Bone morphogenetic proteins induce cardiomyocyte differentiation through the mitogen-activated protein kinase kinase kinase TAK1 and cardiac transcription factors Csx/Nkx-2.5 and GATA-4

A biodegradable, microstructured, electroconductive and nano-integrated drug eluting patch (MENDEP) for myocardial tissue engineering

We produced a microstructured, electroconductive and nano-functionalized drug eluting cardiac patch (MENDEP) designed to attract endogenous precursor cells, favor their differentiation and counteract adverse ventricular remodeling in situ. MENDEP showed mechanical anisotropy and biaxial strength comparable to porcine myocardium, reduced impedance, controlled biodegradability, molecular recognition ability and controlled drug release activity. In vitro, cytocompatibility and cardioinductivity were demonstrated. Migration tests showed the chemoattractive capacity of the patches and conductivity assays showed unaltered cell-cell interactions and cell beating synchronicity. MENDEP was then epicardially implanted in a rat model of ischemia/reperfusion (I/R). Histological, immunofluorescence and biomarker analysis indicated that implantation did not cause damage to the healthy myocardium. After I/R, MENDEP recruited precursor cells into the damaged myocardium and triggered their differentiation towards the vascular lineage. Under the patch, the myocardial tissue appeared well preserved and cardiac gap junctions were correctly distributed at the level of the intercalated discs. The fibrotic area measured in the I/R group was partially reduced in the patch group. Overall, these results demonstrate that MENDEP was fully retained on the epicardial surface of the left ventricle over 4-week implantation period, underwent progressive vascularization, did not perturb the healthy myocardium and showed great potential in repairing the infarcted area.

Oxidative-stress induced Bmp2-Smad1/5/8 signaling dependent differentiation of early cardiomyocytes from embryonic and adult epicardial cells

Heart failure has become a major life-threatening cause affecting millions globally, characterized by the permanent loss of adult functional cardiomyocytes leading to fibrosis which ultimately deprives the heart of its functional efficacy. Here we investigated the reparative property of embryonic and adult epicardial cells towards cardiomyocyte differentiation under oxidative stress-induced conditions along with the identification of a possible molecular signaling pathway. Isolated epicardial cells from embryonic chick hearts subjected to oxidative stress and hypoxia induction. Initial assessment of successful injury induction reveals hypertrophy of isolated epicardial cells. Detailed marker gene expression analyses and inhibitor studies reveal Bone morphogenic protein (Bmp)2-Smad1/5/8 signaling dependent cardiomyocyte lineage specification via epithelial to mesenchymal transition (EMT) post-injury. EMT is further confirmed by increased proliferation, migration, and differentiation towards cardiomyocyte lineage. We have also established an in-vivo model in adult male rats using Isoproterenol. Successful oxidative stress-mediated injury induction in adult heart was marked by increased activated fibroblasts followed by apoptosis of adult cardiomyocytes. The detailed characterization of adult epicardial cells reveals similar findings to our avian in-vitro data. Both in-vitro and in-vivo results show a significant increase in the expression of cardiomyocyte specific markers indicative of lineage specificity and activation of epicardial cells post oxidative stress mediated injury. Our findings suggest an EMT-induced reactivation of epicardial cells and early cardiomyocyte lineage specification following oxidative stress in a Bmp2- Smad1/5/8 dependent manner. Overall, this regulatory mechanism of cardiomyocyte differentiation induced by oxidative stress may contribute to the field of cardiac repair and regenerative therapeutics.

Human pluripotent stem cell-based models of heart development and disease

The heart is a complex organ composed of distinct cell types, such as cardiomyocytes, cardiac fibroblasts, endothelial cells, smooth muscle cells, neuronal cells and immune cells. All these cell types contribute to the structural, electrical and mechanical properties of the heart. Genetic manipulation and lineage tracing studies in mice have been instrumental in gaining critical insights into the networks regulating cardiac cell lineage specification, cell fate and plasticity. Such knowledge has been of fundamental importance for the development of efficient protocols for the directed differentiation of pluripotent stem cells (PSCs) in highly specialized cardiac cell types. In this review, we summarize the evolution and current advances in protocols for cardiac subtype specification, maturation, and assembly in cardiac microtissues and organoids.

Induction of Senescence by Loss of Gata4 in Cardiac Fibroblasts

Cardiac fibroblasts are a major source of cardiac fibrosis during heart repair processes in various heart diseases. Although it has been shown that cardiac fibroblasts become senescent in response to heart injury, it is unknown how the senescence of cardiac fibroblasts is regulated in vivo. Gata4, a cardiogenic transcription factor essential for heart development, is also expressed in cardiac fibroblasts. However, it remains elusive about the role of Gata4 in cardiac fibroblasts. To define the role of Gata4 in cardiac fibroblasts, we generated cardiac fibroblast-specific Gata4 knockout mice by cross-breeding Tcf21-MerCreMer mice with Gata4fl/fl mice. Using this mouse model, we could genetically ablate Gata4 in Tcf21 positive cardiac fibroblasts in an inducible manner upon tamoxifen administration. We found that cardiac fibroblast-specific deletion of Gata4 spontaneously induces senescence in cardiac fibroblasts in vivo and in vitro. We also found that Gata4 expression in both cardiomyocytes and non-myocytes significantly decreases in the aged heart. Interestingly, when αMHC-MerCreMer mice were bred with Gata4fl/fl mice to generate cardiomyocyte-specific Gata4 knockout mice, no senescent cells were detected in the hearts. Taken together, our results demonstrate that Gata4 deficiency in cardiac fibroblasts activates a program of cellular senescence, suggesting a novel molecular mechanism of cardiac fibroblast senescence.

Heart Failure Pathogenesis Elucidation and New Treatment Method Development

Heart failure (HF) is a leading cause of death worldwide. In Japan, the number of HF patients has increased with its aging population, resulting in "HF pandemic." HF is the final stage of various cardiovascular diseases, including valvular heart disease, ischemic heart disease, atrial fibrillation, and hypertension. Cardiac hypertrophy is a compensatory response to increased workload and maintains cardiac function. Pressure overload due to mechanical stress causes cardiac hypertrophy, whereas continuous cardiac stress reduces wall thickness and consequently causes HF. Understanding the molecular mechanisms underlying this process is crucial to elucidate HF pathophysiology. We demonstrated that ischemia and DNA damage are important in the progression of hypertrophy to HF. Genetic mutations associated with cardiomyopathy and prognosis has been identified. To realize precision medicines for HF, the underlying molecular mechanisms need to be elucidated. In this review, we introduce new paradigms for understanding HF pathophysiology discovered through basic research.

Mechanisms of Regenerative Potential Activation in Cardiac Mesenchymal Cells

Recovery of the contractile function of the heart and the regeneration of the myocardium after ischemic injury are contemporary issues in regenerative medicine and cell biology. This study aimed to analyze early transcriptional events in cardiac tissue after infarction and to explore the cell population that can be isolated from myocardial tissue. We induced myocardial infarction in Wistar rats by permanent ligation of the left coronary artery and showed a change in the expression pattern of Notch-associated genes and Bmp2/Runx2 in post-MI tissues using RNA sequencing and RT-PCR. We obtained primary cardiac mesenchymal cell (CMC) cultures from postinfarction myocardium by enzymatic dissociation of tissues, which retained part of the activation stimulus and had a pronounced proliferative potential, assessed using a "xCELLigence" real-time system. Hypoxia in vitro also causes healthy CMCs to overexpress Notch-associated genes and Bmp2/Runx2. Exogenous activation of the Notch signaling pathway by lentiviral transduction of healthy CMCs resulted in a dose-dependent activation of the Runx2 transcription factor but did not affect the activity of the Bmp2 factor. Thus, the results of this study showed that acute hypoxic stress could cause short-term activation of the embryonic signaling pathways Notch and Bmp in CMCs, and this interaction is closely related to the processes of early myocardial remodeling after a heart attack. The ability to correctly modulate and control the corresponding signals in the heart can help increase the regenerative capacity of the myocardium before the formation of fibrotic conditions.

ASB2 is a novel E3 ligase of SMAD9 required for cardiogenesis

Cardiogenesis requires the orchestrated spatiotemporal tuning of BMP signalling upon the balance between induction and counter-acting suppression of the differentiation of the cardiac tissue. SMADs are key intracellular transducers and the selective degradation of SMADs by the ubiquitin-proteasome system is pivotal in the spatiotemporal tuning of BMP signalling. However, among three SMADs for BMP signalling, SMAD1/5/9, only the specific E3 ligase of SMAD9 remains poorly investigated. Here, we report for the first time that SMAD9, but not the other SMADs, is ubiquitylated by the E3 ligase ASB2 and targeted for proteasomal degradation. ASB2, as well as Smad9, is conserved among vertebrates. ASB2 expression was specific to the cardiac region from the very early stage of cardiac differentiation in embryogenesis of mouse. Knockdown of Asb2 in zebrafish resulted in a thinned ventricular wall and dilated ventricle, which were rescued by simultaneous knockdown of Smad9. Abundant Smad9 protein leads to dysregulated cardiac differentiation through a mechanism involving Tbx2, and the BMP signal conducted by Smad9 was downregulated under quantitative suppression of Smad9 by Asb2. Our findings demonstrate that ASB2 is the E3 ligase of SMAD9 and plays a pivotal role in cardiogenesis through regulating BMP signalling.

The Functions of LncRNA H19 in the Heart

Cardiovascular diseases (CVDs) are major causes of morbidity and mortality worldwide. Great effort has been put into exploring early diagnostic biomarkers and innovative therapeutic strategies for preventing CVD progression over the last two decades. Long non-coding RNAs (lncRNAs) have been identified as novel regulators in cardiac development and cardiac pathogenesis. For example, lncRNA H19 (H19), also known as a fetal gene abundant in adult heart and skeletal muscles and evolutionarily conserved in humans and mice, has a regulatory role in aortic aneurysm, myocardial hypertrophy, extracellular matrix reconstitution, and coronary artery diseases. Yet, the exact function of H19 in the heart remains unknown. This review summarises the functions of H19 in the heart and discusses the challenges and possible strategies of H19 research for cardiovascular disease.

Bmp Signaling Regulates Hand1 in a Dose-Dependent Manner during Heart Development

The bone morphogenetic protein (Bmp) signaling pathway and the basic helix–loop–helix (bHLH) transcription factor Hand1 are known key regulators of cardiac development. In this study, we investigated the Bmp signaling regulation of Hand1 during cardiac outflow tract (OFT) development. In Bmp2 and Bmp4loss-of-function embryos with varying levels of Bmp in the heart, Hand1 is sensitively decreased in response to the dose of Bmp expression. In contrast, Hand1 in the heart is dramatically increased in Bmp4 gain-of-function embryos. We further identified and characterized the Bmp/Smad regulatory elements in Hand1. Combined transfection assays and chromatin immunoprecipitation (ChIP) experiments indicated that Hand1 is directly activated and bound by Smads. In addition, we found that upon the treatment of Bmp2 and Bmp4, P19 cells induced Hand1 expression and favored cardiac differentiation. Together, our data indicated that the Bmp signaling pathway directly regulates Hand1 expression in a dose-dependent manner during heart development.

Tissue engineering techniques for iPSC derived three-dimensional cardiac constructs

Recent developments in applied developmental physiology have provided well-defined methodologies for producing human stem cell derived cardiomyocytes. Cardiomyocytes produced in this way have become commonplace as cardiac physiology research models. This accessibility has also allowed for the development of tissue engineered human heart constructs for drug screening, surgical intervention, and investigating cardiac pathogenesis. However, cardiac tissue engineering is an interdisciplinary field that involves complex engineering and physiological concepts, which limits its accessibility. This review provides a readable, broad reaching, and thorough discussion of major factors to consider for the development of cardiovascular tissues from stem cell derived cardiomyocytes. This review will examine important considerations in undertaking a cardiovascular tissue engineering project, and will present, interpret, and summarize some of the recent advancements in this field. This includes reviewing different forms of tissue engineered constructs, a discussion on cardiomyocyte sources, and an in-depth discussion of the fabrication and maturation procedures for tissue engineered heart constructs.

Gene Therapy: Targeting Cardiomyocyte Proliferation to Repopulate the Ischemic Heart

ABSTRACT

Adult mammalian cardiomyocytes show scarce division ability, which makes the heart ineffective in replacing lost contractile cells after ischemic cardiomyopathy. In the past decades, there have been increasing efforts in the search for novel strategies to regenerate the injured myocardium. Among them, gene therapy is one of the most promising ones, based on recent and emerging studies that support the fact that functional cardiomyocyte regeneration can be accomplished by the stimulation and enhancement of the endogenous ability of these cells to achieve cell division. This capacity can be targeted by stimulating several molecules, such as cell cycle regulators, noncoding RNAs, transcription, and metabolic factors. Therefore, the proposed target, together with the selection of the vector used, administration route, and the experimental animal model used in the development of the therapy would determine the success in the clinical field.

A BMP4-p38 MAPK signaling axis controls ISL1 protein stability and activity during cardiogenesis

During development, cells respond rapidly to intra- and intercellular signals, which induce signaling cascades regulating the activity of transcription factors at the transcriptional and/or post-translational level. The transcription factor ISL1 plays a key role in second heart field development and cardiac differentiation, and its mRNA levels are tightly regulated during cardiogenesis. Here, we show that a BMP-p38 MAPK signaling axis controls ISL1 protein function at the post-translational level. BMP-mediated activation of p38 MAPK leads to ISL1 phosphorylation at S269 by p38, which prevents ISL1 degradation and ensures its transcriptional activity during cardiogenesis. Interfering with p38 MAPK signaling leads to the degradation of ISL1 by the proteasome, resulting in defects in cardiomyocyte differentiation and impaired zebrafish and mouse heart morphogenesis and function. Given the critical role of the tight control of ISL1 activity during cardiac lineage diversification, modulation of BMP4-p38 MAPK signaling could direct differentiation into specific cardiac cell subpopulations.

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ISL1 is phosphorylated by p38 MAPK at serine 269

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A BMP4-p38 MAPK signaling axis controls ISL1 protein stability

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Phosphorylation of ISL1 by p38 regulates its activity during cardiogenesis

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p38 Inhibition in vivo results in ISL1 degradation and second heart field defects

Induced Cardiomyocyte Proliferation: A Promising Approach to Cure Heart Failure

Unlike some lower vertebrates which can completely regenerate their heart, the human heart is a terminally differentiated organ. Cardiomyocytes lost during cardiac injury and heart failure cannot be replaced due to their limited proliferative capacity. Therefore, cardiac injury generally leads to progressive failure. Here, we summarize the latest progress in research on methods to induce cardiomyocyte cell cycle entry and heart repair through the alteration of cardiomyocyte plasticity, which is emerging as an effective strategy to compensate for the loss of functional cardiomyocytes and improve the impaired heart functions.

Precision medicine for heart failure based on molecular mechanisms: The 2019 ISHR Research Achievement Award Lecture

Heart failure is a leading cause of death, and the number of patients with heart failure continues to increase worldwide. To realize precision medicine for heart failure, its underlying molecular mechanisms must be elucidated. In this review summarizing the "The Research Achievement Award Lecture" of the 2019 XXIII ISHR World Congress held in Beijing, China, we would like to introduce our approaches for investigating the molecular mechanisms of cardiac hypertrophy, development, and failure, as well as discuss future perspectives.

Cardiac Development: A Glimpse on Its Translational Contributions

Cardiac development is a complex developmental process that is initiated soon after gastrulation, as two sets of precardiac mesodermal precursors are symmetrically located and subsequently fused at the embryonic midline forming the cardiac straight tube. Thereafter, the cardiac straight tube invariably bends to the right, configuring the first sign of morphological left–right asymmetry and soon thereafter the atrial and ventricular chambers are formed, expanded and progressively septated. As a consequence of all these morphogenetic processes, the fetal heart acquired a four-chambered structure having distinct inlet and outlet connections and a specialized conduction system capable of directing the electrical impulse within the fully formed heart. Over the last decades, our understanding of the morphogenetic, cellular, and molecular pathways involved in cardiac development has exponentially grown. Multiples aspects of the initial discoveries during heart formation has served as guiding tools to understand the etiology of cardiac congenital anomalies and adult cardiac pathology, as well as to enlighten novels approaches to heal the damaged heart. In this review we provide an overview of the complex cellular and molecular pathways driving heart morphogenesis and how those discoveries have provided new roads into the genetic, clinical and therapeutic management of the diseased hearts.

Mitogen-activated protein kinase p38 modulates pacemaker ion channels differentiation in P19-derived pluripotent cells

Signal regulators during early cardiogenetic differentiation for the cellular automaticity are largely unknown. Our investigations were designed to clarify the role of transcription factors and their modulators in P19-derived cardiomyocytes to the expression of cardiac pacemaker ion channels. Transcription factors Csx/Nkx2.5 and GATA4 but not MEF2C were markedly inhibited by p38 MAP kinase inhibition in a distinct manner; expression but not phosphorylation of GATA4 was reduced by inhibition of p38 MAP kinase actions. In the presence of an ERK1/2,5 inhibitor PD98059 or a JNK MAP kinase inhibitor SP600125, P19 cells successfully differentiated into cardiomyocytes displaying spontaneous beatings with expression of three types of pacemaker ion channels. We demonstrate that acquisition of cellular automaticity and the expression of pacemaker ion channels are regulated by the transcription factors, Csx/Nkx2.5 and GATA4, through intracellular signals including p38 MAP kinase in the process of P19-derived pluripotent cells differentiation into cardiomyocytes.

HYDIN loss-of-function inhibits GATA4 expression and enhances atrial septal defect risk

BACKGROUND

Mutations affecting cardiac structural genes can lead to congenital heart diseases (CHDs). Axonemal Central Pair Apparatus Protein (HYDIN) is a ciliary protein previously linked to congenital cardiomyopathy. However, the role of HYDIN in the aetiology of CHDs is thus far unknown. Herein, we explore the function of HYDIN in heart development and CHDs.

METHODS

The function of HYDIN in cardiac differentiation was assessed in vitro using HYDIN siRNAs, HYDIN overexpression, and HYDIN short hairpin RNA (shRNA)-GATA binding protein 4 (GATA4) cDNA rescue constructs in the human embryonic stem cell (hESC) line HES3. To assess Hydin's function in vivo, we generated shRNA-mediated Hydin knockdown transgenic mice. We characterized the functional mechanisms of the most common human HYDIN variant associated with atrial septal defect (ASD) risk (71098693 mutant, c.A2207C) in cardiac-differentiating HES3 cells.

RESULTS

HYDIN functions as a positive regulator of human cardiomyocyte differentiation and promotes expression of cardiac contractile genes in hESC cells. This is mediated through GATA4, a critical transcription factor in heart development. Cardiac-specific Hydin knockdown in vivo leads to Gata4 downregulation and enhanced atrial septal defect (ASD) risk in mice. The c.A2207C HYDIN mutation reduces GATA4 expression in hESC cells.

CONCLUSION

HYDIN loss-of-function inhibits GATA4 expression and enhances ASD risk. We also establish the regulation of a key transcription factor in heart development by a ciliary protein.

Negative chronotropic and inotropic effects of lubiprostone on iPS cell-derived cardiomyocytes via activation of CFTR

Background

Lubiprostone (LBP) is a novel chloride channel opener that has been reported to activate chloride channel protein 2 (ClC-2) and cystic fibrosis transmembrane conductance regulator (CFTR). LBP facilitates fluid secretion by activating CFTR in the intestine and is used as a drug for treating chronic constipation. While ClC-2 and CFTR expression has been confirmed in cardiomyocytes (CMs), the effect of LBP on CMs has not yet been investigated. Thus, the present study aimed to investigate the effect of LBP on CMs using mouse-induced pluripotent stem (iPS) cell-derived CMs (iPS-CMs).

Methods

We induced mouse iPS cells into CMs through embryoid body (EB) formation. We compared the differentiated cells to CMs isolated from adult and fetal mice using gene expression, spontaneous beating rate, and contraction ratio analyses.

Results

Gene expression analysis revealed that, in the iPS-CMs, the mRNA expression of the undifferentiated cell markers Rex1 and Nanog decreased, whereas the expression of the unique cardiomyocyte markers cardiac troponin I (cTnI) and cardiac troponin T (cTNT), increased. Immunostaining showed that the localization of cTnI and connexin-43 in the iPS-CMs was similar to that in the primary fetal CMs (FCMs) and adult CMs (ACMs). LBP decreased the spontaneous beating rate of the iPS-CMs and FCMs, and decreased the contraction ratio of the iPS-CMs and ACMs. The reduction in the beating rate and contraction ratio caused by LBP was inhibited by glycine hydrazide (GlyH), which is a CFTR inhibitor.

Conclusion

These results suggest that LBP stimulates CFTR in CMs and that LBP has negative chronotropic and inotropic effects on CMs. LBP may be useful for treating cardiac diseases such as heart failure, ischemia, and arrhythmia.

Cardiac specific transcription factor Csx/Nkx2.5 regulates transient-outward K+ channel expression in pluripotent P19 cell-derived cardiomyocytes

The homeobox-containing gene Csx/Nkx2.5 codes several cardiac transcription factors and plays a critical role in early cardiogenesis. We investigated the effect of Csx/Nkx2.5 on the expression of cardiac ion channels using P19-derived cardiomyocytes. P19CL6 cells and P19CL6 cells with Csx/Nkx2.5 overexpression (P19CL6-Csx cells) were induced to differentiate into cardiomyocytes by treatment with dimethyl sulfoxide. Action potentials and membrane currents were measured by whole cell patch clamp at different differentiation stage: the early stage (1-5 days after beating had begun) and the late stage (10-15 days after beating). Expression of Csx/Nkx2.5 mRNA was increased as the differentiation stages advanced in both P19CL6 and P19CL6-Csx cells. In action potential configuration, maximal diastolic potentials in P19CL6-Csx cells exhibited more hyperpolarized potential (‒ 64.2 mV) than those in P19CL6 cells (‒ 54.8 mV, p < 0.01) in the early stage. In P19CL6 cells, among 6 different voltage-gated and ligand-operated K+ channels expressed during the early stage, the transient-outward K+ channel was most predominant. By overexpression of Csx/Nkx2.5, developmental decrease in the transient-outward K+ channel was suppressed. Homeobox-containing gene Csx/Nkx2.5 modifies the amount of distinct ionic channels, during differentiation periods, predominantly changing the expression of the transient-outward K+ channel.

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

TAK1/Map3k7 enhances differentiation of cardiogenic endoderm from mouse embryonic stem cells

Specification of the primary heart field in mouse embryos requires signaling from the anterior visceral endoderm (AVE). The nature of these signals is not known. We hypothesized that the TGFβ-activated kinase (TAK1/Map3k7) may act as a cardiogenic factor, based on its expression in heart-inducing endoderm and its requirement for cardiac differentiation of p19 cells. To test this, mouse embryonic stem (ES) cells overexpressing Map3k7 were isolated and differentiated as embryoid bodies (EBs). Map3k7-overexpressing EBs showed increased expression of AVE markers but interestingly, showed little effect on mesoderm formation and had no impact on overall cardiomyocyte formation. To test whether the pronounced expansion of endoderm masks an expansion of cardiac lineages, chimeric EBs were made consisting of Map3k7-overexpressing ES and wild type ES cells harboring a cardiac reporter transgene, MHCα::GFP, allowing cardiac differentiation to be assessed specifically in wild type ES cells. Wild type ES cells co-cultured with Map3k7-overexpressing cells had a 4-fold increase in expression of the cardiac reporter, supporting the hypothesis that Map3k7 increases the formation of cardiogenic endoderm. To further examine the role of Map3k7 in early lineage specification, other endodermal markers were examined. Interestingly, markers that are expressed in both the VE and later in gut development were expanded, whereas transcripts that specifically mark the early definitive (streak-derived) endoderm (DE) were not. To determine if Map3k7 is necessary for endoderm differentiation, EBs were grown in the presence of the Map3k7 specific inhibitor 5Z-7-oxozeaenol. Endoderm differentiation was dramatically decreased in these cells. Western blot analysis showed that known downstream targets of Map3k7 (Jnk, Nemo-like kinase (NLK) and p38 MAPK) were all inhibited. By contrast, transcripts for another TGFβ target, Sonic Hedgehog (Shh) were markedly upregulated, as were transcripts for Gli2 (but not Gli1 and Gli3). Together these data support the hypothesis that Map3k7 governs the formation, or proliferation of cardiogenic endoderm.

The Role of the TGF-β Superfamily in Myocardial Infarction

The members of the transforming growth factor β (TGF-β) superfamily are essential regulators of cell differentiation, phenotype and function, and have been implicated in the pathogenesis of many diseases. Myocardial infarction is associated with induction of several members of the superfamily, including TGF-β1, TGF-β2, TGF-β3, bone morphogenetic protein (BMP)-2, BMP-4, BMP-10, growth differentiation factor (GDF)-8, GDF-11 and activin A. This manuscript reviews our current knowledge on the patterns and mechanisms of regulation and activation of TGF-β superfamily members in the infarcted heart, and discusses their cellular actions and downstream signaling mechanisms. In the infarcted heart, TGF-β isoforms modulate cardiomyocyte survival and hypertrophic responses, critically regulate immune cell function, activate fibroblasts, and stimulate a matrix-preserving program. BMP subfamily members have been suggested to exert both pro- and anti-inflammatory actions and may regulate fibrosis. Members of the GDF subfamily may also modulate survival and hypertrophy of cardiomyocytes and regulate inflammation. Important actions of TGF-β superfamily members may be mediated through activation of Smad-dependent or non-Smad pathways. The critical role of TGF-β signaling cascades in cardiac repair, remodeling, fibrosis, and regeneration may suggest attractive therapeutic targets for myocardial infarction patients. However, the pleiotropic, cell-specific, and context-dependent actions of TGF-β superfamily members pose major challenges in therapeutic translation.

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.

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.

The E3 ubiquitin ligase SMURF1 regulates cell-fate specification and outflow tract septation during mammalian heart development

Smad ubiquitin regulatory factor 1 (SMURF1) is a HECT-type E3 ubiquitin ligase that plays a critical role in vertebrate development by regulating planar cell polarity (PCP) signaling and convergent extension (CE). Here we show that SMURF1 is involved in mammalian heart development. We find that SMURF1 is highly expressed in outflow tract cushion mesenchyme and Smurf1^−/− mouse embryos show delayed outflow tract septation. SMURF1 is expressed in smooth muscle cells of the coronary arteries and great vessels. Thickness of the aortic smooth muscle cell layer is reduced in Smurf1^−/− mouse embryos. We show that SMURF1 is a negative regulator of cardiomyogenesis and a positive regulator of smooth muscle cell and cardiac fibroblast differentiation, indicating that SMURF1 is important for cell-type specification during heart development. Finally, we provide evidence that SMURF1 localizes at the primary cilium where it may regulate bone morphogenetic protein (BMP) signaling, which controls the initial phase of cardiomyocyte differentiation. In summary, our results demonstrate that SMURF1 is a critical regulator of outflow tract septation and cell-type specification during heart development, and that these effects may in part be mediated via control of cilium-associated BMP signaling.

Stretchable Piezoelectric Substrate Providing Pulsatile Mechanoelectric Cues for Cardiomyogenic Differentiation of Mesenchymal Stem Cells

Ex vivo induction of cardiomyogenic differentiation of mesenchymal stem cells (MSCs) before implantation would potentiate therapeutic efficacy of stem cell therapies for ischemic heart diseases because MSCs rarely undergo cardiomyogenic differentiation following implantation. In cardiac microenvironments, electric pulse and cyclic mechanical strain are sequentially produced. However, no study has applied the pulsatile mechanoelectric cues (PMEC) to stimulate cardiomyogenic differentiation of MSCs ex vivo. In this study, we developed a stretchable piezoelectric substrate (SPS) that can provide PMEC to human MSCs (hMSCs) for cardiomyogenic differentiation ex vivo. Our data showed that hMSCs subjected to PMEC by SPS underwent promoted cardiac phenotype development: cell alignment and the expression of cardiac markers (i.e., cardiac transcription factors, structural proteins, ion channel proteins, and gap junction proteins). The enhanced cardiac phenotype development was mediated by the upregulation of cardiomyogenic differentiation-related autocrine factor expression, focal adhesion kinase, and extracellular signal-regulated kinases signaling pathways. Thus, SPS providing electrical and mechanical regulation of stem cells may be utilized to potentiate hMSC therapies for myocardial infarction and provide a tool for the study of stem cell biology.

Downregulation of long non-coding RNA H19 promotes P19CL6 cells proliferation and inhibits apoptosis during late-stage cardiac differentiation via miR-19b-modulated Sox6

Background

Regulating cardiac differentiation to maintain normal heart development and function is very important. At present, biological functions of H19 in cardiac differentiation is not completely clear.

Methods

To explore the functional effect of H19 during cardiac differentiation. Expression levels of early cardiac-specific markers Nkx-2.5 and GATA4, cardiac contractile protein genes α-MHC and MLC-2v were determined by qRT-PCR and western lot. The levels of lncRNA H19 and miR-19b were detected by qRT-PCR. We further predicted the binding sequence of H19 and miR-19b by online softwares starBase v2.0 and TargetScan. The biological functions of H19 and Sox6 were evaluated by CCK-8 kit, cell cycle and apoptosis assay and caspase-3 activity.

Results

The expression levels of α-MHC, MLC-2v and H19 were upregulated, and miR-19b was downregulated significantly in mouse P19CL6 cells at the late stage of cardiac differentiation. Biological function analysis showed that knockdown of H19 promoted cell proliferation and inhibits cell apoptosis. H19 suppressed miR-19b expression and miR-19b targeted Sox6, which inhibited cell proliferation and promoted apoptosis in P19CL6 cells during late-stage cardiac differentiation. Importantly, Sox6 overexpression could reverse the positive effects of H19 knockdown on P19CL6 cells.

Conclusion

Downregulation of H19 promoted cell proliferation and inhibited cell apoptosis during late-stage cardiac differentiation by regulating the negative role of miR-19b in Sox6 expression, which suggested that the manipulation of H19 expression could serve as a potential strategy for heart disease.

GATA4 regulates Fgf16 to promote heart repair after injury

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

Calreticulin secures calcium-dependent nuclear pore competency required for cardiogenesis

Calreticulin deficiency causes myocardial developmental defects that culminate in an embryonic lethal phenotype. Recent studies have linked loss of this calcium binding chaperone to failure in myofibrillogenesis through an as yet undefined mechanism. The purpose of the present study was to identify cellular processes corrupted by calreticulin deficiency that precipitate dysregulation of cardiac myofibrillogenesis related to acquisition of cardiac phenotype. In an embryonic stem cell knockout model, calreticulin deficit (crt(-/-)) compromised nucleocytoplasmic transport of nuclear localization signal-dependent and independent pathways, disrupting nuclear import of the cardiac transcription factor MEF2C. The expression of nucleoporins and associated nuclear transport proteins in derived crt(-/-) cardiomyocytes revealed an abnormal nuclear pore complex (NPC) configuration. Altered protein content in crt(-/-) cells resulted in remodeled NPC architecture that caused decreased pore diameter and diminished probability of central channel occupancy versus wild type counterparts. Ionophore treatment of impaired calcium handling in crt(-/-) cells corrected nuclear pore microarchitecture and rescued nuclear import resulting in normalized myofibrillogenesis. Thus, calreticulin deficiency alters nuclear pore function and structure, impeding myofibrillogenesis in nascent cardiomyocytes through a calcium dependent mechanism. This essential role of calreticulin in nucleocytoplasmic communication competency ties its regulatory action with proficiency of cardiac myofibrillogenesis essential for proper cardiac development.

Nuclear Receptor-Like Structure and Interaction of Congenital Heart Disease-Associated Factors GATA4 and NKX2-5

AIMS

Transcription factor GATA4 is a dosage sensitive regulator of heart development and alterations in its level or activity lead to congenital heart disease (CHD). GATA4 has also been implicated in cardiac regeneration and repair. GATA4 action involves combinatorial interaction with other cofactors such as NKX2-5, another critical cardiac regulator whose mutations also cause CHD. Despite its critical importance to the heart and its evolutionary conservation across species, the structural basis of the GATA4-NKX2-5 interaction remains incompletely understood.

METHODS AND RESULTS

A homology model was constructed and used to identify surface amino acids important for the interaction of GATA4 and NKX2-5. These residues were subjected to site-directed mutagenesis, and the mutant proteins were characterized for their ability to bind DNA and to physically and functionally interact with NKX2-5. The studies identify 5 highly conserved amino acids in the second zinc finger (N272, R283, Q274, K299) and its C-terminal extension (R319) that are critical for physical and functional interaction with the third alpha helix of NKX2-5 homeodomain. Integration of the experimental data with computational modeling suggests that the structural arrangement of the zinc finger-homeodomain resembles the architecture of the conserved DNA binding domain of nuclear receptors.

CONCLUSIONS

The results provide novel insight into the structural basis for protein-protein interactions between two important classes of transcription factors. The model proposed will help to elucidate the molecular basis for disease causing mutations in GATA4 and NKX2-5 and may be relevant to other members of the GATA and NK classes of transcription factors.

Dickkopf Wnt signaling pathway inhibitor 1 regulates the differentiation of mouse embryonic stem cells in vitro and in vivo

Embryonic stem cells (ESCs) are pluripotent stem cells derived from early stage embryos. It remains unclear whether inhibiting the Wnt/β‑catenin signaling pathway using dickkopf Wnt signaling pathway inhibitor 1 (DKK1) impacts on the differentiation potential of mouse ESCs in vitro and in vivo. In the present study, immunohistochemical staining was used to measure the expression of markers of the three germ layers in ESCs and teratomas derived from ESCs. The expression of markers for the Wnt/β‑catenin signaling pathway were detected by reverse transcription‑polymerase chain reaction (RT‑qPCR). Immunohistochemistry and western blotting indicated that the expression levels of octamer‑binding transcription factor 4 in the DKK1‑treated ESC group were significantly greater compared with the control ESCs. Reduced expression levels of NeuroD and bone morphogenetic protein 4 were observed in the DKK1‑treated ESCs and teratomas derived from DKK1‑treated ESCs compared with the control group. Increased expression levels of SOX17 were observed in the DKK1‑treated ESCs compared with the control group. RT‑qPCR indicated that β‑catenin expression was significantly reduced in DKK1‑treated ESCs and teratomas derived from DKK1‑treated ESCs compared with the control groups. Western blotting indicated no alterations in the expression of GSK‑3β, however, the levels of phosphorylated‑GSK‑3β were significantly greater in the DKK1 treatment groups, while cyclin D1 and c‑Myc expression levels were significantly reduced in the DKK1 treatment groups compared with the control groups. These results suggest that inhibiting Wnt signaling in ESCs using DKK1 may promote mouse ESCs to differentiate into endoderm in vitro and in vivo, and suppress the tumorigenicity of ESCs.

Arsenic trioxide alters the differentiation of mouse embryonic stem cell into cardiomyocytes

Chronic arsenic exposure is associated with increased morbidity and mortality for cardiovascular diseases. Arsenic increases myocardial infarction mortality in young adulthood, suggesting that exposure during foetal life correlates with cardiac alterations emerging later. Here, we investigated the mechanisms of arsenic trioxide (ATO) cardiomyocytes disruption during their differentiation from mouse embryonic stem cells. Throughout 15 days of differentiation in the presence of ATO (0.1, 0.5, 1.0 μM) we analysed: the expression of i) marker genes of mesoderm (day 4), myofibrillogenic commitment (day 7) and post-natal-like cardiomyocytes (day 15); ii) sarcomeric proteins and their organisation; iii) Connexin 43 and iv) the kinematics contractile properties of syncytia. The higher the dose used, the earlier the stage of differentiation affected (mesoderm commitment, 1.0 μM). At 0.5 or 1.0 μM the expression of cardiomyocyte marker genes is altered. Even at 0.1 μM, ATO leads to reduction and skewed ratio of sarcomeric proteins and to a rarefied distribution of Connexin 43 cardiac junctions. These alterations contribute to the dysruption of the sarcomere and syncytium organisation and to the impairment of kinematic parameters of cardiomyocyte function. This study contributes insights into the mechanistic comprehension of cardiac diseases caused by in utero arsenic exposure.

CARMEN, a human super enhancer-associated long noncoding RNA controlling cardiac specification, differentiation and homeostasis

Long noncoding RNAs (lncRNAs) are emerging as important regulators of developmental pathways. However, their roles in human cardiac precursor cell (CPC) remain unexplored. To characterize the long noncoding transcriptome during human CPC cardiac differentiation, we profiled the lncRNA transcriptome in CPCs isolated from the human fetal heart and identified 570 lncRNAs that were modulated during cardiac differentiation. Many of these were associated with active cardiac enhancer and super enhancers (SE) with their expression being correlated with proximal cardiac genes. One of the most upregulated lncRNAs was a SE-associated lncRNA that was named CARMEN, (CAR)diac (M)esoderm (E)nhancer-associated (N)oncoding RNA. CARMEN exhibits RNA-dependent enhancing activity and is upstream of the cardiac mesoderm-specifying gene regulatory network. Interestingly, CARMEN interacts with SUZ12 and EZH2, two components of the polycomb repressive complex 2 (PRC2). We demonstrate that CARMEN knockdown inhibits cardiac specification and differentiation in cardiac precursor cells independently of MIR-143 and -145 expression, two microRNAs located proximal to the enhancer sequences. Importantly, CARMEN expression was activated during pathological remodeling in the mouse and human hearts, and was necessary for maintaining cardiac identity in differentiated cardiomyocytes. This study demonstrates therefore that CARMEN is a crucial regulator of cardiac cell differentiation and homeostasis.

Signaling Pathways and Gene Regulatory Networks in Cardiomyocyte Differentiation

Strategies for harnessing stem cells as a source to treat cell loss in heart disease are the subject of intense research. Human pluripotent stem cells (hPSCs) can be expanded extensively in vitro and therefore can potentially provide sufficient quantities of patient-specific differentiated cardiomyocytes. Although multiple stimuli direct heart development, the differentiation process is driven in large part by signaling activity. The engineering of hPSCs to heart cell progeny has extensively relied on establishing proper combinations of soluble signals, which target genetic programs thereby inducing cardiomyocyte specification. Pertinent differentiation strategies have relied as a template on the development of embryonic heart in multiple model organisms. Here, information on the regulation of cardiomyocyte development from in vivo genetic and embryological studies is critically reviewed. A fresh interpretation is provided of in vivo and in vitro data on signaling pathways and gene regulatory networks (GRNs) underlying cardiopoiesis. The state-of-the-art understanding of signaling pathways and GRNs presented here can inform the design and optimization of methods for the engineering of tissues for heart therapies.

Effect of miR-20b on Apoptosis, Differentiation, the BMP Signaling Pathway and Mitochondrial Function in the P19 Cell Model of Cardiac Differentiation In Vitro

Objective

To explore the effect of miR-20b on apoptosis, differentiation, the BMP signaling pathway and mitochondrial function in the P19 cell model of cardiac differentiation in vitro.

Methods

A miR-20b over-expression vector, a miR-20b silencing vector and their corresponding empty vectors were constructed and transfected into P19 cells, separately. Stably miR-20b overexpressing and silenced P19 cell lines were successfully selected by blasticidin and puromycin, separately. The cells were induced to undergo apoptosis in FBS-free-α-MEM. The induced cells were examined by flow cytometry and measurement of their caspase-3 activities. Quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR) was used to evaluate the relative expression of marker genes of cardiomyocytes during differentiation, such as cTnT, GATA4 and ANP. QRT-PCR was also used to detect the mitochondrial DNA (mtDNA) copy number. We investigated the cellular ATP production using a luciferase-based luminescence assay. The reactive oxygen species (ROS) was determined by DCFDA (2’, 7’-Dichlorofluorescein diacetate) and the mitochondrial membrane potential (MMP) was elucidated by a JC-1 fluorescent probe, both using fluorescence microscopy and flow cytometer. The expression of BMP signaling pathway-related proteins were analyzed by Western blotting.

Results

Stably miR-20b overexpressing and silenced P19 cell lines were successfully obtained. MiR-20b overexpression increased apoptosis and promoted differentiation in P19 cells by promoting the activation of the BMP signaling pathway. In addition, miR-20b overexpression induced mitochondrial impairment in P19 cells during differentiation, which was characterized by lower MMP, raised ATP synthesis and increased ROS levels. The effects of miR-20b silencing were the exact opposite to those of overexpression.

Conclusion

Collectively, these results suggested that miR-20b was very important in apoptosis, differentiation and mitochondrial function of P19 cells. MiR-20b may represent a new therapeutic target for congenital heart diseases and provide new insights into the mechanisms of cardiac diseases.

Arsenic inhibits hedgehog signaling during P19 cell differentiation

Arsenic is a toxicant found in ground water around the world, and human exposure mainly comes from drinking water or from crops grown in areas containing arsenic in soils or water. Epidemiological studies have shown that arsenic exposure during development decreased intellectual function, reduced birth weight, and altered locomotor activity, while in vitro studies have shown that arsenite decreased muscle and neuronal cell differentiation. The sonic hedgehog (Shh) signaling pathway plays an important role during the differentiation of both neurons and skeletal muscle. The purpose of this study was to investigate whether arsenic can disrupt Shh signaling in P19 mouse embryonic stem cells, leading to changes muscle and neuronal cell differentiation. P19 embryonic stem cells were exposed to 0, 0.25, or 0.5 μM of sodium arsenite for up to 9 days during cell differentiation. We found that arsenite exposure significantly reduced transcript levels of genes in the Shh pathway in both a time and dose-dependent manner. This included the Shh ligand, which was decreased 2- to 3-fold, the Gli2 transcription factor, which was decreased 2- to 3-fold, and its downstream target gene Ascl1, which was decreased 5-fold. GLI2 protein levels and transcriptional activity were also reduced. However, arsenic did not alter GLI2 primary cilium accumulation or nuclear translocation. Moreover, additional extracellular SHH rescued the inhibitory effects of arsenic on cellular differentiation due to an increase in GLI binding activity. Taken together, we conclude that arsenic exposure affected Shh signaling, ultimately decreasing the expression of the Gli2 transcription factor. These results suggest a mechanism by which arsenic disrupts cell differentiation.

CstF-64 is necessary for endoderm differentiation resulting in cardiomyocyte defects

Although adult cardiomyocytes have the capacity for cellular regeneration, they are unable to fully repair severely injured hearts. The use of embryonic stem cell (ESC)-derived cardiomyocytes as transplantable heart muscle cells has been proposed as a solution, but is limited by the lack of understanding of the developmental pathways leading to specification of cardiac progenitors. Identification of these pathways will enhance the ability to differentiate cardiomyocytes into a clinical source of transplantable cells. Here, we show that the mRNA 3' end processing protein, CstF-64, is essential for cardiomyocyte differentiation in mouse ESCs. Loss of CstF-64 in mouse ESCs results in loss of differentiation potential toward the endodermal lineage. However, CstF-64 knockout (Cstf2(E6)) cells were able to differentiate into neuronal progenitors, demonstrating that some differentiation pathways were still intact. Markers for mesodermal differentiation were also present, although Cstf2(E6) cells were defective in forming beating cardiomyocytes and expressing cardiac specific markers. Since the extraembryonic endoderm is needed for cardiomyocyte differentiation and endodermal markers were decreased, we hypothesized that endodermal factors were required for efficient cardiomyocyte formation in the Cstf2(E6) cells. Using conditioned medium from the extraembryonic endodermal (XEN) stem cell line we were able to restore cardiomyocyte differentiation in Cstf2(E6) cells, suggesting that CstF-64 has a role in regulating endoderm differentiation that is necessary for cardiac specification and that extraembryonic endoderm signaling is essential for cardiomyocyte development.

NEXN inhibits GATA4 and leads to atrial septal defects in mice and humans

AIMS

Cardiac structural genes have been implicated as causative factors for congenital heart diseases (CHDs). NEXN is an F-actin binding protein and previously identified as a disease gene causing cardiomyopathies. Whether NEXN contributes to CHDs aetiologically remains unknown. Here, we explored the function of NEXN in cardiac development.

METHODS AND RESULTS

First, we determine the role of NEXN in cardiac differentiation using mouse P19cl6 in vitro model; we demonstrated that NEXN inhibited cardiac contractile markers, serving as a negative regulator. Interestingly, we found this effect was mediated by GATA4, a crucial transcription factor that controls cardiac development by knockdown, overexpression, and rescue experiment, respectively. We then generated transgenic mouse models and surprisingly, we discovered cardiac-selective expression of the NEXN gene caused atrial septal defects (ASDs). Next, to search for the mutations in NEXN gene in patients suffering from ASDs, we sequenced the exon and exon-intron joint regions of the NEXN gene in 150 probands with isolated ASDs and identified three mutations in the conserved region of NEXN (c.-52-78C>A, K199E, and L227S), which were not found in 500 healthy controls. Finally, we characterize the related mechanisms and found all mutations inhibited GATA4 expression.

CONCLUSION

We identify NEXN as a novel gene for ASD and its function to inhibit GATA4 established a critical regulation of an F-actin binding protein on a transcription factor in cardiac development.

Bone Morphogenetic Protein 9 and 13 Induce C3H10T1/2 Cell Differentiation to Cardiomyocyte-Like Cells In Vitro

The present study aimed to evaluate the effect of bone morphogenetic protein 9 (BMP9) and BMP13 on cardiac differentiation of C3H10T1/2 cells in vitro and to characterize the differentiated cells on their ultrastructure and transmembrane electrophysiological features. C3H10T1/2 cells were transfected with the vectors for BMP9 or BMP13 and differentiated into cardiomyocytes in vitro for up to 28 days. The expression of cardiac-specific genes Gata4 and Mef2c and proteins troponin T (cTnT) and connexin 43 (Cx43) was significantly increased in the cells transfected with BMP9 or BMP13 after differentiation over the controls as evaluated using quantitative RT-PCR, Western blotting, and immunofluorescence staining. Transmission electron microscopy and Masson trichrome staining showed that the specific myocardial leap dish and myofilament-like structure were present in the cells overexpressing BMP9 or BMP13, not in the control cells. Whole-cell patch-clamping study demonstrated the presence of delayed rectifier potassium current, inward rectifier potassium current, and T-type calcium current in the cells overexpressing BMP9 or BMP13. Sodium current was detected in a small number of cells overexpressing BMP9, not in the BMP13-transfected cells or the control cells. The expression of Mef2c gene and Cx43 and cTnT proteins was also significantly higher in the cells overexpressing BMP9 than those overexpressing BMP13. Our data indicate that BMP9 and BMP13 (BMP9 might be more effective) promoted the differentiation of C3H10T1/2 cells into cardiomyocyte-like cells with cellular ultrastructures and ion channel currents similar to mature cardiomyocytes in vitro.

SMAD-PI3K-Akt-mTOR pathway mediates BMP-7 polarization of monocytes into M2 macrophages

Previously we demonstrated that bone morphogenetic protein-7 (BMP-7) treatment polarizes monocytes into M2 macrophages and increases the expression of anti-inflammatory cytokines. Despite these findings, the mechanisms for the observed BMP-7 induced monocyte polarization into M2 macrophages are completely unknown. In this study, we demonstrate the mechanisms involved in the polarization of monocytes into M2 macrophages. Apoptotic conditioned media (ACM) was generated to mimic the stressed conditions, inducing monocyte polarization. Monocytes were treated with ACM along with BMP-7 and/or its inhibitor, follistatin, for 48 hours. Furthermore, an inhibitor of the PI3K pathway, LY-294002, was also studied. Our data show that BMP-7 induces polarization of monocytes into M2 macrophages while significantly increasing the expression of anti-inflammatory markers, arginase-1 and IL-10, and significantly (p<0.05) decreasing the expression of pro-inflammatory markers iNOS, IL-6, TNF-α and MCP-1; (p<0.05). Moreover, addition of the PI3K inhibitor, LY-294002, significantly (p<0.05) decreases upregulation of IL-10 and arginase-1, suggesting involvement of the PI3K pathway in M2 macrophage polarization. Next, following BMP-7 treatment, a significant (p<0.05) increase in p-SMAD1/5/8 and p-PI3K expression resulting in downstream activation of p-Akt and p-mTOR was observed. Furthermore, expression of p-PTEN, an inhibitor of the PI3K pathway, was significantly (p<0.05) increased in the ACM group. However, BMP-7 treatment inhibited its expression, suggesting involvement of the PI3K-Akt-mTOR pathway. In conclusion, we demonstrate that BMP-7 polarizes monocytes into M2 macrophages and enhances anti-inflammatory cytokine expression which is mediated by the activated SMAD-PI3K-Akt-mTOR pathway.

Combination of BMP-2 and 5-AZA is advantageous in rat bone marrow-derived mesenchymal stem cells differentiation into cardiomyocytes

Bone morphogenetic protein-2 (BMP-2) has a crucial role in the development of cardiogenesis, and is used in inducing bone marrow mesenchymal stem cells (BMMSCs) to differentiate into cardiomyocytes. We have examined a combination of BMP-2 and 5-azacytidine (5-AZA) in inducing these differentiation effects. BMMSCs were collected and purified from bone marrow of 4-week-old Sprague-Dawley (SD) rats by density-gradient centrifugation and differential attachment. The fourth passage subculture of BMMSCs, selected by cytometry for purity and identification, was divided into four groups: a control group, BMP-2 treated, 5-AZA treated, and a combination of BMP-2 and 5-AZA treatment. Expression of cardiac Troponin I (cTnI) and Connexin 43 (CX-43) in BMMSCs after induction were detected by immunofluorescence and Western blot. Flow cytometry analysis was used for differentiation rates and apoptosis of induced BMMSCs, through the expression of cardiac Troponin T (cTnT) and Annexin V-FITC & PI kit, respectively. BMP-2 can ameliorate apoptosis of BMMSCs caused by 5-AZA and promote the differentiation of BMMSCs into cardiomyocyte-like cells. Thus a combination of BMP-2 and 5-AZA can significantly improve the cardiac differentiation with fewer cell damage effects, making it a safe and effective method of induction in vitro.

Insulin induces proliferation and cardiac differentiation of P19CL6 cells in a dose-dependent manner

Insulin is a peptide hormone produced by beta cells of the pancreas. The roles of insulin in energy metabolism have been well studied, with most of the attention focused on glucose utilization, but the roles of insulin in cell proliferation and differentiation remain unclear. In this study, we observed for the first time that 10 nmol/L insulin treatment induces cell proliferation and cardiac differentiation of P19CL6 cells, whereas 50 and 100 nmol/L insulin treatment induces P19CL6 cell apoptosis and blocks cardiac differentiation of P19CL6 cells. By using real-time polymerase chain reaction (PCR) and Western blotting analysis, we found that the mRNA levels of cyclin D1 and α myosin heavy chain (α-MHC) are induced upon 10 nmol/L insulin stimulation and inhibited upon 50/100 nmol/L insulin treatment, whereas the mRNA levels of BCL-2-antagonist of cell death (BAD) exists a reverse trend. The similar results were observed in P19CL6 cells expressing GATA-6 or peroxisome proliferator-activated receptor α (PPARα). Our results identified the downstream targets of insulin, cyclin D1, BAD, α-MHC, and GATA-4, elucidate a novel molecular mechanism of insulin in promoting cell proliferation and differentiation.

Pitx2-mediated cardiac outflow tract remodeling

BACKGROUND

Heart morphogenesis involves sequential anatomical changes from a linear tube of a single channel peristaltic pump to a four-chamber structure with two channels controlled by one-way valves. The developing heart undergoes continuous remodeling, including septation.

RESULTS

Pitx2-null mice are characterized by cardiac septational defects of the atria, ventricles, and outflow tract. Pitx2-null mice also exhibited a short outflow tract, including unseptated conus and deformed endocardial cushions. Cushions were characterized with a jelly-like structure, rather than the distinct membrane-looking leaflets, indicating that endothelial mesenchymal transition was impaired in Pitx2(-/-) embryos. Mesoderm cells from the branchial arches and neural crest cells from the otic region contribute to the development of the endocardial cushions, and both were reduced in number. Members of the Fgf and Bmp families exhibited altered expression levels in the mutants.

CONCLUSIONS

We suggest that Pitx2 is involved in the cardiac outflow tract septation by promoting and/or maintaining the number and the remodeling process of the mesoderm progenitor cells. Pitx2 influences the expression of transcription factors and signaling molecules involved in the differentiation of the cushion mesenchyme during heart development.

Eosinophil cationic protein enhances stabilization of β-catenin during cardiomyocyte differentiation in P19CL6 embryonal carcinoma cells

Prior to gastrulation, the Wnt signaling pathway through stabilized β-catenin enhances the differentiation of mouse ES cell into cardiomyocytes. We have recently shown that cardiomyocyte differentiation is enhanced by eosinophil cationic protein (ECP) through accelerated expression of marker genes of early cardiac differentiation. Furthermore, ECP enhanced the expression of Wnt3a in P19CL6 cells which were stimulated to differentiate into cardiomyocytes by DMSO. Following these findings, we evaluated in this study the potential of ECP to activate the Wnt/β-catenin signaling pathway during cardiomyocyte differentiation. Analysis by real time qPCR revealed that ECP increased the expression of Frizzled genes such as Frizzled-1, -2, -4 and -10 in P19CL6 cells in the presence of DMSO. The increased expression of those Wnt receptors was found to inhibit the phosphorylation of β-catenin resulting in the stabilization and translocation of β-catenin into the nucleus of P19CL6 cells during the early stages of cardiomyocyte differentiation. When assessed for β-catenin/TCF transcriptional activity with a TCF-luciferase (TOP/FOP) assay, ECP enhanced luciferase activity in P19CL6 cells during 48 h after transfection with TOP/FOP flash reporter in a stoichiometric manner. Collectively, this suggests that ECP can activate a canonical Wnt/β-catenin signaling pathway by enhancing the stabilization of β-catenin during cardiomyocyte differentiation.

Eosinophil cationic protein enhances cardiomyocyte differentiation of P19CL6 embryonal carcinoma cells by stimulating the FGF receptor signaling pathway

We investigated the functional role of eosinophil cationic protein (ECP) in regulating cardiomyogenesis using mouse P19CL6 embryonic carcinoma cells. ECP was confirmed to accelerate the cardiomyocyte differentiation of P19CL6 cells by enhancing the rate and area size of beating of cardiomyocyte and by facilitating the expression of cardiomyocyte-specific genes, such as GATA4 and α-MHC. Since cardiomyocyte differentiation in vivo is considered to follow mesoderm induction, the induction of Brachyury, a marker of mesoderm, was assessed. Brachyury expression was found to be enhanced after the addition of ECP. This enhancement was due to the stimulation of extracellular signal-regulated kinase (ERK)1/2 phosphorylation by ECP. In this context, treatment with SU5402, an inhibitor of fibroblast growth factor (FGF) receptor 1, suppressed Brachyury expression, phosphorylation of ERK1/2, and cardiomyocyte differentiation induced by ECP. We concluded that ECP might induce mesoderm differentiation through FGF signaling pathway and enhance subsequent cardiomyocyte differentiation in concert with dimethyl sulfoxide in P19CL6 cells. ECP may be a novel factor for cardiomyocyte differentiation, which should be very useful to prepare adequate numbers of cardiomyocytes for therapeutic cell transplantation.

Controlling embryonic stem cell growth and differentiation by automation: enhanced and more reliable differentiation for drug discovery

Despite significant use in basic research, embryonic stem cells have just begun to be used in the drug discovery process. Barriers to the adoption of embryonic stem cells in drug discovery include the difficulty in growing cells and inconsistent differentiation to the desired cellular phenotype. Embryonic stem cell cultures require consistent and frequent handling to maintain the cells in a pluripotent state. In addition, the preferred hanging drop method of embryoid body (EB) differentiation is not amenable to high-throughput methods, and suspension cultures of EBs show a high degree of variability. Murine embryonic stem cells passaged on an automated platform maintained ≥ 90% viability and pluripotency. We also developed a method of EB formation using 384-well microplates that form a single EB per well, with excellent uniformity across EBs. This format facilitated high-throughput differentiation and enabled screens to optimize directed differentiation into a desired cell type. Using this approach, we identified conditions that enhanced cardiomyocyte differentiation sevenfold. This optimized differentiation method showed excellent consistency for such a complex biological process. This automated approach to embryonic stem cell handling and differentiation can provide the high and consistent yields of differentiated cell types required for basic research, compound screens, and toxicity studies.

Tbx6 is a determinant of cardiac and neural cell fate decisions in multipotent P19CL6 cells

Multipotent P19CL6 cells differentiate into cardiac myocytes or neural lineages when stimulated with dimethyl sulfoxide (DMSO) or retinoic acid (RA), respectively. Expression of the transcription factor Tbx6 was found to increase during cardiac myocyte differentiation and to decrease during neural differentiation. Overexpression of Tbx6 was not sufficient to drive P19CL6 cells to a cardiac myocyte fate or to accelerate DMSO-induced differentiation. In contrast, knockdown of Tbx6 dramatically inhibited DMSO-induced differentiation of P19CL6 cells to cardiac myocytes, as evidenced by the loss of striated muscle-specific markers and spontaneous beating. Tbx6 knockdown was also accompanied by almost complete loss of Nkx2.5, a transcription factor involved in the specification of the cardiac myocyte lineage, indicating that Nkx2.5 is downstream of Tbx6. In distinction to its positive role in cardiac myocyte differentiation, Tbx6 knockdown augmented RA-induced differentiation of P19CL6 cells to both neurons and glia, and accelerated the rate of neurite formation. Conversely, Tbx6 overexpression attenuated differentiation to neural lineages. Thus, in the P19CL6 model, Tbx6 is required for cardiac myocyte differentiation and represses neural differentiation. We propose a model in which Tbx6 is a part of a molecular switch that modulates divergent differentiation programs within a single progenitor cell.