Induction and selection of Sox17-expressing endoderm cells generated from murine embryonic stem cells.

Embryonic stem (ES) cells offer a valuable source for generating insulin-producing cells. However, current differentiation protocols often result in heterogeneous cell populations of various developmental stages. Here we show the activin A-induced differentiation of mouse ES cells carrying a homologous dsRed-IRES-puromycin knock-in within the Sox17 locus into the endoderm lineage. Sox17-expressing cells were selected by fluorescence-assisted cell sorting (FACS) and characterized at the transcript and protein level. Treatment of ES cells with high concentrations of activin A for 10 days resulted in up to 19% Sox17-positive cells selected by FACS. Isolated Sox17-positive cells were characterized by defini- tive endoderm-specific Sox17/Cxcr4/Foxa2 transcripts, but lacked pluripotency-associated Oct4 mRNA and protein. The Sox17-expressing cells showed downregulation of extraembryonic endoderm (Sox7, Afp, Sdf1)-, mesoderm (Foxf1, Meox1)- and ectoderm (Pax6, NeuroD6)-specific transcripts. The presence of Hnf4α, Hes1 and Pdx1 mRNA demonstrated the expression of primitive gut/foregut cell-specific markers. Ngn3, Nkx6.1 and Nkx2.2 transcripts in Sox17-positive cells were determined as properties of pancreatic endocrine progenitors. Immunocytochemistry of activin A-induced Sox17-positive embryoid bodies revealed coexpression of Cxcr4 and Foxa2. Moreover, the histochemical demonstration of E-cadherin-, Cxcr4-, Sox9-, Hnf1ß- and Ngn3-positive epithelial-like structures underlined the potential of Sox17-positive cells to further differentiate into the pancreatic lineage. By reducing the heterogeneity of the ES cell progeny, Sox17-expressing cells are a suitable model to evaluate the effects of growth and differentiation factors and of culture conditions to delineate the differentiation process for the generation of pancreatic cells in vitro.

The Janus face of pluripotent stem cells--connection between pluripotency and tumourigenicity.

Pluripotent stem cells have gained special attraction because of their almost unlimited proliferation and differentiation capacity in vitro. These properties substantiate the potential of pluripotent stem cells in basic research and regenerative medicine. Here three types of in vitro cultured pluripotent stem cells (embryonic carcinoma, embryonic stem and induced pluripotent stem cells) are compared in their historical context with respect to their different origin and properties. It became evident that tumourigenicity is an inherent property of pluripotent cells based on p53 down-regulation, expression of tumour-related genes and high telomerase activity that allow unlimited proliferation. In addition, culture-adapted genetic and epigenetic changes may induce tumourigenicity of pluripotent cells. The use of stem cells in regenerative medicine, however, requires non-malignant cell types and strategies that circumvent stages of malignancy.Reprogramming strategies of adult somatic cells that avoid the tumourigenic state of pluripotency may offer alternatives for future biomedical application.

Modulation of calcium-activated potassium channels induces cardiogenesis of pluripotent stem cells and enrichment of pacemaker-like cells.

BACKGROUND: Ion channels are key determinants for the function of excitable cells, but little is known about their role and involvement during cardiac development. Earlier work identified Ca(2+)-activated potassium channels of small and intermediate conductance (SKCas) as important regulators of neural stem cell fate. Here we have investigated their impact on the differentiation of pluripotent cells toward the cardiac lineage. METHODS AND RESULTS: We have applied the SKCa activator 1-ethyl-2-benzimidazolinone on embryonic stem cells and identified this particular ion channel family as a new critical target involved in the generation of cardiac pacemaker-like cells: SKCa activation led to rapid remodeling of the actin cytoskeleton, inhibition of proliferation, induction of differentiation, and diminished teratoma formation. Time-restricted SKCa activation induced cardiac mesoderm and commitment to the cardiac lineage as shown by gene regulation, protein, and functional electrophysiological studies. In addition, the differentiation into cardiomyocytes was modulated in a qualitative fashion, resulting in a strong enrichment of pacemaker-like cells. This was accompanied by induction of the sino-atrial gene program and in parallel by a loss of the chamber-specific myocardium. In addition, SKCa activity induced activation of the Ras-Mek-Erk signaling cascade, a signaling pathway involved in the 1-ethyl-2-benzimidazolinone-induced effects. CONCLUSIONS: SKCa activation drives the fate of pluripotent cells toward mesoderm commitment and cardiomyocyte specification, preferentially into nodal-like cardiomyocytes. This provides a novel strategy for the enrichment of cardiomyocytes and in particular, the generation of a specific subtype of cardiomyocytes, pacemaker-like cells, without genetic modification.

Human embryonic stem cell lines and their use in international research.

Research in human pluripotent stem cells, including human embryonic stem cells (hESC) and human induced pluripotent stem cells (hiPSC), is one of the most dynamic research fields. Despite the high public attention, especially for hESC research, there is only scattered information on the number of hESC lines and the degree, dynamics, and diversification of their use on a global level. In this study we present data on the current number of publicly disclosed hESC lines, on the extent and impact of experimental work involving hESCs, and on the use of specific hESC lines in international research. The results are based on the evaluation of nearly 1,000 research papers published by the end of 2008, which describe experimental work on hESCs, and of a comprehensive database of published hESC lines. The average impact of hESC research papers is high at 7.422, with a predominance of research output by the United States. Of at least 1,071 original hESC lines derived up to November 2009 at 87 institutions in 24 countries, only a fraction is thoroughly characterized. Our data show the global predominance of a few hESC lines in research, but also reveal remarkable country-specific differences. Comparison of hESC and hiPSC application did not show a diminished role for hESC research, but rather revealed that, up to this time, both fields continue to expand, exist independently, and partially overlap.

Present state and future perspectives of using pluripotent stem cells in toxicology research.

The use of novel drugs and chemicals requires reliable data on their potential toxic effects on humans. Current test systems are mainly based on animals or in vitro-cultured animal-derived cells and do not or not sufficiently mirror the situation in humans. Therefore, in vitro models based on human pluripotent stem cells (hPSCs) have become an attractive alternative. The article summarizes the characteristics of pluripotent stem cells, including embryonic carcinoma and embryonic germ cells, and discusses the potential of pluripotent stem cells for safety pharmacology and toxicology. Special attention is directed to the potential application of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) for the assessment of developmental toxicology as well as cardio- and hepatotoxicology. With respect to embryotoxicology, recent achievements of the embryonic stem cell test (EST) are described and current limitations as well as prospects of embryotoxicity studies using pluripotent stem cells are discussed. Furthermore, recent efforts to establish hPSC-based cell models for testing cardio- and hepatotoxicity are presented. In this context, methods for differentiation and selection of cardiac and hepatic cells from hPSCs are summarized, requirements and implications with respect to the use of these cells in safety pharmacology and toxicology are presented, and future challenges and perspectives of using hPSCs are discussed.

Induced human pluripotent stem cells: promises and open questions.

Adult cells have been reprogrammed into induced pluripotent stem (iPS) cells by introducing pluripotency-associated transcription factors. Here, we discuss recent advances and challenges of in vitro reprogramming and future prospects of iPS cells for their use in diagnosis and cell therapy. The generation of patient-specific iPS cells for clinical application requires alternative strategies, because genome-integrating viral vectors may cause insertional mutagenesis. Moreover, when suitable iPS cell lines will be available, efficient and selective differentiation protocols are needed to generate transplantable grafts. Finally, we point to the requirement of a regulatory framework necessary for the commercial use of iPS cells.

Pluripotency associated genes are reactivated by chromatin-modifying agents in neurosphere cells.

Chromatin architecture in stem cells determines the pattern of gene expression and thereby cell identity and fate. The chromatin-modifying agents trichostatin A (TSA) and 5-Aza-2'-deoxycytidine (AzaC) affect histone acetylation and DNA methylation, respectively, and thereby influence chromatin structure and gene expression. In our previous work, we demonstrated that TSA/AzaC treatment of neurosphere cells induces hematopoietic activity in vivo that is long-term, multilineage, and transplantable. Here, we have analyzed the TSA/AzaC-induced changes in gene expression by global gene expression profiling. TSA/AzaC caused both up- and downregulation of genes, without increasing the total number of expressed genes. Chromosome analysis showed no hot spot of TSA/AzaC impact on a particular chromosome or chromosomal region. Hierarchical cluster analysis revealed common gene expression patterns among neurosphere cells treated with TSA/AzaC, embryonic stem (ES) cells, and hematopoietic stem cells. Furthermore, our analysis identified several stem cell genes and pluripotency-associated genes that are induced by TSA/AzaC in neurosphere cells, including Cd34, Cd133, Oct4, Nanog, Klf4, Bex1, and the Dppa family members Dppa2, 3, 4, and 5. Sox2 and c-Myc are constitutively expressed in neurosphere cells. We propose a model in which TSA/AzaC, by removal of epigenetic inhibition, induces the reactivation of several stem cell and pluripotency-associated genes, and their coordinate expression enlarges the differentiation potential of somatic precursor cells.

Differentiation analysis of pluripotent mouse embryonic stem (ES) cells in vitro.

Pluripotent embryonic stem (ES) cells are characterized by their almost unlimited potential to self-renew and to differentiate into virtually any cell type of the organism. Here we describe basic protocols for the in vitro differentiation of mouse ES cells into cells of the cardiac, neuronal, pancreatic, and hepatic lineage. The protocols include (1) the formation of embryoid bodies (EBs) followed by (2) the spontaneous differentiation of EBs into progenitor cells of the ecto-, endo-, and mesodermal germ layer and (3) the directed differentiation of early progenitors into the respective lineages. Differentiation induction via growth and extracellular matrix factors leads to titin-expressing spontaneously beating cardiac cells, tyrosine hydroxylase-expressing dopaminergic neurons, insulin and c-peptide co-expressing pancreatic islet-like clusters, and albumin-positive hepatic cells, respectively. The differentiated cells show tissue-specific proteins and electrophysiological properties (action potentials and ion channels) in cardiac and neuronal cells, glucose-dependent insulin release in pancreatic cells, or glycogen storage and albumin synthesis in hepatic cells. The protocols presented here provide basic systems to study differentiation processes in vitro and to establish strategies for the use of stem cells in regenerative therapies.

Cardiomyogenic stem and progenitor cell plasticity and the dissection of cardiopoiesis.

Cell-based therapies hold promise of repairing an injured heart, and the description of stem and progenitor cells with cardiomyogenic potential is critical to its realization. At the vanguard of these efforts are analyses of embryonic stem cells, which clearly have the capacity to generate large numbers of cardiomyocytes in vitro. Through the use of this model system, a number of signaling mechanisms have been worked out that describes at least partially the process of cardiopoiesis. Studies on adult stem and on progenitor cells with cardiomyogenic potential are still in their infancy, and much less is known about the molecular signals that are required to induce the differentiation to cardiomyocytes. It is also unclear whether the pathways are similar or different between embryonic and adult cell-induced cardiomyogenesis, partly because of the continued controversies that surround the stem cell theory of cardiac self-renewal. Irrespective of any perceived or actual limitations, the study of stem and progenitor cells has provided important insights into the process of cardiomyogenesis, and it is likely that future research in this area will turn the promise of repairing an injured heart into a reality.

Pluripotency of embryonic stem cells.

Embryonic stem (ES) cells derived from pre-implantation embryos have the potential to differentiate into any cell type derived from the three germ layers of ectoderm (epidermal tissues and nerves), mesoderm (muscle, bone, blood), and endoderm (liver, pancreas, gastrointestinal tract, lungs), including fetal and adult cells. Alone, these cells do not develop into a viable fetus or adult animal because they do not retain the potential to contribute to extraembryonic tissue, and in vitro, they lack spatial and temporal signaling cues essential to normal in vivo development. The basis of pluripotentiality resides in conserved regulatory networks composed of numerous transcription factors and multiple signaling cascades. Together, these regulatory networks maintain ES cells in a pluripotent and undifferentiated form; however, alterations in the stoichiometry of these signals promote differentiation. By taking advantage of this differentiation capacity in vitro, ES cells have clearly been shown to possess the potential to generate multipotent stem and progenitor cells capable of differentiating into a limited number of cell fates. These latter types of cells may prove to be therapeutically viable, but perhaps more importantly, the studies of these cells have led to a greater understanding of mammalian development.

Linkage of pluripotent stem cell-associated transcripts to regulatory gene networks.

Knowledge of the transcriptional circuitry responsible for pluripotentiality and self-renewal in embryonic stem cells is tantamount to understanding early mammalian development and a prerequisite to determining their therapeutic potential. Various techniques have employed genomics to identify transcripts that were abundant in stem cells, in an attempt to define the molecular basis of 'stemness'. In this study, we have extended traditional genomic analyses to identify cis-elements that might be implicated in the control of embryonic stem cell-restricted gene promoters. The strategy relied on the generation of a problem-specific list from serial analysis of gene expression profiles and subsequent promoter analyses to identify frameworks of multiple cis-elements conserved in space and orientation among genes from the problem-specific list. Subsequent experimental data suggest that 2 novel transcription factors, B-Myb and Maz, predicted from these models, are implicated either in the maintenance of the undifferentiated stem cell state or in early steps of differentiation.

The transcription factor repertoire of Flt3+ hematopoietic stem cells.

Hematopoietic stem cells maintain the development of all mature blood cells throughout life due to their sustained self-renewal capacity and multilineage differentiation potential. During development into specific cell lineages, the options of stem cells and multipotent progenitor cells become increasingly restricted concomitant with a successive decline in self-renewal potential. Here we describe an Flt3+CD11b+ multipotent progenitor that can be amplified in vitro with a specific combination of cytokines to yield homogeneous populations in high cell numbers. By employing gene expression profiling with DNA microarrays, we studied the transcription factor repertoire of Flt3+CD11b+ progenitors and related it to the transcription factor repertoire of hematopoietic stem cells and embryonic stem cells. We report here on overlapping and nonoverlapping expression patterns of transcription factors in these cells and thus provide novel insights into the dynamic networks of transcriptional regulators in embryonic and adult stem cells. Additionally, the results obtained open the perspective for elucidating lineage and 'stemness' determinants in hematopoiesis.

A chip-based platform for the in vitro generation of tissues in three-dimensional organization.

We describe a multi-purpose platform for the three-dimensional cultivation of tissues. The device is composed of polymer chips featuring a microstructured area of 1-2 cm(2). The chip is constructed either as a grid of micro-containers measuring 120-300 x 300 x 300 microm (h x l x w), or as an array of round recesses (300 microm diameter, 300 microm deep). The micro-containers may be separately equipped with addressable 3D-micro-electrodes, which allow for electrical stimulation of excitable cells and on-site measurements of electrochemically accessible parameters. The system is applicable for the cultivation of high cell densities of up to 8 x 10(6) cells and, because of the rectangular grid layout, allows the automated microscopical analysis of cultivated cells. More than 1000 micro-containers enable the parallel analysis of different parameters under superfusion/perfusion conditions. Using different polymer chips in combination with various types of bioreactors we demonstrated the principal suitability of the chip-based bioreactor for tissue culture applications. Primary and established cell lines have been successfully cultivated and analysed for functional properties. When cells were cultured in non-perfused chips, over time a considerable degree of apoptosis could be observed indicating the need for an active perfusion. The system presented here has also been applied for the differentiation analysis of pluripotent embryonic stem cells and may be suitable for the analysis of the stem cell niche.

Dioxin affects glucose transport via the arylhydrocarbon receptor signal cascade in pluripotent embryonic carcinoma cells.

Intoxication by dioxins such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) leads, among other damages, to early embryo loss, fetal malformations, and cardiovascular toxicity. Apart from binding to the arylhydrocarbon receptor (AhR), the mechanism of TCDD-mediated embryo toxicity is still unclear. We investigated possible modes of a TCDD-mediated toxicity, particularly in glucose metabolism, in pluripotent P19 mouse embryonic carcinoma cells. Undifferentiated P19 cells were exposed to 1-100 nM TCDD and characterized for AhR signaling. For studying cell differentiation, P19 cells were exposed to 10 nM TCDD at stage of embryoid body formation, and analyzed on glucose metabolism and cardiac differentiation during the next 3 wk. TCDD treatment activated the AhR-signaling cascade within 1 h, confirmed by AhR translocation, induction of cytochrome P450 1A1 expression, and activation of the xenobiotic response element. Although cell viability and transcription of the cardiac marker protein alpha-myosin heavy chain were affected, TCDD did not inhibit the differentiation of P19 cells to pulsating cardiomyocytes. TCDD significantly down-regulated the expression levels of the glucose transporter (GLUT) isoforms 1 and 3. After 24-h TCDD treatment, GLUT1 was no longer localized in the plasma membrane of P19 cells. The impaired GLUT expression correlated with a lower glucose uptake in 5-d-old embryoid bodies. The TCDD effects were mediated by AhR, as shown by preculture with the AhR antagonist alpha-naphthoflavone. Our data demonstrate that an AhR-mediated disturbance in GLUT expression and insufficient glucose uptake may be major mechanisms in TCDD embryo toxicity.

Insulin-producing cells.

Embryonic stem (ES) cells offer great potential for cell replacement and tissue engineering therapies because of their almost unlimited proliferation capacity and the potential to differentiate into cellular derivatives of all three primary germ layers. This chapter describes a strategy for the in vitro differentiation of mouse ES cells into insulin-producing cells. The three-step protocol does not select for nestin-expressing cells as performed in previous differentiation systems. It includes (1) the spontaneous differentiation of ES cells via embryoid bodies and (2) the formation of progenitor cells of all three primary germ layers (multilineage progenitors) followed by (3) directed differentiation into the pancreatic lineage. The application of growth and extracellular matrix factors, including laminin, nicotinamide, and insulin, leads to the development of committed pancreatic progenitors, which subsequently differentiate into islet-like clusters that release insulin in response to glucose. During differentiation, transcript levels of pancreas-specific transcription factors (i.e., Pdx1, Pax4) and of genes specific for early and mature beta cells, including insulin, islet amyloid pancreatic peptide, somatostatin, and glucagon, are upregulated. C-peptide/insulin-positive islet-like clusters are formed, which release insulin in response to high glucose concentrations at terminal stages. The differentiated cells reveal functional properties with respect to voltage-activated Na+ and ATP-modulated K+ channels and normalize blood glucose levels in streptozotocin-treated diabetic mice. In conclusion, we demonstrate the efficient differentiation of murine ES cells into insulin-producing cells, which may help in the future to establish ES cell-based therapies in diabetes mellitus.

Electromagnetic fields affect transcript levels of apoptosis-related genes in embryonic stem cell-derived neural progenitor cells.

Mouse embryonic stem (ES) cells were used as an experimental model to study the effects of electromagnetic fields (EMF). ES-derived nestin-positive neural progenitor cells were exposed to extremely low frequency EMF simulating power line magnetic fields at 50 Hz (ELF-EMF) and to radiofrequency EMF simulating the Global System for Mobile Communication (GSM) signals at 1.71 GHz (RF-EMF). Following EMF exposure, cells were analyzed for transcript levels of cell cycle regulatory, apoptosis-related, and neural-specific genes and proteins; changes in proliferation; apoptosis; and cytogenetic effects. Quantitative RT-PCR analysis revealed that ELF-EMF exposure to ES-derived neural cells significantly affected transcript levels of the apoptosis-related bcl-2, bax, and cell cycle regulatory "growth arrest DNA damage inducible" GADD45 genes, whereas mRNA levels of neural-specific genes were not affected. RF-EMF exposure of neural progenitor cells resulted in down-regulation of neural-specific Nurr1 and in up-regulation of bax and GADD45 mRNA levels. Short-term RF-EMF exposure for 6 h, but not for 48 h, resulted in a low and transient increase of DNA double-strand breaks. No effects of ELF- and RF-EMF on mitochondrial function, nuclear apoptosis, cell proliferation, and chromosomal alterations were observed. We may conclude that EMF exposure of ES-derived neural progenitor cells transiently affects the transcript level of genes related to apoptosis and cell cycle control. However, these responses are not associated with detectable changes of cell physiology, suggesting compensatory mechanisms at the translational and posttranslational level.

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.

In vitro differentiation of embryonic stem cells into the pancreatic lineage.

Embryonic stem (ES) cells represent a potential source of transplantable cells for the treatment of diabetes because of their almost unlimited proliferation capacity and the potential to differentiate into insulin-producing cells. The differentiation conditions significantly affect the development of pancreatic cells from ES cells in vitro. Here, we describe an efficient strategy for the in vitro generation of insulin-producing cells. The protocol includes the spontaneous generation of multilineage progenitor cells and their differentiation induction by growth and extracellular matrix factors into C-peptide/insulin-positive islet-like clusters. The differentiated cells release insulin in response to high glucose concentrations. No specific selection for nestin-positive cells is performed at any time of ES cell differentiation.

Pluripotency: capacity for in vitro differentiation of undifferentiated embryonic stem cells.

Embryonic stem (ES) cells, the pluripotent cells of early embryos have been successfully cultured as undifferentiated cells. The cells are characterized by two unique properties, unlimited self-renewal capacity and the ability to differentiate into all cells of the body. Because of the high in vitro differentiation potential, ES cells have been used as model system in cell and developmental biology. Here we present methods that use mouse embryonic stem cells for the in vitro differentiation and characterization of neuronal, cardiac, pancreatic and hepatic cells, derivatives of the ectoderm, mesoderm and endoderm, respectively. In the future, differentiated cells may be also generated from human ES cells by cultivation of early embryos or from reprogrammed cells derived by nuclear transfer. Such cells could represent potential sources for tissue repair of serious human diseases.

Loss of beta 1 integrin function results in upregulation of connexin expression in embryonic stem cell-derived cardiomyocytes.

We show that loss of beta1 integrin function affects connexin (Cx) expression in embryonic stem (ES) cell-derived cardiomyocytes. Both loss of beta1 integrin function and inhibition of integrin clustering by RGD peptides in wild type ES cells correlated with upregulated expression of gap junctional proteins in ES-derived cardiomyocytes. The upregulation of connexin transcript levels in beta1 integrin-deficient cells is paralleled by a higher fraction of cells co-expressing Cx40 and Cx43. These observations demonstrate that the expression of connexins in developing cardiomyocytes is correlated to integrin-dependent mechanisms. Further, we found that upregulated cardiac connexin expression in beta1 integrin-deficient cells is related to Rho- and Wnt-dependent pathways. beta1 integrin-deficient cardiac cells displayed high levels of cytoplasmic gamma- and beta-catenins throughout the differentiation period. The administration of lithium, an activator of beta-catenin-dependent pathways, resulted in up-regulated connexin mRNA levels in wild type cardiomyocytes at intermediate, but not at early stages, indicating that the effects are restricted to advanced stages of cardiac differentiation. On the other hand, inhibition of Rho-dependent integrin signaling by treatment of cardiac cells with exoenzyme C3 resulted in immediate up-regulation of cardiac connexin transcript levels at early differentiation stages. Our data indicate that integrin function affects connexin expression in cardiomyocytes via direct effects on RhoA-dependent signaling mechanisms at early differentiation stages and of beta-catenin/Wnt-dependent pathways at advanced stages.