Дисертації з теми "Beta-Amyloid peptides"

Le but de mon travail de thèse était de caractériser les produits de l'oxydation du peptide beta-amyloïde (Abeta) impliqué dans le développement de la maladie d'Alzheimer. Pour étudier l'effet de la structure de peptide sur les processus redox, les propriétés du peptide Abeta (1-40) ont été comparées au peptide de séquence inverse, Abeta (40-1). Les radicaux libres choisis ont été produits en radiolyse gamma. Les produits finaux ont été caractérisés par des techniques d'analyse diverses (HPLC, GC, MALDI-TOF MS, spectrométrie de fluorescence, spectrométrie raman). Pour établir l'effet de l'environnement sur le processus d'oxydation, peptides ont été oxydés dans trois systèmes différents: solution aqueuse homogène, milieu micellaire (SDS) et système des vésicules phospholipidiques (POPC). En solution aqueuse homogène, les produits d'oxydation sont différents pour les deux peptides. Les résidus facilement oxydables sont Met35 pour Abeta(1-40) et Tyr10 pour Abeta(40-1). La présence des micelles ainsi que des vésicules phospholipidiques change profondément le cours de l'oxydation. Une étude structurale en dichroïsme circulaire nous permet d'avancer des hypothèses pour interpréter ces résultats. Nous avons montré que des produits de dégradation des peptides Abeta peuvent induire d'une manière catalytique l'altération des phospholipides. Cette propriété est attribuée à l'action des atomes d'hydrogène sur le peptide. Nos résultats sont intéressants dans le contexte du développement de la maladie d'Alzheimer, car ils peuvent aider à éclairer le rôle de l'interaction de peptide Abeta(1-40) avec des membranes phospholipidique dans les propriétés redox du peptide
The goal of my thesis work was to characterize oxidation products of beta-amyloid peptide (Abeta), which is implied in the development of Alzheimer's disease. To study the effect of peptide structure on the redox processes, oxidation properties of Abeta(1-40) were compared to the peptide with reverse sequence, Abeta(40-1). Azide and hydroxyl radicals used for oxidation were produced by gamma radiolysis. Final products were characterized by a variety of analytical techniques (HPLC, GC, MALDI-TOF MS, fluorescence and raman spectrometry). To establish the role of peptide environment on its redox properties, oxidation was carried out in three different systems: homogeneous aqueous solution, micellar system (SDS) and in the presence of phospholipids vesicles (POPC). In homogeneous aqueous solution, oxidation products are different for both peptides. The main oxidation targets are Met35 for Abeta(1-40) and Tyr10 for Abeta(40-1). The presence of micelles and phospholipid vesicles has an important impact on the oxidation pathways. These changes could be related to changes in peptide conformations studied by circular dichroism. We have also shown that Abeta degradation products may catalytically induce alternation of phospholipids. This process is initiated by reaction of hydrogen radicals with the peptide. Our results are interesting in the context of the development of Alzheimer's disease as they may bring an insight into the role of Abeta(1-40) interaction with phospholipids membrane for the redox properties of the peptide

Thesis (M.S.)--University of New Orleans, 2005.
Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the Department of Chemistry"--Thesis t.p. Vita. Includes bibliographical references.

Aggregation of the Amyloid β (Aβ) peptide to amyloid fibrils is associated with the outbreak of Alzheimer’s disease. Early aggregation intermediates in form of soluble oligomers are of special interest as they are believed to be the major toxic components in the process. These oligomers are of disordered and transient nature. Therefore, their detailed molecular structure is difficult to access experimentally and often remains unknown. In the present work extensive, fully atomistic replica exchange molecular dynamics simulations were performed to study the preaggregated, monomer states and early aggregation intermediates (dimers, trimers) of Aβ(25-35) and Aβ(10-35)-NH2 in aqueous solution. The folding and aggregation of Aβ(25-35) were studied at neutral pH and 293 K. Aβ(25-35) monomers mainly adopt β-hairpin conformations characterized by a β-turn formed by residues G29 and A30, and a β-sheet between residues N27–K28 and I31–I32 in equilibrium with coiled conformations. The β-hairpin conformations served as initial configurations to model spontaneous aggregation of Aβ(25-35). As expected, within the Aβ(25-35) dimer and trimer ensembles many different poorly populated conformations appear. Nevertheless, we were able to distinguish between disordered and fibril-like oligomers. Whereas disordered oligomers are rather compact with few intermolecular hydrogen bonds (HBs), fibril-like oligomers are characterized by the formation of large intermolecular β-sheets. In most of the fibril-like dimers and trimers individual peptides are fully extended forming in- or out-of-register antiparallel β-sheets. A small amount of fibril-like trimers contained V-shaped peptides forming parallel β-sheets. The dimensions of extended and V-shaped oligomers correspond well to the diameters of two distinct morphologies found for Aβ(25-35) fibrils. The transition from disordered to fibril-like Aβ(25-35) dimers is unfavorable but driven by energy. The lower energy of fibril-like dimers arises from favorable intermolecular HBs and other electrostatic interactions which compete with a loss in entropy. Approximately 25 % of the entropic cost correspond to configurational entropy. The rest relates to solvent entropy, presumably caused by hydrophobic and electrostatic effects. In contrast to the transition towards fibril-like dimers the first step of aggregation is driven by entropy. Here, we compared structural and thermodynamic properties of the individual monomer, dimer and trimer ensembles to gain qualitative information about the aggregation process. The β-hairpin conformation observed for monomers is successively dissolved in dimer and trimer ensembles while instead intermolecular β-sheets are formed. As expected upon aggregation the configurational entropy decreases. Additionally, the solvent accessible surface area (SASA), especially the hydrophobic SASA, decreases yielding a favorable solvation free energy which overcompensates the loss in configurational entropy. In summary, the hydrophobic effect, possibly combined with electrostatic effects, yields an increase in solvent entropy which is believed to be one major driving force towards aggregation. Spontaneous folding of the Aβ(10-35)-NH2 monomer was modeled using two force fields, GROMOS96 43a1 and OPLS/AA, and compared to primary NMR data collected at pH 5.6 and 283 K taken from the literature. Unexpectedly, the two force fields yielded significantly different main conformations. Comparison between experimental and calculated nuclear Overhauser effect (NOE) distances is not sufficient to distinguish between the different force fields. Additionally, the comparison with scalar coupling constants suggest that the chosen protonation in both simulations corresponds to a pH lower than in the experiment. Based on this analysis we were unable to determine which force field yields a better description of this system. Dimerization of Aβ(10-35)-NH2 was studied at neutral pH and 300 K. Dimer conformations arrange in many distinct, poorly populated and rather complex alignments or interlocking patterns which are rather stabilized by side chain interactions than by specific intermolecular hydrogen bonds. Similar to Aβ(25-35) dimers, transition towards β-sheet-rich, fibril-like Aβ(10-35) dimers is driven by energy competing with a loss in entropy. Here, transition is mediated by favorable peptide-solvent and solvent-solvent interactions mainly arising from electrostatic interactions.
Die Aggregation des Amyloid β (Aβ) Peptids zu Amyloidfibrillen wird mit dem Ausbruch der Alzheimer Krankheit in Verbindung gebracht. Die toxische Wirkung auf Zellen wird vor allem den zeitigen Intermediaten in Form von löslichen Oligomeren zugeschrieben. Aufgrund deren ungeordneter und flüchtiger Natur kann die molekulare Struktur solcher zeitigen Oligomere oft experimentell nicht aufgelöst werden. In der vorliegenden Arbeit wurden aufwendige atomistische Replica-Exchange-Molekulardynamik-Simulationen durchgeführt, um die molekulare Struktur von Monomeren und Oligomeren der Fragmente Aβ(25-35) und Aβ(10-35)-NH2 in Wasser zu untersuchen. Die Faltung und Aggregation von Aβ(25-35) wurde bei neutralem pH und 293 K untersucht. Monomere dieses Fragments bilden hauptsächlich β-Haarnadelkonformationen im Gleichgewicht mit Knäulstrukturen. Innerhalb der β-Haarnadelkonformationen bilden die Residuen G29 und A30 einen β-turn, während N27–K28 and I31–I32 ein β-Faltblatt bilden. Diese β-Haarnadelkonformationen bildeten den Ausgangspunkt zur Modellierung spontaner Aggregation. Wie zu erwarten, bilden sich eine Vielzahl verschiedener, gering besetzter Dimer- und Trimerkonformationen. Mit Hilfe einer gröberen Einteilung können diese in ungeordnete und fibrillähnliche Oligomere unterteilt werden. Ungeordnete Oligomere bilden kompakte Strukturen, die nur durch wenige intermolekulare Wasserstoffbrückenbindungen (HBB) stabilisiert sind. Typisch für fibrillähnliche Oligomere ist hingegen die Ausbildung großer intermolekularer β-Faltblätter. In vielen dieser Oligomere finden wir antiparallele, in- oder out-of-register β-Faltblätter gebildet durch vollständig ausgestreckte Peptide. Ein kleiner Teil der fibrillähnlichen Trimere bildet parallele, V-förmige β-Faltblätter. Die Ausdehnungen ausgestreckter und V-förmiger Oligomere entspricht in etwa den Durchmessern von zwei verschiedenen, experimentell gefundenen Fibrillmorphologien für Aβ(25-35). Die Umwandlung von ungeordneten zu fibrillähnlichen Aβ(25-35) Dimeren ist energetisch begünstigt, läuft aber nicht freiwillig ab. Fibrillähnliche Dimere haben eine geringere Energie aufgrund günstiger Peptidwechselwirkungen (HBB, Salzbrücken), welche durch den Verlust an Entropie kompensiert wird. Etwa 25 % entsprechen dem Verlust an Konfigurationsentropie. Der restliche Anteil wird einem Verlust an Lösungsmittelentropie aufgrund von hydrophoben und elektrostatischen Effekten zugesprochen. Im Gegensatz zur Umwandlung in fibrillähnliche Dimere, ist die Assoziation von Monomeren oder Oligomeren entropisch begünstigt. Beim Vergleich thermodynamischer Eigenschaften der Monomer-, Dimer- und Trimersysteme zeigt sich im Verlauf der Aggregation, wie erwartet, eine Abnahme der Konfigurationsentropie. Zusätzlich nimmt die dem Lösungsmittel zugängliche Oberfläche (SASA), insbesondere die hydrophobe SASA, ab. In Verbindung damit beobachten wir eine Abnahme der freien Solvatisierungsenergie, welche den Verlust an Konfigurationsentropie kompensiert. Mit anderen Worten, der hydrophobe Effekt in Kombination mit elektrostatischen Wechselwirkungen führt zu einem Ansteigen der Lösungsmittelentropie und begünstigt damit die Aggegation. Die spontane Faltung des Aβ(10-35)-NH2 Monomers wurde für zwei verschiedene Proteinkraftfelder, GROMOS96 43a1 und OPLS/AA, untersucht und mit primären NMR-Daten aus der Literatur, gemessen bei pH 5.6 und 283 K, verglichen. Beide Kraftfelder generieren unterschiedliche Hauptkonformationen. Der Vergleich zwischen experimentellen und berechneten Kern-Overhauser-Effekt (NOE) Abständen ist nicht ausreichend, um zwischen beiden Kraftfeldern zu unterscheiden. Der Vergleich mit Kopplungskonstanten aus Experiment und Simulation zeigt, dass beide Simulationen einem pH-Wert geringer als 5.6 ensprechen. Basierend auf den bisherigen Ergebnissen können wir nicht entscheiden, welches Kraftfeld eine bessere Beschreibung für dieses System liefert. Die Dimerisierung von Aβ(10-35)-NH2 wurde bei neutralem pH und 300 K untersucht. Wir finden eine Vielzahl verschiedener, gering besetzter Dimerstrukturen, welche eher durch Seitenkettenkontakte als durch spezifische HBB stabilisiert sind. Wie bei den Aβ(25-35) Dimeren, ist die Umwandlung zu β-Faltblattreichen, fibrillähnlichen Aβ(10-35) Dimeren energetisch begünstigt, konkurriert aber mit einem Entropieverlust. Die Umwandlung wird in diesem Fall durch elektrostatische Wechselwirkungen zwischen Peptid und Lösungsmittel und innerhalb des Lösungsmittels bestimmt.

Metal ions are ubiquitously found in all living systems and play vital roles in supporting life forms by performing an array of biological activities. Such biological activities include binding and transforming organic molecules, and also acting as active centers and cofactors for catalysis of various acid-base and redox reactions in biological system. The main focus in bioinorganic chemistry is to elucidate the structural and functional roles of metals in biological systems. Among all transition metal ions, Cu2+ and Fe3+ are especially versatile and important due to their abilities to go through redox efficiently. This dissertation can be divided into four main chapters. The bioinorganic chemistry of Cu- and Fe-containing proteins were briefly discussed in Chapter one. The next chapter focuses on bacitracin, a cyclic peptide-based antibiotic produced by soil bacteria Bacillus subtilis. Bacitracin is a metalloantibiotics that can coordinate with many transition metal ions and exhibit different biological activities. In the first part of Chapter two, the aim is to explore the chemicals interactions in soil micro-ecology by investigating the interactions of different flavonoids and Cu(II)-bacitracin complex. The second part of chapter two demonstrated the binding and oxidation activity of iron(III)-bacitracin. Metal-mediated oxidative stress plays a crucial role in the development of different neurodegenerative diseases. In chapter 3, various synthetic and natural compounds were used to inhibit the oxidation chemistry mediated by Cu(II)-beta-amyloid complex associated with Alzheimer’s disease. Many proteins incorporate copper ions at their active sites for different functions, and among all of the chemistry copper-containing-proteins can perform, one of the most interesting aspect is the ability to bind and activate O2. Therefore, the biomimetic of two different Cu(II) complexes were investigated. In all studies, a combination of kinetic and different spectroscopic methods (UV-vis, NMR and resonance Raman spectroscopy) were used to study their metal binding and activity.

Thesis (M.S.)--George Mason University, 2008.
Vita: p. 48. Thesis director: Dmitri Klimov. Submitted in partial fulfillment of the requirements for the degree of Master of Science in Bioinformatics and Computational Biology. Title from PDF t.p. (viewed Mar. 17, 2009). Includes bibliographical references (p. 45-47). Also issued in print.

Analysis of low-abundance components in small samples remains a challenge within bioanalytical chemistry, and new techniques for sample pretreatments followed by sensitive and informative detection are required. In this thesis, procedures for preconcentration and separation of proteins and peptides in open microchannels fabricated on silicon microchips are presented. Analyte electromigration was induced by applying a voltage along the channel length, and detection was performed either by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) within the open channel, or by sampling a nL fraction containing the preconcentrated analytes from the channel for subsequent nano-electrospray ionization- (nESI-) or MALDI-MS. Utilizing solvent evaporation from the open system during sample supply, sample volumes exceeding the 25-75 nL channel volume could be analyzed. For preconcentration/separation of components in the discrete channel volume a lid of inert fluorocarbon liquid was used for evaporation control. In Papers I and II, aqueous, carrier-free solutions of proteins and peptides were analyzed, and the method was successfully applied for fast and simple preconcentration of amyloid beta (Aβ) peptides, related to Alzheimer’s disease. The impact of possible impurities in the analysis of carrier-free solutions was investigated in Paper III with the 1D simulation software GENTRANS, and a method for open-channel isoelectric focusing in a tailor-made pH gradient was developed. The latter approach was used in Paper IV for preconcentration and purification of Aβ peptides after immunoprecipitation from cerebrospinal fluid and blood plasma, followed by MALDI-MS from a micropillar chip. Paper V includes simulations of an isotachophoretic strategy for selective enrichment of Aβ peptides. GENTRANS simulations were used to select the electrolyte composition, and 2D simulations in a geometry suitable for on-chip implementation were performed using COMSOL Multiphysics.

QC 20160930

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder, characterized by global cognitive decline and progressive memory loss. As many other neurological disorders characterized by “proteinopathy”, pathology of AD includes beta-amyloid plaques and tau neurofibrillary tangles, which imply a crucial role of the cellular degradation systems in maintaining homeostasis of protein turnover. This is especially important for post-mitotic neuronal cells since aggravating protein crisis cannot be alleviated by cell division. Autophagy is a cellular degradation process that removes or recycles long-lived proteins and damaged organelles, with its enhancement being remarkably implicated during the progression of Alzheimer’s disease (AD). The majority of studies have hitherto focused on the mechanism of how oligomeric Ah, as one of the potent toxic species in AD, activates autophagy. However, how autophagy is activated remains to be elucidated. The goal of this study is to reveal the underlying mechanisms of autophagy and the subsequent events. Using imaging and biochemical analysis in primary cultures of rat hippocampal neurons, I found that oligomeric An-induced autophagy was initiated by aggregation of the endoplasmic reticulum (ER), in an mTOR-independent pathway. Ao-triggered autophagosomes were derived from omegasomes, starting from the ER aggregation sites. Aggregation of the ER facilitated the clustering of Atg14L to propel the recruitment of Beclin1 and Vps34, which contributes to generation of omegasomes. I further found that p62 targeted to ER aggregates possibly through the enhanced ubiquitinated ER chaperones trapped at ER aggregation sites, implicating the underlying mechanism for how p62 are recruited to autophagosome formation sites (omegasomes). Herein, I report key steps for activation of AH-triggered autophagy, whereby a mechanistic link between ER aggregation, autophagic activation and recruitment of p62 to autophagosome formation sites is revealed. First, Ao-induced ER aggregation triggers autophagy, via the recruitment of Beclin 1 and Vps34 to Atg14L clusters, which is a promoting factor for omegasome formation at the ER aggregation site. Second, the recruitment of p62 to omegasomes is likely mediated by the attraction of the underlying accumulation of ubiquitinated ER chaperones at the ER aggregation site. Up-regulation of autophagy is an early sign of AD. The activation of autophagy without tightly manipulation may contribute to neuronal damage in AD. In addition, how the autophagic substrates can be efficiently incorporated into the autophagic pathway is important for understanding the sustainability of autophagy. Therefore, my study on elucidating how ER aggregation initiates autophagy and the autophagic substrate/cargo receptor p62 are loaded onto autophagosome formation sites may help us to identify a potential therapeutic strategy or target for AD patients.
published_or_final_version
Anatomy
Doctoral
Doctor of Philosophy

Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed Apr. 3, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 178-202).

Neurotoxic aggregates generated by amyloid beta peptides (Abeta) represent one of the main pathological features of Alzheimer’s Disease (AD). Nowadays many natural and synthetic compounds able to prevent Abeta peptide toxicity and aggregation have already been identified. Several of these compounds are not soluble in water, are chemically unstable and/or show pharmacological activities not directly correlated to AD. Among these, tetracycline, rosmarinic acid and curcumin, were analyzed for their ability to bind Abeta peptides. For this purpose NMR spectroscopy has been mainly employed, with the support of other biophysical methodologies. Obtained the structural information related to those interactions, some derivatives of these molecules, with improved solubility and chemical stability, were synthesized and tested in order to generate new Abeta ligands, useful for the development of new potential diagnostic and therapeutic tools against Alzheimer’s Disease.

Thesis (M.S.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 14, 2008) Includes bibliographical references.

One of the main difficulties for the success of tissue and organ transplantation is the deficiency of techniques that ensure regular and stable vascularisation. The knowledge of mechanisms involved in the formation of new vessels could allow application of clinic strategies to facilitate tissue and organ transplantation on the one hand and the reduction of excessive vascular growth in many pathologies on the other. Angiogenesis is a complex process, where several cell types and mediators interact to establish a specific microenvironment suitable for the formation of new vessels (Bouïs et al, 2006). It occurs in both physiological (embryo development, menstrual cycle, pregnancy, wound healing) and pathological conditions (inflammation, psoriasis, metastasis growth). In the last years an increasing amount of evidence suggests that Alzheimer's disease (AD) is not only a neurodegenerative disease characterized by neuronal degeneration and loss of synaptic connections but it is also a vascular pathology. In fact cerebral microvessel vasoconstriction, degeneration of vessel smooth muscle cells and alteration of the basal membrane have been observed in cerebral capillary AD brains. In particular the possible connection between angiogenesis and AD starts from the observations of increased vascular density close to senile plaques in AD patients in comparison to older non-demented people (Vagnucci and Li, 2003). Senile plaques (extracellular and vascular deposits of proteinaceous material where the major component is β-amyloid peptide, Aβ) together with neuro fibrillary tangles (NFT) (composed of iperphophorylated form of τ protein) represent the main neuropathological alterations founded in AD brains (Robertson et al., 2003). A large amount of in vivo, ex-vivo and in vitro experiments show contradictory data on Aβ peptide angiogenic capability (Paris et al., 2004; Cantara et al., 2004). The aim of the present research is the attempt to understand some of the mechanisms that favour angiogenesis. The research deonstrates that Aβ peptides are pro-angiogenic in vivo, ex-vivo and in vitro on human cerebral endothelial cells while they are anti-angiogenic on rat cerebral endothelial cells, probably as consequence of their cytotoxic effect on these cells. Moreover Aβ1-42 peptide does not affect the release of VEGF-A and the expression of mRNA of VEGF-A on rat cerebral endothelial cells and rat hippocampal astrocytes cultures. Astrocytes release factors that induce angiogenesis and release of IL-6 on rat cerebral endothelial cells independently of the presence of Aβ1-42 peptide. Finally the presence of hVEGF165 inhibits toxic and anti-angiogenic effects of the peptide probably taking away Aβ1-42 through the binding A?-hVEGF165. Other experiments are necessary to understand mechanisms connected to AD although it seems that the result could depend on numerous different cell types in response of Aβ effects. Nevertheless capillary alteration and the hypoxia seem to contribute to the process.
Uno dei principali impedimenti alla ricostruzione di tessuti ed organi nell'ingegneria tessutale è la mancanza di strategie che assicurino costante e stabile vascolarizzazione. L'acquisizione di nuove conoscenze sui meccanismi che intervengono nel processo angiogenico potrebbe permettere una efficace applicazione clinica nella ricostruzione di tessuti e organi da una parte e nella riduzione della eccessiva crescita vascolare in patologie angiogenesi-dipendente dall'altra. L'angiogenesi è un processo complesso in cui numerosi cellule e mediatori cellulari interagiscono per stabilire un microambiente specifico per la crescita di nuovi vasi sanguigni (Bouïs et al, 2006). Questo processo si verifica sia in condizioni fisiologiche (sviluppo embrionale, ciclo mestruale, gravidanza, guarigione di ferite) che patologiche (processi infiammatori, psoriasi, crescita di metastasi). Negli ultimi tempi si sta affermando l'ipotesi che la demenza di Alzheimer (AD) non sia solamente una malattia neurodegenerativa caratterizzata da degenerazione neuronale e perdita delle connessioni sinaptiche ma anche una patologia vascolare. Numerose infatti sono le alterazioni riscontrabili a livello dei capillari cerebrali nei soggetti AD: vasocostrizione dei microvasi cerebrali, degenerazione delle cellule muscolari lisce vasali e alterazione della membrana basale. In particolare desta vasto interesse il possibile legame tra angiogenesi e AD derivante dall'osservazione di una aumentata densità  vascolare in prossimità delle placche senili nei pazienti AD rispetto a soggetti anziani non dementi (Vagnucci and Li, 2003). Le placche senili, depositi extracellulari e vascolari di materiale proteico costituite in prevalenza dal peptide β-amiloide (Aβ), assieme ai grovigli neurofibrillari (NFT), costituiti dalla forma iperfosforilata della proteina τ, rappresentano le principali alterazioni neuro-patologiche riscontrabili nel cervello di soggetti AD (Robertson et al., 2003). Numerosi studi in vivo, ex-vivo e in vitro riportano risultati contraddittori sulla capacità  del peptide Aβ di stimolare il processo angiogenico (Paris et al., 2004; Cantara et al., 2004). Scopo di questo lavoro di ricerca è il tentativo di comprendere alcuni meccanismi che favoriscono questo processo. Da questo lavoro di ricerca è emerso che il peptide Aβ è pro-angiogenico in vivo, ex-vivo e in vitro su cellule endoteliali cerebrali umane e anti-angiogenico su cellule endoteliali cerebrali di ratto, probabilmente come conseguenza dell'effetto citotossico effettuato dal peptide su queste ultime. Inoltre il Aβ1-42 non interferisce sulla via di espressione e rilascio di VEGF da parte di cellule endoteliali cerebrali e di astrociti di ippocampo di ratto in coltura. Gli astrociti secernono sostanze che inducono angiogenesi e rilascio di IL-6 da parte delle cellule endoteliali cerebrali di ratto in coltura indipendentemente dal trattamento con Aβ1-42. Infine la presenza di hVEGF165 inibisce l'effetto tossico e anti-angiogenico del peptide probabilmente in seguito al sequestramento del Aβ1-42 ad opera del legame Aβ1-42-hVEGF165. Altri studi sono necessari al fine di comprendere i meccanismi di angiogenesi correlata con la AD sebbene sembri evidente che essa possa derivare dall'interazione di diversi tipi cellulari in risposta all'effetto del peptide Aβ su di esse. Sembra tuttavia che l'alterazione dell'endotelio capillare e la conseguente ipossia contribuiscano all'attivazione di tale processo.

Alzheimer’s disease (AD) is the most common form of dementia. It was first described in 1906 by Alois Alzheimer. Later on, in 1984 George Glenner and Colin Masters isolated the amyloid-beta (Aβ) peptide from a human brain and associated it to the disease. Since then the amyloid hypothesis has been a rather controversial matter discussed among the scientific community. This is because although Aβ has been targeted by the majority of the drugs in clinical trials not even one has been approved up to date: 13 have been discontinued and 10 are in phase 3 clinical trials. A possible explanation for these devastating numbers is the high complexity of the target due to the variety of aggregation forms that Aβ can adopt. Therefore, understanding the links between protein aggregation and neurotoxicity, and specially obtaining the 3D structures of the aggregates responsible for neurotoxicity is key to design effective diagnostic and therapeutic strategies. Unfortunately, this remains one of the most important unresolved issues in the field. The group of Dr. Carulla has been working on the hypothesis that Aβ interacts with the cell membrane leading to ionic dyshomeostasis. In order to study this scenario, the group has changed the paradigm and treated Aβ as a membrane protein and applied well known methodologies used to characterize this family of proteins to study Aβ. By doing so, the group has proved that Aβ is able to form a type of oligomer in the presence of detergent micelles which adopts a very specific and defined structure with characteristics of a β-barrel assembly and functions as a pore. They refer to these types of oligomer as β-Barrel Pore-Forming Oligomer (βPFO). Hereby we present the work carried out to identify by using different biophysical techniques, the 3D structure of βPFO. As a starting point, we have used detergents to study the oligomerization process in a membrane mimetic environment. Micelles compared to other more native-like biomimetics environments based on lipids, will enable the application of novel mass spectrometry (MS) strategies and well-established solution NMR techniques thus providing high-resolution structural information. Since the accumulation of different amounts of Aβ in the membrane is a plausible scenario in the context of the disease, we have used different Aβ to detergent micelle ratios ([Aβ]:[M]) to study the role of this variable in the oligomerization process of Aβ. Throughout the work done we have optimized not only the ratio but also other conditions such as the buffer and the pH to modulate the preparation of samples enriched in defined oligomer populations. To study the stoichiometry of βPFO, we used with Native Mass Spectrometry which proved to be an adequate technique to preserve the non-covalent interactions of our samples analyse them in the gas phase. One of the key parts of the project consisted in the screening of a wide range of non-ionic detergents compatible with MS. After this work as we were able to identify Pentaethylene Glycol Monooctyl Ether (C8E5) as the best candidate for our samples. To continue working with the different samples we implemented a new approach based on coupling size exclusion chromatography (SEC) directly to a SYNAPT G2. This approach has allowed us to establish that higher molecular weight oligomers are better preserved and therefore better detected as we increase the signal to noise ratio. This enabled us to study different points of the SEC chromatogram and therefore understand better the composition of our samples and our system. For the standard βPFO samples, we reported specific charge states for the octamer and tetramer species. In parallel to complement the native-MS results, we have also worked to develop a method to analyse chemically cross-linked βPFOs by MALDI-MS. After a process of trials and optimizations we established a zero-length cross-linker (DMTMM) which allowed us to cross-link the βPFOs and detect again tetramer and octamer such as in the native-MS approach. In order to assess the relevance and to potentially validate the standard βPFO preparation as a target for AD’s it is crucial to characterize the binding of the Nanobodies to the oligomer. This work will also give us the opportunity to generate Nanobodies that could recognize their specific structures in brain tissue and thus assess whether the oligomers proposed are related to AD’s and if so, evaluate them as new targets for AD. Moreover we are very interested in the potential use of these Nanobodies as novel diagnostics or therapeutics tools.
La malaltia d'Alzheimer (AD) és la forma més comuna de demència. Va ser descrita per primera vegada el 1906 per Alois Alzheimer. Més endavant, al 1984, George Glenner i Colin Masters van aïllar el pèptid amiloide-beta (Aβ) d'un cervell humà i el van associar a la malaltia. Des de llavors, la hipòtesi amiloide ha estat un tema bastant controvertit discutit entre la comunitat científica. Una possible explicació és l’alta complexitat del sistema a causa de la varietat de formes d’agregació que Aβ pot adoptar. Per tant, entendre els vincles entre l'agregació de proteïnes i la neurotoxicitat, i especialment l'obtenció de les estructures 3D dels agregats responsables de la neurotoxicitat, és clau per dissenyar estratègies diagnòstiques i terapèutiques efectives. Malauradament, aquest tema continua sent un dels problemes pendents més importants. El grup de la Dra. Carulla ha estat treballant en la hipòtesi que l'Aβ interactua amb la membrana cel·lular que condueix a una deshomeostasi iònica. Per estudiar aquest escenari, el grup ha canviat el paradigma i ha tractat Aβ com a proteïna de membrana i aplicant tècniques biofísiques ben establertes per a caracteritzar proteïnes de membrana per tal d’estudiar Aβ. D'aquesta manera, el grup ha demostrat que Aβ és capaç de formar un tipus d'oligòmers en presència de micel·les de detergent que adopten una estructura molt específica i definida amb capacitat de formar porus a través de membranes lipídiques. Es refereixen a aquest tipus d’oligòmers com a oligòmers formadors de porus barril β (βPFO). A la present tesi doctoral, presentem l’estudi realitzat per identificar mitjançant diferents tècniques biofísiques, l'estructura 3D de βPFO. Hem utilitzat detergents per estudiar el procés d’oligomerització en un entorn mimètic de membrana. Les micel·les en comparació amb altres entorns biomimètics basats en lípids, permeten l'aplicació d’estratègies d'espectrometria de masses (MS) i de ressonància magnètica nuclear (RMN) ben establertes, proporcionant així informació estructural d'alta resolució. Atès que l’acumulació de diferents quantitats d’Aβ a la membrana és un escenari plausible en el context de la malaltia, hem utilitzat diferents relacions de micel·les Aβ a detergents ([Aβ]: [M]) per estudiar el paper d’aquesta variable en l’oligomerització. procés d'Aβ.

La enfermedad de Alzheimer es un trastorno neurodegenerativo caracterizado por el deterioro cognitivo y progresivo de la memoria. Una de sus principales características es la presencia de depósitos extracelulares de péptido beta-amiloide (Aß), en donde se han encontrado que los cationes metálicos tienen un papel importante. En concreto, se ha encontrado que la interacción del catión metálico activo en redox Cu2+ con Aβ puede interferir en la agregación del amiloide y dar lugar a especies reactivas de oxigeno (ROS). Por eso, es esencial un conocimiento detallado de la estructura de los complejos Cu-Aß1-16 para obtener una mejor comprensión de este proceso crítico. En la última década se han propuesto diversas esferas de coordinación para los complejos Cu2+-Aß, pero esta estructura todavía es controvertida y altamente dependiente del pH. La presente tesis está estructurada en siete capítulos. El Capítulo 1 introduce la enfermedad del Alzheimer como el marco en el que se encuentra la tesis, señalando la importancia de los iones metálicos en los depósitos de péptidos Aß y su papel en la formación de ROS, así como los tratamientos más relevantes utilizados hasta el momento. A continuación, el Capítulo 2 presenta los objetivos que se pretenden alcanzar en esta tesis. Después de esto, el Capítulo 3 repasa los aspectos teóricos generales que hay detrás de la tesis, como la estructura electrónica con la mecánica cuántica o los métodos de mecánica molecular y dinámicas moleculares, así como técnicas de modelado por homología. Sin embargo, los detalles computacionales están descritos en cada sección de resultados, que incluye cuatro capítulos. El primero, Capítulo 4, se presenta la construcción y caracterización de las estructuras 3D de los complejos Cu2+-Aß1-16. En el siguiente, Capítulo 5, se explica el estudio de las especies Cu+-Aß1-16 obtenidas por reducción de los complejos Cu2+-Aß1-16 obtenidos del anterior capítulo junto con las propiedades redox de esta pareja, así como la estabilidad de las especies de Cu+. A continuación, el Capítulo 6 investiga el papel de estas especies en el ciclo catalítico de la formación de H2O2; especialmente, la activación de O2 para obtener superóxido. Por último, algunos péptidos han sido estudiados como quelantes del Cu como posible tratamiento para el Alzheimer en el Capítulo 7. Finalmente el Capítulo 8 aporta unas conclusiones generales de la presente tesis. Además, hay una sección de Referencias con todas las referencias citadas en esta tesis, así como un Apéndice que respaldan la información de los capítulos de resultados.
Alzheimer’s disease is a neurodegenerative disorder characterized by progressive cognitive and memory impairment. One of its main hallmarks is the presence of extracellular deposits of the amyloid-beta peptide (Aß), in which metal cations have been shown to play an important role. In particular, the interaction of the redox active Cu2+ metal cation with Aβ has been found to interfere in amyloid aggregation and to lead to reactive oxygen species (ROS). Thus, a detailed knowledge of the structure of Cu-Aß1-16 complexes is essential to get a better understanding of this critical process. In the last decade many conflicting coordination spheres on the Cu2+-Aß complexes have been proposed, but the structure of these complexes is still disputed and highly pH dependent. The present thesis is structured in seven chapters. Chapter 1 introduces the AD framework in which the thesis is located, pointing out the importance of the presence of metal ions in the Aß deposits and its role in the ROS formation, as well as the most relevant treatments used until now. Then, Chapter 2 introduces the goals that this thesis aims. After that, Chapter 3 overviews the general theoretical aspects behind it, such as electronic structure with quantum mechanics or molecular mechanics and molecular dynamics methods, as well as homology modeling technics. However, the computational details are described in each results topic, which encloses four chapters. The first one, Chapter 4, presents the building and characterization of the 3D structure of Cu2+-Aß1-16 complexes. In the next chapter, Chapter 5, the study of the Cu+-Aß1-16 species obtained by reduction of Cu2+-Aß1-16 complexes from the last chapter along with the redox properties of this couple, as well as the stability of these species, is reported. Then, Chapter 6 investigates the role of these species in the catalytic cycle of the H2O2 formation; specially, the O2 activation in order to obtain the superoxide specie. Lastly, some peptides are studied as Cu chelates as possible AD treatment in Chapter 7. Finally, Chapter 8 addresses general conclusions of the present thesis. Moreover, there is a reference section with all the references cited in this thesis, as well as Appendix parts that support the information given in Chapters 4 to 7.

High levels of the amino acid arginine and low levels of the product citrulline in the cerebrospinal fluid of Alzheimer's patients could mean that there is a decrease in the enzymes that metabolize this amino acid. One such enzyme is neuronal nitric oxide synthase (nNOS). In this study, neuronal nitric oxide synthase (nNOS), sourced from bovine brain was extracted and concentrated using two methods of precipitation: poly (ethylene glycol) 20 000 (PEG) and ammonium sulphate [(NH₄)₂S0₄). These two techniques gave no increase in yield nor fold purification and hence were abandoned in favour of ion exchange chromatography by DEAE-Sepharose. The enzyme was then successfully purified by anion-exchange and after dialysis produced a 38% yield and three fold purification and yielded the highest specific activity of 2.27 U/mg. Neuronal nitric oxide synthase (nNOS) was a heterodimeric protein with a total molecular mass of ± 225 kDa (95 and 130 kDa monomers). The temperature and pH optima of the enzyme were 40⁰C and 6.5, respectively. The kinetic parameters (KM and Vmax) of nNOS were 70 μM and 0.332 μmol.min⁻¹, respectively. Moreover neuronal nitric oxide synthase (nNOS) was relatively stable at 40⁰C (t½ = 3 h). It was also confirmed that β-amyloid peptides inhibited nNOS when bound to the enzyme and that nNOS behaved as a catalyst in fibril formation through association-dissociation between enzyme and β-amyloid peptide. It was further shown that Aβ₁₇₋₂₈ inhibited nNOS the most with a Ki of 1.92 μM and also had the highest Stern-Volmer value (Ksv) of 0.11 μM⁻¹ indicating tight binding affinity to nNOS and easier accessibility to fluor molecules during binding. Congo red, turbidity, thioflavin-T assays and transmission electron microscopy were successfully used to detect and visualize the presence of fibrils by studying the process of fibrillogenesis. Computerized molecular modeling successfully studied protein dynamics and conformational changes of nNOS. These results correlated with resonance energy transfer (FRET) results which revealed the distance of tryptophan residues from the arginine bound at enzyme active site. Both the aforementioned techniques revealed that in the natural state of the enzyme with arginine bound at the active site, the tryptophan residues (TRP₆₂₅ and TRP₇₂₁) were positioned at the surface of the enzyme 28 Å away from the active site. When the amyloid peptide (Aβ₁₇₋₂₈) was bound to the active site, these same two amino acids moved 14 Å closer to the active site. A five residue hydrophobic fragment Aβ₁₇₋₂₁ [Leu₁₇ - Val₁₈ - Phe₁₉ - Phe₂₀ - Ala₁] within Aβ₁₇₋₂₈ was shown by computer modeling to be critical to the binding of the peptide to the active site of nNOS.

As a first project, collision-induced dissociation experiments were carried out using electrospray ionisation mass spectrometry on gas phase complexes involving different poly(methylmetacrylate) oligomers with three amino acids: glycine, leucine, and phenylalanine. After acquiring breakdown diagrams, RRKM modeling was used to fit the experimental data in order to obtain the 0 K activation energy and the entropy of activation. These thermodynamic data were then used to understand the competing dissociation channels observed (except for gas phase complexes involving glycine that had only one dissociation channel). Molecular dynamics simulated annealing calculations were carried on the gas phase complexes to understand further the energetic and entropic effects involved as well as the 3D conformation of these complexes. Valuable insight information was found on the 3D conformations, on a qualitative level. Using rotational constants and vibrational harmonic frequencies, it was possible to evaluate the entropy variation between the experimentally observed competing channels. Reasonable agreement was found between the experimental and theoretical variations of entropies. Finally, the proton affinity of poly(methylmetacrylate) oligomers is being discussed. Even though no absolute values for the proton affinity were found, the experimental and computational results help to understand the variation that accompanies the oligomers length. The second project presents the development an efficient and reproducible screening method for identifying low molecular weight compounds that bind to amyloid beta peptides (Abeta) peptides using electrospray ionization mass spectrometry (ESI-MS). Low molecular weight (LMW) compounds capable of interacting with soluble Abeta may be able to modulate/inhibit the Abeta aggregation process and serve as potential disease-modifying agents for Alzheimer’s disease. The present approach was used to rank the binding affinity of a library of compounds to Abeta1-40 peptide. The results obtained show that low molecular weight compounds bind similarly to Abeta1-42, Abeta1-40, as well as Abeta1-28 peptides and they underline the critical role of Abeta peptide charge motif in binding at physiological pH. Finally, some elements of structure-activity relationship (SAR) involved in the binding affinity of homotaurine to soluble Abeta peptides are discussed. As a third project, the gas phase binding of small molecules to the Abeta1-40 peptide generated by electrospray ionization has been explored with collision-induced dissociation mass spectrometry and kinetic rate theory. This project presents a simple procedure used to theoretically model the experimental breakdown diagrams for the Abeta1-40 peptide complexed with a series of aminosulfonate small molecules, namely homotaurine, 3-cyclohexylamino-2-hydroxy-1-propanesulfonic acid (CAPSO), 3-(1,3,4,9-tetrahydro-2H-beta-carbolin-2-yl) propane-1-sulfonic acid, 3-(1,3,4,9-tetrahydro-2H-beta-carbolin-2-yl)butane-1-sulfonic acid, and 3-(cyclohexylamino) propane-1-sulfonic acid. An alternative method employing an extrapolation procedure for the microcanonical rate constant, k(E), is also discussed.

Alzheimer's disease (AD) is characterized by accumulation and deposition of beta-amyloid (Abeta) peptides in the brain. Deposition of Abeta peptides in cerebrovascular system results in chronic vascular inflammation, neurovascular uncoupling and insufficiency, contributing to neurodegeneration. The purpose of this study was to investigate the inflammatory response in human brain endothelial cells (HBEC) induced by aggregated Abeta 1-40 and the molecular mechanism of the Abeta-stimulated inflammatory gene expression. Primary or immortalized HBEC (iHBEC) were treated with aggregated Abeta1-40, control peptides (scrambled Abeta1-40 or poly-asparagine) or 2mM NaOH (vehicle), in the presence or absence of a specific JNK inhibitor (SP600125, 30 muM) at different time points, and inflammatory gene expression was analyzed by reverse-transcriptase polymerase-chain reaction (RT-PCR). TranSignal Protein/DNA Array was used to profile the activities of transcription factors (TF) in Abeta-stimulated HBEC. Nuclear extracts were isolated to determine interaction of AP-1 with DNA by electrophoretic mobility shift assay (EMSA) and supershift assay. The levels of total c-Jun and phosphorylated c-Jun at Ser73/Ser63 were analyzed through Western blotting, and AP-1 transcriptional activity was evaluated by reporter gene assays. In addition, to test indirect effects of Abeta on iHBEC, conditioned media from Abeta1-42-stimulated primary microglia was used to treat iHBEC at different time points in the presence of SP600125. The results obtained in this study have shown that aggregated Abeta1-40 peptides strongly stimulated the expression of monocyte chemoattractant protein 1 (MCP-1), interleukin 8 (IL-8), interleukin 6 (IL-6) and growth-related oncogene (GRO). TF profiling has revealed that Abeta treatment strongly activated AP-1 in the cells. Electrophoretic migration shift assay (EMSA) and supershift assay have confirmed that AP-1 was strongly activated in HBEC at 2 and 4 h post-Abeta-treatment and physically interacted with AP-1-binding DNA sequence and that c-Jun is a component of the activated AP-1 dimeric complex. Abeta-stimulated AP-1 activity was further confirmed by reporter gene assay. In summary, these experiments have demonstrated that binding and internalization of Abeta peptides at HBEC cellular membrane, possibly through RAGE, stimulated JNK signaling cascade pathway in HBEC which resulted in increased phosphorylation of c-Jun at Ser-73 and that activated AP-1 was responsible for increased expression of inflammatory genes in the cells. Aside from direct action on HBEC, Abeta peptides also stimulated microglia to release pro-inflammatory factors, which in turn, stimulated the expression of inflammatory genes in HBEC. The JNK-AP1 signaling pathway and inflammatory factors characterized in this study may potentially serve as therapeutic targets to relieve Abeta-induced inflammation in Alzheimer's disease. (Abstract shortened by UMI.)

Amyloid-beta protein (Aß) is strongly linked to the aetiology of Alzheimer’s disease (AD). Even though Aß has a central role in AD, this protein is normally produced in healthy humans. It is the aberrant processing of Aß that determines its accumulation and aggregation into large oligomer species that evolve into the fibrillar structures deposited in amyloid plaques in the brain of AD patients. The neurotoxicity observed in AD has been attributed to the oligomeric intermediates, although their stoichiometry and structure still remain unknown. This is the reason why no AD therapeutic approaches tackling Aß aggregation have arrived to the market yet. In the present thesis, we have determined the stoichiometry and the structure of the oligomers formed in the early stages of Aß aggregation. Due to their highly dynamic nature, we have first obtained their covalent counterparts through the use of a photo-induced crosslinking methodology. Successful isolation of cross-linked Aß dimers and trimers has been achieved by means of a disaggregating treatment coupled to size exclusion chromatography. The combined study of these isolated cross-linked species through ion mobility coupled to electrospray ionization mass spectrometry, circular dichroism and molecular dynamics simulations, has shown that Aß dimers and trimers possess a globular shape without defined secondary structure. Moreover, we have proved that these cross-linked oligomers induce calcium influx, an intracellular marker for neurotoxicity, in primary neuroglial cultures, and that these cross-linked species effectively modulate Aß aggregation. Additionally, we have demonstrated that classical SDS-PAGE analysis provides misleading results when determining oligomer stoichiometry. The present thesis was also aimed at providing insights into the role of Aß amyloid fibrils in AD. Aß fibrils had been previously shown to be in dynamic equilibrium with soluble Aß species. The objective was to find evidences on the nature of these soluble species in equilibrium with Aß fibrils. Determination of their stoichiometry has been achieved by incubating Aß fibrils with insulin degrading enzyme, an enzyme which we have demonstrated to specifically proteolyze monomeric Aß. Subsequent analysis of Aß fibrils by hydrogen/deuterium exchange monitored by mass spectrometry has revealed that Aß fibrils are in equilibrium with monomers and low molecular weight oligomers. This equilibrium has been proved to be highly dependent on the physicochemical properties of Aß fibrils.
La proteïna beta amiloide (Aß) es troba estretament lligada a la malaltia d’Alzheimer (MA). Tot i el seu rol central en la malaltia, Aß es produeix de forma regular en humans sans. És el processament aberrant de la proteïna que en determina la seva acumulació i agregació, primer en intermedis oligomèrics transitoris que evolucionen cap a les estructures fibril·lars que composen les plaques amiloides dipositades al cervell dels malalts de la MA. La neurotoxicitat associada a la malaltia s’atribueix a les espècies intermèdies, per bé que se’n desconeix l’estequiometria i l’estructura. En la present tesi doctoral, hem determinat l’estequiometria i l’estructura dels oligòmers d’Aß formats en els estadiatges inicials de l’agregació. Hem provat que aquests oligòmers mostren neurotoxicitat en cultius neuronals primaris. Addicionalment, hem demostrat que el clàssic anàlisi per electroforesi en gel proporciona resultats confusos a l’hora de determinar l’estequiometria dels oligòmers. Els resultats presentats en la tesi doctoral també mostren evidències de que les fibres amiloides d’Aß es troben en equilibri amb monòmers i oligòmers de baix pes molecular. Aquest equilibri ha demostrat ser dependent de les propietats fisicoquímiques de les pròpies fibres d’Aß.

La maladie d'Alzheimer (AD) est un désordre neurodégénératif progressif et la forme la plus commune de démence. A l’heure actuelle, il n'y a aucun remède et la maladie est toujours fatale. Une des caractéristiques histopathologiques de l'AD est la présence de dépôts protéiques, les plaques amyloïdes, dans le cerveau. Ces plaques sont formées par les peptides amyloïdes β (Aβ) de 40 et 42 résidus, qui sont les produits de clivage par des protéases de la protéine précurseur de l’amyloïde (l'APP). L'élucidation de certains des processus clés dans la cause et le développement de l'AD est une étape cruciale pour le développement de traitements nouveaux et efficaces.

Les propriétés conformationnelles du segment transmembranaire (TM) de l’APP peuvent affecter sa protéolyse par la γ-sécrétase. Ces propriétés ne sont pas encore clairement établies. Afin de comprendre le rôle des variations structurelles du TM dans le traitement de l'APP, des détails structurels des peptides APP_TM4K, chimiquement synthétisés, ont été étudiés dans la bicouche lipidique en utilisant la réflexion totale atténuée par spectroscopie infrarouge à transformée de Fourier (ATR-FTIR) et la résonance magnétique nucléaire à l’état solide (ssNMR). Tandis que la structure secondaire globale du peptide APP_TM4K est hélicoidale, une hétérogénéité conformationnelle et orientée a été observée pour le site de clivage γ et, dans une plus faible mesure, pour le site de clivage ζ. Ces variabilités conformationnelles autour des sites de clivage γ et ζ peuvent avoir des implications importantes dans le mécanisme de clivage et donc dans la production d’Aβ. Il a été aussi démontré que la dernière glycine dans le motif de dimérisation GxxxG est transmembranaire. Ceci peut impliquer que la dimérisation via ce motif pourrait servir d’ancrage et conférer une orientation transmembranaire stable au segment transmembranaire de l’APP.

Le peptide amyloïde β est directement lié à la maladie d’Alzheimer. Partant de sa forme monomérique, l’Aβ s'agrège pour produire en final des fibrilles et aussi de manière transitoire toute une gamme d'oligomères, ces derniers étant la plupart neurotoxiques. Une dérégulation de l’homéostasie du Ca2+ dans le cerveau vieillissant et dans des troubles neurodégénératifs joue un rôle crucial dans de nombreux processus et contribue au dysfonctionnement et à la mort cellulaire. Nous avons postulé que le calcium peut permettre ou accélérer l'accumulation d'Aβ. Le modèle d'accumulation d'Aβ (1-40) et celui d'Aβ (1-40) E22G, un peptide amyloïde portant la mutation arctique qui cause une apparition prématurée de la maladie, ont été comparé. Nous avons constaté qu'en présence de Ca2+, l’Aβ (1-40) forme de préférence des oligomères semblables à ceux formés par l’Aβ (1-40) E22G avec ou sans Ca2+, tandis qu'en absence de Ca2+ l'Aβ (1-40) s’agrège sous forme de fibrilles. Les ressemblances morphologiques entre oligomères ont été confirmées par microscopie de force atomique. La distribution des oligomères et des fibrilles dans des échantillons différents a été détectée par électrophorèse sur gel suivie d’une analyse par Western blot, dont les résultats ont été confirmés par des expériences de fluorescence à la thioflavine T. Dans les échantillons sans Ca2+, l’ATR-FTIR révèle la conversion des oligomères en feuillets β antiparallèles en la conformation caractéristique des fibrilles en feuillets β parallèles. En général, ces résultats nous ont ameré à conclure que les ions calcium stimulent la formation d'oligomères d'Aβ (1-40), qui sont impliqués dans la pathogénèse d'AD.

Malgré les progrès énormes obtenus dans la compréhension de la maladie (AD), il reste un défi majeur, celui du développement de médicaments nouveaux et efficaces. Afin d’obtenir des éclaircissements sur le mécanisme d'action de deux nouveaux puissants modulateurs de la γ-sécrétase - le benzyl-carprofen et le sulfonyl-carprofen dans la bicouche lipidique, la technique de RMN à l’état solide a été employée. Précédemment, les dérivés du carprofen ont été localisés dans des membranes de lipides par des expériences de diffusion (scattering) des neutrons. Les contraintes déterminées à partir des expériences de ssNMR ont permis d’affiner leurs positions et d’obtenir une orientation précise dans la double couche lipidique. Ces résultats combinés indiquent que le mécanisme probable de modulation du clivage par la γ-sécrétase est une interaction directe des carprofènes avec le domaine TM de l’APP. Une telle interaction, empêcherait à la formation de dimères d'APP, dimérisation nécessaire au clivage séquentiel par la γ-sécrétase, diminuant ou réduisant ainsi énormément la production d’Aβ, tout particulièrement d’Aβ42.

Les résultats de ce travail apporte de nouvelles informations sur les processus clés impliqués dans l'AD; Production de l'Aβ à partir de l'APP, formation des oligomères d'Aβ et mécanisme d'action potentiel de molécules thérapeutiques. Nous pensons que ces résultats pourront permettre une meilleure compréhension de la maladie et pourront aider dans la conception de nouveaux médicaments contre cette maladie.

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. There is no cure and the disease is fatal. One of the characteristic histopathological markers of AD is the presence of proteinaceous deposits, amyloid plaques, in the brain. These plaques are formed by the amyloid β-peptides (Aβ) 40- and 42-residue-long, which are protease cleavage products of the amyloid precursor protein (APP). Elucidation of some of the key processes in the cause and the development of AD is crucial for the development of new and efficient treatments.

Conformational properties of the transmembrane (TM) segment of APP may affect its proteolytic processing by γ-secretase. These properties have not been definitely established. In addressing the role of structural variations of the TM sequence in APP processing, structural details of the chemically synthesized APP_TM4K peptides within the membrane bilayers were studied using Attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) and solid-state nuclear magnetic resonance (ssNMR) techniques. While the overall secondary structure of the APP_TM4K peptide is an α-helix, conformational and orientational heterogeneity was observed for the γ-cleavage site and, to a smaller extent, for the ζ-cleavage site. Evidence for the conformational variability around γ- and ζ-cleavage sites may have important implications for the cleavage mechanism and hence for the Aβ production. It was also found that the last glycine within the sequence of GxxxG motifs is in the transmembrane orientation, implying that dimerization via these motifs may act as an anchor, confining the TM dimer to the stable transmembrane orientation.

Amyloid β-peptide is directly linked to AD. Starting from its monomeric form, Aβ aggregates into fibrils and / or oligomers, the latter being the most neurotoxic. Dysregulation of Ca2+ homeostasis in aging brains and in neurodegenerative disorders plays a crucial role in numerous processes and contributes to cell dysfunction and death. Here we postulated that calcium may enable or accelerate the aggregation of Aβ. The aggregation pattern of Aβ(1-40) and of Aβ(1-40)E22G, an amyloid peptide carrying the Arctic mutation that causes early onset of the disease, were compared. We found that in the presence of Ca2+, Aβ(1-40) preferentially formed oligomers similar to those formed by Aβ(1-40)E22G with or without added Ca2+, whereas in the absence of added Ca2+ the Aβ(1-40) aggregated to form fibrils. Morphological similarities of the oligomers were confirmed by contact mode atomic force microscopy (AFM) imaging. The distribution of oligomeric and fibrillar species in different samples was detected by gel electrophoresis and Western blot analysis, the results which were further supported by thioflavin T fluorescence experiments. In the samples without Ca2+, Fourier transform infrared spectroscopy revealed conversion of oligomers from an anti-parallel β-sheet to the parallel β-sheet conformation characteristic of fibrils. Overall, these results led us to conclude that calcium ions stimulate the formation of oligomers of Aβ(1-40), that have been implicated in the pathogenesis of AD.

Despite the tremendous progress in understanding AD, there remains the challenge of the development of new and efficient drugs. In order to shed light onto the mechanism of action of two new potent γ-secretase modulators -- benzyl-carprofen and sulfonyl-carprofen within lipid bilayers, ssNMR technique was employed. Using neutron scattering experiments it was previously found that sulfonyl-carprofen and benzyl-carprofen partition into the headgroup region of the lipid bilayer. The orientational constraints derived from the ssNMR experiments refined their position into precise orientation. Combined, these results indicate that carprofen-derivatives can directly interact with the region of APP that mediates dimerization. Such interaction, would interfere with proper APP-dimer formation, which is necessary for the sequential cleavage by γ-secretase, diminishing or greatly reducing Aβ42 production.

Results obtained during this work shed new light onto some of the key processes in AD: Aβ production from APP, formation of Aβ oligomers and insights into the mechanism of action of potential therapeutics. We believe that these results will promote a better understanding of the disease and will help in future drug design.

Doctorat en Sciences
info:eu-repo/semantics/nonPublished

The prion protein (PrPC) is a cell surface glycoprotein that binds Cu2+ ions. The misfolding and oligomerisation of PrPC is responsible for a range of transmissible spongiform encephalopathies (TSEs) in mammals. As changes in PrPC conformation are intimately linked with disease pathogenesis, the effect of Cu2+ ions on the structure and stability of PrPC has been investigated. In chapter 3, urea unfolding studies indicate that Cu2+ ions destabilise the native fold of PrPC. The mid-point of the unfolding transition is reduced by 0.73 ± 0.05 M urea in the presence of Cu2+ ions equating to an appreciable difference in free energy of unfolding (∆∆GU[D]50%), 2.02 ± 0.05 kJmol-1. This suggests that in Prion diseases, Cu2+ ions could destabilise the native fold of PrPC and make the transition to a misfolded state more favourable. Furthermore, Cu2+ induced changes in secondary structure observed for small fragments of the protein are related to the full-length prion protein. An increase in -sheet like character is observed when Cu2+ ions are present, this is due to local Cu2+ ion coordination to the individual binding sites of the amyloidgenic region. Cu2+ induced changes in the secondary structure of the N-terminal domain, PrP(23-126) and full-length PrP(23-231), are attributed to Cu2+ ions binding within the octarepeat region of PrPC. Oxidative stress is also a well-recognised feature of Prion diseases. In chapter 4, the effects of Cu2+ catalysed oxidation of PrP on the structure and stability are discussed. 2D 1H-15N HSQC NMR studies of PrPC indicate that specific key residues are perturbed upon methionine (Met) oxidation by H2O2. These residues are involved in the hydrophobic packing of the structured core of the protein, stabilising its ternary structure. Urea unfolding studies indicate that the oxidation of PrPC by H2O2 and to a greater extent Cu2+ ions with peroxide significantly reduce the thermodynamic stability of PrPC. Cu2+ catalysed oxidation of PrP causes much more significant alteration of the structure. 2D 1H-15N HSQC NMR spectroscopy indicates that the structured C-terminal portion of PrP becomes a large molten-globule, made of monomeric species. FT-IR and far-UV-CD spectroscopy indicate that this molten-globule is rich in β-sheet. These observations supports a hypothesis that oxidation of PrP destabilises the native fold of PrPC, making the transition to PrPSc more energetically favourable. This study gives a structural and thermodynamic explanation for the high levels of oxidised Met residues in scrapie isolates. Finally, in chapter 5 the interaction of PrPC with Aβ peptide, responsible for Alzheimer’s disease (AD), is investigated. In particular, the influence of full length PrP and fragments on the kinetics of Aβ fibril growth is investigated. The complete inhibition Aβ fibril formation is observed when as little as one-twentieth of the molar ratio of PrPC is used. The unstructured N-terminus of PrPC, residues 23 to115, is thought to be crucial for this inhibition, while, residues 116 to 231 have no influence on the fibril formation. Gel filtration chromatography indicates that the complex formed by PrPC with an Aβ oligomer is 12 to 24 monomers in size.

La maladie d'Alzheimer (MA) est la maladie neurodégénérative la plus répandue à travers le monde et reste actuellement incurable. Le peptide beta amyloïde (Abeta), composant principal des plaques séniles retrouvées dans le cerveau des patients, joue un rôle majeur dans le développement de la MA, d'où l'importance de contrôler sa production et/ou son élimination. Dans cette optique, nous travaillons sur des molécules nommées métalloprotéases matricielles (MMPs). Bien qu'ayant été impliquées à la fois dans de nombreux processus physiologiques et pathologiques dans système nerveux, leur rôle dans la MA reste encore relativement inexplorée. Nous avons utilisé comme modèle d'étude des souris qui développent les symptômes de la MA (déclin cognitif, mort des neurones). Nous montrons que deux MMPs, MMP-2 et MT1-MMP, augmentent leurs niveaux d'expression avec le vieillissement de l'animal et donc avec l'aggravation de la pathologie. Ceci a lieu dans l'hippocampe, une région du cerveau qui est particulièrement sensible car elle est impliquée dans l'apprentissage et la mémoire. Par la suite nous avons utilisé des cellules HEKswe qui produisent beaucoup d'Abeta et miment d'une certaine manière ce qui se passe dans le cerveau de la souris, afin de mieux appréhender la signification des augmentations de ces MMPs. Nous montrons que la surexpression de MT1-MMP dans ces cellules favorise la formation d'Abeta, alors que MMP-2 l'empêche. Ces résultats montrent pour la première fois une dualité fonctionnelle au sein de la famille des MMPs, et plus important, révèlent une nouvelle molécule amyloïdogénique (MT1-MMP) qui pourrait devenir à terme une cible thérapeutique
We investigate the role of matrix metalloproteinases in the metabolism of beta amyloid peptide (Abeta) and its amyloid precursor protein (APP) in Alzheimer's disease (AD). Our results in the 5xFAD mouse model of AD indicate a cell-type and age-dependent upregulation of MMP-2 -and MT1-MMP active forms. This is concomitant with the increase of toxic forms of Abeta, but also of cytotoxic C99, a membrane fragment of APP generated by beta-secretase and that gives rise to Abeta after gamma-secretase cleavage. We show in HEK cells overproducing Abeta that while MT1-MMP interacts with APP and boosts C99 and Abeta production, MMP-2 does not interact with APP and degrades Abeta. These results uncover a MMP-specific regulatory crosstalk with amyloid and also MT1-MMP as a new pro-amyloidogenic proteinase. We want now to gain further insight into the mechanisms that support MT1-MMP effects, namely the possible modulation by MT1-MMP of beta- and gamma-secretase activities and/or APP trafficking

Amyloid-beta peptide (Aβ) is strongly linked to the aetiology of Alzheimer’s disease (AD). Aβ is the main component of the amyloid plaques found in the brain of AD patients, however, Aβ is also present in the brain of healthy humans. It has been described that for this peptide to be neurotoxic, aggregation is needed. The accumulation of Aβ causes aggregation from low order oligomers through different intermediate species up to the formation of amyloid fibrils. However, is not the presence of the fibrils what correlates the harmfulness of the disease, but the concentration of soluble oligomeric intermediate species. Nowadays, is accepted that the neurotoxicity of these oligomers is produced on the membrane. From this point, the laboratory of Dr. Carulla developed the beta-barrel Pore Forming Oligomer (βPFO). βPFO, was produced with Aβ42, the most neurotoxic version of Aβ. It was the first described example of a stable, well-defined and homogeneous membrane oligomer with the ability to form pores on lipid membranes. In this thesis, we aim to advance in the characterization of this βPFO and the validation of βPFO as a druggable target for AD. First, as βPFO was described using detergents as a biomimetic membrane environment, we aimed to move towards a more native environment using natural lipids. By using lipid-detergent micelles we studied βPFO. In this work we demonstrated that βPFO is not able to reconstitute into the common 1,2-dihexanoyl-sn-glycero-3-phosphocholine - 1,2-dimyristoyl-sn-glycero-phosphatidylcholine (DHPC-DMPC) bicelles. Therefore, we described a new type of bicelles using dodecylphosphocholine (DPC) and DMPC, not described in the literature in these conditions until then. We showed that βPFO was able to reconstitute into DPC-DMPC bicelles preserving its overall structure and pore-forming function. Then, to advance towards βPFO validation, we immunized an alpaca with βPFO in order to generate Nanobodies. A Nanobody is a fragment of the single-chain antibodies produced by camelids, with many different properties from conventional antibodies, their reduced size, their cavity specificity, their ease of modification and production, etc. Upon the Nanobodies generation, we selected the ones specific against βPFO obtaining 11 different Nanobodies. Using enzyme-linked immunosorbent assay (ELISA) we showed that they had both, a high specificity for βPFO compared to monomeric and fibrillar Aβ42, and a high affinity for them. Moreover, we showed that these generated Nanobodies, were binding to βPFO in different manners affecting differently the protection they could cause to proteolysis. Finally, we demonstrated that upon Nanobody binding on membrane-inserted βPFO, some of the Nanobodies did not affect the current pass across the bilayer while others reduced the current pass and two of them completely blocked the pore formed. In the future, these Nanobodies could serve, not only as a tool to validate as a player βPFO in the context of AD, but also as possible therapeutics.

Une des caractéristiques histopathologiques de la maladie d'Alzheimer (AD) est la présence de plaques amyloïdes formées par les peptides amyloïdes β (Aβ) de 40 et 42 résidus, qui sont les produits de clivage par des protéases de l'APP. Afin de comprendre le rôle des variations structurelles du TM dans le traitement de l'APP, les peptides APP_TM4K ont été étudiés dans la bicouche lipidique en utilisant l’ATR-FTIR et ssNMR. Tandis que la structure secondaire globale du peptide APP_TM4K est hélicoidale, hétérogénéité de conformation et d'orientation a été observée pour le site de clivage γ et , que peuvent avoir des implications dans le mécanisme de clivage et donc dans la production d’Aβ. Les peptides Aβ s'agrègent pour produire des fibrilles et aussi de manière transitoire d'oligomères neurotoxiques. Nous avons constaté qu'en présence de Ca2+, l’Aβ (1-40) forme de préférence des oligomères, tandis qu'en absence de Ca2+ l'Aβ (1-40) s’agrège sous forme de fibrilles. Dans les échantillons sans Ca2+, l’ATR-FTIR révèle la conversion des oligomères en feuillets β antiparallèles en la conformation caractéristique des fibrilles en feuillets β parallèles. Ces résultats nous ont amené à conclure que les Ca2+ stimulent la formation d'oligomères d'Aβ (1-40), qui sont impliqués dans l’AD. Les positions et une orientation précise de deux nouveaux médicaments puissants modulateurs de la γ-sécrétase - le benzyl-carprofen et le sulfonyl-carprofen  dans la bicouche lipidique, ont été obtenus à partir des expériences des ssNMR. Ces résultats indiquent que le mécanisme probable de modulation du clivage par la y-sécrétase est une interaction directe avec le domaine TM de l’APP
A histopathological characteristic of Alzheimer’s disease (AD) is the presence of amyloid plaques formed by amyloid β(A) peptides of 40 and 42 residues-long, which are the cleavage products of APP by proteases. To understand the role of structural changes in the TM domain of APP, APP_TM4K peptides were studied in the lipid bilayer using ATR-FTIR and ssNMR. While the overall secondary structure of the APP_TM4K peptide is helical, conformational and orientational heterogeneity was observed for the y- and for the -cleavage sites, which may have implications for the cleavage mechanism and therefore the production of Aβ. Starting from its monomeric form, Aβ peptides aggregate into fibrils and / or oligomers, the latter being the most neurotoxic. We found that in the presence of Ca2 +, Aβ (1-40) preferably forms oligomers, whereas in the absence of a2 + Aβ (1-40) aggregates into fibrils. In samples without Ca2 +, ATR-FTIR shows conversion from antiparallel β sheet conformation of oligomers into parallel β sheets, characteristic of fibrils. These results led us to conclude that Ca2 +stimulates the formation of oligomers of Aβ (1-40), that have been implicated in the pathogenesis of AD. Position and precise orientation of two new drugs  powerful modulators of γ-secretase  benzyl-carprofen and carprofen sulfonyl  in the lipid bilayer were obtained from neutron scattering and ssNMR experiments. These results indicate that carprofen-derivatives can directly interact with APP. Such interaction would interfere with proper APP-dimer formation, which is necessary for the sequential cleavage by β -secretase, diminishing or greatly reducing Aβ42 production

A neurodegeneração é um processo onde ocorre morte celular progressiva. O tráfego neuronal anterógrado e retrógado, e entre os compartimentos é essencial para a viabilidade celular. As proteínas Rabs pertencem à família de pequenas GTPases, com funções de tráfego de vesículas e organelas, para realizarem sua função as proteínas Rab podem recrutar proteínas motoras como as KIF 1B e KIF 5, responsáveis pelo transporte anterógrado mitocondrial. A associação do distúrbio do tráfego intracelular com doenças neurodegenerativas tem sido tema de estudos recentes. Com isso o objetivo do presente trabalho é analisar a expressão das proteínas Rab, bem como estudar as proteínas motoras que podem contribuir para o esclarecimento sobre os distúrbios no tráfego intracelular que antecedem a formação de agregados proteicos envolvidos em neurodegeneração. Para tanto, utilizou-se o modelo de tratamento com rotenona para indução de agregados em Ratos Lewis idosos que foram expostos a rotenona durante 4 semanas, em seguida foram avaliados os níveis de expressão das proteínas Rab no hipocampo, substância negra e locus coeruleus, por western blotting. Foram analisados também os níveis de expressão das proteínas motoras KIF1B e KIF5 antes e durante a formação de agregados proteicos, em culturas de células, de ratos Lewis neonatos, do hipocampo, substância negra e locus coeruleus tratadas com rotenona por 24 horas ou 48 horas nas concentrações de 0,1nM, 0, 3nM e 0,5nM. Foi observado diminuição dos níveis de expressão das proteínas Rab 1 nas regiões do hipocampo e locus coeruleus. Houve aumento de expressão das Rab 4,5 e 6 no hipocampo, porém na substância negra a expressão da Rab 1 aumentou e da Rab 6 diminuiu. Já no locus coeruleus in vivo a Rab 6 aumentou, mas as Rab 1, 5 e 11 diminuíram sua expressão. Já a expressão da KIF 5 aumentou com o tratamento de 0,1nM de rotenona e diminuiu após 0,5nM do xenobiótico por 48 horas in vitro, na mesma região. Na substância negra aumentaram as KIFs 1B e 5 após o tratamento com 0,5nM por 48 horas in vitro, mas diminuíram as KIF 1B e 5 após o tratamento com 0,3nM por 24 horas e KIF 5 após o tratamento com 0,1nM por 48 horas. Esses resultados permitem concluir que a expressão de proteínas importantes para o tráfego mitocondrial e de vesículas encontram-se alteradas e fazem parte dos eventos intracelulares que antecedem a neurodegeneração
Neurodegeneration is a process that leads to progressive cell death. The anterograde and retrograde neuronal traffic as well as the traffic between compartments are essential for cell viability. The Rab proteins belong to the small GTPases family with function of vesicles and organelle trafficking. Rab proteins can recruit motor proteins such as KIF 1B and KIF 5 that are responsible for anterograde mitochondrial transport. The association of intracellular traffic disturb with neurodegenerative diseases have been theme of recent studies. Thereat the objective of this study is analyze the expression of Rab and motor proteins that can contribute for the understanding about the disturb of the intracellular traffic that precedes protein aggregation involved in neurodegeneration. For this purpose it was employed the model of rotenone treatment for induction of aggregation in aged Lewis rats that were exposed to rotenone during 4 weeks in order to evaluate Rabs expression. The levels of motor proteins KIF 1B and KIF 5 expression were evaluated before and during the formation of protein aggregates in hippocampus, substantia nigra and locus coeruleus cell cultures of neonates Lewis rats, exposed to rotenone for 24 hours or 48 hours in the concentrations of 0.1nM, 0.3nM or 0.5nM. It was observed decreased levels of Rab 1 expression in hippocampus and locus coeruleus. Rabs 4,5 and 6 were increased in the hippocampus, but in the substantia nigra the expression of Rab 1 increased and Rab 6 decreased. In the locus coeruleus the Rab 6 increased, but Rabs 1, 5 and 11 decreased. The expression of KIF 5 increased after 0.1nM of rotenone and decreased after the exposure to 0.5nM of for 48 hours in cultured cell from the locus coeruleus. In the substantia nigra the KIF1B and KIF 5 increased after treatment with 0.5nM for 48 hours in vitro, but these protein decreased after treatment with 0.3nM for 24 hours in vitro, and KIF 5 after treatment with 0.1nM for 48 hours. These results allow us conclude that the expression of important proteins for the mitochondrial and vesicles traffic are altered and participate of intracellular events that precede the neurodegeneration

The Amyloid beta peptide (Ab) is related to Alzheimer’s disease and is suggested to be the molecular pathogenic species of the disease, probably through the neurotoxic effect of Ab oligomers. Here the results from biophysical studies of Ab and fragments thereof, are presented. Pulsed field gradient NMR diffusion experiments show that Ab exists mainly as an unfolded monomer. In addition, the hydrodynamic radius of Ab suggests that Ab has residual secondary structure propensities. CD experiments reveal that Ab has a high propensity to adopt a polyproline type II (PII) helix at low temperature. NMR diffusion measurements as well as the 3JHNH values show that increasing the temperature from 4 C induces a structure transition from PII propensity to a beta strand propensity around 15 C and to a random coil conformation at higher temperature. The small hydrodynamic radius at low temperature may be explained by the presence of a population of a hairpin conformation as was suggested by MD simulations. 15N relaxation and secondary chemical shifts suggest that Ab consists of 6 structural regions, two regions with high PII propensity are separated by a highly mobile region located in the N-terminal part of the peptide. In the C-terminal part two regions with a propensity to adopt b-strand are located, separated by a mobile region. The structural propensities of soluble monomeric Ab agree well with the structure of the peptide in fibril aggregates as well as in SDS micelles. Ab binds zinc specifically and with high affinity. This interaction was studied using heteronuclear correlation experiments. The metal ligands were determined to be three histidines, 6,13 and 14 and the N-terminus. The Ab peptide also binds b-cyclodextrin and the combined use of NMR diffusion experiments and induced chemical shifts show that Ab has at least two binding sites for b-cyclodextrin, and the dissociation constants of these binding sites were determined.

Thesis (M.S.)--University of Missouri-Columbia, 2008.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 14, 2009) Includes bibliographical references.

The aim of the thesis project was to examine what form(s) of Amyloid beta (Aβ) (25-­‐35) peptide interact with phospholipids in vitro and the implications of this for the mechanism of Alzheimer’s Diseases (AD). The mechanism of AD is thought to involve protein folding and misfolding. An increasing amount of evidence has shown that protein misfolding plays an important role in the biological and pathological processes of AD. Although seen as the biomedical markers of those diseases, the roles of amyloid aggregates themselves are still not fully understood. Whether the aggregates, or the monomer, or some other intermediates of Aβ cause AD is still unknown. In order to investigate the membrane-­‐interaction of Aβ and its implications for AD, two forms of Aβ, namely levorotary and dextrorotary (L-­‐ and D-­‐) Aβ isomers were used. Evidence has shown that L-­‐ and D-­‐ peptide can each form aggregates in a humid environment. However, when mixed together, L-­‐ and D-­‐ peptides tend not to form any aggregates. Using the mixtures of L-­‐ and D-­‐ peptides at different proportions and as well as using L-­‐ and D-­‐ alone can help us to determine the toxic form of Aβ. Phospholipids have been used to mimic membrane bilayers. Biological membranes in vivo are a complicated system. They contain three types of lipids, namely phospholipids, glycolipids, and steroids. Different types of cells and different membranes have different proportions of those lipids. Studying the interaction between Aβ and membranes in vivo can be extremely difficult. Artificial membranes, which only contains one kind of lipids, on the other hand, are a useful tool for the study of molecular interactions. Phospholipids are the most abundant type of membrane lipid and thus that can be seen as representative of cell membranes. The interactions of Aβ and different kinds of phospholipids have been investigated in this project. This thesis discusses the secondary structure of Aβ in different environment, the interaction between Aβ and phospholipids at the air-­‐water surface, and the location of Aβ in membranes during the interaction. The study provides useful information of the mechanisms and the origin of AD. At the end of the thesis, a discussion chapter analyses the difficulties of studying Aβ and AD and the potentials and inadequacies of this research.

The role of microglia in Alzheimer’s Disease (AD) pathogenesis is widely acknowledged, and the beta-amyloid (Aβ) peptide which accumulates in AD brain is known to activate a range of microglial functions. In the present thesis, the acute induction of some of these processes is examined using live cell imaging techniques. Aβ causes activation of microglial NADPH oxidase, a membrane-localised enzyme system which produces reactive oxygen species (ROS) thereby engendering oxidative stress. The transfer of electrons across the membrane by this enzyme system to produce ROS generates a potential difference, which will limit enzyme function unless it is dissipated by a compensatory movement of charge. I show that chloride intracellular channel 1 (CLIC1), a protein enriched in microglia and implicated in Aβ- induced microglial-mediated neurotoxicity, mediates a chloride conductance which sustains NADPH oxidase activity. Thus, blockade or knockdown of CLIC1 limits Aβ- induced ROS production. Using a variety of imaging methods, I show that the fascinating CLIC1 protein achieves its functions following an Aβ-induced redoxdependent direct insertion into the plasma membrane from the cytosol. Acute Aβ-induced microglial calcium signalling is also examined. Aβ is shown to elicit rapid and complex changes in microglial cytosolic calcium concentration, although these changes are less frequently observed in microglia than in astrocytes. The changes are not linked to ROS damage nor to voltage-gated calcium channel (VGCC) activity, but may be dependent on CD36 receptor function. The effects of Aβ treatment on subsequent calcium signalling elicited by the neuronal damage signalling molecule adenosine triphosphate (ATP) are investigated, and found to be complex. Aβ causes disruption of microglial calcium homeostasis and a reduction in the response to ATP, despite the calcium levels in the endoplasmic reticulum required for the response being increased. This work suggests that Aβ has diverse and consequential effects on microglial function relevant to AD pathophysiology.

Alzheimer’s disease (AD) is a neurodegenerative disorder. The patho-physiological effects of amyloid beta (Aβ) may be mediated by Aβ-membrane interaction. However, the molecular mechanism of interaction between Aβ and neuronal membrane remains unknown. The aim of the study was to investigate the interaction of a toxic fragment of amyloid beta, Aβ₂₅-₃₅ with the lipid membrane model using model lipid bilayers and beta breaker peptide, KLVFF. Liquid ¹H NMR assay was used to investigate the aggregation properties of Aβ₂₅-₃₅. The sharp NMR peaks of Aβ₂₅-₃₅ appeared immediately after sample preparation and these peaks were lost after 24 hrs incubation. However, on addition of KLVFF to Aβ₂₅-₃₅, the amyloid peptide peaks remain unchanged even after long period of incubation. The data suggest that KLVFF has ability to inhibit the aggregation of Aβ₂₅-₃₅. Magic angle spinning solid state NMR were used to investigate the location and interaction of Aβ₂₅-₃₅ to lipid bilayers. NOESY cross-relaxation rates suggest that the soluble form of Aβ₂₅-₃₅ may interact predominantly with the lipid chains near glycerol region. The cholesterol molecules did not exhibit direct interaction with soluble Aβ₂₅-₃₅. However, cross relaxation rate data suggest that cholesterol may push the soluble Aβ₂₅-₃₅ towards the head region of lipid bilayers. The data indicates that soluble form of Aβ₂₅-₃₅ may enter into lipid bilayers and interact with phospholipids. ²H NMR was used to analyse the effect of Aβ₂₅-₃₅ on lipid phase behaviour. M₁ analysis and methyl splitting data were used to observe the phase transitions. Aβ₂₅-₃₅ lowers the lipid phase transitions temperature in presence and absence of cholesterol. The data suggest that the insoluble form of Aβ₂₅-₃₅ may develop the lipid order (stiffness) and thus lowers the phase transition temperature. The Aβ₂₅-₃₅ plus KLVFF with cholesterol may also significantly raise the phase transition temperature and also elongate the phase transition boundaries, indicating that cholesterol molecules may enhance the lipid order parameter. In conclusion, KLVFF may stop the amyloid beta aggregation either in solution or in the lipid bilayers. Cholesterol molecules may not interact directly with amyloid beta and it may also affect the location of amyloid beta in the lipid bilayers. The results of the study may be important to understand the interactions between Aβ and lipid bilayers which may act as new therapeutic strategies for the development of new drugs for amyloid diseases.

Includes bibliographical references
Angiotensin-1 converting enzyme (ACE) is a zinc metallopeptidase that consists of two homologous catalytic domains (N and C) with different substrate specificities. ACE is a central component of the intrinsic brain renin angiotensin-aldosterone system (BRAAS), well renowned as the regulator of blood pressure. The BRAAS has alternate functions that extend beyond fluid and blood pressure homeostasis into areas such as neurological function. As a result, it is implicated in many neurodegenerative diseases including Alzheimer's disease (AD). ACE's specific mechanistic role in AD is not entirely clear and is somewhat controversial. However, it has been shown that ACE hydrolyses the amyloid beta (Aβ) peptide, the putative causative agent of AD. This study aimed to investigate the molecular basis of ACE hydrolysis of Aβ by determining : 1) the kinetic parameters of five different forms of human ACE with various N-terminal amyloid beta (Aβ) substrates; 2) the specific active site determinants of Aβ-domain selectivity; and 3) the high-resolution crystal structures of the N-domain of ACE in complex with Aβ(1-16), Aβ(10-16), Aβ(4-10), the FRET Aβ(4-10)Y and Aβ(35-42) peptides. For the physiological Aβ(1-16) peptide, a novel ACE cleavage site was found at His14/Gln15. Furthermore, Aβ(1-16 ) was preferentially cleaved by the truncated N-domain; however, the presence of an inactive C-domain in full-length ACE greatly reduced enzyme activity and affected domain-selectivity. Two fluorogenic substrates, designed specifically to assess ACE's mechanism of Aβ hydrolysis Aβ(4-10)Q and Aβ(4-10)Y, underwent endoproteolytic cleavage at the Asp7/Ser8 bond. The Aβ(4-10)Q peptide was a poor substrate of ACE but was N-selective, with a selectivity driven largely by interactions with the domain-specific residues of the S2 and S2' pockets. The selectivity of the S2' residues were confirmed with a similar, more physiological, fluorogenic Aβ(4-10)Y peptide. This work provides further understanding towards the substrate determinants of N-selectivity, highlighting the importance of the S2' Ser357. ACE C-domain hydrolysed Aβ(4-10)Y with modest efficiency compared to the other substrates, where hydrolysis under the same conditions did not occur. Moreover, Aβ(4-10)Y also displayed N-domain selectivity. In contrast to Aβ(1-16) and Aβ(410)Q, both sACE and the double C-domain (CC-sACE) construct showed positive domain cooperativity towards Aβ(4-10)Y. The high-resolution crystal structures of the N-domain in complex with five Aβ peptide fragments provided an overlapping, conserved, molecular mechanism of peptide binding and evidence of the enzyme's broad exoprotease activity. In addition to the kinetic and structural studies, ACE's signalling response to the N-selective Aβ(1-16) and Aβ(1-42) was investigated using immunodetection and mass spectrometry. Similar to the ACE inhibitor lisinopril, the Aβ peptides elicited ACE signalling by phosphorylation of the cytoplasmic Ser1270 residue and JNK activation. The signalling response of ACE was coupled to increased ACE activity an d expression on treatment with Aβ(1-42). These studies allowed us to rationalise the increased ACE activity and expression found in AD, may arise through direct interactions with Aβ. This work provides a kinetic, structural and mechanistic understanding of the selective cleavage of Aβ by the N and C catalytic sites of ACE. Due to the broad substrate specificity of the two domains of ACE, and the overarching N- selectivity of Aβ hydrolysis, these findings provide rationale for further in vivo pharmacological studies on the mechanism of action C- domain-selective inhibitors, in the context of AD.

La malaltia d’Alzheimer es caracteritza per l’acumulació de plaques extracel.lulars amiloides, formades pels anomenats pèptids amiloides (Aβ40). L’homeòstasi del coure (Cu) es veu afectada en l’etiologia de la malaltia d’Alzheimer, encara que el seu rol és un fet controvertit. Per a l’estudi de la influència del Cu(II) en l’agregació del pèptid amiloide, la morfologia i l’estructura secundària dels agregats amiloides formats en presència de Cu(II) s’han utilitzat AFM, TEM, SEM, SAXS, FTIR i espectrometria de fluorescència. A més, els efectes tòxics d’aquests agregats s’han estudiat en cèl.lules neuronals. Els resultats obtinguts mostren que aquests agregats són amorfos i presenten una toxicitat més alta que les fibres. Per a l’estudi dels dendrímers de maltosa com a possibles moduladors de l’agregació i de la toxicitat del pèptide amiloide. S’ha confirmat que aquests dendrimers no són tòxics en cèl.lules neuronals i que són capaços de modular l’agregació i toxicitat del pèptid amiloide. Aquests resultats permeten considerar als dendrimers de maltosa com a possibles eines per a reduir la toxicitat dels pèptids amilodies.
Senile plaques of Alzheimer’s disease patients are composed primarily of the amyloid-β-peptide (Aβ). Recent studies implicate Cu(II) in the aetiology of AD. The role of Cu(II) in ADis currently highly disputed. Influence of Cu(II) on Aβ aggregation and amyloidogenic properties of glycodendrimers were investigated in this thesis. AFM, TEM, SEM, SAXS, FTIR and fluorescence spectroscopy were used to study a morphology and a secondary structure of Aβ-Cu(II) aggregates. The toxic effects of Aβ40-Cu(II) amorphous aggregates was confirmed for neuronal cell lines. It was shown that maltose glycodendrimers can be efficiently used to modulate Alzheimer’s amyloid peptide aggregation and inhibit cell toxicity by facilitating the clustering of amyloid fibrils. These results show that glycodendrimers are promising non-toxic agents in the search for anti-amyloidogenic compounds. It was also suggested that fibril clumping may be anti-amyloid toxicity strategy.

Thesis (Ph. D.)--University of Missouri-Columbia, 2006.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (March 3, 2007) Vita. Includes bibliographical references.

Plaques of amyloid ? peptide (A?) are a hallmark trait of Alzheimer's disease (AD). However, the precise role of A? aggregates is not well understood. Recent studies have identified that naturally occurring N-terminal truncation and pyroglutamylation of A? significantly increases its neurotoxicity by an unknown mechanism. Content of pyroglutamylated A? (pE-A?) in AD brains has been shown to reach up to 50% of total A?. Modified pE-A? co-aggregates with A? by a seeding mechanism and forms structurally distinct and highly toxic oligomers. We studied structural transitions of the full-length A?1-42, its pyroglutamylated form A?pE3-42, their 9:1 (A?1-42/A?pE3-42) and 1:1 molar combinations. Transmission electron microscopy was used to directly visualize the fibrils of the samples in a buffer mimicking physiological environment. Atomic force microscopy measurements were done to determine rate of second nucleation events in fibrils. Thioflavin-T fluorescence indicated that low ionic strength suppressed the aggregation of A?pE3-42 but promoted that of A?1-42, suggesting different paths of fibrillogenesis of unmodified A? and pE-A?. Interestingly, A?pE3-42 at only 10% significantly facilitated the fibrillization of A?1-42 at near physiological ionic strength but had little effect at low salt. Circular dichroism and Fourier transform infrared (FTIR) spectroscopy were used to characterize the structural transitions during fibrillogenesis. In aqueous buffer, both unmodified A? and pE-A? peptides adopted parallel intermolecular ?-structure. Interestingly, A?pE3-42 contained lower ?-sheet content than 13C-A?1-42, while retaining significantly larger fractions of ?-helical and turn structures. Structural details of A? and pE-A? combinations were unveiled by isotope-edited FTIR spectroscopy, using 13C-labeled A?1-42 and unlabeled A?pE3-42. When exposed to environmental humidity, A?pE3-42 not only maintained an increased fraction of ?-helix but also was able to reverse 13C-A?1-42 ?-sheet structure. These data provide a novel structural mechanism for pE-A? hypertoxicity; pE-A? undergoes faster nucleation due to its increased hydrophobicity, thus promoting formation of smaller, hypertoxic oligomers of partial ?-helical structure.
M.S.
Masters
Molecular Biology and Microbiology
Medicine
Biotechnology; Professional Science Master's Track

Les maladies neurodégénératives sont des maladies chroniques progressives touchant le système nerveux central. Tandis que ces maladies ont des origines multifactorielles, leur fréquence augmente avec l'âge. En raison du vieillissement progressif de la population, et de l'absence de traitement, elles deviennent un enjeu majeur de santé publique. Pour exemple, la maladie d'Alzheimer pourrait toucher 1 personne dans le monde sur 85 d'ici 2050. C'est dans ce contexte que les chercheurs étudient différentes pistes pour permettre une meilleure compréhension de cette maladie et de ses mécanismes pathophysiologies. Ils savent aujourd'hui qu'une hyperphosphorylation de la protéine Tau et la production de formes toxiques de peptides beta-amyloïdes s'agglomérant en plaques séniles en sont les principales causes. L'origine de ces dysfonctionnements est quant à elle encore mal connue mais pourrait être élucidée par l'étude des mécanismes biochimiques intracellulaire. Dans ce contexte, nous avons imaginé un dispositif in vitro reposant sur l'utilisation de nanoaiguilles en silicium ayant la faculté de sonder le cytoplasme cellulaire de neurones pour y détecter les biomarqueurs de l'Alzheimer et en suivre l'évolution. Notre travail a reposé sur l'élaboration de ce capteur qui s'est divisée en 3 points. Le premier était la fabrication des nanoaiguilles par développement de techniques peu onéreuse comme la lithographie de nanosphère suivit de méthodes de gravure humide ou sèches. Le second point était l'optimisation de ces aiguilles pour l'identification bimodale de molécules par spectrométrie de masse (SALDI-MS) et par spectrométrie Raman exaltée de surface (SERS). Le troisième point portait sur l'étude de l'interaction entre nos aiguilles et les neurones avec à l'esprit la volonté de capture de biomarqueurs et la préservation de l'intégrité cellulaire. La lithographie de nanosphères a pu être développée, et les aiguilles ont été fabriquées selon 2 voies que sont la gravure humide assistée par métal (MACE) et la gravure sèche par gravure plasma continue. De la rhodamine 6G, des peptides standards ainsi que des peptides beta-amyloïdes ont pu être détectés par SALDI-MS et SERS sur nos réseaux d'aiguilles. Enfin nous avons constaté la biocompatibilité de nos aiguilles avec le milieu cellulaire et caractérisé leur interaction
Neurodegenerative diseases are chronic progressive diseases affecting the central nervous system. While these diseases have multifactorial origins, their prevalence increases with age. Due to the progressive aging of the population and the absence of treatment, they are becoming a crucial public health issue. For example, Alzheimer's disease will affect 1 person out of 85 worldwide by 2050. In this context, researchers are studying various options to gain a better understanding of this disease and its pathophysiological mechanisms. They now know that hyperphosphorylation of the Tau protein and the production of toxic forms of beta-amyloid peptides that aggregate into senile plaques are the main causes. The origin of these dysfunctions is still poorly understood but could be elucidated by studying intracellular biochemical mechanisms. In this context, we have conceived an in vitro device based on the use of silicon nanoneedles with the ability to probe the cytoplasm of neuronal cells to detect Alzheimer's biomarkers and monitor their evolution. Our work was based on the development of this sensor, which was divided into 3 points. The first was the fabrication of nanoneedles through the development of cost-effective techniques such as nanosphere lithography followed by wet or dry etching methods. The second point was the optimization of these needles for the bimodal identification of molecules by mass spectrometry (SALDI-MS) and surface-enhanced Raman spectroscopy (SERS). The third point focused on the study of the interaction between our needles and neurons with the aim of capturing biomarkers and preserving cellular integrity. Nanosphere lithography was successfully developed, and the needles were manufactured using two methods: metal assisted chemical etching (MACE) and dry etching by continuous plasma etching. Rhodamine 6G, standard peptides, and beta-amyloid peptides could be detected by SALDI-MS and SERS on our needle arrays. Finally, we observed the biocompatibility of our needles with the cellular environment and characterized their interaction

It is widely accepted that A-beta (Aβ) generated from amyloid precursor protein (APP) oligomerizes and fibrillizes to form neuritic plaques in the Alzheimer’s disease (AD) brain, yet little is known about the contribution of APP preceding AD pathogenesis. Our data presented here suggest that APP has a functional role in cell cycle regulation and proliferation. First, we demonstrat that APP is pathologically phosphorylated at Thr668 and that P-APP localizes to the centrosomes. Furthermore, P-APP is proteolytically processed in a cell cycle -dependent manner to generate its pathogenic metabolites. Using Stable Isotope Labeling by Amino Acids in Culture (SILAC) and mass spectrometry analyses, we also show that expression of APP results in the expression of proliferation-associated proteins and the phosphorylation of proteins associated with cell cycle regulation and transcription. Here, we demonstrate that APP expression and oligomeric Aβ42 elicit Ras/ERK signaling cascade and glycogen synthase kinase3 (GSK3) activation. Both ERK and GSK3 are known to induce hyperphosphorylation of tau and of APP at Thr668, and our findings suggest that aberrant signaling by APP facilitates these events. Supporting this notion, analysis of human brain samples show increased expression of Ras, activation of GSK3 and phosphorylation of APP and tau, which correlate with Aβ levels in the AD brains. Furthermore, treatment of primary rat neurons with Aβ recapitulate these events and show enhanced Ras-ERK signaling, GSK3 activation, upregulation of cyclin D1, and phosphorylation of APP and tau. The finding that Aβ induces Thr668 phosphorylation on APP, which we show enhances APP proteolysis and Aβ generation, denotes a vicious feed-forward mechanism by which APP and Aβ promote tau hyperphosphorylation and neurodegeneration in AD. Based on these results we hypothesize that aberrant proliferative signaling by APP plays a fundamental role in AD neurodegeneration and an inhibition of this would impede the mitotic catastrophe and neurodegeneration observed in AD.