Distinct Regulation of Developmental and Heart Disease–Induced Atrial Natriuretic Factor Expression by Two Separate Distal Sequences

Silver Nanoparticles Exposure Impairs Cardiac Development by Suppressing the Focal Adhesion Pathway in Zebrafish

Introduction

The potential toxic effects of wastewater discharges containing silver nanoparticles (AgNPs) and their release into aquatic ecosystems on aquatic organisms are becoming a major concern for environmental and human health. However, the potential risks of AgNPs to aquatic organisms, especially for cardiac development by Focal adhesion pathway, are still poorly understood.

Methods

The cardiac development of various concentrations of AgNPs in zebrafish were examined using stereoscopic microscope. The expression levels of cardiac development-related genes were analyzed by qRT-PCR and Whole-mount in situ hybridization (WISH). In addition, Illumina high-throughput global transcriptome analysis was performed to explore the potential signaling pathway involved in the treatment of zebrafish embryos by AgNPs after 72 h.

Results

We systematically investigated the cardiac developing toxicity of AgNPs on the embryos of zebrafish. The results demonstrated that 2 or 4 mg/L AgNPs exposure induces cardiac developmental malformations, such as the appearance of pericardial edema phenotype. In addition, after 72 h of exposure, the mRNA levels of cardiac development-related genes, such as myh7, myh6, tpm1, nppa, tbx5, tbx20, myl7 and cmlc1, were significantly lower in AgNPs-treated zebrafish embryos than in control zebrafish embryos. Moreover, RNA sequencing, KEGG (Kyoto Encyclopedia of Genes) and Genomes and GSEA (gene set enrichment analysis) of the DEGs (differentially expressed genes) between the AgNPs-exposed and control groups indicated that the downregulated DEGs were mainly enriched in focal adhesion pathways. Further investigations demonstrated that the mRNA levels of focal adhesion pathway-related genes, such as igf1ra, shc3, grb2b, ptk2aa, akt1, itga4, parvaa, akt3b and vcla, were significantly decreased after AgNPs treatment in zebrafish.

Conclusion

Thus, our findings illustrated that AgNPs could impair cardiac development by regulating the focal adhesion pathway in zebrafish.

Neuronal nitric oxide synthase required for erythropoietin modulation of heart function in mice

Introduction: Erythropoietin (EPO) acts primarily in regulating red blood cell production mediated by high EPO receptor (EPOR) expression in erythroid progenitor cells. EPO activity in non-erythroid tissue is evident in mice with EPOR restricted to erythroid tissues (ΔEPORE) that become obese, glucose-intolerant, and insulin-resistant. In animal models, nitric oxide synthase (NOS) contributes to EPO activities including erythropoiesis, neuroprotection, and cardioprotection against ischemia-reperfusion injury. However, we found that extended EPO treatment to increase hematocrit compromised heart function, while the loss of neuronal NOS (nNOS) was protective against the deleterious activity of EPO to promote heart failure. Methods: Wild-type (WT) mice, ΔEPORE mice, and nNOS-knockout mice (nNOS-/-) were placed on a high-fat diet to match the ΔEPORE obese phenotype and were treated with EPO for 3 weeks. Hematocrit and metabolic response to EPO treatment were monitored. Cardiac function was assessed by echocardiography and ultrasonography. Results: ΔEPORE mice showed a decrease in the left ventricular outflow tract (LVOT) peak velocity, ejection fraction, and fractional shortening, showing that endogenous non-erythroid EPO response is protective for heart function. EPO treatment increased hematocrit in all mice and decreased fat mass in male WT, demonstrating that EPO regulation of fat mass requires non-erythroid EPOR. EPO treatment also compromised heart function in WT mice, and decreased the pulmonary artery peak velocity (PA peak velocity), LVOT peak velocity, ejection fraction, and fractional shortening, but it had minimal effect in further reducing the heart function in ΔEPORE mice, indicating that the adverse effect of EPO on heart function is not related to EPO-stimulated erythropoiesis. ΔEPORE mice had increased expression of heart failure-associated genes, hypertrophic cardiomyopathy-related genes, and sarcomeric genes that were also elevated with EPO treatment in WT mice. Male and female nNOS-/- mice were protected against diet-induced obesity. EPO treatment in nNOS-/- mice increased the hematocrit that tended to be lower than WT mice and decreased the PA peak velocity but did not affect the LVOT peak velocity, ejection fraction, and fractional shortening, suggesting that nNOS is required for the adverse effect of EPO treatment on heart function in WT mice. EPO treatment did not change expression of heart failure-associated gene expression in nNOS-/- mice. Discussion: Endogenous EPO has a protective effect on heart function. With EPO administration, in contrast to the protective effect to the cardiac injury of acute EPO treatment, extended EPO treatment to increase hematocrit in WT mice adversely affected the heart function with a corresponding increase in expression of heart failure-associated genes. This EPO activity was independent of EPO-stimulated erythropoiesis and required EPOR in non-erythroid tissue and nNOS activity, while nNOS-/- mice were protected from the EPO-associated adverse effect on heart function. These data provide evidence that nNOS contributes to the negative impact on the heart function of high-dose EPO treatment for anemia.

Proteomic and Phosphoproteomic Analysis of Right Ventricular Hypertrophy in the Pulmonary Hypertension Rat Model

Pulmonary arterial hypertension (PAH) is a progressive disease that affects both the lungs and heart. Right ventricle (RV) hypertrophy is a primary pathological feature of PAH; however, its underlying molecular mechanisms remain insufficiently studied. In this study, we employed tandem mass tag (TMT)-based quantitative proteomics for the integrative analysis of the proteome and phosphoproteome of the RV derived from monocrotaline-induced PAH model rats. Compared with control samples, 564 significantly upregulated proteins, 616 downregulated proteins, 622 downregulated phosphopeptides, and 683 upregulated phosphopeptides were identified (P < 0.05, abs (log2 (fold change)) > log2 1.2) in the MCT samples. The quantitative real-time polymerase chain reaction (qRT-PCR) validated the expression levels of top 20 significantly altered proteins, including Nppa (natriuretic peptides A), latent TGF-β binding protein 2 (Ltbp2), periostin, connective tissue growth factor 2 (Ccn2), Ncam1 (neural cell adhesion molecule), quinone reductase 2 (Nqo2), and tropomodulin 4 (Tmod4). Western blotting confirmed the upregulation of Ncam1 and downregulation of Nqo2 and Tmod4 in both MCT-induced and hypoxia-induced PH rat models. Pathway enrichment analyses indicated that the altered proteins are associated with pathways, such as vesicle-mediated transport, actin cytoskeleton organization, TCA cycle, and respiratory electron transport. These significantly changed phosphoproteins were enriched in pathways such as diabetic cardiomyopathy, hypertrophic cardiomyopathy, glycolysis/gluconeogenesis, and cardiac muscle contraction. In summary, this study provides an initial analysis of the RV proteome and phosphoproteome in the progression of PAH, highlighting several RV dysfunction-associated proteins and pathways.

Tbx5 maintains atrial identity in post-natal cardiomyocytes by regulating an atrial-specific enhancer network

Understanding how the atrial and ventricular heart chambers maintain distinct identities is a prerequisite for treating chamber-specific diseases. Here, we selectively knocked out (KO) the transcription factor Tbx5 in the atrial working myocardium to evaluate its requirement for atrial identity. Atrial Tbx5 inactivation downregulated atrial cardiomyocyte (aCM) selective gene expression. Using concurrent single nucleus transcriptome and open chromatin profiling, genomic accessibility differences were identified between control and Tbx5 KO aCMs, revealing that 69% of the control-enriched ATAC regions were bound by TBX5. Genes associated with these regions were downregulated in KO aCMs, suggesting they function as TBX5-dependent enhancers. Comparing enhancer chromatin looping using H3K27ac HiChIP identified 510 chromatin loops sensitive to TBX5 dosage, and 74.8% of control-enriched loops contained anchors in control-enriched ATAC regions. Together, these data demonstrate TBX5 maintains the atrial gene expression program by binding to and preserving the tissue-specific chromatin architecture of atrial enhancers.

The long noncoding RNA Charme supervises cardiomyocyte maturation by controlling cell differentiation programs in the developing heart

Long noncoding RNAs (lncRNAs) are emerging as critical regulators of heart physiology and disease, although the studies unveiling their modes of action are still limited to few examples. We recently identified pCharme, a chromatin-associated lncRNA whose functional knockout in mice results in defective myogenesis and morphological remodeling of the cardiac muscle. Here, we combined Cap-Analysis of Gene Expression (CAGE), single-cell (sc)RNA sequencing, and whole-mount in situ hybridization analyses to study pCharme cardiac expression. Since the early steps of cardiomyogenesis, we found the lncRNA being specifically restricted to cardiomyocytes, where it assists the formation of specific nuclear condensates containing MATR3, as well as important RNAs for cardiac development. In line with the functional significance of these activities, pCharme ablation in mice results in a delayed maturation of cardiomyocytes, which ultimately leads to morphological alterations of the ventricular myocardium. Since congenital anomalies in myocardium are clinically relevant in humans and predispose patients to major complications, the identification of novel genes controlling cardiac morphology becomes crucial. Our study offers unique insights into a novel lncRNA-mediated regulatory mechanism promoting cardiomyocyte maturation and bears relevance to Charme locus for future theranostic applications.

Proteomic Insights into Cardiac Fibrosis: From Pathophysiological Mechanisms to Therapeutic Opportunities

Cardiac fibrosis is a common pathophysiologic process in nearly all forms of heart disease which refers to excessive deposition of extracellular matrix proteins by cardiac fibroblasts. Activated fibroblasts are the central cellular effectors in cardiac fibrosis, and fibrotic remodelling can cause several cardiac dysfunctions either by reducing the ejection fraction due to a stiffened myocardial matrix, or by impairing electric conductance. Recently, there is a rising focus on the proteomic studies of cardiac fibrosis for pathogenesis elucidation and potential biomarker mining. This paper summarizes the current knowledge of molecular mechanisms underlying cardiac fibrosis, discusses the potential of imaging and circulating biomarkers available to recognize different phenotypes of this lesion, reviews the currently available and potential future therapies that allow individualized management in reversing progressive fibrosis, as well as the recent progress on proteomic studies of cardiac fibrosis. Proteomic approaches using clinical specimens and animal models can provide the ability to track pathological changes and new insights into the mechanisms underlining cardiac fibrosis. Furthermore, spatial and cell-type resolved quantitative proteomic analysis may also serve as a minimally invasive method for diagnosing cardiac fibrosis and allowing for the initiation of prophylactic treatment.

NRSF/REST-Mediated Epigenomic Regulation in the Heart: Transcriptional Control of Natriuretic Peptides and Beyond

Reactivation of fetal cardiac genes, including those encoding atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), is a key feature of pathological cardiac remodeling and heart failure. Intensive studies on the regulation of ANP and BNP have revealed the involvement of numerous transcriptional factors in the regulation of the fetal cardiac gene program. Among these, we identified that a transcriptional repressor, neuron-restrictive silencer factor (NRSF), also named repressor element-1-silencing transcription factor (REST), which was initially detected as a transcriptional repressor of neuron-specific genes in non-neuronal cells, plays a pivotal role in the transcriptional regulation of ANP, BNP and other fetal cardiac genes. Here we review the transcriptional regulation of ANP and BNP gene expression and the role of the NRSF repressor complex in the regulation of cardiac gene expression and the maintenance of cardiac homeostasis.

Natriuretic peptides and Forkhead O transcription factors act in a cooperative manner to promote cardiomyocyte cell cycle re-entry in the postnatal mouse heart

Background

Cardiomyocytes proliferate rapidly during fetal life but lose their ability of proliferation soon after birth. However, before terminal withdrawal from the cell cycle, cardiomyocytes undergo another round of cell cycle during early postnatal life in mice. While a transient wave of increased DNA synthesis in cardiomyocyte has been observed in postnatal mouse hearts, the molecular mechanisms describing cardiomyocyte cell cycle re-entry remain poorly understood. Atrial and B-type natriuretic peptides (ANP and BNP) are abundantly expressed in embryonic heart ventricles. After birth, the expression of both genes is strongly reduced in the ventricular myocardium. Forkhead O (FOXO) transcription factors are expressed in both embryonic and postnatal heart ventricles. Their transcriptional activity negatively affects cardiomyocyte proliferation. Upon phosphorylation, FOXO is translocated to the cytoplasm and is transcriptionally inactive. Despite these important findings, it remains largely unknown whether natriuretic peptides and FOXO cooperatively play a role in regulating cardiomyocyte cell cycle activity during early postnatal life.

Results

We observed that the expression of ANP and BNP and the level of phosphorylated FOXO were transiently increased in the postnatal mouse heart ventricles, which coincided with the burst of cardiomyocyte cell cycle re-entry during early postnatal life in mice. Cell culture studies showed that ANP/BNP signaling and FOXO cooperatively promoted cell cycle activity in neonatal mouse cardiomyocytes. The enhanced cell cycle activity observed in combined treatment of ANP/BNP and dominant-negative FOXO (DN-FOXO), which can bind FOXO recognition sites on DNA but cannot activate transcription, was primarily mediated through natriuretic peptide receptor 3 (Npr3). In mice, simultaneous application of ANP and DN-FOXO in postnatal hearts reactivated cell cycle in cardiomyocytes, resulting in reduced scar formation after experimental myocardial infarction.

Conclusions

Our data demonstrate the cooperative effects of natriuretic peptide and DN-FOXO on promoting cardiomyocyte cell cycle activity and mouse cardiac repair and regeneration after injury.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12861-020-00236-y.

Cholecystokinin peptide signaling is regulated by a TBX5-MEF2 axis in the heart

The procholecystokinin (proCCK) gene encodes a secreted peptide known to regulate the digestive, endocrine, and nervous systems. Though recently proposed as a biomarker for heart dysfunction, its physiological role in both the embryonic and adult heart is poorly understood, and there are no reports of tissue-specific regulators of cholecystokinin signaling in the heart or other tissues. In the present study, mRNA of proCCK was observed in cardiac tissues during mouse embryonic development, establishing proCCK as an early marker of differentiated cardiomyocytes which is later restricted to anatomical subdomains of the neonatal heart. Three-dimensional analysis of the expression of proCCK and CCKAR/CCKBR receptors was performed using in situ hybridization and optical projection tomography, illustrating chamber-specific expression patterns in the postnatal heart. Transcription factor motif analyses indicated developmental cardiac transcription factors TBX5 and MEF2C as upstream regulators of proCCK, and this regulatory activity was confirmed in reporter gene assays. proCCK mRNA levels were also measured in the infarcted heart and in response to cyclic mechanical stretch and endothelin-1, indicating dynamic transcriptional regulation which might be leveraged for improved biomarker development. Functional analyses of exogenous cholecystokinin octapeptide (CCK-8) administration were performed in differentiating mouse embryonic stem cells (mESCs), and the results suggest that CCK-8 does not act as a differentiation modulator of cardiomyocyte subtypes. Collectively, these findings indicate that proCCK is regulated at the transcriptional level by TBX5-MEF2 and neurohormonal signaling, informing use of proCCK as a biomarker and future strategies for upstream manipulation of cholecystokinin signaling in the heart and other tissues.

Genetic Dissection of a Super Enhancer Controlling the Nppa-Nppb Cluster in the Heart

RATIONALE

ANP (atrial natriuretic peptide) and BNP (B-type natriuretic peptide), encoded by the clustered genes Nppa and Nppb, are important prognostic, diagnostic, and therapeutic proteins in cardiac disease. The spatiotemporal expression pattern and stress-induction of the Nppa and Nppb are tightly regulated, possibly involving their coregulation by an evolutionary conserved enhancer cluster.

OBJECTIVE

To explore the physiological functions of the enhancer cluster and elucidate the genomic mechanism underlying Nppa-Nppb coregulation in vivo.

METHODS AND RESULTS

By analyzing epigenetic data we uncovered an enhancer cluster with super enhancer characteristics upstream of Nppb. Using CRISPR/Cas9 genome editing, the enhancer cluster or parts thereof, Nppb and flanking regions or the entire genomic block spanning Nppa-Nppb, respectively, were deleted from the mouse genome. The impact on gene regulation and phenotype of the respective mouse lines was investigated by transcriptomic, epigenomic, and phenotypic analyses. The enhancer cluster was essential for prenatal and postnatal ventricular expression of Nppa and Nppb but not of any other gene. Enhancer cluster-deficient mice showed enlarged hearts before and after birth, similar to Nppa-Nppb compound knockout mice we generated. Analysis of the other deletion alleles indicated the enhancer cluster engages the promoters of Nppa and Nppb in a competitive rather than a cooperative mode, resulting in increased Nppa expression when Nppb and flanking sequences were deleted. The enhancer cluster maintained its active epigenetic state and selectivity when its target genes are absent. In enhancer cluster-deficient animals, Nppa was induced but remained low in the postmyocardial infarction border zone and in the hypertrophic ventricle, involving regulatory sequences proximal to Nppa.

CONCLUSIONS

Coordinated ventricular expression of Nppa and Nppb is controlled in a competitive manner by a shared super enhancer, which is also required to augment stress-induced expression and to prevent premature hypertrophy.

Cardiac natriuretic peptides

Investigations into the mixed muscle-secretory phenotype of cardiomyocytes from the atrial appendages of the heart led to the discovery that these cells produce, in a regulated manner, two polypeptide hormones - the natriuretic peptides - referred to as atrial natriuretic factor or atrial natriuretic peptide (ANP) and brain or B-type natriuretic peptide (BNP), thereby demonstrating an endocrine function for the heart. Studies on the gene encoding ANP (NPPA) initiated the field of modern research into gene regulation in the cardiovascular system. Additionally, ANP and BNP were found to be the natural ligands for cell membrane-bound guanylyl cyclase receptors that mediate the effects of natriuretic peptides through the generation of intracellular cGMP, which interacts with specific enzymes and ion channels. Natriuretic peptides have many physiological actions and participate in numerous pathophysiological processes. Important clinical entities associated with natriuretic peptide research include heart failure, obesity and systemic hypertension. Plasma levels of natriuretic peptides have proven to be powerful diagnostic and prognostic biomarkers of heart disease. Development of pharmacological agents that are based on natriuretic peptides is an area of active research, with vast potential benefits for the treatment of cardiovascular disease.

smarce1 mutants have a defective endocardium and an increased expression of cardiac transcription factors in zebrafish

SWI/SNF or BAF chromatin-remodeling complexes are polymorphic assemblies of homologous subunit families that remodel nucleosomes and facilitate tissue-specific gene regulation during development. BAF57/SMARCE1 is a BAF complex subunit encoded in animals by a single gene and is a component of all mammalian BAF complexes. In vivo, the loss of SMARCE1 would lead to the formation of deficient combinations of the complex which might present limited remodeling activities. To address the specific contribution of SMARCE1 to the function of the BAF complex, we generated CRISPR/Cas9 mutations of smarce1 in zebrafish. Smarce1 mutants showed visible defects at 72 hpf, including smaller eyes, abnormal body curvature and heart abnormalities. Gene expression analysis revealed that the mutant embryos displayed defects in endocardial development since early stages, which led to the formation of a misshapen heart tube. The severe morphological and functional cardiac problems observed at 4 dpf were correlated with the substantially increased expression of different cardiac transcription factors. Additionally, we showed that Smarce1 binds to cis-regulatory regions of the gata5 gene and is necessary for the recruitment of the BAF complex to these regions.

Structure and function of the Nppa-Nppb cluster locus during heart development and disease

Atrial natriuretic factor and brain natriuretic peptide are two important biomarkers in clinical cardiology. These two natriuretic peptide hormones are encoded by the paralogous genes Nppa and Nppb, which are evolutionary conserved. Both genes are predominantly expressed by the heart muscle during the embryonic and fetal stages, and in particular Nppa expression is strongly reduced in the ventricles after birth. Upon cardiac stress, Nppa and Nppb are strongly upregulated in the ventricular myocardium. Much is known about the molecular and physiological ques inducing Nppa and Nppb expression; however, the transcriptional regulatory mechanisms of the Nppa-Nppb cluster in vivo has proven to be quite complex and is not well understood. In this review, we will provide recent insights into the dynamic and complex regulation of Nppa and Nppb during heart development and hypertrophy, and the association of this gene cluster with the cardiomyocyte-intrinsic program of heart regeneration.

Optogenetic termination of atrial fibrillation in mice

Aims

The primary goal in the treatment of symptomatic atrial fibrillation/flutter (AF) is to restore sinus rhythm by cardioversion. Electrical shocks are highly effective, but have to be applied under analgo-sedation and can further harm the heart. In order to develop a novel pain-free and less harmful approach, we explored herein the optogenetic cardioversion by light-induced depolarization.

Methods and results

Hearts from mice expressing Channelrhodopsin-2 (ChR2) and the AF-promoting loss-of-function Connexin 40 Ala96Ser mutation were explanted and perfused with low K+ Tyrode's solution and an atrial KATP-channel activator. This new protocol shortened atrial refractoriness as well as slowed atrial conduction and thereby enabled the induction of sustained AF. AF episodes could be terminated by epicardial illumination of the atria with focussed blue light (470 nm, 0.4 mW/mm2) with an efficacy of ∼97% (n = 17 hearts). In > 80% of cases, light directly terminated the AF episode with onset of illumination. Because similar illumination intensity was able to locally inhibit atrial activity, we propose that a light-induced block of electrical activity is responsible for reliable AF termination. The success rate was strongly depending on the illuminated area, applied light intensity and duration of illumination. Importantly, we were also able to demonstrate optogenetic termination of AF in vivo, using epicardial illumination through the open chest (n = 3 hearts). To point towards a translational potential, we systemically injected an adeno-associated virus to express ChR2 in wild type hearts. After 6-8 months, we found robust ChR2 expression in the atria, enabling light-mediated AF termination in six of seven mice tested.

Conclusion

We provide the first evidence for optogenetic termination of atrial tachyarrhythmia in intact hearts from transgenic as well as wild type mice ex and in vivo. Thus, this report could lay the foundation for the development of implantable devices for pain-free termination of AF.

The Efficacy of Cardiac Anti-miR-208a Therapy Is Stress Dependent

MicroRNAs (miRNAs) are important regulators of biology and disease. Recent animal efficacy studies validate the therapeutic benefit of miRNA modulation and underscore the therapeutic value of miRNA-targeting oligonucleotides. However, whether disease conditions (stress) influence the pharmacological effects of an anti-miR is currently unknown. To study the effect of disease on target regulation after anti-miR treatment, we injected animals with anti-miR-208a, a synthetic oligonucleotide that inhibits the cardiomyocyte-specific miR-208a. Our data indicate that the presence of stress increases the number of regulated miR-208a targets, and that higher stress levels correlate with stronger target derepression. Additionally, the type of stress also influences which targets are regulated upon miR-208a inhibition. Studies in a large animal model indicate a similar stress-dependent anti-miR effect. Subsequent in vitro studies suggest that the influence of stress on anti-miR efficacy depends at least in part on increased cellular anti-miR uptake. These data indicate that the pharmacological effect of anti-miRs is stronger under disease conditions, and that both the type and severity of disease determine the therapeutic outcome. These facts will be important for assessing the therapeutic dose and predicting the therapeutic outcome when applying anti-miRs in a clinical setting.

Identification of a regulatory domain controlling the Nppa-Nppb gene cluster during heart development and stress

The paralogous genes Nppa and Nppb are organized in an evolutionarily conserved cluster and provide a valuable model for studying co-regulation and regulatory landscape organization during heart development and disease. Here, we analyzed the chromatin conformation, epigenetic status and enhancer potential of sequences of the Nppa-Nppb cluster in vivo Our data indicate that the regulatory landscape of the cluster is present within a 60-kb domain centered around Nppb Both promoters and several potential regulatory elements interact with each other in a similar manner in different tissues and developmental stages. The distribution of H3K27ac and the association of Pol2 across the locus changed during cardiac hypertrophy, revealing their potential involvement in stress-mediated gene regulation. Functional analysis of double-reporter transgenic mice revealed that Nppa and Nppb share developmental, but not stress-response, enhancers, responsible for their co-regulation. Moreover, the Nppb promoter was required, but not sufficient, for hypertrophy-induced Nppa expression. In summary, the developmental regulation and stress response of the Nppa-Nppb cluster involve the concerted action of multiple enhancers and epigenetic changes distributed across a structurally rigid regulatory domain.

Noncoding RNA in age-related cardiovascular diseases

Eukaryotic gene expression is tightly regulated transcriptionally and post-transcriptionally by a host of noncoding (nc)RNAs. The best-studied class of short ncRNAs, microRNAs, mainly repress gene expression post-transcriptionally. Long noncoding (lnc)RNAs, which comprise RNAs differing widely in length and function, can regulate gene transcription as well as post-transcriptional mRNA fate. Collectively, ncRNAs affect a broad range of age-related physiologic deteriorations and pathologies, including reduced cardiovascular vigor and age-associated cardiovascular disease. This review presents an update of our understanding of regulatory ncRNAs contributing to cardiovascular health and disease as a function of advancing age. We will discuss (1) regulatory ncRNAs that control aging-associated cardiovascular homeostasis and disease, (2) the concepts, approaches, and methodologies needed to study regulatory ncRNAs in cardiovascular aging and (3) the challenges and opportunities that age-associated regulatory ncRNAs present in cardiovascular physiology and pathology. This article is part of a Special Issue entitled "CV Aging".

Long-range regulatory interactions at the 4q25 atrial fibrillation risk locus involve PITX2c and ENPEP

BACKGROUND

Recent genome-wide association studies have uncovered genomic loci that underlie an increased risk for atrial fibrillation, the major cardiac arrhythmia in humans. The most significant locus is located in a gene desert at 4q25, approximately 170 kilobases upstream of PITX2, which codes for a transcription factor involved in embryonic left-right asymmetry and cardiac development. However, how this genomic region functionally and structurally relates to PITX2 and atrial fibrillation is unknown.

RESULTS

To characterise its function, we tested genomic fragments from 4q25 for transcriptional activity in a mouse atrial cardiomyocyte cell line and in transgenic mouse embryos, identifying a non-tissue-specific potentiator regulatory element. Chromosome conformation capture revealed that this region physically interacts with the promoter of the cardiac specific isoform of Pitx2. Surprisingly, this regulatory region also interacts with the promoter of the next neighbouring gene, Enpep, which we show to be expressed in regions of the developing mouse heart essential for cardiac electrical activity.

CONCLUSIONS

Our data suggest that de-regulation of both PITX2 and ENPEP could contribute to an increased risk of atrial fibrillation in carriers of disease-associated variants, and show the challenges that we face in the functional analysis of genome-wide disease associations.

Investigating the transcriptional control of cardiovascular development

Transcriptional regulation of thousands of genes instructs complex morphogenetic and molecular events for heart development. Cardiac transcription factors choreograph gene expression at each stage of differentiation by interacting with cofactors, including chromatin-modifying enzymes, and by binding to a constellation of regulatory DNA elements. Here, we present salient examples relevant to cardiovascular development and heart disease, and review techniques that can sharpen our understanding of cardiovascular biology. We discuss the interplay between cardiac transcription factors, cis-regulatory elements, and chromatin as dynamic regulatory networks, to orchestrate sequential deployment of the cardiac gene expression program.

Brain derived neurotrophic factor contributes to the cardiogenic potential of adult resident progenitor cells in failing murine heart

Aims

Resident cardiac progenitor cells show homing properties when injected into the injured but not to the healthy myocardium. The molecular background behind this difference in behavior needs to be studied to elucidate how adult progenitor cells can restore cardiac function of the damaged myocardium. Since the brain derived neurotrophic factor (BDNF) moderates cardioprotection in injured hearts, we focused on delineating its regulatory role in the damaged myocardium.

Methods and Results

Comparative gene expression profiling of freshly isolated undifferentiated Sca-1 progenitor cells derived either from heart failure transgenic αMHC-CyclinT1/Gαq overexpressing mice or wildtype littermates revealed transcriptional variations. Bdnf expression was up regulated 5-fold during heart failure which was verified by qRT-PCR and confirmed at protein level. The migratory capacity of Sca-1 cells from transgenic hearts was improved by 15% in the presence of 25ng/ml BDNF. Furthermore, BDNF-mediated effects on Sca-1 cells were studied via pulsed Stable Isotope Labeling of Amino acids in Cell Culture (pSILAC) proteomics approach. After BDNF treatment significant differences between newly synthesized proteins in Sca-1 cells from control and transgenic hearts were observed for CDK1, SRRT, HDGF, and MAP2K3 which are known to regulate cell cycle, survival and differentiation. Moreover BDNF repressed the proliferation of Sca-1 cells from transgenic hearts.

Conclusion

Comparative profiling of resident Sca-1 cells revealed elevated BDNF levels in the failing heart. Exogenous BDNF (i) stimulated migration, which might improve the homing ability of Sca-1 cells derived from the failing heart and (ii) repressed the cell cycle progression suggesting its potency to ameliorate heart failure.

RP5-833A20.1/miR-382-5p/NFIA-dependent signal transduction pathway contributes to the regulation of cholesterol homeostasis and inflammatory reaction

OBJECTIVE

Cardiovascular disease caused by atherosclerosis is the number one cause of death in Western countries and threatens to become the major cause of morbidity and mortality worldwide. Long noncoding RNAs are emerging as new players in gene regulation, but how long noncoding RNAs operate in the development of atherosclerosis remains unclear.

APPROACH AND RESULTS

Using microarray analysis, we found that long noncoding RNA RP5-833A20.1 expression was upregulated, whereas nuclear factor IA (NFIA) expression was downregulated in human acute monocytic leukemia macrophage-derived foam cells. Moreover, we showed that long noncoding RNA RP5-833A20.1 may decreases NFIA expression by inducing hsa-miR-382-5p expression in vitro. We found that the RP5-833A20.1/hsa-miR-382-5p/NFIA pathway is essential to the regulation of cholesterol homeostasis and inflammatory responses in human acute monocytic leukemia macrophages. Lentivirus-mediated NFIA overexpression increased high-density lipoprotein cholesterol circulation, reduced low-density lipoprotein cholesterol, and very-low-density lipoprotein cholesterol circulation, decreased circulation of inflammatory cytokines, including interleukin-1β, interleukin-6, tumor necrosis factor-α, and C-reactive protein, enhanced reverse cholesterol transport, and promoted regression of atherosclerosis in apolipoprotein E-deficient mice.

CONCLUSIONS

Our findings indicated that the RP5-833A20.1/miR-382-5p/NFIA pathway was essential to the regulation of cholesterol homeostasis and inflammatory reactions and suggested that NFIA may represent a therapeutic target to ameliorate cardiovascular disease.

A systematic review of fetal genes as biomarkers of cardiac hypertrophy in rodent models of diabetes

Pathological cardiac hypertrophy activates a suite of genes called the fetal gene program (FGP). Pathological hypertrophy occurs in diabetic cardiomyopathy (DCM); therefore, the FGP is widely used as a biomarker of DCM in animal studies. However, it is unknown whether the FGP is a consistent marker of hypertrophy in rodent models of diabetes. Therefore, we analyzed this relationship in 94 systematically selected studies. Results showed that diabetes induced with cytotoxic glucose analogs such as streptozotocin was associated with decreased cardiac weight, but genetic or diet-induced models of diabetes were significantly more likely to show cardiac hypertrophy (P<0.05). Animal strain, sex, age, and duration of diabetes did not moderate this effect. There were no correlations between the heart weight:body weight index and mRNA or protein levels of the fetal genes α-myosin heavy chain (α-MHC) or β-MHC, sarco/endoplasmic reticulum Ca²⁺-ATPase, atrial natriuretic peptide (ANP), or brain natriuretic peptide. The only correlates of non-indexed heart weight were the protein levels of α-MHC (Spearman's ρ = 1, P<0.05) and ANP (ρ = −0.73, P<0.05). These results indicate that most commonly measured genes in the FGP are confounded by diabetogenic methods, and are not associated with cardiac hypertrophy in rodent models of diabetes.

Differential activation of natriuretic peptide receptors modulates cardiomyocyte proliferation during development

Organ development is a highly regulated process involving the coordinated proliferation and differentiation of diverse cellular populations. The pathways regulating cell proliferation and their effects on organ growth are complex and for many organs incompletely understood. In all vertebrate species, the cardiac natriuretic peptides (ANP and BNP) are produced by cardiomyocytes in the developing heart. However, their role during cardiogenesis is not defined. Using the embryonic zebrafish and neonatal mammalian cardiomyocytes we explored the natriuretic peptide signaling network during myocardial development. We observed that the cardiac natriuretic peptides ANP and BNP and the guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2 are functionally redundant during early cardiovascular development. In addition, we demonstrate that low levels of the natriuretic peptides preferentially activate Npr3, a receptor with Gi activator sequences, and increase cardiomyocyte proliferation through inhibition of adenylate cyclase. Conversely, high concentrations of natriuretic peptides reduce cardiomyocyte proliferation through activation of the particulate guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2, and activation of protein kinase G. These data link the cardiac natriuretic peptides in a complex hierarchy modulating cardiomyocyte numbers during development through opposing effects on cardiomyocyte proliferation mediated through distinct cyclic nucleotide signaling pathways.

Long non-coding RNAs and human disease

The central dogma of molecular biology states that DNA is transcribed into RNA, which in turn is translated into proteins. We now know, however, that as much as 50% of the transcriptome has no protein-coding potential, but rather represents an important class of regulatory molecules responsible for the fine-tuning of gene expression. Although the role of small regulatory RNAs [microRNAs and siRNAs (small interfering RNA)] is well defined, another much less characterized category of non-coding transcripts exists, namely lncRNAs (long non-coding RNAs). Pervasively expressed by eukaryotic genomes, lncRNAs can be kilobases long and regulate their targets by influencing the epigenetic control, chromatin status, mRNA processing or translation capacity of their targets. In the present review, I outline the potential mechanisms of action of lncRNAs, the cellular processes that have been associated with them, and also explore some of the emerging evidence for their involvement in common human disease.

Localized and temporal gene regulation in heart development

The heart is a structurally complex and functionally heterogeneous organ. The repertoire of genes active in a given cardiac cell defines its shapes and function. This process of localized or heterogeneous gene expression is regulated to a large extent at the level of transcription, dictating the degree particular genes in a cell are active. Therefore, errors in the regulation of localized gene expression are at the basis of misregulation of the delicate process of heart development and function. In this review, we provide an overview of the origin of the different components of the vertebrate heart, and discuss our current understanding of the regulation of localized gene expression in the developing heart. We will also discuss where future research may lead to gain more insight into this process, which should provide much needed insight into the dysregulation of heart development and function, and the etiology of congenital defects.

In vivo natriuretic peptide reporter assay identifies chemical modifiers of hypertrophic cardiomyopathy signalling

AIMS

Despite increased understanding of the fundamental biology regulating cardiomyocyte hypertrophy and heart failure, it has been challenging to find novel chemical or genetic modifiers of these pathways. Traditional cell-based methods do not model the complexity of an intact cardiovascular system and mammalian models are not readily adaptable to chemical or genetic screens. Our objective was to create an in vivo model suitable for chemical and genetic screens for hypertrophy and heart failure modifiers.

METHODS AND RESULTS

Using the developing zebrafish, we established that the cardiac natriuretic peptide genes (nppa and nppb), known markers of cardiomyocyte hypertrophy and heart failure, were induced in the embryonic heart by pathological cardiac stimuli. This pathological induction was distinct from the developmental regulation of these genes. We created a luciferase-based transgenic reporter line that accurately modelled the pathological induction patterns of the zebrafish nppb gene. Utilizing this reporter line, we were able to show remarkable conservation of pharmacological responses between the larval zebrafish heart and adult mammalian models.

CONCLUSION

By performing a focused screen of chemical agents, we were able to show a distinct response of a genetic model of hypertrophic cardiomyopathy to the histone deacetylase inhibitor, Trichostatin A, and the mitogen-activated protein kinase kinase 1/2 inhibitor, U0126. We believe this in vivo reporter line will offer a unique approach to the identification of novel chemical or genetic regulators of myocardial hypertrophy and heart failure.

Differential role of Nkx2-5 in activation of the atrial natriuretic factor gene in the developing versus failing heart

Atrial natriuretic factor (ANF) is abundantly expressed in atrial cardiomyocytes throughout ontogeny and in ventricular cardiomyocytes in the developing heart. However, during cardiac failure and hypertrophy, ANF expression can reappear in adult ventricular cardiomyocytes. The transcription factor Nkx2-5 is one of the major transactivators of the ANF gene in the developing heart. We identified Nkx2-5 binding at three 5' regulatory elements (kb -34, -31, and -21) and at the proximal ANF promoter by ChIP assay using neonatal mouse cardiomyocytes. 3C analysis revealed close proximity between the distal elements and the promoter region. A 5.8-kb fragment consisting of these elements transactivated a reporter gene in vivo recapitulating endogenous ANF expression, which was markedly reduced in tamoxifen-inducible Nkx2-5 gene knockout mice. However, expression of a reporter gene was increased and expanded toward the outer compact layer in the absence of the transcription repressor Hey2, similar to endogenous ANF expression. Functional Nkx2-5 and Hey2 binding sites separated by 59 bp were identified in the -34 kb element in neonatal cardiomyocytes. In adult hearts, this fragment did not respond to pressure overload, and ANF was induced in the absence of Nkx2-5. These results demonstrate that Nkx2-5 and its responsive cis-regulatory DNA elements are essential for ANF expression selectively in the developing heart.

Atrial natriuretic factor in the developing heart: a signpost for cardiac morphogenesis

The developing heart forms during the early stages of embryogenesis, and misregulated heart development results in congenital heart defects (CHDs). To understand the molecular basis of CHDs, a deep understanding of the morphological and genetic basis of heart development is necessary. Atrial Natriuretic Factor (ANF) is an important and extremely sensitive marker for specific regions of the developing heart, as well as for disturbances in the patterning of the heart. This review summarizes the dynamic expression of ANF in the developing heart and its usefulness in understanding the early molecular defects underlying CHDs.

Systemic molecular and cellular changes induced in rats upon inhalation of JP-8 petroleum fuel vapor

Limited information is available regarding systemic changes in mammals associated with exposures to petroleum/hydrocarbon fuels. In this study, systemic toxicity of JP-8 jet fuel was observed in a rat inhalation model at different JP-8 fuel vapor concentrations (250, 500, or 1000 mg/m(3), for 91 days). Gel electrophoresis and mass spectrometry sequencing identified the alpha-2 microglobulin protein to be elevated in rat kidney in a JP-8 dose-dependent manner. Western blot analysis of kidney and lung tissue extracts revealed JP-8 dependent elevation of inducible heat shock protein 70 (HSP70). Tissue changes were observed histologically (hematoxylin and eosin staining) in liver, kidney, lung, bone marrow, and heart, and more prevalently at medium or high JP-8 vapor phase exposures (500-1000 mg/m(3)) than at low vapor phase exposure (250 mg/m(3)) or non-JP-8 controls. JP-8 fuel-induced liver alterations included dilated sinusoids, cytoplasmic clumping, and fat cell deposition. Changes to the kidneys included reduced numbers of nuclei, and cytoplasmic dumping in the lumen of proximal convoluted tubules. JP-8 dependent lung alterations were edema and dilated alveolar capillaries, which allowed clumping of red blood cells (RBCs). Changes in the bone marrow in response to JP-8 included reduction of fat cells and fat globules, and cellular proliferation (RBCs, white blood cells-WBCs, and megakaryocytes). Heart tissue from JP-8 exposed animals contained increased numbers of inflammatory and fibroblast cells, as well as myofibril scarring. cDNA array analysis of heart tissue revealed a JP-8 dependent increase in atrial natriuretic peptide precursor mRNA and a decrease in voltage-gated potassium (K+) ion channel mRNA.

Gene replacement strategies to test the functional redundancy of basic helix-loop-helix transcription factor

Basic helix-loop-helix (bHLH) transcription factors control developmental decisions for a wide range of embryonic cell types. Hand1 and Hand2 are closely related bHLH proteins that control cardiac, craniofacial, and limb development. Within the developing heart, Hand1 expression becomes restricted predominantly to the left ventricle, whereas Hand2 becomes restricted predominantly to the left ventricle, for which findings have shown each Hand factor to be necessary for normal chamber formation. Forced overexpression of Hand1 throughout the early developing heart induces abnormal interventricular septal development, with resulting pathogenesis of congenital heart defects. To investigate the potential transcriptional mechanisms involved in heart morphogenesis by Hand2, this study used a replacement targeting approach to knock Hand2 into the Hand1 locus and ectopically express one copy of Hand2 within the endogenous Hand1 expression domain in the developing hearts of transgenic mice. The findings show that high-percentage Hand1 ( Hand2 ) chimeras die at birth and exhibit a range of congenital heart defects. These findings suggest that Hand factors may act via unique transcriptional mechanisms mediated by bHLH factor partner choice, supporting the notion that alterations of Hand factor stoichiometry may be as deleterious to normal heart morphogenesis as Hand factor loss of function.

Influence of natriuretic peptide receptor-1 on survival and cardiac hypertrophy during development

The heart adapts to an increased workload through the activation of a hypertrophic response within the cardiac ventricles. This response is characterized by both an increase in the size of the individual cardiomyocytes and an induction of a panel of genes normally expressed in the embryonic and neonatal ventricle, such as atrial natriuretic peptide (ANP). ANP and brain natriuretic peptide (BNP) exert their biological actions through activation of the natriuretic peptide receptor-1 (Npr1). The current study examined mice lacking Npr1 (Npr1(-/-)) activity and investigated the effects of the absence of Npr1 signaling during cardiac development on embryo viability, cardiac structure and gene and protein expression. Npr1(-/-)embryos were collected at embryonic day (ED) 12.5, 15.5 and neonatal day 1 (ND 1). Npr1(-/-)embryos occurred at the expected Mendelian frequency at ED 12.5, but knockout numbers were significantly decreased at ED 15.5 and ND 1. There was no indication of cardiac structural abnormalities in surviving embryos. However, Npr1(-/-)embryos exhibited cardiac enlargement (without fibrosis) from ED 15.5 as well as significantly increased ANP mRNA and protein expression compared to wild-type (WT) mice, but no concomitant increase in expression of the hypertrophy-related transcription factors, Mef2A, Mef2C, GATA-4, GATA-6 or serum response factor (SRF). However, there was a significant decrease in Connexin-43 (Cx43) gene and protein expression at mid-gestation in Npr1(-/-)embryos. Our findings suggest that the mechanism by which natriuretic peptide signaling influences cardiac development in Npr1(-/-) mice is distinct from that seen during the development of pathological cardiac hypertrophy and fibrosis. The decreased viability of Npr1(-/-)embryos may result from a combination of cardiomegaly and dysregulated Cx43 protein affecting cardiac contractility.

Characterization of promoter elements required for cardiac chamber-specific expression

Salmon cardiac natriuretic peptide (sCP, an A-type natriuretic peptide) is an excellent model for the study of cardiac chamber-specific gene expression because it is uniquely specific to the heart and its promoter drives gene expression effectively in mammalian cardiac atrial but not in ventricular cells. We have now prepared hybrid luciferase constructs containing specific sequences from both sCP and BNP 5' promoters. According to our results the simple addition of a short rat BNP proximal promoter fragment to the inert 846 nucleotide sCP proximal promoter increases 100 times the basal activity of the sCP promoter in rat ventricular cardiomyocytes, and also conveys inducibility by mechanical load and endothelin-1. Thus, a small rBNP promoter fragment can transform the prototypical A-type natriuretic peptide regulation of sCP to B-type regulation, a result which argues against a major role of repressors causing the low expression level of A-type peptides in ventricular cardiomyocytes.

Gene expression profiling of the forming atrioventricular node using a novel tbx3-based node-specific transgenic reporter

The atrioventricular (AV) node is a recurrent source of potentially life-threatening arrhythmias. Nevertheless, limited data are available on its developmental control or molecular phenotype. We used a novel AV nodal myocardium-specific reporter mouse to gain insight into the gene programs determining the formation and phenotype of the developing AV node. In this reporter, green fluorescent protein (GFP) expression was driven by a 160-kbp bacterial artificial chromosome with Tbx3 and flanking sequences. GFP was selectively active in the AV canal of embryos and AV node of adults, whereas the Tbx3-positive AV bundle and sinus node were devoid of GFP, demonstrating that distinct regulatory sequences and pathways control expression in the components of the conduction system. Fluorescent AV nodal and complementary Nppa-positive chamber myocardial cell populations of embryonic day 10.5 embryos and of embryonic day 17.5 fetuses were purified using fluorescence-activated cell sorting, and their expression profiles were assessed by genome-wide microarray analysis, providing valuable information concerning their molecular identities. We constructed a comprehensive list of sodium, calcium, and potassium channel genes specific for developing nodal or chamber myocardium. Furthermore, the data revealed that the AV node and the chamber (working) myocardium phenotypes diverge during development but that the functional gene classes characterizing both subtypes are maintained. One of the repertoires identified in the AV node-specific gene profiles consists of multiple neurotrophic factors and semaphorins, not yet appreciated to play a role in nodal development, revealing shared characteristics between nodal and nervous system development.

The Tbx2+ primary myocardium of the atrioventricular canal forms the atrioventricular node and the base of the left ventricle

The primary myocardium of the embryonic heart, including the atrioventricular canal and outflow tract, is essential for septation and valve formation. In the chamber-forming heart, the expression of the T-box transcription factor Tbx2 is restricted to the primary myocardium. To gain insight into the cellular contributions of the Tbx2+ primary myocardium to the components of the definitive heart, genetic lineage tracing was performed using a novel Tbx2Cre allele. These analyses revealed that progeny of Tbx2+ cells provide an unexpectedly large contribution to the Tbx2-negative ventricles. Contrary to common assumption, we found that the embryonic left ventricle only forms the left part of the definitive ventricular septum and the apex. The atrioventricular node, but not the atrioventricular bundle, was found to derive from Tbx2+ cells. The Tbx2+ outflow tract formed the right ventricle and right part of the ventricular septum. In Tbx2-deficient embryos, the left-sided atrioventricular canal was found to prematurely differentiate to chamber myocardium and to proliferate at increased rates similar to those of chamber myocardium. As a result, the atrioventricular junction and base of the left ventricle were malformed. Together, these observations indicate that Tbx2 temporally suppresses differentiation and proliferation of primary myocardial cells. A subset of these Tbx2Cre-marked cells switch off expression of Tbx2, which allows them to differentiate into chamber myocardium, to initiate proliferation, and to provide a large contribution to the ventricles. These findings imply that errors in the development of the early atrioventricular canal may affect a much larger region than previously anticipated, including the ventricular base.