Aβ42 oligomers, but not fibrils, simultaneously bind to and cause damage to ganglioside-containing lipid membranes

2011 ◽  
Vol 439 (1) ◽  
pp. 67-77 ◽  
Author(s):  
Thomas L. Williams ◽  
Benjamin R. G. Johnson ◽  
Brigita Urbanc ◽  
A. Toby A. Jenkins ◽  
Simon D. A. Connell ◽  
...  
Keyword(s):  
Lipid Membranes ◽  
Senile Plaques ◽  
Mechanical Damage ◽  
Amyloid Β ◽  
Fold Increase ◽  
Major Constituent ◽  
Membrane Disruption ◽  
Amyloid Β Peptide ◽  
Aβ Amyloid

Aβ (amyloid-β peptide) assembles to form amyloid fibres that accumulate in senile plaques associated with AD (Alzheimer's disease). The major constituent, a 42-residue Aβ, has the propensity to assemble and form soluble and potentially cytotoxic oligomers, as well as ordered stable amyloid fibres. It is widely believed that the cytotoxicity is a result of the formation of transient soluble oligomers. This observed toxicity may be associated with the ability of oligomers to associate with and cause permeation of lipid membranes. In the present study, we have investigated the ability of oligomeric and fibrillar Aβ42 to simultaneously associate with and affect the integrity of biomimetic membranes in vitro. Surface plasmon field-enhanced fluorescence spectroscopy reveals that the binding of the freshly dissolved oligomeric 42-residue peptide binds with a two-step association with the lipid bilayer, and causes disruption of the membrane resulting in leakage from vesicles. In contrast, fibrils bind with a 2-fold reduced avidity, and their addition results in approximately 2-fold less fluorophore leakage compared with oligomeric Aβ. Binding of the oligomers may be, in part, mediated by the GM1 ganglioside receptors as there is a 1.8-fold increase in oligomeric Aβ binding and a 2-fold increase in permeation compared with when GM1 is not present. Atomic force microscopy reveals the formation of defects and holes in response to oligomeric Aβ, but not preformed fibrillar Aβ. The results of the present study indicate that significant membrane disruption arises from association of low-molecular-mass Aβ and this may be mediated by mechanical damage to the membranes by Aβ aggregation. This membrane disruption may play a key role in the mechanism of Aβ-related cell toxicity in AD.

A copper-binding site in the cytoplasmic domain of BACE1 identifies a possible link to metal homoeostasis and oxidative stress in Alzheimer's disease

2007 ◽  
Vol 35 (3) ◽  
pp. 571-573 ◽  
Author(s):  
C. Dingwall
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Cytoplasmic Domain ◽  
Major Constituent ◽  
Amyloid Β Peptide ◽  
Copper Binding ◽  
App Processing ◽  
Aβ Amyloid

The amyloidogenic processing pathway of the APP (amyloid precursor protein) generates Aβ (amyloid β-peptide), the major constituent in Alzheimer's disease senile plaques. This processing is catalysed by two unusual membrane-localized aspartic proteinases, β-secretase [BACE1 (β-site APP-cleaving enzyme 1)] and the γ-secretase complex. There is a clear link between APP processing and copper homoeostasis in the brain. APP binds copper and zinc in the extracellular domain and Aβ also binds copper, zinc and iron. We have found that a 24-residue peptide corresponding to the C-terminal domain of BACE1 binds a single copper(I) atom with high affinity through cysteine residues. We also observed that the cytoplasmic domain of BACE1 interacts with CCS, the dedicated copper chaperone for SOD1 (superoxide dismutase 1). Overproduction of BACE1 reduces SOD1 activity in cells. Consequently, SOD1 activity, cytosolic copper and ectodomain cleavage of APP are linked through BACE1.

Amyloid β-peptide and Alzheimer's disease

2014 ◽  
Vol 56 ◽  
pp. 99-110 ◽  
Author(s):  
David Allsop ◽  
Jennifer Mayes
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Senile Plaques ◽  
Strong Support ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
Amyloid Cascade Hypothesis ◽  
Sequence Of Events ◽  
Aβ Amyloid ◽  
Amyloid Cascade

One of the hallmarks of AD (Alzheimer's disease) is the formation of senile plaques in the brain, which contain fibrils composed of Aβ (amyloid β-peptide). According to the ‘amyloid cascade’ hypothesis, the aggregation of Aβ initiates a sequence of events leading to the formation of neurofibrillary tangles, neurodegeneration, and on to the main symptom of dementia. However, emphasis has now shifted away from fibrillar forms of Aβ and towards smaller and more soluble ‘oligomers’ as the main culprit in AD. The present chapter commences with a brief introduction to the disease and its current treatment, and then focuses on the formation of Aβ from the APP (amyloid precursor protein), the genetics of early-onset AD, which has provided strong support for the amyloid cascade hypothesis, and then on the development of new drugs aimed at reducing the load of cerebral Aβ, which is still the main hope for providing a more effective treatment for AD in the future.

Structural origin of polymorphism of Alzheimer's amyloid β-fibrils

2012 ◽  
Vol 447 (1) ◽  
pp. 43-50 ◽  
Author(s):  
Audrey Agopian ◽  
Zhefeng Guo
Keyword(s):  
Amyloid Fibrils ◽  
Spin Exchange ◽  
Electron Paramagnetic Resonance Spectroscopy ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Side Chain ◽  
Resonance Spectroscopy ◽  
Amyloid Β Peptide ◽  
Amyloid Proteins ◽  
Aβ Amyloid

Formation of senile plaques containing amyloid fibrils of Aβ (amyloid β-peptide) is a pathological hallmark of Alzheimer's disease. Unlike globular proteins, which fold into unique structures, the fibrils of Aβ and other amyloid proteins often contain multiple polymorphs. Polymorphism of amyloid fibrils leads to different toxicity in amyloid diseases and may be the basis for prion strains, but the structural origin for fibril polymorphism is still elusive. In the present study we investigate the structural origin of two major fibril polymorphs of Aβ40: an untwisted polymorph formed under agitated conditions and a twisted polymorph formed under quiescent conditions. Using electron paramagnetic resonance spectroscopy, we studied the inter-strand side-chain interactions at 14 spin-labelled positions in the Aβ40 sequence. The results of the present study show that the agitated fibrils have stronger inter-strand spin–spin interactions at most of the residue positions investigated. The two hydrophobic regions at residues 17–20 and 31–36 have the strongest interactions in agitated fibrils. Distance estimates on the basis of the spin exchange frequencies suggest that inter-strand distances at residues 17, 20, 32, 34 and 36 in agitated fibrils are approximately 0.2 Å (1 Å=0.1 nm) closer than in quiescent fibrils. We propose that the strength of inter-strand side-chain interactions determines the degree of β-sheet twist, which then leads to the different association patterns between different cross β-units and thus distinct fibril morphologies. Therefore the inter-strand side-chain interaction may be a structural origin for fibril polymorphism in Aβ and other amyloid proteins.

Protein–protein interactions in the assembly and subcellular trafficking of the BACE (β-site amyloid precursor protein-cleaving enzyme) complex of Alzheimer's disease

2007 ◽  
Vol 35 (5) ◽  
pp. 974-979 ◽  
Author(s):  
R.B. Parsons ◽  
B.M. Austen
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Precursor Protein ◽  
Protein Interactions ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Precursor Protein ◽  
Amyloid Β Peptide ◽  
Aβ Amyloid ◽  
Ad Alzheimer’S Disease

The correct assembly of the BACE (β-site amyloid precursor protein-cleaving enzyme or β-secretase) complex and its subsequent trafficking to cellular compartments where it associates with the APP (amyloid precursor protein) is essential for the production of Aβ (amyloid β-peptide), the protein whose aggregation into senile plaques is thought to be responsible for the pathogenesis of AD (Alzheimer's disease). These processes rely upon both transient and permanent BACE–protein interactions. This review will discuss what is currently known about these BACE–protein interactions and how they may reveal novel therapeutic targets for the treatment of AD.

Impairment of the activity of the plasma membrane Ca2+-ATPase in Alzheimer's disease

2011 ◽  
Vol 39 (3) ◽  
pp. 819-822 ◽  
Author(s):  
Ana M. Mata ◽  
María Berrocal ◽  
M. Rosario Sepúlveda
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Plasma Membrane ◽  
Molecular Mechanisms ◽  
Neurodegenerative Disorder ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Inhibitory Effect ◽  
Amyloid Β Peptide ◽  
Aβ Amyloid

AD (Alzheimer's disease) is an age-associated neurodegenerative disorder where the accumulation of neurotoxic Aβ (amyloid β-peptide) in senile plaques is a typical feature. Recent studies point out a relationship between Aβ neurotoxicity and Ca2+ dyshomoeostasis, but the molecular mechanisms involved are still under discussion. The PMCAs (plasma membrane Ca2+-ATPases) are a multi-isoform family of proteins highly expressed in brain that is implicated in the maintenance of low intraneural Ca2+ concentration. Therefore the malfunction of this pump may also be responsible for Ca2+ homoeostasis failure in AD. We have found that the Ca2+-dependence of PMCA activity is affected in human brains diagnosed with AD, being related to the enrichment of Aβ. The peptide produces an inhibitory effect on the activity of PMCA which is isoform-specific, with the greatest inhibition of PMCA4. Besides, cholesterol blocked the inhibitory effect of Aβ, which is consistent with the lack of any Aβ effect on PMCA4 found in cholesterol-enriched lipid rafts isolated from pig brain. These observations suggest that PMCAs are a functional component of the machinery that leads to Ca2+ dysregulation in AD and propose cholesterol enrichment in rafts as a protector of the Aβ-mediated inhibition on PMCA.

Inhibition of Aβ(1–40) fibril formation by cyclophilins

2016 ◽  
Vol 473 (10) ◽  
pp. 1355-1368 ◽  
Author(s):  
Marten Villmow ◽  
Monika Baumann ◽  
Miroslav Malesevic ◽  
Rolf Sachs ◽  
Gerd Hause ◽  
...  
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Amyloid Β ◽  
Fibril Formation ◽  
Water Soluble ◽  
Main Process ◽  
Amyloid Β Peptide ◽  
Cyclophilin D ◽  
Aβ Amyloid

Cyclophilins interact directly with the Alzheimer's disease peptide Aβ (amyloid β-peptide) and are therefore involved in the early stages of Alzheimer's disease. Aβ binding to CypD (cyclophilin D) induces dysfunction of human mitochondria. We found that both CypD and CypA suppress in vitro fibril formation of Aβ(1–40) at substoichiometric concentrations when present early in the aggregation process. The prototypic inhibitor CsA (cyclosporin A) of both cyclophilins as well as the new water-soluble MM258 derivative prevented this suppression. A SPOT peptide array approach and NMR titration experiments confirmed binding of Aβ(1–40) to the catalytic site of CypD mainly via residues Lys16–Glu22. The peptide Aβ(16–20) representing this section showed submicromolar IC50 values for the peptidyl prolyl cis–trans isomerase activity of CypD and CypA and low-micromolar KD values in ITC experiments. Chemical cross-linking and NMR-detected hydrogen–deuterium exchange experiments revealed a shift in the populations of small Aβ(1–40) oligomers towards the monomeric species, which we investigated in the present study as being the main process of prevention of Aβ fibril formation by cyclophilins.

scholarly journals A TrkA-to-p75NTR molecular switch activates amyloid β-peptide generation during aging

2005 ◽  
Vol 391 (1) ◽  
pp. 59-67 ◽  
Author(s):  
Claudio Costantini ◽  
Richard Weindruch ◽  
Giuliano Della Valle ◽  
Luigi Puglielli
Keyword(s):  
Caloric Restriction ◽  
Late Onset ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Normal Aging ◽  
Neurotrophin Receptor ◽  
Tyrosine Kinase Receptor ◽  
Amyloid Β Peptide ◽  
Aβ Amyloid ◽  
Aβ Generation

Aging is the single most important risk factor for AD (Alzheimer's disease). However, the molecular events that connect normal aging to AD are mostly unknown. The abnormal accumulation of Aβ (amyloid β-peptide) in the form of senile plaques is one of the main characteristics of AD. In the present study, we show that two members of the neurotrophin receptor superfamily, TrkA (tyrosine kinase receptor A) and p75NTR (p75 neurotrophin receptor), differentially regulate the processing of APP (amyloid precursor protein): TrkA reduces, whereas p75NTR activates, β-cleavage of APP. The p75NTR-dependent effect requires NGF (nerve growth factor) binding and activation of the second messenger ceramide. We also show that normal aging activates Aβ generation in the brain by ‘switching’ from the TrkA to the p75NTR receptor system. Such an effect is abolished in p75NTR ‘knockout’ animals, and can be blocked by both caloric restriction and inhibitors of nSMase (neutral sphingomyelinase). In contrast with caloric restriction, which prevents the age-associated up-regulation of p75NTR expression, nSMase inhibitors block the activation of ceramide. When taken together, these results indicate that the p75NTR–ceramide signalling pathway activates the rate of Aβ generation in an age-dependent fashion, and provide a new target for both the understanding and the prevention of late-onset AD.

scholarly journals Detection of a Novel Intraneuronal Pool of Insoluble Amyloid β Protein that Accumulates with Time in Culture

1998 ◽  
Vol 141 (4) ◽  
pp. 1031-1039 ◽  
Author(s):  
Daniel M. Skovronsky ◽  
Robert W. Doms ◽  
Virginia M.-Y. Lee
Keyword(s):  
Endoplasmic Reticulum ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Acid Extraction ◽  
Amyloid Β Peptide ◽  
Amyloid Β Protein ◽  
Dependent Manner ◽  
Intermediate Compartment ◽  
Nt2n Neurons

The amyloid-β peptide (Aβ) is produced at several sites within cultured human NT2N neurons with Aβ1-42 specifically generated in the endoplasmic reticulum/intermediate compartment. Since Aβ is found as insoluble deposits in senile plaques of the AD brain, and the Aβ peptide can polymerize into insoluble fibrils in vitro, we examined the possibility that Aβ1-40, and particularly the more highly amyloidogenic Aβ1-42, accumulate in an insoluble pool within NT2N neurons. Remarkably, we found that formic acid extraction of the NT2N cells solubilized a pool of previously undetectable Aβ that accounted for over half of the total intracellular Aβ. Aβ1-42 was more abundant than Aβ1-40 in this pool, and most of the insoluble Aβ1-42 was generated in the endoplasmic reticulum/intermediate compartment pathway. High levels of insoluble Aβ were also detected in several nonneuronal cell lines engineered to overexpress the amyloid-β precursor protein. This insoluble intracellular pool of Aβ was exceptionally stable, and accumulated in NT2N neurons in a time-dependent manner, increasing 12-fold over a 7-wk period in culture. These novel findings suggest that Aβ amyloidogenesis may be initiated within living neurons rather than in the extracellular space. Thus, the data presented here require a reexamination of the prevailing view about the pathogenesis of Aβ deposition in the AD brain.

scholarly journals Dissociation of ERK signalling inhibition from the anti-amyloidogenic action of synthetic ceramide analogues

2012 ◽  
Vol 122 (9) ◽  
pp. 409-420 ◽  
Author(s):  
Hongyun Li ◽  
Genevieve Evin ◽  
Andrew F. Hill ◽  
Ya Hui Hung ◽  
Ashley I. Bush ◽  
...  
Keyword(s):  
Chinese Hamster Ovary Cells ◽  
Neuroblastoma Cells ◽  
Chinese Hamster ◽  
Amyloid Β ◽  
Amyloid Β Peptide ◽  
Principal Mechanism ◽  
Erk Phosphorylation ◽  
Aβ Amyloid ◽  
Aβ Production

Inhibition of GSL (glycosphingolipid) synthesis reduces Aβ (amyloid β-peptide) production in vitro. Previous studies indicate that GCS (glucosylceramide synthase) inhibitors modulate phosphorylation of ERK1/2 (extracellular-signal-regulated kinase 1/2) and that the ERK pathway may regulate some aspects of Aβ production. It is not clear whether there is a causative relationship linking GSL synthesis inhibition, ERK phosphorylation and Aβ production. In the present study, we treated CHO cells (Chinese-hamster ovary cells) and SH-SY5Y neuroblastoma cells, that both constitutively express human wild-type APP (amyloid precursor protein) and process this to produce Aβ, with GSL-modulating agents to explore this relationship. We found that three related ceramide analogue GSL inhibitors, based on the PDMP (D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol) structure, reduced cellular Aβ production and in all cases this was correlated with inhibition of pERK (phosphorylated ERK) formation. Importantly, the L-threo enantiomers of these compounds (that are inferior GSL synthesis inhibitors compared with the D-threo-enantiomers) also reduced ERK phosphorylation to a similar extent without altering Aβ production. Inhibition of ERK activation using either PD98059 [2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one] or U0126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene) had no impact on Aβ production, and knockdown of endogenous GCS using small interfering RNA reduced cellular GSL levels without suppressing Aβ production or pERK formation. Our data suggest that the alteration in pERK levels following treatment with these ceramide analogues is not the principal mechanism involved in the inhibition of Aβ generation and that the ERK signalling pathway does not play a crucial role in processing APP through the amyloidogenic pathway.

scholarly journals Amide solvent protection analysis demonstrates that amyloid-β(1–40) and amyloid-β(1–42) form different fibrillar structures under identical conditions

2007 ◽  
Vol 404 (1) ◽  
pp. 63-70 ◽  
Author(s):  
Anders Olofsson ◽  
Malin Lindhagen-Persson ◽  
A. Elisabeth Sauer-Eriksson ◽  
Anders Öhman
Keyword(s):  
Secondary Structure ◽  
Neurodegenerative Disorder ◽  
Senile Plaques ◽  
Amyloid Β ◽  
Abundant Species ◽  
Detailed Knowledge ◽  
Amyloid Β Peptide ◽  
Amyloid Formation ◽  
Aβ Amyloid ◽  
Protection Pattern

AD (Alzheimer's disease) is a neurodegenerative disorder characterized by self-assembly and amyloid formation of the 39–43 residue long Aβ (amyloid-β)-peptide. The most abundant species, Aβ(1–40) and Aβ(1–42), are both present within senile plaques, but Aβ(1–42) peptides are considerably more prone to self-aggregation and are also essential for the development of AD. To understand the molecular and pathological mechanisms behind AD, a detailed knowledge of the amyloid structures of Aβ-peptides is vital. In the present study we have used quenched hydrogen/deuterium-exchange NMR experiments to probe the structure of Aβ(1–40) fibrils. The fibrils were prepared and analysed identically as in our previous study on Aβ(1–42) fibrils, allowing a direct comparison of the two fibrillar structures. The solvent protection pattern of Aβ(1–40) fibrils revealed two well-protected regions, consistent with a structural arrangement of two β-strands connected with a bend. This protection pattern partly resembles the pattern found in Aβ(1–42) fibrils, but the Aβ(1–40) fibrils display a significantly increased protection for the N-terminal residues Phe4–His14, suggesting that additional secondary structure is formed in this region. In contrast, the C-terminal residues Gly37–Val40 show a reduced protection that suggests a loss of secondary structure in this region and an altered filament assembly. The differences between the present study and other similar investigations suggest that subtle variations in fibril-preparation conditions may significantly affect the fibrillar architecture.

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