Les Cellules Endothéliales Progénitrices ("Endothelial Progenitor Cells", EPCs) sont des précurseurs endothéliaux qui jouent un rôle émergeant en biologie vasculaire. Les EPCs ont été localisées dans le cordon ombilical, la moelle osseuse, le sang périphérique et dans certains tissus régénérateurs. Les interactions des EPCs avec les cellules sanguines et vasculaires peuvent largement influencer leurs propriétés biologiques et dicter leur fonctionnement pendant la réparation endothéliale. Plus spécifiquement, les interactions des EPCs avec les plaquettes circulantes induisent leur migration, leur recrutement et leur différentiation en cellules endothéliales aux sites de lésions vasculaires. Cependant, l’impact d’une telle interaction sur la fonction plaquettaire n’a pas été recherché. Le but de mon projet était de :1) générer des EPCs à partir des cellules mononucléaires du sang humain périphérique ("Peripheral Blood Mononuclear Cells", PBMCs); 2) étudier les interactions adhésives entre les EPCs et les plaquettes; 3) déterminer leur impact sur la fonction plaquettaire et la formation du thrombus et 4) décrire le mécanisme d’action des EPCs sur les plaquettes et le thrombus. Mises en culture sur une surface de fibronectine dans un milieu conditionné, les PBMCs fraîchement isolées possédaient une morphologie ronde et une petite taille. Après cinq jours, les PBMCs adhérentes donnaient naissance à des colonies, puis formaient une monocouche de cellules aplaties caractéristiques des EPCs après dix jours de culture. Les EPCs différenciées étaient positives pour l’Ulex-lectine et l’Acétyle des lipoprotéines de faible densité ("Acetylated Low Density Lipoprotein", Ac-LDL), exprimaient les marqueurs progéniteurs (CD34, P-sélectine, VEGFR2, vWF et VE-Cadhérine) tandis que les marqueurs leucocytaires (CD14, PSGL-1 et L-sélectine) étaient absents. Ces EPCs interagissaient avec les plaquettes activées par un mécanisme dépendant de la P-sélectine plaquettaire, inhibaient l’activation et l’agrégation plaquettaire et réduisaient significativement l’adhésion plaquettaire, principalement par l’action de prostacycline (PGI2). En fait, ceci était associé avec une augmentation de l’expression de la cyclooxygénase-2 (COX-2) et du monoxyde d’azote (NO) synthéthase inductible (iNOS). Toutefois, les effets inhibiteurs des EPCs sur la fonction plaquettaire ont été renversés par une inhibition de la COX et non pas du NO. Bien que les EPCs fussent en mesure de lier les plaquettes via la P-sélectine, leurs effets prédominants étaient médiés essentiellement par une sécrétion paracrine, impliquant la PGI2. Néanmoins, un rapprochement étroit ou un bref contact entre les EPCs et les plaquettes était requis pour que cette fonction soit complètement réalisée. D’ailleurs, cet aspect a été investigué chez des souris déficientes en P-sélectine (P-sel-/-) et chez leurs congénères de phénotype sauvage (Wild Type, WT). Chez les souris WT, les EPCs inhibaient l’agrégation plaquettaire dans le sang complet de manière concentration-dépendante alors que dans les souris P-sel-/-, l’action des EPCs n’avait pas d’effet significatif. De plus, en utilisant un modèle murin de thrombose artérielle, nous avons démontré que l’infusion systémique des EPCs altéraient la formation du thrombus et réduisaient significativement sa masse chez les souris WT, mais non pas chez les souris P-sel-/-. En outre, le nombre des EPCs incorporées au niveau du thrombus et de la paroi vasculaire était visiblement réduit chez les P-sel-/- par rapport aux souris WT. Dans cette étude, nous sommes parvenus à différentier adéquatement des EPCs à partir des PBMCs, nous avons étudié les interactions adhésives entre les EPCs et les plaquettes, et nous avons décrit leur impact sur la fonction plaquettaire et la formation du thrombus. De plus, nous avons identifié la PGI2 comme étant le principal facteur soluble sécrété par les EPCs en culture et responsable de leurs effets inhibiteurs sur l’activation, l’adhésion et l’agrégation plaquettaire in vitro. De surcroît, nous avons élucidé le mécanisme d’action des EPCs sur l’agrégation plaquettaire et la formation du thrombus, in vivo, et nous avons souligné le rôle de la P-sélectine plaquettaire dans ce processus. Ces résultats ajoutent de nouvelles connaissances sur la biologie des EPCs et définissent leur rôle potentiel dans la régulation de la fonction plaquettaire et la thrombogenèse. / Endothelial Progenitor Cells (EPCs) are believed to contribute to vascular biology and endothelial repair. EPCs have been isolated from umbilical cord, bone marrow, peripheral blood and in some regenerative tissues. Interactions of EPCs with vascular and blood cells can largely influence their functional properties and predict their destiny in the target tissues. More specifically, interactions of EPCs with circulating platelets provide the critical signal to ensure their migration and homing at the sites of vascular injury and their differentiation into endothelial cells. However, the functional consequences of such interactions on platelets remain unknown. Accordingly, this project was designed to investigate the impact of EPCs on platelet function and the specific objectives of this study were to: 1) generate EPCs from human peripheral blood mononuclear cells (PBMCs); 2) characterize the adhesive interactions between EPCs and platelets; 3) determine their impact on platelet function and thrombus formation and 4) elucidate the mechanistic action of EPCs on platelets and thrombus. Cultured on fibronectin in conditioned media, PBMCs differentiated, within ten days of culture, into EPCs, which were positive for Ulex-lectin and Ac-LDL (Acetylated Low Density Lipoprotein), and expressed progenitor markers (CD34, VEGFR2, vWF, and VE-Cadherin). These EPCs bind activated platelets through P-selectin-dependent mechanism, inhibited platelet activation, aggregation and adhesion, mainly via prostacyclin (PGI2) secretion. Indeed, this was associated with up-regulation of cyclooxygenase-2 (COX-2) and inducible nitric oxide (NO) synthase (iNOS). However, the effects on platelets were reversed by COX, but not by NO inhibition. Although EPCs bound platelets via platelet P-selectin, their predominant effects occurred via a paracrine secretion, implying PGI2. Nevertheless, a transitory link or brief contact between EPCs and platelets was required for this function to be fully realized. This was further depicted using a murine arterial thrombosis model in P-selectin deficient mice (P sel-/-) and their wild-type counterparts (WT). EPCs significantly impaired, in a concentration dependent-manner, collagen-induced whole blood platelet aggregation in WT mice; whereas in P-sel-/- mice, EPCs had no significant effect. Moreover, in murin model of arterial thrombosis, infusion of EPCs altered thrombus formation and significantly reduced the mass of thrombi generated in WT, but not in P-sel-/- mice. Furthermore, the number of EPCs recruited within the thrombi and along the vascular wall was visually reduced in P-sel-/- mice as compared to WT mice. In this project, we succeeded in adequately differentiating EPCs from PBMCs, we characterized the adhesive interaction between EPCs and platelets, and we addressed the impact of EPCs on platelet function and thrombus formation. Moreover, we identified PGI2 as the principal soluble factor secreted by cultured EPCs and responsible of their inhibitory effects on platelet function in vitro. In addition, using a murine model of arterial carotid injury in WT and P-sel-/- mice, we elucidate the mechanistic action of EPCs on platelet aggregation and thrombus formation, in vivo, and we highlighted the role of platelet P-selectin in this process. These findings add new insights into the biology of EPCs and reveal a potential role for EPCs in regulating platelet function, which in turn may limit thrombogenesis and maintain hemostasis at the sites of vascular injury.

Cette thèse rapporte l’étude des propriétés physicochimiques des nanoparticles polymériques et leur impact sur l’interaction avec les cellules vivantes. Nous nous sommes tout spécialement attachés à étudier l’effet des propriétés adhésives et mécaniques des nanoparticules sur leur capacité de pénétration de la membrane cellulaire. Pour ce faire, nous avons tout d’abord utilisé des nanoparticules d’acide polylactique (PLA) fonctionnalisées en surface avec un ligand des sélectines E et P. Le greffage du ligand sur la particule s’est fait par une nouvelle méthode expérimentale garantissant la présence du ligand à la surface de la particule durant toute sa durée de vie. Cette méthode consiste à mélanger un polymère fonctionnalisé avec le ligand avec un autre polymère non fonctionnalisé. La présence du ligand à la surface des nanoparticules formées à partir de ce mélange de polymères a été confirmée par analyse ToF SIMS. Nous avons pu prouver que les particules possédant le ligand greffé à leur surface démontraient une capacité adhésive supérieure à leurs homologues non fonctionnalisés sur des cellules endothéliales HUVEC activées par différentes drogues. De plus, le captage des particules par les cellules HUVEC est modulé par le niveau d’expression des récepteurs selectine E et P et aussi par la quantité de ligand libre. Ces résultats montrent clairement que le greffage du ligand confère aux particules des propriétés adhésives accrues et spécifiques ce qui permet leur usage postérieure comme vecteur pharmaceutique capable de cibler un récepteur particulier à la surface d’une cellule. Nous avons aussi démontré que l’interaction entre les nanoparticules et la membrane cellulaire peut aussi être contrôlée aussi bien par les propriétés mécaniques de la cellule que de la nanoparticule. Dans une première étape, nous avons mesuré à l’aide de l’appareil de forces de surface l’élasticité de cellules macrophagiques déposées sur différents substrats. En contrôlant l’interaction entre la cellule et le substrat sur lequel elle repose nous avons montré qu’il était possible de modifier à ii volonté les propriétés mécaniques cellulaire. Une augmentation de l’élasticité cellulaire s’accompagne d’une augmentation systématique de l’internalisation de nanoparticules de PLA non fonctionnalisées. Ceci suggère un rôle prépondérant des propriétés mécaniques du cortex cellulaire dans le captage des nanoparticules de PLA. Dans une seconde étape, nous avons étudié l’effet des propriétés mécaniques des nanoparticules sur leur capacité de pénétration cellulaire. Pour ce faire, nous avons synthétisé des particules d’hydrogel dont l’élasticité était contrôlée par le degré d’agent réticulant inclus dans leur formulation. Le contrôle des propriétés mécaniques des nanoparticules a été confirmé par la mesure du module de Young des particules par microscopie de force atomique. L’impact des propriétés mécaniques de ces particules sur leur capacité de pénétration dans les cellules vivantes a été étudié sur des cellules macrophagiques de souris. Les résultats ont montré que la cinétique d’internalisation, la quantité de particules internalisées et le mécanisme d’internalisation dépendent tous du module de Young des nanoparticules. Aucune différence dans le trajet intracellulaire des particules n’a pu être observée malgré le fait que différentes voies d’internalisation aient été observées. Ce dernier résultat peut s’expliquer par le fait que les nanoparticules sont internalisées par plusieurs voie simultanément ce qui facilite leur accumulation dans les organelles digestives intracellulaires. Un modèle simple permettant d’expliquer ces résultats a été proposé et discuté. / This thesis reports the study of physical chemical properties of polymeric nanoparticles and their impact on the interaction with living cells. In particular we endeavoured to study the effect of the adhesive and mechanical properties of the vector on its capacity of penetration of the cellular membrane. With this intention, we firstly used nanoparticules of polylactic acid (PLA) functionalized on their surfaces with a ligand of the selectines E and P receptor. The grafting of the ligand on the particle’s surface was carried out thanks to a new experimental method guaranteeing the presence of the active molecule on the surface of the particle during its whole life cycle. This method consists in mixing a polymer functionalized with the ligand with another polymer not functionalized. The presence of the ligand on the surface of the nanoparticules formed starting from this mixture of polymers was confirmed by ToF SIMS analysis. We could show that the particles having the ligand grafted on their surface exhibit a higher adhesive capacity than their non-functionalized counterpart on endothelial cells HUVEC activated by various drugs. Nanoparticles adhesion on cells membrane was modulated by the level of expression of the receptors selectine E and P and also by the quantity of free ligand. These results show clearly that the functionalized particles possess all the characteristics of a pharmaceutical vector capable of targeting a particular receptor on a cell surface. The interaction between nanoparticules and cellular membrane can also be controlled by the mechanical properties of the cell as well as of the nanoparticule. To demonstrate it we have measured the elasticity of macrophagic cells deposited on various substrates using the SFA. We have thus showed that it was possible to control the cell mechanical properties at will by controlling the interaction between the cell and the substrate on which it rests. An increase of the cell elasticity is accompanied by an increase of the internalization of non-functionalized PLA nanoparticules. This suggests a major role of cytocortical mechanical properties in the capture of hard PLA particles. iv Lastly, we studied the effect of the mechanical properties of the nanoparticules on their cellular penetration capacity. With this intention, we synthesized hydrogel particles whose elasticity was controlled by the degree of crosslinking agent included in their formulation. The control of the mechanical properties of the nanoparticules was confirmed by the measurement of the Young modulus of the particles by AFM. The interaction of these particles with macrophagess showed that the mechanical properties of the particles affect various aspects related to the internalization of the nanoparticles. The internalization kinetics, the quantity of internalized particles and the mechanism of internalization depend all on the Young modulus of the nanoparticules. No differences in the intracellular pathway could be observed in spite of the fact that various pathways of internalization were observed for these nanoparticules. This last result can be explained by the fact that the nanoparticules are internalized by several mechanisms of simultaneously which facilitates their accumulation in intracellular digestive organelles. A simple model explaining these results is proposed and discussed.

Das Ziel dieser Arbeit war die Untersuchung der Rollgeschwindigkeiten von Leukozyten auf humanen kardialen mikrovaskulären Endothelzellen (HCMEC) und humanen umbilikalen venösen Endothelzellen (HUVEC). Die Endothelzellen wurden aus explantierten humanen Herzen sowie aus menschlichen Nabelschnüren unmittelbar postpartal gewonnen. Unter definierten Bedingungen wurden die in einer Flusskammer gemessenen Geschwindigkeiten von L-Selektin exprimierenden Nalm6-IF4 Zellen auf unstimulierten Endothelzellen mit denen auf stimulierten Endothelzellen verglichen. Die langsamere Geschwindigkeit der Leukozyten auf stimulierten Endothelzellen weist darauf hin, dass L-Selektin Liganden auf humanen kardialen mikrovaskulären Endothelzellen erst nach Stimulation exprimiert werden. Die beobachtete Geschwindigkeitsreduktion der Leukozyten ist jedoch von dem in der Literatur beschriebenen Selektin vermittelten Rollen zu unterscheiden. In den Versuchen mit Tunicamycin wurde gezeigt, dass N-glykosidisch gebundene Zucker kritische Bestandteile der Liganden für ihre Interaktion mit L-Selektin sind. Unter den gleichen Versuchsbedingungen wurde auch der Einfluss E-Selektin vermittelter Interaktionen auf die Geschwindigkeit der HL60 Zellen untersucht. Neben dem typischen Rollen wurde hier ebenfalls eine Selektin abhängige Geschwindigkeitsreduktion gesehen. / The aim of the present study was to investigate selectin mediated rolling velocities of leucocytes on human cardiac microvascular endothelial cells (HCMEC) and human umbilical vein endothelial cells (HUVEC). HCMEC were gained from explanted human hearts and HUVEC from umbilical cords immediately postpartum. Flow velocities of L-Selectin expressing Nalm6-IF4 cells on quiesent endothelial cells were compared to those on stimulated endothelial cells. Stimulation of endothelial cells with TNF led to significantly slower velocities of Nalm6-IF4 cells indicating that HCMEC express L-Selectin ligands only after stimulation. The observed reduction of flow velocities differs from rolling of leucocytes described in the literature. Experiments with tunicamycin showed that N-glycosylated carbohydtrate moieties are needed for proper function of L-Selectin ligands. E-Selectin mediated interactions between HL60 cells and endothelial cells were studied under the same conditions. Besides the typical rolling, a selectin mediated reduction of flow velocity was observed.

A hipertensão arterial pulmonar é uma síndrome clínica e hemodinâmica, caracterizada pelo aumento de resistência vascular na microcirculação. A vasoconstrição presente na doença ocorre principalmente devido à disfunção endotelial, induzindo a um estado pró-trombótico onde a participação das plaquetas é inequívoca. A trombina, principal agonista da ativação plaquetária, exerce seus efeitos nas células por meio de receptores ativados por proteases. Através da citometria de fluxo, este trabalho teve por objetivo analisar (1) a expressão do receptor ativado por protease do tipo 1 (PAR-1) na membrana de plaquetas, em seu estado íntegro ou clivado, (2) a atividade, mediante a formação de agregados entre plaquetas e leucócitos e, plaquetas e monócitos após estímulo de receptores ativados por proteases, além (3) da expressão de selectina-P na membrana plaquetária após estimulação. Foram estudados 30 pacientes portadores de hipertensão arterial pulmonar sob tratamento ambulatorial no Instituto do Coração da Faculdade de Medicina da Universidade de São Paulo. A idade destes pacientes variou de 11 a 78 anos, e a média da pressão sistólica da artéria pulmonar foi de 89+29 mmHg. Em 30% dos pacientes, o número de plaquetas esteve abaixo de 150x103/l, e em 40%, o nível do hematócrito apresentou-se acima de 50%. No presente estudo, não foi observada diferença significante na expressão do PAR-1 íntegro em plaquetas de pacientes comparativamente aos controles (p = 0,2). Em contrapartida, as plaquetas dos pacientes apresentaram menor quantidade de receptor clivado (p = 0,01), sugerindo internalização destes receptores. Com relação à avaliação da atividade de PAR-1 através da formação de agregados entre plaquetas e leucócitos e, plaquetas e monócitos após estimulação por agentes capazes de atuar sobre o receptor de trombina, não foram observadas diferenças entre pacientes e controles, ou seja, em ambos os casos houve a formação de agregados (p = 0,2 e p = 0,4, respectivamente). Em relação aos leucócitos, o SFLLRN, estimulou o receptor independentemente do seu estado, íntegro ou clivado, nos pacientes (p < 0,05), enquanto que nos indivíduos normais, a resposta só foi observada quando o receptor íntegro foi estimulado por trombina (p < 0,05). Tanto nos pacientes estudados, como nos controles, a estimulação do PAR-1 plaquetário, promoveu aumento da expressão de selectina-P na superfície plaquetária (p < 0,0001), embora não houvesse diferença entre os grupos (p = 0,9). Estes resultados demonstram que as plaquetas dos pacientes não são refratárias à liberação de seu conteúdo granular, e encontram-se aptas a responder aos estímulos tanto quanto as plaquetas dos controles. Este estudo reforça a importância da terapia antiplaquetária em pacientes com hipertensão arterial pulmonar. / Pulmonary hypertension is a clinical and hemodynamic syndrome, characterized by the increase of vascular resistance in lungs, generally through various mechanisms, involving vasoconstriction and remodeling of the arterial wall. Endothelial dysfunction in pulmonary arterial hypertension leads to a prothrombotic status, in which platelet participation seems to be unequivocal. Thrombin is the most potent platelet activator and exerts its effects on cells, through protease-activated receptors. Flow cytometry procedure was employed to assess (1) platelet protease-activated receptor 1 (PAR-1) expression, in both uncleaved and cleaved forms, (2) PAR-1 activity, through platelet-leukocyte and platelet-monocyte aggregates formation in response to the thrombin receptor stimulus, and finally (3) platelet P-selectin expression after stimulus. Thirty patients with pulmonary arterial hypertension (age 11 to 78 years) under treatment at the Heart Institute, University of São Paulo were enrolled. The systolic pulmonary arterial pressure was 89+29 mmHg. The platelet count was < 150x103/l in 30% of the patients, and the hematocrit level was > 50% in 40% of the patients. In the present study, there was no relevant difference in the level of intact platelet protease-activated receptor 1 expression in patients and controls (p = 0.2). On the other hand, the expression of cleaved receptors was decreased in patients (p = 0.01) platelets, what suggests internalization. There was no difference on platelet-leukocyte, and platelet-monocyte aggregates in response to the thrombin receptor stimulus between patients and controls, in other words, in both cases there was the aggregates formation (p = 0.2). However, aggregates formation in patients appeared to occur predominately in response to an agent (SFLLRN) capable to stimulate the receptor, independent of its state, intact or cleaved (p < 0.05). Otherwise, in healthy individuals, the response occurred especially when the intact receptor was stimulated by thrombin (p < 0.05). In these patients, similarly to the controls, platelet protease-activated receptor 1 stimulation induced membrane P-selectin expression (p < 0.001), although there was no difference between the groups (p = 0.9). These findings suggest that platelets from patients are not refractory to its granular content secretion and are capable to respond to stimulus as the controls platelets. This study re-enforce the importance of anti platelet therapy in pulmonary arterial hypertension patients.

In systemic sclerosis (SSc), interstitial lung disease (ILD) and engagement of the vascular system lead to increased morbidity and mortality. The aim of this thesis was to elucidate, in a consecutively included cohort of SSc (limited and diffuse) patients (n = 33), the T cell cytokine profile driving the disease in ILD and to explore the role of matrix metalloproteinase 9 (MMP-9) and its inhibitor: tissue inhibitor of metalloproteinase 1 (TIMP-1) in the extracellular matrix (ECM) degrading process leading to fibrous scarring and honey combing. Moreover, to characterize the role of nitric oxide (NO) in vascular engagement. Peripheral arterial changes cause Raynaud’s phenomenon and digital ulcers. Nitric oxide (NO) a main inducer of vasodilation is produced by endothelial nitric oxide synthase (eNOS) in response to changes in blood flow or by inflammatory cytokine inducible (i) NOS. In the vascular smooth muscle cell (VSMC) NO activates guanylate cyclase to produce cGMP, causing relaxation. We showed elevated plasma nitrate, a degradation product of NO, and increased urinary excretion of nitrate and cGMP. Plasma nitrate correlated with elevated levels of endothelial adhesion molecules: endothelial (E) selectin and vascular adhesion molecule 1, indicating that the activated endothelium is the site of NO synthesis by iNOS. Endothelial staining for E-selectin and the finding of iNOS and eNOS in SSc skin biopsies supported this notion. In SSc increased vascular stiffness may limit the NO vasodilatory effects. We found normal endothelium-dependent (i.e. flow mediated (FMD%)) and endothelium-independent (i.e. nitroglycerin-induced (NTG%)) vasodilation in the brachial artery. Radial arterial wall stiffness measured as maximum increase in pulse pressure (dP/dtmax) was increased. FMD% and especially NTG% correlated negatively and dP/dtmax positively to measures of endothelial inflammation: plasma- nitrate and adhesion molecule levels. Thus inflammatory vascular wall changes may interfere with dilation as may the presence of nitrate tolerance. We found elevated alveolar MMP-9 in both its pro- and active form in ILD. The levels correlated to decline in lung capacity, pointing at a causal relation. We suggest that neutrophils secrete MMP-9, which may degrade collagen IV, (the main constituent of basal membranes), collagen V, gelatins, proteoglycans and elastin. MMP-9 activity is partly regulated by the binding of pro- and active form to TIMP-1. Alveolar TIMP-1, which even stimulates fibroblast ECM synthesis, was increased independent of ILD. The inflammatory process in ILD is orchestrated by activated T helper (h) lymphocytes. We found a mixed Th1/Th2 reaction in SSc alveolar T cells expressing messenger for interferon gamma (Th1), IL-6 and IL-10 (both Th2). No particular cytokine mRNA profile distinguished alveolar T cells in ILD. Neutrophils invaded the bronchial epithelium, which seemed otherwise inert as levels of inflammatory cytokine sensitive transcription factors and their nuclear translocation tended to be low. The neutrophil recruitment pathway is uncertain as chemoattractants and endothelial adhesion molecules were normally expressed. In conclusion, MMP-9 probably causes degradation of lung tissue in ILD and may represent a future therapeutic target. Alveolar T cells show a mixed Th1/Th2 cytokine profile independent of ILD. Neutrophils invade the bronchial epithelium. Activated endothelium produces increased amounts of NO and adhesion molecules and the level of activation influences brachial arterial FMD% and NTG% and radial arterial compliance. Nitrate tolerance may be present.

Cell adhesion plays an important role in inflammation and immunological responses. Adhesion molecules (e.g., selectins and integrins) are key modulators in mediating these cellular responses, such as leukocyte trafficking under shear stress. In this thesis, we use a bio-membrane force probe (BFP) to study force regulation on kinetics and conformations of selectin and LFA-1 integrin. A new BFP was built up, and a new assay, using thermal fluctuation of the BFP, was developed and used to monitoring selectins and their ligands association and dissociations. The new BFP was also used to investigate the force and force history dependence of selectin-ligand interactions. We found tri-phasic transition of force-dependent off-rates and force-history dependence of selectin/ligaind interactions. The BFP was also used to characterize force-dependent lifetimes of the LFA-1-ICAM-1 interaction. We found that LFA-1/ICAM-1 bonds behaved as catch bond and that LFA-1-ICAM-1's catch bonds were abolished blocking the downward movement of αA domain α7 helix. Finally, the BFP was applied to dynamically probe the global conformational changes of LFA-1 and to characterize force-regulated transitions among different conformational states on a living cell. We observed dynamic transitions of LFA-1 between extended and bent conformations on living cells. The observed average distance change of LFA-1's extensions was about 18nm, while that of the bending was only about 14nm. We also found that forces could facilitate extension but they slow down the bending of LFA-1. The observed transition time of extension was less than 0.1s, while that of contraction was longer than 0.2s. Our observations here are the first in-situ evidence to demonstrate how integrins dynamically transit different conformations and how force regulates these transitions.

Les Cellules Endothéliales Progénitrices ("Endothelial Progenitor Cells", EPCs) sont des précurseurs endothéliaux qui jouent un rôle émergeant en biologie vasculaire. Les EPCs ont été localisées dans le cordon ombilical, la moelle osseuse, le sang périphérique et dans certains tissus régénérateurs. Les interactions des EPCs avec les cellules sanguines et vasculaires peuvent largement influencer leurs propriétés biologiques et dicter leur fonctionnement pendant la réparation endothéliale. Plus spécifiquement, les interactions des EPCs avec les plaquettes circulantes induisent leur migration, leur recrutement et leur différentiation en cellules endothéliales aux sites de lésions vasculaires. Cependant, l’impact d’une telle interaction sur la fonction plaquettaire n’a pas été recherché. Le but de mon projet était de :1) générer des EPCs à partir des cellules mononucléaires du sang humain périphérique ("Peripheral Blood Mononuclear Cells", PBMCs); 2) étudier les interactions adhésives entre les EPCs et les plaquettes; 3) déterminer leur impact sur la fonction plaquettaire et la formation du thrombus et 4) décrire le mécanisme d’action des EPCs sur les plaquettes et le thrombus. Mises en culture sur une surface de fibronectine dans un milieu conditionné, les PBMCs fraîchement isolées possédaient une morphologie ronde et une petite taille. Après cinq jours, les PBMCs adhérentes donnaient naissance à des colonies, puis formaient une monocouche de cellules aplaties caractéristiques des EPCs après dix jours de culture. Les EPCs différenciées étaient positives pour l’Ulex-lectine et l’Acétyle des lipoprotéines de faible densité ("Acetylated Low Density Lipoprotein", Ac-LDL), exprimaient les marqueurs progéniteurs (CD34, P-sélectine, VEGFR2, vWF et VE-Cadhérine) tandis que les marqueurs leucocytaires (CD14, PSGL-1 et L-sélectine) étaient absents. Ces EPCs interagissaient avec les plaquettes activées par un mécanisme dépendant de la P-sélectine plaquettaire, inhibaient l’activation et l’agrégation plaquettaire et réduisaient significativement l’adhésion plaquettaire, principalement par l’action de prostacycline (PGI2). En fait, ceci était associé avec une augmentation de l’expression de la cyclooxygénase-2 (COX-2) et du monoxyde d’azote (NO) synthéthase inductible (iNOS). Toutefois, les effets inhibiteurs des EPCs sur la fonction plaquettaire ont été renversés par une inhibition de la COX et non pas du NO. Bien que les EPCs fussent en mesure de lier les plaquettes via la P-sélectine, leurs effets prédominants étaient médiés essentiellement par une sécrétion paracrine, impliquant la PGI2. Néanmoins, un rapprochement étroit ou un bref contact entre les EPCs et les plaquettes était requis pour que cette fonction soit complètement réalisée. D’ailleurs, cet aspect a été investigué chez des souris déficientes en P-sélectine (P-sel-/-) et chez leurs congénères de phénotype sauvage (Wild Type, WT). Chez les souris WT, les EPCs inhibaient l’agrégation plaquettaire dans le sang complet de manière concentration-dépendante alors que dans les souris P-sel-/-, l’action des EPCs n’avait pas d’effet significatif. De plus, en utilisant un modèle murin de thrombose artérielle, nous avons démontré que l’infusion systémique des EPCs altéraient la formation du thrombus et réduisaient significativement sa masse chez les souris WT, mais non pas chez les souris P-sel-/-. En outre, le nombre des EPCs incorporées au niveau du thrombus et de la paroi vasculaire était visiblement réduit chez les P-sel-/- par rapport aux souris WT. Dans cette étude, nous sommes parvenus à différentier adéquatement des EPCs à partir des PBMCs, nous avons étudié les interactions adhésives entre les EPCs et les plaquettes, et nous avons décrit leur impact sur la fonction plaquettaire et la formation du thrombus. De plus, nous avons identifié la PGI2 comme étant le principal facteur soluble sécrété par les EPCs en culture et responsable de leurs effets inhibiteurs sur l’activation, l’adhésion et l’agrégation plaquettaire in vitro. De surcroît, nous avons élucidé le mécanisme d’action des EPCs sur l’agrégation plaquettaire et la formation du thrombus, in vivo, et nous avons souligné le rôle de la P-sélectine plaquettaire dans ce processus. Ces résultats ajoutent de nouvelles connaissances sur la biologie des EPCs et définissent leur rôle potentiel dans la régulation de la fonction plaquettaire et la thrombogenèse. / Endothelial Progenitor Cells (EPCs) are believed to contribute to vascular biology and endothelial repair. EPCs have been isolated from umbilical cord, bone marrow, peripheral blood and in some regenerative tissues. Interactions of EPCs with vascular and blood cells can largely influence their functional properties and predict their destiny in the target tissues. More specifically, interactions of EPCs with circulating platelets provide the critical signal to ensure their migration and homing at the sites of vascular injury and their differentiation into endothelial cells. However, the functional consequences of such interactions on platelets remain unknown. Accordingly, this project was designed to investigate the impact of EPCs on platelet function and the specific objectives of this study were to: 1) generate EPCs from human peripheral blood mononuclear cells (PBMCs); 2) characterize the adhesive interactions between EPCs and platelets; 3) determine their impact on platelet function and thrombus formation and 4) elucidate the mechanistic action of EPCs on platelets and thrombus. Cultured on fibronectin in conditioned media, PBMCs differentiated, within ten days of culture, into EPCs, which were positive for Ulex-lectin and Ac-LDL (Acetylated Low Density Lipoprotein), and expressed progenitor markers (CD34, VEGFR2, vWF, and VE-Cadherin). These EPCs bind activated platelets through P-selectin-dependent mechanism, inhibited platelet activation, aggregation and adhesion, mainly via prostacyclin (PGI2) secretion. Indeed, this was associated with up-regulation of cyclooxygenase-2 (COX-2) and inducible nitric oxide (NO) synthase (iNOS). However, the effects on platelets were reversed by COX, but not by NO inhibition. Although EPCs bound platelets via platelet P-selectin, their predominant effects occurred via a paracrine secretion, implying PGI2. Nevertheless, a transitory link or brief contact between EPCs and platelets was required for this function to be fully realized. This was further depicted using a murine arterial thrombosis model in P-selectin deficient mice (P sel-/-) and their wild-type counterparts (WT). EPCs significantly impaired, in a concentration dependent-manner, collagen-induced whole blood platelet aggregation in WT mice; whereas in P-sel-/- mice, EPCs had no significant effect. Moreover, in murin model of arterial thrombosis, infusion of EPCs altered thrombus formation and significantly reduced the mass of thrombi generated in WT, but not in P-sel-/- mice. Furthermore, the number of EPCs recruited within the thrombi and along the vascular wall was visually reduced in P-sel-/- mice as compared to WT mice. In this project, we succeeded in adequately differentiating EPCs from PBMCs, we characterized the adhesive interaction between EPCs and platelets, and we addressed the impact of EPCs on platelet function and thrombus formation. Moreover, we identified PGI2 as the principal soluble factor secreted by cultured EPCs and responsible of their inhibitory effects on platelet function in vitro. In addition, using a murine model of arterial carotid injury in WT and P-sel-/- mice, we elucidate the mechanistic action of EPCs on platelet aggregation and thrombus formation, in vivo, and we highlighted the role of platelet P-selectin in this process. These findings add new insights into the biology of EPCs and reveal a potential role for EPCs in regulating platelet function, which in turn may limit thrombogenesis and maintain hemostasis at the sites of vascular injury.

Cette thèse rapporte l’étude des propriétés physicochimiques des nanoparticles polymériques et leur impact sur l’interaction avec les cellules vivantes. Nous nous sommes tout spécialement attachés à étudier l’effet des propriétés adhésives et mécaniques des nanoparticules sur leur capacité de pénétration de la membrane cellulaire. Pour ce faire, nous avons tout d’abord utilisé des nanoparticules d’acide polylactique (PLA) fonctionnalisées en surface avec un ligand des sélectines E et P. Le greffage du ligand sur la particule s’est fait par une nouvelle méthode expérimentale garantissant la présence du ligand à la surface de la particule durant toute sa durée de vie. Cette méthode consiste à mélanger un polymère fonctionnalisé avec le ligand avec un autre polymère non fonctionnalisé. La présence du ligand à la surface des nanoparticules formées à partir de ce mélange de polymères a été confirmée par analyse ToF SIMS. Nous avons pu prouver que les particules possédant le ligand greffé à leur surface démontraient une capacité adhésive supérieure à leurs homologues non fonctionnalisés sur des cellules endothéliales HUVEC activées par différentes drogues. De plus, le captage des particules par les cellules HUVEC est modulé par le niveau d’expression des récepteurs selectine E et P et aussi par la quantité de ligand libre. Ces résultats montrent clairement que le greffage du ligand confère aux particules des propriétés adhésives accrues et spécifiques ce qui permet leur usage postérieure comme vecteur pharmaceutique capable de cibler un récepteur particulier à la surface d’une cellule. Nous avons aussi démontré que l’interaction entre les nanoparticules et la membrane cellulaire peut aussi être contrôlée aussi bien par les propriétés mécaniques de la cellule que de la nanoparticule. Dans une première étape, nous avons mesuré à l’aide de l’appareil de forces de surface l’élasticité de cellules macrophagiques déposées sur différents substrats. En contrôlant l’interaction entre la cellule et le substrat sur lequel elle repose nous avons montré qu’il était possible de modifier à ii volonté les propriétés mécaniques cellulaire. Une augmentation de l’élasticité cellulaire s’accompagne d’une augmentation systématique de l’internalisation de nanoparticules de PLA non fonctionnalisées. Ceci suggère un rôle prépondérant des propriétés mécaniques du cortex cellulaire dans le captage des nanoparticules de PLA. Dans une seconde étape, nous avons étudié l’effet des propriétés mécaniques des nanoparticules sur leur capacité de pénétration cellulaire. Pour ce faire, nous avons synthétisé des particules d’hydrogel dont l’élasticité était contrôlée par le degré d’agent réticulant inclus dans leur formulation. Le contrôle des propriétés mécaniques des nanoparticules a été confirmé par la mesure du module de Young des particules par microscopie de force atomique. L’impact des propriétés mécaniques de ces particules sur leur capacité de pénétration dans les cellules vivantes a été étudié sur des cellules macrophagiques de souris. Les résultats ont montré que la cinétique d’internalisation, la quantité de particules internalisées et le mécanisme d’internalisation dépendent tous du module de Young des nanoparticules. Aucune différence dans le trajet intracellulaire des particules n’a pu être observée malgré le fait que différentes voies d’internalisation aient été observées. Ce dernier résultat peut s’expliquer par le fait que les nanoparticules sont internalisées par plusieurs voie simultanément ce qui facilite leur accumulation dans les organelles digestives intracellulaires. Un modèle simple permettant d’expliquer ces résultats a été proposé et discuté. / This thesis reports the study of physical chemical properties of polymeric nanoparticles and their impact on the interaction with living cells. In particular we endeavoured to study the effect of the adhesive and mechanical properties of the vector on its capacity of penetration of the cellular membrane. With this intention, we firstly used nanoparticules of polylactic acid (PLA) functionalized on their surfaces with a ligand of the selectines E and P receptor. The grafting of the ligand on the particle’s surface was carried out thanks to a new experimental method guaranteeing the presence of the active molecule on the surface of the particle during its whole life cycle. This method consists in mixing a polymer functionalized with the ligand with another polymer not functionalized. The presence of the ligand on the surface of the nanoparticules formed starting from this mixture of polymers was confirmed by ToF SIMS analysis. We could show that the particles having the ligand grafted on their surface exhibit a higher adhesive capacity than their non-functionalized counterpart on endothelial cells HUVEC activated by various drugs. Nanoparticles adhesion on cells membrane was modulated by the level of expression of the receptors selectine E and P and also by the quantity of free ligand. These results show clearly that the functionalized particles possess all the characteristics of a pharmaceutical vector capable of targeting a particular receptor on a cell surface. The interaction between nanoparticules and cellular membrane can also be controlled by the mechanical properties of the cell as well as of the nanoparticule. To demonstrate it we have measured the elasticity of macrophagic cells deposited on various substrates using the SFA. We have thus showed that it was possible to control the cell mechanical properties at will by controlling the interaction between the cell and the substrate on which it rests. An increase of the cell elasticity is accompanied by an increase of the internalization of non-functionalized PLA nanoparticules. This suggests a major role of cytocortical mechanical properties in the capture of hard PLA particles. iv Lastly, we studied the effect of the mechanical properties of the nanoparticules on their cellular penetration capacity. With this intention, we synthesized hydrogel particles whose elasticity was controlled by the degree of crosslinking agent included in their formulation. The control of the mechanical properties of the nanoparticules was confirmed by the measurement of the Young modulus of the particles by AFM. The interaction of these particles with macrophagess showed that the mechanical properties of the particles affect various aspects related to the internalization of the nanoparticles. The internalization kinetics, the quantity of internalized particles and the mechanism of internalization depend all on the Young modulus of the nanoparticules. No differences in the intracellular pathway could be observed in spite of the fact that various pathways of internalization were observed for these nanoparticules. This last result can be explained by the fact that the nanoparticules are internalized by several mechanisms of simultaneously which facilitates their accumulation in intracellular digestive organelles. A simple model explaining these results is proposed and discussed.

We examined the effect of cyclosporin A, tacrolimus, sirolimus and everolimus on the cell growth, viability, proliferation, expression of cellular adhesion molecules (CAM) and leukocyte (PBMC) binding of human macrovascular (coronary artery, saphenous vein) and microvascular endothelial cells (EC). Tacrolimus did not affect EC integrity, growth or expression of CAM. Exclusively, EC from the coronary arteries showed a reduced cellular growth (about 30%) under cyclosporin A and tacrolimus treatment. In contrast, treatment with mTOR inhibitors reduced EC proliferative activity by about 40%, independently of the EC origin. No induction of apoptosis (caspase-3/7 activity) or cytotoxicity (MTS test) was observed. Long-term treatment with high concentrations of sirolimus and everolimus did not enhance the expression of CAM. Stimulation with tumor necrosis factor significantly increased the expression of CAM, independently of the drugs used. None of the mTOR inhibitors influenced the tumor necrosis factor-induced expression of CAM, whereas adhesion of PBMC increased significantly, as described by other papers. In summary, neither calcineurin inhibitors nor mTOR inhibitors activate human micro- and macrovascular EC. Therefore, the investigated drugs are unlikely to contribute to EC activation during transplant-associated vasculopathy. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

A hipertensão arterial pulmonar é uma síndrome clínica e hemodinâmica, caracterizada pelo aumento de resistência vascular na microcirculação. A vasoconstrição presente na doença ocorre principalmente devido à disfunção endotelial, induzindo a um estado pró-trombótico onde a participação das plaquetas é inequívoca. A trombina, principal agonista da ativação plaquetária, exerce seus efeitos nas células por meio de receptores ativados por proteases. Através da citometria de fluxo, este trabalho teve por objetivo analisar (1) a expressão do receptor ativado por protease do tipo 1 (PAR-1) na membrana de plaquetas, em seu estado íntegro ou clivado, (2) a atividade, mediante a formação de agregados entre plaquetas e leucócitos e, plaquetas e monócitos após estímulo de receptores ativados por proteases, além (3) da expressão de selectina-P na membrana plaquetária após estimulação. Foram estudados 30 pacientes portadores de hipertensão arterial pulmonar sob tratamento ambulatorial no Instituto do Coração da Faculdade de Medicina da Universidade de São Paulo. A idade destes pacientes variou de 11 a 78 anos, e a média da pressão sistólica da artéria pulmonar foi de 89+29 mmHg. Em 30% dos pacientes, o número de plaquetas esteve abaixo de 150x103/l, e em 40%, o nível do hematócrito apresentou-se acima de 50%. No presente estudo, não foi observada diferença significante na expressão do PAR-1 íntegro em plaquetas de pacientes comparativamente aos controles (p = 0,2). Em contrapartida, as plaquetas dos pacientes apresentaram menor quantidade de receptor clivado (p = 0,01), sugerindo internalização destes receptores. Com relação à avaliação da atividade de PAR-1 através da formação de agregados entre plaquetas e leucócitos e, plaquetas e monócitos após estimulação por agentes capazes de atuar sobre o receptor de trombina, não foram observadas diferenças entre pacientes e controles, ou seja, em ambos os casos houve a formação de agregados (p = 0,2 e p = 0,4, respectivamente). Em relação aos leucócitos, o SFLLRN, estimulou o receptor independentemente do seu estado, íntegro ou clivado, nos pacientes (p < 0,05), enquanto que nos indivíduos normais, a resposta só foi observada quando o receptor íntegro foi estimulado por trombina (p < 0,05). Tanto nos pacientes estudados, como nos controles, a estimulação do PAR-1 plaquetário, promoveu aumento da expressão de selectina-P na superfície plaquetária (p < 0,0001), embora não houvesse diferença entre os grupos (p = 0,9). Estes resultados demonstram que as plaquetas dos pacientes não são refratárias à liberação de seu conteúdo granular, e encontram-se aptas a responder aos estímulos tanto quanto as plaquetas dos controles. Este estudo reforça a importância da terapia antiplaquetária em pacientes com hipertensão arterial pulmonar. / Pulmonary hypertension is a clinical and hemodynamic syndrome, characterized by the increase of vascular resistance in lungs, generally through various mechanisms, involving vasoconstriction and remodeling of the arterial wall. Endothelial dysfunction in pulmonary arterial hypertension leads to a prothrombotic status, in which platelet participation seems to be unequivocal. Thrombin is the most potent platelet activator and exerts its effects on cells, through protease-activated receptors. Flow cytometry procedure was employed to assess (1) platelet protease-activated receptor 1 (PAR-1) expression, in both uncleaved and cleaved forms, (2) PAR-1 activity, through platelet-leukocyte and platelet-monocyte aggregates formation in response to the thrombin receptor stimulus, and finally (3) platelet P-selectin expression after stimulus. Thirty patients with pulmonary arterial hypertension (age 11 to 78 years) under treatment at the Heart Institute, University of São Paulo were enrolled. The systolic pulmonary arterial pressure was 89+29 mmHg. The platelet count was < 150x103/l in 30% of the patients, and the hematocrit level was > 50% in 40% of the patients. In the present study, there was no relevant difference in the level of intact platelet protease-activated receptor 1 expression in patients and controls (p = 0.2). On the other hand, the expression of cleaved receptors was decreased in patients (p = 0.01) platelets, what suggests internalization. There was no difference on platelet-leukocyte, and platelet-monocyte aggregates in response to the thrombin receptor stimulus between patients and controls, in other words, in both cases there was the aggregates formation (p = 0.2). However, aggregates formation in patients appeared to occur predominately in response to an agent (SFLLRN) capable to stimulate the receptor, independent of its state, intact or cleaved (p < 0.05). Otherwise, in healthy individuals, the response occurred especially when the intact receptor was stimulated by thrombin (p < 0.05). In these patients, similarly to the controls, platelet protease-activated receptor 1 stimulation induced membrane P-selectin expression (p < 0.001), although there was no difference between the groups (p = 0.9). These findings suggest that platelets from patients are not refractory to its granular content secretion and are capable to respond to stimulus as the controls platelets. This study re-enforce the importance of anti platelet therapy in pulmonary arterial hypertension patients.