Implication de la voie de signalisation Src/Stat3 dans l'étiologie de l'hypertension artérielle pulmonaire

Tableau d'honneur de la Faculté des études supérieures et postdoctorales, 2011-2012L’hypertension artérielle pulmonaire (PAH) est une vasculopathie obstructive caractérisée par une oblitération du lumen des artères pulmonaires distales et une augmentation des résistances vasculaires menant à une augmentation des pressions pulmonaires (PAP) et une hypertrophie ventriculaire droite (RVH) compensatrice. Aucun médicament n’est capable à ce jour de stopper le processus, et lorsque l’hypertrophie compensatrice devient insuffisante, le ventricule droit (RV) se dilate et défaille. A l’origine de ce processus se trouve une hyper-prolifération, une résistance à l’apoptose et une augmentation de la motilité des cellules musculaires lisses vasculaires de l’artère pulmonaire (PASMCs), les rendant « pseudo-malignes ». Le laboratoire a précédemment démontré que le facteur de transcription NFAT (Nuclear factor of activated T-cells) est en partie impliqué dans ces désordres cellulaires en provoquant une augmentation des concentrations calciques intracellulaires et stimulant la prolifération ; et une hyperpolarisation du potentiel de membrane mitochondriale (ΔΨm) inhibant ainsi l’apoptose dépendante des mitochondries. Dans le chapitre 2 nous avons démontré pour la première fois dans le réseau vasculaire pulmonaire que le facteur de transcription STAT3 (Signal transducer and activator of transcription 3) est activé et impliqué de façon directe dans la régulation de l’expression de NFAT et de façon indirecte dans son activation via l’oncoprotéine serine/thréonine kinase Pim1 (Provirus integration site for Murine Moloney leukemia virus). L’inhibition de Pim1 in vitro et in vivo (modèle de rat injecté à la monocrotaline) est associée à une diminution de l’activité de NFATc2 et à un retour à un phénotype normal. De plus, les souris déficientes pour le gène Pim1 sont résistantes à une induction de la PAH par hypoxie ou monocrotaline. De plus nous avons démontré que l’expression de Pim1 corrèle avec la sévérité de la maladie dans le modèle expérimental et le modèle humain. Nous avons donc souligné l’intérêt de Pim1 comme cible thérapeutique et outil de diagnostic. Dans le chapitre 3, nous avons mis en évidence l’implication de la plateforme signalétique c-Src (sarcoma Schmidt-Ruppin A-2 viral oncogene homolog)/FAK (Focal adhesion kinase) dans la régulation du phénotype « pseudo malin » en partie par activation de STAT3. L’inhibition de FAK in vitro diminue la prolifération des cellules pathologiques, augmente leur sensibilité a l’apoptose et réduit leur motilité. In vivo, l’inhibition de FAK réduit les pressions pulmonaires et le remodelage vasculaire faisant de FAK une cible thérapeutique intéressante. Dans le chapitre 4 nous proposons finalement une autre option thérapeutique par l’utilisation de la dehydroepiandrosterone. Cette hormone naturelle a précédemment été remarquée comme bénéfique dans le traitement de l’hypertension artérielle pulmonaire de par ses propriétés vasodilatatrices. Nous avons montré ici qu’en inhibant STAT3 la DHEA possède également des propriétés antiprolifératives et que son utilisation clinique est prometteuse. Durant mes travaux de doctorat, j’ai pu donc mettre en évidence l’implication majeure de l’axe Src/FAK/STAT3/Pim1 dans la pathogénèse de l’hypertension artérielle pulmonaire. J’ai pu proposer diverses solutions thérapeutiques qui pourraient apporter de nouvelles issues cliniques plus ou moins rapidement.Pulmonary arterial hypertension (PAH) is an obstructive vasculopathy characterized by distal pulmonary arteries lumen obliteration and increased vascular resistances, leading to a rise in pulmonary arterial pressure (PAP) and a compensatory right ventricular hypertrophy. Currently available therapies do not permit to reverse the established process and when the hypertrophy become insufficient, the right ventricle dilates and fails. This phenomenon is due to enhanced proliferation, survival and motility of pulmonary artery smooth muscle cells (PASMCs), which acquire a pseudo malignant phenotype. Our group previously described that the transcription factor NFAT (Nuclear factor of activated T-cells) is involved in these cellular disorders by increasing intracellular calcium level and enhancing proliferation; and by hyperpolarizing the mitochondrial membrane potential and decreasing mitochondrial-dependant apoptosis. In the Chapter 2, we demonstrated for the first time in the pulmonary vasculature, that STAT3 (Signal transducer and activator of transcription 3) regulates directly NFATc2 expression and indirectly NFATc2 activity via the oncoprotein serine/threonine kinase Pim1 (Provirus integration site for Murine Moloney leukemia virus). In vitro and in vivo Pim1 inhibition (in the monocrotaline rat model) is associated with decreased NFATc2 activity and reversion of the malignant phenotype. Moreover, Pim1 deficient mice are resistant to monocrotaline or hypoxia-induced PAH. Finally, we demonstrated that Pim1 expression correlates with disease progression both in animal and human model. Thus, we underlined Pim1 as a potent therapeutic target and an interesting diagnosis tool. In the chapter 3, we showed that the signaling hub c-Src (sarcoma Schmidt-Ruppin A-2 viral oncogene homolog)/FAK (Focal adhesion kinase) is implicated in the regulation of the PASMCs pseudo malignant phenotype, in part by activating STAT3. FAK inhibition in vitro decreases PASMCs proliferation, survival and motility. In vivo, FAK inhibition is associated with decreased PAP and decreased vascular remodeling, making FAK as an interesting therapeutic target. In the chapter 4, we suggest dehydroepiandrosterone (DHEA) as another therapeutical option. This natural hormone is known to be beneficial in PAH through their vasodilating properties. We showed here that by inhibiting STAT3 activation, DHEA also has anti-proliferating properties. Therefore, clinical use of DHEA for PAH can be promising. During my PhD studies, I showed the critical implication of the Src/FAK/STAT3/Pim1 in PAH pathogenesis. I contributed to increase the knowledge on PAH pathogenesis and suggested some therapeutical solutions that can be useful to improve patient outcome

Pim-1 : a new biomarker in pulmonary arterial hypertension

Provirus integration site for Moloney murine leukemia virus (Pim-1) is an oncoprotein overexpressed in lungs from pulmonary arterial hypertension (PAH) patients and involved in cell proliferation via the activation of the NFAT/STAT3 signaling pathway. We hypothesized that Pim-1 plasma levels would predict the presence of PAH and correlate with disease severity. Pim-1 plasma levels were measured at the time of catheterization in 49 PAH patients, including nonvasoreactive (n = 19) and vasoreactive idiopathic PAH (n = 5), and PAH related to connective tissue disease (n = 16) and congenital heart disease (n = 9). Fifty controls were also recruited. The capacity of Pim-1 to discriminate PAH from controls and its association with disease severity were assessed. Pim-1 plasma levels were higher in PAH than in controls (9.6 ± 4.0 vs. 7.2 ± 2.4 ng/mL, P < 0.01). Pim-1 appropriately discriminated proliferative PAH from controls (AUC = 0.78 to 0.94 using ROC curves). Among PAH patients, Pim-1 correlated with traditional markers of PAH severity. The 1-year survival was 97% and 47% for PAH patients with baseline Pim-1 levels lower and higher than 11.1 ng/mL, respectively (HR 11.4 (3.3–39.7); P <0.01). After adjustment for hemodynamic and biochemical variables, Pim-1 levels remained an independent predictor of mortality (P < 0.01). Pim-1 is a promising new biomarker in PAH

Role for miR-204 in human pulmonary arterial hypertension

Reduced miR-204 expression facilitates the excessive proliferation and apoptosis resistance of pulmonary artery smooth muscle cells characteristic of human pulmonary arterial hypertension

DNA Damage and Pulmonary Hypertension

Pulmonary hypertension (PH) is defined by a mean pulmonary arterial pressure over 25 mmHg at rest and is diagnosed by right heart catheterization. Among the different groups of PH, pulmonary arterial hypertension (PAH) is characterized by a progressive obstruction of distal pulmonary arteries, related to endothelial cell dysfunction and vascular cell proliferation, which leads to an increased pulmonary vascular resistance, right ventricular hypertrophy, and right heart failure. Although the primary trigger of PAH remains unknown, oxidative stress and inflammation have been shown to play a key role in the development and progression of vascular remodeling. These factors are known to increase DNA damage that might favor the emergence of the proliferative and apoptosis-resistant phenotype observed in PAH vascular cells. High levels of DNA damage were reported to occur in PAH lungs and remodeled arteries as well as in animal models of PH. Moreover, recent studies have demonstrated that impaired DNA-response mechanisms may lead to an increased mutagen sensitivity in PAH patients. Finally, PAH was linked with decreased breast cancer 1 protein (BRCA1) and DNA topoisomerase 2-binding protein 1 (TopBP1) expression, both involved in maintaining genome integrity. This review aims to provide an overview of recent evidence of DNA damage and DNA repair deficiency and their implication in PAH pathogenesis

Pim-1: A New Biomarker in Pulmonary Arterial Hypertension

Provirus integration site for Moloney murine leukemia virus (Pim-1) is an oncoprotein overexpressed in lungs from pulmonary arterial hypertension (PAH) patients and involved in cell proliferation via the activation of the NFAT/STAT3 signaling pathway. We hypothesized that Pim-1 plasma levels would predict the presence of PAH and correlate with disease severity. Pim-1 plasma levels were measured at the time of catheterization in 49 PAH patients, including nonvasoreactive ( n = 19) and vasoreactive idiopathic PAH (n = 5), and PAH related to connective tissue disease (n = 16) and congenital heart disease (n = 9). Fifty controls were also recruited. The capacity of Pim-1 to discriminate PAH from controls and its association with disease severity were assessed. Pim-1 plasma levels were higher in PAH than in controls (9.6 ± 4.0 vs. 7.2 ± 2.4 ng/mL, P < 0.01). Pim-1 appropriately discriminated proliferative PAH from controls (AUC = 0.78 to 0.94 using ROC curves). Among PAH patients, Pim-1 correlated with traditional markers of PAH severity. The 1-year survival was 97% and 47% for PAH patients with baseline Pim-1 levels lower and higher than 11.1 ng/mL, respectively (HR 11.4 (3.3-39.7); P < 0.01). After adjustment for hemodynamic and biochemical variables, Pim-1 levels remained an independent predictor of mortality (P < 0.01). Pim-1 is a promising new biomarker in PAH

Krüppel-like Factor 5 contributes to pulmonary artery smooth muscle proliferation and resistance to apoptosis in human pulmonary arterial hypertension

Background Pulmonary arterial hypertension (PAH) is a vascular remodeling disease characterized by enhanced proliferation of pulmonary artery smooth muscle cell (PASMC) and suppressed apoptosis. This phenotype has been associated with the upregulation of the oncoprotein survivin promoting mitochondrial membrane potential hyperpolarization (decreasing apoptosis) and the upregulation of growth factor and cytokines like PDGF, IL-6 and vasoactive agent like endothelin-1 (ET-1) promoting PASMC proliferation. Krüppel-like factor 5 (KLF5), is a zinc-finger-type transcription factor implicated in the regulation of cell differentiation, proliferation, migration and apoptosis. Recent studies have demonstrated the implication of KLF5 in tissue remodeling in cardiovascular diseases, such as atherosclerosis, restenosis, and cardiac hypertrophy. Nonetheless, the implication of KLF5 in pulmonary arterial hypertension (PAH) remains unknown. We hypothesized that KLF5 up-regulation in PAH triggers PASMC proliferation and resistance to apoptosis. Methods and results We showed that KFL5 is upregulated in both human lung biopsies and cultured human PASMC isolated from distal pulmonary arteries from PAH patients compared to controls. Using stimulation experiments, we demonstrated that PDGF, ET-1 and IL-6 trigger KLF-5 activation in control PASMC to a level similar to the one seen in PAH-PASMC. Inhibition of the STAT3 pathway abrogates KLF5 activation in PAH-PASMC. Once activated, KLF5 promotes cyclin B1 upregulation and promotes PASMC proliferation and triggers survivin expression hyperpolarizing mitochondria membrane potential decreasing PASMC ability to undergo apoptosis. Conclusion We demonstrated for the first time that KLF5 is activated in human PAH and implicated in the pro-proliferative and anti-apoptotic phenotype that characterize PAH-PASMC. We believe that our findings will open new avenues of investigation on the role of KLF5 in PAH and might lead to the identification of new therapeutic targets.</p

Effect of fatty acids on human bone marrow mesenchymal stem cell energy metabolism and survival.

Successful stem cell therapy requires the optimal proliferation, engraftment, and differentiation of stem cells into the desired cell lineage of tissues. However, stem cell therapy clinical trials to date have had limited success, suggesting that a better understanding of stem cell biology is needed. This includes a better understanding of stem cell energy metabolism because of the importance of energy metabolism in stem cell proliferation and differentiation. We report here the first direct evidence that human bone marrow mesenchymal stem cell (BMMSC) energy metabolism is highly glycolytic with low rates of mitochondrial oxidative metabolism. The contribution of glycolysis to ATP production is greater than 97% in undifferentiated BMMSCs, while glucose and fatty acid oxidation combined only contribute 3% of ATP production. We also assessed the effect of physiological levels of fatty acids on human BMMSC survival and energy metabolism. We found that the saturated fatty acid palmitate induces BMMSC apoptosis and decreases proliferation, an effect prevented by the unsaturated fatty acid oleate. Interestingly, chronic exposure of human BMMSCs to physiological levels of palmitate (for 24 hr) reduces palmitate oxidation rates. This decrease in palmitate oxidation is prevented by chronic exposure of the BMMSCs to oleate. These results suggest that reducing saturated fatty acid oxidation can decrease human BMMSC proliferation and cause cell death. These results also suggest that saturated fatty acids may be involved in the long-term impairment of BMMSC survival in vivo