NRG-1-induced cardiomyocyte hypertrophy. Role of PI-3-kinase, p70(S6K), and MEK-MAPK-RSK

Nrg1 Regulates Cardiomyocyte Migration and Cell Cycle in Ventricular Development

BACKGROUND

Cardiac ventricles provide the contractile force of the beating heart throughout life. How the primitive endocardium-layered myocardial projections called trabeculae form and mature into the adult ventricles is of great interest for biology and regenerative medicine. Trabeculation is dependent on the signaling protein Nrg1 (neuregulin-1). However, the mechanism of action of Nrg1 and its role in ventricular wall maturation are poorly understood.

METHODS

We investigated the functions and downstream mechanisms of Nrg1 signaling during ventricular chamber development using confocal imaging, transcriptomics, and biochemical approaches in mice with cardiac-specific inactivation or overexpression of Nrg1.

RESULTS

Analysis of cardiac-specific Nrg1 mutant mice showed that the transcriptional program underlying cardiomyocyte-oriented cell division and trabeculae formation depends on endocardial Nrg1 to myocardial ErbB2 (erb-b2 receptor tyrosine kinase 2) signaling and phospho-Erk (phosphorylated extracellular signal-regulated kinase; pErk) activation. Early endothelial loss of Nrg1 and reduced pErk activation diminished cardiomyocyte Pard3 and Crumbs2 (Crumbs Cell Polarity Complex Component 2) protein and altered cytoskeletal gene expression and organization. These alterations are associated with abnormal gene expression related to mitotic spindle organization and a shift in cardiomyocyte division orientation. Nrg1 is crucial for trabecular growth and ventricular wall thickening by regulating an epithelial-to-mesenchymal transition-like process in cardiomyocytes involving migration, adhesion, cytoskeletal actin turnover, and timely progression through the cell cycle G2/M phase. Ectopic cardiac Nrg1 overexpression and high pErk signaling caused S-phase arrest, sustained high epithelial-to-mesenchymal transition-like gene expression, and prolonged trabeculation, blocking compact myocardium maturation. Myocardial trabecular patterning alterations resulting from above- or below-normal Nrg1-dependent pErk activation were concomitant with sarcomere actin cytoskeleton disorganization. The Nrg1 loss- and gain-of-function transcriptomes were enriched for Yap1 (yes-associated protein-1) gene signatures, identifying Yap1 as a potential downstream effector. Furthermore, biochemical and imaging data reveal that Nrg1 influences pErk activation and Yap1 nuclear-cytoplasmic distribution during trabeculation.

CONCLUSIONS

These data establish the Nrg1-ErbB2/ErbB4-Erk axis as a crucial regulator of cardiomyocyte cell cycle progression and migration during ventricular development.

Comparative Analysis of Heart Regeneration: Searching for the Key to Heal the Heart-Part II: Molecular Mechanisms of Cardiac Regeneration

Cardiovascular diseases are the leading cause of death worldwide, among which ischemic heart disease is the most representative. Myocardial infarction results from occlusion of a coronary artery, which leads to an insufficient blood supply to the myocardium. As it is well known, the massive loss of cardiomyocytes cannot be solved due the limited regenerative ability of the adult mammalian hearts. In contrast, some lower vertebrate species can regenerate the heart after an injury; their study has disclosed some of the involved cell types, molecular mechanisms and signaling pathways during the regenerative process. In this 'two parts' review, we discuss the current state-of-the-art of the main response to achieve heart regeneration, where several processes are involved and essential for cardiac regeneration.

STAT5b is a key effector of NRG-1/ERBB4-mediated myocardial growth

The growth factor Neuregulin-1 (NRG-1) regulates myocardial growth and is currently under clinical investigation as a treatment for heart failure. Here, we demonstrate in several in vitro and in vivo models that STAT5b mediates NRG-1/EBBB4-stimulated cardiomyocyte growth. Genetic and chemical disruption of the NRG-1/ERBB4 pathway reduces STAT5b activation and transcription of STAT5b target genes Igf1, Myc, and Cdkn1a in murine cardiomyocytes. Loss of Stat5b also ablates NRG-1-induced cardiomyocyte hypertrophy. Dynamin-2 is shown to control the cell surface localization of ERBB4 and chemical inhibition of Dynamin-2 downregulates STAT5b activation and cardiomyocyte hypertrophy. In zebrafish embryos, Stat5 is activated during NRG-1-induced hyperplastic myocardial growth, and chemical inhibition of the Nrg-1/Erbb4 pathway or Dynamin-2 leads to loss of myocardial growth and Stat5 activation. Moreover, CRISPR/Cas9-mediated knockdown of stat5b results in reduced myocardial growth and cardiac function. Finally, the NRG-1/ERBB4/STAT5b signaling pathway is differentially regulated at mRNA and protein levels in the myocardium of patients with pathological cardiac hypertrophy as compared to control human subjects, consistent with a role of the NRG-1/ERBB4/STAT5b pathway in myocardial growth.

Endothelial Dysfunction in Heart Failure With Preserved Ejection Fraction: What are the Experimental Proofs?

Heart failure with preserved ejection fraction (HFpEF) has been recognized as the greatest single unmet need in cardiovascular medicine. Indeed, the morbi-mortality of HFpEF is high and as the population ages and the comorbidities increase, so considerably does the prevalence of HFpEF. However, HFpEF pathophysiology is still poorly understood and therapeutic targets are missing. An unifying, but untested, theory of the pathophysiology of HFpEF, proposed in 2013, suggests that cardiovascular risk factors lead to a systemic inflammation, which triggers endothelial cells (EC) and coronary microvascular dysfunction. This cardiac small vessel disease is proposed to be responsible for cardiac wall stiffening and diastolic dysfunction. This paradigm is based on the fact that microvascular dysfunction is highly prevalent in HFpEF patients. More specifically, HFpEF patients have been shown to have decreased cardiac microvascular density, systemic endothelial dysfunction and a lower mean coronary flow reserve. Importantly, impaired coronary microvascular function has been associated with the severity of HF. This review discusses evidence supporting the causal role of endothelial dysfunction in the pathophysiology of HFpEF in human and experimental models.

Rho-Proteins and Downstream Pathways as Potential Targets in Sepsis and Septic Shock: What Have We Learned from Basic Research

Sepsis and septic shock are associated with acute and sustained impairment in the function of the cardiovascular system, kidneys, lungs, liver, and brain, among others. Despite the significant advances in prevention and treatment, sepsis and septic shock sepsis remain global health problems with elevated mortality rates. Rho proteins can interact with a considerable number of targets, directly affecting cellular contractility, actin filament assembly and growing, cell motility and migration, cytoskeleton rearrangement, and actin polymerization, physiological functions that are intensively impaired during inflammatory conditions, such as the one that occurs in sepsis. In the last few decades, Rho proteins and their downstream pathways have been investigated in sepsis-associated experimental models. The most frequently used experimental design included the exposure to bacterial lipopolysaccharide (LPS), in both in vitro and in vivo approaches, but experiments using the cecal ligation and puncture (CLP) model of sepsis have also been performed. The findings described in this review indicate that Rho proteins, mainly RhoA and Rac1, are associated with the development of crucial sepsis-associated dysfunction in different systems and cells, including the endothelium, vessels, and heart. Notably, the data found in the literature suggest that either the inhibition or activation of Rho proteins and associated pathways might be desirable in sepsis and septic shock, accordingly with the cellular system evaluated. This review included the main findings, relevance, and limitations of the current knowledge connecting Rho proteins and sepsis-associated experimental models.

p38 Mitogen-activated protein kinase regulates chamber-specific perinatal growth in heart

In the mammalian heart, the left ventricle (LV) rapidly becomes more dominant in size and function over the right ventricle (RV) after birth. The molecular regulators responsible for this chamber-specific differential growth are largely unknown. We found that cardiomyocytes in the neonatal mouse RV had lower proliferation, more apoptosis, and a smaller average size compared with the LV. This chamber-specific growth pattern was associated with a selective activation of p38 mitogen-activated protein kinase (MAPK) activity in the RV and simultaneous inactivation in the LV. Cardiomyocyte-specific deletion of both the Mapk14 and Mapk11 genes in mice resulted in loss of p38 MAPK expression and activity in the neonatal heart. Inactivation of p38 activity led to a marked increase in cardiomyocyte proliferation and hypertrophy but diminished cardiomyocyte apoptosis, specifically in the RV. Consequently, the p38-inactivated hearts showed RV-specific enlargement postnatally, progressing to pulmonary hypertension and right heart failure at the adult stage. Chamber-specific p38 activity was associated with differential expression of dual-specific phosphatases (DUSPs) in neonatal hearts, including DUSP26. Unbiased transcriptome analysis revealed that IRE1α/XBP1-mediated gene regulation contributed to p38 MAPK-dependent regulation of neonatal cardiomyocyte proliferation and binucleation. These findings establish an obligatory role of DUSP/p38/IRE1α signaling in cardiomyocytes for chamber-specific growth in the postnatal heart.

Role of Muscle-Specific Histone Methyltransferase (Smyd1) in Exercise-Induced Cardioprotection against Pathological Remodeling after Myocardial Infarction

Pathological remodeling is the main detrimental complication after myocardial infarction (MI). Overproduction of reactive oxygen species (ROS) in infarcted myocardium may contribute to this process. Adequate exercise training after MI may reduce oxidative stress-induced cardiac tissue damage and remodeling. SET and MYND domain containing 1 (Smyd1) is a muscle-specific histone methyltransferase which is upregulated by resistance training, may strengthen sarcomere assembly and myofiber folding, and may promote skeletal muscles growth and hypertrophy. However, it remains elusive if Smyd1 has similar functions in post-MI cardiac muscle and participates in exercise-induced cardioprotection. Accordingly, we investigated the effects of interval treadmill exercise on cardiac function, ROS generation, Smyd1 expression, and sarcomere assembly of F-actin in normal and infarcted hearts. Adult male rats were randomly divided into five groups (n = 10/group): control (C), exercise alone (EX), sham-operated (S), MI induced by permanent ligation of left anterior descending coronary artery (MI), and MI with interval exercise training (MI + EX). Exercise training significantly improved post-MI cardiac function and sarcomere assembly of F-actin. The cardioprotective effects were associated with increased Smyd1, Trx1, cTnI, and α-actinin expression as well as upregulated ratio of phosphorylated AMP-activated protein kinase (AMPK)/AMPK, whereas Hsp90, MuRF1, brain natriuretic peptide (BNP) expression, ROS generation, and myocardial fibrosis were attenuated. The improved post-MI cardiac function was associated with increased Smyd1 expression. In cultured H9C2 cardiomyoblasts, in vitro treatment with H₂O₂ (50 µmol/L) or AMP-activated protein kinase (AMPK) agonist (AICAR, 1 mmol/L) or their combination for 4 h simulated the effects of exercise on levels of ROS and Smyd1. In conclusion, we demonstrated a novel role of Smyd1 in association with post-MI exercise-induced cardioprotection. The moderate level of ROS-induced upregulation of Smyd1 may be an important target for modulating post-MI cardiac function and remodeling.

Growth factor therapy for cardiac repair: an overview of recent advances and future directions

Heart disease represents a significant public health burden and is associated with considerable morbidity and mortality at the level of the individual. Current therapies for pathologies such as myocardial infarction, cardiomyopathy and heart failure are unable to repair damaged tissue to an extent that provides restoration of function approaching that of the pre-diseased state. Novel approaches to repair and regenerate the injured heart include cell therapy and the use of exogenous factors. Improved understanding of the role of growth factors in endogenous cardiac repair processes has motivated the investigation of their potential as therapeutic agents for cardiac pathology. Despite the disappointing performance of other growth factors in historical clinical trials, insulin-like growth factor 1 (IGF-1), neuregulin and platelet-derived growth factor (PDGF) have recently emerged as new candidate therapies. These growth factors elicit tissue repair through anti-apoptotic, pro-angiogenic and fibrosis-modulating mechanisms and have produced clinically significant functional improvement in preclinical studies. Early human trials suggest that IGF-1 and neuregulin are well tolerated and yield dose-dependent benefit, warranting progression to later phase studies. However, outstanding challenges such as short growth factor serum half-life and insufficient target-organ specificity currently necessitate the development of novel delivery strategies.

Neuregulin-1 promotes mitochondrial biogenesis, attenuates mitochondrial dysfunction, and prevents hypoxia/reoxygenation injury in neonatal cardiomyocytes

Neuregulin-1 (NRG-1)/erythroblastic leukaemia viral oncogene homologues (ErbB) pathway activation plays a crucial role in regulating the adaptation of the adult heart to physiological and pathological stress. In the present study, we investigate the effect of recombined human NRG-1 (rhNRG-1) on mitochondrial biogenesis, mitochondrial function, and cell survival in neonatal rat cardiac myocytes (NRCMs) exposed to hypoxia/reoxygenation (H/R). The results of this study showed that, in the H/R-exposed NRCMs, mitochondrial biogenesis was impaired, as manifested by the decrease of the expression of peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) and mitochondrial membrane proteins, the inner membrane (Tim23), mitofusin 1 (Mfn1), and mitofusin 2 (Mfn2). RhNRG-1 pretreatment effectively restored the expression of PGC-1α and these membrane proteins, upregulated the expression of the anti-apoptosis proteins Bcl-2 and Bcl-xL, preserved the mitochondrial membrane potential, and attenuated H/R-induced cell apoptosis. Blocking PGC-1 expression with siRNA abolished the beneficial role of rhNRG-1 on mitochondrial function and cell survival. The results of the present study strongly suggest that NRG-1/ErbB activation enhances the adaption of cardiomyocytes to H/R injury via promoted mitochondrial biogenesis and improved mitochondrial homeostasis. SIGNIFICANCE OF THE STUDY: The results of this research revealed for the first time the relationship between neuregulin-1 (NRG-1)/erythroblastic leukaemia viral oncogene homologues (ErbB) activation and mitochondrial biogenesis in neonatal cardiomyocytes and verified the significance of this promoted mitochondrial biogenesis in attenuating hypoxia/reoxygenation injury. This finding may open a new field to further understand the biological role of NRG-1/ErbB signalling pathway in cardiomyocyte.

MircroRNA-10b Promotes Human Embryonic Stem Cell-Derived Cardiomyocyte Proliferation via Novel Target Gene LATS1

Adult mammalian cardiomyocytes (CMs) retain a limited proliferative ability, which is insufficient for the repair of CM loss in ischemic cardiac injury. Regulation of the Hippo signaling pathway to promote endogenous CM proliferation has emerged as a promising strategy for heart regeneration. Previous studies have shown that the microRNA cluster miR302-367 negatively regulates the Hippo pathway, promoting CM proliferation. In this study, we identified another microRNA, miR-10b, that regulates the Hippo pathway and promotes cell proliferation in human embryonic stem cell-derived CMs (hESC-CMs). We observed that miR-10b expression was enriched in the early stage of CMs, but its expression was reduced over time. Overexpression of miR-10b promoted CM proliferation, while knockdown of miR-10b suppressed CM proliferation. Moreover, miR-10b protected CMs against apoptosis. miR-10b functions, in part, by directly targeting LATS1, which is a major component of the Hippo pathway. Our study suggests that miR-10b has promising potential for heart regeneration.

Mechanisms of the Multitasking Endothelial Protein NRG-1 as a Compensatory Factor During Chronic Heart Failure

Heart failure is a complex syndrome whose phenotypic presentation and disease progression depends on a complex network of adaptive and maladaptive responses. One of these responses is the endothelial release of NRG (neuregulin)-1—a paracrine growth factor activating ErbB2 (erythroblastic leukemia viral oncogene homolog B2), ErbB3, and ErbB4 receptor tyrosine kinases on various targets cells. NRG-1 features a multitasking profile tuning regenerative, inflammatory, fibrotic, and metabolic processes. Here, we review the activities of NRG-1 on different cell types and organs and their implication for heart failure progression and its comorbidities. Although, in general, effects of NRG-1 in heart failure are compensatory and beneficial, translation into therapies remains unaccomplished both because of the complexity of the underlying pathways and because of the challenges in the development of therapeutics (proteins, peptides, small molecules, and RNA-based therapies) for tyrosine kinase receptors. Here, we give an overview of the complexity to be faced and how it may be tackled.

Glial Growth Factor 2 Regulates Glucose Transport in Healthy Cardiac Myocytes and During Myocardial Infarction via an Akt-Dependent Pathway

Neuregulin (NRG), a paracrine factor in myocytes, promotes cardiac development via the ErbB receptors. NRG-1β also improves cardiac function and cell survival after myocardial infarction (MI), although the mechanisms underlying these cardioprotective effects are not well elucidated. Increased glucose uptake has been shown to be cardio-protective during MI. We hypothesized that treatment with a recombinant version of NRG-1β, glial growth factor 2 (GGF2), will enhance glucose transport in the healthy myocardium and during MI. Cardiac myocytes were isolated from MI and healthy adult rats, and subsequently incubated with or without insulin or GGF2. Glucose uptake was measured using a fluorescent D-glucose analog. The translocation of glucose transporter (GLUT) 4 to the cell surface, the rate-limiting step in glucose uptake, was measured using a photolabeled biotinylation assay in isolated myocytes. Similar to insulin, acute in vitro GGF2 treatment increased glucose uptake in healthy cardiac myocytes (by 40 and 49%, respectively, P = 0.002). GGF2 treatment also increased GLUT4 translocation in healthy myocytes by 184% (P < 0.01), while ErbB 2/4 receptor blockade (by afatinib) abolished these effects. In addition, GGF2 treatment enhanced Akt phosphorylation (at both threonine and serine sites, by 75 and 139%, respectively, P = 0.029 and P = 0.01), which was blunted by ErbB 2/4 receptor blockade. GGF2 treatment increased the phosphorylation of AS160 (an Akt effector) by 72% (P < 0.05), as well as the phosphorylation of PDK-1 and PKC (by 118 and 92%, respectively, P < 0.05). During MI, cardiac GLUT4 translocation was downregulated by 44% (P = 0.004) and was partially rescued by both in vitro insulin and GGF2 treatment. Our data demonstrate that acute GGF2 treatment increased glucose transport in cardiac myocytes by activating the ErbB 2/4 receptors and subsequent key downstream effectors (i.e., PDK-1, Akt, AS160, and PKC). These findings highlight novel mechanisms of action of GGF2, which warrant further investigation in patients with heart failure.

Metabolic Mechanisms of Exercise-Induced Cardiac Remodeling

Exercise has a myriad of physiological benefits that derive in part from its ability to improve cardiometabolic health. The periodic metabolic stress imposed by regular exercise appears fundamental in driving cardiovascular tissue adaptation. However, different types, intensities, or durations of exercise elicit different levels of metabolic stress and may promote distinct types of tissue remodeling. In this review, we discuss how exercise affects cardiac structure and function and how exercise-induced changes in metabolism regulate cardiac adaptation. Current evidence suggests that exercise typically elicits an adaptive, beneficial form of cardiac remodeling that involves cardiomyocyte growth and proliferation; however, chronic levels of extreme exercise may increase the risk for pathological cardiac remodeling or sudden cardiac death. An emerging theme underpinning acute as well as chronic cardiac adaptations to exercise is metabolic periodicity, which appears important for regulating mitochondrial quality and function, for stimulating metabolism-mediated exercise gene programs and hypertrophic kinase activity, and for coordinating biosynthetic pathway activity. In addition, circulating metabolites liberated during exercise trigger physiological cardiac growth. Further understanding of how exercise-mediated changes in metabolism orchestrate cell signaling and gene expression could facilitate therapeutic strategies to maximize the benefits of exercise and improve cardiac health.

Effects of neuregulin-1 on autonomic nervous system remodeling post-myocardial infarction in a rat model

Sympathetic nerve and vagus nerve remodeling play an important part in cardiac function post-myocardial infarction (MI). Increasing evidence indicates that neuregulin-1 (NRG-1) improves cardiac function following heart failure. Since its impact on cardiac function and neural remodeling post-MI is poorly understood, we aimed to investigate the role of NRG-1 in autonomic nervous system remodeling post-MI. Forty-five Sprague-Dawley rats were equally randomized into three groups: sham (with the left anterior descending coronary artery exposed but without ligation), MI (left anterior descending coronary artery ligation), and MI plus NRG-1 (left anterior descending coronary artery ligation followed by intraperitoneal injection of NRG-1 (10 μg/kg, once daily for 7 days)). At 4 weeks after MI, echocardiography was used to detect the rat cardiac function by measuring the left ventricular end-systolic inner diameter, left ventricular diastolic diameter, left ventricular end-systolic volume, left ventricular end-diastolic volume, left ventricular ejection fraction, and left ventricular fractional shortening. mRNA and protein expression levels of tyrosine hydroxylase, growth associated protein-43 (neuronal specific protein), nerve growth factor, choline acetyltransferase (vagus nerve marker), and vesicular acetylcholine transporter (cardiac vagal nerve fiber marker) in ischemic myocardia were detected by real-time PCR and western blot assay to assess autonomous nervous remodeling. After MI, the rat cardiac function deteriorated significantly, and it was significantly improved after NRG-1 injection. Compared with the MI group, mRNA and protein levels of tyrosine hydroxylase and growth associated protein-43, as well as choline acetyltransferase mRNA level significantly decreased in the MI plus NRG-1 group, while mRNA and protein levels of nerve growth factor and vesicular acetylcholine transporters, as well as choline acetyltransferase protein level slightly decreased. Our results indicate that NRG-1 can improve cardiac function and regulate sympathetic and vagus nerve remodeling post-MI, thus reaching a new balance of the autonomic nervous system to protect the heart from injury.

IGF1 and NRG1 Enhance Proliferation, Metabolic Maturity, and the Force-Frequency Response in hESC-Derived Engineered Cardiac Tissues

Insulin-like growth factor 1 (IGF1) and neuregulin-1β (NRG1) play important roles during cardiac development both individually and synergistically. In this study, we analyze how 3D cardiac tissue engineered from human embryonic stem cell- (hESC-) derived cardiomyocytes and 2D-plated hESC-cardiomyocytes respond to developmentally relevant growth factors both to stimulate maturity and to characterize the therapeutic potential of IGF1 and NRG1. When administered to engineered cardiac tissues, a significant decrease in active force production of ~65% was measured in all treatment groups, likely due to changes in cellular physiology. Developmentally related processes were identified in engineered tissues as IGF1 increased hESC-cardiomyocyte proliferation 3-fold over untreated controls and NRG1 stimulated oxidative phosphorylation and promoted a positive force-frequency relationship in tissues up to 3 Hz. hESC-cardiomyocyte area increased significantly with NRG1 and IGF1 + NRG1 treatment in 2D culture and gene expression data suggested increased cardiac contractile components in engineered tissues, indicating the need for functional analysis in a 3D platform to accurately characterize engineered cardiac tissue response to biochemical stimulation. This study demonstrates the therapeutic potential of IGF1 for boosting proliferation and NRG1 for promoting metabolic and contractile maturation in engineered human cardiac tissue.

Effects of neuregulin GGF2 (cimaglermin alfa) dose and treatment frequency on left ventricular function in rats following myocardial infarction

Neuregulins are important growth factors involved in cardiac development and response to stress. Certain isoforms and fragments of neuregulin have been found to be cardioprotective. The effects of a full-length neuregulin-1β isoform, glial growth factor 2 (GGF2; USAN/INN; also called cimaglermin) were investigated in vitro. Various dosing regimens were then evaluated for their effects on left ventricular (LV) function in rats with surgically-induced myocardial infarction. In vitro, GGF2 bound with high affinity to erythroblastic leukemia viral oncogene (ErbB) 4 receptors, potently promoted Akt phosphorylation, as well as reduced cell death following doxorubicin exposure in HL1 cells. Daily GGF2 treatment beginning 7-14 days after left anterior descending coronary artery ligation produced improvements in LV ejection fraction and other measures of LV function and morphology. The improvements in LV function (e.g. 10% point increase in absolute LV ejection fraction) with GGF2 were dose-dependent. LV performance was substantially improved when GGF2 treatment was delivered infrequently, despite a serum half-life of less than 2h and could be maintained for more than 10 months with treatment once weekly or once every 2 weeks. These studies confirm previous findings that GGF2 may improve contractile performance in the failing rat heart and that infrequent exposure to GGF2 may improve LV function and impact remodeling in the failing myocardium. GGF2 is now being developed for the treatment of heart failure in humans.

Identification of candidate genes for congenital heart defects on proximal chromosome 8p

With the application of advanced molecular cytogenetic techniques, the number of patients identified as having abnormal chromosome 8p has increased progressively. Individuals with terminal 8p deletion have been extensively described in previous studies. The manifestations usually include cardiac anomalies, developmental delay/mental retardation, craniofacial abnormalities, and multiple other minor anomalies. However, some patients with proximal deletion also presented with similar phenotypic features. Here we describe a female child with an 18.5-Mb deletion at 8p11.23–p22 that include the cardiac-associated loci NKX2-6 and NRG1. Further mutation screening of these two candidate genes in 143 atrial septal defect patients, two heterozygous mutations NKX2-6 (c.1A > T) and NRG1 (c.1652G > A) were identified. The mutations were described for the first time in patients with congenital heart disease (CHD). The c.1A > T NKX2-6 generated a protein truncated by 45 amino acids with a decreased level of mRNA expression, whereas the NRG1 mutation had no significant effect on protein functions. Our findings suggest that 8p21-8p12 may be another critical region for 8p-associated CHD, and some cardiac malformations might be due to NKX2-6 haploinsufficiency. This study also links the NKX2-6 mutation to ASD for the first time, providing novel insight into the molecular underpinning of this common form of CHD.

Transcription factor ETV1 is essential for rapid conduction in the heart

Rapid impulse propagation in the heart is a defining property of pectinated atrial myocardium (PAM) and the ventricular conduction system (VCS) and is essential for maintaining normal cardiac rhythm and optimal cardiac output. Conduction defects in these tissues produce a disproportionate burden of arrhythmic disease and are major predictors of mortality in heart failure patients. Despite the clinical importance, little is known about the gene regulatory network that dictates the fast conduction phenotype. Here, we have used signal transduction and transcriptional profiling screens to identify a genetic pathway that converges on the NRG1-responsive transcription factor ETV1 as a critical regulator of fast conduction physiology for PAM and VCS cardiomyocytes. Etv1 was highly expressed in murine PAM and VCS cardiomyocytes, where it regulates expression of Nkx2-5, Gja5, and Scn5a, key cardiac genes required for rapid conduction. Mice deficient in Etv1 exhibited marked cardiac conduction defects coupled with developmental abnormalities of the VCS. Loss of Etv1 resulted in a complete disruption of the normal sodium current heterogeneity that exists between atrial, VCS, and ventricular myocytes. Lastly, a phenome-wide association study identified a link between ETV1 and bundle branch block and heart block in humans. Together, these results identify ETV1 as a critical factor in determining fast conduction physiology in the heart.

Mechanisms of Cardiac Regeneration

Adult humans fail to regenerate their hearts following injury, and this failure to regenerate myocardium is a leading cause of heart failure and death worldwide. Although all adult mammals appear to lack significant cardiac regeneration potential, some vertebrates can regenerate myocardium throughout life. In addition, new studies indicate that mammals have cardiac regeneration potential during development and very soon after birth. The mechanisms of heart regeneration among model organisms, including neonatal mice, appear remarkably similar. Orchestrated waves of inflammation, matrix deposition and remodeling, and cardiomyocyte proliferation are commonly seen in heart regeneration models. Understanding why adult mammals develop extensive scarring instead of regeneration is a crucial goal for regenerative biology.

Neuregulin-1β promotes glucose uptake via PI3K/Akt in neonatal rat cardiomyocytes

Nrg1β is critically involved in cardiac development and also maintains function of the adult heart. Studies conducted in animal models showed that it improves cardiac performance under a range of pathological conditions, which led to its introduction in clinical trials to treat heart failure. Recent work also implicated Nrg1β in the regenerative potential of neonatal and adult hearts. The molecular mechanisms whereby Nrg1β acts in cardiac cells are still poorly understood. In the present study, we analyzed the effects of Nrg1β on glucose uptake in neonatal rat ventricular myocytes and investigated to what extent mTOR/Akt signaling pathways are implicated. We show that Nrg1β enhances glucose uptake in cardiomyocytes as efficiently as IGF-I and insulin. Nrg1β causes phosphorylation of ErbB2 and ErbB4 and rapidly induces the phosphorylation of FAK (Tyr(861)), Akt (Thr(308) and Ser(473)), and its effector AS160 (Thr(642)). Knockdown of ErbB2 or ErbB4 reduces Akt phosphorylation and blocks the glucose uptake. The Akt inhibitor VIII and the PI3K inhibitors LY-294002 and Byl-719 abolish Nrg1β-induced phosphorylation and glucose uptake. Finally, specific mTORC2 inactivation after knockdown of rictor blocks the Nrg1β-induced increases in Akt-p-Ser(473) but does not modify AS160-p-Thr(642) or the glucose uptake responses to Nrg1β. In conclusion, our study demonstrates that Nrg1β enhances glucose uptake in cardiomyocytes via ErbB2/ErbB4 heterodimers, PI3Kα, and Akt. Furthermore, although Nrg1β activates mTORC2, the resulting Akt-Ser(473) phosphorylation is not essential for glucose uptake induction. These new insights into pathways whereby Nrg1β regulates glucose uptake in cardiomyocytes may contribute to the understanding of its regenerative capacity and protective function in heart failure.

RSK3 is required for concentric myocyte hypertrophy in an activated Raf1 model for Noonan syndrome

Noonan syndrome (NS) is a congenital disorder resulting from mutations of the Ras-Raf signaling pathway. Hypertrophic cardiomyopathy associated with RAF1 "RASopathy" mutations is a major risk factor for heart failure and death in NS and has been attributed to activation of MEK1/2-ERK1/2 mitogen-activated protein kinases. We recently discovered that type 3 p90 ribosomal S6 kinase (RSK3) is an ERK effector that is required, like ERK1/2, for concentric myocyte hypertrophy in response to pathological stress such as pressure overload. In order to test whether RSK3 also contributes to NS-associated hypertrophic cardiomyopathy, RSK3 knock-out mice were crossed with mice bearing the Raf1(L613V) human NS mutation. We confirmed that Raf1(L613V) knock-in confers a NS-like phenotype, including cardiac hypertrophy. Active RSK3 was increased in Raf1(L613V) mice. Constitutive RSK3 gene deletion prevented the Raf1(L613V)-dependent concentric growth in width of the cardiac myocyte and attenuated cardiac hypertrophy in female mice. These results are consistent with RSK3 being an important mediator of ERK1/2-dependent growth in RASopathy. In conjunction with previously published data showing that RSK3 is important for pathological remodeling of the heart, these data suggest that targeting of this downstream MAP-kinase pathway effector should be considered in the treatment of RASopathy-associated hypertrophic cardiomyopathy.

RSK3: A regulator of pathological cardiac remodeling

The family of p90 ribosomal S6 kinases (RSKs) are pleiotropic effectors for extracellular signal-regulated kinase signaling pathways. Recently, RSK3 was shown to be important for pathological remodeling of the heart. Although cardiac myocyte hypertrophy can be compensatory for increased wall stress, in chronic heart diseases, this nonmitotic cell growth is usually associated with interstitial fibrosis, increased cell death, and decreased cardiac function. Although RSK3 is less abundant in the cardiac myocyte than other RSK family members, RSK3 appears to serve a unique role in cardiac myocyte stress responses. A potential mechanism conferring the unique function of RSK3 in the heart is anchoring by the scaffold protein muscle A-kinase anchoring protein β (mAKAPβ). Recent findings suggest that RSK3 should be considered as a therapeutic target for the prevention of heart failure, a clinical syndrome of major public health significance.

The roles of neuregulin-1 in cardiac development, homeostasis, and disease

Neuregulin-1 (NRG-1) and its signaling receptors, erythroblastic leukemia viral oncogene homologs (ErbB) 2, 3, and 4, have been implicated in both cardiomyocyte development and disease, as well as in homeostatic cardiac function. NRG-1/ErbB signaling is involved in a multitude of cardiac processes ranging from myocardial and cardiac conduction system development to angiogenic support of cardiomyocytes, to cardioprotective effects upon injury. Numerous studies of NRG-1 employ a variety of platforms, including in vitro assays, animal models, and human clinical trials, with equally varying and, sometimes, contradictory outcomes. NRG-1 has the potential to be used as a therapeutic tool in stem cell therapies, tissue engineering applications, and clinical diagnostics and treatment. This review presents a concise summary of the growing body of literature to highlight the temporally persistent significance of NRG-1/ErbB signaling throughout development, homeostasis, and disease in the heart, specifically in cardiomyocytes.

Platelet endothelial cell adhesion molecule-1 mediates endothelial-cardiomyocyte communication and regulates cardiac function

Background

Dilated cardiomyopathy is characterized by impaired contractility of cardiomyocytes, ventricular chamber dilatation, and systolic dysfunction. Although mutations in genes expressed in the cardiomyocyte are the best described causes of reduced contractility, the importance of endothelial‐cardiomyocyte communication for proper cardiac function is increasingly appreciated. In the present study, we investigate the role of the endothelial adhesion molecule platelet endothelial cell adhesion molecule (PECAM‐1) in the regulation of cardiac function.

Methods and Results

Using cell culture and animal models, we show that PECAM‐1 expressed in endothelial cells (ECs) regulates cardiomyocyte contractility and cardiac function via the neuregulin‐ErbB signaling pathway. Conscious echocardiography revealed left ventricular (LV) chamber dilation and systolic dysfunction in PECAM‐1^−/− mice in the absence of histological abnormalities or defects in cardiac capillary density. Despite deficits in global cardiac function, cardiomyocytes isolated from PECAM‐1^−/− hearts displayed normal baseline and isoproterenol‐stimulated contractility. Mechanistically, absence of PECAM‐1 resulted in elevated NO/ROS signaling and NRG‐1 release from ECs, which resulted in augmented phosphorylation of its receptor ErbB2. Treatment of cardiomyocytes with conditioned media from PECAM‐1^−/− ECs resulted in enhanced ErbB2 activation, which was normalized by pre‐treatment with an NRG‐1 blocking antibody. To determine whether normalization of increased NRG‐1 levels could correct cardiac function, PECAM‐1^−/− mice were treated with the NRG‐1 blocking antibody. Echocardiography showed that treatment significantly improved cardiac function of PECAM‐1^−/− mice, as revealed by increased ejection fraction and fractional shortening.

Conclusions

We identify a novel role for PECAM‐1 in regulating cardiac function via a paracrine NRG1‐ErbB pathway. These data highlight the importance of tightly regulated cellular communication for proper cardiac function.

Recombinant neuregulin 1 does not activate cardiomyocyte DNA synthesis in normal or infarcted adult mice

Objectives

Neuregulin 1 signaling plays an important role in cardiac trabecular development, and in sustaining functional integrity in adult hearts. Treatment with neuregulin 1 enhances adult cardiomyocyte differentiation, survival and/or function in vitro and in vivo. It has also been suggested that recombinant neuregulin 1β1 (NRG1β1) induces cardiomyocyte proliferation in normal and injured adult hearts. Here we further explore the impact of neuregulin 1 signaling on adult cardiomyocyte cell cycle activity.

Methods and Results

Adult mice were subjected to 9 consecutive daily injections of recombinant NRG1β1 or vehicle, and cardiomyocyte DNA synthesis was quantitated via bromodeoxyuridine (BrdU) incorporation, which was delivered using mini-osmotic pumps over the entire duration of NRG1β1 treatment. NRG1β1 treatment inhibited baseline rates of cardiomyocyte DNA synthesis in normal mice (cardiomyocyte labelling index: 0.019±0.005% vs. 0.003±0.001%, saline vs. NRG1β1, P<0.05). Acute NRG1β1 treatment did result in activation of Erk1/2 and cardiac myosin regulatory light chain (down-stream mediators of neuregulin signalling), as well as activation of DNA synthesis in non-cardiomyocytes, validating the biological activity of the recombinant protein. In other studies, mice were subjected to permanent coronary artery occlusion, and cardiomyocyte DNA synthesis was monitored via tritiated thymidine incorporation which was delivered as a single injection 7 days post-infarction. Daily NRG1β1 treatment had no impact on cardiomyocyte DNA synthesis in the infarcted myocardium (cardiomyocyte labelling index: 0.039±0.011% vs. 0.027±0.021%, saline vs. NRG1β1, P>0.05).

Summary

These data indicate that NRG1β1 treatment does not increase cardiomyocyte DNA synthesis (and consequently does not increase the rate of cardiomyocyte renewal) in normal or infarcted adult mouse hearts. Thus, any improvement in cardiac structure and function observed following neuregulin treatment of injured hearts likely occurs independently of overt myocardial regeneration.

Anti-remodeling and anti-fibrotic effects of the neuregulin-1β glial growth factor 2 in a large animal model of heart failure

BACKGROUND

Neuregulin-1β (NRG-1β) is a growth factor critical for cardiac development and repair with therapeutic potential for heart failure. We previously showed that the glial growth factor 2 (GGF2) isoform of NRG-1β improves cardiac function in rodents after myocardial infarction (MI), but its efficacy in a large animal model of cardiac injury has not been examined. We therefore sought to examine the effects of GGF2 on ventricular remodeling, cardiac function, and global transcription in post-MI swine, as well as potential mechanisms for anti-remodeling effects.

METHODS AND RESULTS

MI was induced in anesthetized swine (n=23) by intracoronary balloon occlusion. At 1 week post-MI, survivors (n=13) received GGF2 treatment (intravenous, biweekly for 4 weeks; n=8) or were untreated (n=5). At 5 weeks post-MI, fractional shortening was higher (32.8% versus 25.3%, P=0.019), and left ventricular (LV) end-diastolic dimension lower (4.5 versus 5.3 cm, P=0.003) in GGF2-treated animals. Treatment altered expression of 528 genes, as measured by microarrays, including collagens, basal lamina components, and matricellular proteins. GGF2-treated pigs exhibited improvements in LV cardiomyocyte mitochondria and intercalated disk structures and showed less fibrosis, altered matrix structure, and fewer myofibroblasts (myoFbs), based on trichrome staining, electron microscopy, and immunostaining. In vitro experiments with isolated murine and rat cardiac fibroblasts demonstrate that NRG-1β reduces myoFbs, and suppresses TGFβ-induced phospho-SMAD3 as well as αSMA expression.

CONCLUSIONS

These results suggest that GGF2/NRG-1β prevents adverse remodeling after injury in part via anti-fibrotic effects in the heart.

Neuregulin as a heart failure therapy and mediator of reverse remodeling

The beta isoform of Neuregulin-1 (NRG-1β), along with its receptors (ErbB2-4), is required for cardiac development. NRG-1β, as well as the ErbB2 and ErbB4 receptors, is also essential for maintenance of adult heart function. These observations have led to its evaluation as a therapeutic for heart failure. Animal studies and ongoing clinical trials have demonstrated beneficial effects of two forms of recombinant NRG-1β on cardiac function. In addition to the possible role for recombinant NRG-1βs as heart failure therapies, endogenous NRG-1β/ErbB signaling appears to play a role in restoring cardiac function after injury. The potential mechanisms by which NRG-1β may act as both a therapy and a mediator of reverse remodeling remain incompletely understood. In addition to direct effects on cardiac myocytes NRG-1β acts on the vasculature, interstitium, cardiac fibroblasts, and hematopoietic and immune cells, which, collectively, may contribute to NRG-1β's role in maintaining cardiac structure and function, as well as mediating reverse remodeling.

PRAK interacts with DJ-1 and prevents oxidative stress-induced cell death

As a core member of p38 MAPK signal transduction pathway, p38 regulated/activated kinase (PRAK) is activated by cellular stresses. However, the function of PRAK and its downstream interacting partner remain undefined. Using a yeast two-hybrid system, we identified DJ-1 as a potential PRAK interacting protein. We further verified that DJ-1 bound to PRAK in vitro and in vivo and colocalized with PRAK in the nuclei of NIH3T3 cells. Furthermore, following H₂O₂ stimulation the majority of endogenous DJ-1 in PRAK^+/+ cells still remained in the nucleus, whereas most DJ-1 in PRAK^−/− cells translocated from the nucleus into the cytoplasm, indicating that PRAK is essential for DJ-1 to localize in the nucleus. In addition, PRAK-associated phosphorylation of DJ-1 was observed in vitro and in vivo of H₂O₂-challenged PRAK^+/+ cells. Cytoplasmic translocation of DJ-1 in H₂O₂-treated PRAK^−/− cells lost its ability to sequester Daxx, a death protein, in the nucleus, and as a result, Daxx gained access to the cytoplasm and triggered cell death. These data highlight that DJ-1 is the downstream interacting target for PRAK, and in response to oxidative stress PRAK may exert a cytoprotective effect by facilitating DJ-1 to sequester Daxx in the nucleus, thus preventing cell death.

Reciprocal myocardial-endocardial interactions pattern the delay in atrioventricular junction conduction

Efficient blood flow depends on two developmental processes that occur within the atrioventricular junction (AVJ) of the heart: conduction delay, which entrains sequential chamber contraction; and valve formation, which prevents retrograde fluid movement. Defects in either result in severe congenital heart disease; however, little is known about the interplay between these two crucial developmental processes. Here, we show that AVJ conduction delay is locally assigned by the morphogenetic events that initiate valve formation. Our data demonstrate that physical separation from endocardial-derived factors prevents AVJ myocardium from becoming fast conducting. Mechanistically, this physical separation is induced by myocardial-derived factors that support cardiac jelly deposition at the onset of valve formation. These data offer a novel paradigm for conduction patterning, whereby reciprocal myocardial-endocardial interactions coordinate the processes of valve formation with establishment of conduction delay. This, in turn, synchronizes the electrophysiological and structural events necessary for the optimization of blood flow through the developing heart.

Chemotherapy-Induced Cardiotoxicity: Pathophysiology and Prevention

Along with the remarkable progress registered in oncological treatment that led to increased survival of cancer patients, treatment-related comorbidities have also become an issue for these long-term survivors. Of particular interest is the development of cardiotoxic events, which, even when asymptomatic, not only have a negative impact on the patient`s cardiac prognosis, but also considerably restrict therapeutic opportunities. The pathophysiology of cytostatic-induced cardiotoxicity implies a series of complex and intricate mechanisms, whose understanding enables the development of preventive and therapeutic strategies. Securing cardiac function is an ongoing challenge for the pharmaceutical industry and the physicians who have to deal currently with these adverse reactions. This review focuses on the main mechanism of cardiac toxicity induced by anticancer drugs and especially on the current strategies applied for preventing and minimizing the cardiac side effects.

Harnessing Hippo in the heart: Hippo/Yap signaling and applications to heart regeneration and rejuvenation

The adult mammalian heart exhibits limited regenerative capacity after myocardial injury, a shortcoming that is responsible for the current lack of definitive treatments for heart failure. A search for approaches that might enhance adult heart regeneration has led to interest in the Hippo/Yap signaling pathway, a recently discovered signaling pathway that regulates cell proliferation and organ growth. Here we provide a brief overview of the Hippo/Yap pathway and its known roles in the developing and adult heart. We discuss the implications of Hippo/Yap signaling for regulation of cardiomyocyte death and regeneration.

Signalling between microvascular endothelium and cardiomyocytes through neuregulin

Heterocellular communication in the heart is an important mechanism for matching circulatory demands with cardiac structure and function, and neuregulins (Nrgs) play an important role in transducing this signal between the hearts' vasculature and musculature. Here, we review the current knowledge regarding Nrgs, explaining their roles in transducing signals between the heart's microvasculature and cardiomyocytes. We highlight intriguing areas being investigated for developing new, Nrg-mediated strategies to heal the heart in acquired and congenital heart diseases, and note avenues for future research.

Neuregulin-1β induces embryonic stem cell cardiomyogenesis via ErbB3/ErbB2 receptors

NRG-1β (neuregulin-1β) serves multiple functions during embryonic heart development by signalling through ErbB family receptor tyrosine kinases (ErbB2, ErbB3 and ErbB4). Previous studies reported that NRG-1β induces cardiomyogenesis of mESCs (mouse embryonic stem cells) at the later stages of differen-tiation through ErbB4 receptor activation. In the present study we systematically examined NRG-1β induction of cardiac myocytes in mESCs and identified a novel time window, the first 48 h, for NRG-1β-based cardiomyogenesis. At this time point ErbB3, but not ErbB4, is expressed. In contrast with the later differentiation of mESCs in which NRG-1β induces cardiomyogenesis via the ErbB4 receptor, we found that knocking down ErbB3 or ErbB2 with siRNA during the early differentiation inhibited NRG-1β-induced cardiomyogenesis in mESCs. Microarray analysis of RNA expression at this early time point indicated that NRG-1β treatment in mESCs resulted in gene expression changes important to differentiation including up-regulation of components of PI3K (phosphoinositide 3-kinase), a known mediator of the NRG-1β/ErbB signalling pathway, as well as activation of CREB (cAMP-response-element-binding protein). Further study demonstrated that the NRG-1β-induced phosphorylation of CREB was required for cardiomyogenesis of mESCs. In summary, we report a previously unrecognized role for NRG-1β/ErbB3/CREB signalling at the pre-mesoderm stage for stem cell cardiac differentiation.

Erbin is a negative modulator of cardiac hypertrophy

ErbB2 interacting protein (Erbin) is a widely expressed protein and participates in inhibition of several intracellular signaling pathways. Its mRNA has been found to be present in relatively high levels in the heart. However, its physiological role in the heart has not been explored. In the present work, we elucidated the role of Erbin in cardiac hypertrophy. Cardiac hypertrophy was induced in mice either by isoproterenol administration or by aortic constriction. The level of Erbin was significantly decreased in both models. Erbin(-/-) mice rapidly develop decompensated cardiac hypertrophy, and following severe pressure overload all Erbin(-/-) mice died from heart failure. Down-regulation of Erbin expression was also observed in biopsies derived from human failing hearts. It is known that Erbin inhibits Ras-mediated activation of the extracellular signal-regulated kinase (ERK) by binding to Soc-2 suppressor of clear homolog (Shoc2). Our data clearly show that ERK phosphorylation is enhanced in the heart tissues of Erbin(-/-) mice. Furthermore, we clearly demonstrate here that Erbin associates with Shoc2 in both whole hearts and in cardiomyocytes, and that in the absence of Erbin, Raf is phosphorylated and binds Shoc2, resulting in ERK phosphorylation. In conclusion, Erbin is an inhibitor of pathological cardiac hypertrophy, and this inhibition is mediated, at least in part, by modulating ERK signaling.

Emerging paradigms in cardiomyopathies associated with cancer therapies

The cardiovascular care of cancer patients (cardio-oncology) has emerged as a new discipline in clinical medicine, given recent advances in cancer therapy, and is driven by the cardiovascular complications that occur as a direct result of cancer therapy. Traditional therapies such as anthracyclines and radiation have been recognized for years to have cardiovascular complications. Less expected were the cardiovascular effects of targeted cancer therapies, which were initially thought to be specific to cancer cells and would spare any adverse effects on the heart. Cancers are typically driven by mutations, translocations, or overexpression of protein kinases. The majority of these mutated kinases are tyrosine kinases, though serine/threonine kinases also play key roles in some malignancies. Several agents were developed to target these kinases, but many more are in development. Major successes have been largely restricted to agents targeting human epidermal growth factor receptor-2 (mutated or overexpressed in breast cancer), BCR-ABL (chronic myelogenous leukemia and some cases of acute lymphoblastic leukemia), and c-Kit (gastrointestinal stromal tumor). Other agents targeting more complex malignancies, such as advanced solid tumors, have had successes, but have not extended life to the degree seen with chronic myelogenous leukemia. Years before the first targeted therapy, Judah Folkman correctly proposed that to address solid tumors one had to target the inherent neoangiogenesis. Unfortunately, emerging evidence confirms that angiogenesis inhibitors cause cardiac complications, including hypertension, thrombosis, and heart failure. And therein lies the catch-22. Nevertheless, cardio-oncology has the potential to be transformative as the human cardiomyopathies that arise from targeted therapies can provide insights into the normal function of the heart.

Time-dependent regulation of neuregulin-1β/ErbB/ERK pathways in cardiac differentiation of mouse embryonic stem cells

Neuregulin-1β (NRG-1β)/ErbB signaling plays crucial roles in the cardiac differentiation of mouse embryonic stem cells (ESCs), but its roles and the underlying mechanisms in cardiac differentiation are incompletely understood. This study showed that NRG-1β significantly increased the percentage of beating embryoid bodies (EBs) and up-regulated the gene expressions of Nkx2.5, GATA4, α-actin, MLC-2v, and ANF in a time-dependent manner, with no effect on the gene expressions of HCN4 and Tbx3. Inhibition of ErbB receptors with AG1478 significantly decreased the percentage of beating EBs; down-regulated the gene expressions of Nkx2.5, GATA4, MLC-2v, ANF, and α-actin; and concomitantly up-regulated the gene expressions of HCN4 and Tbx3 in a time-dependent manner. Moreover, the up-regulation of transcripts for Nkx2.5 and GATA4 by NRG-1β was blocked by the extracellular signal-related kinases (ERK) 1/2 inhibitor, U0126. However, U0126 could not inhibit the transcript up-regulations of MLC-2v and ANF by NRG-1β. The protein quantitation results were consistent with those of gene quantitation. Our results suggest that NRG-1β/ErbB signaling plays critical roles in the cardiac differentiation of mouse ESCs and in the subtype specification of cardiomyocytes in a time-dependent manner. The ERK1/2 pathway may be involved in the early cardiogenesis, but not in the subtype specification of cardiomyocytes.

Neuregulin in cardiovascular development and disease

Studies in genetically modified mice have demonstrated that neuregulin-1 (NRG-1), along with the erythroblastic leukemia viral oncogene homolog (ErbB) 2, 3, and 4 receptor tyrosine kinases, is necessary for multiple aspects of cardiovascular development. These observations stimulated in vitro and in vivo animal studies, implicating NRG-1/ErbB signaling in the regulation of cardiac cell biology throughout life. Cardiovascular effects of ErbB2-targeted cancer therapies provide evidence in humans that ErbB signaling plays a role in the maintenance of cardiac function. These and other studies suggest a conceptual model in which a key function of NRG-1/ErbB signaling is to mediate adaptations of the heart to physiological and pathological stimuli through activation of intracellular kinase cascades that regulate tissue plasticity. Recent work implicates NRG-1/ErbB signaling in the regulation of multiple aspects of cardiovascular biology, including angiogenesis, blood pressure, and skeletal muscle responses to exercise. The therapeutic potential of recombinant NRG-1 as a potential treatment for heart failure has been demonstrated in animal models and is now being explored in clinical studies. NRG-1 is found in human serum and plasma, and it correlates with some clinical parameters, suggesting that it may have value as an indicator of prognosis. In this review, we bring together this growing literature on NRG-1 and its significance in cardiovascular development and disease.

Clarifying off-target effects for torcetrapib using network pharmacology and reverse docking approach

Background

Torcetrapib, a cholesteryl ester transfer protein (CETP) inhibitor which raises high-density lipoprotein (HDL) cholesterol and reduces low-density lipoprotein (LDL) cholesterol level, has been documented to increase mortality and cardiac events associated with adverse effects. However, it is still unclear the underlying mechanisms of the off-target effects of torcetrapib.

Results

In the present study, we developed a systems biology approach by combining a human reassembled signaling network with the publicly available microarray gene expression data to provide unique insights into the off-target adverse effects for torcetrapib. Cytoscape with three plugins including BisoGenet, NetworkAnalyzer and ClusterONE was utilized to establish a context-specific drug-gene interaction network. The DAVID functional annotation tool was applied for gene ontology (GO) analysis, while pathway enrichment analysis was clustered by ToppFun. Furthermore, potential off-targets of torcetrapib were predicted by a reverse docking approach. In general, 10503 nodes were retrieved from the integrative signaling network and 47660 inter-connected relations were obtained from the BisoGenet plugin. In addition, 388 significantly up-regulated genes were detected by Significance Analysis of Microarray (SAM) in adrenal carcinoma cells treated with torcetrapib. After constructing the human signaling network, the over-expressed microarray genes were mapped to illustrate the context-specific network. Subsequently, three conspicuous gene regulatory networks (GRNs) modules were unearthed, which contributed to the off-target effects of torcetrapib. GO analysis reflected dramatically over-represented biological processes associated with torcetrapib including activation of cell death, apoptosis and regulation of RNA metabolic process. Enriched signaling pathways uncovered that IL-2 Receptor Beta Chain in T cell Activation, Platelet-Derived Growth Factor Receptor (PDGFR) beta signaling pathway, IL2-mediated signaling events, ErbB signaling pathway and signaling events mediated by Hepatocyte Growth Factor Receptor (HGFR, c-Met) might play decisive characters in the adverse cardiovascular effects associated with torcetrapib. Finally, a reverse docking algorithm in silico between torcetrapib and transmembrane receptors was conducted to identify the potential off-targets. This screening was carried out based on the enriched signaling network analysis.

Conclusions

Our study provided unique insights into the biological processes of torcetrapib-associated off-target adverse effects in a systems biology visual angle. In particular, we highlighted the importance of PDGFR, HGFR, IL-2 Receptor and ErbB1tyrosine kinase might be direct off-targets, which were highly related to the unfavorable adverse effects of torcetrapib and worthy of further experimental validation.

Pooled analysis of cardiac safety in patients with cancer treated with pertuzumab

BACKGROUND

Pertuzumab, a human epidermal growth factor receptor (HER) 2 dimerization inhibitor, has demonstrated promising efficacy in combination with trastuzumab in patients with metastatic breast cancer. As HER signaling pathways are not only involved in oncogenesis, but also in myocardial homeostasis, an analysis of cardiac safety data was undertaken in a large group of patients treated with pertuzumab.

PATIENTS AND METHODS

A complete database of patients treated with full-dose pertuzumab was used to describe the incidence of asymptomatic left ventricular systolic dysfunction (LVSD) and symptomatic heart failure (HF).

RESULTS

Information for 598 unique patients was available for the current analysis. Of the patients treated with pertuzumab alone (n = 331) or pertuzumab in combination with a non-anthracycline-containing cytotoxic (n = 175) or trastuzumab (n = 93), 23 (6.9%), 6 (3.4%), and 6 (6.5%), respectively, developed asymptomatic LVSD and 1 (0.3%), 2 (1.1%), and 1 (1.1%), respectively, displayed symptomatic HF. None of the 15 patients receiving both pertuzumab and erlotinib demonstrated LVSD.

CONCLUSIONS

Patients treated with pertuzumab experienced relatively low levels of asymptomatic LVSD or symptomatic HF. There was no notable increase in cardiac side-effects when pertuzumab was given in combination with other anticancer agents.

Cardiac regeneration

The heart is a pump that is comprised of cardiac myocytes and other cell types and whose proper function is critical to quality of life. The ability to trigger regeneration of heart muscle following injury eludes adult mammals, a deficiency of great clinical impact. Major research efforts are attempting to change this through advances in cell therapy or activating endogenous regenerative mechanisms that exist only early in life. In contrast with mammals, lower vertebrates like zebrafish demonstrate an impressive natural capacity for cardiac regeneration throughout life. This review will cover recent progress in the field of heart regeneration with a focus on endogenous regenerative capacity and its potential manipulation.

Cardiotoxicity of molecularly targeted agents

Cardiac toxicity of molecularly targeted cancer agents is increasingly recognized as a significant side effect of chemotherapy. These new potent therapies may not only affect the survival of cancer cells, but have the potential to adversely impact normal cardiac and vascular function. Unraveling the mechanisms by which these therapies affect the heart and vasculature is crucial for improving drug design and finding alternative therapies to protect patients predisposed to cardiovascular disease. In this review, we summarize the classification and side effects of currently approved molecularly targeted chemotherapeutics.

Cardiotoxicity

Cancer treatment has improved extraordinarily in recent years. The development of targeted therapies has widened the cardiotoxic spectrum of antineoplastic drugs. Optimum management of cardiovascular disease before and during antineoplastic treatment is essential to reduce morbidity and mortality in cancer patients. This article reviews the incidence and characteristics of cardiotoxic effects of antineoplastic drugs with special focus on the pathophysiological mechanisms. It also emphasizes the importance of early detection and correction of cardiovascular risk factors and the relevance of close cardiac monitoring during antineoplastic treatment in order to reduce cardiotoxicity.

Therapeutic effects of neuregulin-1 in diabetic cardiomyopathy rats

Background

Diabetic cardiomyopathy (DCM) is a disorder of the heart muscle in people with diabetes, which is characterized by both systolic and diastolic dysfunction. The effective treatment strategy for DCM has not been developed.

Methods

Rats were divided into 3 groups with different treatment. The control group was only injected with citrate buffer (n = 8). The diabetes group and diabetes treated group were injected with streptozotocin to induce diabetes. After success of diabetes induction, the rats with diabetes were treated with (diabetes treated group, n = 8) or without (diabetes group, n = 8) recombinant human Neuregulin-1 (rhNRG-1). All studies were carried out 16 weeks after induction of diabetes. Cardiac catheterization was performed to evaluate the cardiac function. Apoptotic cells were determined by TUNEL staining. Left ventricular (LV) sections were stained with Masson to investigate myocardial collagen contents. Related gene expressions were analyzed by quantitative real-time PCR (qRT-PCR).

Results

Diabetes impaired cardiac function manifested by reduced LV systolic pressure (LVSP), maximum rate of LV pressure rise and fall (+dp/dt max and -dp/dt max) and increased LV end-diastolic pressure (LVEDP). The rhNRG-1 treatment could significantly alleviate these symptoms and improve heart function. More TUNEL staining positive cells were observed in the diabetic group than that in the control group, and the rhNRG-1 treatment decreased apoptotic cells number. Furthermore, qRT-PCR assay demonstrated that rhNRG-1 treatment could decrease the expression of bax and caspase-3 and increase that of bcl-2. Collagen volume fraction was higher in the diabetic group than in the control group. Fibrotic and fibrotic related mRNA (type I and type III collagen) levels in the myocardium were significantly reduced by administration of rhNRG-1.

Conclusion

rhNRG-1 could significantly improve the heart function and reverse the cardiac remodeling of DCM rats with chronic heart failure. These results support the clinical possibility of applying rhNRG-1 as an optional therapeutic strategy for DCM treatment in the future.

Neuregulin-1β for the treatment of systolic heart failure

The Neuregulin-1 gene encodes a family of ligands that act through the ErbB family of receptor tyrosine kinases to regulate morphogenesis of many tissues. Work in isolated cardiac cells as well as genetically altered mice demonstrates that neuregulin-1/ErbB signaling is a paracrine signaling system that functions in endocardial-endothelial/cardiomyocyte interactions to regulate tissue organization during development as well as maintain cardiac function throughout life. Treatment of animals with cardiac dysfunction with recombinant neuregulin-1beta improves cardiac function. This has led to ongoing early phase clinical studies examining neuregulin-1beta as a potential novel therapeutic for heart failure. In this review we synthesize the literature behind this rapidly evolving area of translational research. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure."

Cytostatic drugs, neuregulin activation of erbB receptors, and angiogenesis

Cytostatic drugs were developed to target specific molecular pathways shown to drive tumor growth. Although this approach has been very successful in treating cancers, its use is often hindered by off-target toxic effects. An example of this is trastuzumab, which targets the erbB2 kinase receptor. This drug successfully decreases tumor growth but adversely affects cardiac function. This observation led to important studies elucidating the importance of the erbB pathway in cardioprotection and angiogenesis. This review addresses the problem of off-target effects of cytostatic drugs (specifically trastuzumab) and their effect on cardiac function, summarizes the neuregulin-1 (NRG)/erbB signaling pathway, and discusses its importance in cardiac myocytes. It also highlights important findings showing the role of NRG/erbB signaling in microvascular preservation and angiogenesis, with a brief discussion of preclinical and clinical data regarding treatment of cardiovascular disease with NRG.

Neuregulin-1β regulation of embryonic endothelial progenitor cell survival

Endothelial progenitor cells (EPCs) are mobilized into the vascular space and home to damaged tissues, where they promote repair in part through a process of angiogenesis. Neuregulins (NRGs) are ligands in the epidermal growth factor family that signal through type I receptor tyrosine kinases in the erbB family (erbB2, erbB3, and erbB4) and regulate endothelial cell biology, promoting angiogenesis. Stimuli such as ischemia and exercise that promote EPC mobilization also induce cleavage and release of transmembrane NRG from cardiac microvascular endothelial cells (CMECs). We hypothesized that NRG/erbB signaling may regulate EPC biology. Using an embryonic (e)EPC cell line that homes to and repairs injured myocardium, we were able to detect erbB2 and erbB3 transcripts. Identical receptor expression was found in EPCs isolated from rat bone marrow and human whole blood. NRG treatment of eEPCs induces phosphorylation of kinases including Akt, GSK-3β, and Erk1/2 and the nuclear accumulation and transcriptional activation of β-catenin. NRG does not induce eEPC proliferation or migration but does protect eEPCs against serum deprivation-induced apoptosis. These results suggest a role for tissue-derived NRG in the regulation of EPC survival.