Small-angle X-ray scattering characterization of a [Formula: see text]-amyloid model in phantoms

OBJECTIVE

We present a method to prepare an amyloid model at scalable quantities for phantom studies to evaluate small-angle x-ray scattering systems for amyloid detection. Two amyloid models were made from a plasma protein with and without heating. Both models mimic the [Formula: see text]-sheet structure of the [Formula: see text]-amyloid ([Formula: see text]) plaques in Alzheimer's disease. Amyloid detection is based on the distinct peaks in the scattering signature of the [Formula: see text]-sheet structure. We characterized the amyloid models using a spectral small-angle x-ray scattering (sSAXS) prototype with samples in a plastic syringe and within a cylindrical polymethyl methacrylate (PMMA) phantom.

RESULTS

sSAXS data show that we can detect the scattering peaks characteristic of amyloid [Formula: see text]-sheet structure in both models around 6 and 13 [Formula: see text]. The [Formula: see text] model prepared without heating provides a stronger signal in the PMMA phantom. The methods described can be used to prepare models in sufficiently large quantities and used in samples with different packing density to assess the performance of [Formula: see text] quantification systems.

Hidden Aggregation Hot-Spots on Human Apolipoprotein E: A Structural Study

Human apolipoprotein E (apoE) is a major component of lipoprotein particles, and under physiological conditions, is involved in plasma cholesterol transport. Human apolipoprotein E found in three isoforms (E2; E3; E4) is a member of a family of apolipoproteins that under pathological conditions are detected in extracellular amyloid depositions in several amyloidoses. Interestingly, the lipid-free apoE form has been shown to be co-localized with the amyloidogenic Aβ peptide in amyloid plaques in Alzheimer’s disease, whereas in particular, the apoE4 isoform is a crucial risk factor for late-onset Alzheimer’s disease. Evidence at the experimental level proves that apoE self-assembles into amyloid fibrilsin vitro, although the misfolding mechanism has not been clarified yet. Here, we explored the mechanistic insights of apoE misfolding by testing short apoE stretches predicted as amyloidogenic determinants by AMYLPRED, and we computationally investigated the dynamics of apoE and an apoE–Αβ complex. Our in vitro biophysical results prove that apoE peptide–analogues may act as the driving force needed to trigger apoE aggregation and are supported by the computational apoE outcome. Additional computational work concerning the apoE–Αβ complex also designates apoE amyloidogenic regions as important binding sites for oligomeric Αβ; taking an important step forward in the field of Alzheimer’s anti-aggregation drug development.

Visualization of neuritic plaques in Alzheimer's disease by polarization-sensitive optical coherence microscopy

One major hallmark of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) is the deposition of extracellular senile plaques and vessel wall deposits composed of amyloid-beta (Aβ). In AD, degeneration of neurons is preceded by the formation of Aβ plaques, which show different morphological forms. Most of them are birefringent owing to the parallel arrangement of amyloid fibrils. Here, we present polarization sensitive optical coherence microscopy (PS-OCM) for imaging mature neuritic Aβ plaques based on their birefringent properties. Formalin-fixed, post-mortem brain samples of advanced stage AD patients were investigated. In several cortical brain regions, neuritic Aβ plaques were successfully visualized in tomographic and three-dimensional (3D) images. Cortical grey matter appeared polarization preserving, whereas neuritic plaques caused increased phase retardation. Consistent with the results from PS-OCM imaging, the 3D structure of senile Aβ plaques was computationally modelled for different illumination settings and plaque sizes. Furthermore, the birefringent properties of cortical and meningeal vessel walls in CAA were investigated in selected samples. Significantly increased birefringence was found in smaller vessels. Overall, these results provide evidence that PS-OCM is able to assess amyloidosis based on intrinsic birefringent properties.

RNA aptamer probes as optical imaging agents for the detection of amyloid plaques

Optical imaging using multiphoton microscopy and whole body near infrared imaging has become a routine part of biomedical research. However, optical imaging methods rely on the availability of either small molecule reporters or genetically encoded fluorescent proteins, which are challenging and time consuming to develop. While directly labeled antibodies can also be used as imaging agents, antibodies are species specific, can typically not be tagged with multiple fluorescent reporters without interfering with target binding, and are bioactive, almost always eliciting a biological response and thereby influencing the process that is being studied. We examined the possibility of developing highly specific and sensitive optical imaging agents using aptamer technology. We developed a fluorescently tagged anti-Aβ RNA aptamer, β55, which binds amyloid plaques in both ex vivo human Alzheimer’s disease brain tissue and in vivo APP/PS1 transgenic mice. Diffuse β55 positive halos, attributed to oligomeric Aβ, were observed surrounding the methoxy-XO4 positive plaque cores. Dot blots of synthetic Aβ aggregates provide further evidence that β55 binds both fibrillar and non-fibrillar Aβ. The high binding affinity, the ease of probe development, and the ability to incorporate multiple and multimodal imaging reporters suggest that RNA aptamers may have complementary and perhaps advantageous properties compared to conventional optical imaging probes and reporters.

Amyloid generation and dysfunctional immunoproteasome activation with disease progression in animal model of familial Alzheimer's disease

Double-transgenic amyloid precursor protein/presenilin 1 (APP/PS1) mice express a chimeric mouse/human APP bearing the Swedish mutation (Mo/HuAPP695swe) and a mutant human PS1-dE9 both causative of familial Alzheimer's disease (FAD). Transgenic mice show impaired memory and learning performance from the age of 6 months onwards. Double-transgenic APP/PS1 mice express altered APP and PS1 mRNAs and proteins, reduced β-secretase 1 (BACE1) mRNA and normal BACE1 protein, all of which suggest a particular mechanism of amyloidogenesis when compared with sporadic AD. The first β-amyloid plaques in APP/PS1 mice appear at 3 months, and they increase in number and distribution with disease progression in parallel with increased levels of brain soluble β-amyloid 1-42 and 1-40, but also with reduced 1-42/1-40 ratio with age. Amyloid deposition in plaques is accompanied by altered mitochondria and increased oxidative damage, post-translational modifications and accumulation of altered proteins at the dystrophic neurites surrounding plaques. Degradation pathways are also modified with disease progression including activation of the immunoproteasome together with variable alterations of the different protease activities of the ubiquitin-proteasome system. Present observations show modifications in the production of β-amyloid and activation and malfunction of the subcellular degradation pathways that have general implications in the pathogenesis of AD and more particularly in specificities of FAD amyloidogenesis.

Ultrastructural studies in APP/PS1 mice expressing human ApoE isoforms: implications for Alzheimer's disease

Alzheimer's disease is characterized in part by extracellular aggregation of the amyloid-β peptide in the form of diffuse and fibrillar plaques in the brain. Electron microscopy (EM) has made an important contribution in understanding of the structure of amyloid plaques in humans. Classical EM studies have revealed the architecture of the fibrillar core, characterized the progression of neuritic changes, and have identified the neurofibrillary tangles formed by paired helical filaments (PHF) in degenerating neurons. Clinical data has strongly correlated cognitive impairment in AD with the substantial synapse loss observed in these early ultrastructural studies. Animal models of AD-type brain amyloidosis have provided excellent opportunities to study amyloid and neuritic pathology in detail and establish the role of neurons and glia in plaque formation. Transgenic mice overexpressing mutant amyloid precursor protein (APP) alone with or without mutant presenilin 1 (PS1), have shown that brain amyloid plaque development and structure grossly recapitulate classical findings in humans. Transgenic APP/PS1 mice expressing human apolioprotein E isoforms also develop amyloid plaque deposition. However no ultrastructural data has been reported for these animals. Here we show results from detailed EM analysis of amyloid plaques in APP/PS1 mice expressing human isoforms of ApoE and compare these findings with EM data in other transgenic models and in human AD. Our results show that similar to other transgenic animals, APP/PS1 mice expressing human ApoE isoforms share all major cellular and subcellular degenerative features and highlight the identity of the cellular elements involved in Aβ deposition and neuronal degeneration.

Subependymal plaques in scrapie-affected hamster brains--why are they so different from compact kuru plaques?

We report here routine thin-section and immunogold electron microscopic studies on diffuse plaques in scrapie-affected hamster brains. These plaques were not discernible by routine HE staining. Ultrastructurally, plaques were recognized as areas of low electron density containing haphazardly-oriented fibrils, but not as stellate compact structures typical of mouse scrapie models; hence we labelled them "loose plaques". Following immunohistochemistry at the electron microscopy level, fibrils within plaques were heavily decorated with PrP-conjugated gold particles. Loose plaques were located beneath the basal border of the ependymal cells and around blood vessels in the adjacent subependymal neuropil. When dystrophic neurites containing electron-dense inclusion bodies, some of them autophagic vacuoles [59], were seen within the plaque perimeter, they always remained PrP-negative. Some microglial cells were observed in close contact with PrP-positive plaques, and secondary lysosomes within these cells were heavily decorated with gold particles.

TgCRND8 amyloid precursor protein transgenic mice exhibit an altered gamma-secretase processing and an aggressive, additive amyloid pathology subject to immunotherapeutic modulation

We investigated the morphology and biochemistry of the amyloid-beta (Abeta) peptides produced in TgCRND8 Tg mice carrying combined amyloid precursor protein (APP) Swedish (K670M/N671L) and Indiana (V717F) mutations. Histological analyses employing amyloid-specific staining and electron microscopy revealed that the TgCRND8 Tg mice produce an aggressive pathology, evident as early as 3 months of age, that is a composite of core plaques and peculiar floccular diffuse parenchymal deposits. The Abeta peptides were purified using combined FPLC-HPLC, Western blots, and immunoprecipitation methods and characterized by MALDI-TOF/SELDI-TOF mass spectrometry. The C-terminal APP peptides, assessed by Western blot experiments and mass spectrometry, suggested an alteration in the order of secretase processing, yielding a C-terminal fragment pattern that is substantially different from that observed in sporadic Alzheimer's disease (AD). This modified processing pattern generated longer Abeta peptides, as well as those ending at residues 40/42/43, which may partially explain the early onset and destructive nature of familial AD caused by APP mutations. Despite an aggressive pathology that extended to the cerebellum and white matter, these animals tolerated the presence of an imposing amount of Abeta load. Abeta immunization resulted in an impressive 7-fold reduction in the number of amyloid core plaques and, as previously demonstrated, a significant memory recovery. However, given the phylogenetic distance and the differences in APP processing and Abeta chemistry between Tg mice and AD, caution should be applied in projecting mouse therapeutic interventions onto human subjects.

Mitochondrial degeneration in dystrophic neurites of senile plaques may lead to extracellular deposition of fine filaments

Recent data show that amyloid precursor protein accumulates inside axons after disruption of fast axonal transport, but how this leads to mature plaques with extracellular amyloid remains unclear. To investigate this issue, primitive plaques in prefrontal cortex of aged rhesus monkeys were reconstructed using serial section electron microscopy. The swollen profiles of dystrophic neurites were found to be diverticula from the main axis of otherwise normal neurites. Microtubules extended from the main neurite axis into the diverticulum to form circular loops or coils, providing a transport pathway for trapping organelles. The quantity and morphology of organelles contained within diverticula suggested a progression of degeneration. Primitive diverticula contained microtubules and normal mitochondria, while larger, presumably older, diverticula contained large numbers of degenerating mitochondria. In advanced stages of degeneration, apparent autophagosomes derived from mitochondria exhibited a loose lamellar to filamentous internal structure. Similar filamentous material and remnants of mitochondria were visible in the extracellular spaces of plaques. This progression of degeneration suggests that extracellular filaments originate inside degenerating mitochondria of neuritic diverticula, which may be a common process in diverse diseases.

Differential binding and activation of caspase-3 in cultured hippocampal neurons by assembly forms of A beta 1-42

Amyloid-beta (A beta) peptides, the primary constituents of amyloid plaques in the brain in Alzheimer's disease (AD), may cause AD, but how they do so is not clear. A beta peptides spontaneously aggregate, or self-assemble, to generate several distinct macromolecular and morphological forms that can differ significantly in their effects on cells. We have compared different assembly forms of A beta(1-42) (A beta 42) for their ability to trigger apoptosis in cultured hippocampal neurons at a submicromolar concentration and for their binding to such neurons. Fibrillar A beta 42 caused both morphological changes indicative of apoptosis and specific activation of caspase-3, a characteristic marker of neurodegeneration in AD, in hippocampal neurons, whereas other preparations tested did not do so under the same conditions. More aggregated forms of A beta 42, including both fibrils and a mixture of assembly forms termed A beta-derived diffusible ligands (ADDLs), bound to neurons much more extensively and at lower concentrations than preparations that contained smaller forms. Fibrillar A beta 42, in particular, bound to neurons at concentrations as low as 1 nM. Colocalization studies showed that fibrillar A beta 42 bound almost exclusively at nonsynaptic sites. These results show differences between assembly forms of A beta 42 in the ability to trigger apoptotic signaling in CNS neurons, and they directly demonstrate differences between assembly forms in the binding to CNS neurons, a possible first step in the pathogenesis of AD. These results suggest that fibrillar A beta 42 contributes to the pathogenesis of AD.

Methylene Blue Inhibits Amyloid Aβ Oligomerization by Promoting Fibrillization

Amyloid plaques are hallmark neuropathological lesions in Alzheimer's disease, which consist of abnormally aggregated Abeta protein. Multiple Abeta aggregated species have been identified, and neurotoxicity appears to be correlated with the amount of nonfibrillar oligomers. Therefore, selective inhibition of Abeta oligomer formation has emerged as an attractive means of therapeutic intervention. To investigate whether small molecules can modulate aggregation to achieve selective inhibition of neurotoxic amyloid oligomers, Abeta aggregation was assayed in vitro in the presence of methylene blue, using immunoreactivity with the prefibrillar oligomer-specific antibody A11, transmission electron microscopy, and turbidity assays. Methylene blue inhibited oligomerization when used at substoichiometric concentrations relative to that of the Abeta monomer. Inhibition of Abeta oligomerization was achieved concomitant with promotion of fibrillization, suggesting that oligomer and fibril formation are distinct and competing pathways. Methylene blue-mediated promotion of fiber formation occurred via a dose-dependent decrease in the lag time and an increase in the fibrillization rate, consistent with promotion of both filament nucleation and elongation. Addition of methylene blue to preformed oligomers resulted in oligomer loss and promotion of fibrillization. The data show that Abeta oligomer formation is inhibited by promoting fibril formation, which suggests that the relative pathological significance of oligomers and fibrils may be tested in vivo using methylene blue. If Abeta oligomers represent the primary pathogenic species, then inhibition of this highly toxic species via promotion of formation of less toxic aggregates may be therapeutically useful.

Genetically augmenting tau levels does not modulate the onset or progression of Abeta pathology in transgenic mice

The two hallmark pathologies of Alzheimer's disease (AD) are amyloid plaques, composed of the small amyloid-beta (Abeta) peptide, and neurofibrillary tangles, comprised aggregates of the microtubule binding protein, tau. The molecular linkage between these two lesions, however, remains unknown. Based on human and mouse studies, it is clear that the development of Abeta pathology can trigger tau pathology, either directly or indirectly. However, it remains to be established if the interaction between Abeta and tau is bidirectional and whether the modulation of tau will influence Abeta pathology. To address this question, we used the 3xTg-AD mouse model, which is characterized by the age-dependent buildup of both plaques and tangles. Here we show that genetically augmenting tau levels and hyperphosphorylation in the 3xTg-AD mice has no effect on the onset and progression of Abeta pathology. These data suggest that the link between Abeta and tau is predominantly if not exclusively unidirectional, which is consistent with the Abeta cascade hypothesis and may explain why tauopathy-only disorders are devoid of any Abeta pathology.

High sensitivity analysis of amyloid-beta peptide composition in amyloid deposits from human and PS2APP mouse brain

Cortical amyloid-beta (Abeta) deposition is considered essential in Alzheimer's disease (AD) and is also detectable in nondemented individuals with pathologic aging (PA). The present work presents a detailed analysis of the Abeta composition in various plaque types from human AD and PA cases, compared with plaque Abeta isolated from PS2APP mice. To determine minute amounts of Abeta from 30 to 50 laser-dissected amyloid deposits, we used a highly sensitive mass spectrometry procedure after restriction protease lysyl endopeptidase (Lys-C) digestion. This approach allowed the analysis of the amino-terminus and, including a novel ionization modifier, for the first time the carboxy-terminus of Abeta at a detection limit of approximately 200 fmol. In addition, full length Abeta 40/42 and pyroglutamate 3-42 were analyzed using a highly sensitive urea-based Western blot procedure. Generally, Abeta fragments were less accessible in human deposits, indicative of more posttranslational modifications. Thioflavine S positive cored plaques in AD were found to contain predominantly Abeta 42, whereas thioflavine S positive compact plaques and vascular amyloid consist mostly of Abeta 40. Diffuse plaques from AD and PA, as well as from PS2APP mice are composed predominantly of Abeta 1-42. Despite biochemical similarities in human and PS2APP mice, immuno-electron microscopy revealed an extensive extracellular matrix associated with Abeta fibrils in AD, specifically in diffuse plaques. Amino-terminal truncations of Abeta, especially pyroglutamate 3-40/42, are more frequently found in human plaques. In cored plaques we measured an increase of N-terminal truncations of approximately 20% between Braak stages IV to VI. In contrast, diffuse plaques of AD and PA cases, show consistently only low levels of amino-terminal truncations. Our data support the concept that diffuse plaques represent initial Abeta deposits but indicate a structural difference for Abeta depositions in human AD compared with PS2APP mice already at the stage of diffuse plaque formation.

Blood-borne factors inhibit Alzheimer's β-amyloid fibril formation in vitro

Soluble amyloid beta-protein (Abeta) does not aggregate to beta-amyloid fibrils (fAbeta) in the brain of normal humans. We recently found that the cerebrospinal fluid (CSF) from non-Alzheimer's disease (AD) subjects inhibited the formation of fAbeta(1-40) and fAbeta(1-42) more strongly than that from AD subjects, although the CSF obtained from both groups inhibited the fAbetas formation in vitro. Here, we examined the influence of plasma obtained from AD, non-AD and healthy control (CTL) subjects on the formation of fAbeta(1-40) and fAbeta(1-42) in vitro. Although the plasma obtained from all groups inhibited the formation of fAbeta(1-40) and fAbeta(1-42), the plasma from non-AD and CTL subjects inhibited the formation of fAbetas more strongly than that from AD subjects. These results indicate that the plasma as well as CSF in AD would provide a molecular environment favorable for fAbeta formation, suggesting a decrease of specific inhibitory factors and/or increase of specific accelerating factors.

Strain fidelity of chronic wasting disease upon murine adaptation

Chronic wasting disease (CWD), a prion disease of deer and elk, is highly prevalent in some regions of North America. The establishment of mouse-adapted CWD prions has proven difficult due to the strong species barrier between mice and deer. Here we report the efficient transmission of CWD to transgenic mice overexpressing murine PrP. All mice developed disease 500 +/- 62 days after intracerebral CWD challenge. The incubation period decreased to 228 +/- 103 days on secondary passage and to 162 +/- 6 days on tertiary passage. Mice developed very large, radially structured cerebral amyloid plaques similar to those of CWD-infected deer and elk. PrP(Sc) was detected in spleen, indicating that murine CWD was lymphotropic. PrP(Sc) glycoform profiles maintained a predominantly diglycosylated PrP pattern, as seen with CWD in deer and elk, across all passages. Therefore, all pathological, biochemical, and histological strain characteristics of CWD appear to persist upon repetitive serial passage through mice. These findings indicate that the salient strain-specific properties of CWD are encoded by agent-intrinsic components rather than by host factors.

Ultrastructural characteristics of tau filaments in tauopathies: Immuno-electron microscopic demonstration of tau filaments in tauopathies

The microtubule-associated protein tau aggregates into filaments in the form of neurofibrillary tangles, neuropil threads and argyrophilic grains in neurons, in the form of variable astrocytic tangles in astrocytes and in the form of coiled bodies and argyrophilic threads in oligodendrocytes. These tau filaments may be classified into two types, straight filaments or tubules with 9-18 nm diameters and "twisted ribbons" composed of two parallel aligned components. In the same disease, the fine structure of tau filaments in glial cells roughly resembles that in neurons. In sporadic tauopathies, individual tau filaments show characteristic sizes, shapes and arrangements, and therefore contribute to neuropathologic differential diagnosis. In frontotemporal dementias caused by tau gene mutations, variable filamentous profiles were observed in association with mutation sites and insoluble tau isoforms, including straight filaments or tubules, paired helical filament-like filaments, and twisted ribbons. Pre-embedding immunoelectron microscopic studies were carried out using anti-3-repeat tau and anti-4-repeat tau specific antibodies, RD3 and RD4. Straight tubules in neuronal and astrocytic Pick bodies were immunolabeled by the anti-3-repeat tau antibody. The anti-4-repeat tau antibody recognized abnormal tubules comprising neurofibrillary tangles, coiled bodies and argyrophilic threads in progressive supranuclear palsy (PSP) and corticobasal degeneration. In the pre-embedding immunoelectron microscopic study using the phosphorylated tau AT8 antibody, tuft-shaped astrocytes of PSP were found to be composed of bundles of abnormal tubules in processes and perikarya of protoplasmic astrocytes. In this study, the 3-repeat tau or 4-repeat tau epitope was detected in situ at the ultrastructural level in abnormal tubules in representative pathological lesions in Pick's disease, PSP and corticobasal degeneration.

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.

Linker histone H1 binds to disease associated amyloid-like fibrils

Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most prevalent neurodegenerative diseases of the central nervous system. These two diseases share a common feature in that a normally soluble peptide (amyloid-beta) or protein (alpha-synuclein) aggregates into an ordered fibrillar structure. As well as structural similarities observed between fibrillar aggregates related to these diseases, common pathological processes of increased oxidative injury, excitotoxicity and altered cell cycle are also evident. It was the aim of this study to identify novel interacting proteins to the amyloid-like motif and therefore identify common potential pathways between neurodegenerative diseases that share biophysical properties common to classical amyloid fibrils. Optimal ageing of recombinant proteins to form amyloid-like fibrils was determined by electron microscopy, Congo red birefringement and photo-induced cross-linking. Using pull-down assays the strongest detected interacting protein to the amyloid-like motifs of amyloid-beta, alpha-synuclein and lysozyme was identified as histone H1. The interaction with the amyloid-like motif was confirmed by techniques including surface plasmon resonance and immunohistochemistry. Histone H1 is known to be an integral part of chromatin within the nucleus, with a primary role of binding DNA that enters and exits from the nucleosome, and facilitating the shift in equilibrium of chromatin towards a more condensed form. However, phosphorylated histone H1 is predominantly present in the cytoplasm and as yet the functional significance of this translocation is unknown. This study also found that histone H1 is localised within the cytoplasm of neurons and astrocytes from areas affected by disease as well as amyloid plaques, supporting the hypothesis that histone H1 favoured binding to an ordered fibrillar motif. We conclude that the binding of histone H1 to a general amyloid-like motif indicates that histone H1 may play an important common role in diseases associated with amyloid-like fibrils.

A functional polymorphism within plasminogen activator urokinase (PLAU) is associated with Alzheimer's disease

A number of susceptibility loci for Alzheimer's disease (AD) have been identified including a region on Chromosome 10q21-q22. Within this region the plasminogen activator urokinase gene (PLAU) was considered as a reasonable candidate from its functional implication in plasmin generation, a serine protease capable of degrading beta-Amyloid (Abeta) protein. We screened 56 single nucleotide polymorphisms (SNPs) around PLAU using 1751 individuals from four independent case-control samples (Munich, N=679; Bonn N=282; Brescia (Italy) N=219; Perth (Australia) N=557 and one discordant sib-pair sample (Munich N=622). In brain tissue samples of neuropathologically confirmed cases with AD (N=33) we analyzed plaque counts according to the risk allele. We identified that one functional exonic SNP (rs2227564) is associated with development of AD using the four independent case-control samples (Munich, P=0.02; Bonn, P=0.005; Brescia (Italy), P=0.001; Perth (Australia), P=0.03) and the discordant sib-pair sample (P=0.001). In brain tissue, from neuropathologically confirmed cases with AD, we identified significantly higher plaque counts in carriers of the risk allele (N=6; 60.3+/-16.9) compared with non-carriers (N=9; 26.3+/-8.8; P=0.007). This study provides compelling evidence of a genetic and functional involvement of a common PLAU variant into the pathogenesis of AD. Further functional investigations are warranted to elucidate the specific role of PLAU, respectively, PLAU variants in the metabolism of Abeta proteins.

New techniques for imaging, digitization and analysis of three-dimensional neural morphology on multiple scales

Cognitive impairment in normal aging and neurodegenerative diseases is accompanied by altered morphologies on multiple scales. Understanding of the role of these structural changes in producing functional deficits in brain aging and neuropsychiatric disorders requires accurate three-dimensional representations of neuronal morphology, and realistic biophysical modeling that can directly relate structural changes to altered neuronal firing patterns. To date however, tools capable of resolving, digitizing and analyzing neuronal morphology on both local and global scales, and with sufficient throughput and automation, have been lacking. The precision of existing image analysis-based morphometric tools is restricted at the finest scales, where resolution of fine dendritic features and spine geometry is limited by the skeletonization methods used, and by quantization errors arising from insufficient imaging resolution. We are developing techniques for imaging, reconstruction and analysis of neuronal morphology that capture both local and global structural variation. To minimize quantization error and evaluate more precisely the fine geometry of dendrites and spines, we introduce a new shape analysis technique, the Rayburst sampling algorithm that uses the original grayscale data rather than the segmented images for precise, continuous radius estimation, and multidirectional radius sampling to represent non-circular branch cross-sections and anisotropic structures such as dendritic spine heads, with greater accuracy. We apply the Rayburst technique to 3D neuronal shape analysis at different scales. We reconstruct and digitize entire neurons from stacks of laser-scanning microscopy images, as well as globally complex structures such as multineuron networks and microvascular networks. We also introduce imaging techniques necessary to recover detailed information on three-dimensional mass distribution and surface roughness of amyloid beta plaques from human Alzheimer's disease patients and from the Tg2576 mouse that expresses the "Swedish" mutation of the amyloid precursor protein. By providing true three-dimensional morphometry of complex histologic structures on multiple scales, the tools described in this report will enable multiscale biophysical modeling studies capable of testing potential mechanisms by which altered dendritic structure, spine geometry and network branching patterns that occur in normal aging and in many brain disorders, determine deficits of functions such as working memory and cognition.

Nursing management of the patient with Alzheimer's disease

Alzheimer's disease (AD) is a progressive, degenerative, debilitating illness that affects all races and both sexes. In 2002 the numbers of women over the age of 90 years with AD were higher compared with men of the same age group (Office for National Statistics (ONS), 2004). Although there are no data identifying the number of women suffering from AD compared with men, it could be concluded from these data (ONS, 2004) that more women than men suffer from AD. The number of individuals suffering from AD is increasing as people are living longer. Analysis of postmortem brain tissue in patients with AD has identified senile plaques in the hippocampal region, neurofibrillary tangles in the brain cells and also a decline in levels of acetylcholine in the brain. There is no known cure for the illness and therefore patients will ultimately require constant care in the community or in special units in residential homes. The National Service Framework for Long-Term Conditions (Department of Health, 2005) gives clear guidelines for healthcare providers in caring for these patients.

Targeting the Alpha 7 Nicotinic Acetylcholine Receptor to Reduce Amyloid Accumulation in Alzheimers Disease Pyramidal Neurons

Although there is still no known effective preventative treatment or cure for Alzheimer's disease (AD), the development of new drugs that target pathological features that appear early in the course of this disease and alleviate some of the early cognitive and memory symptoms is a laudable goal that may be one step closer. To date, the acetylcholinesterase inhibitors have been the most widely used AD drugs and have been somewhat successful in slowing loss of cognition. In the last few years, a number of studies have demonstrated that amyloid beta (1-42) (Abeta42), the predominant Abeta peptide species in amyloid plaques, first accumulates in vulnerable neurons prior to plaque formation. Recently, we have shown that many (if not most) amyloid plaques in the entorhinal cortex of AD brains are actually the lysis remnants of degenerated, Abeta42-overburdened neurons. Furthermore, the most vulnerable neurons appear to be those that abundantly express the alpha7 nicotinic acetylcholine receptor (alpha7nAChR), and internalization of Abeta42 appears to be facilitated by the high-affinity binding of Abeta42 to the alpha7nAChR on neuronal cell surfaces, followed by endocytosis of the resulting complex and its accumulation within the lysosomal compartment. This mechanism provides a reasonable explanation for the selective vulnerability of cholinergic and cholinoceptive neurons in AD brains and for the fact that Abeta42 is the dominant Abeta peptide species in both intraneuronal accumulations and amyloid plaques. In view of the pathophysiological consequences of Abeta42 binding to alpha7nAChR on neuronal surfaces that stem from excessive intraneuronal Abeta42 accumulation, the alpha7nAChR could be an important therapeutic target for treatment of AD. In addition, it further emphasizes the potential merits of new and effective therapeutic strategies pointed towards the goal of lowering of Abeta42 levels in the blood and cerebrospinal fluid as well as blocking Abeta42 in the blood from penetrating the blood-brain barrier and entering into the brain parenchyma.

Cerebrospinal fluid of Alzheimer patients promotes beta-amyloid fibril formation in vitro

Cerebral deposition of amyloid beta-peptide (Abeta) is an invariant feature of Alzheimer's disease (AD). To answer why soluble Abeta does not aggregate to beta-amyloid fibrils (fAbeta) in the brain of normal humans, we examined the influence of cerebrospinal fluid (CSF) obtained from AD and non-AD patients on the formation of fAbeta(1-40) and fAbeta(1-42) in vitro, by using fluorescence spectroscopy with thioflavin T and electron microscopy. Although the CSF obtained from both groups inhibited the formation of both fAbeta(1-40) and fAbeta(1-42), the CSF from non-AD patients inhibited the formation of fAbetas more strongly than that from AD patients. In AD patients, the final levels of fAbetas formation showed a significant negative correlation with the Abeta(1-42) level in CSF. These results indicate that fAbeta deposition in the brain of AD may be enhanced by the decrease of specific inhibitory factors and/or by the increase of specific accelerating factors in CSF.

Type-specific evolution of amyloid plaque and angiopathy in APPsw mice

To clarify how Abeta deposits start in the brain, we examined the early to late stages of senile plaques and amyloid angiopathy in APPsw mice. All types of human senile plaques were observed in the mouse brains. The premature forms of cored plaques appeared first in the cerebral cortex of mice at 7-8 months old. Then, amyloid angiopathy emerged, followed by diffuse plaques consisting of Abeta1-42. Modifications of the N-terminus of Abeta were late phase phenomena. The premature forms of cored plaques were composed of central Abeta1-40 amyloid cores, surrounding amorphous Abeta1-42 deposits, and accumulation of Abeta1-42 in some peripheral cells. These cells were incorporated in amyloid cores, and these plaques developed to large cored plaques composed of Abeta1-40 and Abeta1-42. The size and number of cored plaques were increased with age. These findings indicate different evolution paths for cored plaques and diffuse plaques, and suggest the presence of a pathway that initiates with the intracellular accumulation of Abeta1-42 and leads to the development of classic plaques in human brain tissues.

Modelling of amyloid beta-peptide induced lesions using roller-drum incubation of hippocampal slice cultures from neonatal rats

Pronounced neurodegeneration of hippocampal pyramidal neurons has been shown in Alzheimer's disease. The aim of this study was to establish an organotypic in vitro model for investigating effects of the amyloid beta (Abeta)-peptide on pyramidal neuron degeneration, glial cell activation and tau phosphorylation. Tissue cultures in a quasi-monolayer were obtained using roller-drum incubation of hippocampal slices from neonatal Sprague Dawley rats. Neuronal populations identified included N-methyl-D-aspartate (NMDA-R1) receptor immunoreactive pyramidal neurons, and neurons immunopositive for glutamic acid decarboxylase-65 (GAD65) or gamma amino butyric acid (GABA). Many neurons expressed phosphorylated tau as shown by pS(396), AD2 and PHF-tau immunostaining. Astrocytes, microglial cells and macrophages were also identified. The Abeta(25-35) peptide formed fibrillar networks within 2 days as demonstrated by electron microscopy. In the presence of the neurotoxic Abeta(25-35) peptide, but not Abeta(35-25), deposits developed in the tissue that were stainable with Thioflavine T and Congo red and showed the characteristic birefringence of Abeta plaques. Following Abeta(25-35) exposure, neurodegenerative cells were observed with Fluoro-Jade B staining. Further characterization of pyramidal neurons immunopositive for NMDA-R1 showed a decrease of cell number in the immediate surrounding of Abeta(25-35) deposits in a time- and concentration-dependent fashion. Similar effects on pyramidal neurons were obtained following exposure to the full-length, Abeta(1-40) peptide. Also, a loss of neuronal processes was seen with GAD65, but not GABA, immunohistochemistry after exposure to Abeta(25-35). Abeta(25-35)-exposed neurons immunopositive for phospho-tau showed degenerating, bent and often fragmented processes. Astrocytes showed increased GFAP-positive reactivity after Abeta(25-35) exposure and formation of large networks of processes. No obvious effect on microglial cells and macrophages could be seen after the Abeta(25-35) exposure. The developed in vitro system may constitute a useful tool for screening novel drugs against Abeta-induced alterations of tau and degeneration of hippocampal neurons.

Alpha-Synuclein aggregation in pathological aging and Alzheimer's disease: the impact of beta-amyloid plaque level

In central nervous system diseases, abnormal aggregation of one protein is often associated with aggregation of other proteins. To begin to assess whether beta-amyloid (Abeta) is associated with alpha-synuclein (AS) aggregation [secondary Lewy body (LB) formation], we used immunohistochemical techniques to compare the amygdala of 11 subjects with pathological aging and 18 with Alzheimer's disease. Overall, Abeta-40 plaque level was greater in cases with secondary AS aggregates. Abeta-42 plaque level was not associated with AS aggregation. Abeta-40 plaque levels cannot be ruled out as a factor involved in secondary LB formation.

Soluble Abeta oligomers ultrastructurally localize to cell processes and might be related to synaptic dysfunction in Alzheimer's disease brain

Soluble Abeta oligomers have recently been considered to be responsible for cognitive dysfunction prior to senile plaque (SP) formation in Alzheimer's disease (AD) brain. To investigate the ultrastructural localization of soluble Abeta oligomers, we conducted the post-embedding immunoelectron microscopic (IEM) study using an antibody against a molecular mimic of oligomeric Abeta. We examined autopsied brains from AD patients and nondemented subjects. Oligomer-specific immunoreactions detected by IEM tended to be found with higher density (1) in AD than in nondemented brains and (2) at the axon and axon terminal in AD than in nondemented brains. These findings imply that soluble Abeta oligomers might be related to synaptic dysfunction in AD brain.

Immersion autometallographic tracing of zinc ions in Alzheimer beta-amyloid plaques

An easy to perform autometallographic technique (AMG) for capturing zinc ions in Alzheimer plaques is presented. The possibility of visualizing loosely bound or free zinc ions in tissue by immersion autometallography (iZnS(AMG)) is a relatively recent development. The iZnS(AMG) staining is caused by zinc-sulphur nanocrystals created in 1-2 mm thick brain slices that are immersed in a 0.1% sodium sulphide, 3% glutaraldehyde phosphate buffered solution, the NeoTimm Solution (NTS), for 3 days. When the zinc-sulphur nanocrystals are subsequently silver-enhanced by autometallography, the plaques are readily identified as spheres of dark interlacing strands of different sizes, embedded in the pattern of zinc-enriched terminals. The zinc specificity of the iZnS(AMG) technique was tested by immersion of brain slides in the chelator DEDTC prior to the NTS immersion. The iZnS(AMG) detection of zinc ions is easily standardized and can be used in the quantification of plaques with stereological methods. This technique is the first to detect zinc in plaques in the cerebellum of transgenic PS1/APP mice and the first to detect zinc ions in plaques and dystrophic neurites at electron microscopical levels.

Part of membrane-bound Abeta exists in rafts within senile plaques in Tg2576 mouse brain

To clarify whether rafts are the site of abnormal amyloid beta protein (Abeta) deposition, we examined the ultrastructural localization of both flotillin-1 (pre-embedding) and Abeta (post-embedding) in Tg2576 mouse brains. After observing the exact areas of senile plaques by reflection contrast microscopy, we observed these same plaques under an electron microscope. Membrane-bound Abeta was predominantly observed on plasma membranes of small processes in diffuse plaques. Non-fibrillar and fibrillar Abeta was increased in primitive plaques, and the fibrillar form was predominant in mature plaques. The number of flotillin-1-positive rafts per field in mature plaques was prominently less than those outside of the plaques, in diffuse plaques and in primitive plaques. The colocalization of flotillin-1 with Abeta42 appeared approximately 10% of flotillin-1-positive rafts within senile plaques, while there was no colocalization found outside of the plaques. This study ultrastructurally demonstrated that part of membrane-bound Abeta exists in lipid rafts within senile plaques, and suggests that rafts could be one of the sites for initial Abeta deposition.

Oligomeric proteins ultrastructurally localize to cell processes, especially to axon terminals with higher density, but not to lipid rafts in Tg2576 mouse brain

We examined the ultrastructural localization of oligomeric proteins, Abeta42, and flotillin-1 in Tg2576 mouse brains by triple immunoelectron microscopy. Oligomer-specific immunoreactions localized to cell processes, especially to axon terminals with higher density in Tg than in nonTg mouse brains. The oligomer was less frequently colocalized to flotillin-1-immunoreactive rafts than Abeta42, suggesting that rafts are one of the sites of polymeric Abeta deposition, but not of oligomeric proteins including Abeta.

The contribution of microscopy to the study of Alzheimer's disease, amyloid plaques and Abeta fibrillogenesis

A broad survey is presented in this chapter, dealing with the impact that microscopy has made to the study of Alzheimer's disease, amyloid plaques and amyloid-beta fibrillogenesis. This includes classical light microscopy and the modem immunolabelling and confocal microscopies, together with the contribution of transmission electron microscopy and atomic force microscopy. Whilst usefully standing alone, the individual microscopies often contribute most effectively when they are integrated with cellular, biophysical and molecular approaches.

Cells of monocyte/microglial lineage are involved in both microvessel amyloidosis and fibrillar plaque formation in APPsw tg mice

Ultrastructural three-dimensional reconstruction indicates that deposition of amyloid in the wall of capillaries and in perivascular plaques in APP(SW) transgenic mice (Tg2576) represents two steps of one pathological process associated with inflammation of the vascular wall and perivascular space with cells of monocyte/microglia lineage and fibrillar amyloid-beta deposition. Plaque growth is associated with an increase in the number of microglial cells from two in the smallest plaque to 113 in the largest plaque; however, the growth in the number of microglial cells does not result in amyloid deposit degradation. On the contrary, an increase in the number and volume of microglial cells correlates with the growth of amyloid star from 62 to 34,460 microm(3), and an increase of the plaque volume from 1555 to 284,497 microm(3) (r=0.9). Growth in the number of microglial cells in the absence of morphological evidence of fibrillar amyloid internalization and phagocytosis indicates that microglial cells do not remove amyloid in Tg2576 mice. The study suggests that (a) the mechanism of capillary amyloidosis and plaque formation is similar, (b) the cells of monocyte/macrophage lineage play a critical role in fibrillar amyloid deposition in both types of lesions, and (c) treatment of one of these two forms of brain amyloidosis may affect both types of pathological changes.

Mostly separate distributions of CLAC- versus Abeta40- or thioflavin S-reactivities in senile plaques reveal two distinct subpopulations of beta-amyloid deposits

Collagenous Alzheimer amyloid plaque component (CLAC) is a unique non-Abeta amyloid component of senile plaques (SP) derived from a transmembrane collagen termed CLAC-precursor. Here we characterize the chronological and spatial relationship of CLAC with other features of SP amyloid in the brains of patients with Alzheimer's disease (AD), Down syndrome (DS), and of PSAPP transgenic mice. In AD and DS cerebral cortex, CLAC invariably colocalized with Abeta42 but often lacked Abeta40- or thioflavin S (thioS)-reactivities. Immunoelectron microscopy of CLAC-positive SP showed labeling of fibrils that are more loosely dispersed compared to typical amyloid fibrils in CLAC-negative SP. In DS cerebral cortex, diffuse plaques in young patients were negative for CLAC, whereas a subset of SP became CLAC-positive in patients aged 35 to 50 years, before the appearance of Abeta40. In DS cases over 50 years of age, Abeta40-positive SP dramatically increased, whereas CLAC burden remained at a constant level. In PSAPP transgenic mice, CLAC was positive in the diffuse Abeta deposits surrounding huge-cored plaques. Thus, CLAC and Abeta40 or thioS exhibit mostly separate distribution patterns in SP, suggesting that CLAC is a relatively early component of SP in human brains that may have inhibitory effects against the maturation of SP into beta-sheet-rich amyloid deposits.

Cognitive correlates of Aβ deposition in male and female mice bearing amyloid precursor protein and presenilin-1 mutant transgenes

Several transgenic mouse models of Alzheimer's disease (AD) have been developed that exhibit beta-amyloid (Abeta) neuropathology and behavioural deficits. However, not all studies have investigated the relationship between the development of cognitive impairment and neuropathology. Therefore, temporal changes in cognition were investigated in male and female double-mutant APPswexPS1.M146V (TASTPM) transgenic mice using an object recognition test and correlated with the development of cerebral Abeta neuropathology. Both male and female TASTPM mice exhibited similar significant cognitive impairment at 6, 8 and 10 months of age in the object recognition test, compared to wild-type littermates. There was no such cognitive impairment at 3 or 4 months of age. Quantitative immunohistochemistry using a battery of Abeta antibodies demonstrated that cerebral Abeta deposition was first apparent in 3-month-old mice, and it increased with age. The early appearance of cerebral Abeta deposits in the double-transgenic TASTPM mice supports the evidence that mutations in the PS1 gene accelerate Abeta deposition. The cerebral Abeta load was greater in female than in male TASTPM mice at all ages investigated. In the electron microscope, mature Abeta plaques comprising a fibrillar core surrounded by degenerating neurites and reactive glia were first observed in the cortex of TASTPM mice at 6 months of age, the same age at which cognitive impairment became apparent. These results suggest that the cognitive impairment in TASTPM mice is related to the disruption of neural connectivity and not simply Abeta deposition, which first occurs 3 months earlier.

Characterisation of cytoskeletal abnormalities in mice transgenic for wild-type human tau and familial Alzheimer's disease mutants of APP and presenilin-1

To study the role of Abeta amyloid deposits in the generation of cytoskeletal lesions, we have generated a transgenic mouse line coexpressing in the same neurons a wild-type human tau isoform (0N3R), a mutant form of APP (751SL) and a mutant form of PS1 (M146L). These mice developed early cerebral extracellular deposits of Abeta, starting at 2.5 months. A somatodendritic neuronal accumulation of transgenic tau protein was observed in tau only and in tau/PS1/APP transgenic mice, including in neurons adjacent to Abeta deposits. The phosphorylation status of this somatodendritic tau was similar in the two transgenic lines. The Abeta deposits were surrounded by a neuritic reaction composed of axonal dystrophic processes, immunoreactive for many phosphotau epitopes and for the human tau transgenic protein. Ultrastructural observation showed in these dystrophic neurites a disorganisation of the microtubule and the neurofilament network but animals that were observed up to 18 months of age did not develop neurofibrillary tangles. These results indicate that overexpression of mutant PS1, mutant APP and of wild-type human tau were not sufficient per se to drive the formation of neurofibrillary tangles in a transgenic model. The Abeta deposits, however, were associated to marked changes in cytoskeletal organisation and in tau phosphorylation in adjacent dystrophic neurites.

Chlamydia pneumoniae induces Alzheimer-like amyloid plaques in brains of BALB/c mice

Amyloid deposits resembling plaques found in Alzheimer's disease (AD) brains were formed in the brains of non-transgenic BALB/c mice following intranasal infection with Chlamydia pneumoniae. The mice were infected at 3 months of age with C. pneumoniae isolated from an AD brain. Infection was confirmed by light and electron microscopy in olfactory tissues of the mice. C. pneumoniae was still evident in these tissues 3 months after the initial infection indicating that a persistent infection had been established. Amyloid beta (Abeta) 1-42 immunoreactive deposits were identified in the brains of infected BALB/c mice up to 3 months post-infection with the density, size, and number of deposits increasing as the infection progressed. A subset of deposits exhibited thioflavin-s labeling. Intracellular Abeta1-42 labeling was observed in neuronal cells. Experimental induction of amyloid deposition in brains of non-transgenic BALB/c mice following infection with C. pneumoniae may be a useful model for furthering our understanding of mechanisms, linked to infection, involved in the initiation of the pathogenesis of sporadic AD.

Diffusion tensor imaging detects age-dependent white matter changes in a transgenic mouse model with amyloid deposition

Increasing evidence demonstrates that there is marked damage and dysfunction not only in the gray matter but also in the white matter in Alzheimer's disease (AD). In this study, transgenic mice overexpressing beta-amyloid precursor protein (APP) under control of the platelet-derived growth factor promoter (PDAPP mice) were examined using diffusion tensor magnetic resonance imaging (DTI) to evaluate the extent of white matter injury before and following the development of AD-like pathology. The profile of DTI parameters was significantly different in old PDAPP mice compared to that of old control mice following the development of AD-like pathology. No difference in DTI parameters was observed between the young PDAPP and control mice. Our results suggest that as amyloid beta (Abeta) deposition and levels increase over time in PDAPP mice, these changes lead to primary or secondary white matter injury that can be detected by DTI.

Insulin inhibits amyloid beta-induced cell death in cultured human brain pericytes

Amyloid-beta (Abeta) deposition in the cerebral arterial and capillary walls is one of the characteristics of Alzheimer's disease and hereditary cerebral hemorrhage with amyloidosis-Dutch type. In vitro, Abeta1-40, carrying the "Dutch" mutation (DAbeta1-40), induced reproducible degeneration of cultured human brain pericytes (HBP), by forming fibrils at the cell surface. Thus, this culture system provides an useful model to study the vascular pathology seen in Alzheimer's disease. In this study, we used this model to investigate the effects of insulin on Abeta-induced degeneration of HBP, as it has been mentioned previously that insulin is able to protect neurons against Abeta-induced cell-death. The toxic effect of DAbeta1-40 on HBP was inhibited by insulin in a dose-dependent matter. Insulin interacted with Abeta and inhibited fibril formation of Abeta in a cell-free assay, as well as at the cell surface of HBP. Our data indicate that the formation of a fibril network is essential for Abeta-induced cell death in HBP. Additionally, insulin may be involved in the regulation of Abeta fibrillization in AD.

Effect of different anti-Abeta antibodies on Abeta fibrillogenesis as assessed by atomic force microscopy

Extensive data suggest that the conversion of the amyloid-beta (Abeta) peptide from soluble to insoluble forms is a key factor in the pathogenesis of Alzheimer's disease (AD). In recent years, atomic force microscopy (AFM) has provided useful insights into the physicochemical processes involving Abeta morphology, and it can now be used to explore factors that either inhibit or promote fibrillogenesis. We used ex situ AFM to explore the impact of anti-Abeta antibodies directed against different domains of Abeta on fibril formation. For the AFM studies, two monoclonal antibodies (m3D6 and m266.2) were incubated in solution with Abeta(1-42) with a molar ratio of 1:10 (antibody to Abeta) over several days. Fibril formation was analyzed quantitatively by determining the number of fibrils per microm(2) and by aggregate size analysis. m3D6, which is directed against an N-terminal domain of Abeta (amino acid residues 1-5) slowed down fibril formation. However, m266.2, which is directed against the central domain of Abeta (amino acid residues 13-28) appeared to completely prevent the formation of fibrils over the course of the experiment. Inhibition of fibril formation by both antibodies was also confirmed by thioflavin-T (ThT) fluorescence experiments carried out with Abeta(1-40) incubated for five days. However, unlike AFM results, ThT did not differentiate between the samples incubated with m3D6 versus m266.2. These results indicate that AFM can be not only reliably used to study the effect of different molecules on Abeta aggregation, but that it can provide additional information such as the role of epitope specificity of antibodies as potential inhibitors of fibril formation.

Amyloid plaques in transmissible spongiform encephalopathies (prion diseases)

Amyloid plaques are encountered in all cases of kuru and Gerstmann-Straussler-Scheinker disease (GSS) and in some 10-15% of sporadic Creutzfeldt-Jakob disease (sCJD) cases. In variant Creutzfeldt-Jakob (vCJD) the particular type of plaque known as "florid" or "daisy" plaque exists in 100% of cases. By electron microscopy several types of amyloid plaque were delineated, corresponding to those seen by PrP immunohistochemistry. Unicentric "kuru" plaques consisted of stellate arrangements (stars or cores) of amyloid bundles emanating from a dense interwoven centre. A proportion of kuru plaques formed very dense stars, reminiscent of sea urchins in shape. Others presented a looser pattern. Amyloid stars were enveloped by astrocytic processes. High-power electron micrographs revealed that amyloid bundles were concealed within grooves of obscure cellular origin. Interestingly, basement membranes lined with electron-dense material were observed at the periphery of many amyloid plaques of GSS. Dystrophic neurites were seen only rarely. Microglial cells formed a significant part of the amyloid plaques. Occasionally clusters composed of several kuru plaques were found. These were intermediate forms to multi-centric plaques, which consisted of several merging stellate cores. Smaller amyloid deposits surrounded larger cores. In contrast to the kuru plaques, associated with a limited number of dystrophic neurites (DN), numerous such structures were seen at the periphery. The DN were filled with abnormal organelles such as electron-dense bodies, multi-vesicular bodies and multilamellar bodies and thus were indistinguishable from those seen in scrapie and CJD or Alzheimer's disease, except that they did not contain paired helical filaments (PHF). Instead, piled neurofilaments were often detected in the centres of DN. Similar DN were observed but these were not associated with any plaques. The last and, by the same token, the rarest type of plaque was the purely neuritic plaque. These consisted of large areas filled with DN of different sizes and shapes (sometimes bizarre) but not amyloid bundles. Analogously to the kuru and multi-centric plaques, astrocytic processes were observed at the periphery. By means of light microscopy and semi-thin (1 microm) sections discrete PrP-immunopositive plaques were observed (data not shown), in the subependymal region but not in the deep brain neuroparenchyma, in both 263K and 22C-H scrapie-infected hamster brains. These plaques were not discernible by routine haematoxylin and eosin staining. Ultrastructurally, plaques were recognised as areas of low electron density containing haphazardly-oriented fibrils which, when immunogold techniques were applied, were heavily decorated with PrP-conjugated gold particles.

Identification of neuronal plasma membrane microdomains that colocalize beta-amyloid and presenilin: implications for beta-amyloid precursor protein processing

Alzheimer's disease (AD) is associated with the accumulation of extracellular deposits of the beta-amyloid protein (Abeta). Abeta is a result of misprocessing of the beta-amyloid precursor protein (APP). Gamma-secretase is involved in APP misprocessing and one hypothesis holds that this secretase is identical to PS1. We tested this hypothesis by determining whether PS is co-localised with Abeta in situ. Using confocal analyses and a sensitive immunogold procedure we show that PS and Abeta are co-localised within discrete microdomains of neuronal plasma membranes in AD patients and in aged dogs, an established model of human brain aging. Our data indicate that APP misprocessing occurs in discrete plasma membrane domains of neurons and provide evidence that PS1 is critically involved in Abeta formation.

Degeneration of beta-amyloid-associated cholinergic structures in transgenic APP SW mice

Cholinergic dysfunction is a consistent feature of Alzheimer's disease, and the interrelationship between beta-amyloid deposits, inflammation and early cholinergic cell loss is still not fully understood. To characterize the mechanisms by which beta-amyloid and pro-inflammatory cytokines may exert specific degenerating actions on cholinergic cells ultrastructural investigations by electron microscopy were performed in brain sections from transgenic Tg2576 mice that express the Swedish double mutation of the human amyloid precursor protein and progressively develop beta-amyloid plaques during aging. Both light and electron microscopical investigations of the cerebral cortex of 19-month-old transgenic mice revealed a number of pathological tissue responses in close proximity of beta-amyloid plaques, such as activated microglia, astroglial proliferation, increased number of fibrous astrocytes, brain edema, degeneration of nerve cells, dendrites and axon terminals. Ultrastructural detection of choline acetyl transferase (ChAT)-immunostaining in cerebral cortical sections of transgenic mice clearly demonstrated degeneration of ChAT-immunoreactive fibres in the environment of beta-amyloid plaques and activated glial cells suggesting a role of beta-amyloid and/or inflammation in specific degeneration of cholinergic synaptic structures.

Direct observation of amyloid fibril growth monitored by thioflavin T fluorescence

Real-time monitoring of fibril growth is essential to clarify the mechanism of amyloid fibril formation. Thioflavin T (ThT) is a reagent known to become strongly fluorescent upon binding to amyloid fibrils. Here, we show that, by monitoring ThT fluorescence with total internal reflection fluorescence microscopy (TIRFM), amyloid fibrils of beta2-microgobulin (beta2-m) can be visualized without requiring covalent fluorescence labeling. One of the advantages of TIRFM would be that we selectively monitor fibrils lying along the slide glass, so that we can obtain the exact length of fibrils. This method was used to follow the kinetics of seed-dependent beta2-m fibril extension. The extension was unidirectional with various rates, suggesting the heterogeneity of the amyloid structures. Since ThT binding is common to all amyloid fibrils, the present method will have general applicability for the analysis of amyloid fibrils. We confirmed this with the octapeptide corresponding to the C terminus derived from human medin and the Alzheimer's amyloid beta-peptide.

Origin and turnover of microglial cells in fibrillar plaques of APPsw transgenic mice

Activated microglial cells are an integral component of fibrillar plaques in brains of subjects with Alzheimer's disease (AD) and in brains of transgenic mice overexpressing amyloidogenic fragments of human amyloid precursor protein (APP). The aim of this ultrastructural study of fibrillar plaques was to characterize the origin of microglial cells involved in cored plaque formation. Computer-aided three-dimensional reconstruction of plaques and microvessels in APPsw transgenic mice shows perivascular development of cored plaques. Perivascular location of almost all examined plaques and the infiltration at the interface between vessels and plaques with cells of monocyte/microglia lineage indicates that plaques are formed by inflammatory cells of blood origin. The increase in the number of microglial cells from 1 or 2 in an early plaque to more than 100 in a several-month-old plaque does not result in plaque degradation, but is associated with amyloid core growth and progression of neuronal degeneration, and suggests that recruitment of inflammatory cells of blood origin sustains plaque growth. Infiltration of the plaque with cells of blood origin and degeneration of 10-46% of inflammatory cells in large plaques, which is especially frequent at the interface between capillary wall and plaque, suggest their accelerated turnover.

Amyloid beta plaque-associated proteins C1q and SAP enhance the Abeta1-42 peptide-induced cytokine secretion by adult human microglia in vitro

Pro-inflammatory cytokines released by activated microglia could be a driving force in Alzheimer's disease (AD) pathology. We evaluated whether the presence of complement factor C1q and serum amyloid P component (SAP) in Abeta deposits is related to microglial activation. Activated microglia accumulate in SAP- and C1q-immunoreactive fibrillar amyloid beta (Abeta) plaques in AD temporal cortex. No clustered microglia are seen in SAP- and C1q-positive circumscript, non-fibrillar, tau-negative Abeta plaques in AD caudate nucleus and non-demented control temporal cortex. In addition, no clustered microglia were observed in C1q- and SAP-negative, irregular shaped, diffuse plaques in AD caudate nucleus and in non-demented control temporal cortex, which suggests that microglia are attracted and activated in Abeta deposits of certain fibrillarity that, in addition, have fixed SAP and C1q. Therefore, the effects of Abeta(1-42), SAP and C1q on cytokine secretion by human postmortem microglia in vitro were assessed. Abeta(1-42) alone had little to no effect. Abeta(1-42) peptides in combination with C1q or C1q and SAP increased microglial interleukin (IL)-6 secretion four- and eightfold, respectively. Tumor necrosis factor (TNF)-alpha, as well as intracellular IL-1alpha and IL-1beta levels, also increased upon exposure of microglia to Abeta(1-42)-SAP-C1q complexes. Combined with earlier findings, that amyloid and activated microglia accumulate at a relatively early stage of cognitive decline in AD patients, this suggests that clustering of activated, cytokine-secreting microglia in SAP- and C1q-containing Abeta deposits precedes neurodegenerative changes in AD, and thus may provide a "therapeutic window".

Beta-amyloid peptide potentiates inflammatory responses induced by lipopolysaccharide, interferon -gamma and 'advanced glycation endproducts' in a murine microglia cell line

beta-Amyloid (Abeta) plaques are characteristic hallmarks of Alzheimer's disease (AD). In AD, it has been suggested that activation of microglial cells might be the link between Abeta deposition and neuronal degeneration. Activated microglia are associated with senile plaques and produce free radicals and inflammatory cytokines. However, it is still not clear whether Abeta needs a prestimulated environment to exert its proinflammatory potential. Advanced glycation endproducts (AGEs), protein-bound oxidation products of sugars, have been shown to accumulate in senile plaques and could induce a silent but chronic inflammation in the AD brain. We tested whether Abeta acts as an amplifier of a submaximal proinflammatory response initiated by exposure to chicken egg albumin-AGE, lipopolysaccharide or interferon-gamma. Synthetic Abeta was used to produce three different samples (Abeta-fibrilar; Abeta-aggregated; Abeta-AGE), which were characterized for beta-sheeted fibrils by the thioflavin-T test and electron microscopy. As markers of microglial activation, nitric oxide, interleukin-6, macrophage-colony stimulation factor and tumour necrosis factor-alpha production was measured. All three Abeta samples alone could not induce a detectable microglial response. The combination of Abeta preparations, however, with the coinducers provoked a strong microglial response, whereby Abeta-AGE and fibrilar Abeta were more potent inflammatory signals than aggregated Abeta. Thus, Abeta in senile plaques can amplify microglial activation by a coexisting submaximal inflammatory stimulus. Hence, anti-inflammatory therapeutics could either target the primary proinflammatory signal (e.g. by limiting AGE-formation by AGE inhibitors or cross-link breakers) or the amplifyer Abeta (e.g. by limiting Abeta production by beta- or gamma-secretase inhibitors).

Characterization of an O-glycosylated plaque-associated protein from Alzheimer disease brain

In this work we characterized a 90-kDa glycoprotein from Alzheimer disease (9OAzgp) brain extracts that is recognized by the GalNAc-specific lectin from Amaranthus leucocarpus (ALL), as determined through Western blot. The 90Azgp was purified by electro-elution, and its amino acid sequence determined from peptides obtained after trypsin digestion through MALDI-TOF (Matrix-assisted laser desorption ionization-time of flight), and compared with the relative values obtained from the NCBInr (Swiss-Prot 10/01/2001) database. The 90Azgp showed 32% and 42% homology with the KIAA0310 protein from human brain and the human gastric mucin, respectively. Presence of O-glycosidically linked glycans in the proteins recognized by ALL was confirmed by inhibition of the lectin-glycoprotein interaction through hapten-inhibition assays and also by elimination of the O-glycosidically linked glycans after treatment with O-glycanase from Diplococcus pneumoniae. Electron transmission microscopy confirmed that the receptor recognized by the lectin is processed in the Golgi apparatus of AD neurons. Although the specific role of this glycoprotein has not been identified, considering that the presence of this lectin receptor co-localized with neuritic plaques and in AD sprouting neurons, it could suggest that the O-glycosyl-protein identified by the A. leucocarpus lectin participates in the pathogenesis of neurodegenerative diseases.