Cardiomyocyte proliferation, a target for cardiac regeneration

International audienceCardiac diseases, characterized by cardiomyocyte loss, lead to dramatic impairment of cardiac function and ultimately to congestive heart failure. Despite significant advances, conventional treatments do not correct the defects in cardiac muscle cell numbers and the prognosis of congestive heart failure remains poor. The existence, in adult mammalian heart, of low but detectable cardiomyocyte proliferative capacities has shifted the target of regenerative therapy toward new therapeutical strategy. Indeed, the stimulation of terminally differentiated cardiomyocyte proliferation represents the main therapeutic approach for heart regeneration. Increasing evidence demonstrating that the loss of mammalian cardiomyocyte renewal potential shortly after birth causes the loss of regenerative capacities, strongly support the hypothesis that a detailed understanding of the molecular mechanisms controlling fetal and postnatal cardiomyocyte proliferation is essential to identify targets for cardiac regeneration. Here, we will review major developmental mechanisms regulating fetal cardiomyocyte proliferation and will describetheimpactofthedevelopmentalswitch,operatingatbirthanddrivingpostnatalheartmaturation,ontheregulationofadultcardiomyocyteproliferation,all these mechanisms representing potential targets for cardiac repair and regeneration

Hes1 Is Expressed in the Second Heart Field and Is Required for Outflow Tract Development

Background: Rapid growth of the embryonic heart occurs by addition of progenitor cells of the second heart field to the poles of the elongating heart tube. Failure or perturbation of this process leads to congenital heart defects. In order to provide further insight into second heart field development we characterized the insertion site of a transgene expressed in the second heart field and outflow tract as the result of an integration site position effect. Results: Here we show that the integration site of the A17-Myf5-nlacZ-T55 transgene lies upstream of Hes1, encoding a basic helix-loop-helix containing transcriptional repressor required for the maintenance of diverse progenitor cell populations during embryonic development. Transgene expression in a subset of Hes1 expression sites, including the CNS, pharyngeal epithelia, pericardium, limb bud and lung endoderm suggests that Hes1 is the endogenous target of regulatory elements trapped by the transgene. Hes1 is expressed in pharyngeal endoderm and mesoderm including the second heart field. Analysis of Hes1 mutant hearts at embryonic day 15.5 reveals outflow tract alignment defects including ventricular septal defects and overriding aorta. At earlier developmental stages, Hes1 mutant embryos display defects in second heart field proliferation, a reduction in cardiac neural crest cells and failure to completely extend the outflow tract. Conclusions: Hes1 is expressed in cardiac progenitor cells in the early embryo and is required for development of the arteria

A transposable element into the human long noncoding RNA CARMEN is a switch for cardiac precursor cell specification.

AIMS The major cardiac cell types composing the adult heart arise from common multipotent precursor cells. Cardiac lineage decisions are guided by extrinsic and cell-autonomous factors, including recently discovered long noncoding RNAs (lncRNAs). The human lncRNA CARMEN, which is known to dictate specification towards the cardiomyocyte (CM) and the smooth muscle cell (SMC) fates, generates a diversity of alternatively spliced isoforms. METHODS AND RESULTS The CARMEN locus can be manipulated to direct human primary cardiac precursor cells (CPCs) into specific cardiovascular fates. Investigating CARMEN isoform usage in differentiating CPCs represents therefore a unique opportunity to uncover isoform-specific function in lncRNAs. Here, we identify one CARMEN isoform, CARMEN-201, to be crucial for SMC commitment. CARMEN-201 activity is encoded within an alternatively-spliced exon containing a MIRc short interspersed nuclear element. This element binds the transcriptional repressor REST (RE1 Silencing Transcription Factor), targets it to cardiogenic loci, including ISL1, IRX1, IRX5, and SFRP1, and thereby blocks the CM gene program. In turn, genes regulating SMC differentiation are induced. CONCLUSIONS These data show how a critical physiological switch is wired by alternative splicing and functional transposable elements in a long noncoding RNA. They further demonstrated the crucial importance of the lncRNA isoform CARMEN-201 in SMC specification during heart development

Régénération cardiaque : les leçons du développement

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Signaling pathways controling second heart field development

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FGF10 Signaling in Heart Development, Homeostasis, Disease and Repair

International audienceEssential muscular organ that provides the whole body with oxygen and nutrients, the heart is the first organ to function during embryonic development. Cardiovascular diseases, including acquired and congenital heart defects, are the leading cause of mortality in industrialized countries. Fibroblast Growth Factors (FGFs) are involved in a variety of cellular responses including proliferation, differentiation, and migration. Among the 22 human/mouse FGFs, the secreted FGF10 ligand through the binding of its specific receptors (FGFR1b and FGFR2b) and subsequent activation of downstream signaling is known to play essential role in cardiac development, homeostasis and disease. FGF10 is one of the major marker of the early cardiac progenitor cells and a crucial regulator of differentiated cardiomyocyte proliferation in the developing embryo. Increasing evidence support the hypothesis that a detailed understanding of developmental processes is essential to identify targets for cardiac repair and regeneration. Indeed the activation of resident cardiomyocyte proliferation together with the injection of cardiac progenitors represent the most promising therapeutical strategies for cardiac regenerative medicine. The recent findings showing that FGF10 promotes adult cardiomyocyte cell cycle reentry and directs stem cell differentiation and cell reprogramming toward the cardiogenic lineage provide new insights into therapeutical strategies for cardiac regeneration and repair

THE OLD AND NEW FACES OF CYCLIC AMP - Lessons from cAMP compartmentation in isolated cardiac myocytes

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Interhelical interaction and receptor phosphorylation regulate activation kinetics of different human beta1-adrenoceptor variants

International audienceG protein-coupled receptors represent the largest class of drug targets, but genetic variation within G protein-coupled receptors leads to variable drug responses and, thereby, compromises their therapeutic application. One of the most intensely studied examples is a hyperfunctional variant of the human β1-adrenoceptor that carries an arginine at position 389 in helix 8 (Arg-389-ADRB1). However, the mechanism underlying the higher efficacy of the Arg-389 variant remained unclear to date. Despite its hyperfunctionality, we found the Arg-389 variant of ADRB1 to be hyperphosphorylated upon continuous stimulation with norepinephrine compared with the Gly-389 variant. Using ADRB1 sensors to monitor activation kinetics by fluorescence resonance energy transfer, Arg-389-ADRB1 exerted faster activation speed and arrestin recruitment than the Gly-389 variant. Both activation speed and arrestin recruitment depended on phosphorylation of the receptor, as shown by knockdown of G protein-coupled receptor kinases and phosphorylation-deficient ADRB1 mutants. Structural modeling of the human β1-adrenoceptor suggested interaction of the side chain of Arg-389 with opposing amino acid residues in helix 1. Site-directed mutagenesis of Lys-85 and Thr-86 in helix 1 revealed that this interaction indeed determined ADRB1 activation kinetics. Taken together, these findings indicate that differences in interhelical interaction regulate the different activation speed and efficacy of ADRB1 variants

By promoting cardiac regeneration FGF10 preserves cardiac remodeling and function after myocardial infarction

5th Congress of the ESC-Council-on-Basic-Cardiovascular-Science on Frontiers in Cardio Vascular Biology, Vienna, AUSTRIA, APR 20-22, 2018International audienc

PPARγ and NOTCH Regulate Regional Identity in the Murine Cardiac Outflow Tract

International audienceBackground: The arterial pole of the heart is a hotspot for life-threatening forms of congenital heart defects (CHDs). Development of this cardiac region occurs by addition of Second Heart Field (SHF) progenitor cells to the embryonic outflow tract (OFT) and subsequently the base of the ascending aorta and pulmonary trunk. Understanding the cellular and genetic mechanisms driving arterial pole morphogenesis is essential to provide further insights into the cause of CHDs. Methods: A synergistic combination of bioinformatic analysis and mouse genetics as well as embryo and explant culture experiments were used to dissect the cross-regulatory transcriptional circuitry operating in future subaortic and subpulmonary OFT myocardium. Results: Here, we show that the lipid sensor PPARγ (peroxisome proliferator–activated receptor gamma) is expressed in future subpulmonary myocardium in the inferior wall of the OFT and that PPARγ signaling-related genes display regionalized OFT expression regulated by the transcription factor TBX1 (T-box transcription factor 1). Modulating PPARγ activity in ex vivo cultured embryos treated with a PPARγ agonist or antagonist or deleting Pparγ in cardiac progenitor cells using Mesp1-Cre reveals that Pparγ is required for addition of future subpulmonary myocardium and normal arterial pole development. Additionally, the non-canonical DLK1 (delta-like noncanonical Notch ligand 1)/NOTCH (Notch receptor 1)/HES1 (Hes family bHLH transcription factor 1) pathway negatively regulates Ppar γ in future subaortic myocardium in the superior OFT wall. Conclusions: Together these results identify Pparγ as a regulator of regional transcriptional identity in the developing heart, providing new insights into gene interactions involved in congenital heart defects