Cardiac α-Actin ( ACTC1 ) Gene Mutation Causes Atrial-Septal Defects Associated With Late-Onset Dilated Cardiomyopathy

The Genetic Factors Influencing Cardiomyopathies and Heart Failure across the Allele Frequency Spectrum

Heart failure (HF) remains a major cause of mortality and morbidity worldwide. Understanding the genetic basis of HF allows for the development of disease-modifying therapies, more appropriate risk stratification, and personalised management of patients. The advent of next-generation sequencing has enabled genome-wide association studies; moving beyond rare variants identified in a Mendelian fashion and detecting common DNA variants associated with disease. We summarise the latest GWAS and rare variant data on mixed and refined HF aetiologies, and cardiomyopathies. We describe the recent understanding of the functional impact of titin variants and highlight FHOD3 as a novel cardiomyopathy-associated gene. We describe future directions of research in this field and how genetic data can be leveraged to improve the care of patients with HF.

Human Genetics of Atrial Septal Defect

Although atrial septal defects (ASD) can be subdivided based on their anatomical location, an essential aspect of human genetics and genetic counseling is distinguishing between isolated and familiar cases without extracardiac features and syndromic cases with the co-occurrence of extracardiac abnormalities, such as developmental delay. Isolated or familial cases tend to show genetic alterations in genes related to important cardiac transcription factors and genes encoding for sarcomeric proteins. By contrast, the spectrum of genes with genetic alterations observed in syndromic cases is diverse. Currently, it points to different pathways and gene networks relevant to the dysregulation of cardiomyogenesis and ASD pathogenesis. Therefore, this chapter reflects the current knowledge and highlights stable associations observed in human genetics studies. It gives an overview of the different types of genetic alterations in these subtypes, including common associations based on genome-wide association studies (GWAS), and it highlights the most frequently observed syndromes associated with ASD pathogenesis.

Human Genetics of Congenital Heart Defects

Congenital heart diseases (or congenital heart defects/disorders; CHDs) are structural abnormalities of the heart and/or great vessels that are present at birth. CHDs include an extensive range of defects that may be minor and require no intervention or may be life-limiting and require complex surgery shortly after birth. This chapter reviews the current knowledge on the genetic causes of CHD.

Molecular Pathways and Animal Models of Atrial Septal Defect

The relative simplicity of the clinical presentation and management of an atrial septal defect belies the complexity of the developmental pathogenesis. Here, we describe the anatomic development of the atrial septum and the venous return to the atrial chambers. Experimental models suggest how mutations and naturally occurring genetic variation could affect developmental steps to cause a defect within the oval fossa, the so-called secundum defect, or other interatrial communications, such as the sinus venosus defect or ostium primum defect.

Anti-tumor target screening of sea cucumber saponin Frondoside A: a bioinformatics and molecular docking analysis

Cancer remains the leading cause of death worldwide. In spite of significant advances in targeted and immunotherapeutic approaches, clinical outcomes for cancer remain poor. The aim of the present study was to investigate the potential mechanisms and therapeutic targets of Frondoside A for the treatment of liver, pancreatic, and bladder cancers. The data presented in our study demonstrated that Frondoside A reduced the viability and migration of HepG2, Panc02, and UM-UC-3 cancer cell in vitro. Moreover, we utilized the GEO database to screen and identify for differentially expressed genes (DEGs) in liver, pancreatic, and bladder cancers, which resulted in the identification of 714, 357, and 101 DEGs, respectively. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation were performed using the Metascape database for DEGs that were significantly associated with cancer development. The protein-protein interaction (PPI) networks of the identified DEGs in liver, pancreatic, and bladder cancers were analyzed using Cytoscape 3.9.0 software, and subsequently identified potential key genes that were associated with these networks. Subsequently, their prognostic values were assessed by gene expression level analysis and Kaplan-Meier survival analysis (GEPIA). Furthermore, we utilized TIMER 2.0 to investigate the correlation between the expression of the identified key gene and cancer immune infiltration. Finally, molecular docking simulations were performed to assess the affinity of Frondoside A and key genes. Our results showed a significant correlation between these DEGs and cancer progression. Combined, these analyses revealed that Frondoside A involves in the regulation of multiple pathways, such as drug metabolism, cell cycle in liver cancer by inhibiting the expression of CDK1, TOP2A, CDC20, and KIF20A, and regulates protein digestion and absorption, receptor interaction in pancreatic cancer by down-regulation of ASPM, TOP2A, DLGAP5, TPX2, KIF23, MELK, LAMA3, and ANLN. While in bladder cancer, Frondoside A regulates muscle contraction, complement and coagulation cascade by increase FLNC expression. In conclusion, the present study offers valuable insights into the molecular mechanism underlying the anticancer effects of Frondoside A, and suggests that Frondoside A can be used as a functional food supplement or further developed as a natural anti-cancer drug.

Dilated cardiomyopathy: causes, mechanisms, and current and future treatment approaches

Dilated cardiomyopathy is conventionally defined as the presence of left ventricular or biventricular dilatation or systolic dysfunction in the absence of abnormal loading conditions (eg, primary valve disease) or significant coronary artery disease sufficient to cause ventricular remodelling. This definition has been recognised as overly restrictive, as left ventricular hypokinesis without dilation could be the initial presentation of dilated cardiomyopathy. The causes of dilated cardiomyopathy comprise genetic (primary dilated cardiomyopathy) or acquired factors (secondary dilated cardiomyopathy). Acquired factors include infections, toxins, cancer treatment, endocrinopathies, pregnancy, tachyarrhythmias, and immune-mediated diseases. 5-15% of patients with acquired dilated cardiomyopathy harbour a likely pathogenic or pathogenic gene variant (ie, gene mutation). Therefore, the diagnostic tests and therapeutic approach should always consider both genetic and acquired factors. This Seminar will focus on the current multidimensional diagnostic and therapeutic approach and discuss the underlying pathophysiology that could drive future treatments aiming to repair or replace the existing gene mutation, or target the specific inflammatory, metabolic, or pro-fibrotic drivers of genetic or acquired dilated cardiomyopathy.

Actin polymerization and depolymerization in developing vertebrates

Development is a complex process that occurs throughout the life cycle. F-actin, a major component of the cytoskeleton, is essential for the morphogenesis of tissues and organs during development. F-actin is formed by the polymerization of G-actin, and the dynamic balance of polymerization and depolymerization ensures proper cellular function. Disruption of this balance results in various abnormalities and defects or even embryonic lethality. Here, we reviewed recent findings on the structure of G-actin and F-actin and the polymerization of G-actin to F-actin. We also focused on the functions of actin isoforms and the underlying mechanisms of actin polymerization/depolymerization in cellular and organic morphogenesis during development. This information will extend our understanding of the role of actin polymerization in the physiologic or pathologic processes during development and may open new avenues for developing therapeutics for embryonic developmental abnormalities or tissue regeneration.

Cardiovascular Complications in Patients with Prostate Cancer: Potential Molecular Connections

Cardiovascular diseases (CVDs) and complications are often seen in patients with prostate cancer (PCa) and affect their clinical management. Despite acceptable safety profiles and patient compliance, androgen deprivation therapy (ADT), the mainstay of PCa treatment and chemotherapy, has increased cardiovascular risks and metabolic syndromes in patients. A growing body of evidence also suggests that patients with pre-existing cardiovascular conditions show an increased incidence of PCa and present with fatal forms of the disease. Therefore, it is possible that a molecular link exists between the two diseases, which has not yet been unraveled. This article provides insight into the connection between PCa and CVDs. In this context, we present our findings linking PCa progression with patients' cardiovascular health by performing a comprehensive gene expression study, gene set enrichment (GSEA) and biological pathway analysis using publicly available data extracted from patients with advanced metastatic PCa. We also discuss the common androgen deprivation strategies and CVDs most frequently reported in PCa patients and present evidence from various clinical trials that suggest that therapy induces CVD in PCa patients.

USP25 Ameliorates Pathological Cardiac Hypertrophy by Stabilizing SERCA2a in Cardiomyocytes

BACKGROUND

Pathological cardiac hypertrophy can lead to heart failure and is one of the leading causes of death globally. Understanding the molecular mechanism of pathological cardiac hypertrophy will contribute to the treatment of heart failure. DUBs (deubiquitinating enzymes) are essential to cardiac pathophysiology by precisely controlling protein function, localization, and degradation. This study set out to investigate the role and molecular mechanism of a DUB, USP25 (ubiquitin-specific peptidase 25), in pathological cardiac hypertrophy.

METHODS

The role of USP25 in myocardial hypertrophy was evaluated in murine cardiomyocytes in response to Ang II (angiotensin II) and transverse aortic constriction stimulation and in hypertrophic myocardium tissues of heart failure patients. Liquid chromotography with mass spectrometry/mass spectrometry analysis combined with Co-IP was used to identify SERCA2a (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase 2A), an antihypertrophy protein, as an interacting protein of USP25. To clarify the molecular mechanism of USP25 in the regulation of SERCA2a, we constructed a series of mutant plasmids of USP25. In addition, we overexpressed USP25 and SERCA2a in the heart with adenoassociated virus serotype 9 vectors to validate the biological function of USP25 and SERCA2a interaction.

RESULTS

We revealed increased protein level of USP25 in murine cardiomyocytes subject to Ang II and transverse aortic constriction stimulation and in hypertrophic myocardium tissues of patients with heart failure. USP25 deficiency aggravated cardiac hypertrophy and cardiac dysfunction under Ang II and transverse aortic constriction treatment. Mechanistically, USP25 bound to SERCA2a directly via its USP (ubiquitin-specific protease) domain and cysteine at position 178 of USP25 exerts deubiquitination to maintain the stability of the SERCA2a protein by removing the K48 ubiquitin chain and preventing proteasomal pathway degradation, thereby maintaining calcium handling in cardiomyocytes. Moreover, restoration of USP25 expression via adenoassociated virus serotype 9 vectors in USP25^-/- mice attenuated Ang II-induced cardiac hypertrophy and cardiac dysfunction, whereas myocardial overexpression of SERCA2a could mimic the effect of USP25.

CONCLUSIONS

We confirmed that USP25 inhibited cardiac hypertrophy by deubiquitinating and stabilizing SERCA2a.

The actin cytoskeleton: Morphological changes in pre- and fully developed lung cancer

Actin, a primary component of the cell cytoskeleton can have multiple isoforms, each of which can have specific properties uniquely suited for their purpose. These monomers are then bound together to form polymeric filaments utilizing adenosine triphosphate hydrolysis as a source of energy. Proteins, such as Arp2/3, VASP, formin, profilin, and cofilin, serve important roles in the polymerization process. These filaments can further be linked to form stress fibers by proteins called actin-binding proteins, such as α-actinin, myosin, fascin, filamin, zyxin, and epsin. These stress fibers are responsible for mechanotransduction, maintaining cell shape, cell motility, and intracellular cargo transport. Cancer metastasis, specifically epithelial mesenchymal transition (EMT), which is one of the key steps of the process, is accompanied by the formation of thick stress fibers through the Rho-associated protein kinase, MAPK/ERK, and Wnt pathways. Recently, with the advent of "field cancerization," pre-malignant cells have also been demonstrated to possess stress fibers and related cytoskeletal features. Analytical methods ranging from western blot and RNA-sequencing to cryo-EM and fluorescent imaging have been employed to understand the structure and dynamics of actin and related proteins including polymerization/depolymerization. More recent methods involve quantifying properties of the actin cytoskeleton from fluorescent images and utilizing them to study biological processes, such as EMT. These image analysis approaches exploit the fact that filaments have a unique structure (curvilinear) compared to the noise or other artifacts to separate them. Line segments are extracted from these filament images that have assigned lengths and orientations. Coupling such methods with statistical analysis has resulted in development of a new reporter for EMT in lung cancer cells as well as their drug responses.

De novo and inherited variants in coding and regulatory regions in genetic cardiomyopathies

BACKGROUND

Cardiomyopathies are a leading cause of progressive heart failure and sudden cardiac death; however, their genetic aetiology remains poorly understood. We hypothesised that variants in noncoding regulatory regions and oligogenic inheritance mechanisms may help close the diagnostic gap.

METHODS

We first analysed whole-genome sequencing data of 143 parent-offspring trios from Genomics England 100,000 Genomes Project. We used gene panel testing and a phenotype-based, variant prioritisation framework called Exomiser to identify candidate genes in trios. To assess the contribution of noncoding DNVs to cardiomyopathies, we intersected DNVs with open chromatin sequences from single-cell ATAC-seq data of cardiomyocytes. We also performed a case-control analysis in an exome-negative cohort, including 843 probands and 19,467 controls, to assess the association between noncoding variants in known cardiomyopathy genes and disease.

RESULTS

In the trio analysis, a definite or probable genetic diagnosis was identified in 21 probands according to the American College of Medical Genetics guidelines. We identified novel DNVs in diagnostic-grade genes (RYR2, TNNT2, PTPN11, MYH7, LZR1, NKX2-5), and five cases harbouring a combination of prioritised variants, suggesting that oligogenic inheritance and genetic modifiers contribute to cardiomyopathies. Phenotype-based ranking of candidate genes identified in noncoding DNV analysis revealed JPH2 as the top candidate. Moreover, a case-control analysis revealed an enrichment of rare noncoding variants in regulatory elements of cardiomyopathy genes (p = .035, OR = 1.43, 95% Cl = 1.095-1.767) versus controls. Of the 25 variants associated with disease  (p< 0.5), 23 are novel and nine are predicted to disrupt transcription factor binding motifs.

CONCLUSION

Our results highlight complex genetic mechanisms in cardiomyopathies and reveal novel genes for future investigations.

KLF13 Loss‐of‐Function Mutations Underlying Familial Dilated Cardiomyopathy

Background

Dilated cardiomyopathy (DCM), characterized by progressive left ventricular enlargement and systolic dysfunction, is the most common type of cardiomyopathy and a leading cause of heart failure and cardiac death. Accumulating evidence underscores the critical role of genetic defects in the pathogenesis of DCM, and >250 genes have been implicated in DCM to date. However, DCM is of substantial genetic heterogeneity, and the genetic basis underpinning DCM remains elusive in most cases.

Methods and Results

By genome‐wide scan with microsatellite markers and genetic linkage analysis in a 4‐generation family inflicted with autosomal‐dominant DCM, a new locus for DCM was mapped on chromosome 15q13.1–q13.3, a 4.77‐cM (≈3.43 Mbp) interval between markers D15S1019 and D15S1010, with the largest 2‐point logarithm of odds score of 5.1175 for the marker D15S165 at recombination fraction (θ)=0.00. Whole‐exome sequencing analyses revealed that within the mapping chromosomal region, only the mutation in the KLF13 gene, c.430G>T (p.E144X), cosegregated with DCM in the family. In addition, sequencing analyses of KLF13 in another cohort of 266 unrelated patients with DCM and their available family members unveiled 2 new mutations, c.580G>T (p.E194X) and c.595T>C (p.C199R), which cosegregated with DCM in 2 families, respectively. The 3 mutations were absent from 418 healthy subjects. Functional assays demonstrated that the 3 mutants had no transactivation on the target genes ACTC1 and MYH7 (2 genes causally linked to DCM), alone or together with GATA4 (another gene contributing to DCM), and a diminished ability to bind the promoters of ACTC1 and MYH7 . Add, the E144X‐mutant KLF13 showed a defect in intracellular distribution.

Conclusions

This investigation indicates KLF13 as a new gene predisposing to DCM, which adds novel insight to the molecular pathogenesis underlying DCM, implying potential implications for prenatal prevention and precision treatment of DCM in a subset of patients.

Mutational Assessment in NKX2-5 and ACTC1 Genes in Patients with Congenital Cardiac Septal Defect (CCSD) from Ethnic Kashmiri Population

(1) Background globe. The etiology of CHDs is complex and involves both genetic and non-genetic factors. Although, significant progress has been made in deciphering the genetic components involved in CHDs, recent reports have revealed that mutations in Nk2 homeobox5 (NKX2-5) and actin alpha cardiac muscle1 (ACTC1) genes play a key role in CHDs such as atrial and ventricular septum defects. Therefore, the present study evaluates the role of key hotspot mutations in NKX2-5 and ACTC1 genes of congenital cardiac septal defect (CCSD) in ethnic Kashmiri population. (2) Methods: A total of 112 confirmed CHD patients were included in the current study, of which 30 patients were evaluated for mutational analysis for hotspot mutations of NKX2-5 and ACTC1 genes. The total genomic DNA was extracted from the samples (cardiac tissue/blood) and were subjected to amplification for NKX2-5 (exon 1 and 2), and ACTC1 (exon 2) genes by using PCR specific primers to analyze the hotspot mutations in respective exons. The amplified products obtained were sent to Macrogen Korea for sequencing by Sanger’s method. (3) Results: Our results confirmed that not a single mutation was found in either hotspot exon 1 and 2 of NKX2-5 and exon 2 of ACTC1 in the patients included in the current study. Interestingly, a novel synonymous nucleotide variation leading to G > C transversion (GCG > GCC) was found in exon 2 of NKX2-5 gene of CCSD patient. (4) Conclusions: The current findings demonstrated the role of NKX2-5 and ACTC1 in cardiac development. The study will provide an insight in understanding the genetic etiology and highlights the role of newly identified mutations in patients with CDS’s in ethnic Kashmiri population. In silico findings revealed amino acid changes, splice site variation and the creation of new site. Furthermore, the study warrants complete screening of genes involved in CCSDs.

Myocardial Injury Caused by Chronic Alcohol Exposure—A Pilot Study Based on Proteomics

Chronic alcohol exposure can cause myocardial degenerative diseases, manifested as cardiac insufficiency, arrhythmia, etc. These are defined as alcoholic cardiomyopathy (ACM). Alcohol-mediated myocardial injury has previously been studied through metabolomics, and it has been proved to be involved in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway concerning unsaturated fatty acids biosynthesis and oxidative phosphorylation, which tentatively explored the mechanism of ACM induced by chronic drinking. To further study alcohol-induced myocardial injury, myocardial specimens from a previously successfully established mouse model of ACM were subjected to histological, echocardiographic, and proteomic analyses, and validated by real-time quantitative polymerase chain reaction (qPCR). Results of histopathology and echocardiography showed the hypertrophy of cardiomyocytes, the dilation of ventricles, and decreased cardiac function. Proteomic results, available via ProteomeXchange with identifier PXD032949, revealed 56 differentially expressed proteins (DEPs) were identified, which have the potential to be involved in the KEGG pathway related to fatty acid biosynthesis disorders, lipid metabolism disorders, oxidative stress, and, ultimately, in the development of dilated cardiomyopathy (DCM). The present study further elucidates the underlying effects of myocardial injury due to chronic alcohol intake, laying a foundation for further studies to clarify the potential mechanisms of ACM.

Dilated cardiomyopathy in the era of precision medicine: latest concepts and developments

Dilated cardiomyopathy (DCM) is an umbrella term entailing a wide variety of genetic and non-genetic etiologies, leading to left ventricular systolic dysfunction and dilatation, not explained by abnormal loading conditions or coronary artery disease. The clinical presentation can vary from asymptomatic to heart failure symptoms or sudden cardiac death (SCD) even in previously asymptomatic individuals. In the last 2 decades, there has been striking progress in the understanding of the complex genetic basis of DCM, with the discovery of additional genes and genotype-phenotype correlation studies. Rigorous clinical work-up of DCM patients, meticulous family screening, and the implementation of advanced imaging techniques pave the way for a more efficient and earlier diagnosis as well as more precise indications for implantable cardioverter defibrillator implantation and prevention of SCD. In the era of precision medicine, genotype-directed therapies have started to emerge. In this review, we focus on updates of the genetic background of DCM, characteristic phenotypes caused by recently described pathogenic variants, specific indications for prevention of SCD in those individuals and genotype-directed treatments under development. Finally, the latest developments in distinguishing athletic heart syndrome from subclinical DCM are described.

Fibulin-3 Deficiency Protects Against Myocardial Injury Following Ischaemia/ Reperfusion in in vitro Cardiac Spheroids

Myocardial infarction (MI, or heart attack) is a leading cause of death worldwide. Myocardial ischaemia reperfusion (I/R) injury typical of MI events is also associated with the development of cardiac fibrosis and heart failure in patients. Fibulin-3 is an extracellular matrix component that plays a role in regulating MI response in the heart. In this study, we generated and compared in vitro cardiac spheroids (CSs) from wild type (WT) and fibulin-3 knockout (Fib-3 KO) mice. These were then exposed to pathophysiological changes in oxygen (O₂) concentrations to mimic an MI event. We finally measured changes in contractile function, cell death, and mRNA expression levels of cardiovascular disease genes between WT and Fib-3 KO CSs. Our results demonstrated that there are significant differences in growth kinetics and endothelial network formation between WT and Fib-3 KO CSs, however, they respond similarly to changes in O₂ concentrations. Fib-3 deficiency resulted in an increase in viability of cells and improvement in contraction frequency and fractional shortening compared to WT I/R CSs. Gene expression analyses demonstrated that Fib-3 deficiency inhibits I/R injury and cardiac fibrosis and promotes angiogenesis in CSs. Altogether, our findings suggest that Fib-3 deficiency makes CSs resistant to I/R injury and associated cardiac fibrosis and helps to improve the vascular network in CSs.

Comparison of Outcome in Patients With Familial Versus Spontaneous Atrial Septal Defect

Patients with atrial septal defects (ASDs) have increased mortality and morbidity. This can only partly be explained by hemodynamic changes caused by the ASD, suggesting additional underlying causes. Patients with an ASD have an increased burden of pathogenic gene variants in ASD-related genes, indicating genetics as an important factor in etiology. Inheritance of genetic variants with high impact can cause ASD in relatives (familial ASD). This study aimed to investigate whether lifelong outcomes were different in patients with familial ASD compared with patients with sporadic ASD. We used health registries and a nationwide cohort of 2,151 patients with ASD to compare the incidences of atrial fibrillation or flutter (together abbreviated as AF), heart failure, and mortality between patients with familial and sporadic ASD using Cox proportional hazard ratio and Fine and Gray analysis. Patients with familial ASD experienced AF and heart failure earlier in life than patients with sporadic ASD, with hazard ratios of 1.6 and 1.7, respectively. Subdistribution hazard ratios showed an increased risk of AF and heart failure in patients with familial ASD compared with patients with sporadic ASDs (2.3 and 3.1, respectively). Our results suggest that genetic variants with high impact may influence the outcomes of patients with ASD. In conclusion, patients with familial ASD have an increased risk and an earlier onset of AF and heart failure compared with patients with sporadic ASD, hence clinical awareness of arrhythmias and heart failure in patients with familial ASD may lead to timely treatment.

Co-Overexpression of GRK5/ACTC1 Correlates With the Clinical Parameters and Poor Prognosis of Epithelial Ovarian Cancer

Background: The prognosis of epithelial ovarian cancer (EOC) is poor, and the present prognostic predictors of EOC are neither sensitive nor specific.

Objective: The aim of this study was to search the prognostic biomarkers of EOC and to investigate the expression of G protein-coupled receptor kinase 5 (GRK5) and actin alpha cardiac muscle 1 (ACTC1) in EOC tissues (both paraffin-embedded and fresh-frozen tissues) and to explore their association with clinicopathological parameters and prognostic value in patients with EOC.

Methods: A total of 172 paraffin-embedded cancer tissues of EOC patients diagnosed and operated at the memorial hospital of Sun Yat-sen University between December 2009 and March 2017 and 41 paratumor tissues were collected and the expression of GRK5 and ACTC1 was examined using immunohistochemistry. Furthermore, 16 fresh-frozen EOC tissues and their matched paratumor tissues were collected from the Integrated Hospital of Traditional Chinese Medicine, Southern Medical University, between August 2013 and November 2019 and subjected to reverse-transcription quantitative PCR analysis to detect the mRNA expression of GRK5 and ACTC1.

Results: The expression of GRK5 and ACTC1 was both higher in cancer tissues than in paratumor tissues. GRK5 expression was positively correlated with ACTC1 expression. In addition, GRK5, ACTC1, and GRK5/ACTC1 expression was associated with the recurrence-free survival and overall survival of EOC patients. Furthermore, multivariate logistic regression analysis indicated that GRK5+/ACTC1+ co-expression, intestinal metastasis, postoperative chemotherapy, platinum resistance, and hyperthermic intraperitoneal chemotherapy were independent prognostic factors of EOC.

Conclusion: GRK5 and ACTC1 are both upregulated in EOC compared with those in paratumor tissues. The co-expression of GRK5+/ACTC1+ rather than GRK5 or ACTC1 is an independent prognostic biomarker of EOC.

Understanding the molecular basis of cardiomyopathy

Inherited cardiomyopathies are a major cause of mortality and morbidity worldwide and can be caused by mutations in a wide range of proteins located in different cellular compartments. The present review is based on Dr. Ju Chen's 2021 Robert M. Berne Distinguished Lectureship of the American Physiological Society Cardiovascular Section, in which he provided an overview of the current knowledge on the cardiomyopathy-associated proteins that have been studied in his laboratory. The review provides a general summary of the proteins in different compartments of cardiomyocytes associated with cardiomyopathies, with specific focus on the proteins that have been studied in Dr. Chen's laboratory.

Dilated cardiomyopathy: a new insight into the rare but common cause of heart failure

Heart failure is a global health burden responsible for high morbidity and mortality with a prevalence of greater than 60 million individuals worldwide. One of the major causes of heart failure is dilated cardiomyopathy (DCM), characterized by associated systolic dysfunction. During the last few decades, there have been remarkable advances in our understanding about the genetics of dilated cardiomyopathy. The genetic causes were initially thought to be associated with mutations in genes encoding proteins that are localized to cytoskeleton and sarcomere only; however, with the advancement in mechanistic understanding, the roles of ion channels, Z-disc, mitochondria, nuclear proteins, cardiac transcription factors (e.g., NKX-2.5, TBX20, GATA4), and the factors involved in calcium homeostasis have also been identified and found to be implicated in both familial and sporadic DCM cases. During past few years, next-generation sequencing (NGS) has been established as a diagnostic tool for genetic analysis and it has added significantly to the existing candidate gene list for DCM. The animal models have also provided novel insights to develop a better treatment strategy based on phenotype-genotype correlation, epigenetic and phenomic profiling. Most of the DCM biomarkers that are used in routine genetic and clinical testing are structural proteins, but during the last few years, the role of mi-RNA has also emerged as a biomarker due to their accessibility through noninvasive methods. Our increasing genetic knowledge can improve the clinical management of DCM by bringing clinicians and geneticists on one platform, thereby influencing the individualized clinical decision making and leading to precision medicine.

Genetic Association Between Hypoplastic Left Heart Syndrome and Cardiomyopathies

BACKGROUND

Hypoplastic left heart syndrome (HLHS) with risk of poor outcome has been linked to MYH6 variants, implicating overlap in genetic etiologies of structural and myopathic heart disease.

METHODS

Whole genome sequencing was performed in 197 probands with HLHS, 43 family members, and 813 controls. Data were filtered for rare, segregating variants in 3 index families comprised of an HLHS proband and relative(s) with cardiomyopathy. Whole genome sequencing data from cases and controls were compared for rare variant burden across 56 cardiomyopathy genes utilizing a weighted burden test approach, accounting for multiple testing using a Bonferroni correction.

RESULTS

A pathogenic MYBPC3 nonsense variant was identified in the first proband who underwent cardiac transplantation for diastolic heart failure, her father with left ventricular noncompaction, and 2 fourth-degree relatives with hypertrophic cardiomyopathy. A likely pathogenic RYR2 missense variant was identified in the second proband, a second-degree relative with aortic dilation, and a fourth-degree relative with dilated cardiomyopathy. A pathogenic RYR2 exon 3 in-frame deletion was identified in the third proband diagnosed with catecholaminergic polymorphic ventricular tachycardia and his father with left ventricular noncompaction and catecholaminergic polymorphic ventricular tachycardia. To further investigate HLHS-cardiomyopathy gene associations in cases versus controls, rare variant burden testing of 56 genes revealed enrichment in MYH6 (P=0.000068). Rare, predicted-damaging MYH6 variants were identified in 10% of probands in our cohort-4 with familial congenital heart disease, 4 with compound heterozygosity (3 with systolic ventricular dysfunction), and 4 with MYH6-FLNC synergistic heterozygosity.

CONCLUSIONS

Whole genome sequencing in multiplex families, proband-parent trios, and case-control cohorts revealed defects in cardiomyopathy-associated genes in patients with HLHS, which may portend impaired functional reserve of the single-ventricle circulation.

Detection and functional characterization of a novel MEF2A variation responsible for familial dilated cardiomyopathy

OBJECTIVES

Dilated cardiomyopathy (DCM) represents the most frequent form of cardiomyopathy, leading to heart failure, cardiac arrhythmias and death. Accumulating evidence convincingly demonstrates the crucial role of genetic defects in the pathogenesis of DCM, and over 100 culprit genes have been implicated with DCM. However, DCM is of substantial genetic heterogeneity, and the genetic determinants underpinning DCM remain largely elusive.

METHODS

Whole-exome sequencing and bioinformatical analyses were implemented in a consanguineous Chinese family with DCM. A total of 380 clinically annotated control individuals and 166 more DCM index cases then underwent Sanger sequencing analysis for the identified genetic variation. The functional characteristics of the variant were delineated by utilizing a dual-luciferase assay system.

RESULTS

A heterozygous variation in the MEF2A gene (encoding myocyte enhancer factor 2A, a transcription factor pivotal for embryonic cardiogenesis and postnatal cardiac adaptation), NM_001365204.1: c.718G>T; p. (Gly240*), was identified, and verified by Sanger sequencing to segregate with autosome-dominant DCM in the family with complete penetrance. The nonsense variation was neither detected in 760 control chromosomes nor found in 166 more DCM probands. Functional analyses revealed that the variant lost transactivation on the validated target genes MYH6 and FHL2, both causally linked to DCM. Furthermore, the variation nullified the synergistic activation between MEF2A and GATA4, another key transcription factor involved in DCM.

CONCLUSIONS

The findings firstly indicate that MEF2A loss-of-function variation predisposes to DCM in humans, providing novel insight into the molecular mechanisms of DCM and suggesting potential implications for genetic testing and prognostic evaluation of DCM patients.

Advances in Stem Cell Modeling of Dystrophin-Associated Disease: Implications for the Wider World of Dilated Cardiomyopathy

Familial dilated cardiomyopathy (DCM) is mostly caused by mutations in genes encoding cytoskeletal and sarcomeric proteins. In the pediatric population, DCM is the predominant type of primitive myocardial disease. A severe form of DCM is associated with mutations in the DMD gene encoding dystrophin, which are the cause of Duchenne Muscular Dystrophy (DMD). DMD-associated cardiomyopathy is still poorly understood and orphan of a specific therapy. In the last 5 years, a rise of interest in disease models using human induced pluripotent stem cells (hiPSCs) has led to more than 50 original studies on DCM models. In this review paper, we provide a comprehensive overview on the advances in DMD cardiomyopathy disease modeling and highlight the most remarkable findings obtained from cardiomyocytes differentiated from hiPSCs of DMD patients. We will also describe how hiPSCs based studies have contributed to the identification of specific myocardial disease mechanisms that may be relevant in the pathogenesis of DCM, representing novel potential therapeutic targets.

Data on the role of cardiac α-actin (ACTC1) gene mutations on SRF-signaling

We recently reported a novel, heterozygous, and non-synonymous ACTC1 mutation (p.Gly247Asp or G247D) in a large, multi-generational family, causing atrial-septal defect followed by late-onset dilated cardiomyopathy (DCM). We also found that the G247D ACTC1 mutation negatively regulated serum response (SRF)-signaling thereby contributing to the late-onset DCM observed in human patients carrying this mutation (“A cardiac α-actin (ACTC1) p. Gly247Asp mutation inhibits SRF-signaling in vitro in neonatal rat cardiomyocytes” [1]). There are some ACTC1 mutations known to date, majority of which, though, have not been investigated for their functional consequence. We thus aimed at determining the functional impact of various ACTC1 gene mutations on SRF-signaling using SM22-response element driven firefly luciferase activity assays in C2C12 cells.

Downregulation of Cypher induces apoptosis in cardiomyocytes via Akt/p38 MAPK signaling pathway

Background: Dilated cardiomyopathy (DCM) is considered as the most common form of non-ischemic cardiomyopathy with a high mortality worldwide. Cytoskeleton protein Cypher plays an important role in maintaining cardiac function. Genetic studies in human and animal models revealed that Cypher is involved in the development of DCM. However, the underlying molecular mechanism is not fully understood. Accumulating evidences suggest that apoptosis in myocytes may contribute to DCM. Thus, the purpose of this study is to define whether lack of Cypher in cardiomyocytes can elevate apoptosis signaling and lead to DCM eventually. Methods and Results: Cypher-siRNA sufficiently inhibited Cypher expression in cardiomyocytes. TUNEL-positive cardiomyocytes were increased in both Cypher knockdown neonatal rat cardiomyocytes and Cypher knockout mice hearts, which were rare in the control group. Flow cytometry further confirmed that downregulation of Cypher significantly increased myocytes apoptosis in vitro. Cell counting kit-8 assay revealed that Cypher knockdown in H9c2 cells significantly reduced cell viability. Cypher knockdown was found to increase cleaved caspase-3 expression and suppress p21, ratio of bcl-2 to Bax. Cypher-deficiency induced apoptosis was linked to downregulation of Akt activation and elevated p-p38 MAPK accumulation. Pharmacological activation of Akt with SC79 attenuated apoptosis with enhanced phosphorylation of Akt and reduced p-p38 MAPK and Bax expression. Conclusions: Downregulation of Cypher participates in the promotion of cardiomyocytes apoptosis through inhibiting Akt dependent pathway and enhancing p38 MAPK phosphorylation. These findings may provide a new potential therapeutic strategy for the treatment of DCM.

A cardiac α-actin (ACTC1) p. Gly247Asp mutation inhibits SRF-signaling in vitro in neonatal rat cardiomyocytes

We recently identified a novel, heterozygous, and non-synonymous ACTC1 mutation (p.Gly247Asp or G247D) in a large, multi-generational family, causing atrial-septal defect followed by late-onset dilated cardiomyopathy (DCM). Molecular dynamics studies revealed possible actin polymerization defects as G247D mutation resides at the juncture of side-chain interaction, which was indeed confirmed by in vitro actin polymerization assays. Since polymerization/de-polymerization is important for the activation of Rho-GTPase-mediated serum response factor (SRF)-signaling, we studied the effect of G247D mutation using luciferase assay. Overexpression of native human ACTC1 in neonatal rat cardiomyocytes (NRVCMs) strongly activated SRF-signaling both in C2C12 cells and NRVCMs, whereas, G247D mutation abolished this activation. Mechanistically, we found reduced GTP-bound Rho-GTPase and increased nuclear localization of globular actin in NRVCMs overexpressing mutant ACTC1 possibly causing inhibition of SRF-signaling activation. In conclusion, our data suggests that human G247D ACTC1 mutation negatively regulates SRF-signaling likely contributing to the late-onset DCM observed in mutation carrier patients.