Factors affecting functional outcome after autologous skeletal myoblast transplantation

MicroRNA-214 protects L6 skeletal myoblasts against hydrogen peroxide-induced apoptosis

MicroRNAs (miRNAs) have been reported as key gene regulators, and they control many fundamental biological processes. Previously, we demonstrated that miR-214 had a protective effect against myocardial apoptosis and myocardial fibrosis. In this study, we sought to investigate the expression of miR-214 in L6 skeletal myoblast (SKM), the regulatory effect of miR-214 on hydrogen peroxide (H₂O₂) induced cell apoptosis and the underlying mechanisms of the antiapoptotic effect. MiR-214 expression was up-regulated by H₂O₂ in a dose and time-dependent manner in L6 SKMs. To investigate the regulatory effects of miR-214 on L6 SKM, both gain-of-function and loss-of-function approaches were applied. The results showed that miR-214 improved cell survival and inhibited cell apoptosis, and blockage of miR-214 abrogated the protective effect on cell survival and resistance to apoptosis. Phosphatase and tensin homolog (PTEN) was negatively regulated by miR-214, and PTEN inhibitor obviously reversed the effect of miR-214 blockage on enhancing cell apoptosis. In addition, miR-214 up-regulated antiapoptotic protein Bcl-2, down-regulated proapoptotic protein Bax, prevented release of cytochrome c and inhibited caspase-3 activation. In summary, H₂O₂-induced injury increases miR-214 expression in L6 SKM, and miR-214 contributes to the protection of L6 SKM against apoptosis via lowering PTEN and subsequently inhibiting the mitochondrial-mediated caspase-dependent apoptotic signaling pathway.

RGDfK-Peptide Modified Alginate Scaffold for Cell Transplantation and Cardiac Neovascularization

Cell implantation for tissue repair is a promising new therapeutic strategy. Although direct injection of cells into tissue is appealing, cell viability and retention are not very good. Cell engraftment and survival following implantation are dependent on a sufficient supply of oxygen and nutrients through functional microcirculation as well as a suitable local microenvironment for implanted cells. In this study, we describe the development of a porous, biocompatible, three-dimensional (3D) alginate scaffold covalently modified with the synthetic cyclic RGDfK (Arg-Gly-Asp-D-Phe-Lys) peptide. Cyclic RGDfK peptide is protease resistant, highly stable in aqueous solutions, and has high affinity for cellular integrins. Cyclic RGDfK-modified alginate scaffolds were generated using a novel silicone sheet sandwich technique in combination with freeze-gelation, resulting in highly porous nonimmunogenic scaffolds that promoted both human and rodent cell survival in vitro, and neoangiogenesis in vivo. Two months following implantation in abdominal rectus muscles in rats, cyclic RGDfK-modified scaffolds were fully populated by host cells, especially microvasculature without an overt immune response or fibrosis, whereas unmodified control scaffolds did not show cell ingrowth. Importantly, modified scaffolds that were seeded with human mesenchymal precursor cells and were patched to the epicardial surface of infarcted myocardium induced myocardial neoangiogenesis and significantly improved cardiac function. In summary, purified cyclic RGDfK peptide-modified 3D alginate scaffolds are biocompatible and nonimmunogenic, enhance cell viability, promote angiogenesis, and may be used as a means to deliver cells to myocardial infarct areas to improve neovascularization and cardiac function.

Myoblast Therapy: From Bench to Bedside

Myoblasts are defined as stem cells containing skeletal muscle cell precursors. A decade of experimental work has revealed many properties of myoblasts, including the stability of resulting hybrid myofibers without immune suppression, the persistence of transgene expression, and the lack of tumorigenicity. Early phase clinical trials also showed that myoblast-based therapy is a promising approach for many intractable clinical conditions, including both muscle-related and non-muscle-related diseases. The potential application of myoblast therapy may be in the treatment of genetic muscle diseases, cardiomyocyte damaged heart diseases, and urinary incontinence. This review will provide an overview of myoblast biology, along with discussion of the potential application in clinical medicine. In addition, problems in current myoblast therapy and possible future improvements will be addressed.

Long-Term Cell Survival and Hemodynamic Improvements after Neonatal Cardiomyocyte and Satellite Cell Transplantation into Healed Myocardial Cryoinfarcted Lesions in Rats

Cell engraftment is a new strategy for the repair of ischemic myocardial lesions. The hemodynamic effectiveness of this strategy, however, is not completely elucidated yet. In a rat model of cryothermia-induced myocardial dysfunction, we investigated whether syngeneic transplantation of neonatal cardiomyocytes or satellite cells is able to improve left ventricular performance. Myocardial infarction was induced in female Lewis rats by a standardized cryolesion to the obtuse margin of the left ventricle. After 4 weeks, 5 × 106 genetically male neonatal cardiomyocytes (n= 16) or satellite cells (n = 16) were engrafted into the myocardial scar. Sham-transplanted animals (n = 15) received injections with cell-free medium. Sham-operated animals (n = 15) served as controls. Left ventricular performance was analyzed 4 months after cell engraftment. Chimerism after this sex-mismatched transplantation was evaluated by detection of PCR-amplified DNA of the Y chromosome. The average heart weight of the infarcted animals significantly exceeded that of controls (p < 0.05). In sham-transplanted animals, mean aortic pressure, left ventricular systolic pressure, aortic flow (indicator of cardiac output), and left ventricular systolic reserve were significantly lower (p < 0.05) compared with sham-operated controls. This was associated with deterioration of ventricular diastolic function (maximal negative dP/dt, time constants of isovolumic relaxation; p < 0.05). Transplantation of satellite cells was found more effective than transplantation of neonatal cardiomyocytes, resulting in i) normalization of mean aortic pressure compared with sham-operated controls, and ii) significantly improved left ventricular systolic pressure and aortic flow (p < 0.05) compared with sham-transplanted animals. Left ventricular systolic reserve and diastolic function, however, were improved by neither satellite cell nor neonatal cardiomyocyte transplantation. Analysis of male genomic DNA revealed 3.98 ± 2.70 ng in hearts after neonatal cardiomyocyte engraftment and 6.16 ± 4.05 ng in hearts after satellite cell engraftment, representing approximately 103 viable engrafted cells per heart. Our study demonstrates i) long-term survival of both neonatal cardiomyocytes and satellite cells after transplantation into cryoinfarcted rat hearts, ii) slight superiority of satellite cells over neonatal cardiomyocytes in improving global left ventricular pump performance, and iii) no effect of both transplant procedures on diastolic dysfunction.

Targeting the pathway of GSK-3β/nerve growth factor to attenuate post-infarction arrhythmias by preconditioned adipose-derived stem cells

Adipose-derived stem cell (ADSC) transplantation is a promising new therapy to improve cardiac function after myocardial infarction. However, its low efficacy of transdifferentiation hampers its usefulness. Glycogen synthase kinase-3β (GSK-3β) signal has been shown to play a role in preconditioning-induced cardioprotection. We assessed whether n-butylidenephthalide (BP) primed ADSCs can attenuate arrhythmias by a GSK-3β-dependent pathway after myocardial infarction. Male Wistar rats after coronary ligation was randomly allocated to receive intramyocardial injection of vehicle, ADSCs, BP-preconditioned ADSCs, (BP+lithium)-preconditioned ADSCs, (BP+SB216763)-preconditioned ADSCs, and (BP+LY294002)-preconditioned ADSCs. ADSCs were primed for 16h before implantation. After 4weeks of implantation, ADSCs were retained in myocardium, reduced fibrosis and improved cardiac function. Sympathetic hyperinnervation was blunted after administering ADSCs, assessed by immunofluorescent analysis, and Western blotting and real-time quantitative RT-PCR of nerve growth factor. Arrhythmic scores during programmed stimulation in the ADSC-treated infarcted rats were significantly lower than vehicle. BP-preconditioned ADSCs had superior cardioprotection, greater ADSC engraftment and transdifferentiation, and antiarrhythmic effects compared with ADSCs alone. Simultaneously, BP increased the levels of phospho-Akt and down-regulated GSK-3β activity. The effects of BP against sympathetic hyperinnervation were blocked by LY294002, a PI3K inhibitor. Addition of either lithium or SB216763 did not have additional effects compared with BP alone. Compared with ADSC alone, BP-primed ADSC implantation improved stem cell engraftment and attenuated sympathetic hyperinnervation and arrhythmias through a PI3K/Akt/GSK-3β-dependent pathway, suggesting that a synergic action was achieved between BP pretreatment and ADSCs.

Externally Applied Static Magnetic Field Enhances Cardiac Retention and Functional Benefit of Magnetically Iron-Labeled Adipose-Derived Stem Cells in Infarcted Hearts

: Although adipose-derived stem cells (ASCs) hold the promise of effective therapy for myocardial infarction, low cardiac retention of implanted ASCs has hindered their therapeutic efficiency. We investigated whether an externally applied static magnetic field (SMF) enhances cardiac localization of "magnetic" cells and promotes heart function recovery when ASCs are preloaded with superparamagnetic iron oxide (SPIO) nanoparticles. The influence of SMF (0.1 Tesla) on the biological activities of SPIO-labeled ASCs (_SPIOASCs) was investigated first. Fifty-six female rats with myocardial infarction underwent intramyocardial injection of cell culture medium (CCM) or male _SPIOASCs with or without the subcutaneous implantable magnet (CCM-magnet or _SPIOASC-magnet). Four weeks later, endothelial differentiation, angiogenic cytokine secretion, angiogenesis, cardiomyocyte apoptosis, cell retention, and cardiac performance were examined. The 0.1-Tsela SMF did not adversely affect the viability, proliferation, angiogenic cytokine secretion, and DNA integrity of _SPIOASCs. The implanted _SPIOASCs could differentiate into endothelial cell, incorporate into newly formed vessels, and secrete multiple angiogenic cytokines. Four weeks after cell transplantation, the number of cardiac _SPIOASCs was significantly increased, vascular density was markedly enlarged, fewer apoptotic cardiomyocytes were present, and heart contractile function was substantially improved in the _SPIOASC-magnet treated rats in comparison with the _SPIOASC-treated rats. The _SPIOASCs could differentiate into endothelial cells, incorporate into vessels, promote angiogenesis, and inhibit ischemic cardiomyocyte apoptosis. An externally applied SMF offered a secure environment for biological properties of _SPIOASCs, increased the cardiac retention of implanted magnetic _SPIOASCs, and further enhanced heart function recovery after myocardial infarction.

SIGNIFICANCE

This pilot proof-of-concept study suggests that a 0.1-Tesla static magnetic field does not adversely affect the viability, proliferation, angiogenic cytokine secretion, or DNA integrity of the superparamagnetic iron oxide-labeled adipose-derived stem cells (_SPIOASCs). Implantation of adipose-derived stem cells promotes myocardial neovascularization and inhibits ischemic cardiomyocyte apoptosis through endothelial differentiation, incorporation into vessels, and paracrine factor secretion. An externally applied static magnetic field enhanced myocardial retention of intramyocardially injected "magnetic" _SPIOASCs and promoted cardiac function recovery after myocardial infarction. With further preclinical optimization, this approach may improve the outcome of current stem cell therapy for ischemic myocardial infarction.

Diazoxide protects L6 skeletal myoblasts from H2O2-induced apoptosis via the phosphatidylinositol-3 kinase/Akt pathway

OBJECTIVES AND DESIGN

Transplanted cell survival might greatly improve the therapeutic efficacy of cell therapy. Diazoxide (DZ), a highly selective mitochondrial ATP-sensitive potassium channel opener, is known to suppress cell apoptosis and protect cells in oxidative stressed ischemic environment. We explored the mechanisms involved in DZ pre-treatment-induced anti-apoptotic effect on L6 skeletal myoblast (SKM).

MATERIALS AND METHODS

L6 SKMs were divided into control group, H2O2 group, DZ + H2O2 group and DZ + LY + H2O2 group. Treatments of 400 μmol/L H2O2 for 24 h alone, or after 200 μmol/L DZ pre-treatment for 30 min, or after DZ and 50 μmol/L LY294002 co-administration for 30 min were performed. The cell apoptosis rates were assessed by flow cytometric analysis. The changes of mitochondrial membrane potential were determined by JC-1 mitochondrial staining. The activation of phosphatidylinositol-3 kinase (PI3K)/Akt, caspase-9 and caspase-3 was detected by western blot.

RESULTS

Compared with the H2O2 group, DZ pre-treatment protected cells from H2O2-induced damage, increased Akt phosphorylation, prevented mitochondrial membrane depolarization as well as the activation of caspase-9 and caspase-3 and decreased the cell apoptosis rate. However, the DZ-induced cytoprotective and anti-apoptosis effects were partly inhibited by co-administration of a PI3K inhibitor, LY294002.

CONCLUSIONS

These data suggest that DZ pre-treatment contributes to protection of L6 SKMs against apoptosis at least partly by activating the PI3K/Akt pathway and subsequently inhibiting the mitochondrial-mediated caspase-dependent apoptotic signalling pathway.

Application and Progress of Combined Mesenchymal Stem Cell Transplantation in the Treatment of Ischemic Cardiomyopathy

Treatment of ischemic cardiomyopathy caused by myocardial infarction (MI) using mesenchymal stem cell (MSC) transplantation is a widely researched field, with promising clinical application. However, the low survival rate of transplanted cells has a severe impact on treatment outcome. Currently, research is focused on investigating the strategy of combining genetic engineering, tissue engineering materials, and drug/hypoxia preconditioning to improve ischemic cardiomyopathy treatment outcome using MSC transplantation treatment (MSCTT). This review discusses the application and progress of these techniques.

Modulation of Alloimmune Responses by Interleukin-10 Prevents Rejection of Implanted Allogeneic Smooth Muscle Cells and Restores Postinfarction Ventricular Function

Interleukin-10 (IL-10) gene transduction into allogeneic smooth muscle cells (SMCs) was evaluated to improve the long-term benefits of allogeneic cell transplantation into infarcted myocardium. Allogeneic cells, including SMCs, have been demonstrated to restore cardiac function and repair the infarcted myocardium, but late rejection of the transplanted cells by the host immune system may reverse the benefits of cell therapy. In a rat myocardial infarction model, three groups of rats were injected with either unmodified autologous, unmodified allogeneic, or allogeneic + IL-10 SMCs into the infarct region. Three weeks later, most of the allogeneic cells were rejected, whereas autologous cells were engrafted in the myocardium. IL-10 gene transduction of the allogeneic SMCs significantly improved the cell survival. To understand the mechanism of this improved survival, we evaluated the host immune responses against the SMCs. Allogeneic SMCs expressing IL-10 decreased leukocyte-mediated cytotoxicity in coculture, decreased the number of cytotoxic CD8+ T-cells, and increased the number of CD4+CD25+ regulatory T-cells in vitro and in vivo. Furthermore, IL-10 prevented the production of antidonor antibodies by the recipients against the allogeneic SMCs. Transplantation of unmodified autologous SMCs, but not unmodified allogeneic SMCs, significantly improved fractional shortening and left ventricular dimensions compared to the media-injected control group. However, IL-10 gene-enhanced allogeneic SMCs improved ventricular function, increased wall thickness, and decreased scar length in association with their enhanced survival. We conclude that IL-10 gene-enhanced cell therapy with allogeneic SMCs prevents detrimental alloimmune responses in the recipient, thereby increasing the survival of transplanted allogeneic SMCs and more effectively restoring cardiac function.

Comparison of Magnetic Intensities for Mesenchymal Stem Cell Targeting Therapy on Ischemic Myocardial Repair: High Magnetic Intensity Improves Cell Retention but Has no Additional Functional Benefit

Magnetic targeting has the potential to enhance the therapeutic effects of stem cells through increasing retention of transplanted cells. To investigate the effects of magnetic targeting intensities on cell transplantation, we performed different magnetic intensities for mesenchymal stem cell (MSC)-targeting therapy in a rat model of ischemia/reperfusion. Rat MSCs labeled with superparamagnetic oxide nanoparticles (SPIOs) were injected into the left ventricular (LV) cavity of rats during a brief aorta and pulmonary artery occlusion. The 0.15 Tesla (T), 0.3 T, and 0.6 T magnets were placed 0∼1 mm above the injured myocardium during and after the injection of 1 × 10(6) MSCs. Fluorescence imaging and quantitative PCR revealed that magnetic targeting enhanced cell retention in the heart at 24 h in a magnetic field strength-dependent manner. Compared with the 0 T group, three magnetic targeting groups enhanced varying cell engraftment at 3 weeks, at which time LV remodeling was maximally attenuated, and the therapeutic benefit (LV ejection fraction) was also highest in the 0.3 T groups. Interestingly, due to the low MSC engraftment resulting from microvascular embolisms, the 0.6 T group failed to translate into additional therapeutic outcomes, though it had the highest cell retention. Magnetic targeting enhances cell retention in a magnetic field strength-dependent manner. However, too high of a magnetic intensity may result in microembolization and consequently undermine the functional benefits of cell transplantation.

The rejuvenation of aged stem cells for cardiac repair

Rejuvenation is one of the greatest challenges of modern science. Aging affects every tissue and organ in the body, leading to a deterioration of normal function and inhibition of repair mechanisms. Cell therapy has received much attention for its potential to regenerate organs, but in the context of cardiac repair, the initial clinical trials in aged patients did not replicate the dramatic benefits recorded in preclinical studies with young animals. The benefits of autologous cell therapy are reduced in the elderly, the largest target group for regenerative medicine. Adult stem cell functionality decreases with age which impairs tissue regeneration. In this review we discuss the age-related changes in stem cell function, with particular attention to stem cell therapy in heart disease. We also focus on possible mechanisms of adult stem cell aging and targets for rejuvenation strategies to reverse the aging process. We provide useful insights on how to apply this knowledge to advance cellular therapies for heart disease.

Sca-1+ cardiac progenitor cell therapy with cells overexpressing integrin-linked kinase improves cardiac function after myocardial infarction

BACKGROUND

This study was to investigate the effect of integrin-linked kinase (ILK) on the transplantation efficiency of stem cell antigen-1-positive cardiac progenitor cells (Sca-1 CPCs) in a mouse myocardial infarction (MI) model.

METHODS

Sca-1 CPCs were isolated from C57/BL6 mice heart tissues and genetically modified with adenovirus vector containing green fluorescent protein (GFP)/ILK or GFP. Cell viability, migration, DNA synthesis, proliferation, and apoptosis were assessed in vitro. Immediately after MI, treated animals received 5×10 GFP-CPC or ILK-CPC transplantation into the peri-infarct myocardium. Cardiac function, exercise ability, cardiac morphology, angiogenesis, cardiomyocyte apoptosis, as well as ILK-related protein expression were measured. Acute and long-term cell survival after cell transplantation was assessed.

RESULTS

Overexpression of ILK increased the viability, migration, DNA synthesis, proliferation, and survival of Sca-1 CPCs in vitro. Protein expression of phosphorylated Akt and cyclin D1 were up-regulated. In our in vivo experiment, more transplanted cells were found in the peri-infarct myocardium in ILK-CPC group 3 days after cell transplantation, but there was no difference between the two groups 4 weeks later. ILK-CPC group showed reduced infarct size 7 days after cell transplantation. Long-term observation showed improved cardiac function indicated by higher percent fractional shortening and lower left ventricular end systolic diameter/left ventricular end diastolic diameter, better exercise ability, increased angiogenesis, decreased fibrosis and apoptosis, as well as up-regulation of ILK, Cdc42, and Aurora B protein expression in ILK-CPC group 4 weeks after cell transplantation.

CONCLUSIONS

ILK-overexpressed Sca-1 CPCs showed improved therapeutic efficacy in MI.

Noninvasive in vivo tracking of mesenchymal stem cells and evaluation of cell therapeutic effects in a murine model using a clinical 3.0 T MRI

Cardiac cell therapy with mesenchymal stem cells (MSCs) represents a promising treatment approach for end-stage heart failure. However, little is known about the underlying mechanisms and the fate of the transplanted cells. The objective of the presented work is to determine the feasibility of magnetic resonance imaging (MRI) and in vivo monitoring after transplantation into infarcted mouse hearts using a clinical 3.0 T MRI device. The labeling procedure of bone marrow-derived MSCs with micron-sized paramagnetic iron oxide particles (MPIOs) did not affect the viability of the cells and their cell type-defining properties when compared to unlabeled cells. Using a clinical 3.0 T MRI scanner equipped with a dedicated small animal solenoid coil, 10(5) labeled MSCs could be detected and localized in the mouse hearts for up to 4 weeks after intramyocardial transplantation. Weekly ECG-gated scans using T1-weighted sequences were performed, and left ventricular function was assessed. Histological analysis of hearts confirmed the survival of labeled MSCs in the target area up to 4 weeks after transplantation. In conclusion, in vivo tracking of labeled MSCs using a clinical 3.0 T MRI scanner is feasible. In combination with assessment of heart function, this technology allows the monitoring of the therapeutic efficacy of regenerative therapies in a small animal model.

AG490 improves the survival of human myoblasts in vitro and in vivo

Cell therapies consist in transplanting healthy cells into a disabled tissue with the goal to repopulate it and restore its function at least partially. In muscular diseases, most of the time, myoblasts are chosen for their expansion capacity in culture. Nevertheless, cell transplantation has limitations, among them, death of the transplanted cells, during the days following the graft. One possibility to counteract this problem is to enhance the proliferation of the transplanted myoblasts before their fusion with the existing muscle fibers. AG490 is a specific inhibitor of janus tyrosine kinase 2 (JAK2). The hypothesis is to block myoblast differentiation with AG490, thus permitting their proliferation. The inhibition of myoblast fusion by AG490 was confirmed in this study by gene expression and with a myosin heavy chain staining (MyHC). Moreover, cell survival was estimated by flow cytometry. AG490 was found to protect myoblasts in vitro from apoptosis induced by H(2)O(2) or by preventing attachment of cells to their substrate. Finally, in an in vivo model of muscle regeneration, when AG490 was coinjected with the myoblasts their survival was increased by 45% at 5 days after their transplantation.

Extracellular GC-rich DNA activates TLR9- and NF-kB-dependent signaling pathways in human adipose-derived mesenchymal stem cells (haMSCs)

INTRODUCTION

The content of GC-rich ribosomal repeats (rDNA) in cell-free DNA (cfDNA) of patients with various diseases is several times higher as compared with genomic DNA (gDNA) and cfDNA of healthy donors. rDNA may act as Toll-like receptor 9 (TLR9) ligands and affect human adipose-derived mesenchymal stem cells (haMSCs). Here we explore effects of human cfDNAs and model rDNA fragments on cultured haMSCs.

AREAS COVERED

Both cfDNAs and cloned rDNA stimulate expression of TLR9 (qRT-PCR). Treatment with cloned rDNA leads to an increase in the number of TLR9(+) cells (FACS), expression levels for both TLR9 and Myd88, the translocation of nuclear factor-kappa B to the nuclei and up-regulation of TNFα and IL-10 cytokines (ELISA). As shown by an analysis of γH2AX-foci and MTT test, the preconditioning of haMSCs with cloned rDNA fragment increases the resistance of these cells to irradiation at 2Gy, while the treatments with control gDNA did not stimulate either TLR9- or NF-kB-dependent signaling pathways.

EXPERT OPINION

GC-rich sequences present in cfDNA stimulate endogenous stems cells when body is exposed to adverse conditions. GC-rich fragments of human DNA may be used for preconditioning of therapeutic MSCs aiming at an increase in their survival in the ailing body.

Activation of IL-11/STAT3 pathway in preconditioned human skeletal myoblasts blocks apoptotic cascade under oxidant stress

AIM

To determine whether our novel approach of diazoxide-induced stem cell preconditioning might be extrapolated to human skeletal myoblasts to support their survival under lethal oxidant stress.

METHODS & RESULTS

Using an in vitro model of H(2)O(2) treatment of human skeletal myoblasts, we report the ability of diazoxide-preconditioned human skeletal myoblasts to express cytokines and growth factors, which act in an autocrine and paracrine fashion to promote their own survival. Preconditioning of skeletal myoblasts was cytoprotective and significantly reduced their apoptotic index (p < 0.05). IL-11 gene and protein expression was significantly increased in preconditioned skeletal myoblasts. Transfection of skeletal myoblasts with IL-11-specific siRNA incurred their death under oxidant stress. The cytoprotective effect of diazoxide preconditioning was blocked by Erk1/2 inhibitor PD98059 (20-100 µM), which abrogated STAT-3 phosphorylation, thus confirming a possible involvement of Erk1/2/STAT3 signaling downstream of IL-11 in cell survival. We also investigated the time course of subcellular changes and signaling pathway of skeletal myoblasts apoptosis under oxidant stress before and after preconditioning. Apoptosis was induced in skeletal myoblasts with 100-500 µM H(2)O(2) for time points ranging from 1 to 24 h. Release of lactate dehydrogenase, disruption of the mitochondrial membrane potential and cytochrome-c translocation into cytoplasm were the earliest signs of apoptosis. Total Akt protein remained unchanged whereas marked reduction in pAkt was observed in the native skeletal myoblasts. Terminal dUTP nick end-labeling and annexin-V positivity were significantly increased after 4 h. Ultra-structure studies showed condensed chromatin, shriveled nuclei and swollen mitochondria.

CONCLUSION

These data suggest that skeletal myoblasts undergo apoptosis under oxidant stress in a time-dependent manner and preconditioning of skeletal myoblasts significantly prevented their apoptosis via IL-11/STAT3 signaling.

Regenerating functional heart tissue for myocardial repair

Heart disease is one of the leading causes of death worldwide and the number of patients with the disease is likely to grow with the continual decline in health for most of the developed world. Heart transplantation is one of the only treatment options for heart failure due to an acute myocardial infarction, but limited donor supply and organ rejection limit its widespread use. Cellular cardiomyoplasty, or cellular implantation, combined with various tissue-engineering methods aims to regenerate functional heart tissue. This review highlights the numerous cell sources that have been used to regenerate the heart as well as cover the wide range of tissue-engineering strategies that have been devised to optimize the delivery of these cells. It will probably be a long time before an effective regenerative therapy can make a serious impact at the bedside.

Functional regeneration of ischemic myocardium by transplanted cells overexpressing stromal cell-derived factor-1 (SDF-1): intramyocardial injection versus scaffold-based application

OBJECTIVE

Stromal cell-derived factor-1 (SDF-1) is a potent chemotaxin. Increased SDF-1 levels can be found in ischemic myocardium and might protect against ischemia-reperfusion injury. We hypothesized that transplantation of stem cells overexpressing SDF-1 might improve cardiac function after myocardial infarction (MI). We compared intramyocardial injection with a scaffold-based application of SDF-1-transfected cells.

METHODS

Skeletal myoblasts (SkMs) were isolated and expanded from newborn Lewis rats. Cells were transfected with pcDNA3-huSDF-1 and seeded on polyurethane (PU) scaffolds or diluted in medium for cell injection. Two weeks after myocardial infarction, seeded scaffolds were implanted epicardially into rats (group: PU-SDF-1-SkM) or the injection solution was applied intramyocardially (Inj-SDF-1-SkM). Additional groups were treated with non-transfected myoblasts either by injection (Inj-SkM) or by scaffold-based application (PU-SkM) or received a sham operation (Sham). Before this intervention and 6 weeks later, hemodynamic parameters were measured. Infarction size and neovascularization were assessed by histology at study end.

RESULTS

In sham animals, we detected a clear decrease in systolic function from intervention to study end. In group Inj-SkM and PU-SkM, all hemodynamic parameters that were assessed remained unchanged during observation time. Systolic function as measured by dP/dt(max) and SB-Emax was significantly improved in groups Inj-SDF-1-SkM and PU-SDF-1-SkM at study end without a difference between the two SDF-1 groups. Diastolic function measured by post-interventional dP/dt(min) was also increased in group Inj-SDF-1-SkM but not in PU-SDF-1-SkM. Histological analysis revealed a reduced infarction size in all treatment groups at study end but enhanced neovascularization was not observable.

CONCLUSIONS

Transplantation of myoblasts overexpressing SDF-1 improves cardiac function after MI. The restoration of hemodynamic parameters is accompanied by a reduction in infarction size. This reverse remodeling capacity is independent of a scaffold-based application of the SDF-1-transfected cells.

Preconditioning approach in stem cell therapy for the treatment of infarcted heart

Nearly two decades of research in regenerative medicine have been focused on the development of stem cells as a therapeutic option for treatment of the ischemic heart. Given the ability of stem cells to regenerate the damaged tissue, stem-cell-based therapy is an ideal approach for cardiovascular disorders. Preclinical studies in experimental animal models and clinical trials to determine the safety and efficacy of stem cell therapy have produced encouraging results that promise angiomyogenic repair of the ischemically damaged heart. Despite these promising results, stem cell therapy is still confronted with issues ranging from uncertainty about the as-yet-undetermined "ideal" donor cell type to the nonoptimized cell delivery strategies to harness optimal clinical benefits. Moreover, these lacunae have significantly hampered the progress of the heart cell therapy approach from bench to bedside for routine clinical applications. Massive death of donor cells in the infarcted myocardium during acute phase postengraftment is one of the areas of prime concern, which immensely lowers the efficacy of the procedure. An overview of the published data relevant to stem cell therapy is provided here and the various strategies that have been adopted to develop and optimize the protocols to enhance donor stem cell survival posttransplantation are discussed, with special focus on the preconditioning approach.

A double-blind, randomized, controlled, multicenter study to assess the safety and cardiovascular effects of skeletal myoblast implantation by catheter delivery in patients with chronic heart failure after myocardial infarction

BACKGROUND

We sought to determine the safety and preliminary efficacy of transcatheter intramyocardial administration of myoblasts in patients with heart failure (HF).

METHODS

MARVEL is a randomized placebo-controlled trial of image-guided, catheter-based intramyocardial injection of placebo or myoblasts (400 or 800 million) in patients with class II to IV HF and ejection fraction <35%. Primary end points were frequency of serious adverse events (safety) and changes in 6-minute walk test and Minnesota Living With HF score (efficacy). Of 330 patients intended for enrollment, 23 were randomized (MARVEL-1) before stopping the study for financial reasons.

RESULTS

At 6 months, similar numbers of events occurred in each group: 8 (placebo), 7 (low dose), and 8 (high dose), without deaths. Ventricular tachycardia responsive to amiodarone was more frequent in myoblast-treated patients: 1 (placebo), 3 (low dose), and 4 (high dose). A trend toward improvement in functional capacity was noted in myoblast-treated groups (Δ6-minute walk test of -3.6 vs +95.6 vs +85.5 m [placebo vs low dose vs high dose; P = .50]) without significant changes in Minnesota Living With HF scores.

CONCLUSIONS

In HF patients with chronic postinfarction cardiomyopathy, transcatheter administration of myoblasts in doses of 400 to 800 million cells is feasible and may lead to important clinical benefits. Ventricular tachycardia may be provoked by myoblast injection but appears to be a transient and treatable problem. A large-scale outcome trial of myoblast administration in HF patients with postinfarction cardiomyopathy is feasible and warranted.

Mesenchymal stem cell delivery into rat infarcted myocardium using a porous polysaccharide-based scaffold: a quantitative comparison with endocardial injection

The use of mesenchymal stem cells (MSCs) for tissue regeneration is often hampered by modest engraftment in host tissue. This study was designed to quantitatively compare MSCs engraftment rates after delivery using a polysaccharide-based porous scaffold or endocardial (EC) injection in a rat myocardial infarction model. Cellular engraftment was measured by quantitative reverse transcription-polymerase chain reaction using MSCs previously transduced with a lentiviral vector that expresses green fluorescent protein (GFP). The use of a scaffold promoted local cellular engraftment and survival. The number of residual GFP(+) cells was greater with the scaffold than after EC injection (9.7% vs. 5.1% at 1 month and 16.3% vs. 6.1% at 2 months, respectively [n=5]). This concurred with a significant increase in mRNA vascular endothelial growth factor level in the scaffold group (p<0.05). Clusters of GFP+ cells were detected in the peri-infarct area, mainly phenotypically consistent with immature MSCs. Functional assessment by echocardiography at 2 months postinfarct also showed a trend toward a lower left ventricular dilatation and a reduced fibrosis in the scaffold group in comparison to direct injection group (n=10). These findings demonstrate that using a porous biodegradable scaffold is a promising method to improve cell delivery and engraftment into damaged myocardium.

Role of stem cells in cardiovascular biology

This review article addresses the controversy as to whether the adult heart possesses an intrinsic growth reserve. If myocyte renewal takes place in healthy and diseased organs, the reconstitution of the damaged tissue lost upon pathological insults might be achieved by enhancing a natural occurring process. Evidence in support of the old and new view of cardiac biology is critically discussed in an attempt to understand whether the heart is a static or dynamic organ. According to the traditional concept, the heart exerts its function until death of the organism with the same or lesser number of cells that are present at birth. This paradigm was challenged by documentation of the cell cycle activation and nuclear and cellular division in a subset of myocytes. These observations raised the important question of the origin of replicating myocytes. Several theories have been proposed and are presented in this review article. Newly formed myocytes may derive from a pre-existing pool of cells that has maintained the ability to divide. Alternatively, myocytes may be generated by activation and commitment of resident cardiac stem cells or by migration of progenitor cells from distant organs. In all cases, parenchymal cell turnover throughout lifespan results in a heterogeneous population consisting of young, adult, and senescent myocytes. With time, accumulation of old myocytes has detrimental effects on cardiac performance and may cause the development of an aging myopathy.

Repeated intracoronary infusion of peripheral blood stem cells with G-CSF in patients with refractory ischemic heart failure--a pilot study

BACKGROUND

Recent investigations have suggested the clinical efficacy of granulocyte colony-stimulating factor (G-CSF) infusion alone or in combination with a single dose delivery of peripheral blood stem cells (PBSC) infusion in patients with myocardial infarction (MI) and congestive heart failure (HF). The current study tested the feasibility and effect of repeated intracoronary infusions PBSC and the mobilization of G-CSF in patients with refractory HF after MI.

METHODS AND RESULTS

Patients with recent large MI and a lower left ventricular ejection fraction (LVEF) were enrolled into one of the following 3 groups: Group R (n=15) received repeated intracoronary infusion of PBSC and one-dose of G-CSF; Group S (n=15) received a single infusion of PBSC and a G-CSF dose; and Group C (n=15) received neither PBSC nor a G-CSF dose. Cardiac performance was evaluated by echocardiography and single photon-emission computed tomography (SPECT). All the patients underwent 12-month follow-up. LVEF in Group R (47.00±4.90%) was significantly higher than that in Group S (44.40±3.87%, P<0.01) and Group C (40.80±3.41%, P<0.01). Similarly, the improvement of myocardial perfusion assessed by SPECT in Group R was more than that in Group S (P=0.012) and Group C (P<0.01). Neither death nor new MI occurred.

CONCLUSIONS

Repeated intracoronary infusions of PBSC plus mobilization of G-CSF might be an optional effective strategy for treating patients with refractory HF after recent large MI.

One-year follow-up of feasibility and safety of the first U.S., randomized, controlled study using 3-dimensional guided catheter-based delivery of autologous skeletal myoblasts for ischemic cardiomyopathy (CAuSMIC study)

OBJECTIVES

The aim of this study was to test safety and feasibility of myoblast transplantation with the Biosense-NOGA (Diamond Bar, California) 3-dimensional-guided endomyocardial delivery system.

BACKGROUND

Previous Phase-1 trials showed feasibility of epicardial injection of myoblasts. However, catheter-based delivery has several advantages: it can be applied on high-risk patients, the procedure can be repeated, and it is associated with less morbidity and mortality.

METHODS

Twenty-three subjects, with previous myocardial infarction and heart failure, New York Heart Association (NYHA) functional class II to IV, were enrolled, 11 control and 12 treatment subjects. To assess safety, physical exam, electrocardiogram, continuous rhythm monitoring, quality of life assessments, and heart function were evaluated at baseline and follow-up until 1 year.

RESULTS

There was favorable safety: no difference between groups in arrhythmias, and no deaths. Treated subjects showed sustained improvements in NYHA and Minnesota Living with Heart Failure Questionnaire (MLHFQ) compared with control subjects (NYHA, -1.0 point in treatment vs. +0.3 point in control group, p < 0.0004; MLHFQ, -14 point in treatment vs. +1 point in the control group, p = 0.004). Blinded core laboratory echocardiography evaluations showed sustained reductions in the treatment versus control in end diastolic diameter (-0.03 cm vs. +0.05 cm, p = 0.07) and end systolic diameter (-0.05 cm vs. +0.1 cm, p = 0.07). Finally, NOGA voltage mapping demonstrated improved voltage measurements (+1.0 mV, p = 0.008).

CONCLUSIONS

This trial of myoblast transplantation via catheter into heart failure patients demonstrated safety and feasibility. Treated patients showed improvement in NYHA, MLHFQ, ventricular viability, and evidence of reverse ventricular remodeling. These data demonstrate positive safety outcomes and warrant initiation of larger phase 2, double-blind, placebo-controlled clinical trials.

Implantation of mouse embryonic stem cell-derived cardiac progenitor cells preserves function of infarcted murine hearts

Stem cell transplantation holds great promise for the treatment of myocardial infarction injury. We recently described the embryonic stem cell-derived cardiac progenitor cells (CPCs) capable of differentiating into cardiomyocytes, vascular endothelium, and smooth muscle. In this study, we hypothesized that transplanted CPCs will preserve function of the infarcted heart by participating in both muscle replacement and neovascularization. Differentiated CPCs formed functional electromechanical junctions with cardiomyocytes in vitro and conducted action potentials over cm-scale distances. When transplanted into infarcted mouse hearts, CPCs engrafted long-term in the infarct zone and surrounding myocardium without causing teratomas or arrhythmias. The grafted cells differentiated into cross-striated cardiomyocytes forming gap junctions with the host cells, while also contributing to neovascularization. Serial echocardiography and pressure-volume catheterization demonstrated attenuated ventricular dilatation and preserved left ventricular fractional shortening, systolic and diastolic function. Our results demonstrate that CPCs can engraft, differentiate, and preserve the functional output of the infarcted heart.

Aging impairs the angiogenic response to ischemic injury and the activity of implanted cells: combined consequences for cell therapy in older recipients

OBJECTIVE

Cell therapy has received much attention for its potential to regenerate ischemic organs, but initial clinical trials in aged patients did not replicate the dramatic benefits recorded in preclinical studies with young animals. This study was designed to improve our understanding of age-related changes in the response to ischemic injury and the regenerative capacity of implanted cells in the context of cell therapy for older recipients.

METHODS AND RESULTS

Restoration of regional perfusion after hind limb femoral artery ligation was impaired (P < .05) in old (vs young) rats, reflecting approximately 50% reductions in circulating endothelial progenitor cells and the release of vascular endothelial growth factor/basic fibroblast growth factor. Bone marrow stromal cells from young or old donors implanted into the ischemic hind limbs of young or old rats restored regional perfusion. Specifically, we documented significantly greater (P < .05) angiogenic potential in young (vs old) donor cells when recipient age was controlled and greater (P < .05) regenerative responses in young (vs old) recipients when donor cell age was controlled. Contributing to these differences were significantly greater survival in young (vs old) donor cells (in vitro and after implantation) and about 2-fold more production of vascular endothelial growth factor/basic fibroblast growth factor and mobilization of endogenous endothelial progenitor cells in young (vs old) rats in response to ischemia.

CONCLUSIONS

The outcome of cell therapy in older recipients is determined by a combination of age effects on the donor cells and on the recipients' endogenous responses. Donor cell age and recipient age are equally important contributors to the outcome of cell therapy; thus, novel biointerventions will need to target both components of the process.

Repairing skeletal muscle: regenerative potential of skeletal muscle stem cells

Skeletal muscle damaged by injury or by degenerative diseases such as muscular dystrophy is able to regenerate new muscle fibers. Regeneration mainly depends upon satellite cells, myogenic progenitors localized between the basal lamina and the muscle fiber membrane. However, other cell types outside the basal lamina, such as pericytes, also have myogenic potency. Here, we discuss the main properties of satellite cells and other myogenic progenitors as well as recent efforts to obtain myogenic cells from pluripotent stem cells for patient-tailored cell therapy. Clinical trials utilizing these cells to treat muscular dystrophies, heart failure, and stress urinary incontinence are also briefly outlined.

Scaffold-free human cardiac tissue patch created from embryonic stem cells

Progress in cardiac tissue engineering has been limited by (1) unfavorable cell and host responses to biomaterial scaffolds, (2) lack of suitable human cardiomyocyte sources, and (3) lack of fabrication techniques for scalable production of engineered tissue constructs. Here we report a novel and scalable method to generate scaffold-free human cardiac tissue patches. Human embryonic stem cells were differentiated to cardiomyocytes using activin A and BMP4 and placed into suspension on a rotating orbital shaker. Cells aggregated to form macroscopic disc-shaped patches of beating tissue after 2 days. Patch diameter was directly proportional to input cell number (approximately 11 mm with 12 million cells), and patches were 300-600 mum thick. Cardiomyocytes were concentrated around the patch edges and exhibited increased purity and maturation with time, comprising approximately 80% of total cells after 11 days. Noncardiac cell elements, primarily epithelium, were present at day 2 but were diminished markedly at later time points. Cardiomyocyte proliferation occurred throughout the patches at day 2 but declined by day 8. Patches exhibited automaticity and synchronous calcium transients, indicating electromechanical coupling. These novel scaffold-free human myocardial patches address critical challenges related to human cell sourcing and tissue fabrication that previously inhibited progress in cardiac tissue engineering.

Repeated implantation of skeletal myoblast in a swine model of chronic myocardial infarction

AIMS

Although transplantation of skeletal myoblast (SkM) in models of chronic myocardial infarction (MI) induces an improvement in cardiac function, the limited engraftment remains a major limitation. We analyse in a pre-clinical model whether the sequential transplantation of autologous SkM by percutaneous delivery was associated with increased cell engraftment and functional benefit.

METHODS AND RESULTS

Chronically infarcted Goettingen minipigs (n = 20) were divided in four groups that received either media control or one, two, or three doses of SkM (mean of 329.6 x 10(6) cells per dose) at intervals of 6 weeks and were followed for a total of 7 months. At the time of sacrifice, cardiac function was significantly better in animals treated with SkM in comparison with the control group. A significantly greater increase in the DeltaLVEF was detected in animals that received three doses vs. a single dose of SkM. A correlation between the total number of transplanted cells and the improvement in LVEF and DeltaLVEF was found (P < 0.05). Skeletal myoblast transplant was associated with an increase in tissue vasculogenesis and decreased fibrosis (collagen vascular fraction) and these effects were greater in animals receiving three doses of cells.

CONCLUSION

Repeated injection of SkM in a model of chronic MI is feasible and safe and induces a significant improvement in cardiac function.

Sca-1+ stem cell survival and engraftment in the infarcted heart: dual role for preconditioning-induced connexin-43

BACKGROUND

We report that elevated connexin-43 (Cx-43) in stem cells preconditioned with insulin-like growth factor-1 (IGF-1) is cytoprotective and reprograms the cells for cardiomyogenic differentiation.

METHODS AND RESULTS

Sca-1+ cells were preconditioned with 100 nmol/L IGF-1 for 30 minutes followed by 8 hours of oxygen glucose deprivation to assess the cytoprotective effects of preconditioning. LDH release assay, cytochrome c release, and mitochondrial membrane potential assay showed improved survival of preconditioned Sca-1+ cells under oxygen glucose deprivation compared with nonpreconditioned Sca-1+ cells via PI3K/Akt-dependent caspase-3 downregulation. We observed PI3K/Akt-dependent upregulation of cardiac-specific markers including MEF-2c (2.5-fold), GATA4 (3.1-fold), and Cx-43 (3.5-fold). Cx-43 inhibition with specific RNA interference reduced cell survival under oxygen glucose deprivation and after transplantation. In vivo studies were performed in a female rat model of acute myocardial infarction (n=78). Animals were grouped to receive intramyocardially 70 microL Dulbecco modified Eagles medium without cells (group 1) or containing male 1 x 10(6) nonpreconditioned Sca-1+ cells (group 2) or preconditioned Sca-1+ (group 3) cells labeled with PKH26. Survival of the preconditioned Sca-1+ cells was 5.5-fold higher in group 3 compared with group 2 at 7 days after transplantation. Confocal imaging after actinin and Cx-43 specific immunostaining showed extensive engraftment and myogenic differentiation of preconditioned Sca-1+ cells. Compared with group 2, group 3 showed increased blood vessel density (22.3+/-1.7 per microscopic field; P<0.0001) and attenuated infarction size (23.3+/-3.6%; P=0.002). Heart function indices including ejection fraction (56.2+/-3.5; P=0.029) and fractional shortening (24.3+/-2.1; P=0.03) were improved in group 3 compared with group 2.

CONCLUSIONS

Preconditioning with IGF-1 reprograms Sca-1+ for prosurvival signaling and cardiomyogenic differentiation with an important role for Cx-43 in this process.

Dose-response relationship of mesenchymal stem cell transplantation and functional regeneration after severe skeletal muscle injury in rats

Various therapeutic strategies that aim to influence clinical outcome after severe skeletal muscle trauma have been considered. One such method, the local transplantation of stem cells, has been shown to improve tissue regeneration. The number of cells required for successful regeneration, however, remains unclear. The aim of this study was therefore to examine the correlation between the number of transplanted bone marrow-derived mesenchymal stem cells (MSCs) and the resulting muscle function. One week after inducing an open crush trauma in 34 female Sprague Dawley rats, increasing quantities of autologous MSCs (0.1 x 10(6), 1 x 10(6), 2.5 x 10(6), and 10 x 10(6) cells) or saline solution (control group) were transplanted into the left soleus muscle of the rat hind limb. At 4 weeks posttrauma, the outcome was assessed by measuring muscle contraction forces following an indirect fast twitch and tetanic stimulation. A logarithmic dose-response relationship was observed for both maximum twitch and tetanic contraction forces (R(2) = 0.9 for fast twitch [p = 0.004]; R(2) = 0.87 [p = 0.002] for tetanic contraction). The transplantation of 10 x 10(6) cells resulted in the most pronounced improvement of muscle force. MSC therapy represents a promising new tool for the treatment of skeletal muscle trauma that shows potential for aiding in the prevention of severe functional deficiencies. The logarithmic dose-response relationship demonstrates the association between the number of transplanted cells and the resulting muscle forces, as well as the amount of MSCs required for promoting muscular regeneration.

Cell-based therapy for heart failure: skeletal myoblasts

Satellite cells are committed precursor cells residing in the skeletal muscle. These cells provide an almost unlimited regeneration potential to the muscle, contrary to the heart, which, although proved to contain cardiac stem cells, possesses a very limited ability for self-renewal. The idea that myoblasts (satellite cell progenies) may repopulate postinfarction scar occurred around the mid-1990s. Encouraging results of preclinical studies triggered extensive research, which led to the onset of clinical trials. These trials have shown that autologous skeletal myoblast transplantation to cure heart failure is feasible and relatively safe (observed incidences of arrhythmia). Because most of the initial studies on myoblast application into postischemic heart have been carried out as an adjunct to routine surgical procedures, the true clinical outcome of such therapy in regard to cell implantation is blurred and requires to be elucidated. The mechanism by which implantation of skeletal myoblast may improve heart function is not clear, especially in the light of inability of these cells to couple electromechanically with a host myocardium. Successful myoblast therapy depends on a number of factors, including: delivery to the target tissue, long-term survival, efficacious engraftment, differentiation into cardiomyocytes, and integration into the new, unique microenvironment. All these steps constitute a potential goal for cell manipulation aiming to improve the overall outcome of such therapy. Precise understanding of the mechanism by which cells improve cardiac function is essential in giving the sensible direction of further research.

Allogeneic mesenchymal precursor cell therapy to limit remodeling after myocardial infarction: the effect of cell dosage

BACKGROUND

This experiment assessed the dose-dependent effect of a unique allogeneic STRO-3-positive mesenchymal precursor cell (MPC) on postinfarction left ventricular (LV) remodeling. The MPCs were administered in a manner that would simulate an off-the-self, early postinfarction, preventative approach to cardiac cell therapy in a sheep transmural myocardial infarct (MI) model.

METHODS

Allogeneic MPCs were isolated from male crossbred sheep. Forty-six female sheep underwent coronary ligation to produce a transmural LV anteroapical infarction. One hour after infarction, the borderzone myocardium received an injection of 25, 75, 225, or 450 x 10(6) MPCs, or cell medium. Echocardiography was performed at 4 and 8 weeks after MI to quantify LV end-diastolic (LVEDV) and end-systolic volumes (LVESV), ejection fraction (EF), and infarct expansion. CD31 and smooth muscle actin (SMA) immunohistochemical staining was performed on infarct and borderzone specimens to quantify vascular density.

RESULTS

Compared with controls, low-dose (25 and 75 x 10(6) cells) MPC treatment significantly attenuated infarct expansion and increases in LVEDV and LVESV. EF was improved at all cell doses. CD31 and SMA immunohistochemical staining demonstrated increased vascular density in the borderzone only at the lower cell doses. There was no evidence of myocardial regeneration within the infarct.

CONCLUSION

Allogeneic STRO-3 positive MPCs attenuate the remodeling response to transmural MI in a clinically relevant large-animal model. This effect is associated with vasculogenesis and arteriogenesis within the borderzone and infarct and is most pronounced at lower cell doses.

Allogeneic mesenchymal precursor cell therapy to limit remodeling after myocardial infarction: the effect of cell dosage

BACKGROUND

This experiment assessed the dose-dependent effect of a unique allogeneic STRO-3-positive mesenchymal precursor cell (MPC) on postinfarction left ventricular (LV) remodeling. The MPCs were administered in a manner that would simulate an off-the-self, early postinfarction, preventative approach to cardiac cell therapy in a sheep transmural myocardial infarct (MI) model.

METHODS

Allogeneic MPCs were isolated from male crossbred sheep. Forty-six female sheep underwent coronary ligation to produce a transmural LV anteroapical infarction. One hour after infarction, the borderzone myocardium received an injection of 25, 75, 225, or 450 x 10(6) MPCs, or cell medium. Echocardiography was performed at 4 and 8 weeks after MI to quantify LV end-diastolic (LVEDV) and end-systolic volumes (LVESV), ejection fraction (EF), and infarct expansion. CD31 and smooth muscle actin (SMA) immunohistochemical staining was performed on infarct and borderzone specimens to quantify vascular density.

RESULTS

Compared with controls, low-dose (25 and 75 x 10(6) cells) MPC treatment significantly attenuated infarct expansion and increases in LVEDV and LVESV. EF was improved at all cell doses. CD31 and SMA immunohistochemical staining demonstrated increased vascular density in the borderzone only at the lower cell doses. There was no evidence of myocardial regeneration within the infarct.

CONCLUSION

Allogeneic STRO-3 positive MPCs attenuate the remodeling response to transmural MI in a clinically relevant large-animal model. This effect is associated with vasculogenesis and arteriogenesis within the borderzone and infarct and is most pronounced at lower cell doses.

Adult progenitor cell transplantation influences contractile performance and calcium handling of recipient cardiomyocytes

Adult progenitor cell transplantation has been proposed for the treatment of heart failure, but the mechanisms effecting functional improvements remain unknown. The aim of this study was to test the hypothesis that, in failing hearts treated with cell transplantation, the mechanical properties and excitation-contraction coupling of recipient cardiomyocytes are altered. Adult rats underwent coronary artery ligation, leading to myocardial infarction and chronic heart failure. After 3 wk, they received intramyocardial injections of either 10(7) green fluorescence protein (GFP)-positive bone marrow mononuclear cells or 5 x 10(6) GFP-positive skeletal myoblasts. Four weeks after injection, both cell types increased ejection fraction and reduced cardiomyocyte size. The contractility of isolated GFP-negative cardiomyocytes was monitored by sarcomere shortening assessment, Ca(2+) handling by indo-1 and fluo-4 fluorescence, and electrophysiology by patch-clamping techniques. Injection of either bone marrow cells or skeletal myoblasts normalized the impaired contractile performance and the prolonged time to peak of the Ca(2+) transient observed in failing cardiomyocytes. The smaller and slower L-type Ca(2+) current observed in heart failure normalized after skeletal myoblast, but not bone marrow cell, transplantation. Measurement of Ca(2+) sparks suggested a normalization of sarcoplasmic reticulum Ca(2+) leak after skeletal myoblast transplantation. The increased Ca(2+) wave frequency observed in failing myocytes was reduced by either bone marrow cells or skeletal myoblasts. In conclusion, the morphology, contractile performance, and excitation-contraction coupling of individual recipient cardiomyocytes are altered in failing hearts treated with adult progenitor cell transplantation.

Myogenic endothelial cells purified from human skeletal muscle improve cardiac function after transplantation into infarcted myocardium

OBJECTIVES

The aim of this study was to evaluate the therapeutic potential of human skeletal muscle-derived myoendothelial cells for myocardial infarct repair.

BACKGROUND

We have recently identified and purified a novel population of myoendothelial cells from human skeletal muscle. These cells coexpress myogenic and endothelial cell markers and produce robust muscle regeneration when injected into cardiotoxin-injured skeletal muscle.

METHODS

Myoendothelial cells were isolated from biopsies of human skeletal muscle using a fluorescence-activated cell sorter along with populations of regular myoblasts and endothelial cells. Acute myocardial infarction was induced in male immune-deficient mice, and cells were directly injected into the ischemic area. Cardiac function was assessed by echocardiography, and donor cell engraftment, angiogenesis, scar tissue, endogenous cardiomyocyte proliferation, and apoptosis were all evaluated by immunohistochemistry.

RESULTS

A greater improvement in left ventricular function was observed after intramyocardial injection of myoendothelial cells when compared with that seen in hearts injected with myoblast or endothelial cells. Transplanted myoendothelial cells generated robust engraftments within the infarcted myocardium, and also stimulated angiogenesis, attenuation of scar tissue, and proliferation and survival of endogenous cardiomyocytes more effectively than transplanted myoblasts or endothelial cells.

CONCLUSIONS

Our findings suggest that myoendothelial cells represent a novel cell population from human skeletal muscle that may hold promise for cardiac repair.

Stem cells for cardiac regeneration by cell therapy and myocardial tissue engineering

Congestive heart failure, which often occurs progressively following a myocardial infarction, is characterized by impaired myocardial perfusion, ventricular dilatation, and cardiac dysfunction. Novel treatments are required to reverse these effects - especially in older patients whose endogenous regenerative responses to currently available therapies are limited by age. This review explores the current state of research for two related approaches to cardiac regeneration: cell therapy and tissue engineering. First, to evaluate cell therapy, we review the effectiveness of various cell types for their ability to limit ventricular dilatation and promote functional recovery following implantation into a damaged heart. Next, to assess tissue engineering, we discuss the characteristics of several biomaterials for their potential to physically support the infarcted myocardium and promote implanted cell survival following cardiac injury. Finally, looking ahead, we present recent findings suggesting that hybrid constructs combining a biomaterial with stem and supporting cells may be the most effective approaches to cardiac regeneration.

Paracrine effects of cell transplantation: strategies to augment the efficacy of cell therapies

Within the last few years, it has become evident that the beneficial effect of cell transplantation on ventricular function and myocardial perfusion is in large part mediated through paracrine effects on the host myocardium. Studies in which medium conditioned by cultured cells, usually mesenchymal stem cells, were injected into infarcted animal hearts have provided definitive evidence of this mechanism of action. Paracrine effects of the donor cells include but are not limited to angiogenesis, mobilization of both circulating and bone-marrow-derived stem cells, activation of cardiac-resident stem cells (CRSCs), and stabilization of the extracellular matrix (ECM). These paracrine effects can be augmented by transplantation of cells modified to express therapeutically useful transgenes, or by preconditioning through hypoxic or pharmacologic means. Strategies to enhance the paracrine effects of cell transplantation may thus be employed in the next generation of cell therapies, with greater functional benefit.

Ultrasound-mediated microbubble destruction enhances the efficacy of bone marrow mesenchymal stem cell transplantation and cardiac function

1. Application of ultrasound (US) to intravascular microbubble (MB) contrast agents causes small capillary ruptures. The purpose of the present study was to examine the effects of US-mediated MB destruction on bone marrow mesenchymal stem cell (BMSC) transplantation into the infarcted myocardium and to evaluate whether this approach could improve cardiac function. 2. Ultrasound was applied to the anterior chest of rabbits after intravenous injection of MB followed by infusion of BMSC. There were four groups investigated: (i) a control group, in which neither US nor MB were used prior to infusion of BMSC; (ii) one group subjected to US alone prior to infusion of BMSC; (iii) another group injected with MB prior to infusion of BMSC; and (iv) a group in which US was applied to MB prior to the infusion of BMSC. Cardiac function was evaluated by echocardiography 24 h and 4 weeks after cell transplantation. All rabbits were killed to enable histological and immunochemical examination. 3. Echocardiography 24 h after infusion of BMSC indicated no difference in cardiac function between any of the groups, as assessed by left ventricular ejection fraction (LVEF), left ventricular end-diastolic dimensions (LVDD), left ventricular systolic diameter (LVSD) and fractional shortening (FS%; all P > 0.05). However, 4 weeks after BMSC transplantation, there was a significant improvement in LVEF in the group subjected to US plus MB compared with the control, US alone and MB alone groups (59.5 +/- 3.5, 52.5 +/- 5.5, 52.8 +/- 5.2 and 51.1 +/- 3.5%, respectively; all P < 0.05). In addition, treatment with US plus MB significantly reduced LVDD and LVSD and increased capillary density in the infarcted area. 4. In conslusion, the results of the present study indicate that using US-mediated MB destruction prior to BMSC transplantation into the infarcted myocardium improves the effectiveness of cardiac cell therapy and cardiac function in rabbits.

Systems approaches to preventing transplanted cell death in cardiac repair

Stem cell transplantation may repair the injured heart, but tissue regeneration is limited by death of transplanted cells. Most cell death occurs in the first few days post-transplantation, likely from a combination of ischemia, anoikis and inflammation. Interventions known to enhance transplanted cell survival include heat shock, over-expressing anti-apoptotic proteins, free radical scavengers, anti-inflammatory therapy and co-delivery of extracellular matrix molecules. Combinatorial use of such interventions markedly enhances graft cell survival, but death still remains a significant problem. We review these challenges to cardiac cell transplantation and present an approach to systematically address them. Most anti-death studies use histology to assess engraftment, which is time- and labor-intensive. To increase throughput, we developed two biochemical approaches to follow graft viability in the mouse heart. The first relies on LacZ enzymatic activity to track genetically modified cells, and the second quantifies human genomic DNA content using repetitive Alu sequences. Both show linear relationships between input cell number and biochemical signal, but require correction for the time lag between cell death and loss of signal. Once optimized, they permit detection of as few as 1 graft cell in 40,000 host cells. Pro-survival effects measured biochemically at three days predict long-term histological engraftment benefits. These methods permitted identification of carbamylated erythropoietin (CEPO) as a pro-survival factor for human embryonic stem cell-derived cardiomyocyte grafts. CEPO's effects were additive to heat shock, implying independent survival pathways. This system should permit combinatorial approaches to enhance graft viability in a fraction of the time required for conventional histology.