x, 156 leaves : ill. ; 29 cm Notes Typescript. (Another copy on microfilm is located in Archives) Thesis (Ph.D.) -- University of Oregon Includes vita and abstract Bibliography: leaves 150-156

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / VÃrias estratÃgias tÃm sido utilizadas para que materiais, quando em contato com sangue, possam reduzir a adsorÃÃo de proteÃnas do plasma e, consequentemente, a probabilidade de formaÃÃo de trombos. AlÃm disso, outro problema associado à a calcificaÃÃo, descrita como um processo de formaÃÃo de fosfato de cÃlcio, que à a causa primÃria de falhas em tecidos moles e implantes devido à deposiÃÃo destes sais. A quitosana e a carragenana sÃo dois polÃmeros que apresentam propriedades que os tornam promissores para utilizaÃÃo como biomateriais. A quitosana, em funÃÃo dos grupos amino em sua estrutura, pode promover a adesÃo plaquetÃria, sendo necessÃria uma modificaÃÃo quÃmica, como reaÃÃes de sulfonataÃÃo, que visam diminuir a adsorÃÃo de proteÃnas plasmÃticas. A presenÃa de grupos sulfato na carragenana pode contribuir para a obtenÃÃo de superfÃcies com propriedades antitrombogÃnicas sem a necessidade de modificaÃÃo quÃmica da estrutura. A formaÃÃo de complexos polieletrolÃticos (PECs) alia a biocompatibilidade superior da quitosana com a densidade de carga da carragenana, gerada pela presenÃa dos grupos sulfato. Esse trabalho teve por objetivo estudar os efeitos da calcificaÃÃo e da trombogenicidade de filmes de quitosana e carragenana caracterizando-os atravÃs de tÃcnicas de microscopia e espectroscopia, assim como realizar estudo de revestimento de superfÃcie metÃlica utilizando estes polÃmeros. Observou-se uma diminuiÃÃo nos efeitos de calcificaÃÃo para as blendas de quitosana e carragenana e nos filmes sulfonatados (Ca/P 0,11 ou ausÃncia de fÃsforo), reduzindo a formaÃÃo e deposiÃÃo de sais de cÃlcio quando comparados com a quitosana natural (Ca/P 2,78). Ensaios de adesÃo plaquetÃria mostraram melhoria das superfÃcies de quitosana quando modificadas pela sulfonataÃÃo, ou quando misturadas com carragenana, apresentando adesÃo, em mÃdia, de 1 a 2 plaquetas/0,01 mmÂ, contra a formaÃÃo de trombos em filme de quitosana. No ensaio de revestimento, a modificaÃÃo da superfÃcie metÃlica foi evidenciada pela alteraÃÃo da quantidade percentual de carbono e oxigÃnio na composiÃÃo quÃmica da superfÃcie quando comparado o aÃo eletropolido bruto e apÃs a inserÃÃo da quitosana. As sucessivas mudanÃas sofridas pelo Ãngulo de contato reforÃam o sucesso do grafting dos polÃmeros, atravÃs da formaÃÃo de uma camada hidrofÃlica tanto para quitosana natural quanto para a sulfonatada. Pelos resultados obtidos, pode-se inferir que a quitosana sulfonatada e as blendas de quitosana/carragenana mostram-se promissoras para serem utilizadas como biomateriais em contato com sangue. / Various strategies have been proposed to reduce the plasma proteins adsorption and consequently the probability of thrombus formation on materials when contacted with blood. Furthermore, another problem associated with biomaterials is the calcification process, which is described as calcium phosphate formation, which is the primary cause of failures in soft tissues and implants. Chitosan and carrageenan are two polymers that show properties that make them promising for use as biomaterials. Chitosan, due to amino groups in its structure, may promote platelet adhesion, being necessary to perform a chemical modification on it, such as sulfonation reactions, in order to reduce plasma protein adsorption. The presence of sulfate groups in carrageenan structure may contribute to obtain surfaces with antithrombogenic properties without the need of chemical modification on its structure. The formation of polyelectrolyte complexes (PECs) combines the high biocompatibility of chitosan with the charge density of carrageenan, generated by the presence of sulfate groups. This work aimed to study the effects of calcification and thrombogenicity of chitosan and carrageenan films, characterizing them by microscopy and spectroscopy techniques. We also conducted the study of metal surfaces coating using these polymers. A reduction in the effects of calcification for chitosan and carrageenan blends and for sulfonated chitosan films (Ca/P 0.11 or phosphate absence) was observed, reducing the formation and deposition of calcium salts when compared with pristine chitosan (Ca/P 2.78). Assays of platelet adhesion for chitosan surfaces when modified by sulfonation reaction or when blended with carrageenan, showed adhesion on average of 1 to 2 platelets/0.01mm2 against thrombus formation on chitosan film. For the coating essays, the modification on metal surface was characterized by the changing of carbon and oxygen percentage amount on the chemical composition surface, comparing the raw electropolished steel and grafted chitosan. The successive changes observed in the contact angle reinforce the success of the grafting of polymers, forming a hydrophilic layer both for pristine and sulfonated chitosan. From the results obtained, it can be inferred that the sulfonated chitosan and chitosan/carrageenan blends are promising for use as biomaterials in blood contact.

Orientador: Marisa Masumi Beppu / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-09T18:10:57Z (GMT). No. of bitstreams: 1 Aimoli_CassianoGomes_M.pdf: 6283050 bytes, checksum: 378aeffd560aaaa8a34ccdde9885c054 (MD5) Previous issue date: 2007 / Resumo: A utilização de materiais biologicamente compatíveis é de crescente interesse no meio científico e tecnológico. Associados à utilização de biomateriais em diversas áreas, estão fenômenos como a calcificação, que pode ser prejudicial e patogênica no caso de próteses cardíacas e lentes de contato, mas que pode ser indispensável para a produção de resinas de adsorção e substratos mais mecanicamente resistentes. Nesse contexto, a quitosana desponta como material de grande importância, já que além de ser biocompatível, é derivada do segundo biomaterial mais abundante na natureza: a quitina. Entretanto, a sua utilização com a finalidade de se promover calcificação é muito pouco estudada e pouco se sabe sobre os mecanismos e fenômenos associados. Visando o entendimento detalhado sobre o mecanismo de calcificação deste material, foram realizados três diferentes experimentos, envolvendo a deposição de fosfatos e carbonatos de cálcio sobre substratos de quitosana natural e modificada quimicamente. Inicialmente, foi realizada a investigação dos estágios iniciais de deposição através de ensaios de curta duração. Em seguida, foram realizados ensaios em condições de deposição similares àquelas observadas nos organismos vivos e por fim, testes de calcificação quimicamente induzida foram feitos com o objetivo de se observar a influência do substrato sobre os depósitos formados. Os resultados indicam que em ambos os substratos utilizados o mecanismo geral de calcificação segue os estágios de nucleação e crescimento. Em estágios iniciais, a quitosana acetilada parece produzir uma deposição mais lenta enquanto que a quitosana natural provoca uma nucleação mais rápida e menos organizada em estágios iniciais. Porém em estágios posteriores de crescimento, este substrato aparentemente exerce maior influência sobre os aglomerados em crescimento que a quitosana acetilada / Abstract: The use of biocompatible materials presents increasing interest in the scientific and technological areas. Calcification phenomena are widely associated to the use of biomaterials. It can be desirable for production of resins for adsorption and mechanically resistant materials, but it can be harmful and pathogenic in cardiac valves and contact lenses. In this context, chitosan appears as a material of great importance, since besides being biocompatible, it is derived from the most abundant biomaterial in the nature: chitin. However, its use as substrate for calcification is not extensively studied and its mechanism remains still unknown. Three different experiments involving the deposition of calcium phosphates and carbonates on pristine and acetylated chitosan were conducted in order to understand the mechanism of calcification on this material. Initially, dense membranes underwent calcium compounds deposition through preliminary experiments. Afterwards, deposition in similar conditions to those observed in the living organisms had been conducted and finally, quick tests to induce calcification were done with the intention to observe the influence of the substrate on the deposits. The results indicate that the general mechanism of calcification seems to follow the stages of nucleation and growth in pristine and acetylated chitosan. In initial stages, the acetylated chitosan seems to induce a slower deposition whereas the pristine chitosan seems to provoke an less organized and faster nucleation and in initial stages. However, in the latest stages of growth, pristine chitosan apparently promotes a significant influence on the aglomerates / Mestrado / Engenharia de Processos / Mestre em Engenharia Química

A calcificação ocorre pela formação de depósitos de cálcio em diferentes matrizes envolvendo fatores mecânicos, químicos e biológicos. Alguns compósitos, polímeros e proteínas são utilizados na formação de matrizes por promover maior eficiência no processo de mineralização. Estima-se que a fibroína da seda apresente também esta finalidade. A fibroína é uma proteína fibrosa extraída do casulo do bicho-da-seda (Bombyx mori), que pode ser processada como filme, membrana, esponja, pó, gel e aplicada em ossos e cartilagens, enxertos vasculares, reparação de nervos e córnea, como sistema de liberação de drogas, suturas, ligamentos, peles, tendões e substrato para cultura de células. Nesse trabalho houve a preparação de micropartículas de fibroína da seda através de dois procedimentos distintos, um por borrifamento em N&sup2 e outro por borrifamento em Na2HPO4 e o processo de calcificação realizado foi por imersão alternada de soluções tamponadas de cálcio e fosfato. As caracterizações realizadas foram Espectroscopia de Absorção no Infravermelho (FT-IR), Análise Termogravimétrica (TGA), Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Energia Dispersiva (EDS) e Calorimetria Exploratória Diferencial (DSC). Os resultados obtidos mostraram que a calcificação das micropartículas de fibroína ocorre pelas duas metodologias empregadas. O teor de calcificação foi de aproximadamente 29% para micropartículas borrifadas em N&sup2 e de aproximadamente 80% para as micropartículas borrifadas em Na2HPO4. As micropartículas de fibroína calcificadas, não apresentaram transição térmica até a temperatura de 120°C, possibilitando a esterilização em autoclave a seco. / Calcification occurs by the formation of calcium deposits in different matrices involving mechanical factors, chemical and biological. Some composites, polymers, and proteins are used in forming matrices to promote higher efficiency in the process of mineralization. It is estimated that the silk fibroin also present for this purpose. The fibroin is a fibrous protein extracted from silkworm cocoon silkworm (Bombyx mori), which can be processed as film, membrane, sponge, powder, gel and applied in bone and cartilage, vascular grafts, nerve repair and corneal as a delivery system for drugs, sutures, ligaments, skins, tendons and substrate for cell culture. In this work was the preparation of microparticles of silk fibroin by two different procedures, sputter under N&sup2 and in other sputter Na2HPO4 and calcification process was performed by immersion of alternating buffered solutions of calcium and phosphate. The characterizations were performed Absorption Spectroscopy Infrared (FT-IR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Differential Scanning Calorimetry (DSC). The results showed that the calcification of fibroin microparticles occurs by the two methodologies. The calcified fibroin microparticles showed no thermal transition temperature to 120°C, enabling autoclaving of the microparticles dry

Despite high temperature and salinity conditions that challenge reef growth in other oceans, the Red Sea maintains amongst the most biodiverse and productive coral reefs worldwide. It is therefore an important region for the exploration of coral reef functioning, and expected to contribute valuable insights towards the understanding of coral reefs in challenging environments. This dissertation assessed the baseline variability of in situ abiotic conditions (temperature, dissolved oxygen, pH, and total alkalinity, among others) in the central Red Sea and highlights these environmental regimes in a global context. Further, focus was directed on biotic factors (biofilm community dynamics, calcification and bioerosion), which underlie reef growth processes and are crucial for maintaining coral reef functioning and ecosystem services. Using full-year data from an environmental cross-shelf gradient, the dynamic interplay of abiotic and biotic factors was investigated. In situ observations demonstrate that central Red Sea coral reefs were highly variable on spatial, seasonal, and diel scales, and exhibited comparably high temperature, high salinity, and low dissolved oxygen levels, which on the one hand reflect future ocean predictions. Under these conditions epilithic bacterial and algal assemblages were mainly driven by variables (i.e., temperature, salinity, dissolved oxygen) which are predicted to change strongly in the progression of global climate change, implying an influential bottom up effect on reef-building communities. On the other hand, measured alkalinity and other carbonate chemistry value were close to the estimates of preindustrial global ocean surface water and thus in favor of reef growth processes. Despite this beneficial carbonate chemistry, calcification and carbonate budgets in the reefs were not higher than in other coral reef regions. In this regard, seasonal calcification patterns suggest that summer temperatures may be exceeding the optima of calcifiers. As a possible interpretation of the here observed environmental regimes, it can be concluded that the central Red Sea may be less sensitive to ocean acidification, but is already impacted by ocean warming. Importantly, this dissertation provides valuable present-day baseline data of the natural variability of relevant abiotic drivers together with benthic community and reef growth dynamics. These data will be important for future comparative studies and efforts to quantify the impact of future environmental change in the region.

Le premier axe de ce travail de thèse s'est d'abord orienté vers la détermination des causes biochimiques de la résistance aux AVK liée au polymorphisme du gène Vkorcl. Ainsi, 26 mutations spontanées ont été répertoriées sur le gène Vkorcl chez des hommes recevant des doses augmentées d'AVK. Cependant, l'association entre la résistance et les réelles causes pharmacogénétiques, a parfois été établie de manière un peu hâtive. Nous avons donc, dans un premier temps, voulu confirmer ou non ces liens de causalités, en caractérisant le profile enzymatique de chaque mutant. L'expression hétérologue de ces enzymes mutées, par la levure Pichia pastoris, n'a permis de révéler uniquement 6 mutations réellement impliquées dans le phénotype résistant. De la même manière, nous avons ensuite déterminé l'efficacité d'un nouvel AVK, la Tecarfarine, sur ces mêmes mutants. Cet AVK, contournant toute forme de résistance liée aux polymorphismes des CYP450, présente un avantage relatif face à certaines SNP de Vkorcl. Dans un second temps, nous avons établi les caractéristiques catalytiques d'une nouvelle enzyme paralogue de VKORC1, la VKORC1-L1. Etant également dotée d'une activité vitamine K époxyde réductase, nous voulions éclaircir sont rôle biologique ainsi que sa répartition dans les différents tissus. La VKORC1-L1 apparait alors bien plus résistante aux AVK que VKORC1 malgré une forte homologie de structure. Les propriétés catalytiques de VKORC1-L1 et sa répartition biologique oriente alors sont rôle vers l'activation des PVKD extra- hépatiques, expliquant l'absence d'influence des traitements AVK sur les autres processus vitamine K dépendants. Enfin, grâce à ces résultats, une étude Structure/Fonction de ces 2 enzymes, basée sur la mutagénèse dirigée, nous a permis de révéler certains AA de VKORC1- L1 responsable de son phénotype résistant. Cette étude nous a alors permis de mieux comprendre l'implication de différents acides aminés dans l'interaction avec les AVK chez VKORC1 et VKORC1-L1 et de dévoiler un peu plus leur mécanisme enzymatique. Le deuxième axe de ce travail s'est construit, cette fois-ci, autour des conséquences biochimiques et physiologiques des ces SNP de Vkorcl chez l'homme et le rongeur. Nous avons alors révélé chez le rat des mutations responsables de la perte de vitamine K sous forme de 3-OH au sein du cycle de recyclage. Une explication mécanistique à alors été apportée afin de mieux comprendre cette altération du cycle de recyclage conduisant à terme vers un état de subcarence chez ces animaux. Cet état de subcarence en vitamine K est alors décrit comme le « coût biologique de la résistance aux AVK ». Ce coût biologique va alors avoir des répercussions sur de nombreux processus liés à la vitamine K, comme la calcification des tissus mous mené par la MGP. Nous avons alors tenté de créer un modèle animal, à partir d'une souche de rat possédant une mutation en positon 139 sur Vkorcl causant cette fuite sous forme de 3-OH vitamine K. Ce modèle animal mime parfaitement la calcification au niveau de la média artérielle, de part une simple diminution de l'apport en vitamine K dans l'alimentation, pendant environ 5 semaines. Ces calcifications s'observent dans les artères de multiples organes et reproduisent ce qu'il se manifeste chez les personnes âgées ou souffrant d'IRC. Ce modèle pourra donc à l'avenir supplanter les autres modèles de calcifications artérielles, nécessitant des traitements lourds et une attention toute particulière. Le modèle développé dans cette étude est simple à mettre en place, assez court, peu onéreux et permettra à terme d'étudier des maladies cardiovasculaires comme l'hypertension systolique isolée / .

Giant clams (Tridacninae subfamily) are prominent members of Indo-Pacific corals reefs, including the Red Sea, where they play multiple roles and are of distinct ecological significance for these communities. Tridacninae stand out among other bivalves as one of the few molluscan groups that live in a symbiosis with dinoflagellate Symbiodiniaceae. This relationship is comparable to the symbiosis of corals and their associated algae, where the symbionts provide a substantial amount of the respiratory carbon demand of the host through their photosynthetic activity. Their photosymbiosis restricts the distribution of the Tridacninae holobiont (i.e. giant clam host, symbiotic algae and associated bacteria) to the sunlit, shallow waters of the euphotic zone, where organisms receive sufficient incident light to maintain their high rates of primary production and calcification. However, giant clams in these shallow reefs are simultaneously exposed to potentially high and damaging levels of solar (UV) radiation. This thesis includes research on the Red Sea Tridacna spp. holobiont from an ecosystem to microscale level. It assess the abundance and distribution of Red Sea giant clams, including their associated symbiotic microalgae and bacterial microbiome. Further, it describes the strong light-dependency of calcification and primary production of Red Sea Tridacna maxima clams and reports on the effective photo-protective mechanisms that have been evolved by these clams to thrive in shallow reefs, despite levels of high solar irradiance. Tridacninae developed effective behavioral mechanisms for photo-protection, by which the clam is able to flexibly adjust its shell gaping behavior to incident light levels within a narrow time frame. On a microscale, Tridacninae use advanced photonic structures (iridocytes) within their tissues to mitigate the potential negative effects of high solar UV radiation, and to promote the photosynthesis of their symbiotic algae. Understanding the role of the Tridacna spp. holobiont for Red Sea coral reefs, its contributions to overall productivity, and its abundances in the region may serve as a baseline for further studies on this charismatic invertebrate. It may also contribute to the conservation efforts from local to regional scales, and eventually aid the protection of Tridacninae in the Red Sea and elsewhere.

Scleractinian corals represent the foundation species of one of the most diverse and productive ecosystem on earth, coral reefs. Corals not only constitute the trophic basis of these ecosystems, but also provide essential habitats and shelter for a wide variety of marine species, many of which are commercially relevant. They also provide other important ecosystem services such as food provision, shoreline protection and opportunities for ecotourism. Despite the ecological importance of corals, very little is known about how their soft-bodied ancestor evolved the ability to form a calcified skeleton and became the ecosystem builders they are today. Corallimorpharia are closely related to reef-building corals but lack the ability to form calcified skeletons. Here we assembled and annotated two draft genomes of the corallimorpharians, Amplexidiscus fenestrafer and Discosoma sp., and further provided an online interface to facilitate the use of these resources. The two genomes can not only inform on the current evolutionary gap in genomic resources for the subclass of Hexacorallia but also provide important resources for comparative genomic studies aiming at understanding the evolution of coral specific traits. Our broad phylogenomic approach using whole genome data, including phylogenetic analyses of nuclear encoding genes as well as genome-wide presence/absence information and synteny conservation from six hexacorallian species, provides robust evidence that corallimorpharians are a monophyletic sister group of scleractinians, therefore rejecting the “naked coral” hypothesis. Being the closest non-calcifying relative of scleractinian corals, corallimorpharians appear to be the best candidates to understand the evolutionary origin of coral calcification. Molecular divergence analysis of scleractinian coral and Corallimorpharia genes suggests that the soft-bodied ancestor of corals evolved the ability to calcify within approximately 80 million years after the divergence of these two orders. To uncover the molecular basis of coral skeletal formation and growth, we integrate genomic and transcriptomic data as well as skeletal proteomic data, and show that gene and domain duplications have been the main evolutionary mechanisms underlying the evolution of calcification in scleractinian corals.

The uptake of CO2 by the ocean is causing major changes in its chemistry. These changes are likely to have detrimental effects on many organisms with a severe impact on calcifying species. With future OA, marine organisms will be submitted to hypercapnia (increased pCO2) and acidosis (decreased pH). Skeleton production and maintenance could be impacted due to the increased energetic cost to calcify in less favourable conditions and direct corrosive effect of undersaturated seawater resulting in dissolution of calcium-carbonate unprotected structures. Postmetamorphic echinoderms (juveniles and adults) endoskeleton is made of high magnesium-calcite, one of the most soluble form of CaCO3. Because of their low metabolism and their heavily calcified skeleton, echinoderms were designated as species particularly at risk under OA. However, the effects of OA on calcification and on skeleton maintenance vary among closely related taxa. Hypotheses explaining these contrasted tolerance to OA were stated: (1) regulation of the acid-base balance, which occurs in some echinoderms taxa and not others, plays a major role; (2) populations living in highly fluctuating habitats are adapted or selected, which may confer them a better resistance to acidified conditions. The goal of this thesis was to evaluate these hypotheses using a comparative approach in asteroids (two species) and regular euechinoids (five species). The chosen species differ by their ability to regulate their acid-base physiology and by the amplitude of fluctuations in their habitats. The impacts of OA on corrosion and mechanical properties of their skeletal elements as well as, in selected species, the expression of biomineralization-related genes were investigated. All samples were obtained from individuals exposed to acidified conditions during long-term aquarium experiments or in situ exposures (CO2 vents).Bending and compression mechanical tests analysed by Weibull statistics and expression of biomineralization-related genes appeared particularly unitive endpoints. On the contrary, occurrence of corrosion, i.e. observation in scanning electron microscopy, did not match with mechanical effects, and nanoindentation never revealed differences according to treatment. The results showed that species which were not able to regulate their acid-base physiology also presented the most affected skeleton integrity when submitted to OA. This was particularly true for the temperate sea star Asterias rubens and the Mediterranean sea urchin Arbacia lixula whose skeleton was significantly impacted. In the latter, this went together with a down-regulation of biomineralization-related genes. Temperate and tropical sea urchins that regulated their acid-base physiology (Paracentrotus lividus, Echinometra sp. B and sp. C) presented no or very limited impact of OA on their skeleton and biomineralization-related gene expression (P. lividus). The Antarctic species (the sea star Odontaster validus and the sea urchin Sterechinus neumayeri) showed no sign of acid-base physiology regulation but also no impact of acidified conditions on their skeleton. This could be linked to their particularly low metabolism or to food availability. Living in fluctuating habitats did not appear to confer a particular resistance of the skeleton in front of OA. In particular, the sea star A. rubens from Kiel Fjord, living in highly fluctuating sea water conditions, was impacted by acidified conditions they transiently encounter every year. The same was true for the temperate sea urchin A. lixula. So, it appears that sea stars and sea urchins living in fluctuating habitats might already be at the limit of their tolerance window if they do not regulate their acid-base physiology. In conclusion, it appears that the acid-base regulation may be the key biological trait to address the impact of OA on the skeleton of adult echinoderms. Studies coupling mechanical testing and analysing biomineralization-related gene expression should be extended to more taxa (within and outside echinoderms) to ascertain the relationship between OA sensitivity and absence of acid-base regulation. / Depuis la Révolution Industrielle, la concentration en dioxyde de carbone (CO2) atmosphérique augmente continuellement. Les océans absorbent en partie ce CO2, ce qui induit une diminution de la concentration en ions carbonate ainsi qu’une augmentation de la concentration en protons, processus connus sous le nom d’acidification des océans (AO). Ces changements sont susceptibles d'avoir des effets néfastes sur une variété d'organismes marins qui seront soumis à l’hypercapnie (augmentation de la pCO2) et à l’acidose (diminution du pH). De plus, la calcification fait l’objet d’une attention particulière étant donné la remontée des horizons de saturation en carbonate de calcium dans les océans. La production ainsi que le maintien du squelette pourraient être limités en raison de l'augmentation du coût énergétique de la calcification dans des conditions moins favorables. Cependant, les effets de l’AO sur la calcification et sur le maintien du squelette varient selon les taxons voire au sein d’un même taxon. Des hypothèses ont donc été émises quant aux mécanismes sous-tendant ces différences. Une meilleure résistance face à l’AO pourrait aller de pair avec (1) une capacité à réguler le pH des fluides extracellulaires, (2) une préadaptation due à l’occupation d’habitats fortement fluctuants.Les échinodermes post-métamorphiques (juvéniles et adultes), espèces marines clés, possèdent une biologie générale assez semblable et sont constitués d’un endosquelette composé de calcite hautement magnésienne, une des formes les plus solubles de carbonate de calcium. En raison de leur faible métabolisme et de leur squelette fortement calcifié, les échinodermes ont été désignés comme des espèces particulièrement vulnérables sous l’effet de l’AO. Toutefois, de récentes études montrent que le squelette de certaines espèces d’échinodermes au stade adulte n’est pas affecté lorsque les organismes sont soumis à de bas pH d’eau de mer. L'objectif principal de la présente thèse était d’évaluer les différentes hypothèses par une approche comparative chez les astéroïdes (deux espèces) et les euéchinoïdes réguliers (cinq espèces). Les espèces choisies se différencient par leur capacité à réguler leur physiologie acide-base et par l’amplitude des fluctuations de leur habitat. Les effets de l’AO sur la corrosion et les propriétés mécaniques de leurs éléments squelettiques, ainsi que, chez certaines espèces, l’expression de gènes liés à la biominéralisation ont été étudiés. Tous les échantillons ont été obtenus à partir d’individus exposés à des conditions acidifiées lors d’expériences à long terme ou d’expositions in situ (évents à CO2).Les résultats ont montré que les espèces qui n'étaient pas en mesure de réguler leur physiologie acide-base (l’étoile de mer Asterias rubens et l’oursin Arbacia lixula) présentaient également des squelettes plus affectés lorsqu'elles étaient soumises à l'AO. Les oursins tempérés et tropicaux qui régulent leur physiologie acide-base (Parancetrotus lividus, Echinometra spp.) n’ont présenté aucun impact ou un impact très limité de l’AO sur leur squelette et l’expression des gènes liés à la biominéralisation (P. lividus). Les espèces antarctiques (l’oursin Sterechinus neumayeri et l'étoile de mer Odontaster validus) n’ont montré aucun signe de régulation de la physiologie acide-base mais également aucun impact sur leur squelette dû à une diminution du pH de l'eau de mer. Cela pourrait être lié à leur métabolisme bas ou à la disponibilité de nourriture dans leur environnement. Vivre dans des habitats fluctuants ne semble pas conférer une résistance particulière du squelette face à l’AO. En particulier, l’étoile de mer A. rubens du Fjord de Kiel, qui vit dans des conditions très fluctuantes, a été affectée par des conditions d’acidification qu’elles rencontrent de manière transitoire chaque année. Il en va de même pour l’oursin tempéré A. lixula. Il semble donc que les étoiles de mer et les oursins vivant dans des habitats fluctuants pourraient déjà être à la limite de leur fenêtre de tolérance lorsqu’ils ne régulent pas leur physiologie acide-base. En conclusion, la régulation de la physiologie acide-base est une caractéristiques biologique clé pour adresser les effets de l’AO sur le squelette des échinodermes adultes. Les études couplant les tests mécaniques à l’analyse de l’expression de gènes liés à la biominéralisation devraient être étendues à plus de taxons (au sein et en dehors de échinodermes) afin de déterminer la relation entre la sensibilité de la calcification face à l’AO et l’absence de régulation acide-base. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

L’évaluation de la sténose aortique (SA) par échocardiographie Doppler aboutit à une classification discordante de la sévérité chez environ 30 % des patients. La tomodensitométrie qui mesure la calcification valvulaire aortique, un indice de sévérité anatomique, peut alors être utile pour corroborer la sévérité de la SA. De précédentes études ont montré une bonne corrélation entre la sévérité hémodynamique mesurée par échocardiographie Doppler et la sévérité anatomique définie par la calcification valvulaire aortique mesurée par tomodensitométrie. Cependant, l’impact du phénotype de la valve aortique (bicuspide versus tricuspide) et de l’âge sur cette relation entre sévérité hémodynamique et sévérité anatomique reste inconnu. Or, ces deux facteurs sont hautement impliqués dans le développement de la SA. En effet, les patients ayant une valve aortique bicuspide ont une prédisposition à développer une SA, et ce, généralement plus tôt que les patients avec une valve aortique tricuspide. L’hypothèse principale de l’étude est que le phénotype de la valve aortique et l’âge influencent la relation entre la sévérité hémodynamique et la calcification valvulaire aortique de la SA. L’objectif principal de l’étude est d’évaluer l’impact du phénotype de la valve aortique et de l’âge sur la relation entre la sévérité hémodynamique et la calcification valvulaire aortique de la SA. / Assessment of aortic stenosis (AS) by Doppler echocardiography leads to discordant severity grading in around 30% of patients. Computed tomography which measures aortic valve calcification, an indication of anatomic severity, can then be useful to corroborate AS severity. Previous studies have shown a good correlation between hemodynamic severity measured by Doppler echocardiography and anatomic severity defined by aortic valve calcification measured by computed tomography. However, the impact of aortic valve phenotype (bicuspid versus tricuspid) and age on this relation between hemodynamic severity and anatomic severity remains unknown. Yet, these two factors are highly implicated in AS development. Indeed, patients with a bicuspid aortic valve have a predisposition to develop AS, and this, generally earlier than patients with a tricuspid aortic valve. The main hypothesis of the study is that aortic valve phenotype and age influence the relationship between haemodynamic severity and aortic valve calcification of AS. The main objective of the study is to assess the impact of aortic valve phenotype and age on the relationship between haemodynamic severity and aortic valve calcification of AS.