Myocardial regeneration strategies using human embryonic stem cell-derived cardiomyocytes

Automated grouping of action potentials of human embryonic stem cell-derived cardiomyocytes

Methods for obtaining cardiomyocytes from human embryonic stem cells (hESCs) are improving at a significant rate. However, the characterization of these cardiomyocytes (CMs) is evolving at a relatively slower rate. In particular, there is still uncertainty in classifying the phenotype (ventricular-like, atrial-like, nodal-like, etc.) of an hESC-derived cardiomyocyte (hESC-CM). While previous studies identified the phenotype of a CM based on electrophysiological features of its action potential, the criteria for classification were typically subjective and differed across studies. In this paper, we use techniques from signal processing and machine learning to develop an automated approach to discriminate the electrophysiological differences between hESC-CMs. Specifically, we propose a spectral grouping-based algorithm to separate a population of CMs into distinct groups based on the similarity of their action potential shapes. We applied this method to a dataset of optical maps of cardiac cell clusters dissected from human embryoid bodies. While some of the nine cell clusters in the dataset are presented with just one phenotype, the majority of the cell clusters are presented with multiple phenotypes. The proposed algorithm is generally applicable to other action potential datasets and could prove useful in investigating the purification of specific types of CMs from an electrophysiological perspective.

Human-induced pluripotent stem cell-derived cardiomyocytes exhibit temporal changes in phenotype

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) have been recently derived and are used for basic research, cardiotoxicity assessment, and phenotypic screening. However, the hiPS-CM phenotype is dependent on their derivation, age, and culture conditions, and there is disagreement as to what constitutes a functional hiPS-CM. The aim of the present study is to characterize the temporal changes in hiPS-CM phenotype by examining five determinants of cardiomyocyte function: gene expression, ion channel functionality, calcium cycling, metabolic activity, and responsiveness to cardioactive compounds. Based on both gene expression and electrophysiological properties, at day 30 of differentiation, hiPS-CMs are immature cells that, with time in culture, progressively develop a more mature phenotype without signs of dedifferentiation. This phenotype is characterized by adult-like gene expression patterns, action potentials exhibiting ventricular atrial and nodal properties, coordinated calcium cycling and beating, suggesting the formation of a functional syncytium. Pharmacological responses to pathological (endothelin-1), physiological (IGF-1), and autonomic (isoproterenol) stimuli similar to those characteristic of isolated adult cardiac myocytes are present in maturing hiPS-CMs. In addition, thyroid hormone treatment of hiPS-CMs attenuated the fetal gene expression in favor of a more adult-like pattern. Overall, hiPS-CMs progressively acquire functionality when maintained in culture for a prolonged period of time. The description of this evolving phenotype helps to identify optimal use of hiPS-CMs for a range of research applications.

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 stem cells in safety pharmacology and toxicology

Embryonic stem (ES) cells undergo self-renewal and are pluripotent, i.e., they can give rise to all the types of specialised cells in the body. Scientific knowledge on ES cells is increasing rapidly, leading to opportunities for establishment of ES cell-based in vitro tests for drug discovery, preclinical safety pharmacology and toxicology. The main properties of ES cells making them useful in in vitro assays are that they have a normal diploid karyotype and can provide a large number of cells for high-throughput assays. Human ES cells additionally have the potential to provide solutions to problems related to interspecies differences and methods for screening for human polymorphisms, thus supporting robust human hazard identification and optimised drug discovery strategies. Importantly, ES cell based assays could be potential tools to reduce and perhaps replace, animal experiments. This chapter will describe ongoing research in the use of ES cells in toxicology and safety pharmacology, focusing on the major areas of progress, namely, embryotoxicology, cardiotoxicology and hepatoxicology.

Increased cardiogenesis in P19-GFP teratocarcinoma cells expressing the propeptide IGF-1Ea

The mechanism implicated in differentiation of endogenous cardiac stem cells into cardiomyocytes to regenerate the heart tissue upon an insult remains elusive, limiting the therapeutical goals to exogenous cell injection and/or gene therapy. We have shown previously that cardiac specific overexpression of the insulin-like growth factor 1 propeptide IGF-1Ea induces beneficial myocardial repair after infarct. Although the mechanism is still under investigation, the possibility that this propeptide may be involved in promoting stem cell differentiation into the cardiac lineage has yet to be explored. To investigate whether IGF-1Ea promote cardiogenesis, we initially modified P19 embryonal carcinoma cells to express IGF-1Ea. Taking advantage of their cardiomyogenic nature, we analyzed whether overexpression of this propeptide affected cardiac differentiation program. The data herein presented showed for the first time that constitutively overexpressed IGF-1Ea increased cardiogenic differentiation program in both undifferentiated and DMSO-differentiated cells. In details, IGF-1Ea overexpression promoted localization of alpha-actinin in finely organized sarcomeric structure compared to control cells and upregulated the cardiac mesodermal marker NKX-2.5 and the ventricular structural protein MLC2v. Furthermore, activated IGF-1 signaling promoted cardiac mesodermal induction in undifferentiated cells independently of cell proliferation. This analysis suggests that IGF-1Ea may be a good candidate to improve both in vitro production of cardiomyocytes from pluripotent stem cells and in vivo activation of the differentiation program of cardiac progenitor cells.

Myocardial regeneration in heart failure: integrated development of biological therapeutic approaches

Heart failure currently constitutes one of the greatest health problems in the Western world. Its incidence, far from diminishing or even remaining stable, is actually still increasing in association with the aging of the population and its lifestyle. A better knowledge of physiopathological mechanisms has allowed for the development of new therapeutic focal points and lines of research. Nevertheless, its treatment is complex and encompasses a multidisciplinary approach. Patients in an advanced stage still have a very high mortality rate in spite of receiving optimum medical care. The development of new therapeutic techniques that afford a better prognosis has therefore been essential. Of these, and leaving aside surgical treatments, myocardial regeneration by means of cellular therapy, new concepts in tissue engineering and their results, and the applications of new advances in the field of immunomodulation have all recently experienced development. In this article, the aim is to bring the latest concepts in the physiopathology and humoral response of cardiac failure up to date as well as doing the same with the therapeutic approaches in this area.

Stem Cell Therapy in Acute Myocardial Infarction: A Pot of Gold or Pandora's Box

Stem cell therapy for conditions characterized by myocyte loss in myocardial infarction and heart failure is intuitively appealing. Stem cells from various sources, including heart itself in preclinical and animal studies, have shown the potential to improve the function of ventricular muscle after ischaemic injury. The clinical experience from worldwide studies have indicated the safety profile but with modest benefits. The predominant mechanisms of transplanted cells for improving cardiac function have pointed towards paracrine effects rather than transdifferentiation into cardiomyocytes. Thus, further investigations should be encouraged towards bench side and bedside to resolve various issues for ensuring the correct type and dosing of cells, time, and method of delivery and identify correct mechanism of functional improvement. An interdisciplinary effort at the scientific, clinical, and the government front will bring successful realization of this therapy for healing the heart and may convert what seems now a Pandora's Box into a Pot of Gold.

Comparative analysis of adherence, viability, proliferation and morphology of umbilical cord tissue-derived mesenchymal stem cells seeded on different titanium-coated expanded polytetrafluoroethylene scaffolds

Umbilical cord tissue comprises an attractive new source for mesenchymal stem cells. Umbilical cord tissue-derived mesenchymal stem cells (UCMSC) exhibit self-renewal, multipotency and immunological naivity, and they can be obtained without medical intervention. The transfer of UCMSC to the ischemic region of the heart may have a favorable impact on tissue regeneration. Benefit from typical cell delivery by injection to the infarcted area is often limited due to poor cell retention and survival. Another route of administration is to use populated scaffolds implanted into the infarcted zone. In this paper, the seeding efficiency of UCMSC on uncoated and titanium-coated expanded polytetrafluoroethylene (ePTFE) scaffolds with different surface structures was determined. Dualmesh (DM) offers a corduroy-like surface in contrast to the comparatively planar surface of cardiovascular patch (CVP). The investigation of adherence, viability and proliferation of UCMSC demonstrates that titanium-coated scaffolds are superior to uncoated scaffolds, independent of the surface structure. Microscopic images reveal spherical UCMSC seeded on uncoated scaffolds. In contrast, UCMSC on titanium-coated scaffolds display their characteristic spindle-shaped morphology and a homogeneous coverage of CVP. In summary, titanium coating of clinically approved CVP enhances the retention of UCMSC and thus offers a potential cell delivery system for the repair of the damaged myocardium.

Is tissue engineering a new paradigm in medicine? Consequences for the ethical evaluation of tissue engineering research

Ex-vivo tissue engineering is a quickly developing medical technology aiming to regenerate tissue through the introduction of an ex-vivo created tissue construct instead of restoring the damaged tissue to some level of functionality. Tissue engineering is considered by some as a new medical paradigm. We analyse this claim and identify tissue engineering's fundamental characteristics, focusing on the aim of the intervention and on the complexity and continuity of the process. We inquire how these features have an impact not only on the scientific research itself but also on the ethical evaluation of this research. We suggest that viewing tissue engineering as a new medical paradigm allows us to develop a wider perspective for successful investigation instead of focusing on isolated steps of the tissue engineering process in an anecdotal way, which may lead to an inadequate ethical evaluation. We argue that the concept of tissue engineering as a paradigm may benefit the way we address the ethical challenges presented by tissue engineering.

Pre-transplantation specification of stem cells to cardiac lineage for regeneration of cardiac tissue

Myocardial infarction (MI) is a lead cause of mortality in the Western world. Treatment of acute MI is focused on restoration of antegrade flow which inhibits further tissue loss, but does not restore function to damaged tissue. Chronic therapy for injured myocardial tissue involves medical therapy that attempts to minimize pathologic remodeling of the heart. End stage therapy for chronic heart failure (CHF) involves inotropic therapy to increase surviving cardiac myocyte function or mechanical augmentation of cardiac performance. Not until the point of heart transplantation, a limited resource at best, does therapy focus on the fundamental problem of needing to replace injured tissue with new contractile tissue. In this setting, the potential for stem cell therapy has garnered significant interest for its potential to regenerate or create new contractile cardiac tissue. While to date adult stem cell therapy in clinical trials has suggested potential benefit, there is waning belief that the approaches used to date lead to regeneration of cardiac tissue. As the literature has better defined the pathways involved in cardiac differentiation, preclinical studies have suggested that stem cell pretreatment to direct stem cell differentiation prior to stem cell transplantation may be a more efficacious strategy for inducing cardiac regeneration. Here we review the available literature on pre-transplantation conditioning of stem cells in an attempt to better understand stem cell behavior and their readiness in cell-based therapy for myocardial regeneration.

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.

Involvement of NF-kappaB and AP-1 activation in icariin promoted cardiac differentiation of mouse embryonic stem cells

Icariin has been reported to facilitate the differentiation of mouse embryonic stem (ES) cells into cardiomyocytes; however, the mechanism on cardiomyogenic cell lineage differentiation has not been fully elucidated yet. In the present studies, an underlying signaling network including p38, extracellular signal-regulated kinase 1, 2 (ERK1, 2), nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) transcription factors c-jun and c-fos was assumed in icariin induced cardiomyogenesis. Icariin rapidly activated p38 and ERK1, 2 in embryoid bodies, treatment with p38 antagonist 4-(4-Fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)-1H-imidazole (SB203580) or ERK1, 2 inhibitor 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene (U0126) significantly abolished icariin induced cardiac commitment, MEF2C gene expression and nuclear translocation, as well as cardiac-specific protein alpha-actinin expression, indicating that p38 and ERK1, 2 are specifically involved in icariin stimulated cardiomyogenic cell lineage differentiation of ES cells. Further, IkappaBalpha phosphorylation and NF-kappaB p65 translocation to the nucleus appeared rapidly when embryoid bodies exposed to icariin, and the expression of IkappaBalpha or NF-kappaB p65 in cytoplasm was decreased concomitantly. Moreover, icariin increased c-jun and c-fos mRNA and protein expression. Either SB203580 or U0126 displayed inhibitory effect on icariin induced NF-kappaB and AP-1 activation. It could be concluded that p38 and ERK1, 2 are activated in a coordinated manner, which in turn contribute to NF-kappaB and AP-1 activation in icariin induced cardiomyogenic cell lineage differentiation of mouse ES cells.

Cell therapy in congestive heart failure

Congestive heart failure (CHF) has emerged as a major worldwide epidemic and its main causes seem to be the aging of the population and the survival of patients with post-myocardial infarction. Cardiomyocyte dropout (necrosis and apoptosis) plays a critical role in the progress of CHF; thus treatment of CHF by exogenous cell implantation will be a promising medical approach. In the acute phase of cardiac damage cardiac stem cells (CSCs) within the heart divide symmetrically and/or asymmetrically in response to the change of heart homeostasis, and at the same time homing of bone marrow stem cells (BMCs) to injured area is thought to occur, which not only reconstitutes CSC population to normal levels but also repairs the heart by differentiation into cardiac tissue. So far, basic studies by using potential sources such as BMCs and CSCs to treat animal CHF have shown improved ventricular remodelling and heart function. Recently, however, a few of randomized, double-blind, placebo-controlled clinical trials demonstrated mixed results in heart failure with BMC therapy during acute myocardial infarction.

Do stem cells in the heart truly differentiate into cardiomyocytes?

Chronic congestive heart failure (CHF) is a common consequence of heart muscle or valve damage and remains a major cause of morbidity and mortality worldwide. There are increasing interests to treat cardiac failure by stem cell-based therapy. Many types of stem cells or progenitor cells have been suggested for cellular therapy of heart failure. While stem cell-based therapy was initially thought to be achieved by transdifferentiation of stem cells into myocardial cells including cardiomyocytes it has become clear that this may be rather an infrequent event. Instead cardiac regeneration may result from vascular differentiation of stem cells or even from stem cell-mediated reverse remodelling. Thus the term stem cell-mediated cardiac regeneration covers the spectrum from stem cell transdifferentiation into cardiomyocytes to cell-mediated pharmacotherapy. In this review we revise stem cell-based cardiac regeneration both in experimental models and in clinical application. We have limited our discussion on some selected types of stem cells, with particular emphasis on their differentiation potential, current status and perspectives on their future applications.