Genes in congenital heart disease: atrioventricular valve formation

Circular RNA circZFPM2 regulates cardiomyocyte hypertrophy and survival

Hypertrophic cardiomyopathy (HCM) constitutes the most common genetic cardiac disorder. However, current pharmacotherapeutics are mainly symptomatic and only partially address underlying molecular mechanisms. Circular RNAs (circRNAs) are a recently discovered class of non-coding RNAs and emerged as specific and powerful regulators of cellular functions. By performing global circRNA-specific next generation sequencing in cardiac tissue of patients with hypertrophic cardiomyopathy compared to healthy donors, we identified circZFPM2 (hsa_circ_0003380). CircZFPM2, which derives from the ZFPM2 gene locus, is a highly conserved regulatory circRNA that is strongly induced in HCM tissue. In vitro loss-of-function experiments were performed in neonatal rat cardiomyocytes, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), and HCM-patient-derived hiPSC-CMs. A knockdown of circZFPM2 was found to induce cardiomyocyte hypertrophy and compromise mitochondrial respiration, leading to an increased production of reactive oxygen species and apoptosis. In contrast, delivery of recombinant circZFPM2, packaged in lipid-nanoparticles or using AAV-based overexpression, rescued cardiomyocyte hypertrophic gene expression and promoted cell survival. Additionally, HCM-derived cardiac organoids exhibited improved contractility upon CM-specific overexpression of circZFPM2. Multi-Omics analysis further promoted our hypothesis, showing beneficial effects of circZFPM2 on cardiac contractility and mitochondrial function. Collectively, our data highlight that circZFPM2 serves as a promising target for the treatment of cardiac hypertrophy including HCM.

Genetic Variants of CITED2 Gene Promoter in Human Atrial Septal Defects: Case-Control Study and Cellular Functional Verification

Atrial septal defect (ASD) is one of the most common forms of congenital heart disease (CHD). Genetic variants in the coding region of the CITED2 gene are known to be significantly correlated with CHD, but the role of variants in the promoter region of CITED2 is unknown. We investigated variants in the promoter of the CITED2 gene in 625 subjects (332 ASD and 293 healthy controls) through Sanger sequencing. Four variants in the CITED2 gene promoter were found only in eight ASD patients with zero occurrence in the control subjects (one case of g.4078A>C(rs1165649373), one case of g.4240C>A(rs1235857801), four cases of g.4935C>T(rs111470468), two cases of g.5027C>T(rs112831934)). Cellular functional analysis showed that these four variants significantly changed the transcriptional activity of the CITED2 gene promoter in HEK-293 and HL-1 cells. Electrophoretic mobility change assay results and JASPAR database analysis demonstrated that these variants created or destroyed a series of possible transcription factor binding sites, resulting in changes in the expression of CITED2 protein. We conclude that the variants of CITED2 promoter in ASD patients affect the transcriptional activity and are likely involved in the occurrence and development of ASD. These findings provide new perspectives on the pathogenesis and potential therapeutic insights of ASD.

Activation of Nkx2.5 transcriptional program is required for adult myocardial repair

The cardiac developmental network has been associated with myocardial regenerative potential. However, the embryonic signals triggered following injury have yet to be fully elucidated. Nkx2.5 is a key causative transcription factor associated with human congenital heart disease and one of the earliest markers of cardiac progenitors, thus it serves as a promising candidate. Here, we show that cardiac-specific RNA-sequencing studies reveal a disrupted embryonic transcriptional profile in the adult Nkx2.5 loss-of-function myocardium. nkx2.5-/- fish exhibit an impaired ability to recover following ventricular apex amputation with diminished dedifferentiation and proliferation. Complex network analyses illuminate that Nkx2.5 is required to provoke proteolytic pathways necessary for sarcomere disassembly and to mount a proliferative response for cardiomyocyte renewal. Moreover, Nkx2.5 targets embedded in these distinct gene regulatory modules coordinate appropriate, multi-faceted injury responses. Altogether, our findings support a previously unrecognized, Nkx2.5-dependent regenerative circuit that invokes myocardial cell cycle re-entry, proteolysis, and mitochondrial metabolism to ensure effective regeneration in the teleost heart.

Epigenetics in Congenital Heart Disease

Embryonic heart development is an intricate process that mainly involves morphogens, transcription factors, and cardiac genes. The precise spatiotemporal expression of these genes during different developmental stages underlies normal heart development. Thus, mutation or aberrant expression of these genes may lead to congenital heart disease (CHD). However, evidence demonstrates that the mutation of genes accounts for only a small portion of CHD cases, whereas the aberrant expression regulated by epigenetic modification plays a predominant role in the pathogenesis of CHD. In this review, we provide essential knowledge on the aberrant epigenetic modification involved in the pathogenesis of CHD. Then, we discuss recent advances in the identification of novel epigenetic biomarkers. Last, we highlight the epigenetic roles in some adverse intrauterine environment‐related CHD, which may help the prevention, diagnosis, and treatment of these kinds of CHD.

Identification of Rare Variants in Right Ventricular Outflow Tract Obstruction Congenital Heart Disease by Whole-Exome Sequencing

Background

Pulmonary atresia (PA) is a kind of congenital heart disease characterized by right ventricular outflow tract obstruction. It is divided into PA with intact ventricular septum (PA/IVS) whose favorable form is pulmonary valvular stenosis (PS), and PA with ventricular septal defect (PA/VSD) whose favorable form is tetralogy of Fallot (TOF). Due to limitations in genetics etiology, whole-exome sequencing (WES) was utilized to identify new variants associated with the diseases.

Methods

The data from PS-PA/IVS (n = 74), TOF-PA/VSD (n = 100), and 100 controls were obtained. The common sites between PS and PA/IVS, PA/VSD and TOF, were compared. The novel rare damage variants, and candidate genes were identified by gene-based burden analysis. Finally, the enrichment analysis of differential genes was conducted between case and control groups.

Results

Seventeen rare damage variants located in seven genes were predicted to be associated with the PS through burden analysis. Enrichment analysis identified that the Wnt and cadherin signaling pathways were relevant to PS-PA/IVS.

Conclusion

This study put forth seven candidate genes (APC, PPP1R12A, PCK2, SOS2, TNR, MED13, and TIAM1), resulting in PS-PA/IVS. The Wnt and cadherin signaling pathways were identified to be related to PS-PA/IVS by enrichment analysis. This study provides new evidence for exploring the genetic mechanism of PS-PA/IVS.

Cardiac forces regulate zebrafish heart valve delamination by modulating Nfat signaling

In the clinic, most cases of congenital heart valve defects are thought to arise through errors that occur after the endothelial–mesenchymal transition (EndoMT) stage of valve development. Although mechanical forces caused by heartbeat are essential modulators of cardiovascular development, their role in these later developmental events is poorly understood. To address this question, we used the zebrafish superior atrioventricular valve (AV) as a model. We found that cellularized cushions of the superior atrioventricular canal (AVC) morph into valve leaflets via mesenchymal–endothelial transition (MEndoT) and tissue sheet delamination. Defects in delamination result in thickened, hyperplastic valves, and reduced heart function. Mechanical, chemical, and genetic perturbation of cardiac forces showed that mechanical stimuli are important regulators of valve delamination. Mechanistically, we show that forces modulate Nfatc activity to control delamination. Together, our results establish the cellular and molecular signature of cardiac valve delamination in vivo and demonstrate the continuous regulatory role of mechanical forces and blood flow during valve formation.

Why do developing zebrafish atrioventricular heart valves become hyperplastic under certain hemodynamic conditions? This study suggests that part of the answer lies in how the mechanosensitive Nfat pathway regulates the valve mesenchymal-to-endothelial transition.

The role of DNA methylation in syndromic and non-syndromic congenital heart disease

Congenital heart disease (CHD) is a common structural birth defect worldwide, and defects typically occur in the walls and valves of the heart or enlarged blood vessels. Chromosomal abnormalities and genetic mutations only account for a small portion of the pathogenic mechanisms of CHD, and the etiology of most cases remains unknown. The role of epigenetics in various diseases, including CHD, has attracted increased attention. The contributions of DNA methylation, one of the most important epigenetic modifications, to CHD have not been illuminated. Increasing evidence suggests that aberrant DNA methylation is related to CHD. Here, we briefly introduce DNA methylation and CHD and then review the DNA methylation profiles during cardiac development and in CHD, abnormalities in maternal genome-wide DNA methylation patterns are also described. Whole genome methylation profile and important differentially methylated genes identified in recent years are summarized and clustered according to the sample type and methodologies. Finally, we discuss the novel technology for and prospects of CHD-related DNA methylation.

Nfatc1 Promotes Interstitial Cell Formation During Cardiac Valve Development in Zebrafish

RATIONALE

The transcription factor NFATC1 (nuclear factor of activated T-cell 1) has been implicated in cardiac valve formation in humans and mice, but we know little about the underlying mechanisms. To gain mechanistic understanding of cardiac valve formation at single-cell resolution and insights into the role of NFATC1 in this process, we used the zebrafish model as it offers unique attributes for live imaging and facile genetics.

OBJECTIVE

To understand the role of Nfatc1 in cardiac valve formation.

METHODS AND RESULTS

Using the zebrafish atrioventricular valve, we focus on the valve interstitial cells (VICs), which confer biomechanical strength to the cardiac valve leaflets. We find that initially atrioventricular endocardial cells migrate collectively into the cardiac jelly to form a bilayered structure; subsequently, the cells that led this migration invade the ECM (extracellular matrix) between the 2 endocardial cell monolayers, undergo endothelial-to-mesenchymal transition as marked by loss of intercellular adhesion, and differentiate into VICs. These cells proliferate and are joined by a few neural crest-derived cells. VIC expansion and a switch from a promigratory to an elastic ECM drive valve leaflet elongation. Functional analysis of Nfatc1 reveals its requirement during VIC development. Zebrafish nfatc1 mutants form significantly fewer VICs due to reduced proliferation and impaired recruitment of endocardial and neural crest cells during the early stages of VIC development. With high-speed microscopy and echocardiography, we show that reduced VIC formation correlates with valvular dysfunction and severe retrograde blood flow that persist into adulthood. Analysis of downstream effectors reveals that Nfatc1 promotes the expression of twist1b-a well-known regulator of epithelial-to-mesenchymal transition.

CONCLUSIONS

Our study sheds light on the function of Nfatc1 in zebrafish cardiac valve development and reveals its role in VIC formation. It also further establishes the zebrafish as a powerful model to carry out longitudinal studies of valve formation and function.

The Combined Use of Ultrasound and Fetal Magnetic Resonance Imaging for a Comprehensive Fetal Neurological Assessment in Fetal Congenital Cardiac Defects: Scientific Impact Paper No. 60

Heart problems are common in newborn babies, affecting approximately 5-10 in 1000 babies. Some are more serious than others, but most babies born with heart problems do not have other health issues. Of those babies who have a serious heart problem, almost 1 in 4 will have heart surgery in their first year. In the UK, pregnant women are offered a scan at around 20 weeks to try and spot any heart problems. In most cases there is not a clear reason for the problem, but sometimes other issues, such as genetic conditions, are discovered. In recent years the care given to these babies after they are born has improved their chances of surviving. However, it is recognised that babies born with heart problems have a risk of delays in their learning and development. This may be due to their medical condition, or as a result of surgery and complications after birth. In babies with heart problems, there is a need for more research on ultrasound and magnetic resonance imaging (MRI) to understand how the brain develops and why these babies are more likely to have delays in learning and development. This paper discusses the way ultrasound and MRI are used in assessing the baby's brain. Ultrasound is often used to spot any problems, looking at how the baby's brain develops in pregnancy. Advances in ultrasound technologies have made this easier. MRI is well-established and safe in pregnancy, and if problems in the brain have been seen on ultrasound, MRI may be used to look at these problems in more detail. While it is not always clear what unusual MRI findings can mean for the baby in the long term, increased understanding may mean parents can be given more information about possible outcomes for the baby and may help to improve the counselling they are offered before their baby's birth.

Focal adhesions are essential to drive zebrafish heart valve morphogenesis

Gunawan et al. analyze at single-cell resolution collective endocardial cell migration into the extracellular matrix and the cellular rearrangements forming leaflets during zebrafish heart valve formation. They show that focal adhesion activity driven by Integrin α5β1 and Talin1 are essential to drive cardiac valve morphogenesis in zebrafish.

Elucidating the morphogenetic events that shape vertebrate heart valves, complex structures that prevent retrograde blood flow, is critical to understanding valvular development and aberrations. Here, we used the zebrafish atrioventricular (AV) valve to investigate these events in real time and at single-cell resolution. We report the initial events of collective migration of AV endocardial cells (ECs) into the extracellular matrix (ECM), and their subsequent rearrangements to form the leaflets. We functionally characterize integrin-based focal adhesions (FAs), critical mediators of cell–ECM interactions, during valve morphogenesis. Using transgenes to block FA signaling specifically in AV ECs as well as loss-of-function approaches, we show that FA signaling mediated by Integrin α5β1 and Talin1 promotes AV EC migration and overall shaping of the valve leaflets. Altogether, our investigation reveals the critical processes driving cardiac valve morphogenesis in vivo and establishes the zebrafish AV valve as a vertebrate model to study FA-regulated tissue morphogenesis.

Wnt4 is required for ostia development in the Drosophila heart

The Drosophila ostia are valve-like structures in the heart with functional similarity to vertebrate cardiac valves. The Wnt/β-catenin signaling pathway is critical for valve development in zebrafish and mouse, but the key ligand(s) for valve induction remains unclear. We observed high levels of Wnt4 gene expression in Drosophila ostia progenitor cells, immediately prior to morphological differentiation of these cells associated with ostia formation. This differentiation was blocked in Wnt4 mutants and in flies expressing canonical Wnt signaling pathway inhibitors but not inhibitors of the planar cell polarity pathway. High levels of Wnt4 dependent activation of a canonical Wnt signaling reporter was observed specifically in ostia progenitor cells. In vertebrate valve formation Wnt signaling is active in cells undergoing early endothelial-mesenchymal transition (EMT) and the Wnt9 homolog of Drosophila Wnt4 is expressed in valve progenitors. In demonstrating an essential role for Wnt4 in ostia development we have identified similarities between molecular and cellular events associated with early EMT during vertebrate valve development and the differentiation and partial delamination of ostia progenitor cells in the process of ostia formation.

Effect of LYRM1 knockdown on proliferation, apoptosis, differentiation and mitochondrial function in the P19 cell model of cardiac differentiation in vitro

To explore the effects of LYRM1 knockdown on proliferation, apoptosis, differentiation and mitochondrial function in the embryonic carcinoma (P19) cell model of cardiac differentiation. Knockdown of LYRM1 using small interfering RNA (siRNA) was confirmed by quantitative real-time PCR. Cell Counting Kit-8(CCK-8) proliferation assays and cell cycle analysis demonstrated that LYRM1 gene silencing significantly inhibited P19 cell proliferation. Flow cytometry and measurement of their caspase-3 activities revealed that knockdown of LYRM1 increased P19 cell apoptosis. Observation of morphological changes using an inverted microscope and expression analysis of specific differentiation marker genes using quantitative real-time PCR and Western blotting revealed that knockdown of LYRM1 significantly inhibited the differentiation of P19 cells into cardiomyocytes. Furthermore, real-time quantitative PCR applied to detect mitochondrial DNA (mtDNA) copy number implied that there was no significant difference in the LYRM1 knockdown group compared with the control group. Cellular ATP production investigated by luciferase-based luminescence assay was dramatically decreased in differentiated cells transfected with LYRM1 RNAi. Fluorescence microscopy and flow cytometery were used to detect the reactive oxygen species (ROS) and the mitochondrial membrane potential (MMP) showed that the level of ROS was dramatically increased and MMP was obviously decreased in differentiated cells transfected with LYRM1 RNAi. Collectively, knockdown of LYRM1 promoted apoptosis and suppressed proliferation and differentiation in P19 cells. In addition, knockdown of LYRM1 induced mitochondrial impairment in P19 cells during differentiation, which was reflected by decreased ATP synthesis, lower MMP and increased ROS levels.

Functional Analysis of Two Novel Mutations in TWIST1 Protein Motifs Found in Ventricular Septal Defect Patients

The aim of this study was to investigate the possible genetic effect of sequence variations in TWIST1 on the pathogenesis of ventricular septal defect in humans. We examined the coding region of TWIST1 in a cohort of 196 Chinese people with non-syndromic ventricular septal defect patients and 200 healthy individuals as the controls. We identified two novel potential disease-associated mutations, NM_000474.3:c.247G>A (G83S) and NM_000474.3:c.283A>G (S95G). Both of them were identified for the first time and were not observed in the 200 controls without congenital heart disease. Using a dual-luciferase reporter assay, we showed that both of the mutations significantly down-regulated the repressive effect of TWIST1 on the E-cadherin promoter. Furthermore, a mammalian two-hybrid assay showed that both of the mutations significantly affected the interaction between TWIST1 and KAT2B. New mutations in the transcription factor TWIST1 that affect protein function were identified in 1.0 % (2/196) of Chinese patients with ventricular septal defect. Our data show, for the first time, that TWIST1 has a potential causative effect on the development of ventricular septal defect.

How to make a heart valve: from embryonic development to bioengineering of living valve substitutes

Cardiac valve disease is a significant cause of ill health and death worldwide, and valve replacement remains one of the most common cardiac interventions in high-income economies. Despite major advances in surgical treatment, long-term therapy remains inadequate because none of the current valve substitutes have the potential for remodeling, regeneration, and growth of native structures. Valve development is coordinated by a complex interplay of signaling pathways and environmental cues that cause disease when perturbed. Cardiac valves develop from endocardial cushions that become populated by valve precursor mesenchyme formed by an epithelial-mesenchymal transition (EMT). The mesenchymal precursors, subsequently, undergo directed growth, characterized by cellular compartmentalization and layering of a structured extracellular matrix (ECM). Knowledge gained from research into the development of cardiac valves is driving exploration into valve biomechanics and tissue engineering directed at creating novel valve substitutes endowed with native form and function.

Distinct signaling pathways activated by "extracellular" and "intracellular" serotonin in heart valve development and disease

Cardiac valve diseases are often due to developmental anomalies that progressively lead to the abnormal distribution and organization of extracellular matrix proteins overtime. Whereas mechanisms underlying adult valvulopathies are unknown, previous work has shown a critical involvement of the monoamine serotonin in disease pathogenesis. In particular, the interaction of serotonin with its receptors can activate transforming growth factor-β1 (TGF-β1) signaling, which in turn promotes extracellular matrix gene expression. Elevated levels of circulating serotonin can lead to aberrant TGF-β1 signaling with significant effects on cardiac valve structure and function. Additional functions of serotonin have recently been reported in which internalization of serotonin, through the serotonin transporter SERT, can exert important cytoskeletal functions in lieu of simply being degraded. Recent findings demonstrate that intracellular serotonin regulates cardiac valve remodeling, and perturbation of this pathway can also lead to heart valve defects. Thus, both extracellular and intracellular mechanisms of serotonin action appear to be operative in heart valve development, functionality, and disease. This review summarizes some of the salient aspects of serotonin activity during cardiac valve development and disease pathogenesis with an understanding that further elaboration of intracellular and extracellular serotonin pathways may lead to beneficial treatments for heart valve disease.

Krüppel-like factor 2 is required for normal mouse cardiac development

Krüppel-like factor 2 (KLF2) is expressed in endothelial cells in the developing heart, particularly in areas of high shear stress, such as the atrioventricular (AV) canal. KLF2 ablation leads to myocardial thinning, high output cardiac failure and death by mouse embryonic day 14.5 (E14.5) in a mixed genetic background. This work identifies an earlier and more fundamental role for KLF2 in mouse cardiac development in FVB/N mice. FVB/N KLF2−/− embryos die earlier, by E11.5. E9.5 FVB/N KLF2−/− hearts have multiple, disorganized cell layers lining the AV cushions, the primordia of the AV valves, rather than the normal single layer. By E10.5, traditional and endothelial-specific FVB/N KLF2−/− AV cushions are hypocellular, suggesting that the cells accumulating at the AV canal have a defect in endothelial to mesenchymal transformation (EMT). E10.5 FVB/N KLF2−/− hearts have reduced glycosaminoglycans in the cardiac jelly, correlating with the reduced EMT. However, the number of mesenchymal cells migrating from FVB/N KLF2−/− AV explants into a collagen matrix is reduced considerably compared to wild-type, suggesting that the EMT defect is not due solely to abnormal cardiac jelly. Echocardiography of E10.5 FVB/N KLF2−/− embryos indicates that they have abnormal heart function compared to wild-type. E10.5 C57BL/6 KLF2−/− hearts have largely normal AV cushions. However, E10.5 FVB/N and C57BL/6 KLF2−/− embryos have a delay in the formation of the atrial septum that is not observed in a defined mixed background. KLF2 ablation results in reduced Sox9, UDP-glucose dehydrogenase (Ugdh), Gata4 and Tbx5 mRNA in FVB/N AV canals. KLF2 binds to the Gata4, Tbx5 and Ugdh promoters in chromatin immunoprecipitation assays, indicating that KLF2 could directly regulate these genes. In conclusion, KLF2−/− heart phenotypes are genetic background-dependent. KLF2 plays a role in EMT through its regulation of important cardiovascular genes.

Association of growth/differentiation factor 1 gene polymorphisms with the risk of congenital heart disease in the Chinese Han population

There is evidence suggesting that genetic variants of Nodal signaling may be associated with risk of congenital heart diseases (CHDs), in which several polymorphisms, such as Nodal rs1904589, have been considered to be implicated in the accumulation of the genetic burden of CHD risk with interacting genes. We hypothesized that genetic variants of GDF1, a protein that heterodimerizes with Nodal, may be related to increased CHD susceptibility. In this study, four tagSNPs of GDF1 were genotyped in 310 non-syndromic CHD patients and 320 healthy controls by using PCR-based DHPLC and RFLP. The results showed no statistically significant differences in genotype and allele frequencies between CHDs and controls with any of the analyzed variants of GDF1. However, a weak statistical association existed between GDF1 rs4808870 and conotruncal defects (CTDs) (uncorrected P = 0.027). Further stratified analysis for subtype revealed the SNP AA genotype and A allele have statistical significance in pulmonary atresia (PA) (corrected P = 1.01 × 10(-3) and 0.015, respectively), especially in pulmonary atresia with intact ventricular septum (PA + IVS) (corrected P = 1.67 × 10(-3) and 0.034, respectively). Furthermore, two haplotypes, TGGT and CAGT, were found to be significantly associated with increased CHD susceptibility (corrected P = 3.20 × 10(-3) and 2.73 × 10(-7), respectively). In summary, our results provide evidence that genetic variations of the Nodal-like factor, GDF1 may be associated with CHD risk, and these variations contribute at least in part to the development of some subtypes of CTD in the Chinese Han population.

Myxomatous mitral valve disease in dogs: does size matter?

Myxomatous mitral valve disease (MMVD) is the most commonly diagnosed cardiovascular disease in the dog accounting for more than 70% of all cardiovascular disease in dogs. As are most canine diseases with genetic underpinnings, risk of MMVD is greatly increased in a subset of breeds. What is uncommon is that the vast majority of the breeds at elevated risk for MMVD are small or toy breeds with average adult weights under 9 kg. These breeds appear to have little in common other than their diminutive size. In the following review we propose a number of mechanisms by which relatively unrelated small breeds may have developed a predisposition for chronic valvular disorders. Although factors such as age are key in the expression of MMVD, taking a comprehensive look at the commonalities, as well as the differences, between the susceptible breeds may assist in finding the causal variants responsible for MMVD and translating them to improved treatments for both dogs and humans.

A de novo 1.1Mb microdeletion of chromosome 19p13.11 provides indirect evidence for EPS15L1 to be a strong candidate for split hand split foot malformation

We describe a 3.5 year old girl presenting with short stature, developmental delay, marked muscular hypotonia with ataxia, premature pubarche, and dysmorphic features. A 1.07-1.12Mb-sized de novo microdeletion of chromosome 19p13.11 is most likely the cause for the clinical phenotype. The patient did not show any abnormalities of the extremities which contrasts with the finding of one previously reported patient with an overlapping deletion presenting with split hand and foot malformation (SHFM). The remarkable difference is that in the previously described patient but not in the patient reported herein the genes EPS15L1 and CALR3 were deleted. As EPS15L1 has been associated with limb development previously, the presented case provides indirect evidence that this may be a new candidate gene for SHFM. A possible genotype-phenotype correlation is provided based on literature review and comparison of our patient to the previously reported patients with overlapping or partly overlapping copy number variations in 19p13.11.

In vitro epithelial-to-mesenchymal transformation in human adult epicardial cells is regulated by TGFβ-signaling and WT1

Adult epicardial cells are required for endogenous cardiac repair. After myocardial injury, they are reactivated, undergo epithelial-to-mesenchymal transformation (EMT) and migrate into the injured myocardium where they generate various cell types, including coronary smooth muscle cells and cardiac interstitial fibroblasts, which contribute to cardiac repair. To understand what drives epicardial EMT, we used an in vitro model for human adult epicardial cells. These cells have an epithelium-like morphology and markedly express the cell surface marker vascular cell adhesion marker (VCAM-1). In culture, epicardial cells spontaneously undergo EMT after which the spindle-shaped cells now express endoglin. Both epicardial cells before and after EMT express the epicardial marker, Wilms tumor 1 (WT1). Adding transforming growth factor beta (TGFβ) induces loss of epithelial character and initiates the onset of mesenchymal differentiation in human adult epicardial cells. In this study, we show that TGFβ-induced EMT is dependent on type-1 TGFβ receptor activity and can be inhibited by soluble VCAM-1. We also show that epicardial-specific knockdown of Wilms tumor-1 (WT1) induces the process of EMT in human adult epicardial cells, through transcriptional regulation of platelet-derived growth factor receptor alpha (Pdgfrα), Snai1 and VCAM-1. These data provide new insights into the process of EMT in human adult epicardial cells, which might provide opportunities to develop new strategies for endogenous cell-based cardiac repair.

Heart chamber size in zebrafish is regulated redundantly by duplicated tbx2 genes

The Tbx2 transcription factor is implicated in growth control based on its association with human cancers. In the heart, Tbx2 represses cardiac differentiation to mediate development of the atrioventricular canal (AVC). The zebrafish genome retains two tbx2 genes, and both are required for formation of the AVC. Here, we show that both genes are also expressed earlier in the primitive heart tube, and we describe a previously unrecognized role for Tbx2 in promoting proliferation of presumptive myocardium at the heart tube stage. In contrast to single knockdowns, depletion of both gene products causes chamber defects, resulting in an expanded atrium and a smaller ventricle, associated with decreased proliferation of ventricular cardiomyocytes. The phenotype correlates with changes in the expression for known cardiac growth factors. Therefore, in zebrafish, two tbx2 genes are functionally redundant for regulating chamber development, while each gene is required independently for development of the AVC.

Treatment of congenital heart disease: risk-reducing measures in young adults

Adults with congenital heart disease form a new and relatively young population, since surgical treatment of heart defects became available three to four decades ago. Owing to improved survival this population is steadily growing in number and age. Little is known regarding long-term survival; however, late complications occur frequently. During adulthood, almost half of the patients have one or more complication, such as endocarditis, stroke, systemic or pulmonary hypertension, aortic aneurysm or dissection and arrhythmias. Heart failure and sudden cardiac death are the main causes of death. Treatment of adults with congenital heart disease is aimed at the reduction of symptoms, but also at minimizing the risk and severity of late complications. In this article the most recent advances in the treatment of congenital heart disease will be discussed. The main focus of the article will be on pharmacological, interventional and surgical interventions that reduce the risk of heart failure, arrhythmias, vascular complications, pulmonary hypertension and endocarditis.

Maternal genome-wide DNA methylation patterns and congenital heart defects

The majority of congenital heart defects (CHDs) are thought to result from the interaction between multiple genetic, epigenetic, environmental, and lifestyle factors. Epigenetic mechanisms are attractive targets in the study of complex diseases because they may be altered by environmental factors and dietary interventions. We conducted a population based, case-control study of genome-wide maternal DNA methylation to determine if alterations in gene-specific methylation were associated with CHDs. Using the Illumina Infinium Human Methylation27 BeadChip, we assessed maternal gene-specific methylation in over 27,000 CpG sites from DNA isolated from peripheral blood lymphocytes. Our study sample included 180 mothers with non-syndromic CHD-affected pregnancies (cases) and 187 mothers with unaffected pregnancies (controls). Using a multi-factorial statistical model, we observed differential methylation between cases and controls at multiple CpG sites, although no CpG site reached the most stringent level of genome-wide statistical significance. The majority of differentially methylated CpG sites were hypermethylated in cases and located within CpG islands. Gene Set Enrichment Analysis (GSEA) revealed that the genes of interest were enriched in multiple biological processes involved in fetal development. Associations with canonical pathways previously shown to be involved in fetal organogenesis were also observed. We present preliminary evidence that alterations in maternal DNA methylation may be associated with CHDs. Our results suggest that further studies involving maternal epigenetic patterns and CHDs are warranted. Multiple candidate processes and pathways for future study have been identified.

The changing epidemiology of congenital heart disease

Congenital heart disease is the most common congenital disorder in newborns. Advances in cardiovascular medicine and surgery have enabled most patients to reach adulthood. Unfortunately, prolonged survival has been achieved at a cost, as many patients suffer late complications, of which heart failure and arrhythmias are the most prominent. Accordingly, these patients need frequent follow-up by physicians with specific knowledge in the field of congenital heart disease. However, planning of care for this population is difficult, because the number of patients currently living with congenital heart disease is difficult to measure. Birth prevalence estimates vary widely according to different studies, and survival rates have not been well recorded. Consequently, the prevalence of congenital heart disease is unclear, with estimates exceeding the number of patients currently seen in cardiology clinics. New developments continue to influence the size of the population of patients with congenital heart disease. Prenatal screening has led to increased rates of termination of pregnancy. Improved management of complications has changed the time and mode of death caused by congenital heart disease. Several genetic and environmental factors have been shown to be involved in the etiology of congenital heart disease, although this knowledge has not yet led to the implementation of preventative measures. In this Review, we give an overview of the etiology, birth prevalence, current prevalence, mortality, and complications of congenital heart disease.

NKX2-5: an update on this hypermutable homeodomain protein and its role in human congenital heart disease (CHD)

Congenital heart disease (CHD) is among the most prevalent and fatal of all birth defects. Deciphering its causes, however, is complicated, as many patients affected by CHD have no family history of the disease. There is also widespread heterogeneity of cardiac malformations within affected individuals. Nonetheless, there have been tremendous efforts toward a better understanding of the molecular and cellular events leading to CHD. Notably, certain cardiac-specific transcription factors have been implicated in mammalian heart development and disruption of their activity has been demonstrated in CHD. The homeodomain transcription factor NKX2-5 is an important member of this group. Indeed, more than 40 heterozygous NKX2-5 germline mutations have been observed in individuals with CHD, and these are spread along the coding region, with many shown to impact protein function. Thus, NKX2-5 appears to be hypermutable, yet the overall detection frequency in sporadic CHD is about 2% and NKX2-5 mutations are one-time detections with single-positives or private to families. Furthermore, there is lack of genotype-phenotype correlation, in which the same cardiac malformations have been exhibited in different NKX2-5 mutations or the same NKX2-5 mutation associated with diverse malformations. Here, we summarize published NKX2-5 germline mutations and explore different avenues in disease pathogenesis to support the notion of a multifactorial cause of CHD where possibly several genes and associated pathways are involved.

LYRM1, a gene that promotes proliferation and inhibits apoptosis during heart development

Congenital heart disease (CHD) is the most common type of birth defect, but its underlying molecular mechanisms remain unidentified. Previous studies determined that Homo sapiens LYR motif containing 1 (LYRM1) is a novel nucleoprotein expressed at the highest level in adipose tissue and in high levels in heart tissue. The LYRM1 gene may play an important role in the development of the human heart. This study was designed to identify the biological characteristics of the LYRM1 gene in heart development. On the basis of expression-specific differentiation markers identified with quantitative real-time RT-PCR and the morphology of LYRM1-overexpressing cells during differentiation, ectopic expression was not found to significantly affect differentiation of P19 cells into cardiomyocytes. MTT assays and cell cycle analysis showed that LYRM1 dramatically increases the proliferation of P19 cells. Furthermore, data from annexin V-FITC binding and caspase-3 activity revealed that LYRM1 can inhibit the apoptosis of P19 cells. Our data suggest that LYRM1 might have the potential to modulate cell growth, apoptosis, and heart development.

A de novo mutation in NKX2.5 associated with atrial septal defects, ventricular noncompaction, syncope and sudden death

BACKGROUND

Mutations in transcription factor NKX2.5 cause congenital heart disease (CHD). We identified a CHD family with atrial septal defects (ASDs), atrioventricular block, ventricular noncompaction, syncope and sudden death. Our objective is to identify the disease-causing mutation in the CHD family.

METHODS

Direct DNA sequence analysis was used to identify the CHD mutation. The functional effects of the mutation were characterized by a luciferase reporter assay and immunostaining.

RESULTS

A novel, de novo 2-bp insertion (c.512insGC) was identified in exon 2 of NKX2.5. Mutation c.512insGC co-segregates with CHD in the family, and is not present in 200 controls. Functional studies indicate that the c.512insGC mutation impedes nuclear localization of NKX2.5 and causes a total loss of transactivation activity of NKX2.5. Furthermore, no NKX2.5 mutation was identified in 125 sporadic Chinese CHD patients.

CONCLUSIONS

(1) NKX2.5 mutation c.512insGC is associated with ASDs, syncope and sudden death. It is the second de novo mutation identified in NKX2.5. (2) NKX2.5 mutations are rare in sporadic CHD patients. (3) This study for the first time identifies association between a NKX2.5 mutation and ventricular noncompaction. Our results significantly expand the phenotypic spectrum of NKX2.5 mutations.

Integration of a Notch-dependent mesenchymal gene program and Bmp2-driven cell invasiveness regulates murine cardiac valve formation

Cardiac valve formation is crucial for embryonic and adult heart function. Valve malformations constitute the most common congenital cardiac defect, but little is known about the molecular mechanisms regulating valve formation and homeostasis. Here, we show that endocardial Notch1 and myocardial Bmp2 signal integration establish a valve-forming field between 2 chamber developmental domains. Patterning occurs through the activation of endocardial epithelial-to-mesenchymal transition (EMT) exclusively in prospective valve territories. Mice with constitutive endocardial Notch1 activity ectopically express Hey1 and Heyl. They also display an activated mesenchymal gene program in ventricles and a partial (noninvasive) EMT in vitro that becomes invasive upon BMP2 treatment. Snail1, TGF-β2, or Notch1 inhibition reduces BMP2-induced ventricular transformation and invasion, whereas BMP2 treatment inhibits endothelial Gsk3β, stabilizing Snail1 and promoting invasiveness. Integration of Notch and Bmp2 signals is consistent with Notch1 signaling being attenuated after myocardial Bmp2 deletion. Notch1 activation in myocardium extends Hey1 expression to nonchamber myocardium, represses Bmp2, and impairs EMT. In contrast, Notch deletion abrogates endocardial Hey gene transcription and extends Bmp2 expression to the ventricular endocardium. This embryonic Notch1-Bmp2-Snail1 relationship may be relevant in adult valve disease, in which decreased NOTCH signaling causes valve mesenchyme cell formation, fibrosis, and calcification.

13q13.1-q13.2 deletion in tetralogy of Fallot: clinical report and a literature review

Recent advances in microarray technology are helping to identify more genetic anomalies associated with tetralogy of Fallot and other congenital heart defects. We report on a 24-year-old woman with a syndromic form of tetralogy of Fallot who was found to have a novel de novo deletion of the proximal long arm of chromosome 13. History of developmental delay and learning difficulties, mild dysmorphic facial features, and anal atresia prompted genetic investigations. A review of the literature on deletions that overlap this region showed that several were associated with major congenital heart defects. The results suggest that the 13q13.1-q13.2 region may harbour a gene or genes important in cardiac development.

Gene expression profiling in the fetal cardiac tissue after folate and low-dose trichloroethylene exposure

BACKGROUND

Previous studies show gene expression alterations in rat embryo hearts and cell lines that correspond to the cardio-teratogenic effects of trichloroethylene (TCE) in animal models. One potential mechanism of TCE teratogenicity may be through altered regulation of calcium homeostatic genes with a corresponding inhibition of cardiac function. It has been suggested that TCE may interfere with the folic acid/methylation pathway in liver and kidney and alter gene regulation by epigenetic mechanisms. According to this hypothesis, folate supplementation in the maternal diet should counteract TCE effects on gene expression in the embryonic heart.

APPROACH

To identify transcriptional targets altered in the embryonic heart after exposure to TCE, and possible protective effects of folate, we used DNA microarray technology to profile gene expression in embryonic mouse hearts with maternal TCE exposure and dietary changes in maternal folate.

RESULTS

Exposure to low doses of TCE (10 ppb) caused extensive alterations in transcripts encoding proteins involved in transport, ion channel, transcription, differentiation, cytoskeleton, cell cycle, and apoptosis. Exogenous folate did not offset the effects of TCE exposure on normal gene expression, and both high and low levels of folate produced additional significant changes in gene expression.

CONCLUSIONS

A mechanism by which TCE induces a folate deficiency does not explain altered gene expression patterns in the embryonic mouse heart. The data further suggest that use of folate supplementation, in the presence of this toxin, may be detrimental and not protective of the developing embryo.

Pathogenic mechanisms of congenital heart disease

Congenital heart disease (CHD) is the most common type of birth defect. Despite the many advances in the understanding of cardiac development and the identification of many genes related to cardiac development, the fundamental etiology for the majority of cases of congenital heart disease remains unknown. This review summarizes normal cardiac development, and outlines the recent discoveries of the genetic causes of congenital heart disease and provides possible strategies for exploring genetic causes.

Dominant-negative ALK2 allele associates with congenital heart defects

BACKGROUND

Serious congenital heart defects occur as a result of improper atrioventricular septum (AVS) development during embryogenesis. Despite extensive knowledge of the genetic control of AVS development, few genetic lesions have been identified that are responsible for AVS-associated congenital heart defects.

METHODS AND RESULTS

We sequenced 32 genes known to be important in AVS development in patients with AVS defects and identified 11 novel coding single-nucleotide polymorphisms that are predicted to impair protein function. We focused on variants identified in the bone morphogenetic protein receptor, ALK2, and subjected 2 identified variants to functional analysis. The coding single-nucleotide polymorphisms R307L and L343P are heterozygous missense substitutions and were each identified in single individuals. The L343P allele had impaired functional activity as measured by in vitro kinase and bone morphogenetic protein-specific transcriptional response assays and dominant-interfering activity in vivo. In vivo analysis of zebrafish embryos injected with ALK2 L343P RNA revealed improper atrioventricular canal formation.

CONCLUSIONS

These data identify the dominant-negative allele ALK2 L343P in a patient with AVS defects.