Wnt/β-catenin and Bmp signals control distinct sets of transcription factors in cardiac progenitor cells

Genetic association and functional validation of ZFP36L2 in non-syndromic orofacial cleft subtypes

BACKGROUND

Non-syndromic orofacial cleft (NSOC) is one of the most common craniofacial malformations with complex etiology. This study aimed to explore the role of specific SNPs in ZFP36L2 and its functional relevance in zebrafish models.

METHODS

We analyzed genetic data of the Chinese Han population from two previous GWAS, comprising of 2512 cases and 2255 controls. Based on the Hardy-Weinberg Equilibrium (HWE) and minor allele frequency (MAF), SNPs in the ZFP36L2 were selected for association analysis. In addition, zebrafish models were used to clarify the in-situ expression pattern of zfp36l2 and the impact of its Morpholino-induced knockdown.

RESULTS

Via association analysis, rs7933 in ZFP36L2 was significantly associated with various non-syndromic cleft lip-only subtypes, potentially conferring a protective effect. Zebrafish embryos showed elevated expression of zfp36l2 in the craniofacial region during critical stages of oral cavity formation. Furthermore, Morpholino-induced knockdown of zfp36l2 led to craniofacial abnormalities, including cleft lip, which was partially rescued by the addition of zfp36l2 mRNA.

CONCLUSION

Our findings highlight the significance of ZFP36L2 in the etiology of NSOC, supported by both human genetic association data and functional studies in zebrafish. These results pave the way for further exploration of targeted interventions for craniofacial malformations.

Oxidative-stress induced Bmp2-Smad1/5/8 signaling dependent differentiation of early cardiomyocytes from embryonic and adult epicardial cells

Heart failure has become a major life-threatening cause affecting millions globally, characterized by the permanent loss of adult functional cardiomyocytes leading to fibrosis which ultimately deprives the heart of its functional efficacy. Here we investigated the reparative property of embryonic and adult epicardial cells towards cardiomyocyte differentiation under oxidative stress-induced conditions along with the identification of a possible molecular signaling pathway. Isolated epicardial cells from embryonic chick hearts subjected to oxidative stress and hypoxia induction. Initial assessment of successful injury induction reveals hypertrophy of isolated epicardial cells. Detailed marker gene expression analyses and inhibitor studies reveal Bone morphogenic protein (Bmp)2-Smad1/5/8 signaling dependent cardiomyocyte lineage specification via epithelial to mesenchymal transition (EMT) post-injury. EMT is further confirmed by increased proliferation, migration, and differentiation towards cardiomyocyte lineage. We have also established an in-vivo model in adult male rats using Isoproterenol. Successful oxidative stress-mediated injury induction in adult heart was marked by increased activated fibroblasts followed by apoptosis of adult cardiomyocytes. The detailed characterization of adult epicardial cells reveals similar findings to our avian in-vitro data. Both in-vitro and in-vivo results show a significant increase in the expression of cardiomyocyte specific markers indicative of lineage specificity and activation of epicardial cells post oxidative stress mediated injury. Our findings suggest an EMT-induced reactivation of epicardial cells and early cardiomyocyte lineage specification following oxidative stress in a Bmp2- Smad1/5/8 dependent manner. Overall, this regulatory mechanism of cardiomyocyte differentiation induced by oxidative stress may contribute to the field of cardiac repair and regenerative therapeutics.

The benign nature and rare occurrence of cardiac myxoma as a possible consequence of the limited cardiac proliferative/ regenerative potential: a systematic review

BACKGROUND

Cardiac Myxoma is a primary tumor of heart. Its origins, rarity of the occurrence of primary cardiac tumors and how it may be related to limited cardiac regenerative potential, are not yet entirely known. This study investigates the key cardiac genes/ transcription factors (TFs) and signaling pathways to understand these important questions.

METHODS

Databases including PubMed, MEDLINE, and Google Scholar were searched for published articles without any date restrictions, involving cardiac myxoma, cardiac genes/TFs/signaling pathways and their roles in cardiogenesis, proliferation, differentiation, key interactions and tumorigenesis, with focus on cardiomyocytes.

RESULTS

The cardiac genetic landscape is governed by a very tight control between proliferation and differentiation-related genes/TFs/pathways. Cardiac myxoma originates possibly as a consequence of dysregulations in the gene expression of differentiation regulators including Tbx5, GATA4, HAND1/2, MYOCD, HOPX, BMPs. Such dysregulations switch the expression of cardiomyocytes into progenitor-like state in cardiac myxoma development by dysregulating Isl1, Baf60 complex, Wnt, FGF, Notch, Mef2c and others. The Nkx2-5 and MSX2 contribute predominantly to both proliferation and differentiation of Cardiac Progenitor Cells (CPCs), may possibly serve roles based on the microenvironment and the direction of cell circuitry in cardiac tumorigenesis. The Nkx2-5 in cardiac myxoma may serve to limit progression of tumorigenesis as it has massive control over the proliferation of CPCs. The cardiac cell type-specific genetic programming plays governing role in controlling the tumorigenesis and regenerative potential.

CONCLUSION

The cardiomyocytes have very limited proliferative and regenerative potential. They survive for long periods of time and tightly maintain the gene expression of differentiation genes such as Tbx5, GATA4 that interact with tumor suppressors (TS) and exert TS like effect. The total effect such gene expression exerts is responsible for the rare occurrence and benign nature of primary cardiac tumors. This prevents the progression of tumorigenesis. But this also limits the regenerative and proliferative potential of cardiomyocytes. Cardiac Myxoma develops as a consequence of dysregulations in these key genes which revert the cells towards progenitor-like state, hallmark of CM. The CM development in carney complex also signifies the role of TS in cardiac cells.

Ghrelin promotes cardiomyocyte differentiation of adipose tissue‑derived mesenchymal stem cells by DDX17‑mediated regulation of the SFRP4/Wnt/β‑catenin axis

Adipose tissue‑derived mesenchymal stem cells (ADMSCs) differentiate into cardiomyocytes and may be an ideal cell source for myocardial regenerative medicine. Ghrelin is a gastric‑secreted peptide hormone involved in the multilineage differentiation of MSCs. To the best of our knowledge, however, the role and potential downstream regulatory mechanism of ghrelin in cardiomyocyte differentiation of ADMSCs is still unknown. The mRNA and protein levels were measured by reverse transcription‑quantitative PCR and western blotting. Immunofluorescence staining was used to show the expression and cellular localization of cardiomyocyte markers and β‑catenin. RNA sequencing was used to explore the differentially expressed genes (DEGs) that regulated by ghrelin. The present study found that ghrelin promoted cardiomyocyte differentiation of ADMSCs in a concentration‑dependent manner, as shown by increased levels of cardiomyocyte markers GATA binding protein 4, α‑myosin heavy chain (α‑MHC), ISL LIM homeobox 1, NK2 homeobox 5 and troponin T2, cardiac type. Ghrelin increased β‑catenin accumulation in nucleus and decreased the protein expression of secreted frizzled‑related protein 4 (SFRP4), an inhibitor of Wnt signaling. RNA sequencing was used to determine the DEGs regulated by ghrelin. Functional enrichment showed that DEGs were more enriched in cardiomyocyte differentiation‑associated terms and Wnt pathways. Dead‑box helicase 17 (DDX17), an upregulated DEG, showed enhanced mRNA and protein expression levels following ghrelin addition. Overexpression of DDX17 promoted protein expression of cardiac‑specific markers and β‑catenin and enhanced the fluorescence intensity of α‑MHC and β‑catenin. DDX17 upregulation inhibited protein expression of SFRP4. Rescue assay confirmed that the addition of SFRP4 partially reversed ghrelin‑enhanced protein levels of cardiac‑specific markers and the fluorescence intensity of α‑MHC. In conclusion, ghrelin promoted cardiomyocyte differentiation of ADMSCs by DDX17‑mediated regulation of the SFRP4/Wnt/β‑catenin axis.

WNT/β-catenin pathway is a key regulator of cardiac function and energetic metabolism

The WNT/β-catenin pathway is a master regulator of cardiac development and growth, and its activity is low in healthy adult hearts. However, even this low activity is essential for maintaining normal heart function. Acute activation of the WNT/β-catenin signaling cascade is considered to be cardioprotective after infarction through the upregulation of prosurvival genes and reprogramming of metabolism. Chronically high WNT/β-catenin pathway activity causes profibrotic and hypertrophic effects in the adult heart. New data suggest more complex functions of β-catenin in metabolic maturation of the perinatal heart, establishing an adult pattern of glucose and fatty acid utilization. Additionally, low basal activity of the WNT/β-catenin cascade maintains oxidative metabolism in the adult heart, and this pathway is reactivated by physiological or pathological stimuli to meet the higher energy needs of the heart. This review summarizes the current state of knowledge of the organization of canonical WNT signaling and its function in cardiogenesis, heart maturation, adult heart function, and remodeling. We also discuss the role of the WNT/β-catenin pathway in cardiac glucose, lipid metabolism, and mitochondrial physiology.

Overexpression of PYGO1 promotes early cardiac lineage development in human umbilical cord mesenchymal stromal/stem cells by activating the Wnt/β-catenin pathway

Cardiovascular disease still has the highest mortality. Gene-modified mesenchymal stromal/stem cells could be a promising therapy. Pygo plays an important role in embryonic development and regulates life activities with a variety of regulatory mechanisms. Therefore, this study aimed to investigate whether the overexpression of the PYGO1 gene can promote the differentiation of human umbilical cord-derived mesenchymal stromal/stem cells (HUC-MSCs) into early cardiac lineage cells and to preliminary explore the relevant mechanisms. In this study, HUC-MSCs were isolated by the explant method and were identified by flow cytometry and differentiation assay, followed by transfected with lentivirus carrying the PYGO1 plasmid. In PYGO1 group (cells were incubated with lentiviral-PYGO1), the mRNA expressions of cardiac differentiation-specific markers (MESP1, NKX2.5, GATA4, MEF2C, ISL1, TBX5, TNNT2, ACTC1, and MYH6 genes) and the protein expressions of NKX2.5 and cTnT were significantly up-regulated compared with the NC group (cells were incubated with lentiviral-empty vector). In addition, the proportion of NKX2.5, GATA4, and cTnT immunofluorescence-positive cells increased with the inducement time. Overexpression of PYGO1 statistically significantly increased the relative luciferase expression level of Topflash plasmid, the protein expression level of β-catenin and the mRNA expression level of CYCLIND1. Compared with the control group, decreased protein levels of NKX2.5 and cTnT were detected in PYGO1 group after application of XAV-939, the specific inhibitor of the canonical Wnt/β-catenin pathway. Our study suggests that overexpression of PYGO1 significantly promotes the differentiation of HUC-MSCs into early cardiac lineage cells, which is regulated by the canonical Wnt/β-catenin signaling.

Progesterone Receptor Modulates Extraembryonic Mesoderm and Cardiac Progenitor Specification during Mouse Gastrulation

Progesterone treatment is commonly employed to promote and support pregnancy. While maternal tissues are the main progesterone targets in humans and mice, its receptor (PGR) is expressed in the murine embryo, questioning its function during embryonic development. Progesterone has been previously associated with murine blastocyst development. Whether it contributes to lineage specification is largely unknown. Gastrulation initiates lineage specification and generation of the progenitors contributing to all organs. Cells passing through the primitive streak (PS) will give rise to the mesoderm and endoderm. Cells emerging posteriorly will form the extraembryonic mesodermal tissues supporting embryonic growth. Cells arising anteriorly will contribute to the embryonic heart in two sets of distinct progenitors, first (FHF) and second heart field (SHF). We found that PGR is expressed in a posterior–anterior gradient in the PS of gastrulating embryos. We established in vitro differentiation systems inducing posterior (extraembryonic) and anterior (cardiac) mesoderm to unravel PGR function. We discovered that PGR specifically modulates extraembryonic and cardiac mesoderm. Overexpression experiments revealed that PGR safeguards cardiac differentiation, blocking premature SHF progenitor specification and sustaining the FHF progenitor pool. This role of PGR in heart development indicates that progesterone administration should be closely monitored in potential early-pregnancy patients undergoing infertility treatment.

Genome-wide methylome pattern predictive network analysis reveal mesenchymal stem cell's propensity to undergo cardiovascular lineage

Mesenchymal stem cells (MSCs) differentiation toward cardiovascular lineage prediction using the global methylome profile will highlight its prospective utility in regenerative medicine. We examined the propensity prediction to cardiovascular lineage using 5-Aza, a well-known cardiac lineage inducer. The customized 180 K microarray was performed and further analysis of global differentially methylated regions by Ingenuity pathway analysis (IPA) in both MSCs and 5-AC-treated MSCs. The cluster enrichment tools sorted differentially enriched genes and further annotated to construct the interactive networks. Prediction analysis revealed pathways pertaining to the cardiovascular lineage found active in the native MSCs, suggesting its higher propensity to undergo cardiac, smooth muscle cell, and endothelial lineages in vitro. Interestingly, gene interaction network also proposed majorly stemness gene network NANOG and KLF6, cardiac-specific transcription factors GATA4, NKX2.5, and TBX5 were upregulated in the native MSCs. Furthermore, the expression of cardiovascular lineage specific markers such as Brachury, CD105, CD90, CD31, KDR and various forms of ACTIN (cardiac, sarcomeric, smooth muscle) were validated in native MSCs using real time PCR and immunostaining and blotting analysis. In 5-AC-treated MSCs, mosaic interactive networks were observed to persuade towards osteogenesis and cardiac lineage, indicating that 5-AC treatment resulted in nonspecific lineage induction in MSCs, while MSCs by default have a higher propensity to undergo cardiovascular lineage.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03058-2.

Resuscitating the Field of Cardiac Regeneration: Seeking Answers from Basic Biology

Heart failure (HF) is one of the leading causes for hospital admissions worldwide. HF patients are classified based on the chronic changes in left ventricular ejection fraction (LVEF) as preserved (LVEF ≥ 50%), reduced (LVEF ≤ 40%), or mid-ranged (40% < LVEF < 50%) HFs. Treatments nowadays can prevent HFrEF progress, whereas only a few of the treatments have been proven to be effective in improving the survival of HFpEF. In this review, numerous mediators involved in the pathogenesis of HF are summarized. The regional upstream signaling and their diagnostic and therapeutic potential are also discussed. Additionally, the recent challenges and development in cardiac regenerative therapy that hold opportunities for future research and clinical translation are discussed.

Injectable AuNP-HA matrix with localized stiffness enhances the formation of gap junction in engrafted human induced pluripotent stem cell-derived cardiomyocytes and promotes cardiac repair

Cell therapy offers a promising paradigm for heart tissue regeneration. Human induced pluripotent stem cells (hiPS) and their cardiac derivatives are emerging as a novel treatment for post-myocardial infarction repair. However, the immature phenotype and function of hiPS-derived cardiomyocytes (hiPS-CMs), particularly poor electrical coupling, limit their potential as a therapy. Herein, we developed a hybrid gold nanoparticle (AuNP)-hyaluronic acid (HA) hydrogel matrix encapsulating hiPS-CMs to overcome this limitation. Methacrylate-modified-HA was used as the backbone and crosslinked with a matrix metalloproteinase-2 (MMP-2) degradable peptide to obtain a MMP-2-responsive hydrogel; RGD peptide was introduced as an adhesion point to enhance biocompatibility; AuNPs were incorporated to regulate the mechanical and topological properties of the matrix by significantly increasing its stiffness and surface roughness, thereby accelerating gap junction formation in hiPS-CMs and orchestrating calcium handling via the α_nβ1integrin-mediated ILK-1/p-AKT/GATA4 pathway. Transplanted AuNP-HA-hydrogel-encapsulated-hiPS-CMs developed more robust gap junctions in the infarcted mice heart and resynchronized electrical conduction of the ventricle post-myocardial infarction. The hiPS-CMs delivered by the hydrogels exerted stronger angiogenic effects, which also contributed to the recovery process. This study provides insight into constructing an injectable biomimetic for structural and functional renovation of the injured heart.

Heart organoids and tissue models for modeling development and disease

Organoids, or miniaturized organs formed in vitro, hold potential to revolutionize how researchers approach and answer fundamental biological and pathological questions. In the context of cardiac biology, development of a bona fide cardiac organoid enables study of heart development, function, and pathogenesis in a dish, providing insight into the nature of congenital heart disease and offering the opportunity for high-throughput probing of adult heart disease and drug discovery. Recently, multiple groups have reported novel methods for generating in vitro models of the heart; however, there are substantial conceptual and methodological differences. In this review we will evaluate recent cardiac organoid studies through the lens of the core principles of organoid technology: patterned self-organization of multiple cell types resembling the in vivo organ. Based on this, we will classify systems into the following related types of tissues: developmental cardiac organoids, chamber cardiac organoids, microtissues, and engineered heart tissues. Furthermore, we highlight the interventions which allow for organoid formation, such as modulation of highly conserved cardiogenic signaling pathways mediated by developmental morphogens. We expect that consolidation and categorization of existing organoid models will help eliminate confusion in the field and facilitate progress towards creation of an ideal cardiac organoid.

Neuregulin-1, in a Conducive Milieu with Wnt/BMP/Retinoic Acid, Prolongs the Epicardial-Mediated Cardiac Regeneration Capacity of Neonatal Heart Explants

Rationale: Cardiac sympathetic nerves are required for endogenous repair of the mammalian neonatal heart in vivo, but the underlying mechanism is unclear. Objective: We tested the hypothesis that a combination of cardiac developmental growth factors Wnt3a, BMP4 and Neuregulin (NRG-1), compensate for denervation and support cardiac regeneration in explanted neonatal mammalian hearts. Methods and Results: Hearts from 2-day old neonatal mice were harvested, lesioned at the apex and grown ex vivo for 21 days under defined conditions. Hearts grown in canonical cardiomyocyte culture media underwent complete coagulative necrosis, a process resembling ischemic cell death, by day 14. However, the addition of Wnt3a, BMP-4 and NRG-1, maintained cellular integrity and restored the endogenous regenerative program. None of these factors alone, or in any paired combination, were sufficient to induce regeneration in culture. rNRG-1 alone significantly reduced the accumulation of double strand DNA damage at Day 3; (-NRG-1: 60±12%; +NRG-1: 8±3%; P<0.01) and prevented coagulative necrosis at Day 14. Short-term addition of rWnt3a and rBMP-4 (day 0-3, NRG-1+) increased WT1 expression (a marker of epicardial cells) 7-fold, epicardial proliferation (78±17 cells vs. 21±9 cells; P<0.05), migration and recellularization (80±22 vs. zero cells; P<0.01; n=6) at the injury site on day 14. Conclusions: A novel explant culture system maintains three-dimensional neonatal mouse hearts and the mammalian neonatal cardiac regenerative program ex vivo. We identified that rNRG-1, plus short-term activation of Wnt- and BMP-signaling, promotes cardiac repair via epicardial cell activation, their proliferation and migration to the injury site, followed by putative cardiomyocyte recruitment. This novel technique will facilitate future studies of mammalian cardiac regeneration and may be useful in cardiac-specific drug testing.

Overexpression and Activation of αvβ3 Integrin Differentially Affects TGFβ2 Signaling in Human Trabecular Meshwork Cells

Studies from our laboratory have suggested that activation of αvβ3 integrin-mediated signaling could contribute to the fibrotic-like changes observed in primary open angle glaucoma (POAG) and glucocorticoid-induced glaucoma. To determine how αvβ3 integrin signaling could be involved in this process, RNA-Seq analysis was used to analyze the transcriptomes of immortalized trabecular meshwork (TM) cell lines overexpressing either a control vector or a wild type (WT) or a constitutively active (CA) αvβ3 integrin. Compared to control cells, hierarchical clustering, PANTHER pathway and protein-protein interaction (PPI) analysis of cells overexpressing WT-αvβ3 integrin or CA-αvβ3 integrin resulted in a significant differential expression of genes encoding for transcription factors, adhesion and cytoskeleton proteins, extracellular matrix (ECM) proteins, cytokines and GTPases. Cells overexpressing a CA-αvβ3 integrin also demonstrated an enrichment for genes encoding proteins found in TGFβ2, Wnt and cadherin signaling pathways all of which have been implicated in POAG pathogenesis. These changes were not observed in cells overexpressing WT-αvβ3 integrin. Our results suggest that activation of αvβ3 integrin signaling in TM cells could have significant impacts on TM function and POAG pathogenesis.

Differentiation and Application of Human Pluripotent Stem Cells Derived Cardiovascular Cells for Treatment of Heart Diseases: Promises and Challenges

Human pluripotent stem cells (hPSCs) are derived from human embryos (human embryonic stem cells) or reprogrammed from human somatic cells (human induced pluripotent stem cells). They can differentiate into cardiovascular cells, which have great potential as exogenous cell resources for restoring cardiac structure and function in patients with heart disease or heart failure. A variety of protocols have been developed to generate and expand cardiovascular cells derived from hPSCs in vitro. Precisely and spatiotemporally activating or inhibiting various pathways in hPSCs is required to obtain cardiovascular lineages with high differentiation efficiency. In this concise review, we summarize the protocols of differentiating hPSCs into cardiovascular cells, highlight their therapeutic application for treatment of cardiac diseases in large animal models, and discuss the challenges and limitations in the use of cardiac cells generated from hPSCs for a better clinical application of hPSC-based cardiac cell therapy.

SOX17 Loss-of-Function Mutation Underlying Familial Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) refers to a rare, progressive disorder that is characterized by occlusive pulmonary vascular remodeling, resulting in increased pulmonary arterial pressure, right-sided heart failure, and eventual death. Emerging evidence from genetic investigations of pediatric-onset PAH highlights the strong genetic basis underpinning PAH, and deleterious variants in multiple genes have been found to cause PAH. Nevertheless, PAH is of substantial genetic heterogeneity, and the genetic defects underlying PAH in the overwhelming majority of cases remain elusive. In this investigation, a consanguineous family suffering from PAH transmitted as an autosomal-dominant trait was identified. Through whole-exome sequencing and bioinformatic analyses as well as Sanger sequencing analyses of the PAH family, a novel heterozygous SOX17 mutation, NM_022454.4: c.379C>T; p. (Gln127*), was found to co-segregate with the disease in the family, with complete penetrance. The nonsense mutation was neither observed in 612 unrelated healthy volunteers nor retrieved in the population genetic databases encompassing the Genome Aggregation Database, the Exome Aggregation Consortium database, and the Single Nucleotide Polymorphism database. Biological analyses using a dual-luciferase reporter assay system revealed that the Gln127*-mutant SOX17 protein lost the ability to transcriptionally activate its target gene NOTCH1. Moreover, the Gln127*-mutant SOX17 protein exhibited no inhibitory effect on the function of CTNNB1-encode β-catenin, which is a key player in vascular morphogenesis. This research firstly links SOX17 loss-of-function mutation to familial PAH, which provides novel insight into the molecular pathogenesis of PAH, suggesting potential implications for genetic and prognostic risk evaluation as well as personalized prophylaxis of the family members affected with PAH.

Understanding Heart Field Progenitor Cells for Modeling Congenital Heart Diseases

PURPOSE OF REVIEW

Heart development is a meticulously coordinated process that involves the specification of two distinct populations of cardiac progenitor cells, namely the first and the second heart field. Disruption of heart field progenitors can result in congenital heart defects. In this review, we aim to describe the signaling pathways and transcription factors that link heart field development and congenital heart disease.

RECENT FINDINGS

Single-cell transcriptomics, lineage-tracing mouse models, and stem cell-based in vitro modeling of cardiogenesis have significantly improved the spatiotemporal characterization of cardiac progenitors. Additionally, novel functional genomic studies have now linked more genetic variants with congenital heart disease. Dysregulation of cardiac progenitor cells causes malformations that can be lethal. Ongoing research will continue to shed light on cardiac morphogenesis and help us better understand and treat patients with congenital heart disease.

The Role of Epigenetics in Congenital Heart Disease

Congenital heart disease (CHD) is the most common birth defect among newborns worldwide and contributes to significant infant morbidity and mortality. Owing to major advances in medical and surgical management, as well as improved prenatal diagnosis, the outcomes for these children with CHD have improved tremendously so much so that there are now more adults living with CHD than children. Advances in genomic technologies have discovered the genetic causes of a significant fraction of CHD, while at the same time pointing to remarkable complexity in CHD genetics. For this reason, the complex process of cardiogenesis, which is governed by multiple interlinked and dose-dependent pathways, is a well investigated process. In addition to the sequence of the genome, the contribution of epigenetics to cardiogenesis is increasingly recognized. Significant progress has been made dissecting the epigenome of the heart and identified associations with cardiovascular diseases. The role of epigenetic regulation in cardiac development/cardiogenesis, using tissue and animal models, has been well reviewed. Here, we curate the current literature based on studies in humans, which have revealed associated and/or causative epigenetic factors implicated in CHD. We sought to summarize the current knowledge on the functional role of epigenetics in cardiogenesis as well as in distinct CHDs, with an aim to provide scientists and clinicians an overview of the abnormal cardiogenic pathways affected by epigenetic mechanisms, for a better understanding of their impact on the developing fetal heart, particularly for readers interested in CHD research.

Cardiomyocyte Proliferation and Maturation: Two Sides of the Same Coin for Heart Regeneration

In the past few decades, cardiac regeneration has been the central target for restoring the injured heart. In mammals, cardiomyocytes are terminally differentiated and rarely divide during adulthood. Embryonic and fetal cardiomyocytes undergo robust proliferation to form mature heart chambers in order to accommodate the increased workload of a systemic circulation. In contrast, postnatal cardiomyocytes stop dividing and initiate hypertrophic growth by increasing the size of the cardiomyocyte when exposed to increased workload. Extracellular and intracellular signaling pathways control embryonic cardiomyocyte proliferation and postnatal cardiac hypertrophy. Harnessing these pathways could be the future focus for stimulating endogenous cardiac regeneration in response to various pathological stressors. Meanwhile, patient-specific cardiomyocytes derived from autologous induced pluripotent stem cells (iPSCs) could become the major exogenous sources for replenishing the damaged myocardium. Human iPSC-derived cardiomyocytes (iPSC-CMs) are relatively immature and have the potential to increase the population of cells that advance to physiological hypertrophy in the presence of extracellular stimuli. In this review, we discuss how cardiac proliferation and maturation are regulated during embryonic development and postnatal growth, and explore how patient iPSC-CMs could serve as the future seed cells for cardiac cell replacement therapy.

Molecular Signatures and Networks of Cardiomyocyte Differentiation in Humans and Mice

Cardiomyocyte differentiation derived from embryonic stem cells (ESCs) is a complex process involving molecular regulation of multiple levels. In this study, we first identify and compare differentially expressed gene (DEG) signatures of ESC-derived cardiomyocyte differentiation (ESCDCD) in humans and mice. Then, the multiscale embedded gene co-expression network analysis (MEGENA) of the human ESCDCD dataset is performed to identify 212 significantly co-expressed gene modules, which capture well the regulatory information of cardiomyocyte differentiation. Three modules respectively involved in the regulation of stem cell pluripotency, Wnt, and calcium pathways are enriched in the DEG signatures of the differentiation phase transition in the two species. Three human-specific cardiomyocyte differentiation phase transition modules are identified. Moreover, the potential regulation mechanisms of transcription factors during cardiomyocyte differentiation are also illustrated. Finally, several novel key drivers of ESCDCD are identified with the evidence of their expression during mouse embryonic cardiomyocyte differentiation. Using an integrative network analysis, the core molecular signatures and gene subnetworks (modules) underlying cardiomyocyte lineage commitment are identified in both humans and mice. Our findings provide a global picture of gene-gene co-regulation and identify key regulators during ESCDCD.

Single-Cell Transcriptomic Analysis of Cardiac Progenitor Differentiation

PURPOSE OF REVIEW

Emerging single-cell RNA sequencing technologies hold great promises to boost our understanding of the heterogeneity and molecular regulation of diverse cell phenotypes during organ development. In this review, we aimed at summarizing recent advances in employing single-cell transcriptomic analysis to depict the landscape of embryonic heart development, in particular, focusing on cardiac progenitor (CP) differentiation.

RECENT FINDINGS

Recent studies unbiasedly cataloged and characterized cardiac cell types in the spatial and temporal resolution during early heart development. Pseudo-time analysis revealed a temporal continuum of the differentiation progress from embryonic day (E) 6.5 to E9.5, implicating early cardiac lineage restriction during mouse gastrulation. First and second heart field (FHF and SHF) CPs adopted different differentiation strategies and underwent distinct transcriptional regulation. Collectively, the comprehensive molecular atlases yield a rich resource for identification of the key cardiac regulators and signaling molecules within the key cardiac gene regulatory network (GRN) governing cardiac cell fate determinations. This review offers insights into the exquisite process and its regulation of CP differentiation at single-cell resolution. As single-cell technologies continuously grow and evolve, computational integration of multimodal single-cell data with well-designed experimental validation promises to further delineate molecular basis in deploying cardiac progenitors of distinct sources with anatomical information.

GATA4 Is Required for Budding Morphogenesis of Posterior Foregut Endoderm in a Model of Human Stomach Development

Three-dimensional gastrointestinal organoid culture systems provide innovative and tractable models to investigate fundamental developmental biology questions using human cells. The goal of this study was to explore the role of the zinc-finger containing transcription factor GATA4 in gastric development using an organoid-based model of human stomach development. Given GATA4′s vital role in the developing mouse gastrointestinal tract, we hypothesized that GATA4 plays an essential role in human stomach development. We generated a human induced pluripotent stem cell (hiPSC) line stably expressing an shRNA targeted against GATA4 (G4KD-hiPSCs) and used an established protocol for the directed differentiation of hiPSCs into stomach organoids. This in vitro model system, informed by studies in multiple non-human model systems, recapitulates the fundamental processes of stomach development, including foregut endoderm patterning, specification, and subsequent tissue morphogenesis and growth, to produce three-dimensional fundic or antral organoids containing functional gastric epithelial cell types. We confirmed that GATA4 depletion did not disrupt hiPSC differentiation to definitive endoderm (DE). However, when G4KD-hiPSC-derived DE cells were directed to differentiate toward budding SOX2+, HNF1B+ posterior foregut spheroids, we observed a striking decrease in the emergence of cell aggregates, with little to no spheroid formation and budding by GATA4-depleted hiPSCs. In contrast, control hiPSC-derived DE cells, expressing GATA4, formed aggregates and budded into spheroids as expected. These data support an essential role for GATA4 during the earliest stages of human stomach development.

Notch and interacting signalling pathways in cardiac development, disease, and regeneration

Cardiogenesis is a complex developmental process involving multiple overlapping stages of cell fate specification, proliferation, differentiation, and morphogenesis. Precise spatiotemporal coordination between the different cardiogenic processes is ensured by intercellular signalling crosstalk and tissue-tissue interactions. Notch is an intercellular signalling pathway crucial for cell fate decisions during multicellular organismal development and is aptly positioned to coordinate the complex signalling crosstalk required for progressive cell lineage restriction during cardiogenesis. In this Review, we describe the role of Notch signalling and the crosstalk with other signalling pathways during the differentiation and patterning of the different cardiac tissues and in cardiac valve and ventricular chamber development. We examine how perturbation of Notch signalling activity is linked to congenital heart diseases affecting the neonate and adult, and discuss studies that shed light on the role of Notch signalling in heart regeneration and repair after injury.

Augmenting canonical Wnt signalling in therapeutically inert cells converts them into therapeutically potent exosome factories

Cardiosphere-derived cells (CDCs) are therapeutic candidates with disease-modifying bioactivity, but their variable potency has complicated their clinical translation. Transcriptomic analyses of CDCs from human donors have revealed that the therapeutic potency of these cells correlates with Wnt/β-catenin signalling and with β-catenin protein levels. Here, we show that skin fibroblasts engineered to overexpress β-catenin and the transcription factor Gata4 become immortal and therapeutically potent. Transplantation of the engineered fibroblasts into a mouse model of acute myocardial infarction led to improved cardiac function and mouse survival. And in the mdx mouse model of Duchenne muscular dystrophy, exosomes secreted by the engineered fibroblasts improved exercise capacity and reduced skeletal-muscle fibrosis. We also demonstrate that exosomes from high-potency CDCs exhibit enhanced levels of miR-92a (a known potentiator of the Wnt/β-catenin pathway), and that they activate cardioprotective bone-morphogenetic-protein signalling in cardiomyocytes. Our findings show that the modulation of canonical Wnt signalling can turn therapeutically inert mammalian cells into immortal exosome factories for cell-free therapies.

Overexpression of β-catenin and the transcription factor Gata4 in skin fibroblasts converts them into therapeutically active cells that secrete reparative exosomes as shown in mice models of myocardial infarction and Duchenne muscular dystrophy.

The lncRNA Locus Handsdown Regulates Cardiac Gene Programs and Is Essential for Early Mouse Development

Precisely controlled gene regulatory networks are required during embryonic development to give rise to various structures, including those of the cardiovascular system. Long non-coding RNA (lncRNA) loci are known to be important regulators of these genetic programs. We have identified a novel and essential lncRNA locus Handsdown (Hdn), active in early heart cells, and show by genetic inactivation that it is essential for murine development. Hdn displays haploinsufficiency for cardiac development as Hdn-heterozygous adult mice exhibit hyperplasia in the right ventricular wall. Transcriptional activity of the Hdn locus, independent of its RNA, suppresses its neighboring gene Hand2. We reveal a switch in a topologically associated domain in differentiation of the cardiac lineage, allowing the Hdn locus to directly interact with regulatory elements of the Hand2 locus.

Analysis of Uncharacterized mKiaa1211 Expression during Mouse Development and Cardiovascular Morphogenesis

Mammalian Kiaa1211 and Kiaa1211-like are a homologous pair of uncharacterized, highly conserved genes cloned from fetal and adult brain cDNA libraries. Herein we map the in utero spatiotemporal expression of mKiaa1211 and mKiaa1211L mRNA and their expression patterns in postnatal testis, skin, gastrointestinal, and adipose progenitor tissues. Significantly, mKiaa1211 is present throughout the early stages of mouse heart development, particularly in the second heart field (SHF) lineage as it differentiates from mesenchymal cells into cardiomyocytes. We also show that mKiaa1211 is expressed within several early neuronal tissues destined to give rise to central, peripheral, and sympathetic nervous system structures. Expression profiling revealed that the paralog mKiaa1211L is not expressed during the normal developmental process and that mKiaa1211 expression was noticeably absent from most adult terminally differentiated tissues. Finally, we confirm that a previously uncharacterized CRISPR/CAS-generated mKiaa1211 mouse mutant allele is hypomorphic.

From Molecular Mechanisms to Clinical Management of Antineoplastic Drug-Induced Cardiovascular Toxicity: A Translational Overview

Significance: Antineoplastic therapies have significantly improved the prognosis of oncology patients. However, these treatments can bring to a higher incidence of side-effects, including the worrying cardiovascular toxicity (CTX). Recent Advances: Substantial evidence indicates multiple mechanisms of CTX, with redox mechanisms playing a key role. Recent data singled out mitochondria as key targets for antineoplastic drug-induced CTX; understanding the underlying mechanisms is, therefore, crucial for effective cardioprotection, without compromising the efficacy of anti-cancer treatments. Critical Issues: CTX can occur within a few days or many years after treatment. Type I CTX is associated with irreversible cardiac cell injury, and it is typically caused by anthracyclines and traditional chemotherapeutics. Type II CTX is generally caused by novel biologics and more targeted drugs, and it is associated with reversible myocardial dysfunction. Therefore, patients undergoing anti-cancer treatments should be closely monitored, and patients at risk of CTX should be identified before beginning treatment to reduce CTX-related morbidity. Future Directions: Genetic profiling of clinical risk factors and an integrated approach using molecular, imaging, and clinical data may allow the recognition of patients who are at a high risk of developing chemotherapy-related CTX, and it may suggest methodologies to limit damage in a wider range of patients. The involvement of redox mechanisms in cancer biology and anticancer treatments is a very active field of research. Further investigations will be necessary to uncover the hallmarks of cancer from a redox perspective and to develop more efficacious antineoplastic therapies that also spare the cardiovascular system.

Single cell expression analysis reveals anatomical and cell cycle-dependent transcriptional shifts during heart development

The heart is a complex organ composed of multiple cell and tissue types. Cardiac cells from different regions of the growing embryonic heart exhibit distinct patterns of gene expression, which are thought to contribute to heart development and morphogenesis. Single cell RNA sequencing allows genome-wide analysis of gene expression at the single cell level. Here, we have analyzed cardiac cells derived from early stage developing hearts by single cell RNA-seq and identified cell cycle gene expression as a major determinant of transcriptional variation. Within cell cycle stage-matched CMs from a given heart chamber, we found that CMs in the G2/M phase downregulated sarcomeric and cytoskeletal markers. We also identified cell location-specific signaling molecules that may influence the proliferation of other nearby cell types. Our data highlight how variations in cell cycle activity selectively promote cardiac chamber growth during development, reveal profound chamber-specific cell cycle-linked transcriptional shifts, and open the way to deeper understanding of pathogenesis of congenital heart disease.

Human Pluripotent Stem Cell-Derived Multipotent Vascular Progenitors of the Mesothelium Lineage Have Utility in Tissue Engineering and Repair

In this report we describe a human pluripotent stem cell-derived vascular progenitor (MesoT) cell of the mesothelium lineage. MesoT cells are multipotent and generate smooth muscle cells, endothelial cells, and pericytes and self-assemble into vessel-like networks in vitro. MesoT cells transplanted into mechanically damaged neonatal mouse heart migrate into the injured tissue and contribute to nascent coronary vessels in the repair zone. When seeded onto decellularized vascular scaffolds, MesoT cells differentiate into the major vascular lineages and self-assemble into vasculature capable of supporting peripheral blood flow following transplantation. These findings demonstrate in vivo functionality and the potential utility of MesoT cells in vascular engineering applications.

Cardiotrophic Growth Factor-Driven Induction of Human Muse Cells Into Cardiomyocyte-Like Phenotype

Multilineage-differentiating stress-enduring (Muse) cells are endogenous nontumorigenic stem cells collectable as stage-specific embryonic antigen 3 (SSEA-3) + from various organs including the bone marrow and are pluripotent-like. The potential of human bone marrow-derived Muse cells to commit to cardiac lineage cells was evaluated. We found that (1) initial treatment of Muse cells with 5'-azacytidine in suspension culture successfully accelerated demethylation of cardiac marker Nkx2.5 promoter; (2) then transferring the cells onto adherent culture and treatment with early cardiac differentiation factors including wingless-int (Wnt)-3a, bone morphogenetic proteins (BMP)-2/4, and transforming growth factor (TGF) β1; and (3) further treatment with late cardiac differentiation cytokines including cardiotrophin-1 converted Muse cells into cardiomyocyte-like cells that expressed α-actinin and troponin-I with a striation-like pattern. MLC2a expression in the final step suggested differentiation of the cells into an atrial subtype. MLC2v, a marker for a mature ventricular subtype, was expressed when cells were treated with Dickkopf-related protein 1 (DKK-1) and Noggin, inhibitors of Wnt3a and BMP-4, respectively, between steps (2) and (3). None of the steps included exogenous gene transfection, making induced cells feasible for future clinical application.

Role of c-Kit in Myocardial Regeneration and Aging

c-Kit, a type III receptor tyrosine kinase (RTK), is involved in multiple intracellular signaling whereby it is mainly considered a stem cell factor receptor, which participates in vital functions of the mammalian body, including the human. Furthermore, c-kit is a necessary yet not sufficient marker to detect and isolate several types of tissue-specific adult stem cells. Accordingly, c-kit was initially used as a marker to identify and enrich for adult cardiac stem/progenitor cells (CSCs) that were proven to be clonogenic, self-renewing and multipotent, being able to differentiate into cardiomyocytes, endothelial cells and smooth muscle cells in vitro as well as in vivo after myocardial injury. Afterwards it was demonstrated that c-kit expression labels a heterogenous cardiac cell population, which is mainly composed by endothelial cells while only a very small fraction represents CSCs. Furthermore, c-kit as a signaling molecule is expressed at different levels in this heterogenous c-kit labeled cardiac cell pool, whereby c-kit low expressers are enriched for CSCs while c-kit high expressers are endothelial and mast cells. This heterogeneity in cell composition and expression levels has been neglected in recent genetic fate map studies focusing on c-kit, which have claimed that c-kit identifies cells with robust endothelial differentiation potential but with minimal if not negligible myogenic commitment potential. However, modification of c-kit gene for Cre Recombinase expression in these Cre/Lox genetic fate map mouse models produced a detrimental c-kit haploinsufficiency that prevents efficient labeling of true CSCs on one hand while affecting the regenerative potential of these cells on the other. Interestingly, c-kit haploinsufficiency in c-kit-deficient mice causes a worsening myocardial repair after injury and accelerates cardiac aging. Therefore, these studies have further demonstrated that adult c-kit-labeled CSCs are robustly myogenic and that the adult myocardium relies on c-kit expression to regenerate after injury and to counteract aging effects on cardiac structure and function.

Heterogeneity of Adult Cardiac Stem Cells

Cardiac biology and heart regeneration have been intensively investigated and debated in the last 15 years. Nowadays, the well-established and old dogma that the adult heart lacks of any myocyte-regenerative capacity has been firmly overturned by the evidence of cardiomyocyte renewal throughout the mammalian life as part of normal organ cell homeostasis, which is increased in response to injury. Concurrently, reproducible evidences from independent laboratories have convincingly shown that the adult heart possesses a pool of multipotent cardiac stem/progenitor cells (CSCs or CPCs) capable of sustaining cardiomyocyte and vascular tissue refreshment after injury. CSC transplantation in animal models displays an effective regenerative potential and may be helpful to treat chronic heart failure (CHF), obviating at the poor/modest results using non-cardiac cells in clinical trials. Nevertheless, the degree/significance of cardiomyocyte turnover in the adult heart, which is insufficient to regenerate extensive damage from ischemic and non-ischemic origin, remains strongly disputed. Concurrently, different methodologies used to detect CSCs in situ have created the paradox of the adult heart harboring more than seven different cardiac progenitor populations. The latter was likely secondary to the intrinsic heterogeneity of any regenerative cell agent in an adult tissue but also to the confusion created by the heterogeneity of the cell population identified by a single cell marker used to detect the CSCs in situ. On the other hand, some recent studies using genetic fate mapping strategies claimed that CSCs are an irrelevant endogenous source of new cardiomyocytes in the adult. On the basis of these contradictory findings, here we critically reviewed the available data on adult CSC biology and their role in myocardial cell homeostasis and repair.

Intensive Glucose Control Reduces the Risk Effect of TRIB3, SMARCD3, and ATF6 Genetic Variation on Diabetic Vascular Complications

Type 2 diabetes mellitus is a complex disease. Our previous study revealed that TRIB3 genetic variations were strongly associated with diabetic vascular complications, although TRIB3 regulation pathways remain poorly understood. We used two extreme treatment groups from a 2 × 2 factorial randomized controlled trial to identify a positive association, which was further validated in patients receiving cross treatment to test the effect of genetic polymorphisms among the different treatment groups. A gene-centric score (GS)-weighted model including the three associated genetic variations TRIB3 rs2295490, ATF6 rs12086247, and SMARCD3 rs58125572 was used. The results of the GS model indicated a 46% reduction in the risk of primary vascular complications in patients bearing more than two risk alleles [hazard ratio (HR) 0.54, 95% confidence interval (CI) 0.38-0.76, p < 0.001], following intensive glucose control treatment when compared with patients who received standard glucose control treatment. Furthermore, these patients benefited from active blood pressure-lowering treatment (HR 0.39, 95% CI 0.24-0.64, p < 0.001). However, no significant difference was observed between the two interventions in patients with fewer than two risk alleles (HR 1.09, 95% CI 0.86-1.39, p = 0.47). These results indicate that genetic variants in these three genes may be useful biomarkers for individualized drug therapy in diabetic patients.

The status of MAPK cascades contributes to the induction and activation of Gata4 and Nkx2.5 during the stepwise process of cardiac differentiation

Cardiac differentiation in vitro is a complex, stepwise process that is rigidly governed by a subset of transcription factors and signaling cascades. In this study, we investigated the cooperation of cardiac-specific transcription factors Gata4 and Nkx2.5, as well as mitogen-activated protein kinase (MAPK) cascades. P19 embryonic carcinoma cells were induced into spontaneously beating cardiomyocytes utilizing a two-step protocol that comprised an early stage and a late stage of differentiation. During early-stage differentiation in suspension culture, P19 cells aggregated to form embryoid bodies (EBs), and the Gata4 and Nkx2.5 genes were induced. However, Gata4 expressed at the early stage of differentiation was incapable of activating downstream gene expression, as it was localized in the cytoplasm and prone to degradation. After EBs were plated for late-stage differentiation in adherent culture, the MAPK cascades were highly activated and contributed to the activation of Gata4 and Nkx2.5. Specifically, we revealed that p38 signaling participated in regulating the localization and stabilization of Gata4 and Nkx2.5. Additionally, the JNK cascade regulated late-stage cardiac differentiation; JNK kinase reduced Gata4 stabilization and conversely alleviated Nkx2.5 degradation by direct interaction and phosphorylation of Nkx2.5. Finally, we found that the C-terminal domain of Nkx2.5 was required for its stabilization under conditions of oxidative stress and JNK activation. Overall, our results indicated that the induction and activation of Gata4 and Nkx2.5 during early- and late-stage cardiac differentiation was closely associated with the function of the MAPK signaling cascades.

Rare variants in SOX17 are associated with pulmonary arterial hypertension with congenital heart disease

BACKGROUND

Pulmonary arterial hypertension (PAH) is a rare disease characterized by distinctive changes in pulmonary arterioles that lead to progressive pulmonary arterial pressures, right-sided heart failure, and a high mortality rate. Up to 30% of adult and 75% of pediatric PAH cases are associated with congenital heart disease (PAH-CHD), and the underlying etiology is largely unknown. There are no known major risk genes for PAH-CHD.

METHODS

To identify novel genetic causes of PAH-CHD, we performed whole exome sequencing in 256 PAH-CHD patients. We performed a case-control gene-based association test of rare deleterious variants using 7509 gnomAD whole genome sequencing population controls. We then screened a separate cohort of 413 idiopathic and familial PAH patients without CHD for rare deleterious variants in the top association gene.

RESULTS

We identified SOX17 as a novel candidate risk gene (p = 5.5e-7). SOX17 is highly constrained and encodes a transcription factor involved in Wnt/β-catenin and Notch signaling during development. We estimate that rare deleterious variants contribute to approximately 3.2% of PAH-CHD cases. The coding variants identified include likely gene-disrupting (LGD) and deleterious missense, with most of the missense variants occurring in a highly conserved HMG-box protein domain. We further observed an enrichment of rare deleterious variants in putative targets of SOX17, many of which are highly expressed in developing heart and pulmonary vasculature. In the cohort of PAH without CHD, rare deleterious variants of SOX17 were observed in 0.7% of cases.

CONCLUSIONS

These data strongly implicate SOX17 as a new risk gene contributing to PAH-CHD as well as idiopathic/familial PAH. Replication in other PAH cohorts and further characterization of the clinical phenotype will be important to confirm the precise role of SOX17 and better estimate the contribution of genes regulated by SOX17.

Molecular basis of functional myogenic specification of Bona Fide multipotent adult cardiac stem cells

Ischemic Heart Disease (IHD) remains the developed world's number one killer. The improved survival from Acute Myocardial Infarction (AMI) and the progressive aging of western population brought to an increased incidence of chronic Heart Failure (HF), which assumed epidemic proportions nowadays. Except for heart transplantation, all treatments for HF should be considered palliative because none of the current therapies can reverse myocardial degeneration responsible for HF syndrome. To stop the HF epidemic will ultimately require protocols to reduce the progressive cardiomyocyte (CM) loss and to foster their regeneration. It is now generally accepted that mammalian CMs renew throughout life. However, this endogenous regenerative reservoir is insufficient to repair the extensive damage produced by AMI/IHD while the source and degree of CM turnover remains strongly disputed. Independent groups have convincingly shown that the adult myocardium harbors bona-fide tissue specific cardiac stem cells (CSCs). Unfortunately, recent reports have challenged the identity and the endogenous myogenic capacity of the c-kit expressing CSCs. This has hampered progress and unless this conflict is settled, clinical tests of repair/regenerative protocols are unlikely to provide convincing answers about their clinical potential. Here we review recent data that have eventually clarified the specific phenotypic identity of true multipotent CSCs. These cells when coaxed by embryonic cardiac morphogens undergo a precisely orchestrated myogenic commitment process robustly generating bona-fide functional cardiomyocytes. These data should set the path for the revival of further investigation untangling the regenerative biology of adult CSCs to harness their potential for HF prevention and treatment.

SMAD6 overexpression leads to accelerated myogenic differentiation of LMNA mutated cells

LMNA gene encodes lamins A and C, two major components of the nuclear lamina, a network of intermediate filaments underlying the inner nuclear membrane. Most of LMNA mutations are associated with cardiac and/or skeletal muscles defects. Muscle laminopathies include Emery-Dreifuss Muscular Dystrophy, Limb-Girdle Muscular Dystrophy 1B, LMNA-related Congenital Muscular Dystrophy and Dilated Cardiomyopathy with conduction defects. To identify potential alterations in signaling pathways regulating muscle differentiation in LMNA-mutated myoblasts, we used a previously described model of conditionally immortalized murine myoblasts: H-2K cell lines. Comparing gene expression profiles in wild-type and Lmna^∆8–11 H-2K myoblasts, we identified two major alterations in the BMP (Bone Morphogenetic Protein) pathway: Bmp4 downregulation and Smad6 overexpression. We demonstrated that these impairments lead to Lmna^∆8–11 myoblasts premature differentiation and can be rescued by downregulating Smad6 expression. Finally, we showed that BMP4 pathway defects are also present in myoblasts from human patients carrying different heterozygous LMNA mutations.

The TGFβ superfamily in cardiac dysfunction

TGFβ superfamily includes the transforming growth factor βs (TGFβs), bone morphogenetic proteins (BMPs), growth and differentiation factors (GDFs) and Activin/Inhibin families of ligands. Among the 33 members of TGFβ superfamily ligands, many act on multiple types of cells within the heart, including cardiomyocytes, cardiac fibroblasts/myofibroblasts, coronary endothelial cells, smooth muscle cells, and immune cells (e.g. monocytes/macrophages and neutrophils). In this review, we highlight recent discoveries on TGFβs, BMPs, and GDFs in different cardiac residential cellular components, in association with functional impacts in heart development, injury repair, and dysfunction. Specifically, we will review the roles of TGFβs, BMPs, and GDFs in cardiac hypertrophy, fibrosis, contractility, metabolism, angiogenesis, and regeneration.

Physiology of Cardiac Development: From Genetics to Signaling to Therapeutic Strategies

The heart is one of the first organs to form and function during embryonic development. It is comprised of multiple cell lineages, each integral for proper cardiac development, and include cardiomyocytes, endothelial cells, epicardial cells and neural crest cells. The molecular mechanisms regulating cardiac development and morphogenesis are dependent on signaling crosstalk between multiple lineages through paracrine interactions, cell-ECM interactions, and cell-cell interactions, which together, help facilitate survival, growth, proliferation, differentiation and migration of cardiac tissue. Aberrant regulation of any of these processes can induce developmental disorders and pathological phenotypes. Here, we will discuss each of these processes, the genetic factors that contribute to each step of cardiac development, as well as the current and future therapeutic targets and mechanisms of heart development and disease. Understanding the complex interactions that regulate cardiac development, proliferation and differentiation is not only vital to understanding the causes of congenital heart defects, but to also finding new therapeutics that can treat both pediatric and adult cardiac disease in the near future.

Human Pluripotent Stem Cell Differentiation into Functional Epicardial Progenitor Cells

Human pluripotent stem cells (hPSCs) are widely used to study cardiovascular cell differentiation and function. Here, we induced differentiation of hPSCs (both embryonic and induced) to proepicardial/epicardial progenitor cells that cover the heart during development. Addition of retinoic acid (RA) and bone morphogenetic protein 4 (BMP4) promoted expression of the mesodermal marker PDGFRα, upregulated characteristic (pro)epicardial progenitor cell genes, and downregulated transcription of myocardial genes. We confirmed the (pro)epicardial-like properties of these cells using in vitro co-culture assays and in ovo grafting of hPSC-epicardial cells into chick embryos. Our data show that RA + BMP4-treated hPSCs differentiate into (pro)epicardial-like cells displaying functional properties (adhesion and spreading over the myocardium) of their in vivo counterpart. The results extend evidence that hPSCs are an excellent model to study (pro)epicardial differentiation into cardiovascular cells in human development and evaluate their potential for cardiac regeneration.

The canonical way to make a heart: β-catenin and plakoglobin in heart development and remodeling

The main mediator of the canonical Wnt pathway, β-catenin, is a major effector of embryonic development, postnatal tissue homeostasis, and adult tissue regeneration. The requirement for β-catenin in cardiogenesis and embryogenesis has been well established. However, many questions regarding the molecular mechanisms by which β-catenin and canonical Wnt signaling regulate these developmental processes remain unanswered. An interesting question that emerged from our studies concerns how β-catenin signaling is modulated through interaction with other factors. Recent experimental data implicate new players in canonical Wnt signaling, particularly those which modulate β-catenin function in many its biological processes, including cardiogenesis. One of the interesting candidates is plakoglobin, a little-studied member of the catenin family which shares several mechanistic and functional features with its close relative, β-catenin. Here we have focused on the function of β-catenin in cardiogenesis. We also summarize findings on plakoglobin signaling function and discuss possible interplays between β-catenin and plakoglobin in the regulation of embryonic heart development. Impact statement Heart development, function, and remodeling are complex processes orchestrated by multiple signaling networks. This review examines our current knowledge of the role of canonical Wnt signaling in cardiogenesis and heart remodeling, focusing primarily on the mechanistic action of its effector β-catenin. We summarize the generally accepted understanding of the field based on experimental in vitro and in vivo data, and address unresolved questions in the field, specifically relating to the role of canonical Wnt signaling in heart maturation and regeneration. What are the modulators of canonical Wnt, and particularly what are the potential roles of plakoglobin, a close relative of β-catenin, in regulating Wnt signaling?Answers to these questions will enhance our understanding of the mechanism by which the canonical Wnt signaling regulates development of the heart and its regeneration after damage.

Adult cardiac stem cells are multipotent and robustly myogenic: c-kit expression is necessary but not sufficient for their identification

Multipotent adult resident cardiac stem cells (CSCs) were first identified by the expression of c-kit, the stem cell factor receptor. However, in the adult myocardium c-kit alone cannot distinguish CSCs from other c-kit-expressing (c-kit^pos) cells. The adult heart indeed contains a heterogeneous mixture of c-kit^pos cells, mainly composed of mast and endothelial/progenitor cells. This heterogeneity of cardiac c-kit^pos cells has generated confusion and controversy about the existence and role of CSCs in the adult heart. Here, to unravel CSC identity within the heterogeneous c-kit-expressing cardiac cell population, c-kit^pos cardiac cells were separated through CD45-positive or -negative sorting followed by c-kit^pos sorting. The blood/endothelial lineage-committed (Lineage^pos) CD45^posc-kit^pos cardiac cells were compared to CD45^neg(Lineage^neg/Lin^neg) c-kit^pos cardiac cells for stemness and myogenic properties in vitro and in vivo. The majority (~90%) of the resident c-kit^pos cardiac cells are blood/endothelial lineage-committed CD45^posCD31^posc-kit^pos cells. In contrast, the Lin^negCD45^negc-kit^pos cardiac cell cohort, which represents ⩽10% of the total c-kit^pos cells, contain all the cardiac cells with the properties of adult multipotent CSCs. These characteristics are absent from the c-kit^neg and the blood/endothelial lineage-committed c-kit^pos cardiac cells. Single Lin^negc-kit^pos cell-derived clones, which represent only 1-2% of total c-kit^pos myocardial cells, when stimulated with TGF-β/Wnt molecules, acquire full transcriptome and protein expression, sarcomere organisation, spontaneous contraction and electrophysiological properties of differentiated cardiomyocytes (CMs). Genetically tagged cloned progeny of one Lin^negc-kit^pos cell when injected into the infarcted myocardium, results in significant regeneration of new CMs, arterioles and capillaries, derived from the injected cells. The CSC's myogenic regenerative capacity is dependent on commitment to the CM lineage through activation of the SMAD2 pathway. Such regeneration was not apparent when blood/endothelial lineage-committed c-kit^pos cardiac cells were injected. Thus, among the cardiac c-kit^pos cell cohort only a very small fraction has the phenotype and the differentiation/regenerative potential characteristics of true multipotent CSCs.

Graphene Sheet-Induced Global Maturation of Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Human induced pluripotent stem cells (hiPSCs) can proliferate infinitely. Their ability to differentiate into cardiomyocytes provides abundant sources for disease modeling, drug screening and regenerative medicine. However, hiPSC-derived cardiomyocytes (hiPSC-CMs) display a low degree of maturation and fetal-like properties. Current in vitro differentiation methods do not mimic the structural, mechanical, or physiological properties of the cardiogenesis niche. Recently, we present an efficient cardiac maturation platform that combines hiPSCs monolayer cardiac differentiation with graphene substrate, which is a biocompatible and superconductive material. The hiPSCs lines were successfully maintained on the graphene sheets and were able to differentiate into functional cardiomyocytes. This strategy markedly increased the myofibril ultrastructural organization, elevated the conduction velocity, and enhanced both the Ca²⁺ handling and electrophysiological properties in the absence of electrical stimulation. On the graphene substrate, the expression of connexin 43 increased along with the conduction velocity. Interestingly, the bone morphogenetic proteins signaling was also significantly activated during early cardiogenesis, confirmed by RNA sequencing analysis. Here, we reasoned that graphene substrate as a conductive biomimetic surface could facilitate the intrinsic electrical propagation, mimicking the microenvironment of the native heart, to further promote the global maturation of hiPSC-CMs. Our findings highlight the capability of electrically active substrates to influence cardiomyocyte development. We believe that application of graphene sheets will be useful for simple, fast, and scalable maturation of regenerated cardiomyocytes.

Genome-Wide Temporal Profiling of Transcriptome and Open Chromatin of Early Cardiomyocyte Differentiation Derived From hiPSCs and hESCs

RATIONALE

Recent advances have improved our ability to generate cardiomyocytes from human induced pluripotent stem cells (hiPSCs) and human embryonic stem cells (hESCs). However, our understanding of the transcriptional regulatory networks underlying early stages (ie, from mesoderm to cardiac mesoderm) of cardiomyocyte differentiation remains limited.

OBJECTIVE

To characterize transcriptome and chromatin accessibility during early cardiomyocyte differentiation from hiPSCs and hESCs.

METHODS AND RESULTS

We profiled the temporal changes in transcriptome and chromatin accessibility at genome-wide levels during cardiomyocyte differentiation derived from 2 hiPSC lines and 2 hESC lines at 4 stages: pluripotent stem cells, mesoderm, cardiac mesoderm, and differentiated cardiomyocytes. Overall, RNA sequencing analysis revealed that transcriptomes during early cardiomyocyte differentiation were highly concordant between hiPSCs and hESCs, and clustering of 4 cell lines within each time point demonstrated that changes in genome-wide chromatin accessibility were similar across hiPSC and hESC cell lines. Weighted gene co-expression network analysis (WGCNA) identified several modules that were strongly correlated with different stages of cardiomyocyte differentiation. Several novel genes were identified with high weighted connectivity within modules and exhibited coexpression patterns with other genes, including noncoding RNA LINC01124 and uncharacterized RNA AK127400 in the module related to the mesoderm stage; E-box-binding homeobox 1 (ZEB1) in the module correlated with postcardiac mesoderm. We further demonstrated that ZEB1 is required for early cardiomyocyte differentiation. In addition, based on integrative analysis of both WGCNA and transcription factor motif enrichment analysis, we determined numerous transcription factors likely to play important roles at different stages during cardiomyocyte differentiation, such as T and eomesodermin (EOMES; mesoderm), lymphoid enhancer-binding factor 1 (LEF1) and mesoderm posterior BHLH transcription factor 1 (MESP1; from mesoderm to cardiac mesoderm), meis homeobox 1 (MEIS1) and GATA-binding protein 4 (GATA4) (postcardiac mesoderm), JUN and FOS families, and MEIS2 (cardiomyocyte).

CONCLUSIONS

Both hiPSCs and hESCs share similar transcriptional regulatory mechanisms underlying early cardiac differentiation, and our results have revealed transcriptional regulatory networks and new factors (eg, ZEB1) controlling early stages of cardiomyocyte differentiation.

Cardiac Regeneration: Lessons From Development

Palliative surgery for congenital heart disease has allowed patients with previously lethal heart malformations to survive and, in most cases, to thrive. However, these procedures often place pressure and volume loads on the heart, and over time, these chronic loads can cause heart failure. Current therapeutic options for initial surgery and chronic heart failure that results from failed palliation are limited, in part, by the mammalian heart's low inherent capacity to form new cardiomyocytes. Surmounting the heart regeneration barrier would transform the treatment of congenital, as well as acquired, heart disease and likewise would enable development of personalized, in vitro cardiac disease models. Although these remain distant goals, studies of heart development are illuminating the path forward and suggest unique opportunities for heart regeneration, particularly in fetal and neonatal periods. Here, we review major lessons from heart development that inform current and future studies directed at enhancing cardiac regeneration.

Transforming growth factor β: A potential biomarker and therapeutic target of ventricular remodeling

Transforming growth factor β (TGF-β) is a multifunctional cytokine that is synthesized by many types of cells and regulates the cell cycle. Increasing evidence has led to TGF-β receiving increased and deserved attention in recent years because it may play a potentially novel and critical role in the development and progression of myocardial fibrosis and the subsequent progress of ventricular remodeling (VR). Numerous studies have highlighted a crucial role of TGF-β in VR and suggest potential therapeutic targets of the TGF-β signaling pathways for VR. Changes in TGF-β activity may elicit anti-VR activity and may serve as a novel therapeutic target for VR therapy. This review we discusses the smad-dependent signaling pathway, such as TGF-β/Smads, TGF-β/Sirtuins, TGF-β/BMP, TGF-β/miRNAs, TGF-β/MAPK, and Smad-independent signaling pathway of TGF-β, such as TGF-β/PI3K/Akt, TGF-β/Rho/ROCK,TGF-β/Wnt/β-catenin in the cardiac fibrosis and subsequent progression of VR. Furthermore, agonists and antagonists of TGF-β as potential therapeutic targets in VR are also described.

Transcriptome dynamics of human pluripotent stem cell-derived contracting cardiomyocytes using an embryoid body model with fetal bovine serum

Current cardiomyocyte (CM) differentiation protocols did not promote the sufficient expression of genes involved in oxidative phosphorylation for generating adult-like mature CMs.

BMP4 promotes mouse iPS cell differentiation to male germ cells via Smad1/5, Gata4, Id1 and Id2

Generation of male germ cells from pluripotent cells could provide male gametes for treating male infertility and offer an ideal model for unveiling molecular mechanisms of spermatogenesis. However, the influence and exact molecular mechanisms, especially downstream effectors of BMP4 signaling pathways, in male germ cell differentiation of the induce pluripotent stem (iPS) cells, remain unknown. This study was designed to explore the role and mechanism of BMP4 signaling in the differentiation of mouse iPS cells to male germ cells. Embryoid body (EB) formation and recombinant BMP4 or Noggin were utilized to evaluate the effect of BMP4 on male germ cell generation from mouse iPS cells. Germ cell-specific genes and proteins as well as the downstream effectors of BMP4 signaling pathway were assessed using real-time PCR and Western blots. We found that BMP4 ligand and its multiple receptors, including BMPR1a, BMPR1b and BMPR2, were expressed in mouse iPS cells. Real-time PCR and Western blots revealed that BMP4 could upregulate the levels of genes and proteins for germ cell markers in iPS cells-derived EBs, whereas Noggin decreased their expression in these cells. Moreover, Smad1/5 phosphorylation, Gata4 transcription and the transcripts of Id1 and Id2 were enhanced by BMP4 but decreased when exposed to Noggin. Collectively, these results suggest that BMP4 promotes the generation of male germ cells from iPS cells via Smad1/5 pathway and the activation of Gata4, Id1 and Id2 This study thus offers novel insights into molecular mechanisms underlying male germ cell development.

CIBZ Regulates Mesodermal and Cardiac Differentiation of by Suppressing T and Mesp1 Expression in Mouse Embryonic Stem Cells

The molecular mechanisms underlying mesodermal and cardiac specification from embryonic stem cells (ESCs) are not fully understood. Here, we showed that the BTB domain-containing zinc finger protein CIBZ is expressed in mouse ESCs but is dramatically downregulated during ESC differentiation. CIBZ deletion in ESCs induced specification toward mesoderm phenotypes and their differentiation into cardiomyocytes, whereas overexpression of CIBZ delayed these processes. During ESC differentiation, CIBZ loss-and-gain-of-function data indicate that CIBZ negatively regulates the expressions of Brachyury (T) and Mesp1, the key transcriptional factors responsible for the specification of mammalian mesoderm and cardiac progenitors, respectively. Chromatin immunoprecipitation assays showed that CIBZ binds to T and Mesp1 promoters in undifferentiated ESCs, and luciferase assays indicate that CIBZ suppresses T and Mesp1 promoters. These findings demonstrate that CIBZ is a novel regulator of mesodermal and cardiac differentiation of ESCs, and suggest that CIBZ-mediated cardiac differentiation depends on the regulation of these two genes.

Paracrine nitric oxide induces expression of cardiac sarcomeric proteins in adult progenitor cells through soluble guanylyl cyclase/cyclic-guanosine monophosphate and Wnt/β-catenin inhibition

AIM

Cardiac progenitor cells (CPC) from adult hearts can differentiate to several cell types composing the myocardium but the underlying molecular pathways are poorly characterized. We examined the role of paracrine nitric oxide (NO) in the specification of CPC to the cardiac lineage, particularly through its inhibition of the canonical Wnt/β-catenin pathway, a critical step preceding cardiac differentiation.

METHODS AND RESULTS

Sca1 + CPC from adult mouse hearts were isolated by magnetic-activated cell sorting and clonally expanded. Pharmacologic NO donors increased their expression of cardiac myocyte-specific sarcomeric proteins in a concentration and time-dependent manner. The optimal time window for NO efficacy coincided with up-regulation of CPC expression of Gucy1a3 (coding the alpha1 subunit of guanylyl cyclase). The effect of paracrine NO was reproduced in vitro upon co-culture of CPC with cardiac myocytes expressing a transgenic NOS3 (endothelial nitric oxide synthase) and in vivo upon injection of CPC in infarcted hearts from cardiac-specific NOS3 transgenic mice. In mono- and co-cultures, this effect was abrogated upon inhibition of soluble guanylyl cyclase or nitric oxide synthase, and was lost in CPC genetically deficient in Gucy1a3. Mechanistically, NO inhibits the constitutive activity of the canonical Wnt/β-catenin in CPC and in cell reporter assays in a guanylyl cyclase-dependent fashion. This was paralleled with decreased expression of β-catenin and down-regulation of Wnt target genes in CPC and abrogated in CPC with a stabilized, non-inhibitable β-catenin.

CONCLUSIONS

Exogenous or paracrine sources of NO promote the specification towards the myocyte lineage and expression of cardiac sarcomeric proteins of adult CPC. This is contingent upon the expression and activity of the alpha1 subunit of guanylyl cyclase in CPC that is necessary for NO-mediated inhibition of the canonical Wnt/β-catenin pathway.