Homing of intravenously infused embryonic stem cell-derived cells to injured hearts after myocardial infarction

Greater angiogenic and immunoregulatory potency of bFGF and 5-aza-2'-deoxycytidine pre-treated menstrual blood stem cells in compare to bone marrow stem cells in rat model of myocardial infarction

BACKGROUND

This study is designed to compare the menstrual blood stem cells (MenSCs) and bone marrow stem cells (BMSCs)-secreted factors with or without pre-treatment regimen using basic fibroblast growth factor (bFGF) and 5-aza-2'-deoxycytidine (5-aza) and also regenerative capacity of pre-treated MenSCs and/or BMSCs in a rat model of myocardial infarction (MI).

METHODS

BMSCs and MenSCs were pre-treated with bFGF and 5-aza for 48 h and we compared the paracrine activity by western blotting. Furthermore, MI model was created and the animals were divided into sham, MI, pre-treated BMSCs, and pre-treated MenSCs groups. The stem cells were administrated via tail vain. 35 days post-MI, serum and tissue were harvested for further investigations.

RESULTS

Following pre-treatment, vascular endothelium growth factor, hypoxia-inducible factor-1, stromal cell-derived factor-1, and hepatocyte growth factor were significantly increased in secretome of MenSCs in compared to BMSCs. Moreover, systemic administration of pre-treated MenSCs, leaded to improvement of cardiac function, preservation of myocardium from further subsequent injuries, promotion the angiogenesis, and reduction the level of NF-κB expression in compared to the pre-treated BMSCs. Also, pre-treated MenSCs administration significantly decreased the serum level of Interleukin 1 beta (IL-1β) in compared to the pre-treated BMSCs and MI groups.

CONCLUSIONS

bFGF and 5-aza pre-treated MenSCs offer superior cardioprotection compare to bFGF and 5-aza pre-treated BMSCs following MI.

Successful Derivation of an Induced Pluripotent Stem Cell Line from a Genetically Nonpermissive Enhanced Green Fluorescent Protein-Transgenic FVB/N Mouse Strain

The embryonic stem cell line derivation from nonpermissive mouse strains is a challenging and highly inefficient process. The cellular reprogramming strategy provides an alternative route for generating pluripotent stem cell (PSC) lines from such strains. In this study, we successfully derived an enhanced green fluorescent protein (EGFP)-transgenic "N9" induced pluripotent stem cell (iPS cell, iPSC) line from the FVB/N strain-derived mouse embryonic fibroblasts (MEFs). The exposure of MEFs to human OCT4, SOX2, KLF4, and c-MYC (OSKM) transgenes via lentiviral transduction resulted in complete reprogramming. The N9 iPS cell line demonstrated all the criteria of a typical mouse PSC line, including normal colony morphology and karyotype (40,XY), high replication and propagation efficiencies, expression of the pluripotency-associated genes, spontaneous differentiation to three germ lineage-derived cell types, and robust potential of chimeric blastocyst formation. Taken together, using human OSKM genes for transduction, we report, for the first time, the successful derivation of an EGFP-expressing iPS cell line from a genetically nonpermissive transgenic FVB/N mouse. This cell line could provide opportunities for designing protocols for efficient derivation of PSC lines from other nonpermissive strains and developing mouse models of human diseases.

Stem Cell Homing: a Potential Therapeutic Strategy Unproven for Treatment of Myocardial Injury

Despite advances in the prevention and therapeutic modalities of ischemic heart disease, morbidity and mortality post-infarction heart failure remain big challenges in modern society. Stem cell therapy is emerging as a promising therapeutic strategy. Stem cell homing, the ability of stem cells to find their destination, is receiving more attention. Identification of specific cues and understanding the signaling pathways that direct stem cells to targeted destination will improve stem cell homing efficiency. This review discusses the cellular and molecular mechanism of stem cell homing at length in the light of literature and analyzes the problem and considerations of this approach as a treatment strategy for the treatment of ischemic heart disease clinically.

Important roles of the Ca2+-sensing receptor in vascular health and disease

Ca²⁺-sensing receptor (CaSR), a member of G protein-coupled receptor family, is widely expressed in the vascular system, including perivascular neurons, vascular endothelial cells (VECs) and vascular smooth muscle cells (VSMCs). When stimulated, CaSR can further increase the cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) in two ways: intracellular Ca²⁺ release from endo/sarcoplasmic reticulum (ER/SR) and extracellular Ca²⁺ entry through Ca²⁺-permeable cation channels. In endothelium, increased Ca²⁺ subsequently activate nitric oxide synthase (NOS) and intermediate conductance Ca²⁺-activated K⁺ channels (IKCa), resulting in vasodilation through NOS-mediated NO release or membrane hyperpolarization. In VSMCs, CaSR-induced intracellular Ca²⁺ increase causes blood vessel constriction. CaSR activation predominantly induces vasorelaxation of whole vascular tissues through VECs-dependent mechanisms; however, CaSR-induced Ca²⁺ signaling in VSMCs may play a braking role in CaSR-mediated vasorelaxation. Emerging evidence reveals the importance of CaSR in the regulation of vascular tone and blood pressure. Here, we summarized recent advances in CaSR-mediated vascular reaction and the underlying mechanisms in different species, including humans. In addition, several studies have demonstrated that CaSR dysfunction may be associated with some fatal vascular diseases, such as pulmonary arterial hypertension, primary hypertension, diabetes, acute myocardial infarction and vascular calcification. With the advance of studies on CaSR in vascular health and disease, it is expected positive modulators or negative modulators of CaSR used for the treatment of specific diseases may be promising therapeutic options for the prevention and/or treatment of vascular diseases.

Calcium-sensing receptor-mediated mitogen-activated protein kinase pathway improves the status of transplanted mouse embryonic stem cells in rats with acute myocardial infarction

Several studies have identified the critical role of calcium-sensing receptors (CaSRs) in cardiac ischaemia/reperfusion injury and cardiac hypertrophy and have demonstrated that CaSRs induce myocardial apoptosis by activating MAPKs. Using acute myocardial infarction rat models, we found that a combination therapy of CaSR inhibition and embryonic stem cell (ESC) transplantation after acute myocardial infarction (AMI) leads to a dramatic reduction in the infarct size; a significant increase in the maximum rising and falling rate (+dp/dtmax and -dp/dtmax, respectively) of left ventricular pressure; a significant decrease in left ventricular end-diastolic pressure; a significant decrease in the mRNA expression level of CaSR, Bax, Bcl-2, cleaved caspase-3, cleaved caspase-9, p-ERK, p-JNK and p-P38 protein together with apoptosis indexes in the C and E groups; and a significant decrease in cTnT levels as well as LDH and CK activity. These findings indicate that cardiac function could be enhanced significantly by combination therapy with CaSR inhibition and ESC transplantation; the effect was better than ESC transplantation alone, and the mechanism might be associated with a reduction in cell apoptosis via the inhibition of the MAPK pathway. Apoptosis could be reduced through CaSR, which regulates the MAPK pathway and apoptosis-related protein. Our study indicated that CaSR inhibitors have a pivotal role in the treatment of AMI.

Angiopellosis as an Alternative Mechanism of Cell Extravasation

Stem cells possess the ability to home in and travel to damaged tissue when injected intravenously. For the cells to exert their therapeutic effect, they must cross the blood vessel wall and enter the surrounding tissues. The mechanism of extravasation injected stem cells employ for exit has yet to be characterized. Using intravital microscopy and a transgenic zebrafish line Tg(fli1a:egpf) with GFP-expressing vasculature, we documented the detailed extravasation processes in vivo for injected stem cells in comparison to white blood cells (WBCs). While WBCs left the blood vessels by the standard diapedesis process, injected cardiac and mesenchymal stem cells underwent a distinct method of extravasation that was markedly different from diapedesis. Here, the vascular wall undergoes an extensive remodeling to allow the cell to exit the lumen, while the injected cell remains distinctively passive in activity. We termed this process Angio-pello-sis, which represents an alternative mechanism of cell extravasation to the prevailing theory of diapedesis. Stem Cells 2017;35:170-180 Video Highlight: https://youtu.be/i5EI-ZvhBps.

Magnetic resonance imaging with superparamagnetic iron oxide fails to track the long-term fate of mesenchymal stem cells transplanted into heart

MRI for in vivo stem cell tracking remains controversial. Here we tested the hypothesis that MRI can track the long-term fate of the superparamagnetic iron oxide (SPIO) nanoparticles labelled mesenchymal stem cells (MSCs) following intramyocardially injection in AMI rats. MSCs (1 × 10⁶) from male rats doubly labeled with SPIO and DAPI were injected 2 weeks after myocardial infarction. The control group received cell-free media injection. In vivo serial MRI was performed at 24 hours before cell delivery (baseline), 3 days, 1, 2, and 4 weeks after cell delivery, respectively. Serial follow-up MRI demonstrated large persistent intramyocardial signal-voids representing SPIO during the follow-up of 4 weeks, and MSCs did not moderate the left ventricular dysfunction. The TUNEL analysis confirmed that MSCs engrafted underwent apoptosis. The histopathological studies revealed that the site of cell injection was infiltrated by inflammatory cells progressively and the iron-positive cells were macrophages identified by CD68 staining, but very few or no DAPI-positive stem cells at 4 weeks after cells transplantation. The presence of engrafted cells was confirmed by real-time PCR, which showed that the amount of Y-chromosome-specific SRY gene was consistent with the results. MRI may not reliably track the long-term fate of SPIO-labeled MSCs engraftment in heart.

Stem cell therapy for heart failure

The last decade has witnessed the publication of a large number of clinical trials, primarily using bone marrow-derived stem cells as the injected cell. Much has been learned through these "first-generation" clinical trials. The considerable advances in our understanding include (1) cell therapy is safe, (2) cell therapy has been modestly effective, (3) the recognition that in humans bone marrow-derived stem cells do not transdifferentiate into cardiomyocytes or new blood vessels (or at least in sufficient numbers to have any effect). The primary mechanism of action for cell therapy is now believed to be through paracrine effects that include the release of cytokines, chemokines, and growth factors that inhibit apoptosis and fibrosis, enhance contractility, and activate endogenous regenerative mechanisms through endogenous circulating or site-specific stem cells. The new direction for clinical trials includes the use of stem cells capable of cardiac lineage, such as endogenous cardiac stem cells.

SCF promotes dental pulp progenitor migration, neovascularization, and collagen remodeling - potential applications as a homing factor in dental pulp regeneration

Stem cell factor (SCF) is a powerful chemokine that binds to the c-Kit receptor CD117 and has shown promise as a homing agent capable of progenitor cell recruitment. In the present study we have documented high levels of both SCF and its receptor c-Kit in differentiating dental pulp (DP) cells and in the sub-odontoblastic layer of Höhl. In vitro studies using human DP progenitors revealed a significant increase in cell proliferation after100 nM SCF application, explained by a 2-fold upregulation in cyclin D3 and FGF2 cell cycle regulators, and a 7-fold increase in CDK4 expression. DP cell migration in the presence of SCF was up-regulated 2.7-fold after a 24 h culture period, and this effect was accompanied by cytoskeletal rearrangement, a 1.5-fold increase in polymeric F-actin over G-actin, and a 1.8-fold increase in RhoA expression. Explaining the signaling effect of SCF on DP migration, PI3K/Akt and MEK/ERK pathway inhibitors were demonstrated to significantly reduce DP cell migration, while SCF alone doubled the number of migrated cells. ERK and AKT phosphorylation were dramatically upregulated already 3-5 min after SCF addition to the culture medium and declined thereafter, classifying SCF as a fast acting chemokine. When applied as an agent to promote tissue regeneration in subcutaneously implanted collagen sponges, SCF resulted in a 7-fold increase in the cell number in the implanted tissue construct, a more than 9-fold increase in capillaries, as well as collagen sponge remodeling and collagen fiber neogenesis. Together, these studies demonstrate the suitability of SCF as a potent aid in the regeneration of dental pulp and other mesenchymal tissues, capable of inducing cell homing, angiogenesis, and tissue remodeling.

Soluble factors secreted by differentiating embryonic stem cells stimulate exogenous cell proliferation and migration

INTRODUCTION

Stem cells are being investigated as catalysts of tissue regeneration to either directly replace or promote cellularity lost as a result of traumatic injury or degenerative disease. In many reports, despite low numbers of stably integrated cells, the transient presence of cells delivered or recruited to sites of tissue remodeling globally benefits functional recovery. Such findings have motivated the need to determine how paracrine factors secreted from transplanted cells may be capable of positively impacting endogenous repair processes and somatic cell responses.

METHODS

Embryonic stem cells were differentiated as embryoid bodies (EBs) in vitro and media conditioned by EBs were collected at different intervals of time. Gene and protein expression analysis of several different growth factors secreted by EBs were examined by polymerase chain reaction and enzyme-linked immunosorbent assay analysis, respectively, as a function of time. The proliferation and migration of fibroblasts and endothelial cells treated with EB conditioned media was examined compared with unconditioned and growth media controls.

RESULTS

The expression of several growth factors, including bone morphogenic protein-4, insulin-like growth factors and vascular endothelial growth factor-A, increased during the course of embryonic stem cell (ESC) differentiation as EBs. Conditioned media collected from EBs at different stages of differentiation stimulated proliferation and migration of both fibroblasts and endothelial cells, based on 5-bromo-2'-deoxyuridine incorporation and transwell assays, respectively.

CONCLUSIONS

Overall, these results demonstrate that differentiating ESCs express increasing amounts of various growth factors over time that altogether are capable of stimulating mitogenic and motogenic activity of exogenous cell populations.

Regulation of multiple transcription factors by reactive oxygen species and effects of pro-inflammatory cytokines released during myocardial infarction on cardiac differentiation of embryonic stem cells

BACKGROUND

The mechanism of how reactive oxygen species (ROS) regulate cardiac differentiation in the long-run is unclear and the effect of pro-inflammatory cytokines secreted during myocardial infarction on the cardiac differentiation of embryonic stem cells (ESCs) is unknown. The aims of this study were 1) to investigate the effect of ROS on cardiac differentiation and the regulations of transcription factors in ESC differentiation cultures and 2) to investigate the effect of pro-inflammatory cytokines on the expression of cardiac structural genes and whether this effect is mediated through ROS signaling.

METHODS

ESCs were differentiated using hanging drop method. Degree of cardiac differentiation was determined by the appearance of beating embryoid bodies (EBs) and by the expression of cardiac genes using real-time PCR and Western blot. Intracellular ROS level was examined by confocal imaging.

RESULTS

H2O2-treated EBs were found to have enhanced cardiac differentiation in the long run as reflected by, firstly, an earlier appearance of beating EBs, and secondly, an upregulation in cardiac structural protein expression at both mRNA and protein levels. Also, ROS upregulated the expression of several cardiac-related transcription factors, and increased the post-translationally-activated transcription factors SRF and AP-1. IL-1β, IL-10, IL-18 and TNF-α upregulated the expression of cardiac structural proteins and increased the ROS level in differentiating EBs. In addition, ROS scavenger reversed the cardiogenic effect of IL-10 and IL-18.

CONCLUSIONS

These results demonstrated that ROS enhance cardiac differentiation of ESCs through upregulating the expression and activity of multiple cardiac-related transcription factors. IL-1β, IL-10, IL-18 and TNF-α enhance cardiac differentiation and ROS may serve as the messenger in cardiogenic signaling from these cytokines.

Monocyte chemotactic protein-1 promotes the myocardial homing of mesenchymal stem cells in dilated cardiomyopathy

Dilated cardiomyopathy (DCM) is the most common form of non-ischemic cardiomyopathy that leads to heart failure. Mesenchymal stem cells (MSCs) are under active investigation currently as a potential therapy for DCM. However, little information is available about the therapeutic potential of intravenous administration of MSCs for DCM. Moreover, how MSCs home to the myocardium in DCM is also unclear. DCM was induced by intraperitoneally administering Doxorubicin and MSCs or vehicles were infused through the internal jugular vein. Cardiac functions including the percentage of fractional shortening, left ventricular diastolic dimension, left ventricular end-diastolic pressure, and left ventricular maximum dp/dt were evaluated by echocardiographic and hemodynamic studies. Fibrosis was determined by Masson’s trichrome staining. The mRNA expression levels of monocyte chemotactic protein-1 (MCP-1), stromal cell-derived factor-1 (SDF-1), macrophage inflammatory protein-1α (MIP-1α), and monocyte chemotactic protein-3 (MCP-3) were determined using real time polymerase chain reactions and the protein expression level of MCP-1 was detected with Western blot. The MSCs expression of C-C chemokine receptor type 2 (CCR2), a MCP-1 receptor, was confirmed by Western blot and flow cytometry analysis. The chemotactic effects of MCP-1/CCR2 were checked by assessing the migration in vitro and in vivo. MSCs transplantation improved the cardiac function and decreased the myocardial fibrosis of mice with DCM. MCP-1 was up-regulated in dilated myocardial tissue both at the mRNA and protein level while SDF-1, MIP-1α and MCP-3 remain unchanged. CCR2 was present in MSCs. MCP-1 promoted MSCs migration in vitro while CCR2 inhibition decreased the migration of MCP-1 to the dilated heart. This study provides direct evidences that peripheral intravenous infusion of MSCs can support the functional recovery of DCM. In addition, novel insights into the myocardial homing factor of MSCs in DCM are presented. Modulation of MCP-1/CCR2 signaling system might be a novel therapeutic strategy for DCM.

Translational research and therapeutic applications of stem cell transplantation in periodontal regenerative medicine

Stem cells have received a great deal of interest from the research community as potential therapeutic "tools" for a variety of chronic debilitating diseases that lack clinically effective therapies. Stem cells are also of interest for the regeneration of tooth-supporting tissues that have been lost to periodontal disease. Indeed, substantial data have demonstrated that the exogenous administration of stem cells or their derivatives in preclinical animal models of periodontal defects can restore damaged tissues to their original form and function. As we discuss here, however, considerable hurdles must be overcome before these findings can be responsibly translated to novel clinical therapies. Generally, the application of stem cells for periodontal therapy in clinics will not be realized until the best cell(s) to use, the optimal dose, and an effective mode of administration are identified. In particular, we need to better understand the mechanisms of action of stem cells after transplantation in the periodontium and to learn how to preciously control stem cell fates in the pathological environment around a tooth. From a translational perspective, we outline the challenges that may vary across preclinical models for the evaluation of stem cell therapy in situations that require periodontal reconstruction and the safety issues that are related to clinical applications of human stem cells. Although clinical trials that use autologous periodontal ligament stem cells have been approved and have already been initiated, proper consideration of the technical, safety, and regulatory concerns may facilitate, rather than inhibit, the clinical translation of new therapies.

Cell delivery in cardiac regenerative therapy

There is a growing interest in the clinical application of stem cells as a novel therapeutic approach for treatment of myocardial infarction and prevention of subsequent heart failure. Transplanted stem cells improve cardiac functions through multiple mechanisms, which include but are not limited to promoting angiogenesis, replacing dead cardiomyocytes, modulating cardiac remodeling. Most of the results obtained so far are exciting and very promising, spawning an increasing number of clinical trials recently. However, many problems still remain to be resolved such as the best delivery method for transplantation of cells to the injured myocardium and the issue of how to optimize the delivery of targeted cells is of exceptional clinical relevance. In this review, we focus on the different delivery strategies in cardiac regenerative therapy, as well as provide a brief overview of current clinical trials utilizing cell-based therapy in patients with ischemic heart disease.

Role of GATA-4 in differentiation and survival of bone marrow mesenchymal stem cells

Cell and tissue regeneration is a relatively new research field and it incorporates a novel application of molecular genetics. Combinatorial approaches for stem-cell-based therapies wherein guided differentiation into cardiac lineage cells and cells secreting paracrine factors may be necessary to overcome the limitations and shortcomings of a singular approach. GATA-4, a GATA zinc-finger transcription factor family member, has been shown to regulate differentiation, growth, and survival of a wide range of cell types. In this chapter, we discuss whether overexpression of GATA-4 increases mesenchymal stem cell (MSC) transdifferentiation into cardiac phenotype and enhances the MSC secretome, thereby increasing cell survival and promoting postinfarction cardiac angiogenesis. MSCs engineered with GATA-4 enhance their capacity to differentiate into cardiac cell phenotypes, improve survival of the cardiac progenitor cells and their offspring, and modulate the paracrine activity of stem cells to support their angiomyogenic potential and cardioprotective effects.

Reduction of infarct size by intravenous injection of uncultured adipose derived stromal cells in a rat model is dependent on the time point of application

Stem cell therapy is a promising tool to improve outcome after acute myocardial infarction (AMI), but needs to be optimized since results from clinical applications remain ambiguous. A potent source of stem cells is the stromal vascular fraction of adipose tissue (SVF), which contains high numbers of adipose derived stem cells (ASC). We hypothesized that: 1) intravenous injection can be used to apply stem cells to the heart. 2) Uncultured SVF cells are easier and safer when cultured ASCs. 3) Transplantation after the acute inflammation period of AMI is favorable over early injection. For this, AMI was induced in rats by 40min of coronary occlusion. One or seven days after AMI, rats were intravenously injected with vehicle, 5×10(6) uncultured rat SVF cells or 1×10(6) rat ASCs. Rats were analyzed 35 days after AMI. Intravenous delivery of both fresh SVF cells and cultured ASCs 7 days after AMI significantly reduced infarct size compared to vehicle. Similar numbers of stem cells were found in the heart, after treatment with fresh SVF cells and cultured ASCs. Importantly, no adverse effects were found after injection of SVF cells. Using cultured ASCs, however, 3 animals had shortness of breath, and one animal died during injection. In contrast to application at 7 days post AMI, injection of SVF cells 1 day post AMI resulted in a small but non-significant infarct reduction (p=0.35). Taken together, intravenous injection of uncultured SVF cells subsequent to the acute inflammation period, is a promising stem cell therapy for AMI.

Effects of histocompatibility and host immune responses on the tumorigenicity of pluripotent stem cells

Pluripotent stem cells hold great promises for regenerative medicine. They might become useful as a universal source for a battery of new cell replacement therapies. Among the major concerns for the clinical application of stem cell-derived grafts are the risks of immune rejection and tumor formation. Pluripotency and tumorigenicity are closely linked features of pluripotent stem cells. However, the capacity to form teratomas or other tumors is not sufficiently described by inherited features of a stem cell line or a stem cell-derived graft. The tumorigenicity always depends on the inability of the recipient to reject the tumorigenic cells. This review summarizes recent data on the tumorigenicity of pluripotent stem cells in immunodeficient, syngeneic, allogeneic, and xenogeneic hosts. The effects of immunosuppressive treatment and cell differentiation are discussed. Different immune effector mechanisms appear to be involved in the rejection of undifferentiated and differentiated cell populations. Elements of the innate immune system, such as natural killer cells and the complement system, which are active also in syngeneic recipients, appear to preferentially reject undifferentiated cells. This effect could reduce the risk of tumor formation in immunocompetent recipients. Cell differentiation apparently increases susceptibility to rejection by the adaptive immune system in allogeneic hosts. The current data suggest that the immune system of the recipient has a major impact on the outcome of pluripotent stem cell transplantation, whether it is rejection, engraftment, or tumor development. This has to be considered when the results of experimental transplantation models are interpreted and even more when translation into clinics is planned.

A novel vascularized patch enhances cell survival and modifies ventricular remodeling in a rat myocardial infarction model

OBJECTIVE

Although stem cells hold a great therapeutic potential for injured tissues, limited survival of transplanted stem cells has hindered the clinical application of this technology. We hypothesized that an omentum-based stem cell-supporting patch could provide adequate nutrients and microenvironment to prolong cell survival. We examined this hypothesis in rats with experimental myocardial infarction.

METHODS

The omentum-based supporting patch was constructed by stitching polylactic acid-co-glycolic acid polymer seeded with mesenchymal stem cells from male Sprague-Dawley rats. Eight weeks after the experimental myocardial infarction, which was created by ligating the left coronary artery of female Sprague-Dawley rats, mesenchymal stem cells were transplanted with (n = 16) or without (n = 14) the supporting patch. After 4 weeks, transplanted mesenchymal stem cell survival, ventricular remodeling, and cardiac performance were examined.

RESULTS

Significantly more cells survived after 4 weeks in rats transplanted with mesenchymal stem cells on the supporting patch assessed by means of polymerase chain reaction detection of the Sry gene than seen in those without the supporting patch (2.61 ± 0.40 vs 1.19 ± 0.12, P < .05). Rats with myocardial infarction that received mesenchymal stem cells with the patch also had significantly improved ventricular remodeling and cardiac function than those without the patch. Wrapping infarcted myocardium with omentum alone did not change the myocardial function.

CONCLUSIONS

The omentum-based cell-supporting patch provided a favorable microenvironment for transplanted mesenchymal stem cell survival, which resulted in favorable ventricular remodeling and restoration of cardiac function in rats with experimental myocardial infarction. Further validation of the technique in human subjects could make mesenchymal stem cell transplantation a viable therapeutic option for patients with cardiac disease.

Embryonic stem cell transplantation: promise and progress in the treatment of heart disease

Cardiovascular diseases remain the leading cause of death worldwide, and the burden is equally shared between men and women around the globe. Cardiomyocytes that die in response to disease processes or aging are replaced by scar tissue instead of new muscle cells. Although recent reports suggest an intrinsic capacity for the mammalian myocardium to regenerate via endogenous stem/progenitor cells, the magnitude of such a response appears to be minimal and has yet to be realized fully in cardiovascular patients. Despite the advances in pharmacotherapy and new biomedical technologies, the prognosis for patients diagnosed with end-stage heart failure appears to be grave. While heart transplantation is a viable option, this life-saving intervention suffers from an acute shortage of cardiac organ donors. In view of these existing issues, donor cell transplantation is emerging as a promising strategy to regenerate diseased myocardium. Studies from multiple laboratories have shown that transplantation of donor cells (e.g. fetal cardiomyocytes, skeletal myoblasts, smooth muscle cells, and adult stem cells) can improve the function of diseased hearts over a short period of time (1-4 weeks). While long-term follow-up studies are warranted, it is generally perceived that the beneficial effects of transplanted cells are mainly due to increased angiogenesis or favorable scar remodeling in the engrafted myocardium. Although skeletal myoblasts and bone marrow stem cells hold the highest potential for implementation of autologous therapies, initial results from phase I trials are not promising. In contrast, transplantation of fetal cardiomyocytes has been shown to confer protection against the induction of ventricular tachycardia in experimental myocardial injury models. Furthermore, results from multiple laboratories suggest that fetal cardiomyocytes can couple functionally with host myocytes, stimulate formation of new blood vessels, and improve myocardial function. While it is neither practical nor ethical to test the potential of fetal cardiomyocytes in clinical trials, embryonic stem (ES) cells serve as a novel source for generation of unlimited quantities of cardiomyocytes for myocardial repair. The initial success in the application of ES cells to partially repair and improve myocardial function in experimental models of heart disease has been quite promising. However, multiple hurdles need to be crossed before the potential benefits of ES cells can be translated to the clinic. In this review, we summarize the current knowledge of cardiomyocyte derivation and enrichment from ES-cell cultures and provide a brief survey of factors increasing cardiomyogenic induction in both mouse and human ES cultures. Subsequently, we summarize the current state of research using mouse and human ES cells for the treatment of heart disease in various experimental models. Furthermore, we discuss the challenges that need to be overcome prior to the successful clinical utilization of ES-derived cardiomyocytes for the treatment of end-stage heart disease. While we are optimistic that the researchers in this field will sail across the hurdles, we also suggest that a more cautious approach to the validation of ES cardiomyocytes in experimental models would certainly prevent future disappointments, as seen with skeletal myoblast studies.

Colony-forming cells in rat myocardium after destructive exposure and intramyocardial transplantation of bone marrow cells

The content of colony-forming cells in myocardial cell culture from the perinecrotic zone of rat heart was evaluated on day 40 after cryodestruction. The mean cellularity after cryodestruction was 12-fold lower than in intact animals. Intramyocardial transplantation of bone marrow cells (mononuclears, mesenchymal stem cells, and mesenchymal stem cells treated with 5-azacitidine) into the perinecrotic zone increased the content of colony-forming cells. After transplantation of mesenchymal stem cells and mesenchymal stem cells treated with 5-azacitidine, the number of colonies reached 33 +/- 7 and 11 +/- 3, the mean cellularity being 2975 +/- 80 and 1105 +/- 42 cells/cm2, respectively. Hence, intramyocardial transplantation of mesenchymal stem cells created an appreciable pool of colony-forming cells in the myocardial perinecrotic zone. Treatment with 5-azacitidine reduced survival of mesenchymal stem cells after intramyocardial transplantation.

Cell delivery mechanisms for tissue repair

Many cell populations, derived from both adult tissues and embryonic stem cells, show promise for the treatment of a variety of diseases. Although the major effort in stem cell therapies in the past has been identifying potentially therapeutic cells, it is now clear that developing systems to deliver these cells and promote their efficient engraftment will provide an equally challenging task. More sophisticated pretransplantation manipulations and material carriers may dramatically improve the survival, engraftment, and fate control of transplanted stem cells and their ultimate clinical utility.

Adhesion proteins, stem cells, and arrhythmogenesis

Cell-transplantation therapy is a promising treatment option that is being actively explored as a way to repair cardiac muscle. The ultimate goal is to reconstitute the architecture of the cardiac muscle and to reestablish electrical propagation, while avoiding hypertrophy and scar formation. In this review, we focus on recent advances in the field as well as the difficulties encountered when the engraftment of cells into the host tissue is to be confirmed and functionally characterized. This is critical since incomplete or partial engraftment of transplanted cells within the host cardiac network exacerbates the heterogeneity already present in the injured myocardium and increases its propensity to arrhythmia. We conclude with a brief discussion of how the modulation of cell adhesion via modification of coupling proteins within transplanted cells may facilitate engraftment and alleviate the arrhythmogenic potential of cardiac grafts.

Stem cells and their potential in cell-based cardiac therapies

Stem cells are potential agents for the treatment of myocardial infarcts among other heart diseases. Over the past decade, the scientific community has extensively used a wide variety of cells and examined their capacity to both regenerate the infarcted myocardium and improve functionally the diseased hearts. Some of the cells used include skeletal myoblasts, bone marrow-derived cells, adult cardiac resident stem cells, mesenchymal stem cells, and both mouse and human embryonic stem cells (Nat Biotechnol 2005;23:845-856). The reported cardiogenic capacity of the utilitized stem cells is assayed both in vitro through the use of differentiation paradigms and in vivo through transplantation into a variety of animal models of cardiac disease. The purpose of this review article is to summarize recent stem cell applications in cell-based cardiac therapies and their outcomes.

A promising technique for transplantation of bone marrow-derived endothelial progenitor cells into rat heart

OBJECTIVE

To investigate the feasibility of intracoronary application of endothelial progenitor cells and the subsequent distribution within the heart.

METHODS

Endothelial progenitors cells (EPCs) cultured from rat bone marrow were identified by double-positive staining with Dil-Ac-LDL and BS1-lectin. Twenty-four hours before cell transplantation, EPCs were labeled with 5-bromo-2'-deoxyuridine (BrdU). Cells (5 x 10(5) in 250-microl medium) were injected into healthy rats, either as intracoronary application (n=11) or as intramyocardial injection (n = 6). At 15 min or 3 days posttransplantation, hearts as well as other organs (lung, liver, kidney, and spleen) were collected and processed for subsequent BrdU immunohistochemistry. The number of BrdU-positive cells per tissue area was counted.

RESULTS

Compared to intramyocardial injection, intracoronary administration resulted in more than twice as much positive cells in the heart (P < .05), with no local differences within the heart. Whereas after 15 min, EPCs were equally distributed in all examined organs (except for the spleen), cells that were still present after 3 days, approximately 10%, were selectively restricted to the heart.

CONCLUSIONS

Our data indicate that the intracoronary application provides a promising technique for EPC transplantation in the rat heart.

Antiapoptotic effect of implanted embryonic stem cell-derived early-differentiated cells in aging rats after myocardial infarction

This study tested whether implanted embryonic stem cell-derived early-differentiated cells (EDCs) lead to improvement in cardiac function by preventing cardiac apoptosis in aging rats after myocardial infarction. Cardiac apoptosis after transplantation of EDCs was assessed in situ by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling reaction (TUNEL) staining as well as by measurements of protein levels of cleaved caspases 3, Bax, and Bcl-2. Our results indicate that cell transplantation improved cardiac function at 6-months observation. The frequency of apoptotic cells in the peri-infarcted myocardium 3 days after cell transplantation was significantly decreased in the cell transplantation group. EDC therapy decreased the protein levels of cleaved caspase 3 and Bax, and increased the level of Bcl-2 in comparison to myocardial infarction control. Additionally, the number of apoptotic cells decreased significantly in cardiomyocytes precocultured with EDCs. This study demonstrates that functional improvement of EDC transplantation may at least in part be related to a reduction in cardiomyocyte apoptosis.

Cellular transplantation: future therapeutic options

PURPOSE OF REVIEW

Cardiac transplantation is a complex undertaking and an imperfect solution to end-stage heart failure. Cellular transplantation has been proposed as an alternative solution; however, clinical trials at present are small and show variable results. The mechanisms behind stem cell therapy have not yet been elucidated.

RECENT FINDINGS

Several large trials have been presented that address the question of bone marrow stem cells as therapy for acute myocardial infarction, and also the possible benefits of therapy with granulocyte colony-stimulating factor. Although some trials show a modest improvement in ejection fraction or reduction of infarct size, other trials show no change with treatment. Fewer clinical data are available on the treatment of chronic left ventricular systolic function. Many questions remain such as what cell type to use, dosing, the ideal timing for therapy, and the technique of cell delivery. Finally, further research continues on the cellular milieu, enhancement of cell engraftment, proliferation, and survival.

SUMMARY

This review briefly examines the background for stem cell therapy, as well as the larger clinical trials of stem cell therapy for acute myocardial infarction and chronic left ventricular systolic dysfunction, and possible pharmacologic enhancement options.

Donor cell transplantation for myocardial disease: does it complement current pharmacological therapies?This paper is one of a selection of papers published in this Special Issue, entitled Young Investigators' Forum

Heart failure secondary to ischemic heart disease, hypertension, and myocardial infarction is a common cause of death in developed countries. Although pharmacological therapies are very effective, poor prognosis and shorter life expectancy of heart disease patients clearly indicate the need for alternative interventions to complement the present therapies. Since the progression of heart disease is associated with the loss of myocardial cells, the concept of donor cell transplantation into host myocardium is emerging as an attractive strategy to repopulate the damaged tissue. To this end, a number of donor cell types have been tested for their ability to increase the systolic function of diseased hearts in both experimental and clinical settings. Although initial clinical trials with bone marrow stem cells are encouraging, long-term consequences of such interventions are yet to be rigorously examined. While additional laboratory studies are required to address several issues in this field, there is also a clear need for further characterization of drug interactions with donor cells in these interventions. Here, we provide a brief summary of current pharmacological and cell-based therapies for heart disease. Further, we discuss the potential of various donor cell types in myocardial repair, mechanisms underlying functional improvement in cell-based therapies, as well as potential interactions between pharmacological and cell-based therapies.

Nuclear imaging in cardiac cell therapy

Cardiac stem cell therapy is an innovative and promising therapeutic approach for heart failure. However, despite an increasing body of existing experimental and human data, it still presents a substantial challenge for basic scientists and clinical researchers. Several issues concerning biologic mechanisms of therapy remain to be answered, and unequivocal proof of clinical efficacy is needed. The variety of different available cell types and different methods for cell delivery to the myocardium raises further questions about the most useful therapeutic approach. Nuclear imaging not only provides accurate noninvasive information about myocardial perfusion, contractile function and viability, which enables assessment of clinical benefits of therapy. The rapidly developing field of molecular imaging has also brought up more specific tracers targeting cellular and subcellular biologic events, which are expected to shed more light upon mechanisms of cell therapy. Moreover, nuclear imaging is well suited for tracking of transplanted cells by use of direct radionuclide labeling or genetic labeling with reporter genes that can be targeted by radioactive reporter probes. Such a broad spectrum of available in vivo information is expected to significantly impact the future development of cell therapy towards a clinically accepted treatment.