p300 Functions as a coactivator of transcription factor GATA-4

Epigenetic modifications and emerging therapeutic targets in cardiovascular aging and diseases

The complex mechanisms underlying the development of cardiovascular diseases remain not fully elucidated. Epigenetics, which modulates gene expression without DNA sequence changes, is shedding light on these mechanisms and their heritable effects. This review focus on epigenetic regulation in cardiovascular aging and diseases, detailing specific epigenetic enzymes such as DNA methyltransferases (DNMTs), histone acetyltransferases (HATs), and histone deacetylases (HDACs), which serve as writers or erasers that modify the epigenetic landscape. We also discuss the readers of these modifications, such as the 5-methylcytosine binding domain proteins, and the erasers ten-eleven translocation (TET) proteins. The emerging role of RNA methylation, particularly N6-methyladenosine (m6A), in cardiovascular pathogenesis is also discussed. We summarize potential therapeutic targets, such as key enzymes and their inhibitors, including DNMT inhibitors like 5-azacytidine and decitabine, HDAC inhibitors like belinostat and givinotide, some of which have been approved by the FDA for various malignancies, suggesting their potential in treating cardiovascular diseases. Furthermore, we highlight the role of novel histone modifications and their associated enzymes, which are emerging as potential therapeutic targets in cardiovascular diseases. Thus, by incorporating the recent studies involving patients with cardiovascular aging and diseases, we aim to provide a more detailed and updated review that reflects the advancements in the field of epigenetic modification in cardiovascular diseases.

Deciphering the Landscape of GATA-Mediated Transcriptional Regulation in Gastric Cancer

Gastric cancer (GC) is an asymptomatic malignancy in early stages, with an invasive and cost-ineffective diagnostic toolbox that contributes to severe global mortality rates on an annual basis. Ectopic expression of the lineage survival transcription factors (LS-TFs) GATA4 and 6 promotes stomach oncogenesis. However, LS-TFs also govern important physiological roles, hindering their direct therapeutic targeting. Therefore, their downstream target genes are particularly interesting for developing cancer-specific molecular biomarkers or therapeutic agents. In this work, we couple inducible knockdown systems with chromatin immunoprecipitation and RNA-seq to thoroughly detect and characterize direct targets of GATA-mediated transcriptional regulation in gastric cancer cells. Our experimental and computational strategy provides evidence that both factors regulate the expression of several coding and non-coding RNAs that in turn mediate for their cancer-promoting phenotypes, including but not limited to cell cycle, apoptosis, ferroptosis, and oxidative stress response. Finally, the diagnostic and prognostic potential of four metagene signatures consisting of selected GATA4/6 target transcripts is evaluated in a multi-cancer panel of ~7000 biopsies from nineteen tumor types, revealing elevated specificity for gastrointestinal tumors. In conclusion, our integrated strategy uncovers the landscape of GATA-mediated coding and non-coding transcriptional regulation, providing insights regarding their molecular and clinical function in gastric cancer.

Epigenetic Regulation of Mammalian Cardiomyocyte Development

The heart is the first organ formed during mammalian development and functions to distribute nutrients and oxygen to other parts of the developing embryo. Cardiomyocytes are the major cell types of the heart and provide both structural support and contractile function to the heart. The successful differentiation of cardiomyocytes during early development is under tight regulation by physical and molecular factors. We have reviewed current studies on epigenetic factors critical for cardiomyocyte differentiation, including DNA methylation, histone modifications, chromatin remodelers, and noncoding RNAs. This review also provides comprehensive details on structural and morphological changes associated with the differentiation of fetal and postnatal cardiomyocytes and highlights their differences. A holistic understanding of all aspects of cardiomyocyte development is critical for the successful in vitro differentiation of cardiomyocytes for therapeutic purposes.

Non-canonical functions of EZH2 in cancer

Mutations in chromatin modifying genes frequently occur in many kinds of cancer. Most mechanistic studies focus on their canonical functions, while therapeutic approaches target their enzymatic activity. Recent studies, however, demonstrate that non-canonical functions of chromatin modifiers may be equally important and therapeutically actionable in different types of cancer. One epigenetic regulator that demonstrates such a dual role in cancer is the histone methyltransferase EZH2. EZH2 is a core component of the polycomb repressive complex 2 (PRC2), which plays a crucial role in cell identity, differentiation, proliferation, stemness and plasticity. While much of the regulatory functions and oncogenic activity of EZH2 have been attributed to its canonical, enzymatic activity of methylating lysine 27 on histone 3 (H3K27me3), a repressive chromatin mark, recent studies suggest that non-canonical functions that are independent of H3K27me3 also contribute towards the oncogenic activity of EZH2. Contrary to PRC2's canonical repressive activity, mediated by H3K27me3, outside of the complex EZH2 can directly interact with transcription factors and oncogenes to activate gene expression. A more focused investigation into these non-canonical interactions of EZH2 and other epigenetic/chromatin regulators may uncover new and more effective therapeutic strategies. Here, we summarize major findings on the non-canonical functions of EZH2 and how they are related to different aspects of carcinogenesis.

Dynamic changes in P300 enhancers and enhancer-promoter contacts control mouse cardiomyocyte maturation

Cardiomyocyte differentiation continues throughout murine gestation and into the postnatal period, driven by temporally regulated expression changes in the transcriptome. The mechanisms that regulate these developmental changes remain incompletely defined. Here, we used cardiomyocyte-specific ChIP-seq of the activate enhancer marker P300 to identify 54,920 cardiomyocyte enhancers at seven stages of murine heart development. These data were matched to cardiomyocyte gene expression profiles at the same stages and to Hi-C and H3K27ac HiChIP chromatin conformation data at fetal, neonatal, and adult stages. Regions with dynamic P300 occupancy exhibited developmentally regulated enhancer activity, as measured by massively parallel reporter assays in cardiomyocytes in vivo, and identified key transcription factor-binding motifs. These dynamic enhancers interacted with temporal changes of the 3D genome architecture to specify developmentally regulated cardiomyocyte gene expressions. Our work provides a 3D genome-mediated enhancer activity landscape of murine cardiomyocyte development.

Identification and Characterization of p300-Mediated Lysine Residues in Cardiac SERCA2a

Impaired calcium uptake resulting from reduced expression and activity of the cardiac sarco-endoplasmic reticulum Ca²⁺ ATPase (SERCA2a) is a hallmark of heart failure (HF). Recently, new mechanisms of SERCA2a regulation, including post-translational modifications (PTMs), have emerged. Our latest analysis of SERCA2a PTMs has identified lysine acetylation as another PTM which might play a significant role in regulating SERCA2a activity. SERCA2a is acetylated, and that acetylation is more prominent in failing human hearts. In this study, we confirmed that p300 interacts with and acetylates SERCA2a in cardiac tissues. Several lysine residues in SERCA2a modulated by p300 were identified using in vitro acetylation assay. Analysis of in vitro acetylated SERCA2a revealed several lysine residues in SERCA2a susceptible to acetylation by p300. Among them, SERCA2a Lys514 (K514) was confirmed to be essential for SERCA2a activity and stability using an acetylated mimicking mutant. Finally, the reintroduction of an acetyl-mimicking mutant of SERCA2a (K514Q) into SERCA2 knockout cardiomyocytes resulted in deteriorated cardiomyocyte function. Taken together, our data demonstrated that p300-mediated acetylation of SERCA2a is a critical PTM that decreases the pump's function and contributes to cardiac impairment in HF. SERCA2a acetylation can be targeted for therapeutic aims for the treatment of HF.

CRdb: a comprehensive resource for deciphering chromatin regulators in human

Chromatin regulators (CRs) regulate epigenetic patterns on a partial or global scale, playing a critical role in affecting multi-target gene expression. As chromatin immunoprecipitation sequencing (ChIP-seq) data associated with CRs are rapidly accumulating, a comprehensive resource of CRs needs to be built urgently for collecting, integrating, and processing these data, which can provide abundant annotated information on CR upstream and downstream regulatory analyses as well as CR-related analysis functions. This study established an integrative CR resource, named CRdb (http://cr.liclab.net/crdb/), with the aim of curating a large number of available resources for CRs and providing extensive annotations and analyses of CRs to help biological researchers clarify the regulation mechanism and function of CRs. The CRdb database comprised a total of 647 CRs and 2,591 ChIP-seq samples from more than 300 human tissues and cell types. These samples have been manually curated from NCBI GEO/SRA and ENCODE. Importantly, CRdb provided the abundant and detailed genetic annotations in CR-binding regions based on ChIP-seq. Furthermore, CRdb supported various functional annotations and upstream regulatory information on CRs. In particular, it embedded four types of CR regulatory analyses: CR gene set enrichment, CR-binding genomic region annotation, CR-TF co-occupancy analysis, and CR regulatory axis analysis. CRdb is a useful and powerful resource that can help in exploring the potential functions of CRs and their regulatory mechanism in diseases and biological processes.

GATA4 Regulates Developing Endocardium Through Interaction With ETS1

BACKGROUND

The pioneer transcription factor (TF) GATA4 (GATA Binding Protein 4) is expressed in multiple cardiovascular lineages and is essential for heart development. GATA4 lineage-specific occupancy in the developing heart underlies its lineage specific activities. Here, we characterized GATA4 chromatin occupancy in cardiomyocyte and endocardial lineages, dissected mechanisms that control lineage specific occupancy, and analyzed GATA4 regulation of endocardial gene expression.

METHODS

We mapped GATA4 chromatin occupancy in cardiomyocyte and endocardial cells of embryonic day 12.5 (E12.5) mouse heart using lineage specific, Cre-activated biotinylation of GATA4. Regulation of GATA4 pioneering activity was studied in cell lines stably overexpressing GATA4. GATA4 regulation of endocardial gene expression was analyzed using single cell RNA sequencing and luciferase reporter assays.

RESULTS

Cardiomyocyte-selective and endothelial-selective GATA4 occupied genomic regions had features of lineage specific enhancers. Footprints within cardiomyocyte- and endothelial-selective GATA4 regions were enriched for NKX2-5 (NK2 homeobox 5) and ETS1 (ETS Proto-Oncogene 1) motifs, respectively, and both of these TFs interacted with GATA4 in co-immunoprecipitation assays. In stable NIH3T3 cell lines expressing GATA4 with or without NKX2-5 or ETS1, the partner TFs re-directed GATA4 pioneer binding and augmented its ability to open previously inaccessible regions, with ETS1 displaying greater potency as a pioneer partner than NKX2-5. Single-cell RNA sequencing of embryonic hearts with endothelial cell-specific Gata4 inactivation identified Gata4-regulated endocardial genes, which were adjacent to GATA4-bound, endothelial regions enriched for both GATA4 and ETS1 motifs. In reporter assays, GATA4 and ETS1 cooperatively stimulated endothelial cell enhancer activity.

CONCLUSIONS

Lineage selective non-pioneer TFs NKX2-5 and ETS1 guide the activity of pioneer TF GATA4 to bind and open chromatin and create active enhancers and mechanistically link ETS1 interaction to GATA4 regulation of endocardial development.

Angiotensin II Mediates Cardiomyocyte Hypertrophy in Atrial Cardiomyopathy via Epigenetic Transcriptional Regulation

Aims

European Heart Rhythm Association established an expert consensus to define, characterize, and classify atrial cardiomyopathy into four subgroups based on their histopathological features. The predominant pathological feature of classes I and III is the hypertrophy of atrial cardiomyocytes. Here, we aim to investigate the mechanism of epigenetic transcriptional regulation of cardiomyocyte hypertrophy in atrial cardiomyopathy.

Methods and Results

Compared with that of sinus rhythm control individuals, the myocardium of patients with atrial fibrillation exhibited increased levels of angiotensin II (AngII), chromatin-bound myocyte enhancer factor 2 (MEF2), acetylated histone H4 (H4ac), and H3K27ac; upregulation of hypertrophy-related genes; and decreased levels of histone deacetylase (HDAC) 4 and HDAC5 bound to the promoters of hypertrophy-related genes. Furthermore, incubation of atrial cardiomyocytes with AngII increased their cross-sectional area and improved the expression of hypertrophy-related genes. AngII also promoted the phosphorylation of HDAC4 and HDAC5 and induced their nuclear export. RNA sequencing analyses revealed that AngII significantly upregulated genes associated with cardiac hypertrophy. Chromatin immunoprecipitation showed that this correlated with increased levels of chromatin-bound MEF2, H4ac, and H3K27ac and decreased HDAC4 and HDAC5 enrichment in the promoters of hypertrophy-related genes. Moreover, these AngII-induced prohypertrophic effects could be partially reverted by treatment with the AngII receptor blocker losartan.

Conclusions

AngII had a prohypertrophic effect on atrial cardiomyopathy which was epigenetic-dependent. Patients with atrial fibrillation manifest an increased susceptibility to hypertrophy and exhibit epigenetic characteristics that are permissive for the transcription of hypertrophy-related genes. AngII induces histone acetylation via the cytoplasmic-nuclear shuttling of HDACs, which constitutes a novel mechanism of atrial hypertrophy regulation and might provide a promising therapeutic strategy for atrial cardiomyopathy.

Innate Immune Nod1/RIP2 Signaling Is Essential for Cardiac Hypertrophy but Requires Mitochondrial Antiviral Signaling Protein for Signal Transductions and Energy Balance

BACKGROUND

Cardiac hypertrophy is a key biological response to injurious stresses such as pressure overload and, when excessive, can lead to heart failure. Innate immune activation by danger signals, through intracellular pattern recognition receptors such as nucleotide-binding oligomerization domain 1 (Nod1) and its adaptor receptor-interacting protein 2 (RIP2), might play a major role in cardiac remodeling and progression to heart failure. We hypothesize that Nod1/RIP2 are major contributors to cardiac hypertrophy, but may not be sufficient to fully express the phenotype alone.

METHODS

To elucidate the contribution of Nod1/RIP2 signaling to cardiac hypertrophy, we randomized Nod1^-/-, RIP2^-/-, or wild-type mice to transverse aortic constriction or sham operations. Cardiac hypertrophy, fibrosis, and cardiac function were examined in these mice.

RESULTS

Nod1 and RIP2 proteins were upregulated in the heart after transverse aortic constriction, and this was paralleled by increased expression of mitochondrial proteins, including mitochondrial antiviral signaling protein (MAVS). Nod1^-/- and RIP2^-/- mice subjected to transverse aortic constriction exhibited better survival, improved cardiac function, and decreased cardiac hypertrophy. Downstream signal transduction pathways that regulate inflammation and fibrosis, including NF (nuclear factor) κB and MAPK (mitogen-activated protein kinase)-GATA4/p300, were reduced in both Nod1^-/- and RIP2^-/- mice after transverse aortic constriction compared with wild-type mice. Coimmunoprecipitation of extracted cardiac proteins and confocal immunofluorescence microscopy showed that Nod1/RIP2 interaction was robust and that this complex also included MAVS as an essential component. Suppression of MAVS expression attenuated the complex formation, NF κB signaling, and myocyte hypertrophy. Interrogation of mitochondrial function compared in the presence or ablation of MAVS revealed that MAVS serves to suppress mitochondrial energy output and mediate fission/fusion related dynamic changes. The latter is possibly linked to mitophagy during cardiomyocytes stress, which may provide an intriguing link between innate immune activation and mitochondrial energy balance under stress or injury conditions.

CONCLUSIONS

We have identified that innate immune Nod1/RIP2 signaling is a major contributor to cardiac remodeling after stress. This process is critically joined by and regulated through the mitochondrial danger signal adapter MAVS. This novel complex coordinates remodeling, inflammatory response, and mitochondrial energy metabolism in stressed cardiomyocytes. Thus, Nod1/RIP2/MAVS signaling complex may represent an attractive new therapeutic approach toward heart failure.

Deacetylase-independent function of SIRT6 couples GATA4 transcription factor and epigenetic activation against cardiomyocyte apoptosis

SIRT6 deacetylase activity improves stress resistance via gene silencing and genome maintenance. Here, we reveal a deacetylase-independent function of SIRT6, which promotes anti-apoptotic gene expression via the transcription factor GATA4. SIRT6 recruits TIP60 acetyltransferase to acetylate GATA4 at K328/330, thus enhancing its chromatin binding capacity. In turn, GATA4 inhibits the deacetylase activity of SIRT6, thus ensuring the local chromatin accessibility via TIP60-promoted H3K9 acetylation. Significantly, the treatment of doxorubicin (DOX), an anti-cancer chemotherapeutic, impairs the SIRT6-TIP60-GATA4 trimeric complex, blocking GATA4 acetylation and causing cardiomyocyte apoptosis. While GATA4 hyperacetylation-mimic retains the protective effect against DOX, the hypoacetylation-mimic loses such ability. Thus, the data reveal a novel SIRT6-TIP60-GATA4 axis, which promotes the anti-apoptotic pathway to prevent DOX toxicity. Targeting the trimeric complex constitutes a new strategy to improve the safety of DOX chemotherapy in clinical application.

Functional genetic variants of the GATA4 gene promoter in acute myocardial infarction

Coronary artery disease (CAD), including acute myocardial infarction (AMI), is a common complex disease; however, the genetic causes remain largely unknown. Recent epidemiological investigations indicated that the incidence of CAD in patients with congenital heart diseases is markedly higher than that observed in healthy controls. It was therefore hypothesized that the dysregulated expression of cardiac developmental genes may be involved in CAD development. GATA binding protein 4 (GATA4) serves essential roles in heart development and coronary vessel formation. In the present study, the GATA4 gene promoter was analyzed in patients with AMI (n=395) and in ethnically‑matched healthy controls (n=397). A total of 14 DNA variants were identified, including two single‑nucleotide polymorphisms. Three novel heterozygous DNA variants (g.31806C>T, g.31900G>C and g.32241C>T) were reported in three patients with AMI. These DNA variants significantly increased the activity of the GATA4 gene promoter. The electrophoretic mobility shift assay revealed that the DNA variant g.32241C>T influenced the binding ability of transcription factors. Taken together, the DNA variants may alter GATA4 gene promoter activity and affect GATA4 levels, thus contributing to AMI development.

Transcription Factors Activate Genes through the Phase-Separation Capacity of Their Activation Domains

Gene expression is controlled by transcription factors (TFs) that consist of DNA-binding domains (DBDs) and activation domains (ADs). The DBDs have been well characterized, but little is known about the mechanisms by which ADs effect gene activation. Here, we report that diverse ADs form phase-separated condensates with the Mediator coactivator. For the OCT4 and GCN4 TFs, we show that the ability to form phase-separated droplets with Mediator in vitro and the ability to activate genes in vivo are dependent on the same amino acid residues. For the estrogen receptor (ER), a ligand-dependent activator, we show that estrogen enhances phase separation with Mediator, again linking phase separation with gene activation. These results suggest that diverse TFs can interact with Mediator through the phase-separating capacity of their ADs and that formation of condensates with Mediator is involved in gene activation.

GATA transcription factors in development and disease

The GATA family of transcription factors is of crucial importance during embryonic development, playing complex and widespread roles in cell fate decisions and tissue morphogenesis. GATA proteins are essential for the development of tissues derived from all three germ layers, including the skin, brain, gonads, liver, hematopoietic, cardiovascular and urogenital systems. The crucial activity of GATA factors is underscored by the fact that inactivating mutations in most GATA members lead to embryonic lethality in mouse models and are often associated with developmental diseases in humans. In this Primer, we discuss the unique and redundant functions of GATA proteins in tissue morphogenesis, with an emphasis on their regulation of lineage specification and early organogenesis.

The pioneer factor activity of c-Myb involves recruitment of p300 and induction of histone acetylation followed by acetylation-induced chromatin dissociation

Background

The concept of pioneer transcription factors is emerging as an essential part of the epigenetic regulation, taking place during cell development and differentiation. However, the precise molecular mechanism underlying pioneer factor activity remains poorly understood. We recently reported that the transcription factor c-Myb acts as a pioneer factor in haematopoiesis, and a point mutation in its DNA binding domain, D152V, is able to abrogate this function.

Results

Here, we show that specific histone modifications, including H3K27ac, prevent binding of c-Myb to histone tails, representing a novel effect of histone modifications, namely restricting binding of a pioneer factor to chromatin. Furthermore, we have taken advantage of the pioneer-defect D152V mutant to investigate mechanisms of c-Myb’s pioneer factor activity. We show that c-Myb-dependent transcriptional activation of a gene in inaccessible chromatin relies on c-Myb binding to histones, as well as on c-Myb interacting with the histone acetyltransferase p300. ChIP assays show that both wild type and the D152V mutant of c-Myb bind to a selected target gene at its promoter and enhancer, but only wild-type c-Myb causes opening and activation of the locus. Enhancement of histone acetylation restores activation of the same gene in the absence of c-Myb, suggesting that facilitating histone acetylation is a crucial part of the pioneer factor function of c-Myb.

Conclusions

We suggest a pioneer factor model in which c-Myb binds to regions of closed chromatin and then recruits histone acetyltransferases. By binding to histones, c-Myb facilitates histone acetylation, acting as a cofactor for p300 at c-Myb bound sites. The resulting H3K27ac leads to chromatin opening and detachment of c-Myb from the acetylated chromatin. We propose that the latter phenomenon, acetylation-induced chromatin dissociation, represents a mechanism for controlling the dynamics of pioneer factor binding to chromatin.

Electronic supplementary material

The online version of this article (10.1186/s13072-018-0208-y) contains supplementary material, which is available to authorized users.

Persistence of risk factors associated with maternal cardiovascular disease following aberrant inflammation in rat pregnancy

Introduction

Pre-eclampsia is associated with increased risk of subsequent cardiovascular and metabolic disease in the affected mothers. While aberrant inflammation contributes to the pathophysiology of pre-eclampsia, it is unclear whether maternal inflammation contributes to the increased risk of disease. Here, we determined the effect of aberrant inflammation in pregnancy on cardiovascular and metabolic disease risk factors.

Methods

Wistar rats were administered low doses of lipopolysaccharide (LPS) on gestational days (GD) 13.5-16.5 to induce inflammation. Controls included pregnant rats treated with saline and nonpregnant rats treated with LPS or saline. We previously showed that LPS-treated pregnant rats exhibit key features of pre-eclampsia. Echocardiographic parameters, heart weight, blood pressure, blood lipids, pulse-wave velocity, and glucose tolerance, were assessed at 16 weeks postpartum. Messenger RNA levels of transcription factors associated with cardiac growth were measured in left ventricular tissue; histone modifications and global DNA methylation were determined in hearts and livers at GD 17.5 and at 16 weeks postpartum.

Results

Compared with saline-treated pregnant rats and nonpregnant rats treated with LPS or saline, LPS-treated pregnant rats exhibited left ventricular hypertrophy and increased blood cholesterol and low-density lipoprotein levels at 16 weeks postdelivery. LPS-treated rats had increased left ventricular mRNA levels of hypertrophy-associated transcription factors at GD 17.5 and increased levels of modified histones in hearts and livers at GD 17.5 and 16 weeks postpartum. Other parameters remained unchanged.

Conclusion

Aberrant inflammation during pregnancy results in persistent alterations in maternal physiological parameters and epigenetic modifications that could contribute to the pathophysiology of cardiovascular disease.

A novel acetyltransferase p300 inhibitor ameliorates hypertension-associated cardio-renal fibrosis

Hypertension-associated end-organ damage commonly leads to cardiac and renal fibrosis. As no effective anti-fibrotic therapy currently exists, the unchecked progression of fibrogenesis manifests as cardio-renal failure and early death. We have previously shown that FATp300-p300 with intrinsic factor acetyltransferase activity-is an essential epigenetic regulator of fibrogenesis, and is elevated in several fibrotic tissues. In this report, we investigate the therapeutic efficacy of a novel FATp300 inhibitor, L002, in a murine model of hypertensive cardio-renal fibrosis. Additionally, we examine the effects of L002 on cellular pro-fibrogenic processes and provide mechanistic insights into its antifibrogenic action. Utilizing cardiac fibroblasts, podocytes, and mesangial cells, we demonstrate that L002 blunts FATp300-mediated acetylation of specific histones. Further, incubating cells with L002 suppresses several pro-fibrogenic processes including cellular proliferation, migration, myofibroblast differentiation and collagen synthesis. Importantly, systemic administration of L002 in mice reduces hypertension-associated pathological hypertrophy, cardiac fibrosis and renal fibrosis. The anti-hypertrophic and anti-fibrotic effects of L002 were independent of blood pressure regulation. Our work solidifies the role of epigenetic regulator FATp300 in fibrogenesis and establishes it as a pharmacological target for reducing pathological matrix remodeling and associated pathologies. Additionally, we discover a new therapeutic role of L002, as it ameliorates hypertension-induced cardio-renal fibrosis and antagonizes pro-fibrogenic responses in fibroblasts, podocytes and mesangial cells.

The Role of GATA in Mammalian Reproduction

GATA transcription factors are emerging as critical players in mammalian reproductive development and function. GATA-4 contributes to fetal male gonadal development by regulating genes mediating Müllerian duct regression and the onset of testosterone production. GATA-2 expression appears to be sexually dimorphic being transiently expressed in the germ cell lineage of the fetal ovary but not the fetal testis. In the reproductive system, GATA-1 is exclusively expressed in Sertoli cells at specific seminiferous tubule stages. In addition, GATA-4 and GATA-6 are localized primary to ovarian and testicular somatic cells. The majority of cell transfection studies demonstrate that GATA-1 and GATA-4 can stimulate inhibin subunit gene promoter constructs. Other studies provide strong evidence that GATA-4 and GATA-6 can activate genes mediating gonadal cell steroidogenesis. GATA-2 and GATA-3 are found in pituitary and placental cells and can regulate alpha-glycoprotein subunit gene expression. Gonadal expression and activation of GATAs appear to be regulated in part by gonadotropin signaling via the cyclic AMP-protein kinase A pathway. This review will cover the current knowledge regarding GATA expression and function at all levels of the reproductive axis.

Emerging Field of Cardiomics: High-Throughput Investigations into Transcriptional Regulation of Cardiovascular Development and Disease

Congenital heart defects remain a leading cause of infant mortality in the western world, despite decades of research focusing on cardiovascular development and disease. With the recent emergence of several high-throughput technologies including RNA sequencing, chromatin-immunoprecipitation-coupled sequencing, mass-spectrometry-based proteomics analyses, and the numerous variations of these strategies, investigations into cardiac development have been transformed from candidate-based studies into whole-genome, -transcriptome, and -proteome undertakings. In this review, we discuss several reports that have emerged from our laboratory and others over the past 5 years that emphasize the versatility of large dataset-based investigations of cardiogenic transcription factors, from phenotypic validations and new gene implications to the identification of novel roles of well-studied transcriptional regulators.

Tyrosine phosphorylation of RACK1 triggers cardiomyocyte hypertrophy by regulating the interaction between p300 and GATA4

The zinc finger protein GATA4 is a transcription factor involved in cardiomyocyte hypertrophy. It forms a functional complex with the intrinsic histone acetyltransferase (HAT) p300. The HAT activity of p300 is required for the acetylation and transcriptional activity of GATA4, as well as for cardiomyocyte hypertrophy and the development of heart failure. In the present study, we have identified Receptor for Activated Protein Kinase C1 (RACK1) as a novel GATA4-binding protein using tandem affinity purification and mass spectrometry analyses. We found that exogenous RACK1 repressed phenylephrine (PE)-induced hypertrophic responses, such as myofibrillar organization, increased cell size, and hypertrophy-associated gene transcription, in cultured cardiomyocytes. RACK1 physically interacted with GATA4 and the overexpression of RACK1 reduced PE-induced formation of the p300/GATA4 complex and the acetylation and DNA binding activity of GATA4. In response to hypertrophic stimulation in cultured cardiomyocytes and in the hearts of hypertensive heart disease model rats, the tyrosine phosphorylation of RACK1 was increased, and the binding between GATA4 and RACK1 was reduced. In addition, the tyrosine phosphorylation of RACK1 was required for the disruption of the RACK1/GATA4 complex and for the formation of the p300/GATA4 complex. These findings demonstrate that RACK1 is involved in p300/GATA4-dependent hypertrophic responses in cardiomyocytes and is a promising therapeutic target for heart failure.

Unique functions of Gata4 in mouse liver induction and heart development

Gata4 and Gata6 are closely related transcription factors that are essential for the development of a number of embryonic tissues. While they have nearly identical DNA-binding domains and similar patterns of expression, Gata4 and Gata6 null embryos have strikingly different embryonic lethal phenotypes. To determine whether the lack of redundancy is due to differences in protein function or Gata4 and Gata6 expression domains, we generated mice that contained the Gata6 cDNA in place of the Gata4 genomic locus. Gata4(Gata6/Gata6) embryos survived through embryonic day (E)12.5 and successfully underwent ventral folding morphogenesis, demonstrating that Gata6 is able to replace Gata4 function in extraembryonic tissues. Surprisingly, Gata6 is unable to replace Gata4 function in the septum transversum mesenchyme or the epicardium, leading to liver agenesis and lethal heart defects in Gata4(Gata6/Gata6) embryos. These studies suggest that Gata4 has evolved distinct functions in the development of these tissues that cannot be performed by Gata6, even when it is provided in the identical expression domain. Our work has important implications for the respective mechanisms of Gata function during development, as well as the functional evolution of these essential transcription factors.

Elucidating the mechanisms of transcription regulation during heart development by next-generation sequencing

Dysregulation of transcription is associated with the pathogenesis of cardiovascular diseases, including congenital heart diseases and heart failure. However, it remains unclear how transcription factors regulate transcription in the heart and which genes are associated with cardiovascular diseases in humans. Development of genome-wide analyses using next-generation sequencers provides powerful methods to determine how these transcription factors and chromatin regulators control gene expressions and to identify causative genes in cardiovascular diseases. These technologies have revealed that transcription during heart development is elaborately regulated by multiple cardiac transcription factors. In this review, we discuss the recent progress toward understanding the molecular mechanisms of how transcriptional dysregulation leads to cardiovascular diseases.

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.

GATA-dependent transcriptional and epigenetic control of cardiac lineage specification and differentiation

Heart progenitor cells differentiate into various cell types including pacemaker and working cardiomyocytes. Cell-type specific gene expression is achieved by combinatorial interactions between tissue-specific transcription factors (TFs), co-factors, and chromatin remodelers and DNA binding elements in regulatory regions. Dysfunction of these transcriptional networks may result in congenital heart defects. Functional analysis of the regulatory DNA sequences has contributed substantially to the identification of the transcriptional network components and combinatorial interactions regulating the tissue-specific gene programs. GATA TFs have been identified as central players in these networks. In particular, GATA binding elements have emerged as a platform to recruit broadly active histone modification enzymes and cell-type-specific co-factors to drive cell-type-specific gene programs. Here, we discuss the role of GATA factors in cell fate decisions and differentiation in the developing heart.

Dynamic GATA4 enhancers shape the chromatin landscape central to heart development and disease

How stage-specific enhancer dynamics modulate gene expression patterns essential for organ development, homesostasis, and disease is not well understood. Here, we addressed this question by mapping chromatin occupancy of GATA4—a master cardiac transcription factor—in heart development and disease. We find that GATA4 binds and participaes in establishing active chromatin regions by stimulating H3K27ac deposition, which facilitates GATA4-driven gene expression. GATA4 chromatin occupancy changes markedly between fetal and adult heart, with a limitted binding sites overlap. Cardiac stress restored GATA4 occupancy to a subset of fetal sites, but many stress-associated GATA4 binding sites localized to loci not occupied by GATA4 during normal heart development. Collectively, our data show that dynamic, context-specific transcription factors occupancy underlies stage-specific events in development, homeostasis, and disease.

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.

A large permissive regulatory domain exclusively controls Tbx3 expression in the cardiac conduction system

RATIONALE

The evolutionary conserved Tbx3/Tbx5 gene cluster encodes T-box transcription factors that play crucial roles in the development and homeostasis of the cardiac conduction system in human and mouse. Both genes are expressed in overlapping patterns and function in strictly tissue-specific and dose-dependent manners, yet, their regulation is poorly understood.

OBJECTIVE

To analyze the mechanism underlying the complex regulation of the Tbx3/Tbx5 cluster.

METHODS AND RESULTS

By probing the 3-dimensional architecture of the Tbx3/Tbx5 cluster using high-resolution circular chromosome conformation capture sequencing in vivo, we found that its regulatory landscape is in a preformed conformation similar in embryonic heart, limbs, and brain. Tbx3 and its flanking gene desert form a 1 Mbp loop between CCCTC-binding factor (CTCF)-binding sites that is separated from the neighboring Tbx5 loop. However, Ctcf inactivation did not result in transcriptional regulatory interaction between Tbx3 and Tbx5. Multiple sites within the Tbx3 locus contact the promoter, including sites corresponding to regions known to contain variations in the human genome influencing conduction. We identified an atrioventricular-specific enhancer and a pan-cardiac enhancer that contact the promoter and each other and synergize to activate transcription in the atrioventricular conduction system.

CONCLUSIONS

We provide a high-resolution model of the 3-dimensional structure and function of the Tbx3/Tbx5 locus and show that the locus is organized in a preformed, permissive structure. The Tbx3 locus forms a CTCF-independent autonomous regulatory domain with multiple combinatorial regulatory elements that control the precise pattern of Tbx3 in the cardiac conduction system.

Chromatin modifications remodel cardiac gene expression

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

GATA-dependent regulatory switches establish atrioventricular canal specificity during heart development

The embryonic vertebrate heart tube develops an atrioventricular canal that divides the atrial and ventricular chambers, forms atrioventricular conduction tissue and organizes valve development. Here we assess the transcriptional mechanism underlying this localized differentiation process. We show that atrioventricular canal-specific enhancers are GATA-binding site-dependent and act as switches that repress gene activity in the chambers. We find that atrioventricular canal-specific gene loci are enriched in H3K27ac, a marker of active enhancers, in atrioventricular canal tissue and depleted in H3K27ac in chamber tissue. In the atrioventricular canal, Gata4 activates the enhancers in synergy with Bmp2/Smad signalling, leading to H3K27 acetylation. In contrast, in chambers, Gata4 cooperates with pan-cardiac Hdac1 and Hdac2 and chamber-specific Hey1 and Hey2, leading to H3K27 deacetylation and repression. We conclude that atrioventricular canal-specific enhancers are platforms integrating cardiac transcription factors, broadly active histone modification enzymes and localized co-factors to drive atrioventricular canal-specific gene activity.

The atrioventricular canal partitions the developing vertebrate heart. Here, the authors show that the cardiac transcription factor Gata4 together with histone modification enzymes and localized co-factors binds atrioventricular canal-specific enhancers, thereby repressing gene activity in the cardiac chambers.

Activation of GATA4 gene expression at the early stage of cardiac specification

Currently, there are no effective treatments to directly repair damaged heart tissue after cardiac injury since existing therapies focus on rescuing or preserving reversibly damaged tissue. Cell-based therapies using cardiomyocytes generated from stem cells present a promising therapeutic approach to directly replace damaged myocardium with new healthy tissue. However, the molecular mechanisms underlying the commitment of stem cells into cardiomyocytes are not fully understood and will be critical to guide this new technology into the clinic. Since GATA4 is a critical regulator of cardiac differentiation, we examined the molecular basis underlying the early activation of GATA4 gene expression during cardiac differentiation of pluripotent stem cells. Our studies demonstrate the direct involvement of histone acetylation and transcriptional coactivator p300 in the regulation of GATA4 gene expression. More importantly, we show that histone acetyltransferase (HAT) activity is important for GATA4 gene expression with the use of curcumin, a HAT inhibitor. In addition, the widely used histone deacetylase inhibitor valproic acid enhances both histone acetylation and cardiac specification.

Dysregulation of histone acetyltransferases and deacetylases in cardiovascular diseases

Cardiovascular disease (CVD) remains a leading cause of mortality worldwide despite advances in its prevention and management. A comprehensive understanding of factors which contribute to CVD is required in order to develop more effective treatment options. Dysregulation of epigenetic posttranscriptional modifications of histones in chromatin is thought to be associated with the pathology of many disease models, including CVD. Histone acetyltransferases (HATs) and deacetylases (HDACs) are regulators of histone lysine acetylation. Recent studies have implicated a fundamental role of reversible protein acetylation in the regulation of CVDs such as hypertension, pulmonary hypertension, diabetic cardiomyopathy, coronary artery disease, arrhythmia, and heart failure. This reversible acetylation is governed by enzymes that HATs add or HDACs remove acetyl groups respectively. New evidence has revealed that histone acetylation regulators blunt cardiovascular and related disease states in certain cellular processes including myocyte hypertrophy, apoptosis, fibrosis, oxidative stress, and inflammation. The accumulating evidence of the detrimental role of histone acetylation in cardiac disease combined with the cardioprotective role of histone acetylation regulators suggests that the use of histone acetylation regulators may serve as a novel approach to treating the millions of patients afflicted by cardiac diseases worldwide.

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.

Signaling and transcriptional networks in heart development and regeneration

The mammalian heart is the first functional organ, the first indicator of life. Its normal formation and function are essential for fetal life. Defects in heart formation lead to congenital heart defects, underscoring the finesse with which the heart is assembled. Understanding the regulatory networks controlling heart development have led to significant insights into its lineage origins and morphogenesis and illuminated important aspects of mammalian embryology, while providing insights into human congenital heart disease. The mammalian heart has very little regenerative potential, and thus, any damage to the heart is life threatening and permanent. Knowledge of the developing heart is important for effective strategies of cardiac regeneration, providing new hope for future treatments for heart disease. Although we still have an incomplete picture of the mechanisms controlling development of the mammalian heart, our current knowledge has important implications for embryology and better understanding of human heart disease.

Evolutionary conservation of Nkx2.5 autoregulation in the second heart field

The cardiac homeobox gene Nkx2.5 plays a key and dosage-sensitive role in the differentiation of outflow tract and right ventricle from progenitors of the second heart field (SHF) and Nkx2.5 mutation is strongly associated with human outflow tract congenital heart disease (OFT CHD). Therefore defining the regulatory mechanisms controlling Nkx2.5 expression in SHF populations serves an important function in understanding the etiology of complex CHD. Through a comparative analysis of regulatory elements controlling SHF expression of Nkx2.5 in the chicken and mouse, we have found evidence that Nkx2.5 autoregulation is important for maintaining Nkx2.5 expression during SHF differentiation in both species. However the mechanism of Nkx2.5 maintenance differs between placental mammals and non-mammalian vertebrates: in chick Nkx2.5 binds directly to a genomic enhancer element that is required to maintain Nkx2.5 expression in the SHF. In addition, it is likely that this is true in other non-mammalian vertebrates given that they possess a similar genomic organization. By contrast, in placental mammals, Nkx2.5 autoregulation in the SHF functions indirectly through Mef2c. These data underscore a tight relationship in mammals between Nkx2.5 and Mef2c in SHF transcriptional regulation, and highlight the potential for evolutionary cis-regulatory analysis to identify core, conserved components of the gene networks controlling heart development.

Histone acetylation as a therapeutic target

The recent developments in the field of epigenetics have changed the way the covalent modifications were perceived from mere chemical tags to important biological recruiting platforms as well as decisive factors in the process of transcriptional regulation and gene expression. Over the years, the parallel investigations in the area of epigenetics and disease have also shown the significance of the epigenetic modifications as important regulatory nodes that exhibit dysfunction in disease states. In the present scenario where epigenetic therapy is also being considered at par with the conventional therapeutic strategies, this article reviews the role of histone acetylation as an epigenetic mark involved in different biological processes associated with normal as well as abnormal gene expression states, modulation of this acetylation by small molecules and warrants the possibility of acetylation as a therapeutic target.

Regulation of GATA4 transcriptional activity in cardiovascular development and disease

Transcription factors regulate formation and function of the heart, and perturbation of transcription factor expression and regulation disrupts normal heart structure and function. Multiple mechanisms regulate the level and locus-specific activity of transcription factors, including transcription, translation, subcellular localization, posttranslational modifications, and context-dependent interactions with other transcription factors, chromatin remodeling enzymes, and epigenetic regulators. The zinc finger transcription factor GATA4 is among the best-studied cardiac transcriptional factors. This review focuses on molecular mechanisms that regulate GATA4 transcriptional activity in the cardiovascular system, providing a framework to investigate and understand the molecular regulation of cardiac gene transcription by other transcription factors.

Role of GATA-4 in differentiation and survival of bone marrow mesenchymal stem cells

Cell and tissue regeneration is a relatively new research field and it incorporates a novel application of molecular genetics. Combinatorial approaches for stem-cell-based therapies wherein guided differentiation into cardiac lineage cells and cells secreting paracrine factors may be necessary to overcome the limitations and shortcomings of a singular approach. GATA-4, a GATA zinc-finger transcription factor family member, has been shown to regulate differentiation, growth, and survival of a wide range of cell types. In this chapter, we discuss whether overexpression of GATA-4 increases mesenchymal stem cell (MSC) transdifferentiation into cardiac phenotype and enhances the MSC secretome, thereby increasing cell survival and promoting postinfarction cardiac angiogenesis. MSCs engineered with GATA-4 enhance their capacity to differentiate into cardiac cell phenotypes, improve survival of the cardiac progenitor cells and their offspring, and modulate the paracrine activity of stem cells to support their angiomyogenic potential and cardioprotective effects.

PRC2 directly methylates GATA4 and represses its transcriptional activity

Polycomb-repressive complex 2 (PRC2) promotes tissue-specific differentiation by depositing trimethylated histone H3 Lys 27 (H3K27me3) epigenetic marks to silence ectopic gene expression programs. Here, we show that EZH2, the catalytic subunit of PRC2, is required for cardiac morphogenesis. Both in vitro and in fetal hearts, EZH2 interacted with cardiac transcription factor GATA4 and directly methylated it at Lys 299. PRC2 methylation of GATA4 attenuated its transcriptional activity by reducing its interaction with and acetylation by p300. Our results reveal a new mechanism of PRC2-mediated transcriptional repression in which PRC2 methylates a transcription factor to inhibit its transcriptional activity.

Epigenetic modifications of stem cells: a paradigm for the control of cardiac progenitor cells

Stem cells of all types are characterized by the ability to self-renew and to differentiate. Multiple lines of evidence suggest that both maintenance of stemness and lineage commitment, including determination of the cardiomyogenic lineage, are tightly controlled by epigenetic mechanisms such as DNA methylation, histone modifications, and ATP-dependent chromatin remodeling. Epigenetic mechanisms are intrinsically reversible, interdependent, and highly dynamic in regulation of chromatin structure and specific gene transcription programs, thereby contributing to stem cell homeostasis. Here, we review the current understanding of epigenetic mechanisms involved in regulation of stem cell self-renewal and differentiation and in the control of cardiac progenitor cell commitment during heart development. Further progress in this area will help to decipher the epigenetic landscape in stem and progenitor cells and facilitate manipulation of stem cells for regenerative applications.

Curcumin ameliorates cardiac inflammation in rats with autoimmune myocarditis

Curcumin is a natural polyphenolic compound abundant in the rhizome of the perennial herb turmeric, Curcuma longa. It is commonly used as a dietary spice and coloring agent in cooking, and is used anecdotally as an herb in traditional Indian and Chinese medicine. It has been reported that curcumin has the potential to protect against cardiac inflammation through suppression of GATA-4 and nuclear factor-κB (NF-κB); however, no study to date has addressed the effect of curcumin on experimental autoimmune myocarditis (EAM) in rats. In this study, 8-week-old male Lewis rats were immunized with cardiac myosin to induce EAM. They were then divided randomly into a treatment or vehicle group and orally administrated curcumin (50 mg/kg/d) or 1% gum arabic, respectively, for 3 weeks after myosin injection. We performed hemodynamic, echocardiographic, hematoxylin and eosin staining, mast cell staining and Western blotting studies to evaluate the protective effect of curcumin in the acute phase of EAM. Cardiac functional parameters measured by hemodynamic and echocardiographic studies were significantly improved by curcumin treatment. Furthermore, curcumin reduced the heart weight-to-body weight ratio, area of inflammatory lesions and the myocardial protein level of NF-κB, interleukin (IL)-1β, tumor necrosis factor (TNF)-α and GATA-4. Our results indicate that curcumin has the potential to protect against cardiac inflammation through suppression of IL-1β, TNF-α, GATA-4 and NF-κB expresses, and may provide a novel therapeutic strategy for autoimmune myocarditis.

GATA-4 promotes myocardial transdifferentiation of mesenchymal stromal cells via up-regulating IGFBP-4

BACKGROUND AIMS

GATA-4 is a cardiac transcription factor and plays an important role in cell lineage differentiation during development. We investigated whether overexpression of GATA-4 increases adult mesenchymal stromal cell (MSC) transdifferentiation into a cardiac phenotype in vitro.

METHODS

MSC were harvested from rat bone marrow (BM) and transduced with GATA-4 (MSC(GATA-4)) using a murine stem cell virus (pMSCV) retroviral expression system. Gene expression in MSC(GATA-4) was analyzed using quantitative reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting. Native cardiomyocytes (CM) were isolated from ventricles of neonatal rats. Myocardial transdifferentiation of MSC was determined by immunostaining and electrophysiologic recording. The transdifferentiation rate was calculated directly from flow cytometery.

RESULTS

The expression of cardiac genes, including brain natriuretic peptide (BNP), Islet-1 and α-sarcomeric actinin (α-SA), was up-regulated in MSC(GATA-4) compared with control cells that were transfected with Green Fluorescent Protein (GFP) only (MSC(Null)). At the same time, insulin-like growth factor-binding protein (IGFBP)-4 was significantly up-regulated in MSC(GATA-4). A synchronous beating of MSC with native CM was detected and an action potential was recorded. Some GFP (+) cells were positive for α-SA staining after MSC were co-cultured with native CM for 7 days. The transdifferentiation rate was significantly higher in MSC(GATA-4). Functional studies indicated that the differentiation potential of MSC(GATA-4) was decreased by knockdown of IGFBP-4.

CONCLUSIONS

Overexpression of GATA-4 significantly increases MSC differentiation into a myocardial phenotype, which might be associated with the up-regulation of IGFBP-4.