolic ROS levels were elevated to 142.1 and 120.5% relative to controls only in cells from aged PS1M146L animals. Additionally, brain tissue HNE levels were positively correlated with mitochondrial ROS levels in splenic lymphocytes, indicating that oxidative stress can be detected in different tissues of PS1 transgenic mice. Antioxidant defenses (activities of antioxidant enzymes Cu/Zn-SOD, GPx, or GR) or susceptibility to in vitro oxidative stimulation was unaltered. In summary, these results demonstrate that the PS1M146L mutation increases mitochondrial ROS formation and oxidative damage in aged mice. Hence, oxidative stress caused by the combined effects of aging and PS1 mutations may be causative for triggering neurodegenerative events in FAD patients.

Differences in regional brain atrophy in genetic forms of Alzheimer's disease

Multiple degenerative hallmarks characterize Alzheimer's disease: insoluble protein deposition, neuronal loss and cortical atrophy. Atrophy begins in the medial temporal lobe and becomes global by end stage. In a small proportion of cases, these tissue changes are caused by mutations in three known genes. These cases are affected earlier in life and have more abundant protein deposition, which may indicate greater tissue atrophy and degeneration. This issue remains unresolved. Grey matter atrophy in different cortical regions was determined in genetic cases of Alzheimer's disease (N = 13) and compared to sporadic cases (N = 13) and non-diseased controls (N = 23). Genetic mutations were found to influence the degree and regional pattern of atrophy. The majority of cases had greater medial temporal atrophy than sporadic disease, suggesting that abnormalities affecting Abeta metabolism selectively increase hippocampal degeneration. Cases with mutations in presenilin-1 demonstrated additional increased frontotemporal atrophy. This effect may be due to the influence of presenilin-1 on tau phosphorylation and metabolism. These differences may explain the earlier onset ages in these different forms of Alzheimer's disease.

Metabolism of amyloid beta peptide and pathogenesis of Alzheimer's disease. Towards presymptomatic diagnosis, prevention and therapy

The conversion of what has been interpreted as "normal brain aging" to Alzheimer's disease (AD) via a transition state, i.e. mild cognitive impairment, appears to be a continuous process caused primarily by aging-dependent accumulation of amyloid beta peptide (Abeta) in the brain. This notion give us a hope that, by manipulating the Abeta levels in the brain, we may be able not only to prevent and cure the disease but also to partially control some very significant aspects of brain aging. Abeta is constantly produced from its precursor and immediately catabolized under normal conditions, whereas dysmetabolism of Abeta seems to lead to pathological deposition upon aging. We have focused our attention on elucidation of the unresolved mechanism of Abeta catabolism in the brain. In this review, we describe a new approach to prevent AD development by reducing Abeta burdens in aging brains through up-regulation the catabolic mechanism involving neprilysin that can degrade both monomeric and oligomeric forms of Abeta. The strategy of combining presymptomatic diagnosis with preventive medicine seems to be the most pragmatic in both medical and socio-economical terms. We also introduce a novel non-invasive amyloid imaging approach using a high-power magnetic resonance imaging (MRI) for the presymptomatic diagnosis of AD.

Mutagenesis of the central hydrophobic cluster in Abeta42 Alzheimer's peptide. Side-chain properties correlate with aggregation propensities

Protein misfolding and deposition underlie an increasing number of debilitating human disorders. Alzheimer's disease is pathologically characterized by the presence of numerous insoluble amyloid plaques in the brain, composed primarily of the 42 amino acid human beta-amyloid peptide (Abeta42). Disease-linked mutations in Abeta42 occur in or near a central hydrophobic cluster comprising residues 17-21. We exploited the ability of green fluorescent protein to act as a reporter of the aggregation of upstream fused Abeta42 variants to characterize the effects of a large set of single-point mutations at the central position of this hydrophobic sequence as well as substitutions linked to early onset of the disease located in or close to this region. The aggregational properties of the different protein variants clearly correlated with changes in the intrinsic physicochemical properties of the side chains at the point of mutation. Reduction in hydrophobicity and beta-sheet propensity resulted in an increase of in vivo fluorescence indicating disruption of aggregation, as confirmed by the in vitro analysis of synthetic Abeta42 variants. The results confirm the key role played by the central hydrophobic stretch on Abeta42 deposition and support the hypothesis that sequence tunes the aggregation propensities of polypeptides.

Presenilin immunoreactivity in Alzheimer's disease

The role of presenilin (PS) mutations in familial Alzheimer's disease (AD) may be as a toxic gain of function, but in sporadic disease their contribution is more difficult to understand. In this study, we investigated PS proteins in sporadic AD by comparing the immunocytochemical profiles in sporadic AD with control brains using a quantitative immunocytochemical approach to both the N- and C-terminals of PS1 and PS2. Ten patients with pathologically proven AD (using modified Consortium to Establish a Registry for Alzheimer's Disease [CERAD] criteria) and 10 controls were age- and sex-matched. The immunocytochemical primary antibodies were affinity-purified goat polyclonal antibodies and the secondary antibodies were biotinylated donkey anti-goat to the N- and C-terminal of both PS1 and PS2. The number of PS-containing neurones was quantified manually and without the knowledge of the diagnosis. We found no significant differences in the number of PS1- and PS2-containing neurones in three anatomical regions for both N- and C-terminals between AD and controls. Our findings argue in favour of functional changes in PS molecules contributing to the pathogenesis of AD and are consistent with the hypothesis of dysfunction of the entire gamma-secretase complex, of which PS proteins are a constituent.

Transient abundance of presenilin 1 fragments/nicastrin complex associated with synaptogenesis during development in rat cerebellum

Immunolocalization and expression of endogenous nicastrin (NCT) and presenilin 1 (PS1) fragments during postnatal development of rat cerebellum were investigated with fragment-specific antibodies. Immunoblotting for NCT revealed the expected mature and immature species, which gradually declined during development. In contrast, the expression of PS1 N-terminal fragment exhibited a peak at postnatal day 14 (P14) and declined thereafter. This chronological change was similarly observed with PS1 C-terminal fragment. Immunoprecipitation of NCT indicated its physical association with PS1 fragments. Colocalization of these molecules to the endoplasmic reticulum in cerebellar Purkinje cells indicates that they are organized into a complex in developing neurons. In addition, active sites of synaptogenesis, the base of the external granular layer and glomeruli, contained PS1 fragments and smaller amount of NCT. Isolated synaptic fraction contained both PS1 and NCT, suggesting their functional association within synapses. Transient abundance of NCT and PS1 fragments as a complex, when (P14) and where synaptogenesis is active, is consistent with intracellular trafficking of this complex in developing neurons and suggests its role as gamma-secretase in synaptogenesis.

Clinical phenotypic heterogeneity of Alzheimer's disease associated with mutations of the presenilin-1 gene

It is now 10 years since the first report of mutations in the presenilin genes that were deterministic for familial autosomal dominant Alzheimer's disease. The most common of these mutations occurs in the presenilin-1 gene (PSEN1) located on chromosome 14. In the ensuing decade, more than 100 PSEN1 mutations have been described. The emphasis of these reports has largely been on the novelty of the mutations and their potential pathogenic consequences rather than detailed clinical, neuropsychological, neuroimaging and neuropathological accounts of patients with the mutation. This article reviews the clinical phenotypes of reported PSEN1 mutations, emphasizing their heterogeneity, and suggesting that other factors, both genetic and epigenetic,must contribute to disease phenotype.

Aberrant accentuation of neurofibrillary degeneration in the hippocampus of Alzheimer's disease with amyloid precursor protein 717 and presenilin-1 gene mutations

This study reports correlation of the hippocampal neurofibrillary tangles (NFT) density with beta-amyloid (Abeta) precursor protein (APP) 717 mutation, presenilin (PS)-1 mutation and apolipoprotein E (Apo-E) e4 alleles (E4), being graded as 3 forms (no-E4, one-E4 and two-E4) in autopsied brains from patients with familial and non-familial Alzheimer's disease (AD). We studied the density of NFT-free neurons, intracellular NFT (I-NFT), extracellular NFT (E-NFT) and total NFT (I-NFT plus E-NFT) in the six hippocampal subdivisions: cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. The APP mutation cases showed significantly higher total NFT density in the CA1-CA2 region, and the PS-1 mutation cases also showed higher density of total NFT in the CA1-CA3 than non-familial cases. Moreover, high densities of the E-NFT contributed to these high total NFT densities. Non-familial AD cases showed a stereotypical NFT distribution with entorhinal accentuation in the hippocampus irrespective of E4 frequency. Thus, APP and PS-1 mutations predominantly affect the CA regions with profound neurodegeneration, which contributes early and severe clinical features of familial AD.

Deficient cerebral clearance of vasculotropic mutant Dutch/Iowa Double A beta in human A betaPP transgenic mice

Cerebral amyloid angiopathy (CAA) is a prominent pathological feature of Alzheimer's disease and related familial CAA disorders. However, the mechanisms that account for the cerebral vascular accumulation of amyloid beta-peptide (A beta) have not been defined. Recently, we reported novel transgenic mice (Tg-SwDI) expressing neuronally derived Swedish/Dutch/Iowa vasculotropic mutant human A beta precursor (A betaPP) that develop early-onset and robust accumulation of fibrillar cerebral microvascular A beta. Deficient clearance of Dutch/Iowa mutant A beta from brain across the capillary blood-brain barrier into the circulation may contribute to its potent cerebral accumulation. To further evaluate this theory, we generated a new transgenic mouse (Tg-Sw) that is nearly identical to Tg-SwDI, except lacking the Dutch/Iowa A beta mutations. Tg-Sw and Tg-SwDI mice expressed comparable levels of human A betaPP in brain and not in peripheral tissues. However, Tg-SwDI mice strongly accumulated Dutch/Iowa mutant A beta in brain, particularly in the cerebral microvasculature, whereas Tg-Sw mice exhibited no accumulations of wild-type A beta. Conversely, Tg-SwDI mice had no detectable Dutch/Iowa mutant A beta in plasma whereas Tg-Sw mice exhibited consistent levels of human wild-type A beta in plasma. Together, these findings suggest that while wild-type A beta is readily transported out of brain into plasma, Dutch/Iowa mutant A beta is deficient in this clearance process, likely contributing to its robust accumulation in the cerebral vasculature.

Etiology of sporadic Alzheimer’s disease: Somatostatin, neprilysin, and amyloid β peptide

We recently demonstrated that amyloid beta peptide (Abeta) is catabolized primarily by a neutral endopeptidase, neprilysin, in the brain and that a neuropeptide, somatostatin (SST), regulates brain Abeta level via modulation of neprilysin activity. Because SST expression in the brain declines upon aging in various mammals including rodents, apes and humans, we hypothesize that the aging-dependent reduction of SST triggers accumulation of Abeta in the brain by suppressing neprilysin action. This hypothesis accounts for the fact that aging is the predominant risk factor for Sporadic Alzheimer's disease.

Deciphering the molecular basis of memory failure in Alzheimer's disease

Acutely developing lesions of the brain have been highly instructive in elucidating the neural systems underlying memory in humans and animal models. Much less has been learned from chronic neurodegenerative disorders that insidiously impair memory. But the advent of a detailed molecular hypothesis for the development of Alzheimer's disease and the creation of compelling mouse models thereof have begun to change this situation. Experiments in rodents suggest that soluble oligomers of the amyloid beta protein (Abeta) may discretely interfere with synaptic mechanisms mediating aspects of learning and memory, including long-term potentiation. In humans, memory impairment correlates strongly with cortical levels of soluble Abeta species, which include oligomers. Local inflammatory changes, neurofibrillary degeneration, and neurotransmitter deficits all contribute to memory impairment, but available evidence suggests that these develop as a consequence of early Abeta accumulation. Accordingly, attempts to slow memory and cognitive loss by decreasing cerebral Abeta levels have entered human trials.

CA1 hippocampal neuronal loss in familial Alzheimer's disease presenilin-1 E280A mutation is related to epilepsy

PURPOSE

Alzheimer disease (AD) and epilepsy are brain disorders frequently associated with neuronal cell loss in mesial temporal lobe structures, but presenting different patterns of damage. Recently it was proposed that a causal relation may exist between AD pathology and the appearance of epilepsy in some cases with AD. This study aimed to determine the neuronal loss in CA1 hippocampal region from patients bearing the presenilin-1 [E280A] mutation (PS1[E280A]) associated with seizures.

METHODS

Coronal sections from the hippocampal formation (anterior one third) from controls (n = 5) and familial AD (FAD; n = 8) patients were stained by using thionin and thioflavine-S staining to evaluate the number of neurons in the CA1 field, beta-plaques, and neurofibrillary tangles, respectively.

RESULTS

Two distinct patterns of neuronal loss in the CA1 field of FAD patients were found: (a) diffuse-patchy neuronal loss (three FAD nonepilepsy patients) characterized by both a general decrease of neurons and the presence of multiple, small regions devoid of neurons; and (b) sclerotic-like neuronal loss (five FAD epilepsy patients) similar to that found typically in the CA1 field of epilepsy patients with hippocampal sclerosis.

CONCLUSIONS

This investigation shows for the first time CA1 neuronal depopulation in a subpopulation of patients (five of eight) bearing the PS1[E280A] mutation with epileptic seizures, indicating a relation between hippocampal neuronal loss and epileptic seizures in FAD patients.

Age-dependent neurodegeneration and Alzheimer-amyloid plaque formation in transgenic Drosophila

Beta-amyloid peptides that are cleaved from the amyloid precursor protein (APP) play a critical role in Alzheimer's disease (AD) pathophysiology. Here, we show that in Drosophila, the targeted expression of the key genes of AD, APP, the beta-site APP-cleaving enzyme BACE, and the presenilins led to the generation of beta-amyloid plaques and age-dependent neurodegeneration as well as to semilethality, a shortened life span, and defects in wing vein development. Genetic manipulations or pharmacological treatments with secretase inhibitors influenced the activity of the APP-processing proteases and modulated the severity of the phenotypes. This invertebrate model of amyloid plaque pathology demonstrates Abeta-induced neurodegeneration as a basic biological principle and may allow additional genetic analyses of the underlying molecular pathways.

Baculoviruses expressing the human familial Alzheimer's disease presenilin 1 mutation lacking exon 9 increase levels of an amyloid beta-like protein in Sf9 cells

Presenilin 1 (PS1) plays a pivotal role in the production of the amyloid-beta protein (Abeta) that is central to the pathogenesis of Alzheimer's disease. PS1 regulates the intramembranous proteolysis of a 99-amino-acid C-terminal fragment of the amyloid precursor protein (APP-C99), a cleavage event that releases Abeta following a reaction catalyzed by an enzyme termed 'gamma-secretase'. The molecular mechanism of PS1-mediated, gamma-secretase cleavage remains largely unresolved. In particular, controversy surrounds whether PS1 includes the catalytic site of the gamma-secretase protease or whether instead PS1 mediates gamma-secretase activity indirectly, perhaps by regulating the trafficking or presentation of substrates to the 'authentic' protease, which may be a molecule distinct from PS1. To address this issue, the baculovirus expression system was used to co-express: (i) APP-C99; (ii) a pathogenic, constitutively active mutant form of PS1 lacking exon 9 (PS1DeltaE9); (iii) nicastrin and (iv) tropomyosin in Spodoptera frugiperda (Sf9) cells. Cells infected with APP-C99 alone produced an Abeta-like species, and levels of this species were enhanced by the addition of baculoviruses bearing the PS1DeltaE9 mutation. The addition to APP-C99-infected cells of baculoviruses bearing nicastrin, also a transmembrane protein, had a neutral or inhibitory effect on the reaction; tropomyosin viruses had the same effect as nicastrin viruses. These results suggest that PS1DeltaE9 molecules expressed in Sf9 cells retain the ability to modulate Abeta levels. Baculoviral-expressed PS1DeltaE9 provides a source of microgram quantities of bioactive molecules for use as starting material for purifying and reconstituting gamma-secretase activity from its individual purified component parts.

Neuropathological and clinical phenotype of an Italian Alzheimer family with M239V mutation of presenilin 2 gene

Presenilin 1 and 2 are 2 highly homologous genes involved in familial Alzheimer disease. While more than 100 mutations in presenilin 1 are known to segregate with the disease in familial Alzheimer disease, only 9 mutations of presenilin 2 have been identified to date. We report the clinical and neuropathological phenotype of FLO10, the large Italian Alzheimer kindred associated with methionine to valine substitution at residue 239 of presenilin 2. The patients showed a remarkable variability in age of onset of symptoms, disease duration, and clinical presentation. The neuropathological study of 2 patients revealed peculiar features in addition to neurofibrillary changes and A beta amyloid deposits in the neuropil and vessel wall. Ectopic neurons in the subcortical white matter, often containing neurofibrillary tangles, were found in both patients, one of whom presented with epilepsy. Furthermore, 1 patient showed an unusually high number of ghost tangles in the cerebral cortex. These observations indicate that the Alzheimer kindred FLO10 associated with M239V mutation of presenilin 2 is characterized by some peculiarities of the clinical and neuropathologic phenotype compared to sporadic Alzheimer disease.

Clinical, pathological, and biochemical spectrum of Alzheimer disease associated with PS-1 mutations

Three genes have been implicated in the etiology of early-onset autosomal-dominant Alzheimer disease (AD): the amyloid precursor protein, the presenilin-1, and presenilin-2 genes. Approximately half of autosomal-dominant AD cases are associated with mutations in the presenilin-1 (PS-1) gene on the long arm of Chromosome 14. Marked allelic heterogeneity characterizes families with PS-1 gene mutations; more than 100 different mutations have been found in independent families thus far. With the exception of age at onset, the clinical phenotype is similar to late-onset AD, although some rare specific phenotypes have been described. These mutations lead to enhanced deposition of total Abeta and Abeta42 (but not Abeta40) in the brain, compared with sporadic AD. There is a considerable heterogeneity in the histological profiles among brains from patients with different mutations, and although some lead to predominantly parenchymal deposition of Abeta in the form of diffuse and cored plaques, others show predominantly vascular deposition, with severe amyloid angiopathy. Only some mutations are associated with enhanced neurofibrillary tangle formation and increased neuronal loss compared with sporadic AD. However, there is an important clinical and pathological variability even among family members with the same mutation, which suggests the involvement of other genetic or environmental factors that modulate the clinical expression of the disease. This represents a valuable model for identifying such factors and has potential implications for the development of new therapeutic strategies for delaying disease onset.

Pedigree disequilibrium test (PDT) replicates association and linkage between DRD4 and ADHD in multigenerational and extended pedigrees from a genetic isolate

Association/linkage between dopamine D4 receptor (DRD4) polymorphisms and attention-deficit/hyperactivity disorder (ADHD) has been suggested by case-control- and nuclear-family-based studies. Here, we present a candidate gene analysis for DRD4 using 14 extended and multigenerational families segregating ADHD derived from the 'Paisa' community of Antioquia, Colombia, a genetic isolate. Two DRD4 polymorphisms (a 120 bp tandem duplication at the promoter and a 48 bp-VNTR at exon 3), reported associated to ADHD, were genotyped. Parametric and non-parametric linkage analyses, and a family-based association test (FBAT), the pedigree disequilibrium test (PDT), were applied to search for evidence of association/linkage. Two-point LOD scores were significantly negative, with values ranging from -3.21 (P=0.011158) to -7.66 (P=0.000091 at theta=0). Non-parametrical analysis resulted in nonsignificant evidence for linkage. The PDT showed a moderate trend toward significance of association/linkage between the 7-repeat (7R) allele at the 48 bp VNTR and ADHD (P=0.0578). Furthermore, the haplotype analysis shows a significant association/linkage of the 7R-240 bp haplotype (P=0.0467) with ADHD. Results suggest that either a moderate DRD4 genetic effect, or linkage disequilibrium of DRD4 with an ADHD disease locus in the vicinity or the linkage to a phenotypic component of the ADHD spectrum could be underlying this association/linkage. These results provide further evidence for the association of ADHD to genetic variation in or near to DRD4 and replicate the previously reported association between ADHD and the 7R allele.

Luteinizing hormone, a reproductive regulator that modulates the processing of amyloid-beta precursor protein and amyloid-beta deposition

Hormonal changes associated with the dysregulation of the hypothalamic-pituitary-gonadal (HPG) axis following menopause/andropause have been implicated in the pathogenesis of Alzheimer's disease (AD). Experimental support for this has come from studies demonstrating an increase in amyloid-beta (Abeta) deposition following ovariectomy/castration. Because sex steroids and gonadotropins are both part of the HPG feedback loop, any loss in sex steroids results in a proportionate increase in gonadotropins. To assess whether Abeta generation was due to the loss of serum 17beta-estradiol or to the up-regulation of serum gonadotropins, we treated C57Bl/6J mice with the anti-gonadotropin leuprolide acetate, which suppresses both sex steroids and gonadotropins. Leuprolide acetate treatment resulted in a 3.5-fold (p < 0.0001) and a 1.5-fold (p < 0.024) reduction in total brain Abeta1-42 and Abeta1-40 concentrations, respectively, after 8 weeks of treatment. To further explore the role of gonadotropins in promoting amyloidogenesis, M17 neuroblastoma cells were treated with the gonadotropin luteinizing hormone (LH) at concentrations equivalent to early adulthood (10 mIU/ml) or post-menopause/andropause (30 mIU/ml). LH did not alter amyloid-beta precursor protein (AbetaPP) expression but did alter AbetaPP processing toward the amyloidogenic pathway as evidenced by increased secretion and insolubility of Abeta, decreased alphaAbetaPP secretion, and increased AbetaPP-C99 levels. These results suggest the marked increases in serum LH following menopause/andropause as a physiologically relevant signal that could promote Abeta secretion and deposition in the aging brain. Suppression of the age-related increase in serum gonadotropins using anti-gonadotropin agents may represent a novel therapeutic strategy for AD.

Mutant presenilin (A260V) affects Rab8 in PC12D cell

Most familial early-onset Alzheimer's disease (FAD) is caused by mutations in the presenilin-1 (PS1) gene. Abeta is derived from amyloid precursor protein (APP) and an increased concentration of Abeta 42 is widely believed to be a pathological hallmark of abnormal PS function. Therefore, the interaction between PS1 and APP is a central theme in attempts to clarify the molecular mechanism of AD. To examine the effect of PS1 mutations on APP metabolism, we made PC12D cell lines that express human PS1 or mutant PS1 (A260V). In PC12D cells expressing the PS1A260V mutant, we found that Rab8, a GTPase involved in transport from the trans-Golgi network (TGN) to the plasma membrane (PM), was significantly reduced in PC12D cells expressing the A260V mutant and that APP C-terminal fragment (CTF), the direct precursor of Abeta, accumulated in the heavy membrane fraction including membrane vesicles involved in TGN-to-PM transport. Furthermore, the total intracellular Abeta production was reduced in these cells. Combined together, we have observed that PS1 mutation disturbs membrane vesicle transport, resulting in prolonged residence of APP CTF during TGN-to-PM transport pathway. Therefore, it is highly likely that reduction of Abeta is closely related to the retention of APP CTF during TGN-to-PM transport.

Notch and Presenilin: regulated intramembrane proteolysis links development and degeneration

Intensive studies of three proteins--Presenilin, Notch, and the amyloid precursor protein (APP)--have led to the recognition of a direct intersection between early development and late-life neurodegeneration. Notch signaling mediates many different intercellular communication events that are essential for determining the fates of neural and nonneural cells during development and in the adult. The Notch receptor acts in a core pathway as a membrane-bound transcription factor that is released to the nucleus by a two-step cleavage mechanism called regulated intramembrane proteolysis (RIP). The second cleavage is effected by Presenilin, an unusual polytopic aspartyl protease that apparently cleaves Notch and numerous other single-transmembrane substrates within the lipid bilayer. Another Presenilin substrate, APP, releases the amyloid ss-protein that can accumulate over time in limbic and association cortices and help initiate Alzheimer's disease. Elucidating the detailed mechanism of Presenilin processing of membrane proteins is important for understanding diverse signal transduction pathways and potentially for treating and preventing Alzheimer's disease.

Altered Abeta formation and long-term potentiation in a calsenilin knock-out

Calsenilin has been identified as a presenilin-binding protein, a transcription factor regulating dynorphin expression, and a beta-subunit of Kv4 channels and could, thus, be a multifunctional protein. To study these functions of calsenilin in vivo and to determine the neuroanatomical expression pattern of calsenilin, we generated mice with a disruption of the calsenilin gene by the targeted insertion of the beta-galactosidase gene. We found that calsenilin expression (as represented by beta-galactosidase activity) is very restricted but overlaps better with that of presenilins and Kv4 channels than with dynorphin, suggesting that calsenilin may regulate presenilin and Kv4 channels in brain. Abeta peptide levels are reduced in calsenilin knock-out mice, demonstrating that calsenilin affects presenilin-dependent gamma-cleavage in vivo. Furthermore, long-term potentiation (LTP) in dentate gyrus of hippocampus, in which calsenilin is strongly and selectively expressed, is enhanced in calsenilin knock-out mice. This enhancement of LTP coincides with a downregulation of the Kv4 channel-dependent A-type current and can be mimicked in wild-type animals by a Kv4 channel blocker. The data presented here show that lack of calsenilin affects both Abeta formation and the A-type current. We suggest that these effects are separate events, caused by a common mechanism possibly involving protein transport.

Two novel presenilin-1 mutations (Y256S and Q222H) are associated with early-onset Alzheimer's disease

Mutations in the gene encoding presenilin 1 (PS-1) account for 50% of early-onset familial Alzheimer's disease (EOFAD) cases. In this study, we identified two missense mutations in the coding sequence of the presenilin (PS-1) gene in two EOFAD pedigrees. AD was confirmed in one pedigree by autopsy. Mutation analysis of PCR products amplified from genomic DNA templates showed two novel PS-1 mutations resulting in Gln222His and Tyr256Ser. The two novel mutations are located within predicted transmembrane domains five (TM-5) and six (TM-6), respectively, and are associated with very early ages of onset. The Tyr256Ser is associated with one of the youngest age of AD onset, 25 years, which is consistent with a drastic change in function of the altered PS-1 protein. A morphometric analysis of the cortical degenerative changes of the Tyr256Ser case, showed severe involvement of the primary motor cortex, which correlated well with the pyramidal changes, including tetraspasticity. Immunoblot analysis showed the Tyr256Ser case had the greatest expression of Abeta(1-40) and Abeta(1-42), which was confirmed by ELISA, compared to other PS-1 mutant FAD cases and age-matched controls and, thus, contributes to the severity of the disease pathology.

Apolipoprotein Eepsilon4 modifies Alzheimer's disease onset in an E280A PS1 kindred

We previously have identified a large kindred from Colombia in which Alzheimer's disease (AD) is caused by the E280A presenilin 1 (PS1) mutation. The objective of this study was to examine whether environmental and genetic factors are responsible for variation in the phenotypic expression of the E280A PS1 mutation. We genotyped coding and promoter polymorphisms of the APOE gene in carriers of the E280A PS1 mutation. Kaplan-Meier product-limit and Cox proportional hazard models were used in the statistical analyses. DNA was available from 114 carriers of the E280A PS1 mutation, including 52 subjects with AD. APOE epsilon 4 allele carriers were more likely to develop AD at an earlier age than subjects without the epsilon 4 allele (hazard ratio, 2.07; 95% confidence interval, 1.07-3.99; p = 0.030). Subjects with low education were more likely to develop AD later than those with higher education (hazard ratio, 0.476; 95% confidence interval, 0.26-0.87). Low educational level was associated with rural residence (p < 0.001). Promoter APOE variants did not influence either the onset or the duration of the disease. This study is the first to our knowledge to demonstrate that genetic and environmental factors influence age of onset in a kindred with a familial AD mutation.

Intramembrane proteolysis by presenilin and presenilin-like proteases

Regulated intramembrane proteolysis is a novel mechanism involving proteases that hydrolyze their substrates in a hydrophobic environment. Presenilin (PS) 1 and PS 2 are required for intramembrane cleavage of an increasing number of type I membrane proteins, including the amyloid precursor protein of Alzheimer's disease and the Notch receptor, which signals during differentiation and development. Mutagenesis, affinity labeling, biochemical isolation, and reconstitution in cells reveal that PS, in complex with co-factors nicastrin, APH-1 and PEN-2, apparently contains the active site of gamma-secretase, a novel membrane aspartyl protease. In addition, other related aspartyl proteases have been identified. These include members of the type-4 prepilin peptidase family in bacteria, which are known proteases and carry a GD motif conserved in PS. A group of multi-pass membrane proteins found in eukaryotes also contain YD and LGXGD motifs in two transmembrane domains that are conserved in PS and postulated to constitute an aspartyl protease active site. Among these is signal peptide peptidase (SPP), which cleaves remnant signal peptides derived from signal-peptidase-mediated ectodomain shedding. SPP cuts type II membrane proteins, illustrating that PS-like proteases play a key role in intramembrane proteolysis of single-pass membrane proteins oriented in either direction.

Neuropsychological study of familial Alzheimer's disease caused by mutation E280A in the presenilin 1 gene

In Antioquia, Colombia, investigators have recently discovered the largest family with the E280A mutation in the presenilin 1 gene that causes one type of familial Alzheimer's disease (FAD). The current study compares two groups within this family: those diagnosed with Alzheimer's disease (AD) in its early stage (nine subjects) and relatives (carriers) who did not show any signs of dementia (nine subjects). A battery of the following neuropsychological tests was administered to subjects in both groups: the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), a Phonological Verbal Fluency test, the Visual "A" Cancellation Test, memory of three phrases, the Rey-Osterrieth Complex Figure, and the Trail Making Test Part A. Statistical analyses of the average test scores of each group showed that the AD group scored significantly (p < 0.01 or p < 0.05) lower on 29 of the 43 neuropsychological variables measured (67 percent). Therefore, this specific battery was useful in discriminating subjects with AD from their healthy relatives who are carriers of the disease. The AD group as a whole presented slight dementia with predominant deficits in memory, language, praxis, and attention. This profile is similar to those reported in subjects with sporadic AD in its early stage and confirms the findings found in other neuropsychological studies of subjects with FAD linked to mutations in chromosome 14.

Early-onset Alzheimer's disease with presenilin-1 M139V mutation: clinical, neuropsychological and neuropathological study

The clinical, neuropsychological and neuropathological features of a patient with early-onset Alzheimer's disease as a result of the M139V presenilin-1 (PSEN-1) mutation are presented, and compared with previous reports of patients with the same mutation. Similarities, such as the age at onset and the relative preservation of naming skills, and differences, such as the significant basal ganglia, thalamic and cerebellar pathology, are noted. This clinical and pathological heterogeneity in patients with the same PSEN-1 mutation suggests phenotype modulation by genetic and/or epigenetic factors.

gamma-Secretase cleavage site specificity differs for intracellular and secretory amyloid beta

The final step in A beta generation is the cleavage of the C-terminal 99 amino acid residues of the amyloid precursor protein by gamma-secretase. gamma-Secretase activity is closely linked to the multi-transmembrane-spanning proteins presenilin 1 and presenilin 2. To elucidate whether the cleavage site specificities of gamma-secretase leading to the formation of secreted and intracellular A beta are identical, we made use of point mutations close to the gamma-cleavage site, known to have a dramatic effect on the 42/40 ratio of secreted A beta. We found that the selected point mutations only marginally influenced the 42/40 ratio of intracellular A beta, suggesting differences in the gamma-secretase cleavage site specificity for the generation of secreted and intracellular A beta. The analysis of the subcellular compartments involved in the generation of intracellular A beta revealed that A beta is not generated in the early secretory pathway in the human SH-SY5Y neuroblastoma cell line. In this study we identified late Golgi compartments to be involved in the generation of intracellular A beta. Moreover, we demonstrate that the presence of processed PS1 is not sufficient to obtain gamma-secretase processing of the truncated amyloid precursor protein construct C99, proposing the existence of an additional factor downstream of the endoplasmic reticulum and early Golgi required for the formation of an active gamma-secretase complex.

Physiologic and pathologic events mediated by intramembranous and juxtamembranous proteolysis

Intramembranous proteolysis (IP) is a recently recognized mechanism for transmembrane signal transduction that involves proteolysis of transmembrane proteins within their membrane-spanning domains. Juxtamembranous proteolysis (JP) is similar, but proteolytic cleavage of a transmembrane protein occurs at a site close to, but not within, the transmembrane domain of the target protein. In both IP and JP, a soluble domain of a transmembrane protein is released from its membrane tether. This domain can then transmit a signal either locally or at some distance from the site of cleavage. In certain signaling pathways, JP and IP are linked. JP on one side of the membrane results in secondary IP, which then releases a signaling domain from the membrane. Whereas well-characterized proteases such as caspases, the proteasome, and metalloprotease disintegrins, have been implicated in JP, three families of multipass membrane proteases (MpMPs) have now been shown to carry out IP. Recent studies of events mediated by IP and JP indicate that they regulate key cellular signaling events including pathways involved in sterol regulation, cell fate selection, and growth regulation. Moreover, IP and JP have important roles in certain diseases such as Alzheimer's disease. Because some of the proteases mediating IP and JP can be selectivity inhibited, inhibitors targeting these proteases are likely to alter both physiologic and pathologic events triggered by IP and JP.

Presenilin-1 mutation L271V results in altered exon 8 splicing and Alzheimer's disease with non-cored plaques and no neuritic dystrophy

The mutation L271V in exon 8 of the presenilin-1 (PS-1) gene was detected in an Alzheimer's disease pedigree. Neuropathological examination of affected individuals identified variant, large, non-cored plaques without neuritic dystrophy, reminiscent of cotton wool plaques. Biochemical analysis of L271V mutation showed that it increased secretion of the 42-amino acid amyloid-beta peptide, suggesting a pathogenic mutation. Analysis of PS-1 transcripts from the brains of two mutation carriers revealed a 17-50% increase in PS-1 transcripts with deletion of exon 8 (PS-1deltaexon8) compared with unrelated Alzheimer's disease brains. Exon trapping analysis confirmed that L271V mutation enhanced the deletion of exon 8. Western blots of brain lysates indicated that PS-1deltaexon8 was overexpressed in an affected individual. Biochemical analysis of PS-1deltaexon8 in COS and BD8 cells indicate the splice isoform is not intrinsically active but interacts with wild-type PS-1 to generate amyloid-beta. Western blots of cell lysates immunoprecipitated with anti-Tau or anti-GSK-3beta antibodies indicated that PS-1deltaexon8, unlike wild-type PS-1, does not interact directly with Tau or GSK-3beta, potential modifiers of neuritic dystrophy. We postulate that variant plaques observed in this family are due in part to the effects of PS-1deltaexon8 and that interaction between PS-1 and various protein complexes are necessary for neuritic plaque formation.

Dentate gyrus volume is reduced before onset of plaque formation in PDAPP mice: a magnetic resonance microscopy and stereologic analysis

High-resolution magnetic resonance microscopy (MRM) was used to determine regional brain volumetric changes in a mouse model of Alzheimer's disease. These transgenic (Tg) mice overexpress human mutant amyloid precursor protein (APP) V717F under control of platelet-derived growth factor promoter (PDAPP mice), and cortical and hippocampal beta-amyloid (Abeta) deposits accumulate in heterozygotes after 8-10 mos. We used MRM to obtain 3D volumetric data on mouse brains imaged in their skulls to define genotype- and age-related changes. Hippocampal, cerebellar, and brain volumes and corpus callosum length were quantified in 40-, 100-, 365-, and 630-day-old mice. Measurements taken at age 100 days, before Abeta deposition, revealed a 12.3% reduction of hippocampus volume in Tg mice compared with WT controls. This reduction persisted without progression to age 21 mos. A significant 18% increase in hippocampal volume occurred between 40 and 630 days in WT mice, and no corresponding significant increase occurred in Tg mice. Cavalieri volume estimates of hippocampal subfields from 100-day-old Tg mice further localized a 28% volume deficit in the dentate gyrus. In addition, corpus callosum length was reduced by approximately 25% in Tg mice at all ages analyzed. In summary, reduced hippocampal volume and corpus callosum length can be detected by MRM before Abeta deposition. We conclude that overexpression of APP and amyloid may initiate pathologic changes before the appearance of plaques, suggesting novel targets for the treatment of Alzheimer's disease and further reinforcing the need for early diagnosis and treatment.

Deciphering the genetic basis of Alzheimer's disease

A remarkable rise in life expectancy during the past century has made Alzheimer's disease (AD) the most common form of progressive cognitive failure in humans. Compositional analyses of the classical brain lesions, the senile (amyloid) plaques and neurofibrillary tangles, preceded and has guided the search for genetic alterations. Four genes have been unequivocally implicated in inherited forms of AD, and mutations or polymorphisms in these genes cause excessive cerebral accumulation of the amyloid beta-protein and subsequent neuronal and glial pathology in brain regions important for memory and cognition. This understanding of the genotype-to-phenotype conversions of familial AD has led to the development of pharmacological strategies to lower amyloid beta-protein levels as a way of treating or preventing all forms of the disease.

Bradykinin receptor modulation in cellular models of aging and Alzheimer's disease

Human fibroblast cell culture systems have been used to model both molecular events associated with the aging process and the biochemical anomalies found in the aging-associated neurodegenerative disorder Alzheimer's disease (AD). We demonstrate modulation of bradykinin (BK) B2 receptors that results in Intermediate (I, Kd 2.5-5 nM) and Low (L, Kd 44 nM) receptor affinity states in two cellular model systems that target aging and aging-associated disorders: the human lung fibroblast cell line WI-38 model for cellular aging and a skin fibroblast cell line from a patient with early onset familial Alzheimer's disease. In both cellular models the generation of I and L BK B2 receptors is extremely rapid, occurring within 1 min of activation of protein kinase C (PKC) by phorbol ester. Blocking phosphoprotein phosphatase activity further augments the cellular content of I and L receptors in the Alzheimer's skin fibroblast cell line. These two lines of evidence suggest that a phosphorylation cascade modifying the receptors is responsible for the I and L states. The I and L receptors remain biologically active and enhance cellular responsiveness to elevated levels of BK that are found in tissue injury, one of the major risk factors for development of Alzheimer's disease. The Alzheimer's disease skin fibroblast cell line presents a cellular environment highly enriched in the amyloid Abeta1-42 peptide that is the hallmark of Alzheimer's plaque lesions in the brain. This Abeta-rich environment may serve to foster the signal transduction mechanism that generates I and L BK B2 receptors.