Exome sequencing in multiplex families with left-sided cardiac defects has high yield for disease gene discovery

Molecular genetics of congenital heart disease

Congenital heart disease (CHD) is the most prevalent human birth defect and remains a leading cause of mortality in childhood. Although advancements in surgical and medical interventions have significantly reduced mortality rates among infants with critical CHDs, many survivors experience substantial cardiac and extracardiac comorbidities that affect their quality of life. The etiology of CHD is multifactorial, involving both genetic and environmental factors, yet a definitive cause remains unidentified in many cases. Recent advancements in genetic testing technologies have improved our ability to identify the genetic causes of CHD. This review presents an updated summary of the established genetic contributions to CHD, including chromosomal aberrations and mutations in genes associated with transcription factors, cardiac structural proteins, chromatin modifiers, cilia-related proteins, and cell signaling pathways. Furthermore, we discuss recent findings that support the roles of non-coding mutations and complex inheritance in the etiology of CHD.

Protective role of Tongxinluo in mitigating myocardial fibrosis in mice with acute myocardial infarction via neuregulin-1 upregulation and Inhibition of endothelium-interstitial transition

Acute myocardial infarction (AMI) is a leading cause of heart failure, often accompanied by myocardial fibrosis (MF), characterized by excessive extracellular matrix accumulation. Endothelial-to-mesenchymal transition (EndMT) plays a key role in MF progression post-AMI. Neuregulin-1 (NRG-1), a growth factor with cardioprotective properties, has emerged as a potential therapeutic target. Tongxinluo (TXL), a traditional Chinese medicine, mitigates MF by upregulating NRG-1. This study elucidates the mechanisms underlying the protective effects of NRG-1 and TXL against MF following AMI. Left anterior descending artery ligation established a model for mice with AMI. Adeno-associated virus was used to modulate NRG-1 expression in the myocardium. Echocardiography assessed cardiac function, and histological staining was used to evaluate MF. Expression levels of markers for myofibroblasts (α-SMA, FSP-1) and endothelial cells (CD31, VE-cadherin) were analysed to investigate EndMT. The involvement of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling pathway in NRG-1's protective mechanism was validated using biochemical methods. Tongxinluo was administered to mice with AMI via gavage for 4 weeks, and its effects on cardiac function, MF and EndMT were assessed. Overexpression of NRG-1 in mice with AMI ameliorated cardiac dysfunction and reduced interstitial and perivascular fibrosis, whereas NRG-1 deficiency exacerbated these effects. NRG-1 protected against EndMT, as evidenced by changes in myofibroblast and endothelial cell markers. The PI3K/AKT signalling pathway was involved in NRG-1's protective mechanism against MF. The administration of TXL to mice with AMI improved cardiac function and reduced MF by activating NRG-1. Furthermore, TXL inhibited EndMT post-AMI through the NRG-1/PI3K/AKT pathway. NRG-1 and TXL protect against MF post-AMI by mitigating EndMT through the PI3K/AKT pathway. These findings suggest that targeting NRG-1 or using TXL may be promising therapeutic strategies for MF following AMI.

Hsf1 is essential for proteotoxic stress response in smyd1b-deficient embryos and fish survival under heat shock

Molecular chaperones play critical roles in post-translational maintenance in protein homeostasis. Previous studies have shown that loss of Smyd1b function results in defective myofibril organization and dramatic upregulation of heat shock protein gene (hsp) expression in muscle cells of zebrafish embryos. To investigate the molecular mechanisms and functional importance of this stress response, we characterized changes of gene expression in smyd1b knockdown and knockout embryos using RNA-seq. The results showed that the top upregulated genes encode mostly cytosolic heat shock proteins. Co-IP assay revealed that the upregulated cytosolic Hsp70s associate with myosin chaperone UNC45b which is critical for myosin protein folding and sarcomere assembly. Strikingly, several hsp70 genes also display muscle-specific upregulation in response to heat shock-induced stress in zebrafish embryos. To investigate the regulation of hsp gene upregulation and its functional significance in muscle cells, we generated heat shock factor 1 (hsf-/-) knockout zebrafish mutants and analyzed hsp gene expression and muscle phenotype in the smyd1b-/-single and hsf1-/-;smyd1b-/- double-mutant embryos. The results showed that knockout of hsf1 blocked the hsp gene upregulation and worsened the muscle defects in smyd1b-/- mutant embryos. Moreover, we demonstrated that Hsf1 is essential for fish survival under heat shock (HS) conditions. Together, these studies uncover a correlation between Smyd1b deficiency and the Hsf1-activated heat shock response (HSR) in regulating muscle protein homeostasis and myofibril assembly and demonstrate that the Hsf1-mediated hsp gene upregulation is vital for the survival of zebrafish larvae under thermal stress conditions.

Heart Morphogenesis Requires Smyd1b for Proper Incorporation of the Second Heart Field in Zebrafish

Background/Objectives: Abnormal development of the second heart field significantly contributes to congenital heart defects, often caused by disruptions in tightly regulated molecular pathways. Smyd1, a gene encoding a protein with SET and MYND domains, is essential for heart and skeletal muscle development. Mutations in SMYD1 result in severe cardiac malformations and misregulation of Hand2 expression in mammals. This study examines the role of Smyd1b in zebrafish cardiac morphogenesis to elucidate its function and the mechanisms underlying congenital heart defects. Methods: Smyd1b (still heart) mutant embryos were analyzed for cardiac defects, and changes in gene expression related to heart development using live imaging, in situ hybridization, quantitative PCR and immunofluorescent comparisons and analysis. Results: Smyd1b mutants displayed severe cardiac defects, including failure to loop, severe edema, and an expansion of cardiac jelly linked to increased has2 expression. Additionally, the expression of key cardiac transcription factors, such as gata4, gata5, and nkx2.5, was notably reduced, indicating disrupted transcriptional regulation. The migration of cardiac progenitors was impaired and the absence of Islet-1-positive cells in the mutant hearts suggests a failed contribution of SHF progenitor cells. Conclusions: These findings underscore the essential role of Smyd1b in regulating cardiac morphogenesis and the development of the second heart field. This study highlights the potential of Smyd1b as a key factor in understanding the genetic and molecular mechanisms underlying congenital heart defects and cardiac development.

Genetic variants in patients with recurrent pericarditis

AIMS

Presence of family cases and multiple recurrences of pericarditis suggest the existence of a possible genetic background in at least 10% of cases. The aim of the present study is to describe the genetic landscape of a cohort of patients with multiple recurrences (at least two recurrences).

METHODS

Retrospective cohort study of consecutive adult patients referred for at least two episodes of recurrences in a tertiary referral centre. Genetic testing was performed by whole exome sequencing (WES).

RESULTS

Our cohort included 108 consecutive patients with recurrent pericarditis [median age 32 years, interquartile range (IQR) 18.5; 67.6% females, all Caucasian, idiopathic aetiology in 71.1%] with a median number of recurrences of 5 (IQR 2). Overall, 16 patients (14.8%) had variants in genes related to the inflammatory response. Eleven variants were located in genes already associated with recurrent pericarditis (NLRP3, TNFRSF1A and MEFV) and five in inflammation/immunodeficiency-related genes (IFIH1, NFKBIA, JAK1, NOD2 and ALPK1). Furthermore, we identified 10 patients with variants located in genes associated with conduction system-related diseases, and 22 variants in 21 patients with genes associated with heart structural-related diseases.

CONCLUSION

In this first observational study using WES to assess genetic variants in patients with multiple recurrences of pericarditis, about 15% of patients bore at least one variant that may be related to the disease. These findings highlight the importance of addressing the role of genetic predisposition in recurrent pericarditis. Moreover, 28.7% of patients carry variants in different cardiac genes, worthy of a deeper investigation.

SMYD1 modulates the proliferation of multipotent cardiac progenitor cells derived from human pluripotent stem cells during myocardial differentiation through GSK3β/β-catenin&ERK signaling

BACKGROUND

The histone-lysine N-methyltransferase SMYD1, which is specific to striated muscle, plays a crucial role in regulating early heart development. Its deficiency has been linked to the occurrence of congenital heart disease. Nevertheless, the precise mechanism by which SMYD1 deficiency contributes to congenital heart disease remains unclear.

METHODS

We established a SMYD1 knockout pluripotent stem cell line and a doxycycline-inducible SMYD1 expression pluripotent stem cell line to investigate the functions of SMYD1 utilizing an in vitro-directed myocardial differentiation model.

RESULTS

Cardiomyocytes lacking SMYD1 displayed drastically diminished differentiation efficiency, concomitant with heightened proliferation capacity of cardiac progenitor cells during the early cardiac differentiation stage. These cellular phenotypes were confirmed through experiments inducing the re-expression of SMYD1. Transcriptome sequencing and small molecule inhibitor intervention suggested that the GSK3β/β-catenin&ERK signaling pathway was involved in the proliferation of cardiac progenitor cells. Chromatin immunoprecipitation demonstrated that SMYD1 acted as a transcriptional activator of GSK3β through histone H3 lysine 4 trimethylation. Additionally, dual-luciferase analyses indicated that SMYD1 could interact with the promoter region of GSK3β, thereby augmenting its transcriptional activity. Moreover, administering insulin and Insulin-like growth factor 1 can enhance the efficacy of myocardial differentiation in SMYD1 knockout cells.

CONCLUSIONS

Our research indicated that the participation of SMYD1 in the GSK3β/β-catenin&ERK signaling cascade modulated the proliferation of cardiac progenitor cells during myocardial differentiation. This process was partly reliant on the transcription of GSK3β. Our research provided a novel insight into the genetic modification effect of SMYD1 during early myocardial differentiation. The findings were essential to the molecular mechanism and potential interventions for congenital heart disease.

Feto-placental and coronary endothelial genes implicated in miscarriage, congenital heart disease and stillbirth, a systematic review and meta-analysis

The first trimester placenta is very rarely investigated for placental vascular formation in developmental or diseased contexts. Defects in placental formation can cause heart defects in the fetus, and vice versa. Determining the causality is therefore difficult as both organs develop concurrently and express many of the same genes. Here, we performed a systematic review to determine feto-placental and coronary endothelial genes implicated in miscarriages, stillbirth and congenital heart defects (CHD) from human genome wide screening studies. 4 single cell RNAseq datasets from human first/early second trimester cardiac and placental samples were queried to generate a list of 1187 endothelial genes. This broad list was cross-referenced with genes implicated in the pregnancy disorders above. 39 papers reported feto-placental and cardiac coronary endothelial genes, totalling 612 variants. Vascular gene variants were attributed to the incidence of miscarriage (8 %), CHD (4 %) and stillbirth (3 %). The most common genes for CHD (NOTCH, DST, FBN1, JAG1, CHD4), miscarriage (COL1A1, HERC1), and stillbirth (AKAP9, MYLK), were involved in blood vessel and cardiac valve formation, with roles in endothelial differentiation, angiogenesis, extracellular matrix signaling, growth factor binding and cell adhesion. NOTCH1, AKAP12, CHD4, LAMC1 and SOS1 showed greater relative risk ratios with CHD. Many of the vascular genes identified were expressed highly in both placental and heart EC populations. Both feto-placental and cardiac vascular genes are likely to result in poor endothelial cell development and function during human pregnancy that leads to higher risk of miscarriage, congenital heart disease and stillbirth.

Expression of Smyd1b_tv1 by Alternative Splicing in Cardiac Muscle is Critical for Sarcomere Organization in Cardiomyocytes and Heart Function

Smyd1, a member of the Smyd lysine methyltransferase family, plays an important role in myofibrillogenesis of skeletal and cardiac muscles. Loss of Smyd1b (a Smyd1 ortholog) function in zebrafish results in embryonic death from heart malfunction. smyd1b encodes two isoforms, Smyd1b_tv1 and Smyd1b_tv2, differing by 13 amino acids due to alternative splicing. While smyd1 alternative splicing is evolutionarily conserved, the isoform-specific expression and function of Smyd1b_tv1 and Smyd1b_tv2 remained unknown. Here we analyzed their expression and function in skeletal and cardiac muscles. Our analysis revealed expression of smyd1b_tv1 predominately in cardiac and smyd1b_tv2 in skeletal muscles. Using zebrafish models expressing only one isoform, we demonstrated that Smyd1b_tv1 is essential for cardiomyocyte differentiation and fish viability, whereas Smyd1b_tv2 is dispensable for heart development and fish survival. Cellular and biochemical analyses revealed that Smyd1b_tv1 differs from Smyd1b_tv2 in protein localization and binding with myosin chaperones. While Smyd1b_tv2 diffused in the cytosol of muscle cells, Smyd1b_tv1 was localized to M-lines and essential for sarcomere organization in cardiomyocytes. Co-IP analysis revealed a stronger binding of Smyd1b_tv1 with chaperones and cochaperones compared with Smyd1b_tv2. Collectively, these findings highlight the nonequivalence of Smyd1b isoforms in cardiomyocyte differentiation, emphasizing the critical role of Smyd1b_tv1 in cardiac function.

Expanding the phenotypic spectrum of NOTCH1 variants: clinical manifestations in families with congenital heart disease

Pathogenic variants in NOTCH1 are associated with non-syndromic congenital heart disease (CHD) and Adams-Oliver syndrome (AOS). The clinical presentation of individuals with damaging NOTCH1 variants is characterized by variable expressivity and incomplete penetrance; however, data on systematic phenotypic characterization are limited. We report the genotype and phenotype of a cohort of 33 individuals (20 females, 13 males; median age 23.4 years, range 2.5-68.3 years) from 11 families with causative NOTCH1 variants (9 inherited, 2 de novo; 9 novel), ascertained from a proband with CHD. We describe the cardiac and extracardiac anomalies identified in these 33 individuals, only four of whom met criteria for AOS. The most common CHD identified was tetralogy of Fallot, though various left- and right-sided lesions and septal defects were also present. Extracardiac anomalies identified include cutis aplasia (5/33), cutaneous vascular anomalies (7/33), vascular anomalies of the central nervous system (2/10), Poland anomaly (1/33), pulmonary hypertension (2/33), and structural brain anomalies (3/14). Identification of these findings in a cardiac proband cohort supports NOTCH1-associated CHD and NOTCH1-associated AOS lying on a phenotypic continuum. Our findings also support (1) Broad indications for NOTCH1 molecular testing (any familial CHD, simplex tetralogy of Fallot or hypoplastic left heart); (2) Cascade testing in all at-risk relatives; and (3) A thorough physical exam, in addition to cardiac, brain (structural and vascular), abdominal, and ophthalmologic imaging, in all gene-positive individuals. This information is important for guiding the medical management of these individuals, particularly given the high prevalence of NOTCH1 variants in the CHD population.

Novel pathogenic GATA6 variant associated with congenital heart disease, diabetes mellitus and necrotizing enterocolitis

BACKGROUND

Pathogenic GATA6 variants have been associated with congenital heart disease (CHD) and a spectrum of extracardiac abnormalities, including pancreatic agenesis, congenital diaphragmatic hernia, and developmental delay. However, the comprehensive genotype-phenotype correlation of pathogenic GATA6 variation in humans remains to be fully understood.

METHODS

Exome sequencing was performed in a family where four members had CHD. In vitro functional analysis of the GATA6 variant was performed using immunofluorescence, western blot, and dual-luciferase reporter assay.

RESULTS

A novel, heterozygous missense variant in GATA6 (c.1403 G > A; p.Cys468Tyr) segregated with affected members in a family with CHD, including three with persistent truncus arteriosus. In addition, one member had childhood onset diabetes mellitus (DM), and another had necrotizing enterocolitis (NEC) with intestinal perforation. The p.Cys468Tyr variant was located in the c-terminal zinc finger domain encoded by exon 4. The mutant protein demonstrated an abnormal nuclear localization pattern with protein aggregation and decreased transcriptional activity.

CONCLUSIONS

We report a novel, familial GATA6 likely pathogenic variant associated with CHD, DM, and NEC with intestinal perforation. These findings expand the phenotypic spectrum of pathologic GATA6 variation to include intestinal abnormalities.

IMPACT

Exome sequencing identified a novel heterozygous GATA6 variant (p.Cys468Tyr) that segregated in a family with CHD including persistent truncus arteriosus, atrial septal defects and bicuspid aortic valve. Additionally, affected members displayed extracardiac findings including childhood-onset diabetes mellitus, and uniquely, necrotizing enterocolitis with intestinal perforation in the first four days of life. In vitro functional assays demonstrated that GATA6 p.Cys468Tyr variant leads to cellular localization defects and decreased transactivation activity. This work supports the importance of GATA6 as a causative gene for CHD and expands the phenotypic spectrum of pathogenic GATA6 variation, highlighting neonatal intestinal perforation as a novel extracardiac phenotype.

Cardiomyocyte intercellular signalling increases oxidative stress and reprograms the global- and phospho-proteome of cardiac fibroblasts

Pathological reprogramming of cardiomyocyte and fibroblast proteome landscapes drive the initiation and progression of cardiac fibrosis. Although the secretome of dysfunctional cardiomyocytes is emerging as an important driver of pathological fibroblast reprogramming, our understanding of the downstream molecular players remains limited. Here, we show that cardiac fibroblast activation (αSMA+) and oxidative stress mediated by the secretome of TGFβ-stimulated cardiomyocytes is associated with a profound reprogramming of their proteome and phosphoproteome landscape. Within the fibroblast global proteome there was a striking dysregulation of proteins implicated in extracellular matrix, protein localisation/metabolism, KEAP1-NFE2L2 pathway, lysosomes, carbohydrate metabolism, and transcriptional regulation. Kinase substrate enrichment analysis of phosphopeptides revealed potential role of kinases (CK2, CDK2, PKC, GSK3B) during this remodelling. We verified upregulated activity of casein kinase 2 (CK2) in secretome-treated fibroblasts, and pharmacological CK2 inhibitor TBB (4,5,6,7-Tetrabromobenzotriazole) significantly abrogated fibroblast activation and oxidative stress. Our data provides molecular insights into cardiomyocyte to cardiac fibroblast crosstalk, and the potential role of CK2 in regulating cardiac fibroblast activation and oxidative stress.

CRISPR-based knockout and base editing confirm the role of MYRF in heart development and congenital heart disease

High-throughput DNA sequencing studies increasingly associate DNA variants with congenital heart disease (CHD). However, functional modeling is a crucial prerequisite for translating genomic data into clinical care. We used CRISPR-Cas9-mediated targeting of 12 candidate genes in the vertebrate model medaka (Oryzias latipes), five of which displayed a novel cardiovascular phenotype spectrum in F0 (crispants): mapre2, smg7, cdc42bpab, ankrd11 and myrf, encoding a transcription factor recently linked to cardiac-urogenital syndrome. Our myrf mutant line showed particularly prominent embryonic cardiac defects recapitulating phenotypes of pediatric patients, including hypoplastic ventricle. Mimicking human mutations, we edited three sites to generate specific myrf single-nucleotide variants via cytosine and adenine base editors. The Glu749Lys missense mutation in the conserved intramolecular chaperon autocleavage domain fully recapitulated the characteristic myrf mutant phenotype with high penetrance, underlining the crucial function of this protein domain. The efficiency and scalability of base editing to model specific point mutations accelerate gene validation studies and the generation of human-relevant disease models.

CASZ1: Current Implications in Cardiovascular Diseases and Cancers

Castor zinc finger 1 (CASZ1) is a C2H2 zinc finger family protein that has two splicing variants, CASZ1a and CASZ1b. It is involved in multiple physiological processes, such as tissue differentiation and aldosterone antagonism. Genetic and epigenetic alternations of CASZ1 have been characterized in multiple cardiovascular disorders, such as congenital heart diseases, chronic venous diseases, and hypertension. However, little is known about how CASZ1 mechanically participates in the pathogenesis of these diseases. Over the past decades, at first glance, paradoxical influences on cell behaviors and progressions of different cancer types have been discovered for CASZ1, which may be explained by a "double-agent" role for CASZ1. In this review, we discuss the physiological function of CASZ1, and focus on the association of CASZ1 aberrations with the pathogenesis of cardiovascular diseases and cancers.

Identification of Two Homozygous Variants in MYBPC3 and SMYD1 Genes Associated with Severe Infantile Cardiomyopathy

Mutations in cardiac genes are one of the primary causes of infantile cardiomyopathy. In this study, we report the genetic findings of two siblings carrying variations in the MYBPC3 and SMYD1 genes. The first patient is a female proband exhibiting hypertrophic cardiomyopathy (HCM) and biventricular heart failure carrying a truncating homozygous MYBPC3 variant c.1224-52G>A (IVS13-52G>A) and a novel homozygous variant (c.302A>G; p.Asn101Ser) in the SMYD1 gene. The second patient, the proband's sibling, is a male infant diagnosed with hypertrophic cardiomyopathy and carries the same homozygous MYBPC3 variant. While this specific MYBPC3 variant (c.1224-52G>A, IVS13-52G>A) has been previously reported to be associated with adult-onset hypertrophic cardiomyopathy, this is the first report linking it to infantile cardiomyopathy. In addition, this work describes, for the first time, a novel SMYD1 variant (c.302A>G; p.Asn101Ser) that has never been reported. We performed a histopathological evaluation of tissues collected from both probands and show that these variants lead to myofibrillar disarray, reduced and irregular mitochondrial cristae and cardiac fibrosis. Together, these results provide critical insight into the molecular functionality of these genes in human cardiac physiology.

Graded mesoderm assembly governs cell fate and morphogenesis of the early mammalian heart

Using four-dimensional whole-embryo light sheet imaging with improved and accessible computational tools, we longitudinally reconstruct early murine cardiac development at single-cell resolution. Nascent mesoderm progenitors form opposing density and motility gradients, converting the temporal birth sequence of gastrulation into a spatial anterolateral-to-posteromedial arrangement. Migrating precardiac mesoderm does not strictly preserve cellular neighbor relationships, and spatial patterns only become solidified as the cardiac crescent emerges. Progenitors undergo a mesenchymal-to-epithelial transition, with a first heart field (FHF) ridge apposing a motile juxta-cardiac field (JCF). Anchored along the ridge, the FHF epithelium rotates the JCF forward to form the initial heart tube, along with push-pull morphodynamics of the second heart field. In Mesp1 mutants that fail to make a cardiac crescent, mesoderm remains highly motile but directionally incoherent, resulting in density gradient inversion. Our practicable live embryo imaging approach defines spatial origins and behaviors of cardiac progenitors and identifies their unanticipated morphological transitions.

Considering the Genetic Architecture of Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is among the most severe cardiovascular malformations and understanding its causes is crucial to making progress in prevention and treatment. Genetic analysis is a broadly useful tool for dissecting complex causal mechanisms and it is playing a significant role in HLHS research. However, unlike classical Mendelian disorders where a relatively small number of genes are largely determinative of the occurrence and severity of the disease, the picture in HLHS is complex. De novo single-gene and copy number variant (CNV) disorders make an important contribution, but there is emerging evidence for causal contributions from lower penetrance and common variation. Integrating this emerging knowledge into clinical diagnostics and translating the findings into effective prevention and treatment remain challenges for the future.