Functional characteristics of ES cell-derived cardiac precursor cells identified by tissue-specific expression of the green fluorescent protein

Stem Cell Therapy for the Management of Type 1 Diabetes: Advances and Perspectives

Due to insulin resistance and excessive blood sugar levels, type 1 diabetes mellitus (T1DM) is characterized by pancreatic cell loss. This condition affects young people at a higher rate than any other chronic autoimmune disease. Regardless of the method, exogenous insulin cannot substitute for insulin produced by a healthy pancreas. An emerging area of medicine is pancreatic and islet transplantation for type 1 diabetics to restore normal blood sugar regulation. However, there are still obstacles standing in the way of the widespread use of these therapies, including very low availability of pancreatic and islets supplied from human organ donors, challenging transplantation conditions, high expenses, and a lack of easily accessible methods. Efforts to improve Type 1 Diabetes treatment have been conducted in response to the disease's increasing prevalence. Type 1 diabetes may one day be treated with stem cell treatment. Stem cell therapy has proven to be an effective treatment for type 1 diabetes. Recent progress in stem cell-based diabetes treatment is summarised, and the authors show how to isolate insulin-producing cells (IPCs) from a variety of progenitor cells.

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Evidence for a critical role of catecholamines for cardiomyocyte lineage commitment in murine embryonic stem cells

Catecholamine release is known to modulate cardiac output by increasing heart rate. Although much is known about catecholamine function and regulation in adults, little is known about the presence and role of catecholamines during heart development. The present study aimed therefore to evaluate the effects of different catecholamines on early heart development in an in vitro setting using embryonic stem (ES) cell-derived cardiomyocytes. Effects of catecholamine depletion induced by reserpine were examined in murine ES cells (line D3, αPIG44) during differentiation. Cardiac differentiation was assessed by immunocytochemistry, qRT-PCR, quantification of beating clusters, flow cytometry and pharmacological approaches. Proliferation was analyzed by EB cross-section measurements, while functionality of cardiomyocytes was studied by extracellular field potential (FP) measurements using microelectrode arrays (MEAs). To further differentiate between substance-specific effects of reserpine and catecholamine action via α- and β-receptors we proved the involvement of adrenergic receptors by application of unspecific α- and β-receptor antagonists. Reserpine treatment led to remarkable down-regulation of cardiac-specific genes, proteins and mesodermal marker genes. In more detail, the average ratio of ∼40% spontaneously beating control clusters was significantly reduced by 100%, 91.1% and 20.0% on days 10, 12, and 14, respectively. Flow cytometry revealed a significant reduction (by 71.6%, n = 11) of eGFP positive CMs after reserpine treatment. By contrast, reserpine did not reduce EB growth while number of neuronal cells in reserpine-treated EBs was significantly increased. MEA measurements of reserpine-treated EBs showed lower FP frequencies and weak responsiveness to adrenergic and muscarinic stimulation. Interestingly we found that developmental inhibition after α- and β-adrenergic blocker application mimicked developmental changes with reserpine. Using several methodological approaches our data suggest that reserpine inhibits cardiac differentiation. Thus catecholamines play a critical role during development.

Human embryonic stem cell-derived cardiomyocytes: drug discovery and safety pharmacology

Human embryonic stem cells (hESCs) can provide potentially unlimited quantities of a wide range of human cell types that can be used in drug discovery and development, basic research and regenerative medicine. In this review, the authors describe the differentiation of hESCs into cardiomyocytes and outline the properties of hESC-derived cardiomyocytes (hESC-CMs), including their cardiac-type action potentials and contractile characteristics. In vitro cellular assays using hESC-CMs, which can be genetically engineered to create target-specific reporters as well as human disease models, will have applications at multiple stages of the drug discovery process. Furthermore, cardiac safety pharmacology assays evaluating the risk of proarrhythmic side effects associated with QT prolongation may be enhanced in their predictive value with the use of hESC-CMs.

Improvement of cardiac efficacy and safety models in drug discovery by the use of stem cell-derived cardiomyocytes

BACKGROUND

The pharmaceutical industry suffers from high attrition rates during late phases of drug development. Improved models for early evaluation of drug efficacy and safety are needed to address this problem. Recent developments have illustrated that human stem cell-derived cardiomyocytes are attractive for using as a model system for different cardiac diseases and as a model for screening, safety pharmacology and toxicology.

OBJECTIVE

In this review, we discuss contemporary drug discovery models and their characteristics for cardiac efficacy testing and safety assessment. Additionally, we evaluate various sources of stem cells and how these cells could potentially improve early screening and safety models.

CONCLUSION

We conclude that human stem cells offer a source of physiologically relevant cells that show great potential as a future tool in cardiac drug discovery. However, some technical challenges related to cell differentiation and production and also to validation of improved platforms remain and must be overcome before successful application can become a reality.

Embryonic stem cells: An alternative approach to developmental toxicity testing

Stem cells in the body have a unique ability to renew themselves and give rise to more specialized cell types having functional commitments. Under specified growth conditions, these cell types remain unspecialized but can be triggered to become specific cell type of the body such as heart, nerve, or skin cells. This ability of embryonic stem cells for directed differentiation makes it a prominent candidate as a screening tool in revealing safer and better drugs. In addition, genetic variations and birth defects caused by mutations and teratogens affecting early human development could also be studied on this basis. Moreover, replacement of animal testing is needed because it involves ethical, legal, and cost issues. Thus, there is a strong requirement for validated and reliable, if achievable, human stem cell-based developmental assays for pharmacological and toxicological screening.

Functional expression and modulation of the L-type Ca2+ current in embryonic heart cells

Voltage-dependent L-type Ca2+ channels (VDCCs) are critically involved in excitation contraction coupling and regulation of the force of contraction. An important mechanism contributing to the adaptation of heart function is modulation of the L-type Ca2+ current (I(Ca-L)) by hormones of the autonomous nervous system. The signaling pathways underlying this regulation in the adult heart are well understood. However, VDCC expression and its regulation in the embryonic heart are less understood. This report therefore provides a short overview of the current knowledge on this topic using embryonic stem cells and the mouse as model systems.

Simvastatin modulates mouse embryonic stem cell-derived chondrogenesis in vitro

It has been studied in detail that cellular differentiation during chondrogenesis can be recapitulated in vitro by differentiation of embryonic stem (ES) cells as embryoid bodies (EBs). We here used this model system of cartilage development to analyze the effect of simvastatin, a potentially embryotoxic substance. Statins are a group of drugs used to treat hypercholesterolaemia. We found that simvastatin activated cartilage nodule formation during EB differentiation. Extended application of simvastatin resulted in enhanced expression of cartilage marker molecules and prolonged persistence of cartilage nodules. Expression of collagen type II was upregulated during simvastatin-induced chondrogenic ES cell differentiation as demonstrated by quantitative real time PCR. However, immunostaining for cartilage marker molecules revealed that cartilage nodules within simvastatin-treated EBs were defective, bearing cavities of cell loss. Furthermore, caspase activity was reduced in comparison to untreated controls indicating reduced apoptosis. Taken together, we may speculate that simvastatin prolongs survival of chondrocytes and disrupts cellular integrity of cartilage nodules during EB development by affecting apoptotic mechanisms. The study underlines that ES cell-derived EBs are a useful in vitro model to screen substances for their embryotoxic and teratogenic potential.

Estrogen controls embryonic stem cell proliferation via store-operated calcium entry and the nuclear factor of activated T-cells (NFAT)

Embryonic stem cells (ESCs) can self-renew indefinitely and differentiate into all cell lineages. Calcium is a universal second messenger which regulates a number of cellular pathways. Previous studies showed that store-operated calcium channels (SOCCs) but not voltage-operated calcium channels are present in mouse ESCs (mESCs). In this study, store-operated calcium entry (SOCE) was found to exist in mESCs using confocal microscopy. SOCC blockers lanthanum, 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365 reduced mESC proliferation in a concentration-dependent manner, suggesting that SOCE is important for ESC proliferation. Pluripotent markers, Sox-2, Klf-4, and Nanog, were down-regulated by 2-APB, suggesting that self-renewal property of mESCs relies on SOCE. 17β-estradiol (E2) enhanced mESC proliferation. This enhanced proliferation was associated with an increment of SOCE. Both stimulated proliferation and increased SOCE could be reversed by SOCC blockers suggesting that E2 mediates its stimulatory effect on proliferation via enhancing SOCE. Also, cyclosporin A and INCA-6, inhibitors of calcineurin [phosphatase that de-phosphorylates and activates nuclear factor of activated T-cells (NFAT)], reversed the proliferative effect of E2, indicating that NFAT is involved in E2-stimulated proliferation. Interestingly, E2 caused the nuclear translocation of NFATc4, and this could be reversed by 2-APB. These results suggested that NFATc4 is the downstream target of E2-induced SOCE. The present investigation provides the first line of evidence that SOCE and NFAT are crucial for ESCs to maintain their unique characteristics. In addition, the present investigation also provides novel information on the mechanisms of how E2, an important female sex hormone, affects ESC proliferation.

Analysis of altered gene expression specific to embryotoxic chemical treatment during embryonic stem cell differentiation into myocardiac and neural cells

Embryonic stem cells (ES cells), pluripotent cells derived from the inner cell mass of blastocysts, differentiate in vitro into a variety of cell types representing all three germ layers. They therefore constitute one of the most promising in vitro tools for developmental toxicology. To assess the developmental toxicity of chemicals using ES cells easily, identification of effective marker genes is a high priority. We report here altered gene expression during ES cell differentiation into myocardiac and neural cells on treatment with some embryotoxic and non-embryotoxic chemicals. Decreases in several undifferentiated markers such as Oct3/4 and Nanog, and elevated expression of genes associated with heart development or the central nervous system, respectively, were found on microarray analysis. Under differentiation of ES cells into myocardic cells, 107 genes were substantially up-regulated. Decrease in the expression of 13 genes of these (Hand1, Pim2, Tbx20, Myl4, Myl7, Hbb-bh1, Hba-a1, Col1a2, Hba-x, Cmya1, Pitx2, Smyd1 and Adam19) was observed specifically by embryotoxic chemicals. Of the 107 genes up-regulated under differentiation into neurons, 22 genes (Map2, Cpe, Marcks, Ptbp2, Sox11, Tubb2b, Vim, Arx, Emx2, Pax6, Basp1, Ddr1, Ndn, Sfrp, Ttc3, Ubqln2, Six3, Dcx, L1cam, Reln, Wnt1 and Nnat) showed reduced expression specifically by embryotoxic chemicals. Almost all gene sets identified in this study are known to be indispensable for differentiation and development of heart and brain tissues, and thus may serve in early detection or prediction of embryotoxicity of chemicals in vitro.

What does it take to make a heart?

Ever increasing advances are being made in our quest to understand what it takes to direct pluripotent precursor cells to adopt a specific developmental fate. Eventually, the obvious goal is that targeted manipulation of these precursor cells will result in an efficient and reliable production of tissue-specific cells, which can be safely employed for therapeutic purposes. We have gained an incredible insight as to which molecular pathways are involved in governing neural, skeletal and cardiac muscle fate decisions. However, we still face the challenge of how to direct, for example, a cardiac fate in stem cells in the amounts needed to be employed for regenerative means. Equally importantly, we need to resolve critical questions such as: can the in vitro generated cardiomyocytes actually functionally replace damaged heart tissue? Here I will provide an overview of the molecules and signalling pathways that have first been demonstrated in embryological studies to function in cardiogenesis, and summarize how this knowledge is being applied to differentiate mouse and human embryonic stem cells into cardiomyocytes.

MicroRNA profiling during cardiomyocyte-specific differentiation of murine embryonic stem cells based on two different miRNA array platforms

MicroRNA (miRNA) plays a critical role in a wide variety of biological processes. Profiling miRNA expression during differentiation of embryonic stem cells will help to understand the regulation pathway of differentiation, which in turn may elucidate disease mechanisms. The identified miRNAs could then serve as a new group of possible therapeutic targets. In the present paper, miRNA expression profiles were determined during cardiomyocyte-specific differentiation and maturation of murine embryonic stem (ES) cells. For this purpose a homogeneous cardiomyocyte population was generated from a transgenic murine ES cell line. Two high throughput array platforms (Affymetrix and Febit) were used for miRNA profiling in order to compare the effect of the platforms on miRNA profiling as well as to increase the validity of target miRNA identification. Four time points (i.e. day 0, day 12, day 19 and day 26) were chosen for the miRNA profiling study, which corresponded to different stages during cardiomyocyte-specific differentiation and maturation. Fifty platform and pre-processing method-independent miRNAs were identified as being regulated during the differentiation and maturation processes. The identification of these miRNAs is an important step for characterizing and understanding the events involved in cardiomyocyte-specific differentiation of ES cells and may also highlight candidate target molecules for therapeutic purposes.

Derivation of functional ventricular cardiomyocytes using endogenous promoter sequence from murine embryonic stem cells

The purpose of this study is to establish a murine embryonic stem cell (mESC) line for isolation of functional ventricular cardiomyocytes (VCMs) and then to characterize the derived VCMs. By crossing the myosin light chain 2v (Mlc2v)-Cre mouse line with the reporter strain Rosa26-yellow fluorescent protein (YFP), we generated mESC lines from these double transgenic mice, in which Cre-mediated removal of a stop sequence results in the expression of YFP under the control of the ubiquitously active Rosa26 promoter specifically in the VCM. After induction of differentiation via embryoid body (EB) formation, contracting YFP(+) cells were detected within EBs and isolated by fluorescence-activated cell sorting. N-cadherin, the cadherin expressed in cardiomyocytes, and the major cardiac connexin (Cx) isoform, Cx43, were detected in the respective adherens and gap junctions in these VCMs. Using current clamp recordings we demonstrated that mESC-derived VCMs exhibited action potential characteristics comparable to those of neonatal mouse VCMs. Real-time intracellular calcium [Ca(2+)](i) imaging showed rhythmic intracellular calcium transients in these VCMs. The amplitude and frequency of calcium transients were increased by isoproterenol stimulation, suggesting the existence of functional β-adrenergic signaling. Moreover, [Ca(2+)](i) oscillations responded to increasing frequencies of external electrical stimulation, indicating that VCMs have functional excitation-contraction coupling, a key factor for the ultimate cardiac contractile performance. The present study makes possible the production of homogeneous and functional VCMs for basic research as well as for cardiac repair and regeneration.

The use of gating technology in bioengineering insulin-secreting cells from embryonic stem cells

Embryonic stem cells display the ability to differentiate in vitro into a variety of cell types. This process is induced by embryoid body formation, addition of several soluble growth factors to the culture medium and other strategies. However, none of the used factors is capable to drive differentiation to only one specific celltype. The use of gating technology has allowed to partially overcome this problem. The rational behind this technique is based on the transfection of stem cells with a transgene carrying expression cassettes for a cell type specific promoter, regulating expression ofa selectable marker to select one cell lineage from other cell lineages.Using this system, we have obtained insulin-secreting cells by transfecting mouse embryonic stem cells with a DNA construct providing resistance to neomycin under the control of the regulatory regions of the human insulin gene. Furthermore, gating technology has been successfully used to isolate other cell types such as cardiomyocytes and neural precursors from undifferentiated embryonic stem cells. This review focuses on the possibilities offered by this technology in embryonic stem cell bioengineering, mainly to obtain insulin-secreting cells. Advantages and considerations of this selection system will be also discussed.

Chondrocytes derived from mouse embryonic stem cells

Our knowledge of cellular differentiation processes during chondro- and osteogenesis, in particular the complex interaction of differentiation factors, is still limited. We used the model system of embryonic stem (ES) cell differentiation in vitro via cellular aggregates, so called embryoid bodies (EBs), to analyze chondrogenic and osteogenic differentiation. ES cells differentiated into chondrocytes and osteocytes throughout a series of developmental stages resembling cellular differentiation events during skeletal development in vivo. A lineage from pluripotent ES cells via mesenchymal, prechondrogenic cells, chondrocytes and hypertrophicchondrocytes up to osteogenic cells was characterized. Furthermore, we found evidence for another osteogenic lineage, bypassing the chondrogenic stage. Together our results suggest that this in vitro system will be helpful to answer so far unacknowledged questions regarding chondrogenic and osteogenic differentiation. For example, we isolated an as yet unknown cDNA fragment from ES cell-derived chondrocytes, which showed a developmentally regulated expression pattern during EB differentiation. Considering ES cell differentiation as an alternative approach for cellular therapy, we used two different methods to obtain pure chondrocyte cultures from the heterogenous EBs. First, members of the transforming growth factor (TGF)-beta family were applied and found to modulate chondrogenic differentiation but were not effective enough to produce sufficient amounts of chondrocytes. Second, chondrocytes were isolated from EBs by micro-manipulation. These cells initially showed dedifferentiation into fiboblastoid cells in culture, but later redifferentiated into mature chondrocytes. However, a small amount of chondrocytes isolated from EBs transdifferentiated into other mesenchymal cell types, indicating that chondrocytes derived from ES cells posses a distinct differentiation plasticity.

Mechanical phenotyping of mouse embryonic stem cells: increase in stiffness with differentiation

Atomic force microscopy (AFM) has emerged as a promising tool to characterize the mechanical properties of biological materials and cells. In our studies, undifferentiated and early differentiating mouse embryonic stem cells (mESCs) were assessed individually using an AFM system to determine if we could detect changes in their mechanical properties by surface probing. Probes with pyramidal and spherical tips were assessed, as were different analytical models for evaluating the data. The combination of AFM probing with a spherical tip and analysis using the Hertz model provided the best fit to the experimental data obtained and thus provided the best approximation of the elastic modulus. Our results showed that after only 6 days of differentiation, individual cell stiffness increased significantly with early differentiating mESCs having an elastic modulus two- to threefold higher than undifferentiated mESCs, regardless of cell line (R1 or D3 mESCs) or treatment. Single-touch (indentation) probing of individual cells is minimally invasive compared to other techniques. Therefore, this method of mechanical phenotyping should prove to be a valuable tool in the development of improved methods of identification and targeted cellular differentiation of embryonic, adult, and induced-pluripotent stem cells for therapeutic and diagnostic purposes.

Mechanical phenotyping of stem cells

Elasticity and visco-elasticity are mechanical properties of cells which directly reflect cellular composition, internal structure (cytoskeleton), and external interactions (cell-cell and/or cell-surface). A variety of techniques involving probing, pulling, or deforming cells have been used to characterize these mechanical properties. With continuing advances in the technology, it may be possible to establish mechanical phenotypes that can be used to identify cells at specific points of differentiation and dedifferentiation with direct applications to regenerative medicine, therapeutics, and diagnostics.

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.

Mammalian artificial chromosomes and clinical applications for genetic modification of stem cells: an overview

Modifying multipotent, self-renewing human stem cells with mammalian artificial chromosomes (MACs), present a promising clinical strategy for numerous diseases, especially ex vivo cell therapies that can benefit from constitutive or overexpression of therapeutic gene(s). MACs are nonintegrating, autonomously replicating, with the capacity to carry large cDNA or genomic sequences, which in turn enable potentially prolonged, safe, and regulated therapeutic transgene expression, and render MACs as attractive genetic vectors for "gene replacement" or for controlling differentiation pathways in progenitor cells. The status quo is that the most versatile target cell would be one that was pluripotent and self-renewing to address multiple disease target cell types, thus making multilineage stem cells, such as adult derived early progenitor cells and embryonic stem cells, as attractive universal host cells. We will describe the progress of MAC technologies, the subsequent modifications of stem cells, and discuss the establishment of MAC platform stem cell lines to facilitate proof-of-principle studies and preclinical development.

Differential gene expressions in atrial and ventricular myocytes: insights into the road of applying embryonic stem cell-derived cardiomyocytes for future therapies

Myocardial infarction has been the leading cause of morbidity and mortality in developed countries over the past few decades. The transplantation of cardiomyocytes offers a potential method of treatment. However, cardiomyocytes are in high demand and their supply is extremely limited. Embryonic stem cells (ESCs), which have been isolated from the inner cell mass of blastocysts, can self-renew and are pluripotent, meaning they have the ability to develop into any type of cell, including cardiomyocytes. This suggests that ESCs could be a good source of genuine cardiomyocytes for future therapeutic purposes. However, problems with the yield and purity of ESC-derived cardiomyocytes, among other hurdles for the therapeutic application of ESC-derived cardiomyocytes (e.g., potential immunorejection and tumor formation problems), need to be overcome before these cells can be used effectively for cell replacement therapy. ESC-derived cardiomyocytes consist of nodal, atrial, and ventricular cardiomyocytes. Specifically, for treatment of myocardial infarction, transplantation of a sufficient quantity of ventricular cardiomyocytes, rather than nodal or atrial cardiomyocytes, is preferred. Hence, it is important to find ways of increasing the yield and purity of specific types of cardiomyocytes. Atrial and ventricular cardiomyocytes have differential expression of genes (transcription factors, structural proteins, ion channels, etc.) and are functionally distinct. This paper presents a thorough review of differential gene expression in atrial and ventricular myocytes, their expression throughout development, and their regulation. An understanding of the molecular and functional differences between atrial and ventricular myocytes allows discussion of potential strategies for preferentially directing ESCs to differentiate into chamber-specific cells, or for fine tuning the ESC-derived cardiomyocytes into specific electrical and contractile phenotypes resembling chamber-specific cells.

Global transcriptional profiles of beating clusters derived from human induced pluripotent stem cells and embryonic stem cells are highly similar

Background

Functional and molecular integrity of cardiomyocytes (CMs) derived from induced pluripotent stem (iPS) cells is essential for their use in tissue repair, disease modelling and drug screening. In this study we compared global transcriptomes of beating clusters (BCs) microdissected from differentiating human iPS cells and embryonic stem (ES) cells.

Results

Hierarchical clustering and principal component analysis revealed that iPS-BCs and ES-BCs cluster together, are similarly enriched for cardiospecific genes and differ in expression of only 1.9% of present transcripts. Similarly, sarcomeric organization, electrophysiological properties and calcium handling of iPS-CMs were indistinguishable from those of ES-CMs. Gene ontology analysis revealed that among 204 genes that were upregulated in iPS-BCs vs ES-BCs the processes related to extracellular matrix, cell adhesion and tissue development were overrepresented. Interestingly, 47 of 106 genes that were upregulated in undifferentiated iPS vs ES cells remained enriched in iPS-BCs vs ES-BCs. Most of these genes were found to be highly expressed in fibroblasts used for reprogramming and 34% overlapped with the recently reported iPS cell-enriched genes.

Conclusions

These data suggest that iPS-BCs are transcriptionally highly similar to ES-BCs. However, iPS-BCs appear to share some somatic cell signature with undifferentiated iPS cells. Thus, iPS-BCs may not be perfectly identical to ES-BCs. These minor differences in the expression profiles may occur due to differential cellular composition of iPS-BCs and ES-BCs, due to retention of some genetic profile of somatic cells in differentiated iPS cell-derivatives, or both.

Current status of myocardial regeneration and cell transplantation

Recent studies have shown that cardiomyocytes can be induced to differentiate from several types of stem cells. Techniques to purify and transplant stem-cell-derived cardiomyocytes have also been developed, and the transplanted cells have been demonstrated to reside in the recipient hearts for long periods. Recently, cardiomyocyte cell sheets enabling transplantation of viable tissue have been reported. Promising results have also been obtained using cytokines to mobilize stem cells in vivo as a potential treatment for heart failure. However, a number of hurdles remain in the quest to treat heart failure by cell transplantation without the need for a donor at the preclinical stage. In the next phase, the field needs to develop innovations to specifically differentiate cardiomyocytes from stem cells, to purify cardiomyocytes from contaminating cells in a cell mixture using a high-throughput method, and to establish and maintain artificial regenerated tissue using tissue engineering for transplantation.

Temporal and contextual orchestration of cardiac fate by WNT-BMP synergy and threshold

Cardiomyogenic development proceeds with a cascade of intricate signalling events that operate in a temporo-spatial fashion to specify cardiac cell fate during early embryogenesis. In fact, conflicting reports exist regarding the role of Wnt/β-catenin signalling during cardiomyogenesis. Here, we describe a dose-dependent and temporal effect of Wnt/β-catenin signalling on in vitro cardiomyogenesis using embryonic stem cells (ESCs) as a model system. We could demonstrate that canonical Wnt activation during early stage of differentiation either through ligand or by GSK3β inhibition helped in maintaining Oct4 and Nanog expressions, and in parallel, it promoted mesoderm and endoderm inductions. In contrast, it led to attenuation in cardiomyogenesis that was reversed by moderate concentration of DKK1, but not soluble Fz8. However, higher DKK1 could also block cardiomyogenesis, suggesting thereby governance of a particular signalling threshold underlying this developmental event. Interestingly, Wnt signalling activation at early stage modulated BMP4 expression in a stage-specific manner. Wnt activation, synchronized with BMP4 and brachyury up-regulation at early stage, correlated well with mesoderm induction. Conversely, Wnt activation led to BMP4 and Wnt5a down-regulation at late stage culminating in cardiomyogenic attenuation. Our findings suggested the existence of precise regulatory machinery with context-dependent role of Wnt for fine tuning mesoderm induction and its derivatives, through establishment of Wnt gradient during ESCs’ differentiation. Moreover, contrary to mere activation/inhibition, a specific threshold of Wnt and BMP and their synergy seemed necessary for providing the guiding cues in orchestrating mesoderm induction and subsequent cardiomyogenesis.

Progressive maturation in contracting cardiomyocytes derived from human embryonic stem cells: Qualitative effects on electrophysiological responses to drugs

The field of drug testing currently needs a new integrated assay system, as accurate as systems using native tissues, that will allow us to predict arrhythmia risks of candidate drugs and the relationship between genetic mutations and acquired electrophysiological phenotypes. This could be accomplished by combining the microelectrode array (MEA) system with cardiomyocytes (CMs) derived from human embryonic stem cells (hESC) and induced pluripotential stem cells. CMs have been successfully induced from both types, but their maturation process is not systematically controlled; this results in loss of beating potency and insufficient ion channel function. We generated a transgenic hESC line that facilitates maintenance of hESC-CM clusters every 2 weeks by expressing GFP driven by a cardiac-specific alphaMHC promoter, thereby producing a compact pacemaker lineage within a ventricular population over a year. Further analyses, including quantitative RT-PCR, patch-clamp, and MEA-mediated QT tests, demonstrated that replating culturing continuously enhanced gene expression, ionic current amplitudes, and resistance to K(+) channel blockades in hESC-CMs. Moreover, temporal three-dimensional (3D) culturing accelerated maturation by restoring the global gene repressive status established in the adhesive status. Replating/3D culturing thus produces hESC-CMs that act as functional syncytia suitable for use in regenerative medicine and accurate drug tests.

Electrophysiological development of transplanted embryonic stem cell-derived cardiomyocytes in the hearts of syngeneic mice

BACKGROUND AND AIMS

We undertook this study in order to investigate the electrophysiological properties of grafted mouse embryonic stem cell (ES)-derived cardiomyocytes in mouse hearts.

METHODS

We generated transgenic D3 ES cells that carry the alpha-myosin heavy-chain promoter-driven enhanced green fluorescent protein (EGFP) gene. ES-derived cardiomyocytes (10 days) were purified by fluorescent-activated cell sorting and then transplanted into the left ventricle of syngeneic mice. Finally, hearts were removed and the EGFP+ cardiomyocytes were dissociated from the host heart for patch clamp study.

RESULTS

Morphological studies showed that EGFP+ cardiomyocytes were round and small before transplantation. Majority of cells were larger and longer with clear cross striations at the fourth week. Colocalization of EGFP and 4',6-diamidino-2-phenylindole-labeled nuclei of transplanted cells with cardiomyocyte markers for cardiac troponin T, as detected by immunofluorescent microscopy, indicated the survival of grafted cells. The patch clamp study revealed that the ES-derived cardiomyocytes possessed pacemaker-like action potential (AP) before transplantation. Four weeks after transplantation, grafted cells retained the characteristic of intermediate embryonic ventricular-like AP distinct from triangular AP of adult mouse ventricular myocytes, along with the loss of cellular excitability and downregulation of pacemaker current, suggesting that these grafted cells were not as mature as native ventricular cells.

CONCLUSIONS

Transplanted ES-derived cardiomyocytes display accelerated differentiation and loss of automaticity, indicating that the long-term effectiveness of ES cell-based biological pacemakers can also be problematic.

Interrogating functional integration between injected pluripotent stem cell-derived cells and surrogate cardiac tissue

Myocardial infarction resulting in irreversible loss of cardiomyocytes (CMs) remains a leading cause of heart failure. Although cell transplantation has modestly improved cardiac function, major challenges including increasing cell survival, engraftment, and functional integration with host tissue, remain. Embryonic stem cells (ESCs), which can be differentiated into cardiac progenitors (CPs) and CMs, represent a candidate cell source for cardiac cell therapy. However, it is not known what specific cell type or condition is the most appropriate for transplantation. This problem is exasperated by the lack of efficient and predictive strategies to screen the large numbers of parameters that may impact cell transplantation. We used a cardiac tissue model, engineered heart tissue (EHT), and quantitative molecular and electrophysiological analyses, to test transplantation conditions and specific cell populations for their potential to functionally integrate with the host tissue. In this study, we validated our analytical platform using contractile mouse neonatal CMs (nCMs) and noncontractile cardiac fibroblasts (cFBs), and screened for the integration potential of ESC-derived CMs and CPs (ESC-CMs and -CPs). Consistent with previous in vivo studies, cFB injection interfered with electrical signal propagation, whereas injected nCMs improved tissue function. Purified bioreactor-generated ESC-CMs exhibited a diminished capacity for electrophysiological integration; a result correlated with lower (compared with nCMs) connexin 43 expression. ESC-CPs, however, appeared able to appropriately mature and integrate into EHT, enhancing the amplitude of tissue contraction. Our results support the use of EHT as a model system to accelerate development of cardiac cell therapy strategies.

Differentiation induction of mouse embryonic stem cells into sinus node-like cells by suramin

BACKGROUND

Embryonic stem (ES) cells differentiate into cardiac phenotypes representing early pacemaker-, atrial-, ventricular-, and sinus node-like cells, however, ES-derived specification into sinus nodal cells is not yet known. By using the naphthylamine derivative of urea, suramin, we were able to follow the process of cardiac specialization into sinus node-like cells.

METHODS

Differentiating mouse ES cells were treated with suramin (500 µM) from day 5 to 7 of embryoid body formation, and cells were analysed for their differentiation potential via morphological analysis, flow cytometry, RT-PCR, immunohistochemistry and patch clamp analysis.

RESULTS

Application of suramin resulted in an increased number of cardiac cells, but inhibition of neuronal, skeletal muscle and definitive endoderm differentiation. Immediately after suramin treatment, a decreased mesendoderm differentiation was found. Brachyury, FGF10, Wnt8 and Wnt3a transcript levels were significantly down-regulated, followed by a decrease in mesoderm- and cardiac progenitor-specific markers BMP2, GATA4/5, Wnt11, Isl1, Nkx2.5 and Tbx5 immediately after removal of the substance. With continued differentiation, a significant up-regulation of Brachyury, FGF10 and GATA5 transcript levels was observed, whereas Nkx2.5, Isl1, Tbx5, BMP2 and Wnt11 levels were normalized to control levels. At advanced differentiation stages, sinus node-specific HCN4, Tbx2 and Tbx3 transcript levels were significantly up-regulated. Immunofluorescence and patch-clamp analysis confirmed the increased number of sinus node-like cells, and electrophysiological analysis revealed a lower number of atrial- and ventricular-like cardiomyocytes following suramin treatment.

CONCLUSION

We conclude that the interference of suramin with the cardiac differentiation process modified mesoderm- and cardiac-specific gene expression resulting in enhanced formation of sinus node-like cells.

Functional characterization of cardiomyocytes derived from murine induced pluripotent stem cells in vitro

Several types of terminally differentiated somatic cells can be reprogrammed into a pluripotent state by ectopic expression of Klf4, Oct3/4, Sox2, and c-Myc. Such induced pluripotent stem (iPS) cells have great potential to serve as an autologous source of cells for tissue repair. In the process of developing iPS-cell-based therapies, the major goal is to determine whether differentiated cells derived from iPS cells, such as cardiomyocytes (CMs), have the same functional properties as their physiological in vivo counterparts. Therefore, we differentiated murine iPS cells to CMs in vitro and characterized them by RT-PCR, immunocytochemistry, and electrophysiology. As key markers of cardiac lineages, transcripts for Nkx2.5, alphaMHC, Mlc2v, and cTnT could be identified. Immunocytochemical stainings revealed the presence of organized sarcomeric actinin but the absence of mature atrial natriuretic factor. We examined characteristics and developmental changes of action potentials, as well as functional hormonal regulation and sensitivity to channel blockers. In addition, we determined expression patterns and functionality of cardiac-specific voltage-gated Na+, Ca2+, and K+ channels at early and late differentiation stages and compared them with CMs derived from murine embryonic stem cells (ESCs) as well as with fetal CMs. We conclude that iPS cells give rise to functional CMs in vitro, with established hormonal regulation pathways and functionally expressed cardiac ion channels; CMs generated from iPS cells have a ventricular phenotype; and cardiac development of iPS cells is delayed compared with maturation of native fetal CMs and of ESC-derived CMs. This difference may reflect the incomplete reprogramming of iPS cells and should be critically considered in further studies to clarify the suitability of the iPS model for regenerative medicine of heart disorders.

Pericellular matrix of decidua-derived mesenchymal cells: a potent human-derived substrate for the maintenance culture of human ES cells

In routine culture, human embryonic stem (hES) cells are maintained on either feeder cells or special culture substrates such as Matrigel. However, to expand hES cells for clinical applications, it is desirable to minimize animal-derived materials in the culture for safety reasons. In this report, we show that the pericellular matrix prepared from human decidua-derived mesenchymal cells (PCM-DM) is a potent substrate material that supports the growth and pluripotency of hES cells as efficiently as Matrigel does. This supporting activity of PCM-DM is stable and can be preserved for several months in the refrigerator. PCM-DM-based culture is compatible with non-conditioned commercial defined medium, and with the maintenance of dissociated hES cells in the presence of ROCK inhibitor. Since decidual mesenchymal cells can be prepared and expanded in a large quantity, PCM-DM is a practical human-derived substitute for the animal-derived substrates for use in clinical-grade culture of hES cells.

Lack of laminin gamma1 in embryonic stem cell-derived cardiomyocytes causes inhomogeneous electrical spreading despite intact differentiation and function

Laminins form a large family of extracellular matrix (ECM) proteins, and their expression is a prerequisite for normal embryonic development. Herein we investigated the role of the laminin gamma1 chain for cardiac muscle differentiation and function using cardiomyocytes derived from embryonic stem cells deficient in the LAMC1 gene. Laminin gamma1 (-/-) cardiomyocytes lacked basement membranes (BM), whereas their sarcomeric organization was unaffected. Accordingly, electrical activity and hormonal regulation were found to be intact. However, the inadequate BM formation led to an increase of ECM deposits between adjacent cardiomyocytes, and this resulted in defects of the electrical signal propagation. Furthermore, we also found an increase in the number of pacemaker areas. Thus, although laminin and intact BM are not essential for cardiomyocyte development and differentiation per se, they are required for the normal deposition of matrix molecules and critical for intact electrical signal propagation.

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.

Stem cell sources for regenerative medicine

Tissue-resident stem cells or primitive progenitors play an integral role in homeostasis of most organ systems. Recent developments in methodologies to isolate and culture embryonic and somatic stem cells have many new applications poised for clinical and preclinical trials, which will enable the potential of regenerative medicine to be realized. Here, we overview the current progress in therapeutic applications of various stem cells and discuss technical and social hurdles that must be overcome for their potential to be realized.

Substrate rigidity regulates Ca2+ oscillation via RhoA pathway in stem cells

Substrate rigidity plays crucial roles in regulating cellular functions, such as cell spreading, traction forces, and stem cell differentiation. However, it is not clear how substrate rigidity influences early cell signaling events such as calcium in living cells. Using highly sensitive Ca(2+) biosensors based on fluorescence resonance energy transfer (FRET), we investigated the molecular mechanism by which substrate rigidity affects calcium signaling in human mesenchymal stem cells (HMSCs). Spontaneous Ca(2+) oscillations were observed inside the cytoplasm and the endoplasmic reticulum (ER) using the FRET biosensors targeted at subcellular locations in cells plated on rigid dishes. Lowering the substrate stiffness to 1 kPa significantly inhibited both the magnitudes and frequencies of the cytoplasmic Ca(2+) oscillation in comparison to stiffer or rigid substrate. This Ca(2+) oscillation was shown to be dependent on ROCK, a downstream effector molecule of RhoA, but independent of actin filaments, microtubules, myosin light chain kinase, or myosin activity. Lysophosphatidic acid, which activates RhoA, also inhibited the frequency of the Ca(2+) oscillation. Consistently, either a constitutive active mutant of RhoA (RhoA-V14) or a dominant negative mutant of RhoA (RhoA-N19) inhibited the Ca(2+) oscillation. Further experiments revealed that HMSCs cultured on gels with low elastic moduli displayed low RhoA activities. Therefore, our results demonstrate that RhoA and its downstream molecule ROCK may mediate the substrate rigidity-regulated Ca(2+) oscillation, which determines the physiological functions of HMSCs.

Enhanced proliferation of monolayer cultures of embryonic stem (ES) cell-derived cardiomyocytes following acute loss of retinoblastoma

Background

Cardiomyocyte (CM) cell cycle analysis has been impeded because of a reliance on primary neonatal cultures of poorly proliferating cells or chronic transgenic animal models with innate compensatory mechanisms.

Methodology/Principal Findings

We describe an in vitro model consisting of monolayer cultures of highly proliferative embryonic stem (ES) cell-derived CM. Following induction with ascorbate and selection with puromycin, early CM cultures are >98% pure, and at least 85% of the cells actively proliferate. During the proliferative stage, cells express high levels of E2F3a, B-Myb and phosphorylated forms of retinoblastoma (Rb), but with continued cultivation, cells stop dividing and mature functionally. This developmental transition is characterized by a switch from slow skeletal to cardiac TnI, an increase in binucleation, cardiac calsequestrin and hypophosphorylated Rb, a decrease in E2F3, B-Myb and atrial natriuretic factor, and the establishment of a more negative resting membrane potential. Although previous publications suggested that Rb was not necessary for cell cycle control in heart, we find following acute knockdown of Rb that this factor actively regulates progression through the G1 checkpoint and that its loss promotes proliferation at the expense of CM maturation.

Conclusions/Significance

We have established a unique model system for studying cardiac cell cycle progression, and show in contrast to previous reports that Rb actively regulates both cell cycle progression through the G1 checkpoint and maturation of heart cells. We conclude that this in vitro model will facilitate the analysis of cell cycle control mechanisms of CMs.

Cardiac regenerative medicine

Severe heart failure is associated with damage to the myocardium that is irreversible with current medical therapies. Recent experimental and clinical studies, however, have opened the possibility of solving many of the associated problems, making this an exciting and tangible goal. There are many potential cell sources for regenerative cardiac medicine, including bone marrow stem cells, endothelial progenitor cells, skeletal myocytes, adult cardiac stem cells, and embryonic stem (ES) cells. Although ES cells are highly proliferative and suitable for mass production, they are not autologous, and an efficient protocol is yet to be established to ensure selective cardiomyocyte induction. Recent studies have successfully established inducible pluripotent stem (iPS) cells from mouse and human fibroblasts by the gene transfer of 4 transcription factors that are strongly expressed in ES cells: Oct3/4, Sox2, Klf4 and c-Myc. iPS cells can differentiate into all 3 germ layer-derived cells and are syngeneic, indicating that they can become an ideal cell source for regenerative medicine. Despite these successes, the accumulating evidence from fields as diverse as developmental biology, stem cell biology and tissue engineering must be integrated to achieve the full potential of cardiac regenerative medicine.

Emerging roles of inositol 1,4,5-trisphosphate signaling in cardiac myocytes

Inositol 1,4,5-trisphosphate (IP(3)) is a ubiquitous intracellular messenger regulating diverse functions in almost all mammalian cell types. It is generated by membrane receptors that couple to phospholipase C (PLC), an enzyme which liberates IP(3) from phosphatidylinositol 4,5-bisphosphate (PIP(2)). The major action of IP(3), which is hydrophilic and thus translocates from the membrane into the cytoplasm, is to induce Ca(2+) release from endogenous stores through IP(3) receptors (IP(3)Rs). Cardiac excitation-contraction coupling relies largely on ryanodine receptor (RyR)-induced Ca(2+) release from the sarcoplasmic reticulum. Myocytes express a significantly larger number of RyRs compared to IP(3)Rs (~100:1), and furthermore they experience substantial fluxes of Ca(2+) with each heartbeat. Therefore, the role of IP(3) and IP(3)-mediated Ca(2+) signaling in cardiac myocytes has long been enigmatic. Recent evidence, however, indicates that despite their paucity cardiac IP(3)Rs may play crucial roles in regulating diverse cardiac functions. Strategic localization of IP(3)Rs in cytoplasmic compartments and the nucleus enables them to participate in subsarcolemmal, bulk cytoplasmic and nuclear Ca(2+) signaling in embryonic stem cell-derived and neonatal cardiomyocytes, and in adult cardiac myocytes from the atria and ventricles. Intriguingly, expression of both IP(3)Rs and membrane receptors that couple to PLC/IP(3) signaling is altered in cardiac disease such as atrial fibrillation or heart failure, suggesting the involvement of IP(3) signaling in the pathology of these diseases. Thus, IP(3) exerts important physiological and pathological functions in the heart, ranging from the regulation of pacemaking, excitation-contraction and excitation-transcription coupling to the initiation and/or progression of arrhythmias, hypertrophy and heart failure.

Efficient stem cell labeling for MRI studies

Iron oxide particles are especially suited for cell tracking experiments due to their extraordinarily molar relaxivity as compared with other paramagnetic nuclei. We have compared different iron oxide particles (Sinerem, Endorem and magnetic microspheres) for their suitability to label embryonic stem cells (D3 cell line). In addition to detectability thresholds, particular attention has been paid to the evaluation of long-term stability of the labelling procedure (up to 4 weeks) as well as to toxic and other adverse effects on cell viability. Comparative studies were performed using neural progenitor cells (C17.2) and dendritic cells. The present study indicates strong dependence of the label efficiency and stability on the iron oxide particles and cell lines in use.

Genetic modification of cells for transplantation

Progress in gene therapy has produced promising results that translate experimental research into clinical treatment. Gene modification has been extensively employed in cell transplantation. The main barrier is an effective gene delivery system. Several viral vectors were utilized in end-stage differentiated cells. Recently, successful applications were described with adenovirus-associated vectors. As an alternative, embryonic stem cell- and stem cell-like systems were established for generation of tissue-specified gene-modified cells. Owing to the feasibility for genetic manipulations and the self-renewing potency of these cells they can be used in a way enabling large-scale in vitro production. This approach offers the establishment of in vitro cell culture systems that will deliver sufficient amounts of highly purified, immunoautologous cells suitable for application in regenerative medicine. In this review, the current technology of gene delivery systems to cells is recapitulated and the latest developments for cell transplantation are discussed.