New 3D multi-scale modeling approaches for the structural analysis of native and prosthetic Aortic Valves (AV) are investigated. Three different nonlinear hyperelastic constitutive material models for the mechanical behavior of the AV tissue are introduced. The first is the well-known Holzapfel hyperelastic, anisotropic and homogeneous model. The second model, termed the Collagen Fiber Network (CFN), is a heterogeneous model that recognizes the hyperelastic collagen and elastin layers using different layered finite elements. The third hyperelastic model is implemented using a new nonlinear micromechanical formulation of the High Fidelity Generalized Method of Cells (HFGMC) originally proposed by Aboudi. The latter two material models are heterogeneous and explicitly recognize the in-situ tissue constituents. Initially, a full scale 3D structural model of a polymeric-based prosthetic AV model is studied. This model is verified using deformation metrics obtained from images taken with high speed cameras during in-vitro experiments. The predictions from the proposed polymeric AV model are in good agreement with the test data. Next, the three tissue material models are examined in their ability to predict the anisotropic material behavior of porcine AV leaflet tissue. The Holzapfel model is calibrated from the overall anisotropic uni- and biaxial stress-strain data while the in-situ elastin and collagen constituents in the CFN and HFGMC models are calibrated to match the overall effective responses. Dynamic structural analysis is performed for the porcine AV with applied transvalvular pressure measured from repeated in-vitro tests conducted in this study. Principal stretches are computed from the experimental measurements and compared with the AV material-structural predictions. The proposed multi-scale modeling approach for the native AV is capable of predicting the structural behavior during the entire cardiac cycle without suffering from numerical convergence problems. Finally, new nonlinear micromechanical formulations based on the HFGMC method are developed and applied for various types of tissue materials including the human arterial wall layers and porcine AV leaflets. The proposed hyperelastic HFGMC model is compared to the CFN model and the Holzapfel models. It is shown that the HFGMC is an effective modeling approach for the arteries especially when the collagen fiber network has a periodic microstructure.

Background：Aortic stenosis (AS) is the commonest valve disease in the West. Aortic valve replacement (AVR) remains the only available management for AS and results in improved symptoms and recovery of ventricular functions. In addition, it is well known that AVR results in disruption of LV function mainly in the form of reversal of septal motion as well as depression of right ventricular (RV) systolic function. The aim of this thesis was to study, in detail, the early and mid-term response of ventricular function to AVR procedures (surgical and TAVI) as well as post operative patients’ exercise capacity. Methods：We studied LV and RV function by Doppler echocardiography and speckle tracking echocardiography (STE) in the following 4 groups; (1) 30 severe AS patients (age 62±11 years, 19 male) with normal LV ejection fraction (EF) who underwent AVR, (2) 20 severe AS patients (age 79±6 years, 14 male) who underwent TAVI, (3) 30 healthy controls (age 63±11 years, 16 male), (4) 21 healthy controls (age 57±9 years, 14 male) who underwent exercise echocardiography. Results: After one week of TAVI, the septal radial motion and RV tricuspid annulus peak systolic excursion (TAPSE) were not different from before, while surgical AVR had significantly reversed septal radial motion and TAPSE dropped by 70% compared to before. The extent of the reversed septal motion correlated with that of TAPSE (r=0.78, p<0.001) in the patients as a whole after AVR and TAVI (Study I). Compared with controls, the LV twist function was increased in AS patients before and normalized after 6 months of surgical AVR. In controls, the LV twist correlated with LV fractional shortening (r=0.81, p<0.001), a relationship which became weak in patients before (r=0.52, p<0.01) and after AVR (r=0.34, p=ns) (Study II). After 6 months of surgical AVR, the reversed septal radial motion was still significantly lower than before. The septal peak displacement also decreased and its time became prolonged. In contrast, the LV lateral wall peak displacement increased and the time to peak displacement was early. The accentuated lateral wall peak displacement correlated with the septal peak displacement time delay (r=0.60, p<0.001) and septal-lateral time delay (r=0.64, p<0.001) (Study III). In 21 surgical AVR patients who performed exercise echocardiography, the LV function was normal at rest but different from controls with exercise. At peak exercise, oxygen consumption (pVO2) was lower in patients than controls. Although patients could achieve cardiac output (CO) and heart rate (HR) similar to controls at peak exercise, the LV systolic and early diastolic myocardial velocities and strain rate as well as their delta changes were significantly lower than controls. pVO2 correlated with peak exercise LV myocardial function in the patients group only, and the systolic global longitudinal strain rate (GLSRs) at peak exercise was the only independent predictor of pVO2 in multivariate regression analysis (p=0.03) (Study IV). Conclusion: Surgical AVR is an effective treatment for AS patients, but results in reversed septal radial motion and reduced TAPSE. The newly developed TAVI procedure maintains RV function which results in preservation of septal radial motion. In AS, the LV twist function is exaggerated, normalizes after AVR but loses its relationship with basal LV function. While the reversed septal motion results in decreased and delayed septal longitudinal displacement which is compensated for by the accentuated lateral wall displacement and the time early. These patients remain suffering from limited exercise capacity years after AVR.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2006. / Härtill 6 uppsatser.

Made available in DSpace on 2015-01-26T13:21:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-08-26Bitstream added on 2015-01-26T13:30:38Z : No. of bitstreams: 1 000798818.pdf: 341307 bytes, checksum: a33a2c9977f57c10c36e049053a2657c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Após uma agressão, o coração remodela-se para manter estável a sua função; entretanto, a remodelação cardíaca (RC) é tempo dependente e a longo prazo pode ser prejudicial. A estenose aórtica supravalvar (EAo) tem sido utilizado para promover o desenvolvimento gradual de hipertrofia ventricular esquerda. Constatouse que ratos desenvolvem hipertrofia ventricular esquerda, disfunção diastólica e melhoria da função sistólica após 2 e 6 semanas de EAo, manutenção da disfunção diastólica e deterioração do desempenho sistólico na 12ª semana e, na 18ª semana há acentuação da disfunção sistólica e aparecimento de insuficiência cardíaca. Diferentes fatores poderiam contribuir para a disfunção no modelo experimental de EAo como o déficit de oxigênio ou de substrato energético. Em condições aeróbicas normais, aproximadamente 70% da produção de energia miocárdica deriva do metabolismo de ácidos graxos, sendo a contribuição glicolítica em torno de 30%. Estudos mostram que o fator responsável pela escolha do substrato energético cardíaco são os níveis plasmáticos elevados de ácidos graxos e triglicérides. Estudos utilizando modelos experimentais de insuficiência cardíaca constataram que o aumento na oferta de energia por lipídeos, não alteraram ou promoveram melhoria da RC. O objetivo deste trabalho foi testar a hipótese que a maior disponibilidade de energia proveniente dos lipídeos ricos em ácidos graxos saturados restaura o equilíbrio energético miocárdico, atenuando o processo de remodelação patológica (RP). Com a finalidade de testar esta hipótese, foram avaliadas a estrutura, a função e o metabolismo miocárdico de ratos com EAo, tratados com dieta hiperlipídica saturada. Foram utilizados ratos Wistar machos, com 21 dias de idade, separados em grupo controle (Sham) e estenose aórtica supravalvar (EAo); após 6 semanas da cirurgia, os ratos foram redistribuídos em mais dois ... / After an aggression, the heart undergoes remodeling to maintain its function stable; however, cardiac remodeling (CR) is time dependent and, in long term, may be harmful. The supravalvular aortic stenosis (AS) has been used to promote gradual development of left ventricular hypertrophy. It was observed that rats develop left ventricular hypertrophy, diastolic dysfunction and improved systolic function after 2 and 6 weeks of AS. After 12 weeks, diastolic dysfunction is maintained and systolic performance deteriorates; around the 18th week, systolic dysfunction is accentuated and signs of heart failure appear. Different factors could contribute to the dysfunction in the experimental model of AS, such as oxygen or energy substrate deficit. Under normal aerobic conditions, approximately 70% of myocardial energy production comes from fatty acid metabolism, and glycolysis contribution is around 30%. Studies have showed that the responsible factor for the choice of cardiac energy substrate is the elevated plasma levels of fatty acids and triglycerides. Studies that used experimental models of heart failure found that the increase in energy supply by lipids did not change or improved RC. The aim of this study was to test the hypothesis that the increased energy availability derived from lipids rich in saturated fatty acids restores myocardial energy balance, attenuating the pathological remodeling process. In order to test this hypothesis, we have evaluated the myocardial structure, function and metabolism of rats with AS fed with saturated high-fat diet. Male Wistar rats, 21 days old, were distributed into control group (Sham) or supravalvular aortic stenosis (AS); 6 weeks after surgery, rats were redistributed into two groups: fed with saturated high-fat diet or normolipidic diet (AS-N, n=12; Sham-N, n=14; AS-H, n=14 and Sham-H, n=14). The nutritional profile was determined. RC was characterized by the ...

Orientador: Antonio Carlos Cicogna / Banca: André Soares Leopoldo / Banca: Silvio Assis de Oliveira Júnior / Banca: Marcos Ferreira Minicucci / Banca: Paula Schmidt Azevedo Gaiolla / Resumo: Após uma agressão, o coração remodela-se para manter estável a sua função; entretanto, a remodelação cardíaca (RC) é tempo dependente e a longo prazo pode ser prejudicial. A estenose aórtica supravalvar (EAo) tem sido utilizado para promover o desenvolvimento gradual de hipertrofia ventricular esquerda. Constatouse que ratos desenvolvem hipertrofia ventricular esquerda, disfunção diastólica e melhoria da função sistólica após 2 e 6 semanas de EAo, manutenção da disfunção diastólica e deterioração do desempenho sistólico na 12ª semana e, na 18ª semana há acentuação da disfunção sistólica e aparecimento de insuficiência cardíaca. Diferentes fatores poderiam contribuir para a disfunção no modelo experimental de EAo como o déficit de oxigênio ou de substrato energético. Em condições aeróbicas normais, aproximadamente 70% da produção de energia miocárdica deriva do metabolismo de ácidos graxos, sendo a contribuição glicolítica em torno de 30%. Estudos mostram que o fator responsável pela escolha do substrato energético cardíaco são os níveis plasmáticos elevados de ácidos graxos e triglicérides. Estudos utilizando modelos experimentais de insuficiência cardíaca constataram que o aumento na oferta de energia por lipídeos, não alteraram ou promoveram melhoria da RC. O objetivo deste trabalho foi testar a hipótese que a maior disponibilidade de energia proveniente dos lipídeos ricos em ácidos graxos saturados restaura o equilíbrio energético miocárdico, atenuando o processo de remodelação patológica (RP). Com a finalidade de testar esta hipótese, foram avaliadas a estrutura, a função e o metabolismo miocárdico de ratos com EAo, tratados com dieta hiperlipídica saturada. Foram utilizados ratos Wistar machos, com 21 dias de idade, separados em grupo controle (Sham) e estenose aórtica supravalvar (EAo); após 6 semanas da cirurgia, os ratos foram redistribuídos em mais dois ... / Abstract: After an aggression, the heart undergoes remodeling to maintain its function stable; however, cardiac remodeling (CR) is time dependent and, in long term, may be harmful. The supravalvular aortic stenosis (AS) has been used to promote gradual development of left ventricular hypertrophy. It was observed that rats develop left ventricular hypertrophy, diastolic dysfunction and improved systolic function after 2 and 6 weeks of AS. After 12 weeks, diastolic dysfunction is maintained and systolic performance deteriorates; around the 18th week, systolic dysfunction is accentuated and signs of heart failure appear. Different factors could contribute to the dysfunction in the experimental model of AS, such as oxygen or energy substrate deficit. Under normal aerobic conditions, approximately 70% of myocardial energy production comes from fatty acid metabolism, and glycolysis contribution is around 30%. Studies have showed that the responsible factor for the choice of cardiac energy substrate is the elevated plasma levels of fatty acids and triglycerides. Studies that used experimental models of heart failure found that the increase in energy supply by lipids did not change or improved RC. The aim of this study was to test the hypothesis that the increased energy availability derived from lipids rich in saturated fatty acids restores myocardial energy balance, attenuating the pathological remodeling process. In order to test this hypothesis, we have evaluated the myocardial structure, function and metabolism of rats with AS fed with saturated high-fat diet. Male Wistar rats, 21 days old, were distributed into control group (Sham) or supravalvular aortic stenosis (AS); 6 weeks after surgery, rats were redistributed into two groups: fed with saturated high-fat diet or normolipidic diet (AS-N, n=12; Sham-N, n=14; AS-H, n=14 and Sham-H, n=14). The nutritional profile was determined. RC was characterized by the ... / Mestre

Introdução: A deposição de cálcio junto aos folhetos valvares esta intimamente relacionada à fisiopatologia da estenose valvar aórtica degenerativa (EAD). A tomografia computadorizada com multidetectores (TCMD), além de possibilitar o delineamento tridimensional das estruturas cardíacas, permite a quantificação da intensidade da calcificação valvar. Atualmente, a relação entre a localização dos depósitos valvares de cálcio e a gravidade hemodinâmica na estenose aórtica permanece incerta. Objetivo: Avaliar se a topografia da calcificação valvar influencia a repercussão hemodinâmica na EAD. Métodos: Trata-se de estudo prospectivo, unicêntrico, incluindo 97 pacientes com EAD moderada ou importante. O escore de cálcio da valva aórtica foi calculado a partir da TCMD sem contraste. A topografia da calcificação valvar foi avaliada através de análise tomográfica específica com infusão de baixa dose de contraste endovenoso, objetivando uma detalhada segmentação anatômica dos planos valvares. A medida da atenuação, expressa em unidades Hounsfield (UH), foi utilizada para quantificar o conteúdo de cálcio na região central e periférica do plano valvar aórtico. Resultados: Pacientes com EAD importante apresentaram escore de cálcio valvar aórtico superior ao dos portadores de EAD moderada (3131 ± 1828 unidades Agatston [UA] e 1302 ± 846 UA, respectivamente; p < 0,001). Quanto à topografia da calcificação, pacientes com EAD importante exibiram atenuações significativamente maiores no centro do plano valvar do que em sua periferia (507,4 ± 181,7 UH vs. 449,8 ± 114,5 UH; p = 0,001). Inversamente, pacientes com EAD moderada apresentaram menor atenuação na região central do que na periferia valvar (308,7 ± 92,9 UH vs. 347,6 ± 84,2 UH, p < 0,001). A razão da atenuação centro/periferia também foi significativamente maior nos pacientes com EAD importante (1,14 ± 0,32 vs. 0,89 ± 0,13; p < 0,001), permanecendo significativamente associada à presença de EAD importante mesmo após ajuste para o grau subjacente de calcificação Resumo valvar. Conclusão: A gravidade da EAD parece resultar não apenas do grau de calcificação, mas também da localização dos depósitos valvares de cálcio / Introduction: The pathophysiology of degenerative aortic valve stenosis (AS) is intimately related to the development of calcific deposits in the valve structure. Multidetector computed tomography (MDCT), a reliable method to delineate the tridimensional heart geometry, has been shown to accurately quantify the global aortic valve calcium content. Currently, the relationship between calcium location and hemodynamic disease severity is poorly understood. Objective: The present prospective study was conducted to test the hypothesis of whether the location of valve calcification influences the functional severity of AS. Methods: Prospective, single-arm study including 97 patients with diagnosed moderate or severe AS. Aortic valve calcium score was calculated from nocontrast multidetector computed tomography (MDCT). \"Low-contrast- os \" MDCT images were acquired for segmentation of the cardiac anatomy, with the attenuation, expressed in Hounsfield units (HU), used to quantify the calcium content at the central and peripheral regions of the aortic valve zone. Results: The calcium score was higher among patients with severe AS compared to patients without severe AS (3131±1828 Agatston units [AU] vs. 1302±846 AU respectively; p < 0.001). Patients with severe AS had significantly higher attenuations at the center of the valve than at its periphery (507.4±181.7 HU vs. 449.8±114.5 HU; p=0.001). Conversely, patients without severe AS had lower attenuation at the center than at the periphery of the valve (308.7 ± 92.9 HU vs. 347.6±84.2 HU; p < 0.001). The center/periphery attenuation ratio was significantly higher for patients with severe AS than for those without severe disease (1.14±0.32 vs. 0.89 ± 0.13; p < 0.001), and remained significantly associated with the presence of severe AS even after adjusting for the underlying degree of valve calcification. Conclusion: The severity of degenerative aortic valve stenosis appears to result not only from the degree of calcification but also from the localization of the calcific deposits within the valve

Abstract The stem cell is a primitive cell that is capable of dividing to reproduce itself and can give rise to a selection of differentiated progeny. Stem cells are thought to be involved in or even main factors in many diseases. In postnatal humans, mesenchymal tissues have the capacity to regenerate from stem cells called mesenchymal stem cells (MSC). It is currently thought that these cells will become the basis of therapy for many diseases. In the present study, a novel in vitro method was developed to examine human bone marrow derived MSC differentiation into osteoblast lineage, and to study the role of MSC in a variety of mesenchymal diseases. The ability of MSCs to differentiate into osteoblasts was investigated during aging. In addition, the interindividual variability in the osteogenesis of MSCs and in the osteoblastic response of MSC to estrogen and testosterone was studied. Furthermore, an ex vivo model using a human aortic valve microenvironment was developed to explore whether the extracellular matrix influences the osteoblastic differentiation of the MSC. Finally, the role of MSC in neurofibromatosis type 1 (NF1) related congenital pseudarthrosis of the tibia (CPT) was studied. It was found that after menopause the osteogenic potential of MSCs does not decrease. It was also found that estrogen receptor (ER) alpha genotype confers interindividual variability of response to estrogen and testosterone in MSC derived osteoblasts. In addition, it was found that the non-calcified valves with living valve cells inhibited osteogenesis of co-cultured MSCs, whereas the calcified and devitalised valves promoted differentiation towards an osteoblastic lineage. Finally, MSCs from NF1-related pseudarthrosis showed altered NF1 gene expression, poor osteoblastic differentiation and bone formation. In conclusion, MSC can be easily isolated from the bone marrow and MSC has the capacity to regenerate tissue even at later stages of life. These results could help explain the contradictory effects of 17β-estradiol (E2) on osteoblasts in vitro and might also provide new insights into understanding the differences in responses to hormone replacement therapy. It seems that adult stem cells from bone marrow undergo milieu-dependent differentiation to express phenotypes that are similar to cells in the local microenvironment. Finally, the NF1 gene was shown to have a role in bone development and remodelling.

Einleitung: Das Ziel dieser Arbeit war die Darstellung der Ergebnisse der Ross- Operation in der Kinderherzchirurgie der Universitätsmedizin Göttingen als Verfahren des AKE durch die eigene Pulmonalklappe (Autograft) bei Kindern und Jugendlichen unter besonderer Berücksichtigung der Haltbarkeit und Funktion des pulmonalen Autografts und der postoperativen Entwicklung des hypertrophierten linken Ventrikels. Zu diesem Zwecke wurden retrospektiv klinische Daten bezüglich der linksventrikulären Funktion und Haltbarkeit des pulmonalen Autografts und der klinischen Belastbarkeit ausgewertet. Patienten und Methoden: Untersucht wurden die Entwicklung der Neo-Aortenklappe (Autograftklappe) und des linken Ventrikels nach Ross-Operation bei 31 Patienten unter 21 Jahren, die zwischen 1994 und 2008 in Göttingen operiert wurden. Das Alter der untersuchten Patienten betrug zum Operationszeitpunkt zwischen 6 Monaten und 20 Jahren (Mittelwert: 133 Monate b= 11,1 Jahre). Der Nachbeobachtungszeitraum variierte zwischen 10 Monaten und 14 Jahren (Mittelwert: 67 Monate b= 5,6 Jahre). Retrospektiv wurden 2 verfügbare postoperative Echokardiographien bezüglich der Durchmesser des Aortenklappenrings, der Aortenwurzel, des sino-tubulären Übergangs, des LVESD, des LVEDD, des IVS und der linksventrikulären HW ausgewertet. Zur Vergleichbarkeit des untersuchten Kollektivs mit gesunden Kindern und Jugendlichen wurden mit Hilfe von Regressionskurven nach Daubeney et al. (1999) und Pettersen et al. (2008) Z-Werte für die gemessenen Durchmesser bestimmt und ihre Entwicklung durch statistische Methoden ausgewertet. Ergebnisse: Im untersuchten Patientenkollektiv konnte kein signifikanter Anstieg der Z-Werte der Durchmesser der Neo-Aortenklappe und des linken Ventrikels beobachtet werden. Die Z-Werte des Neo-Aortenwurzel-Durchmessers und des LVEDD näherten sich im Verlauf signifikant den Normkurven an. Bei keinem Patienten wurde ein Ersatz des Autografts notwendig. 1 Patient benötigte eine operative Revision der Neo-Aortenklappe in Form einer supravalvul¨aren Kürzung und Ummantelung der Autograft-Wurzel bzw. des sino-tubulären Übergangs. Bei 15 Patienten kam es im Verlauf zu einer Autograftinsuffizienz ersten Grades. Diese beobachteten Einschränkungen der Neo-Aortenklappenfunktion im Sinne einer geringen oder trivialen Insuffizienz waren ohne klinische Relevanz. 1 Patientin verstarb unmittelbar postoperativ an einer intrazerebralen Blutung. Zu weiteren schwerwiegenden Komplikationen kam es nicht. Die Haltbarkeit des Pulmonalis-Ersatzes durch einen Homograft oder einen Xenograft war bereits innerhalb der ersten postoperativen Dekade limitiert. Im postoperativen Nachbeobachtungszeitraum benötigten 5 Patienten einen Austausch des Implantats. Bei den ausgetauschten Homografts handelte es sich in 3 Fällen um Pulmonalis-Homografts und in 2 Fällen um Aortenhomografts. Fazit: Die Ross-Operation ist ein Verfahren des AKE, das besonders für Kinder und Jugendliche auf Grund des Wachstumspotentials, der exzellenten Hämodynamik, der Regenerationsfähigkeit, der Infektresistenz, der uneingeschränkten natürlichen Funktion und der Athrombogenität besonders geeignet ist. Auch für Frauen mit Kinderwunsch und junge Männer mit Risikoprofil (durch Sport oder verletzungsträchtige Berufstätigkeit) oder Patienten mit Kontraindikation für eine Phenprocoumon-Therapie ist die Ross- Operation wegen der nicht notwendigen Marcumarisierung eine attraktive Behandlungsoption. Die befürchtete Dilatation des Autografts im Langzeitverlauf konnte nicht beobachtet werden.

Abstract Calcified aortic valve disease represents a spectrum of disease spanning from mild aortic valve sclerosis to severe aortic valve stenosis (AS), being an actively regulated disease process and showing some hallmarks of atherosclerosis. The calcified aortic valve lesion develops endothelial injury and is characterized by inflammation, lipid accumulation, renin-angiotensin system activation and fibrosis. There is no approved pharmacological treatment available in AS. This study was aimed to characterize gene expression of endothelial factors in aortic valves in patients representing different stages of calcified aortic valve disease to reveal new targets for pharmacological interventions in AS. Aortic valves obtained from 75 patients undergoing valve replacement surgery were studied. Expression of natriuretic peptides (ANP, BNP and CNP), their processing enzymes (corin and furin), natriuretic receptors (NPR-A, NPR-B and NPR-C), endothelin-1 (ET-1), endothelin converting enzyme-1 (ECE-1), endothelin receptors A and B (ETA and ETB), and apelin pathway (apelin and its receptor APJ) was characterized by reverse-transcriptase polymerase chain reaction (RT-PCR) and immunohistochemistry. AS was characterized by distinct downregulation of gene expression of CNP, its processing enzyme furin and the target receptor NPR-B. Furthermore, increased amount of ET-1 and its target receptor ETA as well as imbalance between ETA and ETB receptors and downregulated endothelial nitric oxide synthase (eNOS) gene expression were observed. Finally, gene expression of apelin and APJ receptor were significantly upregulated in stenotic valves when compared to controls in combination with disequilibrium between expression of angiotensin II receptors AT1 and AT2. The study provides a better understanding of molecular mechanisms associated with calcific aortic valve disease and suggest potential targets for novel therapeutic interventions.

Les pathologies valvulaires aortiques sont des pathologies plurifactorielles, comportant un déterminisme génétique indiscutable mais peu caractérisé. Ma thèse a pour but d’étudier le rôle du facteur de transcription Krox20 au cours du développement et de la maturation valvulaire à travers l’analyse de modèles murins. Nous avons montré que ce gène est nécessaire au développement et à la maturation de la valve aortique. L’invalidation de Krox20 chez la souris conduit à une hypertrophie des feuillets aortiques dès les stades fœtaux et à des insuffisances aortiques chez l’adulte. Ces anomalies sont associées à des défauts d’organisation de la matrice extracellulaire en partie liée à une régulation directe de l’expression des collagènes de type I et III. 25% des souris déficientes pour Krox20 présentent une bicuspidie de la valve aortique. Nous avons observé une diminution de l’expression de eNos chez ces mutants et pu mettre en évidence une interaction génétique entre Krox20 et eNos. De plus, nous avons identifié une sous population de cellules des crêtes neurales cardiaques impliquées dans l’apparition de la bicuspidie chez les mutants Krox20. Afin d’explorer le rôle de Krox20 dans la calcification de la valve aortique, nous avons étudié les conséquences de la surexpression de ce gène dans un modèle et montré que lcela induisait une activation de gènes pro-fibrotiques et pro-ostéogénique sans conduire à des dépôts calciques. Krox20 est donc un facteur de transcription important pour la valvulogenèse et à l’homéostasie valvulaire chez l’adulte. Mes travaux ont contribué à l’identification de Krox20 comme gène candidat potentiel aux valvulopathies rencontrées chez l’homme. / Long seen as a consequence of aging and mechanical wear of aortic cusps, aortic valve diseases are currently considered multifactorial diseases, with an indisputable genetic determinism but not well characterized. My thesis aims to study the role of the transcription factor Krox20 during development and maturation of the valve through the analysis of mouse models. We have shown that this gene is necessary for the development and maturation of the aortic valve. Indeed, the deletion of Krox20 in the mouse leads to thickened aortic leaflets from the fetal stage and the onset of aortic valve disease in adults. These anomalies are associated with defects in the organization of the extracellular matrix and more particularly to direct regulsation of collagen type I and type III expression. Our analysis showed that 25% Krox20-/- mice have a bicuspid aortic valve. The analysis of this model has allowed us to identify a population of cardiac neural crest cells involved in the occurrence of this phenotype. In addition, we were able to observe a down regulation of eNos in Krox20-/- embryos and show a genetic interaction between Krox20 and eNos. To address the role of Krox20 in the process of calcification of the aortic valve, we have studied the effects of its overexpression. Our preliminary results indicate that this overexpression leads to activation of pro-fibrotic and pro-osteogenic genes, however, this is not sufficient to induce calcification of aortic valve leaflets.Therefore Krox20 is important for valvulogenesis but also for valvular homeostasis in the adult. My work has contributed to the identification of a potential candidate gene involved in human valve diseases.