Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.24.56 (insulin-degrading enzyme)
 737 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Considerable evidence indicates that the amyloid-beta (Abeta) peptide, a proteolytic fragment of the amyloid precursor protein, is the pathogenic agent in Alzheimer's disease (AD). A number of proteases have been reported as capable of degrading Abeta, among them: neprilysin, insulin-degrading enzyme, endothelin-converting enzyme-1 and -2, angiotensin-converting enzyme and plasmin. These proteases, originating from a variety of cell types, degrade Abeta of various conformational states and in different cellular locations. We report here the isolation of a serine protease from serum-free conditioned medium of human neuroblastoma cells. Tandem mass spectrometry (MS/MS)-based sequencing of the isolated protein identified acyl peptide hydrolase (APH; EC3.4.19.1) as the active peptidase. APH is one of four members of the prolyl oligopeptidase family of serine proteases expressed in a variety of cells and tissues, including erythrocytes, liver and brain, but its precise biological activity is unknown. Here, we describe the identification of APH as an Abeta-degrading enzyme, and we show that the degradation of Abeta by APH isolated from transfected cells is inhibited by APH-specific inhibitors, as well as by synthetic Abeta peptide. In addition, we cloned APH from human brain and from neuroblastoma cells. Most importantly, our results indicate that APH expression in AD brain is lower than in age-matched controls.
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PMID:Acyl peptide hydrolase, a serine proteinase isolated from conditioned medium of neuroblastoma cells, degrades the amyloid-beta peptide. 1724 Nov 60

The beta amyloid (Abeta) cascade has been at the forefront of the hypothesis used to describe the pathogenesis of Alzheimer's disease (AD). It is generally accepted that drugs that can regulate the processing of the amyloid precursor protein (APP) toward the non-amyloidogenic pathway may have a therapeutic potential. Previous studies have shown that protein kinase C (PKC) hypofunction has an important role in AD pathophysiology. Therefore, the effects of a new PKC activator, alpha-APP modulator [(2S,5S)-(E,E)-8-(5-(4-(trifluoromethyl)phenyl)-2,4-pentadienoylamino)benzolactam (TPPB)], on APP processing were investigated. Using PC12 cells and SH-SY5Y(APP695) cells, it was found that TPPB promoted the secretion of sAPPalpha without affecting full-length expression of APP. The increase in sAPPalpha by TPPB was blocked by inhibitors of PKC, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and tyrosine kinase, suggesting the involvement of these signal transduction pathways. TPPB increased alpha-secretase activity [a disintegrin and metalloproteinase (ADAM)10 and 17], as shown by direct fluorescence activity detection and Western blot analysis. TPPB-induced sAPPalpha release was blocked by the metalloproteinase inhibitor TAPI-2, furin inhibitor CMK and by the protein-trafficking inhibitor brefeldin. The results also showed that TPPB decreased beta-secretase activity, Abeta40 release and beta site APP-cleaving enzyme 1 (BACE1) expression, but did not significantly affect neprilysin (NEP) and insulin-degrading enzyme (IDE) expression. Our data indicate that TPPB could direct APP processing towards the non-amyloidogenic pathway by increasing alpha-secretase activity, and suggest its therapeutic potential in AD.
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PMID:New protein kinase C activator regulates amyloid precursor protein processing in vitro by increasing alpha-secretase activity. 1765 Jan 13

Neurodegenerative diseases associated with abnormal protein folding and ordered aggregation require an initial trigger which may be infectious, inherited, post-inflammatory or idiopathic. Proteolytic cleavage to generate vulnerable precursors, such as amyloid-beta peptide (Abeta) production via beta and gamma secretases in Alzheimer's Disease (AD), is one such trigger, but the proteolytic removal of these fragments is also aetiologically important. The levels of Abeta in the central nervous system are regulated by several catabolic proteases, including insulysin (IDE) and neprilysin (NEP). The known association of human acetylcholinesterase (hAChE) with pathological aggregates in AD together with its ability to increase Abeta fibrilization prompted us to search for proteolytic triggers that could enhance this process. The hAChE C-terminal domain (T40, AChE(575-614)) is an exposed amphiphilic alpha-helix involved in enzyme oligomerisation, but it also contains a conformational switch region (CSR) with high propensity for conversion to non-native (hidden) beta-strand, a property associated with amyloidogenicity. A synthetic peptide (AChE(586-599)) encompassing the CSR region shares homology with Abeta and forms beta-sheet amyloid fibrils. We investigated the influence of IDE and NEP proteolysis on the formation and degradation of relevant hAChE beta-sheet species. By combining reverse-phase HPLC and mass spectrometry, we established that the enzyme digestion profiles on T40 versus AChE(586-599), or versus Abeta, differed. Moreover, IDE digestion of T40 triggered the conformational switch from alpha- to beta-structures, resulting in surfactant CSR species that self-assembled into amyloid fibril precursors (oligomers). Crucially, these CSR species significantly increased Abeta fibril formation both by seeding the energetically unfavorable formation of amyloid nuclei and by enhancing the rate of amyloid elongation. Hence, these results may offer an explanation for observations that implicate hAChE in the extent of Abeta deposition in the brain. Furthermore, this process of heterologous amyloid seeding by a proteolytic fragment from another protein may represent a previously underestimated pathological trigger, implying that the abundance of the major amyloidogenic species (Abeta in AD, for example) may not be the only important factor in neurodegeneration.
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PMID:Heterologous amyloid seeding: revisiting the role of acetylcholinesterase in Alzheimer's disease. 1765 79

Proteolytic enzymes constitute around 2% of the human genome and are involved in many stages of cell development from fertilization to death (apoptosis). The identification of many novel proteases from genome-sequencing programs has suggested them as potential new therapeutic targets. In addition, several well-characterized metallopeptidases were recently shown to possess new biological roles in neuroinflammation and neurodegeneration. As a result of these studies, metabolism of the neurotoxic and inflammatory amyloid peptide (Abeta) is considered as a physiologically relevant process with several metallopeptidases being suggested for the role of amyloid-degrading enzymes. These include the neprilysin (NEP) family of metalloproteinases (including its homologue endothelin-converting enzyme), insulin-degrading enzyme, angiotensin-converting enzyme, plasmin, and, possibly, some other enzymes. NEP also has a role in metabolism of sensory and inflammatory neuropeptides such as tachykinins and neurokinins. The existence of natural enzymatic mechanisms for removal of amyloid peptides has extended the therapeutic avenues in Alzheimer's disease (AD) and neurodegeneration. The proteolytic events underlying AD are highly compartmentalized in the cell and formation of amyloid peptide from its precursor molecule APP (amyloid precursor protein) takes place both within intracellular compartments and in the plasma membrane, especially in lipid raft domains. Degradation of amyloid peptide by metallopeptidases can also be both intra- and extracellular depending on the activity of membrane-bound enzymes and their soluble partners. Soluble forms of proteases can be secreted or released from the cell surface through the activity of "sheddases"-another group of proteolytic enzymes involved in key cellular regulatory functions. The activity of proteases involved in amyloid metabolism depends on numerous factors (e.g., genetic, environmental, age), and some conditions (e.g., hypoxia and ischemia) shift the balance of amyloid metabolism toward accumulation of higher concentrations of Abeta. In this regard, regulation of the activity of amyloid-degrading enzymes should be considered as a viable strategy in neuroprotection.
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PMID:New insights into the roles of metalloproteinases in neurodegeneration and neuroprotection. 1767 58

Fibrillar amyloid-beta protein (fAbeta) is the principal component of amyloid plaques in the brains of patients with Alzheimer's disease (AD). We have recently reported that activity of trypsin is inhibited by fAbeta and that trypsin can bind to fAbeta. Neprilysin and insulysin are important proteases for the clearance of soluble Abeta. Here, we report that fAbeta also binds to neprilysin and insulysin, which results in the inhibition of their proteolytic activities. These findings suggest that clearance of soluble Abeta may be defective in AD because of binding of proteases to amyloid plaques, leading to inactivation of proteases that are required for catabolism of Abeta. The identification of compounds that can inhibit binding of proteases to fAbeta may, therefore, be of significance for therapeutic intervention in AD. Congo red and Thioflavin T are widely used for histopathological examination of amyloid plaques because of their strong affinity to fibrillar amyloid proteins. We examined the effect of Congo red and Thioflavin T (potent fAbeta-binding compounds) on the binding of different proteases to fAbeta. While Congo red inhibited the binding of trypsin, neprilysin and insulysin to fAbeta, Thioflavin T did not have any effect. The effect of Congo red was concentration-dependent and the inhibitory effect was in the order of trypsin > insulysin > neprilysin. When the effect of prebound-Congo red to fAbeta was examined, trypsin was unable to bind to this complex suggesting that Congo red may have better affinity than trypsin for binding to fAbeta. Based on these results, we propose that the inhibition of binding of proteases to amyloid plaques may help in reducing the deposition of Abeta in AD.
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PMID:Binding of proteases to fibrillar amyloid-beta protein and its inhibition by Congo red. 1805 60

Internally quenched fluorogenic substrates are commonly used for measuring enzyme activity in biological samples and allow high sensitivity and continuous real-time measurement that is well suited for high throughput analysis. We describe the development and optimisation of an immunocapture-based assay that uses the fluorogenic peptide substrate (Mca-RPPGFSAFK(Dnp)) and allows the specific measurement of insulin-degrading enzyme (IDE) activity in brain tissue homogenates. This fluorogenic substrate can be cleaved by a number of enzymes including neprilysin (NEP), endothelin-converting enzyme-1 (ECE-1) and angiotensin-converting enzyme (ACE), as well as IDE, and we have previously shown that discrimination between these individual enzymes is not readily achieved in tissue homogenates, even in the presence of selective inhibitors and pH conditions. We tested a panel of IDE antibodies to isolate and capture IDE from brain tissue homogenates and found that immunocapture with antibody to the inactive domain of IDE prior to the addition of fluorogenic substrate allows sensitive (linear at 156-2500ng/ml) and specific measurement of IDE activity and negligible cross-reactivity with NEP, ACE or ECE-1. This assay should allow the measurement of IDE enzyme levels in a variety of biological tissues and may be useful in study of diseases such as Alzheimer's disease and insulin-dependent diabetes.
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PMID:Immunocapture-based fluorometric assay for the measurement of insulin-degrading enzyme activity in brain tissue homogenates. 1822 86

In Alzheimer's disease (AD) Abeta accumulates because of imbalance between the production of Abeta and its removal from the brain. There is increasing evidence that in most sporadic forms of AD, the accumulation of Abeta is partly, if not in some cases solely, because of defects in its removal--mediated through a combination of diffusion along perivascular extracellular matrix, transport across vessel walls into the blood stream and enzymatic degradation. Multiple enzymes within the central nervous system (CNS) are capable of degrading Abeta. Most are produced by neurons or glia, but some are expressed in the cerebral vasculature, where reduced Abeta-degrading activity may contribute to the development of cerebral amyloid angiopathy (CAA). Neprilysin and insulin-degrading enzyme (IDE), which have been most extensively studied, are expressed both neuronally and within the vasculature. The levels of both of these enzymes are reduced in AD although the correlation with enzyme activity is still not entirely clear. Other enzymes shown capable of degrading Abetain vitro or in animal studies include plasmin; endothelin-converting enzymes ECE-1 and -2; matrix metalloproteinases MMP-2, -3 and -9; and angiotensin-converting enzyme (ACE). The levels of plasmin and plasminogen activators (uPA and tPA) and ECE-2 are reported to be reduced in AD. Reductions in neprilysin, IDE and plasmin in AD have been associated with possession of APOEepsilon4. We found no change in the level or activity of MMP-2, -3 or -9 in AD. The level and activity of ACE are increased, the level being directly related to Abeta plaque load. Up-regulation of some Abeta-degrading enzymes may initially compensate for declining activity of others, but as age, genetic factors and diseases such as hypertension and diabetes diminish the effectiveness of other Abeta-clearance pathways, reductions in the activity of particular Abeta-degrading enzymes may become critical, leading to the development of AD and CAA.
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PMID:Abeta-degrading enzymes in Alzheimer's disease. 1836 35

The steady state concentration of the Alzheimer's amyloid-beta peptide in the brain represents a balance between its biosynthesis from the transmembrane amyloid precursor protein (APP), its oligomerisation into neurotoxic and stable species and its degradation by a variety of amyloid-degrading enzymes, principally metallopeptidases. These include, among others, neprilysin (NEP) and its homologue endothelin-converting enzyme (ECE), insulysin (IDE), angiotensin-converting enzyme (ACE) and matrix metalloproteinase-9 (MMP-9). In addition, the serine proteinase, plasmin, may participate in extracellular metabolism of the amyloid peptide under regulation of the plasminogen-activator inhibitor. These various amyloid-degrading enzymes have distinct subcellular localizations, and differential responses to aging, oxidative stress and pharmacological agents and their upregulation may provide a novel and viable therapeutic strategy for prevention and treatment of Alzheimer's disease. Potential approaches to manipulate expression levels of the key amyloid-degrading enzymes are highlighted.
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PMID:Amyloid-degrading enzymes as therapeutic targets in Alzheimer's disease. 1839 6

Apolipoprotein E is associated with age-related risk for Alzheimer's disease and plays critical roles in Abeta homeostasis. We report that ApoE plays a role in facilitating the proteolytic clearance of soluble Abeta from the brain. The endolytic degradation of Abeta peptides within microglia by neprilysin and related enzymes is dramatically enhanced by ApoE. Similarly, Abeta degradation extracellularly by insulin-degrading enzyme is facilitated by ApoE. The capacity of ApoE to promote Abeta degradation is dependent upon the ApoE isoform and its lipidation status. The enhanced expression of lipidated ApoE, through the activation of liver X receptors, stimulates Abeta degradation. Indeed, aged Tg2576 mice treated with the LXR agonist GW3965 exhibited a dramatic reduction in brain Abeta load. GW3965 treatment also reversed contextual memory deficits. These data demonstrate a mechanism through which ApoE facilitates the clearance of Abeta from the brain and suggest that LXR agonists may represent a novel therapy for AD.
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PMID:ApoE promotes the proteolytic degradation of Abeta. 1854 81

Early microglial accumulation in Alzheimer's disease (AD) delays disease progression by promoting clearance of beta-amyloid (Abeta) before formation of senile plaques. However, persistent Abeta accumulation despite increasing microglial numbers suggests that the ability of microglia to clear Abeta may decrease with age and progression of AD pathology. To determine the effects of aging and Abeta deposition on microglial ability to clear Abeta, we used quantitative PCR to analyze gene expression in freshly isolated adult microglia from 1.5-, 3-, 8-, and 14-month-old transgenic PS1-APP mice, an established mouse model of AD, and from their nontransgenic littermates. We found that microglia from old PS1-APP mice, but not from younger mice, have a twofold to fivefold decrease in expression of the Abeta-binding scavenger receptors scavenger receptor A (SRA), CD36, and RAGE (receptor for advanced-glycosylation endproducts), and the Abeta-degrading enzymes insulysin, neprilysin, and MMP9, compared with their littermate controls. In contrast, PS1-APP microglia had a 2.5-fold increase in the proinflammatory cytokines IL-1beta (interleukin-1beta) and tumor necrosis factor alpha (TNFalpha), suggesting that there is an inverse correlation between cytokine production and Abeta clearance. In support of this possibility, we found that incubation of cultured N9 mouse microglia with TNFalpha decreased the expression of SRA and CD36 and reduced Abeta uptake. Our data indicate that, although early microglial recruitment promotes Abeta clearance and is neuroprotective in AD, as disease progresses, proinflammatory cytokines produced in response to Abeta deposition downregulate genes involved in Abeta clearance and promote Abeta accumulation, therefore contributing to neurodegeneration. Antiinflammatory therapy for AD should take this dichotomous microglial role into consideration.
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PMID:Microglial dysfunction and defective beta-amyloid clearance pathways in aging Alzheimer's disease mice. 1870 98


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