La « semicarbazide-sensitive amine oxidase » (SSAO) catalyse la déamination oxydative des amines primaires en aldéhyde, peroxyde d’hydrogène et ammoniac. Elle participe à la différenciation cellulaires, l’inflammation et la transmigration leucocytaire à travers l’endothélium lymphatique. Nos objectifs ont été d’étudier le rôle de la SSAO (i) dans la différenciation chondrocytaire hypertrophique, en relation avec le développement de l’arthrose en utilisant des chondrocytes de rat en culture primaire et des genoux arthrosiques de patients (ii) dans le développement de l’athérosclérose en invalidant des souris ApoE-/- qui développent naturellement l’athérosclérose pour le gène de la SSAO. Au niveau articulaire, la SSAO a été détectée dans le cartilage de rat et humain. In vitro, la SSAO (activité et expression) augmentent au cours de la différenciation terminale de chondrocytes de rat. Son inhibition par le LJP1586 entraîne un retard de différenciation chondrocytaire. La SSAO augmente également dans les zones arthrosiques du cartilage humain parallèlement à l’augmentation de l’hypertrophie. La SSAO jouerait donc un rôle dans la différenciation terminale des chondrocytes (hypertrophie) possiblement via le transport de glucose et dans le développement de la maladie. Au niveau vasculaire, les souris femelles ApoE-/-SSAO-/- de 25 semaines présentent une augmentation de la surface des plaques d’athérome par rapport aux ApoE-/-. Ceci est associée à une diminution de l’expression d’α-actine dans le média sous les plaques et de smMHC dans l’aorte abdominale (AA) sans modification ni de l’infiltration des lymphocytes T; ni des monocytes/ macrophages dans la paroi artérielle, ni du profil cytokinique pro-/anti-inflammatoire dans la rate. A 15 semaines, les souris femelles ApoE-/-SSAO-/-, sm-MHC a diminué dans les AA de ces souris par rapport aux ApoE-/- ainsi qu’une réorientation du trafic des cellules immunitaires vers la paroi aortique sans modification significative de la surface des plaques a été détecté. La SSAO jouerait donc un rôle précoce dans le développement de l’athérosclérose via une modification du trafic des cellules immunitaires et du phénotype des CML dans la paroi / The semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidative deamination of primary amines into aldehydes, hydrogen peroxide and ammonia. The SSAO was implicated in cellular differentiation, inflammation and transmigration of leukocyte through the lymphatic. The objectives of this work were to study the role of SSAO (i) in chondrocyte differentiation and in the development of osteoarthritis using rat chondrocyte primary cell culture and osteroarthritic samples from patients. (ii) in the development of atherosclerosis using ApoE-/- mice, which develop naturally atherosclerosis, invalidated for the SSAO gene. Concerning the articulation, the SSAO (expression and activity) was detected in the rat and human cartilage. In vitro, SSAO increases during chondrocyte terminal differentiation (hypertrophy) and the inhibition of its activity by LJP1586, decreases the level of differentiation. In human arthritic cartilage, SSAO was higher that in healthy cartilage, in association with an increase in hypertrophic markers. The SSAO plays a role in the terminal differentiation of chondrocytes and might be involved in the development of osteoarthritis. At the vascular level, 25 week-old female ApoE-/-SSAO-/- mice presented a 50% increase in plaque surface associated with an 80% decrease in α-actin expression in the media of aortic sinus and a decrease in sm-MCH in abdominal aortas (AA) compared to ApoE-/- mice. These results were not due neither to a modification of monocytes/ macrophages, Tcell infiltration in the plaque nor in a pro- or anti-inflammatory cytokine change in spleen. In 15 week-old ApoE-/-SSAO-/- mice, even if no modification of plaque surface was found, a decrease in sm-MHC was noticed in the AA from ApoE-/-SSAO-/- compare to ApoE-/- mice. More over, the immune cell trafficking was increased in the aortic wall of ApoE-/-SSAO-/- compared to ApoE-/- mice. Thus, SSAO is involved in the early development of atherosclerosis in changing the immune cell trafficking and the VSMC phenotype

La rigidité artérielle et la fibrose ont une valeur prédictive dans le développement des maladies cardiovasculaires (CV). Ces 2 phénotypes impliquent les cellules musculaires lisses vasculaires (CMLVs) notamment des récepteurs membranaires et les protéines du cytosquelette. Les objectifs ont été d’étudier : (i) l’influence du récepteur minéralocorticoïde (MR) sur la réactivité vasculaire, (ii) le rôle de l’intégrine αvβ3 dans le développement de la rigidité artérielle et la fibrose vasculaire, et (iii) l’impact de la vimentine et la synémine sur la structure et la fonction artérielle. Ces trois études ont utilisées des souris avec invalidation génétiques des protéines d’intérêt. Résultats : l’absence du MR diminue la réactivité vasculaire en altérant le couplage contraction/relaxation des CMLVs via des mécanismes Ca2+- et NO-dépendants (une diminution de la vasoconstriction en réponse au Ca2+ extracellulaire et une altération de la vasorelaxation endothélium-dépendante en réponse à l’acétylcholine). L’invalidation de la sous-unité αv prévient la fibrose en réponse à l’administration d’angiotensine II. L’absence de la vimentine et non celle de la synémine augmente la rigidité artérielle via des changements des adhésions focales des CMLVs mais aussi des cellules endothéliales. En conclusion, les récepteurs membranaires et protéines intracellulaires étudiées influencent la fonction et la structure des artères grâce à des actions spécifiques sur le tonus musculaire, la mécanotransduction et l’organisation ultra-structurale des CMLVs. Ces études montrent au niveau cellulaire et moléculaire le déterminisme plurifactoriel des phénotypes de rigidité-fibrose de la paroi artérielle. Ces résultats nécessitent des travaux plus mécanistiques pour affirmer l’implication de ces protéines dans les maladies CV liées au vieillissement / Arterial stiffness and fibrosis have a predictive value in the development of cardiovascular diseases (CV). These two phenotypes involve vascular smooth muscle cells (VSMCs) including membrane receptors and cytoskeletal proteins. The objectives were to examine: (i) the influence of the mineralocorticoid receptor (MR) on vascular reactivity, (ii) the role of avb3 integrin in the development of arterial stiffness and vascular fibrosis, and (iii) the impact of vimentin and synemin on arterial structure and function. The mice with genetic invalidation of the proteins of interest were used in these three studies. Results: the absence of MR decreased vascular reactivity by altering the contraction/relaxation coupling of VSMC through Ca2+- and NO-dependent mechanisms (a decrease of vasoconstriction in response to extracellular Ca2+ and impaired endothelium-dependent vasorelaxation in response to acetylcholine). The invalidation of the αv subunit prevented fibrosis in response to the administration of angiotensin II. The absence of vimentin, and not that of the synemin, increased arterial stiffness via changes in focal adhesions of VSMCs as well as endothelial cells. In conclusion, the studied membrane receptors and intracellular proteins that influenced the structure and function of arteries through specific actions on muscle tone, the mechanotransduction and the ultra-structural organization of VSMCs. These studies show the multifactorial dependency of the stiffness-fibrosis phenotypes of the arterial wall at the cellular and molecular levels. These results require more mechanistic work to determine the role of these proteins in CV diseases related to aging

As coronárias derivam do proepicárdio, uma estrutura formada por precursores dos constituintes de vasos coronários, células endoteliais e musculares lisas (CoSMC). In vivo observa-se um marcante atraso entre a diferenciação endotelial e a integração de CoSMC à parede do vaso. O objetivo deste trabalho foi identificar os mecanismos que inibem a diferenciação a CoSMC in vivo. Baseados na perda progressiva da expressão de raldh2, a principal enzima de síntese de ácido retinóico (AR), nós exploramos a sinalização por AR como um possível inibidor da diferenciação a CoSMC. Através de um vetor adenoviral de expressão de raldh2 e da inibição in vivo da síntese de AR nós demonstramos que a sinalização por AR bloqueia a diferenciação a CoSMC dos precursores coronários. Nós também identificamos o VEGF como um fator chave no controle da diferenciação a CoSMC. Em conjunto, nossos dados suportam o modelo que a síntese de AR e VEGF durante o desenvolvimento cardíaco foi co-optada para o bloqueio da diferenciação a CoSMC até o estabelecimento de uma vasta malha vascular. / Coronary vessels derive from the proepicardium (PE), a structure formed by precursor of coronary vessels cells, endothelial and smooth muscle cells (CoSMC). In vivo there is a clear gap between the endothelial differentiation and the integration of CoSMC into the vascular tubes. The aim of this work was to understand the mechanisms controlling the delayed in vivo CoSMC differentiation. Based on the progressive loss of expression of raldh2, the main retinoic acid (RA) synthesizing enzyme, we explored the RA signaling as a possible candidate inhibitor of CoSMC differentiation. Using a adenoviral raldh2 expression system and in vivo inhibition of RA synthesis we showed that RA signaling act as a brake to slow CoSMC differentiation in PE-derived cells. We also identified VEGF as key factor acting on the control of CoSMC differentiation. Together our results support a model that AR and VEGF synthesis during cardiac development was co-opted to block the CoSMC differentiation of coronary precursors before an extensive endothelial network of tubes is established.

cAMP-elevating agents such as adenosine and epinephrine (after binding to beta-adrenergic receptor) contribute to local vascular dilation and some of these dilations are endothelium-dependent. Previous intracellular Ca 2+ imaging studies in mouse microvessel endothelial cells reported that addition of adenosine or epinephrine induced a Ca2+ influx which is blocked by CNG channel blockers such as L-cis-diltiazem or LY83583. Inside-out patch clamp studies confirmed the existence of a cAMP-activated current in endothelial cells, strongly suggesting a functional role of CNG, in particular CNGA2, channels in endothelial cells. The current study went further to show that similar Ca2+ influx in response to adenosine or epinephrine occurred in endothelial cells in freshly isolated mouse aortic strips and was again blocked by L-cis-diltiazem. By measuring the isometric force developed in mouse aortic strips, we showed that CNGA2 channel-mediated Ca2+ influx in endothelial cells contributed to the endothelium-dependent vascular dilatation in response to adenosine and epinephrine. / In conclusion, cyclic nucleotides playa vital role in the regulation of intracellular Ca2+ concentration in vascular cells and Jurket T cells. / In Jurkat T cells, cyclic nucleotides regulated Ca2+ mobilization in a different way. Fluorescence-imaging studies showed that cGMP inhibited store-operated Ca2+ influx and histamine-induced Ca 2+ rise in Jurkat T cells through activation of PKG. / Thromboxane A2 (TxA2)-induced smooth muscle contraction has been implicated in cardiovascular, renal and respiratory diseases. This contraction can partly be attributed to TxA2-induced Ca2+ influx, which activates the Ca2+-calmodulin-MLCK pathway. This study aims to identify the channels that mediate TxA2-induced Ca2+ influx in vascular smooth muscle cells. Application of U-46619, a thromboxane A2 mimic, resulted in a constriction in endothelium-denuded small mesenteric artery segments. The constriction relied on the presence of extracellular Ca2+, because removal of extracellular Ca2+ abolished the constriction. This constriction was partially inhibited by a L-type Ca2+ channel inhibitor nifedipine (0.5-1 muM). The remaining component was inhibited by L-cis-diltiazem, a selective inhibitor for CNG channels, in a dose-dependent manner, Another CNG channel blocker LY83583 [6-(phenylamino)-5,8-quinolinedione] had similar effect. In primary cultured smooth muscle cells derived from rat aorta, application of U46619 (100 nM) induced a rise in cytosolic Ca2+, which was inhibited by L-cis-diltiazem. Immunoblot experiments confirmed the presence Of CNGA2 protein in vascular smooth muscle cells, These data suggest a functional role of CNG channels in U-46619-induced Ca 2+ influx and contraction of smooth muscle cells. / Leung, Yuk Ki. / "August 2010." / Adviser: Yao Xiaoxiang. / Source: Dissertation Abstracts International, Volume: 73-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 116-132). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

O dimorfismo sexual relacionado à hipertensão arterial surge na adolescência e persiste por toda vida adulta. Homens apresentam maior incidência de doenças cardiovasculares quando comparados a mulheres de mesma faixa etária. O mesmo perfil é observado em modelos animais de hipertensão, nos quais machos apresentam maiores níveis pressóricos quando comparados a fêmeas. Dessa forma, a testosterona é frequentemente relacionada à hipertensão arterial. Entretanto, os mecanismos pelos quais a testosterona exerce efeitos vasculares ainda não estão esclarecidos. O objetivo deste trabalho foi investigar os efeitos da testosterona sobre a geração de espécies reativas de oxigênio (EROs), importantes mediadores do processo hipertensivo, em células da musculatura lisa vascular (CMLV) de ratos normotensos e espontaneamente hipertensos (SHR). Os receptores para andrógenos, as fontes de EROs (papel da NADPH oxidase), bem como os efeitos funcionais celulares (migração celular) relacionados aos efeitos da testosterona também foram analisados. Para tanto, CMLV do leito mesentérico de ratos Wistar (W), Wistar-Kyoto (WKY) e SHR foram isoladas, cultivadas e estimuladas com testosterona 10-7mol/L em diferentes tempos, de acordo com cada protocolo. Sempre que necessário, as células foram pré-incubadas por 30 minutos com inibidores específicos para o estudo dos mecanismos envolvidos, tais como: flutamida (inibidor do receptor clássico para andrógenos), apocinina (inibidor da NADPH oxidase), PP2 (inibidor da c-Src), actinomicina D (inibidor da transcrição gênica) e cicloheximida (inibidor da síntese protéica). Nossos resultados indicam que a testosterona induz a geração de EROs por mecanismos dependentes do tempo e da linhagem de ratos, de modo que células isoladas de animais SHR são mais sensíveis a testosterona. Esta geração ocorre por dois mecanismos principais: um mediado pelo receptor clássico para andrógenos (AR) e outro mediado pelo receptor de membrana para andrógenos (ARm), resultando em efeitos genômicos e não-genômicos, respectivamente. Enquanto os efeitos genômicos são comuns, isto é, são observados em células de animais normotensos e hipertensos, os efeitos não-genômicos são específicos, e ocorrem exclusivamente em células de animais hipertensos. A geração genômica de EROs, mediada pelo AR, depende da modulação da expressão de subunidades da NADPH oxidase. Por outro lado, a geração não-genômica, é mediada pelo ARm, independe de síntese protéica, e ocorre devido à ativação de vias de sinalização específicas, reguladoras do complexo enzimático NADPH oxidase. As EROs formadas a partir do estímulo com a testosterona tanto por mecanismos genômicos ou não-genômicos levam a migração celular por mecanismos mediados pelo RA. Nossos resultados sugerem que a testosterona tem papel importante na função de células da musculatura lisa vascular, o que pode contribuir para algumas alterações vasculares características do processo hipertensivo. Portanto, nosso trabalho é o primeiro a demonstrar que a testosterona regula vias de sinalização redox em CMLV levando a efeitos funcionais importantes, relacionados ao remodelamento vascular, os quais podem contribuir para o desenvolvimento e manutenção da hipertensão arterial. / Sexual dimorphism related to hypertension begins at childhood and persists through adulthood. The incidence of cardiovascular diseases is higher in men when compared to age-matched women. Although testosterone has been associated to the sexual dimorphism in hypertension, the mechanisms whereby testosterone acts in the vasculature remain unclear. The main objective of this study was to determine whether testosterone induces reactive oxygen species (ROS) generation, key players on hypertension, in vascular smooth muscle cells (VSMC) isolated from normotensive and hypertensive rats. The signaling pathways and the androgen receptors activated by testosterone, the role of NADPH oxidase in ROS generation and the cellular outcomes (cell migration) were also determined. Accordingly, VSMC isolated from the mesenteric bed of Wistar (W), Wistar-Kyoto (WKY) and spontaneously hypertensive (SHR) rats were stimulated with testosterone 10-7mol/L for different periods of time, according to each protocol. Whenever appropriate, cells were pre-incubated with specific inhibitors, such as flutamide 10-5mol/L (nuclear androgen receptor antagonist), apocynin 3x10-5mol/L (NADPH oxidase inhibitor), PP2 10-5mol/L (c-Src inhibitor), actinomycin D 10-5mol/L (inhibitor of gene transcription), and cycloheximide 10-5mol/L (protein synthesis inhibitor). Our findings demonstrate that testosterone induces ROS formation in a time and strain-dependent manner. Augmentation of ROS formation is higher in SHR-VSCMC, indicating an increased sensitivity of SHR-VSMC to testosterone stimuli. Testosterone-induced ROS production occurs by two main mechanisms: the first mediated through the classical androgen receptor (AR) and the second mediated through membrane-associated androgen receptor (ARm), leading to genomic and non-genomic effects, respectively. Whereas the genomic effects occur in VSMC from both strains, non-genomic effects are only observed in SHR-VSMC. The genomic ROS production is mediated through AR and depends on modulation of NADPH oxidase subunits. On the other hand, non-genomic ROS formation is mediated through RAm, does not rely on protein synthesis and occurs via specific signaling pathways that regulate NADPH oxidase. Genomic and non-genomic ROS production by testosterone leads to a common final effect: VSMC migration, indicating that testosterone plays a key role in VSMC function. These results indicate that testosterone signals through redox-sensitive pathways, important in c-Src-mediated migration of VSMCs in SHR. Such processes may contribute to vascular remodeling in hypertension.

Han, Jianguo. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 66-76). / Abstracts in English and Chinese. / Declaration --- p.i / Acknowledgement --- p.□ / Publication --- p.□ / Abstract (English) --- p.□xi / Abstract (Chinese) --- p.□ / Abbreviations --- p.ix / List of figures / tables --- p.x / Chapter Chapter 1. --- General Introduction / Chapter 1.1 --- Role of vascular smooth muscle cells in the control of coronary circulation --- p.1 / Chapter 1.1.1 --- Potassium channels in the coronary smooth muscle cells --- p.2 / Chapter 1.1.1.1 --- Voltage -dependent potassium (Kv) channels --- p.3 / Chapter 1.1.1.2 --- Inward rectifier K+ (Kir) channels --- p.4 / Chapter 1.1.1.3 --- ATP-sensitive potassium (Katp) channels --- p.4 / Chapter 1.1.2 --- BKCa channels in the regulation of vascular function --- p.6 / Chapter 1.1.2.1 --- The structure of BKCa channels --- p.6 / Chapter 1.1.2.2 --- Role of BKCa channels in the regulation of vascular function --- p.6 / Chapter 1.2 --- Functional alteration of the coronary SMCs during cardiac surgery --- p.7 / Chapter 1.2.1 --- Effect of ischemia on the function of SMCs in the coronary circulation --- p.8 / Chapter 1.2.2 --- Effect of cardioplegic/organ preservation solutions on the function of SMCs in the coronary circulation --- p.11 / Chapter Chapter 2. --- Materials and Methods --- p.14 / Chapter 2.1 --- Isometric force study in small coronary arteries --- p.14 / Chapter 2.1.1 --- Preparation of porcine small coronary arteries --- p.14 / Chapter 2.1.2 --- Experiment procedure --- p.15 / Chapter 2.1.2.1 --- Mounting of small coronary arteries --- p.15 / Chapter 2.1.2.2 --- Normalization procedure for small coronary arteries --- p.16 / Chapter 2.1.2.3 --- Precontraction and relaxation --- p.17 / Chapter 2.1.3 --- Data acquisition and analysis --- p.17 / Chapter 2.2 --- Patch-clamp electrophysiology --- p.18 / Chapter 2.2.1 --- Preparation of porcine coronary arteries --- p.18 / Chapter 2.2.2 --- Enzymatic dissociation of coronary arterial SMCs --- p.18 / Chapter 2.2.3 --- Primary cell culture --- p.19 / Chapter 2.2.4 --- Recording of BKca channel currents --- p.19 / Chapter 2.3 --- Statistical analysis --- p.21 / Chapter 2.4 --- Chemicals --- p.21 / Chapter Chapter 3. --- The Effect of Ischemia on BKCa channels in the Isolated SMCs of Coronary Arteries --- p.22 / Chapter 3.1 --- Abstract --- p.22 / Chapter 3.2 --- Introduction --- p.23 / Chapter 3.3 --- Experimental design and analysis --- p.25 / Chapter 3.3.1 --- Isometric force study in small coronary arteries --- p.25 / Chapter 3.3.2 --- Effect of ischemia on NS1619-induced relaxation in small coronary arteries --- p.26 / Chapter 3.3.3 --- Effect of ischemia on smooth muscle BKca channel currents --- p.27 / Chapter 3.3.3.1 --- Preparation of porcine coronary artery --- p.27 / Chapter 3.3.3.2 --- Enzymatic dissociation of coronary arterial SMCs --- p.27 / Chapter 3.3.3.3 --- Recording of BKCa channel currents --- p.27 / Chapter 3.3.4 --- Data acquisition and analysis --- p.28 / Chapter 3.4 --- Results --- p.28 / Chapter 3.4.1 --- Electrophysiological studies --- p.28 / Chapter 3.4.1.1 --- Effect of IBTX on the whole cell outward currents --- p.29 / Chapter 3.4.1.2 --- Effect of ischemia on the IBTX-sensitive BKca currents --- p.30 / Chapter 3.4.2 --- Relaxation studies --- p.30 / Chapter 3.4.2.1 --- Resting force --- p.30 / Chapter 3.4.2.2 --- U46619-induced contraction force --- p.31 / Chapter 3.4.2.3 --- Effect of IBTX on the NS1619-induced relaxation --- p.31 / Chapter 3.4.2.4 --- Effect of ischemia on the NS1619-induced relaxation --- p.31 / Chapter 3.5 --- Discussion --- p.32 / Chapter 3.5.1 --- Functional changes of the coronary smooth muscle BKca channels after ischemic exposure --- p.33 / Chapter 3.5.2 --- Role of BKca channels in SMCs during ischemia --- p.33 / Chapter 3.5.3 --- Clinical implications --- p.35 / Chapter Chapter 4. --- The Effect of Hyperkalemia on BKCa channels in the Isolated SMCs of Coronary Arteries --- p.41 / Chapter 4.1 --- Abstract --- p.41 / Chapter 4.2 --- Introduction --- p.42 / Chapter 4.3 --- Experimental design and analysis --- p.44 / Chapter 4.3.1 --- Isometric force study in small coronary arteries --- p.44 / Chapter 4.3.1.1 --- Effect of hyperkalemia on NS1619-mediated relaxation in small coronary arteries --- p.44 / Chapter 4.3.2. --- Effect of hyperkalemia on BKCa currents of SMCs --- p.45 / Chapter 4.3.2.1 --- Preparation of porcine coronary arteries --- p.45 / Chapter 4.3.2.2 --- Enzymatic dissociation of coronary arterial SMCs --- p.45 / Chapter 4.3.2.3 --- Recording of BKca channel currents --- p.46 / Chapter 4.3.3. --- Data acquisition and analysis --- p.46 / Chapter 4.4 --- Results --- p.47 / Chapter 4.4.1 --- Effect of hyperkalemia on the iberiotoxin-sensitive BKCa channel currents --- p.47 / Chapter 4.4.2 --- Relaxation studies --- p.48 / Chapter 4.4.2.1 --- Resting force --- p.48 / Chapter 4.4.2.2 --- U46619- and high K+-induced contraction force --- p.48 / Chapter 4.4.2.3 --- Effect of high K+ on the NS1619-induced relaxation --- p.48 / Chapter 4.4.2.4 --- Effect of IBTX on the NS1619-induced relaxation --- p.49 / Chapter 4.5 --- Discussion --- p.49 / Chapter 4.5.1 --- Role of BKCa channels in the isolated SMCs in hyperkalemic solution --- p.50 / Chapter 4.5.2 --- Functional changes of BKCa channels in coronary SMCs in hyperkalemia exposure --- p.51 / Chapter 4.5.3 --- Clinical implications --- p.52 / Chapter Chapter 5. --- General Discussion --- p.58 / Chapter 5.1 --- BKCa channels in porcine coronary SMCs --- p.59 / Chapter 5.2 --- Alteration of BKCa function related to ischemia in porcine coronary SMCs --- p.60 / Chapter 5.3 --- Alteration of BKCa function related to hyperkalemia in porcine coronary SMCs --- p.61 / Chapter 5.4 --- Limitation of the study --- p.62 / Chapter 5.5 --- Future investigations --- p.63 / Chapter 5.6 --- Conclusions --- p.63 / References --- p.66

La trans-différenciation des cellules musculaires lisses vasculaires (CMLV) vers un phénotype migratoire, prolifératif et sécrétoire joue un rôle clé dans la progression des lésions athéromateuses et l’hyperplasie intimale qui sous-tend la resténose post-angioplastie. Nos travaux suggèrent que la transition phénotypique des CMLV implique, chez le rat, la souris et l’Homme, l’expression de novo de l’Adénylyl Cyclase 8 (AC8), une enzyme catalysant la synthèse de l’AMP cyclique (AMPc) (Clément et al., 2006; Gueguen et al., 2010; Keuylian et al., 2012; résultats non publiés). Ce travail de thèse avait pour objectif d’appréhender le rôle de l’AC8 dans la trans-différenciation des CMLV en évaluant son impact sur la signalisation AMPc. L’étude des dynamiques de production du second messager avec le biosenseur T-Epac-VV montre que l’AC8 inhibe les hausses d’AMPc dans les CMLV trans-différenciées à l’Interleukine-1β. Cette fonction non canonique est assurée par de nouvelles isoformes d’AC8 que nous avons identifiées et clonées, les AC8E1 à 4, qui partagent une délétion des cinq premiers domaines transmembranaires. Des dosages de l’accumulation d’AMPc couplés à des expériences de co-immunoprécipitation et d’immunocytochimie révèlent que les AC8E exprimées de façon hétérologue dans des cellules HEK s’hétéro-dimérisent avec les AC en transit dans le réticulum, suppriment leur activité enzymatique et préviennent leur adressage à la membrane plasmique. L’induction des AC8E dans les CMLV trans-différenciées pourrait prévenir les effets vasculoprotecteurs de l’AMPc (Douglas et al., 2005; Katakami et al., 2010), favorisant ainsi l’acquisition et/ou le maintien du phénotype synthétique. / The phenotypic switch of vascular smooth muscle cells (VSMC) towards a migratory, proliferative and secretory state plays a key role in atherosclerotic plaque expansion and intimal hyperplasia leading to post-angioplasty restenosis. Our previous results suggest that the trans-differentiation of rat, mouse and human VSMC involves the de novo expression of the Adenylyl Cyclase 8 (AC8), an enzyme that catalyzes the synthesis of cyclic AMP (cAMP) (Clement et al., 2006; Gueguen et al., 2010; Keuylian et al., 2012; unpublished results). The main goal of my PhD was to decipher the impact of AC8 expression on cAMP signaling in trans-differentiated VSMC. Using the FRET-based biosensor T-Epac-VV, we showed that the de novo expression of AC8 limits increases in cellular cAMP. This non-canonical function relies on a new family of AC8 isoforms that we have identified and cloned: the AC8E1 to 4. They share a common deletion of the first five transmembrane domains. The biochemical characterization of AC8E over-expressed in HEK cells allowed us to elucidate their functioning. cAMP accumulation assays, co-immunoprecipitation experiments and immunocytochemistry revealed that AC8E hetero-dimerize with functional AC during their maturation in the reticulum, suppress their enzymatic activity and prevent their traffic to the plasma membrane. Numerous studies have shown that increases in cAMP concentration within trans-differentiated VSMC antagonize pathological vascular remodeling (Douglas et al., 2005; Katakami et al., 2010). Thus, the induction of AC8E in trans-differentiated VSMC could prevent the vasculoprotective effects of cAMP and promote the acquisition of a synthetic phenotype.

Chez les patients souffrant d'insuffisance rénale chronique, les calcifications vasculaires représentent la première cause de mortalité. Elles résultent de la trans-différenciation des cellules musculaires lisses (CMLs) en cellules de type ostéoblastique et/ou chondrocytaire, en réponse à des cytokines inflammatoires ou à une hyperphosphatémie. Les CMLs forment alors des cristaux par l'activité de la phosphatase alcaline non-spécifique du tissu (TNAP). A la lumière de résultats récents, nous avons émis l'hypothèse que la TNAP module la trans différenciation des CMLs. Nos objectifs étaient donc de déterminer l'effet de la TNAP dans la trans-différenciation des CMLs, et d'étudier les mécanismes impliqués dans son induction, avec un intérêt particulier pour les microRNAs. Nous avons observé que l'ajout de phosphatase alcaline purifiée ou la surexpression de TNAP stimule l'expression de marqueurs chondrocytaires en culture de CMLs et de cellules souches mésenchymateuses. De plus, l'inhibition de la TNAP bloque la maturation de chondrocytes primaires. Nous excluons un rôle des cristaux formés par la TNAP, puisque l'ajout de cristaux seuls ou associés à une matrice collagénique n'a pas reproduit les effets de la TNAP. Nous suspectons que la TNAP agit en hydrolysant le pyrophosphate inorganique (PPi). En effet, c'est la TNAP qui hydrolyse le PPi en culture de CMLs et de chondrocytes, et le PPi mime les effets de l'inhibition de TNAP en culture de chondrocytes. Enfin, nous rapportons le profil de microRNA des artères cultivées en conditions hyperphosphatémiques. Ces résultats pourraient être particulièrement importants dans le développement de nouvelles approches thérapeutiques / In patients with chronic kidney disease (CKD), vascular calcification represents the main cause of mortality. Vascular calcification results from the trans-differentiation of vascular smooth muscle cells (VSMCs) into cells similar to osteoblasts and/or chondrocytes, in response to inflammatory cytokines or hyperphosphatemia. Calcifying VSMCs form calcium phosphate crystals through the activity of tissue nonspecific alkaline phosphatase (TNAP). In light of recent findings, we hypothesized that TNAP also modulates VSMC trans-differentiation. Our objectives were therefore to determine the effect of TNAP activity on VSMC trans-differentiation, and secondly to investigate the molecular mechanisms involved in TNAP expression in aortas, with a particular interest in microRNAs. We first observed that addition of purified alkaline phosphatase or TNAP over-expression stimulates the expression of chondrocyte markers in culture of the mouse and rat VSMC lines, and of mesenchymal stem cells. Moreover, TNAP inhibition blocks the maturation of mouse primary chondrocytes and reduces mineralization. We exclude a role for crystals in TNAP effects, since addition of crystals alone or associated to a collagenous matrix fails to mimic TNAP effects. We rather suspect that TNAP acts through the hydrolysis of inorganic pyrophosphate (PPi). Indeed, PPi is hydrolyzed by TNAP in VSMCs and chondrocytes and addition of PPi mimics the effects of TNAP inhibition on chondrocyte maturation. Finally, we report microRNA signature of aortic explants treated under hyperphosphatemic conditions that induce vascular calcification. These results could be of particular importance in patients with CKD

Abstract not available

Thesis (Ph. D.)--University of Missouri--Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 186-210). Also available on the Internet.