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1.
β-Amyloid peptide (Aβ), the main constituent of senile plaques and diffuse amyloid deposits in Alzheimer's diseased brain, was shown to initiate the development of oxidative stress in neuronal cell cultures. Toxic lots of Aβ form free radical species in aqueous solution. It was proposed that Aβ-derived free radicals can directly damage cell proteins via oxidative modification. Recently we reported that synthetic Aβ can interact with glutamine synthetase (GS) and induce inactivation of this enzyme. In the present study we present the evidence that toxic Aβ(25-35) induces the oxidation of pure GS in vitro. It was found that inactivation of GS by Aβ, as well as the oxidation of GS by metal-catalyzed oxidation system, is accompanied by an increase of protein carbonyl content. As it was reported previously by our laboratory, radicalization of Aβ is not iron or peroxide-dependent. Our present observations consistently show that toxic Aβ does not need iron or peroxide to oxidize GS. However, treatment of GS with the peptide, iron and peroxide together significantly stimulates the protein carbonyl formation. Here we report also that Aβ(25-35) induces carbonyl formation in BSA. Our results demonstrate that P-peptide, as well as other free radical generators, induces carbonyl formation when brought into contact with different proteins.  相似文献   

2.
It is generally believed that amyloid β peptides (Aβ) are the key mediators of Alzheimer's disease. Therapeutic interventions have been directed toward impairing the synthesis or accelerating the clearance of Aβ. An equilibrium between blood and brain Aβ exists mediated by carriers that transport Aβ across the blood–brain barrier. Passive immunotherapy has been shown to be effective in mouse models of AD, where the plasma borne antibody binds plasma Aβ causing an efflux of Aβ from the brain. As an alternative to passive immunotherapy we have considered the use of Aβ-degrading peptidases to lower plasma Aβ levels. Here we compare the ability of three Aβ-degrading peptidases to degrade Aβ. Biotinylated peptidases were coupled to the surface of biotinylated erythrocytes via streptavidin. These erythrocyte-bound peptidases degrade Aβ peptide in plasma. Thus, peptidases bound to or expressed on the surface of erythroid cells represent an alternative to passive immunotherapy.  相似文献   

3.
The functional differences between male and female brains commit to the existence of androgen that the testis secretes during the perinatal period. Androgen exerts its action on the brain after conversion to estrogen by brain aromatase. The aromatase appears in some neural nuclei such as in the hypothalamus and amygdala, and has been indicated to be involved in the expression of sexuality by the results of neurobehavioral analyses involving aromatase-knockout mice. We analyzed the brain-specific promoter in order to clarify the control mechanism for the expression of brain aromatase, which is deeply concerned in the sexual differentiation of the brain. The 202 bp upstream region of brain-specific exon 1 contains at least three kinds of cis-acting elements, Arom-A, -Aβ and -B. In particular, the binding activities as to the Aβ sequence show a tissue-specific pattern. Gel shift analysis revealed that the Aβ binding factor recognizes the TTGGCCCCT sequence. Aβ binding activity is detectable at the perinatal stage, but is undetectable at the adult stage in the brain. Furthermore, a protein which binds to the Aβ sequence was purified from the fetal mouse brain. The molecular mass of the Aβ binding protein was estimated to be 49 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.  相似文献   

4.
Poon WY  Malik-Hall M  Wood JN  Okuse K 《FEBS letters》2004,570(1-3):114-118
In human brain the Aβ peptide is produced mainly by neurons and the overexpression of amyloid precursor protein (APP) that involves an increase in Aβ secretion, has been observed in some areas of the Alzheimer's disease patients brain. We have generated two stably transfected human neuroblastoma lines which overexpress APP; both of them secreted Aβ and showed morphological changes and cell death with apoptotic program characteristics. Interestingly, coculture experiments with the untransfected human neuroblastoma cell line showed that the Aβ peptide was not responsible for the death in those cell lines; additionally, we indicate that upon cell death, Aβ peptide is secreted into cell medium.  相似文献   

5.

Background

The deposition and oligomerization of amyloid β (Aβ) peptide plays a key role in the pathogenesis of Alzheimer''s disease (AD). Aβ peptide arises from cleavage of the membrane-associated domain of the amyloid precursor protein (APP) by β and γ secretases. Several lines of evidence point to the soluble Aβ oligomer (AβO) as the primary neurotoxic species in the etiology of AD. Recently, we have demonstrated that a class of fluorene molecules specifically disrupts the AβO species.

Methodology/Principal Findings

To achieve a better understanding of the mechanism of action of this disruptive ability, we extend the application of electron paramagnetic resonance (EPR) spectroscopy of site-directed spin labels in the Aβ peptide to investigate the binding and influence of fluorene compounds on AβO structure and dynamics. In addition, we have synthesized a spin-labeled fluorene (SLF) containing a pyrroline nitroxide group that provides both increased cell protection against AβO toxicity and a route to directly observe the binding of the fluorene to the AβO assembly. We also evaluate the ability of fluorenes to target multiple pathological processes involved in the neurodegenerative cascade, such as their ability to block AβO toxicity, scavenge free radicals and diminish the formation of intracellular AβO species.

Conclusions

Fluorene modified with pyrroline nitroxide may be especially useful in counteracting Aβ peptide toxicity, because they posses both antioxidant properties and the ability to disrupt AβO species.  相似文献   

6.
The accumulation of fibrillar aggregates of beta Amyloid (Aβ) in Alzheimer's Disease (AD) brain is associated with chronic brain inflammation. Although activated microglia (μglia) can potentially clear toxic amyloid, chronic activation may lead to excessive production of neurotoxins. Recent epidemiological and clinical data have raised questions about the use of anti-inflammatory steroids (glucocorticoids, Gcs) and estrogens for treatment or prevention of AD. Since very little is known about steroid effects on μglial interactions with amyloid, we investigated the effects of the synthetic Gc dexamethasone (DXM) and 17-β estradiol (E2) in vitro in a murine μglial-like N9 cell line on toxin production and intracellular Aβ accumulation. To determine whether the steroid alterations of Aβ uptake in vitro had relevance in vivo, we examined the effects of these steroids on Aβ accumulation and μglial responses to Aβ infused into rat brain. Our in vitro data demonstrate for the first time that Gc dose-dependently enhanced μglial Aβ accumulation and support previous work showing that E2 enhances Aβ uptake. Despite both steroids enhancing uptake, degradation was impeded, particularly with Gcs. Distinct differences between the two steroids were observed in their effect on toxin production and cell viability. Gc dose-dependently increased toxicity and potentiated Aβ induction of nitric oxide, while E2 promoted cell viability and inhibited Aβ induction of nitric oxide. The steroid enhancement of μglial uptake and impedence of degradation observed in vitro were consistent with observations from in vivo studies. In the brains of Aβ-infused rats, the μglial staining in entorhinal cortex layer 3, not associated with Aβ deposits was increased in response to Aβ infusion and this effect was blocked by feeding rats prednisolone. In contrast, E2 enhanced μglial staining in Aβ-infused rats. Aβ-immunoreactive (ir) deposits were quantitatively smaller, appeared denser, and were associated with robust μglial responses. Despite the fact that steroid produced a smaller more focal deposit, total extracted Aβ in cortical homogenate was elevated. Together, the in vivo and in vitro data support a role for steroids in plaque compaction. Our data are also consistent with the hypothesis that although E2 is less potent than Gc in impeding Aβ degradation, long term exposure to both steroids could reduce Aβ clearance and clinical utility. These data showing Gc potentiation of Aβ-induced μglial toxins may help explain the lack of epidemiological correlation for AD. The failure of both steroids to accelerate Aβ degradation may explain their lack of efficacy for treatment of AD.  相似文献   

7.
Senile plaque composed of amyloid-beta (Aβ) in the brain is one of the hallmarks of Alzheimer disease (AD). Removal of Aβ from the brain is the most important therapeutic strategy for AD. The solubility of Aβ is critical for its endocytosis, transcytosis and removal from the brain. Our recent study has found that the extracellular domain of p75NTR, the neurotrophin receptor, plays an important role in the solubility of Aβ and might be one of the endogenous mechanisms in the regulation of Aβ plaque formation. The physiologically shedded extracellular domain of p75NTR is able to inhibit Aβ aggregation and diasggregate preformed Aβ fibrils, while the full p75NTR expressed on neurites, endothelial cells and smooth muscle cells in blood-brain barrier (BBB) might initiate Aβ endocytosis and degradation, and/or remove Aβ from the brain via BBB. Understanding the roles of p75NTR in the solubility and clearance of Aβ may allow targetting p75NTR as a unique opportunity to develop therapeutic drugs for the prevention and treatment of AD.Key words: Alzheimer disease, amyloid-β, p75NTR, extracellular domain, blood-brain barrier, clearanceSenile plaque in the brain is one of the hallmarks of Alzheimer disease (AD). The main component of the senile plaques is amyloid-beta (Aβ), which is a metabolic product of amyloid precursor protein (APP). The steady-state level of Aβ in the normal brain is maintained by the balance between its production and clearance. However in the AD brain this balance is broken due to either over-production of Aβ or a reduction in Aβ clearance;1,2 thus Aβ accumulates in the brain and forms amyloid plaques which cause dementia and neurodegeneration in patients. Based on the Aβ hypothesis proposed a decade ago, Aβ plays a causal and pivotal role in the development of AD.3 Therefore, removal of Aβ from the brain is the most important therapeutic strategy for AD.4 To reach this goal, it is essential to understand how the Aβ metabolism is regulated in the AD brain. Despite the dramatic progress has been made in the understanding of how Aβ is produced from APP, the mechanisms of Aβ aggregation, metabolism and clearance from the brain remain unclear so far. Only 5% of AD (familial cases) is due to the over-production of Aβ because of mutations in the APP gene or in the APP processing enzymes, while the majority (95%) of so-called sporadic or late-onset AD (LOAD) are likely caused by dysfunctions in Aβ solubility or aggregation, endocytosis, degradation, transcytosis and removal.The solubility of Aβ is critical for its endocytosis, transcytosis and removal from the brain. In AD patients, one of the most consistent biomarkers found so far is the reduction of Aβ level in the cerebral spinal fluid (CSF).5 This is the most convincing evidence that there is a reduction in the solubility of Aβ and an increase in the Aβ aggregation and beta-sheet formation in AD patients. In sporadic cases of AD, the polymorphism of the Aβ-binding protein ApoE4 is highly associated with AD. It is known that other variants of ApoE proteins have a higher binding affinity to Aβ than ApoE4. It is likely that ApoE protein plays a critical role in the solubility of Aβ.6 The reduction in the Aβ binding ability of ApoE4 may reduce the solubility of Aβ. Thus ApoE protein may act on Aβ keeping it soluble and preventing its aggregation, and ApoE4 variant may reduce Aβ solubility and increase aggregation in the brain. It is not fully understood at this time, what other proteins that might regulate Aβ solubility and prevent its aggregation. Understanding the endogenous mechanism of suppressing Aβ aggregation and enhancing its removal will help to target Aβ for developing disease-modifying drugs.The neurotrophin receptor p75NTR may be such the protein which plays critical roles in the Aβ solubility and prevents Aβ aggregation and deposition in the brain. During the investigation into the functions of p75NTR in the development of AD in a recent study, we have found that the extracellular domain of p75NTR regulates the deposition of Aβ in a mouse model of AD.7 In p75NTR gene-knockout APPswe/PS1dE9 mice, soluble Aβ which reflects the steady-state level of Aβ production, is reduced in the brain. The serum Aβ level, which is associated with the level of soluble Aβ in the brain, is also reduced in p75NTR-knockout animals. In comparison, we found that p75NTR knockout increases the insoluble Aβ as reflected by the increased amyloid plaques and formic acid-extracted Aβ levels. Our results indicate that p75NTR may play critical roles in the solubility of Aβ in the brain of AD mice. To test the hypothesis, we have made recombinant extracellular domain-fused with human immunoglobulin Fc fragment and tested its effects in the solubility of Aβ in vitro. We have found that the recombinant extracellular domain of p75NTR has a very strong effect on the solubility of Aβ. It reduces Aβ oligomerization and fibrillization, solubilizes fibrilized Aβ. Most interestingly, when injected into the hippocampus of AD mice, it reduces the number and size of Aβ plaques. Thus, we have clearly demonstrated that the extracellular domain plays an important role in the solubility of Aβ and might be one of endogenous mechanisms in the regulation of Aβ plaque formation in patients.How might p75NTR play a role in the Aβ plaque formation or deposition in AD brain? One of the features of the Aβ pathology is that Aβ exclusively deposits in the neocortex, hippocampus and vessel walls. These areas are also the projection area of p75NTR positive fibers. The close anatomical association between p75NTR expression and Aβ deposition strongly suggests that p75NTR is involved in the initiation and development of Aβ deposition in the brain. Interestingly, we have observed there is a spatial relationship between p75NTR fibers and Aβ plaques in the brain of AD mice. We have found that p75NTR positive neurites locates in the center of compact senile plaques, while p75NTR negative degenerative neurites locate in the outer region of Aβ plaques.7 This phenomenon suggests that p75NTR positive neurodegenerative fibers may play a seeding role to initiate the Aβ aggregation and plaque formation. It is known that Aβ can bind to the extracellular domain of p75NTR.8 Normally, Aβ-bound p75NTR is likely endocytosed and degraded in the lysosomes, but the degenerated neurites may be abnormal in the endocytosis of the Aβ-p75NTR complex. Thus Aβ which binds to p75NTR on the cell surface may act as seeds to initiate the cascade of Aβ aggregation and beta-sheet formation.On the other hand, the extracellular domain of p75NTR after enzymatic shedding may play a different role than the membranous p75NTR. It is known that the p75NTR extracellular domain is physiologically shedded by TACE to generate a soluble and diffusible factor.9 The physiological function of the shedded diffusible extracellular domain of p75NTR remains unknown. During the aging process and during the development of AD, p75NTR expression is upregulated,10,11 and presumably the production of the diffusible extracellar domain of p75NTR is also increased. The increased extracellular domain of the p75NTR is likely a critical factor to maintain the solubility of Aβ, acting in concert with ApoE and other Aβ-binding proteins such as low-density lipoprotein receptor-related protein-1 (LRP1).12 Indeed, in our animal experiment, we have found that knockout of p75NTR significantly increases the insoluble Aβ, even though the production of Aβ is reduced in p75NTR knockout neurons.7 Our data have provided strong evidence that the brain Aβ deposition and amyloid plaque formation may be mainly due to the decreased Aβ solubility or decreased Aβ clearance.The solubility of Aβ goes hand in hand with the clearance of Aβ because only the solubilized Aβ can be endocytosed and degraded in lysosomes by neurons, microglia and astrocytes, and be transported from the brain to the blood for degradation and clearance.4 Whether p75NTR plays any roles in the endocytosis of Aβ and degradation is unclear. Our data of increased Aβ deposition in the brain of p75NTR knockout mice may also be explained by the decreased endocytosis of Aβ via p75NTR. It is likely that p75NTR may play a role in Aβ endocytosis, as p75NTR is a receptor of Aβ and mediates its toxicity in neurons.8 p75NTR ligands can trigger a clathrin-dependent endocytosis of both p75NTR and its ligands.13 If p75NTR normally mediates Aβ endocytosis, the knockout of p75NTR would reduce the removal of Aβ by endocytosis and lead to the increased deposition in the brain.Normally, p75NTR is also expressed in endothelial cells and smooth muscle cells of blood vessels, vessel-innervating sympathetic and sensory neurons and choroid plexus in the brain.14,15 This raises the possibility that p75NTR within blood vessels may play a role in transport and trafficking of Aβ from the brain to the blood. It is well known that LRP1 plays important roles in the transport and transcytosis of Aβ and clears Aβ from the brain.12 LRP1 on the cell-surface of the blood-brain barrier (BBB) can bind, transcytose and transport Aβ from the brain to the blood. p75NTR expressed on the BBB may play similar roles in the removal of Aβ in a similar manner to the Aβ binding proteins, LRP1 and G-glycoprotein, expressed on the BBB. Future studies should test roles of p75NTR in the endocytosis, transcytosis and clearance of Aβ by different cells such as neurons, endothelial cells and smooth muscle cells. The levels of shedded diffusible p75NTR in the brain and blood of AD patients should be determined as a biomarker and correlated with Aβ levels or Aβ plaques to reveal its potential roles in the solubility and clearance of Aβ in AD patients.In summary, our studies have provided strong evidence that p75NTR is an essential molecule to keep the solubility of Aβ during development of AD. We speculate that p75NTR might also play many vital roles in removing Aβ from brain (Fig. 1). However, it is still far from certain how p75NTR regulates the solubility of Aβ and suppresses its deposition in the AD brain. Understanding the roles of p75NTR in the solubility and clearance of Aβ may help using p75NTR as a target to develop therapeutic drugs for the prevention and treatment of AD.Open in a separate windowFigure 1Schematic diagram depicting functions of p75NTR in Aβ solubility and clearance. p75NTR locates on the neurites, epithelial cells and smooth muscle cells of the blood-brain barrier (BBB). Binding of Aβ to p75NTR on neurites may initiate the endocytosis of Aβ and its degradation in the neurons. Shedding of p75NTR from the cell membrane releases the soluble extracellular domain (p75NTR-ECD), which is capable of inhibiting Aβ aggregation and disaggregating preformed Aβ fibrils. p75NTR at BBB might be able to transport Aβ from the brain to blood.  相似文献   

8.
Waters J 《PloS one》2010,5(12):e15709

Background

Many recent studies of the effects of amyloid-β protein (Aβ) on brain tissue from amyloid precursor protein (APP) overexpressing mice have concluded that Aβ oligomers in the extracellular space can profoundly affect synaptic structure and function. As soluble proteins, oliomers of Aβ can diffuse through brain tissue and can presumably exit acute slices, but the rate of loss of Aβ species by diffusion from brain slices and the resulting reduced concentrations of Aβ species in brain slices are unknown.

Methodology/Principal Findings

Here I combine measurements of Aβ1–42 diffusion and release from acute slices and simple numerical models to measure the concentration of Aβ1–42 in intact mice (in vivo) and in acute slices from CRND8 mice. The in vivo concentration of diffusible Aβ1–42 in CRND8 mice was 250 pM at 6 months of age and 425 pM at 12 months of age. The concentration of Aβ1–42 declined rapidly after slice preparation, reaching a steady-state concentration within one hour. 50 µm from the surface of an acute slice the steady-state concentration of Aβ was 15–30% of the concentration in intact mice. In more superficial regions of the slice, where synaptic physiology is generally studied, the remaining Aβ is less than 15%. Hence the concentration of Aβ1–42 in acute slices from CRND8 mice is less than 150 pM.

Conclusions/Significance

Aβ affects synaptic plasticity in the picomolar concentration range. Some of the effects of Aβ may therefore be lost or altered after slice preparation, as the extracellular Aβ concentration declines from the high picomolar to the low picomolar range. Hence loss of Aβ by diffusion may complicate interpretation of the effects of Aβ in experiments on acute slices from APP overexpressing mice.  相似文献   

9.

Background

A typical pathological feature of Alzheimer''s disease (AD) is the appearance in the brain of senile plaques made up of β-amyloid (Aβ) and neurofibrillary tangles. AD is also associated with an abnormal accumulation of some metal ions, and we have recently shown that one of these, aluminum (Al), plays a relevant role in affecting Aβ aggregation and neurotoxicity.

Methodology

In this study, employing a microarray analysis of 35,129 genes, we investigated the effects induced by the exposure to the Aβ1–42-Al (Aβ-Al) complex on the gene expression profile of the neuronal-like cell line, SH-SY5Y.

Principal Findings

The microarray assay indicated that, compared to Aβ or Al alone, exposure to Aβ-Al complex produced selective changes in gene expression. Some of the genes selectively over or underexpressed are directly related to AD. A further evaluation performed with Ingenuity Pathway analysis revealed that these genes are nodes of networks and pathways that are involved in the modulation of Ca2+ homeostasis as well as in the regulation of glutamatergic transmission and synaptic plasticity.

Conclusions and Significance

Aβ-Al appears to be largely involved in the molecular machinery that regulates neuronal as well as synaptic dysfunction and loss. Aβ-Al seems critical in modulating key AD-related pathways such as glutamatergic transmission, Ca2+ homeostasis, oxidative stress, inflammation, and neuronal apoptosis.  相似文献   

10.
Increasing evidence implicates interactions between Aβ-peptides and membrane lipids in Alzheimer's disease. To gain insight into the potential role of the free amino group of the N-terminus of Aβ29-42 fragment in these processes, we have investigated the ability of Aβ29-42 unprotected and Aβ29-42 N-protected to interact with negatively-charged liposomes and have calculated the interaction with membrane lipids by conformational analysis. Using vesicles mimicking the composition of neuronal membranes, we show that both peptides have a similar capacity to induce membrane fusion and permeabilization. The fusogenic effect is related to the appearance of non-bilayer structures where isotropic motions occur as shown by 31P and 2H NMR studies. The molecular modeling calculations confirm the experimental observations and suggest that lipid destabilization could be due to the ability of both peptides to adopt metastable positions in the presence of lipids. In conclusion, the presence of a free or protected (acetylated) amino group in the N-terminus of Aβ29-42 is therefore probably not crucial for destabilizing properties of the C-terminal fragment of Aβ peptides.  相似文献   

11.
12.
Banks WA  Terrell B  Farr SA  Robinson SM  Nonaka N  Morley JE 《Peptides》2002,23(12):2223-2226
Vaccinations against amyloid β protein (AβP) reduce amyloid deposition and reverse learning and memory deficits in mouse models of Alzheimer’s disease. This has raised the question of whether circulating antibodies, normally restricted by the blood–brain barrier (BBB), can enter the brain [Nat. Med. 7 (2001) 369–372]. Here, we show that antibody directed against AβP does cross the BBB at a very low rate. Entry is by way of the extracellular pathways with about 0.11% of an intravenous (i.v.) dose entering the brain by 1 h. Clearance of antibody from brain increasingly dominates over time, but antibody is still detectable in brain 72 h after i.v. injection. Uptake and clearance is not altered in mice overexpressing AβP. This ability to enter and exit the brain even in the presence of increased brain ligand supports the use of antibody in the treatment of Alzheimer’s and other diseases of the brain.  相似文献   

13.
Wong HE  Kwon I 《PloS one》2011,6(10):e25752

Background

Alzheimer''s disease (AD) is the most common form of dementia. AD is a degenerative brain disorder that causes problems with memory, thinking and behavior. It has been suggested that aggregation of amyloid-beta peptide (Aβ) is closely linked to the development of AD pathology. In the search for safe, effective modulators, we evaluated the modulating capabilities of erythrosine B (ER), a Food and Drug Administration (FDA)-approved red food dye, on Aβ aggregation and Aβ-associated impaired neuronal cell function.

Methodology/Principal Findings

In order to evaluate the modulating ability of ER on Aβ aggregation, we employed transmission electron microscopy (TEM), thioflavin T (ThT) fluorescence assay, and immunoassays using Aβ-specific antibodies. TEM images and ThT fluorescence of Aβ samples indicate that protofibrils are predominantly generated and persist for at least 3 days. The average length of the ER-induced protofibrils is inversely proportional to the concentration of ER above the stoichiometric concentration of Aβ monomers. Immunoassay results using Aβ-specific antibodies suggest that ER binds to the N-terminus of Aβ and inhibits amyloid fibril formation. In order to evaluate Aβ-associated toxicity we determined the reducing activity of SH-SY5Y neuroblastoma cells treated with Aβ aggregates formed in the absence or in the presence of ER. As the concentration of ER increased above the stoichiometric concentration of Aβ, cellular reducing activity increased and Aβ-associated reducing activity loss was negligible at 500 µM ER.

Conclusions/Significance

Our findings show that ER is a novel modulator of Aβ aggregation and reduces Aβ-associated impaired cell function. Our findings also suggest that xanthene dye can be a new type of small molecule modulator of Aβ aggregation. With demonstrated safety profiles and blood-brain permeability, ER represents a particularly attractive aggregation modulator for amyloidogenic proteins associated with neurodegenerative diseases.  相似文献   

14.

Background

It is becoming increasingly evident that deficits in the cortex and hippocampus at early stages of dementia in Alzheimer’s disease (AD) are associated with synaptic damage caused by oligomers of the toxic amyloid-β peptide (Aβ42). However, the underlying molecular and cellular mechanisms behind these deficits are not fully understood. Here we provide evidence of a mechanism by which Aβ42 affects synaptic transmission regulating neurotransmitter release.

Methodology/Findings

We first showed that application of 50 nM Aβ42 in cultured neurones is followed by its internalisation and translocation to synaptic contacts. Interestingly, our results demonstrate that with time, Aβ42 can be detected at the presynaptic terminals where it interacts with Synaptophysin. Furthermore, data from dissociated hippocampal neurons as well as biochemical data provide evidence that Aβ42 disrupts the complex formed between Synaptophysin and VAMP2 increasing the amount of primed vesicles and exocytosis. Finally, electrophysiology recordings in brain slices confirmed that Aβ42 affects baseline transmission.

Conclusions/Significance

Our observations provide a necessary and timely insight into cellular mechanisms that underlie the initial pathological events that lead to synaptic dysfunction in Alzheimer’s disease. Our results demonstrate a new mechanism by which Aβ42 affects synaptic activity.  相似文献   

15.
Alzheimer disease is a progressive neurodegenerative brain disorder that leads to major debilitating cognitive deficits. It is believed that the alterations capable of causing brain circuitry dysfunctions have a slow onset and that the full blown disease may take several years to develop. Therefore, it is important to understand the early, asymptomatic, and possible reversible states of the disease with the aim of proposing preventive and disease-modifying therapeutic strategies. It is largely unknown how amyloid β-peptide (Aβ), a principal agent in Alzheimer disease, affects synapses in brain neurons. In this study, we found that similar to other pore-forming neurotoxins, Aβ induced a rapid increase in intracellular calcium and miniature currents, indicating an enhancement in vesicular transmitter release. Significantly, blockade of these effects by low extracellular calcium and a peptide known to act as an inhibitor of the Aβ-induced pore prevented the delayed failure, indicating that Aβ blocks neurotransmission by causing vesicular depletion. This new mechanism for Aβ synaptic toxicity should provide an alternative pathway to search for small molecules that can antagonize these effects of Aβ.  相似文献   

16.
Nonaka N  Banks WA  Mizushima H  Shioda S  Morley JE 《Peptides》2002,23(12):2197-2202
The blood–brain barrier (BBB) controls the exchange of peptides and regulatory proteins between the central nervous system (CNS) and the blood. Transport across the BBB of such regulatory substances is altered in animal models of Alzheimer’s disease. These alterations could lead to cognitive impairments or diminish their therapeutic potential. Here, we measured the transport rate of radioactively labeled pituitary adenylate cyclase-activating polypeptide (PACAP) from blood into whole brain and into 11 brain regions in three groups of mice: young (2 months old) ICR, young (2 months old) SAMP8, and aged (12 months old) SAMP8 mice. The SAMP8 is a strain which develops impaired learning and memory with aging that correlates with an age-related increase in brain levels of amyloid β protein (AβP). PACAP is a powerful neurotrophin that may have a therapeutic role in neurodegenerative diseases. We found that I-PACAP crossed the BBB fastest at the hypothalamus and the hippocampus in all three groups. Slower transport rates into the whole brain, the olfactory bulb, the hypothalamus, and the hippocampus for aged SAMP8 mice was likely related to differences both from strain and expression of AβP with aging.  相似文献   

17.
18.
Postmenopausal estrogen depletion is a characterized risk factor for Alzheimer disease (AD), a human disorder linked to high levels of β-amyloid peptide (Aβ) in brain tissue. Previous studies suggest that estrogen negatively regulates the level of Aβ in the brain, but the molecular mechanism is unknown. Here, we provide evidence that estrogen promotes Aβ degradation mainly through a principal Aβ degrading enzyme, neprilysin, in neuroblastoma SH-SY5Y cells. We also demonstrate that up-regulation of neprilysin by estrogen is dependent on both estrogen receptor α and β (ERα and ERβ), and ligand-activated ER regulates expression of neprilysin through physical interactions between ER and estrogen response elements (EREs) identified in the neprilysin gene. These results were confirmed by in vitro gel shift and in vivo chromatin immunoprecipitation analyses, which demonstrate specific binding of ERα and ERβ to two putative EREs in the neprilysin gene. The EREs also enhance ERα- and ERβ-dependent reporter gene expression in a yeast model system. Therefore, the study described here provides a putative mechanism by which estrogen positively regulates expression of neprilysin to promote degradation of Aβ, reducing risk for AD. These results may lead to novel approaches to prevent or treat AD.  相似文献   

19.

Background

We describe molecular processes that can facilitate pathogenesis of Alzheimer''s disease (AD) by analyzing the catalytic cycle of a membrane-imbedded protease γ-secretase, from the initial interaction with its C99 substrate to the final release of toxic Aβ peptides.

Results

The C-terminal AICD fragment is cleaved first in a pre-steady-state burst. The lowest Aβ42/Aβ40 ratio is observed in pre-steady-state when Aβ40 is the dominant product. Aβ42 is produced after Aβ40, and therefore Aβ42 is not a precursor for Aβ40. The longer more hydrophobic Aβ products gradually accumulate with multiple catalytic turnovers as a result of interrupted catalytic cycles. Saturation of γ-secretase with its C99 substrate leads to 30% decrease in Aβ40 with concomitant increase in the longer Aβ products and Aβ42/Aβ40 ratio. To different degree the same changes in Aβ products can be observed with two mutations that lead to an early onset of AD, ΔE9 and G384A. Four different lines of evidence show that γ-secretase can bind and cleave multiple substrate molecules in one catalytic turnover. Consequently depending on its concentration, NotchΔE substrate can activate or inhibit γ-secretase activity on C99 substrate. Multiple C99 molecules bound to γ-secretase can affect processive cleavages of the nascent Aβ catalytic intermediates and facilitate their premature release as the toxic membrane-imbedded Aβ-bundles.

Conclusions

Gradual saturation of γ-secretase with its substrate can be the pathogenic process in different alleged causes of AD. Thus, competitive inhibitors of γ-secretase offer the best chance for a successful therapy, while the noncompetitive inhibitors could even facilitate development of the disease by inducing enzyme saturation at otherwise sub-saturating substrate. Membrane-imbedded Aβ-bundles generated by γ-secretase could be neurotoxic and thus crucial for our understanding of the amyloid hypothesis and AD pathogenesis.  相似文献   

20.
Puccio S  Chu J  Praticò D 《PloS one》2011,6(1):e15163

Background

Numerous studies show that high circulating level of glucocorticosteroids is a biochemical characteristic of Alzheimer''s disease (AD). These stress hormones can increase the amount of AD-like pathology in animal models of the disease. Since they also up-regulate the 5-Lipoxygenase (5-LO), an enzyme which modulates amyloid beta (Aβ) formation, in the present paper we tested the hypothesis that this enzymatic pathway is involved in the glucocorticoid-induced pro-amyloidotic effect.

Methodology/Principal Findings

Incubation of neuronal cells with dexamethasone resulted in a significant increase in 5-LO activity and Aβ formation. By contrast, pharmacological inhibition of 5-LO prevented the dexamethasone-dependent increase in Aβ levels. Mouse embryonic fibroblasts responded with a significant increase in Aβ formation after dexamethasone challenge. However, this effect was abolished when dexamethasone was incubated with fibroblasts genetically deficient for 5-LO. No difference in the glucocorticoid receptor levels was observed between the two groups. Finally, treatment of wild type mice with dexamethasone resulted in a significant increase in endogenous brain Aβ levels, which was prevented in mice genetically lacking 5-LO.

Conclusions

These findings suggest that 5-LO plays a functional role in the glucocorticoid-induced brain AD-like amyloid pathology.  相似文献   

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