Alzheimer's Aß42 and Aß40 form mixed oligomers with direct molecular interactions.

Formation of Aß oligomers and fibrils plays a central role in the pathogenesis of Alzheimer's disease. There are two major forms of Aß in the brain: Aß42 and Aß40. Aß42 is the major component of the amyloid plaques, but the overall abundance of Aß40 is several times that of Aß42. In vitro experiments show that Aß42 and Aß40 affect each other's aggregation. In mouse models of Alzheimer's disease, overexpression of Aß40 has been shown to reduce the plaque pathology, suggesting that Aß42 and Aß40 also interact in vivo. Here we address the question of whether Aß42 and Aß40 interact with each other in the formation of oligomers using electron paramagnetic resonance (EPR) spectroscopy. When the Aß42 oligomers were formed using only spin-labeled Aß42, the dipolar interaction between spin labels that are within 20 Å range broadened the EPR spectrum and reduced its amplitude. Oligomers formed with a mixture of spin-labeled Aß42 and wild-type Aß42 gave an EPR spectrum with higher amplitude due to weakened spin-spin interactions, suggesting molecular mixing of labeled and wild-type Aß42. When spin-labeled Aß42 and wild-type Aß40 were mixed to form oligomers, the resulting EPR spectrum also showed reduced amplitude, suggesting that wild-type Aß40 can also form oligomers with spin-labeled Aß42. Therefore, our results suggest that Aß42 and Aß40 form mixed oligomers with direct molecular interactions. Our results point to the importance of investigating Aß42-Aß40 interactions in the brain for a complete understanding of Alzheimer's pathogenesis and therapeutic interventions.

CRANAD-28: A Robust Fluorescent Compound for Visualization of Amyloid Beta Plaques.

CRANAD-28, a difluoroboron curcumin analogue, has been demonstrated in earlier reports to successfully label amyloid beta (Aß) plaques for imaging both ex vivo and in vivo. CRANAD-28's imaging brightness, ability to penetrate the blood brain barrier, and low toxicity make the compound a potentially potent imaging tool in Alzheimer's research. In this study, the Aß-labeling ability of CRANAD-28 was investigated in further detail using histological staining to assess different criteria, including stained Aß plaque brightness, Aß plaque size, and Aß plaque number count. The results of this study demonstrated CRANAD-28 to be superior across all criteria assessed. Furthermore, CRANAD-28 and IBA-1 antibody were used to label Aß-plaques and microglia respectively. Statistical analysis with Spearman regression revealed a statistically significant negative correlation between the size of labeled Aß plaques and surrounding microglia density. This finding provides interesting insight into Aß plaque and microglia dynamism in AD pathology and corroborates the findings of previous studies. In addition, we found that CRANAD-28 provided distinct spectral signatures for Aßs in the core and periphery of the plaques. Based on the study's results, CRANAD-28 could be considered as an alternative standard for imaging Aß-plaques in future research studies.

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 Aß 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-Αß 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-Αß complex also designates apoE amyloidogenic regions as important binding sites for oligomeric Αß; taking an important step forward in the field of Alzheimer's anti-aggregation drug development.

Doublecortin expression in CD8+ T-cells and microglia at sites of amyloid-ß plaques: A potential role in shaping plaque pathology?

INTRODUCTION: One characteristic of Alzheimer's disease is the formation of amyloid-ß plaques, which are typically linked to neuroinflammation and surrounded by inflammatory cells such as microglia and infiltrating immune cells. METHODS: Here, we describe nonneurogenic doublecortin (DCX) positive cells, DCX being generally used as a marker for young immature neurons, at sites of amyloid-ß plaques in various transgenic amyloid mouse models and in human brains with plaque pathology. RESULTS: The plaque-associated DCX+ cells were not of neurogenic identity, instead most of them showed coexpression with markers for microglia (ionized calcium-binding adapter molecule 1) and for phagocytosis (CD68 and TREM2). Another subpopulation of plaque-associated DCX+ cells was negative for ionized calcium-binding adapter molecule 1 but was highly positive for the pan-leukocyte marker CD45. These hematopoietic cells were identified as CD3-and CD8-positive and CD4-negative T-cells. DISCUSSION: Peculiarly, the DCX+/ionized calcium-binding adapter molecule 1+ microglia and DCX+/CD8+ T-cells were closely attached, suggesting that these two cell types are tightly interacting and that this interaction might shape plaque pathology.

Protective properties of lysozyme on ß-amyloid pathology: implications for Alzheimer disease.

The hallmarks of Alzheimer disease are amyloid-ß plaques and neurofibrillary tangles accompanied by signs of neuroinflammation. Lysozyme is a major player in the innate immune system and has recently been shown to prevent the aggregation of amyloid-ß1-40 in vitro. In this study we found that patients with Alzheimer disease have increased lysozyme levels in the cerebrospinal fluid and lysozyme co-localized with amyloid-ß in plaques. In Drosophila neuronal co-expression of lysozyme and amyloid-ß1-42 reduced the formation of soluble and insoluble amyloid-ß species, prolonged survival and improved the activity of amyloid-ß1-42 transgenic flies. This suggests that lysozyme levels rise in Alzheimer disease as a compensatory response to amyloid-ß increases and aggregation. In support of this, in vitro aggregation assays revealed that lysozyme associates with amyloid-ß1-42 and alters its aggregation pathway to counteract the formation of toxic amyloid-ß species. Overall, these studies establish a protective role for lysozyme against amyloid-ß associated toxicities and identify increased lysozyme in patients with Alzheimer disease. Therefore, lysozyme has potential as a new biomarker as well as a therapeutic target for Alzheimer disease.

Increased misfolding and truncation of tau in APP/PS1/tau transgenic mice compared to mutant tau mice.

Neurofibrillary degeneration in transgenic models of tauopathies has been observed to be enhanced when these models are crossed with transgenic models developing an Aß pathology. The mechanisms leading to this enhanced tau pathology are not well understood. We have performed a detailed analysis of tau misprocessing in a new transgenic mouse model combining APP, PS1 and tau mutations (5xFAD×Tg30 mice) by comparison with littermates expressing only a FTD mutant tau (Tg30 mice). These 5xFAD×Tg30 mice showed a more severe deficient motor phenotype than Tg30 mice and developed with age a dramatically accelerated NFT load in the brain compared to Tg30 mice. Insoluble tau in 5xFAD×Tg30 mice compared to insoluble tau in Tg30 mice showed increased phosphorylation, enhanced misfolding and truncation changes mimicking more closely the post-translational changes characteristic of PHF-tau in Alzheimer's disease. Endogenous wild-type mouse tau was recruited at much higher levels in insoluble tau in 5xFAD×Tg30 than in Tg30 mice. Extracellular amyloid load, Aß40 and Aß42, ß-CTFs and ß-CTF phosphorylation levels were lower in 5xFAD×Tg30 mice than in 5xFAD mice. Despite this reduction of Aß, a significant hippocampal neuronal loss was observed in 5xFAD×Tg30 but not in 5xFAD mice indicating its closer association with increased tau pathology. This 5xFAD×Tg30 model thus mimics more faithfully tau pathology and neuronal loss observed in AD and suggests that additional post-translational changes in tau and self-recruitment of endogenous tau drive the enhanced tau pathology developing in the presence of Aß pathology.

Atomic force microscopy to study molecular mechanisms of amyloid fibril formation and toxicity in Alzheimer's disease.

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by dementia and memory loss for which no cure or effective prevention is currently available. Neurodegeneration in AD is linked to formation of amyloid plaques found in brain tissues of Alzheimer's patients during post-mortem examination. Amyloid plaques are composed of amyloid fibrils and small oligomers - insoluble protein aggregates. Although amyloid plaques are found on the neuronal cell surfaces, the mechanism of amyloid toxicity is still not well understood. Currently, it is believed that the cytotoxicity is a result of the nonspecific interaction of small soluble amyloid oligomers (rather than longer fibrils) with the plasma membrane. In recent years, nanotechnology has contributed significantly to understanding the structure and function of lipid membranes and to the study of the molecular mechanisms of membrane-associated diseases. We review the current state of research, including applications of the latest nanotechnology approaches, on the interaction of lipid membranes with the amyloid-ß (Aß) peptide in relation to amyloid toxicity. We discuss the interactions of Aß with model lipid membranes with a focus to demonstrate that composition, charge and phase of the lipid membrane, as well as lipid domains and rafts, affect the binding of Aß to the membrane and contribute to toxicity. Understanding the role of the lipid membrane in AD at the nanoscale and molecular level will contribute to the understanding of the molecular mechanism of amyloid toxicity and may aid into the development of novel preventive strategies to combat AD.

Mechanism of amyloid plaque formation suggests an intracellular basis of Abeta pathogenicity.

The formation of extracellular amyloid plaques is a common patho-biochemical event underlying several debilitating human conditions, including Alzheimer's disease (AD). Considerable evidence implies that AD damage arises primarily from small oligomeric amyloid forms of Abeta peptide, but the precise mechanism of pathogenicity remains to be established. Using a cell culture system that reproducibly leads to the formation of Alzheimer's Abeta amyloid plaques, we show here that the formation of a single amyloid plaque represents a template-dependent process that critically involves the presence of endocytosis- or phagocytosis-competent cells. Internalized Abeta peptide becomes sorted to multivesicular bodies where fibrils grow out, thus penetrating the vesicular membrane. Upon plaque formation, cells undergo cell death and intracellular amyloid structures become released into the extracellular space. These data imply a mechanism where the pathogenic activity of Abeta is attributed, at least in part, to intracellular aggregates.

Cross-seeding effects of amyloid ß-protein and α-synuclein.

Amyloid ß-protein (Aß) and α-synuclein (αS) are the primary components of amyloid plaques and Lewy bodies (LBs), respectively. Previous in vitro and in vivo studies have suggested that interactions between Aß and αS are involved in the pathogenesis of Alzheimer's disease and LB diseases. However, the seeding effects of their aggregates on their aggregation pathways are not completely clear. To investigate the cross-seeding effects of Aß and αS, we examined how sonicated fibrils or cross-linked oligomers of Aß40, Aß42, and αS affected their aggregation pathways using thioflavin T(S) assay and electron microscopy. Fibrils and oligomers of Aß40, Aß42, and αS acted as seeds, and affected the aggregation pathways within and among species. The seeding effects of αS fibrils were higher than those of Aß40 and Aß42 fibrils in the Aß40 and Aß42 aggregation pathways, respectively. We showed that Aß and αS acted as seeds and affected each other's aggregation pathways in vitro, which may contribute to our understanding of the molecular mechanisms of interactions between Alzheimer's disease and LB diseases pathologies.

Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer's mice hippocampus.

Dystrophic neurites associated with amyloid plaques precede neuronal death and manifest early in Alzheimer's disease (AD). In this work we have characterized the plaque-associated neuritic pathology in the hippocampus of young (4- to 6-month-old) PS1(M146L)/APP(751SL) mice model, as the initial degenerative process underlying functional disturbance prior to neuronal loss. Neuritic plaques accounted for almost all fibrillar deposits and an axonal origin of the dystrophies was demonstrated. The early induction of autophagy pathology was evidenced by increased protein levels of the autophagosome marker LC3 that was localized in the axonal dystrophies, and by electron microscopic identification of numerous autophagic vesicles filling and causing the axonal swellings. Early neuritic cytoskeletal defects determined by the presence of phosphorylated tau (AT8-positive) and actin-cofilin rods along with decreased levels of kinesin-1 and dynein motor proteins could be responsible for this extensive vesicle accumulation within dystrophic neurites. Although microsomal Aß oligomers were identified, the presence of A11-immunopositive Aß plaques also suggested a direct role of plaque-associated Aß oligomers in defective axonal transport and disease progression. Most importantly, presynaptic terminals morphologically disrupted by abnormal autophagic vesicle buildup were identified ultrastructurally and further supported by synaptosome isolation. Finally, these early abnormalities in axonal and presynaptic structures might represent the morphological substrate of hippocampal dysfunction preceding synaptic and neuronal loss and could significantly contribute to AD pathology in the preclinical stages.

Gerstmann-Sträussler-Scheinker disease.

Gerstmann-Sträussler-Scheinker (GSS) is a slowly progressive hereditary autosomal dominant disease (OMIM: 137440) and the first human transmissible spongiform encephalopathy (TSE) in which a mutation in a gene encoding for prion protein (PrP) was discovered. The first "H" family had been known by the Viennese neuropsychiatrists since the XXth century and was reported by Gerstmann, Sträussler and Scheinker in 1936. In this chapter we present the clinical, neuropathological and molecular data on GSS with the mutations in the PRNP gene: at codons 102, 105, 117, 131, 145, 187, 198, 202, 212, 217 and 232. In several families with GSS the responsible mutations are unknown.

ß-Secretase-1 elevation in aged monkey and Alzheimer's disease human cerebral cortex occurs around the vasculature in partnership with multisystem axon terminal pathogenesis and ß-amyloid accumulation.

Alzheimer's disease (AD) is the most common dementia-causing disorder in the elderly; it may be related to multiple risk factors, and is characterized pathologically by cerebral hypometabolism, paravascular ß-amyloid peptide (Aß) plaques, neuritic dystrophy, and intra-neuronal aggregation of phosphorylated tau. To explore potential pathogenic links among some of these lesions, we examined ß-secretase-1 (BACE1) alterations relative to Aß deposition, neuritic pathology and vascular organization in aged monkey and AD human cerebral cortex. Western blot analyses detected increased levels of BACE1 protein and ß-site-cleavage amyloid precursor protein C-terminal fragments in plaque-bearing human and monkey cortex relative to controls. In immunohistochemistry, locally elevated BACE1 immunoreactivity (IR) occurred in AD but not in control human cortex, with a trend for increased overall density among cases with greater plaque pathology. In double-labeling preparations, BACE1 IR colocalized with immunolabeling for Aß but not for phosphorylated tau. In perfusion-fixed monkey cortex, locally increased BACE1 IR co-existed with intra-axonal and extracellular Aß IR among virtually all neuritic plaques, ranging from primitive to typical cored forms. This BACE1 labeling localized to swollen/sprouting axon terminals that might co-express one or another neuronal phenotype markers (GABAergic, glutamatergic, cholinergic, or catecholaminergic). Importantly, these BACE1-labeled dystrophic axons resided near to or in direct contact with blood vessels. These findings suggest that plaque formation in AD or normal aged primates relates to a multisystem axonal pathogenesis that occurs in partnership with a potential vascular or metabolic deficit. The data provide a mechanistic explanation for why senile plaques are present preferentially near the cerebral vasculature.

Morphological alterations to neurons of the amygdala and impaired fear conditioning in a transgenic mouse model of Alzheimer's disease.

Patients with Alzheimer's disease (AD) suffer from impaired memory and emotional disturbances, the pathogenesis of which is not entirely clear. In APP/PS1 transgenic mice, a model of AD in which amyloid beta (Abeta) accumulates in the brain, we have examined neurons in the lateral nucleus of the amygdala (LA), a brain region crucial to establish cued fear conditioning. We found that although there was no neuronal loss in this region and Abeta plaques only occupy less than 1% of its volume, these mice froze for shorter times after auditory fear conditioning when compared to their non-transgenic littermates. We performed a three-dimensional analysis of projection neurons and of thousands of dendritic spines in the LA. We found changes in dendritic tree morphology and a substantial decrease in the frequency of large spines in plaque-free neurons of APP/PS1 mice. We suggest that these morphological changes in the neurons of the LA may contribute to the impaired auditory fear conditioning seen in this AD model.

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.

Unobstructed Multiscale Imaging of Tissue Sections for Ultrastructural Pathology Analysis by Backscattered Electron Scanning Microscopy.

Ultrastructural analysis of healthy, diseased, or experimental tissues is essential in diagnostic and investigative pathology. Evaluation of large tissue areas with suborganelle resolution is challenging because biological structures ranging from several millimeters to nanometers in size need to be identified and imaged while maintaining context over multiple scales. Imaging with field emission scanning electron microscopes (FE-SEMs) is uniquely suited for this task. We describe an efficient workflow for the preparation and unobstructed multiscale imaging of tissue sections with backscattered electron scanning electron microscopy (BSE-SEM) for applications in ultrastructural pathology. We demonstrate that a diverse range of tissues, processed by conventional electron microscopy protocols and avoiding the use of mordanting agents, can be imaged on standard glass slides over multiple scales, from the histological to the ultrastructural level, without any visual obstructions. Our workflow takes advantage of the very large scan fields possible with modern FE-SEMs that allow for the acquisition of wide-field overview images which can be explored at the ultrastructural level by digitally zooming into the images. Examples from applications in pulmonary research and neuropathology demonstrate the versatility and efficiency of this method. This BSE-SEM-based multiscale imaging procedure promises to substantially simplify and accelerate ultrastructural tissue analysis in pathology.

Immunoelectron microscopy and mass spectrometry for classification of amyloid deposits.

Amyloidosis is a shared name for several rare, complex and serious diseases caused by extra-cellular deposits of different misfolded proteins. Accurate characterization of the amyloid protein is essential for patient care. Immunoelectron microscopy (IEM) and laser microdissection followed by tandem mass spectrometry (LMD-MS) are new gold standards for molecular subtyping. Both methods perform superiorly to immunohistochemistry, but their complementarities, strengths and weaknesses across amyloid subtypes and organ biopsy origin remain undefined. Therefore, we performed a retrospective study of 106 Congo Red positive biopsies from different involved organs; heart, kidney, lung, gut mucosa, skin and bone marrow. IEM, performed with gold-labelled antibodies against kappa light chains, lambda light chains, transthyretin and amyloid A, identified specific staining of amyloid fibrils in 91.6%; in six biopsies amyloid fibrils were not identified, and in two, the fibril subtype could not be established. LMD-MS identified amyloid protein signature in 98.1%, but in nine the amyloid protein could not be clearly identified. MS identified protein subtype in 89.6%. Corresponding specificities ranged at organ level from 94-100%. Concordance was 89.6-100% for different amyloid subtypes. Importantly, combined use of both methods increased the diagnostic classification to 100%. Some variety in performances at organ level was observed.

Dengzhan Shengmai capsules and their active component scutellarin prevent cognitive decline in APP/PS1 mice by accelerating Aß aggregation and reducing oligomers formation.

There is currently no effective treatment to prevent the progress of Alzheimer's disease (AD). The traditional Chinese herbs Dengzhan Shengmai (DZSM) capsules and their active component scutellarin possess multiple effects and are clinically used for the treatment of cerebrovascular diseases. Scutellarin has been reported to affect Aß aggregation. However, the effects of DZSM capsules on AD remain unknown. Through in vivo experiments, our study proved that the alleviating effects of DZSM capsules on cognitive deficits of AD mice were due to the role of scutellarin, which up-regulated low toxic amyloid plaques and down-regulated highly toxic soluble Aß42 and Aß40 levels in cortex. In vitro, we confirmed scutellarin's role in accelerating transforming Aß42 monomers into high-molecular-mass aggregates by biochemical assays, which supported the results observed in drug-treated APP/PS1 mice. In detail, the 1:10 ratio of scutellarin/Aß42 mixtures promoted production of large ß-sheet-rich fibrils whereas the 1:1 ratio promoted production of protofibrils. In addition, the binding between scutellarin and Aß monomers was quantified by microscale thermophoresis test and the apparent dissociation constant (Kd) was 1284.4 ±â€¯238.8 µM. What's more, binding regions between scutellarin and Aß fibrils were predicted by computational docking models and scutellarin might bind parallel to the long axis of Aß42 fibrils targeting hydrophobic grooves at residues 35-36 or 39. In conclusion, DZSM capsules protected against cognitive defects of AD through scutellarin-mediated acceleration of Aß aggregation into fibrils or protofibrils and reduction of soluble Aß oligomers, thus suggesting potential clinical applications of DZSM capsules and scutellarin in the treatment of AD.

Bis(ethylmaltolato)oxidovanadium(iv) inhibited the pathogenesis of Alzheimer's disease in triple transgenic model mice.

Vanadium compounds have been reported to mimic the anti-diabetes effects of insulin on rodent models, but their effects on Alzheimer's disease (AD) have rarely been explored. In this paper, 9-month-old triple transgenic AD model mice (3×Tg-AD) received bis(ethylmaltolato)oxidovanadium(iv) (BEOV) at doses of 0.2 mmol L-1 (68.4 µg mL-1) and 1.0 mmol L-1 (342 µg mL-1) for 3 months. BEOV at both doses was found to improve contextual memory and spatial learning in AD mice. It also improved glucose metabolism and protected neuronal synapses in the AD brain, as evidenced respectively by 18F-labeled fluoro-deoxyglucose positron emission tomography (18F-FDG-PET) scanning and by transmission electron microscopy. Inhibitory effects of BEOV on ß-amyloid (Aß) plaques and neuronal impairment in the cortex and hippocampus of fluorescent AD mice were visualized three-dimensionally by applying optical clearing technology to brain slices before confocal laser scanning microscopy. Western blot analysis semi-quantitatively revealed the altered levels of Aß42 in the brains of wildtype, AD, and AD treated with 0.2 and 1.0 mmol L-1 BEOV mice (70.3%, 100%, 83.2% and 56.8% in the hippocampus; 82.4%, 100%, 66.9% and 42% in the cortex, respectively). The mechanism study showed that BEOV increased the expression of peroxisome proliferator-activated receptor γ (PPARγ) (140%, 100%, 142% and 160% in the hippocampus; 167%, 100%, 124% and 133% in the cortex) to inactivate the JAK2/STAT3/SOCS-1 pathway and to block the amyloidogenesis cascade, thus attenuating Aß-induced insulin resistance in AD models. BEOV also reduced protein tyrosine phosphatase 1B (PTP1B) expression (74.8%, 100%, 76.5% and 53.8% in the hippocampus; 71.8%, 100%, 94.2% and 81.8% in cortex) to promote insulin sensitivity and to stimulate the PI3K/Akt/GSK3ß pathway, subsequently reducing tau hyperphosphorylation (phosphorylated tau396 levels were 51.1%, 100%, 56.1% and 50.2% in the hippocampus; 22.2%, 100%, 36.1%, and 24% in the cortex). Our results suggested that BEOV reduced the pathological hallmarks of AD by targeting the pathways of PPARγ and PTP1B in 3×Tg AD mice.

Triple-transgenic Alzheimer's disease mice exhibit region-specific abnormalities in brain myelination patterns prior to appearance of amyloid and tau pathology.

Alzheimer's disease (AD) is a progressively debilitating brain disorder pathologically defined by extracellular amyloid plaques, intraneuronal neurofibrillary tangles, and synaptic disintegrity. AD has not been widely considered a disease of white matter, but more recent evidence suggests the existence of abnormalities in myelination patterns and myelin attrition in AD-afflicted human brains. Herein, we demonstrate that triple-transgenic AD (3xTg-AD) mice, which harbor the human amyloid precursor protein Swedish mutant transgene, presenilin knock-in mutation, and tau P301L mutant transgene, exhibit significant region-specific alterations in myelination patterns and in oligodendrocyte marker expression profiles at time points preceding the appearance of amyloid and tau pathology. These immunohistochemical signatures are coincident with age-related alterations in axonal and myelin sheath ultrastructure as visualized by comparative electron microscopic examination of 3xTg-AD and nontransgenic mouse brain tissue. Overall, these findings indicate that 3xTg-AD mice represent a viable model in which to examine mechanisms underlying AD-related myelination and neural transmission defects that occur early during presymptomatic stages of the disease process.

Ultrastructural study of florid plaques in variant Creutzfeldt-Jakob disease: a comparison with amyloid plaques in kuru, sporadic Creutzfeldt-Jakob disease and Gerstmann-Sträussler-Scheinker disease.

BACKGROUND: Although the histological features of the amyloid plaques in variant Creutzfeldt-Jakob disease (vCJD) are distinct from those in other forms of prion disease [kuru, sporadic Creutzfeldt-Jakob disease (sCJD) and Gerstmann-Sträussler-Scheinker disease (GSS)], their ultrastructural features have only been described in a single case report. AIMS: To study vCJD plaques systematically and compare them with plaques in kuru, sCJD, GSS and Alzheimer disease (AD). METHODS: Amyloid plaques were studied by transmission electron microscopy and image analysis in five cases of vCJD, three cases of GSS, two cases of sCJD, one case of kuru and five cases of AD. Immunohistochemistry was performed on paraffin sections from one case of vCJD, two cases of GSS, one case of kuru and two cases of sCJD. RESULTS: The florid plaques in vCJD were either compact or more diffuse; in both forms, the radiating fibrils were organized into thick 'tongues', in contrast to kuru plaques. Dystrophic neurites (DNs) containing lysosomal electron-dense bodies or vesicles surrounded florid plaques. Microglial cells were found within florid plaques; occasional amyloid fibrils were identified in membrane-bound pockets of microglial cells. In vCJD, there was significant tau immunoreactivity in DNs around florid plaques while, in sCJD, GSS and kuru, minimal tau immunoreactivity was observed around plaques. CONCLUSIONS: The ultrastructure of the florid plaques and DNs in vCJD is more reminiscent of neuritic plaques in AD than kuru or multicentric plaques. These findings may reflect differences both in the strains of the transmissible agents responsible for these disorders and in host factors.