The transcription factors GATA4 and GATA6 regulate cardiomyocyte hypertrophy in vitro and in vivo

Regulation of Cardiac Transcription Factor GATA4 by Post-Translational Modification in Cardiomyocyte Hypertrophy and Heart Failure

Heart failure is a leading cause of cardiovascular mortality in industrialized countries. During development and deterioration of heart failure, cardiomyocytes undergo maladaptive hypertrophy, and changes in the cellular phenotype are accompanied by reinduction of the fetal gene program. Gene expression in cardiomyocytes is regulated by various nuclear transcription factors, co-activators, and co-repressors. The zinc finger protein GATA4 is one such transcription factor involved in the regulation of cardiomyocyte hypertrophy. In response to hypertrophic stimuli such as those involving the sympathetic nervous and renin-angiotensin systems, changes in protein interaction and/or post-translational modifications of GATA4 cause hypertrophic gene transcription in cardiomyocytes. In this article, we focus on cardiac nuclear signaling molecules, especially GATA4, that are promising as potential targets for heart failure therapy.

Myocardial plasticity: cardiac development, regeneration and disease

The adult mammalian heart is unable to recover from myocardial cell loss due to cardiac ischemia and infarction because terminally differentiated cardiomyocytes proliferate at a low rate. However, cardiomyocytes in other vertebrate animal models such as zebrafish, axolotls, newts and mammalian mouse neonates are capable of de-differentiating in order to promote cardiomyocyte proliferation and subsequent cardiac regeneration after injury. Although de-differentiation may occur in adult mammalian cardiomyocytes, it is typically associated with diseased hearts and pathologic remodeling rather than repair and regeneration. Here, we review recent studies of cardiac development, regeneration and disease that highlight how changes in myocardial identity (plasticity) is regulated and impacts adaptive and maladaptive cardiac responses.

An Integrative Transcriptomic Analysis for Identifying Novel Target Genes Corresponding to Severity Spectrum in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease resulting from a recessive mutation in the SMN1 gene. This disease affects multiple organ systems with varying degrees of severity. Exploration of the molecular pathological changes occurring in different cell types in SMA is crucial for developing new therapies. This study collected 39 human microarray datasets from ArrayExpress and GEO databases to build an integrative transcriptomic analysis for recognizing novel SMA targets. The transcriptomic analysis was conducted through combining weighted correlation network analysis (WGCNA) for gene module detection, gene set enrichment analysis (GSEA) for functional categorization and filtration, and Cytoscape (visual interaction gene network analysis) for target gene identification. Seven novel target genes (Bmp4, Serpine1, Gata6, Ptgs2, Bcl2, IL6 and Cntn1) of SMA were revealed, and are all known in the regulation of TNFα for controlling neural, cardiac and bone development. Sequentially, the differentially expressed patterns of these 7 target genes in mouse tissues (e.g., spinal cord, heart, muscles and bone) were validated in SMA mice of different severities (pre-symptomatic, mildly symptomatic, and severely symptomatic). In severely symptomatic SMA mice, TNFα was up-regulated with attenuation of Bmp4 and increase of Serpine1 and Gata6 (a pathway in neural and cardiac development), but not in pre-symptomatic and mildly symptomatic SMA mice. The severely symptomatic SMA mice also had the elevated levels of Ptgs2 and Bcl2 (a pathway in skeletal development) as well as IL6 and Cntn1 (a pathway in nervous system development). Thus, the 7 genes identified in this study might serve as potential target genes for future investigations of disease pathogenesis and SMA therapy.

TNF-insulin crosstalk at the transcription factor GATA6 is revealed by a model that links signaling and transcriptomic data tensors

Signal transduction networks coordinate transcriptional programs activated by diverse extracellular stimuli, such as growth factors and cytokines. Cells receive multiple stimuli simultaneously, and mapping how activation of the integrated signaling network affects gene expression is a challenge. We stimulated colon adenocarcinoma cells with various combinations of the cytokine tumor necrosis factor (TNF) and the growth factors insulin and epidermal growth factor (EGF) to investigate signal integration and transcriptional crosstalk. We quantitatively linked the proteomic and transcriptomic data sets by implementing a structured computational approach called tensor partial least squares regression. This statistical model accurately predicted transcriptional signatures from signaling arising from single and combined stimuli and also predicted time-dependent contributions of signaling events. Specifically, the model predicted that an early-phase, AKT-associated signal downstream of insulin repressed a set of transcripts induced by TNF. Through bioinformatics and cell-based experiments, we identified the AKT-repressed signal as glycogen synthase kinase 3 (GSK3)-catalyzed phosphorylation of Ser(37) on the long form of the transcription factor GATA6. Phosphorylation of GATA6 on Ser(37) promoted its degradation, thereby preventing GATA6 from repressing transcripts that are induced by TNF and attenuated by insulin. Our analysis showed that predictive tensor modeling of proteomic and transcriptomic data sets can uncover pathway crosstalk that produces specific patterns of gene expression in cells receiving multiple stimuli.

PKG-1α mediates GATA4 transcriptional activity

GATA4, a zinc-finger transcription factor, is central for cardiac development and diseases. Here we show that GATA4 transcriptional activity is mediated by cell signaling via cGMP dependent PKG-1α activity. Protein kinase G (PKG), a serine/tyrosine specific kinase is the major effector of cGMP signaling. We observed enhanced transcriptional activity elicited by co-expressed GATA4 and PKG-1α. Phosphorylation of GATA4 by PKG-1α was detected on serine 261 (S261), while the C-terminal activation domain of GATA4 associated with PKG-1α. GATA4's DNA binding activity was enhanced by PKG-1α via by both phosphorylation and physical association. More importantly, a number of human disease-linked GATA4 mutants exhibited impaired S261 phosphorylation, pointing to defective S261 phosphorylation in the elaboration of human heart diseases. We showed S261 phosphorylation was favored by PKG-1α but not by PKA, and several other kinase signaling pathways such as MAPK and PKC. Our observations demonstrate that cGMP-PKG signaling mediates transcriptional activity of GATA4 and links defective GATA4 and PKG-1α mutations to the development of human heart disease.

GATA4 regulates Fgf16 to promote heart repair after injury

Although the mammalian heart can regenerate during the neonatal stage, this endogenous regenerative capacity is lost with age. Importantly, replication of cardiomyocytes has been found to be the key mechanism responsible for neonatal cardiac regeneration. Unraveling the transcriptional regulatory network for inducing cardiomyocyte replication will, therefore, be crucial for the development of novel therapies to drive cardiac repair after injury. Here, we investigated whether the key cardiac transcription factor GATA4 is required for neonatal mouse heart regeneration. Using the neonatal mouse heart cryoinjury and apical resection models with an inducible loss of GATA4 specifically in cardiomyocytes, we found severely depressed ventricular function in the Gata4-ablated mice (mutant) after injury. This was accompanied by reduced cardiomyocyte replication. In addition, the mutant hearts displayed impaired coronary angiogenesis and increased hypertrophy and fibrosis after injury. Mechanistically, we found that the paracrine factor FGF16 was significantly reduced in the mutant hearts after injury compared with littermate controls and was directly regulated by GATA4. Cardiac-specific overexpression of FGF16 via adeno-associated virus subtype 9 (AAV9) in the mutant hearts partially rescued the cryoinjury-induced cardiac hypertrophy, promoted cardiomyocyte replication and improved heart function after injury. Altogether, our data demonstrate that GATA4 is required for neonatal heart regeneration through regulation of Fgf16, suggesting that paracrine factors could be of potential use in promoting myocardial repair.

Phenanthrene exposure induces cardiac hypertrophy via reducing miR-133a expression by DNA methylation

Growing evidence indicates that there is an emerging link between environmental pollution and cardiac hypertrophy, while the mechanism is unclear. The objective of this study was to examine whether phenanthrene (Phe) could cause cardiac hypertrophy, and elucidate the molecular mechanisms involved. We found that: 1) Phe exposure increased the heart weight and cardiomyocyte size of rats; 2) Phe exposure led to enlarged cell size, and increased protein synthesis in H9C2 cells; 3) Phe exposure induced important markers of cardiac hypertrophy, such as atrial natriuretic peptide, B-type natriuretic peptide, and c-Myc in H9C2 cells and rat hearts; 4) Phe exposure perturbed miR-133a, CdC42 and RhoA, which were key regulators of cardiac hypertrophy, in H9C2 cells and rat hearts; 5) Phe exposure induced DNA methyltransferases (DNMTs) in H9C2 cells and rat hearts; 6) Phe exposure led to methylation of CpG sites within the miR-133a locus and reduced miR-133a expression in H9C2 cells; 7) DNMT inhibition and miR-133a overexpression could both alleviate the enlargement of cell size and perturbation of CdC42 and RhoA caused by Phe exposure. These results indicated that Phe could induce cardiomyocyte hypertrophy in the rat and H9C2 cells. The mechanism might involve reducing miR-133a expression by DNA methylation.

Inhibitory effect of hsa-miR-590-5p on cardiosphere-derived stem cells differentiation through downregulation of TGFB signaling

The cardiac cells generation via stem cells differentiation is a promising approach to restore the myocardial infarction. Promoted by our primary bioinformatics analysis as well as some previously published data on potential role of hsa-miR-590-3p in cardiogenesis, we have tried to decipher the role of miR-590-5p during the course of differentiation of cardiosphere-derived cells (CDCs). The differentiation induction of CDCs by TGFB1 was confirmed by real-time PCR, ICC, and flow cytometry. The expression pattern of hsa-miR-590-5p and some related genes were examined during the differentiation process. In order to study the role of miR-590-5p in cardiac differentiation, the effect of miR-590 overexpression in CDCs was studied. Evaluating the expression patterns of miR-590 and its potential targets (TGFBRs) during the course of differentiation, demonstrated a significant downregulation of miR-590 and an upregulation of TGFBR2, following the treatment of CDCs with TGFB1. Therefore, we proposed a model in which TGFB1 exerts its differentiation induction via downregulation of miR-590, and hence the higher transcriptional expression level of TGFBR2. In accordance with our proposed model, transfection of CDCs by a pLenti-III-hsa-mir-590-GFP expression vector before or after the first TGFB1 treatment caused a significant alteration in the expression levels of TGFBRs. Moreover, our data revealed that overexpression of miR-590 before TGFB1 induction was able to attenuate the CDCs differentiation probably via the reduction of TGFBR2 expression level. Altogether, our data suggest an inhibitory role of miR-590 during the cardiac differentiation of CDCs which its suppression might elevate the rate of differentiation.

Phosphorylation of the chromatin remodeling factor DPF3a induces cardiac hypertrophy through releasing HEY repressors from DNA

DPF3 (BAF45c) is a member of the BAF chromatin remodeling complex. Two isoforms have been described, namely DPF3a and DPF3b. The latter binds to acetylated and methylated lysine residues of histones. Here, we elaborate on the role of DPF3a and describe a novel pathway of cardiac gene transcription leading to pathological cardiac hypertrophy. Upon hypertrophic stimuli, casein kinase 2 phosphorylates DPF3a at serine 348. This initiates the interaction of DPF3a with the transcriptional repressors HEY, followed by the release of HEY from the DNA. Moreover, BRG1 is bound by DPF3a, and is thus recruited to HEY genomic targets upon interaction of the two components. Consequently, the transcription of downstream targets such as NPPA and GATA4 is initiated and pathological cardiac hypertrophy is established. In human, DPF3a is significantly up-regulated in hypertrophic hearts of patients with hypertrophic cardiomyopathy or aortic stenosis. Taken together, we show that activation of DPF3a upon hypertrophic stimuli switches cardiac fetal gene expression from being silenced by HEY to being activated by BRG1. Thus, we present a novel pathway for pathological cardiac hypertrophy, whose inhibition is a long-term therapeutic goal for the treatment of the course of heart failure.

Bnip3 Binds and Activates p300: Possible Role in Cardiac Transcription and Myocyte Morphology

Bnip3 is a hypoxia-regulated member of the Bcl-2 family of proteins that is implicated in apoptosis, programmed necrosis, autophagy and mitophagy. Mitochondria are thought to be the primary targets of Bnip3 although its activities may extend to the ER, cytoplasm, and nucleus. Bnip3 is induced in the heart by ischemia and pressure-overload, and may contribute to cardiomyopathy and heart failure. Only mitochondrial-dependent programmed death actions have been described for Bnip3 in the heart. Here we describe a novel activity of Bnip3 in cultured cardiac myocytes and transgenic mice overexpressing Bnip3 in the heart (Bnip3-TG). In cultured myocytes Bnip3 bound and activated the acetyltransferase p300, increased acetylation of histones and the transcription factor GATA4, and conferred p300 and GATA4-sensitive cellular morphological changes. In intact Bnip3-TG hearts Bnip3 also bound p300 and GATA4 and conferred enhanced GATA4 acetylation. Bnip3-TG mice underwent age-dependent ventricular dilation and heart failure that was partially prevented by p300 inhibition with curcumin. The results suggest that Bnip3 regulates cardiac gene expression and perhaps myocyte morphology by activating nuclear p300 acetyltransferase activity and hyperacetylating histones and p300-selective transcription factors.

Orphan Nuclear Receptor Nur77 Inhibits Cardiac Hypertrophic Response to Beta-Adrenergic Stimulation

The orphan nuclear receptor Nur77 plays critical roles in cardiovascular diseases, and its expression is markedly induced in the heart after beta-adrenergic receptor (β-AR) activation. However, the functional significance of Nur77 in β-AR signaling in the heart remains unclear. By using Northern blot, Western blot, and immunofluorescent staining assays, we showed that Nur77 expression was markedly upregulated in cardiomyocytes in response to multiple hypertrophic stimuli, including isoproterenol (ISO), phenylephrine (PE), and endothelin-1 (ET-1). In a time- and dose-dependent manner, ISO increases Nur77 expression in the nuclei of cardiomyocytes. Overexpression of Nur77 markedly inhibited ISO-induced cardiac hypertrophy by inducing nuclear translocation of Nur77 in cardiomyocytes. Furthermore, cardiac overexpression of Nur77 by intramyocardial injection of Ad-Nur77 substantially inhibited cardiac hypertrophy and ameliorated cardiac dysfunction after chronic infusion of ISO in mice. Mechanistically, we demonstrated that Nur77 functionally interacts with NFATc3 and GATA4 and inhibits their transcriptional activities, which are critical for the development of cardiac hypertrophy. These results demonstrate for the first time that Nur77 is a novel negative regulator for the β-AR-induced cardiac hypertrophy through inhibiting the NFATc3 and GATA4 transcriptional pathways. Targeting Nur77 may represent a potentially novel therapeutic strategy for preventing cardiac hypertrophy and heart failure.

The alpha1-adrenergic receptors in cardiac hypertrophy: signaling mechanisms and functional implications

Cardiac hypertrophy is a complex remodeling process of the heart induced by physiological or pathological stimuli resulting in increased cardiomyocyte size and myocardial mass. Whereas cardiac hypertrophy can be an adaptive mechanism to stressful conditions of the heart, prolonged hypertrophy can lead to heart failure which represents the primary cause of human morbidity and mortality. Among G protein-coupled receptors, the α1-adrenergic receptors (α1-ARs) play an important role in the development of cardiac hypertrophy as demonstrated by numerous studies in the past decades, both in primary cardiomyocyte cultures and genetically modified mice. The results of these studies have provided evidence of a large variety of α1-AR-induced signaling events contributing to the defining molecular and cellular features of cardiac hypertrophy. Recently, novel signaling mechanisms have been identified and new hypotheses have emerged concerning the functional role of the α1-adrenergic receptors in the heart. This review will summarize the main signaling pathways activated by the α1-AR in the heart and their functional implications in cardiac hypertrophy.

Constitutive activities of estrogen-related receptors: Transcriptional regulation of metabolism by the ERR pathways in health and disease

The estrogen-related receptors (ERRs) comprise a small group of orphan nuclear receptor transcription factors. The ERRα and ERRγ isoforms play a central role in the regulation of metabolic genes and cellular energy metabolism. Although less is known about ERRβ, recent studies have revealed the importance of this isoform in the maintenance of embryonic stem cell pluripotency. Thus, ERRs are essential to many biological processes. The development of several ERR knockout and overexpression models and the application of advanced functional genomics have allowed rapid advancement of our understanding of the physiology regulated by ERR pathways. Moreover, it has enabled us to begin to delineate the distinct programs regulated by ERRα and ERRγ that have overlapping effects on metabolism and growth. The current review primarily focuses on the physiologic roles of ERR isoforms related to their metabolic regulation; therefore, the ERRα and ERRγ are discussed in the greatest detail. We emphasize findings from gain- and loss-of-function models developed to characterize ERR control of skeletal muscle, heart and musculoskeletal physiology. These models have revealed that coordinating metabolic capacity with energy demand is essential for seemingly disparate processes such as muscle differentiation and hypertrophy, innate immune function, thermogenesis, and bone remodeling. Furthermore, the models have revealed that ERRα- and ERRγ-deficiency in mice accelerates progression of pathologic processes and implicates ERRs as etiologic factors in disease. We highlight the human diseases in which ERRs and their downstream metabolic pathways are perturbed, including heart failure and diabetes. While no natural ligand has been identified for any of the ERR isoforms, the potential for using synthetic small molecules to modulate their activity has been demonstrated. Based on our current understanding of their transcriptional mechanisms and physiologic relevance, the ERRs have emerged as potential therapeutic targets for treatment of osteoporosis, muscle atrophy, insulin resistance and heart failure in humans.

IGF-2R-Gαq signaling and cardiac hypertrophy in the low-birth-weight lamb

The cardiac insulin-like growth factor 2 receptor (IGF-2R) can induce cardiomyocyte hypertrophy in a heterotrimeric G protein receptor-coupled manner involving αq (Gαq) or αs (Gαs). We have previously shown increased left ventricular weight and cardiac IGF-2 and IGF-2R gene expression in low-birth-weight (LBW) compared with average-birth-weight (ABW) lambs. Here, we have investigated the cardiac expression of IGF-2 gene variants, the degree of histone acetylation, and the abundance of proteins in the IGF-2R downstream signaling pathway in ABW and LBW lambs. Samples from the left ventricle of ABW and LBW lambs were collected at 21 days of age. There was increased phospho-CaMKII protein with decreased HDAC 4 abundance in the LBW compared with ABW lambs. There was increased GATA 4 and decreased phospho-troponin I abundance in LBW compared with ABW lambs, which are markers of pathological cardiac hypertrophy and impaired or reduced contractility, respectively. There was increased histone acetylation of H3K9 at IGF-2R promoter and IGF-2R intron 2 differentially methylated region in the LBW lamb. In conclusion, histone acetylation of IGF-2R may lead to increased IGF-2R mRNA expression and subsequently mediate Gαq signaling early in life via CaMKII, resulting in an increased risk of left ventricular hypertrophy and cardiovascular disease in adult life.

GLUT12 deficiency during early development results in heart failure and a diabetic phenotype in zebrafish

Cardiomyopathies-associated metabolic pathologies (e.g., type 2 diabetes and insulin resistance) are a leading cause of mortality. It is known that the association between these pathologies works in both directions, for which heart failure can lead to metabolic derangements such as insulin resistance. This intricate crosstalk exemplifies the importance of a fine coordination between one of the most energy-demanding organs and an equilibrated carbohydrate metabolism. In this light, to assist in the understanding of the role of insulin-regulated glucose transporters (GLUTs) and the development of cardiomyopathies, we have developed a model for glut12 deficiency in zebrafish. GLUT12 is a novel insulin-regulated GLUT expressed in the main insulin-sensitive tissues, such as cardiac muscle, skeletal muscle, and adipose tissue. In this study, we show that glut12 knockdown impacts the development of the embryonic heart resulting in abnormal valve formation. Moreover, glut12-deficient embryos also exhibited poor glycemic control. Glucose measurements showed that these larvae were hyperglycemic and resistant to insulin administration. Transcriptome analysis demonstrated that a number of genes known to be important in cardiac development and function as well as metabolic mediators were dysregulated in these larvae. These results indicate that glut12 is an essential GLUT in the heart where the reduction in glucose uptake due to glut12 deficiency leads to heart failure presumably due to the lack of glucose as energy substrate. In addition, the diabetic phenotype displayed by these larvae after glut12 abrogation highlights the importance of this GLUT during early developmental stages.

Sulforaphane suppresses cardiac hypertrophy by inhibiting GATA4/GATA6 expression and MAPK signaling pathways

SCOPE

Sulforaphane (SFN) is a naturally occurring isothiocynate compound found in cruciferous vegetables. Here, we report the effect of SFN on cardiac hypertrophy and propose an underlying mechanism.

METHODS AND RESULTS

SFN suppresses cardiomyocyte hypertrophy induced by hypertrophic stimuli in vitro and in vivo. SFN suppresses the expression of fetal genes, including atrial natriuretic peptide, brain natriuretic peptide, and beta myosin heavy chain. We used an siRNA technique and atrial natriuretic peptide promoter with mutated GATA binding sites to demonstrate that SFN mediates cardiac hypertrophy by modulating transcription factors GATA4/6.

CONCLUSION

These results suggest that SFN has the potential to prevent cardiac hypertrophy by downregulating GATA4/6 and mitogen-activated protein kinase signaling pathways.

Erythropoietin protects myocardium against ischemia-reperfusion injury under moderate hyperglycemia

Erythropoietin (EPO), an essential hormone for erythropoiesis, provides protection against myocardial ischemia/reperfusion (I/R) injury. Hyperglycemia during acute myocardial infarction aggravates organ damage and attenuates the efficacies of various protective measures. This study aimed to investigate the protective role of EPO against myocardial I/R injury under a clinically relevant moderate hyperglycemic condition and its associated mechanisms. Eighty-two Sprague-Dawley rats were randomly assigned to six groups: normoglycemia-Sham, normoglycemia-I/R-control-saline (IRC), normoglycemia-I/R-EPO (IRE), hyperglycemia-Sham, hyperglycemia-IRC, and hyperglycemia-IRE. The rats received 1.2 g/kg dextrose or same volume of normal saline depending on the group. I/R was induced by a 30 min period of ischemia followed by reperfusion for 4 h. For 1 h before I/R injury, intravenous 4000 IU/kg of EPO was administered. EPO pretreatment significantly reduced the number of apoptotic cells and the infarct size compared with those of the control groups. EPO increased GATA-4 phosphorylation and acetylation against I/R in hyperglycemic myocardium. It also enhanced ERK induced GATA-4 post-translational modifications such as increased GATA-4 phosphorylation and acetylation, and decreased GATA-4 ubiquitination following hypoxia-reoxygenation in H9c2 cells in hyperglycemic medium. Increased GATA-4 stability by EPO diminished I/R-related down-regulation of Bcl-2 and reduction of caspase-3 activities in hyperglycemic myocardium. In conclusion, EPO pretreatment before I/R injury conveyed significant myocardial protection under moderate hyperglycemic condition through mechanisms involved in reduction of caspase-3 activity and up-regulation of Bcl-2 in association with enhanced ERK-induced GATA-4 stability.

Carboxy terminus of GATA4 transcription factor is required for its cardiogenic activity and interaction with CDK4

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Carboxy terminal region of GATA4 is required for cardiogenesis in Xenopus pluripotent explants and in embryos.

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Carboxy terminus of GATA4 interacts with CDK4.

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CDK4 enhances transcriptional and cardiogenic activity of GATA4.

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GATA4-Tbx5 and GATA4-FOG2 interactions are not required for cardiogenesis.

GATA4-6 transcription factors regulate numerous aspects of development and homeostasis in multiple tissues of mesodermal and endodermal origin. In the heart, the best studied of these factors, GATA4, has multiple distinct roles in cardiac specification, differentiation, morphogenesis, hypertrophy and survival. To improve understanding of how GATA4 achieves its numerous roles in the heart, here we have focused on the carboxy-terminal domain and the residues required for interaction with cofactors FOG2 and Tbx5. We present evidence that the carboxy terminal region composed of amino acids 362–400 is essential for mediating cardiogenesis in Xenopus pluripotent explants and embryos. In contrast, the same region is not required for endoderm-inducing activity of GATA4. Further evidence is presented that the carboxy terminal cardiogenic region of GATA4 does not operate as a generic transcriptional activator. Potential mechanism of action of the carboxy terminal end of GATA4 is provided by the results showing physical and functional interaction with CDK4, including the enhancement of cardiogenic activity of GATA4 by CDK4. These results establish CDK4 as a GATA4 partner in cardiogenesis. The interactions of GATA4 with its other well described cofactors Tbx5 and FOG2 are known to be involved in heart morphogenesis, but their requirement for cardiac differentiation is unknown. We report that the mutations that disrupt interactions of GATA4 with Tbx5 and FOG2, G295S and V217G, respectively, do not impair cardiogenic activity of GATA4. These findings add support to the view that distinct roles of GATA4 in the heart are mediated by different determinants of the protein. Finally, we show that the rat GATA4 likely induces cardiogenesis cell autonomously or directly as it does not require activity of endodermal transcription factor Sox17, a GATA4 target gene that induces cardiogenesis non-cell autonomously.

GATA6 loss-of-function mutations contribute to familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM), the most prevalent form of primary heart muscle disease, is the third most common cause of heart failure and the most frequent reason for cardiac transplantation. Mounting evidence has demonstrated that genetic risk factors are crucial in the pathogenesis of DCM. However, DCM is genetically heterogeneous, and the genetic basis of DCM in a large majority of cases remains unclear. In the current study, the coding exons and flanking introns of the GATA6 gene, which encodes a zinc‑finger transcription factor essential for cardiogenesis, was sequenced in 140 unrelated patients with DCM, and two novel heterozygous mutations, p.C447Y and p.H475R, were identified in two index patients with DCM, respectively. Analysis of the pedigrees showed that in each family the mutation co-segregated with DCM transmitted in an autosomal-dominant pattern, with complete penetrance. The missense mutations were absent in 400 control chromosomes and predicted to be disease-causing by MutationTaster or probably damaging by PolyPhen-2. The alignment of multiple GATA6 proteins across species revealed that the altered amino acids were completely conserved evolutionarily. The functional assays showed that the mutated GATA6 proteins were associated with significantly reduced transcriptional activation in comparison with their wild-type counterpart. To the best of our knowledge, this is the first study on the association of GATA6 loss-of-function mutations with enhanced susceptibility to familial DCM, which provides novel insight into the molecular mechanism of DCM and suggests potential implications for the antenatal prophylaxis and allele-specific treatment of DCM.

Small heterodimer partner blocks cardiac hypertrophy by interfering with GATA6 signaling

RATIONALE

Small heterodimer partner (SHP; NR0B2) is an atypical orphan nuclear receptor that lacks a conventional DNA-binding domain. Through interactions with other transcription factors, SHP regulates diverse biological events, including glucose metabolism in liver. However, the role of SHP in adult heart diseases has not yet been demonstrated.

OBJECTIVE

We aimed to investigate the role of SHP in adult heart in association with cardiac hypertrophy.

METHODS AND RESULTS

The roles of SHP in cardiac hypertrophy were tested in primary cultured cardiomyocytes and in animal models. SHP-null mice showed a hypertrophic phenotype. Hypertrophic stresses repressed the expression of SHP, whereas forced expression of SHP blocked the development of hypertrophy in cardiomyocytes. SHP reduced the protein amount of Gata6 and, by direct physical interaction with Gata6, interfered with the binding of Gata6 to GATA-binding elements in the promoter regions of natriuretic peptide precursor type A. Metformin, an antidiabetic agent, induced SHP and suppressed cardiac hypertrophy. The metformin-induced antihypertrophic effect was attenuated either by SHP small interfering RNA in cardiomyocytes or in SHP-null mice.

CONCLUSIONS

These results establish SHP as a novel antihypertrophic regulator that acts by interfering with GATA6 signaling. SHP may participate in the metformin-induced antihypertrophic response.

Prevalence and spectrum of GATA4 mutations associated with sporadic dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is the most frequent type of primary myocardial disorder responsible for substantial morbidity and mortality. DCM is the third most common cause of heart failure and the most common reason for heart transplantation. A recent study has implicated GATA4 mutation in the pathogenesis of familial DCM. However, the prevalence and spectrum of GATA4 mutations associated with sporadic DCM remain unclear. In this study, the coding exons and exon-intron boundaries of the GATA4 gene, which encodes a cardiac transcription factor crucial for normal cardiogenesis, were sequenced in 220 unrelated patients with sporadic DCM. A total of 200 unrelated ethnically-matched healthy individuals used as controls were genotyped. The functional characteristics of the mutant GATA4 were assayed in contrast to its wild-type counterpart using a luciferase reporter assay system. As a result, 3 novel heterozygous GATA4 mutations, p.V39L, p.P226Q and p.T279S, were identified in 3 unrelated patients with sporadic DCM, with a mutational prevalence of approximately 1.36%. The missense mutations were absent in 400 control chromosomes and the altered amino acids were completely conserved evolutionarily across species. Functional analysis showed that the GATA4 mutants were consistently associated with significantly decreased transcriptional activity and markedly reduced the synergistic activation between GATA4 and NKX2-5. This study firstly links GATA4 mutations to increased susceptibility to sporadic DCM and provides novel insight into the molecular etiology underlying DCM, suggesting the potential implications for the early prophylaxis and allele-specific treatment of this common form of cardiomyopathy.

Inhibition of cardiomyocyte hypertrophy by protein arginine methyltransferase 5

Protein arginine methyltransferase 5 (PRMT5), a protein arginine methyltransferase that catalyzes the symmetrical dimethylation of arginine residues within target proteins, has been implicated in many essential cellular processes ranging from the regulation of gene expression to cell proliferation and differentiation. PRMT5 is highly expressed in the heart; the functional role of PRMT5 in the heart, however, remains largely elusive. In the present study, we show that PRMT5 specifically interacts with GATA4 in both co-transfected HEK293T cells and neonatal rat cardiomyocytes by co-immunoprecipitation. Importantly, this interaction leads to the arginine methylation of GATA4 at positions of 229, 265, and 317, which leads to an inhibition of the GATA4 transcriptional activity, predominantly through blocking the p300-mediated acetylation of GATA4 in cardiomyocytes. Moreover, overexpression of PRMT5 substantially inhibited the acetylation of GATA4 and cardiac hypertrophic responses in phenylephrine-stimulated cardiomyocytes, whereas knockdown of PRMT5 induced GATA4 activation and cardiomyocyte hypertrophy. Furthermore, in response to phenylephrine stimulation, PRMT5 translocates into the cytoplasm, thus relieving its repression on GATA4 activity in the nucleus and leading to hypertrophic gene expression in cardiomyocytes. These findings indicate that PRMT5 is an essential regulator of myocardial hypertrophic signaling and suggest that strategies aimed at activating PRMT5 in the heart may represent a potential therapeutic approach for the prevention of cardiac hypertrophy and heart failure.

Apocynum Tablet Protects against Cardiac Hypertrophy via Inhibiting AKT and ERK1/2 Phosphorylation after Pressure Overload

Background. Cardiac hypertrophy occurs in many cardiovascular diseases. Apocynum tablet (AT), a traditional Chinese medicine, has been widely used in China to treat patients with hypertension. However, the underlying molecular mechanisms of AT on the hypertension-induced cardiac hypertrophy remain elusive. The current study evaluated the effect and mechanisms of AT on cardiac hypertrophy. Methods. We created a mouse model of cardiac hypertrophy by inducing pressure overload with surgery of transverse aortic constriction (TAC) and then explored the effect of AT on the development of cardiac hypertrophy using 46 mice in 4 study groups (combinations of AT and TAC). In addition, we evaluated the signaling pathway of phosphorylation of ERK1/2, AKT, and protein expression of GATA4 in the cardioprotective effects of AT using Western blot. Results. AT inhibited the phosphorylation of Thr202/Tyr204 sites of ERK1/2, Ser473 site of AKT, and protein expression of GATA4 and significantly inhibited cardiac hypertrophy and cardiac fibrosis at 2 weeks after TAC surgery (P < 0.05). Conclusions. We experimentally demonstrated that AT inhibits cardiac hypertrophy via suppressing phosphorylation of ERK1/2 and AKT.

An emerging role for the miR-26 family in cardiovascular disease

In response to acute myocardial infarction (MI), a complex series of cellular and molecular signaling events orchestrate the myocardial remodeling that ensues weeks to months after injury. Clinical, epidemiological, and pathological studies demonstrate that inadequate or impaired angiogenesis after myocardial injury is often associated with decreased left ventricular (LV) function and clinical outcomes. The microRNA family, miR-26, plays diverse roles in regulating key aspects of cellular growth, development, and activation. Recent evidence supports a central role for the miR-26 family in cardiovascular disease by controlling critical signaling pathways, such as BMP/SMAD1 signaling, and targets relevant to endothelial cell growth, angiogenesis, and LV function post-MI. Emerging studies of the miR-26 family in other cell types including vascular smooth muscle cells, cardiac fibroblasts, and cardiomyocytes suggest that miR-26 may bear important implications for a range of cardiovascular repair mechanisms. This review examines the current knowledge of the miR-26 family's role in key cell types that critically control cardiovascular disease under pathological and physiological stimuli.

An analysis of the global expression of microRNAs in an experimental model of physiological left ventricular hypertrophy

Background

MicroRNAs (miRs) are a class of small non-coding RNAs that regulate gene expression. Studies of transgenic mouse models have indicated that deregulation of a single miR can induce pathological cardiac hypertrophy and cardiac failure. The roles of miRs in the genesis of physiological left ventricular hypertrophy (LVH), however, are not well understood.

Objective

To evaluate the global miR expression in an experimental model of exercise-induced LVH.

Methods

Male Balb/c mice were divided into sedentary (SED) and exercise (EXE) groups. Voluntary exercise was performed on an odometer-monitored metal wheels for 35 days. Various tests were performed after 7 and 35 days of training, including a transthoracic echocardiography, a maximal exercise test, a miR microarray (miRBase v.16) and qRT-PCR analysis.

Results

The ratio between the left ventricular weight and body weight was increased by 7% in the EXE group at day 7 (p<0.01) and by 11% at day 35 of training (p<0.001). After 7 days of training, the microarray identified 35 miRs that were differentially expressed between the two groups: 20 were up-regulated and 15 were down-regulated in the EXE group compared with the SED group (p = 0.01). At day 35 of training, 25 miRs were differentially expressed: 15 were up-regulated and 10 were decreased in the EXE animals compared with the SED animals (p<0.01). The qRT-PCR analysis demonstrated an increase in miR-150 levels after 35 days and a decrease in miR-26b, miR-27a and miR-143 after 7 days of voluntary exercise.

Conclusions

We have identified new miRs that can modulate physiological cardiac hypertrophy, particularly miR-26b, -150, -27a and -143. Our data also indicate that previously established regulatory gene pathways involved in pathological LVH are not changed in physiological LVH.

Art27 interacts with GATA4, FOG2 and NKX2.5 and is a novel co-repressor of cardiac genes

Transcription factors play a crucial role in regulation of cardiac biology. FOG-2 is indispensable in this setting, predominantly functioning through a physical interaction with GATA-4. This study aimed to identify novel co-regulators of FOG-2 to further elaborate on its inhibitory activity on GATA-4. The Art27 transcription factor was identified by a yeast-2-hybrid library screen to be a novel FOG-2 protein partner. Characterisation revealed that Art27 is co-expressed with FOG-2 and GATA-4 throughout cardiac myocyte differentiation and in multiple structures of the adult heart. Art27 physically interacts with GATA-4, FOG-2 and other cardiac transcription factors and by this means, down-regulates their activity on cardiac specific promoters α-myosin heavy chain, atrial natriuretic peptide and B-type natriuretic peptide. Regulation of endogenous cardiac genes by Art27 was shown using microarray analysis of P19CL6-Mlc2v-GFP cardiomyocytes. Together these results suggest that Art27 is a novel transcription factor that is involved in downregulation of cardiac specific genes by physically interacting and inhibiting the activity of crucial transcriptions factors involved in cardiac biology.

Comparing the effect of equiaxial cyclic mechanical stimulation on GATA4 expression in adipose-derived and bone marrow-derived mesenchymal stem cells

Myocardium is prone to mechanical stimuli among which pulsatile blood flow exerts both radial and longitudinal strains on the heart. Recent studies have shown that mechanical stimulation can notably influence regeneration of cardiac muscle cells. GATA4 is a cardiac-specific transcription factor that plays an important role in late embryonic heart development. Our study aimed at investigating the effect of equiaxial cyclic strain on GATA4 expression in adipose-derived (ASCs) and bone marrow-derived (BMSCs) mesenchymal stem cells. For this reason, both ASCs and BMSCs were studied in four distinct groups of chemical, mechanical, mechano-chemical and negative control. According to this categorisation, the cells were exposed to cyclic mechanical loading and/or 5-azacytidine as the chemical factor. The level of GATA4 expression was then quantified using real-time PCR method on the first, fourth and seventh days. The results show that: (1) equiaxial cyclic stimulation of mesenchymal stem cells could promote GATA4 expression from the early days of induction and as it went on, its combination with chemical factor elevated expression; (2) cyclic strain could accelerate GATA4 expression compared to the chemical factor; (3) in this regard, these results indicate a higher capacity of ASCs than BMSCs to express GATA4.

Parsing the roles of the transcription factors GATA-4 and GATA-6 in the adult cardiac hypertrophic response

The transcriptional code that programs cardiac hypertrophy involves the zinc finger-containing DNA binding factors GATA-4 and GATA-6, both of which are required to mount a hypertrophic response of the adult heart. Here we performed conditional gene deletion of Gata4 or Gata6 in the mouse heart in conjunction with reciprocal gene replacement using a transgene encoding either GATA-4 or GATA-6 in the heart as a means of parsing dosage effects of GATA-4 and GATA-6 versus unique functional roles. We determined that GATA-4 and GATA-6 play a redundant and dosage-sensitive role in programming the hypertrophic growth response of the heart following pressure overload stimulation. However, non-redundant functions were identified in allowing the heart to compensate and resist heart failure after pressure overload stimulation, as neither Gata4 nor Gata6 deletion was fully rescued by expression of the reciprocal transgene. For example, only Gata4 heart-specific deletion blocked the neoangiogenic response to pressure overload stimulation. Gene expression profiling from hearts of these gene-deleted mice showed both overlapping and unique transcriptional codes, which is presented. These results indicate that GATA-4 and GATA-6 play a dosage-dependent and redundant role in programming cardiac hypertrophy, but that each has a more complex role in maintaining cardiac homeostasis and resistance to heart failure following injury that cannot be compensated by the other.

Cardiac alpha1-adrenergic receptors: novel aspects of expression, signaling mechanisms, physiologic function, and clinical importance

Adrenergic receptors (AR) are G-protein-coupled receptors (GPCRs) that have a crucial role in cardiac physiology in health and disease. Alpha1-ARs signal through Gαq, and signaling through Gq, for example, by endothelin and angiotensin receptors, is thought to be detrimental to the heart. In contrast, cardiac alpha1-ARs mediate important protective and adaptive functions in the heart, although alpha1-ARs are only a minor fraction of total cardiac ARs. Cardiac alpha1-ARs activate pleiotropic downstream signaling to prevent pathologic remodeling in heart failure. Mechanisms defined in animal and cell models include activation of adaptive hypertrophy, prevention of cardiac myocyte death, augmentation of contractility, and induction of ischemic preconditioning. Surprisingly, at the molecular level, alpha1-ARs localize to and signal at the nucleus in cardiac myocytes, and, unlike most GPCRs, activate "inside-out" signaling to cause cardioprotection. Contrary to past opinion, human cardiac alpha1-AR expression is similar to that in the mouse, where alpha1-AR effects are seen most convincingly in knockout models. Human clinical studies show that alpha1-blockade worsens heart failure in hypertension and does not improve outcomes in heart failure, implying a cardioprotective role for human alpha1-ARs. In summary, these findings identify novel functional and mechanistic aspects of cardiac alpha1-AR function and suggest that activation of cardiac alpha1-AR might be a viable therapeutic strategy in heart failure.

A novel GATA4 loss-of-function mutation responsible for familial dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is the most common form of primary myocardial disorder and is associated with substantial morbidity and mortality. Increasing evidence suggests that genetic risk factors play an important role in the pathogenesis of idiopathic DCM. However, DCM is a genetically heterogeneous disease, and the genetic defects responsible for DCM in an overwhelming majority of cases remain to be identified. In the present study, the entire coding region and the splice junction sites of the GATA4 gene, which encodes a cardiac transcription factor essential for cardiogenesis, were sequenced in 150 unrelated patients with idiopathic DCM. The available relatives of the index patient harboring an identified mutation and 200 unrelated ethnically matched healthy individuals used as controls were genotyped. The functional characteristics of the mutant GATA4 were delineated in contrast to its wild-type counterpart using a luciferase reporter assay system. As a result, a novel heterozygous GATA4 mutation, p.V291L, was identified in a family with DCM inherited in an autosomal dominant pattern, which co-segregated with DCM in the family with complete penetrance. The missense mutation was absent in 400 control chromosomes, and the altered amino acid was completely conserved evolutionarily among species. Functional analysis revealed that the GATA4 mutant was associated with significantly diminished transcriptional activity. The findings expand the mutational spectrum of GATA4 linked to DCM and provide novel insight into the molecular etiology involved in DCM, suggesting the potential implications in the early prophylaxis and allele-specific treatment for this common type of cardiomyopathy.

Histone deacetylase signaling in cardioprotection

Cardiovascular disease (CVD) represents a major challenge for health care systems, both in terms of the high mortality associated with it and the huge economic burden of its treatment. Although CVD represents a diverse range of disorders, they share common compensatory changes in the heart at the structural, cellular, and molecular level that, in the long term, can become maladaptive and lead to heart failure. Treatment of adverse cardiac remodeling is therefore an important step in preventing this fatal progression. Although previous efforts have been primarily focused on inhibition of deleterious signaling cascades, the stimulation of endogenous cardioprotective mechanisms offers a potent therapeutic tool. In this review, we discuss class I and class II histone deacetylases, a subset of chromatin-modifying enzymes known to have critical roles in the regulation of cardiac remodeling. In particular, we discuss their molecular modes of action and go on to consider how their inhibition or the stimulation of their intrinsic cardioprotective properties may provide a potential therapeutic route for the clinical treatment of CVD.

Tgfβ-Smad and MAPK signaling mediate scleraxis and proteoglycan expression in heart valves

Mature heart valves are complex structures consisting of three highly organized extracellular matrix layers primarily composed of collagens, proteoglycans and elastin. Collectively, these diverse matrix components provide all the necessary biomechanical properties for valve function throughout life. In contrast to healthy valves, myxomatous valve disease is the most common cause of mitral valve prolapse in the human population and is characterized by an abnormal abundance of proteoglycans within the valve tri-laminar structure. Despite the clinical significance, the etiology of this phenotype is not known. Scleraxis (Scx) is a basic-helix-loop-helix transcription factor that we previously showed to be required for establishing heart valve structure during remodeling stages of valvulogenesis. In this study, we report that remodeling heart valves from Scx null mice express decreased levels of proteoglycans, particularly chondroitin sulfate proteoglycans (CSPGs), while overexpression in embryonic avian valve precursor cells and adult porcine valve interstitial cells increases CSPGs. Using these systems we further identify that Scx is positively regulated by canonical Tgfβ2 signaling during this process and this is attenuated by MAPK activity. Finally, we show that Scx is increased in myxomatous valves from human patients and mouse models, and overexpression in human mitral valve interstitial cells modestly increases proteoglycan expression consistent with myxomatous mitral valve phenotypes. Together, these studies identify an important role for Scx in regulating proteoglycans in embryonic and mature valve cells and suggest that imbalanced regulation could influence myxomatous pathogenesis.

Regulation of fetal gene expression in heart failure

During the processes leading to adverse cardiac remodeling and heart failure, cardiomyocytes react to neurohumoral stimuli and biomechanical stress by activating pathways that induce pathological hypertrophy. The gene expression patterns and molecular changes observed during cardiac hypertrophic remodeling bare resemblance to those observed during fetal cardiac development. The re-activation of fetal genes in the adult failing heart is a complex biological process that involves transcriptional, posttranscriptional and epigenetic regulation of the cardiac genome. In this review, the mechanistic actions of transcription factors, microRNAs and chromatin remodeling processes in regulating fetal gene expression in heart failure are discussed.

BET bromodomains mediate transcriptional pause release in heart failure

Heart failure (HF) is driven by the interplay between regulatory transcription factors and dynamic alterations in chromatin structure. Pathologic gene transactivation in HF is associated with recruitment of histone acetyl-transferases and local chromatin hyperacetylation. We therefore assessed the role of acetyl-lysine reader proteins, or bromodomains, in HF. Using a chemical genetic approach, we establish a central role for BET family bromodomain proteins in gene control during HF pathogenesis. BET inhibition potently suppresses cardiomyocyte hypertrophy in vitro and pathologic cardiac remodeling in vivo. Integrative transcriptional and epigenomic analyses reveal that BET proteins function mechanistically as pause-release factors critical to expression of genes that are central to HF pathogenesis and relevant to the pathobiology of failing human hearts. This study implicates epigenetic readers as essential effectors of transcriptional pause release during HF pathogenesis and identifies BET coactivator proteins as therapeutic targets in the heart.

miR-145 inhibits isoproterenol-induced cardiomyocyte hypertrophy by targeting the expression and localization of GATA6

Excessive βAR stimulation is an independent factor in inducing pathological cardiac hypertrophy. Here, we report miR-145 regulates both expression and localization of GATA6, thereby protecting the heart against cardiomyocyte hypertrophy induced by isoproterenol (ISO). The protective activity of miR-145 was associated with down-regulation of ANF, BNP and β-MHC expression, a decreased rate of protein synthesis, inhibited cardiomyocyte growth and the modulation of several signaling pathways including ERK1/2, JNK and Akt-GSK3β. The anti-hypertrophic effect was abrogated by exogenous over-expression of transcription factor GATA6 which was further identified as a direct target of miR-145. In addition, GSK3β antagonists, LiCl and TDZD8, restored the nuclear accumulation of GATA6, which was attenuated by miR-145 Finally, we observed a dynamic pattern of miR-145 expression in ISO-treated NRCMs and in the hearts of TAC mice. Together, our results identify miR-145 as an important regulator in cardiac hypertrophy.

Transcription factors in heart: promising therapeutic targets in cardiac hypertrophy

Regulation of gene expression is central to cell growth, differentiation and diseases. Context specific and signal dependent regulation of gene expression is achieved to a large part by transcription factors. Cardiac transcription factors regulate heart development and are also involved in stress regulation of the adult heart, which may lead to cardiac hypertrophy. Hypertrophy of cardiac myocytes is an outcome of the imbalance between prohypertrophic factors and anti-hypertrophic factors. This is initially a compensatory mechanism but sustained hypertrophy may lead to heart failure. The growing knowledge of transcriptional control mechanisms is helpful in the development of novel therapies. This review summarizes the role of cardiac transcription factors in cardiac hypertrophy, emphasizing their potential as attractive therapeutic targets to prevent the onset of heart failure and sudden death as they can be converging targets for current therapy.

Interferon regulatory factor 3 is a negative regulator of pathological cardiac hypertrophy

Interferon regulatory factor (IRF) 3, a member of the highly conserved IRF family transcription factors, plays a pivotal role in innate immune response, apoptosis, and oncogenesis. Recent studies have implicated IRF3 in a wide range of host defense. However, whether IRF3 induces defensive responses to hypertrophic stresses such as biomechanical stress and neurohumoral factors remains unclear. Herein, we employed an IRF3-deficient mouse model, cardiac-specific IRF3-overexpression mouse model and isolated cardiomyocytes to investigate the role of IRF3 in cardiac hypertrophy induced by aortic banding (AB) or isoproterenol (ISO). The extent of cardiac hypertrophy was quantitated by echocardiography as well as by pathological and molecular analysis. Our results demonstrate that IRF3 deficiency profoundly exacerbated cardiac hypertrophy, whereas overexpression of IRF3 in the heart significantly blunted pathological cardiac remodeling induced by pressure overload. Similar results were also observed in cultured cardiomyocytes upon the treatment with ISO. Mechanistically, we discovered that IRF3 interacted with ERK2 and thereby inhibited the ERK1/2 signaling. Furthermore, inactivation of ERK1/2 by U0126 offset the IRF3-deficient-mediated hypertrophic response induced by aortic banding. Altogether, these data demonstrate that IRF3 plays a protective role in AB-induced hypertrophic response by inactivating ERK1/2 in the heart. Therefore, IRF3 could be a new target for the prevention and therapy of cardiac hypertrophy and failure.

SUMOylation regulates the transcriptional repression activity of FOG-2 and its association with GATA-4

Friend of GATA 2 (FOG-2), a co-factor of several GATA transcription factors (GATA-4, -5 and 6), is a critical regulator of coronary vessel formation and heart morphogenesis. Here we demonstrate that FOG-2 is SUMOylated and that this modification modulates its transcriptional activity. FOG-2 SUMOylation occurs at four lysine residues (K312, 471, 915, 955). Three of these residues are part of the characteristic SUMO consensus site (ψKXE), while K955 is found in the less frequent TKXE motif. Absence of SUMOylation did not affect FOG-2′s nuclear localization. However, mutation of the FOG-2 SUMOylation sites, or de-SUMOylation, with SENP-1 or SENP-8 resulted in stronger transcriptional repression activity in both heterologous cells and cardiomyocytes. Conversely, increased FOG-2 SUMOylation by overexpression of SUMO-1 or expression of a SUMO-1-FOG-2 fusion protein rendered FOG-2 incapable of repressing GATA-4-mediated activation of the B-type natriuretic peptide (BNP) promoter. Moreover, we demonstrate both increased interaction between a FOG-2 SUMO mutant and GATA-4 and enhanced SUMOylation of wild-type FOG-2 by co-expression of GATA-4. These data suggest a new dynamics in which GATA-4 may alter the activity of FOG-2 by influencing its SUMOylation status.

Cyclin D2 rescues size and function of GATA4 haplo-insufficient hearts

Transcription factor GATA4 is a key regulator of cardiomyocyte growth, and differentiation and 50% reduction in GATA4 levels results in hypoplastic hearts. Search for GATA4 targets/effectors revealed cyclin D(2) (CD2), a member of the D-type cyclins (D(1), D(2), and D(3)) that play a vital role in cell growth and differentiation as a direct transcriptional target and a mediator of GATA4 growth in postnatal cardiomyocytes. GATA4 associates with the CD2 promoter in cardiomyocytes and is sufficient to induce endogenous CD2 transcription and to dose-dependently activate the CD2 promoter in heterologous cells. Cardiomyocyte-specific overexpression of CD2 results in enhanced postnatal cardiac growth because of increased cardiomyocyte proliferation. When these transgenic mice are crossed with Gata4 heterozygote mice, they rescue the hypoplastic cardiac phenotype of Gata4(+/-) mice and enhance cardiomyocyte survival and heart function. The data uncover a role for CD2 in the postnatal heart as an effector of GATA4 in myocyte growth and survival. The finding that postnatal upregulation of a cell-cycle gene in GATA4 haplo-insufficient hearts may be protective opens new avenues for maintaining or restoring cardiac function in GATA4-dependent cardiac disease.

Expression of cardiac GATA4 and downstream genes after exercise training in the db/db mouse

GATA4 is a transcriptional factor expressed in heart that regulates the synthesis of structural and cardioprotective genes. We have demonstrated that low GATA4 expression in the db/db mouse heart is associated with reduced expression of key downstream genes, including oxytocin (OT) natriuretic peptide (A-, B-type), nitric oxide synthase (eNOS), and myosin heavy chain (α-MHC). In this study, the effect of exercise on GATA4 expression and related genes was determined in the db/db mouse, a model that represents human type 2 diabetes. Vascular endothelial growth factor (VEGF) and hypoxia-induced factor-α expression were also measured after 8 weeks of treadmill running. Compared with control littermates, db/db mice exhibited hyperglycemia and obesity, and exercise failed to improve these parameters. GATA4 expression was reduced in db/db hearts and this was associated with reduced expression of OT, OTR, ANP, BNP, eNOS, α-MHC, and ratio of α- to β-MHC, whereas mRNA expression of β-MHC and VEGF remained unchanged compared with control hearts. Exercise training increased GATA4 expression (mRNA and protein) but most genes regulated by GATA4 were not observed to increase accordingly. However, protein expression of eNOS, mRNA expression of α-MHC, ratio of α- to β-MHC, and protein expression of VEGF were increased in db/db hearts after exercise. In conclusion, while GATA4 expression is increased following exercise, not all structural and cardioprotective genes are expressed, suggesting other transcription factors may be involved in this regulation. Regardless of this effect, the positive effect of exercise training on key protective genes is evident in the db/db mouse heart.