Genetic causes of human heart failure

Non-ischemic dilated cardiomyopathy and cardiac fibrosis

Cardiac fibrosis is associated with non-ischemic dilated cardiomyopathy, increasing its morbidity and mortality. Cardiac fibroblast is the keystone of fibrogenesis, being activated by numerous cellular and humoral factors. Macrophages, CD4+ and CD8+ T cells, mast cells, and endothelial cells stimulate fibrogenesis directly by activating cardiac fibroblasts and indirectly by synthetizing various profibrotic molecules. The synthesis of type 1 and type 3 collagen, fibronectin, and α-smooth muscle actin is rendered by various mechanisms like transforming growth factor-beta/small mothers against decapentaplegic pathway, renin angiotensin system, and estrogens, which in turn alter the extracellular matrix. Investigating the underlying mechanisms will allow the development of diagnostic and prognostic tools and discover novel specific therapies. Serum biomarkers aid in the diagnosis and tracking of cardiac fibrosis progression. The diagnostic gold standard is cardiac magnetic resonance with gadolinium administration that allows quantification of cardiac fibrosis either by late gadolinium enhancement assessment or by T1 mapping. Therefore, the goal is to stop and even reverse cardiac fibrosis by developing specific therapies that directly target fibrogenesis, in addition to the drugs used to treat heart failure. Cardiac resynchronization therapy had shown to revert myocardial remodeling and to reduce cardiac fibrosis. The purpose of this review is to provide an overview of currently available data.

Long non-coding RNAs link extracellular matrix gene expression to ischemic cardiomyopathy

AIMS

Ischemic cardiomyopathy (ICM) resulting from myocardial infarction is a major cause of heart failure (HF). Recently, thousands of long non-coding RNAs (lncRNAs) have been discovered and implicated in a variety of biological processes. However, the role of most lncRNAs in HF remains largely unknown. The aim of this study is to test the hypothesis that the expression and function of lncRNAs are differentially regulated in diseased hearts.

METHODS AND RESULTS

In this study, we performed RNA deep sequencing of protein-coding and non-coding RNAs from cardiac samples of patients with ICM ( n  = 15) and controls ( n  = 15). Genome-wide transcriptome analysis confirmed that many protein-coding genes previously known to be involved in HF were altered in ICM hearts. Among the 145 differentially expressed lncRNAs identified in ICM hearts, we found a set of 35 lncRNAs that display strong positive expression correlation. Expression correlation coefficient analyses of differentially expressed lncRNAs and protein-coding genes revealed a strong association between lncRNAs and extracellular matrix (ECM) protein-coding genes. We overexpressed or knocked down selected lncRNAs in cardiac fibroblasts and our results suggest that lncRNAs are important regulators of fibrosis and the expression of ECM synthesis genes. Moreover, we show that lncRNAs participate in the TGF-β pathway to modulate the expression of ECM genes and myofibroblast differentiation.

CONCLUSION

Our studies demonstrate that the expression of many lncRNAs is dynamically regulated in ICM. lncRNAs regulate the expression and function of ECM and cardiac fibrosis during the development of ICM. Our results further indicate that lncRNAs may represent novel regulators of heart function and cardiac disorders, including ICM.

Profilin modulates sarcomeric organization and mediates cardiomyocyte hypertrophy

Aims

Heart failure is often preceded by cardiac hypertrophy, which is characterized by increased cell size, altered protein abundance, and actin cytoskeletal reorganization. Profilin is a well-conserved, ubiquitously expressed, multifunctional actin-binding protein, and its role in cardiomyocytes is largely unknown. Given its involvement in vascular hypertrophy, we aimed to test the hypothesis that profilin-1 is a key mediator of cardiomyocyte-specific hypertrophic remodelling.

Methods and results

Profilin-1 was elevated in multiple mouse models of hypertrophy, and a cardiomyocyte-specific increase of profilin in Drosophila resulted in significantly larger heart tube dimensions. Moreover, adenovirus-mediated overexpression of profilin-1 in neonatal rat ventricular myocytes (NRVMs) induced a hypertrophic response, measured by increased myocyte size and gene expression. Profilin-1 silencing suppressed the response in NRVMs stimulated with phenylephrine or endothelin-1. Mechanistically, we found that profilin-1 regulates hypertrophy, in part, through activation of the ERK1/2 signalling cascade. Confocal microscopy showed that profilin localized to the Z-line of Drosophila myofibrils under normal conditions and accumulated near the M-line when overexpressed. Elevated profilin levels resulted in elongated sarcomeres, myofibrillar disorganization, and sarcomeric disarray, which correlated with impaired muscle function.

Conclusion

Our results identify novel roles for profilin as an important mediator of cardiomyocyte hypertrophy. We show that overexpression of profilin is sufficient to induce cardiomyocyte hypertrophy and sarcomeric remodelling, and silencing of profilin attenuates the hypertrophic response.

Associations of Polymorphisms in HRH2, HRH3, DAO, and HNMT Genes with Risk of Chronic Heart Failure

The pathophysiological functions of cardiac histamine level and related histamine receptors during the development of chronic heart failure (CHF) were intensively investigated previously. However, the relevance of polymorphisms in histamine-related genes, such as HRH2, HRH3, DAO, and HNMT, with CHF remains largely neglected. This study herein aims to analyze the clinical associations of polymorphisms in those genes with CHF risk. A total of 333 unrelated Chinese Han CHF patients and 354 ethnicity-matched healthy controls were recruited and 11 single nucleotide polymorphisms (SNPs) were genotyped. We found that the HRH3 rs3787429 polymorphism was associated with CHF risk (p < 0.001). The T allele of rs3787429 exhibited protective effect against CHF under the dominant (ORs = 0.455; 95% CIs = 0.322–0.642) and additive models (ORs = 0.662; 95% CIs = 0.523–0.838), while, for SNPs in HRH2, DAO, and HNMT, no significant associations were observed in the present study. These findings for the first time screen out one SNP (rs3787429) of HRH3 gene that was significantly associated with CHF in Chinese Han population, which may be a novel biomarker for personal prevention and treatment of CHF and provides novel highlights for investigating the contribution of this disease.

Pressure Overload by Transverse Aortic Constriction Induces Maladaptive Hypertrophy in a Titin-Truncated Mouse Model

Mutations in the giant sarcomeric protein titin (TTN) are a major cause for inherited forms of dilated cardiomyopathy (DCM). We have previously developed a mouse model that imitates a TTN truncation mutation we found in a large pedigree with DCM. While heterozygous Ttn knock-in mice do not display signs of heart failure under sedentary conditions, they recapitulate the human phenotype when exposed to the pharmacological stressor angiotensin II or isoproterenol. In this study we investigated the effects of pressure overload by transverse aortic constriction (TAC) in heterozygous (Het) Ttn knock-in mice. Two weeks after TAC, Het mice developed marked impairment of left ventricular ejection fraction (p < 0.05), while wild-type (WT) TAC mice did not. Het mice also trended toward increased ventricular end diastolic pressure and volume compared to WT littermates. We found an increase in histologically diffuse cardiac fibrosis in Het compared to WT in TAC mice. This study shows that a pattern of DCM can be induced by TAC-mediated pressure overload in a TTN-truncated mouse model. This model enlarges our arsenal of cardiac disease models, adding a valuable tool to understand cardiac pathophysiological remodeling processes and to develop therapeutic approaches to combat heart failure.

The natural history of acute dilated cardiomyopathy

INTRODUCTION

Acute dilated cardiomyopathy (ADCM) is a frequent cause for referral for cardiac transplantation yet its prognosis and natural history on contemporary therapy remain uncertain.

METHODS

The Multicenter Intervention in Myocarditis and Acute Cardiomyopathy (IMAC)-2 trial enrolled 373 patients at 12 academic medical centers with left ventricular ejection fraction (LVEF) ≤ 40%, heart failure symptoms < 6 months duration, and a diagnostic evaluation consistent with idiopathic cardiomyopathy or acute myocarditis. The natural history of ADCM in an earlier era (1975-2000) was also examined via a MEDLINE search of published observational studies.

RESULTS

Mean age of the IMAC-2 study cohort was 45 ± 4 years and 38% were female. Mean initial LVEF was 24% ± 8% and increased to 40% ± 12% during treatment with ACE-I/ARB (82%), and a beta-blocker (94%). Transplantation-free survival at 1, 2, and 4 years was 94%, 92%, and 86%, respectively. This survival rate was substantially higher than the prior era. Multivariate predictors of improvement in LVEF were smaller LV dimension and higher systolic blood pressure whereas black race and higher initial New York Heart Association functional class were associated with lower final LVEF. Genotypic variation did not correlate with response to pharmacological therapy.

CONCLUSION

Earlier diagnosis and aggressive pharmacologic and device-based therapy of ADCM has led to improved prognosis.

At the Start of the Sarcomere: A Previously Unrecognized Role for Myosin Chaperones and Associated Proteins during Early Myofibrillogenesis

The development of striated muscle in vertebrates requires the assembly of contractile myofibrils, consisting of highly ordered bundles of protein filaments. Myofibril formation occurs by the stepwise addition of complex proteins, a process that is mediated by a variety of molecular chaperones and quality control factors. Most notably, myosin of the thick filament requires specialized chaperone activity during late myofibrillogenesis, including that of Hsp90 and its cofactor, Unc45b. Unc45b has been proposed to act exclusively as an adaptor molecule, stabilizing interactions between Hsp90 and myosin; however, recent discoveries in zebrafish and C. elegans suggest the possibility of an earlier role for Unc45b during myofibrillogenesis. This role may involve functional control of nonmuscle myosins during the earliest stages of myogenesis, when premyofibril scaffolds are first formed from dynamic cytoskeletal actin. This paper will outline several lines of evidence that converge to build a model for Unc45b activity during early myofibrillogenesis.

Coding sequence mutations identified in MYH7, TNNT2, SCN5A, CSRP3, LBD3, and TCAP from 313 patients with familial or idiopathic dilated cardiomyopathy

BACKGROUND

More than 20 genes have been reported to cause idiopathic and familial dilated cardiomyopathy (IDC/FDC), but the frequency of genetic causation remains poorly understood.

METHODS AND RESULTS

Blood samples were collected and DNA prepared from 313 patients, 183 with FDC and 130 with IDC. Genomic DNA underwent bidirectional sequencing of six genes, and mutation carriers were followed up by evaluation of additional family members. We identified in 36 probands, 31 unique protein-altering variants (11.5% overall) that were not identified in 253 control subjects (506 chromosomes). These included 13 probands (4.2%) with 12 beta-myosin heavy chain (MYH7) mutations, nine probands (2.9%) with six different cardiac troponin T (TNNT2) mutations, eight probands (2.6%) carrying seven different cardiac sodium channel (SCN5A) mutations, three probands (1.0%) with three titin-cap or telethonin (TCAP) mutations, three probands (1.0%) with two LIM domain binding 3 (LDB3) mutations, and one proband (0.3%) with a muscle LIM protein (CSRP3) mutation. Four nucleotide changes did not segregate with phentoype and/or did not alter a conserved amino acid and were therefore considered unlikely to be disease-causing. Mutations in 11 probands were assessed as likely disease-causing, and in 21 probands were considered possibly disease-causing. These 32 probands included 14 of the 130 with IDC (10.8%) and 18 of 183 with FDC (9.8%)

CONCLUSIONS

Mutations of these six genes each account for a small fraction of the genetic cause of FDC/IDC. The frequency of possible or likely disease-causing mutations in these genes is similar for IDC and FDC.

Deciphering modifications in swine cardiac troponin I by top-down high-resolution tandem mass spectrometry

Cardiac troponin I (cTnI) is an important regulatory protein in cardiac muscle, and its modification represents a key mechanism in the regulation of cardiac muscle contraction and relaxation. cTnI is often referred to as the "gold-standard" serum biomarker for diagnosing patients with acute cardiac injury since it is unique to the heart and released into the circulation following necrotic death of cardiac tissue. The swine (Sus scrofa) heart model is extremely valuable for cardiovascular research since the heart anatomy and coronary artery distribution of swine are almost identical to those of humans. Herein, we report a comprehensive characterization of the modifications in swine cTnI using top-down high-resolution tandem mass spectrometry in conjugation with immunoaffinity chromatography purification. High-resolution high accuracy mass spectrometry revealed that swine cTnI affinity purified from domestic pig hearts was N-terminally acetylated and phosphorylated. Electron capture disassociation is uniquely suited for localization of labile phosphorylations, which unambiguously identified Ser22/Ser23 as the only basally phosphorylated sites that are well-known to be regulated by protein kinase A and protein kinase C. Moreover, a combination of tandem mass spectrometry with sequence homology alignment effectively localized a single amino acid polymorphism, V116A, representing a novel genetic variant of swine cTnI. Overall, our studies demonstrated the unique power of top-down high-resolution tandem mass spectrometry in the characterization of protein modifications, including labile phosphorylation and unexpected sequence variants.

Nonischemic ST segment elevation in hypertrophic cardiomyopathy due to chest wall deformity from kyphoscoliosis

A 57-year-old male was admitted with suspected acute coronary syndrome. He reported experiencing moderate chest pain when walking during the day prior to admission, but had very prominent ST segment elevations in the precordial electrocardiography (EKG) leads. A physical examination revealed remarkable severe kyphoscoliosis with chest deformity. The patient's cardiac troponin levels remained normal, while cardiac ultrasound and magnetic resonance imaging of the chest confirmed hypertrophic cardiomyopathy (HCM) with severe thickening of the interventricular septum. Ischemic heart disease was ruled out by myocardial perfusion imaging with (99m)Tc-MIBI during rest and dipyridamole-induced stress without showing irreversible or reversible myocardial ischemia. Our diagnosis was that the chest pain was noncardiac in origin and that the pronounced ST segment elevations in the precordial EKG leads reflected the severely hypertrophic interventricular septum through the normally thick left ventricular free wall. The patient's chest wall deformity brought his septum and the ventricular free wall nearly parallel to the left side of the chest wall, allowing for complete expression of the reciprocal EKG pattern of septal hypertrophy. We suggest that EKG findings should always be interpreted with the chest wall shape being kept in mind.

Genomic analysis of genetic markers associated with inherited cardiomyopathy (round heart disease) in the turkey (Meleagris gallopavo)

In turkeys, spontaneous cardiomyopathy or round heart (RH) disease is characterised by dilated ventricles and cardiac muscle hypertrophy. Although the aetiology of RH is still unknown, the disease can have a significant economic impact on turkey producers. In an initial attempt to identify genomic regions associated with RH, we utilised the chicken genome sequence to target short DNA sequences (sequence-characterised amplified regions, SCARs) identified in previous studies that had significant differences in frequency distribution between RH+ and RH- turkeys. SCARs were comparatively aligned with the chicken whole-genome sequence to identify flanking regions for primer design. Primers from 32 alignments were tested and target sequences were successfully amplified for 30 loci (94%). Comparative re-sequencing identified putative SNPs in 20 of the 30 loci (67%). Genetically informative SNPs at 16 loci were genotyped in the UMN/NTBF turkey mapping population. As a result of this study, 34 markers were placed on the turkey/chicken comparative map and 15 markers were added to the turkey genetic linkage map. The position of these markers relative to cardiac-related genes is presented. In addition, analysis of genotypes at 109 microsatellite loci presumed to flank the SCAR sequences in the turkey genome identified four significant associations with RH.

Genetics in Heart Failure: Where Are We Headed?

Heart failure is a complex disease with many precipitating factors. Novel insights into the genetic background of heart failure have boosted new areas of research that gave rise to the concept of genetic predisposition for heart failure. Various genetic defects and variances have been identified and subsequently linked to the onset of or progression to heart failure. Nevertheless, our understanding of the genetic basis for heart failure is incomplete because we lack knowledge of the functionality of genetic variances. We also do not understand the impact of genetic variances in noncoding DNA because of logistic problems in performing whole-genome scans and difficulties in statistical evaluation of large amounts of data generated by the genetic boom. It is expected that in the future we will be able to overcome these problems and apply the knowledge gained by genetic analyses to target and optimize treatment.

Genetics of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice. Despite its prevalence, relatively little is known regarding the primary mechanisms of AF and, therefore, current treatment practices focus mainly on controlling the disorder and preventing its complications once it is already present. The study of the pathogenesis of AF is complicated by the varied clinical presentation of the arrhythmia and its coexistence with other cardiac pathologies. This article reviews current efforts to delineate the fundamental mechanisms of AF, with a focus on genetic studies. Identification of the underlying etiology may result in the development of more targeted and effective therapies for AF.