Hand2 is an essential regulator for two Notch-dependent functions within the embryonic endocardium

Epigenetic determinants and non-myocardial signaling pathways contributing to heart growth and regeneration

Congenital heart disease is the most common birth defect worldwide. Defective cardiac myogenesis is either a major presentation or associated with many types of congenital heart disease. Non-myocardial tissues, including endocardium and epicardium, function as a supporting hub for myocardial growth and maturation during heart development. Recent research findings suggest an emerging role of epigenetics in nonmyocytes supporting myocardial development. Understanding how growth signaling pathways in non-myocardial tissues are regulated by epigenetic factors will likely identify new disease mechanisms for congenital heart diseases and shed lights for novel therapeutic strategies for heart regeneration.

A disrupted compartment boundary underlies abnormal cardiac patterning and congenital heart defects

Failure of septation of the interventricular septum (IVS) is the most common congenital heart defect (CHD), but mechanisms for patterning the IVS are largely unknown. We show that a Tbx5+/Mef2cAHF+ progenitor lineage forms a compartment boundary bisecting the IVS. This coordinated population originates at a first- and second heart field interface, subsequently forming a morphogenetic nexus. Ablation of Tbx5+/Mef2cAHF+ progenitors cause IVS disorganization, right ventricular hypoplasia and mixing of IVS lineages. Reduced dosage of the CHD transcription factor TBX5 disrupts boundary position and integrity, resulting in ventricular septation defects (VSDs) and patterning defects, including Slit2 and Ntn1 misexpression. Reducing NTN1 dosage partly rescues cardiac defects in Tbx5 mutant embryos. Loss of Slit2 or Ntn1 causes VSDs and perturbed septal lineage distributions. Thus, we identify essential cues that direct progenitors to pattern a compartment boundary for proper cardiac septation, revealing new mechanisms for cardiac birth defects.

Identification and characterization of Hand2 upstream genomic enhancers active in developing stomach and limbs

BACKGROUND

The bHLH transcription factor HAND2 plays important roles in the development of the embryonic heart, face, limbs, and sympathetic and enteric nervous systems. To define how and when HAND2 regulates these developmental systems, requires understanding the transcriptional regulation of Hand2.

RESULTS

Remarkably, Hand2 is flanked by an extensive upstream gene desert containing a potentially diverse enhancer landscape. Here, we screened the regulatory interval 200 kb proximal to Hand2 for putative enhancers using evolutionary conservation and histone marks in Hand2-expressing tissues. H3K27ac signatures across embryonic tissues pointed to only two putative enhancer regions showing deep sequence conservation. Assessment of the transcriptional enhancer potential of these elements using transgenic reporter lines uncovered distinct in vivo enhancer activities in embryonic stomach and limb mesenchyme, respectively. Activity of the identified stomach enhancer was restricted to the developing antrum and showed expression within the smooth muscle and enteric neurons. Surprisingly, the activity pattern of the limb enhancer did not overlap Hand2 mRNA but consistently yielded a defined subectodermal anterior expression pattern within multiple transgenic lines.

CONCLUSIONS

Together, these results start to uncover the diverse regulatory potential inherent to the Hand2 upstream regulatory interval.

Distinct HAND2/HAND2-AS1 Expression Levels May Fine-Tune Mesenchymal and Epithelial Cell Plasticity of Human Mesenchymal Stem Cells

We previously developed several successful decellularization strategies that yielded porcine cardiac extracellular matrices (pcECMs) exhibiting tissue-specific bioactivity and bioinductive capacity when cultured with various pluripotent and multipotent stem cells. Here, we study the tissue-specific effects of the pcECM on seeded human mesenchymal stem cell (hMSC) phenotypes using reverse transcribed quantitative polymerase chain reaction (RT-qPCR) arrays for cardiovascular related gene expression. We further corroborated interesting findings at the protein level (flow cytometry and immunological stains) as well as bioinformatically using several mRNA sequencing and protein databases of normal and pathologic adult and embryonic (organogenesis stage) tissue expression. We discovered that upon the seeding of hMSCs on the pcECM, they displayed a partial mesenchymal-to-epithelial transition (MET) toward endothelial phenotypes (CD31+) and morphologies, which were preceded by an early spike (~Day 3 onward after seeding) in HAND2 expression at both the mRNA and protein levels compared to that in plate controls. The CRISPR-Cas9 knockout (KO) of HAND2 and its associated antisense long non-coding RNA (HAND2-AS1) regulatory region resulted in proliferation arrest, hypertrophy, and senescent-like morphology. Bioinformatic analyses revealed that HAND2 and HAND2-AS1 are highly correlated in expression and are expressed in many different tissue types albeit at distinct yet tightly regulated expression levels. Deviation (downregulation or upregulation) from these basal tissue expression levels is associated with a long list of pathologies. We thus suggest that HAND2 expression levels may possibly fine-tune hMSCs' plasticity through affecting senescence and mesenchymal-to-epithelial transition states, through yet unknown mechanisms. Targeting this pathway may open up a promising new therapeutic approach for a wide range of diseases, including cancer, degenerative disorders, and aging. Nevertheless, further investigation is required to validate these findings and better understand the molecular players involved, potential inducers and inhibitors of this pathway, and eventually potential therapeutic applications.

The people behind the papers - Beth Firulli and Anthony Firulli

HAND2 is an important regulator of cardiac morphogenesis and is expressed throughout the heart. A new paper in Development dissects the gene regulatory networks downstream of HAND2 in the endocardium. To find out more about this research, we caught up with co-first author Beth Firulli and corresponding author Anthony (Tony) Firulli, Professor at Indiana Medical School. Co-first author Rajani George has left the Firulli lab and was not available for our interview.

Single cell evaluation of endocardial Hand2 gene regulatory networks reveals HAND2-dependent pathways that impact cardiac morphogenesis

The transcription factor HAND2 plays essential roles during cardiogenesis. Hand2 endocardial deletion (H2CKO) results in tricuspid atresia or double inlet left ventricle with accompanying intraventricular septum defects, hypo-trabeculated ventricles and an increased density of coronary lumens. To understand the regulatory mechanisms of these phenotypes, single cell transcriptome analysis of mouse E11.5 H2CKO hearts was performed revealing a number of disrupted endocardial regulatory pathways. Using HAND2 DNA occupancy data, we identify several HAND2-dependent enhancers, including two endothelial enhancers for the shear-stress master regulator KLF2. A 1.8 kb enhancer located 50 kb upstream of the Klf2 TSS imparts specific endothelial/endocardial expression within the vasculature and endocardium. This enhancer is HAND2-dependent for ventricular endocardium expression but HAND2-independent for Klf2 vascular and valve expression. Deletion of this Klf2 enhancer results in reduced Klf2 expression within ventricular endocardium. These data reveal that HAND2 functions within endocardial gene regulatory networks including shear-stress response.

Molecular Genetic Study on HAND2 Gene Promoter in Ventricular Septal Defect

Ventricular septal defect (VSD), the most common type of congenital heart disease (CHD), is primarily caused by cardiac dysplasia. Heart and neural crest derivatives expressed 2 (HAND2) participates in developing the right heart. The loss of HAND2 expression in humans is closely connected with ventricular septal defects. We used a case-control study to analyze the genetic variations in the HAND2 promoter region in VSD patients and controls. Some statistical analysis methods were used to analyze the association of single nucleotide polymorphisms (SNPs) with VSD. The dual-luciferase reporter assay and electrophoretic mobility shift assay (EMSA) were used to conduct functional analysis and molecular mechanism study of genetic variations. Through sequencing, we identified nine genetic variants in patients with VSD. The SNP rs2276940 G>T and rs2276941 G>A were associated with an increased risk of VSD. The dual-luciferase reporter assay showed that SNP rs2276940 G>T and rs138531627 C>G decreased the transcriptional activity of the HAND2 promoter. Transcription factors (TFs) predicting suggested that all three SNPs may change the binding of TFs. The result of EMSA showed that rs138531627 C>G may create a new binding site for TFs while rs2276940 G>T enhanced the binding affinity for TFs. These results indicated that genetic variants of the HAND2 promoter may increase the risk of VSD, and the molecular mechanism may be the change of the binding affinity of TFs.

Generation of a recombinant version of a biologically active cell-permeant human HAND2 transcription factor from E. coli

Transcription factor HAND2 has a significant role in vascularization, angiogenesis, and cardiac neural crest development. It is one of the key cardiac factors crucial for the enhanced derivation of functional and mature myocytes from non-myocyte cells. Here, we report the generation of the recombinant human HAND2 fusion protein from the heterologous system. First, we cloned the full-length human HAND2 gene (only protein-coding sequence) after codon optimization along with the fusion tags (for cell penetration, nuclear translocation, and affinity purification) into the expression vector. We then transformed and expressed it in Escherichia coli strain, BL21(DE3). Next, the effect (in terms of expression) of tagging fusion tags with this recombinant protein at two different terminals was also investigated. Using affinity chromatography, we established the one-step homogeneous purification of recombinant human HAND2 fusion protein; and through circular dichroism spectroscopy, we established that this purified protein had retained its secondary structure. We then showed that this purified human protein could transduce the human cells and translocate to its nucleus. The generated recombinant HAND2 fusion protein showed angiogenic potential in the ex vivo chicken embryo model. Following transduction in MEF2C overexpressing cardiomyoblast cells, this purified recombinant protein synergistically activated the α-MHC promoter and induced GFP expression in the α-MHC-eGFP reporter assay. Prospectively, the purified bioactive recombinant HAND2 protein can potentially be a safe and effective molecular tool in the direct cardiac reprogramming process and other biological applications.

Left ventricular noncompaction: a disorder with genotypic and phenotypic heterogeneity-a narrative review

Background and Objective

Left ventricular noncompaction (LVNC) is a cardiomyopathy characterized by excessive trabecular formation and deep recesses in the ventricular wall, with a bilaminar structure consisting of an endocardial noncompaction layer and an epicardial compacted layer. Although genetic variants have been reported in patients with LVNC, understanding of LVNC and its pathogenesis has not yet been fully elucidated. We addressed the latest findings on genes reported to be associated with LVNC morphogenesis and possible pathologies to understand the diverse spectrum between genotype and phenotype in LVNC. Also, the latest findings and issues related to the diagnosis of LVNC were summarized.

Methods

This article is written as a commentary narrative review and will provide an update on the current literature and available data on common forms of LVNC published in the past 30 years in English through to May 2022 using PubMed.

Key Content and Findings

Familial forms of LVNC are frequent, and autosomal dominant mode of inheritance has been predominantly observed. Several of the candidate causative genes are also mutated in other cardiomyopathies, suggesting a possible shared molecular and/or cellular etiology. The most common gene functions were sarcomere function whereas genes in mice LVNC models were involved in heart development. Echocardiography and cardiac magnetic resonance imaging (CMR) are useful for diagnosis although there are no unified criteria due to overdiagnosis of imaging, poor consistency between techniques, and lack of association between trabecular severity and adverse clinical outcomes.

Conclusions

This review reflects the current lack of clarity regarding the pathogenesis and significance of LVNC and showed the complexity of imaging diagnostic criteria, interpretation of the role of LVNC as a cause, and uncertainty regarding the specific genetic basis of LVNC.

Neonatal Deletion of Hand1 and Hand2 within Murine Cardiac Conduction System Reveals a Novel Role for HAND2 in Rhythm Homeostasis

The cardiac conduction system, a network of specialized cells, is required for the functioning of the heart. The basic helix loop helix factors Hand1 and Hand2 are required for cardiac morphogenesis and have been implicated in cardiac conduction system development and maintenance. Here we use embryonic and post-natal specific Cre lines to interrogate the role of Hand1 and Hand2 in the function of the murine cardiac conduction system. Results demonstrate that loss of HAND1 in the post-natal conduction system does not result in any change in electrocardiogram parameters or within the ventricular conduction system as determined by optical voltage mapping. Deletion of Hand2 within the post-natal conduction system results in sex-dependent reduction in PR interval duration in these mice, suggesting a novel role for HAND2 in regulating the atrioventricular conduction. Surprisingly, results show that loss of both HAND factors within the post-natal conduction system does not cause any consistent changes in cardiac conduction system function. Deletion of Hand2 in the embryonic left ventricle results in inconsistent prolongation of PR interval and susceptibility to atrial arrhythmias. Thus, these results suggest a novel role for HAND2 in homeostasis of the murine cardiac conduction system and that HAND1 loss potentially rescues the shortened HAND2 PR phenotype.

Endocardial Regulation of Cardiac Development

The endocardium is a specialized form of endothelium that lines the inner side of the heart chambers and plays a crucial role in cardiac development. While comparatively less studied than other cardiac cell types, much progress has been made in understanding the regulation of and by the endocardium over the past two decades. In this review, we will summarize what is currently known regarding endocardial origin and development, the relationship between endocardium and other cardiac cell types, and the various lineages that endocardial cells derive from and contribute to. These processes are driven by key molecular mechanisms such as Notch and BMP signaling. These pathways in particular have been well studied, but other signaling pathways and mechanical cues also play important roles. Finally, we will touch on the contribution of stem cell modeling in combination with single cell sequencing and its potential translational impact for congenital heart defects such as bicuspid aortic valves and hypoplastic left heart syndrome. The detailed understanding of cellular and molecular processes in the endocardium will be vital to further develop representative stem cell-derived models for disease modeling and regenerative medicine in the future.

Delving into the Molecular World of Single Ventricle Congenital Heart Disease

PURPOSE OF REVIEW

Given a general lack of emphasis on the molecular underpinnings of single ventricle (SV) congenital heart diseases (CHD), our review highlights and summarizes recent advances in uncovering the genetic and molecular mechanisms in SV CHD etiology.

RECENT FINDINGS

While common SV-associated genetic mutations were found in key cardiac transcription factors, other mutations were sporadic. With advances in genetic sequencing technologies and animal models, more disease-associated factors have been identified to act in critical cardiac signaling pathways such as NOTCH, Wnt, and TGF signaling. Recent studies have also revealed that different cardiac lineages play different roles in disease pathogenesis. SV defects are attributed to complex combinations of genetic mutations, indicating that sophisticated spatiotemporal regulation of gene transcription networks and functional cellular pathways govern disease progression. Future studies will warrant in-depth investigations into better understanding how different genetic factors converge to influence common downstream cellular pathways, resulting in SV abnormalities.

Protein tyrosine phosphatase receptor zeta 1 deletion triggers defective heart morphogenesis in mice and zebrafish

Protein tyrosine phosphatase receptor-ζ1 (PTPRZ1) is a transmembrane tyrosine phosphatase receptor highly expressed in embryonic stem cells. In the present work, gene expression analyses of Ptprz1^−/− and Ptprz1^+/+ mice endothelial cells and hearts pointed to an unidentified role of PTPRZ1 in heart development through the regulation of heart-specific transcription factor genes. Echocardiography analysis in mice identified that both systolic and diastolic functions are affected in Ptprz1^−/− compared with Ptprz1^+/+ hearts, based on a dilated left ventricular (LV) cavity, decreased ejection fraction and fraction shortening, and increased angiogenesis in Ptprz1^−/− hearts, with no signs of cardiac hypertrophy. A zebrafish ptprz1^−/− knockout was also generated and exhibited misregulated expression of developmental cardiac markers, bradycardia, and defective heart morphogenesis characterized by enlarged ventricles and defected contractility. A selective PTPRZ1 tyrosine phosphatase inhibitor affected zebrafish heart development and function in a way like what is observed in the ptprz1^−/− zebrafish. The same inhibitor had no effect in the function of the adult zebrafish heart, suggesting that PTPRZ1 is not important for the adult heart function, in line with data from the human cell atlas showing very low to negligible PTPRZ1 expression in the adult human heart. However, in line with the animal models, Ptprz1 was expressed in many different cell types in the human fetal heart, such as valvar, fibroblast-like, cardiomyocytes, and endothelial cells. Collectively, these data suggest that PTPRZ1 regulates cardiac morphogenesis in a way that subsequently affects heart function and warrant further studies for the involvement of PTPRZ1 in idiopathic congenital cardiac pathologies.

NEW & NOTEWORTHY Protein tyrosine phosphatase receptor ζ1 (PTPRZ1) is expressed in fetal but not adult heart and seems to affect heart development. In both mouse and zebrafish animal models, loss of PTPRZ1 results in dilated left ventricle cavity, decreased ejection fraction, and fraction shortening, with no signs of cardiac hypertrophy. PTPRZ1 also seems to be involved in atrioventricular canal specification, outflow tract morphogenesis, and heart angiogenesis. These results suggest that PTPRZ1 plays a role in heart development and support the hypothesis that it may be involved in congenital cardiac pathologies.

The adult heart requires baseline expression of the transcription factor Hand2 to withstand RV pressure overload

AIMS

Research on the pathophysiology of right ventricular (RV) failure has, in spite of the associated high mortality and morbidity, lagged behind compared to the left ventricle (LV).Previous work from our lab revealed that the embryonic basic helix-loop-helix transcription factor heart and neural crest derivatives expressed-2 (Hand2) is re-expressed in the adult heart and activates a 'fetal gene program' contributing to pathological cardiac remodeling under conditions of LV pressure overload. As such, ablation of cardiac expression of Hand2 conferred protection to cardiac stress and abrogated the maladaptive effects that were observed upon increased expression levels. In this study, we aimed to understand the contribution of Hand2 to RV remodeling in response to pressure overload induced by pulmonary artery banding (PAB).

METHODS AND RESULTS

In the present study, Hand2F/F and MCM- Hand2F/F mice were treated with tamoxifen (control and knockout, respectively) and subjected to six weeks of RV pressure overload induced by PAB. Echocardiographic- and MRI-derived hemodynamic parameters as well as molecular remodeling were assessed for all experimental groups and compared to sham-operated controls. Six weeks after PAB, levels of Hand2 expression increased in the control banded animals but, as expected, remained absent in the knockout hearts. Despite the dramatic differences in Hand2 expression, pressure overload resulted in impaired cardiac function independently of the genotype. In fact, Hand2 depletion seems to sensitize the RV to pressure overload as these mice develop more hypertrophy and more severe cardiac dysfunction. Higher expression levels of HAND2 were also observed in RV samples of human hearts from patients with pulmonary hypertension. In turn, the LV of RV-pressure overloaded hearts was also dramatically affected as reflected by changes in shape, decreased LV mass and impaired cardiac function. RNA sequencing revealed a distinct set of genes that are dysregulated in the pressure-overloaded RV, compared to the previously described pressure-overloaded LV.

CONCLUSIONS

Cardiac-specific depletion of Hand2 is associated with severe cardiac dysfunction in conditions of RV pressure overload. While inhibiting Hand2 expression can prevent cardiac dysfunction in conditions of LV pressure overload, the same does not hold true for conditions of RV pressure overload. This study highlights the need to better understand the molecular mechanisms driving pathological remodeling of the RV in contrast to the LV, in order to better diagnose and treat patients with RV or LV failure.

TRANSLATIONAL PERSPECTIVE

RV failure associated with pulmonary hypertension reduces long-term survival rate to 55% within 3 years, suggesting that 3 years after diagnosis almost half of the patients will die. To revert these numbers an adequate RV-specific and, therefore, more efficient treatment is needed. Our work suggests that current therapies and potential mechanisms underlying LV failure may not be suitable for RV failure. While Hand2 deletion is favorable in LV response to stress, it is particularly detrimental in the RV under similar conditions, and thus, highlighting potential severe consequences of not differentiating therapeutic targets or treatment for RV or LV failure.

Generation and characterization of cardiac valve endothelial-like cells from human pluripotent stem cells

The cardiac valvular endothelial cells (VECs) are an ideal cell source that could be used for making the valve organoids. However, few studies have been focused on the derivation of this important cell type. Here we describe a two-step chemically defined xeno-free method for generating VEC-like cells from human pluripotent stem cells (hPSCs). HPSCs were specified to KDR⁺/ISL1⁺ multipotent cardiac progenitors (CPCs), followed by differentiation into valve endothelial-like cells (VELs) via an intermediate endocardial cushion cell (ECC) type. Mechanistically, administration of TGFb1 and BMP4 may specify VEC fate by activating the NOTCH/WNT signaling pathways and previously unidentified targets such as ATF3 and KLF family of transcription factors. When seeded onto the surface of the de-cellularized porcine aortic valve (DCV) matrix scaffolds, hPSC-derived VELs exhibit superior proliferative and clonogenic potential than the primary VECs and human aortic endothelial cells (HAEC). Our results show that hPSC-derived valvular cells could be efficiently generated from hPSCs, which might be used as seed cells for construction of valve organoids or next generation tissue engineered heart valves.

Cheng et al. provide a detailed characterization of the differentiation of human pluripotent stem cells to valve endothelial cells and their function. Their results show that the valve endothelial-like cells express key markers for valve endothelial cells, exhibiting proliferative and clonogenic potential.

The E3 ubiquitin-protein ligase Rbx1 regulates cardiac wall morphogenesis in zebrafish

Cardiac trabeculae are muscular ridge-like structures within the ventricular wall that are crucial for cardiac function. In zebrafish, these structures first form primarily through the delamination of compact wall cardiomyocytes (CMs). Although defects in proteasomal degradation have been associated with decreased cardiac function, whether they also affect cardiac development has not been extensively analyzed. Here we report a role during cardiac wall morphogenesis in zebrafish for the E3 ubiquitin-protein ligase Rbx1, which has been shown to regulate the degradation of key signaling molecules. Although development is largely unperturbed in zebrafish rbx1 mutant larvae, they exhibit CM multi-layering. This phenotype is not affected by blocking ErbB signaling, but fails to manifest itself in the absence of blood flow/cardiac contractility. Surprisingly, rbx1 mutants display ErbB independent Notch reporter expression in the myocardium. We generated tissue-specific rbx1 overexpression lines and found that endothelial, but not myocardial, specific rbx1 expression normalizes the cardiac wall morphogenesis phenotype. In addition, we found that pharmacological activation of Hedgehog signaling ameliorates the multi-layered myocardial wall phenotype in rbx1 mutants. Collectively, our data indicate that endocardial activity of Rbx1 is essential for cardiac wall morphogenesis.

Direct Reprogramming Induces Vascular Regeneration Post Muscle Ischemic Injury

Reprogramming non-cardiomyocytes (non-CMs) into cardiomyocyte (CM)-like cells is a promising strategy for cardiac regeneration in conditions such as ischemic heart disease. Here, we used a modified mRNA (modRNA) gene delivery platform to deliver a cocktail, termed 7G-modRNA, of four cardiac-reprogramming genes—Gata4 (G), Mef2c (M), Tbx5 (T), and Hand2 (H)—together with three reprogramming-helper genes—dominant-negative (DN)-TGFβ, DN-Wnt8a, and acid ceramidase (AC)—to induce CM-like cells. We showed that 7G-modRNA reprogrammed 57% of CM-like cells in vitro. Through a lineage-tracing model, we determined that delivering the 7G-modRNA cocktail at the time of myocardial infarction reprogrammed ∼25% of CM-like cells in the scar area and significantly improved cardiac function, scar size, long-term survival, and capillary density. Mechanistically, we determined that while 7G-modRNA cannot create de novo beating CMs in vitro or in vivo, it can significantly upregulate pro-angiogenic mesenchymal stromal cells markers and transcription factors. We also demonstrated that our 7G-modRNA cocktail leads to neovascularization in ischemic-limb injury, indicating CM-like cells importance in other organs besides the heart. modRNA is currently being used around the globe for vaccination against COVID-19, and this study proves this is a safe, highly efficient gene delivery approach with therapeutic potential to treat ischemic diseases.

The physiological and pathological functions of VEGFR3 in cardiac and lymphatic development and related diseases

Vascular endothelial growth factor receptors (VEGFRs) are part of the evolutionarily conserved VEGF signalling pathways that regulate the development and maintenance of the body's cardiovascular and lymphovascular systems. VEGFR3, encoded by the FLT4 gene, has an indispensable and well-characterized function in development and establishment of the lymphatic system. Autosomal dominant VEGFR3 mutations, that prevent the receptor functioning as a homodimer, cause one of the major forms of hereditary primary lymphoedema; Milroy disease. Recently, we and others have shown that FLT4 variants, distinct to those observed in Milroy disease cases, predispose individuals to Tetralogy of Fallot, the most common cyanotic congenital heart disease, demonstrating a novel function for VEGFR3 in early cardiac development. Here, we examine the familiar and emerging roles of VEGFR3 in the development of both lymphovascular and cardiovascular systems, respectively, compare how distinct genetic variants in FLT4 lead to two disparate human conditions, and highlight the research still required to fully understand this multifaceted receptor.

The Endocardium and Heart Valves

Endocardial cells are specialized endothelial cells that, during embryogenesis, form a lining on the inside of the developing heart, which is maintained throughout life. Endocardial cells are an essential source for several lineages of the cardiovascular system including coronary endothelium, endocardial cushion mesenchyme, cardiomyocytes, mural cells, fibroblasts, liver vasculature, adipocytes, and hematopoietic cells. Alterations in the differentiation programs that give rise to these lineages has detrimental effects, including premature lethality or significant structural malformations present at birth. Here, we will review the literature pertaining to the contribution of endocardial cells to valvular, and nonvalvular lineages and highlight critical pathways required for these processes. The lineage differentiation potential of embryonic, and possibly adult, endocardial cells has therapeutic potential in the regeneration of damaged cardiac tissue or treatment of cardiovascular diseases.

Mis-Expression of a Cranial Neural Crest Cell-Specific Gene Program in Cardiac Neural Crest Cells Modulates HAND Factor Expression, Causing Cardiac Outflow Tract Phenotypes

Congenital heart defects (CHDs) occur with such a frequency that they constitute a significant cause of morbidity and mortality in both children and adults. A significant portion of CHDs can be attributed to aberrant development of the cardiac outflow tract (OFT), and of one of its cellular progenitors known as the cardiac neural crest cells (NCCs). The gene regulatory networks that identify cardiac NCCs as a distinct NCC population are not completely understood. Heart and neural crest derivatives (HAND) bHLH transcription factors play essential roles in NCC morphogenesis. The Hand1^PA/OFT enhancer is dependent upon bone morphogenic protein (BMP) signaling in both cranial and cardiac NCCs. The Hand1^PA/OFT enhancer is directly repressed by the endothelin-induced transcription factors DLX5 and DLX6 in cranial but not cardiac NCCs. This transcriptional distinction offers the unique opportunity to interrogate NCC specification, and to understand why, despite similarities, cranial NCC fate determination is so diverse. We generated a conditionally active transgene that can ectopically express DLX5 within the developing mouse embryo in a Cre-recombinase-dependent manner. Ectopic DLX5 expression represses cranial NCC Hand1^PA/OFT-lacZ reporter expression more effectively than cardiac NCC reporter expression. Ectopic DLX5 expression induces broad domains of NCC cell death within the cranial pharyngeal arches, but minimal cell death in cardiac NCC populations. This study shows that transcription control of NCC gene regulatory programs is influenced by their initial specification at the dorsal neural tube.

Endocardial Notch Signaling Promotes Cardiomyocyte Proliferation in the Regenerating Zebrafish Heart through Wnt Pathway Antagonism

Previous studies demonstrate that the regenerative zebrafish heart responds to injury by upregulating Notch receptors in the endocardium and epicardium. Moreover, global suppression of Notch activity following injury impairs cardiomyocyte proliferation and induces scarring. However, the lineage-specific requirements for Notch signaling and full array of downstream targets remain unidentified. Here, we demonstrate that inhibition of endocardial Notch signaling following ventricular amputation compromises cardiomyocyte proliferation and stimulates fibrosis. RNA sequencing uncovered reduced levels of two transcripts encoding secreted Wnt antagonists, Wif1 and Notum1b, in Notch-suppressed hearts. Like Notch receptors, wif1 and notum1b are induced following injury in the endocardium and epicardium. Small-molecule-mediated activation of Wnt signaling is sufficient to impair cardiomyocyte proliferation and induce scarring. Last, Wnt pathway suppression partially restored cardiomyocyte proliferation in hearts experiencing endocardial Notch inhibition. Taken together, our data demonstrate that Notch signaling supports cardiomyocyte proliferation by dampening myocardial Wnt activity during zebrafish heart regeneration.

The highly regenerative zebrafish heart responds to injury by upregulating Notch receptors in the endocardium and epicardium to support myocardial proliferation and regeneration. Zhao et al. demonstrate that endocardial (EC) Notch signaling augments the expression of secreted endocardial Wnt antagonists that dampen myocardial Wnt signaling to support regenerative cardiomyocyte renewal.

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.

The lncRNA Hand2os1/Uph locus orchestrates heart development through regulation of precise expression of Hand2

Exploration and dissection of potential actions and effects of long noncoding RNA (lncRNA) in animals remain challenging. Here, using multiple knockout mouse models and single cell RNA sequencing, we demonstrate that the divergent lncRNA Hand2os1/Uph has a key complex modulatory effect on the expression of its neighboring gene HAND2 and subsequently on heart development and function. Short deletion of the Hand2os1 promoter in mouse diminishes Hand2os1 transcription to ∼8-32%, but fails to affect HAND2 expression and yields no discernable heart phenotypes. Interestingly, full-length deletion of Hand2os1 in mouse causes moderate yet prevalent upregulation of HAND2 in hundreds of cardiac cells, leading to profound biological consequences, including dysregulated cardiac gene programs, congenital heart defects and perinatal lethality. We propose that the Hand2os1 locus dampens HAND2 expression to restrain cardiomyocyte proliferation, thereby orchestrating a balanced development of cardiac cell lineages. This study highlights the regulatory complexity of the lncRNA Hand2os1 on HAND2 expression, emphasizing the need for complementary genetic and single cell approaches to delineate the function and primary molecular effects of an lncRNA in animals.

HAND2-mediated epithelial maintenance and integrity in cardiac outflow tract morphogenesis

During embryogenesis, epithelial organization is the prerequisite for organogenesis, in particular, for establishing the tubular structure. Recent studies provided hints about epithelial formation in early heart development, which has not been systemically explored. Here, we revealed a gradient of HAND2 protein in the cardiac progenitors in the anterior dorsal pericardial wall (aDPW) and adjacent transition zone (TZ) in the outflow tract (OFT). Deletion of Hand2 caused cell arrest and accumulation in the TZ leading to defective morphogenesis. While apicobasal cell polarity was unaffected, the key epithelial elements of adherens junction and cell-matrix adhesion were disrupted in the TZ of Hand2 mutant mice, indicating poorly formed epithelium. RNA-seq analysis revealed altered regulation of the contractile fiber and actin cytoskeleton, which affected cardiomyocyte differentiation. Furthermore, we have identified Stars as being transcriptionally controlled by HAND2. STARS facilitates actin polymerization that is essential for anchoring the adhesive molecules to create cell adhesion. Thus, we have uncovered a new function of HAND2 in mediating epithelial maintenance and integrity in OFT morphogenesis. Meanwhile, this study provides insights to understanding cardiac progenitor contribution to OFT development.

Molecular discoveries and treatment strategies by direct reprogramming in cardiac regeneration

Cardiac tissue has minimal endogenous regenerative capacity in response to injury. Treatment options are limited following tissue damage after events such as myocardial infarction. Current strategies are aimed primarily at injury prevention, but attention has been increasingly targeted toward the development of regenerative therapies. This review focuses on recent developments in the field of cardiac fibroblast reprogramming into induced cardiomyocytes. Early efforts to produce cardiac regeneration centered around induced pluripotent stem cells, but clinical translation has proved elusive. Currently, techniques are being developed to directly transdifferentiate cardiac fibroblasts into induced cardiomyocytes. Viral vector-driven expression of a combination of transcription factors including Gata4, Mef2c, and Tbx5 induced cardiomyocyte development in mice. Subsequent combinational modifications have extended these results to human cell lines and increased efficacy. The miRNAs including combinations of miR-1, miR-133, miR-208, and miR-499 can improve or independently drive regeneration of cardiomyocytes. Similar results could be obtained by combinations of small molecules with or without transcription factor or miRNA expression. The local tissue environment greatly impacts favorability for reprogramming. Modulation of signaling pathways, especially those mediated by VEGF and TGF-β, enhance differentiation to cardiomyocytes. Current reprogramming strategies are not ready for clinical application, but recent breakthroughs promise regenerative cardiac therapies in the near future.

Myocardial Notch1-Rbpj deletion does not affect NOTCH signaling, heart development or function

During vertebrate cardiac development NOTCH signaling activity in the endocardium is essential for the crosstalk between endocardium and myocardium that initiates ventricular trabeculation and valve primordium formation. This crosstalk leads later to the maturation and compaction of the ventricular chambers and the morphogenesis of the cardiac valves, and its alteration may lead to disease. Although endocardial NOTCH signaling has been shown to be crucial for heart development, its physiological role in the myocardium has not been clearly established. Here we have used mouse genetics to evaluate the role of NOTCH in myocardial development. We have inactivated the unique and ubiquitous NOTCH effector RBPJ in early cardiomyocytes progenitors, and examined its consequences in cardiac development and function. Our results show that mice with Tnnt2-Cre-mediated myocardial-specific deletion of Rbpj develop to term, with homozygous mutant animals showing normal expression of cardiac development markers, and normal adult heart function. Similar observations have been obtained after Notch1 deletion with Tnnt2-Cre. We have also deleted Rbpj in both myocardial and endocardial progenitor cells, using the Nkx2.5-Cre driver, resulting in ventricular septal defect (VSD), double outlet right ventricle (DORV), and bicuspid aortic valve (BAV), due to NOTCH signaling abrogation in the endocardium of cardiac valves. Our data demonstrate that NOTCH-RBPJ inactivation in the myocardium does not affect heart development or adult cardiac function.

NOTCH maintains developmental cardiac gene network through WNT5A

NOTCH and WNT signaling pathways play critical roles in cardiac chamber formation. Here we explored the potential interactions between the two pathways in this developmental process by using genetically modified mouse models and whole embryo culture systems. By deletion of Notch1 to inactivate NOTCH1 signaling in the endocardium in vivo and ex vivo rescue experiments, we showed that myocardial WNT5A mediated endocardial NOTCH1 signaling to maintain the gene regulatory network essential for cardiac chamber formation. Furthermore, genetic deletion of β-catenin in the myocardium and inhibition of the WNT/Ca²⁺ signaling by FK506 resulted in a similar disruption of the gene regulatory network as inactivation of endocardial NOTCH1 signaling. Together, these findings identify WNT5A as a key myocardial factor that mediates the endocardial NOTCH signaling to maintain the gene regulatory network essential for cardiac chamber formation through WNT/β-catenin and WNT/Ca²⁺ signaling pathways.

Hand Factors in Cardiac Development

Congenital heart defects account for 1% of infant mortality and 10% of in utero deaths. As the vertebrate embryo develops, multiple tissue types develop in tandem to morphologically pattern the functional heart. Underlying cardiac development is a network of transcription factors known to tightly control these morphological events. Members of the Twist family of basic helix-loop-helix transcription factors, Hand1 and Hand2, are essential to this process. The expression patterns and functional role of Hand factors in neural crest cells, endocardium, myocardium, and epicardium is indicative of their importance during cardiogenesis; however, to date, an extensive understanding of the transcriptional targets of Hand proteins and their overall mechanism of action remain unclear. In this review, we summarize the recent findings that further outline the crucial functions of Hand factors during heart development and in post-natal heart function. Anat Rec, 302:101-107, 2019. © 2018 Wiley Periodicals, Inc.

The HAND1 frameshift A126FS mutation does not cause hypoplastic left heart syndrome in mice

Aims

To test if a human Hand1 frame shift mutation identified in human samples is causative of hypoplastic left heart syndrome (HLHS).

Methods and results

HLHS is a poorly understood single ventricle congenital heart defect that affects two to three infants in every 10 000 live births. The aetiologies of HLHS are largely unknown. The basic helix-loop-helix transcription factor HAND1 is required for normal heart development. Interrogation of HAND1 sequence from fixed HLHS tissues identified a somatic frame-shift mutation at Alanine 126 (NP_004812.1 p.Ala126Profs13X defined as Hand1A126fs). Hand1A126fs creates a truncated HAND1 protein that predictively functions as dominant negative. To determine if this mutation is causative of HLHS, we engineered a conditional Hand1A126fs mouse allele. Activation of this allele with Nkx2.5Cre results in E14.5 lethality accompanied by cardiac outflow tract and intraventricular septum abnormalities. Using αMHC-Cre or Mef2CAHF-Cre to activate Hand1A126fs results in reduced phenotype and limited viability. Left ventricles of Hand1A126FS mutant mice are not hypoplastic.

Conclusions

Somatically acquired Hand1A126FS mutation is not causative of HLHS. Hand1A126FS mutation does exhibit embryonic lethal cardiac defects that reflect a dominant negative function supporting the critical role of Hand1 in cardiogenesis.

Mechanisms of Trabecular Formation and Specification During Cardiogenesis

Trabecular morphogenesis is a key morphologic event during cardiogenesis and contributes to the formation of a competent ventricular wall. Lack of trabeculation results in embryonic lethality. The trabecular morphogenesis is a multistep process that includes, but is not limited to, trabecular initiation, proliferation/growth, specification, and compaction. Although a number of signaling molecules have been implicated in regulating trabeculation, the cellular processes underlying mammalian trabecular formation are not fully understood. Recent works show that the myocardium displays polarity, and oriented cell division (OCD) and directional migration of the cardiomyocytes in the monolayer myocardium are required for trabecular initiation and formation. Furthermore, perpendicular OCD is an extrinsic asymmetric cell division that contributes to trabecular specification, and is a mechanism that causes the trabecular cardiomyocytes to be distinct from the cardiomyocytes in compact zone. Once the coronary vasculature system starts to function in the embryonic heart, the trabeculae will coalesce with the compact zone to thicken the heart wall, and abnormal compaction will lead to left ventricular non-compaction (LVNC) and heart failure. There are many reviews about compaction and LVNC. In this review, we will focus on the roles of myocardial polarity and OCD in trabecular initiation, formation, and specification.

Control of cardiac jelly dynamics by NOTCH1 and NRG1 defines the building plan for trabeculation

In vertebrate hearts, the ventricular trabecular myocardium develops as a sponge-like network of cardiomyocytes that is critical for contraction and conduction, ventricular septation, papillary muscle formation and wall thickening through the process of compaction ¹ . Defective trabeculation leads to embryonic lethality^2-4 or non-compaction cardiomyopathy (NCC) ⁵ . There are divergent views on when and how trabeculation is initiated in different species. In zebrafish, trabecular cardiomyocytes extrude from compact myocardium ⁶ , whereas in chicks, chamber wall thickening occurs before overt trabeculation ⁷ . In mice, the onset of trabeculation has not been described, but is proposed to begin at embryonic day 9.0, when cardiomyocytes form radially oriented ribs ² . Endocardium-myocardium communication is essential for trabeculation, and numerous signalling pathways have been identified, including Notch^2,8 and Neuregulin (NRG) ⁴ . Late disruption of the Notch pathway causes NCC ⁵ . Whereas it has been shown that mutations in the extracellular matrix (ECM) genes Has2 and Vcan prevent the formation of trabeculae in mice^9,10 and the matrix metalloprotease ADAMTS1 promotes trabecular termination ³ , the pathways involved in ECM dynamics and the molecular regulation of trabeculation during its early phases remain unexplored. Here we present a model of trabeculation in mice that integrates dynamic endocardial and myocardial cell behaviours and ECM remodelling, and reveal new epistatic relationships between the involved signalling pathways. NOTCH1 signalling promotes ECM degradation during the formation of endocardial projections that are critical for individualization of trabecular units, whereas NRG1 promotes myocardial ECM synthesis, which is necessary for trabecular rearrangement and growth. These systems interconnect through NRG1 control of Vegfa, but act antagonistically to establish trabecular architecture. These insights enabled the prediction of persistent ECM and cardiomyocyte growth in a mouse NCC model, providing new insights into the pathophysiology of congenital heart disease.

HAND2 Target Gene Regulatory Networks Control Atrioventricular Canal and Cardiac Valve Development

The HAND2 transcriptional regulator controls cardiac development, and we uncover additional essential functions in the endothelial to mesenchymal transition (EMT) underlying cardiac cushion development in the atrioventricular canal (AVC). In Hand2-deficient mouse embryos, the EMT underlying AVC cardiac cushion formation is disrupted, and we combined ChIP-seq of embryonic hearts with transcriptome analysis of wild-type and mutants AVCs to identify the functionally relevant HAND2 target genes. The HAND2 target gene regulatory network (GRN) includes most genes with known functions in EMT processes and AVC cardiac cushion formation. One of these is Snai1, an EMT master regulator whose expression is lost from Hand2-deficient AVCs. Re-expression of Snai1 in mutant AVC explants partially restores this EMT and mesenchymal cell migration. Furthermore, the HAND2-interacting enhancers in the Snai1 genomic landscape are active in embryonic hearts and other Snai1-expressing tissues. These results show that HAND2 directly regulates the molecular cascades initiating AVC cardiac valve development.

Notch signaling regulates Hey2 expression in a spatiotemporal dependent manner during cardiac morphogenesis and trabecular specification

Hey2 gene mutations in both humans and mice have been associated with multiple cardiac defects. However, the currently reported localization of Hey2 in the ventricular compact zone cannot explain the wide variety of cardiac defects. Furthermore, it was reported that, in contrast to other organs, Notch doesn’t regulate Hey2 in the heart. To determine the expression pattern and the regulation of Hey2, we used novel methods including RNAscope and a Hey2^CreERT2 knockin line to precisely determine the spatiotemporal expression pattern and level of Hey2 during cardiac development. We found that Hey2 is expressed in the endocardial cells of the atrioventricular canal and the outflow tract, as well as at the base of trabeculae, in addition to the reported expression in the ventricular compact myocardium. By disrupting several signaling pathways that regulate trabeculation and/or compaction, we found that, in contrast to previous reports, Notch signaling and Nrg1/ErbB2 regulate Hey2 expression level in myocardium and/or endocardium, but not its expression pattern: weak expression in trabecular myocardium and strong expression in compact myocardium. Instead, we found that FGF signaling regulates the expression pattern of Hey2 in the early myocardium, and regulates the expression level of Hey2 in a Notch1 dependent manner.

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.

In Vivo Visualization of Cardiomyocyte Apicobasal Polarity Reveals Epithelial to Mesenchymal-like Transition during Cardiac Trabeculation

Despite great strides in understanding cardiac trabeculation, many mechanistic aspects remain unclear. To elucidate how cardiomyocyte shape changes are regulated during this process, we engineered transgenes to label their apical and basolateral membranes. Using these tools, we observed that compact-layer cardiomyocytes are clearly polarized while delaminating cardiomyocytes have lost their polarity. The apical transgene also enabled the imaging of cardiomyocyte apical constriction in real time. Furthermore, we found that Neuregulin signaling and blood flow/cardiac contractility are required for cardiomyocyte apical constriction and depolarization. Notably, we observed the activation of Notch signaling in cardiomyocytes adjacent to those undergoing apical constriction, and we showed that this activation is positively regulated by Neuregulin signaling. Inhibition of Notch signaling did not increase the percentage of cardiomyocytes undergoing apical constriction or of trabecular cardiomyocytes. These studies provide information about cardiomyocyte polarization and enhance our understanding of the complex mechanisms underlying ventricular morphogenesis and maturation.

Hand factor ablation causes defective left ventricular chamber development and compromised adult cardiac function

Coordinated cardiomyocyte growth, differentiation, and morphogenesis are essential for heart formation. We demonstrate that the bHLH transcription factors Hand1 and Hand2 play critical regulatory roles for left ventricle (LV) cardiomyocyte proliferation and morphogenesis. Using an LV-specific Cre allele (Hand1^LV-Cre), we ablate Hand1-lineage cardiomyocytes, revealing that DTA-mediated cardiomyocyte death results in a hypoplastic LV by E10.5. Once Hand1-linage cells are removed from the LV, and Hand1 expression is switched off, embryonic hearts recover by E16.5. In contrast, conditional LV loss-of-function of both Hand1 and Hand2 results in aberrant trabeculation and thickened compact zone myocardium resulting from enhanced proliferation and a breakdown of compact zone/trabecular/ventricular septal identity. Surviving Hand1;Hand2 mutants display diminished cardiac function that is rescued by concurrent ablation of Hand-null cardiomyocytes. Collectively, we conclude that, within a mixed cardiomyocyte population, removal of defective myocardium and replacement with healthy endogenous cardiomyocytes may provide an effective strategy for cardiac repair.

The left ventricle of the heart drives blood flow throughout the body. Impaired left ventricle function, associated either with heart failure or with certain, severe cardiac birth defects, constitutes a significant cause of mortality. Understanding how heart muscle grows is vital to developing improved treatments for these diseases. Unfortunately, genetic tools necessary to study the left ventricle have been lacking. Here we engineer the first mouse line to enable specific genetic study of the left ventricle. We show that, unlike in the adult heart, the embryonic left ventricle is remarkably tolerant of cell death, as remaining cells have the capacity to proliferate and to restore heart function. Conversely, disruption of two related genes, Hand1 and Hand2, within the left ventricle causes cells to assume the wrong identity, and to consequently overgrow and impair cardiac function. Ablation of these mutant cells rescues heart function. We conclude that selective removal of defective heart muscle and replacement with healthy cells may provide an effective therapy to treat heart failure.

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.

A HAND to TBX5 Explains the Link Between Thalidomide and Cardiac Diseases

Congenital heart disease is the leading cause of death in the first year of life. Mutations only in few genes have been linked to some cases of CHD. Thalidomide was used by pregnant women for morning sickness but was removed from the market because it caused severe malformations including CHDs. We used both in silico docking software, and in vitro molecular and biochemical methods to document a novel interaction involving Thalidomide, TBX5, and HAND2. Thalidomide binds readily to TBX5 through amino acids R81, R82, and K226 all implicated in DNA binding. It reduces TBX5 binding to DNA by 40%, and suppresses TBX5 mediated activation of the NPPA and VEGF promoters by 70%. We documented a novel interaction between TBX5 and HAND2, and showed that a p.G202V HAND2 variant associated with CHD and coronary artery diseases found in a large Lebanese family with high consanguinity, drastically inhibited this interaction by 90%. Similarly, thalidomide inhibited the TBX5/HAND2 physical interaction, and the in silico docking revealed that the same amino acids involved in the interaction of TBX5 with DNA are also involved in its binding to HAND2. Our results establish a HAND2/TBX5 pathway implicated in heart development and diseases.

Contribution of G protein-coupled estrogen receptor 1 (GPER) to 17β-estradiol-induced developmental toxicity in zebrafish

Exposure to 17β-estradiol (E2) influences the regulation of multiple signaling pathways, and E2-mediated disruption of signaling events during early development can lead to malformations such as cardiac defects. In this study, we investigated the potential role of the G-protein estrogen receptor 1 (GPER) in E2-induced developmental toxicity. Zebrafish embryos were exposed to E2 from 2h post fertilization (hpf) to 76 hpf with subsequent transcriptional measurements of heart and neural crest derivatives expressed 2 (hand2), leucine rich repeat containing 10 (lrrc10), and gper at 12, 28 and 76 hpf. Alteration in the expression of lrrc10, hand2 and gper was observed at 12 hpf and 76 hpf, but not at 28 hpf. Expression of these genes was also altered after exposure to G1 (a GPER agonist) at 76 hpf. Expression of lrrc10, hand2 and gper all coincided with the formation of cardiac edema at 76 hpf as well as other developmental abnormalities. While co-exposure of G1 with G36 (a GPER antagonist) rescued G1-induced abnormalities and altered gene expression, co-exposure of E2 with G36, or ICI 182,780 (an estrogen receptor antagonist) did not rescue E2-induced cardiac deformities or gene expression. In addition, no effects on the concentrations of downstream ER and GPER signaling molecules (cAMP or calcium) were observed in embryo homogenates after E2 treatment. These data suggest that the impacts of E2 on embryonic development at this stage are complex and may involve multiple receptor and/or signaling pathways.

The epigenetic landscape of age-related diseases: the geroscience perspective

In this review, we summarize current knowledge regarding the epigenetics of age-related diseases, focusing on those studies that have described DNA methylation landscape in cardio-vascular diseases, musculoskeletal function and frailty. We stress the importance of adopting the conceptual framework of “geroscience”, which starts from the observation that advanced age is the major risk factor for several of these pathologies and aims at identifying the mechanistic links between aging and age-related diseases. DNA methylation undergoes a profound remodeling during aging, which includes global hypomethylation of the genome, hypermethylation at specific loci and an increase in inter-individual variation and in stochastic changes of DNA methylation values. These epigenetic modifications can be an important contributor to the development of age-related diseases, but our understanding on the complex relationship between the epigenetic signatures of aging and age-related disease is still poor. The most relevant results in this field come from the use of the so called “epigenetics clocks” in cohorts of subjects affected by age-related diseases. We report these studies in final section of this review.

MicroRNA-1 upregulation promotes myocardiocyte proliferation and suppresses apoptosis during heart development

Previous studies have investigated the role of microRNAs (miRs) in heart development to reveal the miRNA mechanism of action in congenital heart disease (CHD) in children. The present study aimed to investigate the role of miR‑1 in heart development in P19 cells. The mRNA level for miR‑1 in P19 cells was detected before or after cardiomyocyte differentiation, using reverse transcription‑quantitative polymerase chain reaction analysis. Expression of cardiomyocyte differentiation markers was also analyzed. The effect of miR‑1 overexpression on the viability and apoptosis of differentiated P19 cells was assessed using MTT and Annexin V‑FITC assays, respectively. Furthermore, the effects of miR-1 on expression of markers of cell proliferation and apoptosis were also analyzed in differentiated P19 cells using western blotting. The results demonstrated that P19 cells were successfully differentiated into cardiomyocytes, and that endogenous miR‑1 expression was significantly decreased in differentiated P19 cells compared with undifferentiated P19 cells. Overexpression of miR‑1 resulted in increased viability in differentiated P19 cells and decreased apoptosis, compared with the normal control. In addition, expression of heart and neural crest derivatives expressed transcript 2 (Hand2) was increased in differentiated cells with miR‑1 overexpressed compared with normal cells, while caspase‑3 cleavage was decreased by miR‑1 overexpression. In conclusion, the present study suggested that miR-1 upregulation may be important in regulating cell proliferation and apoptosis in P19 differentiated cardiomyocytes by increasing Hand2 expression and suppressing caspase‑3 cleavage. The present study aimed to provide a theoretical basis for the explanation of the mechanism of CHD and investigate miR‑1 as a potential therapeutic target for its clinical treatment.

New concepts for an old problem: the diagnosis of endometrial hyperplasia

BACKGROUND

Endometrial hyperplasia (EH) is a uterine pathology representing a spectrum of morphological endometrial alterations. It is predominantly characterized by an increase in the endometrial gland-to-stroma ratio when compared to normal proliferative endometrium. The clinical significance of EH lies in the associated risk of progression to endometrioid endometrial cancer (EC) and 'atypical' forms of EH are regarded as premalignant lesions. Traditional histopathological classification systems for EH exhibit wide and varying degrees of diagnostic reproducibility and, as a consequence, standardized patient management can be challenging.

OBJECTIVE AND RATIONALE

EC is the most common gynaecological malignancy in developed countries. The incidence of EC is rising, with alarming increases described in the 40-44-year-old age group. This review appraises the current EH classification systems used to stratify women at risk of malignant progression to EC. In addition, we summarize the evidence base regarding the use of immunohistochemical biomarkers for EH and discuss an emerging role for genomic analysis.

SEARCH METHODS

PubMed, Medline and the Cochrane Database were searched for original peer-reviewed primary and review articles, from January 2000 to January 2016. The following search terms were used: 'endometrial hyperplasia', 'endometrial intraepithelial neoplasia', 'atypical hyperplasia', 'complex atypical hyperplasia', 'biomarker', 'immunohistochemistry', 'progression', 'genomic', 'classification' and 'stratification'.

OUTCOMES

Recent changes to EH classification reflect our current understanding of the genesis of endometrioid ECs. The concept of endometrial intraepithelial neoplasia (EIN) as a mutationally activated, monoclonal pre-malignancy represents a fundamental shift from the previously held notion that unopposed oestrogenic stimulation causes ever-increasing hyperplastic proliferation, with accumulating cytological atypia that imperceptibly leads to the development of endometrioid EC. Our review highlights several key biomarker candidates that have been described as both diagnostic tools for EH and markers of progression to EC. We propose that, moving forwards, a 'panel' approach of combinations of the immunohistochemical biomarkers described in this review may be more informative since no single candidate can currently fill the entire role.

WIDER IMPLICATIONS

EC has historically been considered a predominantly postmenopausal disease. Owing in part to the current unprecedented rates of obesity, we are starting to see signs of a shift towards a rising incidence of EC amongst pre- and peri-menopausal woman. This creates unique challenges both diagnostically and therapeutically. Furthering our understanding of the premalignant stages of EC development will allow us to pursue earlier diagnosis and facilitate appropriate stratification of women at risk of developing EC, permitting timely and appropriate therapeutic interventions.

Advances in molecular genetics for pulmonary atresia

Genetic and environmental factors may be similar in certain CHD. It has been widely accepted that it is the cumulative effect of these risk factors that results in disease. Pulmonary atresia is a rare type of complex cyanotic CHD with a poor prognosis. Understanding the molecular mechanism of pulmonary atresia is essential for future diagnosis, prevention, and therapeutic approaches. In this article, we reviewed several related copy number variants and related genetic mutations, which were identified in patients with pulmonary atresia, including pulmonary atresia with ventricular septal defect and pulmonary atresia with intact ventricular septum.

Genome-wide DNA promoter methylation and transcriptome analysis in human adipose tissue unravels novel candidate genes for obesity

Objective/methods

DNA methylation plays an important role in obesity and related metabolic complications. We examined genome-wide DNA promoter methylation along with mRNA profiles in paired samples of human subcutaneous adipose tissue (SAT) and omental visceral adipose tissue (OVAT) from non-obese vs. obese individuals.

Results

We identified negatively correlated methylation and expression of several obesity-associated genes in our discovery dataset and in silico replicated ETV6 in two independent cohorts. Further, we identified six adipose tissue depot-specific genes (HAND2, HOXC6, PPARG, SORBS2, CD36, and CLDN1). The effects were further supported in additional independent cohorts. Our top hits might play a role in adipogenesis and differentiation, obesity, lipid metabolism, and adipose tissue expandability. Finally, we show that in vitro methylation of SORBS2 directly represses gene expression.

Conclusions

Taken together, our data show distinct tissue specific epigenetic alterations which associate with obesity.

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Obesity-associated differences in DNA promoter methylation and transcriptome in human adipose tissue (ETV6).

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Depot-specific analyses revealed novel/known genes (HAND2, HOXC6, PPARG, SORBS2, CD36, CLDN1).

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EWAS revealed SSPN and CCDC125 associated to BMI in SAT or OVAT, respectively.

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Differentially methylated genes overlap in part with GWAS hits for obesity and fat distribution.

A HAND2 Loss-of-Function Mutation Causes Familial Ventricular Septal Defect and Pulmonary Stenosis

Congenital heart disease (CHD) is the most common developmental abnormality, and is the leading noninfectious cause of mortality in neonates. Increasing evidence demonstrates that genetic defects play an important role in the pathogenesis of CHD. However, CHD exhibits substantial heterogeneity, and the genetic determinants for CHD remain unknown in the overwhelming majority of cases. In the current study, the coding exons and flanking introns of the HAND2 gene, which encodes a basic helix-loop-helix transcription factor essential for normal cardiovascular development, were sequenced in 192 unrelated patients with CHD, and a novel heterozygous mutation, p.S65I, was identified in a patient with congenital ventricular septal defect (VSD). Genetic analysis of the index patient’s pedigree revealed that the mutation was present in all seven affected family members available, but absent in the 13 unaffected family members examined. Besides, in addition to VSD, five of the proband’s close relatives also had pulmonary stenosis (PS), and the proband’s son also had double outlet right ventricle (DORV). The missense mutation, which altered an evolutionarily conserved amino acid, was absent in 300 unrelated, ethnically matched healthy individuals. Biological analyses using a dual-luciferase reporter assay system showed that the mutant HAND2 was associated with significantly diminished transcriptional activity. Furthermore, the mutation abolished the synergistic activation between HAND2 and GATA4, as well as NKX2.5—two other cardiac core transcriptional factors that have been causally linked to CHD. These findings indicate that HAND2 loss-of-function mutation contributes to human CHD, perhaps via its interaction with GATA4 and NKX2.5.

Single-Cell Lineage Tracing Reveals that Oriented Cell Division Contributes to Trabecular Morphogenesis and Regional Specification

The cardiac trabeculae are sheet-like structures extending from the myocardium that function to increase surface area. A lack of trabeculation causes embryonic lethality due to compromised cardiac function. To understand the cellular and molecular mechanisms of trabecular formation, we genetically labeled individual cardiomyocytes prior to trabeculation via the brainbow multicolor system and traced and analyzed the labeled cells during trabeculation by whole-embryo clearing and imaging. The clones derived from labeled single cells displayed four different geometric patterns that are derived from different patterns of oriented cell division (OCD) and migration. Of the four types of clones, the inner, transmural, and mixed clones contributed to trabecular cardiomyocytes. Further studies showed that perpendicular OCD is an extrinsic asymmetric cell division that putatively contributes to trabecular regional specification. Furthermore, N-Cadherin deletion in labeled clones disrupted the clonal patterns. In summary, our data demonstrate that OCD contributes to trabecular morphogenesis and specification.

Endocardial Notch Signaling in Cardiac Development and Disease

The Notch signaling pathway is an ancient and highly conserved signaling pathway that controls cell fate specification and tissue patterning in the embryo and in the adult. Region-specific endocardial Notch activity regulates heart morphogenesis through the interaction with multiple myocardial-, epicardial-, and neural crest-derived signals. Mutations in NOTCH signaling elements cause congenital heart disease in humans and mice, demonstrating its essential role in cardiac development. Studies in model systems have provided mechanistic understanding of Notch function in cardiac development, congenital heart disease, and heart regeneration. Notch patterns the embryonic endocardium into prospective territories for valve and chamber formation, and later regulates the signaling processes leading to outflow tract and valve morphogenesis and ventricular trabeculae compaction. Alterations in NOTCH signaling in the endocardium result in congenital structural malformations that can lead to disease in the neonate and adult heart.