Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2006. / Härtill 3 uppsatser.

Thesis (M.Sc.). / Written for the Dept. of Neurology & Neurosurgery. Title from title page of PDF (viewed 2008/05/14). Includes bibliographical references.

Thesis (Ph.D. in Biochemistry) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 128-144). Free to UCD affiliates. Online version available via ProQuest Digital Dissertations;

Gut-associated lymphoid tissues such as Peyer’s patches (PP) are inductive sites for immune response in the intestine. Unlike other peripheral lymphoid tissues, gut-associated lymphoid tissues lack afferent lymphatics and can directly sample mucosal antigens by specialized epithelial cells in the follicular associated epithelia (FAE), known as M cells. M cells derive from Lgr5+ intestinal stem cells in intestinal crypts, where the daughter cells of Lgr5+ cells differentiate into M cells after stimulation from the cytokine receptor activator of nuclear factor-κB ligand (RANKL). RANKL is produced by stromal cells within the sub-epithelial dome (SED) residing below the FAE. The transcytosis of antigens across the FAE by M cells is an important initial step in the induction of efficient mucosal immune responses against certain pathogenic bacteria as well as the commensal bacterial flora. However some pathogens, for example orally-acquired prions, may also exploit M cells to infect the host. M cells have been implicated in the uptake of orally acquired prions from the gut lumen. After oral exposure, the accumulation of prions in PP is important for their efficient spread to the nervous system. Previous studies have also shown that pathogen-induced inflammation increases M cell density and this effect can be mimicked by exogenous administration of RANKL. This has led to the hypothesis tested in this thesis that inflammation-related enhancement of M cell differentiation aids the delivery of prions into the lamina propria of villi. The administration of RANKL resulted in increased M cell density in the gut epithelium of mice. Consequently, RANKL treatment enhanced the accumulation of orally-administered prions in PP, decreased disease incubation time and increased prion disease susceptibility. These data indicate the importance of M cells in prion disease pathogenesis and highlight the potential of M cells as vaccine targets against prion disease. The fate and terminal differentiation of distinct intestinal epithelial cell lineages from their uncommitted precursors is dependent on their intrinsic expression of one or more specific transcription factors during their development. Alongside inducing M cell differentiation, RANKL stimulation can also induce the nuclear translocation of the NF-κB transcription factor subunit c-Rel. A comparison of the genes encoding the individual NF-κB subunits c-Rel, Rel-A and Rel-B revealed that they were expressed at the mRNA level in the FAE and by M cells. A c-Rel-deficiency in mice did not influence the expression of RANKL or RANK in PP. The subsequent induction of M cell maturation in the FAE was also unaffected in, indicating that c-Rel is dispensable for the RANKL-mediated differentiation and functional maturation of M cells. The factors implicated in Lgr5+ intestinal stem cell proliferation and their differentiation into M cells are poorly understood. Some reports have indicated that crypt-associated macrophages may provide extrinsic factors that assist Lgr5+ intestinal stem cell proliferation. In this thesis, the ablation of macrophages in the gut resulted in dysregulation of crypt microarchitecture, depleting Paneth cells and the Lgr5+ stem cells. This adversely affected the subsequent differentiation of intestinal epithelial cell lineages and impeded the functional development of M cells. These data reveal a previously unknown role for macrophages in the maintenance of intestinal crypts and intestinal stem cell proliferation and differentiation.

Prions are infectious protein entities capable of self-replication. Prions are the causal agents behind the transmissible spongiform encephalopathies causing neurodegeneration and death in affected organisms. Prions have been identified in yeast with the best-characterized prions being [PSI+] and [PIN+], whose respective native proteins are the Sup35 translation termination factor and Rnq1 (function unknown). Autophagy is a cellular housekeeping mechanism mediating the degradation of damaged proteins and superfluous organelles. It is a highly sequential process regulated by autophagy related genes (ATGs). Autophagy has also been implicated in the clearance of amyloidogenic proteins including prions. However, the mechanistic basis underlying this activity is poorly understood, and a key objective of this project was to characterize how autophagy prevents spontaneous prion formation. Our study found that the deletion of core ATGs correlated with an increase in de novo [PSI+] and [PIN+] formation as well as Sup35 aggregation. Enhancement of autophagic flux through spermidine treatment attenuated the increased levels of de novo [PSI+] formation in mutants that normally show elevated levels of [PSI+] formation. Defective autophagy correlated with increased oxidatively damaged Sup35 in an atg1 mutant whereas anaerobic growth abrogated the increased [PSI+] formation in the atg1 mutant to wild-type levels. Our data suggest that autophagy serves a protective role in the clearance of oxidatively damaged Sup35 proteins that otherwise has a higher propensity towards [PSI+] prion formation. We also investigated the role of prion formation and autophagy during yeast chronological ageing which is the time that non-dividing cells remain viable. Prion diseases are associated with advanced age which correlates with a decline in cellular protective mechanisms including autophagy. Our study found an age dependent increase in the frequency of de novo [PSI+] formation with chronological age of yeast cells, more so in an atg1 mutant relative to the wild-type. Autophagy competent cells carrying the [PSI+] and [PIN+] prions also had improved chronological lifespan relative to prion free cells and atg1 cells. Cells carrying the [PSI+] prion elicited elevated autophagic flux that may promote improved lifespan thus suggesting a beneficial role of the [PSI+] prion during chronological ageing. The actin cytoskeleton provides the structural framework essential for a multitude of cellular processes to occur. We investigated the role of the Arp2/3 complex responsible for branching of actin filaments towards prion formation. Knockout mutants of the nucleation promoting factors of the Arp2/3 complex, in particular the abp1 mutant, showed reduced de novo [PSI+] formation and Sup35 aggregation under basal and oxidative stress conditions. Similarly, treatment with latrunclin A, an actin monomer-sequestering drug also abrogated de novo [PSI+] formation. Colocalization studies revealed that Sup35 often does not colocalize with Rnq1, a marker for the insoluble protein deposit (IPOD) in an abp1 mutant. This suggests a role for the Abp1 protein in the efficient transport of Sup35 molecules to the IPOD that may facilitate de novo [PSI+] prion formation under vegetative states and oxidant challenges.

La maladie de Huntington (MH) est une maladie neurodégénérative autosomique dominante qui affecte environ 3 à 8 personnes sur 100 000 dans le monde. La MH est causée par une mutation du gène HTT, lequel code pour la protéine huntingtine (HTT). Cette mutation consiste en une expansion de 35 répétitions CAG à même l'exon 1 du gène et aboutit à une répétition de la séquence polyglutamine (polyQ) au sein du segment N-terminal de la protéine HTT. Les personnes atteintes de MH développent des troubles moteurs, cognitifs et psychiatriques sévères, principalement à l'âge adulte. L'âge d’apparition des symptômes est généralement inversement proportionnel au nombre de répétitions CAG bien que la symptomatologie varie considérablement d'un patient à l'autre. L'origine de la MH est associée à l'expression de la protéine HTT mutée (mHTT) qui, en raison de son expansion polyQ, adopte une conformation pathogène et s'accumule en petits et/ou gros agrégats cytotoxiques. Bien que l'on suppose que ces événements soient responsables de la neurodégénérescence, le mécanisme sous-jacent aux voies physiopathologiques menant à l'apparition de la maladie et à la mort neuronale est toujours à l'étude. Un nombre croissant d'observations suggère que la mHTT possède des capacités de type prion, c’est-à-dire une aptitude à recruter des protéines endogènes normales et les corrompre afin de créer des agrégats toxiques; capacités qui sont également connues pour d'autres protéines, notamment l'amyloïde, la tau et la a-synucléine, associées à diverses maladies neurodégénératives. Nous avons émis l'hypothèse que le mHTT se propage de cellule en cellule et qu'elle se comporter tel un prion, contribuant à influencer le développement de la MH. Afin de tester cette hypothèse, des fibrilles synthétiques de mHTT ont été administrées à plusieurs lignées cellulaires ainsi qu'à des souris de différentes souches génétiques. Suite à une période d'incubation, les effets des fibrilles de mHTT sur la viabilité cellulaire, le comportement animal et les caractéristiques neuropathologiques ont été examiné. Nous avons ainsi observé que les fibrilles de mHTT provoquaient la mort cellulaire et des changements morphologiques des cellules cultivées, tandis qu’elles induisaient un phénotype comportemental transitoire de la maladie chez des souris saines. Les fibrilles de mHTT pouvaient également exacerber les déficits moteurs, anxieux et cognitifs de type MH dans un modèle de souris huntingtonien. Ainsi, notre étude suggère que la mHTT extracellulaire peut se propager de cellule à cellule et, une fois recrutée au sein de la cellule, provoquer des changements pathologiques. À la lumière de ces observations, nous croyons que la mHTT extracellulaire pourrait représenter une cible attrayante pour le développement de futures stratégies thérapeutiques. De surcroît, la plupart des traitements en études cliniques sont conçus pour cibler le gène HTT dans le but de diminuer l'expression de la protéine, ignorant la quantité importante de mHTT déjà présente dans le système à l'âge adulte. Par conséquent, une thérapie combinatoire ciblant, à la fois l'expression de mHTT et la mHTT extracellulaire préexistante, pourrait se révéler une voie prometteuse pour le traitement de la MH. / Huntington’s disease (HD) is an autosomal dominant neurodegenerative disease that affects approximately 3 - 8 people in 100,000 individuals worldwide. HD is caused by a mutation in the HTT gene, which codes for the protein huntingtin (HTT), consisting of an expansion of 35 CAG repeats in the exon 1 of the gene and resulting in the elongated polyglutamine (polyQ) stretch at the N-terminal fragment of the protein HTT. Individuals who suffer from HD develop severe motor, cognitive and psychiatric impairments, which primarily manifest in adulthood. The onset of the disease is usually inversely proportional to the CAG repeat expansion, however, HD comes with a high variability of symptoms. HD is also associated with the expression of the mutated HTT (mHTT) protein. The mHTT protein adopts a pathogenic conformation, which accumulates in small and/or large cytotoxic aggregates. Although these events are suspected to contribute to neurodegeneration, the exact mechanisms underlying the pathophysiological pathways leading to disease onset and neuronal death are still under investigation. A growing body of evidence suggests that mHTT possesses prion-like capacities – the capacity to spread between cells and seed disease – a phenomenon associated with other proteins such as amyloid, tau and a-synuclein, all involved in various neurodegenerative diseases. We hypothesized that mHTT propagates in a non-autonomous manner and behaves in a prion-like fashion to influence the onset and severity of HD. To address this, exogenous synthetic mHTT fibrils were administered to several cell lines and to mice of different genetic backgrounds. Following an incubation period, the effects of mHTT fibrils on cellular viability, animal behavior and neuropathological features were examined. We observed that mHTT fibrils provoked cell death and morphological changes in cultured cells, induced transient HD-related behavioral phenotypes in healthy mice and exacerbated motor, anxiety-like and cognitive deficits in an HD mouse model. Our study suggests that extracellular mHTT can propagate between cellular elements and once uptaken, trigger pathological changes. In light of these observations, we believe that extracellular mHTT could represent an appealing target for future therapeutic strategies. Current disease-modifying treatments tested in the clinic are designed to target the HTT gene to decrease the expression of the protein, overlooking the mHTT load outside of the cell boundaries and/or which has accumulated in the system prior to the application of gene silencing/editing. Hence, a combinational therapy addressing both the intracellular and extracellular expression of mHTT could serve as a more global treatment of HD.

Les maladies à prions sont des maladies neurodégénératives et transmissibles. Elles sont à l'origine de formes infectieuses comme la maladie de Creutzfeldt-Jakob iatrogène secondaire à un traitement par hormone de croissance d'origine humaine (MCJ post-hGH). La compréhension des facteurs gouvernant la physiopathologie de ces formes demeure parcellaire. Notre objectif a été de les étudier en analysant la cohorte des patients français exposés à l'hGH. Les analyses épidémiologiques, ont montré, à partir de données quantifiées, pour la première fois chez l'homme, une relation entre la dose d'exposition et le risque de développer la maladie d'une part et la durée de la période d'incubation d'autre part. La modélisation de la période d'incubation, a permis d'estimer que 95% des cas sont déjà apparus et d'évaluer l'influence du polymorphisme au codon 129 du gène codant la protéine prion sur la période d'incubation. L'étude descriptive a montré des similarités clinico-pathologiques entre tous les cas de maladies à prion humaines par contamination périphérique laissant supposer un rôle important de la voie d'exposition. Les expériences de transmission à la souris transgénique devraient permettre de valider les hypothèses que nous avons émises sur l'identité des souches présentes dans les lots contaminés. Ce travail a donc permis de mieux caractériser les facteurs impliqués dans la transmission des maladies à prions chez l'homme et de fournir un cadre méthodologique et des informations qui pourraient être utiles pour évaluer le risque de transmission potentielle des autres protéinopathies du système nerveux central pour lesquelles un mécanisme " prion like " a été proposé. / Prion diseases are fatal and transmissible neurodegenerative disorders. Infectious forms include iatrogenic Creutzfeldt-Jakob disease after human cadaver-sourced growth hormone treatment (hGH-iCJD). Our understanding of the factors governing the pathophysiology of infection, upon exposure to an exogenous prion, remains very limited in humans. The aim of this study was to better understand these phenomena using data from the French cohort of patients who were exposed to this at risk treatment. Using Cox hazards model, we provided the first epidemiological evidence of a relationship between dose of exposure and disease occurrence on one hand and incubation time on the other hand. Incubation period modelling by Weibull distribution estimated that 95% of the cases have already occurred. In a descriptive study, we showed that clinical and neuropathological features resembled other forms of infectious prion diseases after a peripheral contamination supporting a major role of the route of exposure. We also performed experimental transmission to transgenic mice expressing human PrP to test our hypotheses about the infecting prion strain that were transmitted to French hGH-iCJD patients. To conclude, we identified factors implicated in human prion transmission and provided a methodological frame and useful information that could help to evaluate the transmission risk associated with other brain proteinopathies such as Alzheimer and Parkinson’s diseases for which a prion-like mechanism has been proposed.

L’étude de l’interaction entre des protéines et leurs ligands est essentielle pour la compréhension de leur rôle physiologique ainsi que de leur rôle dans la mise en place de pathologies. En particulier, dans le cas de maladies neurodégénératives, comme les maladies d’Alzheimer ou de Creutzfeld-Jacob, ou d’autres pathologies liées au mépliement de protéines, la compréhension des interactions entre protéines, qui peuvent modifier de façon considérable le paysage conformationnel des partenaires, est une des clés pour décrypter les étapes moléculaires élémentaires induisant une cascade d’événements qui mènent à la formation d’assemblages protéiques de grande taille. Dans le cadre de cette thèse, nous avons étudié la dynamique de taille de trois types d’assemblages protéines/ peptides.Interactions faibles impliquées dans la structuration d’assemblages de PrPSc et dans l’équilibre entre les formes PrPSc et suPrP : Dans un premier temps, l’étude des étapes précoces de la réplication du prion nous a permis de mettre en évidence une voie de diversification structurale qui implique une voie de templating secondaire. En utilisant une méthode de solubilisation en conditions natives et une approche reposant sur une série de souches différentes, nous avons démontré que, pour toutes les souches testées, les assemblages de prion ont la propriété de se dépolymériser en deux ensembles discrets d’assemblages oligomériques, dont la taille varie entre des dimères et tétramères. Des approches d’amplification de prion in vitro et in vivo ont démontré que ces assemblages oligomériques comportent toute l’information nécessaire à la réplication ainsi que les déterminants structuraux de la souche. Le motif de glycosylation, la cartographie par épitopes ainsi que l’empreinte PK ont mis en évidence des différences structurales entre les espèces oligomériques, soulignant la coexistence d’ensembles d’assemblages structuralement distincts au sein d’une souche donnée. Des expériences de dépliement partiel ont montré la présence d’une dynamique constitutionnelle entre les assemblages reposant sur un échange de matière et un réarrangement structurel à l’échelle de l’unité élémentaire (suPrP) ainsi qu’une diversité structurale au sein des assemblages de prion.Partenaires et oxydation de la PrPc: Bien que des travaux préalables aient mis en évidence l’existence d’interactions entre PrP et Aβ, Aβ1-40 ne forme que des complexes très instables avec la PrP monomérique. La spectrométrie de masse n’a pas permis de mettre en évidence cette interaction, même après optimisation des paramètres en conditions natives ou via des mesures indirectes reposant sur des échanges hydrogène - deutérium d’amide. L’oxydation radioloytique de la PrPC a été étudiée par SEC couplée à la mobilité ionique et la spectrométrie de masse, montrant la formation d’assemblages de haut poids moléculaires associée à des changements de structure.Fortes interactions peptide/peptide : Le système Synapt G2Si (Waters), qui combine de la mobilité ionique avec de la spectrométrie de masse, a été utilisé pour l’analyse d’une série de peptides issus de la capside externe du birnavirus de l’IBDV. Ces peptides peuvent former des complexes avec des énergies de liaison intermoléculaires proches de l’énergie de la liaison peptidique. En plus de la mise en évidence des changements structuraux au sein de ces complexes liés à l’introduction de mutations dans la séquence peptidique, des déviations par rapport aux attentes expérimentales ont été observées au cours de ce travail lors de mesures en conditions de mobilité ionique. Ces écarts ont pu être reliés à la conception de la cellule Tri-Wave de l’instrument, qui conduit à un mélange des différents gaz tampon qui ne peut être évité. De ce fait, les biais introduits par ce mélange influencent les paramètres de modélisation et la comparaison entre instruments pour tous les utilisateurs de ce modèle d’instrument. / Interactions between proteins and their ligands play a crucial in the understanding of their physiological function as well as their role in disease mechanisms. Especially in all forms of neurodegenerative diseases like Alzheimer, Creutzfeld-Jacob disease and others pathologies due to protein misfolding, the understanding of protein interaction, which can cause a dramatic change in the conformational landscape of the binding partners, is key in the deciphering of elementary molecular steps leading to cascade of events finally resulting in the formation of large protein assemblies. In the scope of this thesis we studied the size dynamic of three types of protein/peptides assemblies.Weak interactions involved in the structuration of PrPSc assemblies and in the detailed balanced between PrPSc and suPrP: The earliest steps in prion protein conversion were studied using both in vitro bona fide prion amplification method. We showed that the early step of the replication leads to a deterministic diversification process involving a secondary templating pathway. Furthermore, by using a native solubilization method and through a multi-strain approach. We demonstrated a generic property of prion assemblies to depolymerize into two discreet sets of oligomeric assemblies with a size ranging between dimers and tetramers for all tested strains. Both in vitro and in vivo prion amplification approaches showed that the oligomeric assemblies harbour all the replicative information as well as the strain structural determinant. Glycopattern, epitope-mapping and PK fingerprint revealed structural differences between the oligomeric species highlighting the coexistence of structurally distinct set of assemblies within a given strain. Partial unfolding experiments demonstrated the existence of a constitutional dynamic between the assemblies based on material exchange and structural rearrangement at the level of the elementary subunits (suPrP).PrPc partners and oxidative modifications: Although previous work had shown the existence of interactions between PrP and Aβ, monomeric Aβ1-40 forms only very weak complexes with monomeric PrP and mass spectrometry, even after optimization of the native instrument settings or by indirect measurements based on amide hydrogen deuterium exchange was not able to detect this interaction. Oxidation of PrPc was also suggested as a pathway towards pathology: the appearance and structural changes induced by gamma-radiolysis of water on PrPc were studied by mass spectrometry and ion mobility.Strong peptide/peptide interactions: The Waters Synapt G2Si instrumental set-up which couples ion mobility with mass spectrometry was used for the analysis of a collection of peptides derived from the shell of the IBDV binavirus. These peptides can form complexes with binding energies close or similar to the binding energy of the peptide bond. In addition to a better description of the changes in structure of these complexes varying with the mutations introduced in peptide sequence, we observed deviation from expected instrument characteristics when performing ion mobility measurements. Due to the design of the Tri-wave module in the Waters Synapt G2Si mass spectrometer, a mixture of the different buffer gases intrinsically cannot be avoided. Consequently, these biased measurements influence the outcome of modelling approaches and the inter-instrument comparison for all users of this instrument type.

Le diagnostic de la maladie d’Alzheimer (MA) est tardif et présente un manque de fiabilité en regard de l’examen neuropathologique postmortem permettant de confirmer ce diagnostic. En effet, les présentations cliniques de la MA peuvent être multiples et parfois atypiques. Des anomalies dans les concentrations des protéines tau, tau phosphorylées et amyloïdes bêta, au sein du liquide céphalorachidien (LCR), ont permis d’améliorer le diagnostic du vivant du patient. Nous avons évalué la performance de ces marqueurs, dans le LCR, utilisés pour le diagnostic de la MA dans les formes syndromiques atypiques. L’utilisation de ces marqueurs augmente la précision du diagnostic lors de ces différentes présentations cliniques. De plus, nous avons mis au point un test diagnostic biochimique postmortem des différentes tauopathies permettant de mieux les caractériser en complément de l’examen neuropathologique. Enfin, nous avons conçu et caractérisé des anticorps spécifiquement dirigés contre la protéine tau phosphorylée en position 231. Cet outil nous a permis de développer un test ELISA dans le LCR. Des résultats préliminaires suggéreraient une interaction in vivo entre les protéines tau et Prion. Ces résultats, décrits pour la première fois, sont corrélés à nos observations histologiques / Diagnosis of Alzheimer’s disease (AD) is late with a lack of reliability with regard to postmortem neuropathological examination that permits to confirm this diagnosis. Indeed, many clinical presentations of AD can occur and sometimes atypical. Anomalies in cerebrospinal fluid (CSF) levels of tau, phosphorylated tau and amyloid beta proteins permitted to improve antemortem diagnosis. We evaluated biomarkers performance, into CSF, used for AD diagnosis in syndromal atypical forms. The use of these biomarkers increases the accuracy of diagnosis during these different clinical presentations. Moreover, we adjusted a biochemical postmortem diagnosis test of tauopathies giving the interest to better characterize them in addition to neuropathological examination. Finally, we developed and characterized antibodies specifically directed against phosphorylated tau protein on 231 epitope. This tool permitted to make an ELISA test in CSF. Preliminary results may suggest an in vivo interation between tau and Prion proteins. These results, described for the first time, correlated with our histological observations

Despite intensive research, the cellular and molecular mechanisms involved in human cellular susceptibility to prion infection remain poorly defined, in part due to the continuing lack of cultured human cells that are susceptible to infection with human prions. Such culture models would present distinct advantages including speed and expense compared with animal models, and would provide systems in which to investigate the interaction between PrPC and PrPSc, the basis of cellular susceptibility, the nature of the species barrier and the mechanism of prion propagation in situ. This study sought to examine whether non-neuronal cells might provide opportunities to establish human cell lines replicating human prions. A human follicular dendritic cell-like cell line (termed HK) was obtained, further characterised and then tested for its ability to support human prion replication. The mechanisms of internalisation, intracellular trafficking and the eventual fate of exogenous PrPSc taken up by these cells were also examined. This thesis similarly examined the cellular response of human embryonic stem cells (hESC) to acute exposure to human and animal prions. PrPC was found to be abundantly expressed by HK cells and HK cell extracts were found to support conversion to PrPSc in a cell-free conversion assay. However, HK cells exposed to infectious brain homogenates failed to accumulate PrPSc or become infected in vitro. Exposed HK and hESC did display a readily detectable, time dependent uptake of PrPSc from medium spiked with prion-infected brain homogenates that was independent of the species, disease phenotype and PRNP codon 129 genotype of the human source and the recipient cells. The exposed cells showed intensely labelled intracellular accumulations of PrPSc with coarse granular morphology, largely in the juxtanuclear region of cytoplasm. However, when the brain-spiked medium was withdrawn and cells were given control medium, the intensity and extent of PrPSc immunostaining rapidly diminished. Co-localisation studies implicated caveolae-mediated endocytic uptake of exogenous PrPSc, apparently preceding uptake via clathrin coated pits in HK cells. Evidence suggesting that the endosomal recycling compartment and lysosomes are involved in intracellular trafficking and degradation of exogenous PrPSc was also found. Understanding the cell biology of these processes may help to explain why the majority of cultured cells are refractory to prion infection in vitro. Internalization of misfolded PrP and its subsequent degradation in the lysosomal compartment might function as a self-protective cellular mechanism, serving to eliminate non-native, presumably dysfunctional and potentially dangerous PrP conformers, whether generated endogenously or acquired through exposure to exogenous prion infectivity.