1.
Phosphorus Dendrimers Affect Alzheimer's (Aβ1-28) Peptide and MAP-Tau Protein Aggregation.
Abstract
Alzheimer's disease (AD) is characterized by pathological aggregation of β-amyloid peptides and MAP-Tau protein. β-amyloid (Aβ) is a peptide responsible for extracellular Alzheimer's plaque formation. Intracellular MAP-Tau aggregates appear as a result of hyperphosphorylation of this cytoskeletal protein. Small, oligomeric forms of Aβ are intermediate products that appear before the amyloid plaques are formed. These forms are believed to be most neurotoxic. Dendrimers are highly branched polymers, which may find an application in regulation of amyloid fibril formation. Several biophysical and biochemical methods, like circular dichroism (CD), fluorescence intensity of thioflavin T and thioflavin S, transmission electron microscopy, spectrofluorimetry (measuring quenching of intrinsic peptide fluorescence) and MTT-cytotoxicity assay, were applied to characterize interactions of cationic phosphorus-containing dendrimers of generation 3 and generation 4 (CPDG3, CPDG4) with the fragment of amyloid peptide (Aβ1-28) and MAP-Tau protein. We have demonstrated that CPDs are able to affect β-amyloid and MAP-Tau aggregation processes. A neuro-2a cell line (N2a) was used to test cytotoxicity of formed fibrils and intermediate products during the Aβ1-28 aggregation. It has been shown that CPDs might have a beneficial effect by reducing the system toxicity. Presented results suggest that phosphorus dendrimers may be used in the future as agents regulating the fibrilization processes in Alzheimer's disease.
p53, a Pivotal Effector of a Functional Cross-Talk Linking Presenilins and Pen-2.
Source
Institut de Pharmacologie Moléculaire et Cellulaire et Institut de NeuroMédecine Moléculaire, Equipe Labellisée Fondation pour la Recherche Médicale, Valbonne, France.
Abstract
The γ-secretase is a multiprotein complex responsible for the ultimate cut yielding amyloid-β peptides and their N-terminal truncated species. This complex is composed of at least four distinct entities, namely presenilin-1 (PS1) or PS2, anterior pharynx defective-1, presenilin enhancer-2 (Pen-2) and nicastrin. Very few studies examined the transcriptional regulation of this complex, and more precisely, whether some of the members functionally interact. Here, we summarize our previous data documenting the fact that Pen-2 controls cell death in a p53-dependent manner and our recent demonstration of a pivotal role of p53 as a regulator of Pen-2 transcription. As PS trigger amyloid precursor protein intracellular domain-dependent regulation of p53, our studies delineate a feedback control mechanism by which PS and Pen-2 functionally interact in a p53-dependent manner.
Copyright © 2011 S. Karger AG, Basel.
Fibrillar Amyloid-β1-42 Modifies Actin Organization Affecting the Cofilin Phosphorylation State: A Role for Rac1/cdc42 Effector Proteins and the Slingshot Phosphatase.
Source
Laboratory of Cellular and Molecular Neurosciences, University of Chile and International Center for Biomedicine (ICC), Santiago, Chile.
Abstract
The neuronal cytoskeleton regulates numerous processes that occur in normal homeostasis. Under pathological conditions such as those of Alzheimer's disease (AD), major alterations in cytoskeleton organization have been observed and changes in both microtubules and actin filaments have been reported. Many neurodegenerative consequences of AD are linked to the production and accumulation of amyloid peptides (Aβ) and their oligomers, produced from the internal cleavage of the amyloid-β protein precursor. We previously reported that fibrillar Aβ1-42 (fAβ) treatment of hippocampal neurons induced an increase in Rac1 and Cdc42 activities linking fAβ effects with changes in actin dynamics. Here we show fAβ-induces increased activity of PAK1 and cyclin-dependent kinase 5, and that p21-activated kinase (PAK1) activation targets the LIMK1-cofilin signaling pathway. Increased cofilin dephosphorylation under conditions of enhanced LIM-Kinase 1 (LIMK1) activity suggests that fAβ co-stimulates bifurcating pathways impacting cofilin phosphorylation. Overexpression of slingshot (SSH) prevents the augment of F-actin induced by fAβ after 24 h, suggesting that fAβ-induced changes in actin assembly involve both LIMK1 and SSH. These results suggest that fAb may alter the PAK1/LIMK1/cofilin axis and therefore actin organization in AD.
The Effect of Amyloidogenic Peptides on Bacterial Aging Correlates with Their Intrinsic Aggregation Propensity.
Source
Institut de Biotecnologia i Biomedicina and Departament de Bioquímica i Biologia Molecular, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain.
Abstract
The formation of aggregates by misfolded proteins is thought to be inherently toxic, affecting cell fitness. This observation has led to the suggestion that selection against protein aggregation might be a major constraint on protein evolution. The precise fitness cost associated with protein aggregation has been traditionally difficult to evaluate. Moreover, it is not known if the detrimental effect of aggregates on cell physiology is generic or depends on the specific structural features of the protein deposit. In bacteria, the accumulation of intracellular protein aggregates reduces cell reproductive ability, promoting cellular aging. Here, we exploit the cell division defects promoted by the intracellular aggregation of Alzheimer's-disease-related amyloid β peptide in bacteria to demonstrate that the fitness cost associated with protein misfolding and aggregation is connected to the protein sequence, which controls both the in vivo aggregation rates and the conformational properties of the aggregates. We also show that the deleterious impact of protein aggregation on bacterial division can be buffered by molecular chaperones, likely broadening the sequential space on which natural selection can act. Overall, the results in the present work have potential implications for the evolution of proteins and provide a robust system to experimentally model and quantify the impact of protein aggregation on cell fitness.
Copyright © 2011 Elsevier Ltd. All rights reserved.
Noncore Residues Influence the Kinetics of Functional TTR(105-)(115)-BasedAmyloid Fibril Assembly.
Source
Department of Chemical and Biomolecular Engineering, The University of Melbourne, Parkville VIC 3010, Australia; Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Parkville VIC 3010, Australia.
Abstract
Mutations in the polypeptide sequence that forms the core structure of amyloid fibrils are known to impact on fibril assembly and stability, but the effect of changes on noncore residues, particularly relating to functionalized fibrils where the fibril core is preserved, has not been systematically examined. In this study, the short peptide sequence TTR(105-115) (also known as TTR1) and the functionalized variants TTR1-RGD and TTR1-RAD are used as a model system to investigate the effect of noncore residues on the kinetics of fibril assembly. The noncore residues in TTR1-RGD and TTR1-RAD influence the rate of fibril assembly in non-seeded samples with the glycine residue at position 15 increasing the rate of aggregation compared to alanine. Mature TTR1-RGD fibrils were also found to fragment more readily, indicating possible differences in mechanical properties. Fragments of each type of fibril are capable of self- and cross-seeding, generating fibrils with a highly similar cross-β core structure. The similar rates of assembly observed for self-seeded samples reflect the similar free energy of elongation calculated for these peptides, while the morphology of cross-seeded fibrils is determined by the properties of the monomeric peptide and its macromolecular arrangement within the protofilaments and fibrils. These findings illustrate that noncore residues impact on fibril formation and fibril properties and demonstrate that the influence of noncore residues should be considered when designing sequences for the production of self-assembling functional fibrillar materials.
Copyright © 2011 Elsevier Ltd. All rights reserved.
Structural Basis of C-terminal β-Amyloid Peptide Binding by the Antibody Ponezumab for the Treatment of Alzheimer's Disease.
Source
Rinat, Pfizer Inc., 230 East Grand Avenue, South San Francisco, CA 94080, USA.
Abstract
Alzheimer's disease, the most common cause of dementia in the elderly and characterized by the deposition and accumulation of plaques, is composed in part of β-amyloid (Aβ) peptides, loss of neurons, and the accumulation of neurofibrillary tangles. Here, we describe ponezumab, a humanized monoclonal antibody, and show how it binds specifically to the carboxyl (C)-terminus of Aβ40. Ponezumab can label Aβ that is deposited in brain parenchyma found in sections from Alzheimer's disease casualties and in transgenic mouse models that overexpress Aβ. Importantly, ponezumab does not label full-length, non-cleaved amyloid precursor protein on the cell surface. The C-terminal epitope of ponezumab appears to be available for binding soluble Aβ present in the circulation because systemic administration of ponezumab greatly elevates plasma Aβ40 levels in a dose-dependent fashion after administration to a mouse model that overexpress human Aβ. Administration of ponezumab to transgenic mice also led to a dose-dependent reduction in hippocampal amyloid load. To further explore the nature of ponezumab binding to Aβ40, we determined the X-ray crystal structure of ponezumab in complex with Aβ40 and found that the Aβ40 carboxyl moiety makes extensive contacts with ponezumab. Furthermore, the structure-function analysis supported this critical requirement for carboxy group of AβV40 in the Aβ-ponezumab interaction. These findings provide novel structural insights into the in vivo conformation of the C-terminus of Aβ40 and the brain Aβ-lowering efficacy that we observed following administration of ponezumab in transgenic mouse models.
Copyright © 2011 Elsevier Ltd. All rights reserved.
Hypoxia Due to Cardiac Arrest Induces a Time-Dependent Increase in SerumAmyloid β Levels in Humans.
Source
Department of Psychiatry and Neurochemistry, The Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden.
Abstract
Amyloid β (Aβ) peptides are proteolytic products from amyloid precursor protein (APP) and are thought to play a role in Alzheimer disease (AD) pathogenesis. While much is known about molecular mechanisms underlying cerebral Aβ accumulation in familial AD, less is known about the cause(s) of brain amyloidosis in sporadic disease. Animal and postmortem studies suggest that Aβ secretion can be up-regulated in response to hypoxia. We employed a new technology (Single Molecule Arrays, SiMoA) capable of ultrasensitive protein measurements and developed a novel assay to look for changes in serum Aβ42 concentration in 25 resuscitated patients with severe hypoxia due to cardiac arrest. After a lag period of 10 or more hours, very clear serum Aβ42 elevations were observed in all patients. Elevations ranged from approximately 80% to over 70-fold, with most elevations in the range of 3-10-fold (average approximately 7-fold). The magnitude of the increase correlated with clinical outcome. These data provide the first direct evidence in living humans that ischemia acutely increases Aβ levels in blood. The results point to the possibility that hypoxia may play a role in the amyloidogenic process of AD.
Contributions of brain insulin resistance and deficiency in amyloid-related neurodegeneration in Alzheimer's disease.
Source
Departments of Pathology, Neurosurgery, Neurology, and Medicine, Rhode Island Hospital and the Warren Alpert Medical School of Brown University, Providence, RI, USA.
Abstract
Alzheimer's disease (AD) is the most common cause of dementia in North America. Growing evidence supports the concept that AD is fundamentally a metabolic disease that results in progressive impairment in the brain's capacity to utilize glucose and respond to insulin and insulin-like growth factor (IGF) stimulation. Moreover, the heterogeneous nature of AD is only partly explained by the brain's propensity to accumulate aberrantly processed, misfolded and aggregated oligomeric structural proteins, including amyloid-β peptides and hyperphosphorylated tau. Evidence suggests that other factors, including impaired energy metabolism, oxidative stress, neuroinflammation, insulin and IGF resistance, and insulin/IGF deficiency in the brain should be incorporated into an overarching hypothesis to develop more realistic diagnostic and therapeutic approaches to AD. In this review, the interrelationship between impaired insulin and IGF signalling and amyloid-β pathology is discussed along with potential therapeutic approaches. Impairments in brain insulin/IGF signalling lead to increased expression of amyloid-β precursor protein (AβPP) and accumulation of AβPP-Aβ. In addition, they promote oxidative stress and deficits in energy metabolism, leading to the activation of pro-AβPP-Aβ-mediated neurodegeneration cascades. Although brain insulin/IGF resistance and deficiency can be induced by primary or secondary disease processes, the soaring rates of peripheral insulin resistance associated with obesity, diabetes mellitus and metabolic syndrome quite likely play major roles in the current AD epidemic. Both clinical and experimental data have linked chronic hyperinsulinaemia to cognitive impairment and neurodegeneration with increased AβPP-Aβ accumulation/reduced clearance in the CNS. Correspondingly, both the restoration of insulin responsiveness and the use of insulin therapy can lead to improved cognitive performance, although with variable effects on brain AβPP-Aβ load. On the other hand, experimental evidence supports the concept that the toxic effects of AβPP-Aβ can promote insulin resistance. Together, these findings suggest that a positive feedback loop of progressive neurodegeneration can develop whereby insulin resistance drives AβPP-Aβ accumulation, and AβPP-Aβ fibril toxicity drives brain insulin resistance. This phenomenon could explain why measuring AβPP-Aβ levels in cerebrospinal fluid or imaging of the brain has proven to be inadequate as a stand-alone biomarker for diagnosing AD, and why the clinical trial results of anti-AβPP-Aβ monotherapy have been disappointing. Instead, the aggregate data suggest that brain insulin resistance and deficiency must also be therapeutically targeted to halt AD progression or reverse its natural course. The positive therapeutic effects of different treatments that address the role of brain insulin/IGF resistance and deficiency, including the use of intranasal insulin delivery, incretins and insulin sensitizer agents are discussed along with potential benefits of lifestyle changes to modify risk for developing mild cognitive impairment or AD. Altogether, the data strongly support the notion that we must shift toward the implementation of multimodal rather than unimodal diagnostic and therapeutic strategies for AD.
Reevaluation of Copper(I) Affinity for Amyloid-β Peptides by Competition with Ferrozine-An Unusual Copper(I) Indicator.
Source
CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, 31077 Toulouse, (France); Université de Toulouse, UPS, INPT, LCC, 31077 Toulouse (France), Fax: (+33) 5-61-55-30-03.
Abstract
The association constant of ferrozine (5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine-4,4''-disulfonic acid) with Cu(I) to form the chromophoric [Cu(I) (Fz)(2) ](3-) complex was determined by UV/Vis titration experiments in Hepes buffer (0.1 m, pH 7.4). An association constant close to 10(12) M(-2) , which is significantly weaker than those of the well-known, water-soluble, Cu(I) chelators bicinchoninic acid and 2,9-dimethyl-4,7-diphenyl-1,10-phenantroline disulfonic acid, was found. The [Cu(I) (Fz)(2) ](3-) chromophore was used in UV/Vis competition experiments to determine Cu(I) binding affinity for the amyloid-β peptide involved in Alzheimer's disease and for a series of pertinent mutants. An association constant of approximately 10(7) M(-1) was found; this is much weaker than that reported for dithiothreitol and confirms that imidazoles are harder ligands than thiolates. Each His mutation (H6A, H13A, and H14A) impacts the peptide affinity for Cu(I) . The native human amyloid-β peptide was found to be a fourfold-stronger Cu(I) ligand than the murine peptide, which differs by three point mutations (R5G, Y10F, and H13R) from the human one.
Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Propyl isomerase Pin1 promotes APP protein turnover by inhibiting GSK3β kinase activity: A novel mechanism for Pin1 to protect against Alzheimer's disease.
Source
Beth Israel Deaconese Medical Center, United States;
Abstract
Alzheimer's disease (AD) is characterized by the presence of senile plaques of amyloid-beta peptides (Aβ) derived fromamyloid precursor protein (APP) and neurofibrillary tangles composed of hyperphosphorylated tau. Increasing APP gene dosage or expression has been shown to cause familial early-onset AD. However, whether protein stability of APP is regulated is unclear. The prolyl isomerase Pin1 and glycogen synthase 3β (GSK3β) have been shown to have the opposite effects on APP processing and tau hyperphosphorylation, relevant to the pathogenesis of AD. However, nothing is known about their relationship. In this study, we found that Pin1 binds to the pT330-P motif in GSK3β to inhibit its kinase activity. Furthermore, Pin1 promotes protein turnover of APP by inhibiting GSK3β activity. A point mutation either at T330, the Pin1-binding site in GSK3β, or T668, the GSK3β phosphorylation site in APP, abolished the regulation of GSK3β activity, T668 phosphorylation and APP stability by Pin1, resulting in reduced non-amyloidogenic APP processing and increased APP levels. These results uncover a novel role of Pin1 in inhibiting GSK3β kinase activity to reduce APP protein levels, providing a previously unrecognized mechanism by which Pin1 protects against Alzheimer's disease.
Differing modes of interaction between monomeric Aβ(1-40) peptides and model lipid membranes: an AFM study.
Source
Nanoscale Function Group, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
Abstract
Membrane interactions with β-amyloid peptides are implicated in the pathology of Alzheimer's disease and cholesterol has been shown to be key modulator of this interaction, yet little is known about the mechanism of this interaction. Using atomic force microscopy, we investigated the interaction of monomeric Aβ(1-40) peptides with planar mica-supported bilayers composed of DOPC and DPPC containing varying concentrations of cholesterol. We show that below the bilayer melting temperature, Aβ monomers adsorb to, and assemble on, the surface of DPPC bilayers to form layers that grow laterally and normal to the bilayer plane. Above the bilayer melting temperature, we observe protofibril formation. In contrast, in DOPC bilayers, Aβ monomers exhibit a detergent-like action, forming defects in the bilayer structure. The kinetics of both modes of interaction significantly increases with increasing membrane cholesterol content. We conclude that the mode and rate of the interaction of Aβ monomers with lipid bilayers are strongly dependent on lipid composition, phase state and cholesterol content.
Copyright © 2011. Published by Elsevier Ireland Ltd.
Hydrophobic interactions in the formation of secondary structures in smallpeptides.
Source
Department of Biochemistry and Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada M5S 1A8 and Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7.
Abstract
Effects of the attractive and repulsive parts of hydrophobic interactions on α helices and β sheets in small peptides are investigated using a simple atomic potential. Typically, a physical spatial range of attraction tends to favor β sheets, but α helices would be favored if the attractive range were more extended. We also found that desolvation barriers favor β sheets in collapsed conformations of polyalanine, polyvaline, polyleucine, and three fragments of amyloid peptidestested in this study. Our results provide insight into the multifaceted role of hydrophobicity in secondary structure formation, including the α to β transitions in certain amyloid peptides.
Slow Amyloid Nucleation via α-Helix-Rich Oligomeric Intermediates in Short Polyglutamine-Containing Huntingtin Fragments.
Source
Department of Structural Biology and Pittsburgh Institute for Neurodegenerative Disease, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
Abstract
The 17-amino-acid N-terminal segment (htt(NT)) that leads into the polyglutamine (polyQ) segment in the Huntington's disease protein huntingtin (htt) dramatically increases aggregation rates and changes the aggregation mechanism, compared to a simple polyQ peptide of similar length. With polyQ segments near or above the pathological repeat length threshold of about 37, aggregation of htt N-terminal fragments is so rapid that it is difficult to tease out mechanistic details. We describe here the use of very short polyQ repeat lengths in htt N-terminal fragments to slow this disease-associated aggregation. Although all of these peptides, in addition to htt(NT) itself, form α-helix-rich oligomeric intermediates, only peptides with Q(N) of eight or longer mature into amyloid-like aggregates, doing so by a slow increase in β-structure. The final amyloid-like aggregates not only feature the expected high β-sheet content but also retain an element of solvent-exposed α-helix. The α-helix-rich oligomeric intermediates appear to be both on- and off-pathway, with some oligomers serving as the pool from within which nuclei emerge, while others serve as a reservoir for release of monomers to support fibril elongation. Based on a regular pattern of multimers observed in analytical ultracentrifugation, and a concentration dependence of α-helix formation in CD spectroscopy, it is likely that these oligomers assemble via a four-helix assembly unit. PolyQ expansion in these peptides appears to enhance the rates of both oligomer formation and nucleation from within the oligomer population, by structural mechanisms that remain unclear.
Copyright © 2011 Elsevier Ltd. All rights reserved.
Effects of different force fields and temperatures on the structural character of abeta (12-28) Peptide in aqueous solution.
Source
Shandong Provincial Key Laboratory of Functional Macromolecular Biophysics, Dezhou University, 566 University Rd. West, Dezhou 253023, China; E-Mails: qiayilai@mail.ustc.edu.cn (Z.C.); leiliusid@gmail.com (L.L.); zhaoll@sina.com (L.Z.).
Abstract
The aim of this work is to investigate the effects of different force fields and temperatures on the structural character of Aβ (12-28) peptide in aqueous solution. Moreover, the structural character of Aβ (12-28) peptide is compared with otheramyloid peptides (such as H1 and α-syn12 peptide). The two independent temperature replica exchange molecular dynamics (T-REMD) simulations were completed by using two different models (OPLS-AA/TIP4P and GROMOS 43A1/SPC). We compared the models by analyzing the distributions of backbone dihedral angles, the secondary structure propensity, the free energy surface and the formation of β-hairpin. The results show that the mostly populated conformation state is random coil for both models. The population of β-hairpin is below 8 percent for both models. However, the peptide modeled by GROMOS 43A1 form β-hairpin with turn located at residues F19-E22, while the peptide modeled by OPLS-AA form β-hairpin with turn located at residues L17-F20.
BACE1 Trafficking and Alzheimer's Disease Pathogenesis.
Source
Department of Pathology, and Mental Health Research Institute, The University of Melbourne, Parkville VIC 3010, Australia.
Abstract
BACE1 cleaves the amyloid precursor protein (APP) at the β-secretase site to initiate the production of Aβ peptides. These accumulate to form toxic oligomers and the amyloid plaques associated with Alzheimer's disease (AD). An increase of BACE1 levels in the brain of AD patients has been mostly attributed to alterations of its intracellular trafficking. Golgi-associated adaptor proteins, GGA sort BACE1 for export to the endosomal compartment, which is its major cellular site of BACE1 activity. BACE1 undergoes recycling between endosome, trans-Golgi network (TGN), and the plasma membrane, from where it is endocytosed and either further recycled or retrieved to the endosome. Phosphorylation of Ser498 facilitates BACE1 recognition by GGA1 for retrieval to the endosome. Ubiquitination of BACE1 C-terminal Lys501 signals GGA3 for exporting BACE1 to the lysosome for degradation. In addition, the retromer mediates the retrograde transport of BACE1 from endosome to TGN. Decreased levels of GGA proteins and increased levels of retromer-associated sortilin have been associated with AD. Both would promote the co-localization of BACE1 and APP in the TGN and endosomes. Decreased levels of GGA3 also impair BACE1 degradation. Further understanding of BACE1 trafficking and its regulation may offer new therapeutic approaches for the treatment of Alzheimer's disease. © 2011 The Authors Journal of Neurochemistry© 2011 International Society for Neurochemistry.
© 2011 The Authors Journal of Neurochemistry © 2011 International Society for Neurochemistry.
125I-Labeled single-chain monoclonal antibody, NS4F5, that targets the GlcNS6S-IdoA2S motif of heparan sulfate proteoglycans for the in vivo imaging of peripheral amyloidosis.
Authors
Source
Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2011.
2011 Nov 04 [updated 2011 Dec 01].
Excerpt
Peripheral amyloidosis is the extracellular deposition of insoluble protein fibrils in various organs of animals, including humans, and these deposits are considered to be biomarkers for diseases such as Alzheimer’s disease (AD), light chain amyloidosis (AL), etc (1). The fibrils are made up of disease-specific aggregated proteins or peptides (e.g., Aβpeptides for AD, light chains for AL or multiple myeloma, and reactive amyloidosis (AA)) that incorporate heparin sulfate proteoglycans (HSPG; heparin belongs to the heparan sulfate family of proteoglycans that contain the (GlcNS6S-IdoA2S)3 motif)) and the serum amyloid P component (SAP) within their structure during disease progression. A characteristic feature of the protein fibrils is that the constituent proteins form a secondary cross-β pleated sheet structure that is resistant to proteolytic digestion (for structural details, see Goldsbury et al. (2)). In addition, clinical symptoms of amyloidosis in a patient are influenced by the degree to which an organ is involved in the disease (3).The HSPG contain diverse types of oligosaccharides that are sulfated on the hydroxyl moieties to varying degrees, and these hypersulfated structures are distinct, are found specifically in the amyloid deposits, and differ from one another depending on the organ where they are located (4). In addition, the HSPG contain stretches of the disaccharide GlcNS6S-IdoA2S (HSNS4F5; these motifs are abundantly found in heparin, but have limited presence in the HS of normal tissues) that inhibit cell proliferation and induce apoptosis but do not affect the attachment of cells to collagen I (5). Because the HSPG in the amyloids are hypersulfated compared to the proteoglycans in normal tissues, HSPG are considered to be suitable for the detection of amyloids with imaging techniques and to diagnose and monitor amyloidosis progression and to determine the prognosis for a patient with amyloidosis (1). Whole-body scintigraphy with radioiodinated SAP is commonly used in Europe for the detection of amyloidosis in the various parts of the body, but this technique is not approved by the United States Food and Drug Administration for clinical use in United States because the SAP used to generate the tracer is isolated from human sources (1). In an attempt to develop an amyloidimaging agent that would not require the use of human materials, Wall et al. showed that a 125I-labeled synthetic heparin-binding peptide, p5, could be used with single-photon emission computed tomography (SPECT) to detectamyloid deposits in H2/huIL-6 transgenic mice with severe systemic AA amyloidosis (AA mice) (1). In another study, Wall et al. evaluated the use of 125I-labeled single chain (scFv) antibodies (Abs) directed against HS for the detection of amyloids in AA mice that are prone to develop amyloidosis at ~4–5 months of age as described elsewhere (6). Among these radioiodinated scFv Abs, NS4F5, which binds specifically to HSNS4F5 (5), has been determined to be the most suitable for the noninvasive imaging of amyloids in the transgenic animals (6).
Sections
125I-Labeled heparin-binding peptides that target heparan sulfate proteoglycans for the in vivo imaging of peripheral amyloidosis.
Authors
Source
Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2011.
2011 Nov 02 [updated 2011 Dec 01].
Excerpt
Peripheral amyloidosis is the extracellular deposition of insoluble protein fibrils in various organs of animals, including humans, and these deposits are considered to be biomarkers for diseases such as Alzheimer’s disease (AD), light chain amyloidosis (AL), etc (1). The fibrils are made up of disease-specific aggregated proteins or peptides (e.g., Aβpeptides for AD, light chains for AL or multiple myeloma, and reactive amyloidosis (AA)) that incorporate heparin sulfate proteoglycans (HSPG; heparin belongs to the heparan sulfate family of proteoglycans that contain the (GlcNS6S-IdoA2S)3 motif) and the serum amyloid P component (SAP) within their structure during disease progression. A characteristic feature of the protein fibrils is that the constituent proteins form a secondary cross-β pleated sheet structure that is resistant to proteolytic digestion (for structural details, see Goldsbury et al. (2)). The HSPG contain diverse types of oligosaccharides that are sulfated on the hydroxyl moieties to varying degrees, and these hypersulfated structures are distinct, are found specifically in the amyloid deposits, and differ from one another depending on the organ where they are located (3). In addition, clinical symptoms in patients are influenced by the degree to which an organ is involved in the disease (4). Because the HSPG are hypersulfated compared to proteoglycans found in normal tissues, HSPG are considered to be relevant biomarkers for use with noninvasive imaging to detect, diagnose, and monitor amyloidosis progression and to determine the prognosis for a patient with amyloidosis (1). Whole-body scintigraphy with radioiodinated SAP is commonly used in Europe for the detection of amyloidosis in the various parts of the body, but this technique is not approved for clinical use in the United States by the U.S. Food and Drug Administration because the SAP in the tracer is isolated from human sources (1). In an attempt to develop an amyloid imaging agent that does not require the use of materials of human origin, Wall et al. studied the biodistribution of seven 125I-labeled synthetic heparin-binding peptides with small-animal single-photon emission computed tomography (SPECT) to evaluate their use in the detection of amyloid deposits in mice with severe systemic AA amyloidosis (1).
Sections
Structure-based design of conformation- and sequence-specific antibodies against amyloid β
Source
Center for Biotechnology and Interdisciplinary Studies, Department of Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180.
Abstract
Conformation-specific antibodies that recognize aggregated proteins associated with several conformational disorders (e.g., Parkinson and prion diseases) are invaluable for diagnostic and therapeutic applications. However, no systematic strategy exists for generating conformation-specific antibodies that target linear sequence epitopes within misfolded proteins. Here we report a strategy for designing conformation- and sequence-specific antibodies against misfolded proteins that is inspired by the molecular interactions governing protein aggregation. We find that grafting small amyloidogenic peptides (6-10 residues) from the Aβ42 peptide associated with Alzheimer's disease into the complementarity determining regions of a domain (V(H)) antibody generates antibody variants that recognize Aβ soluble oligomers and amyloid fibrils with nanomolar affinity. We refer to these antibodies as gammabodies for grafted amyloid-motif antibodies. Gammabodies displaying the central amyloidogenic Aβ motif () are reactive with Aβ fibrils, whereas those displaying the amyloidogenic C terminus () are reactive with Aβ fibrils and oligomers (and weakly reactive with Aβ monomers). Importantly, we find that the grafted motifs target the corresponding peptide segments within misfolded Aβ conformers. Aβ gammabodies fail to cross-react with other amyloidogenic proteins and scrambling their grafted sequences eliminates antibody reactivity. Finally, gammabodies that recognize Aβ soluble oligomers and fibrils also neutralize the toxicity of each Aβ conformer. We expect that our antibody design strategy is not limited to Aβ and can be used to readily generate gammabodies against other toxic misfolded proteins.
Zn induced structural aggregation patterns of β-amyloid peptides by first-principle simulations and XAS measurements.
Source
University of Udine, Department of Chemistry, Physics and Environment, via del Cotonificio 108, 33100 Udine, Italy.
Abstract
We show in this paper that in the presence of Zn ions a peculiar structural aggregation pattern of β-amyloid peptides in which metal ions are sequentially coordinated to either three or four histidines of nearby peptides is favored. To stabilize this configuration a deprotonated imidazole ring from one of the histidines forms a bridge connecting two adjacent Zn ions. Though present in zeolite imidazolate frameworks, remarkably in biological compounds this peculiar Zn-imidazolate-Zn topology is only found in enzymes belonging to the Cu,Zn-superoxide dismutase family in the form of an imidazolate bridging Cu and Zn. The results we present are obtained by combining X-ray absorption spectroscopy experimental data with detailed first-principle molecular dynamics simulations.
Ginsenoside Rg1 attenuates β-amyloid generation via suppressing PPARγ-regulated BACE1 activity in N2a-APP695 cells.
Abstract
The level of β-site APP-cleaving enzyme 1 (BACE1) has been documented to increase in the brains of patients with Alzheimer's disease, which has resulted in elevation of β-amyloid (Aβ) peptides. As a transcription factor binding site of the BACE1 promoter, peroxisome proliferator-activated receptor-γ (PPARγ) response element regulates the activity of the BACE1 promoter activity, indicating that PPARγ may become a potential target for Alzheimer's disease treatment. Recent studies have demonstrated that ginsenoside Rg1 which is an effective component of extracts of ginseng can prevent memory loss and improve cognitive function in a variety of animal models. However, the underlying mechanism remains unclear. In the present study, we found that Rg1 decreased the levels of Aβ(1-40) and Aβ(1-42) secreted in N2a-APP695 cells. The expression levels of both BACE1 mRNA and protein as well as β-CTFs, a cleavaged C-terminal fragment of APP by BACE1, were reduced in cells treated with Rg1. Moreover, Rg1 treatment led to a translocation of PPARγ from cytoplasm to nuclear. Intriguingly, Rg1, like pioglitazone (a PPARγ agonist), suppressed BACE1 activity in N2a-APP695 cells, while its effect on BACE1 activity was attenuated by GW9662 (a PPARγ antagonist). These results indicate that Rg1 may be a PPARγ agonist to enhance the binding of nuclear PPARγ to the BACE1 promoter, which may in turn inhibit the transcription and translation of BACE1, suppress the activity of BACE1, and ultimately attenuate Aβ generation. Therefore, ginsenoside Rg1 may serve as a promising agent in modulating Aβ-related pathology in Alzheimer's disease.
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