Cardiogenesis In Embryonic Stem Cells Research Articles

Trajectory mapping of human embryonic stem cell cardiogenesis reveals lineage branch points and an ISL1 progenitor-derived cardiac fibroblast lineage.

A family of multipotent heart progenitors plays a central role in the generation of diverse myogenic and nonmyogenic lineages in the heart. Cardiac progenitors in particular play a significant role in lineages involved in disease, and have also emerged to be a strong therapeutic candidate. Based on this premise, we aimed to deeply characterize the progenitor stage of cardiac differentiation at a single-cell resolution. Integrated comparison with an embryonic 5-week human heart transcriptomic dataset validated lineage identities with their late stage in vitro counterparts, highlighting the relevance of an in vitro differentiation for progenitors that are developmentally too early to be accessed in vivo. We utilized trajectory mapping to elucidate progenitor lineage branching points, which are supported by RNA velocity. Nonmyogenic populations, including cardiac fibroblast-like cells and endoderm, were found, and we identified TGFBI as a candidate marker for human cardiac fibroblasts in vivo and in vitro. Both myogenic and nonmyogenic populations express ISL1, and its loss redirected myogenic progenitors into a neural-like fate. Our study provides important insights into processes during early heart development.

PinX1t, a Novel PinX1 Transcript Variant, Positively Regulates Cardiogenesis of Embryonic Stem Cells.

BackgroundPin2/TRF1‐interacting protein, PinX1, was previously identified as a tumor suppressor. Here, we discovered a novel transcript variant of mPinX1 (mouse PinX1), mPinX1t (mouse PinX1t), in embryonic stem cells (ESCs). The aims of this investigation were (1) to detect the presence of mPinX1 and mPinX1t in ESCs and their differentiation derivatives; (2) to investigate the role of mPinX1 and mPinX1t on regulating the characteristics of undifferentiated ESCs and the cardiac differentiation of ESCs; (3) to elucidate the molecular mechanisms of how mPinX1 and mPinX1t regulate the cardiac differentiation of ESCs.Methods and ResultsBy 5′ rapid amplification of cDNA ends, 3′ rapid amplification of cDNA ends, and polysome fractionation followed by reverse transcription–polymerase chain reaction, mPinX1t transcript was confirmed to be an intact mRNA that is actively translated. Western blot confirmed the existence of mPinX1t protein. Overexpression or knockdown of mPinX1 (both decreased mPinX1t expression) both decreased while overexpression of mPinX1t increased the cardiac differentiation of ESCs. Although both mPinX1 and mPinX1t proteins were found to bind to cardiac transcription factor mRNAs, only mPinX1t protein but not mPinX1 protein was found to bind to nucleoporin 133 protein, a nuclear pore complex component. In addition, mPinX1t‐containing cells were found to have a higher cytosol‐to‐nucleus ratio of cardiac transcription factor mRNAs when compared with that in the control cells. Our data suggested that mPinX1t may positively regulate cardiac differentiation by enhancing export of cardiac transcription factor mRNAs through interacting with nucleoporin 133.ConclusionsWe discovered a novel transcript variant of mPinX1, the mPinX1t, which positively regulates the cardiac differentiation of ESCs.

Cardiogenesis of embryonic stem cells with liquid marble micro-bioreactor.

A liquid marble micro-bioreactor is prepared by placing a drop of murine embryonic stem cell (ESC) (Oct4B2-ESC) suspension onto a polytetrafluoroethylene (PTFE) particle bed. The Oct4B2-ESC aggregates to form embryoid bodies (EBs) with relatively uniform size and shape in a liquid marble within 3 d. For the first time, the feasibility of differentiating ESC into cardiac lineages within liquid marbles is being investigated. Without the addition of growth factors, suspended EBs from liquid marbles express various precardiac mesoderm markers including Flk-1, Gata4, and Nkx2.5. Some of the suspended EBs exhibit spontaneous contraction. These results indicate that the liquid marble provides a suitable microenvironment to induce EB formation and spontaneous cardiac mesoderm differentiation. Some of the EBs are subsequently plated onto gelatin-coated tissue culture dishes. Plated EBs express mature cardiac markers atrial myosin light chain 2a (MLC2a) and ventricular myosin light chain (MLC2v), and the cardiac structural marker α-actinin. More than 60% of the plated EBs exhibit spontaneous contraction and express mature cardiomyocyte marker cardiac troponin T (cTnT), indicating that these EBs have differentiated into functional cardiomyocytes. Together, these results demonstrate that the liquid-marble technique is an easily employed, cost effective, and efficient approach to generate EBs and facilitating their cardiogenesis.

Angiomodulin is required for cardiogenesis of embryonic stem cells and is maintained by a feedback loop network of p63 and Activin-A

The transcription factor p63, member of the p53 gene family, encodes for two main isoforms, TAp63 and ΔNp63 with distinct functions on epithelial homeostasis and cancer. Recently, we discovered that TAp63 is essential for in vitro cardiogenesis and heart development in vivo. TAp63 is expressed by embryonic endoderm and acts on cardiac progenitors by a cell-non-autonomous manner. In the present study, we search for cardiogenic secreted factors that could be regulated by TAp63 and, by ChIP-seq analysis, identified Angiomodulin (AGM), also named IGFBP7 or IGFBP-rP1. We demonstrate that AGM is necessary for cardiac commitment of embryonic stem cells (ESCs) and its regulation depends on TAp63 isoform. TAp63 directly activates both AGM and Activin-A during ESC cardiogenesis while these secreted factors modulate TAp63 gene expression by a feedback loop mechanism. The molecular circuitry controlled by TAp63 on AGM/Activin-A signaling pathway and thus on cardiogenesis emphasizes the importance of p63 during early cardiac development.

Abstract 135: A Novel TGFb Selective Inhibitor Drives Cardiogenesis in Embryonic Stem Cells

The early signals that drive embryonic stem cells (ESC) to cardiomyocytes are well characterized, but little is known about the pathways that control the later stages of differentiation. Genetic studies in animals are however challenging to study these later steps of heart development and are thus incapable of providing useful information for controlling ESC differentiation. Therefore, we have implemented unbiased high throughput screens on mouse ESC (mESC) to discover small molecules that probe these steps of differentiation to unravel novel biological mechanisms that control cardiac fate. From over 17000 unique molecules, screened in a serum assay relying on a cardiac specific Myh6-GFP reporter to monitor cardiogenesis, we identified a dihydropyridine (DHP), which are well-known L-type calcium channel inhibitors. Subsequent pathway analysis in combination with a structure activity relationship study of over 200 DHP analogs pinpointed the activity specifically to the Activin A/TGFb pathway, with high inhibition efficiency for TGFb signals and poor to none for Activin A signals. Further functional characterization of DHP in the TGFb pathway demonstrated that DHP acts upstream of Smad2/3, positioning the activity at the receptor level, where DHP downregulates the amount of TGFb receptors on the cell surface and targets them for degradation. This TGFb selective inhibitor was then applied in mESC to probe the effects of inhibiting TGFb specifically at several stages of differentiation. When given early in differentiation DHP blocked all mesoderm, indicating that, in serum differentiated cultures, TGFb is essential for mesoderm induction. Secondly, when DHP was added during mesoderm patterning, cardiogenesis was enhanced specifically, whereas other cardiovascular lineages such as smooth muscle, blood and endothelial cells were not affected. In summary, we have identified a new probe of TGFb signaling that shows that TGFb signaling governs cardiopoietic fate by inhibiting formation of cardiomyocytes. Additionally, our molecule and its mechanism have important implications for congenital heart disease, since deficient TGFb signaling leads to vascular and cardiac defects, and elevated signaling underlies Loeys-Deitz syndrome.

Expression of Junctophilin 1 during cardiogenesis of mouse embryonic stem cells and rat embryos

To investigate the expression of Junctophilin 1 (JP1) in cardiogenesis of mammalian. Cardiac differentiation of embryonic stem cells (ESCs) was generated by hanging drop method. Fetal heart was obtained from the rats aged d 14-20 of gestation. The expression of JP1 and JP2 during cardiogenesis of ESCs and rat embryos was analyzed by RT-PCR or Western blotting. Immunofluorescence staining was employed to reveal the distribution of JP1 and JP2 in embryoid body (EB), probing for merging of JP1 and JP2 and cardiac sarcomeric α-Actinin or Troponin-T. Percentage of JP1 and JP2-positive staining cells was analyzed quantitatively by FCS on d17. JP1 mRNA was up-regulated at the early stage (d 5-11) and then decreased. The expression of JP1 protein was up-regulated at the early stage (d 7-9), then decreased gradually and disappeared after d 15. While JP2 gene and protein expression increased in a time-dependent manner during cardiogenesis of rat embryos. The results of immunofluorescence staining showed that there was a parallel co-localization of JP2 with Troponin-T or α-Actinin on d17, while JP1 failed to express in the sarcomeric positive area at the same time point. Furthermore, FCS analysis showed that about 16.59% of cells were JP2-positive, while no cells were stained positively for JP1 in d17 EBs. JP1 gene is expressed during the whole process of cardiogenesis, while JP1 protein only appears on the early stage. The expression of JP1 in cardiogenesis of ESCs is consistent with that of rat embryos.

SRC kinase family inhibitor PP2 promotes DMSO-induced cardiac differentiation of P19 cells and inhibits proliferation

BackgroundIt has been reported recently that PP2, a Src family kinase inhibitor, promotes selective cardiogenesis in embryonic stem cells. However, there is no other research proved pro-cardiogenic characteristic of PP2 so far. In this study, we explored the potential cardiogenic effect of PP2 on P19 cells differentiation. MethodsP19-αMHC-EGFP cell line was established by transfecting P19 cells with αMHC-EGFP vector in order to evaluate cardiogenesis with EGFP. P19-αMHC-EGFP cells and P19 cells were induced to differentiate into cardiomyocytes with 1%DMSO, 5μmol/L PP2, or both 1%DMSO and 5μmol/L PP2. Differentiated cells from P19-αMHC-EGFP cells were then assessed under confocal microscope. Western-blot and RT-PCR were also performed to detect expression of cardiac troponin I and cardiac transcription factors respectively. In addition, the effects of PP2 on proliferation of P19 cells were further examined using Cell Counting Kit-8. ResultsEGFP positive cells were firstly detected on day 7 and PP2 alone cannot induce efficient cardiac differentiation of P19-αMHC-EGFP cells. However PP2 supplementation dramatically increases DMSO induced cardiac differentiation than DMSO alone. It was also found that PP2 inhibit proliferation of P19 cells in both a dose-dependent manner and a time-dependent manner. ConclusionPP2 alone cannot substitute DMSO to induce cardiac differentiation, however, PP2 supplementation drastically promotes DMSO-induced cardiac differentiation of P19 cells. The increased percentages of differentiated cardiac myocytes is partly resulting from cell proliferative inhibit effect of PP2 in undifferentiated P19 cells. P19-αMHC-EGFP cell line has the potential to be used for regenerative therapies in experimental models of heart repair.

Directed Differentiation of Human Embryonic Stem Cells to Interrogate the Cardiac Gene Regulatory Network

The limited ability of the heart to regenerate has prompted development of new systems to produce cardiomyocytes for therapeutics. While differentiation of human embryonic stem cells (hESCs) into cardiomyocytes has been well documented, the process remains inefficient and/or expensive, and progress would be facilitated by better understanding the early genetic events that cause cardiac specification. By maintaining a transgenic cardiac-specific MYH6-monomeric red fluorescent protein (mRFP) reporter hESC line in conditions that promote pluripotency, we tested the ability of combinations of 15 genes to induce cardiac specification. Screening identified GATA4 plus TBX5 as the minimum requirement to activate the cardiac gene regulatory network and produce mRFP(+) cells, while a combination of GATA4, TBX5, NKX2.5, and BAF60c (GTNB) was necessary to generate beating cardiomyocytes positive for cTnI and α-actinin. Including the chemotherapeutic agent, Ara-C, from day 10 of induced differentiation enriched for cTnI/α-actinin double positive cells to 45%. Transient expression of GTNB for 5-7 days was necessary to activate the cardiogenesis through progenitor intermediates in a manner consistent with normal heart development. This system provides a route to test the effect of different factors on human cardiac differentiation and will be useful in understanding the network failures that underlie disease phenotypes.

Abstract 5442: Oxidative Stress Regulates Cardiac Stem Cell Differentiation in a MicroRNA-Mediated Mechanism

Oxidative stress, specifically hydrogen peroxide (H 2 O 2 ) is significantly increased following myocardial infarction and its effect on adult cardiac stem cell (CSC) differentiation is largely unknown. To promote endogenous and implanted CSC differentiation into functional cardiac cells in ischemic tissue, mechanisms of deleterious redox signaling on cardiomyogenesis must be determined. Our data demonstrate that H 2 O 2 time- and dose-dependently inhibits Nkx2.5 expression in CSCs exposed to differentiating medium. Since overexpression of microRNA (miR)-1 increases embryonic stem cell cardiac differentiation, we hypothesized that H 2 O 2 regulates CSC differentiation in a miRNA-mediated mechanism. CSCs exposed to H 2 O 2 (1–100 μ M) in differentiating media demonstrated time-dependent, decreased expression of miR1 compared to cells exposed to differentiating media alone (1 μ M: 37±7.6% decrease from Day 5 control; 100 μ M: 47±11% decrease from Day 8 control). MiR133a, essential for normal cardiac development, was not time-dependently regulated by H 2 O 2 , suggesting it is not redox sensitive. Since cardiac differentiation in Drosophila is regulated by miR-1 binding to the Notch ligand Delta and Notch activation attenuates embryonic stem cell cardiogenesis, we next examined the effect of miR1 on the Notch pathway in CSCs. Delta1 expression increased 24±5% above the time-matched control exposed to differentiating media alone after 8 days exposure to H 2 O 2 (0.1 μ M). Since miR1 exhibited the inverse response to H 2 O 2 , the data support Delta1 as a target for miR1-mediated silencing in CSCs. In summary, our data suggest a mechanism for redox-mediated attenuation of CSC differentiation. H 2 O 2 decreases miR1 expression, which prevents normal Delta1 silencing by miR-1 that occurs during differentiation. This failure of Delta1 degradation increases Notch activation, which subsequently suppresses cardiogenic differentiation. This study underscores the importance of H 2 O 2 scavenging following cardiac injury to promote CSC differentiation, and suggests that targeting anti-cardiogenic miRNA regulation may be a promising strategy for successful CSC-based therapy.

Natural and Synthetic Regulators of Embryonic Stem Cell Cardiogenesis

Debilitating cardiomyocyte loss underlies the progression to heart failure. Although there have been significant advances in treatment, current therapies are intended to improve or preserve heart function rather than regenerate lost myocardium. A major hurdle in implementing a cell-based regenerative therapy is the inefficient differentiation of cardiomyocytes from either endogenous or exogenous stem cell sources. Moreover, cardiomyocytes that develop in human embryonic stem cell (hESC) or human-induced pluripotent stem cell (hIPSC) cultures are comparatively immature, even after prolonged culture, and differences in their calcium handling, ion channel, and force generation properties relative to adult cardiomyocytes raise concerns of improper integration and function after transplantation. Thus, the discovery of natural and novel small molecule synthetic regulators of differentiation and maturation would accelerate the development of stem-cell-based myocardial therapies. Here, we document recent advances in defining natural signaling pathways that direct the multistep cardiomyogenic differentiation program and the development of small molecules that might be used to enhance differentiation as well as the potential characteristics of lead candidates for pharmaceutical stimulation of endogenous myocardial replacement.

Abstract 3832: Mir429 Regulates NO-dependent Differentiation Of Mouse Embryonic Stem Cells

BACKGROUND: microRNAs (miRs) are emerging as important regulators of many cell functions and, possibly, also embryonic stem cells (ES) differentiation. Recently, it has been shown that specific microRNAs may allow ES to discriminate among different developmental lineages. Nitric oxide is a key regulator of vascular function and induces cardiogenesis in embryonic stem cells; however, no data are available about the effect of NO on microRNAs expression patterns, neither in adult nor in stem cells. METHODS AND RESULTS: mouse ES were deprived of Leukemia Inhibitory Factor (LIF) and treated with the NO donor diethylenetriamine nitric oxide adduct (DETA/NO) for 90 minutes and microRNA microarray analysis was performed. Among the differentially expressed microRNAs, we focused on miR429, belonging to the miR200 mirRNA family, which regulates epithelial to mesenchymal transition, targeting ZEB transcription factors. ES cells (5x10 5 ) were exposed from 90 minutes to 24 hours to DETA/NO in the absence of LIF and real time PCR experiments, were performed. We found that miR429 progressively increased along the whole time course, in the presence of DETA/NO, to be upregulated 8 fold with respect to control cells at the 24 hours time point. Moreover, we found that, consistently with miR429 upregulation, NO treatment down-modulated ZEB2/Sip1 transcription factor expression in ES cells. Both antagomir429 and ZEB2/Sip1 overexpression blocked NO-dependent expression of cardiovascular markers, such as Flk-1 and SM22α, in ES, while inducing ES proliferation, indicating the mir429/ZEB circuitry as an important regulator of ES cell fate. To our knowledge, these data identify the first, NO-dependent, microRNA-based mechanism regulating ES development and indicate ZEB2/Sip1 as a novel, potential “stem” gene.

Not All Hypertrophy Is Created Equal

See related article, pages 1164–1174 Cardiac hypertrophy is the natural response of myocardium to various stressors, including neurohormonal stimuli, hemodynamic overload, and injury. In the face of continued stress, pathological hypertrophy progresses to a loss of cardiomyocytes, the development of fibrosis, and, ultimately, heart failure. Emerging evidence has shown that glycogen synthase kinase-3β (GSK-3β) is an important negative regulator of cardiomyocyte hypertrophy, yet inhibition of GSK-3β has been shown to reduce cell death after ischemia reperfusion. Therefore, it has been difficult to predict what the consequences of chronic inhibition of GSK-3 in the heart would be because it might be a balance between the potential for the aggravation of cardiac hypertrophy versus antiapoptotic effects. In this issue of Circulation Research , Hirotani and colleagues report that sustained inhibition of GSK-3β in postneonatal hearts results in well-compensated “physiologic” cardiac hypertrophy and, most intriguingly, exerts protective effects against the development of “pathological” hypertrophy and heart failure with pressure overload.1 Although there are a number of concerns that need to be addressed before targeting GSK-3 for the treatment of heart failure, this “best of both worlds” outcome provides an interesting and favorable rationale for such intervention. The GSK-3 family of protein kinases is encoded by 2 genes, α and β. They are highly conserved throughout evolution and are critical to the regulation of diverse biological processes ranging from organ development to cell death, including cell growth, cell cycling, cytoskeletal organization, and metabolism.2,3 Furthermore, dysregulation of GSK-3β has been implicated in the pathogenesis of many human diseases including Alzheimer disease, diabetes, and tumorgenesis.4–8 GSK-3α (51 kDa) is the larger of the two and has a glycine-rich N terminus of unknown function. GSK-3β (47 kDa) and α share significant sequence homology (97%) in their kinase domains, however the homology between the …

Activation of MEK–ERK by heregulin-β1 promotes the development of cardiomyocytes derived from ES cells

We have previously shown that heregulin-beta1 (HRG-β1) was involved in the development and survival of cardiomyocytes derived from embryonic stem (ES) cells. This study was conducted to investigate the intracellular signal mechanisms by which HRG-β1 stimulates cardiogenesis in ES cells. The treatment with ErbB receptor inhibitor decreased the population of cardiomyocytes and transcripts levels of cardiac genes (Nkx2.5, β-MHC, cTnI, and MLC2a). The phosphorylation of ERK and development of cardiomyocytes by treatment with HRG-β1 was suppressed upon treatment with MEK1 inhibitor. Furthermore, cardiomyocytes and level of MHC protein were significantly increased by overexpression of wild type MEK1 or constitutive active MEK1, but not dominant negative MEK1. These results suggest that HRG-β1 promotes the development of cardiomyocytes predominantly by activation of MEK–ERK.

Creating Prodynorphin-Expressing Stem Cells Alerted for a High-Throughput of Cardiogenic Commitment

The development of cell therapy for the rescue of damaged heart muscle is a major area of inquiry. Within this context, the establishment of a cardiogenic cell line may remarkably facilitate the molecular dissection of cardiac fate specification, a low-efficiency and still poorly understood process, paving the way for novel approaches in the use of stem cells for cardiac repair. We used GTR1 cells, a derivative of mouse R1 embryonic stem cells bearing the puromycin-resistance gene driven by the cardiomyocyte-specific alpha-myosin heavy chain promoter, affording a gene trapping selection of a virtually pure population of embryonic stem cell-derived cardiomyocytes. Third-generation lentiviral vectors were used to overexpress the prodynorphin gene, previously shown to orchestrate a dynorphinergic system acting as a major conductor of embryonic stem cell cardiogenesis. Lentiviral prodynorphin transduction remarkably enhanced the transcription of GATA-4 and Nkx-2.5, two cardiac lineage-promoting genes, resulting in a dramatic increase in the number of spontaneously beating cardiomyocytes. Transduced cells also exhibited a subcellular redistribution patterning of protein kinase C-beta, -delta and -epsilon, a major requirement in cardiac lineage commitment. This activation resulted from a sustained increase in the transcription of targeted protein kinase C genes. Prodynorphin transduction was selective in nature and failed to activate genes responsible for skeletal myogenesis or neuronal specification. The cell line developed in this study provides a powerful in vitro model of cardiomyogenesis that may help clarify the cascade of transcriptional activation and signaling networks that push multipotent cells to take on the identity of a cardiac myocyte.

Induction of Cardiogenesis in Embryonic Stem Cells via Downregulation of Notch1 Signaling

Embryonic stem cells represent an attractive source of cardiomyocytes for cell-replacement therapies. However, before embryonic stem cells can be successfully used for the treatment of cardiac diseases, the precise molecular mechanisms that underlie their cardiogenic differentiation must be identified. A network of intrinsic and extrinsic factors regulates embryonic stem cell self-renewal and differentiation into a variety of different cell lineages. Here, we show that Notch signaling takes place in some but not all embryonic stem cells and that the Notch pathway is shut down during the course of differentiation concomitantly with downregulation of Notch receptor and ligand expression. Moreover, gain- and loss-of-function experiments for Notch signaling components show that this pathway is a crucial regulator of cardiomyocyte differentiation within ES cells. Differentiation of ES cells into cardiomyocytes is favored by inactivation of the Notch1 receptor, whereas endogenous Notch signaling promotes differentiation of ES cells into the neuronal lineage. We conclude that Notch signaling influences the cell fate decision between mesodermal and the neuroectodermal cell fates during embryonic stem cell differentiation. These findings should help to optimize the production of specific cell types via modulation of the Notch pathways and, in particular, to improve the production of embryonic stem cell-derived cardiomyocytes.

Focal Adhesion Kinase Signaling Regulates Cardiogenesis of Embryonic Stem Cells

The signaling steps that induce cardiac differentiation in embryonic stem (ES) cells are incompletely understood. We examined the effect of adhesion signaling including Src and focal adhesion kinase (FAK) on cardiogenesis in mouse ES cells using alpha-myosin heavy chain promoter-driven enhanced green fluorescent protein or luciferase as reporters. Cardiac transcription factors including Nkx2.5 and Tbx5 mRNA were first expressed at day 4 in hanging drop embryoid bodies, and adhesion of embryoid bodies to surfaces at or before that day strongly inhibited differentiation of ES cells to cardiomyocytes. Since adhesion signaling could suppress cardiogenesis through Src kinases, embryoid bodies were exposed to the small molecule PP2, known as a Src family kinase inhibitor. PP2 during embryoid body adhesion dramatically increased cardiomyocyte differentiation and decreased mRNA expression of neuronal cellular adhesion molecule and alpha-fetoprotein, neuroectodermal, and endodermal markers, respectively. Surprisingly, although there was an interaction between Src and FAK in cardiogenesis, the procardiogenic effect of PP2 appeared incompletely explained by Src kinase inhibition, since another Src family kinase inhibitor, SU6656, failed to induce cardiogenesis. Instead, PP2 specifically inhibited adhesion-induced FAK phosphorylation. In ES cells stably expressing FAK-related nonkinase, which functions as a dominant negative FAK, cell migration from embryoid bodies was inhibited, whereas alpha-myosin heavy chain expression and myosin-stained cardiomyocytes were increased, suggesting that reducing cell motility may contribute to cardiogenesis. These data indicate that FAK is a key regulator of cardiogenesis in mouse ES cells and that FAK signaling within embryoid bodies can direct stem cell lineage commitment.

Butyric and Retinoic Mixed Ester of Hyaluronan: A NOVEL DIFFERENTIATING GLYCOCONJUGATE AFFORDING A HIGH THROUGHPUT OF CARDIOGENESIS IN EMBRYONIC STEM CELLS

Embryonic stem (ES) cells can differentiate into specialized cells, including cardiac myocytes, but the efficiency is typically low and the process is incompletely understood. Achieving a high throughput of cardiogenesis from pluripotent cells is therefore a major requirement for future approaches in cardiac cell therapy. Here, we developed a novel ester of hyaluronan linked to both butyric and retinoic acid (HBR), coaxing pluripotent ES cells into a cardiogenic decision. In mouse ES cells, HBR remarkably increased the expression of GATA-4 and Nkx-2.5, acting as cardiac lineage-promoting genes in different animal species, including humans. HBR also enhanced prodynorphin gene expression and the synthesis and secretion of dynorphin B, an endorphin playing a major role in ES cell cardiogenesis. These effects occurred at the transcriptional level. HBR also primed the expression of cardiac-specific transcripts and highly enhanced the yield of spontaneously beating ES-derived cardiomyocytes. These results demonstrate the potential for chemically modifying the gene program of cardiac differentiation in ES cells without the aid of gene transfer technologies and may pave the way for novel approaches in tissue engineering and myocardial regeneration.

Identification of Plateled-derived Growth Factor-BB as Cardiogenesis-Inducing Factor in Mouse Embryonic stem cells under Serum-free Conditions

Background/Aims: Embryonic stem (ES) cells may represent an alternative source of functionally mature cardiomyocytes for the treatment of heart diseases. ES cells spontaneously differentiate into spheroidal aggregates, also referred to as embryoid bodies (EBs). The identification of growth factors playing a decisive role in cardiogenesis is a crucial issue for the generation of mature cardiomyocytes. Methods: In order to identify growth factors promoting cardiac development, we established a new differentiation protocol using a defined serum-replacement medium (SRM) containing 5µg/ml insulin and 5µg/ml transferrin in combination with Dulbecco’s Modified Eagle Medium (DMEM). Furthermore, we added platelet-derived growth factor-BB (PDGF-BB) or sphingosine-1-phosphate (SPP) to promote cardiac differentiation. Results: Using SRM/DMEM, we obtained a 6-fold increase of cardiac specific myosin heavy chain α and β (cMHCα/β) in relation to 0,2% foetal calf serum (FCS)/DMEM (= 100%). Stimulation of EBs with PDGF-BB in the presence of SRM/DMEM resulted in a further 2,6-fold enhancement in comparison with the SRM/DMEM-induced increase of cMHCα/β (= 100%). A parallel increase in the number of beating EBs was observed. Similar results were obtained after stimulation of EBs with 5µg/ml SPP. Conclusion: We established a serum-free protocol and identify PDGF-BB and SPP as potent factors promoting cardiogenesis in ES cells.

Vital staining of cardiac myocytes during embryonic stem cell cardiogenesis in vitro.

Mouse embryonic stem (ES) cells differentiate in vitro into a variety of cell types, including spontaneously contracting cardiac myocytes. The primary aim of this work was to use vital stain techniques for real-time detection of developing cardiac myocytes in ES cell differentiation cultures. The -440 to +6 human cardiac alpha-actin promoter was used to direct expression of the Escherichia coli reporter gene lacZ (pHCActlacZ) into ES cell-derived cardiac myocytes during cardiogenesis in vitro. Undifferentiated ES cells were electroporated with HCActlacZ together with a plasmid containing the neomycin gene under the direction of the phosphoglycerate kinase promoter, and stable transformants were selected in G418. Individual clones were screened for activation of lacZ gene expression in cardiac myocytes developing in vitro. Results showed that expression of the HCActlacZ reporter construct was activated very early during the ES cell differentiation program, at a time point before the appearance of spontaneous contractile activity. The earliest detection was at day 6 of differentiation, when approximately 25% of the differentiation cultures expressed the reporter construct, with expression increasing to approximately 70% at day 9 and continuing throughout the duration of spontaneous contractile activity exhibited by the ES cell-derived cardiac myocytes. Indirect immunofluorescence assays provide evidence that expression was restricted to the cardiac myocytes in culture. In the present study, we show vital staining of transgene expression in living cardiac myocytes using lipophilic fluorogenic beta-galactopyranoside substrates for real-time detection of the reporter gene during continuous contraction of the ES cell myocytes in vitro. The vital stain approach used in the present study will permit the identification of differentiating ES cells that are committed to the cardiac lineage for analysis of gene expression at early time points of ES cell cardiogenesis and, in addition, will aid in selecting genetically modified ES cell cardiac myocytes for use in functional studies.

Myosin Heavy Chain Expression in Contracting Myocytes Isolated During Embryonic Stem Cell Cardiogenesis

Mouse embryonic stem (ES) cells are totipotent cells derived from the inner cell mass of the preimplantation blastocyst and are capable of differentiating in vitro into cardiac myocytes. Attached cultures of differentiating ES cells were established to document the timing of contractile development by microscopic observation and to permit the microdissection of cardiac myocytes from culture. The onset of spontaneous contraction varied markedly in differentiation culture, with contraction being maintained on average for 9 days (range, 1 to 75 days). Indirect immunofluorescence in microscopy showed that myosin expression was localized to the contracting cardiac myocytes in culture. Myosin heavy chain (MHC) isoform expression in microdissected ES cell-derived cardiac myocytes was determined by means of sodium dodecyl sulfate-polyacryl-amide gel electrophoresis. The distribution of MHC isoform expression in isolated ES cell cardiac myocytes was as follows: 27% expressed the beta-MHC isoform, 33% expressed both the alpha- and beta-MHC isoforms, and 40% expressed the alpha-MHC isoform. MHC phenotype was correlated to the duration of continuous contractile activity of the myocytes. Myocytes that had just initiated spontaneous contractile activity predominantly expressed the beta-MHC (average days of contraction before isolation, 2.5 +/- 0.7). The alpha-MHC isoform was detected after mouse prolonged contractile activity in vitro (1 to 5 weeks). A strong correlation was obtained between MHC phenotype and days of contraction of the cardiac myocyte preparations isolated from ES cell cultures (r = .93). The apparent transition in MHC isoform expression during ES cell differentiation parallels the beta- to alpha-MHC isoform transition characteristic of murine cardiac development in vivo. These findings are evidence that ES cell cardiac myocyte differentiation follows the normal developmental program of murine cardiogenesis.