Fibroblast growth factor signals regulate a wave of Hedgehog activation that is essential for coronary vascular development

Dissection of zebrafish shha function using site-specific targeting with a Cre-dependent genetic switch

Despite the extensive use of zebrafish as a model organism in developmental biology and regeneration research, genetic techniques enabling conditional analysis of gene function are limited. In this study, we generated Zwitch, a Cre-dependent invertible gene-trap cassette, enabling the establishment of conditional alleles in zebrafish by generating intronic insertions via in vivo homologous recombination. To demonstrate the utility of Zwitch, we generated a conditional sonic hedgehog a (shha) allele. Homozygous shha mutants developed normally; however, shha mutant embryos globally expressing Cre exhibited strong reductions in endogenous shha and shha target gene mRNA levels and developmental defects associated with null shha mutations. Analyzing a conditional shha mutant generated using an epicardium-specific inducible Cre driver revealed unique roles for epicardium-derived Shha in myocardial proliferation during heart development and regeneration. Zwitch will extend the utility of zebrafish in organ development and regeneration research and might be applicable to other model organisms.

DOI:http://dx.doi.org/10.7554/eLife.24635.001

Proteomic characterization of epicardial-myocardial signaling reveals novel regulatory networks including a role for NF-κB in epicardial EMT

Signaling between the epicardium and underlying myocardium is crucial for proper heart development. The complex molecular interactions and regulatory networks involved in this communication are not well understood. In this study, we integrated mass spectrometry with bioinformatics to systematically characterize the secretome of embryonic chicken EPDC-heart explant (EHE) co-cultures. The 150-protein secretome dataset established greatly expands the knowledge base of the molecular players involved in epicardial-myocardial signaling. We identified proteins and pathways that are implicated in epicardial-myocardial signaling for the first time, as well as new components of pathways that are known to regulate the crosstalk between epicardium and myocardium. The large size of the dataset enabled bioinformatics analysis to deduce networks for the regulation of specific biological processes and predicted signal transduction nodes within the networks. We performed functional analysis on one of the predicted nodes, NF-κB, and demonstrate that NF-κB activation is an essential step in TGFβ2/PDGFBB-induced cardiac epithelial-to-mesenchymal transition. In summary, we have generated a global perspective of epicardial-myocardial signaling for the first time, and our findings open exciting new avenues for investigating the molecular basis of heart development and regeneration.

Approaches to augment vascularisation and regeneration of the adult heart via the reactivated epicardium

Survival rates following myocardial infarction have increased in recent years but current treatments for post-infarction recovery are inadequate and cannot induce regeneration of damaged hearts. Regenerative medicine could provide disease-reversing treatments by harnessing modern concepts in cell and developmental biology. A recently-established paradigm in regenerative medicine is that regeneration of a tissue can be achieved by reactivation of the coordinated developmental processes that originally formed the tissue. In the heart, the epicardium has emerged as an important regulator of cardiac development and reactivation of epicardial developmental processes may provide a means to enable cardiac regeneration. Indeed, in adult mouse hearts, treatment with thymosin β4 and other drug-like molecules reactivates the epicardium and improves outcomes after myocardial infarction by inducing regenerative paracrine signalling, neovascularisation and de novo cardiomyocyte production. However, there are considerable limitations to current methods of epicardial reactivation that prevent direct translation into clinical practice. Here, we describe the rationale for targeting the epicardium and the successes and limitations of this approach. We consider how several recent advances in epicardial biology could be used to overcome these limitations. These advances include insight into epicardial signalling and heterogeneity, epicardial modulation of inflammation and epicardial remodelling of extracellular matrix.

Coronary Artery Development: Progenitor Cells and Differentiation Pathways

Coronary artery disease (CAD) is the number one cause of death worldwide and involves the accumulation of plaques within the artery wall that can occlude blood flow to the heart and cause myocardial infarction. The high mortality associated with CAD makes the development of medical interventions that repair and replace diseased arteries a high priority for the cardiovascular research community. Advancements in arterial regenerative medicine could benefit from a detailed understanding of coronary artery development during embryogenesis and of how these pathways might be reignited during disease. Recent research has advanced our knowledge on how the coronary vasculature is built and revealed unexpected features of progenitor cell deployment that may have implications for organogenesis in general. Here, we highlight these recent findings and discuss how they set the stage to interrogate developmental pathways during injury and disease.

Targeting the hedgehog signaling pathway for cardiac repair and regeneration

The hedgehog (Hh) signaling pathway is involved in the angiogenesis and development of the coronary vasculature in the embryonic heart. Recently, the Hh signal pathway has emerged as an important regulator that can increase cardiomyocyte proliferation, inhibit cardiomyocyte death and apoptosis, recruit endothelial progenitor cell (EPCs) into sites of myocardial ischemia, and direct stem cells to differentiate into cardiac muscle lineage. Experimental studies have tried to target the Hh signaling pathway for cardiac repair and regeneration. The purpose of this review is to discuss the role of the Hh signal pathway in cardiac repair and regeneration as well as the current strategies targeting the Hh signaling pathway and its potential in heart diseases.

Primitive Embryonic Macrophages are Required for Coronary Development and Maturation

RATIONALE

It is now recognized that macrophages residing within developing and adult tissues are derived from diverse progenitors including those of embryonic origin. Although the functions of macrophages in adult organisms are well studied, the functions of macrophages during organ development remain largely undefined. Moreover, it is unclear whether distinct macrophage lineages have differing functions.

OBJECTIVE

To address these issues, we investigated the functions of macrophage subsets resident within the developing heart, an organ replete with embryonic-derived macrophages.

METHODS AND RESULTS

Using a combination of flow cytometry, immunostaining, and genetic lineage tracing, we demonstrate that the developing heart contains a complex array of embryonic macrophage subsets that can be divided into chemokine (C-C motif) receptor 2(-) and chemokine (C-C motif) receptor 2(+) macrophages derived from primitive yolk sac, recombination activating gene 1(+) lymphomyeloid, and Fms-like tyrosine kinase 3(+) fetal monocyte lineages. Functionally, yolk sac-derived chemokine (C-C motif) receptor 2(-) macrophages are instrumental in coronary development where they are required for remodeling of the primitive coronary plexus. Mechanistically, chemokine (C-C motif) receptor 2(-) macrophages are recruited to coronary blood vessels at the onset of coronary perfusion where they mediate coronary plexus remodeling through selective expansion of perfused vasculature. We further demonstrate that insulin like growth factor signaling may mediate the proangiogenic properties of embryonic-derived macrophages.

CONCLUSIONS

Together, these findings demonstrate that the embryonic heart contains distinct lineages of embryonic macrophages with unique functions and reveal a novel mechanism that governs coronary development.

Epicardial Epithelial-to-Mesenchymal Transition in Heart Development and Disease

The epicardium is an epithelial monolayer that plays a central role in heart development and the myocardial response to injury. Recent developments in our understanding of epicardial cell biology have revealed this layer to be a dynamic participant in fundamental processes underlying the development of the embryonic ventricles, the coronary vasculature, and the cardiac valves. Likewise, recent data have identified the epicardium as an important contributor to reparative and regenerative processes in the injured myocardium. These essential functions of the epicardium rely on both non-cell autonomous and cell-autonomous mechanisms, with the latter featuring the process of epicardial Epithelial-to-Mesenchymal Transition (EMT). This review will focus on the induction and regulation of epicardial EMT, as it pertains to both cardiogenesis and the response of the myocardium to injury.

Congenital coronary artery anomalies: a bridge from embryology to anatomy and pathophysiology--a position statement of the development, anatomy, and pathology ESC Working Group

Congenital coronary artery anomalies are of major significance in clinical cardiology and cardiac surgery due to their association with myocardial ischaemia and sudden death. Such anomalies are detectable by imaging modalities and, according to various definitions, their prevalence ranges from 0.21 to 5.79%. This consensus document from the Development, Anatomy and Pathology Working Group of the European Society of Cardiology aims to provide: (i) a definition of normality that refers to essential anatomical and embryological features of coronary vessels, based on the integrated analysis of studies of normal and abnormal coronary embryogenesis and pathophysiology; (ii) an animal model-based systematic survey of the molecular and cellular mechanisms that regulate coronary blood vessel development; (iii) an organization of the wide spectrum of coronary artery anomalies, according to a comprehensive anatomical and embryological classification scheme; (iv) current knowledge of the pathophysiological mechanisms underlying symptoms and signs of coronary artery anomalies, with diagnostic and therapeutic implications. This document identifies the mosaic-like embryonic development of the coronary vascular system, as coronary cell types differentiate from multiple cell sources through an intricate network of molecular signals and haemodynamic cues, as the necessary framework for understanding the complex spectrum of coronary artery anomalies observed in human patients.

Estrogen-induced CCN1 is critical for establishment of endometriosis-like lesions in mice

Endometriosis is a prevalent gynecological disorder in which endometrial tissue proliferates in extrauterine sites, such as the peritoneal cavity, eventually giving rise to painful, invasive lesions. Dysregulated estradiol (E) signaling has been implicated in this condition. However, the molecular mechanisms that operate downstream of E in the ectopic endometrial tissue are unknown. To investigate these mechanisms, we used a mouse model of endometriosis. Endometrial tissue from donor mice was surgically transplanted on the peritoneal surface of immunocompetent syngeneic recipient mice, leading to the establishment of cystic endometriosis-like lesions. Our studies revealed that treatment with E led to an approximately 3-fold increase in the lesion size within a week of transplantation. E also caused a concomitant stimulation in the expression of connective tissue growth factor/Cyr61/Nov (CCN1), a secreted cysteine-rich matricellular protein, in the lesions. Interestingly, CCN1 is highly expressed in human ectopic endometriotic lesions. To address its role in endometriosis, endometrial tissue from Ccn1-null donor mice was transplanted in wild-type recipient mice. The resulting ectopic lesions were reduced up to 75% in size compared with wild-type lesions due to diminished cell proliferation and cyst formation. Notably, loss of CCN1 also disrupted the development of vascular networks in the ectopic lesions and reduced the expression of several angiogenic factors, such as vascular endothelial growth factor-A and vascular endothelial growth factor-C. These results suggest that CCN1, acting downstream of E, critically controls cell proliferation and neovascularization, which support the growth and survival of endometriotic tissue at ectopic sites. Blockade of CCN1 signaling during the early stages of lesion establishment may provide a therapeutic avenue to control endometriosis.

Hematopoietic progenitors are required for proper development of coronary vasculature

RATIONALE

During embryogenesis, hematopoietic cells appear in the myocardium prior to the initiation of coronary formation. However, their role is unknown.

OBJECTIVE

Here we investigate whether pre-existing hematopoietic cells are required for the formation of coronary vasculature.

METHODS AND RESULTS

As a model of for hematopoietic cell deficient animals, we used Runx1 knockout embryos and Vav1-cre; R26-DTA embryos, latter of which genetically ablates 2/3 of CD45(+) hematopoietic cells. Both Runx1 knockout embryos and Vav1-cre; R26-DTA embryos revealed disorganized, hypoplastic microvasculature of coronary vessels on section and whole-mount stainings. Furthermore, coronary explant experiments showed that the mouse heart explants from Runx1 and Vav1-cre; R26-DTA embryos exhibited impaired coronary formation ex vivo. Interestingly, in both models it appears that epicardial to mesenchymal transition is adversely affected in the absence of hematopoietic progenitors.

CONCLUSION

Hematopoietic cells are not merely passively transported via coronary vessel, but substantially involved in the induction of the coronary growth. Our findings suggest a novel mechanism of coronary growth.

Fibroblast Growth Factor 9 Imparts Hierarchy and Vasoreactivity to the Microcirculation of Renal Tumors and Suppresses Metastases

Tumor vessel normalization has been proposed as a therapeutic paradigm. However, normal microvessels are hierarchical and vasoreactive with single file transit of red blood cells through capillaries. Such a network has not been identified in malignant tumors. We tested whether the chaotic tumor microcirculation could be reconfigured by the mesenchyme-selective growth factor, FGF9. Delivery of FGF9 to renal tumors in mice yielded microvessels that were covered by pericytes, smooth muscle cells, and a collagen-fortified basement membrane. This was associated with reduced pulmonary metastases. Intravital microvascular imaging revealed a haphazard web of channels in control tumors but a network of arterioles, bona fide capillaries, and venules in FGF9-expressing tumors. Moreover, whereas vasoreactivity was absent in control tumors, arterioles in FGF9-expressing tumors could constrict and dilate in response to adrenergic and nitric oxide releasing agents, respectively. These changes were accompanied by reduced hypoxia in the tumor core and reduced expression of the angiogenic factor VEGF-A. FGF9 was found to selectively amplify a population of PDGFRβ-positive stromal cells in the tumor and blocking PDGFRβ prevented microvascular differentiation by FGF9 and also worsened metastases. We conclude that harnessing local mesenchymal stromal cells with FGF9 can differentiate the tumor microvasculature to an extent not observed previously.

Up-regulation of fibroblast growth factor (FGF) 9 expression and FGF-WNT/β-catenin signaling in laser-induced wound healing

Fibroblast growth factor (FGF) 9 is secreted by both mesothelial and epithelial cells, and plays important roles in organ development and wound healing via WNT/β-catenin signaling. The aim of this study was to evaluate FGF9 expression and FGF-WNT/β-catenin signaling during wound healing of the skin. We investigated FGF9 expression and FGF-WNT/β-catenin signaling after laser ablation of mouse skin and adult human skin, as well as in cultured normal human epidermal keratinocytes (NHEKs) upon stimulation with recombinant human (rh) FGF9 and rh-transforming growth factor (TGF)-β1. Our results showed that laser ablation of both mouse skin and human skin leads to marked overexpression of FGF9 and FGF9 mRNA. Control NHEKs constitutively expressed FGF9, WNT7b, WNT2, and β-catenin, but did not show Snail or FGF receptor (FGFR) 2 expression. We also found that FGFR2 was significantly induced in NHEKs by rhFGF9 stimulation, and observed that FGFR2 expression was slightly up-regulated on particular days during the wound healing process after ablative laser therapy. Both WNT7b and WNT2 showed up-regulated protein expression during the laser-induced wound healing process in mouse skin; moreover, we discerned that the stimulatory effect of rhFGF9 and rhTGF-β1 activates WNT/β-catenin signaling via WNT7b in cultured NHEKs. Our data indicated that rhFGF9 and/or rhTGF-β1 up-regulate FGFR2, WNT7b, and β-catenin, but not FGF9 and Snail; pretreatment with rh dickkopf-1 significantly inhibited the up-regulation of FGFR2, WNT7b, and β-catenin. Our results suggested that FGF9 and FGF-WNT/β-catenin signaling may play important roles in ablative laser-induced wound healing processes.

Cellular origin and developmental program of coronary angiogenesis

Coronary artery disease causes acute myocardial infarction and heart failure. Identifying coronary vascular progenitors and their developmental program could inspire novel regenerative treatments for cardiac diseases. The developmental origins of the coronary vessels have been shrouded in mystery and debated for several decades. Recent identification of progenitors for coronary vessels within the endocardium, epicardium, and sinus venosus provides new insights into this question. In addition, significant progress has been achieved in elucidating the cellular and molecular programs that orchestrate coronary artery development. Establishing adequate vascular supply will be an essential component of cardiac regenerative strategies, and these findings raise exciting new strategies for therapeutic cardiac revascularization.

Protein kinases and associated pathways in pluripotent state and lineage differentiation

Protein kinases (PKs) mediate the reversible conversion of substrate proteins to phosphorylated forms, a key process in controlling intracellular signaling transduction cascades. Pluripotency is, among others, characterized by specifically expressed PKs forming a highly interconnected regulatory network that culminates in a finely-balanced molecular switch. Current high-throughput phosphoproteomic approaches have shed light on the specific regulatory PKs and their function in controlling pluripotent states. Pluripotent cell-derived endothelial and hematopoietic developments represent an example of the importance of pluripotency in cancer therapeutics and organ regeneration. This review attempts to provide the hitherto known kinome profile and the individual characterization of PK-related pathways that regulate pluripotency. Elucidating the underlying intrinsic and extrinsic signals may improve our understanding of the different pluripotent states, the maintenance or induction of pluripotency, and the ability to tailor lineage differentiation, with a particular focus on endothelial cell differentiation for anti-cancer treatment, cell-based tissue engineering, and regenerative medicine strategies.

The Role of miR-378a in Metabolism, Angiogenesis, and Muscle Biology

MicroRNA-378a (miR-378a, previously known as miR-378) is one of the small noncoding RNA molecules able to regulate gene expression at posttranscriptional level. Its two mature strands, miR-378a-3p and miR-378a-5p, originate from the first intron of the peroxisome proliferator-activated receptor gamma, coactivator 1 beta (ppargc1b) gene encoding PGC-1β. Embedding in the sequence of this transcriptional regulator of oxidative energy metabolism implies involvement of miR-378a in metabolic pathways, mitochondrial energy homeostasis, and related biological processes such as muscle development, differentiation, and regeneration. On the other hand, modulating the expression of proangiogenic factors such as vascular endothelial growth factor, angiopoietin-1, or interleukin-8, influencing inflammatory reaction, and affecting tumor suppressors, such as SuFu and Fus-1, miR-378a is considered as a part of an angiogenic network in tumors. In the latter, miR-378a can evoke broader actions by enhancing cell survival, reducing apoptosis, and promoting cell migration and invasion. This review describes the current knowledge on miR-378a linking oxidative/lipid metabolism, muscle biology, and blood vessel formation.

KDR identifies a conserved human and murine hepatic progenitor and instructs early liver development

Understanding the fetal hepatic niche is essential for optimizing the generation of functional hepatocyte-like cells (hepatic cells) from human embryonic stem cells (hESCs). Here, we show that KDR (VEGFR2/FLK-1), previously assumed to be mostly restricted to mesodermal lineages, marks a hESC-derived hepatic progenitor. hESC-derived endoderm cells do not express KDR but, when cultured in media supporting hepatic differentiation, generate KDR+ hepatic progenitors and KDR- hepatic cells. KDR+ progenitors require active KDR signaling both to instruct their own differentiation into hepatic cells and to non-cell-autonomously support the functional maturation of cocultured KDR- hepatic cells. Analysis of human fetal livers suggests that similar progenitors are present in human livers. Lineage tracing in mice provides in vivo evidence of a KDR+ hepatic progenitor for fetal hepatoblasts, adult hepatocytes, and adult cholangiocytes. Altogether, our findings reveal that KDR is a conserved marker for endoderm-derived hepatic progenitors and a functional receptor instructing early liver development.

The sinus venosus contributes to coronary vasculature through VEGFC-stimulated angiogenesis

Identifying coronary artery progenitors and their developmental pathways could inspire novel regenerative treatments for heart disease. Multiple sources of coronary vessels have been proposed, including the sinus venosus (SV), endocardium and proepicardium, but their relative contributions to the coronary circulation and the molecular mechanisms regulating their development are poorly understood. We created an ApjCreER mouse line as a lineage-tracing tool to map SV-derived vessels onto the heart and compared the resulting lineage pattern with endocardial and proepicardial contributions to the coronary circulation. The data showed a striking compartmentalization to coronary development. ApjCreER-traced vessels contributed to a large number of arteries, capillaries and veins on the dorsal and lateral sides of the heart. By contrast, untraced vessels predominated in the midline of the ventral aspect and ventricular septum, which are vessel populations primarily derived from the endocardium. The proepicardium gave rise to a smaller fraction of vessels spaced relatively uniformly throughout the ventricular walls. Dorsal (SV-derived) and ventral (endocardial-derived) coronary vessels developed in response to different growth signals. The absence of VEGFC, which is expressed in the epicardium, dramatically inhibited dorsal and lateral coronary growth but left vessels on the ventral side unaffected. We propose that complementary SV-derived and endocardial-derived migratory routes unite to form the coronary vasculature and that the former requires VEGFC, revealing its role as a tissue-specific mediator of blood endothelial development.

VEGF-C and aortic cardiomyocytes guide coronary artery stem development

Coronary arteries (CAs) stem from the aorta at 2 highly stereotyped locations, deviations from which can cause myocardial ischemia and death. CA stems form during embryogenesis when peritruncal blood vessels encircle the cardiac outflow tract and invade the aorta, but the underlying patterning mechanisms are poorly understood. Here, using murine models, we demonstrated that VEGF-C-deficient hearts have severely hypoplastic peritruncal vessels, resulting in delayed and abnormally positioned CA stems. We observed that VEGF-C is widely expressed in the outflow tract, while cardiomyocytes develop specifically within the aorta at stem sites where they surround maturing CAs in both mouse and human hearts. Mice heterozygous for islet 1 (Isl1) exhibited decreased aortic cardiomyocytes and abnormally low CA stems. In hearts with outflow tract rotation defects, misplaced stems were associated with shifted aortic cardiomyocytes, and myocardium induced ectopic connections with the pulmonary artery in culture. These data support a model in which CA stem development first requires VEGF-C to stimulate vessel growth around the outflow tract. Then, aortic cardiomyocytes facilitate interactions between peritruncal vessels and the aorta. Derangement of either step can lead to mispatterned CA stems. Studying this niche for cardiomyocyte development, and its relationship with CAs, has the potential to identify methods for stimulating vascular regrowth as a treatment for cardiovascular disease.

Directed differentiation of embryonic stem cells using a bead-based combinatorial screening method

We have developed a rapid, bead-based combinatorial screening method to determine optimal combinations of variables that direct stem cell differentiation to produce known or novel cell types having pre-determined characteristics. Here we describe three experiments comprising stepwise exposure of mouse or human embryonic cells to 10,000 combinations of serum-free differentiation media, through which we discovered multiple novel, efficient and robust protocols to generate a number of specific hematopoietic and neural lineages. We further demonstrate that the technology can be used to optimize existing protocols in order to substitute costly growth factors with bioactive small molecules and/or increase cell yield, and to identify in vitro conditions for the production of rare developmental intermediates such as an embryonic lymphoid progenitor cell that has not previously been reported.

Fibroblast growth factor signaling affects vascular outgrowth and is required for the maintenance of blood vessel integrity

Angiogenesis contributes to the development of numerous disorders. Even though fibroblast growth factors (FGFs) were discovered as mediators of angiogenesis more than 30 years ago, their role in developmental angiogenesis still remains elusive. We use a recently described chemical probe, SSR128129E (SSR), that selectively inhibits the action of multiple FGF receptors (FGFRs), in combination with the zebrafish model to examine the role of FGF signaling in vascular development. We observe that while FGFR signaling is less important for vessel guidance, it affects vascular outgrowth and is especially required for the maintenance of blood vessel integrity by ensuring proper cell-cell junctions between endothelial cells. In conclusion, our work illustrates the power of a small molecule probe to reveal insights into blood vessel formation and stabilization and thus of broad interest to the vascular biology community.

Connecting the coronaries: how the coronary plexus develops and is functionalized

The establishment of the coronary circulation is one of the final critical steps during heart development. Despite decades of research, our understanding of how the coronary vasculature develops and connects to the aorta remains limited. This review serves two specific purposes: it addresses recent advances in understanding the origin of the coronary endothelium, and it then focuses on the last crucial step of coronary vasculature development, the connection of the coronary plexus to the aorta. The chick and quail animal models have yielded most of the information for how these connections form, starting with a fine network of vessels that penetrate the aorta and coalesce to form two distinct ostia. Studies in mouse and rat confirm that at least some of these steps are conserved in mammals, but gaps still exist in our understanding of mammalian coronary ostia formation. The signaling cues necessary to guide the coronary plexus to the aorta are also incompletely understood. Hypoxia-inducible transcription factor-1 and its downstream targets are among the few identified genes that promote the formation of the coronary stems. Together, this review summarizes our current knowledge of coronary vascular formation and highlights the significant gaps that remain. In addition, it highlights some of the coronary artery anomalies known to affect human health, demonstrating that even seemingly subtle defects arising from incorrect coronary plexus formation can result in significant health crises.

Gi proteins mediate activation of the canonical hedgehog pathway in the myocardium

During myocardial ischemia, upregulation of the hedgehog (Hh) pathway promotes neovascularization and increases cardiomyocyte survival. The canonical Hh pathway activates a transcriptional program through the Gli family of transcription factors by derepression of the seven-transmembrane protein smoothened (Smo). The mechanisms linking Smo to Gli are complex and, in some cell types, involve coupling of Smo to Gi proteins. In the present study, we investigated, for the first time, the transcriptional response of cardiomyocytes to sonic hedgehog (Shh) and the role of Gi protein utilization. Our results show that Shh strongly activates Gli1 expression by quantitative PCR in a Smo-dependent manner in neonatal rat ventricular cardiomyocytes. Microarray analysis of gene expression changes elicited by Shh and sensitive to a Smo inhibitor identified a small subset of 37 cardiomyocyte-specific genes regulated by Shh, including some in the PKA and purinergic signaling pathways. In addition, neonatal rat ventricular cardiomyocytes infected with an adenovirus encoding GiCT, a peptide that impairs receptor-Gi protein coupling, showed reduced activation of Hh targets. In vitro data were confirmed in transgenic mice with cardiomyocyte-inducible GiCT expression. Transgenic GiCT mice showed specific reduction of Gli1 expression in the heart under basal conditions and failed to upregulate the Hh pathway upon ischemia and reperfusion injury, unlike their littermate controls. This study characterizes, for the first time, the transcriptional response of cardiomyocytes to Shh and establishes a critical role for Smo coupling to Gi in Hh signaling in the normal and ischemic myocardium.

Matrix as an interstitial transport system

The extracellular matrix (ECM) is best known for its function as a structural scaffold for the tissue and more recently as a microenvironment to sequester growth factors and cytokines allowing for rapid and localized changes in their activity in the absence of new protein synthesis. In this review, we explore this and additional new aspects of ECM function in mediating cell-to-cell communications. Fibrillar and nonfibrillar components of ECM can limit and facilitate the transport of molecules through the extracellular space while also regulating interstitial hydrostatic pressure. In turn, transmembrane communications via molecules, such as ECM metalloproteinase inducer, thrombospondins, and integrins, can further mediate cell response to extracellular cues and affect ECM composition and tissue remodeling. Other means of cell-to-cell communication include extracellular microRNA transport and its contribution to gene expression in target cells and the nanotube formation between distant cells, which has recently emerged as a novel conduit for intercellular organelle sharing thereby influencing cell survival and function. The information summarized and discussed here are not limited to the cardiovascular ECM but encompass ECM in general with specific references to the cardiovascular system.

BMPER-induced BMP signaling promotes coronary artery remodeling

The connection of the coronary vasculature to the aorta is one of the last essential steps of cardiac development. However, little is known about the signaling events that promote normal coronary artery formation. The bone morphogenetic protein (BMP) signaling pathway regulates multiple aspects of endothelial cell biology but has not been specifically implicated in coronary vascular development. BMP signaling is tightly regulated by numerous factors, including BMP-binding endothelial cell precursor-derived regulator (BMPER), which can both promote and repress BMP signaling activity. In the embryonic heart, BMPER expression is limited to the endothelial cells and the endothelial-derived cushions, suggesting that BMPER may play a role in coronary vascular development. Histological analysis of BMPER(-/-) embryos at early embryonic stages demonstrates that commencement of coronary plexus differentiation is normal and that endothelial apoptosis and cell proliferation are unaffected in BMPER(-/-) embryos compared with wild-type embryos. However, analysis between embryonic days 15.5-17.5 reveals that, in BMPER(-/-) embryos, coronary arteries are either atretic or connected distal to the semilunar valves. In vitro tubulogenesis assays indicate that isolated BMPER(-/-) endothelial cells have impaired tube formation and migratory ability compared with wild-type endothelial cells, suggesting that these defects may lead to the observed coronary artery anomalies seen in BMPER(-/-) embryos. Additionally, recombinant BMPER promotes wild-type ventricular endothelial migration in a dose-dependent manner, with a low concentration promoting and high concentrations inhibiting migration. Together, these results indicate that BMPER-regulated BMP signaling is critical for coronary plexus remodeling and normal coronary artery development.

FGF16 promotes invasive behavior of SKOV-3 ovarian cancer cells through activation of mitogen-activated protein kinase (MAPK) signaling pathway

Uncontrolled cell growth and tissue invasion define the characteristic features of cancer. Several growth factors regulate these processes by inducing specific signaling pathways. We show that FGF16, a novel factor, is expressed in human ovary, and its expression is markedly increased in ovarian tumors. This finding indicated possible involvement of FGF16 in ovarian cancer progression. We observed that FGF16 stimulates the proliferation of human ovarian adenocarcinoma cells, SKOV-3 and OAW-42. Furthermore, through the activation of FGF receptor-mediated intracellular MAPK pathway, FGF16 regulates the expression of MMP2, MMP9, SNAI1, and CDH1 and thus facilitates cellular invasion. Inhibition of FGFR as well as MAPK pathway reduces the proliferative and invasive behavior of ovarian cancer cells. Moreover, ovarian tumors with up-regulated PITX2 expression also showed activation of Wnt/β-catenin pathway that prompted us to investigate possible interaction among FGF16, PITX2, and Wnt pathway. We identified that PITX2 homeodomain transcription factor interacts with and regulates FGF16 expression. Furthermore, activation of the Wnt/β-catenin pathway induces FGF16 expression. Moreover, FGF16 promoter possesses the binding elements of PITX2 as well as T-cell factor (Wnt-responsive), in close proximity, where PITX2 and β-catenin binds to and synergistically activates the same. A detail study showed that both PITX2 and T-cell factor elements and the interaction with their binding partners are necessary for target gene expression. Taken together, our findings indicate that FGF16 in conjunction with Wnt pathway contributes to the cancer phenotype of ovarian cells and suggests that modulation of its expression in ovarian cells might be a promising therapeutic strategy for the treatment of invasive ovarian cancers.

Epicardial GATA factors regulate early coronary vascular plexus formation

During early development, GATA factors have been shown to be important for key events of coronary vasculogenesis, including formation of the epicardium. Myocardial GATA factors are required for coronary vascular (CV) formation; however, the role of epicardial localized GATAs in this process has not been addressed. The current study was conducted to investigate the molecular mechanisms by which the epicardium controls coronary vasculogenesis, focusing on the role of epicardial GATAs in establishing the endothelial plexus during early coronary vasculogenesis. To address the role of epicardial GATAs, we ablated GATA4 and GATA6 transcription factors specifically from the mouse epicardium and found that the number of endothelial cells in the sub-epicardium was drastically reduced, and concomitant coronary vascular plexus formation was significantly compromised. Here we present evidence for a novel role for epicardial GATA factors in controlling plexus formation by recruiting endothelial cells to the sub-epicardium.

Heparan sulfate deficiency disrupts developmental angiogenesis and causes congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common birth malformation with a heterogeneous etiology. In this study, we report that ablation of the heparan sulfate biosynthetic enzyme NDST1 in murine endothelium (Ndst1ECKO mice) disrupted vascular development in the diaphragm, which led to hypoxia as well as subsequent diaphragm hypoplasia and CDH. Intriguingly, the phenotypes displayed in Ndst1ECKO mice resembled the developmental defects observed in slit homolog 3 (Slit3) knockout mice. Furthermore, introduction of a heterozygous mutation in roundabout homolog 4 (Robo4), the gene encoding the cognate receptor of SLIT3, aggravated the defect in vascular development in the diaphragm and CDH. NDST1 deficiency diminished SLIT3, but not ROBO4, binding to endothelial heparan sulfate and attenuated EC migration and in vivo neovascularization normally elicited by SLIT3-ROBO4 signaling. Together, these data suggest that heparan sulfate presentation of SLIT3 to ROBO4 facilitates initiation of this signaling cascade. Thus, our results demonstrate that loss of NDST1 causes defective diaphragm vascular development and CDH and that heparan sulfate facilitates angiogenic SLIT3-ROBO4 signaling during vascular development.

Overexpressing sonic hedgehog peptide restores periosteal bone formation in a murine bone allograft transplantation model

Although activation of hedgehog (Hh) signaling has been shown to induce osteogenic differentiation in vitro and bone formation in vivo, the underlying mechanisms and the potential use of Hh-activated mesenchymal progenitors in bone defect repair remain elusive. In this study, we demonstrated that implantation of periosteal-derived mesenchymal progenitor cells (PDMPCs) that overexpressed an N-terminal sonic hedgehog peptide (ShhN) via an adenoviral vector (Ad-ShhN) restored periosteal bone collar formation in a 4-mm segmental bone allograft model in immunodeficient mice. Ad-ShhN enhanced donor cell survival and microvessel formation in collagen scaffold at 2 weeks after surgery and induced donor cell-dependent bone formation at 6 weeks after surgery. Fluorescence-activated cell sorting analysis further showed that Ad-ShhN-PDMPC-seeded scaffold contained a twofold more CD45(-)Sca-1(+)CD34(+)VEGFR2(+) endothelial progenitors than Ad-LacZ-PDMPC-seeded scaffold at day 7 after surgery. Ad-ShhN-transduced PDMPCs induced a 1.8-fold more CD31(+) microvessel formation than Ad-LacZ-transduced PDMPCs in a coculture of endothelial progenitors and PDMPCs. Taken together, our data show that overexpression of ShhN in mesenchymal progenitors improves bone defect reconstruction by enhancing donor progenitor cell survival, differentiation, and scaffold revascularization at the site of compromised periosteum. Hh agonist-based therapy, therefore, merits further investigation in tissue engineering-based applications aimed at enhancing bone defect repair and reconstruction.

Embryonic heart progenitors and cardiogenesis

The mammalian heart is a highly specialized organ, comprised of many different cell types arising from distinct embryonic progenitor populations during cardiogenesis. Three precursor populations have been identified to contribute to different myocytic and nonmyocytic cell lineages of the heart: cardiogenic mesoderm cells (CMC), the proepicardium (PE), and cardiac neural crest cells (CNCCs). This review will focus on molecular cues necessary for proper induction, expansion, and lineage-specific differentiation of these progenitor populations during cardiac development in vivo. Moreover, we will briefly discuss how the knowledge gained on embryonic heart progenitor biology can be used to develop novel therapeutic strategies for the management of congenital heart disease as well as for improvement of cardiac function in ischemic heart disease.

Tbx18 regulates development of the epicardium and coronary vessels

The epicardium and coronary vessels originate from progenitor cells in the proepicardium. Here we show that Tbx18, a T-box family member highly expressed in the proepicardium, controls critical early steps in coronary development. In Tbx18(-/-) mouse embryos, both the epicardium and coronary vessels exhibit structural and functional defects. At E12.5, the Tbx18-deficient epicardium contains protrusions and cyst-like structures overlying a disorganized coronary vascular plexus that contains ectopic structures resembling blood islands. At E13.5, the left and right coronary stems form correctly in mutant hearts. However, analysis of PECAM-1 whole mount immunostaining, distribution of SM22α(lacZ/+) activity, and analysis of coronary vascular casts suggest that defective vascular plexus remodeling produces a compromised arterial network at birth consisting of fewer distributing conduit arteries with smaller lumens and a reduced capacity to conduct blood flow. Gene expression profiles of Tbx18(-/-) hearts at E12.5 reveal altered expression of 79 genes that are associated with development of the vascular system including sonic hedgehog signaling components patched and smoothened, VEGF-A, angiopoietin-1, endoglin, and Wnt factors compared to wild type hearts. Thus, formation of coronary vasculature is responsive to Tbx18-dependent gene targets in the epicardium, and a poorly structured network of coronary conduit vessels is formed in Tbx18 null hearts due to defects in epicardial cell signaling and fate during heart development. Lastly, we demonstrate that Tbx18 possesses a SRF/CArG box dependent repressor activity capable of inhibiting progenitor cell differentiation into smooth muscle cells, suggesting a potential function of Tbx18 in maintaining the progenitor status of epicardial-derived cells.

Epicardial function of canonical Wnt-, Hedgehog-, Fgfr1/2-, and Pdgfra-signalling

AIMS

The embryonic epicardium is a source of smooth muscle cells and fibroblasts of the coronary vasculature and of the myocardium, but the signalling pathways that control mobilization and differentiation of epicardial cells are only partly known. We aimed to (re-)evaluate the relevance of canonical Wnt-, Hedgehog (Hh)-, Fibroblast growth factor receptor (Fgfr)1/2-, and platelet-derived growth factor receptor alpha (Pdgfra)-signalling in murine epicardial development.

METHODS AND RESULTS

We used a T-box 18 (Tbx18)(cre)-mediated conditional approach to delete and to stabilize, respectively, the downstream mediator of canonical Wnt-signalling, beta-catenin (Ctnnb1), to delete and activate the mediator of Hh-signalling, smoothened (Smo), and to delete Fgfr1/Fgfr2 and Pdgfra in murine epicardial development. We show that epicardial loss of Ctnnb1, Smo, or Fgfr1/Fgfr2 does not affect cardiac development, whereas the loss of Pdgfra prevents the differentiation of epicardium-derived cells into mature fibroblasts. Epicardial expression of a stabilized version of Ctnnb1 results in the formation of hyperproliferative epicardial cell clusters; epicardial expression of a constitutively active version of Smo leads to epicardial thickening and loss of epicardial mobilization.

CONCLUSION

Canonical Wnt-, Hh-, and Fgfr1/Fgfr2-signalling are dispensable for epicardial development, but Pdgfra-signalling is crucial for the differentiation of cardiac fibroblasts from epicardium-derived cells.

Epicardial calcineurin-NFAT signals through Smad2 to direct coronary smooth muscle cell and arterial wall development

AIMS

Congenital coronary artery anomalies produce serious events that include syncope, arrhythmias, myocardial infarction, or sudden death. Studying the mechanism of coronary development will contribute to the understanding of the disease and help design new diagnostic or therapeutic strategies. Here, we characterized a new calcineurin-NFAT signalling which specifically functions in the epicardium to regulate the development of smooth muscle wall of the coronary arteries.

METHODS AND RESULTS

Using tissue-specific gene deletion, we found that calcineurin-NFAT signals in the embryonic epicardium to direct coronary smooth muscle cell development. The smooth muscle wall of coronary arteries fails to mature in mice with epicardial deletion of calcineurin B1 (Cnb1), and accordingly these mutant mice develop cardiac dysfunction with reduced exercise capacity. Inhibition of calcineurin at various developmental windows shows that calcineurin-NFAT signals within a narrow time window at embryonic Day 12.5-13.5 to regulate coronary smooth muscle cell development. Within the epicardium, NFAT transcriptionally activates the expression of Smad2, whose gene product is critical for transducing transforming growth factor β (TGFβ)-Alk5 signalling to control coronary development.

CONCLUSION

Our findings demonstrate new spatiotemporal and molecular actions of calcineurin-NFAT that dictate coronary arterial wall development and a new mechanism by which calcineurin-NFAT integrates with TGFβ signalling during embryonic development.

A novel ex vivo culture method for the embryonic mouse heart

Developmental studies in the mouse are hampered by the inaccessibility of the embryo during gestation. Thus, protocols to isolate and culture individual organs of interest are essential to provide a method of both visualizing changes in development and allowing novel treatment strategies. To promote the long-term culture of the embryonic heart at late stages of gestation, we developed a protocol in which the excised heart is cultured in a semi-solid, dilute Matrigel. This substrate provides enough support to maintain the three-dimensional structure but is flexible enough to allow continued contraction. In brief, hearts are excised from the embryo and placed in a mixture of cold Matrigel diluted 1:1 with growth medium. After the diluted Matrigel solidifies, growth medium is added to the culture dish. Hearts excised as late as embryonic day 16.5 were viable for four days post-dissection. Analysis of the coronary plexus shows that this method does not disrupt coronary vascular development. Thus, we present a novel method for long-term culture of embryonic hearts.

Snai1 is important for avian epicardial cell transformation and motility

BACKGROUND

Formation of the epicardium requires several cellular processes including migration, transformation, invasion, and differentiation in order to give rise to fibroblast, smooth muscle, coronary endothelial and myocyte cell lineages within the developing myocardium. Snai1 is a zinc finger transcription factor that plays an important role in regulating cell survival and fate during embryonic development and under pathological conditions. However, its role in avian epicardial development has not been examined.

RESULTS

Here we show that Snai1 is highly expressed in epicardial cells from as early as the proepicardial cell stage and its expression is maintained as proepicardial cells migrate and spread over the surface of the myocardium and undergo epicardial-to-mesenchymal transformation in the generation of epicardial-derived cells. Using multiple in vitro assays, we show that Snai1 overexpression in chick explants enhances proepicardial cell migration at Hamburger Hamilton Stage (HH St.) 16, and epicardial-to-mesenchymal transformation, cell migration, and invasion at HH St. 24. Further, we demonstrate that Snai1-mediated cell migration requires matrix metalloproteinase activity, and MMP15 is sufficient for this process.

CONCLUSIONS

Together our data provide new insights into the multiple roles that Snai1 has in regulating avian epicardial development.

Regulator of G-protein signaling - 5 (RGS5) is a novel repressor of hedgehog signaling

Hedgehog (Hh) signaling plays fundamental roles in morphogenesis, tissue repair, and human disease. Initiation of Hh signaling is controlled by the interaction of two multipass membrane proteins, patched (Ptc) and smoothened (Smo). Recent studies identify Smo as a G-protein coupled receptor (GPCR)-like protein that signals through large G-protein complexes which contain the Gα_i subunit. We hypothesize Regulator of G-Protein Signaling (RGS) proteins, and specifically RGS5, are endogenous repressors of Hh signaling via their ability to act as GTPase activating proteins (GAPs) for GTP-bound Gα_i, downstream of Smo. In support of this hypothesis, we demonstrate that RGS5 over-expression inhibits sonic hedgehog (Shh)-mediated signaling and osteogenesis in C3H10T1/2 cells. Conversely, signaling is potentiated by siRNA-mediated knock-down of RGS5 expression, but not RGS4 expression. Furthermore, using immuohistochemical analysis and co-immunoprecipitation (Co-IP), we demonstrate that RGS5 is present with Smo in primary cilia. This organelle is required for canonical Hh signaling in mammalian cells, and RGS5 is found in a physical complex with Smo in these cells. We therefore conclude that RGS5 is an endogenous regulator of Hh-mediated signaling and that RGS proteins are potential targets for novel therapeutics in Hh-mediated diseases.

Inhibition of tumor angiogenesis and growth by a small-molecule multi-FGF receptor blocker with allosteric properties

Receptor tyrosine kinases (RTK) are targets for anticancer drug development. To date, only RTK inhibitors that block orthosteric binding of ligands and substrates have been developed. Here, we report the pharmacologic characterization of the chemical SSR128129E (SSR), which inhibits fibroblast growth factor receptor (FGFR) signaling by binding to the extracellular FGFR domain without affecting orthosteric FGF binding. SSR exhibits allosteric properties, including probe dependence, signaling bias, and ceiling effects. Inhibition by SSR is highly conserved throughout the animal kingdom. Oral delivery of SSR inhibits arthritis and tumors that are relatively refractory to anti-vascular endothelial growth factor receptor-2 antibodies. Thus, orally-active extracellularly acting small-molecule modulators of RTKs with allosteric properties can be developed and may offer opportunities to improve anticancer treatment.

FGF10 Signaling Enhances Epicardial Cell Expansion during Neonatal Mouse Heart Repair

Unlike zebrafish and newt hearts, mammalian hearts have limited capacity to regenerate. Upon injury or disease, the adult mammalian hearts form a fibrotic scar. Recently, it was shown that neonatal mouse hearts can regenerate similarly to adult zebrafish hearts. However, this capacity quickly decreases after postnatal day 7 (P7). Understanding the molecular mechanisms underlying neonatal heart regeneration might lead to therapeutic approaches for regenerating adult mammalian hearts. In this study, we utilized an inducible transgenic mouse model to determine the effects of FGF10 growth factor over expression on neonatal mouse heart regeneration/repair. Over expression of FGF10 in myocardium enhanced the expansion of Wt1 positive epicardial cells at 21 days after heart injury through increased proliferation. However, this expansion of epicardial cells did not lead to increased epithelial-to-mesenchymal transition or affect fibroblast formation or fibrosis, as seen by vimentin expression, after heart injury. Furthermore, neither continuous nor transient expression of FGF10 did not affect scar thickness or length after heart injury in neonatal hearts. Our results suggest that FGF10 can regulate epicardial cell expansion of neonatal mouse hearts after injury; however, FGF10 alone is not sufficient to cause beneficial effects on heart repair.

New insights into the developmental mechanisms of coronary vessels and epicardium

During heart development, the epicardium, which originates from the proepicardial organ (PE), is a source of coronary vessels. The PE develops from the posterior visceral mesoderm of the pericardial coelom after stimulation with a combination of weak bone morphogenetic protein and strong fibroblast growth factor (FGF) signaling. PE-derived cells migrate across the heart surface to form the epicardial sheet, which subsequently seeds multipotent subepicardial mesenchymal cells via epithelial-mesenchymal transition, which is regulated by several signaling pathways including retinoic acid, FGF, sonic hedgehog, Wnt, transforming growth factor-β, and platelet-derived growth factor. Subepicardial endothelial progenitors eventually generate the coronary vascular plexus, which acquires an arterial or venous phenotype, connects with the sinus venosus and aortic sinuses, and then matures through the recruitment of vascular smooth muscle cells under the regulation of complex growth factor signaling pathways. These developmental programs might be activated in the adult heart after injury and play a role in the regeneration/repair of the myocardium.

Cardiac gene activation analysis in mammalian non-myoblasic cells by Nkx2-5, Tbx5, Gata4 and Myocd

Cardiac transcription factors are master regulators during heart development. Some were shown to transdifferentiate tail tip and cardiac fibroblasts into cardiomyocytes. However, recent studies have showed that controversies exist. Potential difference in tail tip and cardiac fibroblast isolation may possibly confound the observations. Moreover, due to the use of a cardiac reporter (Myh6) selection strategy for induced cardiomyocyte enrichment, and the lack of tracking signals for each transcription factors, individual roles of each transcription factors in activating cardiac gene expression in mammalian non-myoblastic cells have never been elucidated. Answers to these questions are an important step toward cardiomyocyte regeneration. Because mouse 10T1/2 fibroblasts are non-myoblastic in nature and can be induced to express genes of all three types of muscle cells, they are an ideal model for the analysis of cardiac and non-cardiac gene activation after induction. We constructed bi-cistronic lentiviral vectors, capable of expressing cardiac transcription factors along with different fluorescent tracking signals. By infecting 10T1/2 fibroblasts with Nkx2-5, Tbx5, Gata4 or Myocd cardiac transcription factor lentivirus alone or different combinations, we found that only Tbx5+Myocd and Tbx5+Gata4+Myocd combinations induced Myh6 and Tnnt2 cardiac marker protein expression. Microarray-based gene ontology analysis revealed that Tbx5 alone activated genes involved in the Wnt receptor signaling pathway and inhibited genes involved in a number of cardiac-related processes. Myocd alone activated genes involved in a number of cardiac-related processes and inhibited genes involved in the Wnt receptor signaling pathway and non-cardiac processes. Gata4 alone inhibited genes involved in non-cardiac processes. Tbx5+Gata4+Myocd was the most effective activator of genes associated with cardiac-related processes. Unlike Tbx5, Gata4, Myocd alone or Tbx5+Myocd, Tbx5+Gata4+Myocd activated the fewest genes associated with non-cardiac processes. Conclusively, Tbx5, Gata4 and Myocd play different roles in cardiac gene activation in mammalian non-myoblastic cells. Tbx5+Gata4+Myocd activates the most cardiac and the least non-cardiac gene expression.

Cutaneous wound healing: recruiting developmental pathways for regeneration

Following a skin injury, the damaged tissue is repaired through the coordinated biological actions that constitute the cutaneous healing response. In mammals, repaired skin is not identical to intact uninjured skin, however, and this disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development. Improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for wound healing complications. Here we focus on the roles of several key developmental signaling pathways (Wnt/β-catenin, TGF-β, Hedgehog, Notch) in mammalian cutaneous wound repair, and compare this to their function in skin development. We discuss the varying responses to cutaneous injury across the taxa, ranging from complete regeneration to scar tissue formation. Finally, we outline how research into the role of developmental pathways during skin repair has contributed to current wound therapies, and holds potential for the development of more effective treatments.

Muscle development and obesity: Is there a relationship?

The formation of skeletal muscle from the epithelial somites involves a series of events triggered by temporally and spatially discrete signals resulting in the generation of muscle fibers which vary in their contractile and metabolic nature. The fiber type composition of muscles varies between individuals and it has now been found that there are differences in fiber type proportions between lean and obese animals and humans. Amongst the possible causes of obesity, it has been suggested that inappropriate prenatal environments may 'program' the fetus and may lead to increased risks for disease in adult life. The characteristics of muscle are both heritable and plastic, giving the tissue some ability to adapt to signals and stimuli both pre and postnatally. Given that muscle is a site of fatty acid oxidation and carbohydrate metabolism and that its development can be changed by prenatal events, it is interesting to examine the possible relationship between muscle development and the risk of obesity.

The expanding role of the epicardium and epicardial-derived cells in cardiac development and disease

PURPOSE OF REVIEW

In this review, we aim at presenting and discussing the cellular and molecular mechanisms of embryonic epicardial development that may underlie the origin of congenital heart disease (CHD).

RECENT FINDINGS

New discoveries on the multiple cell lineages that form part of the original pool of epicardial progenitors and the roles played by epicardial transcription factors and morphogens in the regulation of epicardial epithelial-to-mesenchymal transition, epicardial-derived cell (EPDCs) differentiation, coronary blood vessel morphogenesis and cardiac interstitium formation are presented in a comprehensive manner.

SUMMARY

We have provided evidence on the critical participation of epicardial cells and EPDCs in normal and abnormal cardiac development, suggesting the implication of defective epicardial development in various forms of CHD.