Two novel HAND1 mutations in Chinese patients with ventricular septal defect

Novel and deleterious nucleotide variations in the HAND1 gene probably affect miRNA target sites and protein function in pediatric patients with congenital heart disease

BACKGROUND

Congenital heart disease (CHD) is the most prevalent developmental defect and principal cause of infant mortality and affects cardiac and large blood vessel structures in approximately 1% of live births worldwide. To date, numerous studies have related critical genetic dysfunctions to the pathogenesis of CHDs. However, the genetic basis underlying CHD remains largely unknown. In the present study, we investigated the association of nucleotide variations in coding and noncoding regions of the HAND1 gene with the risk of CHD. The HAND1 gene, encoding a helix-loop-helix transcription factor, is particularly relevant for mechanisms underlying CHD since it plays a significant role in heart development.

METHODS AND RESULTS

The genomic DNA of 150 unrelated pediatric patients with CHD was screened by PCR-SSCP and direct sequencing. Four novel and heterozygous missense mutations were identified in the first exon, with three causing amino acid substitutions (p.Val149Met, p.Tyr142His, and p.Leu146Met). In-silico analysis also indicated their deleterious impact on protein structure and function. In addition, we identified five novel nucleotide variants in the 3'UTR region (c.*461, c.*342, c.*529, c.*448, c.*593), potentially altering the target sites of miRNAs. These changes include the loss of certain target sites and the acquisition of new ones.

CONCLUSIONS

These findings confirm the phenotypic association between CHDs and HAND1 mutations and can pave the way for developing new preventive and therapeutic strategies.

HAND factors regulate cardiac lineage commitment and differentiation from human pluripotent stem cells

BACKGROUND

Transcription factors HAND1 and HAND2 (HAND1/2) play significant roles in cardiac organogenesis. Abnormal expression and deficiency of HAND1/2 result in severe cardiac defects. However, the function and mechanism of HAND1/2 in regulating human early cardiac lineage commitment and differentiation are still unclear.

METHODS

With NKX2.5eGFP H9 human embryonic stem cells (hESCs), we established single and double knockout cell lines for HAND1 and HAND2, respectively, whose cardiomyocyte differentiation efficiency could be monitored by assessing NKX2.5-eGFP+ cells with flow cytometry. The expression of specific markers for heart fields and cardiomyocyte subtypes was examined by quantitative PCR, western blot and immunofluorescence staining. Microelectrode array and whole-cell patch clamp were performed to determine the electrophysiological characteristics of differentiated cardiomyocytes. The transcriptomic changes of HAND knockout cells were revealed by RNA sequencing. The HAND1/2 target genes were identified and validated experimentally by integrating with HAND1/2 chromatin immunoprecipitation sequencing data.

RESULTS

Either HAND1 or HAND2 knockout did not affect the cardiomyocyte differentiation kinetics, whereas depletion of HAND1/2 resulted in delayed differentiation onset. HAND1 knockout biased cardiac mesoderm toward second heart field progenitors at the expense of first heart field progenitors, leading to increased expression of atrial and outflow tract cardiomyocyte markers, which was further confirmed by the appearance of atrial-like action potentials. By contrast, HAND2 knockout cardiomyocytes had reduced expression of atrial cardiomyocyte markers and displayed ventricular-like action potentials. HAND1/2-deficient hESCs were more inclined to second heart field lineage and its derived cardiomyocytes with atrial-like action potentials than HAND1 single knockout during differentiation. Further mechanistic investigations suggested TBX5 as one of the downstream targets of HAND1/2, whose overexpression partially restored the abnormal cardiomyocyte differentiation in HAND1/2-deficient hESCs.

CONCLUSIONS

HAND1/2 have specific and redundant roles in cardiac lineage commitment and differentiation. These findings not only reveal the essential function of HAND1/2 in cardiac organogenesis, but also provide important information on the pathogenesis of HAND1/2 deficiency-related congenital heart diseases, which could potentially lead to new therapeutic strategies.

High-risk genes involved in common septal defects of congenital heart disease

The septation defect is one of the main categories of congenital heart disease (CHD). They can affect the septation of the atria leading to atrial septal defect (ASD), septation of ventricles leading to ventricular septal defect (VSD), and formation of the central part of the heart leading to atrioventricular septal defect (AVSD). Disruption of critical genetic factors involved in the proper development of the heart structure leads to CHD manifestation. Because of this, to identify the high-risk genes involved in common septal defects, a comprehensive search of the literature with the help of databases and the WebGestalt analysis tool was performed. The high-risk genes identified in the analysis were checked in 16 Indian whole-exome sequenced samples, including 13 VSD and three Tetralogy of Fallot for in silico validation. This data revealed three variations in GATA4, i.e., c.C1223A at exon 6: c.C602A and c.C1220A at exon 7; and one variation in MYH6, i.e., c.G3883C at exon 28 in two VSD cases. This study supports previously published studies that suggested GATA4 and MYH6 as the high-risk genes responsible for septal defects. Thus, this study contributes to a better understanding of the genes involved in heart development by identifying the high-risk genes and interacting proteins in the pathway.

HAND transcription factors cooperatively specify the aorta and pulmonary trunk

Congenital heart defects (CHDs) affecting the cardiac outflow tract (OFT) constitute a significant cause of morbidity and mortality. The OFT develops from migratory cell populations which include the cardiac neural crest cells (cNCCs) and secondary heart field (SHF) derived myocardium and endocardium. The related transcription factors HAND1 and HAND2 have been implicated in human CHDs involving the OFT. Although Hand1 is expressed within the OFT, Hand1 NCC-specific conditional knockout mice (H1CKOs) are viable. Here we show that these H1CKOs present a low penetrance of OFT phenotypes, whereas SHF-specific Hand1 ablation does not reveal any cardiac phenotypes. Further, HAND1 and HAND2 appear functionally redundant within the cNCCs, as a reduction/ablation of Hand2 on an NCC-specific H1CKO background causes pronounced OFT defects. Double conditional Hand1 and Hand2 NCC knockouts exhibit persistent truncus arteriosus (PTA) with 100% penetrance. NCC lineage-tracing and Sema3c in situ mRNA expression reveal that Sema3c-expressing cells are mis-localized, resulting in a malformed septal bridge within the OFTs of H1CKO;H2CKO embryos. Interestingly, Hand1 and Hand2 also genetically interact within the SHF, as SHF H1CKOs on a heterozygous Hand2 background exhibit Ventricular Septal Defects (VSDs) with incomplete penetrance. Previously, we identified a BMP, HAND2, and GATA-dependent Hand1 OFT enhancer sufficient to drive reporter gene expression within the nascent OFT and aorta. Using these transcription inputs as a probe, we identify a novel Hand2 OFT enhancer, suggesting that a conserved BMP-GATA dependent mechanism transcriptionally regulates both HAND factors. These findings support the hypothesis that HAND factors interpret BMP signaling within the cNCCs to cooperatively coordinate OFT morphogenesis.

The Role of Epigenetics in Congenital Heart Disease

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

HAND1 loss-of-function within the embryonic myocardium reveals survivable congenital cardiac defects and adult heart failure

AIMS

To examine the role of the basic Helix-loop-Helix (bHLH) transcription factor HAND1 in embryonic and adult myocardium.

METHODS AND RESULTS

Hand1 is expressed within the cardiomyocytes of the left ventricle (LV) and myocardial cuff between embryonic days (E) 9.5-13.5. Hand gene dosage plays an important role in ventricular morphology and the contribution of Hand1 to congenital heart defects requires further interrogation. Conditional ablation of Hand1 was carried out using either Nkx2.5 knockin Cre (Nkx2.5Cre) or α-myosin heavy chain Cre (αMhc-Cre) driver. Interrogation of transcriptome data via ingenuity pathway analysis reveals several gene regulatory pathways disrupted including translation and cardiac hypertrophy-related pathways. Embryo and adult hearts were subjected to histological, functional, and molecular analyses. Myocardial deletion of Hand1 results in morphological defects that include cardiac conduction system defects, survivable interventricular septal defects, and abnormal LV papillary muscles (PMs). Resulting Hand1 conditional mutants are born at Mendelian frequencies; but the morphological alterations acquired during cardiac development result in, the mice developing diastolic heart failure.

CONCLUSION

Collectively, these data reveal that HAND1 contributes to the morphogenic patterning and maturation of cardiomyocytes during embryogenesis and although survivable, indicates a role for Hand1 within the developing conduction system and PM development.

Genetic testing for ventricular septal defect

Ventricular septal defects (VSDs) are the commonest heart malformations and may affect the membranous or the muscular septum. Clinical presentation depends on the amount of interventricular flow, which is determined by the size of the defect and the relative resistances of the pulmonary and systemic vascular beds. The prevalence of VSD is estimated at about 5% among infants. Many small malformations present at birth may later undergo spontaneous closure. VSD may have autosomal dominant or autosomal recessive inheritance and may exist as isolated forms or as part of a syndrome. This Utility Gene Test was developed on the basis of an analysis of the literature and existing diagnostic protocols. It is useful for confirming diagnosis, as well as for differential diagnosis, couple risk assessment and access to clinical trials.

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

Aims

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

Methods and results

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

Conclusions

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

HAND1 Loss-of-Function Mutation Causes Tetralogy of Fallot

As the most prevalent form of birth defect in humans worldwide, congenital heart disease (CHD) is responsible for substantial morbidity and is still the leading cause of birth defect-related demises. Increasing evidence demonstrates that genetic defects play an important role in the pathogenesis of CHD, and mutations in multiple genes, especially in those coding for cardiac core transcription factors, have been causally linked to various CHDs. Nevertheless, CHD is a genetically heterogeneous disease and the genetic determinants underpinning CHD in an overwhelming majority of patients remain elusive. In the current study, genomic DNA was extracted from venous blood samples of 165 unrelated patients with CHD, and the coding exons and splicing junction sites of the HAND1 gene, which encodes a basic helix-loop-helix transcription factor essential for cardiovascular development, were sequenced. As a result, a novel heterozygous mutation, p.R118C, was identified in a patient with tetralogy of Fallot (TOF). The missense mutation, which was absent in 600 referential chromosomes, altered the amino acid that was completely conserved evolutionarily. Biological assays with a dual-luciferase reporter assay system revealed that the R118C-mutant HAND1 protein had significantly reduced transcriptional activity when compared with its wild-type counterpart. Furthermore, the mutation significantly decreased the synergistic activation of a downstream target gene between HAND1 and GATA4, another cardiac core transcription factor associated with TOF. To our knowledge, this is the first report on the association of a HAND1 loss-of-function mutation with enhanced susceptibility to TOF in humans. The findings provide novel insight into the molecular etiology underlying TOF, suggesting potential implications for the improved prophylactic and therapeutic strategies for TOF.

Chromosome 5q33 deletions associated with congenital heart defects

Congenital heart defects (CHD) are present in over 1% of all newborns and are the leading cause of birth-defect-related deaths in the United States. We describe two male subjects with CHD, one with an atrial septal defect, a ventricular septal defect, and pulmonary artery stenosis; and the other with tetralogy of Fallot and a right aortic arch, who carry partially overlapping, de novo deletions of chromosome 5q33. The maximum region of overlap between these deletions encompasses HAND1 and SAP30L, two genes that have previously been shown to play a role in cardiac development. HAND1 encodes a basic helix-loop-helix transcription factor. Cardiac-specific ablation of Hand1 in mice causes septal, valvular, and outflow tract defects. SAP30L, its paralog SAP30, and other SAP proteins form part of a multi-subunit complex involved in transcriptional regulation via histone deacetylation. Morpholino knockdown of sap30L in zebrafish, which do not have a distinct sap30 gene, leads to cardiac hypoplasia and cardiac insufficiency. We subsequently identified two other individuals with chromosomal deletions involving HAND1 and SAP30L in whom cardiac-related medical problems were not described. These observations suggest that haploinsufficiency of HAND1 and/or SAP30L may contribute to the development of CHD, although the contribution of other genes on chromosome 5q33 cannot be excluded. Our findings also suggest that the penetrance of CHD associated with 5q33 deletions is incomplete and may be influenced by other genetic, environmental or stochastic factors. © 2016 Wiley Periodicals, Inc.

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

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

Cellular Mechanisms of Drosophila Heart Morphogenesis

Many of the major discoveries in the fields of genetics and developmental biology have been made using the fruit fly, Drosophila melanogaster. With regard to heart development, the conserved network of core cardiac transcription factors that underlies cardiogenesis has been studied in great detail in the fly, and the importance of several signaling pathways that regulate heart morphogenesis, such as Slit/Robo, was first shown in the fly model. Recent technological advances have led to a large increase in the genomic data available from patients with congenital heart disease (CHD). This has highlighted a number of candidate genes and gene networks that are potentially involved in CHD. To validate genes and genetic interactions among candidate CHD-causing alleles and to better understand heart formation in general are major tasks. The specific limitations of the various cardiac model systems currently employed (mammalian and fish models) provide a niche for the fly model, despite its evolutionary distance to vertebrates and humans. Here, we review recent advances made using the Drosophila embryo that identify factors relevant for heart formation. These underline how this model organism still is invaluable for a better understanding of CHD.

Characterization of circulating microRNA expression in patients with a ventricular septal defect

OBJECTIVES

Ventricular septal defect (VSD), one of the most common types of congenital heart disease (CHD), results from a combination of environmental and genetic factors. Recent studies demonstrated that microRNAs (miRNAs) are involved in development of CHD. This study was to characterize the expression of miRNAs that might be involved in the development or reflect the consequences of VSD.

METHODS

MiRNA microarray analysis and reverse transcription-polymerase chain reaction (RT-PCR) were employed to determine the miRNA expression profile from 3 patients with VSD and 3 VSD-free controls. 3 target gene databases were employed to predict the target genes of differentially expressed miRNAs. miRNAs that were generally consensus across the three databases were selected and then independently validated using real time PCR in plasma samples from 20 VSD patients and 15 VSD-free controls. Target genes of validated 8 miRNAs were predicted using bioinformatic methods.

RESULTS

36 differentially expressed miRNAs were found in the patients with VSD and the VSD-free controls. Compared with VSD-free controls, expression of 15 miRNAs were up-regulated and 21 miRNAs were downregulated in the VSD group. 15 miRNAs were selected based on database analysis results and expression levels of 8 miRNAs were validated. The results of the real time PCR were consistent with those of the microarray analysis. Gene ontology analysis indicated that the top target genes were mainly related to cardiac right ventricle morphogenesis. NOTCH1, HAND1, ZFPM2, and GATA3 were predicted as targets of hsa-let-7e-5p, hsa-miR-222-3p and hsa-miR-433.

CONCLUSION

We report for the first time the circulating miRNA profile for patients with VSD and showed that 7 miRNAs were downregulated and 1 upregulated when matched to VSD-free controls. Analysis revealed target genes involved in cardiac development were probably regulated by these miRNAs.

DNA methylation status of NKX2-5, GATA4 and HAND1 in patients with tetralogy of fallot

Background

NKX2-5, GATA4 and HAND1 are essential for heart development, however, little is known regarding their epigenetic regulation in the pathogenesis of tetralogy of fallot (TOF).

Methods

Methylation levels were measured in three regions of NKX2-5 (M1: -1596 bp ~ -1374 bp, M2: -159 bp ~ 217 bp and M3: 1058 bp ~ 1524 bp), one region of GATA4 (M: -392 bp ~ 107 bp) and three regions of HAND1 (M1: -887 bp ~ -414 bp, M2: -436 bp ~ 2 bp and M3: 37 bp ~ 398 bp) using the Sequenom MassARRAY platform. QRT-PCR was used to analyze NKX2-5 and HAND1 mRNA levels in the right ventricular myocardium of TOF patients.

Results

TOF patients had a significantly higher NKX2-5_M3 median methylation level than controls (41.65% vs. 22.18%; p = 0.0074; interquartile range [IQR]: 30.46%–53.35%, N = 30 and 20.07%–24.31%, N = 5; respectively). The HAND1_M1 median methylation level was also significantly higher in TOF patients than controls (30.05% vs. 17.54%; p = 0.0054; IQR: 20.77%–40.89%, N = 30 and IQR: 14.69%–20.64%; N = 6; respectively). The methylation statuses of NKX2-5_M1, NKX2-5_M2, GATA4_M, HAND1_M2 or HAND1_M3 were not significantly different in TOF patients compared to controls. The methylation values for NKX2-5_M3 were negatively correlated with mRNA levels (r = - 0.463, p = 0.010, N = 30) and there was a significant association between HAND1_M1 methylation status and mRNA levels (r = - 0.524, p = 0.003, N = 30) in TOF patients.

Conclusions

Aberrant methylation statuses of the NKX2-5 gene body and HAND1 promoter regions are associated with the regulation of gene transcription in TOF patients and may play an important role in the pathogenesis of TOF.