The bone marrow--cardiac axis of myocardial regeneration

Bone marrow vasculature advanced in vitro models for cancer and cardiovascular research

Cardiometabolic diseases and cancer are among the most common diseases worldwide and are a serious concern to the healthcare system. These conditions, apparently distant, share common molecular and cellular determinants, that can represent targets for preventive and therapeutic approaches. The bone marrow plays an important role in this context as it is the main source of cells involved in cardiovascular regeneration, and one of the main sites of liquid and solid tumor metastasis, both characterized by the cellular trafficking across the bone marrow vasculature. The bone marrow vasculature has been widely studied in animal models, however, it is clear the need for human-specific in vitro models, that resemble the bone vasculature lined by endothelial cells to study the molecular mechanisms governing cell trafficking. In this review, we summarized the current knowledge on in vitro models of bone marrow vasculature developed for cardiovascular and cancer research.

Cardiac Progenitor Cells

Cardiovascular diseases top the list of fatal illnesses worldwide. Cardiac tissues is known to be one of te least proliferative in the human body, with very limited regenraive capacity. Stem cell therapy has shown great potential for treatment of cardiovascular diseases in the experimental setting, but success in human trials has been limited. Applications of stem cell therapy for cardiovascular regeneration necessitate understamding of the complex and unique structure of the heart unit, and the embryologic development of the heart muscles and vessels. This chapter aims to provide an insight into cardiac progenitor cells and their potential applications in regenerative medicine. It also provides an overview of the embryological development of cardiac tissue, and the major findings on the development of cardiac stem cells, their characterization, and differentiation, and their regenerative potential. It concludes with clinical applications in treating cardiac disease using different approaches, and concludes with areas for future research.

Stem cell-based therapies for cardiac diseases: The critical role of angiogenic exosomes

Finding effective treatments for cardiac diseases is among the hottest subjects in medicine; cell-based therapies have brought great promises for managing a broad range of life-threatening heart complications such as myocardial infarction. After clarifying the critical role of angiogenesis in tissue repair and regeneration, various stem/progenitor cell were utilized to accelerate the healing of injured cardiac tissue. Embryonic, fetal, adult, and induced pluripotent stem cells have shown the appropriate proangiogenic potential for tissue repair strategies. The capability of stem cells for differentiating into endothelial lineages was initially introduced as the primary mechanism involved in improving angiogenesis and accelerated heart tissue repair. However, recent studies have demonstrated the leading role of paracrine factors secreted by stem cells in advancing neo-vessel formation. Genetically modified stem cells are also being applied for promoting angiogenesis regarding their ability to considerably overexpress and secrete angiogenic bioactive molecules. Yet, conducting further research seems necessary to precisely identify molecular mechanisms behind the proangiogenic potential of stem cells, including the signaling pathways and regulatory molecules such as microRNAs. In conclusion, stem cells' pivotal roles in promoting angiogenesis and consequent improved cardiac healing and remodeling processes should not be ignored, especially in the case of stem cell-derived extracellular vesicles.

Understanding stem cells and its pivotal role in regenerative medicine

Stem cells (SCs) are clonogenic cells that develop into the specialized cells which later responsible for making up various types of tissue in the human body. SCs are not only the appropriate source of information for cell division, molecular and cellular processes, and tissue homeostasis but also one of the major putative biological aids to diagnose and cure various degenerative diseases. This study emphasises on various research outputs that occurred in the past two decades. This will give brief information on classification, differentiation, detection, and various isolation techniques of SCs. Here, the various signalling pathways which includes WNT, Sonic hedgehog, Notch, BMI1 and C-met pathways and how does it effect on the regeneration of various classes of SCs and factors that regulates the potency of the SCs are also been discussed. We also focused on the application of SCs in the area of regenerative medicine along with the cellular markers that are useful as salient diagnostic or curative tools or in both, by the process of reprogramming, which includes diabetes, cancer, cardiovascular disorders and neurological disorders. The biomarkers that are mentioned in various literatures and experiments include PDX1, FOXA2, HNF6, and NKX6-1 (for diabetes); CD33, CD24, CD133 (for cancer); c-Kit, SCA-1, Wilm's tumor 1 (for cardiovascular disorders); and OCT4, SOX2, c-MYC, EN1, DAT and VMAT2 (for neurological disorders). In this review, we come to know the advancements and scopes of potential SC-based therapies, its diverse applications in clinical fields that can be helpful in the near future.

Functional genomic fabrics are remodeled in a mouse model of Chagasic cardiomyopathy and restored following cell therapy

We previously found that, in a mouse model of Chagas cardiomyopathy, 18% of the 9390 quantified unigenes were significantly regulated by Trypanosoma cruzi infection. However, treatment with bone marrow-derived mononuclear cells (MNCs) resulted in 84% transcriptomic recovery. We have applied new algorithms to reanalyze these datasets with respect to specific pathways [Chagas disease (CHAGAS), cardiac muscle contraction (CMC) and chemokine signaling (CCS)]. In addition to the levels of expression of individual genes we also calculated gene expression variability and coordination of expression of each gene with all others. These additional measures revealed changes in the control of transcript abundances and gene networking in CHAGAS and restoration following MNC treatment, not accessible using the conventional approach limited to the average expression levels. Moreover, our weighted pathway regulation analysis incorporated the contributions of all affected genes, eliminating the arbitrary cut-off criteria of fold-change and/or p-value for significantly regulated genes. The new analyses revealed that T. cruzi infection had large transcriptomic consequences for the CMC pathway and triggered a huge cytokine signaling. Remarkably, MNC therapy not only restored normal expression levels of numerous genes, but it also recovered most of the CHAGAS, CMC and CCS fabrics that were altered by the infection.

Myocardial Ischemia and Mobilization of Circulating Progenitor Cells

Background

The response of progenitor cells (PCs) to transient myocardial ischemia in patients with coronary artery disease remains unknown. We aimed to investigate the PC response to exercise‐induced myocardial ischemia (ExMI) and compare it to flow mismatch during pharmacological stress testing.

Methods and Results

A total of 356 patients with stable coronary artery disease underwent 99mTc‐sestamibi myocardial perfusion imaging during exercise (69%) or pharmacological stress (31%). CD34⁺ and CD34⁺/chemokine (C‐X‐C motif) receptor 4 PCs were enumerated by flow cytometry. Change in PC count was compared between patients with and without myocardial ischemia using linear regression models. Vascular endothelial growth factor and stromal‐derived factor‐1α were quantified. Mean age was 63±9 years; 76% were men. The incidence of ExMI was 31% and 41% during exercise and pharmacological stress testing, respectively. Patients with ExMI had a significant decrease in CD34⁺/chemokine (C‐X‐C motif) receptor 4 (−18%, P=0.01) after stress that was inversely correlated with the magnitude of ischemia (r=−0.19, P=0.003). In contrast, patients without ExMI had an increase in CD34⁺/chemokine (C‐X‐C motif) receptor 4 (14.7%, P=0.02), and those undergoing pharmacological stress had no change. Plasma vascular endothelial growth factor levels increased (15%, P<0.001) in all patients undergoing exercise stress testing regardless of ischemia. However, the change in stromal‐derived factor‐1α level correlated inversely with the change in PC counts in those with ExMI (P=0.03), suggesting a greater decrease in PCs in those with a greater change in stromal‐derived factor‐1α level with exercise.

Conclusions

ExMI is associated with a significant decrease in circulating levels of CD34⁺/chemokine (C‐X‐C motif) receptor 4 PCs, likely attributable, at least in part, to stromal‐derived factor‐1α–mediated homing of PCs to the ischemic myocardium. The physiologic consequences of this uptake of PCs and their therapeutic implications need further investigation.

Translational research of adult stem cell therapy

Congestive heart failure (CHF) secondary to chronic coronary artery disease is a major cause of morbidity and mortality world-wide. Its prevalence is increasing despite advances in medical and device therapies. Cell based therapies generating new cardiomyocytes and vessels have emerged as a promising treatment to reverse functional deterioration and prevent the progression to CHF. Functional efficacy of progenitor cells isolated from the bone marrow and the heart have been evaluated in preclinical large animal models. Furthermore, several clinical trials using autologous and allogeneic stem cells and progenitor cells have demonstrated their safety in humans yet their clinical relevance is inconclusive. This review will discuss the clinical therapeutic applications of three specific adult stem cells that have shown particularly promising regenerative effects in preclinical studies, bone marrow derived mesenchymal stem cell, heart derived cardiosphere-derived cell and cardiac stem cell. We will also discuss future therapeutic approaches.

Oxytocin improves the expression of cardiac specific markers in porcine bone marrow stem cells differentiation

Bone marrow stem cells (BMSCs) treated with 5-azacytidine possess myogenic differentiation potential. Oxytocin (OT) induces cardiomyogenesis in murine embryonic and cardiac stem cells. We attempted to isolate, characterize, and induce OT-mediated cardiomyogenic differentiation of porcine pBMSCs. Cells were treated as: control, OT, and 5-azacytidine groups. During early passages, transcripts of Oct4, GATA4, OT receptor, and phospholamban were expressed. RT-PCR showed upregulation of GATA4 in OT and 5-azacytidine-induced groups. Immunocytochemistry revealed higher expressions of cardiac troponin T and myosin heavy chain in OT than in 5-azacytidine-induced groups (p < 0.01). Western blot analysis showed upregulation of cardiac troponin I in OT-induced pBMSCs (p < 0.01). We infer pBMSCs should be induced during early passages, when expressing transcription factors related to pluripotency and cardiomyogenesis, as well as OT receptor. The more abundant expression of cardiac specific proteins in OT-treated pBMSCs suggests OT could be a more potent cardiomyogenic inducer of pBMSC.

Cardiac stem cells: biology and clinical applications

SIGNIFICANCE

Heart disease is the primary cause of death in the industrialized world. Cardiac failure is dictated by an uncompensated reduction in the number of viable and fully functional cardiomyocytes. While current pharmacological therapies alleviate the symptoms associated with cardiac deterioration, heart transplantation remains the only therapy for advanced heart failure. Therefore, there is a pressing need for novel therapeutic modalities. Cell-based therapies involving cardiac stem cells (CSCs) constitute a promising emerging approach for the replenishment of the lost tissue and the restoration of cardiac contractility.

RECENT ADVANCES

CSCs reside in the adult heart and govern myocardial homeostasis and repair after injury by producing new cardiomyocytes and vascular structures. In the last decade, different classes of immature cells expressing distinct stem cell markers have been identified and characterized in terms of their growth properties, differentiation potential, and regenerative ability. Phase I clinical trials, employing autologous CSCs in patients with ischemic cardiomyopathy, are being completed with encouraging results.

CRITICAL ISSUES

Accumulating evidence concerning the role of CSCs in heart regeneration imposes a reconsideration of the mechanisms of cardiac aging and the etiology of heart failure. Deciphering the molecular pathways that prevent activation of CSCs in their environment and understanding the processes that affect CSC survival and regenerative function with cardiac pathologies, commonly accompanied by alterations in redox conditions, are of great clinical importance.

FUTURE DIRECTIONS

Further investigations of CSC biology may be translated into highly effective and novel therapeutic strategies aiming at the enhancement of the endogenous healing capacity of the diseased heart.

Cardiac stem cell therapy: review of the native cardiac progenitor cells and future direction

Various stem cell types have been tested for regenerating damaged myocardium after myocardial infarction. However, the results of clinical trials have not been consistent, with only some of the trials reporting small improvements in cardiac function. It seems that engraftment and survival of injected cells is limited and transplanted stem cells either do not differentiate into cardiac cells or differentiate into only limited number of cardiac cells. The exact mechanism(s) of cardiac functional improvement by cell therapy are unclear, but paracrine effect may play a central role. The resident cardiac progenitor cells identified within the adult myocardium have distinct advantages over other stem cell types for cardiac cell therapy, as they are likely precommitted to the cardiovascular fate. However, isolating and expanding these cells from cardiac biopsies is a challenge. More recently, direct reprogramming of fibroblasts into cardiomyocytes has given new hope for myocardial regeneration. Here we will review different stem cells used in cardiac cell therapy with a focus on the native cardiac progenitor cells and briefly outline future directions of cardiac cell therapy.

A randomised double-blind control study of early intracoronary autologous bone marrow cell infusion in acute myocardial infarction (REGENERATE-AMI)

INTRODUCTION

Acute myocardial infarction (AMI) remains a major cause of mortality and morbidity worldwide despite the latest therapeutic advances designed to decrease myocardial injury. Preclinical and emerging clinical evidence show that the intracoronary injection of autologous bone marrow mononuclear cells (BMCs) following AMI leads to improvement in left ventricular ejection function (LVEF). In this clinical trial we will for the first time assess the effect of early (<24 h) infusion of autologous BMCs following AMI on cardiac function.

METHODS AND ANALYSIS

REGENERATE-AMI is a double-blind, randomised, multicentre, placebo-controlled trial to determine whether early (<24 h) intracoronary infusion of BMCs improves LVEF after AMI. The study will enrol 100 patients presenting with an anterior AMI demonstrating anterior regional wall motion abnormality. Patients will be randomised to receive intracoronary infusion of BMCs or placebo (0.9% saline). Primary endpoint will be change in LVEF at 1 year compared to baseline, measured by cardiac MRI. Secondary endpoints at 6 months include the change in global LVEF relative to baseline measured by quantitative left ventriculography and echocardiography, as well as major adverse cardiac events which is also measured at 1 year.

ETHICS AND DISSEMINATION

The study will be performed in agreement with the Declaration of Helsinki and is approved by local ethics committee (NRES Committee London West London: 07/Q0603/76).

TRIAL REGISTRATION

http://clincialtrials.gov (NCT00765453). The results of the trial will be published according to the CONSORT statement and will be presented at conferences and reported in peer-reviewed journals.

In vitro protection of adipose tissue-derived mesenchymal stem cells by erythropoietin

Mobilization of stem cells and their differentiation into cardiomyocytes are known to have protective effects after myocardial infarction. The integrity of transplanted mesenchymal stem cells for cardiac regeneration is dependent on cell-cell or cell-matrix interaction, which is adversely affected by reactive oxygen species in an ischemic environment. Treatment with erythropoietin was shown to protect human adipose tissue derived mesenchymal stem cells in an ischemic injury in vitro model. The analyses indicated that expression of erythropoietin receptors played a pivotal role in erythropoietin mediated cell survival. In this study, the anti-apoptotic effect of erythropoietin on stem cells was analyzed in apoptosis-induced human mesenchymal stem cells. Apoptosis was induced in cultured adult human adipose tissue derived mesenchymal stem cells by hydrogen peroxide. A group of cultured cells was also treated with recombinant human erythropoietin in a concentration of 50 ng mL(-1). The degree of apoptosis was analyzed by flow-cytometry and immunohistochemical staining for Caspase 3. The average percentages of apoptotic cells were significantly higher in H2O2-induced stem cells than in cells co-cultured with erythropoietin (63.03 ± 4.96% vs 29 ± 3.41%, p<0.01). We conclude that preconditioning with erythropoietin suppresses apoptosis of mesenchymal stem cells and enhances their survival.

Intracoronary Infusion of Autologous CD133(+) Cells in Myocardial Infarction and Tracing by Tc99m MIBI Scintigraphy of the Heart Areas Involved in Cell Homing

CD133 mesenchymal cells were enriched using magnetic microbead anti-CD133 antibody from bone marrow mononuclear cells (BMMNCs). Flow cytometry and immunocytochemistry analysis using specific antibodies revealed that these cells were essentially 89 ± 4% CD133⁺ and 8 ± 5% CD34⁺. CD133⁺/CD34⁺ BMMNCs secrete important bioactive proteins such as cardiotrophin-1, angiogenic and neurogenic factors, morphogenetic proteins, and proinflammatory and remodeling factors in vitro. Single intracoronary infusions of autologous CD133⁺/CD34⁺ BMMNCs are effective and reduce infarct size in patients as analyzed by Tc99m MIBI myocardial scintigraphy. The majority of patients were treated via left coronary artery. Nine months after cell therapy, 5 out of 8 patients showed a net positive response to therapy in different regions of the heart. Uptake of Tc99 isotope and revitalization of the heart area in inferoseptal region are more pronounced (P = 0.016) as compared to apex and anterosptal regions after intracoronary injection of the stem cells. The cells chosen here have the properties essential for their potential use in cell therapy and their homing can be followed without major difficulty by the scintigraphy. The cell therapy proposed here is safe and should be practiced, as we found, in conjunction with scintigraphic observation of areas of heart which respond optimally to the infusion of autologous CD133⁺/CD34⁺ BMMNCs.

Regeneration in heart disease-Is ECM the key?

The heart possesses a regeneration potential derived from endogenous and exogenous stem and progenitor cell populations, though baseline regeneration appears to be sub-therapeutic. This limitation was initially attributed to a lack of cells with cardiomyogenic potential following an insult to the myocardium. Rather, recent studies demonstrate increased numbers of cardiomyocyte progenitor cells in diseased hearts. Given that the limiting factor does not appear to be cell quantity but rather repletion of functional cardiomyocytes, it is crucial to understand potential mechanisms inhibiting progenitor cell differentiation. One of the extensively studied areas in heart disease is extracellular matrix (ECM) remodeling, with both the composition and mechanical properties of the ECM undergoing changes in diseased hearts. This review explores the influence of ECM properties on cardiomyogenesis and adult cardiac progenitor cells.

Cardiac stem cell therapy: stemness or commitment?

Cardiac stem cell therapy to promote engraftment of de novo beating cardiac muscle cells in cardiomyopathies could potentially improve clinical outcomes for many patients with congestive heart failure. Clinical trials carried out over the last decade for cardiac regeneration have revealed inadequacy of current approaches in cell therapy. Chief among them is the choice of stem cells to achieve the desired outcomes. Initial enthusiasm of adult bone marrow stems cells for myocyte regeneration has largely been relegated to paracrine-driven, donor cell-independent, endogenous cardiac repair. However, true functional restoration in heart failure is likely to require considerable myocyte replacement. In order to match stem cell application to various clinical scenarios, we review the necessity to preprime stem cells towards cardiac fate before myocardial transplantation and if these differentiated stem cells could confer added advantage over current choice of undifferentiated stem cells. We explore differentiation ability of various stem cells to cardiac progenitors/cardiomyocytes and compare their applicability in providing targeted recovery in light of current clinical challenges of cell therapy.

Adult hematopoietic progenitors are multipotent in chimeric mice

Embryonic stem cells (ESCs) and adult somatic cells, induced to pluripotency (iPSCs), can differentiate into multiple cell lineages. We previously reported that adult mammalian bone marrow contains a sub-population of CD34+ cells that express genes of ESCs and genes required to generate iPSCs. They also express lineage genes of the three embryonic germ layers. Are these CD34+ cells multipotent? Here, CD34+ bone marrow stem cells from adult male ROSA mice, which carry two markers: the β-galactosidase gene and the male Y chromosome, were transplanted into blastocysts of wildtype mice. Each female ROSA chimera generated had a distinct pattern of male-derived organs expressing β-galactosidase; e.g., ectodermal brain, dorsal root ganglia and skin; mesodermal heart, bone and bone marrow; and endodermal pancreas, intestine, and liver. Thus, adult mammals carry cells that appear to exhibit a developmental potential reminiscent of ESCs and iPSCs suggesting they could be used for cell replacement therapy.

Functional and transcriptomic recovery of infarcted mouse myocardium treated with bone marrow mononuclear cells

Although bone marrow-derived mononuclear cells (BMNC) have been extensively used in cell therapy for cardiac diseases, little mechanistic information is available to support reports of their efficacy. To address this shortcoming, we compared structural and functional recovery and associated global gene expression profiles in post-ischaemic myocardium treated with BMNC transplantation. BMNC suspensions were injected into cardiac scar tissue 10 days after experimental myocardial infarction. Six weeks later, mice undergoing BMNC therapy were found to have normalized antibody repertoire and improved cardiac performance measured by ECG, treadmill exercise time and echocardiography. After functional testing, gene expression profiles in cardiac tissue were evaluated using high-density oligonucleotide arrays. Expression of more than 18% of the 11981 quantified unigenes was significantly altered in the infarcted hearts. BMNC therapy restored expression of 2099 (96.2%) of the genes that were altered by infarction but led to altered expression of 286 other genes, considered to be a side effect of the treatment. Transcriptional therapeutic efficacy, a metric calculated using a formula that incorporates both recovery and side effect of treatment, was 73%. In conclusion, our results confirm a beneficial role for bone marrow-derived cell therapy and provide new information on molecular mechanisms operating after BMNC transplantation on post ischemic heart failure in mice.

Tanshinone IIA increases recruitment of bone marrow mesenchymal stem cells to infarct region via up-regulating stromal cell-derived factor-1/CXC chemokine receptor 4 axis in a myocardial ischemia model

Systemic administration with bone marrow mesenchymal stem cells (BMSCs) is a promising approach to cure myocardial ischemia (MI), while the efficacy of cell transplantation is limited by the low engraftment of BMSCs. Tanshinone IIA (Tan IIA) has been reported many times for the treatment of MI. Therefore, the present study was performed to investigate whether Tan IIA could increase the migration of BMSCs to ischemic region and its potential mechanisms. In our study, we found that combination treatment with Tan IIA and BMSCs significantly alleviated the infarct size when compared with control group (31.46 ± 3.00% vs. 46.95 ± 6.51%, p<0.05). Results of real-time PCR showed that Tanshinone IIA (Tan IIA) did increase the migration of BMSCs to ischemic region in vivo, which was correlated with cardiac function recovery after MI. Furthermore, 2 μM Tan IIA could enhance the migration capability of BMSCs in vitro (3.69-fold of control), and this enhancement could be blocked by AMD3100 (a CXC chemokine receptor 4 blocker). CXCR4, together with its specific receptor, stromal cell-derived factor-1 (SDF-1) plays a critical role in the stem cell recruitment. Our experiment indicated that Tan IIA could promote SDF-1α expression in the infarct area and enhance the CXCR4 expression of BMSCs in vitro. Therefore, we postulated that Tan IIA could increase the BMSCs migration via up-regulating SDF1/CXCR4 axis.

Bone marrow stem cell derived paracrine factors for regenerative medicine: current perspectives and therapeutic potential

During the past several years, there has been intense research in the field of bone marrow-derived stem cell (BMSC) therapy to facilitate its translation into clinical setting. Although a lot has been accomplished, plenty of challenges lie ahead. Furthermore, there is a growing body of evidence showing that administration of BMSC-derived conditioned media (BMSC-CM) can recapitulate the beneficial effects observed after stem cell therapy. BMSCs produce a wide range of cytokines and chemokines that have, until now, shown extensive therapeutic potential. These paracrine mechanisms could be as diverse as stimulating receptor-mediated survival pathways, inducing stem cell homing and differentiation or regulating the anti-inflammatory effects in wounded areas. The current review reflects the rapid shift of interest from BMSC to BMSC-CM to alleviate many logistical and technical issues regarding cell therapy and evaluates its future potential as an effective regenerative therapy.

MORE for multiple organ dysfunction syndrome: Multiple Organ REanimation, REgeneration, and REprogramming

Those who care for the critically ill and injured rightfully celebrate the advances made by our field over its first 50 yrs. Advances in systems, tissue, and molecular engineering, together defined as "health engineering," will provide unprecedented opportunities to treat multiple organ dysfunction syndrome in the 21st century. In the future, Multiple Organ REanimation, REgeneration, and REprogramming will be responsible for new treatment approaches for those with multiple organ dysfunction syndrome; several examples are presented here. Thus, as we spent the first 50 yrs of care for the critical ill and injured learning how best to hook humans up to machines, we will spend the next 50 yrs understanding better how to liberate patients from mechanical support. It is difficult to know when these advances will be realized given that the rate of change continues to increase and the seemingly impossible goal of reprogramming fully differentiated cells was accomplished recently by manipulating a few transcription factors. It is not unrealistic to expect that in the next couple of decades that it will be possible to dedifferentiate dysfunctional somatic cells in vivo to a more robust, resistant cell phenotype. Our future should be aimed in part at refining our skill sets and refocusing (even rebranding) critical care as health engineering aimed at Multiple Organ REanimation, REgeneration, and REprogramming.

Migration and differentiation of human umbilical cord stem cells after heart injury in chicken embryos

Here we have analyzed the behavior and fate of stem cells from human umbilical cord blood (scHUCBs) when grafted into the myocardial wall of normal and damaged hearts of chicken embryos. We started by characterizing the scHUCBs before grafting and we found that they express precardiogenic genes including Nkx2.5, GATA4, MEF-2, and SERCA2a together with undifferentiation markers as CD34 or c-kit. In grafting experiments using scHUCBs labeled with DiI we observed that these cells were not rejected by the host and survived when implanted in chicken hearts, being able to migrate through the myocardial wall. By 3 days after grafting we found labeled cells with morphological characters of myocardiocytes in concordance with the identification of the expression of human genes for myosin light chain 2a (Mlc2a) and myosin heavy chain-beta (Mhc beta) in the chicken heart. When a small injury was applied to the heart wall, grafted scHUCBs were vigorously attracted by the damaged myocardium. This directed migration was only sustained for 12 h after injury, time period required for healing of the damaged heart wall. The rate of myocardial differentiation of scHUCBs in damaged hearts was not significantly increased with respect to that found when implanted in healthy hearts. However, we found stimulation of endothelial differentiation in injured hearts deduced by the increased expression of human genes for platelet endothelial cell-adhesion molecule 1 or vascular endothelial growth factor receptor 2 and the presence of DiI-labeled endothelial cells. Together all these findings support the embryonic chicken heart as a feasible model for experimentation in stem cell therapy and emphasize the relevance of the physiological conditions of the myocardial host tissue for engraftment and differentiation of exogenously applied scHUCBs.

Regulation of circulating progenitor cells in left ventricular dysfunction

BACKGROUND

Reductions in numbers of circulating progenitor cells (CD34+ cell subsets) have been demonstrated in patients at risk for, or in the presence of, cardiovascular disease. The mediators of these reductions remain undefined. To determine whether neurohumoral factors might regulate circulating CD34+ cell subsets in vivo, we studied complementary canine models of left ventricular (LV) dysfunction.

METHODS AND RESULTS

A pacing model of severe LV dysfunction and a hypertensive renal wrap model in which dogs were randomized to receive deoxycorticosterone acetate (DOCA) were studied. Circulating CD34+ cell subsets including hematopoietic precursor cells (HPCs: CD34+/CD45(dim)/VEGFR2-) and endothelial progenitor cells (EPCs: CD34+/CD45-/VEGFR2+) were quantified. Additionally, the effect of mineralocorticoid excess on circulating progenitor cells in normal dogs was studied. The majority of circulating CD34+ cells expressed CD45dimly and did not express VEGFR2, consistent with an HPC phenotype. HPCs were decreased in response to pacing, and this decrease correlated with plasma aldosterone levels (Spearman rank correlation=-0.67, P=0.03). In the hypertensive renal wrap model, administration of DOCA resulted in decreased HPCs. No changes were seen in EPCs in either model. Normal dogs treated with DOCA exhibited a decrease in HPCs in peripheral blood but not bone marrow associated with decreased telomerase activity.

CONCLUSIONS

This is the first study to demonstrate that mineralocorticoid excess, either endogenous or exogenous, results in reduction in HPCs. These data suggest that mineralocorticoids may induce accelerated senescence of progenitor cells, leading to their reduced survival and decline in numbers.

Endogenous Wnt/beta-catenin signaling is required for cardiac differentiation in human embryonic stem cells

Background

Wnt/β-catenin signaling is an important regulator of differentiation and morphogenesis that can also control stem cell fates. Our group has developed an efficient protocol to generate cardiomyocytes from human embryonic stem (ES) cells via induction with activin A and BMP4.

Methodology/Principal Findings

We tested the hypothesis that Wnt/β-catenin signals control both early mesoderm induction and later cardiac differentiation in this system. Addition of exogenous Wnt3a at the time of induction enhanced cardiac differentiation, while early inhibition of endogenous Wnt/β-catenin signaling with Dkk1 inhibited cardiac differentiation, as indicated by quantitative RT-PCR analysis for β-myosin heavy chain (β-MHC), cardiac troponin T (cTnT), Nkx2.5, and flow cytometry analysis for sarcomeric myosin heavy chain (sMHC). Conversely, late antagonism of endogenously produced Wnts enhanced cardiogenesis, indicating a biphasic role for the pathway in human cardiac differentiation. Using quantitative RT-PCR, we show that canonical Wnt ligand expression is induced by activin A/BMP4 treatment, and the extent of early Wnt ligand expression can predict the subsequent efficiency of cardiogenesis. Measurement of Brachyury expression showed that addition of Wnt3a enhances mesoderm induction, whereas blockade of endogenously produced Wnts markedly inhibits mesoderm formation. Finally, we show that Wnt/β-catenin signaling is required for Smad1 activation by BMP4.

Conclusions/Significance

Our data indicate that induction of mesoderm and subsequent cardiac differentiation from human ES cells requires fine-tuned cross talk between activin A/BMP4 and Wnt/β-catenin pathways. Controlling these pathways permits efficient generation of cardiomyocytes for basic studies or cardiac repair applications.

Stem cells for myocardial repair and regeneration: where are we today?

An overview for the use of stem cells for myocardial repair and regeneration is provided. The overview provides the rationale for use of stem cells in myocardial repair. Potential stem cell types and technological challenges are highlighted.

Cellular cardiomyoplasty: what have we learned?

Restoring blood flow, improving perfusion, reducing clinical symptoms, and augmenting ventricular function are the goals after acute myocardial infarction. Other than cardiac transplantation, no standard clinical procedure is available to restore damaged myocardium. Since we first reported cellular cardiomyoplasty in 1989, successful outcomes have been confirmed by experimental and clinical studies, but definitive long-term efficacy requires large-scale placebo-controlled double-blind randomized trials. On meta-analysis, stem cell-treated groups had significantly improved left ventricular ejection fraction, reduced infarct scar size, and decreased left ventricular end-systolic volume. Fewer myocardial infarctions, deaths, readmissions for heart failure, and repeat revascularizations were additional benefits. Encouraging clinical findings have been reported using satellite or bone marrow stem cells, but understanding of the benefit mechanisms demands additional studies. Adult mammalian ventricular myocardium lacks adequate regeneration capability, and cellular cardiomyoplasty offers a new way to overcome this; the poor retention and engraftment rate and high apoptotic rate of the implanted stem cells limit outcomes. The ideal type and number of cells, optimal timing of cell therapy, and ideal cell delivery method depend on determining the beneficial mechanisms. Cellular cardiomyoplasty has progressed rapidly in the last decade. A critical review may help us to better plan the future direction.

Long-term secondary prevention programs after cardiac rehabilitation for the reduction of future cardiovascular events: focus on regular physical activity

Cardiac rehabilitation/secondary prevention programs are recognized as integral to the comprehensive care of patients with coronary heart disease, and as such are recommended in most contemporary clinical practice guidelines. The interventions are aimed at reducing disability, optimizing cardiovascular risk reduction by drug therapy and promoting healthy behavior. Healthy lifestyle habits must be recognized as capable of substantially reducing the risk for cardiovascular events in patients with coronary heart disease. This review highlights the recommended components of cardiac rehabilitation/secondary prevention programs, with special emphasis on regular physical activity.

Cardiac renewing: interstitial Cajal-like cells nurse cardiomyocyte progenitors in epicardial stem cell niches

Recent studies suggested that various cell lineages exist within the subepicardium and we supposed that this area could host cardiac stem cell niches (CSCNs). Using transmission electron microscopy, we have found at least 10 types of cells coexisting in the subepicardium of normal adult mice: adipocytes, fibroblasts, Schwann cells and nerve fibres, isolated smooth muscle cells, mast cells, macrophages, lymphocytes, interstitial Cajal-like cells (ICLCs) and cardiomyocytes progenitors (CMPs). The latter cells, sited in the area of origin of coronary arteries and aorta, showed typical features of either very immature or developing cardiomyocytes. Some of these cells were connected to each other to form columns surrounded by a basal lamina and embedded in a cellular network made by ICLCs. Complex intercellular communication occurs between the ICLCs and CMPs through electron-dense nanostructures or through shed vesicles. We provide here for the first time the ultrastructural description of CSCN in the adult mice myocardium, mainly containing ICLCs and CMPs. The existence of resident CMPs in different developmental stages proves that cardiac renewing is a continuous process. We suggest that ICLCs might act as supporting nurse cells of the cardiac niches and may be responsible for activation, commitment and migration of the stem cells out of the niches. Briefly, not only resident cardiac stem cells but also ICLCs regulate myocyte turnover and contribute to both cardiac cellular homeostasis and endogenous repair/remodelling after injuries.

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.

Isolation and enrichment of stem cells

Stem cells have the potential to revolutionize tissue regeneration and engineering. Both general types of stem cells, those with pluripotent differentiation potential as well as those with multipotent differentiation potential, are of equal interest. They are important tools to further understanding of general cellular processes, to refine industrial applications for drug target discovery and predictive toxicology, and to gain more insights into their potential for tissue regeneration. This chapter provides an overview of existing sorting technologies and protocols, outlines the phenotypic characteristics of a number of different stem cells, and summarizes their potential clinical applications.

ADSCs differentiated into cardiomyocytes in cardiac microenvironment

The microenvironment plays a critical role in directing the progression of stem cells into differentiated cells. So we investigated the role that cardiac microenvironment plays in directing this differentiation process. Adipose tissue-derived stem cells (ADSCs) were cultured with cardiomyocytes directly ("co-culture directly") or by cell culture insert ("co-culture indirectly"). For co-culture indirectly, differentiated ADSCs were collected and identified. For co-culture directly, ADSCs were labeled with carboxyfluorescein succinimidyl ester (CFSE), Fluorescence-activated cell sorting was used to extract and examine the differentiated ADSCs. The ultrastructure and the expression of cardiac specific proteins and genes were analyzed by SEM, TEM, western blotting, and RT-PCR, respectively. Differentiated ADSCs experienced the co-culture presented cardiac ultrastructure and expressed cardiac specific genes and proteins, and the fractions of ADSCs expressing these markers by co-culture directly were higher than those of co-culture indirectly. These data indicate that in addition to soluble signaling molecules, direct cell-to-cell contact is obligatory in relaying the external cues of the microenvironment controlling the differentiation of ADSCs to cardiomyocytes.

Regulation of cell proliferation by intermediate-conductance Ca2+-activated potassium and volume-sensitive chloride channels in mouse mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) are a promising cell source for regenerative medicine; however, their cellular physiology is not fully understood. The present study aimed at exploring the potential roles of the two dominant functional ion channels, intermediate-conductance Ca(2+)-activated potassium (IK(Ca)) and volume-sensitive chloride (I(Cl.vol)) channels, in regulating proliferation of mouse MSCs. We found that inhibition of IK(Ca) with clotrimazole and I(Cl.vol) with 5-nitro-1-(3-phenylpropylamino) benzoic acid (NPPB) reduced cell proliferation in a concentration-dependent manner. Knockdown of KCa3.1 or Clcn3 with specific short interference (si)RNAs significantly reduced IK(Ca) or I(Cl.vol) density and channel protein and produced a remarkable suppression of cell proliferation (by 24.4 +/- 9.6% and 29.5 +/- 7.2%, respectively, P < 0.05 vs. controls). Flow cytometry analysis showed that mouse MSCs retained at G(0)/G(1) phase (control: 51.65 +/- 3.43%) by inhibiting IK(Ca) or I(Cl.vol) using clotrimazole (2 microM: 64.45 +/- 2.20%, P < 0.05) or NPPB (200 microM: 82.89 +/- 2.49%, P < 0.05) or the specific siRNAs, meanwhile distribution of cells in S phase was decreased. Western blot analysis revealed a reduced expression of the cell cycle regulatory proteins cyclin D1 and cyclin E. Collectively, our results have demonstrated that IK(Ca) and I(Cl.vol) channels regulate cell cycle progression and proliferation of mouse MSCs by modulating cyclin D1 and cyclin E expression.

Potential strategies for myocardial regeneration in pediatric patients

Owing to the heart’s limited ability for self-repair, heart failure is a leading cause of death among all patient populations. Thus, a cell-based regenerative strategy for cardiac repair would be highly attractive. A variety of cell sources have been identified as candidates for myocardial repair, including skeletal myoblasts, various bone marrow stem cells, resident cardiac progenitors and embryonic stem cells. However, nearly all studies geared towards myocardial regeneration, both in animal models and in clinical trials, have focused on adult ischemic disease with regional muscle injury. Pediatric patients suffer from more diverse forms of heart disease, including congenital and acquired cardiomyopathies with global muscle dysfunction, as well as disorders of cardiac development, for example, left ventricular hypoplasia, atrial or ventricular septal defects. In this article, a broad range of cell-based therapies are discussed, emphasizing the rapidly evolving science surrounding these strategies and the outstanding questions before application to pediatric patients. It is probable that many of the cell types and delivery strategies capable of repairing adult myocardial diseases will require additional investigations to take advantage of the unique opportunities and challenges of pediatric patients.

Bones of contention: marrow-derived cells in myocardial regeneration

Almost 7 years have passed since the initial publication reporting that bone marrow cells regenerate infarcted myocardium. The subsequent years produced hundreds of investigations that ran the gamut of findings from validation to disproof. Undeterred by the concurrent debate, clinical trials ensued to test the safety and efficacy of bone marrow-derived cell population for autologous therapy in clinical treatment of myocardial disease. In the following conversational exchange, two scientists with distinct perspectives weigh the pros and cons of pursuing bone marrow stem cell therapy and look toward finding a consensus of where the future lies for regenerative medicine and the heart. The conclusion is that the two camps may not be as far apart as it may seem from the rancor in literature and at meetings, and the potential of one day achieving regenerative therapy is indeed a vision that both parties enthusiastically share.

Separation of adult bone marrow mononuclear cells using the automated closed separation system Sepax

BACKGROUND

The Düsseldorf-based cardiologist Professor Strauer was the first to present a therapeutic concept for the repair of acute infarcted myocardium in 2001: the autologous intracoronary transplantation of unfractionated human bone marrow (BM) mononuclear cells (MNC). The Division of Cardiology, Pneumology and Angiology, University of Duesseldorf Medical School, Duesseldorf, Germany, was also able to show the regenerative potential of BM stem cell transplantation in patients with chronic heart disease (CHD) and peripheral arterial disease (PAD). In the mean time, several clinical trials have been set up worldwide, predominantly by using MNC isolated manually from BM aspirates via density-gradient centrifugation; 374 patients have been treated here with unselected BM MNC since 2001. Altogether 217 BM aspirates have been processed manually. In order to maintain the high standards required for cellular therapeutics, the Sepax cell-separation system was implemented into routine BM processing in 2006. The closed Sepax system provides a reproducible MNC isolation method, and 157 BM samples have been processed with the Sepax device. The results of manual MNC isolation were compared with the Sepax-mediated MNC isolation.

METHODS

The manual Ficoll separation method was compared with the Sepax density gradient-based separation (DGBS) protocol using Ficoll with the kit CS-900 and the Sepax S-100 main processing unit from Biosafe.

RESULTS

Nucleated cell and MNC recovery were significantly higher after Sepax processing (P<0.0001) whereas no significance was found for red blood cell depletion.

DISCUSSION

The Sepax cell-separation system is a time-saving method providing clinical-grade MNC isolated automatically from human BM by Ficoll density centrifugation.

"AKT"ing lessons for stem cells: regulation of cardiac myocyte and progenitor cell proliferation

Cardiac development and postnatal growth depend on activation of AKT, but initial strategies to improve myocardial repair using AKT were stymied by undesirable corollary alterations in myocardial structure and function. These unfortunate precedents were based on high-level expression of constitutively activated AKT, predominantly in the cytoplasm of the cell. Based on subsequent studies establishing that activated AKT accumulates in the nucleus, we reasoned that the location of AKT, not simply the activity level, would be a critical determinant of the phenotypic outcome resulting from AKT activation. Using myocardial-specific expression of nuclear-targeted AKT (AKT/nuc), the proliferation of myocardial stem and progenitor cell populations is enhanced, casting new light on the implementation of AKT activity as a molecular interventional approach for treatment of cardiomyopathic damage resulting from acute injury, chronic stress, or the debilitating changes of aging.

G-CSF-based stem cell therapy for the heart--unresolved issues part B: Stem cells, engraftment, transdifferentiation, and bioengineering

The authors extend their coverage of recent developments in stem cell-based therapy for repairing the heart to cover the basic questions of what stem cells should be used and how best to favor their survivability within the injured heart. The authors focus their attention on those adult stem/progenitor cells that have been best investigated in animal studies for repairing the infarcted heart and are the focus of completed or ongoing clinical trials. In addition, they discuss the promise that resident cardiac stem cells offer and the recent identification of specialized architecturally defined niches within the heart to nurse their development. Bioengineering approaches employing off-the-shelf mesenchymal stem cell patches may soon provide a way to recreate these niches in the scarred heart. Conceivably, these patches might also be seeded with prescribed mixtures of culturally expanded autologous stem/progenitor cells that would lead to new blood vessel and cardiac myocyte formation. The convergence of bioengineering and molecular biology on stem cell therapy would seem to make what was once unimaginable, cardiac regeneration, a clinical reality in less than one generation.