Concise review: stem cells, myocardial regeneration, and methodological artifacts

Reciprocity of Action of Increasing Oct4 and Repressing p53 in Transdifferentiation of Mouse Embryonic Fibroblasts into Cardiac Myocytes

p53 is a barrier to somatic cell reprogramming. Deletion or transient suppression of p53 increases the efficiency of reprogramming of somatic cells into induced pluripotent stem cells. Whether p53 represents an obstacle to a similar process transdifferentiation of somatic cells is unknown. However, it is predicted that inhibition of p53 would promote transdifferentiation of fibroblasts into cardiomyocytes. In this study, the effect of p53 on the capacity of cardiogenic transdifferentiation is evaluated using p53 wild-type (p53^+/+), p53 heterozygous mutant (p53^+/-), and p53 homozygous mutant (p53^-/-) mouse embryonic fibroblasts (MEFs). Repression of p53 in MEFs increases the expression level of mesoderm transcription factors Brachyury (T) and MESP1. The cardiac-specific markers, Myh6 (Myosin, Heavy Chain 6), Myh7 (Myosin, Heavy Chain 7), and cTnI (cardiac muscle troponin I), show elevated expression in p53^+/- and p53^-/- MEFs compared with wild-type MEFs, but cardiac muscle troponin T (cTnT) showed a lower expression level when p53 was inhibited. After induction to cardiac differentiation, cTnT expression increased and markers of endoderm and ectoderm decreased in p53^+/- and p53^-/- MEFs. The effect of an important reprogramming factor Oct4 on cardiac transdifferentiation was also evaluated in the allelic series of p53 MEFs. We found that overexpression of Oct4 significantly enhanced Mesp1, Tbx5, and Isl1 expression in p53^+/+ and p53^+/- MEFs. Oct4 also enhanced cTnT expression in all three cell lines, especially in p53^+/- MEFs. Thus, inhibition of p53 expression and viral expression of Oct4 both promote transdifferentiation of MEFs into cardiomyocytes, establishing reciprocity of action in the process.

Retracted Article: Development of functional hydrogels for heart failure

Hydrogel-based approaches were reviewed for cardiac tissue engineering and myocardial regeneration in ischemia-induced heart failure, with an emphasis on functional studies, translational status, and clinical advancements.

Mesenchymal stem cells and vascular regeneration

In recent years, MSCs have emerged as a promising therapeutic cell type in regenerative medicine. They hold great promise for treating cardiovascular diseases, such as myocardial infarction and limb ischemia. MSCs may be utilized in both cell-based therapy and vascular graft engineering to restore vascular function, thereby providing therapeutic benefits to patients. The efficacy of MSCs lies in their multipotent differentiation ability toward vascular smooth muscle cells, endothelial cells and other cell types, as well as their capacity to secrete various trophic factors, which are potent in promoting angiogenesis, inhibiting apoptosis and modulating immunoreaction. Increasing our understanding of the mechanisms of MSC involvement in vascular regeneration will be beneficial in boosting present therapeutic approaches and developing novel ones to treat cardiovascular diseases. In this review, we aim to summarize current progress in characterizing the in vivo identity of MSCs, to discuss mechanisms involved in cell-based therapy utilizing MSCs, and to explore current and future strategies for vascular regeneration.

Cellular mechanisms underlying cardiac engraftment of stem cells

INTRODUCTION

Over the past decade, it has become clear that long-term engraftment of any ex vivo expanded cell product transplanted into injured myocardium is modest and all therapeutic regeneration is mediated by stimulation of endogenous repair rather than differentiation of transplanted cells into working myocardium. Given that increasing the retention of transplanted cells boosts myocardial function, focus on the fundamental mechanisms limiting retention and survival of transplanted cells may enable strategies to help to restore normal cardiac function. Areas covered: This review outlines the challenges confronting cardiac engraftment of ex vivo expanded cells and explores means of enhancing cell-mediated repair of injured myocardium. Expert opinion: Stem cell therapy has already come a long way in terms of regenerating damaged hearts though the poor retention of transplanted cells limits the full potential of truly cardiotrophic cell products. Multifaceted strategies directed towards fundamental mechanisms limiting the long-term survival of transplanted cells will be needed to enhance transplanted cell retention and cell-mediated repair of damaged myocardium for cardiac cell therapy to reach its full potential.

Cardiomyocyte specific overexpression of a 37 amino acid domain of regulator of G protein signalling 2 inhibits cardiac hypertrophy and improves function in response to pressure overload in mice

Regulator of G protein signalling 2 (RGS2) is known to play a protective role in maladaptive cardiac hypertrophy and heart failure via its ability to inhibit G_q- and G_s- mediated GPCR signalling. We previously demonstrated that RGS2 can also inhibit protein translation and can thereby attenuate cell growth. This G protein-independent inhibitory effect has been mapped to a 37 amino acid domain (RGS2^eb) within RGS2 that binds to eukaryotic initiation factor 2B (eIF2B). When expressed in neonatal rat cardiomyocytes, RGS2^eb attenuates both protein synthesis and hypertrophy induced by G_q- and G_s- activating agents. In the current study, we investigated the potential cardioprotective role of RGS2^eb by determining whether RGS2^eb transgenic (RGS2^eb TG) mice with cardiomyocyte specific overexpression of RGS2^eb show resistance to the development of hypertrophy in comparison to wild-type (WT) controls. Using transverse aortic constriction (TAC) in a pressure-overload hypertrophy model, we demonstrated that cardiac hypertrophy was inhibited in RGS2^eb TG mice compared to WT controls following four weeks of TAC. Expression of the hypertrophic markers atrial natriuretic peptide (ANP) and β-myosin heavy chain (MHC-β) was also reduced in RGS2^eb TG compared to WT TAC animals. Furthermore, cardiac function in RGS2^eb TG TAC mice was significantly improved compared to WT TAC mice. Notably, cardiomyocyte cell size was significantly decreased in TG compared to WT TAC mice. These results suggest that RGS2 may limit pathological cardiac hypertrophy at least in part via the function of its eIF2B-binding domain.

Functional Tissue Engineering: A Prevascularized Cardiac Muscle Construct for Validating Human Mesenchymal Stem Cells Engraftment Potential In Vitro

The influence of somatic stem cells in the stimulation of mammalian cardiac muscle regeneration is still in its early stages, and so far, it has been difficult to determine the efficacy of the procedures that have been employed. The outstanding question remains whether stem cells derived from the bone marrow or some other location within or outside of the heart can populate a region of myocardial damage and transform into tissue-specific differentiated progenies, and also exhibit functional synchronization. Consequently, this necessitates the development of an appropriate in vitro three-dimensional (3D) model of cardiomyogenesis and prompts the development of a 3D cardiac muscle construct for tissue engineering purposes, especially using the somatic stem cell, human mesenchymal stem cells (hMSCs). To this end, we have created an in vitro 3D functional prevascularized cardiac muscle construct using embryonic cardiac myocytes (eCMs) and hMSCs. First, to generate the prevascularized scaffold, human cardiac microvascular endothelial cells (hCMVECs) and hMSCs were cocultured onto a 3D collagen cell carrier (CCC) for 7 days under vasculogenic culture conditions; hCMVECs/hMSCs underwent maturation, differentiation, and morphogenesis characteristic of microvessels, and formed dense vascular networks. Next, the eCMs and hMSCs were cocultured onto this generated prevascularized CCCs for further 7 or 14 days in myogenic culture conditions. Finally, the vascular and cardiac phenotypic inductions were characterized at the morphological, immunological, biochemical, molecular, and functional levels. Expression and functional analyses of the differentiated progenies revealed neo-cardiomyogenesis and neo-vasculogenesis. In this milieu, for instance, not only were hMSCs able to couple electromechanically with developing eCMs but were also able to contribute to the developing vasculature as mural cells, respectively. Hence, our unique 3D coculture system provides us a reproducible and quintessential in vitro 3D model of cardiomyogenesis and a functioning prevascularized 3D cardiac graft that can be utilized for personalized medicine.

Hypertensive Disorders of Pregnancy and Offspring Cardiac Structure and Function in Adolescence

Background

Fetal exposure to preeclampsia is associated with higher blood pressure and later risk of stroke. We aimed to investigate the associations of maternal preeclampsia, gestational hypertension, and maternal blood pressure change in pregnancy with offspring cardiac structure and function in adolescence.

Methods and Results

Using data from a prospective birth cohort study, we included offspring who underwent echocardiography (mean age, 17.7 years; SD, 0.3; N=1592). We examined whether hypertensive disorders of pregnancy were associated with offspring cardiac structure and systolic/diastolic function using linear regression. Using multilevel linear spline models (measurement occasions within women), we also investigated whether rate of maternal systolic/diastolic blood pressure change during pregnancy (weeks 8–18, 18–30, 30–36, and 36 or more) were associated with offspring outcomes. Main models were typically adjusted for maternal age, offspring age and sex, prepregnancy body mass index, parity, glycosuria/diabetes mellitus, education, and maternal smoking. Exposure to maternal preeclampsia (0.025; 95% CI, 0.008–0.043) and gestational hypertension (0.010; 0.002–0.017) were associated with greater relative wall thickness. Furthermore, preeclampsia was also associated with a smaller left ventricular end‐diastolic volume (−9.0 mL; −15 to −3.1). No associations were found between hypertensive disorders of pregnancy and offspring cardiac function. Positive rate of maternal systolic blood pressure change during weeks 8 to 18 was associated with greater offspring left ventricular end‐diastolic volume, left ventricular mass indexed to height^2.7, and E/A.

Conclusions

Adolescent offspring exposed to maternal preeclampsia had greater relative wall thickness and reduced left ventricular end‐diastolic volume, which could be early signs of concentric remodeling and affect future cardiac function as well as risk of cardiovascular disease.

Inhibitory effect of hsa-miR-590-5p on cardiosphere-derived stem cells differentiation through downregulation of TGFB signaling

The cardiac cells generation via stem cells differentiation is a promising approach to restore the myocardial infarction. Promoted by our primary bioinformatics analysis as well as some previously published data on potential role of hsa-miR-590-3p in cardiogenesis, we have tried to decipher the role of miR-590-5p during the course of differentiation of cardiosphere-derived cells (CDCs). The differentiation induction of CDCs by TGFB1 was confirmed by real-time PCR, ICC, and flow cytometry. The expression pattern of hsa-miR-590-5p and some related genes were examined during the differentiation process. In order to study the role of miR-590-5p in cardiac differentiation, the effect of miR-590 overexpression in CDCs was studied. Evaluating the expression patterns of miR-590 and its potential targets (TGFBRs) during the course of differentiation, demonstrated a significant downregulation of miR-590 and an upregulation of TGFBR2, following the treatment of CDCs with TGFB1. Therefore, we proposed a model in which TGFB1 exerts its differentiation induction via downregulation of miR-590, and hence the higher transcriptional expression level of TGFBR2. In accordance with our proposed model, transfection of CDCs by a pLenti-III-hsa-mir-590-GFP expression vector before or after the first TGFB1 treatment caused a significant alteration in the expression levels of TGFBRs. Moreover, our data revealed that overexpression of miR-590 before TGFB1 induction was able to attenuate the CDCs differentiation probably via the reduction of TGFBR2 expression level. Altogether, our data suggest an inhibitory role of miR-590 during the cardiac differentiation of CDCs which its suppression might elevate the rate of differentiation.

Origin and differentiation of vascular smooth muscle cells

Vascular smooth muscle cells (SMCs), a major structural component of the vessel wall, not only play a key role in maintaining vascular structure but also perform various functions. During embryogenesis, SMC recruitment from their progenitors is an important step in the formation of the embryonic vascular system. SMCs in the arterial wall are mostly quiescent but can display a contractile phenotype in adults. Under pathophysiological conditions, i.e. vascular remodelling after endothelial dysfunction or damage, contractile SMCs found in the media switch to a secretory type, which will facilitate their ability to migrate to the intima and proliferate to contribute to neointimal lesions. However, recent evidence suggests that the mobilization and recruitment of abundant stem/progenitor cells present in the vessel wall are largely responsible for SMC accumulation in the intima during vascular remodelling such as neointimal hyperplasia and arteriosclerosis. Therefore, understanding the regulatory mechanisms that control SMC differentiation from vascular progenitors is essential for exploring therapeutic targets for potential clinical applications. In this article, we review the origin and differentiation of SMCs from stem/progenitor cells during cardiovascular development and in the adult, highlighting the environmental cues and signalling pathways that control phenotypic modulation within the vasculature.

Origin of cardiomyocytes in the adult heart

This review article discusses the mechanisms of cardiomyogenesis in the adult heart. They include the re-entry of cardiomyocytes into the cell cycle; dedifferentiation of pre-existing cardiomyocytes, which assume an immature replicating cell phenotype; transdifferentiation of hematopoietic stem cells into cardiomyocytes; and cardiomyocytes derived from activation and lineage specification of resident cardiac stem cells. The recognition of the origin of cardiomyocytes is of critical importance for the development of strategies capable of enhancing the growth response of the myocardium; in fact, cell therapy for the decompensated heart has to be based on the acquisition of this fundamental biological knowledge.

Stem cells for cardiac regeneration and possible roles of the transforming growth factor-β superfamily

Abstract Heart failure is a leading cause of death worldwide. Studies of stem cell biology are essential for developing efficient treatments. Recently, we established and characterized c-kit-positive cardiac stem cells from the adult rat heart. Using a MethoCult culture system with a methyl-cellulose-based medium, stem-like left-atrium-derived pluripotent cells could be regulated to differentiate into skeletal/cardiac myocytes or adipocytes with almost 100% purity. Microarray and pathway analyses of these cells showed that transforming growth factor-β1 (TGF-β1) and noggin were significantly involved in the differentiation switch. Furthermore, TGF-β1 may act as a regulator for this switch because it simultaneously inhibits adipogenesis and activates myogenesis in a dose-dependent manner. However, the effect of TGF-β varies with developmental stage, dosage, and timing of treatment. In the present review, the findings of recent studies, in particular the use of c-kit-positive cardiac stem cells, are discussed. The effects of the TGF-β superfamily on differentiation, especially on adipogenesis and/or myogenesis, have important implications for future regenerative medicine.

Pathologic function and therapeutic potential of exosomes in cardiovascular disease

The heart is a very complex conglomeration of organized interactions between various different cell types that all aid in facilitating myocardial function through contractility, sufficient perfusion, and cell-to-cell reception. In order to make sure that all features of the heart work effectively, it is imperative to have a well-controlled communication system among the different types of cells. One of the most important ways that the heart regulates itself is by the use of extracellular vesicles, more specifically, exosomes. Exosomes are types of nano-vesicles, naturally released from living cells. They are believed to play a critical role in intercellular communication through the means of certain mechanisms including direct cell-to-cell contact, long-range signals as well as electrical and extracellular chemical molecules. Exosomes contain many unique features like surface proteins/receptors, lipids, mRNAs, microRNAs, transcription factors and other proteins. Recent studies indicate that the exosomal contents are highly regulated by various stress and disease conditions, in turn reflective of the parent cell status. At present, exosomes are well appreciated to be involved in the process of tumor and infection disease. However, the research on cardiac exosomes is just emerging. In this review, we summarize recent findings on the pathologic effects of exosomes on cardiac remodeling under stress and disease conditions, including cardiac hypertrophy, peripartum cardiomyopathy, diabetic cardiomyopathy and sepsis-induced cardiovascular dysfunction. In addition, the cardio-protective effects of stress-preconditioned exosomes and stem cell-derived exosomes are also summarized. Finally, we discuss how to epigenetically reprogram exosome contents in host cells which makes them beneficial for the heart.

Stem cell therapies for the treatment of radiation-induced normal tissue side effects

SIGNIFICANCE

Targeted irradiation is an effective cancer therapy but damage inflicted to normal tissues surrounding the tumor may cause severe complications. While certain pharmacologic strategies can temper the adverse effects of irradiation, stem cell therapies provide unique opportunities for restoring functionality to the irradiated tissue bed.

RECENT ADVANCES

Preclinical studies presented in this review provide encouraging proof of concept regarding the therapeutic potential of stem cells for treating the adverse side effects associated with radiotherapy in different organs. Early-stage clinical data for radiation-induced lung, bone, and skin complications are promising and highlight the importance of selecting the appropriate stem cell type to stimulate tissue regeneration.

CRITICAL ISSUES

While therapeutic efficacy has been demonstrated in a variety of animal models and human trials, a range of additional concerns regarding stem cell transplantation for ameliorating radiation-induced normal tissue sequelae remain. Safety issues regarding teratoma formation, disease progression, and genomic stability along with technical issues impacting disease targeting, immunorejection, and clinical scale-up are factors bearing on the eventual translation of stem cell therapies into routine clinical practice.

FUTURE DIRECTIONS

Follow-up studies will need to identify the best possible stem cell types for the treatment of early and late radiation-induced normal tissue injury. Additional work should seek to optimize cellular dosing regimes, identify the best routes of administration, elucidate optimal transplantation windows for introducing cells into more receptive host tissues, and improve immune tolerance for longer-term engrafted cell survival into the irradiated microenvironment.

Mouse strain determines cardiac growth potential

Rationale

The extent of heart disease varies from person to person, suggesting that genetic background is important in pathology. Genetic background is also important when selecting appropriate mouse models to study heart disease. This study examines heart growth as a function of strain, specifically C57BL/6 and DBA/2 mouse strains.

Objective

In this study, we test the hypothesis that two strains of mice, C57BL/6 and DBA/2, will produce varying degrees of heart growth in both physiological and pathological settings.

Methods and Results

Differences in heart dimensions are detectable by echocardiography at 8 weeks of age. Percentages of cardiac progenitor cells (c-kit+ cells) and mononucleated cells were found to be in a higher percentage in DBA/2 mice, and more tri- and quad-nucleated cells were in C57BL/6 mice. Cardiomyocyte turnover shows no significant changes in mitotic activity, however, there is more apoptotic activity in DBA/2 mice. Cardiomyocyte cell size increased with age, but increased more in DBA/2 mice, although percentages of nucleated cells remained the same in both strains. Two-week isoproterenol stimulation showed an increase in heart growth in DBA/2 mice, both at cardiomyocyte and whole heart level. In isoproterenol-treated DBA/2 mice, there was also a greater expression level of the hypertrophy marker, ANF, compared to C57BL/6 mice.

Conclusion

We conclude that the DBA/2 mouse strain has a more immature cardiac phenotype, which correlates to a cardiac protective response to hypertrophy in both physiological and pathological stimulations.

Innate regeneration in the aging heart: healing from within

The concept of the heart as a terminally differentiated organ incapable of replacing damaged myocytes has been at the center of cardiovascular research and therapeutic development for the past 50 years. The progressive decline in myocyte number as a function of age and the formation of scarred tissue after myocardial infarction have been interpreted as irrefutable proofs of the postmitotic characteristic of the heart. However, emerging evidence supports a more dynamic view of the heart in which cell death and renewal are vital components of the remodeling process that governs cardiac homeostasis, aging, and disease. The identification of dividing myocytes in the adult and senescent heart raises the important question concerning the origin of these newly formed cells. In vitro and in vivo findings strongly suggest that replicating myocytes derive from lineage determination of resident primitive cells, supporting the notion that cardiomyogenesis is controlled by activation and differentiation of a stem cell compartment. It is the current view that the myocardium is an organ permissive of tissue regeneration mediated by exogenous and endogenous progenitor cells.

Podocalyxin-like protein 1 is a relevant marker for human c-kit(pos) cardiac stem cells

Cardiac progenitor cells (CPCs) from adult myocardium offer an alternative cell therapy approach for ischaemic heart disease. Improved clinical performance of CPCs in clinical trials requires a comprehensive definition of their biology and specific interactions with the environment. In this work we characterize specific human CPC surface markers and study some of their related functions. c-kit(pos) human CPCs (hCPCs) were characterized for cell surface marker expression, pluripotency, early and late cardiac differentiation markers and therapeutic activity in a rat model of acute myocardial infarction. The results indicate that hCPCs are a mesenchymal stem cell (MSC)-like population, with a similar immunoregulatory capacity. A partial hCPC membrane proteome was analysed by liquid chromatography-mass spectrometry/mass spectrometry and 36 proteins were identified. Several, including CD26, myoferlin and podocalyxin-like protein 1 (PODXL), have been previously described in other stem-cell systems. Suppression and overexpression analysis demonstrated that PODXL regulates hCPC activation, migration and differentiation; it also modulates their local immunoregulatory capacity. Therefore, hCPCs are a resident cardiac population that shares many features with hMSCs, including their capacity for local immunoregulation. Expression of PODXL appears to favour the immature state of hCPCs, while its downregulation facilitates their differentiation. Copyright © 2016 John Wiley & Sons, Ltd.

Potential benefits of cell therapy in coronary heart disease

Cardiovascular disease is the leading cause of morbidity and mortality in the world. In recent years, there has been an increasing interest both in basic and clinical research regarding the field of cell therapy for coronary heart disease (CHD). Several preclinical models of CHD have suggested that regenerative properties of stem and progenitor cells might help restoring myocardial functions in the event of cardiac diseases. Here, we summarize different types of stem/progenitor cells that have been tested in experimental and clinical settings of cardiac regeneration, from embryonic stem cells to induced pluripotent stem cells. Then, we provide a comprehensive description of the most common cell delivery strategies with their major pros and cons and underline the potential of tissue engineering and injectable matrices to address the crucial issue of restoring the three-dimensional structure of the injured myocardial region. Due to the encouraging results from preclinical models, the number of clinical trials with cell therapy is continuously increasing and includes patients with CHD and congestive heart failure. Most of the already published trials have demonstrated safety and feasibility of cell therapies in these clinical conditions. Several studies have also suggested that cell therapy results in improved clinical outcomes. Numerous ongoing clinical trials utilizing this therapy for CHD will address fundamental issues concerning cell source and population utilized, as well as the use of imaging techniques to assess cell homing and survival, all factors that affect the efficacy of different cell therapy strategies.

Modification of a purification and expansion method for human embryonic stem cell-derived cardiomyocytes

OBJECTIVE

This study aimed to develop a simple and efficient purification method for human embryonic stem cell (hESC)-derived cardiomyocytes (CMs) using a low-glucose culture system. In addition, we investigated whether intercellular adhesion between single hESC-CMs plays a critical role in enhancing proliferation of purified hESC-CMs.

METHOD

hESCs were cultured in suspension to form human embryoid bodies (hEBs) from which ∼15% contracting clusters were derived after 15-20 days in culture. To purify CMs from contracting hEBs, we first manually isolated contracting clumps that were re-cultured on gelatin-coated plates with media containing a low concentration of glucose. The purified hESC-CMs were cultured at different densities to examine whether cell-cell contact enhances proliferation of hESC-CMs.

RESULTS

Purified CMs demonstrated spontaneous contraction and strongly expressed the CM-specific markers cardiac troponin T and slow myosin heavy chain. We investigated the purification efficiency by examining the expression levels of cardiac-related genes and the expression of MitoTracker Red dye. In addition, purified hESC-CMs in low-glucose culture demonstrated a 1.5-fold increase in their proliferative capacity compared to those cultured as single hESC-CMs.

CONCLUSION

A low level of glucose is efficient in purifying hESC-CMs and intercellular adhesion between individual hESC-CMs plays a critical role in enhancing hESC-CM proliferation.

Embryonic stem cells facilitate the isolation of persistent clonal cardiovascular progenitor cell lines and leukemia inhibitor factor maintains their self-renewal and myocardial differentiation potential in vitro

Compelling evidence for the existence of somatic stem cells in the heart of different mammalian species has been provided by numerous groups; however, so far it has not been possible to maintain these cells as self-renewing and phenotypically stable clonal cell lines in vitro. Thus, we sought to identify a surrogate stem cell niche for the isolation and persistent maintenance of stable clonal cardiovascular progenitor cell lines, enabling us to study the mechanism of self-renewal and differentiation in these cells. Using postnatal murine hearts with a selectable marker as the stem cell source and embryonic stem cells and leukemia inhibitory factor (LIF)-secreting fibroblasts as a surrogate niche, we succeeded in the isolation of stable clonal cardiovascular progenitor cell lines. These cell lines self-renew in an LIF-dependent manner. They express both stemness transcription factors Oct4, Sox2, and Nanog and early myocardial transcription factors Nkx2.5, GATA4, and Isl-1 at the same time. Upon LIF deprivation, they exclusively differentiate to functional cardiomyocytes and endothelial and smooth muscle cells, suggesting that these cells are mesodermal intermediates already committed to the cardiogenic lineage. Cardiovascular progenitor cell lines can be maintained for at least 149 passages over 7 years without phenotypic changes, in the presence of LIF-secreting fibroblasts. Isolation of wild-type cardiovascular progenitor cell lines from adolescent and old mice has finally demonstrated the general feasibility of this strategy for the isolation of phenotypically stable somatic stem cell lines.

Cardiac stem cells: A promising treatment option for heart failure

Cardiovascular diseases are the most common cause of death in the world. The development of heart failure is mainly due to the loss of cardiomyocytes following myocardial infarction and the absence of endogenous myocardial repair. Numerous studies have focused on cardiac stem cells (CSCs) due to their therapeutic benefit, particularly in the treatment of heart failure. It has previously been demonstrated that CSCs are able to promote the regeneration of cardiomyocytes in animals following myocardial infarction. However, the underlying mechanism(s) remain unclear. This review mainly discusses the cardioprotective effect of CSCs and the effect of CSCs on the function of cardiomyocytes, and compares the efficacies of CSCs from rats, mice and humans, thereby contributing to an improved understanding of CSCs as a promising treatment option for heart failure.

Intracoronary bone marrow cell application for terminal heart failure in children

INTRODUCTION

In spite of tremendous progress in the medical and surgical treatment of children with congenital heart disease and dilated cardiomyopathy achieved during the past few decades, for some children a heart transplant remains the only option. Clinically relevant benefits of intracoronary injection of autologous stem cells on cardiac function and remodelling have been demonstrated in adult patients with acute myocardial infarction. Experience with autologous stem cell therapy in children with severe congenital or acquired pump failure is limited to a small number of case reports.

METHOD AND RESULTS

Between 2006 and 2010, nine severely ill children were treated with intracoronary infusion of autologous bone marrow-derived mononuclear cells as part of a compassionate therapy in our centre. No procedure-related unexpected adverse events occurred. There was one patient on extracorporeal membrane oxygenation who died of haemorrhage unrelated to the procedure; three patients proceeded to heart transplantation once a donor heart became available. The other five patients showed an improvement with respect to New York Heart Association classification (greater than or equal to 1), brain natriuretic peptide serum levels, and ejection fraction.

CONCLUSION

Similar to adults, intracoronary injection of autologous bone marrow cell is technically feasible and safe for children. On the basis of our data, we propose to perform a pilot study for children with congestive heart failure, to formally assess the efficacy of intracoronary autologous bone marrow cell therapy.

Cardiac progenitor cells engineered with Pim-1 (CPCeP) develop cardiac phenotypic electrophysiological properties as they are co-cultured with neonatal myocytes

Stem cell transplantation has been successfully used for amelioration of cardiomyopathic injury using adult cardiac progenitor cells (CPC). Engineering of mouse CPC with the human serine/threonine kinase Pim-1 (CPCeP) enhances regeneration and cell survival in vivo, but it is unknown if such apparent lineage commitment is associated with maturation of electrophysiological properties and excitation-contraction coupling. This study aims to determine electrophysiology and Ca(2+)-handling properties of CPCeP using neonatal rat cardiomyocyte (NRCM) co-culture to promote cardiomyocyte lineage commitment. Measurements of membrane capacitance, dye transfer, expression of connexin 43 (Cx43), and transmission of ionic currents (I(Ca), I(Na)) from one cell to the next suggest that a subset of co-cultured CPCeP and NRCM becomes connected via gap junctions. Unlike NRCM, CPCeP had no significant I(Na), but expressed nifedipine-sensitive I(Ca) that could be measured more consistently with Ba(2+) as permeant ion using ramp-clamp protocols than with Ca(2+) and step-depolarization protocols. The magnitude of I(Ca) in CPCeP increased during culture (4-7 days vs. 1-3 days) and was larger in co-cultures with NRCM and with NRCM-conditioned medium, than in mono-cultured CPCeP. I(Ca) was virtually absent in CPC without engineered expression of Pim-1. Caffeine and KCl-activated Ca(2+)-transients were significantly present in co-cultured CPCeP, but smaller than in NRCM. Conversely, ATP-induced (IP(3)-mediated) Ca(2+) transients were larger in CPCeP than in NRCM. I(NCX) and I(ATP) were expressed in equivalent densities in CPCeP and NRCM. These in vitro studies suggest that CPCeP in co-culture with NRCM: a) develop I(Ca) current and Ca(2+) signaling consistent with cardiac lineage, b) form electrical connections via Cx43 gap junctions, and c) respond to paracrine signals from NRCM. These properties may be essential for durable and functional myocardial regeneration under in vivo conditions.

Reconstitution of aged bone marrow with young cells repopulates cardiac-resident bone marrow-derived progenitor cells and prevents cardiac dysfunction after a myocardial infarction

AIMS

The study was designed to evaluate the mechanisms of cardiac regeneration after injury and to determine how to restore that capacity in aged individuals. The adult heart retains a small population of nascent cells that have myeloid, mesenchymal, and mesodermal capabilities, which play an essential role in the recovery of ventricular function after injury. In aged individuals, these cells are diminished and dysfunctional. We evaluated the derivation of some of these cardiac progenitors and a method to restore their number and function.

METHODS AND RESULTS

We first demonstrated that aged mice have fewer progenitors in both the bone marrow (BM) and the myocardium, which correlated with the extent of cardiac dysfunction after injury. Bone marrow chimerism established in aged mice with young BM donors restored both myocardial progenitors and cardiac function, but neither was restored with aged BM donors. Cardiac micro-chimerism in aged mice was established with young BM cells, which restored cardiac function after injury, even with old peripheral BM cells. The young cardiac-resident BM-derived progenitor cells in the aged myocardium persisted for at least a year, and after myocardial infarction they actively proliferated and enhanced cardiac repair through paracrine mechanisms.

CONCLUSION

Bone marrow reconstitution with young BM cells in aged recipients restored progenitors in both the BM and, most importantly, the myocardium. The number and function of cardiac-resident BM-derived progenitor cells in the aged myocardium prior to injury was the major determinant for successful recovery of cardiac function. The aged heart was rejuvenated with young BM cells.

Bone marrow-derived human mesenchymal stem cells express cardiomyogenic proteins but do not exhibit functional cardiomyogenic differentiation potential

Despite their paracrine activites, cardiomyogenic differentiation of bone marrow (BM)-derived mesenchymal stem cells (MSCs) is thought to contribute to cardiac regeneration. To systematically evaluate the role of differentiation in MSC-mediated cardiac regeneration, the cardiomyogenic differentiation potential of human MSCs (hMSCs) and murine MSCs (mMSCs) was investigated in vitro and in vivo by inducing cardiomyogenic and noncardiomyogenic differentiation. Untreated hMSCs showed upregulation of cardiac tropopin I, cardiac actin, and myosin light chain mRNA and protein, and treatment of hMSCs with various cardiomyogenic differentiation media led to an enhanced expression of cardiomyogenic genes and proteins; however, no functional cardiomyogenic differentiation of hMSCs was observed. Moreover, co-culturing of hMSCs with cardiomyocytes derived from murine pluripotent cells (mcP19) or with murine fetal cardiomyocytes (mfCMCs) did not result in functional cardiomyogenic differentiation of hMSCs. Despite direct contact to beating mfCMCs, hMSCs could be effectively differentiated into cells of only the adipogenic and osteogenic lineage. After intramyocardial transplantation into a mouse model of myocardial infarction, Sca-1(+) mMSCs migrated to the infarcted area and survived at least 14 days but showed inconsistent evidence of functional cardiomyogenic differentiation. Neither in vitro treatment nor intramyocardial transplantation of MSCs reliably generated MSC-derived cardiomyocytes, indicating that functional cardiomyogenic differentiation of BM-derived MSCs is a rare event and, therefore, may not be the main contributor to cardiac regeneration.

Stem cell mediated cardiovascular repair

Recent increase in the interest in stem and progenitor cells may be attributed to their behavioural characteristics. A consensus has been reached that embryonic or adult stem cells have therapeutic potential. As cardiovascular health issues are still the major culprits in many developed countries, stem and progenitor cell driven approaches may give the clinicians a new arsenal to tackle many significant health issues. However, stem and progenitor cell mediated cardiovascular regeneration can be achieved via complex and dynamic molecular mechanisms involving a variety of cells, growth factors, cytokines, and genes. Functional contributions of transplanted cells on target organs and their survival are still critical problems waiting to be resolved. Moreover, the regeneration of contracting myocardial tissue has controversial results in human trials. Thus, moderately favourable clinical results should be interpreted carefully. Determining the behavioural programs, genetic and transcriptional control of stem cells, mechanisms that determine cell fate, and functional characteristics are the primary targets. In addition, ensuring the long-term follow-up of cells with efficient imaging techniques in human clinical studies may provide a resurgence of the initial enthusiasm, which has faded over time. Here, we provide a brief historical perspective on stem cell driven cardiac regeneration and discuss cardiac and vascular repair in the context of translational science.

Pressure overload leads to an increase of cardiac resident stem cells

Recent studies suggest that the mammalian heart possesses some capacity for cardiac regeneration. This regenerative capacity is primarily documented postnatally and after myocardial infarction or pressure overload. Although the cell type that mediates endogenous regeneration is unclear, cardiac stem cells might be considered as potential candidates. To determine the number of c-kit + cardiac resident cells under conditions of pressure overload, we evaluated specimens derived from n = 8 patients with pressure overloaded single right ventricles in comparison to n = 4 explanted hearts from patients with dilated cardiomyopathy and n = 14 biopsies from children after heart transplantation. The age of the patients ranged from 16 days to 19 years. For quantification of cardiac stem cells, c-kit+/mast cell tryptase-/CD45- cells were counted and expressed as percent of the total nuclei. In specimens from patients with dilated cardiomyopathy, 0.13 ± 0.09% c-kit +/mast cell tryptase-/CD45- cells were detected. However, in specimens from patients with pressure overloaded single right ventricles, the numbers of c-kit+/mast cell tryptase-/CD45- cells were significantly higher (0.41 ±0.24%, p < 0.05). Under conditions of pressure overload, the right ventricle shows an approximately three-fold increase in c-kit+/mast cell tryptase-/CD45- cardiac resident cells. Despite the fact that this increased number of c-kit+ cells is not sufficient to prevent the failing heart from congestive heart failure, understanding the mechanism that leads to an increase of presumably cardiac resident stem cells under conditions of pressure overload might help to develop new strategies to enhance endogenous repair.

Using stem cells in skin regeneration: possibilities and reality

Tissue-engineered skin has a long history of clinical applications, yet current treatments are not capable of completely regenerating normal, uninjured skin. Nonetheless, the field has experienced a tremendous development in the past 10 years, encountering the summit of tissue engineering (TE) and the arising of stem cell research. Since then, unique features of these cells such as self-renewal capacity, multi-lineage differentiation potential, and wound healing properties have been highlighted. However, a realistic perspective of their outcome in skin regenerative medicine applications is still absent. This review intends to discuss the directions that adult and embryonic stem cells (ESCs) can take, strengthening the skin regeneration field. Distinctively, a critical overview of stem cells' differentiation potential onto skin main lineages, along with a highlight of their participation in wound healing mechanisms, is herein provided. We aim to compile and review significant work to allow a better understanding of the best skin TE approaches, enabling the embodiment of the materialization of a new era in skin regeneration to come, with a conscious overview of the current limitations.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

Mechanisms of cardiogenesis in cardiovascular progenitor cells

Self-renewing cells of the vertebrate heart have become a major subject of interest in the past decade. However, many researchers had a hard time to argue against the orthodox textbook view that defines the heart as a postmitotic organ. Once the scientific community agreed on the existence of self-renewing cells in the vertebrate heart, their origin was again put on trial when transdifferentiation, dedifferentiation, and reprogramming could no longer be excluded as potential sources of self-renewal in the adult organ. Additionally, the presence of self-renewing pluripotent cells in the peripheral blood challenges the concept of tissue-specific stem and progenitor cells. Leaving these unsolved problems aside, it seems very desirable to learn about the basic biology of this unique cell type. Thus, we shall here paint a picture of cardiovascular progenitor cells including the current knowledge about their origin, basic nature, and the molecular mechanisms guiding proliferation and differentiation into somatic cells of the heart.

Adipose-derived stromal cell therapy improves cardiac function after coronary occlusion in rats

Recent studies have identified adipose tissue as a new source of mesenchymal stem cells for therapy. The purpose of this study was to investigate the therapy with adipose-derived stromal cells (ASCs) in a rat model of healed myocardial infarction (MI). ASCs from inguinal subcutaneous adipose tissue of male Wistar rats were isolated by enzymatic digestion and filtration. Cells were then cultured until passage 3. Four weeks after ligation of the left coronary artery of female rats, a suspension of either 100 µl with phosphate-buffered saline (PBS) + Matrigel + 2 × 10(6) ASCs labeled with Hoechst (n = 11) or 100 µl of PBS + Matrigel (n = 10) was injected along the borders of the ventricular wall scar tissue. A sham-operated group (n = 5) was submitted to the same surgical procedure except permanent ligation of left coronary artery. Cardiac performance was assessed by electro- and echocardiogram. Echo was performed prior to injections (baseline, BL) and 6 weeks after injections (follow-up, FU), and values after treatment were normalized by values obtained before treatment. Hemodynamic measurements were performed 6 weeks after injections. All infarcted animals exhibited cardiac function impairment. Ejection fraction (EF), shortening fractional area (SFA), and left ventricular akinesia (LVA) were similar between infarcted groups before treatment. Six weeks after therapy, ASC group showed significant improvement in all three ECHO indices in comparison to vehicle group. In anesthetized animals dp/dt(+) was also significantly higher in ASCs when compared to vehicle. In agreement with functional improvement, scar area was diminished in the ASC group. We conclude that ASCs improve cardiac function in infarcted rats when administered directly to the myocardium.

Embryonic and foetal Islet-1 positive cells in human hearts are also positive to c-Kit

During embryogenesis, the mammalian heart develops from a primitive heart tube originating from two bilateral primary heart fields located in the lateral plate mesoderm. Cells belongings to the pre-cardiac mesoderm will differentiate into early cardiac progenitors, which express early transcription factors which are also common to the Isl-1 positive cardiac progenitor cells isolated from the developing pharyngeal mesoderm and the foetal and post-natal mice hearts. A second population of cardiac progenitor cells positive to c-Kit has been abundantly isolated from adult hearts. Until now, these two populations have been considered two different sets of progenitor cells present in the heart in different stages of an individual life. In the present study we collected embryonic, foetal and infant hearts, and we tested the hypotheses that c-Kit positive cells, usually isolated from the adult heart, are also present in the intra-uterine life and persist in the adult heart after birth, and that foetal Isl-1 positive cells are also positive to c-Kit. Using immunohistochemistry we studied the temporal distribution of Isl-1 positive and c-Kit/CD105 double positive cells, and by immunofluorescence and confocal analysis we studied the co-localization of c-Kit and Isl-1 positive cells. The results indicated that cardiomyocytes and interstitial cells were positive for c-Kit from the 9th to the 19th gestational week, that cells positive for both c-Kit and CD105 appeared in the interstitium at the 17th gestational week and persisted in the postnatal age, and that the Isl-1 positive cells were a subset of the c-Kit positive population.

Autologous mesenchymal stem cells mobilize cKit+ and CD133+ bone marrow progenitor cells and improve regional function in hibernating myocardium

RATIONALE

Mesenchymal stem cells (MSCs) improve function after infarction, but their mechanism of action remains unclear, and the importance of reduced scar volume, cardiomyocyte proliferation, and perfusion is uncertain.

OBJECTIVE

The present study was conducted to test the hypothesis that MSCs mobilize bone marrow progenitor cells and improve function by stimulating myocyte proliferation in collateral-dependent hibe rnating myocardium.

METHODS AND RESULTS

Swine with chronic hibernating myocardium received autologous intracoronary MSCs (icMSCs; ≈44 ×10(6) cells, n = 10) 4 months after instrumentation and were studied up to 6 weeks later. Physiological and immunohistochemical findings were compared with untreated hibernating animals (n = 7), sham-normal animals (n = 5), and icMSC-treated sham-normal animals (n = 6). In hibernating myocardium, icMSCs increased function (percent wall thickening of the left anterior descending coronary artery 24 ± 4% to 43 ± 5%, P < 0.05), although left anterior descending coronary artery flow reserve (adenosine/rest) remained critically impaired (1.2 ± 0.1 versus 1.2 ± 0.1). Circulating cKit+ and CD133+ bone marrow progenitor cells increased transiently after icMSC administration, with a corresponding increase in myocardial cKit+/CD133+ and cKit+/CD133- bone marrow progenitor cells (total cKit+ from 223 ± 49 to 4415 ± 866/10(6) cardiomyocytes, P < 0.05). In hibernating hearts, icMSCs increased Ki67+ cardiomyocytes (from 410 ± 83 to 2460 ± 610/10(6) nuclei, P < 0.05) and phospho-histone H3-positive cardiomyocytes (from 9 ± 5 to 116 ± 12/10(6) nuclei, P < 0.05). Myocyte nuclear number (from 75 336 ± 5037 to 114 424 ± 9564 nuclei/mm3, P < 0.01) and left ventricular mass (from 2.5 ± 0.1 to 2.8 ± 0.1 g/kg, P < 0.05) increased, yet myocytes were smaller (14.5 ± 0.4 versus 16.5 ± 0.4 μm, P < 0.05), which supports endogenous cardiomyocyte proliferation. In sham-normal animals, icMSCs increased myocardial bone marrow progenitor cells with no effect on myocyte proliferation or regional function.

CONCLUSIONS

Our results indicate that icMSCs improve function in hibernating myocardium independent of coronary flow or reduced scar volume. This arises from stimulation of myocyte proliferation with increases in cKit+/CD133+ bone marrow progenitor cells and cKit+/CD133- resident stem cells, which increase myocyte number and reduce cellular hypertrophy.

Heterogeneity in SDF-1 expression defines the vasculogenic potential of adult cardiac progenitor cells

Rationale

The adult myocardium has been reported to harbor several classes of multipotent progenitor cells (CPCs) with tri-lineage differentiation potential. It is not clear whether c-kit+CPCs represent a uniform precursor population or a more complex mixture of cell types.

Objective

To characterize and understand vasculogenic heterogeneity within c-kit+presumptive cardiac progenitor cell populations.

Methods and Results

c-kit+, sca-1+ CPCs obtained from adult mouse left ventricle expressed stem cell-associated genes, including Oct-4 and Myc, and were self-renewing, pluripotent and clonogenic. Detailed single cell clonal analysis of 17 clones revealed that most (14/17) exhibited trilineage differentiation potential. However, striking morphological differences were observed among clones that were heritable and stable in long-term culture. 3 major groups were identified: round (7/17), flat or spindle-shaped (5/17) and stellate (5/17). Stellate morphology was predictive of vasculogenic differentiation in Matrigel. Genome-wide expression studies and bioinformatic analysis revealed clonally stable, heritable differences in stromal cell-derived factor-1 (SDF-1) expression that correlated strongly with stellate morphology and vasculogenic capacity. Endogenous SDF-1 production contributed directly to vasculogenic differentiation: both shRNA-mediated knockdown of SDF-1 and AMD3100, an antagonist of the SDF-1 receptor CXC chemokine Receptor-4 (CXCR4), reduced tube-forming capacity, while exogenous SDF-1 induced tube formation by 2 non-vasculogenic clones. CPCs producing SDF-1 were able to vascularize Matrigel dermal implants in vivo, while CPCs with low SDF-1 production were not.

Conclusions

Clonogenic c-kit+, sca-1+ CPCs are heterogeneous in morphology, gene expression patterns and differentiation potential. Clone-specific levels of SDF-1 expression both predict and promote development of a vasculogenic phenotype via a previously unreported autocrine mechanism.

Subcellular scaled multiplexed protein patterns for single cell cocultures

Tip-based direct protein printing is a relatively new technique that is useful for controlling the cellular microenvironment with subcellular resolution. Coculture studies have been useful for mimicking the in vivo environment and studying effects on stem or progenitor cell function. However, there are many experimental variables that cannot be properly controlled and may lead to confounding results. Here we demonstrate a technique that allows spatial control of multiple cell types at single cell levels on a substrate. Specifically, 3T3 fibroblasts and C2C12 myoblasts and their respective binding dynamics with fibronectin and laminin demonstrate the single cell coculture concept.

Myocardial regeneration: Roles of stem cells and hydrogels

Heart failure remains the leading cause of morbidity and mortality. Recently, it was reported that the adult heart has intrinsic regenerative capabilities, prompting a great wave of research into applying cell-based therapies, especially with skeletal myoblasts and bone marrow-derived cells, to regenerate heart tissues. While the mechanism of action for the observed beneficial effects of bone marrow-derived cells remains unclear, new cell candidates are emerging, including embryonic stem (ES) and introduced pluripotent stem (iPS) cells, as well as cardiac stem cells (CSCs) from adult hearts. However, the very low engraftment efficiency and survival of implanted cells prevent cell therapy from turning into a clinical reality. Injectable hydrogel biomaterials based on hydrophilic, biocompatible polymers and peptides have great potential for addressing many of these issues by serving as cell/drug delivery vehicles and as a platform for cardiac tissue engineering. In this review, we will discuss the application of stem cells and hydrogels in myocardial regeneration.

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.

Human cord blood CD34+ progenitor cells acquire functional cardiac properties through a cell fusion process

The efficacy of cardiac repair by stem cell administration relies on a successful functional integration of injected cells into the host myocardium. Safety concerns have been raised about the possibility that stem cells may induce foci of arrhythmia in the ischemic myocardium. In a previous work (36), we showed that human cord blood CD34(+) cells, when cocultured on neonatal mouse cardiomyocytes, exhibit excitation-contraction coupling features similar to those of cardiomyocytes, even though no human genes were upregulated. The aims of the present work are to investigate whether human CD34(+) cells, isolated after 1 wk of coculture with neonatal ventricular myocytes, possess molecular and functional properties of cardiomyocytes and to discriminate, using a reporter gene system, whether cardiac differentiation derives from a (trans)differentiation or a cell fusion process. Umbilical cord blood CD34(+) cells were isolated by a magnetic cell sorting method, transduced with a lentiviral vector carrying the enhanced green fluorescent protein (EGFP) gene, and seeded onto primary cultures of spontaneously beating rat neonatal cardiomyocytes. Cocultured EGFP(+)/CD34(+)-derived cells were analyzed for their electrophysiological features at different time points. After 1 wk in coculture, EGFP(+) cells, in contact with cardiomyocytes, were spontaneously contracting and had a maximum diastolic potential (MDP) of -53.1 mV, while those that remained isolated from the surrounding myocytes did not contract and had a depolarized resting potential of -11.4 mV. Cells were then resuspended and cultured at low density to identify EGFP(+) progenitor cell derivatives. Under these conditions, we observed single EGFP(+) beating cells that had acquired an hyperpolarization-activated current typical of neonatal cardiomyocytes (EGFP(+) cells, -2.24 ± 0.89 pA/pF; myocytes, -1.99 ± 0.63 pA/pF, at -125 mV). To discriminate between cell autonomous differentiation and fusion, EGFP(+)/CD34(+) cells were cocultured with cardiac myocytes infected with a red fluorescence protein-lentiviral vector; under these conditions we found that 100% of EGFP(+) cells were also red fluorescent protein positive, suggesting cell fusion as the mechanism by which cardiac functional features are acquired.

Novel therapies in childhood heart failure: today and tomorrow

Heart failure is an important cause of morbidity and mortality in individuals of all ages. The many-faceted nature of the clinical heart failure syndrome has historically frustrated attempts to develop an overarching explanative theory. However, much useful information has been gained by basic and clinical investigation, even though a comprehensive understanding of heart failure has been elusive. Heart failure is a growing problem, in both adult and pediatric populations, for which standard medical therapy, as of 2010, can have positive effects, but these are usually limited and progressively diminish with time in most patients. If we want curative or near-curative therapy that will return patients to a normal state of health at a feasible cost, much better diagnostic and therapeutic technologies need to be developed. This review addresses the vexing group of heart failure etiologies that include cardiomyopathies and other ventricular dysfunctions of various types, for which current therapy is only modestly effective. Although there are many unique aspects to heart failure in patients with pediatric and congenital heart disease, many of the innovative approaches that are being developed for the care of adults with heart failure will be applicable to heart failure in childhood.

Generation of novel reporter stem cells and their application for molecular imaging of cardiac-differentiated stem cells in vivo

Stem cell therapies offer the potential for repair and regeneration of cardiac tissue. To facilitate evaluation of stem cell activity in vivo, we created novel dual-reporter mouse embryonic stem (mES) cell lines that express the firefly luciferase (LUC) reporter gene under the control of the cardiac sodium-calcium exchanger-1 (Ncx-1) promoter in the background of the 7AC5-EYFP mES cell line that constitutively expresses the enhanced yellow fluorescent protein (EYFP). We compared the ability of recombinant clonal cell lines to express LUC before and after induction of cardiac differentiation in vitro. In particular, one of the clonal cell lines (Ncx-1-43LUC mES cells) showed markedly enhanced LUC expression (45-fold increase) upon induction of cardiac differentiation in vitro. Further, cardiac differentiation in these cells was perpetuated over a period of 2-4 weeks after transplantation in a neonatal mouse heart model, as monitored by noninvasive bioluminescence imaging (BLI) and confirmed via postmortem immunofluorescence and histological assessments. In contrast, transplantation of undifferentiated pluripotent Ncx-1-43LUC mES cells in neonatal hearts did not result in detectable levels of cardiac differentiation in these cells in vivo. These results suggest that prior induction of cardiac differentiation in vitro enhances development and maintenance of a cardiomyocyte-like phenotype for mES cells following transplantation into neonatal mouse hearts in vivo. We conclude that the Ncx-1-43LUC mES cell line is a novel tool for monitoring early cardiac differentiation in vivo using noninvasive BLI.

Adult cardiac-derived stem cells: differentiation and survival regulators

At present, heart failure is one of the most concerning diseases worldwide. To develop efficient treatments, it is necessary to gain a better understanding of the biological characteristics of stem cells in the heart. We recently established and characterized c-kit-positive cardiac stem cells obtained from adult rats. Moreover, we established left atrium-derived pluripotent cells that can differentiate either into skeletal/cardiac myocytes or adipocytes in a methylcellulose-based Methocult medium with almost 100% purity. Microarray and signaling pathway analyses showed that transforming growth factor (TGF)-β is a key molecule in the regulation of the differentiation switch. Indeed, TGF-β1 simultaneously inhibits adipogenesis and activates myogenesis in a dose-dependent manner. However, the effect of TGF-β varies with the developmental stage, dosage, and timing of the treatment.

Future research and therapeutic applications of human stem cells: general, regulatory, and bioethical aspects

There is much to be investigated about the specific characteristics of stem cells and about the efficacy and safety of the new drugs based on this type of cells, both embryonic as adult stem cells, for several therapeutic indications (cardiovascular and ischemic diseases, diabetes, hematopoietic diseases, liver diseases). Along with recent progress in transference of nuclei from human somatic cells, as well as iPSC technology, has allowed availability of lineages of all three germ layers genetically identical to those of the donor patient, which permits safe transplantation of organ-tissue-specific adult stem cells with no immune rejection. The main objective is the need for expansion of stem cell characteristics to maximize stem cell efficacy (i.e. the proper selection of a stem cell) and the efficacy (maximum effect) and safety of stem cell derived drugs. Other considerations to take into account in cell therapy will be the suitability of infrastructure and technical staff, biomaterials, production costs, biobanks, biosecurity, and the biotechnological industry. The general objectives in the area of stem cell research in the next few years, are related to identification of therapeutic targets and potential therapeutic tests, studies of cell differentiation and physiological mechanisms, culture conditions of pluripotent stem cells and efficacy and safety tests for stem cell-based drugs or procedures to be performed in both animal and human models in the corresponding clinical trials. A regulatory framework will be required to ensure patient accessibility to products and governmental assistance for their regulation and control. Bioethical aspects will be required related to the scientific and therapeutic relevance and cost of cryopreservation over time, but specially with respect to embryos which may ultimately be used for scientific uses of research as source of embryonic stem cells, in which case the bioethical conflict may be further aggravated.

The human heart: a self-renewing organ

The dogma that the heart is a static organ which contains an irreplaceable population of cardiomyocytes prevailed in the cardiovascular field for the last several decades. However, the recent identification of progenitor cells that give rise to differentiated myocytes has prompted a re-interpretation of cardiac biology. The heart cannot be viewed any longer as a postmitotic organ characterized by a predetermined number of myocytes that is defined at birth and is preserved throughout life. The myocardium constitutes a dynamic entity in which new young parenchymal cells are formed to substitute old damaged dying myocytes. The regenerative ability of the heart was initially documented with a classic morphometric approach and more recently with the demonstration that DNA synthesis, mitosis, and cytokinesis take place in the newly formed myocytes of the normal and pathologic heart. Importantly, replicating myocytes correspond to the differentiated progeny of cardiac stem cells. These findings point to the possibility of novel therapeutic strategies for the diseased heart.

Diazoxide potentiates mesenchymal stem cell survival via NF-kappaB-dependent miR-146a expression by targeting Fas

We have previously reported that preconditioning of bone marrow-derived mesenchymal stem cells (MSCs) with diazoxide (DZ) significantly improved cell survival via NF-κB signaling. Since micro-RNAs (miRNAs) are critical regulators of a wide variety of biological events, including apoptosis, proliferation, and differentiation, it is likely that DZ-induced survival is mediated by miRNAs. Here we show that miR-146a expressed during preconditioning with DZ is a key regulator of stem cell survival. Treatment of MSCs with DZ (200 μM) markedly increased miR-146a expression and promoted cell survival, as evaluated by lactate dehydrogenase release and transferase-mediated dUTP nick-end labeling staining. Interestingly, blocking NF-κB by IKK-γ NEMO binding domain inhibitor peptide did not induce miR-146a expression, indicating NF-κB regulates miR-146a expression. Moreover, blockade of miR-146a expression by antisense miR-146a inhibitor abolished DZ-induced cytoprotective effects, suggesting a critical role of miR-146a in MSC survival. Computational analysis found a consensus putative target site of miR-146a relevant to apoptosis in the 3' untranslated region of Fas mRNA. The role of Fas as a target gene was substantiated by abrogation of miR-146a, which markedly increased Fas protein expression. This was verified by luciferase reporter assay, which showed that forced expression of miR-146a downregulated Fas expression via targeting its 3'-UTR of this gene. Taken together, these data demonstrated that cytoprotection afforded by preconditioning of MSCs with DZ was regulated by miR-146a induction, which may be a novel therapeutic target in cardiac ischemic diseases.