The use of formic acid to embellish amyloid plaque detection in Alzheimer's disease tissues misguides key observations

Macrophagic scavenging of Aβ

No abstract available.

Neurofibrillary Tangles of Aβx-40 in Alzheimer's Disease Brains

The two pathognomonic lesions in the brain of AD patients are senile plaques and intraneuronal neurofibrillary tangles (NFT). Previous studies have demonstrated that amyloid-β (Aβ) is a component of both senile plaques and NFTs, and have showed that intracellular accumulation of Aβ is toxic for cells and precedes the appearance of extracellular amyloid deposits. Here we report that there are numerous intraneuronal NFT and extraneuronal NFT immunoreactive for Aβx-40 in which there is no co-localization with tau staining suggesting the existence of two different neurodegenerating populations associated with the intracellular accumulation of either tau protein or Aβx-40 in AD.

Plaque formation and the intraneuronal accumulation of β-amyloid in Alzheimer's disease

Amyloid plaques and neurofibrillary tangles (NFTs) in the brain are the neuropathological hallmarks of Alzheimer's disease (AD). Amyloid plaques are composed of β-amyloid peptides (Aβ), while NFTs contain hyperphosphorylated tau proteins. Patients with familial AD who have mutations in the amyloid precursor protein (APP) gene have either increased production of Aβ or generate more aggregation-prone forms of Aβ. The findings of familial AD mutations in the APP gene suggest that Aβ plays a central role in the pathophysiology of AD. Aβ42, composed of 42 amino acid residues, aggregates readily and is considered to form amyloid plaque. However, the processes of plaque formation are still not well known. It is generally thought that Aβ is secreted into the extracellular space and aggregates to form amyloid plaques. Aβ as extracellular aggregates and amyloid plaques are thought to be toxic to the surrounding neurons. The intraneuronal accumulation of Aβ has more recently been demonstrated and is reported to be involved in synaptic dysfunction, cognitive impairment, and the formation of amyloid plaques in AD. We herein provide an overview of the process of the intraneuronal accumulation of Aβ and plaque formation, and discuss its implications for the pathology, early diagnosis, and therapy of AD.

Accumulation of amyloid-like Aβ1-42 in AEL (autophagy-endosomal-lysosomal) vesicles: potential implications for plaque biogenesis

Abnormal accumulation of Aβ (amyloid β) within AEL (autophagy-endosomal-lysosomal) vesicles is a prominent neuropathological feature of AD (Alzheimer's disease), but the mechanism of accumulation within vesicles is not clear. We express secretory forms of human Aβ1-40 or Aβ1-42 in Drosophila neurons and observe preferential localization of Aβ1-42 within AEL vesicles. In young animals, Aβ1-42 appears to associate with plasma membrane, whereas Aβ1-40 does not, suggesting that recycling endocytosis may underlie its routing to AEL vesicles. Aβ1-40, in contrast, appears to partially localize in extracellular spaces in whole brain and is preferentially secreted by cultured neurons. As animals become older, AEL vesicles become dysfunctional, enlarge and their turnover appears delayed. Genetic inhibition of AEL function results in decreased Aβ1-42 accumulation. In samples from older animals, Aβ1-42 is broadly distributed within neurons, but only the Aβ1-42 within dysfunctional AEL vesicles appears to be in an amyloid-like state. Moreover, the Aβ1-42-containing AEL vesicles share properties with AD-like extracellular plaques. They appear to be able to relocate to extracellular spaces either as a consequence of age-dependent neurodegeneration or a non-neurodegenerative separation from host neurons by plasma membrane infolding. We propose that dysfunctional AEL vesicles may thus be the source of amyloid-like plaque accumulation in Aβ1-42-expressing Drosophila with potential relevance for AD.

A dual magnetic resonance imaging/fluorescent contrast agent for Cathepsin-D detection

Currently there are no approved biomarkers for the pre-symptomatic diagnosis of Alzheimer's disease (AD). Cathepsin-D (Cat-D) is a lysosomal protease that is present at elevated levels in amyloid plaques and neurons in patients with AD and is also elevated in some cancers. We have developed a magnetic resonance imaging (MRI)/fluorescent contrast agent to detect Cat-D enzymatic activity. The purpose of this study was to investigate the cellular and tissue uptake of this MRI/fluorescent contrast agent. The agent consists of an MRI probe [DOTA-caged metal ion (Gd³⁺ or Tm³⁺)] and a fluorescent probe coupled to a cell-penetrating-peptide sequence by a Cat-D recognition site. The relaxivity of Gd³⁺-DOTA-CAT(cleaved) was measured in 10% heat-treated bovine serum albumin (BSA) phantoms to assess contrast efficacy at magnetic fields ranging from 0.24 mT to 9.4 T. In vitro, Tm³⁺-DOTA-CAT was added to neuronal SN56 cells over-expressing Cat-D and live-cell confocal microscropy was performed at 30 min. Tm³⁺-DOTA-CAT was also intravenously injected into APP/PS1-dE9 Alzheimer's disease mice (n = 9) and controls (n = 8). Cortical and hippocampal uptake was quantified at 30, 60 and 120 min post-injection using confocal microscopy. The liver and kidneys were also evaluated for contrast agent uptake. The relaxivity of Gd³⁺-DOTA-CAT(cleaved) was 3.3 (mM s)⁻¹ in 10% BSA at 9.4 T. In vitro, cells over-expressing Cat-D preferentially took up the contrast agent in a concentration-dependent manner. In vivo, the contrast agent effectively crossed the blood-brain barrier and exhibited a distinct time course of uptake and retention in APP/PS1-dE9 transgenic mice compared with age-matched controls. At clinical and high magnetic field strengths, Gd³⁺-DOTA-CAT produced greater T₁ relaxivity than Gd³⁺-DTPA. Tm³⁺-DOTA-CAT was taken up in a dose-dependent manner in cells over-expressing Cathepsin-D and was shown to transit the blood-brain barrier in vivo. This strategy may be useful for the in vivo detection of enzyme activity and for the diagnosis of Alzheimer's disease.

Amyloid and Alzheimer's disease: inside and out

Alzheimer's disease (AD) is poised to become the most serious healthcare issue of our generation. The leading theory of AD pathophysiology is the Amyloid Cascade Hypothesis, and clinical trials are now proceeding based on this hypothesis. Here, we review the original evidence for the Amyloid Hypothesis, which was originally focused on the extracellular deposition of beta amyloid peptides (Aβ) in large fibrillar aggregates, as well as how this theory has been extended in recent years to focus on highly toxic small soluble amyloid oligomers. We will also examine emerging evidence that Aβ may actually begin to accumulate intracellularly in lysosomes, and the role for intracellular Aβ and lysosomal dysfunction may play in AD pathophysiology. Finally, we will review the clinical implications of these findings.

Early-onset dysfunction of retrosplenial cortex precedes overt amyloid plaque formation in Tg2576 mice

A mouse model of amyloid pathology was used to first examine using a cross sectional design changes in retrosplenial cortex activity in transgenic mice aged 5, 11, 17, and 23 months. Attention focused on: (1) overt amyloid labeled with β-amyloid((1-42)) and Congo Red staining, (2) metabolic function assessed by the enzyme, cytochrome oxidase, and (3) neuronal activity as assessed indirectly by the immediate-early gene (IEG), c-Fos. Changes in cytochrome oxidase and c-Fos activity were observed in the retrosplenial cortex in Tg2576 mice as early as 5 months of age, long before evidence of plaque formation. Subsequent analyses concentrating on this early dysfunction revealed at 5 months pervasive, amyloid precursor protein (APP)-derived peptide accumulation in the retrosplenial cortex and selective afferents (anterior thalamus, hippocampus), which was associated with the observed c-Fos hyporeactivity. These findings indicate that retrosplenial cortex dysfunction occurs during early stages of amyloid production in Tg2576 mice and may contribute to cognitive dysfunction.

Mechanisms of amyloid-Beta Peptide uptake by neurons: the role of lipid rafts and lipid raft-associated proteins

A hallmark pathological feature of Alzheimer's disease (AD) is the accumulation of extracellular plaques composed of the amyloid-beta (Aβ) peptide. Thus, classically experiments were designed to examine Aβ toxicities within the central nervous system (CNS) from the extracellular space. However, a significant amount of evidence now suggests that intraneuronal accumulation of Aβ is neurotoxic and may play an important role in the disease progression of AD. One of the means by which neurons accumulate intracellular Aβ is through uptake of extracellular Aβ peptides, and this process may be a potential link between Aβ generation, synaptic dysfunction, and AD pathology. Recent studies have found that neuronal internalization of Aβ involves lipid rafts and various lipid raft-associated receptor proteins. Uptake mechanisms independent of lipid rafts have also been implicated. The aim of this paper is to summarize these findings and discuss their significance in the pathogenesis of AD.

Morphologically distinct types of amyloid plaques point the way to a better understanding of Alzheimer's disease pathogenesis

The details of the sequence of pathological events leading to neuron death in Alzheimer's disease (AD) are not known. Even the formation of amyloid plaques, one of the major histopathological hallmarks of AD, is not clearly understood; both the origin of the amyloid and the means of its deposition remain unclear. It is still widely considered, however, that amyloid plaques undergo gradual growth in the interstitial space of the brain via continual extracellular deposition of amyloid beta peptides at "seeding sites," and that these growing plaques encroach progressively on neurons and their axons and dendritic processes, eventually leading to neuronal death. Actually, histopathological evidence to support this mechanism is sparse and of uncertain validity. The fact that the amyloid deposits in AD brains that are collectively referred to as plaques are of multiple types and that each seems to have a different origin often is overlooked. We have shown experimentally that many of the so-called "diffuse amyloid plaques," which lack associated inflammatory cells, are either the result of leaks of amyloid from blood vessels at focal sites of blood-brain barrier breaches or are artifacts resulting from grazing sections through the margins of dense core plaques. In addition, we have provided experimental evidence that neuronal death via necrosis leaves a residue that takes the form of a spheroid "cloud" of amyloid, released by cell lysis, surrounding a dense core that often contains neuronal nuclear material. Support for a neuronal origin for these "dense core amyloid plaques" includes their ability to attract inflammatory cells (microglia and immigrant macrophages) and that they contain nuclear and cytoplasmic components that are somewhat resistant to proteolysis by lysosomes released during neuronal cell lysis. We discuss here the clinical and therapeutic importance of recognizing that amyloid deposition occurs both within neurons (intracellular) and in the interstitial (extracellular) space of the brain. For dense core plaques, we propose that the latter location largely follows from the former. This scenario suggests that blocking intraneuronal amyloid deposition should be a primary therapeutic target. This strategy also would be effective for blocking the gradual compromise of neuronal function resulting from this intraneuronal deposition, and the eventual death and lysis of these amyloid-burdened neurons that leads to amyloid release and the appearance of dense core amyloid plaques in the interstitium of AD brains.

Endocytic pathways mediating oligomeric Abeta42 neurotoxicity

BACKGROUND

One pathological hallmark of Alzheimer's disease (AD) is amyloid plaques, composed primarily of amyloid-beta peptide (Abeta). Over-production or diminished clearance of the 42 amino acid form of Abeta (Abeta42) in the brain leads to accumulation of soluble Abeta and plaque formation. Soluble oligomeric Abeta (oAbeta) has recently emerged to be as a likely proximal cause of AD.

RESULTS

Here we demonstrate that endocytosis is critical in mediating oAbeta42-induced neurotoxicity and intraneuronal accumulation of Abeta. Inhibition of clathrin function either with a pharmacological inhibitor, knock-down of clathrin heavy chain expression, or expression of the dominant-negative mutant of clathrin-assembly protein AP180 did not block oAbeta42-induced neurotoxicity or intraneuronal accumulation of Abeta. However, inhibition of dynamin and RhoA by expression of dominant negative mutants reduced neurotoxicity and intraneuronal Abeta accumulation. Pharmacologic inhibition of the dynamin-mediated endocytic pathway by genistein also reduced neurotoxicity.

CONCLUSIONS

These data suggest that dynamin-mediated and RhoA-regulated endocytosis are integral steps for oligomeric Abeta42-induced neurotoxicity and intraneuronal Abeta accumulation.

Accumulation of intraneuronal Abeta correlates with ApoE4 genotype

In contrast to extracellular plaque and intracellular tangle pathology, the presence and relevance of intraneuronal Aβ in Alzheimer’s disease (AD) is still a matter of debate. Human brain tissue offers technical challenges such as post-mortem delay and uneven or prolonged tissue fixation that might affect immunohistochemical staining. In addition, previous studies on intracellular Aβ accumulation in human brain often used antibodies targeting the C-terminus of Aβ and differed strongly in the pretreatments used. To overcome these inconsistencies, we performed extensive parametrical testing using a highly specific N-terminal Aβ antibody detecting the aspartate at position 1, before developing an optimal staining protocol for intraneuronal Aβ detection in paraffin-embedded sections from AD patients. To rule out that this antibody also detects the β-cleaved APP C-terminal fragment (β-CTF, C99) bearing the same epitope, paraffin-sections of transgenic mice overexpressing the C99-fragment were stained without any evidence for cross-reactivity in our staining protocol. The staining intensity of intraneuronal Aβ in cortex and hippocampal tissue of 10 controls and 20 sporadic AD cases was then correlated to patient data including sex, Braak stage, plaque load, and apolipoprotein E (ApoE) genotype. In particular, the presence of one or two ApoE4 alleles strongly correlated with an increased accumulation of intraneuronal Aβ peptides. Given that ApoE4 is a major genetic risk factor for AD and is involved in neuronal cholesterol transport, it is tempting to speculate that perturbed intracellular trafficking is involved in the increased intraneuronal Aβ aggregation in AD.

Intraneuronal beta-amyloid accumulation and synapse pathology in Alzheimer's disease

The aberrant accumulation of aggregated beta-amyloid peptides (Abeta) as plaques is a hallmark of Alzheimer's disease (AD) neuropathology and reduction of Abeta has become a leading direction of emerging experimental therapies for the disease. The mechanism(s) whereby Abeta is involved in the pathophysiology of the disease remain(s) poorly understood. Initially fibrils, and subsequently oligomers of extracellular Abeta have been viewed as the most important pathogenic form of Abeta in AD. More recently, the intraneuronal accumulation of Abeta has been described in the brain, although technical considerations and its relevance in AD have made this a controversial topic. Here, we review the emerging evidence linking intraneuronal Abeta accumulation to the development of synaptic pathology and plaques in AD, and discuss the implications of intraneuronal beta-amyloid for AD pathology, biology, diagnosis and therapy.

Intracellular accumulation of amyloid-Beta - a predictor for synaptic dysfunction and neuron loss in Alzheimer's disease

Despite of long-standing evidence that beta-amyloid (Abeta) peptides have detrimental effects on synaptic function, the relationship between Abeta, synaptic and neuron loss is largely unclear. During the last years there is growing evidence that early intraneuronal accumulation of Abeta peptides is one of the key events leading to synaptic and neuronal dysfunction. Many studies have been carried out using transgenic mouse models of Alzheimer's disease (AD) which have been proven to be valuable model systems in modern AD research. The present review discusses the impact of intraneuronal Abeta accumulation on synaptic impairment and neuron loss and provides an overview of currently available AD mouse models showing these pathological alterations.

Interferon-{gamma} differentially affects Alzheimer's disease pathologies and induces neurogenesis in triple transgenic-AD mice

Inflammatory processes, including the episodic and/ or chronic elaboration of cytokines, have been identified as playing key roles in a number of neurological disorders. Whether these activities impart a disease-resolving and/or contributory outcome depends at least in part on the disease context, stage of pathogenesis, and cellular milieu in which these factors are released. Interferon-gamma (IFNgamma) is one such cytokine that produces pleiotropic effects in the brain. It is protective by ensuring maintenance of virus latency after infection, yet deleterious by recruiting and activating microglia that secrete potentially damaging factors at sites of brain injury. Using the triple-transgenic mouse model of Alzheimer's disease (3xTg-AD), which develops amyloid and tau pathologies in a pattern reminiscent of human Alzheimer's disease, we initiated chronic intrahippocampal expression of IFNgamma through delivery of a serotype-1 recombinant adeno-associated virus vector (rAAV1-IFNgamma). Ten months of IFNgamma expression led to an increase in microglial activation, steady-state levels of proinflammatory cytokine and chemokine transcripts, and severity of amyloid-related pathology. In contrast, these rAAV1-IFNgamma-treated 3xTg-AD mice also exhibited diminished phospho-tau pathology and evidence of increased neurogenesis. Overall, IFNgamma mediates what seem to be diametrically opposed functions in the setting of AD-related neurodegeneration. Gaining an understanding as to how these apparently divergent functions are interrelated and controlled could elucidate new therapeutic strategies designed to harness the neuroprotective activity of IFNgamma.

Formic acid is essential for immunohistochemical detection of aggregated intraneuronal Abeta peptides in mouse models of Alzheimer's disease

The staining protocols so far applied to study intracellular Abeta accumulation in human tissue have been inconsistent with varying use of heat and formic acid (FA) for antigen retrieval. Microwave heat treatment has been reported to enhance the staining of intraneuronal Abeta as compared to no or enzymatic pretreatment. FA is widely used to increase the staining of plaque pathology in AD, yet the effect of FA on intraneuronal Abeta staining has been reported to be low and similar to the effect of heat or even to counteract the enhancing effect of heat pretreatment on intraneuronal Abeta immunohistochemical detection. To overcome these inconsistencies, there is a need for optimization of the staining protocol for intraneuronal Abeta detection and more knowledge is required concerning the effects of the different antigen retrieval methods. In the present work, we optimized the staining protocol for intraneuronal Abeta in paraffin-embedded sections in relation to heat and FA using four different mouse models known to accumulate intraneuronal Abeta peptides. It was found that FA is essential for the staining of highly aggregated intraneuronal Abeta peptides in AD transgenic mouse tissue.

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Abeta accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoepsilon 4 alleles. Parenchymal as well as vascular Abeta deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Abeta peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

Chronic neuron-specific tumor necrosis factor-alpha expression enhances the local inflammatory environment ultimately leading to neuronal death in 3xTg-AD mice

Inflammatory mediators, such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta, appear integral in initiating and/or propagating Alzheimer's disease (AD)-associated pathogenesis. We have previously observed a significant increase in the number of mRNA transcripts encoding the pro-inflammatory cytokine TNF-alpha, which correlated to regionally enhanced microglial activation in the brains of triple transgenic mice (3xTg-AD) before the onset of overt amyloid pathology. In this study, we reveal that neurons serve as significant sources of TNF-alpha in 3xTg-AD mice. To further define the role of neuronally derived TNF-alpha during early AD-like pathology, a recombinant adeno-associated virus vector expressing TNF-alpha was stereotactically delivered to 2-month-old 3xTg-AD mice and non-transgenic control mice to produce sustained focal cytokine expression. At 6 months of age, 3xTg-AD mice exhibited evidence of enhanced intracellular levels of amyloid-beta and hyperphosphorylated tau, as well as microglial activation. At 12 months of age, both TNF receptor II and Jun-related mRNA levels were significantly enhanced, and peripheral cell infiltration and neuronal death were observed in 3xTg-AD mice, but not in non-transgenic mice. These data indicate that a pathological interaction exists between TNF-alpha and the AD-related transgene products in the brains of 3xTg-AD mice. Results presented here suggest that chronic neuronal TNF-alpha expression promotes inflammation and, ultimately, neuronal cell death in this AD mouse model, advocating the development of TNF-alpha-specific agents to subvert AD.

Detailed immunohistochemical characterization of temporal and spatial progression of Alzheimer's disease-related pathologies in male triple-transgenic mice

Background

Several transgenic animal models genetically predisposed to develop Alzheimer's disease (AD)-like pathology have been engineered to facilitate the study of disease pathophysiology and the vetting of potential disease-modifying therapeutics. The triple transgenic mouse model of AD (3xTg-AD) harbors three AD-related genetic loci: human PS1^M146V, human APP^swe, and human tau^P301L. These mice develop both amyloid plaques and neurofibrillary tangle-like pathology in a progressive and age-dependent manner, while these pathological hallmarks are predominantly restricted to the hippocampus, amygdala, and the cerebral cortex the main foci of AD neuropathology in humans. This model represents, at present, one of the most advanced preclinical tools available and is being employed ever increasingly in the study of mechanisms underlying AD, yet a detailed regional and temporal assessment of the subtleties of disease-related pathologies has not been reported.

Methods and results

In this study, we immunohistochemically documented the evolution of AD-related transgene expression, amyloid deposition, tau phosphorylation, astrogliosis, and microglial activation throughout the hippocampus, entorhinal cortex, primary motor cortex, and amygdala over a 26-month period in male 3xTg-AD mice. Intracellular amyloid-beta accumulation is detectable the earliest of AD-related pathologies, followed temporally by phospho-tau, extracellular amyloid-beta, and finally paired helical filament pathology. Pathology appears to be most severe in medial and caudal hippocampus. While astrocytic staining remains relatively constant at all ages and regions assessed, microglial activation appears to progressively increase temporally, especially within the hippocampal formation.

Conclusion

These data fulfill an unmet need in the ever-widening community of investigators studying 3xTg-AD mice and provide a foundation upon which to design future experiments that seek to examine stage-specific disease mechanisms and/or novel therapeutic interventions for AD.

Alzheimer disease models and human neuropathology: similarities and differences

Animal models aim to replicate the symptoms, the lesions or the cause(s) of Alzheimer disease. Numerous mouse transgenic lines have now succeeded in partially reproducing its lesions: the extracellular deposits of Abeta peptide and the intracellular accumulation of tau protein. Mutated human APP transgenes result in the deposition of Abeta peptide, similar but not identical to the Abeta peptide of human senile plaque. Amyloid angiopathy is common. Besides the deposition of Abeta, axon dystrophy and alteration of dendrites have been observed. All of the mutations cause an increase in Abeta 42 levels, except for the Arctic mutation, which alters the Abeta sequence itself. Overexpressing wild-type APP alone (as in the murine models of human trisomy 21) causes no Abeta deposition in most mouse lines. Doubly (APP x mutated PS1) transgenic mice develop the lesions earlier. Transgenic mice in which BACE1 has been knocked out or overexpressed have been produced, as well as lines with altered expression of neprilysin, the main degrading enzyme of Abeta. The APP transgenic mice have raised new questions concerning the mechanisms of neuronal loss, the accumulation of Abeta in the cell body of the neurons, inflammation and gliosis, and the dendritic alterations. They have allowed some insight to be gained into the kinetics of the changes. The connection between the symptoms, the lesions and the increase in Abeta oligomers has been found to be difficult to unravel. Neurofibrillary tangles are only found in mouse lines that overexpress mutated tau or human tau on a murine tau -/- background. A triply transgenic model (mutated APP, PS1 and tau) recapitulates the alterations seen in AD but its physiological relevance may be discussed. A number of modulators of Abeta or of tau accumulation have been tested. A transgenic model may be analyzed at three levels at least (symptoms, lesions, cause of the disease), and a reading key is proposed to summarize this analysis.

Mechanisms of amyloid plaque pathogenesis

The first ultrastructural investigations of Alzheimer's disease noted the prominence of degenerating mitochondria in the dystrophic neurites of amyloid plaques, and speculated that this degeneration might be a major contributor to plaque pathogenesis. However, the fate of these organelles has received scant consideration in the intervening decades. A number of hypotheses for the formation and progression of amyloid plaques have since been suggested, including glial secretion of amyloid, somal and synaptic secretion of amyloid-beta protein from neurons, and endosomal-lysosomal aggregation of amyloid-beta protein in the cell bodies of neurons, but none of these hypotheses fully account for the focal accumulation of amyloid in plaques. In addition to Alzheimer's disease, amyloid plaques occur in a variety of conditions, and these conditions are all accompanied by dystrophic neurites characteristic of disrupted axonal transport. The disruption of axonal transport results in the autophagocytosis of mitochondria without normal lysosomal degradation, and recent evidence from aging, traumatic injury, Alzheimer's disease and transgenic mice models of Alzheimer's disease, suggests that the degeneration of these autophagosomes may lead to amyloid production within dystrophic neurites. The theory of amyloid plaque pathogenesis has thus come full circle, back to the intuitions of the very first researchers in the field.

Immunohistochemical localization of NUB1, a synphilin-1-binding protein, in neurodegenerative disorders

Recently, we showed that NUB1 is a synphilin-1-interacting protein and that NUB1, as well as synphilin-1, accumulates in Lewy bodies in Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and glial cytoplasmic inclusions in multiple system atrophy (MSA). In this study, an investigation was further conducted to elucidate the immunohistochemical localization of NUB1 in various neurodegenerative disorders. In controls, anti-NUB1 antibody weakly immunolabeled neuronal perikarya. In PD and DLB, cortical and brainstem-type Lewy bodies, pale bodies and Lewy neurites were strongly immunolabeled with anti-NUB1. In MSA, NUB1 immunoreactivity was found in the intracytoplasmic inclusions of both neuronal and oligodendroglial cells, neuronal nuclear inclusions, and swollen neurites. No NUB1 immunoreactivity was found in a variety of other neuronal or glial inclusions in other disorders, including Alzheimer's disease, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, motor neuron disease and triplet-repeat diseases. These findings indicate that the abnormal accumulation of NUB1 is specific for alpha-synucleinopathy lesions. However, yeast two-hybrid assay demonstrated that NUB1 did not directly interact with alpha-synuclein.

Intracellular amyloid-beta in Alzheimer's disease

The primal role that the amyloid-beta (Abeta) peptide has in the development of Alzheimer's disease is now almost universally accepted. It is also well recognized that Abeta exists in multiple assembly states, which have different physiological or pathophysiological effects. Although the classical view is that Abeta is deposited extracellularly, emerging evidence from transgenic mice and human patients indicates that this peptide can also accumulate intraneuronally, which may contribute to disease progression.

Small Molecule Inhibitors of Aggregation Indicate That Amyloid β Oligomerization and Fibrillization Pathways Are Independent and Distinct

Alzheimer disease is characterized by the abnormal aggregation of amyloid beta peptide into extracellular fibrillar deposits known as amyloid plaques. Soluble oligomers have been observed at early time points preceding fibril formation, and these oligomers have been implicated as the primary pathological species rather than the mature fibrils. A significant issue that remains to be resolved is whether amyloid oligomers are an obligate intermediate on the pathway to fibril formation or represent an alternate assembly pathway that may or may not lead to fiber formation. To determine whether amyloid beta oligomers are obligate intermediates in the fibrillization pathway, we characterized the mechanism of action of amyloid beta aggregation inhibitors in terms of oligomer and fibril formation. Based on their effects, the small molecules segregated into three distinct classes: compounds that inhibit oligomerization but not fibrillization, compounds that inhibit fibrillization but not oligomerization, and compounds that inhibit both. Several compounds selectively inhibited oligomerization at substoichiometric concentrations relative to amyloid beta monomer, with some active in the low nanomolar range. These results indicate that oligomers are not an obligate intermediate in the fibril formation pathway. In addition, these data suggest that small molecule inhibitors are useful for clarifying the mechanisms underlying protein aggregation and may represent potential therapeutic agents that target fundamental disease mechanisms.

Intraneuronal amyloid β42 enhanced by heating but counteracted by formic acid

Amyloid beta-protein ending at 42 (Abeta42) is the major peptide deposited in Alzheimer's disease (AD) brain. In immunocytochemical studies, formic acid treatment is used to dramatically enhance Abeta immunoreactivity. Recently, Abeta42 has been reported to accumulate in AD neurons. Since heating is known to enhance intracellular protein immunoreactivity, we used an autoclaving protocol to enhance intraneuronal Abeta42 immunoreactivity. Using this protocol, both anti-Abeta42 N-terminal and C-terminal antibodies, but not anti-Abeta40 C-terminal antibody, labeled AD neurons. Moreover, formic acid treatment counteracted such effects of autoclaving. Thus, intraneuronal Abeta42 accumulation may have been underestimated by conventional methods using formic acid only.

Cathepsin D-mediated proteolysis of apolipoprotein E: possible role in Alzheimer's disease

Proteolysis of apolipoprotein E (apoE) may be involved in the pathogenesis of Alzheimer's disease (AD). We previously identified aspartic protease(s) as possibly contributing to the proteolysis of apoE in human brain homogenates. The current study used biochemical and immunohistochemical methods to examine whether cathepsin D (catD) and cathepsin E (catE), candidate aspartic proteases, may be involved in apoE proteolysis. CatD was found to proteolyze both lipid-free recombinant full-length human apoE and lipidated human plasma full-length apoE (apoE4/dipalmitoylphosphatidylcholine-reconstituted discs). CatE was found to proteolyze lipid-free recombinant human apoE to a much greater extent than lipidated apoE. This proteolysis, as well as proteolysis of human apoE added to brain homogenates from apoE-deficient mice, was inhibited by pepstatin A (an aspartic protease inhibitor), but not by phenylmethanesulfonyl fluoride (a serine protease inhibitor). The major apoE fragment obtained with catD included the receptor-binding domain and had an apparent molecular weight similar to that found in human brain homogenates. There was little immunoreactivity for catE in AD brain tissue sections. In contrast, qualitative and quantitative analyses of immunostained sections of the frontal cortex revealed that catD and apoE are colocalized in a subset of predominantly dense-core neuritic plaques and in some neurofibrillary tangles. A positive correlation was observed between estimated duration of illness and the percentage of apoE-positive plaques that were also catD-positive. These results suggest that aspartic proteases, catD in particular, may be involved in proteolysis of apoE and perhaps contribute to the generation of apoE fragments previously implicated in AD pathology.

Intraneuronal Abeta accumulation and origin of plaques in Alzheimer's disease

Plaques are a defining neuropathological hallmark of Alzheimer's disease (AD) and the major constituent of plaques, the beta-amyloid peptide (Abeta), is considered to play an important role in the pathophysiology of AD. But the biological origin of Abeta plaques and the mechanism whereby Abeta is involved in pathogenesis have been unknown. Abeta plaques were thought to form from the gradual accumulation and aggregation of secreted Abeta in the extracellular space. More recently, the accumulation of Abeta has been demonstrated to occur within neurons with AD pathogenesis. Moreover, intraneuronal Abeta accumulation has been reported to be critical in the synaptic dysfunction, cognitive dysfunction and the formation of plaques in AD. Here we provide a historical overview on the origin of plaques and a discussion on potential biological and therapeutic implications of intraneuronal Abeta accumulation for AD.

Collagenase predigestion on paraffin sections enhances collagen immunohistochemical detection without distorting tissue morphology

Reliable immunohistochemical detection of collagen in formalin fixed, paraffin embedded tissues requires protease digestion. While these pan-proteases (pepsin, trypsin, protease K, etc.) enhance collagen detection, they also digest many other tissue proteins and produce poor cellular morphology and unrecognizable cellular structures. Balancing the conditions (protease type, concentration, incubation time and temperature) to digest some, but not all, proteins in a tissue section while optimizing collagen detection requires one to compromise improved collagen immunolabeling with adequate cellular morphology. Furthermore, optimal conditions for digesting tissue proteins to enhance collagen detection vary among tissue types and their fixation. Although brain is not typically subject to these deleterious consequences, structures such as epithelium, spermatids, stroma etc. and other tissues with complicated histology are profoundly affected. To resolve this technical dilemma, we discovered a novel use for collagenase to enhance collagen immunodetection without affecting the noncollagen proteins, thereby preserving tissue morphology. Collagenase, which is typically used in vitro for disassociation of cells, has never been used reliably on formalin fixed, paraffin embedded tissue sections. This new use of collagenase for immunohistochemistry promotes increased collagen immunolabeling, is easy to use, is versatile, and allows preservation of tissue structure that provides maximal and accurate histological information.

Amyloid Pathology and Protein Kinase C (PKC): Possible Therapeutics Effects of PKC Activators

Amyloid beta-protein (Abeta) is one of the most studied peptides in human neurodegenerative disorders. Although much has been learned about the biochemistry of this peptide, fundamental questions such as when and how the Abeta becomes pathologic remain unanswered. In this article we review the recent findings on the biology and pathology of Abeta and the role protein kinase C (PKC) plays in these processes. The potential neuroprotective role of PKC and the possible therapeutic effects of PKC activators in Alzheimer's disease (AD) will be discussed. Briefly, comments will be also addressed on the role of PKC in cell death and neurogenesis in AD.

The microglial phagocytic role with specific plaque types in the Alzheimer disease brain

Alzheimer disease (AD) involves glial inflammation associated with amyloid plaques. The role of the microglial cells in the AD brain is controversial, as it remains unclear if the microglia form the amyloid fibrils of plaques or react to them in a macrophage-phagocytic role. Also, it is not known why microglia are preferentially associated with some amyloid plaque types. This review will provide substantial evidence to support the phagocytic role of microglia in the brain as well as explain why microglia are generally associated with specific plaque types that may be explained through their unique mechanisms of formation. In summary, the data presented suggests that plaque associated microglial activation is typically subsequent to specific amyloid plaque formations in the AD brain.

Evidence linking neuronal cell death to autoimmunity in Alzheimer's disease

The catastrophic loss of cerebral neurons in Alzheimer's disease (AD) is not fully understood. Since serum proteins are known to extravasate into the brain parenchyma in AD due to blood-brain barrier (BBB) dysfunction, this study was designed to explore the possibility that neuronal cell death may be the consequence of the anomalous presence of serum proteins in the brain. As compared to age-matched, non-demented 'control' brain tissues, highly significant increases of immunoglobulins (Igs) were detected in parenchyma, which were associated with vessels in the AD brain tissues. Also, there were dramatic increases of +Ig-neurons in areas with greater parenchymal Ig reactivity. The Ig labeling extended throughout the cell, which showed neurodegenerative apoptotic features that were not observed in -Ig-neurons. Thus, the presence of +Ig-neurons in AD brains implies a critical link between the faulty BBB and neuronal death through an autoimmune mechanism.