Ablation of Nkx2-5 at mid-embryonic stage results in premature lethality and cardiac malformation

Tris(2-chloroethyl) phosphate (TCEP) exposure inhibits the epithelial-mesenchymal transition (EMT), mesoderm differentiation, and cardiovascular development in early chicken embryos

Tris(2-chloroethyl) phosphate (TCEP) is an organophosphorus flame retardant used worldwide and has been detected in the tissues and eggs of wild birds. Our previous study reported that exposure to TCEP induced developmental delay and cardiovascular dysfunction with attenuated heart rate and vasculogenesis in early chicken embryos. This study aimed to investigate the molecular mechanisms underlying the cardiovascular effects of TCEP on chicken embryos using cardiac transcriptome analysis and to examine whether TCEP exposure affects epithelial-mesenchymal transition (EMT) and mesoderm differentiation during gastrulation. Transcriptome analysis revealed that TCEP exposure decreased the expression of cardiac conduction-related genes and transcription factors on day 5 of incubation. In extraembryonic blood vessels, the expression levels of genes related to fibroblast growth factor (FGF) and vascular endothelial growth factor (VEGF) were significantly reduced by TCEP exposure and vasculogenesis was suppressed. TCEP exposure also attenuated Snail family transcriptional repressor 2 (SNAI2) and T-box transcription factor T (TBXT) signaling in the chicken primitive streak, indicating that TCEP inhibits EMT and mesoderm differentiation during gastrulation at the early developmental stage. These effects on EMT and mesoderm differentiation may be related to subsequent phenotypic defects, including suppression of heart development and blood vessel formation.

Pentachloronitrobenzene disturbed murine ventricular wall development by inhibiting cardiomyocyte proliferation via Hec1 downregulation

Exposure to the organochlorine fungicide pentachloronitrobenzene (PCNB) causes developmental abnormalities, including cardiac malformation. However, the molecular mechanism of PCNB cardiotoxicity remains elusive. We found that oral administration of PCNB to pregnant mice induced a hypoplastic wall with significant thinning of the compact myocardium in the developing hearts. PCNB significantly downregulates the expression of Hec1, a member of the NDC80 kinetochore complex, resulting in aberrant spindles, chromosome missegregation and an arrest in cardiomyocyte proliferation. Cardiac-specific ablation of Hec1 sharply inhibits cardiomyocyte proliferation, leading to thinning of the compact myocardium and embryonic lethality. Mechanistically, we found that activating transcription factor 3 (ATF3) transactivates Hec1 expression. Either HEC1 or ATF3 overexpression significantly rescues mitotic defects and restore the decreased proliferative ability of cardiomyocytes caused by PCNB exposure. Our findings highlight that maternal PCNB exposure disrupts embryonic cardiac function by inhibiting cardiomyocyte proliferation and interfering with ventricular wall development, partially attributed to the downregulation of the Atf3-Hec1 axis.

Nkx2.5: a crucial regulator of cardiac development, regeneration and diseases

Cardiomyocytes fail to regenerate after birth and respond to mitotic signals through cellular hypertrophy rather than cellular proliferation. Necrotic cardiomyocytes in the infarcted ventricular tissue are eventually replaced by fibroblasts, generating scar tissue. Cardiomyocyte loss causes localized systolic dysfunction. Therefore, achieving the regeneration of cardiomyocytes is of great significance for cardiac function and development. Heart development is a complex biological process. An integral cardiac developmental network plays a decisive role in the regeneration of cardiomyocytes. During this process, genetic epigenetic factors, transcription factors, signaling pathways and small RNAs are involved in regulating the developmental process of the heart. Cardiomyocyte-specific genes largely promote myocardial regeneration, among which the Nkx2.5 transcription factor is one of the earliest markers of cardiac progenitor cells, and the loss or overexpression of Nkx2.5 affects cardiac development and is a promising candidate factor. Nkx2.5 affects the development and function of the heart through its multiple functional domains. However, until now, the specific mechanism of Nkx2.5 in cardiac development and regeneration is not been fully understood. Therefore, this article will review the molecular structure, function and interaction regulation of Nkx2.5 to provide a new direction for cardiac development and the treatment of heart regeneration.

Application of 4-D ultrasound-derived regional strain and proteomics analysis in Nkx2-5-deficient male mice

The comprehensive characterization of cardiac structure and function is critical to better understanding various murine models of cardiac disease. We demonstrate here a multimodal analysis approach using high-frequency four-dimensional ultrasound (4DUS) imaging and proteomics to explore the relationship between regional function and tissue composition in a murine model of metabolic cardiomyopathy (Nkx2-5183P/+). The presented 4DUS analysis outlines a novel approach to mapping both circumferential and longitudinal strain profiles through a standardized framework. We then demonstrate how this approach allows for spatiotemporal comparisons of cardiac function and improved localization of regional left ventricular dysfunction. Guided by observed trends in regional dysfunction, our targeted Ingenuity Pathway Analysis (IPA) results highlight metabolic dysregulation in the Nkx2-5183P/+ model, including altered mitochondrial function and energy metabolism (i.e., oxidative phosphorylation and fatty acid/lipid handling). Finally, we present a combined 4DUS-proteomics z-score-based analysis that highlights IPA canonical pathways showing strong linear relationships with 4DUS biomarkers of regional cardiac dysfunction. The presented multimodal analysis methods aim to help future studies more comprehensively assess regional structure-function relationships in other preclinical models of cardiomyopathy.NEW & NOTEWORTHY A multimodal approach using both four-dimensional ultrasound (4DUS) and regional proteomics can help enhance our investigations of murine cardiomyopathy models. We present unique 4DUS-derived strain maps that provide a framework for both cross-sectional and longitudinal analysis of spatiotemporal cardiac function. We further detail and demonstrate an innovative 4DUS-proteomics z-score-based linear regression method, aimed at characterizing relationships between regional cardiac dysfunction and underlying mechanisms of disease.

Nkx2-5 Loss of Function in the His-Purkinje System Hampers Its Maturation and Leads to Mechanical Dysfunction

The ventricular conduction or His-Purkinje system (VCS) mediates the rapid propagation and precise delivery of electrical activity essential for the synchronization of heartbeats. Mutations in the transcription factor Nkx2-5 have been implicated in a high prevalence of developing ventricular conduction defects or arrhythmias with age. Nkx2-5 heterozygous mutant mice reproduce human phenotypes associated with a hypoplastic His-Purkinje system resulting from defective patterning of the Purkinje fiber network during development. Here, we investigated the role of Nkx2-5 in the mature VCS and the consequences of its loss on cardiac function. Neonatal deletion of Nkx2-5 in the VCS using a Cx40-CreERT2 mouse line provoked apical hypoplasia and maturation defects of the Purkinje fiber network. Genetic tracing analysis demonstrated that neonatal Cx40-positive cells fail to maintain a conductive phenotype after Nkx2-5 deletion. Moreover, we observed a progressive loss of expression of fast-conduction markers in persistent Purkinje fibers. Consequently, Nkx2-5-deleted mice developed conduction defects with progressively reduced QRS amplitude and RSR' complex associated with higher duration. Cardiac function recorded by MRI revealed a reduction in the ejection fraction in the absence of morphological changes. With age, these mice develop a ventricular diastolic dysfunction associated with dyssynchrony and wall-motion abnormalities without indication of fibrosis. These results highlight the requirement of postnatal expression of Nkx2-5 in the maturation and maintenance of a functional Purkinje fiber network to preserve contraction synchrony and cardiac function.

Effect of maternal pregestational diabetes mellitus on congenital heart diseases

BACKGROUND

The increasing population of diabetes mellitus in adolescent girls and women of childbearing age contributes to a large number of pregnancies with maternal pregestational diabetes mellitus. Congenital heart diseases are a common adverse outcome in mothers with pregestational diabetes mellitus. However, there is little systematic information between maternal pregestational diabetes mellitus and congenital heart diseases in the offspring.

DATA SOURCES

Literature selection was performed in PubMed. One hundred and seven papers were cited in our review, including 36 clinical studies, 26 experimental studies, 31 reviews, eight meta-analysis articles, and six of other types.

RESULTS

Maternal pregestational diabetes mellitus poses a high risk of congenital heart diseases in the offspring and causes variety of phenotypes of congenital heart diseases. Factors such as persistent maternal hyperglycemia, oxidative stress, polymorphism of uncoupling protein 2, polymorphism of adiponectin gene, Notch 1 pathway, Nkx2.5 disorders, dysregulation of the hypoxia-inducible factor 1, and viral etiologies are associated with the occurrence of congenital heart diseases in the offspring of mothers with pregestational diabetes mellitus. Treatment options including blood sugar-reducing, anti-oxidative stress drug supplements and exercise can help to prevent maternal pregestational diabetes mellitus from inducing congenital heart diseases.

CONCLUSIONS

Our review contributes to a better understanding of the association between maternal pregestational diabetes mellitus and congenital heart diseases in the offspring and to a profound thought of the mechanism, preventive and therapeutic measurements of congenital heart diseases caused by maternal pregestational diabetes mellitus.

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.

Effects of constitutively active IKKβ on cardiac development

NF-κB is a major transcription factor regulating cell survival, organ development and inflammation, but its role in cardiac development has been inadequately explored. To examine this function, we generated mice in which IKKβ, an essential kinase for NF-κB activation, was constitutively activated in embryonic cardiomyocytes. For this purpose, we used smooth muscle-22α (SM22α)-Cre mice, which are frequently used for gene recombination in embryonic cardiomyocytes. Embryonic hearts of SM22αCre-CA (constitutively active) IKKβ^flox/flox mice revealed remarkably thin, spongy and hypoplastic myocardium. In exploring the mechanism, we found that the expression of bone morphogenetic protein 10 (BMP10) and T-box transcription factor 20 (Tbx20), major regulators of cardiac development, was significantly downregulated and upregulated, respectively, in the SM22αCre-CAIKKβ^flox/flox mice. We also generated NK2 homeobox 5 (Nkx2.5) Cre-CAIKKβ^flox/wt mice since Nkx2.5 is also expressed in embryonic cardiomyocytes and confirmed that the changes in these genes were also observed. These results implicated that the activation of NF-κB affects cardiac development.

CHD4 is recruited by GATA4 and NKX2-5 to repress noncardiac gene programs in the developing heart

The nucleosome remodeling and deacetylase (NuRD) complex is one of the central chromatin remodeling complexes that mediates gene repression. NuRD is essential for numerous developmental events, including heart development. Clinical and genetic studies have provided direct evidence for the role of chromodomain helicase DNA-binding protein 4 (CHD4), the catalytic component of NuRD, in congenital heart disease (CHD), including atrial and ventricular septal defects. Furthermore, it has been demonstrated that CHD4 is essential for mammalian cardiomyocyte formation and function. A key unresolved question is how CHD4/NuRD is localized to specific cardiac target genes, as neither CHD4 nor NuRD can directly bind DNA. Here, we coupled a bioinformatics-based approach with mass spectrometry analyses to demonstrate that CHD4 interacts with the core cardiac transcription factors GATA4, NKX2-5, and TBX5 during embryonic heart development. Using transcriptomics and genome-wide occupancy data, we characterized the genomic landscape of GATA4, NKX2-5, and TBX5 repression and defined the direct cardiac gene targets of the GATA4-CHD4, NKX2-5-CHD4, and TBX5-CHD4 complexes. These data were used to identify putative cis-regulatory elements controlled by these complexes. We genetically interrogated two of these silencers in vivo: Acta1 and Myh11 We show that deletion of these silencers leads to inappropriate skeletal and smooth muscle gene misexpression, respectively, in the embryonic heart. These results delineate how CHD4/NuRD is localized to specific cardiac loci and explicates how mutations in the broadly expressed CHD4 protein lead to cardiac-specific disease states.

Zebrafish foxc1a controls ventricular chamber maturation by directly regulating wwtr1 and nkx2.5 expression

Chamber maturation is a significant process in cardiac development. Disorders of this crucial process lead to a range of congenital heart defects. Foxc1a is a critical transcription factor reported to regulate the specification of cardiac progenitor cells. However, little is known about the role of Foxc1a in modulating chamber maturation. Previously, we reported that foxc1a-null zebrafish embryos exhibit disrupted heart structures and functions. In this study, we observed that ventricle structure and cardiomyocyte proliferation were abolished during chamber maturation in foxc1a-null zebrafish embryos. To observe the endogenous localization of Foxc1a in the hearts of living embryos, we inserted eyfp at the foxc1a genomic locus using TALEN. Analysis of the knockin zebrafish showed that foxc1a was widely expressed in ventricular cardiomyocytes during chamber development. Cardiac RNA sequencing analysis revealed downregulated expression of the Hippo signaling effector wwtr1. Dual-luciferase and chromatin immunoprecipitation assays revealed that Foxc1a could bind directly to three sites in the wwtr1 promoter region. Furthermore, wwtr1 mRNA overexpression was sufficient to reverse the ventricle defects during chamber maturation. Conditional overexpression of nkx2.5 also partially rescued the ventricular defects during chamber development. These findings demonstrate that wwtr1 and nkx2.5 are direct targets of Foxc1a during ventricular chamber maturation.

Gestational intermittent hyperoxia rescues murine genetic congenital heart disease in part

Cardiac development is a dynamic process, temporally and spatially. When disturbed, it leads to congenital cardiac anomalies that affect approximately 1% of live births. Genetic variants in several loci lead to anomalies, with the transcription factor NKX2-5 being one of the largest. However, there are also non-genetic factors that influence cardiac malformations. We examined the hypothesis that hyperoxia may be beneficial and can rescue genetic cardiac anomalies induced by an Nkx2-5 mutation. Intermittent mild hyperoxia (40% PO₂) was applied for 10 h per day to normal wild-type female mice mated with heterozygous Nkx2-5 mutant males from gestational day 8.5 to birth. Hyperoxia therapy reduced excessive trabeculation in Nkx2-5 mutant mice compared to normoxic conditions (ratio of trabecular layer relative to compact layer area, normoxia 1.84 ± 0.07 vs. hyperoxia 1.51 ± 0.04) and frequency of muscular ventricular septal defects per heart (1.53 ± 0.32 vs. 0.68 ± 0.15); however, the incidence of membranous ventricular septal defects in Nkx2-5 mutant hearts was not changed. Nkx2-5 mutant embryonic hearts showed defective coronary vessel organization, which was improved by intermittent mild hyperoxia. The results of our study showed that mild gestational hyperoxia therapy rescued genetic cardiac malformation induced by Nkx2-5 mutation in part.

Cardiac Development: A Glimpse on Its Translational Contributions

Cardiac development is a complex developmental process that is initiated soon after gastrulation, as two sets of precardiac mesodermal precursors are symmetrically located and subsequently fused at the embryonic midline forming the cardiac straight tube. Thereafter, the cardiac straight tube invariably bends to the right, configuring the first sign of morphological left–right asymmetry and soon thereafter the atrial and ventricular chambers are formed, expanded and progressively septated. As a consequence of all these morphogenetic processes, the fetal heart acquired a four-chambered structure having distinct inlet and outlet connections and a specialized conduction system capable of directing the electrical impulse within the fully formed heart. Over the last decades, our understanding of the morphogenetic, cellular, and molecular pathways involved in cardiac development has exponentially grown. Multiples aspects of the initial discoveries during heart formation has served as guiding tools to understand the etiology of cardiac congenital anomalies and adult cardiac pathology, as well as to enlighten novels approaches to heal the damaged heart. In this review we provide an overview of the complex cellular and molecular pathways driving heart morphogenesis and how those discoveries have provided new roads into the genetic, clinical and therapeutic management of the diseased hearts.

The Mesenchymal Cap of the Atrial Septum and Atrial and Atrioventricular Septation

In this publication, dedicated to Professor Robert H. Anderson and his contributions to the field of cardiac development, anatomy, and congenital heart disease, we will review some of our earlier collaborative studies. The focus of this paper is on our work on the development of the atrioventricular mesenchymal complex, studies in which Professor Anderson has played a significant role. We will revisit a number of events relevant to atrial and atrioventricular septation and present new data on the development of the mesenchymal cap of the atrial septum, a component of the atrioventricular mesenchymal complex which, thus far, has received only moderate attention.

Homocysteine downregulates cardiac homeobox transcription factor NKX2.5 via IGFBP5

Homocysteine (Hcy) is an independent risk factor of congenital heart disease (CHD), but its exact underlying mechanism is unclear. In this study, we collected amniotic fluid (AF) supernatant samples from pregnant women carrying CHD-affected (n = 16) or normal (n = 16) fetuses. We found that Hcy concentrations were higher in the AF of the CHD group when compared with normal pregnancies. Also, Western blot showed that NK2 homeobox 5 (NKX2.5) was decreased and insulin-like growth factor binding protein 5 (IGFBP5) was increased in the AF of the CHD group. In the H9C2 cell culture experiment, 500 μmol/L Hcy downregulated NKX2.5 and upregulated IGFBP5. Real-time PCR and Western blot showed that NKX2.5 expression was reduced in H9C2 cells treated with IGFBP5. Luciferase reporter gene demonstrated that IGFBP5 decreased the transcription of the NKX2.5 promoter. Chromatin immunoprecipitation and electrophoretic mobility shift assay suggested that IGFBP5 binds to the NKX2.5 promoter region. Thus, the data indicated that one of the possible mechanisms by which Hcy is involved in CHD may be that Hcy inhibits NKX2.5 expression partly through IGFBP5.NEW & NOTEWORTHY We found that Hcy and IGFBP5 were increased, whereas NKX2.5 was decreased, in AF of CHD. Meanwhile, Hcy could upregulate IGFBP5 but downregulate NKX2.5, and IGFBP5 inhibited NKX2.5 expression in vitro. Moreover, IGFBP5 can bind to the NKX2.5 promoter region and reduce NKX2.5 transcriptional activity.

Epigenomic and Transcriptomic Dynamics During Human Heart Organogenesis

RATIONALE

There is growing evidence that common variants and rare sequence alterations in regulatory sequences can result in birth defects or predisposition to disease. Congenital heart defects are the most common birth defect and have a clear genetic component, yet only a third of cases can be attributed to structural variation in the genome or a mutation in a gene. The remaining unknown cases could be caused by alterations in regulatory sequences.

OBJECTIVE

Identify regulatory sequences and gene expression networks that are active during organogenesis of the human heart. Determine whether these sites and networks are enriched for disease-relevant genes and associated genetic variation.

METHODS AND RESULTS

We characterized ChromHMM (chromatin state) and gene expression dynamics during human heart organogenesis. We profiled 7 histone modifications in embryonic hearts from each of 9 distinct Carnegie stages (13-14, 16-21, and 23), annotated chromatin states, and compared these maps to over 100 human tissues and cell types. We also generated RNA-sequencing data, performed differential expression, and constructed weighted gene coexpression networks. We identified 177 412 heart enhancers; 12 395 had not been previously annotated as strong enhancers. We identified 92% of all functionally validated heart-positive enhancers (n=281; 7.5× enrichment; P<2.2×10-16). Integration of these data demonstrated novel heart enhancers are enriched near genes expressed more strongly in cardiac tissue and are enriched for variants associated with ECG measures and atrial fibrillation. Our gene expression network analysis identified gene modules strongly enriched for heart-related functions, regulatory control by heart-specific enhancers, and putative disease genes.

CONCLUSIONS

Well-connected hub genes with heart-specific expression targeted by embryonic heart-specific enhancers are likely disease candidates. Our functional annotations will allow for better interpretation of whole genome sequencing data in the large number of patients affected by congenital heart defects.

NOTCH1 is critical for fibroblast-mediated induction of cardiomyocyte specialization into ventricular conduction system-like cells in vitro

Cardiac fibroblasts are present throughout the myocardium and are enriched in the microenvironment surrounding the ventricular conduction system (VCS). Several forms of arrhythmias are linked to VCS abnormalities, but it is still unclear whether VCS malformations are cardiomyocyte autonomous or could be linked to crosstalk between different cell types. We reasoned that fibroblasts influence cardiomyocyte specialization in VCS cells. We developed 2D and 3D culture models of neonatal rat cardiac cells to assess the influence of cardiac fibroblasts on cardiomyocytes. Cardiomyocytes adjacent to cardiac fibroblasts showed a two-fold increase in expression of VCS markers (NAV1.5 and CONTACTIN 2) and calcium transient duration, displaying a Purkinje-like profile. Fibroblast-conditioned media (fCM) was sufficient to activate VCS-related genes (Irx3, Scn5a, Connexin 40) and to induce action potential prolongation, a hallmark of Purkinge phenotype. fCM-mediated response seemed to be spatially-dependent as cardiomyocyte organoids treated with fCM had increased expression of connexin 40 and NAV1.5 primarily on its outer surface. Finally, NOTCH1 activation in both cardiomyocytes and fibroblasts was required for connexin 40 up-regulation (a proxy of VCS phenotype). Altogether, we provide evidence that cardiac fibroblasts influence cardiomyocyte specialization into VCS-like cells via NOTCH1 signaling in vitro.

Nkx2-5 Regulates the Proliferation and Migration of H9c2 Cells

Background

The protein NKX2–5 affects mammalian heart development. In mice, the disruption of Nkx2–5 has been associated with arrhythmias, abnormal myocardial contraction, abnormal cardiac morphogenesis, and death. However, the details of the mechanisms are unclear. This study was designed to investigate them.

Material/Methods

Rat cardiomyocytes from the H9c2 cell line were used in our study. First, we knocked down Nkx2–5 in the H9c2 cells and then validated consequent changes in cell proliferation and migration. We then used RNA sequencing to determine the changes in transcripts. Finally, we validated these results by quantitative reverse transcription-polymerase chain reaction.

Results

We confirmed that Nkx2–5 regulates the proliferation and migration of H9c2 cells. In our experiments, Nkx2–5 regulated the expression of genes related to proliferation, migration, heart development, and disease. Based on bioinformatics analysis, knockdown of Nkx2–5 caused differential expression of genes involved in cardiac development, calcium ion-related biological activity, the transforming growth factor (TGF)-β signaling pathway, pathways related to heart diseases, the MAPK signaling pathway, and other biological processes and signaling pathways.

Conclusions

Nkx2–5 may regulate proliferation and migration of the H9c2 cells through the genes Tgfb-2, Bmp10, Id2, Wt1, Hey1, and Cacna1g; rno-miR-1-3p; the TGF-β signaling pathway; the MAPK signaling pathway; as well as other genes and pathways.

An update on genetic variants of the NKX2-5

NKX2-5 is a homeodomain transcription factor that plays a crucial role in heart development. It is the first gene where a single genetic variant (GV) was found to be associated with congenital heart diseases in humans. In this study, we carried out a comprehensive survey of NKX2-5 GVs to build a unified, curated, and updated compilation of all available GVs. We retrieved a total of 1,380 unique GVs. From these, 970 had information on their frequency in the general population and 143 have been linked to pathogenic phenotypes in humans. In vitro effect was ascertained for 38 GVs. The homeodomain had the biggest cluster of pathogenic variants in the protein: 49 GVs in 60 residues, 23 in its third α-helix, where 11 missense variants may affect protein-DNA interaction or the hydrophobic core. We also pinpointed the likely location of pathogenic GVs in four linear motifs. These analyses allowed us to assign a putative explanation for the effect of 90 GVs. This study pointed to reliable pathogenicity for GVs in helix 3 of the homeodomain and may broaden the scope of functional and structural studies that can be done to better understand the effect of GVs in NKX2-5 function.

Defective coronary vessel organization and reduction of VEGF-A in mouse embryonic hearts with gestational mild hypoxia

BACKGROUND

Vasculature is formed by responding to homeostatic tissue demands including in developing hearts. Hypoxia generally stimulates vascular formation in which vascular endothelial growth factor A (VEGF-A) plays a critical role. Gestational hypoxia increases the risk of low intrauterine growth and low birth weight, both of which are known to increase the risk of the fetus developing cardiovascular defects. In fact, continuous gestational mild hypoxia (14% O₂ ) from the mid-embryonic stage causes cardiac anomalies accompanied by a thinning compact layer in mice in vivo. Because coronary vasculature formation is necessary for compact layers to thicken, we hypothesized that defective coronary vessel organization is related to the thinning compact layer under gestational hypoxia conditions.

RESULTS

Continuous gestational mild hypoxia (14% O₂ ) applied from embryonic day 10.5 (E10.5) reduced the expression of VEGF-A mRNA and proteins by over 60% in E12.5 hearts relative to control normoxic hearts. Formation of CD31-positive vascular plexus, blood islands, and microvessels in embryonic ventricles were stunted by gestational hypoxia compared to control E12.5 hearts.

CONCLUSIONS

Our results suggest that mild hypoxia (14% O₂ ) does not induce coronary vessel organization or VEGF-A expression in developing mouse hearts, opposing the general effects of hypoxia-triggering vascular organization and VEGF-A expression.

Association of Maternal Diabetes Mellitus and Polymorphisms of the NKX2.5 Gene in Children with Congenital Heart Disease: A Single Centre-Based Case-Control Study

BACKGROUND

Congenital heart disease (CHD) is one of the most common birth defects among newborns, accounting for a large proportion of infant mortality worldwide. However, the mechanisms remain largely undefinable. This study aimed to investigate the association of CHD in offspring of mothers with diabetes mellitus (DM) and single nucleotide polymorphisms (SNPs) of NKX2.5.

METHODS AND RESULTS

A case-control study of 620 mothers of CHD patients and 620 mothers of healthy children admitted to Hunan Children's Hospital from November 2017 to December 2019 was conducted. We collected the mothers' information by questionnaire and detected children's NKX2.5 variants with a MassARRAY system. The interaction coefficient (γ) was used to quantify the estimated gene-environment interactions. Univariate and multivariate analyses both showed that the infants had a higher risk of CHD if their mothers had a history of DM, including gestational DM (GDM) during this pregnancy (adjusted odds ratio [aOR = 4.98]), GDM in previous pregnancies (aOR = 4.30), and pregestational DM (PGDM) in the 3 months before this pregnancy (aOR = 6.78). Polymorphisms of the NKX2.5 gene at rs11802669 (C/C vs. T/T: aOR = 4.97; C/T vs. T/T: aOR = 2.15) and rs2277923 (T/T vs. C/C, aOR = 1.74; T/C vs. C/C, aOR = 1.61) were significantly associated with the risk of CHD in offspring. In addition, significant interactions between maternal DM and NKX2.5 genetic variants at rs11802669 (aOR = 8.12) and rs2277923 (aOR = 17.72) affecting the development of CHD were found.

CONCLUSIONS

These results suggest that maternal DM, NKX2.5 genetic variants, and their interactions are significantly associated with the risk of CHD in offspring.

Analysis of NKX2-5 in 439 Chinese Patients with Sporadic Atrial Septal Defect

Background

The NKX2 gene family is made up of core transcription factors that are involved in the morphogenesis of the vertebrate heart. NKx2-5 plays a pivotal role in mouse cardiogenesis, and mutations in NKx2-5 result in an abnormal structure and function of the heart, including atrial septal defect and cardiac electrophysiological abnormalities.

Material/Methods

To investigate the genetic variation of NKX2-5 in Chinese patients with sporadic atrial septal defect, we sequenced the full length of the NKX2-5 gene in the participants of the study. Four hundred thirty-nine patients and 567 healthy unrelated individuals were recruited. Genomic DNA was extracted from the peripheral blood leukocytes of the participants. DNA samples from the participants were amplified by multiplex PCR and sequenced on an Illumina HiSeq platform. Variations were detected by comparison with a standard reference genome and annotation with a variant effect predictor.

Results

Thirty variations were detected in Chinese patients with sporadic atrial septal defect, and 6 single nucleotide polymorphisms (SNPs) had a frequency greater than 1%. Among the 30 variations, the SNPs rs2277923 and rs3729753 were extremely prominent, with a high frequency and odds ratio in patients.

Conclusions

Single nucleotide variations are the prominent genetic variations of NKX2-5 in Chinese patients with sporadic atrial septal defect. The SNPs rs2277923 and rs3729753 are prominent single nucleotide variations (SNVs) in Chinese patients with sporadic atrial septal defect.

Exposure to DBP induces the toxicity in early development and adverse effects on cardiac development in zebrafish (Danio rerio)

Dibutyl phthalate (DBP) is one of the most ubiquitous plasticizers used worldwide and has been frequently detected in soil, water, atmosphere, and other environmental media. DBP has become a ubiquitous environment contaminant and causes serious pollution. However, much attention has been paid to the toxicity of DBP, with only limited attention paid to its detrimental effects on the heart. In the present study, we investigated the toxicity of DBP in zebrafish embryo development, especially adverse effects on cardiac development. Embryos at 4-h post-fertilization (hpf) were exposed to different concentrations of DBP (0, 0.36, 1.8 and 3.6 μM) until 72 hpf. Exposure to DBP resulted in morphological abnormalities in zebrafish embryos. Exposure to 1.8 μM DBP significantly affected the growth, malformation rate, cardiac malformation rate and cardiac looping. Exposure to 3.6 μM DBP significantly affected all endpoints. To preliminarily understand the underlying mechanisms of toxic effects of DBP on the embryo heart, we examined the expression of master cardiac transcription factors such as NKX2.5 and TBX5. The expression of this two transcription factors was significantly reduced with DBP treatment in a dose-dependent manner. Our results demonstrate that exposure to DBP resulted in zebrafish developmental toxicity, pericardial edema, cardiac structure deformities and function alteration, and changed the expression of master cardiac transcription factors such as NKX2.5 and TBX5.

Gene-environment interaction impacts on heart development and embryo survival

Congenital heart disease (CHD) is the most common type of birth defect. In recent years, research has focussed on identifying the genetic causes of CHD. However, only a minority of CHD cases can be attributed to single gene mutations. In addition, studies have identified different environmental stressors that promote CHD, but the additive effect of genetic susceptibility and environmental factors is poorly understood. In this context, we have investigated the effects of short-term gestational hypoxia on mouse embryos genetically predisposed to heart defects. Exposure of mouse embryos heterozygous for Tbx1 or Fgfr1/Fgfr2 to hypoxia in utero increased the incidence and severity of heart defects while Nkx2-5^+/- embryos died within 2 days of hypoxic exposure. We identified the molecular consequences of the interaction between Nkx2-5 and short-term gestational hypoxia, which suggest that reduced Nkx2-5 expression and a prolonged hypoxia-inducible factor 1α response together precipitate embryo death. Our study provides insight into the causes of embryo loss and variable penetrance of monogenic CHD, and raises the possibility that cases of foetal death and CHD in humans could be caused by similar gene-environment interactions.

Mechanism Sharing Between Genetic and Gestational Hypoxia-Induced Cardiac Anomalies

Background: Cardiac development is a dynamic process both temporally and spatially. These complex processes are often disturbed and lead to congenital cardiac anomalies that affect approximately 1% of live births. Disease-causing variants in several genetic loci lead to cardiac anomalies, with variants in transcription factor NKX2-5 gene being one of the largest variants known. Gestational hypoxia, such as seen in high-altitude pregnancy, has been known to affect cardiac development, yet the incidence and underlying mechanisms are largely unknown.

Methods and Results: Normal wild-type female mice mated with heterozygous Nkx2-5 mutant males were housed under moderate hypoxia (14% O₂) or normoxia (20.9% O₂) conditions from 10.5 days of gestation. Wild-type mice exposed to hypoxia demonstrate excessive trabeculation, ventricular septal defects, irregular morphology of interventricular septum as well as atrial septal abnormalities, which overlap with those seen in heterozygous Nkx2-5 mutant mice. Genome-wide transcriptome done by RNA-seq of a 2-day hypoxic exposure on wild-type embryos revealed abnormal transcriptomes, in which approximately 60% share those from Nkx2-5 mutants without hypoxia. Gestational hypoxia reduced the expression of Nkx2-5 proteins in more than one-half along with a reduction in phosphorylation, suggesting that abnormal Nkx2-5 function is a common mechanism shared between genetic and gestational hypoxia-induced cardiac anomalies, at least at a specific developing stage.

Conclusion: The results of our study provide insights into a common molecular mechanism underlying non-genetic and genetic cardiac anomalies.

Deletion of Nkx2-5 in trabecular myocardium reveals the developmental origins of pathological heterogeneity associated with ventricular non-compaction cardiomyopathy

Left ventricular non-compaction (LVNC) is a rare cardiomyopathy associated with a hypertrabeculated phenotype and a large spectrum of symptoms. It is still unclear whether LVNC results from a defect of ventricular trabeculae development and the mechanistic basis that underlies the varying severity of this pathology is unknown. To investigate these issues, we inactivated the cardiac transcription factor Nkx2-5 in trabecular myocardium at different stages of trabecular morphogenesis using an inducible Cx40-creERT2 allele. Conditional deletion of Nkx2-5 at embryonic stages, during trabecular formation, provokes a severe hypertrabeculated phenotype associated with subendocardial fibrosis and Purkinje fiber hypoplasia. A milder phenotype was observed after Nkx2-5 deletion at fetal stages, during trabecular compaction. A longitudinal study of cardiac function in adult Nkx2-5 conditional mutant mice demonstrates that excessive trabeculation is associated with complex ventricular conduction defects, progressively leading to strain defects, and, in 50% of mutant mice, to heart failure. Progressive impaired cardiac function correlates with conduction and strain defects independently of the degree of hypertrabeculation. Transcriptomic analysis of molecular pathways reflects myocardial remodeling with a larger number of differentially expressed genes in the severe versus mild phenotype and identifies Six1 as being upregulated in hypertrabeculated hearts. Our results provide insights into the etiology of LVNC and link its pathogenicity with compromised trabecular development including compaction defects and ventricular conduction system hypoplasia.

During fetal heart morphogenesis, formation of the mature ventricular wall requires coordinated compaction of the inner trabecular layer and growth of the outer layer of myocardium. Arrested trabecular development has been implicated in the pathogenesis of hypertrabeculation associated with ventricular non-compaction cardiomyopathy. However much uncertainty still exists among clinicians concerning the physiopathology of ventricular non-compaction cardiomyopathy, including its clinical characteristics, prognosis, classification and even the definition of hypertrabeculation. In particular, distinguishing between pathological and non-pathological subtypes of non-compaction is currently a major issue. Here we show that deletion of the gene encoding the transcription factor Nkx2-5 at critical steps during trabecular development recapitulates pathological features of hypertrabeculation, providing the first model of ventricular non-compaction cardiomyopathy in adult mice. We demonstrate that excessive trabeculation due to failure of trabecular compaction during fetal development is associated with Purkinje fiber hypoplasia and subendocardial fibrosis. Longitudinal functional studies reveal that these mice present all the clinical signs of symptomatic left ventricular non-compaction cardiomyopathy, including conduction defects, strain defects and progressive heart failure. Our results, including transcriptomic analysis, suggest that pathological features of non-compaction are primarily developmental defects. This study clarifies the origin of the pathological outcomes associated with LVNC and may provide helpful information for clinicians concerning the etiology of this rare cardiomyopathy.

Cardiac-specific developmental and epigenetic functions of Jarid2 during embryonic development

Epigenetic regulation is critical in normal cardiac development. We have demonstrated that the deletion of Jarid2 (Jumonji (Jmj) A/T-rich interaction domain 2) in mice results in cardiac malformations recapitulating human congenital cardiac disease and dysregulation of gene expression. However, the precise developmental and epigenetic functions of Jarid2 within the developing heart remain to be elucidated. Here, we determined the cardiac-specific functions of Jarid2 and the genetic networks regulated by Jarid2. Jarid2 was deleted using different cardiac-specific Cre mice. The deletion of Jarid2 by Nkx2.5-Cre mice (Jarid2^Nkx) caused cardiac malformations including ventricular septal defects, thin myocardium, hypertrabeculation, and neonatal lethality. Jarid2^Nkx mice exhibited elevated expression of neural genes, cardiac jelly, and other key factors including Isl1 and Bmp10 in the developing heart. By employing combinatorial genome-wide approaches and molecular analyses, we showed that Jarid2 in the myocardium regulates a subset of Jarid2 target gene expression and H3K27me3 enrichment during heart development. Specifically, Jarid2 was required for PRC2 occupancy and H3K27me3 at the Isl1 promoter locus, leading to the proper repression of Isl1 expression. In contrast, Jarid2 deletion in differentiated cardiomyocytes by cTnt-Cre mice caused no gross morphological defects or neonatal lethality. Thus, the early deletion of Jarid2 in cardiac progenitors, prior to the differentiation of cardiac progenitors into cardiomyocytes, results in morphogenetic defects manifested later in development. Our studies reveal that there is a critical window during early cardiac progenitor differentiation when Jarid2 is crucial to establish the epigenetic landscape at later stages of development.

Transcriptional activator DOT1L putatively regulates human embryonic stem cell differentiation into the cardiac lineage

Background

Commitment of pluripotent stem cells into differentiated cells and associated gene expression necessitate specific epigenetic mechanisms that modify the DNA and corresponding histone proteins to render the chromatin in an open or closed state. This in turn dictates the associated genetic machinery, including transcription factors, acknowledging the cellular signals provided. Activating histone methyltransferases represent crucial enzymes in the epigenetic machinery that cause transcription initiation by delivering the methyl mark on histone proteins. A number of studies have evidenced the vital role of one such histone modifier, DOT1L, in transcriptional regulation. Involvement of DOT1L in differentiating pluripotent human embryonic stem (hES) cells into the cardiac lineage has not yet been investigated.

Methods

The study was conducted on in-house derived (KIND1) and commercially available (HES3) human embryonic stem cell lines. Chromatin immunoprecipitation (ChIP) was performed followed by sequencing to uncover the cardiac genes harboring the DOT1L specific mark H3K79me2. Following this, dual immunofluorescence was employed to show the DOT1L co-occupancy along with the cardiac progenitor specific marker. DOT1L was knocked down by siRNA to further confirm its role during cardiac differentiation.

Results

ChIP sequencing revealed a significant number of peaks characterizing H3K79me2 occupancy in the proximity of the transcription start site. This included genes like MYOF, NR2F2, NKX2.5, and HAND1 in cardiac progenitors and cardiomyocytes, and POU5F1 and NANOG in pluripotent hES cells. Consistent with this observation, we also show that DOT1L co-localizes with the master cardiac transcription factor NKX2.5, suggesting its direct involvement during gene activation. Knockdown of DOT1L did not alter the pluripotency of hES cells, but it led to the disruption of cardiac differentiation observed morphologically as well as at transcript and protein levels.

Conclusions

Collectively, our data suggests the crucial role of H3K79me2 methyltransferase DOT1L for activation of NKX2.5 during the cardiac differentiation of hES cells.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0810-8) contains supplementary material, which is available to authorized users.

Prevalence and Spectrum of NKX2-5 Mutations Associated With Sporadic Adult-Onset Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM), the most common form of primary myocardial disease, is a leading cause of congestive heart failure and the most common indication for heart transplantation. Recently, NKX2-5 mutations have been involved in the pathogenesis of familial DCM. However, the prevalence and spectrum of NKX2-5 mutations associated with sporadic DCM remain to be evaluated. In this study, the coding regions and flanking introns of the NKX2-5 gene, which encodes a cardiac transcription factor pivotal for cardiac development and structural remodeling, were sequenced in 210 unrelated patients with sporadic adult-onset DCM. A total of 300 unrelated healthy individuals used as controls were also genotyped for NKX2-5. The functional effect of the mutant NKX2-5 was investigated using a dual-luciferase reporter assay system. As a result, two novel heterozygous NKX2-5 mutations, p.R139W and p.E167X, were identified in 2 unrelated patients with sporadic adult-onset DCM, with a mutational prevalence of approximately 0.95%. The mutations were absent in 600 referential chromosomes and the altered amino acids were completely conserved evolutionarily across species. Functional assays revealed that the NKX2-5 mutants were associated with significantly reduced transcriptional activity. Furthermore, the mutations abrogated the synergistic activation between NKX2-5 and GATA4 as well as TBX20, two other cardiac key transcription factors that have been causally linked to adult-onset DCM. This study is the first to associate NKX2-5 loss-of-function mutations with enhanced susceptibility to sporadic DCM, which provides novel insight into the molecular etiology underpinning DCM, and suggests the potential implications for the genetic counseling and personalized treatment of the DCM patients.

Transcription factor-induced activation of cardiac gene expression in human c-kit+ cardiac progenitor cells

Although transplantation of c-kit+ cardiac progenitor cells (CPCs) significantly alleviates post-myocardial infarction left ventricular dysfunction, generation of cardiomyocytes by exogenous CPCs in the recipient heart has often been limited. Inducing robust differentiation would be necessary for improving the efficacy of the regenerative cardiac cell therapy. We assessed the hypothesis that differentiation of human c-kit+ CPCs can be enhanced by priming them with cardiac transcription factors (TFs). We introduced five different TFs (Gata4, MEF2C, NKX2.5, TBX5, and BAF60C) into CPCs, either alone or in combination, and then examined the expression of marker genes associated with the major cardiac cell types using quantitative RT-PCR. When introduced individually, Gata4 and TBX5 induced a subset of myocyte markers. Moreover, Gata4 alone significantly induced smooth muscle cell and fibroblast markers. Interestingly, these gene expression changes brought by Gata4 were also accompanied by morphological changes. In contrast, MEF2C and NKX2.5 were largely ineffective in initiating cardiac gene expression in CPCs. Surprisingly, introduction of multiple TFs in different combinations mostly failed to act synergistically. Likewise, addition of BAF60C to Gata4 and/or TBX5 did not further potentiate their effects on cardiac gene expression. Based on our results, it appears that GATA4 is able to potentiate gene expression programs associated with multiple cardiovascular lineages in CPCs, suggesting that GATA4 may be effective in priming CPCs for enhanced differentiation in the setting of stem cell therapy.

Point mutations in murine Nkx2-5 phenocopy human congenital heart disease and induce pathogenic Wnt signaling

Mutations in the Nkx2-5 gene are a main cause of congenital heart disease. Several studies have addressed the phenotypic consequences of disrupting the Nkx2-5 gene locus, although animal models to date failed to recapitulate the full spectrum of the human disease. Here, we describe a new Nkx2-5 point mutation murine model, akin to its human counterpart disease-generating mutation. Our model fully reproduces the morphological and physiological clinical presentations of the disease and reveals an understudied aspect of Nkx2-5-driven pathology, a primary right ventricular dysfunction. We further describe the molecular consequences of disrupting the transcriptional network regulated by Nkx2-5 in the heart and show that Nkx2-5-dependent perturbation of the Wnt signaling pathway promotes heart dysfunction through alteration of cardiomyocyte metabolism. Our data provide mechanistic insights on how Nkx2-5 regulates heart function and metabolism, a link in the study of congenital heart disease, and confirms that our models are the first murine genetic models to our knowledge to present all spectra of clinically relevant adult congenital heart disease phenotypes generated by NKX2-5 mutations in patients.

Congenital heart defect causing mutation in Nkx2.5 displays in vivo functional deficit

The Nkx2.5 gene encodes a transcription factor that plays a critical role in heart development. In humans, heterozygous mutations in NKX2.5 result in congenital heart defects (CHDs). However, the molecular mechanisms by which these mutations cause the disease remain unknown. NKX2.5-R142C is a mutation that was reported to be associated with atrial septal defect (ASD) and atrioventricular (AV) block in 13-patients from one family. The R142C mutation is located within both the DNA-binding domain and the nuclear localization sequence of NKX2.5 protein. The pathogenesis of CHDs in humans with R142C point mutation is not well understood. To examine the functional deficit associated with this mutation in vivo, we generated and characterized a knock-in mouse that harbours the human mutation R142C. Systematic structural and functional examination of the embryonic, newborn, and adult mice revealed that the homozygous embryos Nkx2.5^R141C/R141C are developmentally arrested around E10.5 with delayed heart morphogenesis and downregulation of Nkx2.5 target genes, Anf, Mlc2v, Actc1 and Cx40. Histological examination of Nkx2.5^R141C/+ newborn hearts showed that 36% displayed ASD, with at least 80% 0f adult heterozygotes displaying a septal defect. Moreover, heterozygous Nkx2.5^R141C/+ newborn mice have downregulation of ion channel genes with 11/12 adult mice manifesting a prolonged PR interval that is indicative of 1st degree AV block. Collectively, the present study demonstrates that mice with the R141C point mutation in the Nkx2.5 allele phenocopies humans with the NKX2.5 R142C point mutation.

Ectopic expression of Cripto-1 in transgenic mouse embryos causes hemorrhages, fatal cardiac defects and embryonic lethality

Targeted disruption of Cripto-1 in mice caused embryonic lethality at E7.5, whereas we unexpectedly found that ectopic Cripto-1 expression in mouse embryos also led to embryonic lethality, which prompted us to characterize the causes and mechanisms underlying embryonic death due to ectopic Cripto-1 expression. RCLG/EIIa-Cre embryos displayed complex phenotypes between embryonic day 14.5 (E14.5) and E17.5, including fatal hemorrhages (E14.5-E15.5), embryo resorption (E14.5-E17.5), pale body surface (E14.5-E16.5) and no abnormal appearance (E14.5-E16.5). Macroscopic and histological examination revealed that ectopic expression of Cripto-1 transgene in RCLG/EIIa-Cre embryos resulted in lethal cardiac defects, as evidenced by cardiac malformations, myocardial thinning, failed assembly of striated myofibrils and lack of heartbeat. In addition, Cripto-1 transgene activation beginning after E8.5 also caused the aforementioned lethal cardiac defects in mouse embryos. Furthermore, ectopic Cripto-1 expression in embryonic hearts reduced the expression of cardiac transcription factors, which is at least partially responsible for the aforementioned lethal cardiac defects. Our results suggest that hemorrhages and cardiac abnormalities are two important lethal factors in Cripto-1 transgenic mice. Taken together, these findings are the first to demonstrate that sustained Cripto-1 transgene expression after E11.5 causes fatal hemorrhages and lethal cardiac defects, leading to embryonic death at E14.5-17.5.

Associations of NKX2-5 Genetic Polymorphisms with the Risk of Congenital Heart Disease: A Meta-analysis

The NKX2-5 gene is a vital regulator of cardiac formation and development. Recently, the roles of NKX2-5 63A>G polymorphism and 606G>C polymorphism in congenital heart disease (CHD) have been extensively studied, with conflicting results. The aim of the present study was to better elucidate the associations between NKX2-5 genetic polymorphisms and CHD risk through a meta-analysis. Eligible articles were searched in PubMed, MEDLINE, EMBASE, Google Scholar and CNKI up to December 2015. Odds ratios (ORs) and 95 % confidence intervals were used to detect any potential associations between NKX2-5 genetic polymorphisms and CHD risk. Heterogeneity between studies was assessed with Q test and I (2) statistic. Subgroup analysis and sensitivity analysis were performed to test the reliability and stability of the results, and funnel plots were applied to estimate publication bias. A total of 13 case-control studies including 2245 CHD patients and 1953 healthy controls were analyzed. The overall meta-analysis results showed that NKX2-5 63A>G polymorphism and 606G>C polymorphism were not significantly associated with CHD risk. Subgroup analysis was further performed for NKX2-5 63A>G polymorphism based on types of CHD and ethnicity of study population, and similar negative results were found in all subgroups. Our findings suggested that NKX2-5 63A>G polymorphism and 606G>C polymorphism may not be implicated in the pathogenesis of CHD.

A novel conditional mouse model for Nkx2-5 reveals transcriptional regulation of cardiac ion channels

Nkx2-5 is one of the master regulators of cardiac development, homeostasis and disease. This transcription factor has been previously associated with a suite of cardiac congenital malformations and impairment of electrical activity. When disease causative mutations in transcription factors are considered, NKX2-5 gene dysfunction is the most common abnormality found in patients. Here we describe a novel mouse model and subsequent implications of Nkx2-5 loss for aspects of myocardial electrical activity. In this work we have engineered a new Nkx2-5 conditional knockout mouse in which flox sites flank the entire Nkx2-5 locus, and validated this line for the study of heart development, differentiation and disease using a full deletion strategy. While our homozygous knockout mice show typical embryonic malformations previously described for the lack of the Nkx2-5 gene, hearts of heterozygous adult mice show moderate morphological and functional abnormalities that are sufficient to sustain blood supply demands under homeostatic conditions. This study further reveals intriguing aspects of Nkx2-5 function in the control of cardiac electrical activity. Using a combination of mouse genetics, biochemistry, molecular and cell biology, we demonstrate that Nkx2-5 regulates the gene encoding Kcnh2 channel and others, shedding light on potential mechanisms generating electrical abnormalities observed in patients bearing NKX2-5 dysfunction and opening opportunities to the study of novel therapeutic targets for anti-arrhythmogenic therapies.

Electrical and mechanical stimulation of cardiac cells and tissue constructs

The field of cardiac tissue engineering has made significant strides over the last few decades, highlighted by the development of human cell derived constructs that have shown increasing functional maturity over time, particularly using bioreactor systems to stimulate the constructs. However, the functionality of these tissues is still unable to match that of native cardiac tissue and many of the stem-cell derived cardiomyocytes display an immature, fetal like phenotype. In this review, we seek to elucidate the biological underpinnings of both mechanical and electrical signaling, as identified via studies related to cardiac development and those related to an evaluation of cardiac disease progression. Next, we review the different types of bioreactors developed to individually deliver electrical and mechanical stimulation to cardiomyocytes in vitro in both two and three-dimensional tissue platforms. Reactors and culture conditions that promote functional cardiomyogenesis in vitro are also highlighted. We then cover the more recent work in the development of bioreactors that combine electrical and mechanical stimulation in order to mimic the complex signaling environment present in vivo. We conclude by offering our impressions on the important next steps for physiologically relevant mechanical and electrical stimulation of cardiac cells and engineered tissue in vitro.

Single nucleotide polymorphism of NKX2-5 gene with sporadic congenital heart disease in Chinese Bai population

BACKGROUND

Congenital heart disease (CHD) is the most common birth abnormality, especially for sporadic CHD. However, the etiology of sporadic CHD is largely unknown. NKX2-5, the earliest sign of cardiac progenitor cell differentiation, plays a key role in cardiac morphogenesis, and the mutation of this gene can cause sporadic CHD.

PURPOSE

To investigate the association of genetic variations of NKX2-5 with sporadic CHD in Chinese Bai people.

METHODS

The whole 2 coding exons and flanking intron sequences of NKX2-5 gene were screened using DNA sequencing in 70 Chinese Bai patients with sporadic CHD and 136 healthy controls.

RESULTS

A novel heterozygous DNA sequence variant (DSV), 1433A>G, was identified in one tetralogy of Fallot (TOF) patient and one persistent left superior vena cava (PLSVC) patient, but none in controls. The frequency of single nucleotide polymorphism (SNP) rs2277923 in CHD group was significantly higher than that in control group. The allele and genotype were associated with the occurrence of CHD.

CONCLUSION

The novel DSV (1433A>G) may be relevant with TOF and PLSVC, and the SNP rs2277923 of NKX2-5 gene contributes to the risk of sporadic CHD in Chinese Bai people.

Investigating the Mechanism of Hyperglycemia-Induced Fetal Cardiac Hypertrophy

Hyperglycemia in diabetic mothers enhances the risk of fetal cardiac hypertrophy during gestation. However, the mechanism of high-glucose-induced cardiac hypertrophy is not largely understood. In this study, we first demonstrated that the incidence rate of cardiac hypertrophy dramatically increased in fetuses of diabetic mothers using color ultrasound examination. In addition, human fetal cardiac hypertrophy was successfully mimicked in a streptozotocin (STZ)-induced diabetes mouse model, in which mouse cardiac hypertrophy was diagnosed using type-M ultrasound and a histological assay. PH3 immunofluorescent staining of mouse fetal hearts and in vitro-cultured H9c2 cells indicated that cell proliferation decreased in E18.5, E15.5 and E13.5 mice, and cell apoptosis in H9c2 cells increased in the presence of high glucose in a dose-dependent manner. Next, we found that the individual cardiomyocyte size increased in pre-gestational diabetes mellitus mice and in response to high glucose exposure. Meanwhile, the expression of β-MHC and BMP-10 was up-regulated. Nkx2.5 immunofluorescent staining showed that the expression of Nkx2.5, a crucial cardiac transcription factor, was suppressed in the ventricular septum, left ventricular wall and right ventricular wall of E18.5, E15.5 and E13.5 mouse hearts. However, cardiac hypertrophy did not morphologically occur in E13.5 mouse hearts. In cultured H9c2 cells exposed to high glucose, Nkx2.5 expression decreased, as detected by both immunostaining and western blotting, and the expression of KCNE1 and Cx43 was also restricted. Taken together, alterations in cell size rather than cell proliferation or apoptosis are responsible for hyperglycemia-induced fetal cardiac hypertrophy. The aberrant expression of Nkx2.5 and its regulatory target genes in the presence of high glucose could be a principal component of pathogenesis in the development of fetal cardiac hypertrophy.

Mouse Model of Human Congenital Heart Disease: Progressive Atrioventricular Block Induced by a Heterozygous Nkx2-5 Homeodomain Missense Mutation

BACKGROUND

Heterozygous human NKX2-5 homeodomain (DNA-binding domain) missense mutations are highly penetrant for varied congenital heart defects, including progressive atrioventricular (AV) block requiring pacemaker implantation. We recently replicated this genetic defect in a murine knockin model, in which we demonstrated highly penetrant, pleiotropic cardiac anomalies. In this study, we examined postnatal AV conduction in the knockin mice.

METHODS AND RESULTS

A murine knockin model (Arg52Gly, Nkx2-5(+/R52G)) in a 129/Sv background was analyzed by histopathology, surface, and telemetry ECG, and in vivo electrophysiology studies, comparing with control Nkx2-5(+/+) mice at diverse postnatal stages, ranging from postnatal day 1 (P1) to 17 months. PR prolongation (first degree AV block) was present at 4 weeks, 7 months, and 17 months of age, but not at P1 in the mutant mice. Advanced AV block was also occasionally demonstrated in the mutant mice. Electrophysiology studies showed that AV nodal function and right ventricular effective refractory period were impaired in the mutant mice, whereas sinus nodal function was not affected. AV nodal size was significantly smaller in the mutant mice than their controls at 4 weeks of age, corresponding to the presence of PR prolongation, but not P1, suggesting, at least in part, that the conduction abnormalities are the result of a morphologically atrophic AV node.

CONCLUSIONS

The highly penetrant and progressive AV block phenotype seen in human heterozygous missense mutations in NKX2-5 homeodomain was replicated in mice by knocking in a comparable missense mutation.

GATA4 transgenic mice as an in vivo model of congenital heart disease

Our previous study indicated that 8 patients from a family with a history of congenital heart disease had simple atrial septal defect (ASD) and carried the same mutation at codon 310 in the GATA4 gene. In the present study, to identify the functional defects caused by this mutation in an in vivo model, the transgene DNA constructs were microinjected into mice to generate a transgenic mouse model. The mice were genotyped using PCR and DNA sequencing. Protein expression was measured by western blot analysis. qPCR was used to determine the copy number of the transgenes. The heart tissue was fixed and sectioned by conventional procedures. The Vevo 2000 system was used to perform echocardiography on the mice. The expression of GATA4 target genes was measured using the real-time PCR system. The incidence of ASD in the heterozygous transgenic mice was found to be greater than that in the wild-type control mice (P<0.05). In addition, the expression of α-myosin heavy chain (α-MHC) in the heart tissues from the homozygous mice was lower than that in the heart tissues from their wild-type littermates (P<0.05). In conclusion, these results suggest that the introduction of GATA4 M310V negatively affects the normal expression of α-MHC. In accordance with previous findings on GATA4 mutation screening and in vitro experiments, this study confirms that GATA4 M310V mutation may lead to the development of the congenital heart defect, ASD.

Copy number variation of GATA4 and NKX2-5 in Chinese fetuses with congenital heart disease

BACKGROUND

Congenital heart disease (CHD) is one of the most common birth defects in newborns. The etiology of CHD has remained largely unknown, but it is assumed to result from the combined effects of genetic and environmental factors. Recent investigations have detected potentially pathogenic copy number variations (CNV) in a proportion of patients with CHD. The present case-control study evaluated whether CNV in the GATA4 and NKX2-5 genes contribute to the pathogenesis of CHD in Chinese fetuses (n = 117), by comparing them with non-CHD control subjects (n = 100).

METHODS

Multiplex ligation-dependent probe amplification with the P311A probe mixture was used to detect CNV.

RESULTS

The normalized signals were within the normal range for all exons in all CHD patients and non-CHD control subjects. Of the 117 CHD patients, three had a deletion of 22q11, and two had a duplication of 22q11.

CONCLUSIONS

There was no evidence of a role for NKX2-5 and GATA4 CNV in fetal CHD; therefore, these CNV may not be common in fetal CHD in China.

An early requirement for nkx2.5 ensures the first and second heart field ventricular identity and cardiac function into adulthood

Temporally controlled mechanisms that define the unique features of ventricular and atrial cardiomyocyte identities are essential for the construction of a coordinated, morphologically intact heart. We have previously demonstrated an important role for nkx genes in maintaining ventricular identity, however, the specific timing of nkx2.5 function in distinct cardiomyocyte populations has yet to be elucidated. Here, we show that heat-shock induction of a novel transgenic line, Tg(hsp70l:nkx2.5-EGFP), during the initial stages of cardiomyocyte differentiation leads to rescue of chamber shape and identity in nkx2.5(-/-) embryos as chambers emerge. Intriguingly, our findings link an early role of this essential cardiac transcription factor with a later function. Moreover, these data reveal that nkx2.5 is also required in the second heart field as the heart tube forms, reflecting the temporal delay in differentiation of this population. Thus, our results support a model in which nkx genes induce downstream targets that are necessary to maintain chamber-specific identity in both early- and late-differentiating cardiomyocytes at discrete stages in cardiac morphogenesis. Furthermore, we show that overexpression of nkx2.5 during the first and second heart field development not only rescues the mutant phenotype, but also is sufficient for proper function of the adult heart. Taken together, these results shed new light on the stage-dependent mechanisms that sculpt chamber-specific cardiomyocytes and, therefore, have the potential to improve in vitro generation of ventricular cells to treat myocardial infarction and congenital heart disease.

A mouse model of human congenital heart disease: high incidence of diverse cardiac anomalies and ventricular noncompaction produced by heterozygous Nkx2-5 homeodomain missense mutation

BACKGROUND

Heterozygous human mutations of NKX2-5 are highly penetrant and associated with varied congenital heart defects. The heterozygous knockout of murine Nkx2-5, in contrast, manifests less profound cardiac malformations, with low disease penetrance. We sought to study this apparent discrepancy between human and mouse genetics. Because missense mutations in the NKX2-5 homeodomain (DNA-binding domain) are the most frequently reported type of human mutation, we replicated this genetic defect in a murine knockin model.

METHODS AND RESULTS

We generated a murine model in a 129/Sv genetic background by knocking-in an Nkx2-5 homeodomain missense mutation previously identified in humans. The mutation was located at homeodomain position 52Arg→Gly (R52G). All the heterozygous neonatal Nkx2-5(+/R52G) mice demonstrated a prominent trabecular layer in the ventricular wall, so called noncompaction, along with diverse cardiac anomalies, including atrioventricular septal defects, Ebstein malformation of the tricuspid valve, and perimembranous and muscular ventricular septal defects. In addition, P10 Nkx2-5(+/R52G) mice demonstrated atrial sepal anomalies, with significant increase in the size of the interatrial communication and fossa ovalis, and decrease in the length of the flap valve compared with control Nkx2-5(+/+) or Nkx2-5(+/-) mice.

CONCLUSIONS

The results of our study demonstrate that heterozygous missense mutation in the murine Nkx2-5 homeodomain (R52G) is highly penetrant and result in pleiotropic cardiac effects. Thus, in contrast to heterozygous Nkx2-5 knockout mice, the effects of the heterozygous knockin mimic findings in humans with heterozygous missense mutation in NKX2-5 homeodomain.

Nkx2-5 suppresses the proliferation of atrial myocytes and conduction system

RATIONALE

Tight control of cardiomyocyte proliferation is essential for the formation of four-chambered heart. Although human mutation of NKX2-5 is linked to septal defects and atrioventricular conduction abnormalities, early lethality and hemodynamic alteration in the mutant models have caused controversy as to whether Nkx2-5 regulates cardiomyocyte proliferation.

OBJECTIVE

In this study, we circumvented these limitations by atrial-restricted deletion of Nkx2-5.

METHOD AND RESULTS

Atrial-specific Nkx2-5 mutants died shortly after birth with hyperplastic working myocytes and conduction system including two nodes and internodal tracts. Multicolor reporter analysis revealed that Nkx2-5-null cardiomyocytes displayed clonal proliferative activity throughout the atria, indicating the suppressive role of Nkx2-5 in cardiomyocyte proliferation after chamber ballooning stages. Transcriptome analysis revealed that aberrant activation of Notch signaling underlies hyperproliferation of mutant cardiomyocytes, and forced activation of Notch signaling recapitulates hyperproliferation of working myocytes but not the conduction system.

CONCLUSIONS

Collectively, these data suggest that Nkx2-5 regulates the proliferation of atrial working and conduction myocardium in coordination with Notch pathway.

Mutational spectrum of the NKX2-5 gene in patients with lone atrial fibrillation

Atrial fibrillation (AF) is the most common form of sustained cardiac arrhythmia in humans and is responsible for substantial morbidity and mortality worldwide. Emerging evidence indicates that abnormal cardiovascular development is involved in the pathogenesis of AF. In this study, the coding exons and splice sites of the NKX2-5 gene, which encodes a homeodomain-containing transcription factor essential for cardiovascular genesis, were sequenced in 146 unrelated patients with lone AF as well as the available relatives of the mutation carriers. A total of 700 unrelated ethnically matched healthy individuals used as controls were genotyped. The disease-causing potential of the identified NKX2-5 variations was predicted by MutationTaster and PolyPhen-2. The functional characteristics of the mutant NKX2-5 proteins were analyzed using a dual-luciferase reporter assay system. As a result, two heterozygous NKX2-5 mutations, including a previously reported p.E21Q and a novel p.T180A mutation, were identified in two families with AF transmitted in an autosomal dominant pattern. The mutations co-segregated with AF in the families with complete penetrance. The detected substitutions, which altered the amino acids highly conserved evolutionarily across species, were absent in 700 control individuals and were both predicted to be causative. Functional analyses demonstrated that the NKX2-5 mutants were associated with significantly decreased transcriptional activity compared with their wild-type counterpart. The findings expand the spectrum of NKX2-5 mutations linked to AF and provide additional evidence that dysfunctional NKX2-5 may confer vulnerability to AF, suggesting the potential benefit for the early prophylaxis and personalized treatment of AF.

Engineered chromosome-based genetic mapping establishes a 3.7 Mb critical genomic region for Down syndrome-associated heart defects in mice

Trisomy 21 (Down syndrome, DS) is the most common human genetic anomaly associated with heart defects. Based on evolutionary conservation, DS-associated heart defects have been modeled in mice. By generating and analyzing mouse mutants carrying different genomic rearrangements in human chromosome 21 (Hsa21) syntenic regions, we found the triplication of the Tiam1-Kcnj6 region on mouse chromosome 16 (Mmu16) resulted in DS-related cardiovascular abnormalities. In this study, we developed two tandem duplications spanning the Tiam1-Kcnj6 genomic region on Mmu16 using recombinase-mediated genome engineering, Dp(16)3Yey and Dp(16)4Yey, spanning the 2.1 Mb Tiam1-Il10rb and 3.7 Mb Ifnar1-Kcnj6 regions, respectively. We found that Dp(16)4Yey/+, but not Dp(16)3Yey/+, led to heart defects, suggesting the triplication of the Ifnar1-Kcnj6 region is sufficient to cause DS-associated heart defects. Our transcriptional analysis of Dp(16)4Yey/+ embryos showed that the Hsa21 gene orthologs located within the duplicated interval were expressed at the elevated levels, reflecting the consequences of the gene dosage alterations. Therefore, we have identified a 3.7 Mb genomic region, the smallest critical genomic region, for DS-associated heart defects, and our results should set the stage for the final step to establish the identities of the causal gene(s), whose elevated expression(s) directly underlie this major DS phenotype.

Lrrc10 is a novel cardiac-specific target gene of Nkx2-5 and GATA4

Cardiac gene expression is precisely regulated and its perturbation causes developmental defects and heart disease. Leucine-rich repeat containing 10 (Lrrc10) is a cardiac-specific factor that is crucial for proper cardiac development and deletion of Lrrc10 in mice results in dilated cardiomyopathy. However, the mechanisms regulating Lrrc10 expression in cardiomyocytes remain unknown. Therefore, we set out to determine trans-acting factors and cis-elements critical for mediating Lrrc10 expression. We identify Lrrc10 as a transcriptional target of Nkx2-5 and GATA4. The Lrrc10 promoter region contains two highly conserved cardiac regulatory elements, which are functional in cardiomyocytes but not in fibroblasts. In vivo, Nkx2-5 and GATA4 endogenously occupy the proximal and distal cardiac regulatory elements of Lrrc10 in the heart. Moreover, embryonic hearts of Nkx2-5 knockout mice have dramatically reduced expression of Lrrc10. These data demonstrate the importance of Nkx2-5 and GATA4 in regulation of Lrrc10 expression in vivo. The proximal cardiac regulatory element located at around -200bp is synergistically activated by Nkx2-5 and GATA4 while the distal cardiac regulatory element present around -3kb requires SRF in addition to Nkx2-5 and GATA4 for synergistic activation. Mutational analyses identify a pair of adjacent Nkx2-5 and GATA binding sites within the proximal cardiac regulatory element that are necessary to induce expression of Lrrc10. In contrast, only the GATA site is functional in the distal regulatory element. Taken together, our data demonstrate that the transcription factors Nkx2-5 and GATA4 cooperatively regulate cardiac-specific expression of Lrrc10.