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Congenital heart malformations often include mitral valve defects which remain largely unexplained. During embryogenesis, a restricted population of endocardial cells within the atrioventricular canal (AVC) undergoes endothelial to mesenchymal transition (EndMT) to give rise to mitral valvular cells. However, the identity, fate decisions of these progenitors as well as the distribution of their derivatives in valve leaflets remain unknown.Here, we use scRNA-seq of genetically labeled mouse AVC endocardial cells and of micro-dissected embryonic and postnatal mitral valves to characterize the developmental road. We uncovered the genetic, cell signaling and metabolic processes underlying specification of the progenitors and how they contribute to subtypes of endothelial and interstitial embryonic and postnatal valvular cells. Using clonal genetic tracing with multicolor reporter, we describe specific modes of growth of endocardial cell-derived clones which build up in a proper manner functional valve leaflets.Our data reveal how both genetic and metabolic specification mechanisms specifically drive the fate of a subset of endocardial cells toward valve progenitors and their distinct clonal contribution to the formation of the valve.

Cornelia de Lange is a rare developmental disorder affecting the formation of many organs following a delay in developmental processes. The disease mainly caused by mutation of the cohesin loader NIPBL is left without any therapeutic strategy. Besides, a short body size and neurological defects, more than half of CdL children feature various cardiac malformations.To mimic the cardiac defects and test a therapeutic preventive strategy, we generated a C57Bl/6 nipbl+/- mouse model of the disease. These mice featured a severe delay in embryonic and postnatal growth.The nipbl-deficient embryonic and neonatal hearts developed ventricular hypertrophy, aortic and valve defects associated with a persistent truncus arteriosus and a ventricular septal defect. The adult hearts then featured a severe aortic senescence phenotype and a stenosis resulting in an increase in aortic flux velocity and persistent left ventricular hypertrophy. Using proteomics and RNA-sequencing in embryos, we identified a dysregulated TGFβ pathway in the outflow tract of embryonic hearts as well as the presence of senescent cells as early as in E13.5 nipbl+/- embryonic hearts. Treatment of pregnant nipbl+/- mice with a TGβR (ALK5) inhibitor from E9.5 to E13.5 rescued the cardiac phenotype as well as the body size of mice at birth.Altogether our data revealed that an exacerbated TFGβ pathway associated with cell senescence is at the origin of many defects in a CdL mouse model. This druggable pathway opens the path toward a potential preventive therapeutic strategy for CdL patients.

Description, Cell reprogramming is at the origin of valve calcification., Cell plasticity plays a key role in embryos by maintaining the differentiation potential of progenitors. Whether postnatal somatic cells revert to an embryonic-like naïve state regaining plasticity and redifferentiate into a cell type leading to a disease remains intriguing. Using genetic lineage tracing and single-cell RNA sequencing, we reveal that Oct4 is induced by nuclear factor κB (NFκB) at embyronic day 9.5 in a subset of mouse endocardial cells originating from the anterior heart forming field at the onset of endocardial-to-mesenchymal transition. These cells acquired a chondro-osteogenic fate. OCT4 in adult valvular aortic cells leads to calcification of mouse and human valves. These calcifying cells originate from the Oct4 embryonic lineage. Genetic deletion of Pou5f1 (Pit-Oct-Unc, OCT4) in the endocardial cell lineage prevents aortic stenosis and calcification of ApoE−/− mouse valve. We established previously unidentified self-cell reprogramming NFκB- and OCT4-mediated inflammatory pathway triggering a dose-dependent mechanism of valve calcification.

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Preservation and development of life depend on the adequate segregation of sister chromatids during mitosis and meiosis. This process is ensured by the cohesin multi-subunit complex. Mutations in this complex have been associated with an increasing number of diseases, termed cohesinopathies. The best characterized cohesinopathy is Cornelia de Lange syndrome (CdLS), in which intellectual and growth retardations are the main phenotypic manifestations. Despite some overlap, the clinical manifestations of cohesinopathies vary considerably. Novel roles of the cohesin complex have emerged during the past decades, suggesting that important cell cycle regulators exert important biological effects through non-cohesion-related functions and broadening the potential pathomechanisms involved in cohesinopathies. This review focuses on non-cohesion-related functions of the cohesin complex, gene dosage effect, epigenetic regulation and TGF-β in cohesinopathy context, especially in comparison to Chronic Atrial and Intestinal Dysrhythmia (CAID) syndrome, a very distinct cohesinopathy caused by a homozygous Shugoshin-1 (SGO1) mutation (K23E) and characterized by pacemaker failure in both heart (sick sinus syndrome followed by atrial flutter) and gut (chronic intestinal pseudo-obstruction) with no intellectual or growth delay. We discuss the possible impact of SGO1 alterations in human pathologies and the potential impact of the SGO1 K23E mutation in the sinus node and gut development and functions. We suggest that the human phenotypes observed in CdLS, CAID syndrome and other cohesinopathies can inform future studies into the less well-known non-cohesion-related functions of cohesin complex genes. Abbreviations: AD: Alzheimer Disease; AFF4: AF4/FMR2 Family Member 4; ANKRD11: Ankyrin Repeat Domain 11; APC: Anaphase Promoter Complex; ASD: Atrial Septal Defect; ATRX: ATRX Chromatin Remodeler; ATRX: Alpha Thalassemia X-linked intellectual disability syndrome; BIRC5: Baculoviral IAP Repeat Containing 5; BMP: Bone Morphogenetic Protein; BRD4: Bromodomain Containing 4; BUB1: BUB1 Mitotic Checkpoint Serine/Threonine Kinase; CAID: Chronic Atrial and Intestinal Dysrhythmia; CDK1: Cyclin Dependent Kinase 1; CdLS: Cornelia de Lange Syndrome; CHD: Congenital Heart Disease; CHOPS: Cognitive impairment, coarse facies, Heart defects, Obesity, Pulmonary involvement, Short stature, and skeletal dysplasia; CIPO: Chronic Intestinal Pseudo-Obstruction; c-kit: KIT Proto-Oncogene Receptor Tyrosine Kinase; CoATs: Cohesin Acetyltransferases; CTCF: CCCTC-Binding Factor; DDX11: DEAD/H-Box Helicase 11; ERG: Transcriptional Regulator ERG; ESCO2: Establishment of Sister Chromatid Cohesion N-Acetyltransferase 2; GJC1: Gap Junction Protein Gamma 1; H2A: Histone H2A; H3K4: Histone H3 Lysine 4; H3K9: Histone H3 Lysine 9; HCN4: Hyperpolarization Activated Cyclic Nucleotide Gated Potassium and Sodium Channel 4;p HDAC8: Histone deacetylases 8; HP1: Heterochromatin Protein 1; ICC: Interstitial Cells of Cajal; ICC-MP: Myenteric Plexus Interstitial cells of Cajal; ICC-DMP: Deep Muscular Plexus Interstitial cells of Cajal; I(f): Pacemaker Funny Current; IP3: Inositol trisphosphate; JNK: C-Jun N-Terminal Kinase; LDS: Loeys-Dietz Syndrome; LOAD: Late-Onset Alzheimer Disease; MAPK: Mitogen-Activated Protein Kinase; MAU: MAU Sister Chromatid Cohesion Factor; MFS: Marfan Syndrome; NIPBL: NIPBL, Cohesin Loading Factor; OCT4: Octamer-Binding Protein 4; P38: P38 MAP Kinase; PDA: Patent Ductus Arteriosus; PDS5: PDS5 Cohesin Associated Factor; P-H3: Phospho Histone H3; PLK1: Polo Like Kinase 1; POPDC1: Popeye Domain Containing 1; POPDC2: Popeye Domain Containing 2; PP2A: Protein Phosphatase 2; RAD21: RAD21 Cohesin Complex Component; RBS: Roberts Syndrome; REC8: REC8 Meiotic Recombination Protein; RNAP2: RNA polymerase II; SAN: Sinoatrial node; SCN5A: Sodium Voltage-Gated Channel Alpha Subunit 5; SEC: Super Elongation Complex; SGO1: Shogoshin-1; SMAD: SMAD Family Member; SMC1A: Structural Maintenance of Chromosomes 1A; SMC3: Structural Maintenance of Chromosomes 3; SNV: Single Nucleotide Variant; SOX2: SRY-Box 2; SOX17: SRY-Box 17; SSS: Sick Sinus Syndrome; STAG2: Cohesin Subunit SA-2; TADs: Topology Associated Domains; TBX: T-box transcription factors; TGF-β: Transforming Growth Factor β; TGFBR: Transforming Growth Factor β receptor; TOF: Tetralogy of Fallot; TREK1: TREK-1 K(+) Channel Subunit; VSD: Ventricular Septal Defect; WABS: Warsaw Breakage Syndrome; WAPL: WAPL Cohesin Release Factor.

International audience; BackgroundGATA1 is an essential transcription factor for both polyploidization and megakaryocyte (MK) differentiation. The polyploidization defect observed in GATA1 variant carriers is not well understood.ObjectiveTo extensively phenotype two pedigrees displaying different variants in the GATA1 gene and determine if GATA1 controls MYH10 expression levels, a key modulator of MK polyploidization.MethodA total of 146 unrelated propositi with constitutional thrombocytopenia were screened on a multigene panel. We described the genotype-phenotype correlation in GATA1 variant carriers and investigated the effect of these novel variants on MYH10 transcription using luciferase constructs.ResultsThe clinical profile associated with the p.L268M variant localized in the C terminal zinc finger was unusual in that the patient displayed bleeding and severe platelet aggregation defects without early-onset thrombocytopenia. p.N206I localized in the N terminal zinc finger was associated, on the other hand, with severe thrombocytopenia (15G/L) in early life. High MYH10 levels were evidenced in platelets of GATA1 variant carriers. Analysis of MKs anti-GATA1 chromatin immunoprecipitation-sequencing data revealed two GATA1 binding sites, located in the 3′ untranslated region and in intron 8 of the MYH10 gene. Luciferase reporter assays showed their respective role in the regulation of MYH10 gene expression. Both GATA1 variants significantly alter intron 8 driven MYH10 transcription.ConclusionThe discovery of an association between MYH10 and GATA1 is a novel one. Overall, this study suggests that impaired MYH10 silencing via an intronic regulatory element is the most likely cause of GATA1-related polyploidization defect.

Right ventricular (RV) failure is a major concern in grown-up congenital heart diseases. Cell-based myocardial repair may be an innovative approach to restore overloaded RV function. A repaired Tetralogy of Fallot pig model was used. After 5 months, cell therapy was surgically administrated using human embryonic stem cell-derived Nkx2.5+ cardiac progenitor cell-seeded collagen patch. A large patch containing 107 cells was engineered to cover the whole RV free wall and applied on the epicardium of 4 pigs (treated group). A control group (n = 4) received a cell-free patch (3) or no patch (1). Myocardial function was assessed by echocardiography using standard and strain parameters before and 2 months after cell graft. The fate of progenitors was tracked using human-and cardiac specific antibodies. Indexed RV diameter and telediastolic RV area significantly decreased in treated group whereas increased in control. The free wall thickness significantly increased in treated group compared to control. In the treated group, RV free wall strain significantly improved by contrast to control (respectively from −13.4 to −15.9% vs. −18.9 to −12.9%, P Fig. 1 ). Although still immature, some cells featured TnT+ actinin+ sarcomeric units. Proliferating small Ki-67+ TnT+ labelled pig myocytes were observed. Expression of collagen genes col1a3, col3a1 monitored in real-Time QPCR reflecting myocardial fibrosis status significantly decreased in the treated group. Human cardiac progenitors migrated and differentiated, contributing together with triggered endogenous mechanism of repair to maintain the RV adaptation to overload and to improve free wall contractility. They also induced a proliferation of host cells supporting potential paracrine effects.

International audience; LMNA mutations in patients are responsible for a dilated cardiomyopathy. Molecular mechanisms underlying the origin and development of the pathology are unknown. Herein, using mouse pluripotent embryonic stem cells (ESCs) and a mouse model both harboring the p.H222P Lmna mutation, we found early defects in cardiac differentiation of mutated ESCs and dilatation of mutated embryonic hearts at E13.5, pointing to a developmental origin of the disease. Using mouse ESCs, we demonstrated that cardiac differentiation of Lmna(H222P/+) was impaired at the mesodermal stage. Expression of Mesp1, a mesodermal cardiogenic gene involved in epithelial-to-mesenchymal transition of epiblast cells, as well as Snail and Twist expression, was decreased in Lmna(H222P/+) cells compared with WT cells in the course of differentiation. In turn, cardiomyocyte differentiation was impaired. ChIP assay of H3K4me1 in differentiating cells revealed a specific decrease of this histone mark on regulatory regions of Mespl and Twist in Lmna(H222P/+) cells. Downregulation or inhibition of LSD1 that specifically demethylated H3K4me1 rescued the epigenetic landscape of mesodermal Lmna(H222P/+) cells and in turn contraction of cardiomyocytes. Inhibition of LSD1 in pregnant mice or neonatal mice prevented cardiomyopathy in E13.5 Lmna(H222P/H222P) offspring and adults, respectively. Thus, LSD1 appeared to be a therapeutic target to prevent or cure dilated cardiomyopathy associated with a laminopathy.

The origins of congenital heart diseases, the most common congenital diseases are still largely unknown. Environmental factors are now emerging as major causes of these diseases. Vitamin D deficiency has become a public health burden, notably for childbearing age, pregnant and breastfeeding women. Since maternal 25-hydroxyvitamin D (25(OH)D) determined fetal and neonatal 25(OH)D status, foetuses exposed to insufficient levels of vitamin D, may feature developmental defects.Herein, we investigated the effects of maternal vitamin D deficiency on cardiovascular defects in early and later life of offsprings in two generations as well as the molecular mechanisms underlying vitamin D effect.Eight weeks before and during pregnancy, C57BL/6JRj female mice received a sufficient or vitamin D deficient diet ((1.0 IU/g in control vs 0.0 IU/g in Vitamin D Deficient (VDD) group). E16.5 Embryos of maternal VDD diet featured hypertrophic heart revealed by a thicker left ventricular (LV) wall and septum. RNAseq analysis of LV revealed 1555 transcripts differentially expressed in the VDD group and among them cardiac transcription factors and constitutive cardiac genes (tbx5, gata4, myl2). Anti-Vitamin D receptor (VDR) Chip-seq from chromatin of E16.5 LV uncovered different targeting of tbx5 and tbx3 loci by VDR in the VDD vs control embryos. Anti-CTCF ChIP-loop experiments focusing on the Tbx3 and Tbx5 loci uncovered a change in the Topology Associated Domains associated with these loci.Echocardiography of 2-months-old VDD offspring revealed a significantly thicker left ventricle and increased fractional shortening while 6-months-old mice featured cardiac decompensation and in turn failing LV.Maternal vitamin D deficiency severely affects heart formation following a change in chromatin conformation on cardiac gene loci and impacts function of adult hearts in two generations. These defects are likely to be at the origin of cardiovascular diseases in the adulthood.

The genome is organized in 3D topology-associated domains to ensure proper gene transcriptional processes. The chromosome conformation capture (3C) is an affordable method to investigate local chromatin structure and dynamics in cells and tissue. Herein I describe an easy to design and a cost-effective protocol.

The genome is organized in 3D topology-associated domains to ensure proper gene transcriptional processes. The chromosome conformation capture (3C) is an affordable method to investigate local chromatin structure and dynamics in cells and tissue. Herein I describe an easy to design and a cost-effective protocol.

MotivationSingle-cell RNA-sequencing (scRNAseq) experiments are becoming a standard tool for bench-scientists to explore the cellular diversity present in all tissues. On one hand, the data produced by scRNASeq is technically complex, with analytical workflows that are still very much an active field of bioinformatics research, and on the other hand, a wealth of biological background knowledge is often needed to guide the investigation. Therefore, there is an increasing need to develop applications geared towards bench-scientists to help them abstract the technical challenges of the analysis, so that they can focus on the Science at play. It is also expected that such applications should support closer collaboration between bioinformaticians and bench-scientists by providing reproducible science tools.ResultsWe present SCHNAPPs, a computer program designed to enable bench-scientists to autonomously explore and interpret single cell RNA-seq expression data and associated annotations. The Shiny-based application allows selecting genes and cells of interest, performing quality control, normalization, clustering, and differential expression analyses, applying standard workflows from Seurat (Stuart et al., 2019) or Scran (Lun et al., 2016) packages, and most of the common visualizations. An R-markdown report can be generated that tracks the modifications, and selected visualizations facilitating communication and reproducibility between bench-scientist and bioinformatician. The modular design of the tool allows to easily integrate new visualizations and analyses by bioinformaticians. We still recommend that a data analysis specialist oversees the analysis and interpretation.AvailabilityThe SCHNAPPs application, docker file, and documentation are available on GitHub: https://c3bi-pasteur-fr.github.io/UTechSCB-SCHNAPPs; Example contribution are available at the following GitHub site: https://github.com/baj12/SCHNAPPsContributions.

Summary: The formation of cardiac valves depends on mechanical forces exerted by blood flow. Endocardial cells lining the interior of the heart are sensitive to these stimuli and respond by rearranging into luminal cells subjected to shear stress and abluminal cells not exposed to it. The mechanisms by which endocardial cells sense these dynamic biomechanical stimuli and how they evoke different cellular responses are largely unknown. Here, we show that blood flow activates two parallel mechanosensitive pathways, one mediated by Notch and the other by Klf2a. Both pathways negatively regulate the angiogenesis receptor Vegfr3/Flt4, which becomes restricted to abluminal endocardial cells. Its loss disrupts valve morphogenesis and results in the occurrence of Notch signaling within abluminal endocardial cells. Our work explains how antagonistic activities by Vegfr3/Flt4 on the abluminal side and by Notch on the luminal side shape cardiac valve leaflets by triggering unique differences in the fates of endocardial cells.

International audience; In utero environment is crucial to ensure normal development of the fetus and to program metabolic health throughout the life. Beside macronutrients, the role of micronutrients, including vitamin D, begins to be explore. The aim of this study was to decipher the impact of maternal vitamin D deficiency (VDD), in normal and high‐fat (HF) diet context, on adipose tissue metabolism and energy homeostasis in offspring, considering sex‐specific responses. Body weight, energy expenditure, and spontaneous activity was differential impacted in juvenile male and female offspring born from VDD mice. In adulthood, a HF diet combined with maternal VDD disrupted glucose homeostasis and adiposity in male offspring but not in females. Such phenotypes were associated to different transcriptomic profiles in adipose tissue, which could be related to differential modulation of plasma 17β‐estradiol concentrations. Thus, maternal VDD sex‐dependently modulated metabolic fate of the offspring, especially when associated with HF diet in adulthood.

Context and objectives Fibro-fatty infiltrations of the sub-epicardium is an important component of the atrial cardiomyopathy that paves the way of atrial fibrillation (AF). We previously reported that epicardium-derived cells (EPDCs) can be a source of adipocytes contributing to fat depot. Here, we examined if EPDCs can contribute also to the fibrotic remodeling of atrial subepicardium. Methods Surgical samples of human right atria were used for histological study and to harvest EPDCs. Clinical and histological data were analyzed using generalized linear models. A model atrial remodeling associated with ischemic heart failure was created in rats and in a genetic lineage tracing WT1CreERT2+/−/Rosa-tdT+/− mice to follow epicardial progenitor fate. Primary cell culture models were used to study EPDC differentiation. Flow cytometry assays and single cell sequencing were used to characterize subpopulations of EPDCs. Results In human atria, epicardium could be a thin cell monolayer or be thick in continuity with dense fibro-fatty infiltrates. The latter aspect predominated in old patient (>70 year) with valve mitral diseases or in AF, clinical conditions associated with an atrial remodeling. This was further established in rat and mouse experimental model of atrial remodeling characterized by a thickening of the epicardium observed one week following the onset of the cardiopathy and, then, followed by a dense fibrotic remodeling of the subepicardium. Cells co-expressing markers of epicardial progenitors and fibroblasts were detected in the subepicardium of diseased atria both in human and murine models. Moreover, a number of myo/fibroblasts from WT1CreERT2+/−/Rosa-tdT+/− mice were detected in diseased atria attesting of their epicardial origin. Distinct EPDC clusters were detected from cells harvested from epicardium whereas only PDGFRa-positive cells could differentiated into fibroblasts. Angiotensin-II induced the differentiation of only PDGFRa-positive cells into fibroblasts. Conclusions Activation of the epicardium is an early event during atrial remodeling that results in the triggering of differentiation of a subpopulation of epicardial progenitors into fibroblasts. Angiotensin-II is part of the signaling switch than regulate the fate of EPDC between fibroblastic or adipogenic lineage. Hence, epicardium by regulating the balance between adipose expansion and fibrosis accumulation appears as an important determinant of the atrial cardiomyopathy. Acknowledgement/Funding ANR-10-IAHU-05

Pluripotent stem cells feature the capacity to differentiate into any somatic cell types including cardiomyocytes. We report a cost-effective and simple protocol for the differentiation of specific ventricular cardiomyocytes. These cells are elongated, do not spontaneously beat, and do not feature any Ca

Epicardium, the mesothelium covering the heart, is composed of multipotent cells and is reactivated following myocardial injury in adults. Herein, we provide evidence for activation of atrial epicardium in aged patients with diseased atria and in murine models of atrial remodeling. Epicardial activation contributed to fibro-fatty infiltration of sub-epicardium that contained a number of cells co-expressing markers of epicardial progenitors and fibroblasts. Indeed, using genetic lineage tracing of adult epicardium, we demonstrate the epicardial origin of fibroblasts within fibro-fatty infiltrates. A subpopulation of adult epicardial-derived cells (aEPDCs) expressing PDGFRα, niched in the sub-epicardium, were isolated and differentiated into myofibroblast in the presence of angiotensin-II. Furthermore, single cell RNA-seq analysis identified several clusters of aEPDCs and revealed transition from adipogenic to fibrogenic cells. In conclusion, a subset of aEPDCs, pre-programmed towards a specific cell fate, contributes to fibro-fatty infiltration of sub-epicardium of diseased atria.

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Pluripotent stem cells feature the capacity to differentiate into any somatic cell types including cardiomyocytes. We report a cost-effective and simple protocol for the differentiation of specific ventricular cardiomyocytes. These cells are elongated, do not spontaneously beat, and do not feature any Ca2+-transient, an index of their stage of maturation toward adult cardiac cells. They represent a suitable model to screen both the efficiency and toxicology of drugs.

During early cardiogenesis, progressive addition of distinct cardiac progenitor cells originating from the second heart field (SHF) contributes to elongation of the forming heart. Whereas the subdivision of the SHF into an anterior and posterior domain is essential for morphogenesis of the definitive heart, the transcriptional programs and upstream regulatory events operating in the different progenitor cell populations remain unclear. Here, we characterize the molecular signature and regulation of anterior and posterior sub-populations of SHF cells. We profiled the transcriptome and chromatin accessibility of purified sub-populations at genome-wide levels and demonstrated that the transcriptional regulator Hoxb1 controls the differentiation of the posterior SHF progenitors during heart morphogenesis. Spatial mis-expression of Hoxb1 in anterior SHF progenitors that normally contribute to right ventricular cardiomyocytes results in hypoplastic right ventricle, revealing how deregulation of a specific sub-population of the SHF can result in congenital heart defects. Expanded activation of Hoxb1 perturbs the anterior transcriptional program and induces increased progenitor cell death in anterior SHF progenitors. Moreover, activation of Hoxb1 in embryonic stem cells arrests cardiac differentiation, whereas Hoxb1-deficient embryos display premature differentiation of cardiac progenitor cells. Our results show that Hoxb1 coordinates a cascade of gene-regulatory events in the SHF essential for proper heart development and provide new insights into how deregulation of SHF sub-population identities can induce congenital heart defects.

International audience; Hyper-activation of extracellular signal-regulated kinase (ERK) 1/2 contributes to heart dysfunction in cardiomyopathy caused by mutations in the lamin A/C gene (LMNA cardiomyopathy). The mechanism of how this affects cardiac function is unknown. We show that active phosphorylated ERK1/2 directly binds to and catalyzes the phosphorylation of the actin depolymerizing factor cofilin-1 on Thr25. Cofilin-1 becomes active and disassembles actin filaments in a large array of cellular and animal models of LMNA cardiomyopathy. In vivo expression of cofilin-1, phosphorylated on Thr25 by endogenous ERK1/2 signaling, leads to alterations in left ventricular function and cardiac actin. These results demonstrate a novel role for cofilin-1 on actin dynamics in cardiac muscle and provide a rationale on how increased ERK1/2 signaling leads to LMNA cardiomyopathy.

The heart is the first organ to be functional in the fetus. Heart formation is a complex morphogenetic process regulated by both genetic and epigenetic mechanisms. Congenital heart diseases (CHD) are the most prominent congenital diseases. Genetics is not sufficient to explain these diseases or the impact of them on patients. Epigenetics is more and more emerging as a basis for cardiac malformations. This review brings the essential knowledge on cardiac biology of development. It further provides a broad background on epigenetics with a focus on three-dimensional conformation of chromatin. Then, we summarize the current knowledge of the impact of epigenetics on cardiac cell fate decision. We further provide an update on the epigenetic anomalies in the genesis of CHD.

Genetically modified mice have advanced our understanding of valve development and related pathologies. Yet, little is known regarding human valvulogenesis in health and diseases. Genuine humanin vitromodels that reproduce valvular (patho)biology are thus needed. We here developed a human pluripotent stem cell-derived model fit to decode the early steps of human valvulogenesis and to recapitulate valve disease traits in a dish.Using cellular based, single cell omics-informed andin vivo-validated approaches, we derived a population of pre-valvular endocardial cells from a pluripotent stem cell source. These human prevalvular cells (HPVCs) expressed gene patterns conforming to the atrio-ventricular canal (AVC) endocardium signature originally established in E9.0 mouse embryos. In fact, HPVC treated with BMP2, cultured onto mouse AVC cushions, or transplanted into the AVC of embryonic mouse hearts, underwent endothelial-to-mesenchymal transition and expressed markers of valve interstitial cells of different valvular layers demonstrating tissue functionality. HPVCs also differentiated into tendinous/chondrogenic cells in line with the valvular repertoire. Extending this valvulogenic model to patient specific iPS cells, we recapitulated features of mitral valve prolapse and uncovered that dysregulation of the SHH pathway is likely to be at the origin of the disease thus providing a putative therapeutic target.Human pluripotent stem cells recapitulate early valvulogenesis and provide a powerful model to systematically decipher the origin and lineage contribution of different valvular cell types in humans as well as to study valve diseases in a dish.

International audience; Mitral valve prolapse (MVP) is a common cardiac valve disease that affects nearly 1 in 40 individuals. It can manifest as mitral regurgitation and is the leading indication for mitral valve surgery. Despite a clear heritable component, the genetic aetiology leading to non-syndromic MVP has remained elusive. Four affected individuals from a large multigenerational family segregating non-syndromic MVP underwent capture sequencing of the linked interval on chromosome 11. We report a missense mutation in the DCHS1 gene, the human homologue of the Drosophila cell polarity gene dachsous (ds), that segregates with MVP in the family. Morpholino knockdown of the zebrafish homologue dachsous1b resulted in a cardiac atrioventricular canal defect that could be rescued by wild-type human DCHS1, but not by DCHS1 messenger RNA with the familial mutation. Further genetic studies identified two additional families in which a second deleterious DCHS1 mutation segregates with MVP. Both DCHS1 mutations reduce protein stability as demonstrated in zebrafish, cultured cells and, notably, in mitral valve interstitial cells (MVICs) obtained during mitral valve repair surgery of a proband. Dchs1(+/-) mice had prolapse of thickened mitral leaflets, which could be traced back to developmental errors in valve morphogenesis. DCHS1 deficiency in MVP patient MVICs, as well as in Dchs1(+/-) mouse MVICs, result in altered migration and cellular patterning, supporting these processes as aetiological underpinnings for the disease. Understanding the role of DCHS1 in mitral valve development and MVP pathogenesis holds potential for therapeutic insights for this very common disease.

Cardiac fibroblasts are a major cell population of the heart and are characterized by their capacity to produce extracellular matrix (ECM). In hearts subjected to pressure overload, excessive fibroblast accumulation is responsible for fibrosis of the myocardium, a major clinical issue. Hence, understanding mechanisms generating fibroblasts in this context has become a key question in the cardiovascular field. Recent studies now point to the activation of resident fibroblasts as the underlying cause of fibrosis. However, de novo generation of fibroblasts from endothelium and circulating hematopoietic cells has also been proposed to significantly contribute to fibrosis. Here, we discuss the latest findings on fibroblast origins, with a particular emphasis on the pressure overload model, and the implication of these findings for the development of anti-fibrotic therapies that are currently lacking.

Heart valve development begins with the endothelial-to-mesenchymal transition (EMT) of endocardial cells. Although lineage studies have demonstrated contributions from cardiac neural crest and epicardium to semilunar and atrioventricular (AV) valve formation, respectively, most valve mesenchyme derives from the endocardial EMT. Specific Cre mouse lines for fate-mapping analyses of valve endocardial cells are limited. Msx1 displayed expression in AV canal endocardium and cushion mesenchyme between E9.5 and E11.5, when EMT is underway. Additionally, previous studies have demonstrated that deletion of Msx1 and its paralog Msx2 results in hypoplastic AV cushions and impaired endocardial signaling. A knock-in tamoxifen-inducible Cre line was recently generated (Msx1CreERT2) and characterized during embryonic development and after birth, and was shown to recapitulate the endogenous Msx1 expression pattern. Here, we further analyze this knock-in allele and track the Msx1-expressing cells and their descendants during cardiac development with a particular focus on their contribution to the valves and their precursors. Thus, Msx1CreERT2 mice represent a useful model for lineage tracing and conditional gene manipulation of endocardial and mesenchymal cushion cells essential to understand mechanisms of valve development and remodeling.

Myocardial infarction is a major cause of adult mortality worldwide. The origin(s) of cardiac fibroblasts that constitute the postinfarct scar remain controversial, in particular the potential contribution of bone marrow lineages to activated fibroblasts within the scar. The aim of this study was to establish the origin(s) of infarct fibroblasts using lineage tracing and bone marrow transplants and a robust marker for cardiac fibroblasts, the Collagen1a1-green fluorescent protein reporter. Using genetic lineage tracing or bone marrow transplant, we found no evidence for collagen-producing fibroblasts derived from hematopoietic or bone marrow lineages in hearts subjected to permanent left anterior descending coronary artery ligation. In fact, fibroblasts within the infarcted area were largely of epicardial origin. Intriguingly, collagen-producing fibrocytes from hematopoietic lineages were observed attached to the epicardial surface of infarcted and sham-operated hearts in which a suture was placed around the left anterior descending coronary artery. In this controversial field, our study demonstrated that the vast majority of infarct fibroblasts were of epicardial origin and not derived from bone marrow lineages, endothelial-to-mesenchymal transition, or blood. We also noted the presence of collagen-producing fibrocytes on the epicardial surface that resulted at least in part from the surgical procedure. T.M. Moore-Morris was supported by American Heart Association postdoctoral fellowship 11POST7310066. P. Cattaneo was supported by the Marie Curie International Outgoing Fellowship within the 7th European Community Framework Program under grant agreement No 623739—The Cardiac Code. M. Cedenilla received funding from the Spanish Ministry of Education, Culture, and Sports, Predoctoral Fellowship program (FPU, AP2008-00508) and Travel Grant Program (TTFPU11-AP2008-00508). J. Bogomolovas is supported by the European Commission’s Marie Sklodowska-Curie Individual Fellowship (Titin Signals, 656636). S.M. Evans is funded by grants from the National Heart, Lung, and Blood Institute and the Leducq Foundation. M. Pucéat and T.M. Moore-Morris acknowledge the generosity of the Leducq Foundation (SHAPEHEART). Sí

Human embryonic stem (HUES) cells are derived from early individual embryos with unique genetic printing. However, how their epigenetic status might affect their potential to differentiate toward specific lineages remains a puzzling question. Using chromatin immunoprecipitation (ChIP)-polymerase chain reaction and ChIP-on-chip, the status of bivalent domains on gene promoters (ie, histone 3 on lysine 4 and histone 3 on lysine 27 trimethylation) was monitored for both undifferentiated and bone morphogenetic protein 2 (BMP2)-induced cardiac-committed cells. A marked difference in the epigenetic profile of HUES cell lines was observed and this was correlated to the pattern of gene expression induced by BMP2 as well as to their potential to generate cardiac progenitors and differentiated myocytes. Thus, the epigenetic H3trimeK4 and H3trimeK27 prints generating bivalent domains on promoters, could be used to predict a preference in their differentiation toward a specific lineage.

During embryogenesis, signaling molecules initiate cell diversification, sometimes via stochastic processes, other times via the formation of long range gradients of activity which pattern entire fields of cells. Such mechanisms are not insensitive to noise (Lander, 2011), yet embryogenesis is a remarkably robust process suggesting that multiple layers of regulations secure patterning during development. In the present study, we present a proof of concept according to which an asymmetric pattern of gene expression obtained from a spatially disorganised population of cells can be guided by the geometry of the environment in a reproducible and robust manner. We used ESC as a model system whithin which multiple developmental cell states coexist (MacArthur and Lemischka, 2013; Smith, 2017; Torres-Padilla and Chambers, 2014). We first present evidence that a reciprocal regulation of genes involved in the establishment of antero-posterior polarity during peri-implantation stages of mouse development is spontaneously occuring within ESC. We then show that a population of cells with primitive streak characteristics localise in regions of high curvature and low cell density. Finally, we show that this patterning did not depend on self-organised gradients of morphogen activity but instead could be attributed to positional rearrangements. Our findings unveil a novel role for tissue geometry in guiding the self-patterning of primitive streak cells and provide a framework to further refine our understanding of symmetry breaking events occuring in ESC aggregates. Finally, this work demonstrates that the self-patterning of a specific population of ESC, Brachyury positive cells in this case, can be directed by providing engineered external geometrical cues.

Recently, a preclinical report assessed the efficacy, safety, and feasibility of using human embryonic stem cells to regenerate infarcted myocardium in a nonhuman primate model. This commentary evaluates that study by pointing out key weaknesses, offering an alternative perspective, and summarizing major unresolved issues. Our conclusion is that significant challenges remain before human embryonic stem cells are ready for use in clinical trials. Ischemic heart disease (IHD) affects millions of patients. The cardiac dysfunction that results from IHD is secondary to the death of cardiac muscle cells. Current IHD treatments are inadequate, and there is a need to develop novel therapies to improve the lives of affected patients. New cellular therapies are being developed for repairing damaged hearts via induction of cardiac myocyte regeneration. In our view, approaches that can regenerate new, functional myocardium need to be tested first in small animal models and then in appropriate large animal models. Those approaches that are shown to be safe and to improve cardiac function in preclinical studies should then be considered for clinical application. In a recent report in Nature , Chong et al1 describe experiments designed to test the potential of human embryonic stem cell–derived cardiac myocytes (hESC-CMs) to regenerate infarcted myocardium in a nonhuman primate model. This study was proposed by the authors as proof of concept for trials of these cells in patients. Our commentary looks at this report with an eye toward safety and efficacy of hESC-CMs. A major advance in the study of Chong et al1 is that an approach has been developed to produce large quantities of hESC-CMs that seem to be sufficient for future use in humans with IHD. The authors were able to amplify 1 billion hESC-CMs, a number purported sufficient to regenerate an adult human infarcted heart. This approach addresses …

Introduction Valves are affected in 1/3 of cardiac congenital diseases. Cardiac valves derive from the process of endothelial-mesenchymal transition (EMT) of endocardial cells in the atrioventricular canal (AVC) and in the outflow tract of embryonic mouse hearts at E9.5 and E10.5, respectively. The origin and fate of endocardial cells as well as how EMT is specifically triggered in a subset of the latter are still poorly understood. Objectives To determine the extent of endocardial cells and valvular cells heterogeneity and in turn to assess whether endocardial cells are already committed to a valvular specific cell type. Methods Clonal analysis: a genetic labeling of endocardial valve progenitors was performed using Brainbow and CAGERT2Cre mouse strains. Single cell sequencing: Tie2Cre/− male was bred with RosatdTomato females. AVC cells were dissected out from E9.5 embryos. Mitral valve leaflets were dissected out from both E16.5 and P0 mice. All cells were enzymatically dissociated and tomato+ cells sorted out by FACS and used for single cell RNA sequencing using the 10X genomics technology. Results and conclusions Preliminary results point to a cell heterogeneity in each cell population so far investigated. A full panel of both clonal analysis and single cell RNA analysis will be presented.

International audience; The abundance of epicardial adipose tissue (EAT) is associated with atrial fibrillation (AF), the most frequent cardiac arrhythmia. However, both the origin and the factors involved in EAT expansion are unknown. Here, we found that adult human atrial epicardial cells were highly adipogenic through an epithelial-mesenchymal transition both in vitro and in vivo. In a genetic lineage tracing the WT1(CreERT2+/-)Rosa(tdT+/-)mouse model subjected to a high-fat diet, adipocytes of atrial EAT derived from a subset of epicardial progenitors. Atrial myocardium secretome induces the adipogenic differentiation of adult mesenchymal epicardium-derived cells by modulating the balance between mesenchymal Wingless-type Mouse Mammary Tumor Virus integration site family, member 10B (Wnt10b)/beta-catenin and adipogenic ERK/MAPK signaling pathways. The adipogenic property of the atrial secretome was enhanced in AF patients. The atrial natriuretic peptide secreted by atrial myocytes is a major adipogenic factor operating at a low concentration by binding to its natriuretic peptide receptor A (NPRA) receptor and, in turn, by activating a cGMP-dependent pathway. Hence, our data indicate cross-talk between EAT expansion and mechanical function of the atrial myocardium.

International audience; Specific gene transcription is a key biological process that underlies cell fate decision during embryonic development. The biological process is mediated by transcription factors which bind genomic regulatory regions including enhancers and promoters of cardiac constitutive genes. DNA is wrapped around histones that are subjected to chemical modifications. Modifications of histones further lead to repressed, activated or poised gene transcription, thus bringing another level of fine tuning regulation of gene transcription. Embryonic Stem cells (ES cells) recapitulate within embryoid bodies (i.e., cell aggregates) or in 2D culture the early steps of cardiac development. They provide in principle enough material for chromatin immunoprecipitation (ChIP), a technology broadly used to identify gene regulatory regions. Furthermore, human ES cells represent a human cell model of cardiogenesis. At later stages of development, mouse embryonic tissues allow for investigating specific epigenetic landscapes required for determination of cell identity. Herein, we describe protocols of ChIP, sequential ChIP followed by PCR or ChIP-sequencing using ES cells, embryoid bodies and cardiac specific embryonic regions. These protocols allow to investigating the epigenetic regulation of cardiac gene transcription.

Background and aims The accumulation of the adipose tissue (AT) in the sup- and subepicardium of the atrial myocardium is associated with a high risk of atrial fibrillation. Here we addressed the question of the cellular origin of atrial AT. Methods Human right atrial specimen obtained during cardiac surgery were used for histological, biochemical studies and to harvest epicardial progenitors. Cells were characterized using flow cytometry, proteomic and genic expression assays and maintained in culture conditions, in some experiments they were co cultured with human atrial myocytes using a Transwell system. Results In atrial section, epicardial progenitors expressing the pre-adipocyte factor 1 (Pref-1) were detected in the epicardial and sub-epicardial layer which contained a number of progenitor cells referred as epicardic progenitorderived cells (EPDCs). Some EPDCs expressed Pref-1 suggesting that they could engaged in the adipocyte pathways. This was tested in vitro using EPDCs harvested from human right atrial samples (n=20). From 1 st to 5-6 cells passages, EPDCs underwent an epithelial-to-mesenchymal transition (EMT), acquired mesenchymal phenotypes and could differentiate into osteocyte or chondrocyte. When cultured using an adipogenic medium, around 40±6% of EPDCs cells showed lipid droplet colored with oil red and expressed mature adipocyte perilipin marker. Culture medium enriched with the secretome of human atria too induced the differentiation of EPDCs in adipocytes (n=6). A shift from pre- to mature adipocytes was indicated by the detection of Pref-1 at 7 but not 30 days of culture, it was the opposite for perilipin. Human atrial myocyte could be the source of pro-adipogenic factor. In fact, after 7 days in coculture, EPDCs are differentiated into adipocytes (n=6). Conclusion Human EPDCs from atria can differentiate into adipocyte; factors secreted by atrial myocytes regulate this differentiation process. The author hereby declares no conflict of interest

Mouse embryonic stem cell lines were derived three decades ago and allow the process of transgenesis and in turn the generation of transgenic mice. In the past and still nowadays, these mice as well as more primitive organisms have provided models to study the first cell decisions in the embryo. Derivation of human embryonic stem cells more than a decade ago has provided a similar cell model for human early embryonic development, an issue that could not be addressed for obvious ethical reasons which limit research on human embryos. These cells allow investigating the genetic and epigenetic mechanisms underlying the first cell decisions in the human embryo. Herein, we use cardiogenesis as an example to reveal the potential of these cells to better understand the first steps of cardiac development.

OCT4 encoded by pou5f1 is one of the most ancient and early transcription factors identified in the embryo. It has been longwise recognized as a gatekeeper for pluripotency of embryonic stem (ES) cell. Uncovered twenty years ago, its fame was built up from its key role in maintaining embryonic stem cell pluripotency in 1998. Since, OCT4 was reported to also instruct stem cell fate through a gene dosage effect. It reached recently a novel glorious hit with its master role in reprogramming somatic cells.

International audience; Embryonic stem cells (ESC) are pluripotent cells capable to give rise to any embryonic cell lineage. In culture, these cells form colonies creating their own niche. Depending upon the molecular and physico-chemical environment, the pluripotent cells oscillate between two metastable states of pluripotency either reminiscent of the inner cell mass of the embryo or the epiblast, a stage of development which give rise to the three embryonic layers, ectoderm, endoderm and mesoderm. Herein, we used PLL/HA nanofilms cross-linked to various degrees to modulate the nanoenvironment of ESCs. Adhesion of ESC on nanofilms increased from native films to highly cross-linked films. The adhesion process was associated with cell proliferation. Expression of genes markers of the ICM decreased with adhesion of cells to cross-linked films. In parallel, genes more reminiscent of the epiblast, were turned on. ESC differentiation within embryoid bodies further revealed that cell pluripotency was better retained when cells did not adhere on native films. We further report that both the stiffness and the chemistry of nanofilms play a key role in modulating the niche of ESC and in turn govern their selfrenewal and fate.