Changes in gene expression in the intact human heart. Downregulation of alpha-myosin heavy chain in hypertrophied, failing ventricular myocardium

Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues

Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.

Direct hydrogel encapsulation of pluripotent stem cells enables ontomimetic differentiation and growth of engineered human heart tissues

Human engineered heart tissues have potential to revolutionize cardiac development research, drug-testing, and treatment of heart disease; however, implementation is limited by the need to use pre-differentiated cardiomyocytes (CMs). Here we show that by providing a 3D poly(ethylene glycol)-fibrinogen hydrogel microenvironment, we can directly differentiate human pluripotent stem cells (hPSCs) into contracting heart tissues. Our straight-forward, ontomimetic approach, imitating the process of development, requires only a single cell-handling step, provides reproducible results for a range of tested geometries and size scales, and overcomes inherent limitations in cell maintenance and maturation, while achieving high yields of CMs with developmentally appropriate temporal changes in gene expression. We demonstrate that hPSCs encapsulated within this biomimetic 3D hydrogel microenvironment develop into functional cardiac tissues composed of self-aligned CMs with evidence of ultrastructural maturation, mimicking heart development, and enabling investigation of disease mechanisms and screening of compounds on developing human heart tissue.

Cellular and molecular basis of RV hypertrophy in congenital heart disease

RV hypertrophy (RVH) is one of the triggers of RV failure in congenital heart disease (CHD). Therefore, improving our understanding of the cellular and molecular basis of this pathology will help in developing strategic therapeutic interventions to enhance patient benefit in the future. This review describes the potential mechanisms that underlie the transition from RVH to RV failure. In particular, it addresses structural and functional remodelling that encompass contractile dysfunction, metabolic changes, shifts in gene expression and extracellular matrix remodelling. Both ischaemic stress and reactive oxygen species production are implicated in triggering these changes and will be discussed. Finally, RV remodelling in response to various CHDs as well as the potential role of biomarkers will be addressed.

Adult mice expressing a Braf Q241R mutation on an ICR/CD-1 background exhibit a cardio-facio-cutaneous syndrome phenotype

Activation of the RAS pathway has been implicated in oncogenesis and developmental disorders called RASopathies. Germline mutations in BRAF have been identified in 50-75% of patients with cardio-facio-cutaneous (CFC) syndrome, which is characterized by congenital heart defects, distinctive facial features, short stature and ectodermal abnormalities. We recently demonstrated that mice expressing a Braf Q241R mutation, which corresponds to the most frequent BRAF mutation (Q257R) in CFC syndrome, on a C57BL/6J background are embryonic/neonatal lethal, with multiple congenital defects, preventing us from analyzing the phenotypic consequences after birth. Here, to further explore the pathogenesis of CFC syndrome, we backcrossed these mice onto a BALB/c or ICR/CD-1 genetic background. On a mixed (BALB/c and C57BL/6J) background, all heterozygous Braf(Q241R/+) mice died between birth and 24 weeks and exhibited growth retardation, sparse and ruffled fur, liver necrosis and atrial septal defects (ASDs). In contrast, 31% of the heterozygous Braf(Q241R/+) ICR mice survived over 74 weeks. The surviving Braf(Q241R/+) ICR mice exhibited growth retardation, sparse and ruffled fur, a hunched appearance, craniofacial dysmorphism, long and/or dystrophic nails, extra digits and ovarian cysts. The Braf(Q241R/+) ICR mice also showed learning deficits in the contextual fear-conditioning test. Echocardiography indicated the presence of pulmonary stenosis and ASDs in the Braf(Q241R/+) ICR mice, which were confirmed by histological analysis. These data suggest that the heterozygous Braf(Q241R/+) ICR mice show similar phenotypes as CFC syndrome after birth and will be useful for elucidating the pathogenesis and potential therapeutic strategies for RASopathies.

The adrenergic system in pulmonary arterial hypertension: bench to bedside (2013 Grover Conference series)

In heart failure with reduced left ventricular ejection fraction (HFrEF), adrenergic activation is a key compensatory mechanism that is a major contributor to progressive ventricular remodeling and worsening of heart failure. Targeting the increased adrenergic activation with β-adrenergic receptor blocking agents has led to the development of arguably the single most effective drug therapy for HFrEF. The pressure-overloaded and ultimately remodeled/failing right ventricle (RV) in pulmonary arterial hypertension (PAH) is also adrenergically activated, which raises the issue of whether an antiadrenergic strategy could be effectively employed in this setting. Anecdotal experience suggests that it will be challenging to administer an antiadrenergic treatment such as a β-blocking agent to patients with established moderate-severe PAH. However, the same types of data and commentary were prevalent early in the development of β-blockade for HFrEF treatment. In addition, in HFrEF approaches have been developed for delivering β-blocker therapy to patients who have extremely advanced heart failure, and these general principles could be applied to RV failure in PAH. This review examines the role played by adrenergic activation in the RV faced with PAH, contrasts PAH-RV remodeling with left ventricle remodeling in settings of sustained increases in afterload, and suggests a possible approach for safely delivering an antiadrenergic treatment to patients with RV dysfunction due to moderate-severe PAH.

Advancing knowledge of right ventricular pathophysiology in chronic pressure overload: Insights from experimental studies

The right ventricle (RV) has to face major changes in loading conditions due to cardiovascular diseases and pulmonary vascular disorders. Clinical experience supports evidence that the RV better compensates for volume than for pressure overload, and for chronic than for acute changes. For a long time, right ventricular (RV) pathophysiology has been restricted to patterns extrapolated from left heart studies. However, the two ventricles are anatomically, haemodynamically and functionally distinct. RV metabolic properties may also result in a different behaviour in response to pathological conditions compared with the left ventricle. In this review, current knowledge of RV pathophysiology is reported in the setting of chronic pressure overload, including recent experimental findings and emerging concepts. After a time-varying compensated period with preserved cardiac output despite overload conditions, RV failure finally occurs, leading to death. The underlying mechanisms involved in the transition from compensatory hypertrophy to maladaptive remodelling are not completely understood.

Aerobic exercise training promotes physiological cardiac remodeling involving a set of microRNAs

Left ventricular (LV) hypertrophy is an important physiological compensatory mechanism in response to chronic increase in hemodynamic overload. There are two different forms of LV hypertrophy, one physiological and another pathological. Aerobic exercise induces beneficial physiological LV remodeling. The molecular/cellular mechanisms for this effect are not totally known, and here we review various mechanisms including the role of microRNA (miRNA). Studies in the heart, have identified antihypertrophic miRNA-1, -133, -26, -9, -98, -29, -378, and -145 and prohypertrophic miRNA-143, -103, -130a, -146a, -21, -210, -221, -222, -27a/b, -199a/b, -208, -195, -499, -34a/b/c, -497, -23a, and -15a/b. Four miRNAs are recognized as cardiac-specific: miRNA-1, -133a/b, -208a/b, and -499 and called myomiRs. In our studies we have shown that miRNAs respond to swimming aerobic exercise by 1) decreasing cardiac fibrosis through miRNA-29 increasing and inhibiting collagen, 2) increasing angiogenesis through miRNA-126 by inhibiting negative regulators of the VEGF pathway, and 3) modulating the renin-angiotensin system through the miRNAs-27a/b and -143. Exercise training also increases cardiomyocyte growth and survival by swimming-regulated miRNA-1, -21, -27a/b, -29a/c, -30e, -99b, -100, -124, -126, -133a/b, -143, -144, -145, -208a, and -222 and running-regulated miRNA-1, -26, -27a, -133, -143, -150, and -222, which influence genes associated with the heart remodeling and angiogenesis. We conclude that there is a potential role of these miRNAs in promoting cardioprotective effects on physiological growth.

Prospects for In Vitro Myofilament Maturation in Stem Cell-Derived Cardiac Myocytes

Cardiomyocytes derived from human stem cells are quickly becoming mainstays of cardiac regenerative medicine, in vitro disease modeling, and drug screening. Their suitability for such roles may seem obvious, but assessments of their contractile behavior suggest that they have not achieved a completely mature cardiac muscle phenotype. This could be explained in part by an incomplete transition from fetal to adult myofilament protein isoform expression. In this commentary, we review evidence that supports this hypothesis and discuss prospects for ultimately generating engineered heart tissue specimens that behave similarly to adult human myocardium. We suggest approaches to better characterize myofilament maturation level in these in vitro systems, and illustrate how new computational models could be used to better understand complex relationships between muscle contraction, myofilament protein isoform expression, and maturation.

Loss of MT1-MMP causes cell senescence and nuclear defects which can be reversed by retinoic acid

MT1-MMP (MMP14) is a collagenolytic enzyme located at the cell surface and implicated in extracellular matrix (ECM) remodeling. Mmp14(-/-) mice present dwarfism, bone abnormalities, and premature death. We demonstrate herein that the loss of MT1-MMP also causes cardiac defects and severe metabolic changes, and alters the cytoskeleton and the nuclear lamina structure. Moreover, the absence of MT1-MMP induces a senescent phenotype characterized by up-regulation of p16(INK4a) and p21(CIP1/WAF) (1), increased activity of senescence-associated β-galactosidase, generation of a senescence-associated secretory phenotype, and somatotroph axis alterations. Consistent with the role of retinoic acid signaling in nuclear lamina stabilization, treatment of Mmp14(-/-) mice with all-trans retinoic acid reversed the nuclear lamina alterations, partially rescued the cell senescence phenotypes, ameliorated the pathological defects in bone, skin, and heart, and extended their life span. These results demonstrate that nuclear architecture and cell senescence can be modulated by a membrane protease, in a process involving the ECM as a key regulator of nuclear stiffness under cell stress conditions.

Nitroxyl (HNO) for treatment of acute heart failure

The loss of contractile function is a hallmark of heart failure. Although increasing intracellular Ca(2+) is a possible strategy for improving contraction, current inotropic agents that achieve this by raising intracellular cAMP levels, such as β-agonists and phosphodiesterase inhibitors, are generally deleterious when administered as long-term therapy due to arrhythmia and myocardial damage. Nitroxyl donors have been shown to improve cardiac function in normal and failing dogs, and in isolated cardiomyocytes they increase fractional shortening and Ca(2+) transients, independently from cAMP/PKA or cGMP/PKG signaling. Instead, nitroxyl targets cysteines in the EC-coupling machinery and myofilament proteins, reversibly modifying them to enhance Ca(2+) handling and myofilament Ca(2+) sensitivity. Phase I-IIa trials with CXL-1020, a novel pure HNO donor, reported declines in left and right heart filling pressures and systemic vascular resistance, and increased cardiac output and stroke volume index. These findings support the concept of nitroxyl donors as attractive agents for the treatment of acute decompensated heart failure.

Antagonistic regulation of mRNA expression and splicing by CELF and MBNL proteins

RNA binding proteins of the conserved CUGBP1, Elav-like factor (CELF) family contribute to heart and skeletal muscle development and are implicated in myotonic dystrophy (DM). To understand their genome-wide functions, we analyzed the transcriptome dynamics following induction of CELF1 or CELF2 in adult mouse heart and of CELF1 in muscle by RNA-seq, complemented by crosslinking/immunoprecipitation-sequencing (CLIP-seq) analysis of mouse cells and tissues to distinguish direct from indirect regulatory targets. We identified hundreds of mRNAs bound in their 3′ UTRs by both CELF1 and the developmentally induced MBNL1 protein, a threefold greater overlap in target messages than expected, including messages involved in development and cell differentiation. The extent of 3′ UTR binding by CELF1 and MBNL1 predicted the degree of mRNA repression or stabilization, respectively, following CELF1 induction. However, CELF1's RNA binding specificity in vitro was not detectably altered by coincubation with recombinant MBNL1. These findings support a model in which CELF and MBNL proteins bind independently to mRNAs but functionally compete to specify down-regulation or localization/stabilization, respectively, of hundreds of mRNA targets. Expression of many alternative 3′ UTR isoforms was altered following CELF1 induction, with 3′ UTR binding associated with down-regulation of isoforms and genes. The splicing of hundreds of alternative exons was oppositely regulated by these proteins, confirming an additional layer of regulatory antagonism previously observed in a handful of cases. The regulatory relationships between CELFs and MBNLs in control of both mRNA abundance and splicing appear to have evolved to enhance developmental transitions in major classes of heart and muscle genes.

Adaptive capacity of the right ventricle: why does it fail?

Only in recent years has the right ventricle (RV) function become appreciated to be equally important to the left ventricle (LV) function to maintain cardiac output. Right ventricular failure is, irrespectively of the etiology, associated with impaired exercise tolerance and poor survival. Since the anatomy and physiology of the RV is distinctly different than that of the LV, its adaptive mechanisms and the pathways involved are different as well. RV hypertrophy is an important mechanism of the RV to preserve cardiac output. This review summarizes the current knowledge on the right ventricle and its response to pathologic situations. We will focus on the adaptive capacity of the right ventricle and the molecular pathways involved, and we will discuss potential therapeutic interventions.

Human umbilical cord blood-derived mononuclear cells improve murine ventricular function upon intramyocardial delivery in right ventricular chronic pressure overload

Introduction

Stem cell therapy has emerged as potential therapeutic strategy for damaged heart muscles. Umbilical cord blood (UCB) cells are the most prevalent stem cell source available, yet have not been fully tested in cardiac regeneration. Herein, studies were performed to evaluate the cardiovascular safety and beneficial effect of mononuclear cells (MNCs) isolated from human umbilical cord blood upon intramyocardial delivery in a murine model of right ventricle (RV) heart failure due to pressure overload.

Methods

UCB-derived MNCs were delivered into the myocardium of a diseased RV cardiac model. Pulmonary artery banding (PAB) was used to produce pressure overload in athymic nude mice that were then injected intramyocardially with UCB-MNCs (0.4 × 10^6 cells/heart). Cardiac functions were then monitored by telemetry, echocardiography, magnetic resonance imaging (MRI) and pathologic analysis of heart samples to determine the ability for cell-based repair.

Results

The cardio-toxicity studies provided evidence that UCB cell transplantation has a safe therapeutic window between 0.4 to 0.8 million cells/heart without altering QT or ST-segments or the morphology of electrocardiograph waves. The PAB cohort demonstrated significant changes in RV chamber dilation and functional defects consistent with severe pressure overload. Using cardiac MRI analysis, UCB-MNC transplantation in the setting of PAB demonstrated an improvement in RV structure and function in this surgical mouse model. The RV volume load in PAB-only mice was 24.09 ± 3.9 compared to 11.05 ± 2.09 in the cell group (mm³, P-value <0.005). The analysis of pathogenic gene expression (BNP, ANP, Acta1, Myh7) in the cell-transplanted group showed a significant reversal with respect to the diseased PAB mice with a robust increase in cardiac progenitor gene expression such as GATA4, Kdr, Mef2c and Nkx2.5. Histological analysis indicated significant fibrosis in the RV in response to PAB that was reduced following UCB-MNC’s transplantation along with concomitant increased Ki-67 expression and CD31 positive vessels as a marker of angiogenesis within the myocardium.

Conclusions

These findings indicate that human UCB-derived MNCs promote an adaptive regenerative response in the right ventricle upon intramyocardial transplantation in the setting of chronic pressure overload heart failure.

Sympathetic nervous system activation and β-adrenoceptor blockade in right heart failure

Right heart failure may develop from pulmonary arterial hypertension or various forms of congenital heart disease. Right ventricular adaptation to the increased afterload is the most important prognostic factor in pulmonary hypertension and congenital heart disease, which share important pathophysiological mechanisms, despite having different aetiologies. There is substantial evidence of increased sympathetic nervous system activation in right heart failure related to both pulmonary hypertension and congenital heart disease. It is unknown to which degree this activation is an adaptive response, a maladaptive response, or if it mainly reflects disease progression. Several experimental studies and clinical trials have been conducted to answer these questions. Here, we review the existing knowledge on sympathetic nervous system activation and the effects of β-adrenoceptor blockade in experimental and clinical right heart failure. This review identifies important gaps in our understanding of the right ventricle and discusses the potential of β-blockers in the treatment of right heart failure.

Neonatal hyperoxic lung injury favorably alters adult right ventricular remodeling response to chronic hypoxia exposure

The development of pulmonary hypertension (PH) requires multiple pulmonary vascular insults, yet the role of early oxygen therapy as an initial pulmonary vascular insult remains poorly defined. Here, we employ a two-hit model of PH, utilizing postnatal hyperoxia followed by adult hypoxia exposure, to evaluate the role of early hyperoxic lung injury in the development of later PH. Sprague-Dawley pups were exposed to 90% oxygen during postnatal days 0-4 or 0-10 or to room air. All pups were then allowed to mature in room air. At 10 wk of age, a subset of rats from each group was exposed to 2 wk of hypoxia (Patm = 362 mmHg). Physiological, structural, and biochemical endpoints were assessed at 12 wk. Prolonged (10 days) postnatal hyperoxia was independently associated with elevated right ventricular (RV) systolic pressure, which worsened after hypoxia exposure later in life. These findings were only partially explained by decreases in lung microvascular density. Surprisingly, postnatal hyperoxia resulted in robust RV hypertrophy and more preserved RV function and exercise capacity following adult hypoxia compared with nonhyperoxic rats. Biochemically, RVs from animals exposed to postnatal hyperoxia and adult hypoxia demonstrated increased capillarization and a switch to a fetal gene pattern, suggesting an RV more adept to handle adult hypoxia following postnatal hyperoxia exposure. We concluded that, despite negative impacts on pulmonary artery pressures, postnatal hyperoxia exposure may render a more adaptive RV phenotype to tolerate late pulmonary vascular insults.

Is cardiac resynchronization therapy for right ventricular failure in pulmonary arterial hypertension of benefit?

Pulmonary arterial hypertension is a manifestation of a group of disorders leading to pulmonary vascular remodeling and increased pulmonary pressures. The right ventricular (RV) response to chronic pressure overload consists of myocardial remodeling, which is in many ways similar to that seen in left ventricular (LV) failure. Maladaptive myocardial remodeling often leads to intraventricular and interventricular dyssychrony, an observation that has led to cardiac resynchronization therapy (CRT) for LV failure. CRT has proven to be an effective treatment strategy in subsets of patients with LV failure resulting in improvement in LV function, heart failure symptoms, and survival. Current therapy for pulmonary arterial hypertension is based on decreasing pulmonary vascular resistance, and there is currently no effective therapy targeting the right ventricle or maladaptive ventricular remodeling in these patients. This review focuses on the RV response to chronic pressure overload, its effect on electromechanical coupling and synchrony, and how lessons learned from left ventricular cardiac resynchronization might be applied as therapy for RV dysfunction in the context of pulmonary arterial hypertension.

Cardiac transcriptome and dilated cardiomyopathy genes in zebrafish

BACKGROUND

Genetic studies of cardiomyopathy and heart failure have limited throughput in mammalian models. Adult zebrafish have been recently pursued as a vertebrate model with higher throughput, but genetic conservation must be tested.

METHODS AND RESULTS

We conducted transcriptome analysis of zebrafish heart and searched for fish homologues of 51 known human dilated cardiomyopathy-associated genes. We also identified genes with high cardiac expression and genes with differential expression between embryonic and adult stages. Among tested genes, 30 had a single zebrafish orthologue, 14 had 2 homologues, and 5 had ≥3 homologues. By analyzing the expression data on the basis of cardiac abundance and enrichment hypotheses, we identified a single zebrafish gene for 14 of 19 multiple-homologue genes and 2 zebrafish homologues of high priority for ACTC1. Of note, our data suggested vmhc and vmhcl as functional zebrafish orthologues for human genes MYH6 and MYH7, respectively, which are established molecular markers for cardiac remodeling.

CONCLUSIONS

Most known genes for human dilated cardiomyopathy have a corresponding zebrafish orthologue, which supports the use of zebrafish as a conserved vertebrate model. Definition of the cardiac transcriptome and fetal gene program will facilitate systems biology studies of dilated cardiomyopathy in zebrafish.

Right ventricular reserve in a piglet model of chronic pulmonary hypertension

Right ventricular (RV) response to exercise or pharmacological stress is not well documented in pulmonary hypertension (PH). We investigated the relationship between RV reserve and ventricular-arterial coupling. Surgical ligation of the left pulmonary artery was performed in 13 Large White piglets (PH group), thereafter weekly embolisations of the right lower lobe were performed for 5 weeks. A control group of six piglets underwent sham procedures. Right heart catheterisation and echocardiography were performed at week 6. Pressure-volume loops were recorded before and after dobutamine infusion. Induction of experimental PH resulted in a higher mean ± sd pulmonary artery pressure (34 ± 9 versus 14 ± 2 mmHg; p<0.01) and in a lower ventricular-arterial coupling efficiency (0.66 ± 0.18 versus 1.24 ± 0.17; p<0.01) compared with controls at 6 weeks. Dobutamine-induced relative changes in RV stroke volume index (SVI) and end-systolic elastance were lower in the PH group (mean ± SD 47 ± 5% versus 20 ± 5%, p<0.01, and 81 ± 37% versus 32 ± 14%, p<0.01, respectively). Change in SVI was strongly associated with resting ventricular-arterial coupling (R(2)=0.74; p<0.01). RV reserve was associated with ventricular-arterial coupling in a porcine model of chronic pressure overload.

Animal model of reversible, right ventricular failure

BACKGROUND

Heart failure is a leading cause of death but very little is known about right ventricular (RV) failure (RVF) and right ventricular recovery (RVR). A robust animal model of reversible, RVF does not exist, which currently limits research opportunities and clinical progress. We sought to develop an animal model of reversible, pressure-overload RVF to study RVF and RVR.

MATERIALS AND METHODS

Fifteen New Zealand rabbits underwent implantation of a fully implantable, adjustable, pulmonary artery band. Animals were assigned to the control, RVF, and RVR groups (n = 5 for each). For the RVF and RVR groups, the pulmonary artery bands were serially tightened to create RVF and released for RVR. Echocardiographic, cardiac magnetic resonance imaging, and histologic analysis were performed.

RESULTS

RV chamber size and wall thickness increased during RVF and regressed during RVR. RV volumes were 1023 μL ± 123 for control, 2381 μL ± 637 for RVF, and 635 μL ± 549 for RVR, and RV wall thicknesses were 0.98 mm ± 0.12 for controls (P = 0.05), 1.72 mm ± 0.60 for RVF, and 1.16 mm ± 0.03 for RVR animals (P = 0.04), respectively. Similarly, heart weight, liver weight, cardiomyocyte size, and the degree of cardiac and hepatic fibrosis increased with RVF and decreased during RVR.

CONCLUSIONS

We report an animal model of chronic, reversible, pressure-overload RVF to study RVF and RVR. This model will be used for preclinical studies that improve our understanding of the mechanisms of RVF and that develop and test RV protective and RVR strategies to be studied later in humans.

Sarcomeric protein isoform transitions in cardiac muscle: a journey to heart failure

Sarcomeric protein isoforms are mainly governed by alternative promoter-driven expression, distinct gene expression, gene mutation and alternative mRNA splicing. The transitions of sarcomeric proteins have been implicated to play a role in the onset and development of human heart failure. In this mini-review, we summarized isoform transitions of several most widely examined sarcomeric proteins including myosin, actin, troponin, tropomyosin, titin and myosin binding protein-C, and the consequence of these abnormal isoform transitions. Even though the isoform transitions of sarcomeric proteins have been described in individual sarcomeric protein reviews, no concise summary of these results has been presented previously. This review is intended to fill this gap and discuss possible future perspectives.

A miR-208-Mef2 axis drives the decompensation of right ventricular function in pulmonary hypertension

RATIONALE

Right ventricular (RV) failure is a major cause of morbidity and mortality in pulmonary hypertension, but its mechanism remains unknown. Myocyte enhancer factor 2 (Mef2) has been implicated in RV development, regulating metabolic, contractile, and angiogenic genes. Moreover, Mef2 regulates microRNAs that have emerged as important determinants of cardiac development and disease, but for which the role in RV is still unclear.

OBJECTIVE

We hypothesized a critical role of a Mef2-microRNAs axis in RV failure.

METHODS AND RESULTS

In a rat pulmonary hypertension model (monocrotaline), we studied RV free wall tissues from rats with normal, compensated, and decompensated RV hypertrophy, carefully defined based on clinically relevant parameters, including RV systolic and end-diastolic pressures, cardiac output, RV size, and morbidity. Mef2c expression was sharply increased in compensating phase of RVH tissues but was lost in decompensation phase of RVH. An unbiased screening of microRNAs in our model resulted to a short microRNA signature of decompensated RV failure, which included the myocardium-specific miR-208, which was progressively downregulated as RV failure progressed, in contrast to what is described in left ventricular failure. With mechanistic in vitro experiments using neonatal and adult RV cardiomyocytes, we showed that miR-208 inhibition, as well as tumor necrosis factor-α, activates the complex mediator of transcription 13/nuclear receptor corepressor 1 axis, which in turn promotes Mef2 inhibition, closing a self-limiting feedback loop, driving the transition from compensating phase of RVH toward decompensation phase of RVH. In our model, serum tumor necrosis factor-α levels progressively increased with time while serum miR-208 levels decreased, mirroring its levels in RV myocardium.

CONCLUSIONS

We describe an RV-specific mechanism for heart failure, which could potentially lead to new biomarkers and therapeutic targets.

Acquisition of a quantitative, stoichiometrically conserved ratiometric marker of maturation status in stem cell-derived cardiac myocytes

There is no consensus in the stem cell field as to what constitutes the mature cardiac myocyte. Thus, helping formalize a molecular signature for cardiac myocyte maturation would advance the field. In the mammalian heart, inactivation of the “fetal” TNNI gene, TNNI1 (ssTnI), together in temporal concert with its stoichiometric replacement by the adult TNNI gene product, TNNI3 (cTnI), represents a quantifiable ratiometric maturation signature. We examined the TNNI isoform transition in human induced pluripotent stem cell (iPSC) cardiac myocytes (hiPSC-CMs) and found the fetal TNNI signature, even during long-term culture. Rodent stem cell-derived and primary myocytes, however, transitioned to the adult TnI profile. Acute genetic engineering of hiPSC-CMs enabled a rapid conversion toward the mature TnI profile. While there is no single marker to denote the mature cardiac myocyte, we propose that tracking the cTnI:ssTnI protein isoform ratio provides a valuable maturation signature to quantify myocyte maturation status across laboratories.

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The TNNI gene switch is a quantitative maturation signal for hiPSC-CMs

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TnI isoform ratio is necessary, but not sufficient, to establish the mature state

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TNNI protein isoform switching is stalled in hiPSC-CMs

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Gene transfer enables acquisition of the mature TNNI signature in hiPSC-CMs

Antithetical regulation of α-myosin heavy chain between fetal and adult heart failure though shuttling of HDAC5 regulating YY-1 function

Molecular switches of myosin isoforms are known to occur in various conditions. Here, we demonstrated the result from fetal heart failure and its potential mechanisms. Fetal and adult heart failure rat models were induced by injections of isoproterenol as previously described, and Go6976 was given to heart failing fetuses. Real-time PCR and Western blot were adopted to measure the expressions of α-MHC, β-MHC and YY-1. Co-immunoprecipitation was performed to analysis whether YY-1 interacts with HDAC5. Besides, histological immunofluorescence assessment was carried out to identify the location of HDAC5. α-MHC was recorded elevated in fetal heart failure which was decreased in adult heart failure. Besides, YY-1 was observed elevated both in fetal and adult failing hearts, but YY-1 could co-immunoprecipitation with HDAC5 only in adult hearts. Nuclear localization of HDAC5 was identified in adult cardiomyocytes, while cytoplasmic localization was identified in fetuses. After Go6976 supplied, HDAC5 shuttled into nucleuses interacted with YY-1. The myosin molecular switches were reversed with worsening cardiac functions and higher mortalities. Regulation of MHC in fetal heart failure was different from adult which provided a better compensation with increased α-MHC. This kind of transition was involved with shuttling of HDAC5 regulating YY-1 function.

The study of fetal rat model of intra-amniotic isoproterenol injection induced heart dysfunction and phenotypic switch of contractile proteins

To establish a reliable isoproterenol induced heart dysfunction fetal rat model and understand the switches of contractile proteins, 45 pregnant rats were divided into 15 mg/kg-once, 15 mg/kg-twice, sham-operated once, sham-operated twice, and control groups. And 18 adult rats were divided into isoproterenol-treated and control groups. H&E staining, Masson staining, and transmission electron microscope were performed. Apoptotic rate assessed by TUNEL analysis and expressions of ANP, BNP, MMP-2, and CTGF of hearts were measured. Intra-amniotic injections of isoproterenol were supplied on E14.5 and E15.5 for fetuses and 7-day continuous intraperitoneal injections were performed for adults. Then echocardiography was performed with M-mode view assessment on E18.5 and 6 weeks later, respectively. Isoproterenol twice treated fetuses exhibited significant changes in histological evaluation, and mitochondrial damages were significantly severe with increased apoptotic rate. ANP and BNP increased and that of MMP-2 increased in isoproterenol twice treated group compared to control group, without CTGF. The isoforms transition of troponin I and myosin heavy chain of fetal heart dysfunction were opposite to adult procedure. The administration of intra-amniotic isoproterenol to fetal rats could induce heart dysfunction and the regulation of contractile proteins of fetuses was different from adult procedure.

Right ventricular dyssynchrony in idiopathic pulmonary arterial hypertension: determinants and impact on pump function

BACKGROUND

Right ventricular (RV) dyssynchrony has been described in pulmonary arterial hypertension (PAH), but no evidence is available on its morphologic determinants and its effect on systolic function. The aim of this study was to evaluate the morphologic determinants of RV dyssynchrony by echocardiographic and cardiac magnetic resonance imaging and its effect on systolic function.

METHODS

In 60 consecutive idiopathic PAH (IPAH) patients with narrow QRS, RV dyssynchrony was evaluated by 2D speckle-tracking echocardiography, calculating the standard deviation of the times to peak systolic strain for the four mid-basal RV segments (RV-SD4). Patients were grouped by the median value of RV-SD4 (19 milliseconds) and compared for RV remodeling and systolic function parameters, WHO class, pulmonary hemodynamics and 6-minute walk test (6MWT).

RESULTS

Despite similar pulmonary vascular resistance and mean pulmonary arterial pressure, patients with RV-SD4 at >19 milliseconds had advanced WHO class and worse 6MWT, RV hemodynamics, RV remodeling and systolic function parameters compared with patients at ≤19 milliseconds. The morphologic determinants of RV dyssynchrony resulted RV end-diastolic area, LV diastolic eccentricity index and RV mass volume ratio (r = 0.69, r(2) = 0.47, p < 0.0001). Finally, we found a significant inverse correlation between RV mid-basal segments post-systolic shortening time and cardiac index (r = -0.64, r(2) = 0.41, p = 0.001), accounting for the significant correlation between RV-SD4 and cardiac index (r = 0.57, r(2) = 0.32, p = 0.003).

CONCLUSIONS

In IPAH with narrow QRS, RV dyssynchrony is associated with RV dilation and eccentric hypertrophy pattern, suggesting a role of segmental wall stress heterogeneity as the major determinant of mechanical delay. Post-systolic shortening, as inefficient contraction, contributes to pump dysfunction.

N-acetylcysteine improves established monocrotaline-induced pulmonary hypertension in rats

Background

The outcome of patients suffering from pulmonary arterial hypertension (PAH) are predominantly determined by the response of the right ventricle to the increase afterload secondary to high vascular pulmonary resistance. However, little is known about the effects of the current available or experimental PAH treatments on the heart. Recently, inflammation has been implicated in the pathophysiology of PAH. N-acetylcysteine (NAC), a well-known safe anti-oxidant drug, has immuno-modulatory and cardioprotective properties. We therefore hypothesized that NAC could reduce the severity of pulmonary hypertension (PH) in rats exposed to monocrotaline (MCT), lowering inflammation and preserving pulmonary vascular system and right heart function.

Methods

Saline-treated control, MCT-exposed, MCT-exposed and NAC treated rats (day 14–28) were evaluated at day 28 following MCT for hemodynamic parameters (right ventricular systolic pressure, mean pulmonary arterial pressure and cardiac output), right ventricular hypertrophy, pulmonary vascular morphometry, lung inflammatory cells immunohistochemistry (monocyte/macrophages and dendritic cells), IL-6 expression, cardiomyocyte hypertrophy and cardiac fibrosis.

Results

The treatment with NAC significantly decreased pulmonary vascular remodeling, lung inflammation, and improved total pulmonary resistance (from 0.71 ± 0.05 for MCT group to 0.50 ± 0.06 for MCT + NAC group, p < 0.05). Right ventricular function was also improved with NAC treatment associated with a significant decrease in cardiomyocyte hypertrophy (625 ± 69 vs. 439 ± 21 μm² for MCT and MCT + NAC group respectively, p < 0.001) and heart fibrosis (14.1 ± 0.8 vs. 8.8 ± 0.1% for MCT and MCT + NAC group respectively, p < 0.001).

Conclusions

Through its immuno-modulatory and cardioprotective properties, NAC has beneficial effect on pulmonary vascular and right heart function in experimental PH.

Chromatin modifications remodel cardiac gene expression

Signalling and transcriptional control involve precise programmes of gene activation and suppression necessary for cardiovascular physiology. Deep sequencing of DNA-bound transcription factors reveals a remarkable complexity of co-activators or co-repressors that serve to alter chromatin modification and regulate gene expression. The regulated complexes characterized by genome-wide mapping implicate the recruitment and exchange of proteins with specific enzymatic activities that include roles for histone acetylation and methylation in key developmental programmes of the heart. As for transcriptional changes in response to pathological stress, co-regulatory complexes are also differentially utilized to regulate genes in cardiac disease. Members of the histone deacetylase (HDAC) family catalyse the removal of acetyl groups from proteins whose pharmacological inhibition has profound effects preventing heart failure. HDACs interact with a complex co-regulatory network of transcription factors, chromatin-remodelling complexes, and specific histone modifiers to regulate gene expression in the heart. For example, the histone methyltransferase (HMT), enhancer of zeste homolog 2 (Ezh2), is regulated by HDAC inhibition and associated with pathological cardiac hypertrophy. The challenge now is to target the activity of enzymes involved in protein modification to prevent or reverse the expression of genes implicated with cardiac hypertrophy. In this review, we discuss the role of HDACs and HMTs with a focus on chromatin modification and gene function as well as the clinical treatment of heart failure.

Right heart adaptation to pulmonary arterial hypertension: physiology and pathobiology

Survival in patients with pulmonary arterial hypertension (PAH) is closely related to right ventricular (RV) function. Although pulmonary load is an important determinant of RV systolic function in PAH, there remains a significant variability in RV adaptation to pulmonary hypertension. In this report, the authors discuss the emerging concepts of right heart pathobiology in PAH. More specifically, the discussion focuses on the following questions. 1) How is right heart failure syndrome best defined? 2) What are the underlying molecular mechanisms of the failing right ventricle in PAH? 3) How are RV contractility and function and their prognostic implications best assessed? 4) What is the role of targeted RV therapy? Throughout the report, the authors highlight differences between right and left heart failure and outline key areas of future investigation.

Gene expression and β-adrenergic signaling are altered in hypoplastic left heart syndrome

BACKGROUND

The purpose of the current study was to define the myocellular changes and adaptation of the β-adrenergic receptor (β-AR) system that occur in the systemic right ventricle (RV) of children with hypoplastic left heart syndrome (HLHS).

METHODS

Explanted hearts from children with HLHS and non-failing controls were used for this study. HLHS patients were divided into 2 groups: "compensated" (C-HLHS), infants listed for primary transplant with normal RV function and absence of heart failure symptoms, and "decompensated" (D-HLHS), patients listed for transplant after failed surgical palliation with RV failure and/or refractory protein-losing enteropathy or plastic bronchitis.

RESULTS

Compared with non-failing control RVs, the HLHS RV demonstrated decreased sarcoplasmic reticulum calcium-adenosine triphosphatase 2a and α-myosin heavy chain (MHC) gene expression, decreased total β-AR due to down-regulation of β1-AR, preserved cyclic adenosine monophosphate levels, and increased calcium/calmodulin-dependent protein kinase II (CaMKII) activity. There was increased atrial natriuretic peptide expression only in the C-HLHS group. Unique to those in the D-HLHS group was increased β-MHC and decreased α-MHC protein expression (MHC isoform switching), increased adenylyl cyclase 5 expression, and increased phosphorylation of the CaMK target site on phospholamban, threonine 17.

CONCLUSIONS

The HLHS RV has an abnormal myocardial gene expression pattern, downregulation of β1-AR, preserved cyclic adenosine monophosphate levels, and increased CaMKII activity compared with the non-failing control RV. There is MHC isoform switching, increased adenylyl cyclase 5, and increased phosphorylation of phospholamban threonine 17 only in the D-HLHS group. Although abnormal gene expression and changes in the β-AR system precede clinically evident ventricular failure in HLHS, additional unique adaptations occur in those with HLHS and failed surgical palliation.

Effect of vildagliptin, a dipeptidyl peptidase 4 inhibitor, on cardiac hypertrophy induced by chronic beta-adrenergic stimulation in rats

Background

Heart failure with left ventricular (LV) hypertrophy is often associated with insulin resistance and inflammation. Recent studies have shown that dipeptidyl peptidase 4 (DPP4) inhibitors improve glucose metabolism and inflammatory status. We therefore evaluated whether vildagliptin, a DPP4 inhibitor, prevents LV hypertrophy and improves diastolic function in isoproterenol-treated rats.

Methods

Male Wistar rats received vehicle (n = 20), subcutaneous isoproterenol (2.4 mg/kg/day, n = 20) (ISO), subcutaneous isoproterenol (2.4 mg/kg/day + oral vildagliptin (30 mg/kg/day, n = 20) (ISO-VL), or vehicle + oral vildagliptin (30 mg/kg/day, n = 20) (vehicle-VL) for 7 days.

Results

Blood pressure was similar among the four groups, whereas LV hypertrophy was significantly decreased in the ISO-VL group compared with the ISO group (heart weight/body weight, vehicle: 3.2 ± 0.40, ISO: 4.43 ± 0.39, ISO-VL: 4.14 ± 0.29, vehicle-VL: 3.16 ± 0.16, p < 0.05). Cardiac catheterization revealed that vildagliptin lowered the elevated LV end-diastolic pressure observed in the ISO group, but other parameters regarding LV diastolic function such as the decreased minimum dp/dt were not ameliorated in the ISO-VL group. Histological analysis showed that vildagliptin attenuated the increased cardiomyocyte hypertrophy and perivascular fibrosis, but it did not affect angiogenesis in cardiac tissue. In the ISO-VL group, quantitative PCR showed attenuation of increased mRNA expression of tumor necrosis factor-α, interleukin-6, insulin-like growth factor-l, and restoration of decreased mRNA expression of glucose transporter type 4.

Conclusions

Vildagliptin may prevent LV hypertrophy caused by continuous exposure to isoproterenol in rats.

Pressure-overload-induced right heart failure

Although pulmonary arterial hypertension originates in the lung and is caused by progressive remodeling of the small pulmonary arterioles, patients die from the consequences of pressure-overload-induced right heart failure. Prognosis is poor, and currently there are no selective treatments targeting the failing right ventricle. Therefore, it is of utmost importance to obtain more insights into the mechanisms of right ventricular adaptation and the transition toward right heart failure. In this review, we propose that the same adaptive mechanisms, which initially preserve right ventricular systolic function and maintain cardiac output, eventually initiate the transition toward right heart failure.

Right ventricular failure and pathobiology in patients with congenital heart disease - implications for long-term follow-up

Right ventricular dysfunction represents a common problem in patients with congenital heart defects, such as Tetralogy of Fallot or pulmonary arterial hypertension. Patients with congenital heart defects may present with a pressure or volume overloaded right ventricle (RV) in a bi-ventricular heart or in a single ventricular circulation in which the RV serves as systemic ventricle. Both subsets of patients are at risk of developing right ventricular failure. Obtaining functional and morphological imaging data of the right heart is technically more difficult than imaging of the left ventricle. In contrast to findings on mechanisms of left ventricular dysfunction, very little is known about the pathophysiologic alterations of the right heart. The two main causes of right ventricular dysfunction are pressure and/or volume overload of the RV. Until now, there are no appropriate models available analyzing the effects of pressure and/or volume overload on the RV. This review intends to summarize clinical aspects mainly focusing on the current research in this field. In future, there will be increasing attention to individual care of patients with right heart diseases. Hence, further investigations are essential for understanding the right ventricular pathobiology.

M-protein is down-regulated in cardiac hypertrophy driven by thyroid hormone in rats

Although it is well known that the thyroid hormone (T3) is an important positive regulator of cardiac function over a short term and that it also promotes deleterious effects over a long term, the molecular mechanisms for such effects are not yet well understood. Because most alterations in cardiac function are associated with changes in sarcomeric machinery, the present work was undertaken to find novel sarcomeric hot spots driven by T3 in the heart. A microarray analysis indicated that the M-band is a major hot spot, and the structural sarcomeric gene coding for the M-protein is severely down-regulated by T3. Real-time quantitative PCR-based measurements confirmed that T3 (1, 5, 50, and 100 physiological doses for 2 days) sharply decreased the M-protein gene and protein expression in vivo in a dose-dependent manner. Furthermore, the M-protein gene expression was elevated 3.4-fold in hypothyroid rats. Accordingly, T3 was able to rapidly and strongly reduce the M-protein gene expression in neonatal cardiomyocytes. Deletions at the M-protein promoter and bioinformatics approach suggested an area responsive to T3, which was confirmed by chromatin immunoprecipitation assay. Functional assays in cultured neonatal cardiomyocytes revealed that depletion of M-protein (by small interfering RNA) drives a severe decrease in speed of contraction. Interestingly, mRNA and protein levels of other M-band components, myomesin and embryonic-heart myomesin, were not altered by T3. We concluded that the M-protein expression is strongly and rapidly repressed by T3 in cardiomyocytes, which represents an important aspect for the basis of T3-dependent sarcomeric deleterious effects in the heart.

Right ventricle in pulmonary hypertension

During heart development chamber specification is controlled and directed by a number of genes and a fetal heart gene expression pattern is revisited during heart failure. In the setting of chronic pulmonary hypertension the right ventricle undergoes hypertrophy, which is likely initially adaptive, but often followed by decompensation, dilatation and failure. Here we discuss differences between the right ventricle and the left ventricle of the heart and begin to describe the cellular and molecular changes which characterize right heart failure. A prevention and treatment of right ventricle failure becomes a treatment goal for patients with severe pulmonary hypertension it follows that we need to understand the pathobiology of right heart hypertrophy and the transition to right heart failure.

Increase in cardiac myosin heavy-chain (MyHC) alpha protein isoform in hibernating ground squirrels, with echocardiographic visualization of ventricular wall hypertrophy and prolonged contraction

Deep hibernators such as golden-mantled ground squirrels (Callospermophilus lateralis) have multiple challenges to cardiac function during low temperature torpor and subsequent arousals. As heart rates fall from over 300 beats min(-1) to less than 10, chamber dilation and reduced cardiac output could lead to congestive myopathy. We performed echocardiography on a cohort of individuals prior to and after several months of hibernation. The left ventricular chamber exhibited eccentric and concentric hypertrophy during hibernation and thus calculated ventricular mass was ~30% greater. Ventricular ejection fraction was mildly reduced during hibernation but stroke volumes were greater due to the eccentric hypertrophy and dramatically increased diastolic filling volumes. Globally, the systolic phase in hibernation was ~9.5 times longer, and the diastolic phase was 28× longer. Left atrial ejection generally was not observed during hibernation. Atrial ejection returned weakly during early arousal. Strain echocardiography assessed the velocity and total movement distance of contraction and relaxation for regional ventricular segments in active and early arousal states. Myocardial systolic strain during early arousal was significantly greater than the active state, indicating greater total contractile movement. This mirrored the increased ventricular ejection fraction noted with early arousal. However, strain rates were slower during early arousal than during the active period, particularly systolic strain, which was 33% of active, compared with the rate of diastolic strain, which was 67% of active. As heart rate rose during the arousal period, myocardial velocities and strain rates also increased; this was matched closely by cardiac output. Curiously, though heart rates were only 26% of active heart rates during early arousal, the cardiac output was nearly 40% of the active state, suggesting an efficient pumping system. We further analyzed proportions of cardiac myosin heavy-chain (MyHC) isoforms in a separate cohort of squirrels over 5 months, including time points before hibernation, during hibernation and just prior to emergence. Hibernating individuals were maintained in both a 4°C cold room and a 20°C warm room. Measured by SDS-PAGE, relative percentages of cardiac MyHC alpha were increased during hibernation, at both hibernacula temperatures. A potential increase in contractile speed, and power, from more abundant MyHC alpha may aid force generation at low temperature and at low heart rates. Unlike many models of cardiomyopathies where the alpha isoform is replaced by the beta isoform in order to reduce oxygen consumption, ground squirrels demonstrate a potential cardioprotective mechanism to maintain cardiac output during torpor.

Hormonal regulation of β-myosin heavy chain expression in the mouse left ventricle

We investigated the influence of sex hormones on the expression of α- and β-cardiac myosin heavy chain isoforms (α-MHC and β-MHC) in C57bl/6 mice of both sexes under physiological and pathological conditions. In the left ventricles (LVs) of fertile female mice, β-MHC expression was tenfold higher compared with the age-matched males, whereas no difference was found in α-MHC expression. These differences disappeared after ovariectomy or in immature mice. We also found a sex-related difference in expression of β-adrenoceptors (β1-AR), as mRNA levels of this gene were 40% lower in fertile females compared with males of the same age but did not differ in prepubertal or ovariectomized animals. Interestingly, the deletion of both β1- and β2-ARs abolished sex difference of β-MHC expression, as mRNA levels in the LVs of knockout males were increased and reached values comparable to those of knockout females. Moreover, the β1-AR antagonist metoprolol induced about a threefold increase in β-MHC expression in adult male mice. The capability of gender to regulate β-MHC expression was also evaluated in the presence of hemodynamic overload. Thoracic aortic coarctation (TAC) produced cardiac hypertrophy along with a 12-fold increase in β-MHC and a 50% decrease in β1-AR expression in males but not in females, thus abolishing the gender difference observed in sham animals for such genes. By contrast, TAC did not change β2-AR expression. In conclusion, our results show that the expression of β-MHC and β1-AR in the LVs undergo gender-related and correlated changes under both physiological and pathological conditions and suggest a role of β1-AR-mediated signaling.

Right ventricular plasticity and functional imaging

Right ventricular (RV) function is a strong independent predictor of outcome in a number of distinct cardiopulmonary diseases. The RV has a remarkable ability to sustain damage and recover function which may be related to unique anatomic, physiologic, and genetic factors that differentiate it from the left ventricle. This capacity has been described in patients with RV myocardial infarction, pulmonary arterial hypertension, and chronic thromboembolic disease as well as post-lung transplant and post-left ventricular assist device implantation. Various echocardiographic and magnetic resonance imaging parameters of RV function contribute to the clinical assessment and predict outcomes in these patients; however, limitations remain with these techniques. Early diagnosis of RV function and better insight into the mechanisms of RV recovery could improve patient outcomes. Further refinement of established and emerging imaging techniques is necessary to aid subclinical diagnosis and inform treatment decisions.

Transgenic rabbit models for studying human cardiovascular diseases

Cardiovascular diseases involve the heart or blood vessels and remain a leading cause of morbidity and mortality in developed countries. A variety of animal models have been used to study cardiovascular diseases and have contributed to our understanding of their pathophysiology and treatment. However, mutations or abnormal expression of specific genes play important roles in the pathophysiology of some heart diseases, for which a closely similar animal model often is not naturally available. With the advent of techniques for specific genomic modification, several transgenic and knockout mouse models have been developed for cardiovascular conditions that result from spontaneous mutations. However, mouse and human heart show marked electrophysiologic differences. In addition, cardiac studies in mouse models are extremely difficult because of their small heart size and fast heart rate. Therefore, larger genetically engineered animal models are needed to overcome the limitations of the mouse models. This review summarizes the transgenic rabbit models that have been developed to study cardiovascular diseases.

Lost in transgenesis: a user's guide for genetically manipulating the mouse in cardiac research

The advent of modern mouse genetics has benefited many fields of diseased-based research over the past 20 years, none perhaps more profoundly than cardiac biology. Indeed, the heart is now arguably one of the easiest tissues to genetically manipulate, given the availability of an ever-growing tool chest of molecular reagents/promoters and "facilitator" mouse lines. It is now possible to modify the expression of essentially any gene or partial gene product in the mouse heart at any time, either gain or loss of function. This review is designed as a handbook for the nonmouse geneticist and/or junior investigator to permit the successful manipulation of any gene or RNA product in the heart, while avoiding artifacts. In the present review, guidelines, pitfalls, and limitations are presented so that rigorous and appropriate examination of cardiac genotype-phenotype relationships can be performed. This review uses examples from the field to illustrate the vast spectrum of experimental and design details that must be considered when using genetically modified mouse models to study cardiac biology.

MAP kinase kinase kinase-2 (MEKK2) regulates hypertrophic remodeling of the right ventricle in hypoxia-induced pulmonary hypertension

Pulmonary hypertension (PH) results in pressure overload of the right ventricle (RV) of the heart, initiating pathological RV remodeling and ultimately leading to right heart failure. Substantial research indicates that signaling through the MAPK superfamily mediates pathological cardiac remodeling. These considerations led us to test the hypothesis that the regulatory protein MAPKKK-2 (MEKK2) contributes to RV hypertrophy in hypoxia-induced PH. Transgenic mice with global knockout of MEKK2 (MEKK2(-/-) mice) and age-matched wild-type (WT) mice were exposed to chronic hypobaric hypoxia (10% O(2), 6 wk) and compared with animals under normoxia. Exposure to chronic hypoxia induced PH in WT and MEKK2(-/-) mice. In response to PH, WT mice showed RV hypertrophy, demonstrated as increased ratio of RV weight to body weight, increased RV wall thickness at diastole, and increased cardiac myocyte size compared with normoxic control animals. In contrast, each of these measures of RV hypertrophy seen in WT mice after chronic hypoxia was attenuated in MEKK2(-/-) mice. Furthermore, chronic hypoxia elicited altered programs of hypertrophic and inflammatory gene expression consistent with pathological RV remodeling in WT mice; MEKK2 deletion selectively inhibited inflammatory gene expression compared with WT mice. The actions of MEKK2 were mediated in part through regulation of the abundance and phosphorylation of its effector, ERK5. In conclusion, signaling by MEKK2 contributes to RV hypertrophy and altered myocardial inflammatory gene expression in response to hypoxia-induced PH. Therapies targeting MEKK2 may protect the myocardium from hypertrophy and pathological remodeling in human PH.

Two distinct phosphorylation events govern the function of muscle FHOD3

Posttranslational modifications such as phosphorylation are universally acknowledged regulators of protein function. Recently we characterised a striated muscle-specific isoform of the formin FHOD3 that displays distinct subcellular targeting and protein half-life compared to its non-muscle counterpart and which is dependent on phosphorylation by CK2 (formerly casein kinase 2). We now show that the two isoforms of FHOD3 are already expressed in the vertebrate embryonic heart. Analysis of CK2 alpha knockout mice showed that phosphorylation by CK2 is also required for proper targeting of muscle FHOD3 to the myofibrils in embryonic cardiomyocytes in situ. The localisation of muscle FHOD3 in the sarcomere varies depending on the maturation state, being either broader or restricted to the Z-disc proper in the adult heart. Following myofibril disassembly, such as that in dedifferentiating adult rat cardiomyocytes in culture, the expression of non-muscle FHOD3 is up-regulated, which is reversed once the myofibrils are reassembled. The shift in expression levels of different isoforms is accompanied by an increased co-localisation with p62, which is involved in autophagy, and affects the half-life of FHOD3. Phosphorylation of three amino acids in the C-terminus of FHOD3 by ROCK1 is sufficient for activation, which results in increased actin filament synthesis in cardiomyocytes and also a broader localisation pattern of FHOD3 in the myofibrils. ROCK1 can directly phosphorylate FHOD3, and FHOD3 seems to be the downstream mediator of the exaggerated actin filament formation phenotype that is induced in cardiomyocytes upon the overexpression of constitutively active ROCK1. We conclude that the expression of the muscle FHOD3 isoform is characteristic of the healthy mature heart and that two distinct phosphorylation events are crucial to regulate the activity of this isoform in thin filament assembly and maintenance.

Dynamic link between histone H3 acetylation and an increase in the functional characteristics of human ESC/iPSC-derived cardiomyocytes

Cardiomyocytes (CMs) derived from human embryonic stem cells (hESCs) or human induced pluripotent stem cells (hiPSCs) are functionally heterogeneous, display insufficient biological efficacy and generally possess the electrophysiological properties seen in fetal CMs. However, a homogenous population of hESC/hiPSC-CMs, with properties similar to those of adult human ventricular cells, is required for use in drug cardiotoxicity screening. Unfortunately, despite the requirement for the functional characteristics of post-mitotic beating cell aggregates to mimic the behavior of mature cardiomyocytes in vitro, few technological improvements have been made in this field to date. Previously, we showed that culturing hESC-CMs under low-adhesion conditions with cyclic replating confers continuous contractility on the cells, leading to a functional increase in cardiac gene expression and electrophysiological properties over time. The current study reveals that culturing hESC/hiPSC-CMs under non-adhesive culture conditions enhances the electrophysiological properties of the CMs through an increase in the acetylation of histone H3 lysine residues, as confirmed by western blot analyses. Histone H3 acetylation was induced chemically by treating primitive hESC/hiPSC-CMs with Trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, resulting in an immediate increase in global cardiac gene expression. In functional analyses using multi-electrode array (MEA) recordings, TSA-treated hESC/hiPSC-CM colonies showed appropriate responses to particular concentrations of known potassium ion channel inhibitors. Thus, the combination of a cell-autonomous functional increase in response to non-adhesive culture and short-term TSA treatment of hESC/hiPSC-CM colonies cultured on MEA electrodes will help to make cardiac toxicity tests more accurate and reproducible via genome-wide chromatin activation.