Beta amyloid Degradation ~ Research Papers on Abeta- Beta amyloid Degradation

Beta amyloid Degradation ~ Research Papers on Abeta- Beta amyloid Degradation

Am J Pathol. 2011 Jan;178(1):306-12. Epub 2010 Dec 23.


Neprilysin-2 Is an Important β-Amyloid Degrading Enzyme.



Hafez D, Huang JY, Huynh AM, Valtierra S, Rockenstein E, Bruno AM, Lu B, Desgroseillers L, Masliah E, Marr RA.



Department of Neuroscience, Rosalind Franklin University of Medicine and Science, North Chicago, Illinois.

Abstract



Proteases that degrade the amyloid-β peptide (Aβ) are important in protecting against Alzheimer's disease (AD), and understanding these proteases is critical to understanding AD pathology. Endopeptidases sensitive to inhibition by thiorphan and phosphoramidon are especially important, because these inhibitors induce dramatic Aβ accumulation (∼30- to 50-fold) and pathological deposition in rodents. The Aβ-degrading enzyme neprilysin (NEP) is the best known target of these inhibitors. However, genetic ablation of NEP results in only modest increases (∼1.5- to 2-fold) in Aβ, indicating that other thiorphan/phosphoramidon-sensitive endopeptidases are at work. Of particular interest is the NEP homolog neprilysin 2 (NEP2), which is thiorphan/phosphoramidon-sensitive and degrades Aβ. We investigated the role of NEP2 in Aβ degradation in vivo through the use of gene knockout and transgenic mice. Mice deficient for the NEP2 gene showed significant elevations in total Aβ species in the hippocampus and brainstem/diencephalon (∼1.5-fold). Increases in Aβ accumulation were more dramatic in NEP2 knockout mice crossbred with APP transgenic mice. In NEP/NEP2 double-knockout mice, Aβ levels were marginally increased (∼1.5- to 2-fold), compared with NEP(-/-)/NEP2(+/+) controls. Treatment of these double-knockout mice with phosphoramidon resulted in elevations of Aβ, suggesting that yet other NEP-like Aβ-degrading endopeptidases are contributing to Aβ catabolism.

Copyright © 2011 American Society for Investigative Pathology. Published by Elsevier Inc. All rights reserved.



PMID: 21224067 [PubMed - in process]



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2.



CNS Neurol Disord Drug Targets. 2011 Jan 11. [Epub ahead of print]

Alzheimer's Disease: From Pathogenesis to Disease-Modifying Approaches.



Galimberti D, Scarpini E.



Department of Neurological Sciences, "Dino Ferrari" Center, University of Milan, IRCCS Fondazione Ospedale Maggiore Policlinico, Via F. Sforza 35, 20122, Milan, Italy. daniela.galimberti@unimi.it.

Abstract



The two major neuropathologic hallmarks of AD are extracellular amyloid beta (A ) plaques and intracellular neurofibrillary tangles (NFTs). A number of additional pathogenic mechanisms, possibly overlapping with A plaques and NFTs formation, have been described, including inflammation, oxidative damage, iron dysregulation, and alterations in cholesterol metabolism. In this review, all of these mechanisms will be discussed and treatments that are under development to interfere with these pathogenic steps will be presented. A primary goal of work in this area is identification of novel compounds that can block the course of the disease in early phases. For this reason they are currently termed "disease modifying" drugs. These drugs are designed to modify pathological steps leading to AD, thus acting on the evolution and progression of the disease. Some of these molecules are undergoing clinical testing whereas others are in preclinical phases of development. Several approaches have been considered, including mainlyA deposition interference by anti- A aggregation agents, vaccination, -secretase inhibition or selective A 42-lowering agents (SALAs), tau deposition interference by methyl thioninium chloride (MTC), and methods for reduction of inflammation and oxidative damage.



PMID: 21222635 [PubMed - as supplied by publisher]



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3.



Curr Alzheimer Res. 2011 Jan 11. [Epub ahead of print]

Neuronal Membranes are Key to the Pathogenesis of Alzheimer's Disease: The Role of Both Raft and Non-Raft Membrane Domains.



Williamson R, Sutherland C.



Biomedical Research Institute, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, Scotland, UK. r.williamson@dundee.ac.uk.

Abstract



Membrane rafts are sterol- and sphingolipid-enriched domains that compartmentalize cellular processes. Membrane rafts isolated from post-mortem AD brain are enriched in both β-amyloid and phosphorylated tau. Proteolytic processing of APP to generate β-amyloid, the principle component of amyloid plaques, can occur in membrane rafts, implicating them in the pathogenesis of Alzheimer's disease (AD). Secondary to their role in β-amyloid generation, membrane rafts have more recently been implicated in the accumulation, aggregation and degradation of β-amyloid, with evidence supporting a specific role for membrane raft gangliosides in the binding and aggregation of β-amyloid. In addition, membrane domain composition has a direct impact on both the generation of β-amyloid and its subsequent toxic actions and as such is a key target for the development of therapeutic strategies. This mini-review will focus on recent advances in our understanding of the relevance of membrane composition, of both raft and non-raft domains, to AD progression in models and in human disease. We will discuss how manipulation of membrane composition can alter both the proteolytic processing of APP and the subsequent binding and aggregation of β-amyloid peptide.



PMID: 21222605 [PubMed - as supplied by publisher]



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Neurobiol Dis. 2011 Jan 7. [Epub ahead of print]

Mechanism mediating oligomeric Aβ clearance by naïve primary microglia.



Yang CN, Shiao YJ, Shie FS, Guo BS, Chen PH, Cho CY, Chen YJ, Huang FL, Tsay HJ.



Institute of Neuroscience, National Yang-Ming University, Taipei 11221, Taiwan.

Abstract



The accumulation of soluble oligomeric amyloid-β peptide (oAβ) proceeds the formation of senile plaques and contributes to synaptic and memory deficits in Alzheimer's disease (AD). The mechanism of mediating microglial oAβ clearance remains unclear and though to occur via scavenger receptors (SRs) in microglia. SRs respond to their ligands in a subtype-specific manner. Therefore, we sought to identify the specific subtypes of SRs that mediate oAβ internalization and proteases that degrade oAβ species in naïve primary microglia. The component of oAβ species were characterized by western blot analysis, analytical ultracentrifugation analysis, and atomic force microscopy. The oAβ species remained soluble in the medium and microglial lysates during incubation at 37°C. SR-A, but not CD36, mediated oAβ internalization in microglia as suggested by the use of subtype-specific neutralizing antibodies and small interfering RNAs (siRNAs). Immunoprecipitation analysis showed that oAβ interacted with SR-A on the plasma membrane. After internalization, over 40% of oAβ vesicles were trafficked toward lysosomes and degraded by cysteine proteases, including cathepsin B. The inhibitors of proteasome, neprilysin, matrix metalloproteinases, and insulin degrading enzyme failed to protect internalized oAβ from degradation. Our study suggests that SR-A and lysosomal cathepsin B are critical in microglial oAβ clearance, providing insight into how microglia are involved in the clearance of oAβ and their roles in the early stages of AD.

Copyright © 2010. Published by Elsevier Inc.



PMID: 21220023 [PubMed - as supplied by publisher]



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5.



Nano Lett. 2011 Jan 10. [Epub ahead of print]

Toward Intrinsic Graphene Surfaces: A Systematic Study on Thermal Annealing and Wet-Chemical Treatment of SiO(2)-Supported Graphene Devices.



Cheng Z, Zhou Q, Wang C, Li Q, Wang C, Fang Y.



National Center for Nanoscience and Technology, 11 Beiyitiao Street, Zhongguancun, Beijing 100190, People's Republic of China.

Abstract



By combining atomic force microscopy and trans-port measurements, we systematically investigated effects of thermal annealing on surface morphologies and electrical properties of single-layer graphene devices fabricated by electron beam lithography on silicon oxide (SiO(2)) substrates. Thermal treatment above 300 °C in vacuum was required to effectively remove resist residues on graphene surfaces. However, annealing at high temperature was found to concomitantly bring graphene in close contact with SiO(2) substrates and induce increased coupling between them, which leads to heavy hole doping and severe degradation of mobilities in graphene devices. To address this problem, a wet-chemical approach employing chloroform was developed in our study, which was shown to enable both intrinsic surfaces and enhanced electrical properties of graphene devices. Upon the recovery of intrinsic surfaces of graphene, the adsorption and assisted fibrillation of amyloid β-peptide (Aβ1-42) on graphene were electrically measured in real time.



PMID: 21218829 [PubMed - as supplied by publisher]



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6.



Mol Brain. 2011 Jan 7;4(1):3. [Epub ahead of print]

APP Processing in Alzheimer's Disease.



Zhang YW, Thompson R, Zhang H, Xu H.

Abstract



ABSTRACT: An important pathological feature of Alzheimer's disease (AD) is the presence of extracellular senile plaques in the brain. Senile plaques are composed of aggregations of small peptides called beta-amyloid (Abeta). Multiple lines of evidence demonstrate that overproduction/aggregation of Abeta in the brain is a primary cause of AD and inhibition of Abeta generation has become a hot topic in AD research. Abeta is generated from beta-amyloid precursor protein (APP) through sequential cleavages first by beta-secretase and then by gamma-secretase complex. Alternatively, APP can be cleaved by alpha-secretase within the Abeta domain to release soluble APPalpha and preclude Abeta generation. Cleavage of APP by caspases may also contribute to AD pathologies. Therefore, understanding the metabolism/processing of APP is crucial for AD therapeutics. Here we review current knowledge of APP processing regulation as well as the patho/physiological functions of APP and its metabolites.



PMID: 21214928 [PubMed - as supplied by publisher]Free Article



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7.



J Neurochem. 2011 Jan 7. doi: 10.1111/j.1471-4159.2010.07070.x. [Epub ahead of print]

Plasmalogen synthesis is regulated via alkyl-dihydroxyacetonephosphate-synthase (AGPS) by amyloid precursor protein (APP) processing and is affected in Alzheimer's disease.



Grimm MO, Kuchenbecker J, Rothhaar TL, Grösgen S, Hundsdörfer B, Burg VK, Friess P, Müller U, Grimm HS, Riemenschneider M, Hartmann T.



Deutsches Institut für DemenzPrävention (DIDP), Neurodegeneration and Neurobiology Psychiatry Neurology Kirrberger Str.1, 66421 Homburg Institute for Pharmacy and Molecular Biotechnology (IPMB), University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany.

Abstract



Lipids play an important role as risk or protective factors in Alzheimer's disease, which is characterized by amyloid plaques composed of aggregated amyloid-beta (Αβ). Plasmalogens are major brain lipids and controversially discussed to be altered in Alzheimer's disease (AD) and whether changes in plasmalogens are cause or consequence of AD pathology. Here we reveal a new physiological function of the amyloid precursor protein (APP) in plasmalogen metabolism. The APP intracellular domain (AICD) was found in vivo and in vitro to increase the expression of the alkyl-dihydroxyacetonephosphate-synthase (AGPS), a rate limiting enzyme in plasmalogen synthesis. Alterations in APP dependent changes of AGPS expression result in reduced protein and plasmalogen levels. Under the pathological situation of AD, increased Aβ level lead to increased reactive oxidative species (ROS) production, reduced AGPS protein and plasmalogen level. Accordingly, phosphatidylethanol plasmalogen (PE-PL) was decreased in the frontal cortex of AD compared to age matched controls. Our findings elucidate that plasmalogens are decreased as a consequence of AD and regulated by APP processing under physiological conditions.

Journal of Neurochemistry © 2011 International Society for Neurochemistry.



PMID: 21214572 [PubMed - as supplied by publisher]



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8.



J Neural Transm. 2011 Jan 6. [Epub ahead of print]

Amyloid-β protein modulates the perivascular clearance of neuronal apolipoprotein E in mouse models of Alzheimer's disease.



Rolyan H, Feike AC, Upadhaya AR, Waha A, Van Dooren T, Haass C, Birkenmeier G, Pietrzik CU, Van Leuven F, Thal DR.



Laboratory of Neuropathology, Institute of Pathology, University of Ulm, Helmholtzstrasse 8/1, 89081, Ulm, Germany.

Abstract



The deposition of amyloid-β protein (Aβ) in the brain is a hallmark of Alzheimer's disease (AD). Apolipoprotein E (apoE) is involved in the clearance of Aβ from brain and the APOE ε4 allele is a major risk factor for sporadic AD. We have recently shown that apoE is drained into the perivascular space (PVS), where it co-localizes with Aβ. To further clarify the role of apoE in perivascular clearance of Aβ, we studied apoE-transgenic mice over-expressing human apoE4 either in astrocytes (GE4) or in neurons (TE4). These animals were crossbred with amyloid precursor protein (APP)-transgenic mice and with APP-presenilin-1 (APP-PS1) double transgenic mice. Using an antibody that specifically detects human apoE (h-apoE), we observed that astroglial expression of h-apoE in GE4 mice leads to its perivascular drainage, whereas neuronal expression in TE4 mice does not, indicating that neuron-derived apoE is usually not the subject of perivascular drainage. However, h-apoE was observed not only in the PVS of APP-GE4 and APP-PS1-GE4 mice, but also in that of APP-TE4 and APP-PS1-TE4 mice. In all these mouse lines, we found co-localization of neuron-derived h-apoE and Aβ in the PVS. Aβ and h-apoE were also found in the cytoplasm of perivascular astrocytes indicating that astrocytes take up the neuron-derived apoE bound to Aβ, presumably prior to its clearance into the PVS. The uptake of apoE-Aβ complexes into glial cells was further investigated in glioblastoma cells. It was mediated by α(2)macroglobulin receptor/low density lipoprotein receptor-related protein (LRP-1) and inhibited by adding receptor-associated protein (RAP). It results in endosomal Aβ accumulation within these cells. These results suggest that neuronal apoE-Aβ complexes, but not neuronal apoE alone, are substrates for LRP-1-mediated astroglial uptake, transcytosis, and subsequent perivascular drainage. Thus, the production of Aβ and its interaction with apoE lead to the pathological perivascular drainage of neuronal apoE and provide insight into the pathological interactions of Aβ with neuronal apoE metabolism.



PMID: 21210284 [PubMed - as supplied by publisher]



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9.



PLoS One. 2010 Dec 30;5(12):e15875.

Alzheimer's aβ peptides with disease-associated N-terminal modifications: influence of isomerisation, truncation and mutation on cu coordination.



Drew SC, Masters CL, Barnham KJ.



Department of Pathology, The University of Melbourne, Melbourne, Victoria, Australia.

Abstract



BACKGROUND: The amyloid-β (Aβ) peptide is the primary component of the extracellular senile plaques characteristic of Alzheimer's disease (AD). The metals hypothesis implicates redox-active copper ions in the pathogenesis of AD and the Cu(2+) coordination of various Aβ peptides has been widely studied. A number of disease-associated modifications involving the first 3 residues are known, including isomerisation, mutation, truncation and cyclisation, but are yet to be characterised in detail. In particular, Aβ in plaques contain a significant amount of truncated pyroglutamate species, which appear to correlate with disease progression.



METHODOLOGY/PRINCIPAL FINDINGS: We previously characterised three Cu(2+)/Aβ1-16 coordination modes in the physiological pH range that involve the first two residues. Based upon our finding that the carbonyl of Ala2 is a Cu(2+) ligand, here we speculate on a hypothetical Cu(2+)-mediated intramolecular cleavage mechanism as a source of truncations beginning at residue 3. Using EPR spectroscopy and site-specific isotopic labelling, we have also examined four Aβ peptides with biologically relevant N-terminal modifications, Aβ1[isoAsp]-16, Aβ1-16(A2V), Aβ3-16 and Aβ3[pE]-16. The recessive A2V mutation preserved the first coordination sphere of Cu(2+)/Aβ, but altered the outer coordination sphere. Isomerisation of Asp1 produced a single dominant species involving a stable 5-membered Cu(2+) chelate at the amino terminus. The Aβ3-16 and Aβ3[pE]-16 peptides both exhibited an equilibrium between two Cu(2+) coordination modes between pH 6-9 with nominally the same first coordination sphere, but with a dramatically different pH dependence arising from differences in H-bonding interactions at the N-terminus.



CONCLUSIONS/SIGNIFICANCE: N-terminal modifications significantly influence the Cu(2+) coordination of Aβ, which may be critical for alterations in aggregation propensity, redox-activity, resistance to degradation and the generation of the Aβ3-× (× = 40/42) precursor of disease-associated Aβ3[pE]-x species.



PMID: 21209855 [PubMed - in process]PMCID: PMC3012727Free PMC Article



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10.



Neurology. 2010 Dec 29. [Epub ahead of print]

{gamma}-Secretase-dependent amyloid-{beta} is increased in Niemann-Pick type C: A cross-sectional study.



Mattsson N, Zetterberg H, Bianconi S, Yanjanin NM, Fu R, Månsson JE, Porter FD, Blennow K.



From the Institute of Neuroscience and Physiology (N.M., H.Z., J.-E.M., K.B.), Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy, University of Gothenburg, Mölndal, Sweden; and Program in Developmental Endocrinology and Genetics (S.B., N.M.Y., R.F., F.D.P.), Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH, DHHS, Bethesda, MD.

Abstract



OBJECTIVE: Niemann-Pick disease type C (NPC) is an inherited disorder characterized by intracellular accumulation of lipids such as cholesterol and glycosphingolipids in endosomes and lysosomes. This accumulation induces progressive degeneration of the nervous system. NPC shows some intriguing similarities with Alzheimer disease (AD), including neurofibrillary tangles, but patients with NPC generally lack amyloid-β (Aβ) plaques. Lipids affect γ-secretase-dependent amyloid precursor protein (APP) metabolism that generates Aβ in vitro, but this has been difficult to prove in vivo. Our aim was to assess the effect of altered lipid constituents in neuronal membranes on amyloidogenic APP processing in humans.



METHODS: We examined Aβ in CSF from patients with NPC (n = 38) and controls (n = 14). CSF was analyzed for Aβ(38), Aβ(40), Aβ(42), α-cleaved soluble APP, β-cleaved soluble APP, total-tau, and phospho-tau.



RESULTS: Aβ release was markedly increased in NPC, with a shift toward the Aβ(42) isoform. Levels of α- and β-cleaved soluble APP were similar in patients and controls. Patients with NPC had increased total-tau. Patients on treatment with miglustat (n = 18), a glucosylceramide synthase blocker, had lower Aβ(42) and total-tau than untreated patients.



CONCLUSION: Increased CSF levels of Aβ(38), Aβ(40), and Aβ(42) and unaltered levels of β-cleaved soluble APP are consistent with increased γ-secretase-dependent Aβ release in the brains of patients with NPC. These results provide the first in vivo evidence that neuronal lipid accumulation facilitates γ-secretase-dependent Aβ production in humans and may be of relevance to AD pathogenesis.



PMID: 21205675 [PubMed - as supplied by publisher]



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11.



Biochem J. 2011 Jan 5. [Epub ahead of print]

AMP-activated protein kinase (AMPK) is a tau kinase, activated in response to β-amyloid exposure.



Thornton C, Bright NJ, Sastre M, Muckett PJ, Carling D.

Abstract



Hyperphosphorylation of tau is a hallmark of Alzheimer's disease and other tauopathies. Although the mechanisms underlying hyperphosphorylation are not fully understood, cellular stresses such as impaired energy metabolism are thought to influence the signalling cascade. The AMPK-related kinases, MARK and BRSK, have been implicated in tau phosphorylation but are insensitive to activation by cellular stress. Here we show that AMPK itself phosphorylates tau on a number of sites including S262 and S396, altering microtubule binding of tau. In primary mouse cortical neurons, CaMKKβ activation of AMPK in response to β-amyloid (Aβ1-42) leads to increased phosphorylation of tau at S262/S356 and S396. Activation of AMPK by Aβ1-42 is inhibited by memantine, a partial antagonist of the N-methyl-D-aspartate (NMDA) receptor and currently licensed for the treatment of Alzheimer's disease. These findings identify a pathway in which Aβ1-42 activates CaMKKβ and AMPK via the NMDA receptor suggesting the possibility that AMPK plays a role in the pathophysiological phosphorylation of tau.



PMID: 21204788 [PubMed - as supplied by publisher]Free Article



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12.



PLoS One. 2010 Dec 21;5(12):e15595.

A novel statistical algorithm for gene expression analysis helps differentiate pregnane x receptor-dependent and independent mechanisms of toxicity.



Mongan MA, Dunn RT, Vonderfecht S, Everds N, Chen G, Su C, Higgins-Garn M, Chen Y, Afshari CA, Williamson TL, Carlock L, Dipalma C, Moss S, Bussiere J, Qualls C, He YD, Hamadeh HK.



Comparative Biology and Safety Sciences, Amgen Inc., Thousand Oaks, California, United States of America.

Abstract



Genome-wide gene expression profiling has become standard for assessing potential liabilities as well as for elucidating mechanisms of toxicity of drug candidates under development. Analysis of microarray data is often challenging due to the lack of a statistical model that is amenable to biological variation in a small number of samples. Here we present a novel non-parametric algorithm that requires minimal assumptions about the data distribution. Our method for determining differential expression consists of two steps: 1) We apply a nominal threshold on fold change and platform p-value to designate whether a gene is differentially expressed in each treated and control sample relative to the averaged control pool, and 2) We compared the number of samples satisfying criteria in step 1 between the treated and control groups to estimate the statistical significance based on a null distribution established by sample permutations. The method captures group effect without being too sensitive to anomalies as it allows tolerance for potential non-responders in the treatment group and outliers in the control group. Performance and results of this method were compared with the Significant Analysis of Microarrays (SAM) method. These two methods were applied to investigate hepatic transcriptional responses of wild-type (PXR(+/+)) and pregnane X receptor-knockout (PXR(-/-)) mice after 96 h exposure to CMP013, an inhibitor of β-secretase (β-site of amyloid precursor protein cleaving enzyme 1 or BACE1). Our results showed that CMP013 led to transcriptional changes in hallmark PXR-regulated genes and induced a cascade of gene expression changes that explained the hepatomegaly observed only in PXR(+/+) animals. Comparison of concordant expression changes between PXR(+/+) and PXR(-/-) mice also suggested a PXR-independent association between CMP013 and perturbations to cellular stress, lipid metabolism, and biliary transport.



PMID: 21203578 [PubMed - in process]PMCID: PMC3006344Free PMC Article



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13.



Int J Alzheimers Dis. 2010 Dec 20;2011:971021.

The role of zinc in Alzheimer's disease.



Watt NT, Whitehouse IJ, Hooper NM.



Institute of Molecular and Cellular Biology, Faculty of Biological Sciences, University of Leeds, Clarendon Way, Leeds LS2 9JT, UK.

Abstract



Zinc, the most abundant trace metal in the brain, has numerous functions, both in health and in disease. Zinc is released into the synaptic cleft of glutamatergic neurons alongside glutamate from where it interacts and modulates NMDA and AMPA receptors. In addition, zinc has multifactorial functions in Alzheimer's disease (AD). Zinc is critical in the enzymatic nonamyloidogenic processing of the amyloid precursor protein (APP) and in the enzymatic degradation of the amyloid-β (Aβ) peptide. Zinc binds to Aβ promoting its aggregation into neurotoxic species, and disruption of zinc homeostasis in the brain results in synaptic and memory deficits. Thus, zinc dyshomeostasis may have a critical role to play in the pathogenesis of AD, and the chelation of zinc is a potential therapeutic approach.



PMID: 21197404 [PubMed - in process]PMCID: PMC3010690Free PMC Article



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14.



Mol Neurodegener. 2010 Dec 30;5(1):62. [Epub ahead of print]

Protein kinase C and rho activated coiled coil protein kinase 2 (ROCK2) modulate Alzheimer's APP metabolism and phosphorylation of the Vps10-domain protein, SorL1.



Lane RF, Small SA, Gatson JW, Ehrlich ME, Gandy S.

Abstract



ABSTRACT:



BACKGROUND: Generation of the amyloid beta (Abeta) peptide of Alzheimer's disease (AD) is differentially regulated through the intracellular trafficking of the amyloid beta precursor protein (APP) within the secretory and endocytic pathways. Protein kinase C (PKC) and rho-activated coiled-coil kinases (ROCKs) are two "third messenger" signaling molecules that control the relative utilization of these two pathways. Several members of the Vps10-domain family of receptors (Vps35, SorL1, SorCS1) play important roles in post-trans-Golgi network (TGN) sorting and generation of APP derivatives, including Abeta at the TGN, endosome and the plasma membrane. We now report that Vps10-domain proteins are candidate substrates for PKC and/or ROCK2 and act as phospho-state-sensitive physiological effectors for post-TGN sorting of APP and its derivatives.



RESULTS: Analysis of the SorL1 cytoplasmic tail revealed multiple consensus sites for phosphorylation by protein kinases. SorL1 was subsequently identified as a phosphoprotein, based on sensitivity of its electrophoretic migration pattern to calf intestine alkaline phosphatase and on its reaction with anti-phospho-serine antibodies. Activation of PKC resulted in increased shedding of the ectodomains of both APP and SorL1, and this was paralleled by an apparent increase in the level of the phosphorylated form of SorL1. ROCK2, the neuronal isoform of another protein kinase, was found to form complexes with SorL1, and both ROCK2 inhibition and ROCK2 knockdown enhanced generation of both soluble APP and Abeta.



CONCLUSION: These results highlight the potential importance of SorL1 in elucidating phospho-state sensitive mechanisms in the regulation of metabolism of APP and Abeta by PKC and ROCK2.



PMID: 21192821 [PubMed - as supplied by publisher]Free Article



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15.



Colloids Surf B Biointerfaces. 2010 Dec 4. [Epub ahead of print]

Using isothermal titration calorimetry to real-time monitor the heat of metabolism: A case study using PC12 cells and Aβ(1-40).



Wang SS, Lin MS, Chen SL, Chang Y, Ruaan RC, Chen WY.



Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan.

Abstract



Isothermal titration calorimetry (ITC) is one of the most powerful means for direct determination of thermodynamic information associated with most physiochemical and biological processes. The deposition and aggregation of β-amyloid (Aβ) on cell membranes was considered as one of the primary factors in having Alzheimer's disease (AD). Recently, a growing body of evidence has suggested that plasma membrane could accelerate the accumulation of Aβ on the plasma membranes. However, the mechanism of AD is still a controversial issue. This study provided a biothermodynamic approach to real-time monitor the heat of metabolism involved in the co-incubation of PC12 cells and Aβ(1-40) by ITC. The effects of Aβ conformation and concentration of oligomeric Aβ on cytotoxicity were successfully distinguished by ITC. This approach with rapid and direct measurement may provide not only real-time information for the effects of Aβ species on living cells but also a platform for the screening of drug candidates for AD.

Copyright © 2010. Published by Elsevier B.V.



PMID: 21190816 [PubMed - as supplied by publisher]



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16.



PLoS One. 2010 Dec 20;5(12):e15645.

The nuclear inclusion a (NIa) protease of turnip mosaic virus (TuMV) cleaves amyloid-β.



Han HE, Sellamuthu S, Shin BH, Lee YJ, Song S, Seo JS, Baek IS, Bae J, Kim H, Yoo YJ, Jung YK, Song WK, Han PL, Park WJ.



Department of Life Science, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea.

Abstract



BACKGROUND: The nuclear inclusion a (NIa) protease of turnip mosaic virus (TuMV) is responsible for the processing of the viral polyprotein into functional proteins. NIa was previously shown to possess a relatively strict substrate specificity with a preference for Val-Xaa-His-Gln↓, with the scissile bond located after Gln. The presence of the same consensus sequence, Val(12)-His-His-Gln(15), near the presumptive α-secretase cleavage site of the amyloid-β (Aβ) peptide led us to hypothesize that NIa could possess activity against Aβ.



METHODOLOGY/PRINCIPAL FINDINGS: Western blotting results showed that oligomeric as well as monomeric forms of Aβ can be degraded by NIa in vitro. The specific cleavage of Aβ was further confirmed by mass spectrometry analysis. NIa was shown to exist predominantly in the cytoplasm as observed by immunofluorescence microscopy. The overexpression of NIa in B103 neuroblastoma cells resulted in a significant reduction in cell death caused by both intracellularly generated and exogenously added Aβ. Moreover, lentiviral-mediated expression of NIa in APP(sw)/PS1 transgenic mice significantly reduced the levels of Aβ and plaques in the brain.



CONCLUSIONS/SIGNIFICANCE: These results indicate that the degradation of Aβ in the cytoplasm could be a novel strategy to control the levels of Aβ, plaque formation, and the associated cell death.



PMID: 21187975 [PubMed - in process]PMCID: PMC3004936Free PMC Article



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Publication Types

Publication Types:



* Research Support, Non-U.S. Gov't



17.



J Mol Biol. 2010 Dec 23. [Epub ahead of print]

Ubiquitin Is a Novel Substrate for Human Insulin-Degrading Enzyme.



Ralat LA, Kalas V, Zheng Z, Goldman RD, Sosnick TR, Tang WJ.



Ben May Department for Cancer Research, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.

Abstract



Insulin-degrading enzyme (IDE) can degrade insulin and amyloid-β, peptides involved in diabetes and Alzheimer's disease, respectively. IDE selects its substrates based on size, charge, and flexibility. From these criteria, we predict that IDE can cleave and inactivate ubiquitin (Ub). Here, we show that IDE cleaves Ub in a biphasic manner, first, by rapidly removing the two C-terminal glycines (k(cat)=2 s(-1)) followed by a slow cleavage between residues 72 and 73 (k(cat)=0.07 s(-1)), thereby producing the inactive 1-74 fragment of Ub and 1-72 fragment of Ub (Ub1-72). IDE is a ubiquitously expressed cytosolic protein, where monomeric Ub is also present. Thus, Ub degradation by IDE should be regulated. IDE is known to bind the cytoplasmic intermediate filament protein nestin with high affinity. We found that nestin potently inhibits the cleavage of Ub by IDE. In addition, Ub1-72 has a markedly increased affinity for IDE (∼90-fold). Thus, the association of IDE with cellular regulators and product inhibition by Ub1-72 can prevent inadvertent proteolysis of cellular Ub by IDE. Ub is a highly stable protein. However, IDE, instead, prefers to degrade peptides with high intrinsic flexibility. Indeed, we demonstrate that IDE is exquisitely sensitive to Ub stability. Mutations that only mildly destabilize Ub (ΔΔG<0.6 kcal/mol) render IDE hypersensitive to Ub with rate enhancements greater than 12-fold. The Ub-bound IDE structure and IDE mutants reveal that the interaction of the exosite with the N-terminus of Ub guides the unfolding of Ub, allowing its sequential cleavages. Together, our studies link the control of Ub clearance with IDE.

Copyright © 2010. Published by Elsevier Ltd.



PMID: 21185309 [PubMed - as supplied by publisher]



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18.



PLoS One. 2010 Dec 16;5(12):e15230.

Amyloid-β triggers the release of neuronal hexokinase 1 from mitochondria.



Saraiva LM, Seixas da Silva GS, Galina A, da-Silva WS, Klein WL, Ferreira ST, De Felice FG.



Programa de Bioquímica e Biofísica Celular, Instituto de Bioquímica Médica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Rio de Janeiro, Brazil.

Abstract



Brain accumulation of the amyloid-β peptide (Aβ) and oxidative stress underlie neuronal dysfunction and memory loss in Alzheimer's disease (AD). Hexokinase (HK), a key glycolytic enzyme, plays important pro-survival roles, reducing mitochondrial reactive oxygen species (ROS) generation and preventing apoptosis in neurons and other cell types. Brain isozyme HKI is mainly associated with mitochondria and HK release from mitochondria causes a significant decrease in enzyme activity and triggers oxidative damage. We here investigated the relationship between Aβ-induced oxidative stress and HK activity. We found that Aβ triggered HKI detachment from mitochondria decreasing HKI activity in cortical neurons. Aβ oligomers further impair energy metabolism by decreasing neuronal ATP levels. Aβ-induced HKI cellular redistribution was accompanied by excessive ROS generation and neuronal death. 2-deoxyglucose blocked Aβ-induced oxidative stress and neuronal death. Results suggest that Aβ-induced cellular redistribution and inactivation of neuronal HKI play important roles in oxidative stress and neurodegeneration in AD.



PMID: 21179577 [PubMed - in process]PMCID: PMC3002973Free PMC Article



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Publication Types, Grant Support

Publication Types:



* Research Support, N.I.H., Extramural

* Research Support, Non-U.S. Gov't



Grant Support:



* R01-AG18877/AG/NIA NIH HHS/United States

* R01-AG22547/AG/NIA NIH HHS/United States



19.



J Biol Chem. 2010 Dec 21. [Epub ahead of print]

Lipoprotein lipase is a novel A{beta}-binding protein that promotes glycosaminoglycan-dependent cellular uptake of A{beta} in astrocytes.



Nishitsuji K, Hosono T, Uchimura K, Michikawa M.



National Center for Geriatrics and Gerontology, Japan.

Abstract



Lipoprotein lipase (LPL) is a member of a lipase family known to hydrolyze triglyceride molecules in plasma lipoprotein particles. LPL also plays a role in the binding of lipoprotein particles to cell-surface molecules including sulfated glycosaminoglycans (GAGs). LPL is predominantly expressed in adipose and muscle, but is also highly expressed in the brain where its specific roles are unknown. It has been shown that LPL is colocalized with senile plaques in Alzheimer's disease (AD) brains and its mutations are associated with the severity of AD pathophysiological features. In this study, we identified a novel function of LPL; that is, LPL binds to amyloid β-protein (Aβ), and promotes cell-surface association and uptake of Aβ in mouse primary astrocytes. The internalized Aβ was degraded within 12 h, mainly in a lysosomal pathway. We also found that sulfated GAGs were involved in the LPL-mediated cellular uptake of Aβ. Apolipoprotein E was dispensable in the LPL-mediated uptake of Aβ. Our findings indicate that LPL is a novel Aβ-binding protein promoting cellular uptake and subsequent degradation of Aβ.



PMID: 21177248 [PubMed - as supplied by publisher]