Cleavage Of Amyloid Research Articles

Chronic basal forebrain activation improves spatial memory, boosts neurotrophin receptor expression, and lowers BACE1 and Aβ42 levels in the cerebral cortex in mice.

The etiology of Alzheimer's dementia has been hypothesized in terms of basal forebrain cholinergic decline, and in terms of reflecting beta-amyloid neuropathology. To study these different biological elements, we activated the basal forebrain in 5xFAD Alzheimer's model mice and littermates. Mice received 5 months of 1 h per day intermittent stimulation of the basal forebrain, which includes cholinergic projections to the cortical mantle. Then, mice were behaviorally tested followed by tissue analysis. The 5xFAD mice performed worse in water-maze testing than littermates. Stimulated groups learned the water maze better than unstimulated groups. Stimulated groups had 2-3-fold increases in frontal cortex immunoblot measures of the neurotrophin receptors for nerve growth factor and brain-derived neurotrophic factor, and a more than 50% decrease in the expression of amyloid cleavage enzyme BACE1. Stimulation also led to lower Aβ42 in 5xFAD mice. These data support a causal relationship between basal forebrain activation and both neurotrophin activation and reduced Aβ42 generation and accumulation. The observation that basal forebrain activation suppresses Aβ42 accumulation, combined with the known high-affinity antagonism of nicotinic receptors by Aβ42, documents bidirectional antagonism between acetylcholine and Aβ42.

Molecular estimation of neurodegeneration pseudotime in older brains

The temporal molecular changes that lead to disease onset and progression in Alzheimer’s disease (AD) are still unknown. Here we develop a temporal model for these unobserved molecular changes with a manifold learning method applied to RNA-Seq data collected from human postmortem brain samples collected within the ROS/MAP and Mayo Clinic RNA-Seq studies. We define an ordering across samples based on their similarity in gene expression and use this ordering to estimate the molecular disease stage–or disease pseudotime-for each sample. Disease pseudotime is strongly concordant with the burden of tau (Braak score, P = 1.0 × 10−5), Aβ (CERAD score, P = 1.8 × 10−5), and cognitive diagnosis (P = 3.5 × 10−7) of late-onset (LO) AD. Early stage disease pseudotime samples are enriched for controls and show changes in basic cellular functions. Late stage disease pseudotime samples are enriched for late stage AD cases and show changes in neuroinflammation and amyloid pathologic processes. We also identify a set of late stage pseudotime samples that are controls and show changes in genes enriched for protein trafficking, splicing, regulation of apoptosis, and prevention of amyloid cleavage pathways. In summary, we present a method for ordering patients along a trajectory of LOAD disease progression from brain transcriptomic data.

Caspase Activation and Caspase-Mediated Cleavage of APP Is Associated with Amyloid β-Protein-Induced Synapse Loss in Alzheimer’s Disease

Amyloid β-protein (Aβ) toxicity is hypothesized to play a seminal role in Alzheimer's disease (AD) pathogenesis. However, it remains unclear how Aβ causes synaptic dysfunction and synapse loss. We hypothesize that one mechanism of Aβ-induced synaptic injury is related to the cleavage of amyloid β precursor protein (APP) at position D664 by caspases that release the putatively cytotoxic C31 peptide. In organotypic slice cultures derived from mice with a knock-in mutation in the APP gene (APP D664A) to inhibit caspase cleavage, Aβ-induced synaptic injury is markedly reduced in two models of Aβ toxicity. Loss of dendritic spines is also attenuated in mice treated with caspase inhibitors. Importantly, the time-dependent dendritic spine loss is correlated with localized activation of caspase-3 but is absent in APP D664A cultures. We propose that the APP cytosolic domain plays an essential role in Aβ-induced synaptic damage in the injury pathway mediated by localized caspase activation.

Exploring beta amyloid cleavage enzyme‐1 inhibition and neuroprotective role of benzimidazole analogues as anti‐alzheimer agents

AbstractBeta amyloid cleavage enzyme‐1 (BACE1) is the key enzyme involved in Aβ peptide formation in Alzheimer's disease pathogenesis. We intend to target this enzyme by exploring benzimidazole analogues against BACE1 as potential anti‐Alzheimer agents. Docking studies were performed to determine the hydrogen bond interactions between the designed molecules and the target protein's active site. Research indicates the relationship between oxidative stress and Aβ effect in precipitating neurodegeneration; hence, the series was also studied in vitro to ascertain its neuroprotective role by performing the lipid peroxidation assay. In silico absorption, distribution, metabolism, and excretion studies were undertaken to assess the drug‐like suitability of the analogues. To judge the effect of the synthesized analogues on central nervous system (CNS), toxicity and memory model studies were conducted on mice. Thus, overall results showcase analogues 11 and 14 as the most promising ones with the dual role of BACE1 inhibition and neuroprotection, along with memory retention.

QSAR Classification Models for Predicting the Activity of Inhibitors of Beta-Secretase (BACE1) Associated with Alzheimer\u2019s Disease

Alzheimer’s disease is one of the most common neurodegenerative disorders in elder population. The β-site amyloid cleavage enzyme 1 (BACE1) is the major constituent of amyloid plaques and plays a central role in this brain pathogenesis, thus it constitutes an auspicious pharmacological target for its treatment. In this paper, a QSAR model for identification of potential inhibitors of BACE1 protein is designed by using classification methods. For building this model, a database with 215 molecules collected from different sources has been assembled. This dataset contains diverse compounds with different scaffolds and physical-chemical properties, covering a wide chemical space in the drug-like range. The most distinctive aspect of the applied QSAR strategy is the combination of hybridization with backward elimination of models, which contributes to improve the quality of the final QSAR model. Another relevant step is the visual analysis of the molecular descriptors that allows guaranteeing the absence of information redundancy in the model. The QSAR model performances have been assessed by traditional metrics, and the final proposed model has low cardinality, and reaches a high percentage of chemical compounds correctly classified.

Beta-secretase/BACE1 promotes APP endocytosis and processing in the endosomes and on cell membrane

Amyloid-β proteins deposition and aggregation occur in extracellular space and form neuritic plaques in Alzheimer’s disease (AD) brain. Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1)/ β-secretase and γ-secretase Presenilin 1 (PSEN1) conduct sequential cleavage of amyloid- β precursor protein (APP) and yield amyloid- β proteins. However the details of the interactions of APP with the enzymes and transportation of catalytic products are unclear. Here we reveal distinctive targeting patterns of the proteins in subcellular organelles in N2A cells. We find all three proteins co-localize in endosomes with APP and PSEN1 co-localize and associate on cell membrane and nucleus. By selectively knocking down BACE1 or PSEN 1 with siRNA, we discover that BACE1 functions as the enzyme initiating the first cleavage step and serves a scaffold for APP and PSEN1 endocytosis. PSEN1 knocking-down only leads to the reduction of BACE1 in cell membrane and nucleus. We conclude that BACE1 facilitates the transportation of APP and formation of the complex with γ-secretase, resulting in the stepwise cleavages of APP. After BACE1 cleavage APP binds to PSEN1 and transfers to cell membrane or nucleus for final processing and amyloid genesis.

Traumatic Brain Injury Alters the Metabolism and Facilitates Alzheimer’s Disease in a Murine Model

A majority of Alzheimer's disease (AD) cases are sporadic without known cause. People who suffered from traumatic brain injury (TBI) are more likely to develop neurodegeneration and cognitive impairments. However, the role of TBI in pathophysiology of AD remains elusive. The present study intended to explore the effect of TBI on metabolism and its role in AD pathogenesis. We subjected double transgenic AD model mice APP23/PS45 to TBI. We found that TBI promoted β-secretase cleavage of amyloid β precursor protein and amyloid β protein deposition, and exuberated the cognitive impairments in AD mouse models. 1H nuclear magnetic resonance (1H-NMR)-based metabolomics with multivariate analysis was performed to investigate the characteristic metabolites and the related metabolic pathways in the serum and urine samples of the mice. TBI affected the metabolic patterns, methylamine metabolism, and amino acid metabolism in serum samples. Urinary metabolites showed that glycolysis and the tricarboxylic acid (TCA) cycle were perturbed. The results indicate that TBI might facilitate Alzheimer's pathogenesis by altering metabolism and inducing mitochondrial dysfunction. The study suggests that metabolite changes could also serve as biomarkers for TBI-induced neurodegeneration.

Curcumin Decreases Hyperphosphorylation of Tau by Down-Regulating Caveolin-1/GSK-3β in N2a/APP695swe Cells and APP/PS1 Double Transgenic Alzheimer's Disease Mice.

Caveolin-1, the marker protein of membranal caveolae, is not only involved in cholesterol regulation, but also participates in the cleavage of amyloid [Formula: see text]-protein precursor (APP) and the generation of [Formula: see text]-amyloid peptide. It has been reported to be tightly related with Tau. In our previous studies, curcumin has been confirmed to play a neuroprotective role in Alzheimer's disease (AD), but its effects on Caveolin-1, Tau and their correlation, and the mechanism is still unknown. As such, in the present study, N2a/WT cells, N2a/APP695swe cell and six-month-old APP/PS1 double transgenic mice were enrolled. After curcumin treatment, the expression of Caveolin-1, Tau and their relationship was detected, and the potential mechanisms were explored. The results showed that in the N2a/APP695swe cells, curcumin not only decreased the number of caveolae, but also made their membrane to be thinner; and curcumin could decreased the expression of phosphorylated Tau (P-Tau(ser404)/Tau) and Caveolin-1 ([Formula: see text]), but the expression of phosphorylated GSK-3[Formula: see text] (P-GSK-3[Formula: see text]/GSK-3[Formula: see text] was increased ([Formula: see text]). In APP/PS1 transgenic mice, the same results were observed. Taken together, our data suggest that curcumin may play an important role in AD via reducing Caveolin-1, inactivating GSK-3[Formula: see text] and inhibiting the abnormal excessive phosphorylation of Tau, which will provide a new theory for AD treatment with curcumin.

Intracellular cleavage of amyloid β by a viral protease NIa prevents amyloid β-mediated cytotoxicity.

Nuclear inclusion a (NIa) of turnip mosaic virus is a cytosolic protease that cleaves amyloid β (Aβ) when heterologously overexpressed. Lentivirus-mediated expression of NIa in the brains of APP(sw)/PS1 mice significantly reduces cerebral Aβ levels and plaque depositions, and improves behavioral deficits. Here, the effects of NIa and neprilysin (NEP), a well-known Aβ-cleaving protease, on oligomeric Aβ-induced cell death were evaluated. NIa cleaved monomeric and oligomeric Aβ at a similar rate, whereas NEP only cleaved monomeric Aβ. Oligomeric Aβ-induced cytotoxicity and mitochondrial dysfunction were significantly ameliorated by NIa, but not by NEP. Endocytosed fluorescently-labeled Aβ localized to mitochondria, and this was significantly reduced by NIa, but not by NEP. These data suggest that NIa may exerts its protective roles by degrading Aβ and thus preventing mitochondrial deposition of Aβ.

Effect of Electroacupuncture Intervention on the Behavior and the Expression of β-site Amyloid Cleavage Enzyme 1 in Cerebral Cortex of SAMP8

Effect of Electroacupuncture Intervention on the Behavior and the Expression of β-site Amyloid Cleavage Enzyme 1 in Cerebral Cortex of SAMP8

F-box Only Protein 2 (Fbxo2) Regulates Amyloid Precursor Protein Levels and Processing

The amyloid precursor protein (APP) is an integral membrane glycoprotein whose cleavage products, particularly amyloid-β, accumulate in Alzheimer disease (AD). APP is present at synapses and is thought to play a role in both the formation and plasticity of these critical neuronal structures. Despite the central role suggested for APP in AD pathogenesis, the mechanisms regulating APP in neurons and its processing into cleavage products remain incompletely understood. F-box only protein 2 (Fbxo2), a neuron-enriched ubiquitin ligase substrate adaptor that preferentially binds high-mannose glycans on glycoproteins, was previously implicated in APP processing by facilitating the degradation of the APP-cleaving β-secretase, β-site APP-cleaving enzyme. Here, we sought to determine whether Fbxo2 plays a similar role for other glycoproteins in the amyloid processing pathway. We present in vitro and in vivo evidence that APP is itself a substrate for Fbxo2. APP levels were decreased in the presence of Fbxo2 in non-neuronal cells, and increased in both cultured hippocampal neurons and brain tissue from Fbxo2 knock-out mice. The processing of APP into its cleavage products was also increased in hippocampi and cultured hippocampal neurons lacking Fbxo2. In hippocampal slices, this increase in cleavage products was accompanied by a significant reduction in APP at the cell surface. Taken together, these results suggest that Fbxo2 regulates APP levels and processing in the brain and may play a role in modulating AD pathogenesis.

Long-Term Treatment of Thalidomide Ameliorates Amyloid-Like Pathology through Inhibition of β-Secretase in a Mouse Model of Alzheimer’s Disease

Thalidomide is a tumor necrosis factor alpha (TNFα) inhibitor which has been found to have abilities against tumor growth, angiogenesis and inflammation. Recently, it has been applied in clinic for the treatment of multiple myeloma as well as some inflammatory diseases. However, whether thalidomide has any therapeutic effects on neurodegenerative disorders, i.e. Alzheimer’s disease (AD) is not clear. AD is characterized by excessive amount of amyloid β peptides (Aβ), which results in a significant release of inflammatory factors, including TNFα in the brain. Studies have shown that inhibition of TNFα reduces amyloid-associated pathology, prevents neuron loss and improves cognition. Our recent report showed that genetic inhibition of TNFα/TNF receptor signal transduction down-regulates β amyloid cleavage enzyme 1 (BACE1) activity, reduces Aβ generation and improves learning and memory deficits. However, the mechanism of thalidomide involving in the mitigation of AD neuropathological features remains unclear. Here, we chronically administrated thalidomide on human APPswedish mutation transgenic (APP23) mice from 9 months old (an onset of Aβ deposits and early stage of AD-like changes) to 12 months old. We found that, in addition of dramatic decrease in the activation of both astrocytes and microglia, thalidomide significantly reduces Aβ load and plaque formation. Furthermore, we found a significant decrease in BACE1 level and activity with long-term thalidomide application. Interestingly, these findings cannot be observed in the brains of 12-month-old APP23 mice with short-term treatment of thalidomide (3 days). These results suggest that chronic thalidomide administration is an alternative approach for AD prevention and therapeutics.

The enhancement of amyloid precursor protein and β-site amyloid cleavage enzyme 1 interaction: Amyloid-β production with aging

Aging is considered a high risk factor for Alzheimer's disease (AD), which is one of the most prevalent neurodegenerative disorders in the elderly population. The major pathologic feature of AD is senile plaques mainly containing amyloid-beta (Abeta) components. However, little direct evidence has shown aging in association with Abeta. Here we show that the protein-protein interaction of amyloid precursor protein (APP) and beta -site amyloid cleavage enzyme 1 (BACE1) is enhanced by the fluorescence resonance energy transfer (FRET) assay during the aging process, and the APP-BACE1 complex accumulates in the endosome in the IMR-90 fibroblast (NHF) cellular aging models. Moreover, enhanced Abeta is observed in aged cells, rat brain homogenates and human serum. Interestingly, addition of the dominant-negative mutant of Rab5, a small G-protein Rab5 involved in the endocytic process, inhibits the aging-related APP-BACE1 interaction and Abeta production, suggesting that endocytosis contributes to AD progression.

Elucidation of insulin degrading enzyme catalyzed site specific hydrolytic cleavage of amyloid β peptide: a comparative density functional theory study

In this B3LYP study, the catalytic mechanisms for the hydrolysis of the three different peptide bonds (Lys28-Gly29, Phe19-Phe20, and His14-Gln15) of Alzheimer amyloid beta (Abeta) peptide by insulin-degrading enzyme (IDE) have been elucidated. For all these peptides, the nature of the substrate was found to influence the structure of the active enzyme-substrate complex. The catalytic mechanism is proposed to proceed through the following three steps: (1) activation of the metal-bound water molecule, (2) formation of the gem-diol intermediate, and (3) cleavage of the peptide bond. With the computed barrier of 14.3, 18.8, and 22.3 kcal/mol for the Lys28-Gly29, Phe19-Phe20, and His14-Gln15 substrates, respectively, the process of water activation was found to be the rate-determining step for all three substrates. The computed energetics show that IDE is the most efficient in hydrolyzing the Lys28-Gly29 (basic polar-neutral nonpolar) peptide bond followed by the Phe19-Phe20 (neutral nonpolar-neutral nonpolar) and His14-Gln15 (basic polar-neutral polar) bonds of the Abeta substrate.

P4-250: Assessment of heparan-mimetics as novel Alzheimer therapeutics

Cleavage of amyloid _–protein precursor (APP) by the protease beta–secretase (BACE1) is a key step in AÎ2 peptide processing. We have recently discovered that the cellular polysaccharide heparan sulfate (HS) is a regulator of BACE1 activity, indicating that it may play a key role in AÎ2 generation and AD pathogenesis. We have also generated heparan–mimetics with potent BACE1 inhibitory activity and low anticoagulant activity as lead compounds for a new class of AD therapeutics. They are effective at lowering AÎ2 production and do not show cytotoxicity in organotypic brain cultures. To test novel heparan–mimetics for toxicity, bioavailability and efficacy in the Tg2576 transgenic mouse model of AD. Mice were injected either with various compounds or saline and evaluated by measuring levels of AÎ2 in the brains as well as by behavioral testing. The compounds showed no evidence of toxicity at any dose. Distribution of radiolabelled compound was measured according to tissue. Pilot efficacy studies showed evidence of promise. The data provides new insights into the in vivo efficacy of heparan–mimetics as BACE1 inhibitors. These studies could underpin the development of new therapeutic strategies for human AD and other neurodegenerative disorders.

Molecular pathology of Alzheimer's disease

Alzheimer's disease (AD) is characterized by the presence of large numbers of senile plaques, neurofibrillary tangles and neuroinflammatory cells. Evidence from genetic studies suggests that the formulation of these plaques is fundamental to the development of AD and that plaques have a central role to play in the instigation of the other pathologies found in AD. To date, four genes have been identified as contributing to the genetic aetiology of AD; amyloid precursor protein, presenilin 1, presenilin 2 and apolipoprotein E. All of these genes have been shown to have a role in the development of senile plaques with some shown to directly facilitate the cleavage of amyloid, the core component of senile plaques, from its parent molecule, amyloid precursor protein. An understanding of the genetic aetiology of AD has led directly to the development of drugs that interfere with the cleavage of intact amyloid from amyloid precursor protein. The aggregation of amyloid molecules is thought to have an important role in the development of tangles and the activation of inflammatory cells. Compounds that disrupt the aggregation of amyloid plaques are already undergoing clinical trials. In addition, studies have shown that amyloid plaques can be removed by active immunization. The formulation of neurofibrillary tangles may be facilitated by activation of several kinases, including GSK-3. More recently, it has been shown that these kinases can be inhibited by drugs including lithium, and so these drugs have now been identified as possible therapeutic agents.

Protein phosphorylation regulates secretion of Alzheimer beta/A4 amyloid precursor protein.

Extracellular deposition of the beta/A4 amyloid peptide is a characteristic feature of the brain in patients with Alzheimer disease. beta/A4 amyloid is derived from the amyloid precursor protein (APP), an integral membrane protein that exists as three major isoforms (APP695, APP751, and APP770). Secreted forms of APP found in blood plasma and cerebrospinal fluid arise by proteolytic cleavage of APP within the beta/A4 amyloid domain, precluding the possibility of amyloidogenesis for that population of molecules. In the present study, we have demonstrated that treatment of PC12 cells with phorbol ester produces a severalfold increase in secretion of APP695, APP751, and APP770. This increase is augmented by simultaneous treatment with the protein phosphatase inhibitor okadaic acid. These data indicate that protein phosphorylation regulates intra-beta/A4 amyloid cleavage and APP secretion. These and other results suggest that APP molecules can normally follow either of two processing pathways: regulated secretion or proteolytic degradation unassociated with secretion.

Cleavage of Amyloid β Peptide During Constitutive Processing of Its Precursor

The amyloid beta peptide (A beta P) is a small fragment of the much larger, broadly distributed amyloid precursor protein (APP). Abundant A beta P deposition in the brains of patients with Alzheimer's disease suggests that altered APP processing may represent a key pathogenic event. Direct protein structural analyses showed that constitutive processing in human embryonic kidney 293 cells cleaves APP in the interior of the A beta P, thus preventing A beta P deposition. A deficiency of this processing event may ultimately prove to be the etiological event in Alzheimer's disease that gives rise to senile plaque formation.