Vascular endothelial growth factor promotes cardiomyocyte differentiation of embryonic stem cells

Improved integration of single-cell transcriptome data demonstrates common and unique signatures of heart failure in mice and humans

BACKGROUND

Cardiovascular research heavily relies on mouse (Mus musculus) models to study disease mechanisms and to test novel biomarkers and medications. Yet, applying these results to patients remains a major challenge and often results in noneffective drugs. Therefore, it is an open challenge of translational science to develop models with high similarities and predictive value. This requires a comparison of disease models in mice with diseased tissue derived from humans.

RESULTS

To compare the transcriptional signatures at single-cell resolution, we implemented an integration pipeline called OrthoIntegrate, which uniquely assigns orthologs and therewith merges single-cell RNA sequencing (scRNA-seq) RNA of different species. The pipeline has been designed to be as easy to use and is fully integrable in the standard Seurat workflow.We applied OrthoIntegrate on scRNA-seq from cardiac tissue of heart failure patients with reduced ejection fraction (HFrEF) and scRNA-seq from the mice after chronic infarction, which is a commonly used mouse model to mimic HFrEF. We discovered shared and distinct regulatory pathways between human HFrEF patients and the corresponding mouse model. Overall, 54% of genes were commonly regulated, including major changes in cardiomyocyte energy metabolism. However, several regulatory pathways (e.g., angiogenesis) were specifically regulated in humans.

CONCLUSIONS

The demonstration of unique pathways occurring in humans indicates limitations on the comparability between mice models and human HFrEF and shows that results from the mice model should be validated carefully. OrthoIntegrate is publicly accessible (https://github.com/MarianoRuzJurado/OrthoIntegrate) and can be used to integrate other large datasets to provide a general comparison of models with patient data.

Investigation of impacts of decellularized heart extracellular matrix and VEGF on cardiomyogenic differentiation of mesenchymal stem cell through Notch/Hedgehog signaling pathways

OBJECTIVE

Decellularization is the process to obtain natural scaffolds with tissue integrity and extracellular matrix components, and recellularization is used to produce tissue-like constructs with specific cell types. In this study, rat bone marrow-derived mesenchymal stem cells (rBM-MSCs) were cultured on decellularized heart extracellular matrix. These cells were then induced to differentiate into cardiomyogenic cells under the stimulatory effect of vascular endothelial growth factor (VEGF) and other chemicals. This study aimed to investigate the effect of the cardiac extracellular matrix and VEGF on cardiomyogenic differentiation in the context of the Notch and Hedgehog signaling pathways.

METHODS

Heart samples extracted from rats were decellularized by serial application of detergent to remove cells from the tissue, and then recellularized with rBM-MSCs. The recellularized tissue matrices were then analyzed for cardiomyogenesis. Cardiomyogenic differentiation was performed on decellularized heart extracellular matrix (ECM; three-dimensional scaffolds) and culture plates (two-dimensional cell culture system) for 28 days to understand the effects of the heart extracellular matrix. In addition, differentiation was induced with and without the stimulatory effect of VEGF to understand the effect of VEGF on cardiomyogenic differentiation of rBM-MSCs.

RESULTS

Immunofluorescence staining showed that decellularization of the heart was performed effectively and successfully. After decellularization process, the heart extracellular matrix was completely free of cells. It was observed that rBM-MSCs transplanted onto the heart extracellular matrix remained viable and proliferated for 21 days after recellularization. The rBM-MSCs promoted cardiomyogenic differentiation in the conventional differentiation medium but were inversely affected by both VEGF and heart extracellular matrix proteins. Lower expression of connexin43 and cardiac troponin I genes was observed in cells induced by either matrix proteins or VEGF, compared to cells differentiated by chemical agents alone.

CONCLUSION

In this study, we investigated the effect of decellularized heart extracellular matrix and VEGF on cardiomyogenic differentiation of rBM-MSCs. On the decellularized cardiac extracellular matrix, rBM-MSCs maintained their viability by adhering to the matrix and proliferating further. The adhesion of the cells to the matrix also produced a physical stimulus that led to the formation of histological structures resembling myocardial layers. Chemical stimulation of the decellularized heart extracellular matrix and cardiomyogenic differentiation supplements resulted in increased expression of cardiomyogenic biomarkers through modulation of the Notch and Hedgehog signaling pathways.

Novel circRNA-miRNA-mRNA networks regulated by maternal exercise in fetal hearts of pregestational diabetes

BACKGROUND

Maternal exercise lowers the incidence of congenital heart defects (CHDs) induced by pregestational diabetes. However, the molecular mechanisms underlying the beneficial effects of maternal exercise remain unclear. The present study aimed to identify circular RNA (circRNA), microRNA (miRNA) and mRNA networks that are regulated by maternal exercise in fetal hearts of pregestational diabetes.

METHODS

Pregestational diabetes was induced in adult C57BL/6 female mice by streptozotocin. The expression profiles of circRNAs, miRNAs and mRNAs in E10.5 fetal hearts of offspring of control and diabetic mothers with or without exercise were analyzed using next generation sequencing. circRNA-miRNA-mRNA networks in fetal hearts were mapped and key candidate transcripts were verified by qPCR analysis.

RESULTS

Pregestational diabetes dysregulated the expression of 206 circRNAs, 66 miRNAs and 391 mRNAs in fetal hearts. Maternal exercise differentially regulated 188 circRNAs, 57 miRNAs and 506 mRNAs in fetal hearts of offspring of pregestational diabetes. A total of 5 circRNAs, 12 miRNAs, and 28 mRNAs were incorporated into a final maternal exercise-associated regulatory network in fetal hearts of offspring of maternal diabetes. Notably, maternal exercise normalized the dysregulated circ_0003226/circ_0015638/miR-351-5p and circ_0002768/miR-3102-3p.2-3p pairs in fetal hearts of pregestational diabetes.

CONCLUSION

Maternal exercise reverses the dysregulated circ_0003226/circ_0015638/miR-351-5p and circ_0002768/miR-3102-3p.2-3p pairs, and partially normalizes circRNA, miRNA, and mRNA expression profiles in fetal hearts of pregestational diabetes. These findings shed new light on the potential mechanisms of the beneficial effects of maternal exercise on the developing heart in diabetic pregnancies.

Promoting early neovascularization by allotransplanted adipose-derived Muse cells in an ovine model of acute myocardial infarction

BACKGROUND

Recent preclinical studies have demonstrated that bone marrow (BM)-derived Muse cells have a homing mechanism to reach damaged cardiac tissue while also being able to reduce myocardial infarct size and improve cardiac function; however, the potential of BM-Muse cells to foster new blood-vessel formation has not been fully assessed. Up to date, adipose tissue (AT)-derived Muse cells remain to be studied in acute myocardial infarction (AMI). The aim of the present study was to analyze in vitro and in vivo the neovascularization capacity of AT-Muse cells while exploring their biodistribution and differentiation potential in a translational ovine model of AMI.

METHODS AND RESULTS

AT-Muse cells were successfully isolated from ovine adipose tissue. In adult sheep, one or more diagonal branches of the left anterior descending coronary artery were permanently ligated for thirty minutes. Sheep were randomized in two groups and treated with intramyocardial injections: Vehicle (PBS, n = 4) and AT-Muse (2x107 AT-Muse cells labeled with PKH26 Red Fluorescent Dye, n = 4). Molecular characterization showed higher expression of angiogenic genes (VEGF, PGF and ANG) and increased number of tube formation in AT-Muse cells group compared to Adipose-derived mesenchymal stromal cells (ASCs) group. At 7 days post-IAM, the AT-Muse group showed significantly more arterioles and capillaries than the Vehicle group. Co-localization of PKH26+ cells with desmin, sarcomeric actin and troponin T implied the differentiation of Muse cells to a cardiac fate; moreover, PKH26+ cells also co-localized with a lectin marker, suggesting a possible differentiation to a vascular lineage.

CONCLUSION

Intramyocardially administered AT-Muse cells displayed a significant neovascularization activity and survival capacity in an ovine model of AMI.

Stem Cell Differentiation into Cardiomyocytes: Current Methods and Emerging Approaches

Cardiovascular diseases (CVDs) are globally known to be important causes of mortality and disabilities. Common treatment strategies for CVDs, such as pharmacological therapeutics impose serious challenges due to the failure of treatments for myocardial necrosis. By contrast, stem cells (SCs) based therapies are seen to be promising approaches to CVDs treatment. In such approaches, cardiomyocytes are differentiated from SCs. To fulfill SCs complete potential, the method should be appointed to generate cardiomyocytes with more mature structure and well-functioning operations. For heart repairing applications, a greatly scalable and medical-grade cardiomyocyte generation must be used. Nonetheless, there are some challenges such as immune rejection, arrhythmogenesis, tumorigenesis, and graft cell death potential. Herein, we discuss the types of potential SCs, and commonly used methods including embryoid bodies related techniques, co-culture, mechanical stimulation, and electrical stimulation and their applications, advantages and limitations in this field. An estimated 17.9 million people died from CVDs in 2019, representing 32 % of all global deaths. Of these deaths, 85 % were due to heart attack and stroke.

A bioinformatics approach for identifying potential molecular mechanisms and key genes involved in COVID-19 associated cardiac remodeling

In 2019 coronavirus disease (COVID-19), whose main complication is respiratory involvement, different organs may also be affected in severe cases. However, COVID-19 associated cardiovascular manifestations are limited at present. The main purpose of this study was to identify potential candidate genes involved in COVID-19-associated heart damage by bioinformatics analysis. Differently expressed genes (DEGs) were identified using transcriptome profiles (GSE150392 and GSE4172) downloaded from the GEO database. After gene and pathway enrichment analyses, PPI network visualization, module analyses, and hub gene extraction were performed using Cytoscape software. A total of 228 (136 up and 92 downregulated) overlapping DEGs were identified at these two microarray datasets. Finally, the top hub genes (FGF2, JUN, TLR4, and VEGFA) were screened out as the critical genes among the DEGs from the PPI network. Identification of critical genes and mechanisms in any disease can lead us to better diagnosis and targeted therapy. Our findings identified core genes shared by inflammatory cardiomyopathy and SARS-CoV-2. The findings of the current study support the idea that these key genes can be used in understanding and managing the long-term cardiovascular effects of COVID-19.

The chromogranin A1-373 fragment reveals how a single change in the protein sequence exerts strong cardioregulatory effects by engaging neuropilin-1

AIM

Chromogranin A (CgA), a 439-residue long protein, is an important cardiovascular regulator and a precursor of various bioactive fragments. Under stressful/pathological conditions, CgA cleavage generates the CgA_1-373 proangiogenic fragment. The present work investigated the possibility that human CgA_1-373 influences the mammalian cardiac performance, evaluating the role of its C-terminal sequence.

METHODS

Haemodynamic assessment was performed on an ex vivo Langendorff rat heart model, while mechanistic studies were performed using perfused hearts, H9c2 cardiomyocytes and in silico.

RESULTS

On the ex vivo heart, CgA_1-373 elicited direct dose-dependent negative inotropism and vasodilation, while CgA_1-372 , a fragment lacking the C-terminal R₃₇₃ residue, was ineffective. Antibodies against the PGPQLR₃₇₃ C-terminal sequence abrogated the CgA_1-373 -dependent cardiac and coronary modulation. Ex vivo studies showed that CgA_1-373 -dependent effects were mediated by endothelium, neuropilin-1 (NRP1) receptor, Akt/NO/Erk1,2 pathways, nitric oxide (NO) production and S-nitrosylation. In vitro experiments on H9c2 cardiomyocytes indicated that CgA_1-373 also induced eNOS activation directly on the cardiomyocyte component by NRP1 targeting and NO involvement and provided beneficial action against isoproterenol-induced hypertrophy, by reducing the increase in cell surface area and brain natriuretic peptide (BNP) release. Molecular docking and all-atom molecular dynamics simulations strongly supported the hypothesis that the C-terminal R₃₇₃ residue of CgA_1-373 directly interacts with NRP1.

CONCLUSION

These results suggest that CgA_1-373 is a new cardioregulatory hormone and that the removal of R₃₇₃ represents a critical switch for turning "off" its cardioregulatory activity.

Cardiotoxic effects of angiogenesis inhibitors

The development of new therapies for cancer has led to dramatic improvements in survivorship. Angiogenesis inhibitors represent one such advancement, revolutionising treatment for a wide range of malignancies. However, these drugs are associated with cardiovascular toxicities which can impact optimal cancer treatment in the short-term and may lead to increased morbidity and mortality in the longer term. Vascular endothelial growth factor inhibitors (VEGFIs) are associated with hypertension, left ventricular systolic dysfunction (LVSD) and heart failure as well as arterial and venous thromboembolism, QTc interval prolongation and arrhythmia. The mechanisms behind the development of VEGFI-associated LVSD and heart failure likely involve the combination of a number of myocardial insults. These include direct myocardial effects, as well as secondary toxicity via coronary or peripheral vascular damage. Cardiac toxicity may result from the 'on-target' effects of VEGF inhibition or 'off-target' effects resulting from inhibition of other tyrosine kinases. Similar mechanisms may be involved in the development of VEGFI-associated right ventricular (RV) dysfunction. Some VEGFIs can be associated with QTc interval prolongation and an increased risk of ventricular and atrial arrhythmia. Further pre-clinical and clinical studies and trials are needed to better understand the impact of VEGFI on the cardiovascular system. Once mechanisms are elucidated, therapies can be investigated in clinical trials and surveillance strategies for identifying VEGFI-associated cardiovascular complications can be developed.

Oxygen Is an Ambivalent Factor for the Differentiation of Human Pluripotent Stem Cells in Cardiac 2D Monolayer and 3D Cardiac Spheroids

Numerous protocols of cardiac differentiation have been established by essentially focusing on specific growth factors on human pluripotent stem cell (hPSC) differentiation efficiency. However, the optimal environmental factors to obtain cardiac myocytes in network are still unclear. The mesoderm germ layer differentiation is known to be enhanced by low oxygen exposure. Here, we hypothesized that low oxygen exposure enhances the molecular and functional maturity of the cardiomyocytes. We aimed at comparing the molecular and functional consequences of low (5% O₂ or LOE) and high oxygen exposure (21% O₂ or HOE) on cardiac differentiation of hPSCs in 2D- and 3D-based protocols. hPSC-CMs were differentiated through both the 2D (monolayer) and 3D (embryoid body) protocols using several lines. Cardiac marker expression and cell morphology were assessed. The mitochondrial localization and metabolic properties were evaluated. The intracellular Ca²⁺ handling and contractile properties were also monitored. The 2D cardiac monolayer can only be differentiated in HOE. The 3D cardiac spheroids containing hPSC-CMs in LOE further exhibited cardiac markers, hypertrophy, steadier SR Ca²⁺ release properties revealing a better SR Ca²⁺ handling, and enhanced contractile force. Preserved distribution of mitochondria and similar oxygen consumption by the mitochondrial respiratory chain complexes were also observed. Our results brought evidences that LOE is moderately beneficial for the 3D cardiac spheroids with hPSC-CMs exhibiting further maturity. In contrast, the 2D cardiac monolayers strictly require HOE.

Vascular endothelial growth factor sustained delivery augmented cell therapy outcomes of cardiac progenitor cells for myocardial infarction

Cell therapy has become a novel promising approach for improvement of cardiac functional capacity in the instances of ventricular remodeling and fibrosis caused by episodes of coronary artery occlusion and hypoxia. The challenge toward enhancing cell engraftment as well as formation of functional tissue, however, necessitated combinatorial approaches. Here, we complemented human embryonic stem cell-derived cardiac progenitor cell (hESC-CPC) therapy by heparin-conjugated, vascular endothelial growth factor (VEGF)-loaded fibrin hydrogel as VEGF delivery system. Transplantation of these cardiac committed cells along with sustained VEGF release could surpass the cardiac repair effects of each constituent alone in a rat model of acute myocardial infarction. The histological sections of rat hearts revealed improved vascularization as well as inclusion of hESC-CPC-derived cardiomyocytes, endothelial, and smooth muscle cells in host myocardium. Thus, co-transplantation of hESC-CPC and proangiogenic factor by a suitable delivery rate may resolve the shortcomings of conventional cell therapy.

Role of Vascular Endothelial Growth Factor and Human Umbilical Vein Endothelial Cells in Designing An In Vitro Vascular-Muscle Cellular Model Using Adipose-Derived Stem Cells

Objective

Researchers have been interested in the creation of a favorable cellular model for use in vascular-muscle tissue engineering. The main objective of this study is to determine the myogenic effects of vascular endothelial growth factor (VEGF) and human umbilical vein endothelial cells (HUVECs) on adipose-derived stem cells (ADSCs) to achieve an in vitro vascular-muscle cellular model.

Materials and Methods

The present experimental research was conducted on two primary groups, namely ADSCs monoculture and ADSCs/HUVECs co-culture that were divided into control, horse serum (HS), and HS/VEGF differentiation subgroups. HUVECs were co-cultured by ADSC in a ratio of 1:1. The myogenic differentiation was evaluated using the reverse transcription-polymerase chain reaction (RT-PCR) and immunofluorescence in different experimental groups. The interaction between ADSCs and HUVECs, as well as the role of ADSCs conditional medium, was investigated for endothelial tube formation assay.

Results

Immunofluorescence staining indicated that Tropomyosin was positive in ADSCs and ADSCs and HUVECs co-culture groups on HS and HS/VEGF culture medium. Furthermore, the MyHC2 gene expression significantly increased in HS and HS/VEGF groups in comparison with the control group (P<0.001). More importantly, there was a significant difference in the mRNA expression of this gene between ADSCs and ADSCs and HUVECs co-culture groups on HS/VEGF culture medium (P<0.05). Current data revealed that the co-culture of ADSCs and HUVECs could develop endothelial network formation in the VEGF-loaded group. Also, the ADSCs-conditioned medium improved the viability and formation of the endothelial tube in the HS and VEGF groups, respectively.

Conclusion

It was concluded that ADSCs/HUVECs co-culture and dual effects of VEGF can lead to the formation of differentiated myoblasts in proximity to endothelial network formations. These in vitro cellular models could be potentially used in vascular-muscle tissue engineering implanted into organ defects where muscle tissue and vascular regeneration were required.

VEGF-A in Cardiomyocytes and Heart Diseases

The vascular endothelial growth factor (VEGF), a homodimeric vasoactive glycoprotein, is the key mediator of angiogenesis. Angiogenesis, the formation of new blood vessels, is responsible for a wide variety of physio/pathological processes, including cardiovascular diseases (CVD). Cardiomyocytes (CM), the main cell type present in the heart, are the source and target of VEGF-A and express its receptors, VEGFR1 and VEGFR2, on their cell surface. The relationship between VEGF-A and the heart is double-sided. On the one hand, VEGF-A activates CM, inducing morphogenesis, contractility and wound healing. On the other hand, VEGF-A is produced by CM during inflammation, mechanical stress and cytokine stimulation. Moreover, high concentrations of VEGF-A have been found in patients affected by different CVD, and are often correlated with an unfavorable prognosis and disease severity. In this review, we summarized the current knowledge about the expression and effects of VEGF-A on CM and the role of VEGF-A in CVD, which are the most important cause of disability and premature death worldwide. Based on clinical studies on angiogenesis therapy conducted to date, it is possible to think that the control of angiogenesis and VEGF-A can lead to better quality and span of life of patients with heart disease.

Robust differentiation of human pluripotent stem cells into endothelial cells via temporal modulation of ETV2 with modified mRNA

Human induced pluripotent stem cell (h-iPSC)-derived endothelial cells (h-iECs) have become a valuable tool in regenerative medicine. However, current differentiation protocols remain inefficient and lack reliability. Here, we describe a method for rapid, consistent, and highly efficient generation of h-iECs. The protocol entails the delivery of modified mRNA encoding the transcription factor ETV2 at the intermediate mesodermal stage of differentiation. This approach reproducibly differentiated 13 diverse h-iPSC lines into h-iECs with exceedingly high efficiency. In contrast, standard differentiation methods that relied on endogenous ETV2 were inefficient and notably inconsistent. Our h-iECs were functionally competent in many respects, including the ability to form perfused vascular networks in vivo. Timely activation of ETV2 was critical, and bypassing the mesodermal stage produced putative h-iECs with reduced expansion potential and inability to form functional vessels. Our protocol has broad applications and could reliably provide an unlimited number of h-iECs for vascular therapies.

Robust differentiation of human pluripotent stem cells into endothelial cells via temporal modulation of ETV2 with modified mRNA

Human induced pluripotent stem cell (h-iPSC)-derived endothelial cells (h-iECs) have become a valuable tool in regenerative medicine. However, current differentiation protocols remain inefficient and lack reliability. Here, we describe a method for rapid, consistent, and highly efficient generation of h-iECs. The protocol entails the delivery of modified mRNA encoding the transcription factor ETV2 at the intermediate mesodermal stage of differentiation. This approach reproducibly differentiated 13 diverse h-iPSC lines into h-iECs with exceedingly high efficiency. In contrast, standard differentiation methods that relied on endogenous ETV2 were inefficient and notably inconsistent. Our h-iECs were functionally competent in many respects, including the ability to form perfused vascular networks in vivo. Timely activation of ETV2 was critical, and bypassing the mesodermal stage produced putative h-iECs with reduced expansion potential and inability to form functional vessels. Our protocol has broad applications and could reliably provide an unlimited number of h-iECs for vascular therapies.

Molecular discoveries and treatment strategies by direct reprogramming in cardiac regeneration

Cardiac tissue has minimal endogenous regenerative capacity in response to injury. Treatment options are limited following tissue damage after events such as myocardial infarction. Current strategies are aimed primarily at injury prevention, but attention has been increasingly targeted toward the development of regenerative therapies. This review focuses on recent developments in the field of cardiac fibroblast reprogramming into induced cardiomyocytes. Early efforts to produce cardiac regeneration centered around induced pluripotent stem cells, but clinical translation has proved elusive. Currently, techniques are being developed to directly transdifferentiate cardiac fibroblasts into induced cardiomyocytes. Viral vector-driven expression of a combination of transcription factors including Gata4, Mef2c, and Tbx5 induced cardiomyocyte development in mice. Subsequent combinational modifications have extended these results to human cell lines and increased efficacy. The miRNAs including combinations of miR-1, miR-133, miR-208, and miR-499 can improve or independently drive regeneration of cardiomyocytes. Similar results could be obtained by combinations of small molecules with or without transcription factor or miRNA expression. The local tissue environment greatly impacts favorability for reprogramming. Modulation of signaling pathways, especially those mediated by VEGF and TGF-β, enhance differentiation to cardiomyocytes. Current reprogramming strategies are not ready for clinical application, but recent breakthroughs promise regenerative cardiac therapies in the near future.

Beyond endothelial cells: Vascular endothelial growth factors in heart, vascular anomalies and placenta

Vascular endothelial growth factors regulate vascular and lymphatic growth. Dysregulation of VEGF signaling is connected to many pathological states, including hemangiomas, arteriovenous malformations and placental abnormalities. In heart, VEGF gene transfer induces myocardial angiogenesis. Besides vascular and lymphatic endothelial cells, VEGFs affect multiple other cell types. Understanding VEGF biology and its paracrine signaling properties will offer new targets for novel treatments of several diseases.

Large-Scale Single-Cell RNA-Seq Reveals Molecular Signatures of Heterogeneous Populations of Human Induced Pluripotent Stem Cell-Derived Endothelial Cells

RATIONALE

Human-induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) have risen as a useful tool in cardiovascular research, offering a wide gamut of translational and clinical applications. However, inefficiency of the currently available iPSC-EC differentiation protocol and underlying heterogeneity of derived iPSC-ECs remain as major limitations of iPSC-EC technology.

OBJECTIVE

Here, we performed droplet-based single-cell RNA sequencing (scRNA-seq) of the human iPSCs after iPSC-EC differentiation. Droplet-based scRNA-seq enables analysis of thousands of cells in parallel, allowing comprehensive analysis of transcriptional heterogeneity.

METHODS AND RESULTS

Bona fide iPSC-EC cluster was identified by scRNA-seq, which expressed high levels of endothelial-specific genes. iPSC-ECs, sorted by CD144 antibody-conjugated magnetic sorting, exhibited standard endothelial morphology and function including tube formation, response to inflammatory signals, and production of NO. Nonendothelial cell populations resulting from the differentiation protocol were identified, which included immature cardiomyocytes, hepatic-like cells, and vascular smooth muscle cells. Furthermore, scRNA-seq analysis of purified iPSC-ECs revealed transcriptional heterogeneity with 4 major subpopulations, marked by robust enrichment of CLDN5, APLNR, GJA5, and ESM1 genes, respectively.

CONCLUSIONS

Massively parallel, droplet-based scRNA-seq allowed meticulous analysis of thousands of human iPSCs subjected to iPSC-EC differentiation. Results showed inefficiency of the differentiation technique, which can be improved with further studies based on identification of molecular signatures that inhibit expansion of nonendothelial cell types. Subtypes of bona fide human iPSC-ECs were also identified, allowing us to sort for iPSC-ECs with specific biological function and identity.

Ascorbic acid induces cardiac differentiation of white adipose tissue-derived stem cells

White adipose tissue (WAT) is the bulk of fatty tissues in humans. Enhancing the potential of WAT-derived stem cells (WATDCs) to generate cardiomyocytes may help supply sufficient number of therapeutically potent cells for heart repair in vivo. Therefore, we investigated whether ascorbic acid (AA) could facilitate the cardiac differentiation of WATDCs and the underlying mechanisms. Our results indicated that AA dose-dependently stimulates the cardiac differentiation of WATDCs, which is supported by the up-regulated expression of cardiac markers and the appearance of myotube-like cell morphologies. Time-course study showed that the front phase (0-4 days) is crucial for the action of AA on cardiac differentiation, which hints that AA may take effect through enhancing the proliferation of cardiac progenitor cells. EdU assay ascertained AA indeed promotes cell growth dose-dependently in the front phase. Further investigation indicated that AA induces the phosphorylation of MEK and ERK, and the synthesis of collagen I (Col I). Interference of MEK/ERK activity or Col I synthesis blocks the cardiomyogenic activity of AA in WATDCs. These findings demonstrated that AA facilitates WATDC cardiogenesis via promoting the proliferation of cardiac progenitor cells through MEK/ERK signaling and collagen synthesis.

Expression of Flk-1 and Cyclin D2 mRNA in the Myocardium of Rats with Doxorubicin-Induced Cardiomyopathy and after Treatment with Betulonic Acid Amide

The expression of VEGFR2 (Flk-1, according to immunohistochemistry) and of cyclin D2 mRNA (according to real-time PCR) in the myocardium of rats is studied in doxorubicin-induced cardiomyopathy and in response to betulonic acid amide. Doxorubicin alone and in combination with betulonic acid amide causes after 3 days a manifest reduction of cyclin D2 mRNA expression (by 38 and 63%, respectively), while injection of betulonic acid amide alone causes a 23-fold increase of cyclin D2 mRNA expression. An increase of cyclin D2 mRNA expression has been detected in all experimental groups after 14 days of experiment, the most pronounced in response to betulonic acid amide (63 times). The expression of Flk-1 in cardiomyocytes increases significantly in response to both chemical agents starting from day 3 of experiment. These results indicate that doxorubicin and betulonic acid amide induce cytoprotective reactions in the myocardium, first at the intracellular, then at the cellular levels.

Constitutive Expression of GATA4 Dramatically Increases the Cardiogenic Potential of D3 Mouse Embryonic Stem Cells

The transcription factor GATA binding protein 4 (GATA4) is a vital regulator of cardiac programming that acts by inducing the expression of many different genes involved in cardiomyogenesis. Here we generated a D3 mouse embryonic stem cell line that constitutively expresses high levels of GATA4 and show that these cells have dramatically increased cardiogenic potential compared to an eGFP-expressing control cell line. Embryoid bodies (EB) derived from the D3-GATA4 line displayed increased levels of cardiac gene expression and showed more abundant cardiomyocyte differentiation than control eGFP EB. These cells and two additional lines expressing lower levels of GATA4 provide a platform to screen previously untested cardiac genes and gene combinations for their ability to further increase the efficiency of cardiomyocyte differentiation beyond that achieved by transgenic GATA4 alone. Non-integrative delivery of identified gene combinations will aid in the production of differentiated cells for the treatment of ischemic cardiomyopathy.

Vascular endothelial growth factor-A gene electrotransfer promotes angiogenesis in a porcine model of cardiac ischemia

This study aimed to assess safety and therapeutic potential of gene electrotransfer as a method for delivery of plasmid encoding vascular endothelial growth factor A to ischemic myocardium in a porcine model. Myocardial ischemia was induced by surgically occluding the left anterior descending coronary artery in swine. Gene electrotransfer following plasmid encoding vascular endothelial growth factor A injection was performed at four sites in the ischemic region. Control groups either received injections of the plasmid without electrotransfer or injections of saline vehicle. Animals were monitored for seven weeks and hearts were evaluated for angiogenesis, myocardial infarct size, and left ventricular contractility. Arteriograms suggest growth of new arteries as early as two weeks post treatment in electrotransfer animals. There is a significant reduction of infarct area and left ventricular contractility is improved in gene electrotransfer treated group compared to controls. There was no significant difference in mortality of animals treated with gene electrotransfer of plasmid encoding vascular endothelial growth factor A from control groups. Gene delivery of plasmid encoding vascular endothelial growth factor A to ischemic myocardium in a porcine model can be accomplished safely with potential for myocardial repair and regeneration.

G-protein Coupled Receptor Signaling in Pluripotent Stem Cell-derived Cardiovascular Cells: Implications for Disease Modeling

Human pluripotent stem cell derivatives show promise as an in vitro platform to study a range of human cardiovascular diseases. A better understanding of the biology of stem cells and their cardiovascular derivatives will help to understand the strengths and limitations of this new model system. G-protein coupled receptors (GPCRs) are key regulators of stem cell maintenance and differentiation and have an important role in cardiovascular cell signaling. In this review, we will therefore describe the state of knowledge concerning the regulatory role of GPCRs in both the generation and function of pluripotent stem cell derived-cardiomyocytes, -endothelial, and -vascular smooth muscle cells. We will consider how far the in vitro disease models recapitulate authentic GPCR signaling and provide a useful basis for discovery of disease mechanisms or design of therapeutic strategies.

Signaling molecules, transcription growth factors and other regulators revealed from in-vivo and in-vitro models for the regulation of cardiac development

Several in-vivo heart developmental models have been applied to decipher the cardiac developmental patterning encompassing early, dorsal, cardiac and visceral mesoderm as well as various transcription factors such as Gata, Hand, Tin, Dpp, Pnr. The expression of cardiac specific transcription factors, such as Gata4, Tbx5, Tbx20, Tbx2, Tbx3, Mef2c, Hey1 and Hand1 are of fundamental significance for the in-vivo cardiac development. Not only the transcription factors, but also the signaling molecules involved in cardiac development were conserved among various species. Enrichment of the bone morphogenic proteins (BMPs) in the anterior lateral plate mesoderm is essential for the initiation of myocardial differentiation and the cardiac developmental process. Moreover, the expression of a number of cardiac transcription factors and structural genes initiate cardiac differentiation in the medial mesoderm. Other signaling molecules such as TGF-beta, IGF-1/2 and the fibroblast growth factor (FGF) play a significant role in cardiac repair/regeneration, ventricular heart development and specification of early cardiac mesoderm, respectively. The role of the Wnt signaling in cardiac development is still controversial discussed, as in-vitro results differ dramatically in relation to the animal models. Embryonic stem cells (ESC) were utilized as an important in-vitro model for the elucidation of the cardiac developmental processes since they can be easily manipulated by numerous signaling molecules, growth factors, small molecules and genetic manipulation. Finally, in the present review the dynamic role of the long noncoding RNA and miRNAs in the regulation of cardiac development are summarized and discussed.

Hydrogels as carriers for stem cell transplantation

Stem cells are a promising source for cell replacement therapy for several degenerative conditions. However, a number of limitations such as low cell survival, uncontrolled and/or low differentiation, induction of host immune response, and the risk of teratoma formation remain as challenges. In this review, we explore the utility of hydrogels as carriers for stem cell delivery and their potential to overcome some of the current limitations in stem cell therapy. We focus on in situ gelling hydrogels, and also discuss other strategies to modulate the immune response to promote controlled stem cell differentiation. Immunomodulatory hydrogels and gels designed to promote cell survival and integration into the host site will likely have a significant effect on enhancing the efficacy of stem cell transplantation as a therapy for debilitating degenerative diseases.

Considerations in designing systems for large scale production of human cardiomyocytes from pluripotent stem cells

Human pluripotent stem cell (hPSC)-derived cardiomyocytes have attracted attention as an unlimited source of cells for cardiac therapies. One of the factors to surmount to achieve this is the production of hPSC-derived cardiomyocytes at a commercial or clinical scale with economically and technically feasible platforms. Given the limited proliferation capacity of differentiated cardiomyocytes and the difficulties in isolating and culturing committed cardiac progenitors, the strategy for cardiomyocyte production would be biphasic, involving hPSC expansion to generate adequate cell numbers followed by differentiation to cardiomyocytes for specific applications. This review summarizes and discusses up-to-date two-dimensional cell culture, cell-aggregate and microcarrier-based platforms for hPSC expansion. Microcarrier-based platforms are shown to be the most suitable for up-scaled production of hPSCs. Subsequently, different platforms for directing hPSC differentiation to cardiomyocytes are discussed. Monolayer differentiation can be straightforward and highly efficient and embryoid body-based approaches are also yielding reasonable cardiomyocyte efficiencies, whereas microcarrier-based approaches are in their infancy but can also generate high cardiomyocyte yields. The optimal target is to establish an integrated scalable process that combines hPSC expansion and cardiomyocyte differentiation into a one unit operation. This review discuss key issues such as platform selection, bioprocess parameters, medium development, downstream processing and parameters that meet current good manufacturing practice standards.

Emulsion electrospun nanofibers as substrates for cardiomyogenic differentiation of mesenchymal stem cells

The potential of cardiomyogenic differentiation of human mesenchymal stem cells (hMSCs) on emulsion electrospun scaffold containing poly(L-lactic acid)-co-poly-(ε-caprolactone), gelatin and vascular endothelial growth factor (PLCL/GV) was investigated in this study. The characterizations of the scaffold were carried out using scanning electron microscope (SEM), transmission electron microscope, water contact angle and porometer. The proliferation of hMSCs showed that 73.4% higher cell proliferation on PLCL/GV scaffolds than that on PLCL scaffold after 20 days of cell culture. Results of 5-chloromethylfluorescein diacetate staining and SEM morphology analysis indicated that hMSCs differentiated on PLCL/GV scaffolds showed irregular morphology of cardiomyocyte phenotype compared to the typical long and thin hMSC phenotype. Immunostaining results showed the expression of alpha actinin and myosin heavy chain. Our studies identified emulsion electrospinning as a method for fabrication of core-shell fibers suitable for the differentiation of stem cells to cardiac cells, with potential application in cardiac regeneration.

Utx is required for proper induction of ectoderm and mesoderm during differentiation of embryonic stem cells

Embryonic development requires chromatin remodeling for dynamic regulation of gene expression patterns to ensure silencing of pluripotent transcription factors and activation of developmental regulators. Demethylation of H3K27me3 by the histone demethylases Utx and Jmjd3 is important for the activation of lineage choice genes in response to developmental signals. To further understand the function of Utx in pluripotency and differentiation we generated Utx knockout embryonic stem cells (ESCs). Here we show that Utx is not required for the proliferation of ESCs, however, Utx contributes to the establishment of ectoderm and mesoderm in vitro. Interestingly, this contribution is independent of the catalytic activity of Utx. Furthermore, we provide data showing that the Utx homologue, Uty, which is devoid of detectable demethylase activity, and Jmjd3 partly compensate for the loss of Utx. Taken together our results show that Utx is required for proper formation of ectoderm and mesoderm in vitro, and that Utx, similar to its C.elegans homologue, has demethylase dependent and independent functions.

The potential role of aerobic exercise to modulate cardiotoxicity of molecularly targeted cancer therapeutics

Molecularly targeted therapeutics (MTT) are the future of cancer systemic therapy. They have already moved from palliative therapy for advanced solid malignancies into the setting of curative-intent treatment for early-stage disease. Cardiotoxicity is a frequent and potentially serious adverse complication of some targeted therapies, leading to a broad range of potentially life-threatening complications, therapy discontinuation, and poor quality of life. Low-cost pleiotropic interventions are therefore urgently required to effectively prevent and/or treat MTT-induced cardiotoxicity. Aerobic exercise therapy has the unique capacity to modulate, without toxicity, multiple gene expression pathways in several organ systems, including a plethora of cardiac-specific molecular and cell-signaling pathways implicated in MTT-induced cardiac toxicity. In this review, we examine the molecular signaling of antiangiogenic and HER2-directed therapies that may underpin cardiac toxicity and the hypothesized molecular mechanisms underlying the cardioprotective properties of aerobic exercise. It is hoped that this knowledge can be used to maximize the benefits of small molecule inhibitors, while minimizing cardiac damage in patients with solid malignancies.

Effective cardiac myocyte differentiation of human induced pluripotent stem cells requires VEGF

Perhaps one of the most significant achievements in modern science is the discovery of human induced pluripotent stem cells (hiPSCs), which have paved the way for regeneration therapy using patients’ own cells. Cardiomyocytes differentiated from hiPSCs (hiPSC-CMs) could be used for modelling patients with heart failure, for testing new drugs, and for cellular therapy in the future. However, the present cardiomyocyte differentiation protocols exhibit variable differentiation efficiency across different hiPSC lines, which inhibit the application of this technology significantly. Here, we demonstrate a novel myocyte differentiation protocol that can yield a significant, high percentage of cardiac myocyte differentiation (>85%) in 2 hiPSC lines, which makes the fabrication of a human cardiac muscle patch possible. The established hiPSCs cell lines being examined include the transgene integrated UCBiPS7 derived from cord blood cells and non-integrated PCBC16iPS from skin fibroblasts. The results indicate that hiPSC-CMs derived from established hiPSC lines respond to adrenergic or acetylcholine stimulation and beat regularly for greater than 60 days. This data also demonstrates that this novel differentiation protocol can efficiently generate hiPSC-CMs from iPSC lines that are derived not only from fibroblasts, but also from blood mononuclear cells.

In vivo cardiac cellular reprogramming efficacy is enhanced by angiogenic preconditioning of the infarcted myocardium with vascular endothelial growth factor

BACKGROUND

In situ cellular reprogramming offers the possibility of regenerating functional cardiomyocytes directly from scar fibroblasts, obviating the challenges of cell implantation. We hypothesized that pretreating scar with gene transfer of the angiogenic vascular endothelial growth factor (VEGF) would enhance the efficacy of this strategy.

METHODS AND RESULTS

Gata4, Mef2c, and Tbx5 (GMT) administration via lentiviral transduction was demonstrated to transdifferentiate rat fibroblasts into (induced) cardiomyocytes in vitro by cardiomyocyte marker studies. Fisher 344 rats underwent coronary ligation and intramyocardial administration of an adenovirus encoding all 3 major isoforms of VEGF (AdVEGF-All6A(+)) or an AdNull control vector (n=12/group). Lentivirus encoding GMT or a GFP control was administered to each animal 3 weeks later, followed by histologic and echocardiographic analyses. GMT administration reduced the extent of fibrosis by half compared with GFP controls (12 ± 2% vs 24 ± 3%, P<0.01) and reduced the number of myofibroblasts detected in the infarct zone by 4-fold. GMT-treated animals also demonstrated greater density of cardiomyocyte-specific marker beta myosin heavy chain 7(+) cells compared with animals receiving GFP with or without VEGF (P<0.01). Ejection fraction was significantly improved after GMT vs GFP administration (12 ± 3% vs -7 ± 3%, P<0.01). Eight (73%) GFP animals but no GMT animals demonstrated decreased ejection fraction during this interval (P<0.01). Also, improvement in ejection fraction was 4-fold greater in GMT/VEGF vs GMT/null animals (17 ± 2% vs 4 ± 1%, P<0.05).

CONCLUSIONS

VEGF administration to infarcted myocardium enhances the efficacy of GMT-mediated cellular reprogramming in improving myocardial function and reducing the extent of myocardial fibrosis compared with the use of GMT or VEGF alone.

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.

Sustained delivery of VEGF from designer self-assembling peptides improves cardiac function after myocardial infarction

Poor vascularization and insufficient oxygen supply are detrimental to the survival of residual cardiomyocytes or transplanted stem cells after myocardial infarction. To prolong and slow the release of angiogenic factors, which stimulate both angiogenesis and vasculogenesis, we constructed a novel self-assembling peptide by attaching the heparin-binding domain sequence LRKKLGKA to the self-assembling peptide RADA16. This designer self-assembling peptide self-assembled into nanofiber scaffolds under physiological conditions, as observed by atomic force microscopy. The injection of designer self-assembling peptides can efficiently provide the sustained delivery of VEGF for at least 1 month. At 4 weeks after transplantation, cardiac function was improved, and scar size and collagen deposition were markedly reduced in the group receiving VEGF with the LRKKLGKA scaffolds compared with groups receiving VEGF alone, LRKKLGKA scaffolds alone or VEGF with RADA16 scaffolds. The microvessel density in the VEGF with LRKKLGKA group was higher than that in the VEGF with RADA16 group. TUNEL and cleaved caspase-3 expression assays showed that the transplantation of VEGF with LRKKLGKA enhanced cell survival in the infarcted heart. These results present the tailor-made peptide scaffolds as a new generation of sustained-release biomimetic biomaterials and suggest that the use of angiogenic factors along with designer self-assembling peptides can lead to myocardial protection, sufficient angiogenesis, and improvement in cardiac function.

Evaluation of endothelial cells differentiated from amniotic fluid-derived stem cells

Amniotic fluid holds great promise as a stem cell source, especially in neonatal applications where autologous cells can be isolated and used. This study examined chemical-mediated differentiation of amniotic fluid-derived stem cells (AFSC) into endothelial cells and verified the function of AFSC-derived endothelial cells (AFSC-EC). AFSC were isolated from amniotic fluid obtained from second trimester amnioreduction as part of therapeutic intervention from pregnancies affected with twin-twin transfusion syndrome. Undifferentiated AFSC were of normal karyotype with a subpopulation of cells positive for the embryonic stem cell marker SSEA4, hematopoietic stem cell marker c-kit, and mesenchymal stem cell markers CD29, CD44, CD73, CD90, and CD105. Additionally, these cells were negative for the endothelial marker CD31 and hematopoietic differentiation marker CD45. AFSC were cultured in endothelial growth media with concentrations of vascular endothelial growth factor (VEGF) ranging from 1 to 100 ng/mL. After 2 weeks, AFSC-EC expressed von Willebrand factor, endothelial nitric oxide synthase, CD31, VE-cadherin, and VEGF receptor 2. Additionally, the percentage of cells expressing CD31 was positively correlated with VEGF concentration up to 50 ng/mL, with no increase at higher concentrations. AFSC-EC showed a decrease in stem cells markers c-kit and SSEA4 and were morphologically similar to human umbilical vein endothelial cells (HUVEC). In functional assays, AFSC-EC formed networks and metabolized acetylated low-density lipoprotein, also characteristic of HUVEC. Nitrate levels for AFSC-EC, an indirect measure of nitric oxide synthesis, were significantly higher than undifferentiated controls and significantly lower than HUVEC. These results indicate that AFSC can differentiate into functional endothelial-like cells and may have the potential to provide vascularization for constructs used in regenerative medicine strategies.

Cobalt chloride pretreatment promotes cardiac differentiation of human embryonic stem cells under atmospheric oxygen level

Our previous study demonstrated the direct involvement of the HIF-1α subunit in the promotion of cardiac differentiation of murine embryonic stem cells (ESCs). We report the use of cobalt chloride to induce HIF-1α stabilization in human ESCs to promote cardiac differentiation. Treatment of undifferentiated hES2 human ESCs with 50 μM cobalt chloride markedly increased protein levels of the HIF-1α subunit, and was associated with increased expression of early cardiac specific transcription factors and cardiotrophic factors including NK2.5, vascular endothelial growth factor, and cardiotrophin-1. When pretreated cells were subjected to cardiac differentiation, a notable increase in the occurrence of beating embryoid bodies and sarcomeric actinin-positive cells was observed, along with increased expression of the cardiac-specific markers, MHC-A, MHC-B, and MLC2V. Electrophysiological study revealed increased atrial- and nodal-like cells in the cobalt chloride-pretreated group. Confocal calcium imaging analysis indicated that the maximum upstroke and decay velocities were significantly increased in both noncaffeine and caffeine-induced calcium transient in cardiomyocytes derived from the cobalt chloride-pretreated cells, suggesting these cells were functionally more mature. In conclusion, our study demonstrated that cobalt chloride pretreatment of hES2 human ESCs promotes cardiac differentiation and the maturation of calcium homeostasis of cardiomyocytes derived from ESCs.

Transcriptome transfer provides a model for understanding the phenotype of cardiomyocytes

We show that the transfer of the adult ventricular myocyte (AVM) transcriptome into either a fibroblast or an astrocyte converts the host cell into a cardiomyocyte. Transcriptome-effected cardiomyocytes (tCardiomyocytes) display morphologies, immunocytochemical properties, and expression profiles of postnatal cardiomyocytes. Cell morphology analysis shows that tCardiomyoctes are elongated and have a similar length-to-width ratio as AVMs. These global phenotypic changes occur in a time-dependent manner and confer electroexcitability to the tCardiomyocytes. tCardiomyocyte generation does not require continuous overexpression of specific transcription factors; for example, the expression level of transcription factor Mef2c is higher in tCardiomyocytes than in fibroblasts, but similar in tCardiomyocytes and AVMs. These data highlight the dominant role of the gene expression profile in developing and maintaining cellular phenotype. The transcriptome-induced phenotype remodeling-generated tCardiomyocyte has significant implications for understanding and modulating cardiac disease development.

VEGF-mediated PI3K class IA and PKC signaling in cardiomyogenesis and vasculogenesis of mouse embryonic stem cells

VEGF-, phosphoinositide 3-kinase (PI3K)- and protein kinase C (PKC)-regulated signaling in cardiac and vascular differentiation was investigated in mouse ES cells and in ES cell-derived Flk-1⁺ cardiovascular progenitor cells. Inhibition of PI3K by wortmannin and LY294002, disruption of PI3K catalytic subunits p110α and p110δ using short hairpin RNA (shRNA), or inhibition of p110α with compound 15e and of p110δ with IC-87114 impaired cardiac and vascular differentiation. By contrast, TGX-221, an inhibitor of p110β, and shRNA knockdown of p110β were without significant effects. Antagonists of the PKC family, i.e. bisindolylmaleimide-1 (BIM-1), GÖ 6976 (targeting PKCα/βII) and rottlerin (targeting PKCδ) abolished vasculogenesis, but not cardiomyogenesis. Inhibition of Akt blunted cardiac as well as vascular differentiation. VEGF induced phosphorylation of PKCα/βII and PKCδ but not PKCζ. This was abolished by PI3K inhibitors and the VEGFR-2 antagonist SU5614. Furthermore, phosphorylation of Akt and phosphoinositide-dependent kinase-1 (PDK1) was blunted upon inhibition of PI3K, but not upon inhibition of PKC by BIM-1, suggesting that activation of Akt and PDK1 by VEGF required PI3K but not PKC. In summary, we demonstrate that PI3K catalytic subunits p110α and p110δ are central to cardiovasculogenesis of ES cells. Akt downstream of PI3K is involved in both cardiomyogenesis and vasculogenesis, whereas PKC is involved only in vasculogenesis.

Ouabain facilitates cardiac differentiation of mouse embryonic stem cells through ERK1/2 pathway

AIM

To investigate the effects of the cardiotonic steroid, ouabain, on cardiac differentiation of murine embyronic stem cells (mESCs).

METHODS

Cardiac differentiation of murine ESCs was enhanced by standard hanging drop method in the presence of ouabain (20 μmol/L) for 7 d. The dissociated ES derived cardiomyocytes were examined by flow cytometry, RT-PCR and confocal calcium imaging.

RESULTS

Compared with control, mESCs treated with ouabain (20 μmol/L) yielded a significantly higher percentage of cardiomyocytes, and significantly increased expression of a panel of cardiac markers including Nkx 2.5, α-MHC, and β-MHC. The α1 and 2- isoforms Na(+)/K(+)-ATPase, on which ouabain acted, were also increased in mESCs during differentiation. Among the three MAPKs involved in the cardiac hypertrophy pathway, ouabain enhanced ERK1/2 activation. Blockage of the Erk1/2 pathway by U0126 (10 μmol/L) inhibited cardiac differentiation while ouabain (20 μmol/L) rescued the effect. Interestingly, the expression of calcium handling proteins, including ryanodine receptor (RyR2) and sacroplasmic recticulum Ca(2+) ATPase (SERCA2a) was also upregulated in ouabain-treated mESCs. ESC-derived cardiomyocyes (CM) treated with ouabain appeared to have more mature calcium handling. As demonstrated by confocal Ca(2+) imaging, cardiomyocytes isolated from ouabain-treated mESCs exhibited higher maximum upstroke velocity (P<0.01) and maximum decay velocity (P<0.05), as well as a higher amplitude of caffeine induced Ca(2+) transient (P<0.05), suggesting more mature sarcoplasmic reticulum (SR).

CONCLUSION

Ouabain induces cardiac differentiation and maturation of mESC-derived cardiomyocytes via activation of Erk1/2 and more mature SR for calcium handling.

Mitogen-activated protein kinase signaling in the heart: angels versus demons in a heart-breaking tale

Among the myriad of intracellular signaling networks that govern the cardiac development and pathogenesis, mitogen-activated protein kinases (MAPKs) are prominent players that have been the focus of extensive investigations in the past decades. The four best characterized MAPK subfamilies, ERK1/2, JNK, p38, and ERK5, are the targets of pharmacological and genetic manipulations to uncover their roles in cardiac development, function, and diseases. However, information reported in the literature from these efforts has not yet resulted in a clear view about the roles of specific MAPK pathways in heart. Rather, controversies from contradictive results have led to a perception that MAPKs are ambiguous characters in heart with both protective and detrimental effects. The primary object of this review is to provide a comprehensive overview of the current progress, in an effort to highlight the areas where consensus is established verses the ones where controversy remains. MAPKs in cardiac development, cardiac hypertrophy, ischemia/reperfusion injury, and pathological remodeling are the main focuses of this review as these represent the most critical issues for evaluating MAPKs as viable targets of therapeutic development. The studies presented in this review will help to reveal the major challenges in the field and the limitations of current approaches and point to a critical need in future studies to gain better understanding of the fundamental mechanisms of MAPK function and regulation in the heart.

Strategies for ensuring that regenerative cardiomyocytes function properly and in cooperation with the host myocardium

In developed countries, in which people have nutrient-rich diets, convenient environments, and access to numerous medications, the disease paradigm has changed. Nowadays, heart failure is one of the major causes of death. In spite of this, the therapeutic efficacies of medications are generally unsatisfactory. Although whole heart transplantation is ideal for younger patients with heart failure, many patients are deemed to be unsuitable for this type of surgery due to complications and/or age. The need for therapeutic alternatives to heart transplantation is great. Regenerative therapy is a strong option. For this purpose, several cell sources have been investigated, including intrinsic adult stem or progenitor cells and extrinsic pluripotent stem cells. Most intrinsic stem cells seem to contribute to a regenerative environment via paracrine factors and/or angiogenesis, whereas extrinsic pluripotent stem cells are unlimited sources of cardiomyocytes. In this review, we summarize the various strategies for using regenerative cardiomyocytes including our recent progressions: non-genetic approaches for the purification of cardiomyocytes and efficient transplantation. We expect that use of intrinsic and extrinsic stem cells in combination will enhance therapeutic effectiveness.

Impact of anti-apoptotic and anti-oxidative effects of bone marrow mesenchymal stem cells with transient overexpression of heme oxygenase-1 on myocardial ischemia

Although mesenchymal stem cells (MSCs) have therapeutic potential for tissue injury, intolerance and poor cell viability limit their reparative capability. Therefore, we examined the impact of bone marrow-derived MSCs, in which heme oxygenase-1 (HO-1) was transiently overexpressed, on the repair of an ischemic myocardial injury. When MSCs and HO-1-overexpressed MSCs (MSCHO-1) were exposed to serum deprivation/hypoxia or H2O2-induced oxidative stress, MSCHO-1 exhibited increased resistance to cell apoptosis compared with MSCs (17 ± 1 vs. 30 ± 2%, P < 0.05) and were markedly resistant to cell death (2 ± 1 vs. 32 ± 2%, P < 0.05). Under these conditions, vascular endothelial growth factor (VEGF) production was 2.1-fold greater in MSCHO-1 than in MSCs. Pretreatment of MSCs and MSCHO-1 with phosphatidylinositol 3-kinase (PI 3-kinase)/protein kinase B (Akt) pathway inhibitors such as LY-294002 (50 μM) or wortmannin (100 nM) significantly decreased VEGF production. In a rat infarction model with MSCs or MSCHO-1 (5 × 106 ± 0.1 × 106 cells/rat) transplantation, the number of TdT-mediated dUTP nick end-labeling-positive cells was significantly lower in the MSCHO-1 group than in the MSC group (12.1 ± 1.0 cells/field vs. 26.5 ± 2.6, P < 0.05) on the 4th day after cell transplantation. On the 28th day, increased capillary density associated with decreased infarction size was observed in the MSCHO-1 group (1,415 ± 47/mm2 with 21.6 ± 2.3%) compared with those in the MSCs group (1,215 ± 43/mm2 with 28.2 ± 2.3%, P < 0.05), although infarction size relative to area at risk was not different in each group at 24 h after transplantation. These results demonstrate that MSCHO-1 exhibit markedly enhanced anti-apoptotic and anti-oxidative capabilities compared with MSCs, thus contributing to improved repair of ischemic myocardial injury through cell survival and VEGF production associated with the PI 3-kinase/Akt pathway.

Cardiogenic induction of pluripotent stem cells streamlined through a conserved SDF-1/VEGF/BMP2 integrated network

Background

Pluripotent stem cells produce tissue-specific lineages through programmed acquisition of sequential gene expression patterns that function as a blueprint for organ formation. As embryonic stem cells respond concomitantly to diverse signaling pathways during differentiation, extraction of a pro-cardiogenic network would offer a roadmap to streamline cardiac progenitor output.

Methods and Results

To resolve gene ontology priorities within precursor transcriptomes, cardiogenic subpopulations were here generated according to either growth factor guidance or stage-specific biomarker sorting. Innate expression profiles were independently delineated through unbiased systems biology mapping, and cross-referenced to filter transcriptional noise unmasking a conserved progenitor motif (55 up- and 233 down-regulated genes). The streamlined pool of 288 genes organized into a core biological network that prioritized the “Cardiovascular Development” function. Recursive in silico deconvolution of the cardiogenic neighborhood and associated canonical signaling pathways identified a combination of integrated axes, CXCR4/SDF-1, Flk-1/VEGF and BMP2r/BMP2, predicted to synchronize cardiac specification. In vitro targeting of the resolved triad in embryoid bodies accelerated expression of Nkx2.5, Mef2C and cardiac-MHC, enhanced beating activity, and augmented cardiogenic yield.

Conclusions

Transcriptome-wide dissection of a conserved progenitor profile thus revealed functional highways that coordinate cardiogenic maturation from a pluripotent ground state. Validating the bioinformatics algorithm established a strategy to rationally modulate cell fate, and optimize stem cell-derived cardiogenesis.

Sphingosine 1-phosphate regulation of extracellular signal-regulated kinase-1/2 in embryonic stem cells

Recent evidence suggests that sphingosine 1-phosphate (S1P) regulates self-renewal of human embryonic stem (ES) cells and differentiation of mouse embryoid bodies (derived from mouse ES cells) to cardiomyocytes. We have investigated the role of S1P in regulating ERK-1/2 signaling in mouse ES cells. In this regard, we found that both mouse ES-D3 and CGR8 cells express S1P(1), S1P(2), S1P(3), and S1P(5) but lack S1P(4). The treatment of ES cells with S1P induced the activation of ERK-1/2 via a mechanism that was not mediated by S1P(1), S1P(2), or S1P(3). This was based on: (i) the failure of S1P(1), S1P(2), or S1P(3) antagonists to inhibit S1P-stimulated ERK-1/2 activation and (ii) the failure of SEW 2871 (S1P(1) receptor agonist) to stimulate ERK-1/2 activation. The treatment of ES cells with phytosphingosine 1-phosphate (phyto-S1P), which we show here is an agonist of the S1P(5) receptor, stimulated ERK-1/2 activation. These findings therefore suggest that S1P(5) may mediate the effects of S1P in terms of regulating ERK-1/2 signaling in ES cells. The S1P-dependent activation of ERK-1/2 was sensitive to inhibition by pertussis toxin (uncouples the G-protein, G(i) from GPCR), bisindolylmaleimide I (PKC inhibitor), and PP2 (c-Src inhibitor), but was not reduced by LY29004 (PI3K inhibitor) suggesting that S1P uses G(i)-, PKC-, and c-Src-dependent mechanisms to activate the ERK-1/2 pathway in ES cells.

Engineering microenvironments for embryonic stem cell differentiation to cardiomyocytes

Embryonic stem cells and induced pluripotent stem cells have the potential to be a renewable source of cardiomyocytes for use in myocardial cell replacement strategies. Although progress has been made towards differentiating stem cells to specific cell lineages, the efficiency is often poor and the number of cells generated is not suitable for therapeutic usage. Recent studies demonstrated that controlling the stem cell microenvironment can influence differentiation. Components of the extracellular matrix are important physiological regulators and can provide mechanical cues, direct differentiation and improve cell engraftment into damaged tissue. Bioreactors are used to control the microenvironment and produce large numbers of desired cells. This article describes recent methods to achieve cardiomyocyte differentiation by engineering the stem cell microenvironment. Successful translation of stem cell research to therapeutic applications will need to address large-scale cardiomyocyte differentiation and purification, assessment of cardiac function and synchronization, and safety concerns.

Myocardial interstitial fluid inhibits proliferation and cardiomyocyte differentiation in pluripotent embryonic stem cells

Several recent studies have demonstrated that the transplantation of pluripotent murine embryonic stem cells (mESCs) can improve or restore the function of infarcted myocardium. Although the extent of remuscularization and its contribution to the restoration of function are unclear, these outcomes are likely strongly influenced by factors in the infarcted and/or ischemic environment. As an initial step toward understanding how the ischemic environment of host myocardium affects transplanted pluripotent cells, we have taken a reductionist approach wherein mESCs are cultured in medium containing ischemic myocardial interstitial fluid (iMIF). iMIF is generated in canine myocardium during eight hourly episodes of transient ischemia and collected on a daily basis, over a 24-day collection period. iMIF strongly reduced the numbers of pluripotent mESCs after 11 days in culture. This inhibitory effect, which was most pronounced for iMIF pools from early time points of the 24-day collection period, resulted from an inhibition of cell proliferation. iMIF also inhibited the differentiation of pluripotent mESCs into cardiomyocytes. By contrast, the expression of vascular smooth muscle and endothelial cell markers was relatively unaffected, consistent with previous findings that iMIF promotes angiogenesis. Taken together, these results suggest that whereas the ischemic/infarcted environment is favorable to stem cell-mediated angiogenesis, it is hostile to cardiac myogenesis. These findings also imply that observations of mESC-mediated improvement of cardiac function after transplantation of pluripotent cells do not reflect remuscularization.

Neuregulin-1 promotes cardiomyocyte differentiation of genetically engineered embryonic stem cell clones

Embryonic stem (ES) cell-derived cardiomyocytes (ESCMs) must be specifically purified in order to prevent teratoma formation, and this confusing issue has hampered their clinical application. We therefore investigated a technique to generate pure labeled ESCMs for possible use in cardiac repair. We generated transgenic ES cell lines expressing enhanced green fluorescent protein (EGFP) under the transcriptional control of the alpha-cardiac myosin heavy chain (alpha-MHC) promoter. Differentiated EGFP-positive ES cells displayed characteristics of CMs. Furthermore, neuregulin-1 (NRG-1) upregulated the expression of the cardiac-restricted transcription factors Nkx2.5 and GATA-4, as well as differentiated CM factors (alpha-MHC, beta-MHC). Immunohistochemistry demonstrated that NRG-1 increased expression of cardiac-specific troponin T in the beating foci of the embryoid bodies. This work revealed a potential method for specifically labeling and enriching ESCMs by combining genetically-engineered ES cell clones and exogenous growth factor treatment.