Molecular Mechanisms of Inherited Cardiomyopathies

Human cardiac β-myosin powerstroke energetics: Thin filament, Pi displacement, and mutation effects

The powerstroke of human cardiac β-myosin is an important stage of the cross-bridge cycle that generates force for muscle contraction. However, the starting structure of this process has never been resolved, and the relative timing of the powerstroke and inorganic phosphate (Pi) release is still controversial. In this study, we generated an atomistic model of myosin on the thin filament and utilized metadynamics simulations to predict the absent starting structure of the powerstroke. We demonstrated that the displacement of Pi from the active site during the powerstroke is likely necessary, reducing the energy barrier of the conformation change. The effects of the presence of the thin filament, the hypertrophic cardiomyopathy mutation R712L, and the binding of mavacamten on the powerstroke process were also investigated.

PLEKHM2 deficiency induces impaired mitochondrial clearance and elevated ROS levels in human iPSC-derived cardiomyocytes

Pleckstrin homology domain-containing family M member 2 (PLEKHM2) is an essential adaptor for lysosomal trafficking and its homozygous truncation have been reported to cause early onset dilated cardiomyopathy (DCM). However, the molecular mechanism of PLEKHM2 deficiency in DCM pathogenesis and progression is poorly understood. Here, we generated an in vitro model of PLEKHM2 knockout (KO) induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to elucidate the potential pathogenic mechanism of PLEKHM2-deficient cardiomyopathy. PLEKHM2-KO hiPSC-CMs developed disease phenotypes with reduced contractility and impaired calcium handling. Subsequent RNA sequencing (RNA-seq) analysis revealed altered expression of genes involved in mitochondrial function, autophagy and apoptosis in PLEKHM2-KO hiPSC-CMs. Further molecular experiments confirmed PLEKHM2 deficiency impaired autophagy and resulted in accumulation of damaged mitochondria, which triggered increased reactive oxygen species (ROS) levels and decreased mitochondrial membrane potential (Δψm). Importantly, the elevated ROS levels caused oxidative stress-induced damage to nearby healthy mitochondria, resulting in extensive Δψm destabilization, and ultimately leading to impaired mitochondrial function and myocardial contractility. Moreover, ROS inhibition attenuated oxidative stress-induced mitochondrial damage, thereby partially rescued PLEKHM2 deficiency-induced disease phenotypes. Remarkably, PLEKHM2-WT overexpression restored autophagic flux and rescued mitochondrial function and myocardial contractility in PLEKHM2-KO hiPSC-CMs. Taken together, these results suggested that impaired mitochondrial clearance and increased ROS levels play important roles in PLEKHM2-deficient cardiomyopathy, and PLEKHM2-WT overexpression can improve mitochondrial function and rescue PLEKHM2-deficient cardiomyopathy.

Low-Salt Diet Regulates the Metabolic and Signal Transduction Genomic Fabrics, and Remodels the Cardiac Normal and Chronic Pathological Pathways

Low-salt diet (LSD) is a constant recommendation to hypertensive patients, but the genomic mechanisms through which it improves cardiac pathophysiology are still not fully understood. Our publicly accessible transcriptomic dataset of the left ventricle myocardium of adult male mice subjected to prolonged LSD or normal diet was analyzed from the perspective of the Genomic Fabric Paradigm. We found that LSD shifted the metabolic priorities by increasing the transcription control for fatty acids biosynthesis while decreasing it for steroid hormone biosynthesis. Moreover, LSD remodeled pathways responsible for cardiac muscle contraction (CMC), chronic Chagas (CHA), diabetic (DIA), dilated (DIL), and hypertrophic (HCM) cardiomyopathies, and their interplays with the glycolysis/glucogenesis (GLY), oxidative phosphorylation (OXP), and adrenergic signaling in cardiomyocytes (ASC). For instance, the statistically (p < 0.05) significant coupling between GLY and ASC was reduced by LSD from 13.82% to 2.91% (i.e., -4.75×), and that of ASC with HCM from 10.50% to 2.83% (-3.71×). The substantial up-regulation of the CMC, ASC, and OXP genes, and the significant weakening of the synchronization of the expression of the HCM, CHA, DIA, and DIL genes within their respective fabrics justify the benefits of the LSD recommendation.

Cardiac proteomic profiling suggests that hypertrophic and dilated cardiomyopathy share a common pathogenetic pathway of the calcium signalling pathway

OBJECTIVE

Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are classified as different diseases but have many similar pathogenic genes and clinical symptoms. Previous research has focused on mutated genes. This study was conducted to identify key molecular mechanisms and explore effective therapeutic targets.

METHODS

Myocardial tissue was harvested from patients with HCM (n = 3) or DCM (n = 4) during surgery. Hearts donated by healthy traffic accident victims were treated as controls (n = 4). Total proteins were extracted for liquid chromatography-tandem mass spectrometry. Differentially expressed proteins (DEPs) were annotated via GO and KEGG analyses. Selected distinguishing protein abundance was confirmed by western blotting.

RESULTS

Compared with the control group, there were 121 and 76 DEPs in the HCM and DCM groups, respectively. GO terms for these two comparisons are associated with contraction-related components and actin binding. Additionally, the most significantly upregulated and downregulated proteins were periostin and tropomyosin alpha-3 chain in both comparisons. Moreover, when comparing the HCM and DCM groups, we found 60 significant DEPs, and the GO and KEGG terms are related to the calcium signalling pathway. Expression of the calcium regulation-related protein peptidyl-prolyl cis-trans isomerase (FKBP1A) was significantly upregulated in multiple samples.

CONCLUSION

HCM and DCM have many mutual pathogenetic pathways. Calcium ion-related processes are among the most significant factors affecting disease development. For HCM and DCM, research on regulating linchpin protein expression or interfering with key calcium-related pathways may be more beneficial than genetic research.

Physiology of intracellular calcium buffering

Calcium signaling underlies much of physiology. Almost all the Ca2+ in the cytoplasm is bound to buffers, with typically only ∼1% being freely ionized at resting levels in most cells. Physiological Ca2+ buffers include small molecules and proteins, and experimentally Ca2+ indicators will also buffer calcium. The chemistry of interactions between Ca2+ and buffers determines the extent and speed of Ca2+ binding. The physiological effects of Ca2+ buffers are determined by the kinetics with which they bind Ca2+ and their mobility within the cell. The degree of buffering depends on factors such as the affinity for Ca2+, the Ca2+ concentration, and whether Ca2+ ions bind cooperatively. Buffering affects both the amplitude and time course of cytoplasmic Ca2+ signals as well as changes of Ca2+ concentration in organelles. It can also facilitate Ca2+ diffusion inside the cell. Ca2+ buffering affects synaptic transmission, muscle contraction, Ca2+ transport across epithelia, and the killing of bacteria. Saturation of buffers leads to synaptic facilitation and tetanic contraction in skeletal muscle and may play a role in inotropy in the heart. This review focuses on the link between buffer chemistry and function and how Ca2+ buffering affects normal physiology and the consequences of changes in disease. As well as summarizing what is known, we point out the many areas where further work is required.

Transcriptomic analysis the mechanisms of anti-osteoporosis of desert-living Cistanche herb in ovariectomized rats of postmenopausal osteoporosis

Desert-living Cistanche herb (DC), as a traditional Chinese medicine for tonifying kidney yang, is often used to treat postmenopausal osteoporosis (PMOP). Total phenylethanoid glycosides are instruction ingredients for discrimination and assay according to the China pharmacopoeia for DC. This research aimed to reveal the anti-osteoporosis mechanism of total phenylethanoid glycosides of DC (PGC) by transcriptomic analysis of ovariectomized rats. Serum levels of BGP were evaluated by ELISA, the bone weight was measured, and transmission electron microscopy was used to examine the ultrastructure of osteoblasts in rats. In addition, micro-CT was used to detect the bone volume (Tb.BS/BV), bone mineral density (Tb.BMD), and bone mineral content (Tb.BMC) in trabecular bone, and the ratio of cortical bone area to total area (Ct.ar/Tt.ar), and the level of bone mineral content (Ct.BMC) in cortical bone. Differential expressed genes (DEGs) after PGC treatment were analyzed by transcriptomics. Then, a bioinformatics analysis of DEGs was carried out through GO enrichment, KEGG enrichment, and selection of the nucleus gene through the protein-protein interaction network. Through qRT-PCR analysis, the DEGs were verified. The analysis results indicated that PGC increased the secretion of osteogenic markers, and ultrastructural characterization of osteoblasts and bone morphology were improved in ovariectomized rats. A total of 269 genes were differentially expressed, including 201 genes that were downregulated and 68 genes that were upregulated between the model group and the PGC group. Bioinformation analysis results prompt the conclusion that PGC could promote the bone metabolism by muscle cell development, myofibril assembly, etc. In addition, our study also found that PGC has a good effect on osteoporosis complicated with cardiomyopathy, and it also provided evidence for the correlation between sarcopenia and osteoporosis.

Case Report: Novel LIM domain-binding protein 3 (LDB3) mutations associated with hypertrophic cardiomyopathy family

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant cardiomyopathy, which is one of the most common reasons for cardiac arrest in children or adolescents. It is characterized by ventricular hypertrophy (usually left ventricle), small ventricular cavity, and reduced ventricular diastolic compliance found by echocardiography in the absence of abnormal load (such as hypertension or aortic stenosis). HCM is usually caused by mutations in genes encoding sarcomere or sarcomere-related genes. Whole exome sequencing (WES) is performed to identify probable causative genes. Through WES, we identified LIM domain-binding protein 3 (LDB3) mutations (R547Q and P323S) respectively in an 11-year-old HCM girl and a 6-year-old HCM boy. Neural network analyses showed that the LDB3 (R547Q and P323S) mutation decreased its protein stability, with confidence scores of -0.9211 and -0.8967. The STRUM server also confirmed that the mutation decreased its protein stability. Thus, LDB3 mutation may be associated with heritable HCM. To our knowledge, this is the first time to report LDB3 heterozygous variants (R547Q and P323S) responsible for heritable HCM.

Computational and biophysical determination of pathogenicity of variants of unknown significance in cardiac thin filament

Point mutations within sarcomeric proteins have been associated with altered function and cardiomyopathy development. Difficulties remain, however, in establishing the pathogenic potential of individual mutations, often limiting the use of genotype in management of affected families. To directly address this challenge, we utilized our all-atom computational model of the human full cardiac thin filament (CTF) to predict how sequence substitutions in CTF proteins might affect structure and dynamics on an atomistic level. Utilizing molecular dynamics calculations, we simulated 21 well-defined genetic pathogenic cardiac troponin T and tropomyosin variants to establish a baseline of pathogenic changes induced in computational observables. Computational results were verified via differential scanning calorimetry on a subset of variants to develop an experimental correlation. Calculations were performed on 9 independent variants of unknown significance (VUS), and results were compared with pathogenic variants to identify high-resolution pathogenic signatures. Results for VUS were compared with the baseline set to determine induced structural and dynamic changes, and potential variant reclassifications were proposed. This unbiased, high-resolution computational methodology can provide unique structural and dynamic information that can be incorporated into existing analyses to facilitate classification both for de novo variants and those where established approaches have provided conflicting information.

Dilated Cardiomyopathy due to the Novel MT-CYB Missense Mutation m.14757T>C

Mitochondrial DNA (mtDNA) mutations frequently manifest with multisystem disease, including cardiomyopathy (CM). Various studies described mutations in protein-encoding mtDNA genes, such as cytochrome-b, manifesting with CM. A detailed clinical, biochemical, and molecular genetic analysis was performed in a 40-year-old male with dilated CM (DCM) to detect the underlying mtDNA defect. Muscle biopsy showed complex-III deficiency, and sequencing of the cytochrome-b gene revealed the pathogenic variant m.14757T>C in MT-CYB, resulting in the replacement of the hydrophobic methionine by the polar threonine (M4T). By application of the PolyPhen algorithm the variant was predicted as pathogenic. The mutation was not found in 100 healthy controls and never reported as a neutral polymorphism despite extensive sequencing of the cytochrome-b gene in 2,704 normal healthy controls from different ethnic backgrounds. In conclusion, the novel variant m.14757T>C in MT-CYB is associated with DCM suggesting a pathophysiologic role of the variant in the development of DCM.

Cardiomyocyte Dysfunction in Inherited Cardiomyopathies

Inherited cardiomyopathies form a heterogenous group of disorders that affect the structure and function of the heart. Defects in the genes encoding sarcomeric proteins are associated with various perturbations that induce contractile dysfunction and promote disease development. In this review we aimed to outline the functional consequences of the major inherited cardiomyopathies in terms of myocardial contraction and kinetics, and to highlight the structural and functional alterations in some sarcomeric variants that have been demonstrated to be involved in the pathogenesis of the inherited cardiomyopathies. A particular focus was made on mutation-induced alterations in cardiomyocyte mechanics. Since no disease-specific treatments for familial cardiomyopathies exist, several novel agents have been developed to modulate sarcomere contractility. Understanding the molecular basis of the disease opens new avenues for the development of new therapies. Furthermore, the earlier the awareness of the genetic defect, the better the clinical prognostication would be for patients and the better the prevention of development of the disease.

Circulating Levels of MicroRNAs in Hypertrophic Cardiomyopathy: The Relationship With Left Ventricular Hypertrophy, Left Atrial Dilatation and Ventricular Depolarisation-Repolarisation Parameters

BACKGROUND

MicroRNAs are small, endogenous, non-coding RNAs that regulate the expression of many genes. It has recently been shown that circulating microRNAs may be biomarkers of hypertrophy and fibrosis in patients with hypertrophic cardiomyopathy (HCM).

OBJECTIVE

To determine whether circulating levels of microRNAs involved in HCM are associated with electrocardiographic and echocardiographic parameters.

METHODS

This study enrolled 20 patients with familial HCM and 20 blood donors. Peripheral serum levels of miR-29a-3p, miR-199a-5p and miR-451a were assessed by quantitative real-time polymerase chain reaction and compared with levels in the control group. Whether circulating levels of miRNAs in HCM patients correlated with electrocardiographic and echocardiographic parameters was also assessed.

RESULTS

Median circulating levels of miR-29a and miR-451a were significantly higher in HCM than the control group. Median miR-199a levels did not differ between groups. However, circulating levels of miR-199a negatively correlated with corrected QT duration (Bazett formula). Median miR-29a levels positively correlated with QRS duration. In addition, circulating levels of miR-29a correlated with maximal wall thickness, left ventricular mass index and left atrial volume index.

CONCLUSIONS

The data suggested that serum levels of miR-29a and miR-451a were significantly increased in HCM patients. As the circulating level of miR-29a correlated with QRS duration, left ventricular hypertrophy and left atrial dilatation, the serum miR-199a level negatively correlated with corrected QT duration. These miRNAs may be seen as potential biomarkers for further research in HCM pathophysiology.

Uncovering Inherited Cardiomyopathy With Human Induced Pluripotent Stem Cells

In the past decades, researchers discovered the contribution of genetic defects to the pathogenesis of primary cardiomyopathy and tried to explain the pathogenesis of these diseases by establishing a variety of disease models. Although human heart tissues and primary cardiomyocytes have advantages in modeling human heart diseases, they are difficult to obtain and culture in vitro. Defects developed in genetically modified animal models are notably different from human diseases at the molecular level. The advent of human induced pluripotent stem cells (hiPSCs) provides an unprecedented opportunity to further investigate the pathogenic mechanisms of inherited cardiomyopathies in vitro using patient-specific hiPSC-derived cardiomyocytes. In this review, we will make a summary of recent advances in in vitro inherited cardiomyopathy modeling using hiPSCs.

Nitric Oxide and Mechano-Electrical Transduction in Cardiomyocytes

The ability§ of the heart to adapt to changes in the mechanical environment is critical for normal cardiac physiology. The role of nitric oxide is increasingly recognized as a mediator of mechanical signaling. Produced in the heart by nitric oxide synthases, nitric oxide affects almost all mechano-transduction pathways within the cardiomyocyte, with roles mediating mechano-sensing, mechano-electric feedback (via modulation of ion channel activity), and calcium handling. As more precise experimental techniques for applying mechanical stresses to cells are developed, the role of these forces in cardiomyocyte function can be further understood. Furthermore, specific inhibitors of different nitric oxide synthase isoforms are now available to elucidate the role of these enzymes in mediating mechano-electrical signaling. Understanding of the links between nitric oxide production and mechano-electrical signaling is incomplete, particularly whether mechanically sensitive ion channels are regulated by nitric oxide, and how this affects the cardiac action potential. This is of particular relevance to conditions such as atrial fibrillation and heart failure, in which nitric oxide production is reduced. Dysfunction of the nitric oxide/mechano-electrical signaling pathways are likely to be a feature of cardiac pathology (e.g., atrial fibrillation, cardiomyopathy, and heart failure) and a better understanding of the importance of nitric oxide signaling and its links to mechanical regulation of heart function may advance our understanding of these conditions.

Novel frameshift variant in MYL2 reveals molecular differences between dominant and recessive forms of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is characterized by thickening of the ventricular muscle without dilation and is often associated with dominant pathogenic variants in cardiac sarcomeric protein genes. Here, we report a family with two infants diagnosed with infantile-onset HCM and mitral valve dysplasia that led to death before one year of age. Using exome sequencing, we discovered that one of the affected children had a homozygous frameshift variant in Myosin light chain 2 (MYL2:NM_000432.3:c.431_432delCT: p.Pro144Argfs*57;MYL2-fs), which alters the last 20 amino acids of the protein and is predicted to impact the most C-terminal of the three EF-hand domains in MYL2. The parents are unaffected heterozygous carriers of the variant and the variant is absent in control cohorts from gnomAD. The absence of the phenotype in carriers and the infantile presentation of severe HCM is in contrast to HCM associated with dominant MYL2 variants. Immunohistochemical analysis of the ventricular muscle of the deceased patient with the MYL2-fs variant showed a marked reduction of MYL2 expression compared to an unaffected control. In vitro overexpression studies further indicate that the MYL2-fs variant is actively degraded. In contrast, an HCM-associated missense variant (MYL2:p.Gly162Arg) and three other MYL2 stop-gain variants (p.E22*, p.K62*, p.E97*) that result in loss of the EF domains are stably expressed but show impaired localization. The degradation of the MYL2-fs can be rescued by inhibiting the cell’s proteasome function supporting a post-translational effect of the variant. In vivo rescue experiments with a Drosophila MYL2-homolog (Mlc2) knockdown model indicate that neither the MYL2-fs nor the MYL2:p.Gly162Arg variant supports normal cardiac function. The tools that we have generated provide a rapid screening platform for functional assessment of variants of unknown significance in MYL2. Our study supports an autosomal recessive model of inheritance for MYL2 loss-of-function variants in infantile HCM and highlights the variant-specific molecular differences found in MYL2-associated cardiomyopathy.

We report a novel frameshift variant in MYL2 that is associated with a severe form of infantile-onset hypertrophic cardiomyopathy. The impact of the variant is only observed in the recessive form of the disease found in the proband and not in the parents who are carriers of the variant. This contrasts with other dominant variants in MYL2 that are associated with cardiomyopathies. We compared the stability of this variant to that of other cardiomyopathy associated MYL2 variants and found molecular differences that correlated with disease pathology. We also show different protein domain requirements for stability and localization of MYL2 in cardiomyocytes. Furthermore, we used a fly model to demonstrate functional deficits due to the variant in the developing heart. Overall, our study shows a molecular mechanism by which loss-of-function variants in MYL2 are recessive while missense variants are dominant. We highlight the use of exome sequencing and functional testing to assist in the diagnosis of rare forms of disease where pathogenicity of the variant is not obvious. The new tools we developed for in vitro functional study and the fly fluorescent reporter analysis will permit rapid analysis of MYL2 variants of unknown significance.

Production of TRPV2-targeting functional antibody ameliorating dilated cardiomyopathy and muscular dystrophy in animal models

Abnormal Ca²⁺ handling is essential in the pathophysiology of degenerative muscle disorders, such as dilated cardiomyopathy (DCM) and muscular dystrophy (MD). Transient receptor potential cation channel, subfamily V, member 2 (TRPV2) is a candidate for Ca²⁺ entry and a potential therapeutic target for degenerative muscle disorders, there are few specific inhibitors for TRPV2. In this study, we produced a monoclonal antibody (designated mAb88-2) and two polyclonal antibodies (pAb591 and pAb592) that selectively recognize TRPV2 from the outside of cells and interact with the turret region of the pore-forming outer gate. These antibodies inhibited Ca²⁺ influx via TRPV2 in cultured cells and substantially reduced TRPV2 in the plasma membrane via cellular internalization. We evaluated the therapeutic efficacy of the functional antibody in δ-sarcoglycan-deficient hamster (J2N-k) models of DCM and MD and in the 4C30 DCM model of murine heart failure. The intraperitoneal administration of the functional antibody (0.5 mg/kg) for 2 weeks (once a week) prevented the progression of cardiac dysfunction, as evaluated by echocardiography and histological staining, and improved the abnormal Ca²⁺ handling (high diastolic Ca²⁺ level and small Ca²⁺ transient peak) in cardiomyocytes isolated from J2N-k hamsters and prevented skeletal muscle damage. Further, the antibody effectively prevented heart failure in the 4C30 mouse model with end-stage DCM. Interestingly, endogenous TRPV2 that accumulated in the cardiac and skeletal muscle sarcolemma disappeared upon antibody administration. Thus, the newly produced antibodies are capable of ameliorating DCM and MD by promoting the cellular internalization of TRPV2; antibodies specific to human TRPV2 may substantially improve the treatment of patients with degenerative muscle diseases.

Genetics and pharmacogenetics in the diagnosis and therapy of cardiovascular diseases

Cardiovascular diseases are the main cause of death worldwide. The ability to accurately define individual susceptibility to these disorders is therefore of strategic importance. Linkage analysis and genome-wide association studies have been useful for the identification of genes related to cardiovascular diseases. The identification of variants predisposing to cardiovascular diseases contributes to the risk profile and the possibility of tailored preventive or therapeutic strategies. Molecular genetics and pharmacogenetics are playing an increasingly important role in the correct clinical management of patients. For instance, genetic testing can identify variants that influence how patients metabolize medications, making it possible to prescribe personalized, safer and more efficient treatments, reducing medical costs and improving clinical outcomes. In the near future we can expect a great increment in information and genetic testing, which should be acknowledged as a true branch of diagnostics in cardiology, like hemodynamics and electrophysiology. In this review we summarize the genetics and pharmacogenetics of the main cardiovascular diseases, showing the role played by genetic information in the identification of cardiovascular risk factors and in the diagnosis and therapy of these conditions. (www.actabiomedica.it)

MLP-deficient human pluripotent stem cell derived cardiomyocytes develop hypertrophic cardiomyopathy and heart failure phenotypes due to abnormal calcium handling

Muscle LIM protein (MLP, CSRP3) is a key regulator of striated muscle function, and its mutations can lead to both hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) in patients. However, due to lack of human models, mechanisms underlining the pathogenesis of MLP defects remain unclear. In this study, we generated a knockout MLP/CSRP3 human embryonic stem cell (hESC) H9 cell line using CRISPR/Cas9 mediated gene disruption. CSRP3 disruption had no impact on the cardiac differentiation of H9 cells and led to confirmed MLP deficiency in hESC-derived cardiomyocytes (ESC-CMs). MLP-deficient hESC-CMs were found to develop phenotypic features of HCM early after differentiation, such as enlarged cell size, multinucleation, and disorganized sarcomeric ultrastructure. Cellular phenotypes of MLP-deficient hESC-CMs subsequently progressed to mimic heart failure (HF) by 30 days post differentiation, including exhibiting mitochondrial damage, increased ROS generation, and impaired Ca²⁺ handling. Pharmaceutical treatment with beta agonist, such as isoproterenol, was found to accelerate the manifestation of HCM and HF, consistent with transgenic animal models of MLP deficiency. Furthermore, restoration of Ca²⁺ homeostasis by verapamil prevented the development of HCM and HF phenotypes, suggesting that elevated intracellular Ca²⁺ concentration is a central mechanism for pathogenesis of MLP deficiency. In summary, MLP-deficient hESC-CMs recapitulate the pathogenesis of HCM and its progression toward HF, providing an important human model for investigation of CSRP3/MLP-associated disease pathogenesis. More importantly, correction of the autonomous dysfunction of Ca²⁺ handling was found to be an effective method for treating the in vitro development of cardiomyopathy disease phenotype.

Role of circular RNAs in cardiovascular diseases

IMPACT STATEMENT

Circular RNAs are important regulators of multiple biological processes such as organogenesis and oncogenesis. Although the bulk of concerning studies focused on revealing their diversified roles in various types of cancers, reports began to accumulate in cardiovascular field these days. We summarize circular RNAs implicated in cardiovascular diseases, aiming to highlight the advances in the knowledge of such diseases and their potential of being promising target for diagnosis and therapy.

Over-expression of a cardiac-specific human dopamine D5 receptor mutation in mice causes a dilated cardiomyopathy through ROS over-generation by NADPH oxidase activation and Nrf2 degradation

Dilated cardiomyopathy (DCM) is a severe disorder caused by medications or genetic mutations. D₅ dopamine receptor (D5R) gene knockout (D5^-/-) mice have cardiac hypertrophy and high blood pressure. To investigate the role and mechanism by which the D5R regulates cardiac function, we generated cardiac-specific human D5R F173L(hD5^F173L-TG) and cardiac-specific human D5R wild-type (hD5^WT-TG) transgenic mice, and H9c2 cells stably expressing hD5^F173L and hD5^WT. We found that cardiac-specific hD5^F173L-TG mice, relative to hD5^WT-TG mice, presented with DCM and increased cardiac expression of cardiac injury markers, NADPH oxidase activity, Nrf2 degradation, and activated ERK1/2/JNK pathway. H9c2-hD5^F173L cells also had an increase in NADPH oxidase activity, Nrf2 degradation, and phospho-JNK (p-JNK) expression. A Nrf2 inhibitor also increased p-JNK expression in H9c2-hD5^F173L cells but not in H9c2-hD5^WT cells. We suggest that the D5R may play an important role in the preservation of normal heart function by inhibiting the production of reactive oxygen species, via inhibition of NADPH oxidase, Nrf2 degradation, and ERK1/2/JNK pathways.

Exploring the Crosstalk Between LMNA and Splicing Machinery Gene Mutations in Dilated Cardiomyopathy

Mutations in the LMNA gene, which encodes for the nuclear lamina proteins lamins A and C, are responsible for a diverse group of diseases known as laminopathies. One type of laminopathy is Dilated Cardiomyopathy (DCM), a heart muscle disease characterized by dilation of the left ventricle and impaired systolic function, often leading to heart failure and sudden cardiac death. LMNA is the second most commonly mutated gene in DCM. In addition to LMNA, mutations in more than 60 genes have been associated with DCM. The DCM-associated genes encode a variety of proteins including transcription factors, cytoskeletal, Ca2+-regulating, ion-channel, desmosomal, sarcomeric, and nuclear-membrane proteins. Another important category among DCM-causing genes emerged upon the identification of DCM-causing mutations in RNA binding motif protein 20 (RBM20), an alternative splicing factor that is chiefly expressed in the heart. In addition to RBM20, several essential splicing factors were validated, by employing mouse knock out models, to be embryonically lethal due to aberrant cardiogenesis. Furthermore, heart-specific deletion of some of these splicing factors was found to result in aberrant splicing of their targets and DCM development. In addition to splicing alterations, advances in next generation sequencing highlighted the association between splice-site mutations in several genes and DCM. This review summarizes LMNA mutations and splicing alterations in DCM and discusses how the interaction between LMNA and splicing regulators could possibly explain DCM disease mechanisms.

Novel inhibitor candidates of TRPV2 prevent damage of dystrophic myocytes and ameliorate against dilated cardiomyopathy in a hamster model

Transient receptor potential cation channel, subfamily V, member 2 (TRPV2) is a principal candidate for abnormal Ca²⁺-entry pathways, which is a potential target for therapy of muscular dystrophy and cardiomyopathy. Here, an in silico drug screening and the following cell-based screening to measure the TRPV2 activation were carried out in HEK293 cells expressing TRPV2 using lead compounds (tranilast or SKF96365) and off-patent drug stocks. We identified 4 chemical compounds containing amino-benzoyl groups and 1 compound (lumin) containing an ethylquinolinium group as candidate TRPV2 inhibitors. Three of these compounds inhibited Ca²⁺ entry through both mouse and human TRPV2, with IC₅₀ of less than 10 μM, but had no apparent effect on other members of TRP family such as TRPV1 and TRPC1. Particularly, lumin inhibited agonist-induced TRPV2 channel activity at a low dose. These compounds inhibited abnormally increased Ca²⁺ influx and prevented stretch-induced skeletal muscle damage in cultured myocytes from dystrophic hamsters (J2N-k). Further, they ameliorated cardiac dysfunction, and prevented disease progression in vivo in the same J2N-k hamsters developing dilated cardiomyopathy as well as muscular dystrophy. The identified compounds described here are available as experimental tools and represent potential treatments for patients with cardiomyopathy and muscular dystrophy.

Troponin through the looking-glass: emerging roles beyond regulation of striated muscle contraction

Troponin is a heterotrimeric Ca²⁺-binding protein that has a well-established role in regulating striated muscle contraction. However, mounting evidence points to novel cellular functions of troponin, with profound implications in cancer, cardiomyopathy pathogenesis and skeletal muscle aging. Here, we highlight the non-canonical roles and aberrant expression patterns of troponin beyond the sarcomeric milieu. Utilizing bioinformatics tools and online databases, we also provide pathway, subcellular localization, and protein-protein/DNA interaction analyses that support a role for troponin in multiple subcellular compartments. This emerging knowledge challenges the conventional view of troponin as a sarcomere-specific protein exclusively involved in muscle contraction and may transform the way we think about sarcomeric proteins, particularly in the context of human disease and aging.

Voluntary Exercise Improves Cardiac Function and Prevents Cardiac Remodeling in a Mouse Model of Dilated Cardiomyopathy

Objective: Despite the indubitable beneficial effect of exercise to prevent of cardiovascular diseases, there is still a lack of studies investigating the impact of exercise in non-ischemic dilated cardiomyopathy. Here, we investigated the impact of voluntary exercise on cardiac function in a mouse model of non-ischemic dilated cardiomyopathy (αMHC-MerCreMer:Sf/Sf), induced by cardiac-specific inactivation of the Serum Response Factor.

Materials and Methods: Seven days after tamoxifen injection, 20 αMHC-MerCreMer:Sf/Sf mice were assigned to sedentary (n = 8) and exercise (n = 12) groups. Seven additional αMHC-MerCreMer:Sf/Sf mice without tamoxifen injection were used as control. The exercise group performed 4 weeks of voluntary running on wheel (1.8 ± 0.12 km/day). Cardiac function, myocardial fibrosis, and mitochondrial energetic pathways were then blindly assessed.

Results: Exercised mice exhibited a smaller decrease of left ventricular (LV) fractional shortening and ejection fraction compared to control mice. This was associated with a lower degree of LV remodeling in exercised mice, as shown by a lower LV end-systolic intrerventricular septal and posterior wall thickness decrease from baseline values compared to sedentary mice. Moreover, exercised mice displayed a reduced gene expression of atrial and brain natriuretic factors. These benefits were associated by a reduced level of myocardial fibrosis. In addition, exercised mice exhibited a higher mitochondrial aconitase, voltage-dependent anion-selective channel 1 and PPAR gamma coactivators-1 alpha proteins levels suggesting that the increase of mitochondrial biogenesis and/or metabolism slowed the progression of dilated cardiomyopathy in exercised animals.

Conclusions: In conclusion, our results support the role of voluntary exercise to improve outcomes in non-ischemic dilated heart failure (HF) and also support its potential for a routine clinical use in the future.

Cardiac vagal control in a knock-in mouse model of dilated cardiomyopathy with a troponin mutation

The aim of this study was to evaluate cardiac vagal nerve activity and identify the abnormality of cardiac vagal control in heart failure caused by dilated cardiomyopathy (DCM) using a knock-in mouse model with a ΔK210 mutation in the cardiac troponin T gene. The effects of electrical stimulation of the cervical vagal nerve at 5 and 10Hz (peripheral vagal control) and α₂-adrennoceptor stimulation by intravenous medetomidine at 0.1mg/kg (central vagal control) were examined in wild-type (WT) mice and DCM mice. Microdialysis technique was applied to the left ventricular myocardium of anesthetized mice and myocardial interstitial acetylcholine (ACh) levels were measured by HPLC as an index of ACh release from cardiac vagal nerve endings. Electrical vagal nerve stimulation increased cardiac interval and myocardial interstitial ACh level in both WT and DCM mice, and these responses did not differ between WT and DCM mice. In contrast, intravenous medetomidine increased cardiac interval and myocardial interstitial ACh level in both WT and DCM mice, but the responses of cardiac interval and myocardial interstitial ACh level were significantly suppressed in DCM mice compared to WT mice. Medetomidine did not affect the myocardial interstitial ACh response induced by vagal nerve stimulation in WT mice. In this mouse model of DCM, peripheral vagal control including ACh release from vagal nerve endings and the postsynaptic response of pacemaker cells was preserved, but central vagal control through α₂-adrenoceptors was impaired.

Cardiac inflammation in genetic dilated cardiomyopathy caused by MYBPC3 mutation

Cardiomyopathies are a leading cause of heart failure and are often caused by mutations in sarcomeric genes, resulting in contractile dysfunction and cellular damage. This may stimulate the production of a robust proinflammatory response. To determine whether myocardial inflammation is associated with cardiac dysfunction in dilated cardiomyopathy (DCM) caused by MYBPC3 mutation, we used the well-characterized cMyBP-C(t/t) mouse model of DCM at 3months of age. Compared to wild type (WT) mice, DCM mice exhibited significantly decreased fractional shortening (36.4±2% vs. 15.5±1.0%, p<0.0001) and significantly increased spleen weight (5.3±0.3 vs. 7.2±0.4mg/mm, p=0.002). Intriguingly, flow cytometry analysis revealed a significant increase in total (CD45+CD11b+Ly6C-MHCII+F480+) macrophages (6.5±1.4% vs. 14.8±1.4%, p=0.002) and classically activated (CD45+CD11b+Ly6C-MHCII+F480+CD206-) proinflammatory (M1) macrophages (3.4±0.8% vs. 10.3±1.2%, p=0.0009) in DCM hearts as compared with WT hearts. These results were further confirmed by immunofluorescence analysis of heart tissue sections. Splenic red pulp (CD11b+Ly6C+MHCIIlowF480hi) macrophages were significantly elevated (1.3±0.1% vs. 2.4±0.1%, p=0.0001) in DCM compared to WT animals. Serum cytokine analysis in DCM animals exhibited a significant increase (0.65±0.2 vs. 2.175±0.5pg/mL, p=0.02) in interleukin (IL)-6 compared to WT animals. Furthermore, RNA-seq analysis revealed the upregulation of inflammatory pathways in the DCM hearts. Together, these data indicate a robust proinflammatory response in DCM hearts, likely in response to cellular damage triggered by MYBPC3 mutation and resultant contractile dysfunction.

The Muscle-Bound Heart

Hypertrophic cardiomyopathy (HCM) is a familial cardiac disease manifested in a wide phenotype and diverse genotype and, thus, presenting unpredictable risks mainly on young adults. Extensive studies are being conducted to categorize patients and link phenotype with genotype for a better management and control of the disease with all its complications. Because the full mechanisms behind HCM are still not revealed, therapeutics are not definitive. Further research is to be conducted for the generation of a complete picture and directed therapy for HCM.

Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility

Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.

An historical approach to the diagnostic biomarkers of acute coronary syndrome

Suspected acute myocardial infarction (AMI) is one of the leading causes of admission to the emergency departments in Western countries but also an increasing cause in many other nations. The diagnosis of AMI involves the evaluation of clinical signs and symptoms, electrocardiographic assessment, and measurement of cardiac circulating biomarkers. In the last sixty years, the use of laboratory markers has changed considerably. Early biomarkers assessment has entailed testing for total enzyme activity of aspartate aminotransferase (AST), lactate dehydrogenase (LDH) and creatine kinase (CK). Advances in electrophoresis allowed the identification of more cardio-specific isoenzymes of both CK and LDH, thus leading to the introduction of the CK-MB and LDH-1 activity assays. Soon thereafter, the development of immunoassays, as well as technical advances in automation, allowed the measurements of the CK-MB in mass rather than in activity and myoglobin. Currently, cardiac troponins have the highest sensitivity and specificity for myocardial necrosis and represent the biochemical gold standard for diagnosing AMI. This review provides a chronology of the major events which marked the evolution of cardiac biomarkers testing and the development of the relative assays from the first introduction of AST in the 1950s to the last high sensitivity troponin immunoassays in the 2010s.

A Restrictive Cardiomyopathy Mutation in an Invariant Proline at the Myosin Head/Rod Junction Enhances Head Flexibility and Function, Yielding Muscle Defects in Drosophila

An "invariant proline" separates the myosin S1 head from its S2 tail and is proposed to be critical for orienting S1 during its interaction with actin, a process that leads to muscle contraction. Mutation of the invariant proline to leucine (P838L) caused dominant restrictive cardiomyopathy in a pediatric patient (Karam et al., Congenit. Heart Dis. 3:138-43, 2008). Here, we use Drosophila melanogaster to model this mutation and dissect its effects on the biochemical and biophysical properties of myosin, as well as on the structure and physiology of skeletal and cardiac muscles. P838L mutant myosin isolated from indirect flight muscles of transgenic Drosophila showed elevated ATPase and actin sliding velocity in vitro. Furthermore, the mutant heads exhibited increased rotational flexibility, and there was an increase in the average angle between the two heads. Indirect flight muscle myofibril assembly was minimally affected in mutant homozygotes, and isolated fibers displayed normal mechanical properties. However, myofibrils degraded during aging, correlating with reduced flight abilities. In contrast, hearts from homozygotes and heterozygotes showed normal morphology, myofibrillar arrays, and contractile parameters. When P838L was placed in trans to Mhc(5), an allele known to cause cardiac restriction in flies, it did not yield the constricted phenotype. Overall, our studies suggest that increased rotational flexibility of myosin S1 enhances myosin ATPase and actin sliding. Moreover, instability of P838L myofibrils leads to decreased function during aging of Drosophila skeletal muscle, but not cardiac muscle, despite the strong evolutionary conservation of the P838 residue.

A Tension-Based Model Distinguishes Hypertrophic versus Dilated Cardiomyopathy

The heart either hypertrophies or dilates in response to familial mutations in genes encoding sarcomeric proteins, which are responsible for contraction and pumping. These mutations typically alter calcium-dependent tension generation within the sarcomeres, but how this translates into the spectrum of hypertrophic versus dilated cardiomyopathy is unknown. By generating a series of cardiac-specific mouse models that permit the systematic tuning of sarcomeric tension generation and calcium fluxing, we identify a significant relationship between the magnitude of tension developed over time and heart growth. When formulated into a computational model, the integral of myofilament tension development predicts hypertrophic and dilated cardiomyopathies in mice associated with essentially any sarcomeric gene mutations, but also accurately predicts human cardiac phenotypes from data generated in induced-pluripotent-stem-cell-derived myocytes from familial cardiomyopathy patients. This tension-based model also has the potential to inform pharmacologic treatment options in cardiomyopathy patients.

Next Generation Sequencing and Linkage Analysis for the Molecular Diagnosis of a Novel Overlapping Syndrome Characterized by Hypertrophic Cardiomyopathy and Typical Electrical Instability of Brugada Syndrome

BACKGROUND

Familial hypertrophic cardiomyopathy (HCM) is an autosomal dominant inherited disorder; mutations in at least 20 genes have been associated. Brugada syndrome (BrS) is an autosomal dominant inherited disorder caused by mutations mainly in theSCN5Agene. A new clinical entity that consists of HCM, typical electrical instability of BrS and sudden death (SD), is described.

METHODS AND RESULTS

The family was constituted by 7 members, 4 of who presented clinical features of HCM and electrical instability of BrS. The clinical presentation of proband was ventricular fibrillation. All members were clinically evaluated by physical examination, 12-lead electrocardiography, 2-dimensional echocardiography, stress test, electrocardiogram Holter, flecainide test, and electrophysiological study. An integrated linkage analysis and next generation sequencing (NGS) approach was used to identify the causative mutation. Linkage with the α-tropomyosin (TPM1) gene on chromosome 15q22 was identified. The NGS study identified a missense mutation within theTPM1gene (c.574G>A; p.E192K), exactly located in a binding domain with polycystin-2 protein. No other pathogenic mutations were identified.

CONCLUSIONS

This is the first report of an association between HCM and BrS, and the first to use a combined approach of linkage and NGS to identify a causative mutation in SD. The present study expands the clinical spectrum of disorders associated with theTPM1gene and may be useful to report novel mechanisms of electrical instability in HCM and BrS.

Atomic resolution probe for allostery in the regulatory thin filament

Calcium binding and dissociation within the cardiac thin filament (CTF) is a fundamental regulator of normal contraction and relaxation. Although the disruption of this complex, allosterically mediated process has long been implicated in human disease, the precise atomic-level mechanisms remain opaque, greatly hampering the development of novel targeted therapies. To address this question, we used a fully atomistic CTF model to test both Ca(2+) binding strength and the energy required to remove Ca(2+) from the N-lobe binding site in WT and mutant troponin complexes that have been linked to genetic cardiomyopathies. This computational approach is combined with measurements of in vitro Ca(2+) dissociation rates in fully reconstituted WT and cardiac troponin T R92L and R92W thin filaments. These human disease mutations represent known substitutions at the same residue, reside at a significant distance from the calcium binding site in cardiac troponin C, and do not affect either the binding pocket affinity or EF-hand structure of the binding domain. Both have been shown to have significantly different effects on cardiac function in vivo. We now show that these mutations independently alter the interaction between the Ca(2+) ion and cardiac troponin I subunit. This interaction is a previously unidentified mechanism, in which mutations in one protein of a complex indirectly affect a third via structural and dynamic changes in a second to yield a pathogenic change in thin filament function that results in mutation-specific disease states. We can now provide atom-level insight that is potentially highly actionable in drug design.

Results of comprehensive diagnostic work-up in 'idiopathic' dilated cardiomyopathy

Objective

Dilated cardiomyopathy (DCM) is characterised by left ventricular dilation and dysfunction not caused by coronary disease, valvular disease or hypertension. Owing to the considerable aetiological and prognostic heterogeneity in DCM, an extensive diagnostic work-up is recommended. We aimed to assess the value of diagnostic testing beyond careful physical examination, blood tests, echocardiography and coronary angiography.

Methods

From October 2008 to November 2012, we prospectively recruited 102 patients referred to our tertiary care hospital with a diagnosis of ‘idiopathic’ DCM based on patient history, physical examination, routine blood tests, echocardiography and coronary angiography. Extended work-up included cardiac MRI, exercise testing, right-sided catheterisation with biopsies, 24 h ECG and genetic testing.

Results

In 15 patients (15%), a diagnosis other than ‘idiopathic’ DCM was made based on additional tests. In 10 patients (10%), a possibly disease-causing mutation was detected. 2 patients were found to have non-compaction cardiomyopathy based on MRI findings; 2 patients had systemic inflammatory disease with cardiac involvement; and in 1 patient, cardiac amyloidosis was diagnosed by endomyocardial biopsy. Only in 5 cases did the results of the extended work-up have direct therapeutic consequences.

Conclusions

In patients with DCM, in whom patient history and routine work-up carry no clues to the aetiology, the diagnostic and therapeutic yield of extensive additional testing is modest.

MicroRNAs Based Therapy of Hypertrophic Cardiomyopathy: The Road Traveled So Far

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease characterized by variable expressivity, age penetrance, and a high heterogeneity. The transcriptional profile (miRNAs, mRNAs), epigenetic modifications, and posttranslational modifications seem to be highly relevant for the onset of the disease. miRNAs, small noncoding RNAs with 22 nucleotides, have been implicated in the regulation of cardiomyocyte function, being differentially expressed in several heart diseases, including HCM. Moreover, a different miRNA expression profile in the various stages of HCM development is also observed. This review summarizes the current knowledge of the profile of miRNAs characteristic of asymptomatic to overt HCM patients, discussing alongside their potential use for diagnosis and therapy. Indeed, the stability and specificity of miRNAs make them suitable targets for use as biomarkers for diagnosis and prognosis and as therapeutical targets.

Mechanical aberrations in hypetrophic cardiomyopathy: emerging concepts

Hypertrophic cardiomyopathy is the most common monogenic disorder in cardiology. Despite important advances in understanding disease pathogenesis, it is not clear how flaws in individual sarcomere components are responsible for the observed phenotype. The aim of this article is to provide a brief interpretative analysis of some currently proposed pathophysiological mechanisms of hypertrophic cardiomyopathy, with a special emphasis on alterations in the cardiac mechanical properties.

Genetic manipulation of cardiac ageing

Ageing in humans is associated with a significant increase in the prevalence of cardiovascular disease. We still do not fully understand the molecular mechanisms underpinning this correlation. However, a number of insights into which genes control cardiac ageing have come from studying hearts of the fruit fly, Drosophila melanogaster. The fly's simple heart tube has similar molecular structure and basic physiology to the human heart. Also, both fly and human hearts experience significant age-related morphological and functional decline. Studies on the fly heart have highlighted the involvement of key nutrient sensing, ion channel and sarcomeric genes in cardiac ageing. Many of these genes have also been implicated in ageing of the mammalian heart. Genes that increase oxidative stress, or are linked to cardiac hypertrophy or neurodegenerative diseases in mammals also affect cardiac ageing in the fruit fly. Moreover, fly studies have demonstrated the potential of exercise and statins to treat age-related cardiac disease. These results show the value of Drosophila as a model to discover the genetic causes of human cardiac ageing.

SERCA2 Haploinsufficiency in a Mouse Model of Darier Disease Causes a Selective Predisposition to Heart Failure

Null mutations in one copy of ATP2A2, the gene encoding sarco/endoplasmic reticulum Ca(2+)-ATPase isoform 2 (SERCA2), cause Darier disease in humans, a skin condition involving keratinocytes. Cardiac function appears to be unimpaired in Darier disease patients, with no evidence that SERCA2 haploinsufficiency itself causes heart disease. However, SERCA2 deficiency is widely considered a contributing factor in heart failure. We therefore analyzed Atp2a2 heterozygous mice to determine whether SERCA2 haploinsufficiency can exacerbate specific heart disease conditions. Despite reduced SERCA2a levels in heart, Atp2a2 heterozygous mice resembled humans in exhibiting normal cardiac physiology. When subjected to hypothyroidism or crossed with a transgenic model of reduced myofibrillar Ca(2+)-sensitivity, SERCA2 deficiency caused no enhancement of the disease state. However, when combined with a transgenic model of increased myofibrillar Ca(2+)-sensitivity, SERCA2 haploinsufficiency caused rapid onset of hypertrophy, decompensation, and death. These effects were associated with reduced expression of the antiapoptotic Hax1, increased levels of the proapoptotic genes Chop and Casp12, and evidence of perturbations in energy metabolism. These data reveal myofibrillar Ca(2+)-sensitivity to be an important determinant of the cardiac effects of SERCA2 haploinsufficiency and raise the possibility that Darier disease patients are more susceptible to heart failure under certain conditions.

GENETIC CAUSES OF DILATED CARDIOMYOPATHY

Dilated cardiomyopathy is a disease of the myocardium characterized by left ventricular dilatation and/or dysfunction, affecting both adult and pediatric populations. Almost half of cases are genetically determined with an autosomal pattern of inheritance. Up to 40 genes have been identified affecting proteins of a wide variety of cellular structures such as the sarcomere, the nuclear envelope, the cytoskeleton, the sarcolemma and the intercellular junction. Novel gene mutations have been recently identified thanks to advances in next-generation sequencing technologies. Genetic screening is an essential tool for early diagnosis, risk assessment, prognostic stratification and, possibly, adoption of primary preventive measures in affected patients and their asymptomatic relatives. The purpose of this article is to review the genetic basis of DCM, the known genotype-phenotype correlations, the role of current genetic sequencing techniques in the discovery of novel pathogenic gene mutations and new therapeutic perspectives.

Study familial hypertrophic cardiomyopathy using patient-specific induced pluripotent stem cells

Aims

Familial hypertrophic cardiomyopathy (HCM) is one the most common heart disorders, with gene mutations in the cardiac sarcomere. Studying HCM with patient-specific induced pluripotent stem-cell (iPSC)-derived cardiomyocytes (CMs) would benefit the understanding of HCM mechanism, as well as the development of personalized therapeutic strategies.

Methods and results

To investigate the molecular mechanism underlying the abnormal CM functions in HCM, we derived iPSCs from an HCM patient with a single missense mutation (Arginine442Glycine) in the MYH7 gene. CMs were next enriched from HCM and healthy iPSCs, followed with whole transcriptome sequencing and pathway enrichment analysis. A widespread increase of genes responsible for ‘Cell Proliferation’ was observed in HCM iPSC-CMs when compared with control iPSC-CMs. Additionally, HCM iPSC-CMs exhibited disorganized sarcomeres and electrophysiological irregularities. Furthermore, disease phenotypes of HCM iPSC-CMs were attenuated with pharmaceutical treatments.

Conclusion

Overall, this study explored the possible patient-specific and mutation-specific disease mechanism of HCM, and demonstrates the potential of using HCM iPSC-CMs for future development of therapeutic strategies. Additionally, the whole methodology established in this study could be utilized to study mechanisms of other human-inherited heart diseases.

Inherited cardiomyopathies

Cardiomyopathies (ie, diseases of the heart muscle) are major causes of morbidity and mortality. A significant percentage of patients with cardiomyopathies have genetic-based, inheritable disease and, over the past 2 decades the genetic causes of these disorders have been increasingly discovered. The genes causing these disorders when they are mutated appear to encode proteins that frame a "final common pathway" for that specific disorder, but the specifics of the phenotype, including age of onset, severity, and outcome is variable for reasons not yet understood. The "final common pathways" for the classified forms of cardiomyopathy include the sarcomere in the primarily diastolic dysfunction disorders hypertrophic cardiomyopathy and restrictive cardiomyopathy, the linkage of the sarcomere and sarcolemma in the systolic dysfunction disorder dilated cardiomyopathy, and the desmosome in arrhythmogenic cardiomyopathy. Left ventricular noncompaction cardiomyopathy (LVNC) is an overlap disorder and it appears that any of these "final common pathways" can be involved depending on the specific form of LVNC. The genetics and mechanisms responsible for these clinical phenotypes will be described.

Survival benefit of ghrelin in the heart failure due to dilated cardiomyopathy

Although ghrelin has been demonstrated to improve cardiac function in heart failure, its therapeutic efficacy on the life expectancy remains unknown. We aim to examine whether ghrelin can improve the life survival in heart failure using a mouse model of inherited dilated cardiomyopathy (DCM) caused by a deletion mutation ΔK210 in cardiac troponin T (cTnT). From 30 days of age, ghrelin (150 μg/kg) was administered subcutaneously to DCM mice once daily, control mice received saline only. The survival rates were compared between the two groups for 30 days. After 30-day treatment, functional and morphological measurements were conducted. Ghrelin-treated DCM mice had significantly prolonged life spans compared with saline-treated control DCM mice. Echocardiography showed that ghrelin reduced left ventricular (LV) end-diastolic dimensions and increased LV ejection fraction. Moreover, histoanatomical data revealed that ghrelin decreased the heart-to-body weight ratio, prevented cardiac remodeling and fibrosis, and markedly decreased the expression of brain natriuretic peptide. Telemetry recording and heart rate variability analysis showed that ghrelin suppressed the excessive cardiac sympathetic nerve activity (CSNA) and recovered the cardiac parasympathetic nerve activity. These results suggest that ghrelin has therapeutic benefits for survival as well as for the cardiac function and remodeling in heart failure probably through suppression of CSNA and recovery of cardiac parasympathetic nerve activity.

Calcium in health and disease

Evolution has exploited the chemical properties of Ca(2+), which facilitate its reversible binding to the sites of irregular geometry offered by biological macromolecules, to select it as a carrier of cellular signals. A number of proteins bind Ca(2+) to specific sites: those intrinsic to membranes play the most important role in the spatial and temporal regulation of the concentration and movements of Ca(2+) inside cells. Those which are soluble, or organized in non-membranous structures, also decode the Ca(2+) message to be then transmitted to the targets of its regulation. Since Ca(2+) controls the most important processes in the life of cells, it must be very carefully controlled within the cytoplasm, where most of the targets of its signaling function reside. Membrane channels (in the plasma membrane and in the organelles) mediate the entrance of Ca(2+) into the cytoplasm, ATPases, exchangers, and the mitochondrial Ca(2+) uptake system remove Ca(2+) from it. The concentration of Ca(2+) in the external spaces, which is controlled essentially by its dynamic exchanges in the bone system, is much higher than inside cells, and can, under conditions of pathology, generate a situation of dangerous internal Ca(2+) overload. When massive and persistent, the Ca(2+) overload culminates in the death of the cell. Subtle conditions of cellular Ca(2+) dyshomeostasis that affect individual systems that control Ca(2+), generate cell disease phenotypes that are particularly severe in tissues in which the signaling function of Ca(2+) has special importance, e.g., the nervous system.

Sizing up models of heart failure: Proteomics from flies to humans

Cardiovascular disease is the leading cause of death in the western world. Heart failure is a heterogeneous and complex syndrome, arising from various etiologies, which result in cellular phenotypes that vary from patient to patient. The ability to utilize genetic manipulation and biochemical experimentation in animal models has made them indispensable in the study of this chronic condition. Similarly, proteomics has been helpful for elucidating complicated cellular and molecular phenotypes and has the potential to identify circulating biomarkers and drug targets for therapeutic intervention. In this review, the use of human samples and animal model systems (pig, dog, rat, mouse, zebrafish, and fruit fly) in cardiac research is discussed. Additionally, the protein sequence homology between these species and the extent of conservation at the level of the phospho-proteome in major kinase signaling cascades involved in heart failure are investigated.

In vivo effects of propyl gallate, a novel Ca(2+) sensitizer, in a mouse model of dilated cardiomyopathy caused by cardiac troponin T mutation

AIMS

We have previously demonstrated that propyl gallate has a Ca(2+) sensitizing effect on the force generation in membrane-permeabilized (skinned) cardiac muscle fibers. However, in vivo beneficial effects of propyl gallate as a novel Ca(2+) sensitizer remain uncertain. In the present study, we aim to explore in vivo effects of propyl gallate.

MAIN METHODS

We compared effects of propyl gallate on ex vivo intact cardiac muscle fibers and in vivo hearts in healthy mice with those of pimobendan, a clinically used Ca(2+) sensitizer. The therapeutic effect of propyl gallate was investigated using a mouse model of dilated cardiomyopathy (DCM) with reduced myofilament Ca(2+) sensitivity due to a deletion mutation ΔK210 in cardiac troponin T.

KEY FINDINGS

Propyl gallate, as well as pimobendan, showed a positive inotropic effect. Propyl gallate slightly increased the blood pressure without changing the heart rate in healthy mice, whereas pimobendan decreased the blood pressure probably through vasodilation via inhibition of phosphodiesterase and increased the heart rate. Propyl gallate prevented cardiac remodeling and systolic dysfunction and significantly improved the life-expectancy of knock-in mouse model of DCM with reduced myofilament Ca(2+) sensitivity due to a mutation in cardiac troponin T. On the other hand, gallate, a similarly strong antioxidant polyphenol lacking Ca(2+) sensitizing action, had no beneficial effects on the DCM mice.

SIGNIFICANCE

These results suggest that propyl gallate might be useful for the treatment of inherited DCM caused by a reduction in the myofilament Ca(2+) sensitivity.

Analysis of the molecular pathogenesis of cardiomyopathy-causing cTnT mutants I79N, ΔE96, and ΔK210

Three troponin T (TnT) mutants that cause hypertrophic, restrictive, and dilated cardiomyopathy (I79N, ΔE96, and ΔK210, respectively), were examined using the thin-filament extraction/reconstitution technique. Effects of Ca(2+), ATP, phosphate, and ADP concentrations on force and its transients were studied at 25°C. Maximal Ca(2+) tension (THC) and Ca(2+)-activatable tension (Tact), respectively, were similar among I79N, ΔE96, and WT, whereas ΔK210 led to a significantly lower THC (∼20% less) and Tact (∼25% less) than did WT. In pCa solution containing 8 mM Pi and ionic strength adjusted to 200 mM, the Ca(2+) sensitivity (pCa50) of I79N (5.63 ± 0.02) and ΔE96 (5.60 ± 0.03) was significantly greater than that of WT (5.45 ± 0.04), but the pCa50 of ΔK210 (5.54 ± 0.04) remained similar to that of WT. Five equilibrium constants were deduced using sinusoidal analysis. All three mutants showed significantly lower K0 (ADP association constant) and larger K4 (equilibrium constant of force generation step) relative to the corresponding values for WT. I79N and ΔK210 were associated with a K2 (equilibrium constant of cross-bridge detachment step) significantly lower than that of ΔE96 and WT. These results demonstrated that at pCa 4.66, the force/cross-bridge is ∼18% less in I79N and ∼41% less in ΔK210 than that in WT. These results indicate that the molecular pathogenesis of the cardiac TnT mutation-related cardiomyopathies is different for each mutation.