Ion channel models are related to non-equilibrium statistical physics, fluid mechanics and electromagnetism. Some classes of ordinary differential equations that model ion channels can be seen as a limit of finite state-space continuous-time Markov chains. The purpose of this thesis is to qualitatively investigate the numerical results of systems of equations that incorporate ion channels modeled by such Markov chains and an electrical circuit model of a single neuron with isopotential extracellular space. This may be useful for making more detailed micro-physical simulations of neurons. A subset of the Rallpack benchmarks is conducted in order to evaluate the accuracy of the electrical circuit model of the transmembrane voltage propagation. In order to test the tau-leap method employed to simulate the Markov-chain based ion channel models a cylindrical geometry is implemented. Convergence properties are presented in terms of mean interspike intervals of the transmembrane voltages for different time- and spatial discretisations. Accuracy of the tau-leap method is presented in relation to the deterministic versions of the ion channel models. The results show that the method used to simulate the transmembrane voltages is accurate and that while the tau-leap method is convergent in the mean interspike interval sense, it is not conclusive how accurate it is compared to the corresponding ordinary differential equations or how efficient it is.

This work presents measurements of the branching fractions for tau decays to 3-prong final states using a data set of 430 million tau lepton pairs, corresponding to an integrated luminosity of $468 fb^-1, collected with the BaBar detector at the PEP-II asymmetric energy e^+e^- storage rings. The tau^- -> 3pi^- eta nu_tau, tau^- ->pi^- 2pi^0 omega nu_tau and tau^- -> f_1(1285) pi^- nu_tau branching fractions are presented as well as a measurement of the non-resonant component of the tau^- -> 3pi^- 3pi^0 nu_tau decay. In addition this work sets a new limit on the branching fraction of the isospin-forbidden, second-class current decay tau^- -> pi^- eta'(958) nu_tau. / Graduate

The dysfunction of tau protein has been implicated in a number of neurodegenerative diseases, including Alzheimer’s disease (AD) and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). In these diseases, the tau protein is aberrantly hyperphosphorylated and aggregated to form neuropathological deposits in the cell body of neurons. Evidence from genetics studies has shown a linkage between tau mutations and autosomal dominantly inherited FTD. In Chapter one, our current understanding of the mechanisms of tauopathies is summarized. In addition, multiple animal models for mechanistic studies of tauopathies are reviewed. In this thesis, endogenous tau genes in zebrafish were identified and investigated in an attempt to establish zebrafish as an animal model for study of tauopathies. Paper 1 describes the identification of two genes, mapta and maptb in zebrafish that represent duplicates of an ancestral tau orthologue. It examines their complex alternative mRNA splicing patterns and their patterns of expression during embryogenesis. Paper 2 (thesis chapter in the form of a manuscript) describes how we might use zebrafish as an animal model to investigate tau function. Two antibodies that detect Mapta and Maptb specifically are described. In addition, we establish that inhibition of Maptb translation causes an impairment of axonogenesis during zebrafish embryogenesis. / Thesis (M.Sc.) -- University of Adelaide, School of Molecular and Biomedical Science, 2010

Frankfurt (Main), Universiẗat, Diss., 2008. / Erscheinungsjahr an der Haupttitelstelle: 2007.

A search for new neutral scalar bosons produced in association with a bottom-quark is performed. The analysis uses data acquired with proton-proton collisions at a center-of-mass energy of 8 TeV and observed with the ATLAS detector at the LHC, corresponding to 20.3 $fb^{-1}$ of integrated luminosity. The search focuses on scalar boson decays into tau lepton pairs, where each decays leptonically ($\tau \rightarrow l \nu_{\tau} \bar{\nu_{l}}$) resulting in one muon, one electron and four neutrinos. No significant excess is observed and upper limits on the signal strength are determined as a function of scalar boson mass.

Currently a grate emphasis is being put on accurate and early diagnosis of Alzheimer's disease (AD), which is important for the introduction of treatments that could postpone the onset of the disease. Antibodies against tau protein appear to be suitable biomarkers for early diagnosis of AD. Therefore, this work deals firstly with preparation of human recombinant tau protein in bacteria and its subsequent use in determining levels of antibodies in blood serum of patients with AD and in normal older persons. A preparation of the tau protein in sufficient purity was achieved for the antibodies measurment by ELISA method and results were statistically analyzed using nonparametric methods. Results were compared with data from Mgr. Jany Švarcové obtained by measuring antibodies in serum of patients with AD and normal elderly using an commercial bovine tau protein. According to the analysis there are differences between the data obtained from human and the bovine tau protein. It was proven that patients with AN have lower levels of antibodies against tau protein than healthy seniors. Recombinant human tau protein was also used to immunize rabbits. The ELISA method confirmed the creation of antibodies against human tau protein in rabbits.

The molecular dynamic of tau protein, its interaction with microtubules and the changes in both that appear in pathological conditions are a focus of research to get an insight in neurodegeneration. It is known that tau binds to microtubules by four homologous repeats in its carboxyterminal half. We want to examine tau and especially its repeat regions and their role for microtubule-interaction in living neurons using live cell imaging. We created multiple tau fragments with different numbers of repeats and expressed them in neuronal differentiated PC12 cells as a model for neurons. We performed fluorescence decay after photoactivation experiments by measuring the change of fluorescence intensity over time in the activated region in the middle of cell processes. From this experiments we were able to determine association and dissociation rates of the respective constructs by fitting and modeling approaches. Fluorescence decay increased with decreasing number of repeats. We found that a minimum number of three repeats required for microtubule interaction. This could also be observed in the tip of the processes. Destabilization of microtubules by colchicine increases the mobility of full length tau and microtubule-interacting fragments, while stabilization with epothilone D has no effect. Pseudophosphorylation of tau does not significantly affect the fluorescence decay, but leads to an increase of the dissociation and association rate. Truncation of the carboyxterminus after amino acid 421 - which simulates caspase 3 cleavage of tau - or amino acid 401 leads to a decrease of fluorescence decay indicating increased binding of these fragments to microtubules and a higher dissociation rate of these fragments. Furthermore we could show that overexpression of full length tau in PC12 cells increases the fraction of polymerized tubulin. The stronger binding caspase cleavage fragment shows a similar microtubule stabilization.

Indiana University-Purdue University Indianapolis (IUPUI) / The pathway leading from soluble and monomeric to hyperphosphorylated, insoluble and filamentous tau protein is at the center of many human neurodegenerative diseases, collectively referred to as tauopathies, such as Alzheimer disease (AD). In this report, we discuss the role of neuroimaging, genetics, and biomarkers in better understanding the underlying brain changes in tauopathies. In Chapters 1 and 2, we review current knowledge of tauopathies, the protein tau and FDG PET studies in AD. In Chapter 3, we investigate glucose metabolism using [18F]FDG PET in a family with multiple systems tauopathy with presenile dementia (MSTD), a primary tauopathy cause by a mutation in MAPT. The results from this study suggest that mutation carriers have lower [18F]FDG uptake, which may precede clinical onset. In Chapter 4, we assessed brain glucose metabolism using [18F]Fluorodeoxyglucose (FDG) positron emission tomography (PET) in individuals with Gerstmann–Sträussler–Scheinker Disease (GSS) with the PRNP F198S mutation. The results from this study suggest hypometabolism in the cerebellar and striatal regions, which may be preceded by hypermetabolism. This chapter also evaluated if [11C]Pittsburgh Compound B (PiB) PET is capable of detecting PrP-amyloid in GSS in individuals with the PRNP P102L and F198S mutations. The results from this study suggest that [11C]PiB is not suitable for in vivo assessment of PrP amyloid plaques in GSS. In Chapter 5, we examine a correlation between two peripheral markers of axonal degeneration, plasma tau and neurofilament light (NFL), and MRI. The results from this study suggest that plasma NFL may be a more specific marker for neurodegeneration relative to plasma tau. In Chapter 6, we attempted to create a tau biological network from gene and protein databases and literature search. We identified over 150 genes that are related to tau protein or MAPT that are involved in different biological functions. Overall, the results of this report support the notion that using a combination of techniques may help model progression of tau pathology. Future studies may establish additional markers that may be used in combination with some of these measures as tools for diagnosis and for the evaluation of treatment efficacy in therapeutic trials.

Tauopathies refer to a group of neurodegenerative diseases that are characterized by pathological aggregations of the microtubule-associated protein Tau (MAPT). Aberrant alternative splicing of Tau exon 10 leads to the imbalanced expression of Tau isoforms that contain either 3 or 4 microtubule binding repeats (3R-Tau or 4R-Tau) and this is sufficient to cause the formation of Tau inclusions. Nonetheless, the exact molecular mechanisms that regulate aberrant Tau exon 10 splicing regulation and subsequent Tau aggregation in tauopathies remain elusive. In my thesis research, I used RNA Antisense Purification by Mass Spectrometry (RAP-MS) to identify upstream regulators of Tau splicing events. Among the 15 identified novel protein candidates, I validated that hnRNPA2B1 and hnRNPC are required to promote 4R-Tau expression, whereas hnRNPH1 supports 3R-Tau expression. Separately, to elucidate the functional difference between 3R- and 4R-Tau isoforms, I performed proximity-dependent biotin identification (BioID2) for all six human central nervous system Tau isoforms in mouse primary neurons. Followed by tandem mass tag (TMT)-labeling proteomics and data analysis, I observed that 4R-Tau proximal proteins are highly enriched in endocytosis, whereas 3R-Tau proximal proteins show top enrichment in fatty acid metabolism. Through further biochemical validations, I found that MAT2A, a S-adenosylmethionine synthase, has higher binding affinity with 3R-Tau versus 4R-Tau. Overall, using novel proteomics methods, I discovered novel Tau splicing regulators and characterized the neuronal Tau isoform-specific proximity proteome networks. These proteins, once validated through future functional studies in cellular and animal models, can represent therapeutic and diagnostic targets for neurodegenerative tauopathies. / Thesis / Doctor of Philosophy (PhD)

Thèse ou mémoire avec insertion d'articles. / La maladie de Huntington (MH) est un désordre neurodégénératif très complexe, caractérisé par un éventail de troubles moteurs, cognitifs et psychiatriques. La maladie origine d'une mutation du gène de la huntingtine (HTT), laquelle mène à la production de la protéine HTT mutée (mHTT) qui s'agrège et interfère avec les fonctions cellulaires. Bien que la mHTT soit au cœur de la pathologie, de plus en plus d'évidences suggèrent que des formes anormales de la protéine Tau se retrouvent dans les structures cérébrales touchées par la MH. Cependant, ses mécanismes de toxicité sont peu connus. Mon projet de thèse avait donc pour but d'élucider la fonction de Tau dans le contexte de la MH. Nous avons choisi d'étudier l'administration de formes fibrillaires de Tau à des modèles murin et cellulaire de la maladie. L'injection intracérébrale de fibrilles a eu pour effet de précipiter et d'exacerber les déficits cognitifs ainsi que les comportements de type anxieux des souris traitées, lesquels étaient accompagnés par une augmentation des niveaux de protéines insolubles et du nombre d'agrégats de mHTT dans les régions du cerveau ciblées par la maladie. Les observations post-mortem ont de surcroit indiqué que les formes fibrillaires de Tau affectent d'autres éléments clés de la MH, tels que la neuroinflammation microgliale et l'atrophie cérébrale. L'exposition de formes pathologiques de Tau à une lignée striatale immortalisée modélisant la MH a également démasqué une altération de la fonctionnalité de la cellule, dépeinte par une augmentation des niveaux de calcium cytosolique. De là, nous avons émis l'hypothèse que l'accumulation d'inclusions de mHTT, suite à l'administration in vivo et in vitro de Tau, serait causée, entre autres, par un dysfonctionnement des voies de clairance protéique. Nous nous sommes plus particulièrement intéressés aux chaperonnes moléculaires, Hsp70 et Hsp90, impliquées dans la protéostase. Nous avons observé que les niveaux solubles de ces protéines étaient effectivement altérés suite à l'exposition aux fibrilles et qu'ils étaient séquestrés à même les agrégats de mHTT. Ces résultats suggèrent une altération du fonctionnement de ces chaperonnes, conduisant à des problèmes de dégradation de protéines pathologiques, et donc une augmentation du nombre d'agrégats mHTT. Nos résultats mettent en lumière les conséquences de Tau sur plusieurs aspects associés à la MH ainsi que sur l'agrégation de la mHTT via un dysfonctionnement de voies de protéostase. Ceci ouvre la voie sur de nouvelles approches thérapeutiques pour traiter la MH, soit en ciblant Tau ou encore en corrigeant/améliorant la dégradation de protéines pathologiques. / Huntington's disease (HD) is a very complex neurodegenerative disorder, characterized by a range of motor, cognitive and psychiatric impairments. The disease originates from a mutation in the huntingtin gene (HTT), which leads to the production of the mutated HTT protein (mHTT) that can in turn aggregate and interfere with cellular functions. Although mHTT is a core feature of the pathology, accumulating evidence suggests that abnormal forms of the Tau protein are also found in brain structures affected by HD but little is known about its mechanisms of toxicity. The aim of my thesis was to elucidate the function of Tau in the pathophysiology of HD. We therefore administered fibrillar forms of Tau to mouse and cell models of the disease. Intracerebral injection of fibrils precipitated and exacerbated cognitive deficits and anxiety-like behaviors in treated mice, which was accompanied by increased levels of insoluble proteins and mHTT aggregates in disease-targeted brain regions. Post-mortem observations further revealed that fibrillar forms of Tau affect other key elements of HD, such as microglial neuroinflammation and brain atrophy. Exposure of pathological forms of Tau to an immortalized striatal cell line also unmasked altered cell functionality, depicted by increased cytosolic calcium levels. From this, we hypothesized that the accumulation of mHTT aggregates, following in vivo and in vitro Tau exposure, would be caused, among other things, by interference of protein clearance pathways. We were particularly interested in the molecular chaperones Hsp70 and Hsp90 involved in proteostasis. We observed that soluble levels of these proteins were indeed altered following exposure to fibrils, and that they were sequestered within mHTT aggregates. These results suggest an alteration in the function of these chaperones, leading to problems with the degradation of pathological proteins, and hence an increase in the number of mHTT aggregates. Our results highlight the consequences of Tau on several aspects associated with HD, as well as on mHTT aggregation via dysfunctional proteostasis pathways. Our findings pave the way for the identification of new therapeutic approaches to treat HD, either by targeting Tau or by correcting/enhancing the degradation of pathological proteins