Nitrosylation of β2-Tubulin Promotes Microtubule Disassembly and Differentiated Cardiomyocyte Beating in Ischemic Mice

BACKGROUND

Beating cardiomyocyte regeneration therapies have revealed as alternative therapeutics for heart transplantation. Nonetheless, the importance of nitric oxide (NO) in cardiomyocyte regeneration has been widely suggested, little has been reported concerning endogenous NO during cardiomyocyte differentiation.

METHODS

Here, we used P19CL6 cells and a Myocardiac infarction (MI) model to confirm NO-induced protein modification and its role in cardiac beating. Two tyrosine (Tyr) residues of β2-tubulin (Y106 and Y340) underwent nitrosylation (Tyr-NO) by endogenously generated NO during cardiomyocyte differentiation from pre-cardiomyocyte-like P19CL6 cells.

RESULTS

Tyr-NO-β2-tubulin mediated the interaction with Stathmin, which promotes microtubule disassembly, and was prominently observed in spontaneously beating cell clusters and mouse embryonic heart (E11.5d). In myocardial infarction mice, Tyr-NO-β2-tubulin in transplanted cells was closely related with cardiac troponin-T expression with their functional recovery, reduced infarct size and thickened left ventricular wall.

CONCLUSION

This is the first discovery of a new target molecule of NO, β2-tubulin, that can promote normal cardiac beating and cardiomyocyte regeneration. Taken together, we suggest therapeutic potential of Tyr-NO-β2-tubulin, for ischemic cardiomyocyte, which can reduce unexpected side effect of stem cell transplantation, arrhythmogenesis.

Zoxazolamine-induced stimulation of cardiomyogenesis from embryonic stem cells is mediated by Ca2+, nitric oxide and ATP release

Ca²⁺-activated potassium (K_Ca) channels of small and intermediate conductance influence proliferation, apoptosis, and cell metabolism. We analysed whether prolonged activation of K_Ca channels by zoxazolamine (ZOX) induces differentiation of mouse embryonic stem (ES) cells towards cardiomyocytes. ZOX treatment of ES cells dose-dependent increased the number and diameter of cardiac foci, the frequency of contractions as well as mRNA expression of the cardiac transcription factor Nkx-2.5, the cardiac markers cardiac troponin I (cTnI), α-myosin heavy chain (α-MHC), ventricular myosin light chain-2 (MLC2v), and the pacemaker hyperpolarization-activated, cyclic nucleotide-gated 4 channel (HCN4). ZOX induced hyperpolarization of membrane potential due to activation of IK_Ca, raised intracellular Ca²⁺ concentration ([Ca²⁺]_i) and nitric oxide (NO) in a Ca²⁺-dependent manner. The Ca²⁺ response to ZOX was inhibited by chelation of Ca²⁺ with BAPTA-AM, release of Ca²⁺ from intracellular stores by thapsigargin and the phospholipase C (PLC) antagonist U73,122. Moreover, the ZOX-induced Ca²⁺ response was blunted by the purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) as well as the specific P2Y₁ antagonist MRS 2,179, suggesting purinergic receptor-stimulated signal transduction. Consequently, ZOX initiated ATP release from differentiating ES cells, which was inhibited by the chloride channel inhibitor NPPB and the gap junction inhibitor carbenoxolone (CBX). The stimulation of cardiomyogenesis by ZOX was blunted by the nitric oxide synthase (NOS) inhibitor l-NAME, as well as CBX and NPPB. In summary, our data suggest that ZOX enhances cardiomyogenesis of ES cells by ATP release presumably through gap junctional hemichannels, purinergic receptor activation and intracellular Ca²⁺ response, thus promoting NO generation.

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.

Cardiomyogenic differentiation is fine-tuned by differential mRNA association with polysomes

BACKGROUND

Cardiac cell fate specification occurs through progressive steps, and its gene expression regulation features are still being defined. There has been an increasing interest in understanding the coordination between transcription and post-transcriptional regulation during the differentiation processes. Here, we took advantage of the polysome profiling technique to isolate and high-throughput sequence ribosome-free and polysome-bound RNAs during cardiomyogenesis.

RESULTS

We showed that polysome-bound RNAs exhibit the cardiomyogenic commitment gene expression and that mesoderm-to-cardiac progenitor stages are strongly regulated. Additionally, we compared ribosome-free and polysome-bound RNAs and found that the post-transcriptional regulation vastly contributes to cardiac phenotype determination, including RNA recruitment to and dissociation from ribosomes. Moreover, we found that protein synthesis is decreased in cardiomyocytes compared to human embryonic stem-cells (hESCs), possibly due to the down-regulation of translation-related genes.

CONCLUSIONS

Our data provided a powerful tool to investigate genes potentially controlled by post-transcriptional mechanisms during the cardiac differentiation of hESC. This work could prospect fundamental tools to develop new therapy and research approaches.

VEGF-B electrotransfer mediated gene therapy induces cardiomyogenesis in a rat model of cardiac ischemia

Atherosclerosis induced myocardial infarction (MI) continues to be a major public health concern. Regenerative therapies that restore cardiac muscle cells are largely absent. The rate of cardiomyogenesis in adults is insufficient to compensate for MI damage. In this study, we explored the capacity of a gene therapy approach to promote cardiomyogenesis. We hypothesized that VEGF-B, critical during fetal heart development, could promote cardiomyogenesis in adult ischemic hearts. Gene electrotransfer (GET), a physical method of in vivo gene delivery, was adapted to the rat model of MI. Favorable pulsing parameters were then used for delivery of pVEGF-B and compared to a sham control in terms of infarct size, cardiomyocyte proliferation and presence of new cardiomyocytes. Ki67 immunoreactivity was used for proliferation analysis. Newly synthetized DNA was labeled with BrdU to identify new cells post-infarction. Cardiac troponin co-localization indicated proliferating and new cardiomyocytes histologically. Eight weeks post-treatment, GET pVEGF-B treated hearts had significantly smaller infarcts than the sham control group (p < 0.04). Proliferating and new cardiomyocytes were only present in the GET of pVEGF-B group, and absent in the controls. In summary, GET pVEGF-B promoted cardiomyogenesis post-MI, demonstrating for the first time direct evidence of myocardial regeneration post-infarction.

MicroRNA-499a-5p Promotes Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells to Cardiomyocytes

Since the adult mammalian heart has limited regenerative capacity, cardiac trauma, disease, and aging cause permanent loss of contractile tissue. This has fueled the development of stem cell-based strategies to provide the damaged heart with new cardiomyocytes. Bone marrow-derived mesenchymal stem cells (BM-MSCs) are capable of self-renewal and differentiation into cardiomyocytes, albeit inefficiently. MicroRNAs (miRNAs, miRs) are non-coding RNAs that have the potential to control stem cell fate decisions and are employed in cardiac regeneration and repair. In this study, we tested the hypothesis that overexpression of miR-499a induces cardiomyogenic differentiation in BM-MSCs. Human BM-MSCs (hBM-MSCs) were transduced with lentiviral vectors encoding miR-499a-3p or miR-499a-5p and analyzed by immunostaining and western blotting methods 14 days post-transduction. MiR-499a-5p-transduced cells adopted a polygonal/rod-shaped (myocyte-like) phenotype and showed an increase in the expression of the cardiomyocyte markers α-actinin and cTnI, as cardiogenic differentiation markers. These results indicate that miR-499a-5p overexpression promotes the cardiomyogenic differentiation of hBM-MSCs and may thereby increase their therapeutic efficiency in cardiac regeneration.

Cardiophysiology Illustrated by Comparing Ventricular Volumes in Healthy Adult Males and Females

Recent advances in cardiac imaging techniques have substantially contributed to a growing interest in the analysis of global cardiac chamber dimensions and regional myocardial deformation. During the cardiac cycle, ventricular luminal volume varies due to the contraction process, which also confers a shape change including substantial alteration of long axis length, as well as rotation of the base compared to the apex. Local deformation can be assessed by strain (rate) analysis. Reviewing the present literature, it must be concluded that there is no single metric available to comprehensively characterize ventricular function. Every candidate advanced thus far has been found to incompletely reflect ventricular performance. This observation is not surprising in view of the complexity of the cardiac pump system. Additionally, sex-specific modifiers may play a role. More than three decades ago, it was shown that on average the ventricular volume is smaller in healthy women compared to matched males. Therefore, the present contribution concerns the interpretation of data derived from the healthy heart in both men and women. Starting from the classical Starling concept, we apply a simple mathematical transformation which permits an insightful representation of ventricular mechanics. Relating end-systolic volume (ESV) to end-diastolic volume creates the ventricular volume regulation graph which features the pertinent working point of an individual heart. This fundamental approach illustrates why certain proposed performance indexes cannot individually reveal the essence of ventricular systolic function. We demonstrate that particular metrics are highly interconnected and just tell us the same story in a different disguise. It is imperative to understand which associations exist and if they expectedly are (nearly) linear or frankly nonlinear. Notably, ejection fraction (EF) is primarily determined by ESV, while in turn EF is not much different from ventriculo-arterial coupling (VAC). Insight into cardiac function is promoted by identification of the paramount/essential components involved. The smaller ESV (p < 0.0001) implies that EF is higher in women and may also have consequences for VAC.

Genome-wide transcriptomics analysis identifies sox7 and sox18 as specifically regulated by gata4 in cardiomyogenesis

The transcription factors GATA4, GATA5 and GATA6 are important regulators of heart muscle differentiation (cardiomyogenesis), which function in a partially redundant manner. We identified genes specifically regulated by individual cardiogenic GATA factors in a genome-wide transcriptomics analysis. The genes regulated by gata4 are particularly interesting because GATA4 is able to induce differentiation of beating cardiomyocytes in Xenopus and in mammalian systems. Among the specifically gata4-regulated transcripts we identified two SoxF family members, sox7 and sox18. Experimental reinstatement of gata4 restores sox7 and sox18 expression, and loss of cardiomyocyte differentiation due to gata4 knockdown is partially restored by reinstating sox7 or sox18 expression, while (as previously reported) knockdown of sox7 or sox18 interferes with heart muscle formation. In order to test for conservation in mammalian cardiomyogenesis, we confirmed in mouse embryonic stem cells (ESCs) undergoing cardiomyogenesis that knockdown of Gata4 leads to reduced Sox7 (and Sox18) expression and that Gata4 is also uniquely capable of promptly inducing Sox7 expression. Taken together, we identify an important and conserved gene regulatory axis from gata4 to the SoxF paralogs sox7 and sox18 and further to heart muscle cell differentiation.

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Gata 4, 5 and 6 have redundant and non-redundant functions in heart development.

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RNA-seq analysis of Gata4, 5 and 6 knockdown experiments was carried out.

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Genes specifically regulated by Gata4, 5 and 6 were identified.

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The SoxF genes sox7 and sox18 were identified as specifically regulated by Gata4.

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Epistasis demonstrates a regulatory axis from Gata4 to Sox7/18 to cardiomyogenesis.

Enhanced cardiomyogenic induction of mouse pluripotent cells by cyclic mechanical stretch

The cardiac milieu is mechanically active with spontaneous contraction beginning from early development and persistent through maturation and homeostasis, suggesting that mechanical loading may provide a biomimetic myocardial developmental signal. In this study, we tested the role of cyclic mechanical stretch loading in the cardiomyogenesis of pluripotent murine embryonic (P19) stem cells. A Flexcell tension system was utilized to apply equiaxial stretch (12% strain, 1.25 Hz frequency) to P19 cell-derived embryoid bodies (EBs). Interestingly, while control EBs without any further stimulation did not exhibit cardiomyogenesis, stretch stimulation alone could induce P19-derived EBs to become spontaneously beating cardiomyocytes (CMs). The beating colony number, average contracting area, and beating rate, as quantified by video capturing and framed image analysis, were even increased for stretch alone case relative to those from known biochemical induction with 5-Azacytidine (5-Aza). Key CM differentiation markers, GATA4 and Troponin T, could also be detected for the stretch alone sample at comparable levels as with 5-Aza treatment. Stretch and 5-Aza co-stimulation produced in general synergistic effects in CM developments. Combined data suggest that stretch loading may serve as a potent trigger to induce functional CM development in both beating dynamics and genomic development, which is still a challenge for myocardial regenerative medicine.

Epac-Rap1-activated mesenchymal stem cells improve cardiac function in rat model of myocardial infarction

INTRODUCTION

Rap1, a member of Ras superfamily of small GTP-binding proteins, is involved in cardiovascular biology in numerous ways. It is an evolutionary conserved regulator of adhesion, polarity, differentiation and growth.

AIMS

Our aim was to analyze Rap1-activated rat bone marrow mesenchymal stem cells (MSCs) for their potential role in adhesion and cardiac differentiation.

METHODS

Myocardial infarction (MI) was produced in Sprague Dawley (SD) rats through occlusion of the left anterior descending coronary artery. MSCs were treated with 8-pCPT-2'-O-Me-cAMP (CPT) to activate Rap1. Normal (untreated) and CPT-treated MSCs were transplanted through intramyocardial injection in respective groups. Cardiac function was assessed by echocardiography at 2 and 4 weeks after cell transplantation. Histological analysis was performed to observe changes at tissue level.

RESULTS

Homing of CPT-treated MSCs was significantly (***P<.001) higher as compared to normal MSCs in the infarcted hearts. This may be due to increase in the gene expression of some of the cell adhesion molecules as evident by qRT-PCR analysis. Significant (***P<.001) improvement in the restoration of heart function in terms of left ventricular diastolic and systolic internal diameters (LVIDd, LVIDs), % ejection fraction, % fraction shortening and end-systolic and end-diastolic volumes were observed in CPT-treated MSCs as compared to the MI model. Histological analyses showed significant (***P<.001) reduction in scar formation in the CPT-treated group. Differentiation of treated MSCs into functional cardiomyocytes was evident through immunohistochemical staining. LV wall thickness was also preserved significantly (***P<.001). Blood vessel formation was more pronounced in CPT-treated group although both cell therapy groups showed significant increase as compared to MI model.

CONCLUSION

Our findings showed that pharmacological activation of Epac-Rap1 improves cardiac function through better survival, adhesion and differentiation of transplanted cells. Transplantation of these MSCs in the infarct area restored functional myocardium.

BRG1 interacts with GLI2 and binds Mef2c gene in a hedgehog signalling dependent manner during in vitro cardiomyogenesis

Background

The Hedgehog (HH) signalling pathway regulates cardiomyogenesis in vivo and in differentiating P19 embryonal carcinoma (EC) cells, a mouse embryonic stem (mES) cell model. To further assess the transcriptional role of HH signalling during cardiomyogenesis in stem cells, we studied the effects of overexpressing GLI2, a primary transducer of the HH signalling pathway, in mES cells.

Results

Stable GLI2 overexpression resulted in an enhancement of cardiac progenitor-enriched genes, Mef2c, Nkx2-5, and Tbx5 during mES cell differentiation. In contrast, pharmacological blockade of the HH pathway in mES cells resulted in lower expression of these genes. Mass spectrometric analysis identified the chromatin remodelling factor BRG1 as a protein which co-immunoprecipitates with GLI2 in differentiating mES cells. We then determined that BRG1 is recruited to a GLI2-specific Mef2c gene element in a HH signalling-dependent manner during cardiomyogenesis in P19 EC cells, a mES cell model.

Conclusions

Thus, we propose a mechanism where HH/GLI2 regulates the expression of Mef2c by recruiting BRG1 to the Mef2c gene, most probably via chromatin remodelling, to ultimately regulate in vitro cardiomyogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-016-0127-8) contains supplementary material, which is available to authorized users.

Peroxiredoxin-2 nitrosylation facilitates cardiomyogenesis of mouse embryonic stem cells via XBP-1s/PI3K pathway

Protein nitrosylation is a ubiquitous post-translational modification in almost all biological systems. However, its function on stem cell biology is so far incompletely understood. Here, we demonstrated that peroxiredoxin 2 (Prdx-2) nitrosylation was involved in cardiomyocyte differentiation of mouse embryonic stem (ES) cells induced by S-nitrosoglutathione (GSNO). We found that temporary GSNO exposure could promote ES cell-derived cardiomyogenesis. Using a stable isotope labeling by amino acids in cell culture (SILAC)-based proteomics approach, coupled with biotin switch technique, a total of 104 nitrosylated proteins were identified. Specifically, one of the antioxidant enzymes, Prdx-2, was abundantly nitrosylated and temporarily reduced in antioxidant activity, causing transient endogenous hydrogen peroxide (H2O2) accumulation and subsequent X-box binding protein-1s/phosphatidylinositol 3-kinase pathway activation. The present study reveals the mechanism in which GSNO favors cardiomyocyte differentiation. Prdx-2 nitrosylation could be a potent strategy to affect the pluripotent stem cell-derived cardiomyogenesis.

Inhibitory effect of progesterone during early embryonic development: Suppression of myocardial differentiation and calcium-related transcriptome by progesterone in mESCs: Progesterone disturb cardiac differentiation of mESCs through lower cytosolic Ca(2.)

Progesterone (PG) and its derivates are used in prevention of spontaneous miscarriage. However, some studies have reported that exposure to PG and its derivates during pregnancy can cause malformations and affect both blood pressure and the cardiovascular system. The effect of PG on cardiomyogenesis of mouse embryonic stem cells (mESCs) is not well known. Expression of Pgr mRNA showed an opposite pattern of beating-ratio during differentiation. PG treatment resulted in reduction of the beating ratio to 60.45±1.54% from 92.17±2.98% in normal differentiation, reduced transcripts of heart morphogenesis and Ca(2+) binding-related genes in the next generation sequencing data and significantly decreased expression levels of Ca(2+)/contraction-related genes including Ryr2, Calm2, Trpv2, and Mylk3, the intracellular Ca(2+) level, and the beating frequency. These results suggest that PG exerts inhibitory effects on differentiation of mESCs into functional cardiomyocytes.

Exogenous expression of homeoprotein EGAM1N prevents in vitro cardiomyogenesis by impairing expression of T and Nkx2.5, but not Mef2c, in mouse embryonic stem cells

Generation of multiple cell types from embryonic stem (ES) cells and induced pluripotent stem cells is crucial to provide materials for regenerative medicine. EGAM1N has been found in preimplantation mouse embryos and mouse ES cells as a functionally unclassified homeoprotein. Recently, we reported that expression of EGAM1N suppressed the in vitro differentiation of ES cells into progenitor cells that arise in early embryogenesis. To clarify the effect of EGAM1N on terminal differentiation, embryoid bodies (EBs) were prepared from ES cells expressing exogenous Egam1n. In EBs expressing Egam1n, cardiomyogenesis was inhibited by impairing the expression of crucial transcription factors Brachyury T and Nkx2.5 in the generation of mesoderm and cardiomyocytes, respectively. Expression levels of Mef2c, another crucial gene for cardiomyogenesis, were unaffected. Conversely, the expression levels of Gata6 and Plat, markers for the primitive endoderm lineage, and Cdx2, a marker for the trophectoderm lineage, were increased. These results suggested that certain cell populations in EBs expressing Egam1n preferentially differentiated to such cell lineages. Our results suggest that EGAM1N not only affects the generation of progenitor cells during early embryogenesis, but also the progression of terminal differentiation, such as cardiomyogenesis, in mouse ES cells.

A Shh coreceptor Cdo is required for efficient cardiomyogenesis of pluripotent stem cells

Sonic hedgehog (Shh) signaling plays an important role for early heart development, such as heart looping and cardiomyogenesis of pluripotent stem cells. A multifunctional receptor Cdo functions as a Shh coreceptor together with Boc and Gas1 to activate Shh signaling and these coreceptors seem to play compensatory roles in early heart development. Thus in this study, we examined the role of Cdo in cardiomyogenesis by utilizing an in vitro differentiation of pluripotent stem cells. Here we show that Cdo is required for efficient cardiomyogenesis of pluripotent stem cells by activation of Shh signaling. Cdo is induced concurrently with Shh signaling activation upon induction of cardiomyogenesis of P19 embryonal carcinoma (EC) cells. Cdo-depleted P19 EC and Cdo(-/-) mouse embryonic stem (ES) cells display decreased expression of key cardiac regulators, including Gata4, Nkx2.5 and Mef2c and this decrease coincides with reduced Shh signaling activities. Furthermore Cdo deficiency causes a stark reduction in formation of mature contractile cardiomyocytes. This defect in cardiomyogenesis is overcome by reactivation of Shh signaling at the early specification stage of cardiomyogenesis. The Shh agonist treatment restores differentiation capacities of Cdo-deficient ES cells into contractile cardiomyocytes by recovering both the expression of early cardiac regulators and structural genes such as cardiac troponin T and Connexin 43. Therefore Cdo is required for efficient cardiomyogenesis of pluripotent stem cells and an excellent target to improve the differentiation potential of stem cells for generation of transplantable cells to treat cardiomyopathies.

Mapping Human Pluripotent-to-Cardiomyocyte Differentiation: Methylomes, Transcriptomes, and Exon DNA Methylation "Memories"

The directed differentiation of human cardiomyocytes (CMs) from pluripotent cells provides an invaluable model for understanding mechanisms of cell fate determination and offers considerable promise in cardiac regenerative medicine. Here, we utilize a human embryonic stem cell suspension bank, produced according to a good manufacturing practice, to generate CMs using a fully defined and small molecule-based differentiation strategy. Primitive and cardiac mesoderm purification was used to remove non-committing and multi-lineage populations and this significantly aided the identification of key transcription factors, lncRNAs, and essential signaling pathways that define cardiomyogenesis. Global methylation profiles reflect CM development and we report on CM exon DNA methylation "memories" persisting beyond transcription repression and marking the expression history of numerous developmentally regulated genes, especially transcription factors.

1,5-Disubstituted benzimidazoles that direct cardiomyocyte differentiation from mouse embryonic stem cells

Cardiomyopathy is the leading cause of death worldwide. Despite progress in medical treatments, heart transplantation is one of the only current options for those with infarcted heart muscle. Stem cell differentiation technology may afford cell-based therapeutics that may lead to the generation of new, healthy heart muscle cells from undifferentiated stem cells. Our approach is to use small molecules to stimulate stem cell differentiation. Herein, we describe a novel class of 1,5-disubstituted benzimidazoles that induce differentiation of stem cells into cardiac cells. We report on the evaluation in vitro for cardiomyocyte differentiation and describe structure-activity relationship results that led to molecules with drug-like properties. The results of this study show the promise of small molecules to direct stem cell lineage commitment, to probe signaling pathways and to develop compounds for the stimulation of stem cells to repair damaged heart tissue.

Stimulation of cardiomyogenesis from mouse embryonic stem cells by nuclear translocation of cardiotrophin-1

BACKGROUND

Cardiotrophin-1 (CT-1) controls cardiomyogenesis of mouse embryonic stem (ES) cells.

OBJECTIVES

To investigate the signaling pathway underlying the action of CT-1 on cardiac cell differentiation.

METHODS

Protein expression was analyzed by western blot technique and cardiac areas by immunohistochemistry. Calcium, reactive oxygen species (ROS) and nitric oxide (NO) were assessed by microfluorometry using fluo-4, H2DCF, and DAF-2DA, respectively. Gene inactivation of CT-1 was achieved by siRNA technology.

RESULTS

CT-1 as well as its receptor gp 130 were transiently upregulated during differentiation of ES cells. Exogenous CT-1 enhanced cardiomyogenesis, increased the cardiac transcription factors MEF2c, Nkx-2.5, TEAD3 and GATA4, the cardiac proteins α-actinin, MLC2a, MYH7, MLC1a, MLC2v and HCN4 as well as vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), fibroblast growth factor-2 (FGF-2) and atrial natriuretic peptide (ANP). CT-1 downregulation by small interfering RNA (siRNA) inhibited cardiomyogenesis and decreased VEGF, PDGF-BB, FGF-2 and ANP expression. CT-1 raised intracellular calcium which was abolished by the intracellular calcium chelator BAPTA, AM and thapsigargin. Moreover, CT-1 treatment increased ROS, followed by NO generation and NOS3 activation. During ES cell differentiation CT-1 was translocated to the cell nucleus. Exogenous CT-1 induced nuclear translocation of endogenous CT-1, which was inhibited by BAPTA, the NOS inhibitor L-N(G)-Nitroarginine methyl ester (l-NAME), the radical scavenger N-(2-mercaptopropionyl)-glycine (NMPG) as well as the janus kinase 2 (JAK2) inhibitor AG490 and the PI3 kinase (PI3K) inhibitor LY294002.

CONCLUSIONS

Nuclear translocation of CT-1 regulates cardiomyogenesis of ES cells and involves calcium, NO, ROS as well as CT-1 regulated signaling pathways.

Identification and characterization of CW108F, a novel β-carboline compound that promotes cardiomyogenesis of stem cells

AIMS

The aim of this study was to identify new compounds that induce cardiomyocyte differentiation of stem cells through cell-based screening and investigate lineage specificity and mechanisms in vitro.

MAIN METHODS

Embryoid bodies (EBs) formed from TC-1/KH2 mouse embryonic stem cells (ESCs) carrying the gene for enhanced green fluorescent protein (EGFP) under the control of the α-myosin heavy chain (MHC) promoter were treated with test compounds. The number of cardiomyocyte-like (EGFP-expressing) cells in EBs was determined by fluorescence-activated cell sorting. Cardiomyocyte differentiation was further confirmed using lineage-specific biochemical assays and by investigating the expression of cardiomyocyte-specific and "stemness"-associated genes. Nuclear factor-kappaB (NF-κB) signaling activity was measured in A549 cells using a reporter-gene assay.

KEY FINDINGS

A β-carboline compound, designated CW108F, increased the number of mouse ESCs expressing α-MHC promoter-driven EGFP and the proportion of beating EBs. CW108F also increased expression of MHC in P19 stem cells, but did not induce osteogenesis of MC3T3-E1 cells, suggesting lineage-specific activity toward cardiomyocytes. CW108F upregulated expression of cardiac-specific GATA-4 and atrial natriuretic factor (ANF) genes in TC-1/KH2 cells, but downregulated expression of the stemness genes, Oct-4 and brachyury. CW108F inhibited NF-κB transcriptional activity, an effect that might contribute to its cardiomyogenesis-promoting activity.

SIGNIFICANCE

The results of this study suggest that the novel β-carboline, CW108F, promotes the differentiation of ESCs into cardiomyocytes and may be useful for investigating molecular pathways of cardiomyogenesis and generating cardiomyocytes from ESCs.

The adult heart responds to increased workload with physiologic hypertrophy, cardiac stem cell activation, and new myocyte formation

Aims

It is a dogma of cardiovascular pathophysiology that the increased cardiac mass in response to increased workload is produced by the hypertrophy of the pre-existing myocytes. The role, if any, of adult-resident endogenous cardiac stem/progenitor cells (eCSCs) and new cardiomyocyte formation in physiological cardiac remodelling remains unexplored.

Methods and results

In response to regular, intensity-controlled exercise training, adult rats respond with hypertrophy of the pre-existing myocytes. In addition, a significant number (∼7%) of smaller newly formed BrdU-positive cardiomyocytes are produced by the exercised animals. Capillary density significantly increased in exercised animals, balancing cardiomyogenesis with neo-angiogenesis. c-kit^pos eCSCs increased their number and activated state in exercising vs. sedentary animals. c-kit^pos eCSCs in exercised hearts showed an increased expression of transcription factors, indicative of their commitment to either the cardiomyocyte (Nkx2.5^pos) or capillary (Ets-1^pos) lineages. These adaptations were dependent on exercise duration and intensity. Insulin-like growth factor-1, transforming growth factor-β1, neuregulin-1, bone morphogenetic protein-10, and periostin were significantly up-regulated in cardiomyocytes of exercised vs. sedentary animals. These factors differentially stimulated c-kit^pos eCSC proliferation and commitment in vitro, pointing to a similar role in vivo.

Conclusion

Intensity-controlled exercise training initiates myocardial remodelling through increased cardiomyocyte growth factor expression leading to cardiomyocyte hypertrophy and to activation and ensuing differentiation of c-kit^pos eCSCs. This leads to the generation of new myocardial cells. These findings highlight the endogenous regenerative capacity of the adult heart, represented by the eCSCs, and the fact that the physiological cardiac adaptation to exercise stress is a combination of cardiomyocyte hypertrophy and hyperplasia (cardiomyocytes and capillaries).