Contribution du modèle Age-Période-Cohorte à l'étude de l'épizootie d'Encéphalopathie Spongiforme Bovine en France et en Europe

Les encéphalopathies spongiformes subaigües transmissibles (ESST) sont des maladies neurodégénératives affectant l'Homme et les animaux, l'issue est toujours fatale. La détection dans le sang de l'agent pathogène responsable de l'infection (protéine prion pathologique)reste difficile à ce jour et l'identification de nouveaux biomarqueurs impliqués dans la physiopathologie des ESST constitue un projet ambitieux et risqué. Dans ce contexte, notre objectif est d'établir un profil protéique corrélé aux ESST. L'utilisation d'un modèle animalbien caractérisé : la tremblante naturelle du mouton, d'une technologie adaptée à l'analyse de profils protéiques : SELDI-TOF MS et d'un fluide biologique : le sérum, a constitué la base de nos travaux de recherche. Dans un premier temps, les protocoles expérimentaux ont été mis en place et optimisés. Puis, ils ont été évalués pour leur pertinence dans la discrimination de moutons pathologiques en phases précoce et tardive de la maladie versus des moutons contrôles par analyse des sérums fractionnés ou non. Des biomarqueurs potentiels de faibles poids moléculaires ont été sélectionnés à l'aide de la méthode statistique SAM et une signature protéique permettant un diagnostic précoce a été établie (87% de sensibilité et 90%de spécificité). Un des biomarqueurs a été identifié comme étant un fragment de la transthyrétine, puis son potentiel discriminant a été évalué en SELDI-TOF MS dans une étude cinétique de hamsters Syriens infectés par la scrapie, en western blot et par dosage ELISA.Finalement, une cohorte de validation constituée de moutons appelés « scrapie-free » a permis de valider les biomarqueurs les plus pertinents. / Transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseasesoccurring in animals and humans for which no ante-mortem diagnostic test in biological fluidsis available. In such pathologies, detection of the pathological form of the prion protein (i.e.,the causative factor) in blood is difficult. Identification of new biomarkers implicated in thepathway of prion infection is relevant. In this context, our objective was to find a proteicprofile correlated to TSEs. We used a well-known TSE model: scrapie in sheep breeding, amass spectrometry technology easy-to-use for proteic profiling: SELDI-TOF MS and abiological fluid: serum. First, experimental tools have been developed and optimized. Thesetools were evaluated for their discriminating potential of control sheep and animals with earlyor late phase scrapie using a large number of serum samples (fractionated or not). Then, usingthe SAM statistical method, potential low molecular weight biomarkers were selected. Amongthese biomarkers, a protein signature pattern was identified; it can discriminate between earlyphase scrapie and control sera (sensitivity of 87% and specificity of 90%). One of theseproteins was identified as a fragment of transthyretin and evaluated as a biomarker using aSELDI-TOF MS kinetic study of sera from scrapie infected Syrian hamsters. This biomarkerwas also confirmed by western blot analysis and ELISA quantitation. Finally, a cohort of freescrapiesheep permits to validate the diagnostic potential of the candidate biomarkers.

No description available.

Nous avons entrepris la caractérisation de la protéine prion pathologique par Western blot à partir d’isolats de petits ruminants et de bovins atteints d’Encéphalopathie Spongiforme Subaiguë Transmissible (ESST) afin d’identifier des signatures moléculaires divergeant de la signature associée à l’ESST affectant habituellement ces animaux ; la tremblante classique pour les petits ruminants et l’ESB classique (ESB-C) pour les bovins. Cette étude a permis d’évaluer la fréquence de phénotypes inhabituels et a contribué à envisager les formes d’ESB atypiques comme sporadiques. Ensuite la transmission des isolats de petits ruminants aux souris C57Bl/6 et TgOvPrP4 a permis d’une part de confirmer l’absence de contamination par l’agent de l’ESB, tout du moins pour les ovins, et d’autre part d’approfondir les connaissances sur la diversité des souches dans les isolats de tremblante. Les travaux de transmission aux souris C57Bl/6 des isolats bovins atteints d’ESB-H ont quant à eux conduit à la description de l’émergence d’une souche présentant les caractéristiques de l’ESB-C suggérant que la forme sporadique d’ESB-H puisse être à l’origine de la contamination initiale des bovins ayant conduit après recyclage par le biais des farines de viande et d’os à l’épizootie d’ESB-C / Molecular characterization using Western blot method has been carried out to identify unusual PrPres pattern from small ruminants and bovines TSE affected. Such analyse allow us to define the frequency of these unusual signature and contribute to consider BSE-H as sporadic form of ruminant TSE. Transmission studies from unusual sheep isolates in C57Bl/6 and TgovPrP4 mice firstly contribute to confirm that none of these sheep isolates was infected by BSE transmission. Secondly, strain characteristics observed through experimental transmission of unusual isolates and classical scrapie affected isolates show results that give some element about strain diversity in both scrapie types. Serial passages of H-BSE in C57Bl/6 mice show the emergence of a prion strain with features similar to classical BSE. Such findings might help to explain the origin of the classical BSE epizootic disease, which could have originated from this kind of sporadic form of BSE

Philosophiae Doctor - PhD / The research was prompted by two main issues prevalent in South African education in the last decade. These were particularly the critical state of the schooling system, especially in the educationally disadvantaged schools (mainly ex-Department of Education and Training) and the relationship of the teacher to teaching and the related issue of teacher upgrading. The resultant effect was that the educationally disadvantaged communities became more and more disadvantaged over time because of decreasing mental stimulation and mental development. The answer lay in finding a theory of intellectual growth and development which takes into account the learning environment of the disadvantaged child. The Educational Support Services Trust (ESST) has been active in addressing this very issue since 1986. It provides appropriate learner-centred mediational texts to disadvantaged pupils around the country. These materials concentrate on the development of practical intelligence by relating leaming to everyday experience. The Teachers' Methodology Project was designed to change the teachers who were using the ESST materials from being disseminators of information to being managers of a learning-centred classroom environment. The idea was to change the way that teachers thought about teaching and learning. This was accomplished by sharing the methodology of the existing pupils' materials and theories of cognition and mediation with them so that they could become adept at mediating at the level of deconstruction of complex ideas and using this knowledge in the construction and development of their own learning materials, thereby contributing to the mental development of their pupils. My experience as a staff member of the ESST and my background in education provided an entry point to this research via Feuerstein et at's (1980,1991) criteria for mediation, Haywood's (1993) mediational teaching style and a range of other theories and ideas including group work and co-operative learning, graphic organisers, and the ESSTs own theory of mediatory text (Sinclair, 1991). These were consolidated into a learning-centred approach to teaching in which the learner, the teacher and the task become part of the total learning-centred environment. The research began as an investigation of the Teachers' Methdology Project (TMP) and an effort to track teachers' development but grew to include the development of the conceptual mediational framework on which the project was based. This resulted in the development of a classroom observation instrument which was used to evaluate how teachers mediated in their classrooms and how they interacted with pupils. The TMP was implemented through a series of workshops during which teachers examined their assumptions about teaching and learning: explored new avenues for facilitating learning; experienced a learning-centred approach to teaching; acquired new strategies for and knowledge of, theories and atttitudes to teaching and learning and were able to reflect on and practise newly acquired skills in a supportive collegial environment. The research employed a qualitative approach and therefore the documentation of the process took considerable effort. An experiential framework (Kolb, 1974) was used to analyse the process and the results. This mediational experiential framework resulted in a methodology which addressed teachers' attitudes and cognition in a life-related way, taking into account their personal knowledge and experience. The methodology is replicable and has been used in basic adult education and other settings. In addition, the methodology can contribute to the understanding of how Outcomes-based Education could be implemented in South Africa.

Dans le but de caractériser chez les ovins l'agent de l'encéphalopathie spongiforme bovine (ESB) responsable du variant de la maladie de Creutzfeldt-Jakob chez l'homme, trois brebis de génotype sensible (2-ARQ/ARQ) ou résistant (1-ARR/ARR) à la tremblante ont été infectées par un cas d'ESB français. La recherche des sites d'accumulation de la protéine prion anormale (PrPsc) a révélé des traces PrPsc chez le mouton ARR/ARR mais n'a pas permis de différencier l'ESB chez les moutons ARQ/ARQ de cas de tremblante naturelle. Chez ces brebis, l'agent de l'ESB a pu être en revanche identifié par l'analyse des sites de clivage de la PrPsc par les protéases comme par l'étude comparée, chez des souris infectées par l'ESB, l'ESB-ovine et la tremblante, de la distribution neuro-anatomique discriminante des dépôts de PrPsc. Ainsi, grâce au maintien de certaines de ses propriétés chez les ovins, il devrait être possible d'identifier l'agent de l'ESB dans les troupeaux par ces approches complémentaires.