Processing of the Alzheimer's disease beta A4 amyloid protein precursor (APP)

Traditional Chinese Nootropic Medicine Radix Polygalae and Its Active Constituent Onjisaponin B Reduce β-Amyloid Production and Improve Cognitive Impairments

Decline of cognitive function is the hallmark of Alzheimer’s disease (AD), regardless of the pathological mechanism. Traditional Chinese medicine has been used to combat cognitive impairments and has been shown to improve learning and memory. Radix Polygalae (RAPO) is a typical and widely used herbal medicine. In this study, we aimed to follow the β-amyloid (Aβ) reduction activity to identify active constituent(s) of RAPO. We found that Onjisaponin B of RAPO functioned as RAPO to suppress Aβ production without direct inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) and γ-secretase activities. Our mechanistic study showed that Onjisaponin B promoted the degradation of amyloid precursor protein (APP). Further, oral administration of Onjisaponin B ameliorated Aβ pathology and behavioral defects in APP/PS1 mice. Taken together, our results indicate that Onjisaponin B is effective against AD, providing a new therapeutic agent for further drug discovery.

Lipidomics of Alzheimer’s disease

Alzheimer’s disease (AD) is a progressive brain disease that leads to an irreversible loss of neurons and cognition. It is the most common cause of dementia and can be considered as a major public health problem. At the histological level, AD is characterized by senile plaques and neurofibrillary tangles. Numerous studies involving genomic, transcriptomic and proteomic approaches have been published in order to understand the molecular mechanisms involved in AD, and to find new biomarkers. Metabolomics, and in particular lipidomics, have recently offered new possibilities due to the development of robust and sensitive analytical methods, such as LC–MS. This review aims to illustrate how lipidomics can help understand the biological mechanisms inherent to AD and how lipids can be considered as relevant biomarkers of AD at early stages.

Dietary lipids and their oxidized products in Alzheimer's disease

Alzheimer's disease (AD) is the commonest form of dementia in the elderly, characterized by memory dysfunction, loss of lexical access, spatial and temporal disorientation, and impaired judgment. A growing body of scientific literature addresses the implication of dietary habits in the pathogenesis of AD. This review reports recent findings concerning the modulation of AD development by dietary lipids, in animals and humans, focusing on the pathogenetic role of lipid oxidation products. Oxidative breakdown products of ω-6 polyunsaturated fatty acids (ω-6 PUFAs), and cholesterol oxidation products (oxysterols), might play a role in favoring β-amyloid deposition, a hallmark of AD's onset and progression. Conversely, ω-3 PUFAs appear to contribute to preventing and treating AD. However, high concentrations of ω-3 PUFAs can also produce oxidized derivatives reacting with important functions of nervous cells. Thus, altered balances between cholesterol and oxysterols, and between ω-3 and ω-6 PUFAs must be considered in AD's pathophysiology. The use of a diet with an appropriate ω-3/ω-6 PUFA ratio, rich in healthy oils, fish and antioxidants, such as flavonoids, but low in cholesterol-containing foods, can be a beneficial component in the clinical strategies of prevention of AD.

Regulation of Notch1 signaling by the APP intracellular domain facilitates degradation of the Notch1 intracellular domain and RBP-Jk

The Notch1 receptor is a crucial controller of cell fate decisions, and is also a key regulator of cell growth and differentiation in a variety of contexts. In this study, we have demonstrated that the APP intracellular domain (AICD) attenuates Notch1 signaling by accelerated degradation of the Notch1 intracellular domain (Notch1-IC) and RBP-Jk, through different degradation pathways. AICD suppresses Notch1 transcriptional activity by the dissociation of the Notch1-IC-RBP-Jk complex after processing by γ-secretase. Notch1-IC is capable of forming a trimeric complex with Fbw7 and AICD, and AICD enhances the protein degradation of Notch1-IC through an Fbw7-dependent proteasomal pathway. AICD downregulates the levels of RBP-Jk protein through the lysosomal pathway. AICD-mediated degradation is involved in the preferential degradation of non-phosphorylated RBP-Jk. Collectively, our results demonstrate that AICD functions as a negative regulator in Notch1 signaling through the promotion of Notch1-IC and RBP-Jk protein degradation.

Surface chemistry of Alzheimer's disease: a Langmuir monolayer approach

Amyloid beta (1-40) and (1-42) peptides are the major constituents of hallmark senile plaques found in Alzheimer's disease (AD) patients. Study of aggregation of Abeta (1-40) and (1-42) peptides and the truncated Abeta fragments could lead towards the mechanism of AD. Langmuir monolayer approach is one of the excellent methods to investigate the mechanism and origin of AD. Particularly, to study the steps involved in the formation and assembly of beta-sheet structures leading to formation of amyloid fibrils. Surface pressure- and surface potential-area isotherms provide information regarding the nature of short-range and long-range interactions between the molecules especially the lipids and the Abeta peptides. Spectroscopic methods like IRRAS, PM-IRRAS, FTIR-ATR, and GIXD at the air-water interface provide insight into the structural characterization, and orientation of the molecules in the Langmuir monolayer.

Notch1 intracellular domain suppresses APP intracellular domain-Tip60-Fe65 complex mediated signaling through physical interaction

The amyloid beta-precursor protein (APP) and the Notch receptor are both type 1 integral transmembrane proteins, and both are cleaved by presenilin-dependent gamma-secretase activity. In this study, we have demonstrated that the Notch intracellular domain (Notch1-IC) suppresses APP-intracellular domain (AICD)-mediated ROS generation and cell death after being processed by gamma secretase. Notch1-IC physically interacts with AICD, Fe65, and Tip60, thereby disrupting the association of the AICD-Fe65-Tip60 trimeric transcription activator complex in AICD signaling. AICD-Fe65-Tip60 mediated reactive oxygen species generation was found to be suppressed by Notch1-IC. Furthermore, AICD-Fe65-Tip60 was shown to mediate cell death in human neuroblastoma cells, and the overexpression of Notch1-IC inhibited cell death induced by AICD-Fe65-Tip60. Collectively, our findings indicate that Notch1-IC plays the role of a negative regulator in AICD signaling via the disruption of the AICD-Fe65-Tip60 trimeric complex.

ε-Glycation, APP and Aβ in ageing and Alzheimer disease: A hypothesis

The post-translational modifications of protein molecules include glycation, which may not only occur enzymatically controlled in N and O position, but also wherever proteins meet reducing sugars non-enzymatically in epsilon position at lysines (non-enzymatic (epsilon) glycation (NEG)). The formation of keto-amines from the amine-sugar compounds (Amadori re-arrangement) and further processing of the largely undigestible Amadori compounds eventually results in insoluble advanced glycation end products (AGEs). The latter can induce or favour disease including mental disorders. Preferential targets of NEG include large cell surface proteins. Ample evidence has been provided that NEG also occurs in the brain where cross-linking of epsilon-glycated proteins, induction of oxidative stress and signalling of AGEs through their specific receptor (RAGE) likely play a role in (brain) ageing and Alzheimer disease (AD). This is underscored by the demonstration of particular interactions between AGE/RAGE and amyloid-beta (Abeta) that favour the aggregation and deposition of Abeta and, perhaps, the formation of Abeta itself. The close relationship between NEG and Abeta, as well as other facts foster the hypothesis that NEG of the large trans-membrane amyloid precursor protein (APP) might be a significant factor in the induction of aberrant APP cleavage with production of Abeta, not only in normal ageing, but also in AD. Blockade of lysine cleavage sites on APP by sugar chains or marker effects induced by NEG akin to ubiquitination of proteins for degradation at lysines could be expected to contribute to altered processing of APP. The hypothesis of epsilon-glycation in APP proposed here and the review of evidences for the significance of NEG in brain ageing and AD are aimed at the stimulation of investigations into the still open question which role NEG plays with respect to APP and its abnormal processing in AD. It can be rendered likely that such research might open new avenues towards decreasing the risk of AD and/or slowing its progression through the prevention of NEG in APP with aberrant APP processing, increased generation of Abeta and the formation of AGEs from epsilon-glycated APP.

Neuropathology of Alzheimer's disease and other dementias

Clinical differentiation of neurodegenerative diseases that produce dementia is imprecise. Neuropathology offers the only way to make a definite diagnosis. The CNS autopsy is also important for clinical quality control and for providing tissue that furthers research into these disabling disorders. This brief article summarizes the major neuropathologic features of largely sporadic disorders that present with late-life dementia. The common causes of dementia discussed are Alzheimer's disease, Lewy body disease, and vascular dementia; less common disorders described are dementia lacking distinctive histopathology, Pick's disease, progressive supranuclear palsy, corticobasal degeneration, and Creutzfeldt-Jakob disease.

Neuroprotective efficacy and mechanisms of novel pyrrolopyrimidine lipid peroxidation inhibitors in the gerbil forebrain ischemia model

A brief period of bilateral carotid occlusion (BCO)-induced forebrain ischemia in gerbils triggers neuronal degeneration and the subsequent expression of amyloid precursor protein (APP), b-amyloid protein (b-AP), and apolipoprotein E (APO-E) in the selectively vulnerable CA1 region of the hippocampus. The increase in immunoreactivity is secondary to the postischemic degeneration of the CA1 neurons and is largely astrocyte-derived as evidenced by a simultaneous increase in glial fibrillary acidic protein (GFAP) staining. Oxygen radical-induced lipid peroxidation has been strongly suggested to play a role in postischemic neuronal damage and Alzheimer's disease. Recent literature suggests a possible link between early oxidative stress and APP overexpression. Therefore, the present investigation examined the effect of two novel brain-penetrating pyrrolopyrimidine lipid peroxidation inhibitors (PNU-101033E and PNU-104067F) on CA1 neurodegeneration and the subsequent increase in APP, b-AP, APO-E, and GFAP immunostaining at 4 days after a 5-minute episode of forebrain ischemia. Using an antibody for lipid peroxidation-derived malondialdehyde (MDA)-modified proteins, the authors also examined the effects of PNU-104067F on MDA immunostaining 2 days after ischemia, before completion of the neuronal loss. At 2 days, the authors also evaluated microglial activation using an antibody to surface major histocompatibility complex class II antigen expressed by activated microglia. Gerbils were treated at 30 mg/kg orally 30 minutes before the BCO and 2 hours after ischemia, followed by daily dosing for the next day (microglia and MDA) and the successive 3 days for APP, b-AP, APO-E, and GFAP immunostaining. APP and APO-E staining was significantly suppressed by 50% and 66%, respectively, with either compound. b-AP immunoreactivity was decreased 56% with both compounds, and GFAP expression was significantly decreased 53% (PNU-101033E) and 60.5% (PNU-104067F). There was a concomitant partial sparing of the CA1 hippocampal neurons by both PNU-101033E and PNU-104067F (P < .01) as determined by cresyl violet histochemistry. PNU-104067F significantly inhibited lipid peroxidation-derived MDA immunostaining and microglia activation (P < .05) at 48 hours after ischemia. Brain-penetrable lipid peroxidation inhibitors may provide attenuation of various glial response proteins after ischemic injury, probably secondary to neuronal protection.

Glycation and microglial reaction in lesions of Alzheimer's disease

Single, double, and triple immunostaining of cryostat sections of elderly normal and Alzheimer disease (AD) brain was performed with monoclonal and polyclonal antibodies to advanced glycation end products (AGE). The sections were counterstained with thioflavin-S or with immunocytochemistry for A beta and also stained with markers for microglia. AGE-immunoreactivity was detected in senile plaques and neurofibrillary tangles (NFT). AGE immunoreactivity was most intense in dense or reticular amyloid deposits and extracellular NFT, while intracellular NFT and diffuse amyloid had less AGE immunoreactivity. This pattern of immunoreactivity was similar to that noted in previous studies with antibodies to apolipoprotein-E (apo-E). Therefore, double labeling with antibodies to apo-E and AGE was performed. AGE immunoreactivity colocalized to a very high degree with apo-E immunoreactivity, except that relatively more intense apo-E immunoreactivity was detected in amyloid deposits and more intense AGE immunoreactivity in NFT. The lesions that were immunostained with antibodies to AGE and apo-E were often, but not always, associated with a local microglial reaction. The results raise the possibility that apo-E or a fragment of apo-E may be glycated. Biochemical studies are needed to determine the extent of possible apo-E glycation in AD. The present results raise the possibility that glycation may serve as one of the signals for activation of microglia associated with amyloid deposits and extracellular NFT.

Evidence for an early inflammatory response in the central nervous system of mice with scrapie

In Alzheimer's disease, the most prevalent of the neurodegenerative diseases, inflammation of the CNS contributes to the pathology and is a target for therapy. In contrast, the group of neurodegenerative conditions known as the Prion Diseases have been widely reported as lacking any inflammatory elements despite the many similarities between the pathologies of Alzheimer's Disease and Prion Diseases We have found evidence for an inflammatory component in mouse scrapie, characterized by microglial activation and T-lymphocyte recruitment, which appears long before any clinical signs of the disease and spreads along well-defined anatomical pathways. These observations emphasize the potential value of murine scrapie as a model for studying the inflammatory pathology of other neurodegenerative diseases.

Apolipoprotein E epsilon 4 allele is associated with deposition of amyloid beta-protein following head injury

Deposition of amyloid beta-protein (A beta) in the brain plays a key role in the pathogenesis of Alzheimer's disease. Apolipoprotein E epsilon 4 allele (apo E-epsilon 4) is a strong risk factor for Alzheimer's disease, and there is in vitro evidence that apo E is directly involved in A beta deposition. Head injury is an epidemiological risk factor for Alzheimer's disease and deposition of A beta occurs in approximately one-third of individuals dying after a severe head injury. We report here that the frequency of apo E-epsilon 4 in those individuals with A beta deposition following head injury (0.52) is higher than in most studies of Alzheimer's disease, while in those head-injured individuals without A beta deposition the apo E-epsilon 4 frequency (0.16) is similar to controls without Alzheimer's disease (P < 0.00001). This finding provides further evidence linking apo E-epsilon 4 with A beta deposition in vivo and suggests that known environmental and genetic risk factors for Alzheimer's disease may act additively. In addition our finding indicates a genetic susceptibility to the effects of a head injury.

The distribution of amyloid beta precursor protein in canine brain

The distribution of amyloid beta precursor protein (APP) in canine brain was investigated. By immunoblot analysis, APP-positive bands corresponding to proteins of 105-120 kilodalton were recognized in all canine brains regardless of the individual age of the dogs. Bands of similar molecular mass were also detected in the meninges, cerebrospinal fluid, and several visceral organs. Immunohistochemical studies were performed using cryostat and paraffin-embedded sections pretreated with formic acid or by the hydrated autoclave method. In the normal canine brain, APP was found to be distributed in the neurons and vascular system. In the brains with SP, obvious accumulation of APP was observed in swollen neurites within amyloid plaques, although the relationship between APP and diffuse plaques was unclear. APP accumulation in swollen axons was also seen around necrotic foci in the brain of one dog with necrotizing purulent encephalitis. These studies revealed that distribution of APP in canine tissues, especially in the brain, and the accumulation of APP in swollen neurites or axons.

Identification and regulation of the high affinity binding site of the Alzheimer's disease amyloid protein precursor (APP) to glycosaminoglycans

The specific binding of the amyloid protein precursor (APP) to glycosaminoglycans (GAG) suggests that APP is a cell adhesion molecule (CAM) and/or substrate adhesion molecule (SAM). In order to characterize this activity of APP in the brain at the molecular level, we have purified and characterized the major APP species from rat brain. The major isoform isolated was sequenced and found to be APP695. In a solid-phase binding assay, the specificity of this brain-specific APP isoform-GAG interaction was analysed. The binding of APP to the glycosaminoglycan heparin was found to be time-dependent and saturable. A strong heparin-binding site within a region conserved in rodent and human APP, APLP1 and APLP2, was identified. Saturable binding to heparin through this binding site was found to occur at nmol concentrations of APP. This putative high-affinity site was then located within a sequence of 22 amino acids in length corresponding to residues 316-337 of APP695. This sequence is encoded by APP exon 9 and the first three codons of exon 10. Since all APP and L-APP isoforms so far described include these exons, the strong heparin binding site is a ubiquitous feature of all APP and L-APP isoforms strongly suggesting that the brain-specific and neuronal, as well as the non-neuronal and peripheral APPs and L-APPs do have CAM- and SAM-like activities. Certain metal ions including zinc (II) have been proposed as risk factors in Alzheimer's disease (AD). Recently we showed that APP binds zinc (II) at higher nmol concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of IgG to amyloid beta A4 peptide via the heavy-chain hinge region with preservation of antigen binding

Amyloid beta A4 peptide is found in the extracellular region of the senile plaque and in the angiopathy of Alzheimer's disease. Several other proteins, including IgG, also reside in these abnormal structures. In an attempt to understand how these structures are assembled and to determine how proteins are recruited, interactions of various proteins with synthetic beta A4 peptide have been examined in vitro. Purified IgG binds directly to synthetic beta A4 peptide with high avidity. The domain between amino acids 12-28 of beta A4 binds IgG. beta A4 peptide binds the hinge region of the immunoglobulin heavy chain, and preserves the ability of the immunoglobulin to bind antigen. A protein which does not bind directly to beta A4 peptide can be targetted to the senile plaque and angiopathy by binding to IgG, which avidly binds beta A4 peptide.

Beta A4 deposits are constant in the brain of the oldest old: an immunocytochemical study of 20 French centenarians

beta A4 deposits occur in the brain of some individuals over 50 years of age. It could be a part of the aging process or indicate a disease found frequently in the elderly. To address this question, beta A4 immunocytochemistry was performed on the brain of 15 nondemented and 5 demented centenarians, some of whom were affected by Alzheimer's disease. We found beta A4 deposits in the parahippocampal and the superior temporal gyri of all the cases, whatever the clinical state. The hippocampus was frequently spared. The lesion density was not correlated with the severity of the mental deterioration. The constant deposition of beta A4 protein in the brain of very old people indicates that this process does not spare a large proportion of this population. This result favors beta A4 accumulation in the brain being an ineluctable age-related process.