Molecular and pharmacological properties of human embryonic stem cell-derived cardiomyocytes

Integration of a fiber-based cell culture and biosensing system for monitoring of multiple protein markers secreted from stem cells

We propose a new platform that can integrate three-dimensional cell culture scaffold and a surface-enhanced Raman spectroscopy (SERS)-based biosensor by stacking them to form a multilayer system, which would allow monitoring of the protein markers secreted from cultured stem cells without periodic cell and/or media collection. The cell culture scaffold supported the proliferation and osteogenic differentiation of adipose-derived mesenchymal stem cells (ADSCs). The SERS capture substrate detected protein markers in combination with SERS tag made with Au-Ag alloy nanoboxes. Incorporating the different Raman reporters into the SERS tag allowed easy identification of target proteins for multiplex assays. The resultant SERS-based immunoassay could detect the pg/mL levels of protein markers without crosstalk and interference. When one ADSC culture scaffold and multiple SERS capture substrates were integrated and incubated in differentiation culture media, our system was sufficiently sensitive to monitor time-dependent secretion of three different osteogenic protein markers from ADSCs during their osteogenic differentiation. Since the sensor and cell culture scaffold can be manipulated independently, various cell and biomarker combinations are possible to obtain relevant information regarding the actual state of the different types of cells.

On-chip spatiotemporal electrophysiological analysis of human stem cell derived cardiomyocytes enables quantitative assessment of proarrhythmia in drug development

We examined a simultaneous combined spatiotemporal field potential duration (FPD) and cell-to-cell conduction time (CT) in lined-up shaped human embryonic stem cell-derived cardiomyocytes (hESC-CMs) using an on-chip multielectrode array (MEA) system to evaluate two origins of lethal arrhythmia, repolarization and depolarization. The repolarization index, FPD, was prolonged by E-4031 and astemizole, and shortened by verapamil, flecainide and terfenadine at 10 times higher than therapeutic plasma concentrations of each drug, but it did not change after lidocaine treatment up to 100 μM. CT was increased by astemizol, flecainide, terfenadine, and lidocaine at equivalent concentrations of Nav1.5 IC50, suggesting that CT may be an index of cardiac depolarization because the increase in CT (i.e., decrease in cell-to-cell conduction speed) was relevant to Nav1.5 inhibition. Fluctuations (short-term variability; STV) of FPD and CT, STVFPD and STVCT also discriminated between torsadogenic and non-torsadogenic compounds with significant increases in their fluctuation values, enabling precise prediction of arrhythmogenic risk as potential new indices.

Key Issues Related to Cryopreservation and Storage of Stem Cells and Cancer Stem Cells: Protecting Biological Integrity

Cryopreservation and biobanking of stem cells are becoming increasingly important as stem cell technology and application attract the interest of industry, academic research, healthcare and patient organisations. Stem cell are already being used in the treatment of some diseases and it is anticipated that stem cell therapy will play a central role in future medicine. Similarly, the discovery of both hematopoietic and solid tumor stem cells and their clinical relevance have profoundly altered paradigms for cancer research as the cancer stem cells are considered promising new targets against cancer. Consequently, long-term cryopreservation and banking of normal and malignant stem cells is crucial and will inevitably become a routine procedure that requires highly regulated and safe methods of specimen storage. There is, however, an increasing amount of evidence showing contradictory results on the impact of cryopreservation and thawing of stem cells, including extensive physical and biological stresses, apoptosis and necrosis, mitochondrial injuries, changes to basal respiration and ATP production, cellular structural damage, telomere shortening and cellular senescence, and DNA damage and oxidative stress. Notably, cell surface proteins that play a major role in stem cell fate and are used as the biomarkers of stem cells are more vulnerable to cold stress than other proteins. There are also data supporting the alteration in some biological features and genetic integrity at the molecular level of the post-thawed stem cells. This article reviews the current and future challenges of cryopreservation of stem cells and stresses the need for further rigorous research on the methodologies for freezing and utilizing cancer stem cells following long-term storage.

Non-Invasive Acoustical sensing of Drug-Induced Effects on the Contractile Machinery of Human Cardiomyocyte Clusters

There is an urgent need for improved models for cardiotoxicity testing. Here we propose acoustic sensing applied to beating human cardiomyocyte clusters for non-invasive, surrogate measuring of the QT interval and other characteristics of the contractile machinery. In experiments with the acoustic method quartz crystal microbalance with dissipation monitoring (QCM-D), the shape of the recorded signals was very similar to the extracellular field potential detected in electrochemical experiments, and the expected changes of the QT interval in response to addition of conventional drugs (E-4031 or nifedipine) were observed. Additionally, changes in the dissipation signal upon addition of cytochalasin D were in good agreement with the known, corresponding shortening of the contraction-relaxation time. These findings suggest that QCM-D has great potential as a tool for cardiotoxicological screening, where effects of compounds on the cardiomyocyte contractile machinery can be detected independently of whether the extracellular field potential is altered or not.

Pluripotent stem cells as a platform for cardiac arrhythmia drug screening

OPINION STATEMENT

Since the first demonstrations of the differentiation of pluripotent stem cells to produce functional human cellular models such as cardiomyocytes, the scientific community has been captivated [1, 2••, 3]. In the time since that seminal work, the field has been catapulted forward by the demonstration that adult somatic cells can be reprogrammed to an induced state of pluripotency [4••], and more recently by the development of efficient and sophisticated genome editing tools [5••, 6••, 7], which together afford a theoretically unlimited supply of relevant genetic disease models. In particular, many of the early successes with induced pluripotent stem cell technology have been realized with cardiac arrhythmia syndromes [8••, 9-15]. There is interest in applying stem cell models in large-scale screens to discover novel therapeutics or drug toxicities. This manuscript aims to discuss the potential role of hPSC-derived cardiomyocyte models in therapeutic arrhythmia screens and review recent advances in the field that bring us closer to this reality.

Pluripotent stem cell derived cardiomyocytes for cardiac repair

OPINION STATEMENT

The adult mammalian heart has limited capacity for regeneration, and any major injury such as a myocardial infarction results in the permanent loss of up to 1 billion cardiomyocytes. The field of cardiac cell therapy aims to replace these lost contractile units with de novo cardiomyocytes to restore lost systolic function and prevent progression to heart failure. Arguably, the ideal cell for this application is the human cardiomyocyte itself, which can electromechanically couple with host myocardium and contribute active systolic force. Pluripotent stem cells from human embryonic or induced pluripotent lineages are attractive sources for cardiomyocytes, and preclinical investigation of these cells is in progress. Recent work has focused on the efficient generation and purification of cardiomyocytes, tissue engineering efforts, and examining the consequences of cell transplantation from mechanical, vascular, and electrical standpoints. Here we discuss historical and contemporary aspects of pluripotent stem cell-based cardiac cell therapy, with an emphasis on recent preclinical studies with translational goals.

Developmental cues for the maturation of metabolic, electrophysiological and calcium handling properties of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cells (hPSCs), including embryonic and induced pluripotent stem cells, are abundant sources of cardiomyocytes (CMs) for cell replacement therapy and other applications such as disease modeling, drug discovery and cardiotoxicity screening. However, hPSC-derived CMs display immature structural, electrophysiological, calcium-handling and metabolic properties. Here, we review various biological as well as physical and topographical cues that are known to associate with the development of native CMs in vivo to gain insights into the development of strategies for facilitated maturation of hPSC-CMs.

Concise review: maturation phases of human pluripotent stem cell-derived cardiomyocytes

Human pluripotent stem cell-derived cardiomyocytes (hPS-CM) may offer a number of advantages over previous cardiac models, however, questions of their immaturity complicate their adoption as a new in vitro model. hPS-CM differ from adult cardiomyocytes with respect to structure, proliferation, metabolism and electrophysiology, better approximating fetal cardiomyocytes. Time in culture appears to significantly impact phenotype, leading to what can be referred to as early and late hPS-CM. This work surveys the phenotype of hPS-CM, including structure, bioenergetics, sensitivity to damage, gene expression, and electrophysiology, including action potential, ion channels, and intracellular calcium stores, while contrasting fetal and adult CM with hPS-CM at early and late time points after onset of differentiation.

Structural and functional maturation of cardiomyocytes derived from human pluripotent stem cells

Despite preclinical studies demonstrating the functional benefit of transplanting human pluripotent stem cell-derived cardiomyocytes (PSC-CMs) into damaged myocardium, the ability of these immature cells to adopt a more adult-like cardiomyocyte (CM) phenotype remains uncertain. To address this issue, we tested the hypothesis that prolonged in vitro culture of human embryonic stem cell (hESC)- and human induced pluripotent stem cell (hiPSC)-derived CMs would result in the maturation of their structural and contractile properties to a more adult-like phenotype. Compared to their early-stage counterparts (PSC-CMs after 20-40 days of in vitro differentiation and culture), late-stage hESC-CMs and hiPSC-CMs (80-120 days) showed dramatic differences in morphology, including increased cell size and anisotropy, greater myofibril density and alignment, sarcomeres visible by bright-field microscopy, and a 10-fold increase in the fraction of multinucleated CMs. Ultrastructural analysis confirmed improvements in the myofibrillar density, alignment, and morphology. We measured the contractile performance of late-stage hESC-CMs and hiPSC-CMs and noted a doubling in shortening magnitude with slowed contraction kinetics compared to the early-stage cells. We then examined changes in the calcium-handling properties of these matured CMs and found an increase in calcium release and reuptake rates with no change in the maximum amplitude. Finally, we performed electrophysiological assessments in hESC-CMs and found that late-stage myocytes have hyperpolarized maximum diastolic potentials, increased action potential amplitudes, and faster upstroke velocities. To correlate these functional changes with gene expression, we performed qPCR and found a robust induction of the key cardiac structural markers, including β-myosin heavy chain and connexin-43, in late-stage hESC-CMs and hiPSC-CMs. These findings suggest that PSC-CMs are capable of slowly maturing to more closely resemble the phenotype of adult CMs and may eventually possess the potential to regenerate the lost myocardium with robust de novo force-producing tissue.

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.

Current status of drug screening and disease modelling in human pluripotent stem cells

The emphasis in human pluripotent stem cell (hPSC) technologies has shifted from cell therapy to in vitro disease modelling and drug screening. This review examines why this shift has occurred, and how current technological limitations might be overcome to fully realise the potential of hPSCs. Details are provided for all disease-specific human induced pluripotent stem cell lines spanning a dozen dysfunctional organ systems. Phenotype and pharmacology have been examined in only 17 of 63 lines, primarily those that model neurological and cardiac conditions. Drug screening is most advanced in hPSC-cardiomyocytes. Responses for almost 60 agents include examples of how careful tests in hPSC-cardiomyocytes have improved on existing in vitro assays, and how these cells have been integrated into high throughput imaging and electrophysiology industrial platforms. Such successes will provide an incentive to overcome bottlenecks in hPSC technology such as improving cell maturity and industrial scalability whilst reducing cost.

Electrophysiological and contractile function of cardiomyocytes derived from human embryonic stem cells

Human embryonic stem cells have emerged as the prototypical source from which cardiomyocytes can be derived for use in drug discovery and cell therapy. However, such applications require that these cardiomyocytes (hESC-CMs) faithfully recapitulate the physiology of adult cells, especially in relation to their electrophysiological and contractile function. We review what is known about the electrophysiology of hESC-CMs in terms of beating rate, action potential characteristics, ionic currents, and cellular coupling as well as their contractility in terms of calcium cycling and contraction. We also discuss the heterogeneity in cellular phenotypes that arises from variability in cardiac differentiation, maturation, and culture conditions, and summarize present strategies that have been implemented to reduce this heterogeneity. Finally, we present original electrophysiological data from optical maps of hESC-CM clusters.

Embryonic template-based generation and purification of pluripotent stem cell-derived cardiomyocytes for heart repair

Cardiovascular disease remains a leading cause of death in Western countries. Many types of cardiovascular diseases are due to a loss of functional cardiomyocytes, which can result in irreversible cardiac failure. Since the adult human heart has limited regenerative potential, cardiac transplantation is still the only effective therapy to address this cardiomyocyte loss. However, drawbacks, such as immune rejection and insufficient donor availability, are limiting this last-resort solution. Recent developments in the stem cell biology field have improved the potential of cardiac regeneration. Improvements in reprogramming strategies of differentiated adult cells into induced pluripotent stem cells, together with increased efficiency of directed differentiation of pluripotent stem cells toward cardiac myocytes, have brought cell-based heart muscle regeneration a few steps closer to the clinic. In this review, we outline the status of research on cardiac regeneration with a focus on directed differentiation of pluripotent stem cells toward the cardiac lineage.

Generation, characterization, and potential therapeutic applications of cardiomyocytes from various stem cells

Heart failure is one of the leading causes of death worldwide. Myocardial cell transplantation emerges as a novel therapeutic strategy for heart failure, but this approach has been hampered by severe shortage of human cardiomyocytes. We have recently induced mouse embryonic stem cells to differentiate into embryoid bodies and eventually, cardiomyocytes. Here, we address recent advancements in cardiomyocyte differentiation from cardiac stem cells and pluripotent stem cells. We highlight the methodologies, using growth factors, endoderm-like cell cocultures, small molecules, and biomaterials, in directing the differentiation of pluripotent stem cells into cardiomyocytes. The characterization and identification of pluripotent stem cell-derived cardiomyocytes by morphological, phenotypic, and functional features are also discussed. Notably, increasing evidence demonstrates that cardiomyocytes may be generated from the stem cells of several tissues outside the cardiovascular system, including skeletal muscles, bone marrow, testes, placenta, amniotic fluid, and adipose tissues. We further address the potential applications of cardiomyocytes derived from various kinds of stem cells. The differentiation of stem cells into functional cardiomyocytes, especially from an extra-cardiac stem cell source, would circumvent the scarcity of heart donors and human cardiomyocytes, and, most importantly, it would offer an ideal and promising cardiomyocyte source for cell therapy and tissue engineering in treating heart failure.

Global transcriptional profiling reveals similarities and differences between human stem cell-derived cardiomyocyte clusters and heart tissue

It is now well documented that human embryonic stem cells (hESCs) can differentiate into functional cardiomyocytes. These cells constitute a promising source of material for use in drug development, toxicity testing, and regenerative medicine. To assess their utility as replacement or complement to existing models, extensive phenotypic characterization of the cells is required. In the present study, we used microarrays and analyzed the global transcription of hESC-derived cardiomyocyte clusters (CMCs) and determined similarities as well as differences compared with reference samples from fetal and adult heart tissue. In addition, we performed a focused analysis of the expression of cardiac ion channels and genes involved in the Ca(2+)-handling machinery, which in previous studies have been shown to be immature in stem cell-derived cardiomyocytes. Our results show that hESC-derived CMCs, on a global level, have a highly similar gene expression profile compared with human heart tissue, and their transcriptional phenotype was more similar to fetal than to adult heart. Despite the high similarity to heart tissue, a number of significantly differentially expressed genes were identified, providing some clues toward understanding the molecular difference between in vivo sourced tissue and stem cell derivatives generated in vitro. Interestingly, some of the cardiac-related ion channels and Ca(2+)-handling genes showed differential expression between the CMCs and heart tissues. These genes may represent candidates for future genetic engineering to create hESC-derived CMCs that better mimic the phenotype of the cardiomyocytes present in the adult human heart.

Timed inhibition of p38MAPK directs accelerated differentiation of human embryonic stem cells into cardiomyocytes

BACKGROUND AIMS

Heart failure therapy with human embryonic stem cell (hESC)-derived cardiomyocytes (hCM) has been limited by the low rate of spontaneous hCM differentiation. As others have shown that p38 mitogen-activated protein kinase (p38MAPK) directs neurogenesis from mouse embryonic stem cells, we investigated whether the p38MAPK inhibitor, SB203580, might influence hCM differentiation.

METHODS

We treated differentiating hESC with SB203580 at specific time-points, and used flow cytometry, immunocytochemistry, quantitative real-time (RT)-polymerase chain reaction (PCR), teratoma formation and transmission electron microscopy to evaluate cardiomyocyte formation.

RESULTS

We observed that the addition of inhibitor resulted in 2.1-fold enrichment of spontaneously beating human embryoid bodies (hEB) at 21 days of differentiation, and that 25% of treated cells expressed cardiac-specific α-myosin heavy chain. This effect was dependent on the stage of differentiation at which the inhibitor was introduced. Immunostaining and teratoma formation assays demonstrated that the inhibitor did not affect hESC pluripotency; however, treated hESC gave rise to hCM exhibiting increased expression of sarcomeric proteins, including cardiac troponin T, myosin light chain and α-myosin heavy chain. This was consistent with significantly increased numbers of myofibrillar bundles and the appearance of nascent Z-bodies at earlier time-points in treated hCM. Treated hEB also demonstrated a normal karyotype by array comparative genomic hybridization and viability in vivo following injection into mouse myocardium.

CONCLUSIONS

These studies demonstrate that p38MAPK inhibition accelerates directed hCM differentiation from hESC, and that this effect is developmental stage-specific. The use of this inhibitor should improve our ability to generate hESC-derived hCM for cell-based therapy.

Cardiac differentiation of pluripotent stem cells

The ability of human pluripotent stem cells to differentiate towards the cardiac lineage has attracted significant interest, initially with a strong focus on regenerative medicine. The ultimate goal to repair the heart by cardiomyocyte replacement has, however, proven challenging. Human cardiac differentiation has been difficult to control, but methods are improving, and the process, to a certain extent, can be manipulated and directed. The stem cell-derived cardiomyocytes described to date exhibit rather immature functional and structural characteristics compared to adult cardiomyocytes. Thus, a future challenge will be to develop strategies to reach a higher degree of cardiomyocyte maturation in vitro, to isolate cardiomyocytes from the heterogeneous pool of differentiating cells, as well as to guide the differentiation into the desired subtype, that is, ventricular, atrial, and pacemaker cells. In this paper, we will discuss the strategies for the generation of cardiomyocytes from pluripotent stem cells and their characteristics, as well as highlight some applications for the cells.

Cryopreservation of human embryonic stem cells derived-cardiomyocytes induced by BMP2 in serum-free condition

Although previous studies showed that cardiomyocytes (CMs) can be generated from human embryonic stem cells (hESCs), the protocols for cryopreservation of hESC-derived CMs is not available to date. Here, we report on the efficient generation of hESC-derived CMs by direct differentiation using BMP2 in a serum-free condition, along with successful cryopreservation of derived CMs using Rho-associated kinase (ROCK) inhibitor. To induce differentiation, hESCs were treated with activin A and BMP2 for 5 days. A mesodermal gene, Brachyury, was expressed from day 3, and cardiac-specific markers such as Nkx2.5 and cTnI were detected at day 14. Furthermore, these cardiac progenitors expressed ion channel-related transcripts such as HCN1 and HCN2 from day 10. Beating clusters were observed from 14 days of differentiation for up to 35 days. Using mass cryopreservation, we froze hESC-derived CMs at 2 stages, at day 12 and 16 (prebeating and postbeating), after treating with ROCK inhibitor, Y-27632. Postthaw survival of CMs was higher in day 12 group compared to day 16, and some cell clusters from day 12 group recovered their contraction. From transmission electron microscope (TEM) analysis, less ultrastructural alterations were observed in day 12 group. Our results provide an insight into the use of BMP2 for cardiac lineage differentiation in a serum-free condition and a possibility of long-term storage of hESC-derived CMs.

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.

Evaluating the utility of cardiomyocytes from human pluripotent stem cells for drug screening

Functional cardiomyocytes can now be derived routinely from hPSCs (human pluripotent stem cells), which collectively include embryonic and induced pluripotent stem cells. This technology presents new opportunities to develop pharmacologically relevant in vitro screens to detect cardiotoxicity, with a view to improving patient safety while reducing the economic burden to industry arising from high drug attrition rates. In the present article, we consider the need for human cardiomyocytes in drug-screening campaigns and review the strategies used to differentiate hPSCs towards the cardiac lineage. During early stages of differentiation, hPSC-cardiomyocytes display gene expression profiles, ultra-structures, ion channel functionality and pharmacological responses reminiscent of an embryonic phenotype, but maturation during extended time in culture has been demonstrated convincingly. Notably, hPSC-cardiomyocytes have been shown to respond in a highly predictable manner to over 40 compounds that have a known pharmacological effect on the human heart. This suggests that further development and validation of the hPSC-cardiomyocyte model as a tool for assessing cardiotoxicity is warranted.

Differentiation of human embryonic stem cells to cardiomyocytes for in vitro and in vivo applications

The ability of human embryonic stem cells to differentiate into spontaneously contracting cardiomyocyte-like cells has attracted substantial interest from the scientific community over the last decade. From having been difficult to control, human cardiomyogenesis in vitro is now becoming a process which, to a certain extent, can be effectively manipulated and directed. Although much research remains, new and improved protocols for guiding pluripotent stem cells to the cardiomyocyte lineage are accumulating in the scientific literature. However, the stem cell derived cardiomyocytes described to date, generally resemble immature embryonic/fetal cardiomyocytes, and they are in some functional and structural aspects different from adult cardiomyocytes. Thus, a future challenge will be to design strategies that eventually may allow the cells to reach a higher degree of maturation in vitro. Nevertheless, the cells which can be prepared using current protocols still have wide spread utility, and they have begun to find their way into the drug discovery platforms used in the pharmaceutical industry. In addition, stem cell derived cardiomyocytes and cardiac progenitors are anticipated to have a tremendous impact on how heart disease will be treated in the future. Here, we will discuss recent strategies for the generation of cardiomyocytes from human embryonic stem cells and recapitulate their features, as well as highlight some in vitro applications for the cells. Finally, opportunities in the area of cardiac regenerative medicine will be illustrated.

Enhancement of cardiomyocyte differentiation from human embryonic stem cells

Several approaches have been used to encourage the differentiation of cardiomyocytes from human embryonic stem cells. However, the differentiation efficiency is low, and appropriate culture protocols are needed to produce adequate numbers of cardiomyocytes for therapeutic cell transplantation. This study investigated the effects of serum on cardiomyocyte differentiation in suspension culture medium during embryoid body (EB) formation by human embryonic stem cells. The addition of ascorbic acid, dimethylsulfoxide and 5-aza-2'-deoxycytidine during days 5-7 at the EB-forming stage resulted in an increase in the numbers of rhythmically contracting clusters of derived cardiomyocytes. Treatment with 0.1 mmol L(-1) ascorbic acid alone, or more notably in combination with 10 micromol L(-1) 5-aza-2'-deoxycytidine, induced the formation of beating cells within EBs. Most of the beating clusters had spontaneous contraction rates similar to those found in human adults, and their contractile activity lasted for up to 194 days.

Cellular models for disease exploring and drug screening

The biopharmaceutical industry has been greatly promoted by the application of drug and disease models, including both animal and cellular models. In particular, the emergence of induced pluripotent stem cells (iPSC) makes it possible to create a large number of disease-specific cells in vitro. This review introduces the most widely applied models and their specialties.

Quantified proarrhythmic potential of selected human embryonic stem cell-derived cardiomyocytes

To improve proarrhythmic predictability of preclinical models, we assessed whether human ventricular-like embryonic stem cell-derived cardiomyocytes (hESC-CMs) can be selected following a standardized protocol. Also, we quantified their arrhythmogenic response and compared this to a contemporary used rabbit Purkinje fiber (PF) model. Multiple transmembrane action potentials (AP) were recorded from 164 hESC-CM clusters (9 different batches), and 12 isolated PFs from New Zealand White rabbits. AP duration (APD), early afterdepolarizations (EADs), triangulation (T), and short-term variability of repolarization (STV) were determined on application of the I(Kr) blocker E-4031 (0.03/0.1/0.3/1 muM). Isoproterenol (0.1 muM) was used to assess adrenergic response. To validate the phenotype, RNA isolated from atrial- and ventricular-like clusters (n=8) was analyzed using low-density Taqman arrays. Based on initial experiments, slow beating rate (<50 bpm) and long APD (>200 ms) were used to select 31 ventricular-like clusters. E-4031 (1 muM) prolonged APD (31/31) and induced EADs only in clusters with APD90>300 ms (11/16). EADs were associated with increased T (1.6+/-0.2 vs 2.0+/-0.3) and STV (2.7+/-1.5 vs 6.9+/-1.9). Rabbit PF reacted in a similar way with regards to EADs (5/12), increased T (1.3+/-0.1 vs 1.9+/-0.4), and STV (1.2+/-0.9 vs 7.1+/-5.6). According to ROC values, hESC-CMs (STV 0.91) could predict EADs at least equivalent to PF (STV 0.69). Isoproterenol shortened APD and completely suppressed EADs. Gene expression analysis revealed that HCN1/2, KCNA5, and GJA5 were higher in atrial/nodal-like cells, whereas KCNJ2 and SCN1B were higher in ventricular-like cells (P<0.05). Selection of hESC-CM clusters with a ventricular-like phenotype can be standardized. The proarrhythmic results are qualitatively and quantitatively comparable between hESC-CMs and rabbit PF. Our results indicate that additional validation of this new safety pharmacology model is warranted.

Cardiac applications for human pluripotent stem cells

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (hiPSCs) can self-renew indefinitely, while maintaining the capacity to differentiate into useful somatic cell types, including cardiomyocytes. As such, these stem cell types represent an essentially inexhaustible source of committed human cardiomyocytes of potential use in cell-based cardiac therapies, high-throughput screening and safety testing of new drugs, and modeling human heart development. These stem cell-derived cardiomyocytes have an unambiguous cardiac phenotype and proliferate robustly both in vitro and in vivo. Recent transplantation studies in preclinical models have provided exciting proof-of-principle for their use in infarct repair and in the formation of a "biological pacemaker". While these successes give reason for cautious optimism, major challenges remain to the successful application of hESCs (or hiPSCs) to cardiac repair, including the need for preparations of high cardiac purity, improved methods of delivery, and approaches to overcome immune rejection and other causes of graft cell death. In this review, we describe the phenotype of hESC- and hiPSC-derived cardiomyocytes, the state of preclinical transplantation studies with these cells, and potential approaches to overcome the aforementioned hurdles.

Substantial variation in the cardiac differentiation of human embryonic stem cell lines derived and propagated under the same conditions--a comparison of multiple cell lines

AIM

The differentiation efficiencies of human embryonic stem cell (hESC) lines differ from each other. To assess this in more detail we studied the cardiac differentiation of eight hESC lines derived in the same laboratory.

RESULTS

Substantial variation in growth and in the ability to form beating areas was seen between the different hESC lines; line HS346 gave the best efficiency (9.4%), while HS293 did not differentiate into beating colonies at all. Nine germ layer and differentiation markers were quantified during early differentiation in four hESC lines. The expression levels of Brachyury T, MESP1 and NKX2.5 were highest in the most efficient cardiac line (HS346). A systematic characterization of the beating cells revealed proper cardiac marker expression, electrophysiological activity, and pharmacological response.

CONCLUSIONS

The hESC lines derived in the same laboratory varied considerably in their potential to differentiate into beating cardiomyocytes. None of the expression markers could clearly predict cardiac differentiation potential, although the expression of early cardiomyogenic genes was upregulated in the best cardiac line. The proper cardiomyocyte characteristics and pharmacological response indicate that these cells could be used as a model for human cardiomyocytes in pharmacological and toxicological analyses when investigating new heart medications or cardiac side-effects.

Human embryonic stem cells and cardiac repair

The muscle lost after a myocardial infarction is replaced with noncontractile scar tissue, often initiating heart failure. Whole-organ cardiac transplantation is the only currently available clinical means of replacing the lost muscle, but this option is limited by the inadequate supply of donor hearts. Thus, cell-based cardiac repair has attracted considerable interest as an alternative means of ameliorating cardiac injury. Because of their tremendous capacity for expansion and unquestioned cardiac potential, pluripotent human embryonic stem cells (hESCs) represent an attractive candidate cell source for obtaining cardiomyocytes and other useful mesenchymal cell types for such therapies. Human embryonic stem cell-derived cardiomyocytes exhibit a committed cardiac phenotype and robust proliferative capacity, and recent testing in rodent infarct models indicates that they can partially remuscularize injured hearts and improve contractile function. Although the latter successes give good reason for optimism, considerable challenges remain in the successful application of hESCs to cardiac repair, including the need for preparations of high cardiac purity, improved methods of delivery, and approaches to overcome immune rejection and other causes of graft cell death. This review will describe the phenotype of hESC-derived cardiomyocytes and preclinical experience with these cells and will consider strategies to overcoming the aforementioned challenges.

Preclinical assessment of cardiac toxicity

The exact prediction of the clinical behavior of drugs represents one of the most difficult duties in preclinical drug development. The use of cell-based assay systems underpins the development of many drug candidates, but owing to the artificial character of many of these systems, cell response and physiological behavior seem to be mutually exclusive. Embryonic stem cell-derived cells represent a system that may address the disconnect between the behavior of cultured cells and cells in situ. While undifferentiated ES cells allow standardization, expansion and genetic manipulation, the differentiated cells provide a reflection of the normal physiological image of their primary counterpart. We compare common models to detect cardiac toxicity with an assay system comprising in vitro differentiated pure cardiomyocytes.

Molecular signature of cardiomyocyte clusters derived from human embryonic stem cells

Human embryonic stem cells (hESCs) can differentiate in vitro into spontaneously contracting cardiomyocytes (CMs). These cells may prove extremely useful for various applications in basic research, drug discovery, and regenerative medicine. To fully use the potential of the cells, they need to be extensively characterized, and the regulatory mechanisms that control hESC differentiation toward the cardiac lineage need to be better defined. In this study, we used microarrays to analyze, for the first time, the global gene expression profile of isolated hESC-derived CM clusters. By comparing the clusters with undifferentiated hESCs and using stringent selection criteria, we identified 530 upregulated and 40 downregulated genes in the contracting clusters. To further characterize the family of upregulated genes in the hESC-derived CM clusters, the genes were classified according to their Gene Ontology annotation. The results indicate that the hESC-derived CM clusters display high similarities, on a molecular level, to human heart tissue. Moreover, using the family of upregulated genes, we created protein interaction maps that revealed topological characteristics. We also searched for cellular pathways among the upregulated genes in the hESC-derived CM clusters and identified eight significantly upregulated pathways. Real-time quantitative polymerase chain reaction and immunohistochemical analysis confirmed the expression of a subset of the genes identified by the microarrays. Taken together, the results presented here provide a molecular signature of hESC-derived CM clusters and further our understanding of the biological processes that are active in these cells.

Cardiomyogenic gene expression profiling of differentiating human embryonic stem cells

Human embryonic stem cells (hESCs) can differentiate into a variety of specialized cell types. Thus, they provide a model system for embryonic development to investigate the molecular processes of cell differentiation and lineage commitment. The development of the cardiac lineage is easily detected in mixed cultures by the appearance of spontaneously contracting areas of cells. We performed gene expression profiling of undifferentiated and differentiating hESCs and monitored 468 genes expressed during cardiac development and/or in cardiac tissue. Their transcription during early differentiation of hESCs through embryoid bodies (EBs) was investigated and compared with spontaneously differentiating hESCs maintained on feeders in culture without passaging (high-density (HD) protocol). We observed a larger variation in the gene expression between cells from a single cell line that were differentiated using two different protocols than in cells from different cell lines that were cultured according to the same protocol. Notably, the EB protocol resulted in more reproducible transcription profiles than the HD protocol. The results presented here provide new information about gene regulation during early differentiation of hESCs with emphasis on the cardiomyogenic program. In addition, we also identified regulatory elements that could prove critical for the development of the cardiomyocyte lineage.

The application of human embryonic stem cell technologies to drug discovery

The isolation of human embryonic stem cells about a decade ago marked the birth of a new era in biomedical research. These pluripotent stem cells possess unique properties that make them exceptionally useful in a range of applications. Discussions about human stem cells are most often focused around the area of regenerative medicine and indeed, the possibility to apply these cells in cell replacement therapies is highly attractive. More imminent, however, is the employment of stem cell technologies for drug discovery and development. Novel improved in vitro models based on physiologically relevant human cells will result in better precision and more cost-effective assays ultimately leading to lower attrition rates and safe new drugs.

Human embryonic stem cells: current technologies and emerging industrial applications

The efficiency and accuracy of the drug development process is severely restricted by the lack of functional human cell systems. However, the successful derivation of pluripotent human embryonic stem (hES) cell lines in the late 1990s is expected to revolutionize biomedical research in many areas. Due to their growth capacity and unique developmental potential to differentiate into almost any cell type of the human body, hES cells have opened novel avenues both in basic and applied research as well as for therapeutic applications. In this review we describe, from an industrial perspective, the basic science that underlies the hES cell technology and discuss the current and future prospects for hES cells in novel and improved stem cell based applications for drug discovery, toxicity testing as well as regenerative medicine.