Gata4 is required for maintenance of postnatal cardiac function and protection from pressure overload-induced heart failure

CircSorbs1 regulates myocardial regeneration and reduces cancer therapy-related cardiovascular toxicity through the Mir-99/GATA4 pathway

Due to the cancer therapy-related cardiovascular toxicity, heart failure following cancer therapy has a significant mortality rate. Gene-targeted therapy promotes the re-entry of existing cardiomyocytes into the cell cycle to achieve myocardial regeneration, which is a promising strategy for preventing and treating heart failure after myocardial infarction. Circular RNAs (circRNAs) are considered as potential targets for myocardial regeneration due to their strong stability, resistance to degradation, and potential role in heart development and cardiovascular diseases. By comparing the myocardial tissue of mice in the sham operation group and the Doxorubicin therapy group (DOX), we observed a significant decrease in Cirsorbs expression in the DOX group. Cirsorbs was predominantly localized in cardiomyocytes and exhibited high conservation. Subsequent investigations revealed that Cirsorbs could promote myocardial proliferation and inhibit myocardial apoptosis. Mechanistic studies further demonstrated that Cirsorbs could bind to miR99 and reduce its expression level. Meanwhile, miR99 was found to bind to GATA4 mRNA and decrease its expression level. The binding of Cirsorbs to miR99 alleviated the repression of miR99, thereby enhancing GATA4 expression and the transcription of downstream cyclin A2 and cyclin E1. This, in turn, increased cardiomyocyte proliferation and reduced apoptosis. In conclusion, Cirsorbs holds promise as an effective target for myocardial regeneration in reducing cancer therapy-related cardiovascular toxicity.

The ENCODE mouse postnatal developmental time course identifies regulatory programs of cell types and cell states

Postnatal genomic regulation significantly influences tissue and organ maturation but is under-studied relative to existing genomic catalogs of adult tissues or prenatal development in mouse. The ENCODE4 consortium generated the first comprehensive single-nucleus resource of postnatal regulatory events across a diverse set of mouse tissues. The collection spans seven postnatal time points, mirroring human development from childhood to adulthood, and encompasses five core tissues. We identified 30 cell types, further subdivided into 69 subtypes and cell states across adrenal gland, left cerebral cortex, hippocampus, heart, and gastrocnemius muscle. Our annotations cover both known and novel cell differentiation dynamics ranging from early hippocampal neurogenesis to a new sex-specific adrenal gland population during puberty. We used an ensemble Latent Dirichlet Allocation strategy with a curated vocabulary of 2,701 regulatory genes to identify regulatory "topics," each of which is a gene vector, linked to cell type differentiation, subtype specialization, and transitions between cell states. We find recurrent regulatory topics in tissue-resident macrophages, neural cell types, endothelial cells across multiple tissues, and cycling cells of the adrenal gland and heart. Cell-type-specific topics are enriched in transcription factors and microRNA host genes, while chromatin regulators dominate mitosis topics. Corresponding chromatin accessibility data reveal dynamic and sex-specific regulatory elements, with enriched motifs matching transcription factors in regulatory topics. Together, these analyses identify both tissue-specific and common regulatory programs in postnatal development across multiple tissues through the lens of the factors regulating transcription.

A Genomic Link From Heart Failure to Atrial Fibrillation Risk: FOG2 Modulates a TBX5/GATA4-Dependent Atrial Gene Regulatory Network

BACKGROUND

The relationship between heart failure (HF) and atrial fibrillation (AF) is clear, with up to half of patients with HF progressing to AF. The pathophysiological basis of AF in the context of HF is presumed to result from atrial remodeling. Upregulation of the transcription factor FOG2 (friend of GATA2; encoded by ZFPM2) is observed in human ventricles during HF and causes HF in mice.

METHODS

FOG2 expression was assessed in human atria. The effect of adult-specific FOG2 overexpression in the mouse heart was evaluated by whole animal electrophysiology, in vivo organ electrophysiology, cellular electrophysiology, calcium flux, mouse genetic interactions, gene expression, and genomic function, including a novel approach for defining functional transcription factor interactions based on overlapping effects on enhancer noncoding transcription.

RESULTS

FOG2 is significantly upregulated in the human atria during HF. Adult cardiomyocyte-specific FOG2 overexpression in mice caused primary spontaneous AF before the development of HF or atrial remodeling. FOG2 overexpression generated arrhythmia substrate and trigger in cardiomyocytes, including calcium cycling defects. We found that FOG2 repressed atrial gene expression promoted by TBX5. FOG2 bound a subset of GATA4 and TBX5 co-bound genomic locations, defining a shared atrial gene regulatory network. FOG2 repressed TBX5-dependent transcription from a subset of co-bound enhancers, including a conserved enhancer at the Atp2a2 locus. Atrial rhythm abnormalities in mice caused by Tbx5 haploinsufficiency were rescued by Zfpm2 haploinsufficiency.

CONCLUSIONS

Transcriptional changes in the atria observed in human HF directly antagonize the atrial rhythm gene regulatory network, providing a genomic link between HF and AF risk independent of atrial remodeling.

RNA binding proteins in cardiovascular development and disease

Congenital heart disease (CHD) is the most common birth defect affecting>1.35 million newborn babies worldwide. CHD can lead to prenatal, neonatal, postnatal lethality or life-long cardiac complications. RNA binding protein (RBP) mutations or variants are emerging as contributors to CHDs. RBPs are wizards of gene regulation and are major contributors to mRNA and protein landscape. However, not much is known about RBPs in the developing heart and their contributions to CHD. In this chapter, we will discuss our current knowledge about specific RBPs implicated in CHDs. We are in an exciting era to study RBPs using the currently available and highly successful RNA-based therapies and methodologies. Understanding how RBPs shape the developing heart will unveil their contributions to CHD. Identifying their target RNAs in the embryonic heart will ultimately lead to RNA-based treatments for congenital heart disease.

Myc beyond Cancer: Regulation of Mammalian Tissue Regeneration

Myc is one of the most well-known oncogenes driving tumorigenesis in a wide variety of tissues. From the brain to blood, its deregulation derails physiological pathways that grant the correct functioning of the cell. Its action is carried out at the gene expression level, where Myc governs basically every aspect of transcription. Indeed, in addition to its role as a canonical, chromatin-bound transcription factor, Myc rules RNA polymerase II (RNAPII) transcriptional pause-release, elongation and termination and mRNA capping. For this reason, it is evident that minimal perturbations of Myc function mirror malignant cell behavior and, consistently, a large body of literature mainly focuses on Myc malfunctioning. In healthy cells, Myc controls molecular mechanisms involved in pivotal functions, such as cell cycle (and proliferation thereof), apoptosis, metabolism and cell size, angiogenesis, differentiation and stem cell self-renewal. In this latter regard, Myc has been found to also regulate tissue regeneration, a hot topic in the research fields of aging and regenerative medicine. Indeed, Myc appears to have a role in wound healing, in peripheral nerves and in liver, pancreas and even heart recovery. Herein, we discuss the state of the art of Myc's role in tissue regeneration, giving an overview of its potent action beyond cancer.

Transcriptomic Characterization of Genes Regulating the Stemness in Porcine Atrial Cardiomyocytes during Primary In Vitro Culture

Heart failure remains a major cause of death worldwide. There is a need to establish new management options as current treatment is frequently suboptimal. Clinical approaches based on autologous stem cell transplant is potentially a good alternative. The heart was long considered an organ unable to regenerate and renew. However, several reports imply that it may possess modest intrinsic regenerative potential. To allow for detailed characterization of cell cultures, whole transcriptome profiling was performed after 0, 7, 15, and 30 days of in vitro cell cultures (IVC) from the right atrial appendage and right atrial wall utilizing microarray technology. In total, 4239 differentially expressed genes (DEGs) with ratio > abs |2| and adjusted p-value ≤ 0.05 for the right atrial wall and 4662 DEGs for the right atrial appendage were identified. It was shown that a subset of DEGs, which have demonstrated some regulation of expression levels with the duration of the cell culture, were enriched in the following GO BP (Gene Ontology Biological Process) terms: "stem cell population maintenance" and "stem cell proliferation". The results were validated by RT-qPCR. The establishment and detailed characterization of in vitro culture of myocardial cells may be important for future applications of these cells in heart regeneration processes.

Poly (ADP-ribose) polymerases 16 triggers pathological cardiac hypertrophy via activating IRE1α-sXBP1-GATA4 pathway

BACKGROUND

Pressure overload-induced pathological cardiac hypertrophy is an independent predecessor of heart failure (HF), which remains the leading cause of worldwide mortality. However, current evidence on the molecular determinants of pathological cardiac hypertrophy is still inadequacy. This study aims to elucidate the role and mechanisms of Poly (ADP-ribose) polymerases 16 (PARP16) in the pathogenesis of pathological cardiac hypertrophy.

METHODS

Gain and loss of function approaches were used to demonstrate the effects of genetic overexpression or deletion of PARP16 on cardiomyocyte hypertrophic growth in vitro. Ablation of PARP16 by transducing the myocardium with serotype 9 adeno-associated virus (AAV9)-encoding PARP16 shRNA were then subjected to transverse aortic construction (TAC) to investigate the effect of PARP16 on pathological cardiac hypertrophy in vivo. Co-immunoprecipitation (IP) and western blot assay were used to detect the mechanisms of PARP16 in regulating cardiac hypertrophic development.

RESULTS

PARP16 deficiency rescued cardiac dysfunction and ameliorated TAC-induced cardiac hypertrophy and fibrosis in vivo, as well as phenylephrine (PE)-induced cardiomyocyte hypertrophic responses in vitro. Whereas overexpression of PARP16 exacerbated hypertrophic responses including the augmented cardiomyocyte surface area and upregulation of the fetal gene expressions. Mechanistically, PARP16 interacted with IRE1α and ADP-ribosylated IRE1α and then mediated the hypertrophic responses through activating the IRE1α-sXBP1-GATA4 pathway.

CONCLUSIONS

Collectively, our results implicated that PARP16 is a contributor to pathological cardiac hypertrophy at least in part via activating the IRE1α-sXBP1-GATA4 pathway, and may be regarded as a new potential target for exploring effective therapeutic interventions of pathological cardiac hypertrophy and heart failure.

Gestational palmitic acid suppresses embryonic GATA-binding protein 4 signaling and causes congenital heart disease

Dysregulated maternal fatty acid metabolism increases the risk of congenital heart disease (CHD) in offspring with an unknown mechanism, and the effect of folic acid fortification in preventing CHD is controversial. Using gas chromatography coupled to either a flame ionization detector or mass spectrometer (GC-FID/MS) analysis, we find that the palmitic acid (PA) concentration increases significantly in serum samples of pregnant women bearing children with CHD. Feeding pregnant mice with PA increased CHD risk in offspring and cannot be rescued by folic acid supplementation. We further find that PA promotes methionyl-tRNA synthetase (MARS) expression and protein lysine homocysteinylation (K-Hcy) of GATA4 and results in GATA4 inhibition and abnormal heart development. Targeting K-Hcy modification by either genetic ablation of Mars or using N-acetyl-L-cysteine (NAC) decreases CHD onset in high-PA-diet-fed mice. In summary, our work links maternal malnutrition and MARS/K-Hcy with the onset of CHD and provides a potential strategy in preventing CHD by targeting K-Hcy other than folic acid supplementation.

Gene Therapy for Cardiomyocyte Renewal: Cell Cycle, a Potential Therapeutic Target

Heart disease is the primary cause of death worldwide. Even though extensive research has been done, and many pharmacological and surgical treatments have been introduced to treat heart disease, the mortality rate still remains high. Gene therapy is widely used to understand molecular mechanisms of myocardial infarction and to treat cardiomyocyte loss. It was reported that adult cardiomyocytes proliferate at a very low rate; thus, targeting their proliferation has become a new regenerative therapeutic approach. Currently, re-activating cardiomyocyte proliferation appears to be one of the most promising methods to promote adult cardiomyocyte renewal. In this article, we highlight gene therapeutic targets of cell proliferation presently being pursued to re-activate the cell cycle of cardiomyocytes, including cell cycle regulators, transcription factors, microRNAs, signal transduction, and other contributing factors. We also summarize gene delivery vectors that have been used in cardiac research and major challenges to be overcome in the translation to the clinical approach and future directions.

Monoamine oxidase A-dependent ROS formation modulates human cardiomyocyte differentiation through AKT and WNT activation

During embryonic development, cardiomyocytes undergo differentiation and maturation, processes that are tightly regulated by tissue-specific signaling cascades. Although redox signaling pathways involved in cardiomyogenesis are established, the exact sources responsible for reactive oxygen species (ROS) formation remain elusive. The present study investigates whether ROS produced by the mitochondrial flavoenzyme monoamine oxidase A (MAO-A) play a role in cardiomyocyte differentiation from human induced pluripotent stem cells (hiPSCs). Wild type (WT) and MAO-A knock out (KO) hiPSCs were generated by CRISPR/Cas9 genome editing and subjected to cardiomyocyte differentiation. Mitochondrial ROS levels were lower in MAO-A KO compared to the WT cells throughout the differentiation process. MAO-A KO hiPSC-derived cardiomyocytes (hiPSC-CMs) displayed sarcomere disarray, reduced α- to β-myosin heavy chain ratio, GATA4 upregulation and lower macroautophagy levels. Functionally, genetic ablation of MAO-A negatively affected intracellular Ca2+ homeostasis in hiPSC-CMs. Mechanistically, MAO-A generated ROS contributed to the activation of AKT signaling that was considerably attenuated in KO cells. In addition, MAO-A ablation caused a reduction in WNT pathway gene expression consistent with its reported stimulation by ROS. As a result of WNT downregulation, expression of MESP1 and NKX2.5 was significantly decreased in MAO-A KO cells. Finally, MAO-A re-expression during differentiation rescued expression levels of cardiac transcription factors, contractile structure, and intracellular Ca2+ homeostasis. Taken together, these results suggest that MAO-A mediated ROS generation is necessary for the activation of AKT and WNT signaling pathways during cardiac lineage commitment and for the differentiation of fully functional human cardiomyocytes.

Genetic and phenotypic profiling of supranormal ejection fraction reveals decreased survival and underdiagnosed heart failure

AIMS

Individuals with supranormal left ventricular ejection fraction (snLVEF; LVEF >70%) have increased mortality. However, the genetic and phenotypic profile of snLVEF remains unknown. This study aimed to determine the relationship of both snLVEF genetic risk and phenotype with survival and underdiagnosed heart failure (HF).

METHODS AND RESULTS

A snLVEF genetic risk score (GRS) was applied and cases of snLVEF were identified in 486 754 individuals across two population-based cohorts (BioMe Biobank and UK Biobank). The snLVEF GRS and phenotype were evaluated for association with survival, as well as HF diagnosis, markers, symptoms, and medications. Of 486 754 participants, the median age was 58 years, 20 069 (4.1%) died, and 10 088 (2.1%) had diagnosed HF. Both snLVEF GRS (hazard ratio [HR] 1.1 for top 10% vs. bottom 10% GRS; p = 0.002) and phenotype (HR 1.4; p = 0.003) were associated with increased all-cause mortality. Both snLVEF GRS and phenotype were associated with reduced HF diagnosis (odds ratio [OR] 0.97 and OR 0.63, respectively; both p ≤0.002). However, the snLVEF GRS and phenotype were both associated with elevated brain natriuretic peptide (BNP) levels (146 and 185 pg/ml increase, respectively; p <0.001), including 268 out of 455 (59%) individuals with snLVEF phenotype who had BNP >100 pg/ml. Among 476 666 participants without HF diagnoses, snLVEF GRS and phenotype were associated with increased HF symptoms (e.g. exertional dyspnoea OR 1.4 and OR 1.3; p <0.003) and HF medications (e.g. loop diuretic OR 1.2 and OR 1.03; p <0.02). Associations were consistent in hypertensive individuals without cardiac comorbidities.

CONCLUSIONS

Genetic predisposition to and presence of snLVEF are associated with decreased survival and underdiagnosed HF.

The regulatory role of pioneer factors during cardiovascular lineage specification – A mini review

Cardiovascular disease (CVD) remains the number one cause of death worldwide. Ischemic heart disease contributes to heart failure and has considerable morbidity and mortality. Therefore, alternative therapeutic strategies are urgently needed. One class of epigenetic regulators known as pioneer factors has emerged as an important tool for the development of regenerative therapies for the treatment of CVD. Pioneer factors bind closed chromatin and remodel it to drive lineage specification. Here, we review pioneer factors within the cardiovascular lineage, particularly during development and reprogramming and highlight the implications this field of research has for the future development of cardiac specific regenerative therapies.

GREAP: a comprehensive enrichment analysis software for human genomic regions

The rapid development of genomic high-throughput sequencing has identified a large number of DNA regulatory elements with abundant epigenetics markers, which promotes the rapid accumulation of functional genomic region data. The comprehensively understanding and research of human functional genomic regions is still a relatively urgent work at present. However, the existing analysis tools lack extensive annotation and enrichment analytical abilities for these regions. Here, we designed a novel software, Genomic Region sets Enrichment Analysis Platform (GREAP), which provides comprehensive region annotation and enrichment analysis capabilities. Currently, GREAP supports 85 370 genomic region reference sets, which cover 634 681 107 regions across 11 different data types, including super enhancers, transcription factors, accessible chromatins, etc. GREAP provides widespread annotation and enrichment analysis of genomic regions. To reflect the significance of enrichment analysis, we used the hypergeometric test and also provided a Locus Overlap Analysis. In summary, GREAP is a powerful platform that provides many types of genomic region sets for users and supports genomic region annotations and enrichment analyses. In addition, we developed a customizable genome browser containing >400 000 000 customizable tracks for visualization. The platform is freely available at http://www.liclab.net/Greap/view/index.

Modeling congenital heart disease: lessons from mice, hPSC-based models, and organoids

In this review, Rao et al. contrast mouse models of CHD, which maintain the anatomical arrangement of the heart, and human cellular models of CHD, which are more likely to capture human-specific biology but lack anatomical structure. They also discuss the recent development of cardiac organoids, which are a promising step toward more anatomically informative human models of CHD.

Congenital heart defects (CHDs) are among the most common birth defects, but their etiology has long been mysterious. In recent decades, the development of a variety of experimental models has led to a greater understanding of the molecular basis of CHDs. In this review, we contrast mouse models of CHD, which maintain the anatomical arrangement of the heart, and human cellular models of CHD, which are more likely to capture human-specific biology but lack anatomical structure. We also discuss the recent development of cardiac organoids, which are a promising step toward more anatomically informative human models of CHD.

Effects of caloric overload before caloric restriction in the murine heart

The beneficial effects of caloric restriction (CR) against cardiac aging and for prevention of cardiovascular diseases are numerous. However, to our knowledge, there is no scientific evidence about how a high-calorie diet (HCD) background influences the mechanisms underlying CR in whole heart tissue (WHT) in experimental murine models. In the current study, CR-treated mice with different alimentary backgrounds were subjected to transthoracic echocardiographic measurements. WHT was then analyzed to determine cardiac energetics, telomerase activity, the expression of energy-sensing networks, tissue-specific adiponectin, and cardiac precursor/cardiac stem cell markers. Animals with a balanced diet consumption before CR presented marked cardiac remodeling with improved ejection fraction (EF) and fractional shortening (FS), enhanced OXPHOS complex I, III, and IV, and CKMT2 enzymatic activity. Mice fed an HCD before CR presented moderate changes in cardiac geometry with diminished EF and FS values, but improved OXPHOS complex IV and CKMT2 activity. Differences in cardiac remodeling, left ventricular systolic/diastolic performance, and mitochondrial energetics, found in the CR-treated mice with contrasting alimentary backgrounds, were corroborated by inconsistencies in the expression of mitochondrial-biogenesis-related markers and associated regulatory networks. In particular, disruption of eNOS and AMPK -PGC-1α-mTOR-related axes. The impact of a past habit of caloric overload on the effects of CR in the WHT is a scarcely explored subject that requires deeper study in combination with analyses of other tissues and organs at higher levels of organization within the organ system. Such research will eventually lead to the development of preventative and therapeutic strategies to promote health and longevity.

Transcription factor GATA4 drives RNA polymerase III-directed transcription and transformed cell proliferation through a filamin A/GATA4/SP1 pathway

RNA polymerase III (pol III) products play fundamental roles in a variety of cellular processes, including protein synthesis and cancer cell proliferation. In addition, dysregulation of pol III-directed transcription closely correlates with tumorigenesis. It is therefore of interest to identify novel pathways or factors governing pol III-directed transcription. Here, we show that transcription factor (TF) GATA binding protein 4 (GATA4) expression in SaOS2 cells was stimulated by the silencing of filamin A (FLNA), a repressor of pol III-directed transcription, suggesting that GATA4 is potentially associated with the regulation of pol III-directed transcription. Indeed, we show that GATA4 expression positively correlates with pol III-mediated transcription and tumor cell proliferation. Mechanistically, we found that GATA4 depletion inhibits the occupancies of the pol III transcription machinery factors at the loci of pol III target genes by reducing expression of both TFIIIB subunit TFIIB-related factor 1 and TFIIIC subunit general transcription factor 3C subunit 2 (GTF3C2). GATA4 has been shown to activate specificity factor 1 (Sp1) gene transcription by binding to the Sp1 gene promoter, and Sp1 has been confirmed to activate pol III gene transcription by directly binding to both Brf1 and Gtf3c2 gene promoters. Thus, the findings from this study suggest that GATA4 links FLNA and Sp1 signaling to form an FLNA/GATA4/Sp1 axis to modulate pol III-directed transcription and transformed cell proliferation. Taken together, these results provide novel insights into the regulatory mechanism of pol III-directed transcription.

N-Acetyl Cysteine, Selenium, and Ascorbic Acid Rescue Diabetic Cardiac Hypertrophy via Mitochondrial-Associated Redox Regulators

Metabolic disorders often lead to cardiac complications. Metabolic deregulations during diabetic conditions are linked to mitochondrial dysfunctions, which are the key contributing factors in cardiac hypertrophy. However, the underlying mechanisms involved in diabetes-induced cardiac hypertrophy are poorly understood. In the current study, we initially established a diabetic rat model by alloxan-administration, which was validated by peripheral glucose measurement. Diabetic rats displayed myocardial stiffness and fibrosis, changes in heart weight/body weight, heart weight/tibia length ratios, and enhanced size of myocytes, which altogether demonstrated the establishment of diabetic cardiac hypertrophy (DCH). Furthermore, we examined the expression of genes associated with mitochondrial signaling impairment. Our data show that the expression of PGC-1α, cytochrome c, MFN-2, and Drp-1 was deregulated. Mitochondrial-signaling impairment was further validated by redox-system dysregulation, which showed a significant increase in ROS and thiobarbituric acid reactive substances, both in serum and heart tissue, whereas the superoxide dismutase, catalase, and glutathione levels were decreased. Additionally, the expression levels of pro-apoptotic gene PUMA and stress marker GATA-4 genes were elevated, whereas ARC, PPARα, and Bcl-2 expression levels were decreased in the heart tissues of diabetic rats. Importantly, these alloxan-induced impairments were rescued by N-acetyl cysteine, ascorbic acid, and selenium treatment. This was demonstrated by the amelioration of myocardial stiffness, fibrosis, mitochondrial gene expression, lipid profile, restoration of myocyte size, reduced oxidative stress, and the activation of enzymes associated with antioxidant activities. Altogether, these data indicate that the improvement of mitochondrial dysfunction by protective agents such as N-acetyl cysteine, selenium, and ascorbic acid could rescue diabetes-associated cardiac complications, including DCH.

Mesenchymal stem cells seeded onto nanofiber scaffold for myocardial regeneration

Cardiac disease is the leading cause of mortality and disability worldwide. We investigated the role of undifferentiated adipose tissue-derived mesenchymal stem cells (ADMSC) alone and ADMSC seeded onto the electro-spun nanofibers (NF) for reconstructing damaged cardiac tissue in isoprenaline-induced myocardial infarction (MI) in rats. ADMSC were sorted by morphological appearance and by detection of cluster of differentiation (CD) surface antigens. The therapeutic potential of ADMSC for treating MI was evaluated by electrocardiogram (ECG), biochemical analysis, molecular genetic analysis and histological examination. Treatment of MI-challenged rats with ADMSC improved ECG findings, which were corroborated by significant decreases in serum lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) enzyme activities together with reduced serum troponin T (cTnT) and connexin 43 (Cx43) levels. MI model rats treated with ADMSC exhibited a significant increase in serum alpha sarcomeric actin (Actn) and GATA binding protein 4 (GATA4), and NK2 homeobox 5 (NKX2.5) gene expression was decreased following treatment with ADMSC. ADMSC also ameliorated damage to cardiac tissue. The effects of ADMSC seeded onto NF were superior to those of ADMSC alone. ADMSC may be useful for mitigation of MI.

Therapeutic and diagnostic targeting of fibrosis in metabolic, proliferative and viral disorders

Fibrosis is a common denominator in many pathologies and crucially affects disease progression, drug delivery efficiency and therapy outcome. We here summarize therapeutic and diagnostic strategies for fibrosis targeting in atherosclerosis and cardiac disease, cancer, diabetes, liver diseases and viral infections. We address various anti-fibrotic targets, ranging from cells and genes to metabolites and proteins, primarily focusing on fibrosis-promoting features that are conserved among the different diseases. We discuss how anti-fibrotic therapies have progressed over the years, and how nanomedicine formulations can potentiate anti-fibrotic treatment efficacy. From a diagnostic point of view, we discuss how medical imaging can be employed to facilitate the diagnosis, staging and treatment monitoring of fibrotic disorders. Altogether, this comprehensive overview serves as a basis for developing individualized and improved treatment strategies for patients suffering from fibrosis-associated pathologies.

Ambient air PM2.5 exposure induces heart injury and cardiac hypertrophy in rats through regulation of miR-208a/b, α/β-MHC, and GATA4

Ambient air fine particulate matter (PM2.5) may increase cardiovascular disease risks. In this study, we investigated the miR-208/GATA4/myosin heavy chain (MHC) regulation mechanisms on cardiac injury in rats after PM2.5 exposure via an animal inhalation device. The results showed that PM2.5 exposure for 2 months caused pathological heart injury, reduced nucleus-cytoplasm ratio, and increased the levels of CK-MB and cTnI, showing cardiac hypertrophy. Oxidative stress and inflammatory responses were also observed in rats' hearts exposed to PM2.5. Of note, PM2.5 exposure for 2-month significantly elevated GATA4 and β-MHC mRNA and protein expression compared with the corresponding controls, along with the high-expression of miR-208b. The ratios of β-MHC/α-MHC expression induced by PM2.5 were remarkably raised in comparison to their controls. It suggested that the up-regulation of miR-208b/β-MHC and GATA4 and the conversion from α-MHC to β-MHC may be the important causes of cardiac hypertrophy in rats incurred by PM2.5.

Fetal Gene Reactivation in Pulmonary Arterial Hypertension: GOOD, BAD, or BOTH?

Pulmonary arterial hypertension is a debilitating chronic disorder marked by the progressive obliteration of the pre-capillary arterioles. This imposes a pressure overload on the right ventricle (RV) pushing the latter to undergo structural and mechanical adaptations that inexorably culminate in RV failure and death. Thanks to the advances in molecular biology, it has been proposed that some aspects of the RV and pulmonary vascular remodeling processes are orchestrated by a subversion of developmental regulatory mechanisms with an upregulation of a suite of genes responsible for the embryo's early growth and normally repressed in adults. In this review, we present relevant background regarding the close relationship between overactivation of fetal genes and cardiopulmonary remodeling, exploring whether the reawakening of developmental factors plays a causative role or constitutes a protective mechanism in the setting of PAH.

Transcriptional factors in calcium mishandling and atrial fibrillation development

Healthy cardiac conduction relies on the coordinated electrical activity of distinct populations of cardiomyocytes. Disruption of cell-cell conduction results in cardiac arrhythmias, a leading cause of morbidity and mortality worldwide. Recent genetic studies have highlighted a major heritable component and identified numerous loci associated with risk of atrial fibrillation, including transcription factor genes, particularly those important in cardiac development, microRNAs, and long noncoding RNAs. Identification of such genetic factors has prompted the search to understand the mechanisms that underlie the genetic component of AF. Recent studies have found several mechanisms by which genetic alterations can result in AF formation via disruption of calcium handling. Loss of developmental transcription factors in adult cardiomyocytes can result in disruption of SR calcium ATPase, sodium calcium exchanger, calcium channels, among other ion channels, which underlie action potential abnormalities and triggered activity that can contribute to AF. This review aims to summarize the complex network of transcription factors and their roles in calcium handling.

Deficit of glucocorticoid-induced leucine zipper amplifies angiotensin-induced cardiomyocyte hypertrophy and diastolic dysfunction

Poor prognosis in heart failure and the lack of real breakthrough strategies validate targeting myocardial remodelling and the intracellular signalling involved in this process. So far, there are no effective strategies to counteract hypertrophy, an independent predictor of heart failure progression and death. Glucocorticoid-induced leucine zipper (GILZ) is involved in inflammatory signalling, but its role in cardiac biology is unknown. Using GILZ-knockout (KO) mice and an experimental model of hypertrophy and diastolic dysfunction, we addressed the role of GILZ in adverse myocardial remodelling. Infusion of angiotensin II (Ang II) resulted in myocardial dysfunction, inflammation, apoptosis, fibrosis, capillary rarefaction and hypertrophy. Interestingly, GILZ-KO showed more evident diastolic dysfunction and aggravated hypertrophic response compared with WT after Ang II administration. Both cardiomyocyte and left ventricular hypertrophy were more pronounced in GILZ-KO mice. On the other hand, Ang II-induced inflammatory and fibrotic phenomena, cell death and reduction in microvascular density, remained invariant between the WT and KO groups. The analysis of regulators of hypertrophic response, GATA4 and FoxP3, demonstrated an up-regulation in WT mice infused with Ang II; conversely, such an increase did not occur in GILZ-KO hearts. These data on myocardial response to Ang II in mice lacking GILZ indicate that this protein is a new element that can be mechanistically involved in cardiovascular pathology.

Gene regulatory programmes of tissue regeneration

Regeneration is the process by which organisms replace lost or damaged tissue, and regenerative capacity can vary greatly among species, tissues and life stages. Tissue regeneration shares certain hallmarks of embryonic development, in that lineage-specific factors can be repurposed upon injury to initiate morphogenesis; however, many differences exist between regeneration and embryogenesis. Recent studies of regenerating tissues in laboratory model organisms - such as acoel worms, frogs, fish and mice - have revealed that chromatin structure, dedicated enhancers and transcriptional networks are regulated in a context-specific manner to control key gene expression programmes. A deeper mechanistic understanding of the gene regulatory networks of regeneration pathways might ultimately enable their targeted reactivation as a means to treat human injuries and degenerative diseases. In this Review, we consider the regeneration of body parts across a range of tissues and species to explore common themes and potentially exploitable elements.

Genetic and Epigenetic Control of Heart Development

A transcriptional program implemented by transcription factors and epigenetic regulators governs cardiac development and disease. Mutations in these factors are important causes of congenital heart disease. Here, we review selected recent advances in our understanding of the transcriptional and epigenetic control of heart development, including determinants of cardiac transcription factor chromatin occupancy, the gene regulatory network that regulates atrial septation, the chromatin landscape and cardiac gene regulation, and the role of Brg/Brahma-associated factor (BAF), nucleosome remodeling and histone deacetylation (NuRD), and Polycomb epigenetic regulatory complexes in heart development.

circRNA Hipk3 Induces Cardiac Regeneration after Myocardial Infarction in Mice by Binding to Notch1 and miR-133a

The synergism between cardiomyogenesis and angiogenesis is essential for cardiac regeneration. Circular RNAs (circRNAs) play pivotal roles in cell growth and angiogenesis, but their functions in cardiac regeneration are not yet known. In this study, we investigated the role and underlying mechanisms of circRNA Hipk3 (circHipk3) in both cardiomyogenesis and angiogenesis during cardiac regeneration. We found that circHipk3 was overexpressed in the fetal or neonatal heart of mice. The transcription factor Gata4 bound to the circHipk3 promoter and increased circHipk3 expression. Cardiomyocyte (CM) proliferation in vitro and in vivo was inhibited by circHipk3 knockdown and increased by circHipk3 overexpression. Moreover, circHipk3 overexpression promoted coronary vessel endothelial cell proliferation, migration, and tube-forming capacity and subsequent angiogenesis. More importantly, circHipk3 overexpression attenuated cardiac dysfunction and decreased fibrotic area after myocardial infarction (MI). Mechanistically, circHipk3 promoted CM proliferation by increasing Notch1 intracellular domain (N1ICD) acetylation, thereby increasing N1ICD stability and preventing its degradation. In addition, circHipk3 acted as a sponge for microRNA (miR)-133a to promote connective tissue growth factor (CTGF) expression, which activated endothelial cells. Our findings suggested that circHipk3 might be a novel therapeutic target for preventing heart failure post-MI.

The role of stretch, tachycardia and sodium-calcium exchanger in induction of early cardiac remodelling

Stretch and tachycardia are common triggers for cardiac remodelling in various conditions, but a comparative characterization of their role in the excitation‐transcription coupling (ETC) and early regulation of gene expression and structural changes is lacking. Here, we show that stretch and tachycardia directly induced hypertrophy of neonatal rat cardiac myocytes and also of non‐myocytes. Both triggers induced similar patterns of hypertrophy but had largely distinct gene expression profiles. ACTA1 served as good hypertrophy marker upon stretch, while RCAN1 was found increased in response to tachycardia in a rate‐dependent fashion. Mechanistically, several calcium‐handling proteins, including the sodium‐calcium exchanger (NCX), contributed to ETC. Phosphorylation of the calcium/calmodulin‐dependent protein kinase II (CaMKII) was elevated and occurred downstream of NCX activation upon tachycardia, but not stretch. Microarray profiling revealed that stretch and tachycardia regulated around 33% and 20% genes in a NCX‐dependent manner, respectively. In conclusion, our data show that hypertrophy induction by stretch and tachycardia is associated with different gene expression profiles with a significant contribution of the NCX.

Atrial fibrillation risk loci interact to modulate Ca2+-dependent atrial rhythm homeostasis

Atrial fibrillation (AF), defined by disorganized atrial cardiac rhythm, is the most prevalent cardiac arrhythmia worldwide. Recent genetic studies have highlighted a major heritable component and identified numerous loci associated with AF risk, including the cardiogenic transcription factor genes TBX5, GATA4, and NKX2-5. We report that Tbx5 and Gata4 interact with opposite signs for atrial rhythm controls compared with cardiac development. Using mouse genetics, we found that AF pathophysiology caused by Tbx5 haploinsufficiency, including atrial arrhythmia susceptibility, prolonged action potential duration, and ectopic cardiomyocyte depolarizations, were all rescued by Gata4 haploinsufficiency. In contrast, Nkx2-5 haploinsufficiency showed no combinatorial effect. The molecular basis of the TBX5/GATA4 interaction included normalization of intra-cardiomyocyte calcium flux and expression of calcium channel genes Atp2a2 and Ryr2. Furthermore, GATA4 and TBX5 showed antagonistic interactions on an Ryr2 enhancer. Atrial rhythm instability caused by Tbx5 haploinsufficiency was rescued by a decreased dose of phospholamban, a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor, consistent with a role for decreased sarcoplasmic reticulum calcium flux in Tbx5-dependent AF susceptibility. This work defines a link between Tbx5 dose, sarcoplasmic reticulum calcium flux, and AF propensity. The unexpected interactions between Tbx5 and Gata4 in atrial rhythm control suggest that evaluating specific interactions between genetic risk loci will be necessary for ascertaining personalized risk from genetic association data.

Electrical stimulation induces differentiation of human cardiosphere-derived cells (hCDCs) to committed cardiomyocyte

Logistic complexities of heart transplantation embossed the necessity of utilizing novel methods, which enable heart regeneration. Human cardiosphere-derived cells (hCDCs) are taken into consideration as a promising cell resource in cell therapy in recent years. In this study, we designed an electrochemical stimulation system, which sends square pulses to the hCDCs and records their electrical response. Morphology, viability and differentiation of hCDCs are monitored at certain time courses of the treatment. Differentiating hCDCs aligned perpendicularly with respect to the direction of applied electric current, and obtained a spindle-like morphology, while they remained viable. At the same time, specific cardiac marker genes including GATA4, cTnT and α-MHC showed a considerable up-regulation. Our findings confirm that hCDCs differentiate to committed cardiomyocytes when hCDCs receive an electrical energy of 0.06 - 0.12 Wh. This amount of electrical energy could be applied to the stem cells using versatile electrical stimulation patterns via commercially available devices.

GATA4-targeted compound exhibits cardioprotective actions against doxorubicin-induced toxicity in vitro and in vivo: establishment of a chronic cardiotoxicity model using human iPSC-derived cardiomyocytes

Doxorubicin is a widely used anticancer drug that causes dose-related cardiotoxicity. The exact mechanisms of doxorubicin toxicity are still unclear, partly because most in vitro studies have evaluated the effects of short-term high-dose doxorubicin treatments. Here, we developed an in vitro model of long-term low-dose administration of doxorubicin utilizing human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Moreover, given that current strategies for prevention and management of doxorubicin-induced cardiotoxicity fail to prevent cancer patients developing heart failure, we also investigated whether the GATA4-targeted compound 3i-1000 has cardioprotective potential against doxorubicin toxicity both in vitro and in vivo. The final doxorubicin concentration used in the chronic toxicity model in vitro was chosen based on cell viability data evaluation. Exposure to doxorubicin at the concentrations of 1–3 µM markedly reduced (60%) hiPSC-CM viability already within 48 h, while a 14-day treatment with 100 nM doxorubicin concentration induced only a modest 26% reduction in hiPCS-CM viability. Doxorubicin treatment also decreased DNA content in hiPSC-CMs. Interestingly, the compound 3i-1000 attenuated doxorubicin-induced increase in pro-B-type natriuretic peptide (proBNP) expression and caspase-3/7 activation in hiPSC-CMs. Moreover, treatment with 3i-1000 for 2 weeks (30 mg/kg/day, i.p.) inhibited doxorubicin cardiotoxicity by restoring left ventricular ejection fraction and fractional shortening in chronic in vivo rat model. In conclusion, the results demonstrate that long-term exposure of hiPSC-CMs can be utilized as an in vitro model of delayed doxorubicin-induced toxicity and provide in vitro and in vivo evidence that targeting GATA4 may be an effective strategy to counteract doxorubicin-induced cardiotoxicity.

Phosphorylation of GATA4 at serine 105 is required for left ventricular remodelling process in angiotensin II-induced hypertension in rats

In this study, we investigated whether local intramyocardial GATA4 overexpression affects the left ventricular (LV) remodelling process and the importance of phosphorylation at serine 105 (S105) for the actions of GATA4 in an angiotensin II (AngII)‐induced hypertension rat model. Adenoviral constructs overexpressing wild‐type GATA4 or GATA4 mutated at S105 were delivered into the anterior LV free wall. AngII (33.3 µg/kg/h) was administered via subcutaneously implanted minipumps. Cardiac function and structure were examined by echocardiography, followed by histological immunostainings of LV sections and gene expression measurements by RT‐qPCR. The effects of GATA4 on cultured neonatal rat ventricular fibroblasts were evaluated. In AngII‐induced hypertension, GATA4 overexpression repressed fibrotic gene expression, reversed the hypertrophic adult‐to‐foetal isoform switch of myofibrillar genes and prevented apoptosis, whereas histological fibrosis was not affected. Overexpression of GATA4 mutated at S105 resulted in LV chamber dilatation, cardiac dysfunction and had minor effects on expression of myocardial remodelling genes. Fibrotic gene expression in cardiac fibroblasts was differently affected by overexpression of wild‐type or mutated GATA4. Our results indicate that GATA4 reduces AngII‐induced responses by interfering with pro‐fibrotic and hypertrophic gene expressions. GATA4 actions on LV remodelling and fibroblasts are dependent on phosphorylation site S105.

Substance P Administered after Myocardial Infarction Upregulates Microphthalmia-Associated Transcription Factor, GATA4, and the Expansion of c-Kit+ Cells

Microphthalmia-associated transcription factor (MITF), a basic helix-loop-helix leucine zipper transcription factor, can govern gene expression by binding to E box elements in the promoter region of its target gene. Although high levels of MITF have been observed in cardiomyocytes and the heart, the role of MITF after myocardial infarction (MI) remains unclear. We investigated the association between substance P (SP)/neurokinin-1 receptor (NK₁R) signaling and MITF expression after MI. Male Sprague-Dawley rats (8 weeks) were randomly divided in two groups: ischemia/reperfusion injury (I/R) and SP injection (5 nmol/kg, SP+I/R). At the end of 7 days, the left ventricle (LV; LV^7daysI/R, LV^7daysSP+I/R) and infarct-related areas (IA; IA^7daysI/R, IA^7daysSP+I/R) from the hearts were collected. Immunofluorescence staining demonstrated that the LV^7daysSP+I/R had a larger population of c-Kit⁺ GATA4^high cells, which markedly upregulated MITF, c-Kit, and GATA4. c-Kit⁺ cells in the explant-derived cells (EDCs) derived from IA^7daysSP+I/R migrated more widely than EDCs IA^7daysI/R. Immunofluorescence staining, western blot analysis, and qRT-PCR assay showed that SP-treated c-Kit⁺ cells exhibited a high expression of c-Kit, GATA4, and MITF. FTY720 (a MITF inhibitor), RP67580 (NK₁R inhibitor), or both inhibited the migration and proliferation of c-Kit⁺ cells increased by SP and blocked the upregulation of c-Kit, GATA4, and MITF. Overall, we suggest that MITF might be a potential regulator in SP-mediated c-Kit⁺ cell expansion post-MI via c-Kit and GATA4.

Paeonol Reverses Adriamycin Induced Cardiac Pathological Remodeling through Notch1 Signaling Reactivation in H9c2 Cells and Adult Zebrafish Heart

Adriamycin is a commonly prescribed chemotherapeutic drug for a wide range of cancers. Adriamycin causes cardiotoxicity as an adverse effect that limits its clinical application in cancer treatment. Several mechanisms have been proposed to explain the toxicity it causes in heart cells. Disruption of inherent cardiac repair mechanism is the least understood mechanism of Adriamycin-induced cardiotoxicity. Adriamycin induces pathological remodeling in cardiac cells by promoting apoptosis, hypertrophy, and fibrosis. We found that Adriamycin inhibited Notch1 in a time- and dose-dependent manner in H9c2 cells. We used Paeonol, a Notch1 activator, and analyzed the markers of apoptosis, hypertrophy, and fibrosis in H9c2 cells in vitro and in adult zebrafish heart in vivo as model systems to study Adriamycin-induced cardiotoxicity. Paeonol activated Notch1 signaling and expression of its downstream target genes effectively in the Adriamycin-treated condition in vitro and in vivo. Also we detected that Notch activation using Paeonol protected the cells from apoptosis, collagen deposition, and hypertrophy response using functional assays. We conclude that Adriamycin induced cardiotoxicity by promoting the pathological cardiac remodeling through inhibition of Notch1 signaling and that the Notch1 reactivation by Paeonol protected the cells and reversed the cardiotoxicity.

Cardiomyocyte Sirt (Sirtuin) 7 Ameliorates Stress-Induced Cardiac Hypertrophy by Interacting With and Deacetylating GATA4

Sirt (Sirtuin) 7, the most recently identified mammalian sirtuin, has been shown to contribute to appropriate wound healing processes after acute cardiovascular insult. However, its role in the development of cardiac remodeling after pressure overload is unclear. Cardiomyocyte-specific Sirt7-knockout and control mice were subjected to pressure overload induced by transverse aortic constriction. Cardiac hypertrophy and functions were then examined in these mice. Sirt7 protein expression was increased in myocardial tissue after pressure overload. Transverse aortic constriction-induced increases in heart weight/tibial length were significantly augmented in cardiomyocyte-specific Sirt7-knockout mice compared with those of control mice. Histological analysis showed that the cardiomyocyte cross-sectional area and fibrosis area were significantly larger in cardiomyocyte-specific Sirt7-deficient mice. Cardiac contractile functions were markedly decreased in cardiomyocyte-specific Sirt7-deficient mice. Mechanistically, we found that Sirt7 interacted directly with GATA4 and that the exacerbation of phenylephrine-induced cardiac hypertrophy by Sirt7 knockdown was decreased by GATA4 knockdown. Sirt7 deacetylated GATA4 in cardiomyocytes and regulated its transcriptional activity. Interestingly, we demonstrated that treatment with nicotinamide mononucleotide, a known key NAD⁺ intermediate, ameliorated agonist-induced cardiac hypertrophies in a Sirt7-dependent manner in vitro. Sirt7 deficiency in cardiomyocytes promotes cardiomyocyte hypertrophy in response to pressure overload. Sirt7 exerts its antihypertrophic effect by interacting with and promoting deacetylation of GATA4.

Transcriptome Analysis of Hypertrophic Heart Tissues from Murine Transverse Aortic Constriction and Human Aortic Stenosis Reveals Key Genes and Transcription Factors Involved in Cardiac Remodeling Induced by Mechanical Stress

Background

Mechanical stress-induced cardiac remodeling that results in heart failure is characterized by transcriptional reprogramming of gene expression. However, a systematic study of genomic changes involved in this process has not been performed to date. To investigate the genomic changes and underlying mechanism of cardiac remodeling, we collected and analyzed DNA microarray data for murine transverse aortic constriction (TAC) and human aortic stenosis (AS) from the Gene Expression Omnibus database and the European Bioinformatics Institute.

Methods and Results

The differential expression genes (DEGs) across the datasets were merged. The Venn diagrams showed that the number of intersections for early and late cardiac remodeling was 74 and 16, respectively. Gene ontology and protein–protein interaction network analysis showed that metabolic changes, cell differentiation and growth, cell cycling, and collagen fibril organization accounted for a great portion of the DEGs in the TAC model, while in AS patients' immune system signaling and cytokine signaling displayed the most significant changes. The intersections between the TAC model and AS patients were few. Nevertheless, the DEGs of the two species shared some common regulatory transcription factors (TFs), including SP1, CEBPB, PPARG, and NFKB1, when the heart was challenged by applied mechanical stress.

Conclusions

This study unravels the complex transcriptome profiles of the heart tissues and highlighting the candidate genes involved in cardiac remodeling induced by mechanical stress may usher in a new era of precision diagnostics and treatment in patients with cardiac remodeling.

From embryogenesis to adulthood: Critical role for GATA factors in heart development and function

Cardiac development is governed by a complex network of transcription factors (TFs) that regulate cell fates in a spatiotemporal manner. Among these, the GATA family of zinc finger TFs plays prominent roles in regulating the development of the myocardium, endocardium, and outflow tract. This family comprises six members three of which, GATA4, 5, and 6, are predominantly expressed in cardiac cells where they activate specific downstream gene targets via interactions with one another and with other TFs and signaling molecules. Their critical function in heart formation is evidenced by the phenotypes of animal models lacking these factors and by the broad spectrum of human congenital heart diseases associated with mutations in their genes. Similarly, in the postnatal heart, these proteins play significant and nonredundant roles in cardiac function, regulating adaptive stress responses including cardiomyocyte hypertrophy and survival, as well as endothelial homeostasis and angiogenesis. As such, decreased expression of either GATA4, 5, or 6 results in impaired cardiovascular homeostasis and increased risk of premature and serious cardiovascular events such as hypertension, arrhythmia, aortopathy, and heart failure. Although a great deal of progress has been made in understanding GATA-dependent regulatory processes in the heart, the molecular mechanisms underlying the specificity of GATA factors and their upstream regulation remain incompletely understood. The knowledge and tools developed since their discovery 25 years ago should accelerate progress toward further elucidation of their mechanisms of action in health and disease. This in turn will greatly improve diagnosis and care for the millions of individuals affected by congenital and acquired cardiac disease worldwide.

Synthesis, Identification, and Structure-Activity Relationship Analysis of GATA4 and NKX2-5 Protein-Protein Interaction Modulators

Transcription factors GATA4 and NKX2-5 directly interact and synergistically activate several cardiac genes and stretch-induced cardiomyocyte hypertrophy. Previously, we identified phenylisoxazole carboxamide 1 as a hit compound, which inhibited the GATA4–NKX2-5 transcriptional synergy. Here, the chemical space around the molecular structure of 1 was explored by synthesizing and characterizing 220 derivatives and structurally related compounds. In addition to the synergistic transcriptional activation, selected compounds were evaluated for their effects on transcriptional activities of GATA4 and NKX2-5 individually as well as potential cytotoxicity. The structure–activity relationship (SAR) analysis revealed that the aromatic isoxazole substituent in the southern part regulates the inhibition of GATA4–NKX2-5 transcriptional synergy. Moreover, inhibition of GATA4 transcriptional activity correlated with the reduced cell viability. In summary, comprehensive SAR analysis accompanied by data analysis successfully identified potent and selective inhibitors of GATA4–NKX2-5 transcriptional synergy and revealed structural features important for it.

Death receptor 5 contributes to cardiomyocyte hypertrophy through epidermal growth factor receptor transactivation

Cardiomyocyte survival and death contributes to many cardiac diseases. A common mechanism of cardiomyocyte death is through apoptosis however, numerous death receptors (DR) have been virtually unstudied in the context of cardiovascular disease. Previous studies have identified TNF-related apoptosis inducing ligand (TRAIL) and its receptor, DR5, as being altered in a chronic catecholamine administration model of heart failure, and suggest a role of non-canonical signaling in cardiomyocytes. Furthermore, multiple clinical studies have identified TRAIL or DR5 as biomarkers in the prediction of severity and mortality following myocardial infarction and in heart failure development risk suggesting a role of DR5 signaling in the heart. While TRAIL/DR5 have been extensively studied as a potential cancer therapeutic due to their ability to selectively activate apoptosis in cancer cells, TRAIL and DR5 are highly expressed in the heart where their function is uncharacterized. However, many non-transformed cell types are resistant to TRAIL-induced apoptosis suggesting non-canonical functions in non-cancerous cell types. Our goal was to determine the role of DR5 in the heart with the hypothesis that DR5 does not induce cardiomyocyte apoptosis but initiates non-canonical signaling to promote cardiomyocyte growth and survival. Histological analysis of hearts from mice treated with a DR5 agonists showed increased hypertrophy with no differences in cardiomyocyte death, fibrosis or function. Mechanistic studies in the heart and isolated cardiomyocytes identified ERK1/2 activation with DR5 agonist treatment which contributed to hypertrophy. Furthermore, epidermal growth factor receptor (EGFR) was activated following DR5 agonist treatment through activation of MMP and HB-EGFR cleavage and specific inhibitors of MMP and EGFR prevented DR5-mediated ERK1/2 signaling and hypertrophy. Taken together, these studies identify a previously unidentified role for DR5 in the heart, which does not promote apoptosis but acts through non-canonical MMP-EGFR-ERK1/2 signaling mechanisms to contribute to cardiomyocyte hypertrophy.

Identification of differentially expressed genes and preliminary validations in cardiac pathological remodeling induced by transverse aortic constriction

Cardiac remodeling predisposes to heart failure if the burden is unresolved, and heart failure is an important cause of mortality in humans. The aim of the present study was to identify the key genes involved in cardiac pathological remodeling induced by pressure overload. Gene expression profiles of the GSE5500, GSE18224, GSE36074 and GSE56348 datasets were downloaded from the Gene Expression Omnibus database. Differentially expressed genes (DEGs), defined as |log2FC|>1 (FC, fold change) and an adjusted P‑value of <0.05, were screened using the R software with the limma package. Gene ontology enrichment analysis was performed and a protein‑protein interaction (PPI) network of the DEGs was constructed. A cardiac remodeling model induced by transverse aortic constriction (TAC) was established. Furthermore, consistent DEGs were further validated using reverse transcription‑quantitative polymerase chain reaction (RT‑PCR) analysis, western blotting and immunohistochemistry in the ventricular tissue samples after TAC or sham operation. A total of 24 common DEGs were identified (23 significantly upregulated and 1 downregulated), of which 9 genes had been previously confirmed to be directly involved in cardiac remodeling. Hence, the level of expression of the other 15 genes was detected in subsequent studies via RT‑PCR. Based on the results of the PPI network analysis and RT‑PCR, we further detected the protein levels of Itgbl1 and Asporin, which were consistent with the results of bioinformatics analysis and RT‑PCR. The expression of Itgbl1, Aspn, Fstl1, Mfap5, Col8a1, Ltbp2, Mfap4, Pamr1, Cnksr1, Aqp8, Meox1, Gdf15 and Srpx was found to be upregulated in a mouse model of cardiac remodeling, while that of Retnla was downregulated. Therefore, the present study identified the key genes implicated in cardiac remodeling, aiming to provide new insight into the underlying mechanism.

A context-specific cardiac β-catenin and GATA4 interaction influences TCF7L2 occupancy and remodels chromatin driving disease progression in the adult heart

Chromatin remodelling precedes transcriptional and structural changes in heart failure. A body of work suggests roles for the developmental Wnt signalling pathway in cardiac remodelling. Hitherto, there is no evidence supporting a direct role of Wnt nuclear components in regulating chromatin landscapes in this process. We show that transcriptionally active, nuclear, phosphorylated(p)Ser675-β-catenin and TCF7L2 are upregulated in diseased murine and human cardiac ventricles. We report that inducible cardiomyocytes (CM)-specific pSer675-β-catenin accumulation mimics the disease situation by triggering TCF7L2 expression. This enhances active chromatin, characterized by increased H3K27ac and TCF7L2 occupancies to cardiac developmental and remodelling genes in vivo. Accordingly, transcriptomic analysis of β-catenin stabilized hearts shows a strong recapitulation of cardiac developmental processes like cell cycling and cytoskeletal remodelling. Mechanistically, TCF7L2 co-occupies distal genomic regions with cardiac transcription factors NKX2–5 and GATA4 in stabilized-β-catenin hearts. Validation assays revealed a previously unrecognized function of GATA4 as a cardiac repressor of the TCF7L2/β-catenin complex in vivo, thereby defining a transcriptional switch controlling disease progression. Conversely, preventing β-catenin activation post-pressure-overload results in a downregulation of these novel TCF7L2-targets and rescues cardiac function. Thus, we present a novel role for TCF7L2/β-catenin in CMs-specific chromatin modulation, which could be exploited for manipulating the ubiquitous Wnt pathway.

Induction of cardiomyocyte proliferation and angiogenesis protects neonatal mice from pressure overload-associated maladaptation

Cardiac pressure overload (for example due to aortic stenosis) induces irreversible myocardial dysfunction, cardiomyocyte hypertrophy and interstitial fibrosis in patients. In contrast to adult, neonatal mice can efficiently regenerate the heart after injury in the first week after birth. To decipher whether insufficient cardiac regeneration contributes to the progression of pressure overload dependent disease, we established a transverse aortic constriction protocol in neonatal mice (nTAC). nTAC in the non-regenerative stage (at postnatal day P7) induced cardiac dysfunction, myocardial fibrosis and cardiomyocyte hypertrophy. In contrast, nTAC in the regenerative stage (at P1) largely prevented these maladaptive responses and was in particular associated with enhanced myocardial angiogenesis and increased cardiomyocyte proliferation, which both supported adaptation during nTAC. A comparative transcriptomic analysis between hearts after regenerative versus non-regenerative nTAC suggested the transcription factor GATA4 as master regulator of the regenerative gene-program. Indeed, cardiomyocyte specific deletion of GATA4 converted the regenerative nTAC into a non-regenerative, maladaptive response. Our new nTAC model can be used to identify mediators of adaptation during pressure overload and to discover novel potential therapeutic strategies.

Developmental origins for semilunar valve stenosis identified in mice harboring congenital heart disease-associated GATA4 mutation

Congenital heart defects affect ∼2% of live births and often involve malformations of the semilunar (aortic and pulmonic) valves. We previously reported a highly penetrant GATA4 p.Gly296Ser mutation in familial, congenital atrial septal defects and pulmonic valve stenosis and showed that mice harboring the orthologous G295S disease-causing mutation display not only atrial septal defects, but also semilunar valve stenosis. Here, we aimed to characterize the role of Gata4 in semilunar valve development and stenosis using the Gata4^G295Ski/wt mouse model. GATA4 is highly expressed in developing valve endothelial and interstitial cells. Echocardiographic examination of Gata4^G295Ski/wt mice at 2 months and 1 year of age identified functional semilunar valve stenosis predominantly affecting the aortic valve with distal leaflet thickening and severe extracellular matrix (ECM) disorganization. Examination of the aortic valve at earlier postnatal timepoints demonstrated similar ECM abnormalities consistent with congenital disease. Analysis at embryonic timepoints showed a reduction in aortic valve cushion volume at embryonic day (E)13.5, predominantly affecting the non-coronary cusp (NCC). Although total cusp volume recovered by E15.5, the NCC cusp remained statistically smaller. As endothelial to mesenchymal transition (EMT)-derived cells contribute significantly to the NCC, we performed proximal outflow tract cushion explant assays and found EMT deficits in Gata4^G295Ski/wt embryos along with deficits in cell proliferation. RNA-seq analysis of E15.5 outflow tracts of mutant embryos suggested a disease state and identified changes in genes involved in ECM and cell migration as well as dysregulation of Wnt signaling. By utilizing a mouse model harboring a human disease-causing mutation, we demonstrate a novel role for GATA4 in congenital semilunar valve stenosis.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: Cellular and molecular characterization of a mutant mouse, harboring a human disease-causing GATA4 variant, identifies cellular deficits in endothelial-to-mesenchymal transition and proliferation that cause abnormal valve remodeling and resultant stenosis.

Copy number variations in individuals with conotruncal heart defects reveal some shared developmental pathways irrespective of 22q11.2 deletion status

Over 50% of patients with 22q11.2 deletion syndrome (DS) have a conotruncal or related cardiac defect (CTRD). We hypothesized that similar genetic variants, developmental pathways and biological functions, contribute to disease risk for CTRD in patients without a 22q11.2 deletion (ND-CTRD) and with a 22q11.2 deletion (DS-CTRD). To test this hypothesis, we performed rare CNV (rCNV)-based analyses on 630 ND-CTRD cases and 602 DS-CTRD cases with comparable cardiac lesions separately and jointly. First, we detected a collection of heart development related pathways from Gene Ontology and Mammalian Phenotype Ontology analysis. We then constructed gene regulation networks using unique genes collected from the rCNVs found in the ND-CTRD and DS-CTRD cohorts. These gene networks were clustered and their predicted functions were examined. We further investigated expression patterns of those unique genes using publicly available mouse embryo microarray expression data from single-cell embryos to fully developed hearts. By these bioinformatics approaches, we identified a commonly shared gene expression pattern in both the ND-CTRD and DS-CTRD cohorts. Computational analysis of gene functions characterized with this expression pattern revealed a collection of significantly enriched terms related to cardiovascular development. By our combined analysis of rCNVs in the ND-CTRD and DS-CTRD cohorts, a group of statistically significant shared pathways, biological functions, and gene expression patterns were identified that can be tested in future studies for their biological relevance.

Synergistic cardiac pathological hypertrophy induced by high-salt diet in IGF-IIRα cardiac-specific transgenic rats

Stress-induced cardiac hypertrophy leads to heart failure. Our previous studies demonstrate that insulin-like growth factor-II receptor (IGF-IIR) signaling is pivotal to hypertrophy regulation. In this study, we show a novel IGF-IIR alternative spliced transcript, IGF-IIRα (150 kDa) play a key role in high-salt induced hypertrophy mechanisms. Cardiac overexpression of IGF-IIRα and high-salt diet influenced cardiac dysfunction by increasing pathophysiological changes with up-regulation of hypertrophy markers, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). We found that, cardiac hypertrophy under high-salt conditions were amplified in the presence of IGF-IIRα overexpression. Importantly, high-salt induced angiotensin II type I receptor (AT1R) up regulation mediated IGF-IIR expressions via upstream mitogen activated protein kinase (MAPK)/silent mating type information regulation 2 homolog 1 (SIRT1)/heat shock factor 1 (HSF1) pathway. Further, G-coupled receptors (Gαq) activated calcineurin/nuclear factor of activated T-cells, cytoplasmic 3 (NFATc3)/protein kinase C (PKC) signaling was significantly up regulated under high-salt conditions. All these effects were observed to be dramatically over-regulated in IGF-IIRα transgenic rats fed with a high-salt diet. Altogether, from the findings, we demonstrate that IGF-IIRα plays a crucial role during high-salt conditions leading to synergistic cardiac hypertrophy.

Gata4 regulates hedgehog signaling and Gata6 expression for outflow tract development

Dominant mutations of Gata4, an essential cardiogenic transcription factor (TF), were known to cause outflow tract (OFT) defects in both human and mouse, but the underlying molecular mechanism was not clear. In this study, Gata4 haploinsufficiency in mice was found to result in OFT defects including double outlet right ventricle (DORV) and ventricular septum defects (VSDs). Gata4 was shown to be required for Hedgehog (Hh)-receiving progenitors within the second heart field (SHF) for normal OFT alignment. Restored cell proliferation in the SHF by knocking-down Pten failed to rescue OFT defects, suggesting that additional cell events under Gata4 regulation is important. SHF Hh-receiving cells failed to migrate properly into the proximal OFT cushion, which is associated with abnormal EMT and cell proliferation in Gata4 haploinsufficiency. The genetic interaction of Hh signaling and Gata4 is further demonstrated to be important for OFT development. Gata4 and Smo double heterozygotes displayed more severe OFT abnormalities including persistent truncus arteriosus (PTA). Restoration of Hedgehog signaling renormalized SHF cell proliferation and migration, and rescued OFT defects in Gata4 haploinsufficiency. In addition, there was enhanced Gata6 expression in the SHF of the Gata4 heterozygotes. The Gata4-responsive repressive sites were identified within 1kbp upstream of the transcription start site of Gata6 by both ChIP-qPCR and luciferase reporter assay. These results suggested a SHF regulatory network comprising of Gata4, Gata6 and Hh-signaling for OFT development.

Gata4 is an important transcription factor that regulates the development of the heart. Human possessing a single copy of Gata4 mutation display congenital heart defects (CHD), including double outlet right ventricle (DORV). DORV is an alignment problem in which both the Aorta and Pulmonary Artery originate from the right ventricle, instead of originating from the left and the right ventricles, respectively. In this study, a Gata4 mutant mouse model was used to study how Gata4 mutations cause DORV. We showed that Gata4 is required in the cardiac precursor cells for the normal alignment of the great arteries. Although Gata4 mutations inhibit the rapid increase in the cardiac precursor cell numbers, resolving this problem does not recover the normal alignment of the great arteries. It indicates that there is a migratory issue of the cardiac precursor cells as they navigate to the great arteries during development. The study further showed that a specific molecular signaling, Hh-signaling and Gata6 are responsible to the Gata4 action in the cardiac precursor cells. Importantly, over-activation of the Hh-signaling pathways rescues the DORV in the Gata4 mutant embryos. This study provides a molecular model to explain the ontogeny of a subtype of CHD.

GATA4 screening in Iranian patients of various ethnicities affected with congenital heart disease: Co-occurrence of a novel de novo translocation (5;7) and a likely pathogenic heterozygous GATA4 mutation in a family with autosomal dominant congenital heart disease

BACKGROUND

Congenital heart disease (CHD) is the most common birth defect and a major health problem around the world. However, its exact etiology has remained unclear. Among various genetic contributing factors, GATA4 transcription factor plays a significant role in the CHD pathogenesis. In this study, GATA4 coding sequence was screened in Iranian patients of various ethnicities.

METHODS

Sixty six individuals with familial CHD referred to our center were recruited in this study. After receiving written informed consent from each individual or their parents, chromosomal analyses and GATA4 variant screening were performed. Pathogenicity of the suspected variants was evaluated using available online software tools: CADD, Mutation Taster, SIFT, and PolyPhen-2.

RESULTS

A total of twelve GATA4 variants were detected including five intronic, 2 exonic and 3 polymorphisms as well as 2 missense mutations, the c.1220C>A and c.1309G>A. Unlike the c.1220C>A, the likely pathogenic heterozygous c.1309G>A has not been previously associated with any phenotype. Here, we not only report, for the first time, a c.1309G>A-related CHD, but also report a novel de novo balanced translocation, 46,XY,t(5;7)(qter13;qter11), in the same patient which may have influenced the disease severity.

CONCLUSION

From screening GATA4 sequence in 66 Iranian patients of various ethnicities, we conclude that cytogenetic analysis and PCR-direct sequencing of different candidate genes may not be the best approach for genetic diagnosis in CHD. Applying novel approaches such as next-generation sequencing (NGS) may provide a better understating of genetic contributing factors in CHD patients for whom conventional methods could not reveal any genetic causative factor.

Sirtuin 6 mediated stem cell cardiomyogenesis on protein coated nanofibrous scaffolds

The cellular niche provides combination of biomolecular and biophysical cues to control stem cell fate. Three-dimensional (3D) aligned nanofibrous scaffolds can effectively augment stem cell cardiomyogenesis. This work aims to understand the role of biomolecular signals from extracellular matrix (ECM) proteins and leverage them to further promote cardiomyogenesis on nanofibrous scaffolds. Human mesenchymal stem cells (hMSCs) were cultured on 3D aligned polycaprolactone scaffolds coated with different ECM proteins. Among multiple coatings tested, collagen coated fibers were most effective in promoting cardiomyogenesis as determined from increased expression of cardiac biomarkers and intracellular calcium flux. At molecular level, enhanced differentiation on collagen coated fibers was associated with an increased level of sirtuin 6 (SIRT6). Depletion of SIRT6 using siRNA attenuated the differentiation process through activation of Wnt signaling pathway. This study, thus, demonstrates that protein coated scaffolds can augment cardiomyogenic differentiation of stem cells through a combination of topographical and biomolecular signals.

Molecular switch model for cardiomyocyte proliferation

This review deals with the human adult cardiomyocyte proliferation as a potential source for heart repair after injury. The mechanism to regain the proliferative capacity of adult cardiomyocytes is a challenge. However, recent studies are promising in showing that the ‘locked’ cell cycle of adult cardiomyocytes could be released through modulation of cell cycle checkpoints. In support of this are the signaling pathways of Notch, Hippo, Wnt, Akt and Jak/Stat that facilitate or inhibit the transition at cell cycle checkpoints. Cyclins and cyclin dependant kinases (CDKs) facilitate this transition which in turn is regulated by inhibitory action of pocket protein e.g. p21, p27 and p57. Transcription factors e.g. E2F, GATA4, TBx20 up regulate Cyclin A, A2, D, E, and CDK4 as promoters of cell cycle and Meis-1 and HIF-1 alpha down regulate cyclin D and E to inhibit the cell cycle. Paracrine factors like Neuregulin-1, IGF-1 and Oncostatin M and Extracellular Matrix proteins like Agrin have been involved in cardiomyocyte proliferation and dedifferentiation processes.

A molecular switch model is proposed that transforms the post mitotic cell into an actively dividing cell. This model shows how the cell cycle is regulated through on- and off switch mechanisms through interaction of transcription factors and signaling pathways with proteins of the cell cycle checkpoints. Signals triggered by injury may activate the right combination of the various pathways that can ‘switch on’ the proliferation signals leading to myocardial regeneration.