Deposition Of Abeta Peptides Research Articles

Isoglutaminyl cyclase contributes to CCL2-driven neuroinflammation in Alzheimer's disease.

The brains of Alzheimer’s disease (AD) patients are characterized by deposits of Abeta peptides and by accompanying chronic inflammation. Here, we provide evidence that the enzyme isoglutaminyl cyclase (isoQC) is a novel factor contributing to both aspects of AD pathology. Two putative substrates of isoQC, N-truncated Abeta peptides and the monocyte chemoattractant chemokine CCL2, undergo isoQC-catalyzed pyroglutamate (pGlu) modification. This triggers Abeta aggregation and facilitates the biological activity of CCL2, which collectively results in the formation of high molecular weight Abeta aggregates, glial cell activation, neuroinflammation and neuronal cell death. In mouse brain, we found isoQC to be neuron-specifically expressed in neocortical, hippocampal and subcortical structures, localized to the endoplasmic reticulum and Golgi apparatus as well as co-expressed with its substrate CCL2. In aged APP transgenic Tg2576 mice, both isoQC and CCL2 mRNA levels are up-regulated and isoQC and CCL2 proteins were found to be co-induced in Abeta plaque-associated reactive astrocytes. Also, in mouse primary astrocyte culture, a simultaneous up-regulation of isoQC and CCL2 expression was revealed upon Abeta and pGlu-Abeta stimulation. In brains of AD patients, the expression of isoQC and CCL2 mRNA and protein is up-regulated compared to controls and correlates with pGlu-Abeta load and with the decline in mini-mental state examination. Our observations provide evidence for a dual involvement of isoQC in AD pathogenesis by catalysis of pGlu-Abeta and pGlu-CCL2 formation which mutually stimulate inflammatory events and affect cognition. We conclude that isoQC inhibition may target both major pathological events in the development of AD.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-015-1395-2) contains supplementary material, which is available to authorized users.

P4-294: Expression of α7 nicotinic acetylcholine receptor by vascular smooth muscle cells facilitates Abeta peptide deposition and promotes cerebrovascular amyloid angiopathy

P4-294: Expression of α7 nicotinic acetylcholine receptor by vascular smooth muscle cells facilitates Abeta peptide deposition and promotes cerebrovascular amyloid angiopathy

Les lésions de la maladie d’Alzheimer. Perspectives thérapeutiques ?

The brain lesions associated with Alzheimer's disease are caused by extracellular accumulation of Abeta peptide and intracellular accumulation of tau protein. Abeta peptide makes the core of the senile plaque (the "focal deposit"); it is also present in the extracellular "diffuse deposits" and in the vessel walls. Neurofibrillary tangles, and neuropil threads are composed of hyperphosphorylated tau that also accumulates in the processes of the corona of the senile plaque. The Abeta deposits first involve the neocortex, while the tau pathology is initially found in the hippocampal region. Abeta deposits first occur in the neocortex, while intracellular tau accumulation mainly affect the hippocampal region. Abeta peptide deposits are initially found in all the neocortical areas, then involve the hippocampus and the subcortical nuclei. Tau lesions successively involve the hippocampal regions, multi- and uni-modal areas and finally the primary cortices in stereotyped stages. Mutations of APP, the precursor of Abeta peptide, cause autosomal dominant familial Alzheimer disease, suggesting that a cascade of reactions link Abeta overproduction, tau pathology and the clinical phenotype. Transgenic mice bearing the mutated human APP gene (APP mice) develop A deposits. Systemic injection of Abeta peptide prevents the deposition of Abeta peptide. However, a clinical trial had to be interrupted when meningoencephalitis occurred in a significant proportion of treated patients. Post mortem studies showed a relative scarcity of Abeta deposits. Forthcoming immunotherapy studies should soon show whether the prevention of Abeta deposition interrupts disease progression.

Angiopathie amyloïde cérébrale

Cerebral amyloid angiopathy is characterised by the presence of protein deposits in the wall of the cerebral vessels. Sporadic forms with deposits of Abeta peptide are the most frequent. The diagnosis of cerebral amyloid angiopathy is only certain when amyloid deposits can be visualized on cerebral tissue by biopsy, that appears in most circumstances to carry too many risks for the expected benefits, or post mortem. The clinical diagnostic criteria are advanced age, morphology of the intracerebral hematomas, occurrence of several episodes of intracerebral haemorrhages and presence of dementia. Recent progresses in the field of MRI make the diagnosis of cerebral amyloid angiopathy easier and more accurate. MRI should be more frequently performed in aged patients.

Dual Binding Site Acetylcholinesterase Inhibitors: Potential New Disease-Modifying Agents for AD

The therapeutic potential of acetylcholinesterase (AChE) inhibitors has been strengthened recently by evidence showing that besides their role in cognitive function, they might contribute to slow down the neurodegeneration in Alzheimer's disease (AD) patients. It is known that AChE exerts secondary noncholinergic functions, related to its peripheral anionic site, in cell adhesion and differentiation, and recent findings also support its role in mediating the processing and deposition of beta-amyloid (Abeta) peptide. AChE is one of the proteins that colocalizes with Abeta peptide deposits in the brain of AD patients and promotes Abeta fibrillogenesis by forming stable AChEA beta complexes. Additionally, it has also been postulated that AChE binds through its peripheral site to the Abeta nonamyloidogenic form and acts as a pathological chaperone inducing a conformational transition to the amyloidogenic form (Inestrosa et al., 1996; Bartolini et al., 2003). Anew series of dual binding site AChE inhibitors has been designed and synthesized as new potent AChE inhibitors, which might simultaneously alleviate cognitive deficits and behave as disease-modifying agents by inhibiting Abeta peptide aggregation through binding to both catalytic and peripheral sites of the enzyme.

The Dualistic Nature of Immune Modulation In Alzheimers Disease: Lessons from the Transgenic Models

There is extensive evidence that changes in immune system activation accompany the pathological changes of Alzheimer's disease (AD), but a mechanistic understanding of how the immune system actually participates in disease pathogenesis is still largely lacking. Because of the complexity of the immunological response, and the difficulty in identifying the key molecular players that underlie any given immunological response, expanding our understanding of the immunological response in AD beyond its descriptive stages has not been a straightforward exercise. The development of transgenic animals that form deposits of Abeta peptide in their brains has provided an unexpected dividend to those interested in the immunological response characterizing AD. Several of these transgenic models develop structures greatly resembling neuritic plaques, a hallmark feature of AD brain that is also a focal point of the immunological response occurring in AD. Genetic and pharmacological manipulation of these Abeta-depositing transgenic mice is providing some intriguing and unexpected insights into the role of innate and adaptive immune mechanisms in the pathogenesis of AD. This review will discuss immunological perspectives that have arisen from research using Abeta-depositing transgenic mice, and place these perspectives in the context of epidemiological and genetic studies that have previously suggested a role for the immune system in AD. The emerging story affirms the likely role of innate and adaptive immune mechanisms in the pathogenesis of AD, but provides a cautionary note as to the difficulties that are likely to face potential immunomodulatory therapies due to the dualistic beneficial and detrimental roles that immune mechanisms appear to play in AD.

BACE1 Cytoplasmic Domain Interacts with the Copper Chaperone for Superoxide Dismutase-1 and Binds Copper

The amyloidogenic pathway leading to the production and deposition of Abeta peptides, major constituents of Alzheimer disease senile plaques, is linked to neuronal metal homeostasis. The amyloid precursor protein binds copper and zinc in its extracellular domain, and the Abeta peptides also bind copper, zinc, and iron. The first step in the generation of Abeta is cleavage of amyloid precursor protein by the aspartic protease BACE1. Here we show that BACE1 interacts with CCS (the copper chaperone for superoxide dismutase-1 (SOD1)) through domain I and the proteins co-immunoprecipitate from rat brain extracts. We have also been able to visualize the co-transport of membranous BACE1 and soluble CCS through axons. BACE1 expression reduces the activity of SOD1 in cells consistent with direct competition for available CCS as overexpression of CCS restores SOD1 activity. Finally, we demonstrate that the twenty-four residue C-terminal domain of BACE1 binds a single Cu(I) atom with high affinity through cysteine residues.

Biological Significance of Isoaspartate and Its Repair System

Isomerization of L-aspartate and deamidation of L-asparagine in proteins or peptides dominantly give rise to L-isoaspartate by a non-enzymatic reaction via succinimide as a intermediate under physiological conditions. Isoaspartates have been identified in a variety of cellular proteins in vivo as well as pathologically deposited proteins in neurodegenerative brain tissue. We described here that the formation of isoaspartate is enhanced in amyloid-beta (Abeta) peptides in Alzheimer's disease (AD). Specific antibodies recognizing isoaspartate of Abeta revealed that isomerized Abeta peptides were deposited in senile plaques as well as amyloid-bearing vessels. Moreover, it was revealed that Abeta peptides, isomerized at position 7 or 23, were differentially deposited in senile plaques and vascular amyloids in AD brains. In vitro experiments showed that the modification at position 23 greatly enhanced the aggregation of Abeta. Furthermore, systematic proline substitution analyses revealed that the beta-turn structure at positions 22 and 23 of Abeta42 plays a crucial role in the aggregation and neurotoxicity of Abeta peptides. It is suggested that spontaneous isomerization at position 23 induces the conformational change to form a beta-turn at position 23, which plays a pathogenic role in the deposition of Abeta peptides in sporadic AD. Protein L-isoaspartyl methyltransferase (PIMT) is a putative protein repair enzyme, which converts L-isoaspartyl residues in damaged proteins to normal L-aspartyl residues. PIMT-deficient mice manifested neurodegenerative changes concomitant with the accumulation of L-isoaspartate in the brain. We discuss here the pathological implications of the formation of isoaspartate in damaged proteins during neurodegeneration in model mice and AD.

Role of Formyl Peptide Receptor–Like 1 (FPRL1/FPR2) in Mononuclear Phagocyte Responses in Alzheimer Disease

Alzheimer disease (AD) is the most common neurodegenerative disease, affecting approx 4 million people in the United States in the year 2000 alone. Amyloid beta (Abeta) deposition, activated glial cells, and neuritic degeneration are the characteristic features of AD. Although the precise cause of AD has yet to be determined, a bulk of evidence suggests that inflammatory responses elicited by elevated Abeta peptides play an important role in the pathogenic process of the disease. In AD brain, mononuclear phagocytes (microglia) accumulate at the sites of Abeta peptide deposition. In vitro, Abeta peptides activate mononuclear phagocytes to release neurotoxic mediators. A number of cell-surface molecules have been reported to act as putative receptors for Abeta peptides, among which the G protein-coupled formyl peptide receptor-like 1 (FPRL1) and its mouse homolog FPR2 have been shown to be expressed by activated microglial cells and mediate the chemotactic activity of the 42 amino acid form of Abeta (Abeta42). FPRL1 also participates in Abeta42 internalization in macrophages and its cytotoxicity for neuronal cells. Therefore, FPRL1 may be involved in the inflammatory aspects of AD. This review discusses recent findings relevant to the function and regulation of FPRL1/FPR2 in mononuclear phagocytes by pro- and antiinflammatory signals and its potential as a therapeutic target in AD.

APP transgenic mice Tg2576 accumulate Abeta peptides that are distinct from the chemically modified and insoluble peptides deposited in Alzheimer's disease senile plaques.

The amyloid (Abeta) peptides generated in Hsiao's APP Tg2576 transgenic (Tg) mice are physically and chemically distinct from those characteristic of Alzheimer's disease (AD). Transgenic mouse Abeta peptides were purified using sequential size-exclusion and reverse-phase chromatographic systems and subjected to amino acid sequencing and mass spectrometry analyses. The mouse Abeta peptides lacked the extensive N-terminal degradations, posttranslational modifications, and cross-linkages abundant in the stable Abeta peptide deposits observed in AD. Truncated Abeta molecules appear to be generated in vivo by hydrolysis at multiple sites rather than by post-mortem C-terminal degradation. In contrast to AD amyloid cores, the Tg mice peptides were soluble in Tris-SDS-EDTA solutions, revealing both monomeric and SDS-stable oligomeric species of Abeta. In contrast to our report on Novartis Pharma APP23 Tg mice [Kuo et al. (2001) J. Biol. Chem. 276, 12991], which maintain high levels of soluble Abeta early on with later development of extensive vascular amyloid, Tg2576 mice exhibited an age-related elevation of soluble Abeta with relatively limited vascular amyloid deposition. The transgenic mouse levels of carboxy-terminal (CT) APP fragments were nearly 10-fold greater than those of human brains, and this condition may contribute to the unique pathology observed in these animals. Immunization of transgenic mice may act to prevent the pathological effects of betaAPP overproduction by binding CT molecules or halting their processing to toxic forms, in addition to having any effects on Abeta itself. Thus, differences in disease evolution and biochemistry must be considered when using transgenic animals to evaluate drugs or therapeutic interventions intended to reduce the Abeta burden in Alzheimer's disease.

Expression of mutant amyloid precursor proteins decreases adhesion and delays differentiation of Hep-1 cells

The amyloid precursor protein (APP) is a type I integral membrane protein and is processed to generate several intra-cellular and secreted fragments. The physiological role of APP and its processed fragments is unclear. Several mutations have been discovered in APP, which are causative of early-onset, familial, neurological disease, including Alzheimer’s disease (FAD). These mutations alter the processing of APP and lead to excess production and extra-cellular deposition of A-beta peptide (Aβ). We have examined the role of APP in a cell culture model of endothelial cell function. The endothelial cell line, Hep-1, was stably transfected with wild-type (wt) and FAD mutant forms of APP (mAPP). Secretion of sAPPα was reduced in cell lines over-expressing mAPP when these cells were grown on several different substrates. Levels of secreted Aβ were increased as measured by ELISA in the mutant cell lines. Cell adhesion to laminin-, fibronectin-, collagen I-, and collagen IV-coated culture flasks was reduced in all mAPP-expressing cell lines, while in lines over-expressing wt-APP, adhesiveness was slightly increased. Cell lines over-expressing mAPP differentiated more slowly into capillary network-like structures on Matrigel™ than those expressing wt-APP. No differences were detected among all cell lines in a migration/invasion assay. The results suggest that APP may have a role in cell adhesiveness and maturation of endothelial cells into capillary-like networks. The reduction in adhesion and differentiation in mutant cell lines may be due to reduced amounts of sAPPα released into the culture media or toxic effects of increased extracellular Aβ.

Laminar specific loss of isocortical presenilin 1 immunoreactivity in Alzheimer's disease. Correlations with the amyloid load and the density of tau-positive neurofibrillary tangles.

Presenilin 1 has been shown to be mutated in a high proportion of cases of familial Alzheimer's disease. Immunoreactive epitopes of the protein have been found mainly in neurones devoid of neurofibrillary tangles - an observation that has led to the conclusion that presenilin 1 could have a protective role. In this study, the relationship between deposits of Abeta peptide (both the 40 and 42 isoforms), tau positive neurofibrillary tangles and presenilin 1-positive neuronal profiles were analysed in three cases of presenilin 1 mutation, four cases of sporadic Alzheimer's disease and five controls. Immunohistochemistry was performed in a sample from the supramarginal gyrus. The proportion of volume occupied by the Abeta1-40 and Abeta1-42 deposits (amyloid load) was evaluated by a point-counting technique. Tau-positive neurofibrillary tangles, and presenilin 1-positive neuronal profiles were directly counted. The location of the lesions in the thickness of the cortex was recorded. The density of PS1-positive neuronal profiles in Alzheimer's disease cases was lower than in the controls. The deficit was significant only in the upper layers of the cortex. The density of presenilin 1 neuronal profiles was negatively correlated with Abeta1-40 and Abeta1-42 loads, and with the density of tau-positive neurofibrillary tangles. Multivariate analysis showed that the Abeta1-42 load was the best determinant of the decrease in presenilin 1-positive neuronal profiles. Presenilin 1-positive neurones appear to be lost rather than protected in the course of Alzheimer disease.

Laminar spongiosis of the dentate gyrus: a sign of disconnection, present in cases of severe Alzheimer's disease.

An extensive laminar spongiosis was found in the outer part of the dentate gyrus in an 84-year-old patient. An old cavitary infarct in the parahippocampal gyrus disconnected the dentate gyrus from the entorhinal area. This finding prompted us to seek laminar spongiosis in Alzheimer's disease, where the neuronal loss in the entorhinal cortex might be severe. The dentate gyrus was systematically examined in a series of prospectively assessed cases either intellectually normal or affected by mental impairment of graded severity. Laminar spongiosis was present in the most severely affected patients. The neuritic crown of the senile plaques seen in the laminar band of spongiosis contained only a few tau- and Bodian-positive fibers, a sign that was taken as evidence of "plaque denervation". By contrast, deposits of Abeta peptide remained abundant but lacked a dense core. These data suggest that dendritic and axonal processes are intermingled in the senile plaque and that the amyloid core is at least partially dependent on the presence of the axonal component.

Aggregation and disaggregation of senile plaques in Alzheimer disease.

We quantitatively analyzed, using laser scanning confocal microscopy, the three-dimensional structure of individual senile plaques in Alzheimer disease. We carried out the quantitative analysis using statistical methods to gain insights about the processes that govern Abeta peptide deposition. Our results show that plaques are complex porous structures with characteristic pore sizes. We interpret plaque morphology in the context of a new dynamical model based on competing aggregation and disaggregation processes in kinetic steady-state equilibrium with an additional diffusion process allowing Abeta deposits to diffuse over the surface of plaques.