Les cellules souches embryonnaires : Du développement myocardique à la médecine régénératrice

Les cellules souches embryonnaires (ES) pluripotentes offrent un modèle de développement précoce du myocarde et apportent de nouveaux espoirs de thérapie cellulaire des maladies dégénératives. Les potentialités cardiogéniques des cellules ES permettent une recherche cognitive sur les réseaux transcriptionnels activés par les morphogènes et qui gouvernent la différenciation cellulaire cardiaque. Bien que les cellules ES humaines soient, comme les cellules de souris, isolées à partir du stade blastocyste de l’embryon, des différences dans le développement embryonnaire des deux espèces entraînent des phénotypes cellulaires et des propriétés spécifiques à chaque espèce. Les enjeux actuels sont donc de comprendre les mécanismes moléculaires des processus de spécification et de différenciation cardiaque des cellules ES humaines afin d’accroître leur potentiel cardiogénique. Ce but atteint, ces cellules permettront l’étude du développement cardiaque précoce, nécessaire à une meilleure compréhension des maladies cardiaques congénitales et ouvriront les perspectives de thérapie régénératrice du myocarde.Embryonic stem cells are capable to recapitulate the first stages of myocardial development. Using mouse embryonic stem cells, transcriptional networks specifying the cardiac fate can be delineated. Furthermore, using members of the TGFβ superfamily to commit mouse ES cells toward a cardiac lineage, recent studies showed that ESC-derived cardiomyocytes were capable to repair post-infarcted myocardium of small and large animals. The next challenges are to validate such results using human ESCs in order to better comprehend cardiac congenital diseases and to foresee a cell therapy of heart failure

"I6 passages: on the reproduction of a human embryonic stem cell line from Israel to France".

The first French clinical trial using human embryonic stem cells for regenerative purposes was launched in 2014, using the I6 stem cell line that was imported from Israel. From Israel to France, national reproductive policies and practices inform how basic scientists produce, manage and circulate cells across countries. Building on an interdisciplinary co-production involving two social scientists and a life scientist, this article suggests that biobanks passage cells from in vitro fertilization to stem cell science and from country to country by modifying their reproductive meaning. Four passages are described: the absence of cells in 2005 when the research started in France; the presence of supernumerary embryos available for research in Israeli IVF biobanks; the production of the I6 stem cell bank in Israel; the importation and laboratory biobanking of the cells in France. Human embryonic stem cell lines can never be completely disentangled from reproduction.Wellcome Trust Grant no. 100606 H2020 Marie Skłodowska-Curie Actions Fondation Fysse

Calreticulin reveals a critical Ca2+ checkpoint in cardiac myofibrillogenesis

Calreticulin (crt) is an ubiquitously expressed and multifunctional Ca2+-binding protein that regulates diverse vital cell functions, including Ca2+ storage in the ER and protein folding. Calreticulin deficiency in mice is lethal in utero due to defects in heart development and function. Herein, we used crt−/− embryonic stem (ES) cells differentiated in vitro into cardiac cells to investigate the molecular mechanisms underlying heart failure of knockout embryos. After 8 d of differentiation, beating areas were prominent in ES-derived wild-type (wt) embryoid bodies (EBs), but not in ES-derived crt−/− EBs, despite normal expression levels of cardiac transcription factors. Crt−/− EBs exhibited a severe decrease in expression and a lack of phosphorylation of ventricular myosin light chain 2 (MLC2v), resulting in an impaired organization of myofibrils. Crt−/− phenotype could be recreated in wt cells by chelating extracellular or cytoplasmic Ca2+ with EGTA or BAPTA, or by inhibiting Ca2+/calmodulin-dependent kinases (CaMKs). An imposed ionomycin-triggered cystolic-free Ca2+ concentration ([Ca2+]c) elevation restored the expression, phosphorylation, and insertion of MLC2v into sarcomeric structures and in turn the myofibrillogenesis. The transcription factor myocyte enhancer factor C2 failed to accumulate into nuclei of crt−/− cardiac cells in the absence of ionomycin-triggered [Ca2+]c increase. We conclude that the absence of calreticulin interferes with myofibril formation. Most importantly, calreticulin deficiency revealed the importance of a Ca2+-dependent checkpoint critical for early events during cardiac myofibrillogenesis

Interplay of Oct4 with Sox2 and Sox17: a molecular switch from stem cell pluripotency to specifying a cardiac fate

Embryonic stem cell pluripotency, once achieved, triggers a switch in promoter affinity for Oct4, which leads to cardiogenesis

Human pre-valvular endocardial cells derived from pluripotent stem cells recapitulate cardiac pathophysiological valvulogenesis

Genetically modified mice have advanced our understanding of valve development and disease. Yet, human pathophysiological valvulogenesis remains poorly understood. Here we report that, by combining single cell sequencing and in vivo approaches, a population of human pre-valvular endocardial cells (HPVCs) can be derived from pluripotent stem cells. HPVCs express gene patterns conforming to the E9.0 mouse atrio-ventricular canal (AVC) endocardium signature. HPVCs treated with BMP2, cultured on mouse AVC cushions, or transplanted into the AVC of embryonic mouse hearts, undergo endothelial-to-mesenchymal transition and express markers of valve interstitial cells of different valvular layers, demonstrating cell specificity. Extending this model to patient-specific induced pluripotent stem cells recapitulates features of mitral valve prolapse and identified dysregulation of the SHH pathway. Concurrently increased ECM secretion can be rescued by SHH inhibition, thus providing a putative therapeutic target. In summary, we report a human cell model of valvulogenesis that faithfully recapitulates valve disease in a dish.We thank the Leducq Fondation for supporting Tui Neri, and funding this research under the framework of the MITRAL network and for generously awarding us for the equipment of our cell imaging facility in the frame of their program “Equipement de Recherche et Plateformes Technologiques” (ERPT to M.P.), the Genopole at Evry and the Fondation de la recherche Medicale (grant DEQ20100318280) for supporting the laboratory of Michel Puceat. Part of this work in South Carolina University was conducted in a facility constructed with support from the National Institutes of Health, Grant Number C06 RR018823 from the Extramural Research Facilities Program of the National Center for Research Resources. Other funding sources: National Heart Lung and Blood Institute: RO1-HL33756 (R.R.M.), COBRE P20RR016434–07 (R.R.M., R.A. N.), P20RR016434–09S1 (R.R.M. and R.A.N.); American Heart Association: 11SDG5270006 (R.A.N.); National Science Foundation: EPS-0902795 (R.R.M. and R.A. N.); American Heart Association: 10SDG2630130 (A.C.Z.), NIH: P01HD032573 (A.C. Z.), NIH: U54 HL108460 (A.C.Z), NCATS: UL1TR000100 (A.C.Z.); EH was supported by a fellowship of the Ministere de la recherche et de l’éducation in France.TM-M was supported by a fellowship from the Fondation Foulon Delalande and the Leducq Foundation. P.v.V. was sponsored by a UC San Diego Cardiovascular Scholarship Award and a Postdoctoral Fellowship from the California Institute for Regenerative Medicine (CIRM) Interdisciplinary Stem Cell Training Program II. S.M.E. was funded by a grant from the National Heart, Lung, and Blood Institute (HL-117649). A.T. is supported by the National Heart, Lung, and Blood Institute (R01-HL134664).S

Cellules souches pluripotentes : un modèle cellulaire de développement cardiaque précoce

Les cellules souches embryonnaires murines dérivées il y a trois décennies ont permis la transgenèse et la génération de souris génétiquement modifiées. Ces animaux et d’autres organismes plus primitifs, dans le passé comme encore aujourd’hui, ont permis l’étude des premières décisions cellulaires dans l’embryon. La dérivation de lignées de cellules souches embryonnaires humaines a apporté un modèle de développement dans un contexte où l’éthique n’autorise pas l’utilisation d’embryon. Il est alors devenu possible d’étudier les mécanismes génétiques et épigénétiques de ces décisions cellulaires humaines. Cette synthèse prend l’exemple de la cardiogénèse, un des premiers évènements cellulaires au cours de l’embryogenèse et montre l’apport des cellules souches dans la biologie du développement cardiaque humain