Embryonic Stem Cell-Derived Cardiac Differentiation: Modulation of Differentiation and “Loss-of-Function” Analysis In Vitro

Improved Survival and Hematopoietic Differentiation of Murine Embryonic Stem Cells on Electrospun Polycaprolactone Nanofiber

OBJECTIVE

Three-dimensional (3D) biomimetic nanofiber scaffolds have widespread ap- plications in biomedical tissue engineering. They provide a suitable environment for cel- lular adhesion, survival, proliferation and differentiation, guide new tissue formation and development, and are one of the outstanding goals of tissue engineering. Electrospinning has recently emerged as a leading technique for producing biomimetic scaffolds with mi- cro to nanoscale topography and a high porosity similar to the natural extracellular matrix (ECM). These scaffolds are comprised of synthetic and natural polymers for tissue engi- neering applications. Several kinds of cells such as human embryonic stem cells (hESCs) and mouse ESCs (mESCs) have been cultured and differentiated on nanofiber scaffolds. mESCs can be induced to differentiate into a particular cell lineage when cultured as em- bryoid bodies (EBs) on nano-sized scaffolds.

MATERIALS AND METHODS

We cultured mESCs (2500 cells/100 µl) in 96-well plates with knockout Dulbecco's modified eagle medium (DMEM-KO) and Roswell Park Memorial Institute-1640 (RPMI-1640), both supplemented with 20% ESC grade fetal bovine serum (FBS) and essential factors in the presence of leukemia inhibitory factor (LIF). mESCs were seeded at a density of 2500 cells/100 µl onto electrospun polycaprolactone (PCL) nanofibers in 96-well plates. The control group comprised mESCs grown on tissue cul- ture plates (TCP) at a density of 2500 cells/100 µl. Differentiation of mESCs into mouse hematopoietic stem cells (mHSCs) was performed by stem cell factor (SCF), interleukin-3 (IL-3), IL-6 and Fms-related tyrosine kinase ligand (Flt3-L) cytokines for both the PCL and TCP groups. We performed an experimental study of mESCs differentiation.

RESULTS

PCL was compared to conventional TCP for survival and differentiation of mESCs to mHSCs. There were significantly more mESCs in the PCL group. Flowcyto- metric analysis revealed differences in hematopoietic differentiation between the PCL and TCP culture systems. There were more CD34+(Sca1+) and CD133+cells subpopulations in the PCL group compared to the conventional TCP culture system.

CONCLUSION

The nanofiber scaffold, as an effective surface, improves survival and differentiation of mESCs into mHSCs compared to gelatin coated TCP. More studies are necessary to understand how the topographical features of electrospun fibers af- fect cell growth and behavior. This can be achieved by designing biomimetic scaffolds for tissue engineering.

Electron microscopic study of mouse embryonic stem cell-derived cardiomyocytes

Differentiation of embryonic stem cell (ESC)-derived embryoid bodies (EBs) is a heterogeneous process. ESCs can differentiate in vitro into different cell types including beating cardiomyocytes. The main aim of the present study was to develop an improved preparation method for scanning electron microscopic study of ESC-derived cardiac bundles and to investigate the fine structural characteristics of mouse ESCs-derived cardiomyocytes using electron microscopy. The mouse ESCs differentiation was induced by EBs' development through hanging drop, suspension and plating stages. Cardiomyocytes appeared in the EBs' outgrowth as beating clusters that grew in size and formed thick branching bundles gradually. Cardiac bundles showed cross striation even when they were observed under an inverted microscope. They showed a positive immunostaining for cardiac troponin I and α-actinin. Transmission and scanning electron microscopy (TEM & SEM) were used to study the structural characteristics of ESC-derived cardiomyocytes. Three weeks after plating, differentiated EBs showed a superficial layer of compact fibrous ECM that made detailed observation of cardiac bundles impossible. We tried several preparation methods to remove unwanted cells and fibers, and finally we revealed the branching bundles of cardiomyocytes. In TEM study, most cardiomyocytes showed parallel arrays of myofibrils with a mature sarcomeric organization marked by H-bands, M-lines and numerous T-tubules. Cardiomyocytes were connected to each other by intercalated discs composed of numerous gap junctions and fascia adherences.

Immunological barriers to stem-cell based cardiac repair

Repair of damaged myocardium with pluripotent stem cell derived cardiomyocytes is becoming increasingly more feasible. Developments in stem cell research emphasize the need to address the foreseeable problem of immune rejection following transplantation. Pluripotent stem cell (PSC) derived cardiomyocytes have unique immune characteristics, some of which are not advantageous for transplantation. Here we review the possible mechanisms of PSC-derived cardiomyocytes rejection, summarize the current knowledge pertaining to immunogenicity of such cells and describe the existing controversies. Myocardial graft rejection can be reduced by modifying PSCs prior to their differentiation into cardiomyocytes. Overall, this approach facilitates the development of universal donor stem cells suitable for the regeneration of many different tissue types.

Functional characterization of embryonic stem cell-derived cardiomyocytes using scanning ion conductance microscopy

We report here the novel use of scanning ion conductance microscopy (SICM) to produce surface images of embryonic stem cell-derived cardiomyocytes (ESCM) to identify individual contracting cardiomyocytes among different cell types. By measuring amplitude and rhythm we can quantitate contraction of ESCM. This method gives, within the same experiment, an assessment of the number and position of ESCM within the layer of mixed cell types, as well as an accurate measure of the response of individual ESCM. Using different modulators of contraction as examples we showed how SICM could be used for recording their responses. We subsequently demonstrated that this model can be used to investigate the protective effect of antiarrhythmogenic drugs.

Icariin-mediated modulation of cell cycle and p53 during cardiomyocyte differentiation in embryonic stem cells

The aim of this study was to investigate the possible inducible effects and to clarify the modulation by icariin of cell cycle and p53 expression in the differentiation of embryonic stem cells into cardiomyocytes in vitro. Embryonic stem cells were cultivated as embryoid bodies in hanging drops and induced to differentiate into cardiomyocytes by icariin at 10(-7) M. Cardiomyocytes were characterized by the expression of sarcomeric proteins, alpha-actinin and cardiac troponin T, by immunocytochemistry. Flow cytometry revealed that 10(-7) M icariin treatment for 48 h significantly induced the accumulation of cells in G0/G1 and reduced the proportion of cells in S phase. A marked increase in apoptosis rate was observed 48 h after icariin treatment. Icariin resulted in significantly increased expressions of p53 mRNA and protein, as determined by reverse transcription-polymerase chain reaction and Western blot analysis. During day 7+0 and 7+9 cardiac developmental stage, 10(-7) M icariin increased the level of p53 mRNA, but caused a parallel decrease in the level of p53 protein. In conclusion, icariin at 10(-7) M facilitated the directional differentiation of embryonic stem cells into cardiomyocytes. Results showed p53 to be an important regulator in the differentiation in embryonic stem cells treated with 10(-7) M icariin, controlling or adjusting the balance between differentiated cells and cells undergoing apoptosis.

Inducible effects of icariin, icaritin, and desmethylicaritin on directional differentiation of embryonic stem cells into cardiomyocytes in vitro

AIM

To investigate the possible inducible effects of icariin, icaritin, and desmethylicaritin on the directional differentiation of embryonic stem (ES) cells into cardiomyocytes in vitro.

METHODS

ES cells were cultivated as embryoid bodies (EBs) in hanging drops with icariin, icaritin, or desmethylicaritin. ES cells treated with retinoic acid and with solvent were used as positive and negative controls, respectively. The cardiomyocytes derived from the ES cells were verified using immunocytochemistry. The expression of cardiac developmental-dependent genes was detected using the reverse transcription-polymerase chain reaction (RT-PCR) method. Cell cycle distribution and apoptosis were analyzed using flow cytometry to determine the partly inducible effect mechanisms involved.

RESULTS

The total percentage of beating EBs treated with 10(-7) mol/L icariin, icaritin, or desmethylicaritin was 87% (P<0.01), 59% (P<0.01), and 49%, respectively. All the beating cardiomyocytes derived from the ES cells expressed cardiac-specific proteins for a-actinin and troponin T. Among them, 10(-7) mol/L icariin treatment resulted in a significantly advanced and increased mRNA level of a-cardiac major histocompatibility complex (MHC) and myosin light chain 2v (MLC-2v) in EBs in the early cardiac developmental stage. Before shifting to the cardiomyocyte phenotype, icariin could evoke the accumulation of ES cells in G0/G1 and accelerate apoptosis of the cell population (P<0.05).

CONCLUSION

Icariin facilitated the directional differentiation of ES cells into cardiomyocytes at a concentration of 10(-7) mol/L. The promoting effect of icariin on cardiac differentiation was related to increasing and accelerating gene expression of a-cardiac MHC and MLC-2v, as well as regulating the cell cycles and inducing apoptosis.

Differentiation of pluripotent embryonic stem cells into cardiomyocytes

Embryonic stem (ES) cells have been established as permanent lines of undifferentiated pluripotent cells from early mouse embryos. ES cells provide a unique system for the genetic manipulation and the creation of knockout strains of mice through gene targeting. By cultivation in vitro as 3D aggregates called embryoid bodies, ES cells can differentiate into derivatives of all 3 primary germ layers, including cardiomyocytes. Protocols for the in vitro differentiation of ES cells into cardiomyocytes representing all specialized cell types of the heart, such as atrial-like, ventricular-like, sinus nodal-like, and Purkinje-like cells, have been established. During differentiation, cardiac-specific genes as well as proteins, receptors, and ion channels are expressed in a developmental continuum, which closely recapitulates the developmental pattern of early cardiogenesis. Exploitation of ES cell-derived cardiomyocytes has facilitated the analysis of early cardiac development and has permitted in vitro "gain-of-function" or "loss-of-function" genetic studies. Recently, human ES cell lines have been established that can be used to investigate cardiac development and the function of human heart cells and to determine the basic strategies of regenerative cell therapy. This review summarizes the current state of ES cell-derived cardiogenesis and provides an overview of how genomic strategies coupled with this in vitro differentiation system can be applied to cardiac research.

Embryonic stem cells as an in vitro model for mutagenicity, cytotoxicity and embryotoxicity studies: present state and future prospects

Primary cultures or established cell lines of vertebrates are commonly used to analyse the mutagenic, embryotoxic or teratogenic potential of environmental factors, drugs and xenobiotics in vitro. However, these cellular systems do not include developmental processes from early embryonic stages up to terminally differentiated cell types. An alternative approach has been offered by permanent lines of pluripotent stem cells of embryonic origin, such as embryonic carcinoma (EC), embryonic stem (ES) and embryonic germ (EG) cells. The undifferentiated stem cell lines are characterized by nearly unlimited self-renewal capacity and have been shown to differentiate in vitro into cells of all three primary germ layers. Pluripotent embryonic stem cell lines recapitulate cellular developmental processes and gene expression patterns of early embryogenesis during in vitro differentiation, data which are summarized in this review. In addition, recent studies are presented which investigated mutagenic, cytotoxic and embryotoxic effects of chemical substances using in vitro systems of pluripotent embryonic stem cells. Furthermore, an outlook is given on future molecular technologies using embryonic stem cells in developmental toxicology and embryotoxicology.

Basis for optimization of in vitro exposure apparatus for health hazard evaluations of mobile communications

The main objective of this paper is to carefully study the fields induced in flasks exposed to RF electromagnetic fields. The study focuses on the widely used 60 mm Petri dishes and rectangular T-75 flasks for the two following cases: 1) cells in homogeneous suspension and 2) cell monolayers. The dependence of the coupling and the homogeneity of the SAR distribution on frequency (0.7 GHz to 2.5 GHz), polarization (E, H and k polarizations) and the amount of medium (1.9 mm to 4.7 mm medium height) is studied. In addition, the effects of the environment, meniscus and field impedance as well as the distortion of the incident field are discussed. Based on these results, advantages and disadvantages of different fundamental designs of apparatus used in the past are compared. These are TEM cells, HF chambers, radial transmission lines (RTL), waveguides and wire patch cells. Furthermore, the major optimization parameters are identified for the development of highly optimized exposure systems, enabling the conduct of high quality experiments.

Embryonic stem cell differentiation: the role of extracellular factors

Embryonic stem (ES) cells have the capacity to self renew and to differentiate into cellular derivatives of the endodermal, ectodermal, and mesodermal lineages. Therefore, ES cells have been used to analyse the effects of exogenous factors on the developmental pattern during in vitro differentiation. By using an in vitro loss-of-function approach based on beta1 integrin-deficient ES cells, it was found that integrin-dependent mechanisms are involved in the regulation of Wnt-1 and BMP-4 expression. Antagonistic effects of the signalling molecules Wnt-1 and BMP-4, morphogens involved in early differentiation events, have been observed in vivo and in vitro: BMP-4 acts as a potent mesoderm inducer, whereas Wnt-1 plays a critical role in the determination of neuroectoderm. Here, we summarise data of ES cell-derived cardiac, myogenic, and neuronal differentiation of wild type and beta1 integrin-deficient ES cells. We present evidence that the interaction of cells with the extracellular matrix via integrins determines the expression of the signalling molecules BMP-4 and Wnt-1, resulting in the activation of the mesodermal and neuroectodermal lineage, respectively. The results support the idea that the influence of the extracellular 'niche' on the developmental fate of pluripotent stem cells is determined not only by soluble factors, but also by the extracellular matrix.

Differentiation of embryonic stem cell-derived dopaminergic neurons is enhanced by survival-promoting factors

Here, we describe the generation of viable and dopamine-producing neurons derived from pluripotent mouse embryonic stem cells. Neurotrophic factors in combination with survival-promoting factors, such as interleukin-1beta, glial cell line-derived neurotrophic factor, neurturin, transforming growth factor-beta(3) and dibutyryl-cyclic AMP, significantly enhanced Nurr1 and tyrosine hydroxylase (TH) mRNA levels, whereas En-1, mash-1 and dopamine-2-receptor mRNA levels were not upregulated. In parallel, mRNA levels of the anti-apoptotic gene bcl-2 were found to be upregulated at terminal stages. Double immunofluorescence analysis revealed increased numbers of TH- and dopamine transporter-, but not gamma-aminobutyric acid- and serotonin-positive neurons in relation to synaptophysin-labeled cells by survival-promoting factors. Moreover, high-performance liquid chromatography analysis showed detectable levels of intracellular dopamine. We conclude that survival-promoting factors enhance differentiation, survival and maintenance of dopaminergic neurons derived from embryonic stem cells.

Potential of embryonic stem cells

Embryonic stem (ES) cells are pluripotent cell lines established from undifferentiated embryonic cells characterized by nearly unlimited self-renewal and differentiation capacity. During differentiation in vitro, ES cells were found to be able to develop into specialized somatic cells types and to recapitulate processes of early embryonic development. These properties allow to use ES cells as model system for studying early embryonic development by gain- or loss-of-function approaches, or to investigate the effects of drugs and environmental factors on differentiation and cell function in embryotoxicity and pharmacology. Now, ES cells derived of human blastocysts may be used for the generation of somatic precursor or differentiated cells in cell and tissue therapy. The review presents data of mouse ES cell differentiation and gives an outlook on future perspectives and problems of using human ES cells in regenerative medicine.

Overexpression of insulin-like growth factor-II in mouse embryonic stem cells promotes myogenic differentiation

Embryonic stem (ES) cells derived from androgenetic or parthenogenetic mouse embryos are important tools for studying the roles of imprinted genes in early development. Androgenetic ES cells have been shown to preferentially differentiate into the myogenic lineage both in vitro and after formation of teratocarcinomas in vivo. To clarify if the maternally imprinted Igf2 gene which is expected to be overexpressed in androgenetic ES cells is sufficient to induce myogenic differentiation, R1 ES cells were transfected with human IGF-II expression vectors. Stable ES cell clones exhibiting human IGF-II mRNA and protein expression were studied vs ES cell clones without IGF-II overexpression in a standard in vitro differentiation system involving culture in "hanging drops" and observation of differentiation of the recovered embryoid bodies (EBs). EBs derived from IGF-II overexpressing ES cells showed stimulated myogenic differentiation evident by the appearance of myoblasts already 3 days after plating and by higher levels of skeletal muscle-specific transcripts (myf5, myoD, myogenin) at earlier stages. Our study demonstrates for the first time that overexpression of IGF-II enhances and accelerates myogenic differentiation of ES cells, which has implications for ES cell-derived tissue engineering.

Embryonic stem cell-derived chondrogenic differentiation in vitro: activation by BMP-2 and BMP-4

Differentiation of mouse embryonic stem (ES) cells via embryoid bodies was established as a suitable model to study development in vitro. Here, we show that differentiation of ES cells in vitro into chondrocytes can be modulated by members of the transforming growth factor-beta family (TGF-beta(1), BMP-2 and -4). ES cell differentiation into chondrocytes was characterized by the appearance of Alcian blue-stained areas and the expression of cartilage-associated genes and proteins. Different stages of cartilage differentiation could be distinguished according to the expression pattern of the transcription factor scleraxis, and the cartilage matrix protein collagen II. The number of Alcian-blue-stained areas decreased slightly after application of TGF-beta(1), whereas BMP-2 or -4 induced chondrogenic differentiation. The inducing effect of BMP-2 was found to be dependent on the time of application, consistent with its role to recruit precursor cells to the chondrogenic fate.

Distant upstream regulatory domains direct high levels of beta -myosin heavy chain gene expression in differentiated embryonic stem cells

Eukaryotic gene transcription takes place in the context of chromatin. In order to study the expression of the beta -myosin heavy chain (MyHC) gene in its appropriate cardiac environment in vitro, embryonic stem cell lines were generated and induced to differentiate into the cardiac lineage. We show that the upstream region of the beta -MyHC gene (-5518 to -2490 relative to the transcriptional start site) directed high levels of transcriptional activity only when stably integrated, but not when expressed extrachromosomally in transient assays. These results are consistent with earlier findings using an in vivo transgenic approach. The expression of beta -MyHC reporter gene constructs was strictly correlated to differentiation status and coincided with the expression of endogenous cardiac marker genes and with morphological differentiation of embryoid bodies in vitro. Using populations of stably transfected cell clones, two domains important for high level expression were identified. The analysis of individual cell clones suggested that the positive regulatory domains act according to the graded model of enhancement. These results show that chromosomal integration is necessary for the appropriate function of the beta -MyHC gene's upstream regulatory region.

Modulation of sarcomere organization during embryonic stem cell-derived cardiomyocyte differentiation

Myofibrillogenesis - sarcomeres - mouse embryonic stem cells - cardiomyocytes - beta1 integrin Mouse embryonic stem (ES) cells, when cultivated as embryoid bodies, differentiate in vitro into cardiomyocytes of ventricle-, atrium- and pacemaker-like cell types characterized by developmentally controlled expression of cardiac-specific genes, structural proteins and ion channels. Using this model system, we show here, (I) that during cardiac myofibrillogenesis sarcomeric proteins are organized in a developmentally regulated manner following the order: titin (Z-disk), alpha-actinin, myomesin, titin (M-band), myosin heavy chain, alpha-actin, cardiac troponin T and M-protein, recapitulating the sarcomeric organization in the chicken embryonal heart in vivo. Our data support the view that the formation of I-Z-I complexes is developmentally delayed with respect to A-band assembly. We show (2) that the process of cardiogenic differentiation in vitro is influenced by medium components: Using a culture medium supplemented with glucose, amino acids, vitamins and selenium ions, we were able to increase the efficiency of cardiac differentiation of wild-type, as well as of beta1 integrin-deficient (beta1-/-) ES cells, and to improve the degree of organization of sarcomeric structures in wild-type and in beta1-/- cardiac cells. The data demonstrate the plasticity of cardiogenesis during the differentiation of wild-type and of genetically modified ES cells.

Embryonic stem cell differentiation models: cardiogenesis, myogenesis, neurogenesis, epithelial and vascular smooth muscle cell differentiation in vitro

Embryonic stem cells, totipotent cells of the early mouse embryo, were established as permanent cell lines of undifferentiated cells. ES cells provide an important cellular system in developmental biology for the manipulation of preselected genes in mice by using the gene targeting technology. Embryonic stem cells, when cultivated as embryo-like aggregates, so-called 'embryoid bodies', are able to differentiate in vitro into derivatives of all three primary germ layers, the endoderm, ectoderm and mesoderm. We established differentiation protocols for the in vitro development of undifferentiated embryonic stem cells into differentiated cardiomyocytes, skeletal muscle, neuronal, epithelial and vascular smooth muscle cells. During differentiation, tissue-specific genes, proteins, ion channels, receptors and action potentials were expressed in a developmentally controlled pattern. This pattern closely recapitulates the developmental pattern during embryogenesis in the living organism. In vitro, the controlled developmental pattern was found to be influenced by differentiation and growth factor molecules or by xenobiotics. Furthermore, the differentiation system has been used for genetic analyses by 'gain of function' and 'loss of function' approaches in vitro.