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

Picomolar amyloid-beta positively modulates synaptic plasticity and memory in hippocampus

Amyloid-beta (Abeta) peptides are produced in high amounts during Alzheimer's disease, causing synaptic and memory dysfunction. However, they are also released in lower amounts in normal brains throughout life during synaptic activity. Here we show that low picomolar concentrations of a preparation containing both Abeta(42) monomers and oligomers cause a marked increase of hippocampal long-term potentiation, whereas high nanomolar concentrations lead to the well established reduction of potentiation. Picomolar levels of Abeta(42) also produce a pronounced enhancement of both reference and contextual fear memory. The mechanism of action of picomolar Abeta(42) on both synaptic plasticity and memory involves alpha7-containing nicotinic acetylcholine receptors. These findings strongly support a model for Abeta effects in which low concentrations play a novel positive, modulatory role on neurotransmission and memory, whereas high concentrations play the well known detrimental effect culminating in dementia.

Presenilin-1 gene intronic polymorphism and late-onset Alzheimer's disease

Presenilin-1 is known to contribute to the pathogenesis of Alzheimer's disease. The association of an intronic polymorphism (rs165932) of the presenilin-1 gene with late-onset Alzheimer's disease has been documented. However, contradicting results have been shown in different populations. The aim of the current study is to determine whether there is an association between the intronic polymorphism of the presenilin-1 gene and late-onset Alzheimer's disease in a cohort of Turkish patients. One hundred and seven participants with dementia of the Alzheimer type and 106 age-matched controls were genotyped according to BamH I restriction site in intron 8 of the presenilin-1 gene. The distribution of genotypes and alleles did not significantly differ according to chi-square test (P = .52, P = .32, respectively), when the control and patients were compared. Consequently, our results showed that the 1/1 genotype does not increase the risk of developing late-onset Alzheimer's disease in the Turkish population.

Mouse models of Alzheimer's dementia: current concepts and new trends

It is lay knowledge now that Alzheimer's dementia (AD) is one of the most devastating diseases afflicting our societies. A major thrust in search for a cure has relied in the development of animal models of the disease. Thanks to progress in the genetics of the rare inherited forms of AD, various transgenic mouse models harboring human mutated proteins were developed, yielding very significant advancements in the understanding of pathological pathways. Although these models led to testing many different new therapies, none of the preclinical successes have translated yet into much needed therapeutic improvements. Further insight into the metabolic disturbances that are probably associated with the onset of the disease may also rely on new animal models of AD involving insulin/IGF-I signaling that could mimic the far most common sporadic forms of AD associated with old age. Combination of models of familial AD that develop severe amyloidosis with those displaying defects in insulin/IGF-I signaling may help clarify the link between putative initial metabolic disturbances and mechanisms of pathological progression.

Histopathological and molecular heterogeneity among individuals with dementia associated with Presenilin mutations

Background

Mutations in the presenilin (PSEN) genes are associated with early-onset familial Alzheimer's disease (FAD). Biochemical characterizations and comparisons have revealed that many PSEN mutations alter γ-secretase activity to promote accumulation of toxic Aβ42 peptides. In this study, we compared the histopathologic and biochemical profiles of ten FAD cases expressing independent PSEN mutations and determined the degradation patterns of amyloid-β precursor protein (AβPP), Notch, N-cadherin and Erb-B4 by γ-secretase. In addition, the levels of Aβ40/42 peptides were quantified by ELISA.

Results

We observed a wide variation in type, number and distribution of amyloid deposits and neurofibrillary tangles. Four of the ten cases examined exhibited a substantial enrichment in the relative proportions of Aβ40 over Aβ42. The AβPP N-terminal and C-terminal fragments and Tau species, assessed by Western blots and scanning densitometry, also demonstrated a wide variation. The Notch-1 intracellular domain was negligible by Western blotting in seven PSEN cases. There was significant N-cadherin and Erb-B4 peptide heterogeneity among the different PSEN mutations.

Conclusion

These observations imply that missense mutations in PSEN genes can alter a range of key γ-secretase activities to produce an array of subtly different biochemical, neuropathological and clinical manifestations. Beyond the broad common features of dementia, plaques and tangles, the various PSEN mutations resulted in a wide heterogeneity and complexity and differed from sporadic AD.

Clair DK, Markesbery WR, Butterfield DA. Oxidative damage in brain from human mutant APP/PS-1 double knock-in mice as a function of age

Oxidative stress is strongly implicated in the progressive decline of cognition associated with aging and neurodegenerative disorders. In the brain, free radical-mediated oxidative stress plays a critical role in the age-related decline of cellular function as a result of the oxidation of proteins, lipids, and nucleic acids. A number of studies indicate that an increase in protein oxidation and lipid peroxidation is associated with age-related neurodegenerative diseases and cellular dysfunction observed in aging brains. Oxidative stress is one of the important factors contributing to Alzheimer's disease (AD), one of whose major hallmarks includes brain depositions of amyloid beta-peptide (Abeta) derived from amyloid precursor protein (APP). Mutation in APP and PS-1 genes, which increases production of the highly amyloidogenic amyloid beta-peptide (Abeta42), is the major cause of familial AD. In the present study, protein oxidation and lipid peroxidation in the brain from knock-in mice expressing human mutant APP and PS-1 were compared with brain from wild type, as a function of age. The results suggest that there is an increased oxidative stress in the brain of wild-type mice as a function of age. In APP/PS-1 mouse brain, there is a basal increase (at 1 month) in oxidative stress compared to the wild type (1 month), as measured by protein oxidation and lipid peroxidation. In addition, age-related elevation of oxidative damage was observed in APP/PS-1 mice brain compared to that of wild-type mice brain. These results are discussed with reference to the importance of Abeta42-associated oxidative stress in the pathogenesis of AD.

Insulin resistance and amyloidogenesis as common molecular foundation for type 2 diabetes and Alzheimer's disease

Characterized as a peripheral metabolic disorder and a degenerative disease of the central nervous system respectively, it is now widely recognized that type 2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) share several common abnormalities including impaired glucose metabolism, increased oxidative stress, insulin resistance and amyloidogenesis. Several recent studies suggest that this is not an epiphenomenon, but rather these two diseases disrupt common molecular pathways and each disease compounds the progression of the other. For instance, in AD the accumulation of the amyloid-beta peptide (Abeta), which characterizes the disease and is thought to participate in the neurodegenerative process, may also induce neuronal insulin resistance. Conversely, disrupting normal glucose metabolism in transgenic animal models of AD that over-express the human amyloid precursor protein (hAPP) promotes amyloid-peptide aggregation and accelerates the disease progression. Studying these processes at a cellular level suggests that insulin resistance and Abeta aggregation may not only be the consequence of excitotoxicity, aberrant Ca(2+) signals, and proinflammatory cytokines such as TNF-alpha, but may also promote these pathological effectors. At the molecular level, insulin resistance and Abeta disrupt common signal transduction cascades including the insulin receptor family/PI3 kinase/Akt/GSK3 pathway. Thus both disease processes contribute to overlapping pathology, thereby compounding disease symptoms and progression.

Dynamics of Abeta turnover and deposition in different beta-amyloid precursor protein transgenic mouse models following gamma-secretase inhibition

Human beta-amyloid precursor protein (APP) transgenic mice are commonly used to test potential therapeutics for Alzheimer's disease. We have characterized the dynamics of beta-amyloid (Abeta) generation and deposition following gamma-secretase inhibition with compound LY-411575 [N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide]. Kinetic studies in preplaque mice distinguished a detergent-soluble Abeta pool in brain with rapid turnover (half-lives for Abeta40 and Abeta42 were 0.7 and 1.7 h) and a much more stable, less soluble pool. Abeta in cerebrospinal fluid (CSF) reflected the changes in the soluble brain Abeta pool, whereas plasma Abeta turned over more rapidly. In brain, APP C-terminal fragments (CTF) accumulated differentially. The half-lives for gamma-secretase degradation were estimated as 0.4 and 0.1 h for C99 and C83, respectively. Three different APP transgenic lines responded very similarly to gamma-secretase inhibition regardless of the familial Alzheimer's disease mutations in APP. Amyloid deposition started with Abeta42, whereas Abeta38 and Abeta40 continued to turn over. Chronic gamma-secretase inhibition lowered amyloid plaque formation to a different degree in different brain regions of the same mice. The extent was inversely related to the initial amyloid load in the region analyzed. No evidence for plaque removal below baseline was obtained. gamma-Secretase inhibition led to a redistribution of intracellular Abeta and an elevation of CTFs in neuronal fibers. In CSF, Abeta showed a similar turnover as in preplaque animals demonstrating its suitability as marker of newly generated, soluble Abeta in plaque-bearing brain. This study supports the use of APP transgenic mice as translational models to characterize Abeta-lowering therapeutics.

The ratio of monomeric to aggregated forms of Abeta40 and Abeta42 is an important determinant of amyloid-beta aggregation, fibrillogenesis, and toxicity

Aggregation and fibril formation of amyloid-beta (Abeta) peptides Abeta40 and Abeta42 are central events in the pathogenesis of Alzheimer disease. Previous studies have established the ratio of Abeta40 to Abeta42 as an important factor in determining the fibrillogenesis, toxicity, and pathological distribution of Abeta. To better understand the molecular basis underlying the pathologic consequences associated with alterations in the ratio of Abeta40 to Abeta42, we probed the concentration- and ratio-dependent interactions between well defined states of the two peptides at different stages of aggregation along the amyloid formation pathway. We report that monomeric Abeta40 alters the kinetic stability, solubility, and morphological properties of Abeta42 aggregates and prevents their conversion into mature fibrils. Abeta40, at approximately equimolar ratios (Abeta40/Abeta42 approximately 0.5-1), inhibits (> 50%) fibril formation by monomeric Abeta42, whereas inhibition of protofibrillar Abeta42 fibrillogenesis is achieved at lower, substoichiometric ratios (Abeta40/Abeta42 approximately 0.1). The inhibitory effect of Abeta40 on Abeta42 fibrillogenesis is reversed by the introduction of excess Abeta42 monomer. Additionally, monomeric Abeta42 and Abeta40 are constantly recycled and compete for binding to the ends of protofibrillar and fibrillar Abeta aggregates. Whereas the fibrillogenesis of both monomeric species can be seeded by fibrils composed of either peptide, Abeta42 protofibrils selectively seed the fibrillogenesis of monomeric Abeta42 but not monomeric Abeta40. Finally, we also show that the amyloidogenic propensities of different individual and mixed Abeta species correlates with their relative neuronal toxicities. These findings, which highlight specific points in the amyloid peptide equilibrium that are highly sensitive to the ratio of Abeta40 to Abeta42, carry important implications for the pathogenesis and current therapeutic strategies of Alzheimer disease.

Introspective analysis of amyloid as the cause of Alzheimer’s disease: alternative model proposed

As the lifespan of the population of developed countries increases, we are faced with managing a disease that is taking almost epidemic proportions and has a high social and economical cost; Alzheimer’s disease (AD). As everyone knows, AD robs the person not only of their memories but also their personalities and leaves only the shell of a once vibrant and functional human being that now requires care 24-h a day. Similar to the race to prevent, treat or cure cancer and heart diseases, it is essential and of extreme urgency to spearhead efforts against AD. To date, there are no effective treatments against AD. Amyloid is largely favored as the cause of the disease. Immense resources and efforts have been dedicated to anti-amyloid therapies and we are at the cusp of finding out if these will work of not. However, the arguments supporting the amyloid hypothesis can be challenged and an alternate model is presented herein.

Behavior of neural stem cells in the Alzheimer brain

Alzheimer's disease (AD) is characterized by the deposition of beta-amyloid peptides (Abeta) and a progressive loss of neurons leading to dementia. Because hippocampal neurogenesis is linked to functions such as learning, memory and mood, there has been great interest in examining the effects of AD on hippocampal neurogenesis. This article reviews the pertinent studies and tries to unite them in one possible disease model. Early in the disease, oligomeric Abeta may transiently promote the generation of immature neurons from neural stem cells (NSCs). However, reduced concentrations of multiple neurotrophic factors and higher levels of fibroblast growth factor-2 seem to induce a developmental arrest of newly generated neurons. Furthermore, fibrillary Abeta and down-regulation of oligodendrocyte-lineage transcription factor-2 (OLIG2) may cause the death of these nonfunctional neurons. Therefore, altering the brain microenvironment for fostering apt maturation of graft-derived neurons may be critical for improving the efficacy of NSC transplantation therapy for AD.

Inhibition and modulation of gamma-secretase for Alzheimer's disease

The 4-kDa amyloid beta-peptide (Abeta) is strongly implicated the pathogenesis of Alzheimer's disease (AD), and this peptide is cut out of the amyloid beta-protein precursor (APP) by the sequential action of beta- and gamma-secretases. gamma-Secretase is a membrane-embedded protease complex that cleaves the transmembrane region of APP to produce Abeta, and this protease is a top target for developing AD therapeutics. A number of inhibitors of the gamma-secretase complex have been identified, including peptidomimetics that block the active site, helical peptides that interact with the initial substrate docking site, and other less peptide-like, more drug-like compounds. To date, one gamma-secretase inhibitor has advanced into late-phase clinical trials for the treatment of AD, but serious concerns remain. The gamma-secretase complex cleaves a number of other substrates, and gamma-secretase inhibitors cause in vivo toxicities by blocking proteolysis of one essential substrate, the Notch receptor. Thus, compounds that modulate gamma-secretase, rather than inhibit it, to selectively alter Abeta production without hindering signal transduction from the Notch receptor would be more ideal. Such modulators have been discovered and advanced, with one compound in late-phase clinical trials, renewing interest in gamma-secretase as a therapeutic target.

Therapeutics for Alzheimer's disease based on the metal hypothesis

Alzheimer's disease is the most common form of dementia in the elderly, and it is characterized by elevated brain iron levels and accumulation of copper and zinc in cerebral beta-amyloid deposits (e.g., senile plaques). Both ionic zinc and copper are able to accelerate the aggregation of Abeta, the principle component of beta-amyloid deposits. Copper (and iron) can also promote the neurotoxic redox activity of Abeta and induce oxidative cross-linking of the peptide into stable oligomers. Recent reports have documented the release of Abeta together with ionic zinc and copper in cortical glutamatergic synapses after excitation. This, in turn, leads to the formation of Abeta oligomers, which, in turn, modulates long-term potentiation by controlling synaptic levels of the NMDA receptor. The excessive accumulation of Abeta oligomers in the synaptic cleft would then be predicted to adversely affect synaptic neurotransmission. Based on these findings, we have proposed the "Metal Hypothesis of Alzheimer's Disease," which stipulates that the neuropathogenic effects of Abeta in Alzheimer's disease are promoted by (and possibly even dependent on) Abeta-metal interactions. Increasingly sophisticated pharmaceutical approaches are now being implemented to attenuate abnormal Abeta-metal interactions without causing systemic disturbance of essential metals. Small molecules targeting Abeta-metal interactions (e.g., PBT2) are currently advancing through clinical trials and show increasing promise as disease-modifying agents for Alzheimer's disease based on the "metal hypothesis."

Mechanism of Ca2+ disruption in Alzheimer's disease by presenilin regulation of InsP3 receptor channel gating

Mutations in presenilins (PS) are the major cause of familial Alzheimer's disease (FAD) and have been associated with calcium (Ca2+) signaling abnormalities. Here, we demonstrate that FAD mutant PS1 (M146L)and PS2 (N141I) interact with the inositol 1,4,5-trisphosphate receptor (InsP3R) Ca2+ release channel and exert profound stimulatory effects on its gating activity in response to saturating and suboptimal levels of InsP3. These interactions result in exaggerated cellular Ca2+ signaling in response to agonist stimulation as well as enhanced low-level Ca2+signaling in unstimulated cells. Parallel studies in InsP3R-expressing and -deficient cells revealed that enhanced Ca2+ release from the endoplasmic reticulum as a result of the specific interaction of PS1-M146L with the InsP3R stimulates amyloid beta processing,an important feature of AD pathology. These observations provide molecular insights into the "Ca2+ dysregulation" hypothesis of AD pathogenesis and suggest novel targets for therapeutic intervention.

Overview on rodent models of Alzheimer's disease

In Alzheimer's disease (AD), characteristic lesions develop in brain regions that subserve cognitive functions, ultimately leading to dementia. There are now several lesioned or transgenic small-animal models of the disease that model select aspects of cognitive deficits and/or recapitulate many, but not all, of the characteristic pathologic lesions observed in AD. This overview describes the most common approaches used to model AD in rodents, highlights their utility, and discusses some of their deficiencies.

Amyloids: friend or foe?

Amyloidogenesis is the aggregation of soluble proteins into structurally conserved fibers. Amyloid fibers are distinguished by their resistance to proteinase K, tinctorial properties and beta-sheet-rich secondary structure. Amyloid formation is a hallmark of many human diseases including Alzheimer's, Huntington's and the prion diseases. Therefore, understanding amyloidogenesis will provide insights into the development of therapeutics that target these debilitating diseases. A new class of ;functional' amyloids promises a unique glimpse at how nature has harnessed the amyloid fiber to accomplish important physiological tasks. Functional amyloids are produced by organisms spanning all aspects of cellular life. Herein we review amyloidogenesis, with special attention focused on the similarities and differences between the best characterized disease-associated amyloidogenic protein amyloid-beta and the formation of several functional amyloids. The implications of studying functional amyloidogenesis and the strategies organisms employ to limit exposure to toxic intermediates will also be discussed.

DNA damage-inducing agents elicit gamma-secretase activation mediated by oxidative stress

According to the amyloid cascade hypothesis, Alzheimer's disease is the consequence of neuronal cell death induced by beta-amyloid (Abeta), which accumulates by abnormal clearance or production. On the other hand, recent studies have shown cell death-induced alteration in amyloid precursor protein (APP) processing, suggesting potential mutual interactions between APP processing and cell death. We have shown previously that the cell death caused by DNA damage-inducing agents (DDIAs) facilitated gamma-secretase activity and Abeta generation in a Bax/Bcl-2-dependent, but caspase-independent manner. Here, we attempted to elucidate the downstream mechanism that modulates gamma-secretase activity in DDIA-treated cells. N-acetyl cysteine, a potent antioxidant, attenuated DDIA-induced enhancement of gamma-secretase activity but failed to rescue cell death. Overexpression of heat shock protein 70, which blocks cytochrome c release from mitochondria, also reduced gamma-secretase activity. Moreover, glutathione depletion significantly facilitated gamma-secretase activity and Abeta generation by enhancing the formation of higher molecular weight gamma-secretase complex before signs of cell death developed. Finally, Abeta treatment, a known inducer of oxidative stress, also increased gamma-secretase activity. Taken together, these results indicate that DDIA-induced gamma-secretase activation is dependent on augmented oxidative stress, and that Abeta and gamma-secretase may activate each other. On the basis of these results, we propose a feed-back loop between oxidative stress and Abeta generation mediated by gamma-secretase activation.

Confronting complexity in late-onset Alzheimer disease: application of two-stage analysis approach addressing heterogeneity and epistasis

Common diseases with a genetic basis are likely to have a very complex etiology, in which the mapping between genotype and phenotype is far from straightforward. A new comprehensive statistical and computational strategy for identifying the missing link between genotype and phenotype has been proposed, which emphasizes the need to address heterogeneity in the first stage of any analysis and gene-gene interactions in the second stage. We applied this two-stage analysis strategy to late-onset Alzheimer disease (LOAD) data, which included functional and positional candidate genes and markers in a region of interest on chromosome 10. Bayesian classification found statistically significant clusterings for independent family-based and case-control datasets, which used the same five markers in leucine-rich repeat transmembrane neuronal 3 (LRRTM3) as the most influential in determining cluster assignment. In subsequent analyses to detect main effects and gene-gene interactions, markers in three genes--urokinase-type plasminogen activator (PLAU), angiotensin 1 converting enzyme (ACE) and cell division cycle 2 (CDC2)--were found to be associated with LOAD in particular subsets of the data based on their LRRTM3 multilocus genotype. All of these genes are viable candidates for LOAD based on their known biological function, even though PLAU, CDC2 and LRRTM3 were initially identified as positional candidates. Further studies are needed to replicate these statistical findings and to elucidate possible biological interaction mechanisms between LRRTM3 and these genes.

Limited clearance of pre-existing amyloid plaques after intracerebral injection of Abeta antibodies in two mouse models of Alzheimer disease

Recent studies have demonstrated the potential utility of antibodies for the treatment of Alzheimer disease (AD). In transgenic mouse models of AD, peripheral and intracerebral administration of Abeta-specific antibodies reduces amyloid burdens to varied extents. The mechanism may involve clearance of pre-existing amyloid plaques or prevention of new amyloid formation. Here, we have used two transgenic models, the inducible CamKII-ttAxtetAPP/swe/ind (Line 107) and the APPswe/PS1dE9 (Line 85), to test the ability of intracerebral injection of Abeta antibodies to clear amyloid. Because the production of Abeta peptides in the Line 107 model is inducible, whereas production in Line 85 mice is constitutive, we could study the effects of antibody on pre-existing plaques versus continuous plaque formation. In Line 85, injection of antibody resulted in modest but statistically significant reductions in amyloid burden (average, 14%-16%). However, injected antibodies had no effect on amyloid burden in Line 107 under conditions in which the production of Abeta was suppressed, indicating that pre-existing plaques are not rapidly cleared. These results indicate that intracerebral injection of Abeta antibodies produces modest reductions in amyloid deposition in these two models and that the mechanism may involve prevention of amyloid formation rather than clearance of pre-existing plaques.

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.

Seladin-1/DHCR24 protects neuroblastoma cells against Abeta toxicity by increasing membrane cholesterol content

The role of brain cholesterol in Alzheimer's disease (AD) is currently a matter of debate. Experimental evidence suggests that reducing circulating and brain cholesterol protects against AD, however recent data indicate that low membrane cholesterol results in neurode-generation and that the cholesterol synthesis catalyst seladin-1 is down-regulated in AD-affected brain regions. We previously reported a significant correlation between resistance to amyloid toxicity and content of membrane cholesterol in differing cultured cell types. Here we provide evidence that Abeta42 pre-fibrillar aggregates accumulate more slowly and in reduced amount at the plasma membrane of human SH-SY5Y neuroblastoma cells overexpressing seladin-1 or treated with PEG-cholesterol than at the membrane of control cells. The accumulation was significantly increased in cholesterol-depleted cells following treatment with the specific seladin-1 inhibitor 5,22E-cholestadien-3-ol or with methyl-beta-cyclodextrin. The resistance to amyloid toxicity and the early cytosolic Ca2+ rise following exposure to Abeta42 aggregates were increased and prevented, respectively, by increasing membrane cholesterol whereas the opposite effects were found in cholesterol-depleted cells. These results suggest that seladin-1-dependent cholesterol synthesis reduces membrane-aggregate interaction and cell damage associated to amyloid-induced imbalance of cytosolic Ca2+. Our findings extend recently reported data indicating that seladin-1 overexpression directly enhances the resistance to Abeta toxicity featuring seladin-1/DHCR 24 as a possible new susceptibility gene for sporadic AD.

Coenzyme Q10 attenuates beta-amyloid pathology in the aged transgenic mice with Alzheimer presenilin 1 mutation

One of the neuropathological features of Alzheimer's disease (AD) is the deposition of senile plaques containing beta-amyloid (A beta). There is limited evidence for the treatment to arrest A beta pathology of AD. In our present study, we tested the effect of coenzyme Q10 (CoQ10), an endogenous antioxidant and a powerful free radical scavenger, on A beta in the aged transgenic mice overexpressing Alzheimer presenilin 1-L235P (leucine-to-proline mutation at codon 235, 16-17 months old). The treatment by feeding the transgenic mice with CoQ10 for 60 days (1,200 mg kg(-1) day(-1)) partially attenuated A beta overproduction and intracellular A beta deposit in the cortex of the transgenic mice compared with the age-matched untreated transgenic mice. Meanwhile, an increased oxidative stress reaction was detected as evidenced by elevated level of malondialdehyde (MDA) and decreased activity of superoxide dismutase (SOD) in the transgenic mice relative to the wild-type mice, and supplementation of CoQ10 partially decreased MDA level and upregulated the activity of SOD. The results indicate that oxidative stress is enhanced in the brain of the transgenic mice, that this enhancement may further promote A beta 42 overproduction in a vicious formation, and that CoQ10 would be beneficial for the therapy of AD.

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.

Pharmacogenomics in Alzheimer's disease

Pharmacological treatment in Alzheimer's disease (AD) accounts for 10-20% of direct costs, and fewer than 20% of AD patients are moderate responders to conventional drugs (donepezil, rivastigmine, galantamine, memantine), with doubtful cost-effectiveness. Both AD pathogenesis and drug metabolism are genetically regulated complex traits in which hundreds of genes cooperatively participate. Structural genomics studies demonstrated that more than 200 genes might be involved in AD pathogenesis regulating dysfunctional genetic networks leading to premature neuronal death. The AD population exhibits a higher genetic variation rate than the control population, with absolute and relative genetic variations of 40-60% and 0.85-1.89%, respectively. AD patients also differ in their genomic architecture from patients with other forms of dementia. Functional genomics studies in AD revealed that age of onset, brain atrophy, cerebrovascular hemodynamics, brain bioelectrical activity, cognitive decline, apoptosis, immune function, lipid metabolism dyshomeostasis, and amyloid deposition are associated with AD-related genes. Pioneering pharmacogenomics studies also demonstrated that the therapeutic response in AD is genotype-specific, with apolipoprotein E (APOE) 4/4 carriers the worst responders to conventional treatments. About 10-20% of Caucasians are carriers of defective cytochrome P450 (CYP) 2D6 polymorphic variants that alter the metabolism and effects of AD drugs and many psychotropic agents currently administered to patients with dementia. There is a moderate accumulation of AD-related genetic variants of risk in CYP2D6 poor metabolizers (PMs) and ultrarapid metabolizers (UMs), who are the worst responders to conventional drugs. The association of the APOE-4 allele with specific genetic variants of other genes (e.g., CYP2D6, angiotensin-converting enzyme [ACE]) negatively modulates the therapeutic response to multifactorial treatments affecting cognition, mood, and behavior. Pharmacogenetic and pharmacogenomic factors may account for 60-90% of drug variability in drug disposition and pharmacodynamics. The incorporation of pharmacogenetic/pharmacogenomic protocols to AD research and clinical practice can foster therapeutics optimization by helping to develop cost-effective pharmaceuticals and improving drug efficacy and safety.

Expanded high-resolution genetic study of 109 Swedish families with Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease that affects approximately 20 million persons all over the world. There are both sporadic and familial forms of AD. We have previously reported a genome-wide linkage analysis on 71 Swedish AD families using 365 genotyped microsatellite markers. In this study, we increased the number of individuals included in the original 71 analysed families besides adding 38 new families. These 109 families were genotyped for 1100 novel microsatellite markers. The present study reports on the linkage data generated from the non-overlapping genotypes from the first genome scan and the genotypes of the present scan, which results in a total of 1289 successfully genotyped markers at an average density of 2.85 cM on 468 individuals from 109 AD families. Non-parametric linkage analysis yielded a significant multipoint LOD score in chromosome 19q13, the region harbouring the major susceptibility gene APOE, both for the whole set of families (LOD=5.0) and the APOE varepsilon4-positive subgroup made up of 63 families (LOD=5.3). Other suggestive linkage peaks that were observed in the original genome scan of 71 Swedish AD families were not detected in this extended analysis, and the previously reported linkage signals in chromosomes 9, 10 and 12 were not replicated.

BACE1 and mutated presenilin-1 differently modulate Abeta40 and Abeta42 levels and cerebral amyloidosis in APPDutch transgenic mice

APPDutch transgenic (tg) mice develop cerebral amyloid angiopathy (CAA) that consists mainly of AbetaDutch40, with virtually no parenchymal amyloid plaques. To modulate cerebral amyloidosis, we crossbred APPDutch mice with either BACE1 tg mice to increase total AbetaDutch, or with G384A-mutated PS1 tg mice to elevate the ratio of AbetaDutch42 to AbetaDutch40. We analyzed all mice at 22 months of age. Compared to APPDutch mice, double-tg APPDutch/BACE1 mice revealed increased CAA mainly due to extensive vascular amyloid accumulation in the thalamus. In addition, they developed parenchymal amyloid in cortex and subiculum. In contrast, APPDutch/G384A-PS1 mice showed extensive, predominantly parenchymal amyloid throughout the entire brain, interestingly, even in the thalamus. The amyloid, composed largely of AbetaDutch42, was different compared to that in APPDutch/BACE1 mice which was composed mainly of AbetaDutch40. In summary, these mouse models reveal a broad variety and region-specificity of parenchymal versus vascular cerebral amyloid. This is partially explained by the absolute amount of neuronally produced AbetaDutch42 and AbetaDutch40 and ratio between the two. We conclude that the absolute levels of Abeta in combination with the ratio of Abeta42 to Abeta40 play a key role in determining the cerebral compartment and brain region in which Abeta is deposited.

A presenilin 1 mutation (Arg278Ser) associated with early onset Alzheimer’s disease and spastic paraparesis

Early onset familial Alzheimer's disease (EOFAD) has been associated with mutations in three genes, of which presenilin 1 (PSEN1) mutations are the most frequent. Several families with an association of progressive dementia and spastic paraplegia caused by PSEN1 mutations have been described. Here we described a novel PSEN1 mutation that was associated with dementia and spastic paraplegia in a family with 5 affected individuals in three generations. The proband was a 44-year-old woman who presented with 5 years history of progressive difficulties in walking, cognition and visuospatial impairment. Her maternal grandmother, mother and two maternal aunts also had similar neurological presentation. Molecular genetic analysis showed a missense mutation predicted to substitute an arginine residue for a serine residue at position 278 in the PSEN1 polypeptide (Arg278Ser). The novel PSEN1 mutation identified in this patient adds to the diverse list of existing mutations causing EOFAD associated with spastic paraparesis.

Angiotensin-converting enzyme converts amyloid beta-protein 1-42 (Abeta(1-42)) to Abeta(1-40), and its inhibition enhances brain Abeta deposition

The abnormal deposition of the amyloid beta-protein (Abeta) in the brain appears crucial to the pathogenesis of Alzheimer's disease (AD). Recent studies have suggested that highly amyloidogenic Abeta(1-42) is a cause of neuronal damage leading to AD pathogenesis and that monomeric Abeta(1-40) has less neurotoxicity than Abeta(1-42). We found that mouse and human brain homogenates exhibit an enzyme activity converting Abeta(1-42) to Abeta(1-40) and that the major part of this converting activity is mediated by the angiotensin-converting enzyme (ACE). Purified human ACE converts Abeta(1-42) to Abeta(1-40) as well as decreases Abeta(1-42)/Abeta(1-40) ratio and degrades Abeta(1-42) and Abeta(1-40). Importantly, the treatment of Tg2576 mice with an ACE inhibitor, captopril, promotes predominant Abeta(1-42) deposition in the brain, suggesting that ACE regulates Abeta(1-42)/Abeta(1-40) ratio in vivo by converting secreted Abeta(1-42) to Abeta(1-40) and degrading Abetas. The upregulation of ACE activity can be a novel therapeutic strategy for AD.

An update on the amyloid hypothesis

Alzheimer's disease (AD) is a devastating neurodegenerative disease. To rationally develop novel therapeutic and/or preventative agents for AD, an understanding of the etiology and pathogenesis of this complex disease is necessary. This article examines the evidence for the amyloid hypothesis of AD pathogenesis and discusses how it relates to the neurological and neuropathological features of AD, the known genetic risk factors and causative mutations, and the heightened risk associated with advanced age.

Peripheral transgene expression of plasma gelsolin reduces amyloid in transgenic mouse models of Alzheimer's disease

The accumulation and deposition of the 40-42-amino acid peptide amyloid beta (Abeta) is thought to be a critical event in the pathology of Alzheimer's disease (AD). Both passive and active immunizations against Abeta in amyloid-depositing transgenic mice have reduced Abeta pathology and improved memory-related behavior. Peripheral treatments with other amyloid-binding agents have also reduced Abeta pathology. The present study demonstrates that peripheral delivery of plasmid DNA coding for the amyloid-binding protein plasma gelsolin reduces brain Abeta in two separate amyloid-depositing transgenic mouse models of AD when inter-litter variability is accounted for. The reduction in Abeta pathology observed is accompanied by an apparent increase in activated and reactive microglia and soluble oligomeric forms of amyloid. These findings demonstrate that peripheral expression of plasma gelsolin may be a suitable gene-therapeutic approach for the prevention or treatment of AD.

Amyloid-beta aggregation

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease in the growing population of elderly people. A hallmark of AD is the accumulation of plaques in the brain of AD patients. The plaques predominantly consist of aggregates of amyloid-beta (Abeta), a peptide of 39-42 amino acids generated in vivo by specific, proteolytic cleavage of the amyloid precursor protein. There is a growing body of evidence that Abeta aggregates are ordered oligomers and the cause rather than a product of AD. The analysis of the assembly pathway of Abeta in vitro and biochemical characterization of Abeta deposits isolated from AD brains indicate that Abeta oligomerization occurs via distinct intermediates, including oligomers of 3-50 Abeta monomers, annular oligomers, protofibrils, fibrils and plaques. Of these, the most toxic species appear to be small Abeta oligomers. This article reviews the current knowledge of the mechanism of Abeta assembly in vivo and in vitro, as well as the influence of inherited amino acid replacements in Abeta and experimental conditions on Abeta aggregation. Challenges regarding the reproducible handling of the Abeta peptide for in vitro assembly studies are discussed.

Cell cycle regulation in the postmitotic neuron: oxymoron or new biology?

Adult CNS neurons are typically described as permanently postmitotic but there is probably nothing permanent about the neuronal cell cycle arrest. Rather, it appears that these highly differentiated cells must constantly keep their cell cycle in check. Relaxation of this vigilance leads to the initiation of a cell cycle and entrance into an altered and vulnerable state, often leading to death. There is evidence that neurons which are at risk of neurodegeneration are also at risk of re-initiating a cell cycle process that involves the expression of cell cycle proteins and DNA replication. Failure of cell cycle regulation might be a root cause of several neurodegenerative disorders and a final common pathway for others.

Altered levels and distribution of IGF-II/M6P receptor and lysosomal enzymes in mutant APP and APP + PS1 transgenic mouse brains

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor participates in the trafficking of lysosomal enzymes from the trans-Golgi network or the cell surface to lysosomes. In Alzheimer's disease (AD) brains, marked up-regulation of the lysosomal system in vulnerable neuronal populations has been correlated with altered metabolic functions. To establish whether IGF-II/M6P receptors and lysosomal enzymes are altered in the brain of transgenic mice harboring different familial AD mutations, we measured the levels and distribution of the receptor and lysosomal enzymes cathepsins B and D in select brain regions of transgenic mice overexpressing either mutant presenilin 1 (PS1; PS1(M146L+L286V)), amyloid precursor protein (APP; APP(KM670/671NL+V717F)) or APP+PS1 (APP(KM670/671NL+V717F)+PS1(M146L+L286V)) transgenes. Our results revealed that levels and expression of the IGF-II/M6P receptor and lysosomal enzymes are increased in the hippocampus and frontal cortex of APP and APP+PS1, but not in PS1, transgenic mouse brains compared with wild-type controls. The changes were more prominent in APP+PS1 than in APP single transgenic mice. Additionally, all beta-amyloid-containing neuritic plaques in the hippocampal and cortical regions of APP and APP+PS1 transgenic mice were immunopositive for both lysosomal enzymes, whereas only a subset of the plaques displayed IGF-II/M6P receptor immunoreactivity. These results suggest that up-regulation of the IGF-II/M6P receptor and lysosomal enzymes in neurons located in vulnerable regions reflects an altered functioning of the endosomal-lysosomal system which may be associated with the increased intracellular and/or extracellular A beta deposits observed in APP and APP+PS1 transgenic mouse brains.

Amyloid-beta in Alzheimer disease: the null versus the alternate hypotheses

For nearly 20 years, the primary focus for researchers studying Alzheimer disease has been centered on amyloid-beta, such that the amyloid cascade hypothesis has become the "null hypothesis." Indeed, amyloid-beta is, by the current definition of the disease, an obligate player in pathophysiology, is toxic to neurons in vitro, and, perhaps most compelling, is increased by all of the human genetic influences on the disease. Therefore, targeting amyloid-beta is the focus of considerable basic and therapeutic interest. However, an increasingly vocal group of investigators are arriving at an "alternate hypothesis" stating that amyloid-beta, while certainly involved in the disease, is not an initiating event but rather is secondary to other pathogenic events. Furthermore and perhaps most contrary to current thinking, the alternate hypothesis proposes that the role of amyloid-beta is not as a harbinger of death but rather a protective response to neuronal insult. To determine which hypothesis relates best to Alzheimer disease requires a broader view of disease pathogenesis and is discussed herein.

Free copper and resting temporal EEG rhythms correlate across healthy, mild cognitive impairment, and Alzheimer’s disease subjects

OBJECTIVE

The present study tested the hypothesis that the serum copper abnormalities were correlated with alterations of resting electroencephalographic (EEG) rhythms across the continuum of healthy elderly (Hold), mild cognitive impairment (MCI), and AD subjects.

METHODS

Resting eyes-closed EEG rhythms delta (2-4Hz), theta (4-8Hz), alpha 1 (8-10.5Hz), alpha 2 (10.5-13Hz), beta 1 (13-20Hz), beta 2 (20-30Hz), and gamma (30-40Hz), estimated by LORETA, were recorded in 17 Hold, 19 MCI, 27 AD- (MMSE< or =20), and 27 AD+ (MMSE20) individuals and correlated with copper biological variables.

RESULTS

Across the continuum of Hold, MCI and AD subjects, alpha sources in parietal, occipital, and temporal areas were decreased, while the magnitude of the delta and theta EEG sources in parietal, occipital, and temporal areas was increased. The fraction of serum copper unbound to ceruloplasmin positively correlated with temporal and frontal delta sources, regardless of the effects of age, gender, and education.

CONCLUSIONS

These results sustain the hypothesis of a toxic component of serum copper that is correlated with functional loss of AD, as revealed by EEG indexes.

SIGNIFICANCE

The present study represents the first demonstration that the fraction of serum copper unbound to ceruloplasmin is correlated with cortical delta rhythms across Hold, MCI, and AD subjects, thus unveiling possible relationships among the biological parameter, advanced neurodegenerative processes, and synchronization mechanisms regulating the relative amplitude of selective EEG rhythms.

Mulberry leaf extract prevents amyloid beta-peptide fibril formation and neurotoxicity

Mulberry leaf has been reported to possess medicinal properties, including hypoglycemic, hypotensive and diuretic effects. Little is known, however, about its medicinal properties for central nervous system disorders, including Alzheimer's disease. Accumulating evidence suggests that amyloid beta-peptide (1-42) plays an important role in the etiology of Alzheimer's disease. Here we show that mulberry leaf extract inhibits the amyloid beta-peptide (1-42) fibril formation by both the thioflavin T fluorescence assay and atomic force microscopy. Furthermore, mulberry leaf extract protected hippocampal neurons against amyloid beta-peptide (1-42)-induced cell death in a concentration-dependent manner. These results suggest that mulberry leaf extract provides a viable treatment for Alzheimer's disease through the inhibition of amyloid beta-peptide (1-42) fibril formation and attenuation of amyloid beta-peptide (1-42)-induced neurotoxicity.

When loss is gain: reduced presenilin proteolytic function leads to increased Abeta42/Abeta40. Talking Point on the role of presenilin mutations in Alzheimer disease

More than 100 missense mutations in presenilin 1 and 2 are associated with early-onset dominant Alzheimer disease. These proteins span the membrane several times and are ostensibly the catalytic component of the gamma-secretase complex, which is responsible for producing the amyloid beta-peptide (Abeta) that deposits in the Alzheimer brain. A common outcome of Alzheimer-associated presenilin mutations is an increase in the ratio of the more aggregation-prone 42-residue form of Abeta to the 40-residue variant, which is often referred to as a presenilin 'gain of function'. An apparent paradox is that most of these mutant presenilins have reduced proteolytic efficiency, which forms part of the counter argument that presenilin 'loss of function' can cause the neuronal dysfunction and death that lead to the disease. In this review, a unifying hypothesis is presented that puts forward a biochemical mechanism by which slower less-efficient forms of the protease can result in a greater proportion of 42-residue Abeta.

Pathological activity of familial Alzheimer's disease-associated mutant presenilin can be executed by six different gamma-secretase complexes

gamma-Secretase is a protease complex, which catalyzes the final of two subsequent cleavages of the beta-amyloid precursor protein (APP) to release the amyloid-beta peptide (Abeta) implicated in Alzheimer's disease (AD) pathogenesis. In human cells, six gamma-secretase complexes exist, which are composed of either presenilin (PS) 1 or 2, the catalytic subunit, nicastrin, PEN-2, and either APH-1a (as S or L splice variants) or its homolog APH-1b. It is not known whether and how different APH-1 species contribute to the pathogenic activity of gamma-secretase complexes with familial AD (FAD)-associated mutant PS. Here we show that all known gamma-secretase complexes are active in APP processing and that all combinations of APH-1 variants with either FAD mutant PS1 or PS2 support pathogenic Abeta(42) production. Since our data suggest that pathogenic gamma-secretase activity cannot be attributed to a discrete gamma-secretase complex, we propose that all gamma-secretase complexes have to be explored and evaluated for their potential as AD drug target.

Structure nor stability of the transmembrane spanning 6/7 domain of presenilin I correlates with pathogenicity

Since its cloning in 1995, missense point mutations in presenilin I (PS-I) have been shown to be responsible for greater than 70% of the cases of early onset familial Alzheimer's disease (EOFAD), which can affect individuals as early as age 18. PS-I is known to be a component of gamma-secretase, the enzyme responsible for cleavage of the amyloid precursor protein (APP) into 42 amino acid peptides that aggregate to form the plaques surrounding neurons of Alzheimer's patients. It has recently been hypothesized that wild-type (wt) PS-I contains an autoinhibitory module that prevents gamma-secretase cleavage of the APP, while pathogenic PS-I point mutants lack a structure necessary for this inhibition. In this work, spectroscopic data is presented that does not correlate structure or stability of the proposed PS-I autoinhibitory module with pathogenicity.

Abeta40 protects non-toxic Abeta42 monomer from aggregation

Abeta40 and Abeta42 are the predominant Abeta species in the human body. Toxic Abeta42 oligomers and fibrils are believed to play a key role in causing Alzheimer's disease (AD). However, the role of Abeta40 in AD pathogenesis is not well established. Emerging evidence indicates a protective role for Abeta40 in AD pathogenesis. Although Abeta40 is known to inhibit Abeta42 fibril formation, it is not clear whether the inhibition acts on the non-toxic monomer or acts on the toxic Abeta42 oligomers. In contrast to conventional methods that detect the appearance of fibrils, in our study Abeta42 aggregation was monitored by the decreasing NMR signals from Abeta42 monomers. In addition, differential NMR isotope labelling enabled the selective observation of Abeta42 aggregation in a mixture of Abeta42 and Abeta40. We found Abeta40 monomers inhibit the aggregation of non-toxic Abeta42 monomers, in an Abeta42/Abeta40 ratio-dependent manner. NMR titration revealed that Abeta40 monomers bind to Abeta42 aggregates with higher affinity than Abeta42 monomers. Abeta40 can also release Abeta42 monomers from Abeta42 aggregates. Thus, Abeta40 likely protects Abeta42 monomers by competing for the binding sites on pre-existing Abeta42 aggregates. Combining our data with growing evidence from transgenic mice and human genetics, we propose that Abeta40 plays a critical, protective role in Alzheimer's by inhibiting the aggregation of Abeta42 monomer. Abeta40 itself, a peptide already present in the human body, may therefore be useful for AD prevention and therapy.

Pin1 in Alzheimer's disease: multiple substrates, one regulatory mechanism?

Presence of neuritic plaques and neurofibrillary tangles in the brain are two neuropathological hallmarks of Alzheimer's disease (AD), although the molecular basis of their coexistence remains elusive. The neurofibrillary tangles are composed of microtubule binding protein Tau, whereas neuritic plaques consist of amyloid-beta peptides derived from amyloid precursor protein (APP). Recently, the peptidyl-prolyl cis/trans isomerase Pin1 has been identified to regulate the function of certain proteins after phosphorylation and to play an important role in cell cycle regulation and cancer development. New data indicate that Pin1 also regulates the function and processing of Tau and APP, respectively, and is important for protecting against age-dependent neurodegeneration. Furthermore, Pin1 is the only gene known so far that, when deleted in mice, can cause both Tau and Abeta-related pathologies in an age-dependent manner, resembling many aspects of human Alzheimer's disease. Moreover, in the human AD brain Pin1 is downregulated or inhibited by oxidative modifications and/or genetic changes. These results suggest that Pin1 deregulation may provide a link between formation of tangles and plaques in AD.

Presenilin-1 C410Y Alzheimer disease plaques contain synaptic proteins

Presenilin-1 (PS-1) mutations are associated with familial Alzheimer's disease (AD). Although beta-amyloid (Abeta) plaques in brain tissue are characteristic of AD patients, space occupying "cotton-wool" plaques (CWPs) lacking dense Abeta cores have also been described in patients with mutations in exon 9 of the PS-1 gene. The composition of CWPs has not been fully described. To better elucidate the composition of these space-occupying plaques, we used immunohistochemistry with antibodies to the synaptic proteins synapsin-1 and synaptophysin, as well as antibodies to tau, Abeta(-42), Abeta(-40), ubiquitin, neurofilament, and glial fibrillary acidic protein. Confocal laser scanning microscopy (CLSM) was utilized to further characterize these plaques. CWPs showed increased synapsin-1 and synaptophysin immunoreactivity relative to the background gray matter. Synaptic protein-containing CWPs occurred in all affected MTL regions, including the granule cell layer of the dentate gyrus, where synaptic terminals are usually sparse. These data suggest that in C410Y PS-1 AD patients, CWPs may constitute a major component of synaptic terminal-specific proteins, and that the C410Y PS-1 mutation may influence either synaptic structure or synaptic protein expression.

Genetic association between polymorphisms of Pen2 gene and late onset Alzheimer's disease in the North Chinese population

Presenilin enhancer 2 (Pen2) is a subunit of the gamma-secretase complex which cleaves amyloid precursor protein (APP) to generate amyloid beta (Abeta). We performed a systematic screening of all Pen2 exons and introns using direct sequencing to assess its role in the risk of developing late onset Alzheimer's disease (LOAD). 947 subjects (LOAD: 467;

CONTROLS

480) were recruited for this study. We obtained three polymorphisms: rs10402601, rs3817622, and rs2293688. Among these three polymorphisms, there was an interaction between rs3817622 and apolipoprotein E (APOE) genotypes (P=0.002). In the subjects with APOE 4 allele, there was a significant difference in the distribution of alleles (P=0.003) and genotypes (P=0.007) between LOAD and control groups. ORs [95% confidence interval (CI)] of allele A and T/A+A/A genotypes were respectively 4.720 (1.517-10.654) and 3.886 (1.381-10.932) with allele T and genotype T/T as a reference. Our results suggest that there is an association between rs3817622 and the development of LOAD in APOE epsilon4 carriers within the northern Chinese population. It is possible allele A of the Pen2 gene increases the risk for LOAD.

Oral vaccination with a viral vector containing Abeta cDNA attenuates age-related Abeta accumulation and memory deficits without causing inflammation in a mouse Alzheimer model

Immunotherapy with Abeta is expected to bring great improvement for Alzheimer disease (AD). However, clinical trials have been suspended because of meningoencephalitics, which accompanied lymphocytic infiltration. We have developed an oral vaccine for AD with a recombinant adeno-associated viral vector carrying Abeta cDNA (AAV/Abeta). The vaccine reduces the amount of Abeta deposited without lymphocytic infiltration in APP transgenic (Tg2576) mice. In the present study, Tg2576 mice showed progressive cognitive impairments in the novel object recognition test, Y-maze test, water maze test, and contextual conditioned fear learning test. A single oral administration of AAV/Abeta to Tg2576 mice at the age of 10 months alleviated progressive cognitive impairment with decreased Abeta deposition, insoluble Abeta, soluble Abeta oligomer (Abeta*56), microglial attraction, and synaptic degeneration induced in the brain regions at the age of 13 months. A histological analysis with hematoxylin and eosin and an immunohistochemical analysis with antibodies against CD3, CD4, CD8, and CD19 suggested there was no lymphocytic infiltration or microhemorrhage in the brain of AAV/Abeta-vaccinated Tg2576 mice at 13 months of age. Taken together, these results suggest that immunotherapy with AAV/Abeta is a safe and effective treatment for AD.

Fifty Hertz electromagnetic field exposure stimulates secretion of beta-amyloid peptide in cultured human neuroglioma

Recent epidemiological studies raise the possibility that individuals with occupational exposure to low frequency (50-60 Hz) electromagnetic fields (LF-EMF), are at increased risk of Alzheimer's disease (AD). However, the mechanisms through which LF-EMF may affect AD pathology are unknown. We here tested the hypothesis that the exposure to LF-EMF may affect amyloidogenic processes. We examined the effect of exposure to 3.1 mT 50 Hz LF-EMF on Abeta secretion in H4 neuroglioma cells stably overexpressing human mutant amyloid precursor protein. We found that overnight exposure to LF-EMF induces a significant increase of amyloid-beta peptide (Abeta) secretion, including the isoform Abeta 1-42, without affecting cell survival. These findings show for the first time that exposure to LF-EMF stimulates Abeta secretion in vitro, thus alluding to a potential link between LF-EMF exposure and APP processing in the brain.

Regulation of γ-Secretase Activity in Alzheimer's Disease

The gamma-secretase complex is an intramembrane aspartyl protease that cleaves its substrates along their transmembrane regions. Sequential proteolytic processing of amyloid precursor protein by beta- and gamma-secretase produces amyloid beta-peptides, which are the major components of amyloid plaques in the brains of Alzheimer's disease patients. The gamma-secretase complex is therefore believed to be critical in the pathogenesis of Alzheimer's disease. Here we review the range of factors found to affect the nature and degree of gamma-secretase complex activity; these include gamma-secretase complex assembly and activation, the integral regulatory subunit CD147, transient or weak binding partners, the levels of cholesterol and sphingolipids in cell membranes, and inflammatory cytokines. Integrated knowledge of the molecular mechanisms supporting the actions of these factors is expected to lead to a comprehensive understanding of the functional regulation of the gamma-secretase complex, and this, in turn, should facilitate the development of novel therapeutic strategies for the treatment of Alzheimer's disease.