Genome-wide analysis of histone marks identifying an epigenetic signature of promoters and enhancers underlying cardiac hypertrophy.

Cardiac hypertrophy, initially an adaptive response of the myocardium to stress, can progress to heart failure. The epigenetic signature underlying this phenomenon is poorly understood. Here, we report on the genome-wide distribution of seven histone modifications in adult mouse cardiomyocytes subjected to a prohypertrophy stimulus in vivo. We found a set of promoters with an epigenetic pattern that distinguishes specific functional classes of genes regulated in hypertrophy and identified 9,207 candidate active enhancers whose activity was modulated. We also analyzed the transcriptional network within which these genetic elements act to orchestrate hypertrophy gene expression, finding a role for myocyte enhancer factor (MEF)2C and MEF2A in regulating enhancers. We propose that the epigenetic landscape is a key determinant of gene expression reprogramming in cardiac hypertrophy and provide a basis for understanding the role of chromatin in regulating this phenomenon.

Therapeutic applications of noncoding RNAs.

PURPOSE OF REVIEW: In this review, we summarize the basic principles underlying the therapeutic use of nonprotein coding (nc)RNAs, such as microRNA (miRNA) and long noncoding RNA, in the cardiovascular field, focusing, where possible, on recent advances that may lead to translation to the clinic for heart failure. RECENT FINDINGS: The number of individual miRNAs associated with a given aspect of heart disease is increasing rapidly, as is the data on miRNA profiles in normal and diseased myocardium. Less is known on the role of long noncoding RNA, and to date only a few have been studied in the heart. Novel oligonucleotide-based therapies have started to trickle into the clinic, but strategies focusing on ncRNA are still in a clinical/preclinical trial phase. SUMMARY: The discovery of functional ncRNAs is leading to a better understanding of the mechanisms underlying cardiovascular physiology. Dysregulation of ncRNAs is being increasingly associated with many diseases affecting the heart and in certain instances may have a pathogenic role. Therapeutic intervention aimed at opposing ncRNA misexpression has been widely demonstrated to be effective in blunting disease in animal models, and may thus have potential in the clinical setting.

MicroRNA-133 controls cardiac hypertrophy.

Growing evidence indicates that microRNAs (miRNAs or miRs) are involved in basic cell functions and oncogenesis. Here we report that miR-133 has a critical role in determining cardiomyocyte hypertrophy. We observed decreased expression of both miR-133 and miR-1, which belong to the same transcriptional unit, in mouse and human models of cardiac hypertrophy. In vitro overexpression of miR-133 or miR-1 inhibited cardiac hypertrophy. In contrast, suppression of miR-133 by 'decoy' sequences induced hypertrophy, which was more pronounced than that after stimulation with conventional inducers of hypertrophy. In vivo inhibition of miR-133 by a single infusion of an antagomir caused marked and sustained cardiac hypertrophy. We identified specific targets of miR-133: RhoA, a GDP-GTP exchange protein regulating cardiac hypertrophy; Cdc42, a signal transduction kinase implicated in hypertrophy; and Nelf-A/WHSC2, a nuclear factor involved in cardiogenesis. Our data show that miR-133, and possibly miR-1, are key regulators of cardiac hypertrophy, suggesting their therapeutic application in heart disease.

Epigenetics: a new mechanism of regulation of heart failure?

Heart failure is a syndrome resulting from a complex genetic predisposition and multiple environmental factors, and is a leading cause of morbidity and mortality. It is frequently accompanied by changes in heart mass, size, and shape, a process known as pathological cardiac remodeling. At the molecular level, these changes are preceded and accompanied by a specific gene expression program characterized by expression of certain 'fetal' genes. This re-expression of fetal genes in the adult heart contributes to the development of the syndrome. Therefore, counteracting the gene expression changes occurring in heart failure could be a therapeutic approach for this pathology. One mechanism of gene expression regulation that has gained importance is epigenetics. This review gives an overview of the roles of some epigenetic mechanisms, such as DNA methylation, histone modifications, ATP-dependent chromatin remodeling, and microRNA-dependent mechanisms, in heart failure.

Unexpectedly low mutation rates in beta-myosin heavy chain and cardiac myosin binding protein genes in Italian patients with hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiac disease. Fourteen sarcomeric and sarcomere-related genes have been implicated in HCM etiology, those encoding ß-myosin heavy chain (MYH7) and cardiac myosin binding protein C (MYBPC3) reported as the most frequently mutated: in fact, these account for around 50% of all cases related to sarcomeric gene mutations, which are collectively responsible for approximately 70% of all HCM cases. Here, we used denaturing high-performance liquid chromatography followed by bidirectional sequencing to screen the coding regions of MYH7 and MYBPC3 in a cohort (n = 125) of Italian patients presenting with HCM. We found 6 MHY7 mutations in 9/125 patients and 18 MYBPC3 mutations in 19/125 patients. Of the three novel MYH7 mutations found, two were missense, and one was a silent mutation; of the eight novel MYBPC3 mutations, one was a substitution, three were stop codons, and four were missense mutations. Thus, our cohort of Italian HCM patients did not harbor the high frequency of mutations usually found in MYH7 and MYBPC3. This finding, coupled to the clinical diversity of our cohort, emphasizes the complexity of HCM and the need for more inclusive investigative approaches in order to fully understand the pathogenesis of this disease.

Therapeutic use of microRNAs in myocardial diseases.

The discovery of regulatory non-coding (nc) RNAs has opened a new world in cell biology. Within this class of ncRNAs, microRNAs (miRNAs) have been found to be involved in many cellular functions. Regarding the cardiovascular system, miRNAs regulate cardiomyocyte size and survival, the action potential, angiogenesis, mitochondrial function, and energetics. Moreover, misexpression of miRNAs has been linked to pathology, and altered levels of certain miRNAs even may cause disease. Thus, the manipulation of miRNAs, by affecting the biological processes in which they are implicated, may be used to improve cardiac function. The expression of microRNAs can be modulated through different approaches. This article reviews these issues in relation to the therapeutic potential of miRNAs for heart failure.

microRNAs in heart disease: putative novel therapeutic targets?

microRNAs (miRs) are short, approximately 22-nucleotide-long non-coding RNAs involved in the control of gene expression. They guide ribonucleoprotein complexes that effect translational repression or messenger RNA degradation to targeted messenger RNAs. miRs were initially thought to be peculiar to the developmental regulation of the nematode worm, in which they were first described in 1993. Since then, hundreds of different miRs have been reported in diverse organisms, and many have been implicated in the regulation of physiological processes of adult animals. Of importance, misexpression of miRs has been uncovered as a pathogenic mechanism in several diseases. Here, we first outline the biogenesis and mechanism of action of miRs, and then discuss their relevance to heart biology, pathology, and medicine.

Akt increases sarcoplasmic reticulum Ca2+ cycling by direct phosphorylation of phospholamban at Thr17.

Cardiomyocytes adapt to physical stress by increasing their size while maintaining cell function. The serine/threonine kinase Akt plays a critical role in this process of adaptation. We previously reported that transgenic overexpression of an active form of Akt (Akt-E40K) in mice results in increased cardiac contractility and cell size, as well as improved sarcoplasmic reticulum (SR) Ca(2+) handling. Because it is not fully elucidated, we decided to study the molecular mechanism by which Akt-E40K overexpression improves SR Ca(2+) handling. To this end, SR Ca(2+) uptake and the phosphorylation status of phospholamban (PLN) were evaluated in heart extracts from wild-type and Akt-E40K mice and mice harboring inducible and cardiac specific knock-out of phosphatidylinositol-dependent kinase-1, the upstream activator of Akt. Moreover, the effect of Akt was assessed in vitro by overexpressing a mutant Akt targeted preferentially to the SR, and by biochemical assays to evaluate potential interaction with PLN. We found that when activated, Akt interacts with and phosphorylates PLN at Thr(17), the Ca(2+)-calmodulin-dependent kinase IIdelta site, whereas silencing Akt signaling, through the knock-out of phosphatidylinositol-dependent kinase-1, resulted in reduced phosphorylation of PLN at Thr(17). Furthermore, overexpression of SR-targeted Akt in cardiomyocytes improved Ca(2+) handling without affecting cell size. Thus, we describe here a new mechanism whereby the preferential translocation of Akt to the SR is responsible for enhancement of contractility without stimulation of hypertrophy.

RNA silencing: small RNA-mediated posttranscriptional regulation of mRNA and the implications for heart electropathophysiology.

Gene silencing refers to the "switching off" of genes within the cell: it can occur at transcriptional and posttranscriptional levels, controlling, respectively, how much mRNA is transcribed from each gene and how much protein is translated from this mRNA. Knowledge of its governing mechanisms is fundamental to our understanding of physiology; moreover, where there is a relevance for pathology, new diagnostic and therapeutic tools may be developed. Recently, families of noncoding RNA (ncRNA)-RNA that does not encode for a protein end-product--have been discovered that function as regulators of gene silencing. This has revolutionized biology by challenging the credence in the centrality of proteins as the regulators of biological processes, and is changing the way we study pathophysiology. In fact, a subfamily of small ncRNAs, called microRNA (miRNA), is now known as one of the most abundant class of regulatory molecules, and over one-third of human genes-including a growing number of key genes of the heart-may be targeted by one or more of the hundreds of miRNAs that exist. Here, we focus on how these small ncRNAs control translation, on the extraordinary consequences this class of regulator is currently known to have on aspects of cardiac excitability, and on the exciting therapeutic potential they have in this field.

Emerging role of microRNAs in cardiovascular biology.

The heart is among the most conserved organs of the body and is susceptible to defects more than any other organ. Heart malformations, in fact, occur in roughly 1% of newborns. Moreover, cardiovascular disease arising during adult life is among the main causes of morbidity and mortality in developed countries. It is not surprising, therefore, that much effort is being channeled into understanding the development, physiology, and pathology of the cardiovascular system. MicroRNAs, a newly discovered class of small ribonucleotide-based regulators of gene expression, are being implicated in an increasing number of biological processes, and the study of their role in cardiovascular biology is just beginning. Here, we briefly overview microRNAs in general and report on the recent findings regarding their importance for the heart and vasculature, in particular. The new insights that are being gained will permit not only a greater understanding of cardiovascular pathologies but also, hopefully, the development of novel therapeutic strategies.

Corrigendum: 3D hydrogel environment rejuvenates aged pericytes for skeletal muscle tissue engineering.

[This corrects the article DOI: 10.3389/fphys.2014.00203.].

MicroRNA and cardiac pathologies.

MicroRNA has been shown to be essential for correct cardiovascular development and physiology in a number of recent reports. Studies have also started to characterize the link between specific microRNAs and aspects of pathogenesis--such as chamber morphogenesis, conduction, and contraction--and between microRNA expression signatures and pathological cardiac phenotypes--such as hypertrophy, ischemic cardiomyopathy, dilated cardiomyopathy, and aortic stenosis. Congenital anomalies of the heart may also be associated with the dysregulation of specific microRNAs. Here we report on the latest findings.

Heart failure: targeting transcriptional and post-transcriptional control mechanisms of hypertrophy for treatment.

Heart failure (HF) is a syndrome caused by diminished heart function that arises from pathologies like hypertension, infarction, and diabetes. Neurohormonal, cardiorenal and cardiocirculatory models have been developed to explain HF but they have not provided sufficient understanding for the elaboration of therapies to conquer the syndrome. In fact, even though progress has been made in improving survival, HF remains a frequent cause of hospitalization and death. Since in most forms of HF, development of the disorder is associated with an alteration of cardiomyocyte structure, perceived as an increase in heart mass due to cell hypertrophy, effort is being directed to address hypertrophy as a therapeutic target. Here, we outline recent understanding of two gene-silencing regulatory mechanisms underlying cardiomyocyte hypertrophy, i.e., transcriptional control by HDACs, and post-transcriptional control by microRNAs.

Physiological myocardial hypertrophy: how and why?

Cardiac hypertrophy is defined by augmentation of ventricular mass as a result of increased cardiomyocyte size, and is the adaptive response of the heart to enhanced hemodynamic loads due to either physiological stimuli (post-natal developmental growth, training, and pregnancy) or pathological states (such as hypertension, valvular insufficiency, etc). The mechanisms leading to hypertrophy during pathological and physiological states are distinct but, in general, evidence indicates that hypertrophy results from the interaction of mechanical forces and neurohormonal factors. Hemodynamic overload creates a mechanical burden on the heart and results in stretch of the myocyte and induction of gene expression of cardiac growth factors. Insulin-like growth factor 1 (IGF1) has recently been shown to be the most important cardiac growth factor involved in physiological hypertrophy. In this review, IGF1 and the pathways it triggers will be discussed.

MicroRNAs control gene expression: importance for cardiac development and pathophysiology.

Growing evidence indicates that microRNAs (miRNAs) are involved in a variety of basic biological processes, including cell proliferation, apoptosis, stress response, hematopoesis, and oncogenesis. In fact, bioinformatic analysis predicts that each miRNA may regulate hundreds of targets, suggesting that miRNAs may play roles in almost every biological pathway. Information from recent studies indicate that miRNAs are involved in the regulation of cardiac development and pathophysiology. Notably, knockout of miRNA-1 was associated with cardiac defects, including regulation of cardiac morphogenesis, electrical conduction, and cell cycle control. Our group has identified a critical role of miRNA-1 and miRNA-133 in determining cardiac hypertrophy and has shown an inverse correlation of expression with cardiac hypertrophy, in vitro, in murine models and in human disease states associated with cardiac hypertrophy. Remarkably, in vivo experiments with a single infusion of antagomir-133 oligonucleotide, a small cholesterol-conjugated RNA sequence suppressing endogenous miRNA, induced marked and sustained cardiac hypertrophy. Shedding light on the role of this new class of RNA molecules in heart physiology and pathology may reveal possible future therapeutic applications for the treatment of heart diseases.