Alzheimer's disease (AD) is characterised by memory loss, insidious cognitive decline, profound neurodegeneration, and the extracellular accumulation of amyloid-beta (Aβ) peptide in senile plaques and intracellular accumulation of tau in neurofibrillary tangles. Synaptic dysfunction and loss is the strongest pathological correlate of cognitive decline in AD with increasing evidence implicating neuropathological forms of both amyloid-beta and tau protein in this process. A large amount of evidence suggests that oligomeric forms of Aβ, associated with senile plaques, are toxic to synapses but the precise localisation of Aβ and which forms are synaptotoxic remain unknown. Using the high-resolution technique, array tomography, this thesis characterised the synaptic localisation of different forms of Aβ oligomers in a mouse model of amyloidopathy. These results show that different oligomeric Aβ species are present in both presynapses and postsynapses. This study highlights the potential of array tomography for rapid testing of aggregation state specific Aβ antibodies in brain tissue. Following these results, the presence of tau at synapses was examined. Despite the knowledge that tau spreads through defined synaptic circuits, it is currently unknown whether synapse loss occurs before the accumulation of tau or as a consequence. To address this, array tomography was used to examine a mouse model in which mutant P301L human tau is expressed primarily in the entorhinal cortex (rTgTauEC). It has previously been shown that rTgTauEC mice exhibit neuronal loss in the entorhinal cortex and synapse density loss in the middle molecular layer (MML) of the dentate gyrus at 24 months of age. The density of tau-expressing and total presynapses, and the spread of tau into the postsynapse in the MML of 3-6, 9, and 18 month old mice were examined. No loss of synapse density was observed in the MML up to 18 months of age, even in axons expressing tau. Despite the maintenance of synapse density, we see spread of human tau from presynaptic terminals to postsynaptic compartments in the MML at very early ages. This indicates that the spread of tau through neural circuits is not due to the degeneration of axon terminals and is an early feature of the disease process. Following examination of both synaptic amyloid-beta and tau in separate models, this thesis then examined how these two proteins may be synergistically working together to drive synaptic pathology. To investigate this a novel mouse model was used in which amyloid-beta deposits are present in combination with non-mutated human tau expression (APP/PS1 + hTau). These results suggested that the addition of human tau expression does not increase plaque associated synapse loss, neither does it increase the proportion of synapses colocalising with amyloid-beta. Similarly the presence of human tau at individual postsynapses was not enhanced in the presence of oligomeric Aβ. Surprisingly, intact long-term recognition memory was observed in APP/PS1 + hTau mice. However a hyperactive phenotype was detected in these mice that could be prevented upon tau suppression. This suggests a synergistic relationship may exist in the presentation of this phenotype. Finally in the last part of this thesis, synapses from post-mortem human Alzheimer's disease and age-matched controls were investigated. It has previously been suggested that both amyloid-beta and tau can interfere with mitochondrial transport to the synapse and mitochondrial function. For this reason the presence of synaptic mitochondria at both the presynapse and postsynapse was determined in order to investigate any alteration in the diseased state. A reduction in the proportion of presynapses with multiple mitochondria present was detected in anterior/posterior transverse temporal cortex (BA41/42). This was not observed in dorsolateral prefrontal cortex (BA46), suggesting either a selective vulnerability of the former brain region or a selective resistance of the latter brain region, to mitochondrial depletion at the synapse. The findings presented in this thesis demonstrate that when investigated in isolation, pathological forms of amyloid-beta are present at a subset of synapses where they may contribute to toxicity, whilst the spread of tau protein is an early feature of the disease process and occurs prior to overt synapse loss. This thesis also explores the proposed synergistic relationship between amyloid-beta and tau using a novel mouse model and human post-mortem brain tissue. Since these two proteins both have been implicated in synaptic dysfunction, investigating Aβ and tau in new mouse models and human brain tissue will be instrumental in furthering our understanding of mechanisms and features of synaptotoxicity that could be important therapeutic targets.

Wu, Chi Chung. / "September 2010." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 86-96). / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (Chinese version) --- p.iii / Acknowledgments --- p.iv / List of Abbreviations --- p.v / List of Tables --- p.vii / List of Figures --- p.viii / Chapter 1. --- INTRODUCTION / Chapter 1.1. --- Neurodegenerative disorders 一 a brief overview --- p.1 / Chapter 1.2. --- Polyglutamine diseases --- p.1 / Chapter 1.3. --- Polyglutamine protein conformers and toxicity --- p.5 / Chapter 1.4. --- in vivo modeling of polyglutamine diseases in Drosophila / Chapter 1.4.1. --- GAL4/UAS transgene expression system in Drosophila --- p.13 / Chapter 1.4.2. --- Temporal control of transgene expression systemin Drosophila --- p.15 / Chapter 1.4.3. --- Drosophila as a model to study polyglutamine diseases --- p.16 / Chapter 1.5. --- in vitro polyglutamine diseases models --- p.19 / Chapter 1.6. --- Aim of study --- p.23 / Chapter 2. --- MATERIALS AND METHODS / Chapter 2.1. --- Drosophila culture and manipulation / Chapter 2.1.1. --- Drosophila culture --- p.25 / Chapter 2.1.2. --- Pseudopupil assay of adult retinal degeneration --- p.25 / Chapter 2.2. --- Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) / Chapter 2.2.1. --- Protein extraction from adult Drosophila heads --- p.26 / Chapter 2.2.2. --- Preparation of SDS-polyacrylamide gel and electrophoresis --- p.27 / Chapter 2.2.3. --- Western blotting --- p.28 / Chapter 2.2.4. --- Immunodetection --- p.29 / Chapter 2.3. --- Solubilization of SDS-insoluble protein --- p.31 / Chapter 2.4. --- Filter retardation assay --- p.31 / Chapter 2.5. --- Immunoprecipitation --- p.32 / Chapter 2.6. --- Nucleocytoplasmic fractionation --- p.33 / Chapter 2.7. --- PCR cloning / Chapter 2.7.1 . --- Drosophila DNA preparation --- p.34 / Chapter 2.7.2. --- Construction of pGEX4T3-MJDflQ27/81 expression plasmid --- p.34 / Chapter 2.8. --- in vitro aggregation assay / Chapter 2.8.1. --- Expression and purification of GST-MJDAQ27/81 protein --- p.36 / Chapter 2.8.2. --- in vitro aggregation --- p.37 / Chapter 2.8.3. --- Native slot-blot --- p.38 / Chapter 2.9. --- Reagents and buffers / Chapter 2.9.1. --- Reagents for Drosophila culture --- p.39 / Chapter 2.9.2. --- Reagents for SDS-PAGE --- p.39 / Chapter 2.9.3. --- Reagents for filter retardation assay --- p.42 / Chapter 2.9.4. --- Reagents for immunoprecipitation --- p.43 / Chapter 2.9.5. --- Reagents for nucleocytoplasmic fractionation --- p.43 / Chapter 2.9.6. --- Reagents for PCR cloning --- p.44 / Chapter 2.9.7. --- Reagents for in vitro aggregation assay --- p.46 / Chapter 3. --- Establishment of a GAL80ts-mediated transgenic Drosophila model of Machado-Joseph Disease (MJD) / Chapter 3.1. --- Introduction --- p.48 / Chapter 3.2. --- Results / Chapter 3.2.1. --- GAL80ts-mediated expression of expanded full-length MJD protein caused progressive neuronal degenerationin Drosophila --- p.49 / Chapter 3.2.2. --- Detection of SDS-insoluble expanded full-length MJD protein and its correlation with neuronal degeneration / Chapter 3.2.2.1. --- Progressive neuronal degeneration is not mediated by progressive accumulation of expanded full-length MJD protein --- p.51 / Chapter 3.2.2.2. --- SDS-soluble expanded full-length MJD protein does not correlate with progressive neuronal degeneration --- p.53 / Chapter 3.2.2.3. --- Progressive accumulation of SDS-insoluble expanded full-length MJD protein correlate with progressive neuronal degeneration --- p.55 / Chapter 3.3. --- Discussion --- p.57 / Chapter 4. --- Detection of conformational changes of expanded full-length MJD protein and its association with neuronal degeneration / Chapter 4.1. --- Introduction --- p.60 / Chapter 4.2. --- Results / Chapter 4.2.1. --- Expanded full-length MJD protein underwent conformational changes from monomer to fibrils and such conformational changes correlated with neuronal degeneration --- p.61 / Chapter 4.2.2. --- Mechanistic studies of how conformational changes of expanded full-length MJD protein triggers neuronal degeneration / Chapter 4.2.2.1. --- Expanded full-length MJD protein gradually accumulated in the nucleus during the course of neurodegeneration --- p.62 / Chapter 4.2.2.2. --- Fibrillar expanded full-length MJD protein caused transcriptional dysregulation of endogenous Hsp70 gene --- p.66 / Chapter 4.2.3. --- Consolidation of the role of fibrillar expanded full-length MJD protein in neuronal degeneration --- p.67 / Chapter 4.3. --- Discussion --- p.72 / Chapter 5. --- Attempts to generate new conformation-specific antibody against recombinant expanded full-length MJD proteins / Chapter 5.1. --- Introduction --- p.75 / Chapter 5.2. --- Results / Chapter 5.2.1. --- Recombinant expanded full-length MJD protein underwent conformational changes during in vitro aggregation --- p.75 / Chapter 5.3. --- Discussion --- p.77 / Chapter 6. --- GENERAL DISCUSSION --- p.81 / Chapter 7. --- CONCLUSION --- p.84 / Chapter 8. --- REFERENCES --- p.86

Protein aggregation, leading to the formation and depositions of amyloids, is a cause for a number of diseases such as Alzheimer’s and Creutzfeld-Jacob’s disease, systemic amyloidoses, type II diabetes and others . More than 20 proteins are associated with protein misfolding diseases and even a larger number of proteins can self-assemble into amyloid in vitro. Relating structural and functional properties of amyloid is of particular interest, as this will lead to the identification of the main factors and mechanisms involved in the process of protein misfolding and aggregation; consequently, this will provide a basis for developing new strategies to treat protein misfolding diseases. The aim of the thesis is to investigate structural aspects of amyloid formation and relate that to the functional properties of amyloid. The first paper describes the amyloid formation of equine lysozyme (EL). We have demonstrated that EL enters an amyloid forming pathways under conditions where the molten globule state is populated. We have found that the morphology of the amyloids depend on the calcium-binding to lysozyme, specifically the holo-protein assembles into short, linear protofilaments, while the apo-EL forms ring-shaped structures. The morphology of EL amyloid significantly differs from the amyloid fibrils of human and hen lysozymes. We have suggested that the stable alpha-helical core of EL, which remains structured in the molten globule intermediate, may obstruct the formation of fibrilar interface and therefore leads to assembly of short, curly fibrils and rings.In the second paper, we describe the cytotoxicity of EL amyloids. We have analysed the amyloid intermediates on the pathway towards amyloid fibrils. The sizes of amyloid oligomers were determined by atomic force microscopy (AFM) and the formation of cross-beta sheet was shown by thioflavin T (ThT) binding. The toxicity studies show that the oligomers formed during amyloid growth phase are toxic to a range of cell lines and cultures and the toxicity is size-dependant.The last manuscript describes a novel method for manufacturing of silver nanowires by the biotemplating using amyloid fibrils. The amyloid assembled from an abundant and cheap hen egg white lysozyme was used as a scaffold for casting ultrathin silver nanowires. We have manufactured nanowires with a diameter of 1.0-2.5 nm and up to 2 micrometers in length. Up to date, it is the thinnest silver nanowires produced by using biotemplating and at least one order of magnitude thinner than nanowires manufactured by chemical synthesis.

Amyloid diseases are a world-wide problem causing great human suffer and large economical costs. Although amyloid deposits, a common denominator in all amyloid disorders, are detrimental to the surrounding tissue, there is a poor correlation between total amyloid burden and clinical symptoms. Soluble oligomers are much more potent to exert a tissue damaging effect.  Alzheimer’s disease (AD) is strongly linked to self-assembly of the amyloid-β (Aβ) peptide. Antibodies selectively targeting cytotoxic Aβ-species are useful both for understanding oligomer formation and for their therapeutic abilities. We hypothesized that the effect of avidity would compensate for a low single site affinity and be enough to selectively target oligomers. To evaluate this hypothesis, we focused on the IgM isotype having ten antigen-binding sites. In accordance with the hypothesis, the IgM isotype effectively bound oligomeric Aβ also in presence of a vast excess of its monomeric counterpart, clearly illustrating the potentiating effect of avidity. As a continuation of this work, we have shown that the avidity effect from a bivalent binding is enough to induce oligomer specificity. This finding facilitates a direct application on the clinically more useful IgG isotype, where the binding properties now can be controlled in detail. The method is general and we have, using this technique, also designed oligomer specific antibodies targeting α-synuclein. Transthyretin (TTR) is an amyloidogenic protein involved in both hereditary and sporadic amyloidosis. The cytotoxicity of TTR is intriguing since studies have shown cytotoxic potential from oligomers, tetramers and even monomers. Elucidation of the molecular properties associated with TTR cytotoxicity is hence of interest. By preventing tetramer dissociation, TTR aggregation and TTR-induced cytotoxicity is abolished. Based on this rationale, a current therapeutic strategy is to stabilize the TTR tetramer with small molecules. The kinetic stability within the spectra of known TTR mutations spans more than three orders of magnitude. However, although the most stable mutants are inert, a poor correlation within the group of cytotoxic variants exists where the cytotoxic effect is not potentiated in proportion to their kinetic stability. Through analysis of a large spectra of TTR variants, our results indicate that TTR induced cytotoxicity requires an intermediate stability of the TTR molecule. The kinetic stability should be low enough to permit tetramer dissociation and the thermodynamic stability high enough to prevent instant aggregation and to allow formation of the cytotoxic fold.

In the first part of this thesis, the synthesis, characterization and investigation of ortho-phenyleneethynylenes containing heterocycles, are presented. These compounds display changes in absorption and emission spectra varying with their functionalization and size. These compounds also have the ability to coordinate with metals. The synthesis of coordination compounds and their crystallographic data are reported. The synthesis and characterization of tetraethynyl thiophene compounds containing pyridines are also presented. These compounds exhibit differences in absorption and emission spectra upon exposure to various metal salts. The final topic to be discussed is the synthesis and characterization of diphenyl amine polymers. These polymers could in principle be used in NLO applications or light emitting devices.

Previous studies of the redox states of linear conjugated oligomers as models for polarons and bipolarons in conjugated polymers do not fully address the influence of intermolecular interactions on the electronic structure of conjugated systems in the solid state. Fusion of oligothiophenes onto a bicyclo[4.4.1]undecane core holds the conjugated oligomers in a permanent cofacial stack. One- and two-electron oxidation of the stacked oligomers affords mono(radical cation)s and dications that serve as models for polarons and bipolarons in p-doped conjugated polymers and demonstrates the effect of pi-stacking on the electronic structure of these species. Installation of phenyl-capped and ferrocenyl-capped oligothiophenes allows us to systematically vary pi-stacked oligomers and study intramolecular charge migration in other linear conjugated molecules.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Virginia, 2001. / Includes bibliographical references (leaves 146-168). Also available online through Digital Dissertations.

Not available / text

Electronic materials are of great interest for use in photovoltaics, sensors, light-emitting diodes, and molecular electronics. Hybrid Inorganic/Organic materials have been studied for device application due to their unique electronic properties. These properties result from the formation of bulk heterojunctions between inorganic (n-type) and organic (p-type) materials. However, due to incomplete pathways for charge transport and poor interfaces between materials, charge trapping and exciton recombination is often high. In an effort to alleviate these problems, we have developed an approach to fabricate bulk heterojunction materials via a seeded growth process. Electropolymerizable Schiff base complexes have been designed, synthesized, and utilized as precursors for conducting metallopolymers. The embedded metal centers are used as seed points for direct growth of size-controllable semiconductor nanoparticles within the polymer film leading to direct electronic communication between the two materials. The synthesis of CdS, CdSe, Ga₂S₃, CuInS₂, CuInSe₂, CuGaS₂, CuGaSe₂, CuGa[subscript x]In[subscript x]-₁S₂, and CuGa[subscript x]In[subscript x]-₁Se₂ has been seen through TEM and EDX. Devices have been fabricated and current studies have focused on the photovoltaic characterization of these materials which have a PCE of 0.11%. As a second but closely related area, polymers have also been studied as organic semiconductors for device applications. However they are hard to process from solution and their polymeric structure can vary. Both of these problems can be solved by using well-defined solution processable oligomers. Thiophene oligomers have been synthesized and characterized through Single Crystal X-Ray Crystallography, Four Point Probe Conductivity, and Powder Diffraction. These oligomers have a well-defined structure and are solution processable from a variety of solvents which can then be used as models to predict and study the properties of polythiophene. / text