Role In Alzheimer's Disease Pathology Research Articles

Sustained Alzheimer's Amyloid Pathology in Myeloid Differentiation Protein-88-Deficient APPswe/PS1 Mice

Background: Most Alzheimer's disease (AD) cases arise sporadically and may involve innate immune activation of microglial expressed Toll-like receptors regulated through the myeloid differentiation protein 88 (MyD88) pathway. Objective: It was the aim of this study to test the innate immune involvement in AD pathology. Methods: We mated APPsw/PS1ΔE9 mice with MyD88-deficient mice. Results: Progeny mice had similar levels of soluble amyloid-β peptides, amyloid plaque density and neuroimmune staining patterns. However, double-transgenic mice did show a significantly reduced life expectancy. Conclusion: Our findings indicate that impaired innate immune responses may play a role in AD pathology.

Glial fibrillary acidic protein isoform expression in plaque related astrogliosis in Alzheimer's disease

In Alzheimer's disease (AD), amyloid plaques are surrounded by reactive astrocytes with an increased expression of intermediate filaments including glial fibrillary acidic protein (GFAP). Different GFAP isoforms have been identified that are differentially expressed by specific subpopulations of astrocytes and that impose different properties to the intermediate filament network. We studied transcript levels and protein expression patterns of all known GFAP isoforms in human hippocampal AD tissue at different stages of the disease. Ten different transcripts for GFAP isoforms were detected at different abundancies. Transcript levels of most isoforms increased with AD progression. GFAPδ-immunopositive astrocytes were observed in subgranular zone, hilus, and stratum–lacunosum–moleculare. GFAPδ-positive cells also stained for GFAPα. In AD donors, astrocytes near plaques displayed increased staining of both GFAPα and GFAPδ. The reading-frame–shifted isoform, GFAP+1, staining was confined to a subset of astrocytes with long processes, and their number increased in the course of AD. In conclusion, the various GFAP isoforms show differential transcript levels and are upregulated in a concerted manner in AD. The GFAP+1 isoform defines a unique subset of astrocytes, with numbers increasing with AD progression. These data indicate the need for future exploration of underlying mechanisms concerning the functions of GFAPδ and GFAP+1 isoforms in astrocytes and their possible role in AD pathology.

Evidence of altered phosphatidylcholine metabolism in Alzheimer's disease

Abberant lipid metabolism is implicated in Alzheimer's disease (AD) pathophysiology, but the connections between AD and lipid metabolic pathways are not fully understood. To investigate plasma lipids in AD, a multiplatform screen (n = 35 by liquid chromatography–mass spectrometry and n = 35 by nuclear magnetic resonance) was developed, which enabled the comprehensive analysis of plasma from 3 groups (individuals with AD, individuals with mild cognitive impairment (MCI), and age-matched controls). This screen identified 3 phosphatidylcholine (PC) molecules that were significantly diminished in AD cases. In a subsequent validation study (n = 141), PC variation in a bigger sample set was investigated, and the same 3 PCs were found to be significantly lower in AD patients: PC 16:0/20:5 (p < 0.001), 16:0/22:6 (p < 0.05), and 18:0/22:6 (p < 0.01). A receiver operating characteristic (ROC) analysis of the PCs, combined with apolipoprotein E (ApoE) data, produced an area under the curve predictive value of 0.828. Confirmatory investigations into the background biochemistry indiciated no significant change in plasma levels of 3 additional PCs of similar structure, total choline containing compounds or total plasma omega fatty acids, adding to the evidence that specific PCs play a role in AD pathology.

Soluble Alpha-APP (sAPPalpha) Regulates CDK5 Expression and Activity in Neurons

A growing body of evidence suggests a role for soluble alpha-amyloid precursor protein (sAPPalpha) in pathomechanisms of Alzheimer disease (AD). This cleavage product of APP was identified to have neurotrophic properties. However, it remained enigmatic what proteins, targeted by sAPPalpha, might be involved in such neuroprotective actions. Here, we used high-resolution two-dimensional polyacrylamide gel electrophoresis to analyze proteome changes downstream of sAPPalpha in neurons. We present evidence that sAPPalpha regulates expression and activity of CDK5, a kinase that plays an important role in AD pathology. We also identified the cytoprotective chaperone ORP150 to be induced by sAPPalpha as part of this protective response. Finally, we present functional evidence that the sAPPalpha receptor SORLA is essential to mediate such molecular functions of sAPPalpha in neurons.

Microsomal prostaglandin E synthase‐1 is induced in alzheimer's disease and its deletion mitigates alzheimer's disease‐like pathology in a mouse model

Epidemiological studies have suggested that long-term use of nonsteroidal anti-inflammatory drugs that inhibit cyclooxygenase (COX) activity can moderate the onset or progression of Alzheimer's disease (AD). Thus it has been suggested that prostaglandin E2 (PGE2 ), a major end-product of COX, may play a pathogenic role in AD, but the involvement of PGE synthase (PGES), a terminal enzyme downstream from COX, has not been fully elucidated. Here we found that, among three PGES enzymes, only microsomal PGES-1 (mPGES-1) is induced, and its expression is associated with β-amyloid (Aβ) plaques in the cerebral cortex in human AD patients and in Tg2576 mice, a transgenic AD mouse model. Furthermore, to investigate whether mPGES-1 contributes to AD-like pathology, we bred mPGES-1-deficient mice with Tg2576 mice. We found that mPGES-1 deletion reduced the accumulation of microglia around senile plaques and attenuated learning impairments in Tg2576 mice. These results indicated that mPGES-1 is induced in the AD brain and thus plays a role in AD pathology. Blockage of mPGES-1 could form the basis for a novel therapeutic strategy for patients with AD.

The Amyloid-β Oligomer Count in Cerebrospinal Fluid is a Biomarker for Alzheimer's Disease

Recent studies indicate that small amyloid-β peptide (Aβ) oligomers are the major toxic species responsible for development and progression of Alzheimer's disease (AD). Therefore, we suggest that the number of Aβ oligomers in body fluids is the most direct and relevant biomarker for AD. Determination of the Aβ oligomer content of cerebrospinal fluid (CSF) samples from 14 AD patients and 12 age-matched controls revealed a clear distinction between both groups. All samples of the control group showed homogenously low numbers of Aβ oligomers, while the samples of the AD group exhibited significantly higher levels of Aβ oligomers. The Aβ oligomer numbers correlated with the patients' Mini-Mental State Examination scores. This indicates that the quantity of Aβ oligomers in CSF reflects the severity of the disease and that Aβ oligomers play a crucial role in AD pathology and in turn can be used as a diagnostic biomarker.

Calcyclin binding protein and Siah-1 interacting protein in Alzheimer's disease pathology: neuronal localization and possible function

The calcyclin binding protein and Siah-1 interacting protein (CacyBP/SIP) protein was shown to play a role in the organization of microtubules. In this work we have examined the neuronal distribution and possible function of CacyBP/SIP in cytoskeletal pathophysiology. We have used brain tissue from Alzheimer's disease (AD) patients and from transgenic mice modeling 2 different pathologies characteristic for AD: amyloid and tau. In the brain from AD patients, CacyBP/SIP was found to be almost exclusively present in neuronal somata, and in control patients it was seen in the somata and neuronal processes. In mice doubly transgenic for amyloid precursor protein and presenilin 1 there was no difference in CacyBP/SIP neuronal localization in comparison with the nontransgenic animals. By contrast in tau transgenic mice, localization of CacyBP/SIP was similar to that observed for AD patients. To find the relation between CacyBP/SIP and tau we examined dephosphorylation of tau by CacyBP/SIP. We found that indeed it exhibited phosphatase activity toward tau. Altogether, our results suggest that CacyBP/SIP might play a role in AD pathology.

Copper dysfunction in Alzheimer's disease: From meta-analysis of biochemical studies to new insight into genetics

The involvement of body copper metabolism in the development of Alzheimer's disease (AD) – the most common form of dementia – is a deeply investigated issue in recent years. Copper is essential for life, but in excess it can be toxic. Recently, it has been hypothesized that copper toxicity may be a contributory factor in the etiology of the neurodegenerative disease AD. Studies on copper evaluation in AD vs. healthy controls collected in the latest 30 years and merged in a meta-analysis demonstrate that serum copper is slightly increased in AD. A specific form of copper, the copper non-bound to ceruloplasmin, or ‘free’ copper, seems to best characterize this increase in copper in AD patients. Clinical studies from us and other groups have demonstrated that free copper is associated with the typical deficits of AD, incipient AD and mild cognitive impairment, and specific cerebrospinal markers. Moreover, very recent data addressing molecular processes underlying copper dysfunction in AD have indicated that genetic variations of K832R and R952K Single Nucleotide Polymorphisms (SNPs) of the Wilson's disease gene ATP7B are associated also with sporadic AD. Specifically, ATP7B encodes for the protein ATPase 7B which controls free copper status in the body, and both R allele in K832R and K allele in R952K ATP7B SNPs are associated with an increased risk of having AD. Even though copper dysfunction cannot be assumed as a determinant of the disease, its causative, rather than associated, role in AD pathology as risk factor can be claimed.

The effects of chronic copper exposure on the amyloid protein metabolisim associated genes’ expression in chronic cerebral hypoperfused rats

The pathogens of Alzheimer's disease (AD) are still unclear, while accumulating evidences have indicated that both genetic and environmental factors are involved in the pathogenesis of AD. Recent studies suggest that AD is primarily a vascular disorder and copper (Cu) may play an important role in AD pathology. However, the consequences of chronic Cu exposure at the presence of other AD risk factors remain to be clarified. To investigate the effects of chronic Cu intake on cerebral hypoperfusion-induced AD pathology, Sprague-Dawley rats suffered bilateral common carotid artery occlusion (2VO) were administrated with 250ppm copper-containing water or not. Morris water maze test showed that Cu exposure for 3 months exacerbated cognitive impairment induced by 2VO. Elevated amyloid precursor protein (APP) and beta-site APP-cleaving enzyme 1 (BACE1) expression in mRNA and protein levels were also observed in brain of Cu-exposed rats suffered 2VO. In contrast, these Cu-exacerbated changes were ameliorated after Cu was withdrawn from drinking water. In summary, our findings demonstrate that chronic Cu exposure might exacerbate AD pathology in 2VO rats.

Air pollution, oxidative stress, and Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia affecting millions of people worldwide and will continue to affect millions more with population aging on the rise. AD causality is multifactorial. Known causal factors include genetic predisposition, age, and sex. Environmental toxins such as air pollution (AP) have also been implicated in AD causation. Exposure to AP can lead to chronic oxidative stress (OS), which is involved in the pathogenesis of AD. Whereas AP plays a role in AD pathology, the epidemiological evidence for this association is limited. Given the significant prevalence of AP exposure combined with increased population aging, epidemiological evidence for this link is important to consider. In this paper, we examine the existing evidence supporting the relationship between AP, OS, and AD and provide recommendations for future research on the population level, which will provide evidence in support of public health interventions.

Genetic association of PICALM polymorphisms with Alzheimer's disease in Han Chinese

PICALM might play an important role in AD pathology through participating in altering synaptic vesicle cycling or APP endocytosis. A recent genome-wide study (GWAS) identified a single nucleotide polymorphism (SNP) rs3851179 in the 5′ to the PICALM gene strongly associated with Alzheimer's disease (AD) in Caucasians. In order to assess the involvement of the PICALM polymorphism in the risk of developing late-onset AD (LOAD), we analyzed the genotype and allele distributions of these three polymorphisms in 609 Han Chinese subjects. Our data showed no significant association between the PICALM rs3851179 polymorphism and LOAD (genotype distribution: P = 0.43; allele frequency: P = 0.25, odds ratio = 0.87, 95% confidence interval = 0.68 to 1.10), even after statistical adjustment for age, gender and apolipoprotein E (APOE) status. Our results suggest that the PICALM polymorphism may not play a major role in the development of LOAD in the Han Chinese population.

Regulation of amyloid precursor protein processing by the Beclin 1 complex.

Autophagy is an intracellular degradation pathway that functions in protein and organelle turnover in response to starvation and cellular stress. Autophagy is initiated by the formation of a complex containing Beclin 1 (BECN1) and its binding partner Phosphoinositide-3-kinase, class 3 (PIK3C3). Recently, BECN1 deficiency was shown to enhance the pathology of a mouse model of Alzheimer Disease (AD). However, the mechanism by which BECN1 or autophagy mediate these effects are unknown. Here, we report that the levels of Amyloid precursor protein (APP) and its metabolites can be reduced through autophagy activation, indicating that they are a substrate for autophagy. Furthermore, we find that knockdown of Becn1 in cell culture increases the levels of APP and its metabolites. Accumulation of APP and APP C-terminal fragments (APP-CTF) are accompanied by impaired autophagosomal clearance. Pharmacological inhibition of autophagosomal-lysosomal degradation causes a comparable accumulation of APP and APP-metabolites in autophagosomes. Becn1 reduction in cell culture leads to lower levels of its binding partner Pik3c3 and increased presence of Microtubule-associated protein 1, light chain 3 (LC3). Overexpression of Becn1, on the other hand, reduces cellular APP levels. In line with these observations, we detected less BECN1 and PIK3C3 but more LC3 protein in brains of AD patients. We conclude that BECN1 regulates APP processing and turnover. BECN1 is involved in autophagy initiation and autophagosome clearance. Accordingly, BECN1 deficiency disrupts cellular autophagy and autophagosomal-lysosomal degradation and alters APP metabolism. Together, our findings suggest that autophagy and the BECN1-PIK3C3 complex regulate APP processing and play an important role in AD pathology.

Suggestive synergy between genetic variants in TF and HFE as risk factors for Alzheimer's disease

Alzheimer's disease (AD) is a complex disease that is likely influenced by many genetic and environmental factors. Citing evidence that iron may play a role in AD pathology, Robson et al. [Robson et al. (2004); J Med Genet 41:261-265] reported that epistatic interaction between rs1049296 (P589S) in the transferrin gene (TF) and rs1800562 (C282Y) in the hemochromatosis gene (HFE) results in significant association with risk for AD. In this study we attempted to replicate their findings in a total of 1,166 cases and 1,404 controls from three European and European American populations. Allele and genotype frequencies were consistent across the three populations. Using synergy factor analysis (SFA) and Logistic Regression analysis we tested each population and the combined sample for interactions between these two SNPs and risk for AD. We observed significant association between bi-carriers of the minor alleles of rs1049296 and rs1800562 in the combined sample using SFA (P = 0.0016, synergy factor = 2.71) and adjusted SFA adjusting for age and presence of the APOE epsilon 4 allele (P = 0.002, OR = 2.4). These results validate those of the previous report and support the hypothesis that iron transport and regulation play a role in AD pathology.

Truncated beta-amyloid peptide channels provide an alternative mechanism for Alzheimer's Disease and Down syndrome.

Full-length amyloid beta peptides (Abeta(1-40/42)) form neuritic amyloid plaques in Alzheimer's disease (AD) patients and are implicated in AD pathology. However, recent transgenic animal models cast doubt on their direct role in AD pathology. Nonamyloidogenic truncated amyloid-beta fragments (Abeta(11-42) and Abeta(17-42)) are also found in amyloid plaques of AD and in the preamyloid lesions of Down syndrome, a model system for early-onset AD study. Very little is known about the structure and activity of these smaller peptides, although they could be the primary AD and Down syndrome pathological agents. Using complementary techniques of molecular dynamics simulations, atomic force microscopy, channel conductance measurements, calcium imaging, neuritic degeneration, and cell death assays, we show that nonamyloidogenic Abeta(9-42) and Abeta(17-42) peptides form ion channels with loosely attached subunits and elicit single-channel conductances. The subunits appear mobile, suggesting insertion of small oligomers, followed by dynamic channel assembly and dissociation. These channels allow calcium uptake in amyloid precursor protein-deficient cells. The channel mediated calcium uptake induces neurite degeneration in human cortical neurons. Channel conductance, calcium uptake, and neurite degeneration are selectively inhibited by zinc, a blocker of amyloid ion channel activity. Thus, truncated Abeta fragments could account for undefined roles played by full length Abetas and provide a unique mechanism of AD and Down syndrome pathologies. The toxicity of nonamyloidogenic peptides via an ion channel mechanism necessitates a reevaluation of the current therapeutic approaches targeting the nonamyloidogenic pathway as avenue for AD treatment.

Overexpression of SOD-2 reduces hippocampal superoxide and prevents memory deficits in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by impaired cognitive function and the deposition of extracellular amyloid plaques and intracellular tangles. Although the proximal cause of AD is not well understood, it is clear that amyloid-beta (Abeta) plays a critical role in AD pathology. Recent studies also implicate mitochondrial abnormalities in AD. We investigated this idea by crossing mice that overexpress mitochondrial superoxide dismutase (SOD-2) with the Tg2576 mouse model of AD that overexpresses the human amyloid precursor protein carrying the Swedish mutation (K670N:M671L). We found that overexpression of SOD-2 decreased hippocampal superoxide, prevented AD-related learning and memory deficits, and reduced Abeta plaques. Interestingly, SOD-2 overexpression did not affect the absolute levels of Abeta(1-40) and Abeta(1-42), but did significantly reduce the Abeta(1-42) to Abeta(1-40) ratio, thereby shifting the balance toward a less amyloidogenic Abeta composition. These findings directly link mitochondrial superoxide to AD pathology and demonstrate the beneficial effects of a mitochondrial anti-oxidant enzyme, hence offering significant therapeutic implications for AD.

Disruption of fast axonal transport is a pathogenic mechanism for intraneuronal amyloid beta

The pathological mechanism by which Abeta causes neuronal dysfunction and death remains largely unknown. Deficiencies in fast axonal transport (FAT) were suggested to play a crucial role in neuronal dysfunction and loss for a diverse set of dying back neuropathologies including Alzheimer's disease (AD), but the molecular basis for pathological changes in FAT were undetermined. Recent findings indicate that soluble intracellular oligomeric Abeta (oAbeta) species may play a critical role in AD pathology. Real-time analysis of vesicle mobility in isolated axoplasms perfused with oAbeta showed bidirectional axonal transport inhibition as a consequence of endogenous casein kinase 2 (CK2) activation. Conversely, neither unaggregated amyloid beta nor fibrillar amyloid beta affected FAT. Inhibition of FAT by oAbeta was prevented by two specific pharmacological inhibitors of CK2, as well as by competition with a CK2 substrate peptide. Furthermore, perfusion of axoplasms with active CK2 mimics the inhibitory effects of oAbeta on FAT. Both oAbeta and CK2 treatment of axoplasm led to increased phosphorylation of kinesin-1 light chains and subsequent release of kinesin from its cargoes. Therefore pharmacological modulation of CK2 activity may represent a promising target for therapeutic intervention in AD.

Small molecule screen reveals differences in the structural landscape of amyloid‐beta oligomers and fibrils

Aggregated amyloid‐β (Aβ) peptide is implicated in the pathology of Alzheimer's disease (AD). In vitro and in vivo, these aggregates are found in a variety of configurations, including globular oligomers and linear fibrils. Despite being composed of identical monomer units, these different quaternary configurations give rise to distinct biological effects; for example, recent evidence suggests that oligomers might play a key role in AD pathology. To identify unique molecular features that might differentiate these architectures, we employed a fluorescence‐based interaction assay to screen a collection of 68 known Aβ ligands. Using this approach, we found that most of the small molecules, including the well‐known compounds Bis‐ANS and Congo Red, interact equally well with both Aβ oligomers and fibrils. However, the fluorescence of five indole‐based compounds was selectively quenched in the presence of oligomers, but remained unchanged after addition of fibrils. These results suggest that amino acids capable of quenching indole fluorescence, such as Lys16, Phe19, Phe20, or Lys28, are relatively exposed in oligomers and buried in fibrils. These differences in accessibility may encompass one mechanism by which different amyloid structures give rise to distinct biological outcomes.

P3-211: Overexpression of the C-terminal fragment of APP altered gene expression profiles in APPV717I-CT100 transgenic mice

Many carboxy-terminal (C-terminal) fragments of the human amyloid precursor protein (APP) are neurotoxic, including β amyloid (Aβ) and APP-CT100. We used a transgenic mouse model expressing the familial Alzheimer's disease (AD) ‘London mutation' with the V717I (valine to isoleucine) substitution within APP-CT100, which includes the Aβ sequence. APPV717I is associated with aggressive early onset dementia and a characteristic increase in the long amyloidogenic form of Aβ (Aβ1–42) in AD brain. β amyloid, in the form of diffuse non-congophilic extracellular plaques, deposits in the brain of transgenic mice expressing APPV717I-CT100 from 6 months of age. To elucidate the neurodegenerative mechanisms of AD, we evaluated several genes that might be involved in APP pathology in 11-month-old APPV717I-CT100 transgenic mice using microarray analysis. We compared the profiles of the altered genes in the hippocampal region of transgenic mice with that of age-matched wild-type transgenic mice. We also clustered the genes associated with apoptosis, cell cycle, cell death, cellular physiology, immune response, signal transduction, and transcription. We selected several genes that might have essential roles in AD pathology and their altered expression in the cortical and hippocampal brain tissues used in the microarray anaysis was confirmed with RT-PCR and Western blot analysis. In addition, the expression pattern of the selected genes was examined in human AD brain by immunohistochemistry and Western blot, and their pathogenic mechanisms were studied in an APP intracellular domain -overexpressing cell culture system. These findings suggest that APPV717I-CT100 overexpression selectively alters the levels of specific transcripts in the brains of transgenic mice. This study provides valuable information about several AD-related genes and their pathogenic roles.

Effect of genetic polymorphism on apolipoprotein E glycosylation and lipoproteins metabolism

Alzheimer's disease (AD) is the leading cause of age‐related dementia and apolipoprotein E (ApoE) is a well‐established genetic risk factor in sporadic AD. ApoE is highly expressed in liver and brain, and has an important role in cholesterol metabolism. In human, there are three alleles (E2, E3 and E4). ApoE4 increases disease susceptibility by binding amyloid‐β (Aβ) and preventing their clearance, leading to Aβ accumulation. ApoE3 is the most common allele but ApoE2 is found to reduce AD risk. ApoE is also associated with hypercholesterolemia, a risk factor for AD. However, the mechanisms underlying ApoE role in AD pathology is poorly understood. ApoE undergoes O‐linked glycosylation and various glycosylated isoforms exist. This diversity is partly due to differential sialylation but the effect and identity of this chemical modification on ApoE function and between ApoE isoforms is unknown. In this study, we will present the glycan profile on different ApoE isoforms. We will also demonstrate ApoE contribution to the biochemical profile of high‐density lipoprotein (HDL), LDL, triglycerides and cholesterol as well as their effect on the expression of several enzymes involved in Aβ metabolism.

Selective Intracellular Release of Copper and Zinc Ions from Bis(thiosemicarbazonato) Complexes Reduces Levels of Alzheimer Disease Amyloid-β Peptide

Copper and zinc play important roles in Alzheimer disease pathology with recent reports describing potential therapeutics based on modulation of metal bioavailability. We examined the ability of a range of metal bis(thiosemicarbazonato) complexes (MII(btsc), where M=CuII or ZnII) to increase intracellular metal levels in Chinese hamster ovary cells overexpressing amyloid precursor protein (APP-CHO) and the subsequent effect on extracellular levels of amyloid-beta peptide (Abeta). The CuII(btsc) complexes were engineered to be either stable to both a change in oxidation state and dissociation of metal or susceptible to intracellular reduction and dissociation of metal. Treatment of APP-CHO cells with stable complexes resulted in elevated levels of intracellular copper with no effect on the detected levels of Abeta. Treatment with complexes susceptible to intracellular reduction increased intracellular copper levels but also resulted in a dose-dependent reduction in the levels of monomeric Abeta. Treatment with less stable ZnII(btsc) complexes increased intracellular zinc levels with a subsequent dose-dependent depletion of monomeric Abeta levels. The increased levels of intracellular bioavailable copper and zinc initiated a signaling cascade involving activation of phosphoinositol 3-kinase and c-Jun N-terminal kinase. Inhibition of these enzymes prevented Abeta depletion induced by the MII(btsc) complexes. Inhibition of metalloproteases also partially restored Abeta levels, implicating metal-driven metalloprotease activation in the extracellular monomeric Abeta depletion. However, a role for alternative metal-induced Abeta metabolism has not been ruled out. These studies demonstrate that MII(btsc) complexes have potential for Alzheimer disease therapy.