Stable fetal cardiomyocyte grafts in the hearts of dystrophic mice and dogs

Navigating the Crossroads of Cell Therapy and Natural Heart Regeneration

Cardiovascular disease remains the leading cause of death worldwide despite significant advances in our understanding of the disease and its treatment. Consequently, the therapeutic potential of cell therapy and induction of natural myocardial regeneration have stimulated a recent surge of research and clinical trials aimed at addressing this challenge. Recent developments in the field have shed new light on the intricate relationship between inflammation and natural regeneration, an intersection that warrants further investigation.

Quantification of Cardiomyocyte Beating Frequency Using Fourier Transform Analysis

Pacemaker cardiomyocytes of the sinoatrial node (SAN) beat more rapidly than cells of the working myocardium. Beating in SAN cells responds to β-adrenergic and cholinergic signaling by speeding up or slowing, respectively. Beat rate has traditionally been assessed using voltage or calcium sensitive dyes, however these may not reflect the true rate of beating because they sequester calcium. Finally, in vitro differentiated cardiomyocytes sometimes briefly pause during imaging giving inaccurate beat rates. We have developed a MATLAB automation to calculate cardiac beat rates directly from video clips based on changes in pixel density at the edges of beating areas. These data are normalized to minimize the effects of secondary movement and are converted to frequency data using a fast Fourier transform (FFT). We find that this gives accurate beat rates even when there are brief pauses in beating. This technique can be used to rapidly assess beating of cardiomyocytes in organoid culture. This technique could also be combined with field scanning techniques to automatically and accurately assess beating within a complex cardiac organoid.

Cardiomyocyte Transplantation in a Porcine Myocardial Infarction Model

Transplantation of cardiomyocytes into the heart is a potential treatment for replacing damaged cardiac muscle. To investigate the feasibility and efficiency of this technique, either a cardiac-derived cell line (HL-1 cells), or normal fetal or neonatal pig cardiomyocytes were grafted into a porcine model of myocardial infarction. The myocardial infarction was created by the placement of an embolization coil in the distal portion of the left anterior descending artery in Yorkshire pigs (n = 9). Four to 5 wk after creation of an infarct, the three preparations of cardiomyocytes were grafted, at 1 × 106 cells/20 μL into normal and into the middle of the infarcted myocardium. The hearts were harvested and processed for histologic examinations 4 to 5 wk after the cell grafts. Histologic evaluation of the graft sites demonstrated that HL-1 cells and fetal pig cardiomyocytes formed stable grafts within the normal myocardium without any detrimental effect including arrhythmia. In addition, a marked increase in angiogenesis was observed both within the grafts and adjacent host myocardium. Electron microscopy studies demonstrated that fetal pig cardiomyocytes and the host myocardial cells were coupled with adherens-type junctions and gap junctions. Histologic examination of graft sites from infarct tissue failed to show the presence of grafted HL-1 cells, fetal, or neonatal pig cardiomyocytes. Cardiomyocyte transplantation may provide the potential means for cell-mediated gene therapy for introduction of therapeutic molecules into the heart.

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.

Stem cell-based therapy: Improving myocardial cell delivery

Stem cell-based therapies form an exciting new class of medicine that attempt to provide the body with the building blocks required for the reconstruction of damaged organs. However, delivering cells to the correct location, while preserving their integrity and functional properties, is a complex undertaking. These challenges have led to the development of a highly dynamic interdisciplinary research field, wherein medical, biological, and chemical sciences have collaborated to develop strategies to overcome the physiological barriers imposed on the cellular therapeutics. In this respect, improving the acute retention and subsequent survival of stem cells is key to effectively increase the effect of the therapy, while proper tissue integration is imperative for stem cells to functionally replace lost cells in damaged organs. In this review, we will use the heart as an example to highlight the current knowledge of therapeutic stem cell utilization, the existing pitfalls and limitations, and the approaches that have been developed to overcome them.

Nano-Enabled Approaches for Stem Cell-Based Cardiac Tissue Engineering

Cardiac diseases are the most prevalent causes of mortality in the world, putting a major economic burden on global healthcare system. Tissue engineering strategies aim at developing efficient therapeutic approaches to overcome the current challenges in prolonging patients survival upon cardiac diseases. The integration of advanced biomaterials and stem cells has offered enormous promises for regeneration of damaged myocardium. Natural or synthetic biomaterials have been extensively used to deliver cells or bioactive molecules to the site of injury in heart. Additionally, nano-enabled approaches (e.g., nanomaterials, nanofeatured surfaces) have been instrumental in developing suitable scaffolding biomaterials and regulating stem cells microenvironment to achieve functional therapeutic outcomes. This review article explores tissue engineering strategies, which have emphasized on the use of nano-enabled approaches in combination with stem cells for regeneration and repair of injured myocardium upon myocardial infarction (MI). Primarily a wide range of biomaterials, along with different types of stem cells, which have utilized in cardiac tissue engineering will be presented. Then integration of nanomaterials and surface nanotopographies with biomaterials and stem cells for myocardial regeneration will be presented. The advantages and challenges of these approaches will be reviewed and future perspective will be discussed.

Tumorigenesis of nuclear transfer-derived embryonic stem cells is reduced through differentiation and enrichment following transplantation in the infarcted rat heart

The aim of the present study was to evaluate the tumorigenic potential of nuclear transfer-derived (nt) mouse embryonic stem cells (mESCs) transplanted into infarcted rat hearts. The nt‑mESCs were cultured using a bioreactor system to develop embryoid bodies, which were induced with 1% ascorbic acid to differentiate into cardiomyocytes. The nt‑mESC‑derived cardiomyocytes (nt‑mESCs‑CMs) were enriched using Percoll density gradient separation to generate nt‑mESCs‑percoll‑enriched (PE)‑CMs. Ischemia was induced by ligating the left anterior descending coronary artery in female Sprague‑Dawley rats. Immunosuppressed rats (daily intraperitoneal injections of cyclosporine A and methylprednisolone) were randomly assigned to receive an injection containing 5x106 mESCs, nt‑mESCs, nt‑mESC‑CMs or nt‑mESC‑PE‑CMs. Analysis performed 8 weeks following transplantation revealed teratoma formation in 80, 86.67 and 33.33% of the rats administered with the mESCs, nt‑mESCs and nt‑mESC‑CMs, respectively, indicating no significant difference between the mESCs and nt‑mESCs; but significance (P<0.05) between the nt‑mESC‑CMs and nt‑mESCs. The mean tumor volumes were 82.72±6.52, 83.17±3.58 and 50.40±5.98 mm3, respectively (P>0.05 mESCs, vs. nt‑mESCs; P<0.05 nt‑mESC‑CMs, vs. nt‑mESCs). By contrast, no teratoma formation was detected in the rats, which received nt‑mESC‑PE‑CMs. Octamer‑binding transcription factor‑4, a specific marker of undifferentiated mESCs, was detected using polymerase chain reaction in the rats, which received nt‑mESCs and nt‑mESC‑CMs, but not in rats administered with nt‑mESC‑PE‑CMs. In conclusion, nt‑mESCs exhibited the same pluripotency as mESCs, and teratoma formation following nt‑mESC transplantation was reduced by cell differentiation and enrichment.

On-chip monitoring of skeletal myoblast transplantation for the treatment of hypoxia-induced myocardial injury

A comprehensive elucidation of the unexpected adverse events that occur in skeletal myoblast transplantation is fundamental for the optimization of myocardial therapeutic effects. However, a well-defined method to study the interactions between skeletal myoblasts and cardiomyocytes during the healing process is out of reach. Here, we describe a microfluidic method for monitoring the interactions between skeletal myoblasts and hypoxia-injured cardiomyocytes in a spatiotemporally-controlled manner, mimicking the in vivo cell transplantation process. A myocardial hypoxia environment was created using an oxygen consumption blocking reagent, carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone. Meanwhile, the interactions between the skeletal L6 myoblasts and hypoxia-injured myocardium H9c2 cells were investigated, and the effects of a L6 conditional medium on H9c2 cells were comparatively analyzed by quantitatively measuring the morphological and pathophysiological dynamics of H9c2 cells. The results showed that skeletal myoblasts could repair hypoxia-injured H9c2 cells mainly through direct cell-to-cell interactions. This simple on-chip assay for investigating myocardial repair processes may provide avenues for the in vitro screening of drug-induced cardiotoxicity.

Cardiac engraftment of genetically-selected parthenogenetic stem cell-derived cardiomyocytes

Parthenogenetic stem cells (PSCs) are a promising candidate donor for cell therapy applications. Similar to embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), PSCs exhibit self-renewing capacity and clonogenic proliferation in vitro. PSCs exhibit largely haploidentical genotype, and as such may constitute an attractive population for allogenic applications. In this study, PSCs isolated from transgenic mice carrying a cardiomyocyte-restricted reporter transgene to permit tracking of donor cells were genetically modified to carry a cardiomyocyte-restricted aminoglycoside phosphotransferase expression cassette (MHC-neo^r/pGK-hygro^r) to permit the generation of highly enriched cardiomyocyte cultures from spontaneously differentiating PSCs by simple selection with the neomycin analogue G148. Following engraftment into isogenic recipient hearts, the selected cardiomyocytes formed a functional syncytium with the host myocardium as evidenced by the presence of entrained intracellular calcium transients. These cells thus constitute a potential source of therapeutic donor cells.

Recombinant neuregulin 1 does not activate cardiomyocyte DNA synthesis in normal or infarcted adult mice

Objectives

Neuregulin 1 signaling plays an important role in cardiac trabecular development, and in sustaining functional integrity in adult hearts. Treatment with neuregulin 1 enhances adult cardiomyocyte differentiation, survival and/or function in vitro and in vivo. It has also been suggested that recombinant neuregulin 1β1 (NRG1β1) induces cardiomyocyte proliferation in normal and injured adult hearts. Here we further explore the impact of neuregulin 1 signaling on adult cardiomyocyte cell cycle activity.

Methods and Results

Adult mice were subjected to 9 consecutive daily injections of recombinant NRG1β1 or vehicle, and cardiomyocyte DNA synthesis was quantitated via bromodeoxyuridine (BrdU) incorporation, which was delivered using mini-osmotic pumps over the entire duration of NRG1β1 treatment. NRG1β1 treatment inhibited baseline rates of cardiomyocyte DNA synthesis in normal mice (cardiomyocyte labelling index: 0.019±0.005% vs. 0.003±0.001%, saline vs. NRG1β1, P<0.05). Acute NRG1β1 treatment did result in activation of Erk1/2 and cardiac myosin regulatory light chain (down-stream mediators of neuregulin signalling), as well as activation of DNA synthesis in non-cardiomyocytes, validating the biological activity of the recombinant protein. In other studies, mice were subjected to permanent coronary artery occlusion, and cardiomyocyte DNA synthesis was monitored via tritiated thymidine incorporation which was delivered as a single injection 7 days post-infarction. Daily NRG1β1 treatment had no impact on cardiomyocyte DNA synthesis in the infarcted myocardium (cardiomyocyte labelling index: 0.039±0.011% vs. 0.027±0.021%, saline vs. NRG1β1, P>0.05).

Summary

These data indicate that NRG1β1 treatment does not increase cardiomyocyte DNA synthesis (and consequently does not increase the rate of cardiomyocyte renewal) in normal or infarcted adult mouse hearts. Thus, any improvement in cardiac structure and function observed following neuregulin treatment of injured hearts likely occurs independently of overt myocardial regeneration.

Modulation of Human Cardiac Progenitors via Hypoxia-ERK Circuit Improves their Functional Bioactivities

Recent accumulating studies have reported that hypoxic preconditioning during ex vivo expansion enhanced the self-renewal or differentiation of various stem cells and provide an important strategy for the adequate modulation of oxygen in culture conditions, which might increase the functional bioactivity of these cells for cardiac regeneration. In this study, we proposed a novel priming protocol to increase the functional bioactivity of cardiac progenitor cells (CPCs) for the treatment of cardiac regeneration. Firstly, patient-derived c-kit⁺ CPCs isolated from the atrium of human hearts by enzymatic digestion and secondly, pivotal target molecules identifi ed their differentiation into specific cell lineages. We observed that hCPCs, in response to hypoxia, strongly activated ERK phosphorylation in ex vivo culture conditioning. Interestingly, pre-treatment with an ERK inhibitor, U0126, significantly enhanced cellular proliferation and tubular formation capacities of CPCs. Furthermore, we observed that hCPCs efficiently maintained the expression of the c-kit, a typical stem cell marker of CPCs, under both hypoxic conditioning and ERK inhibition. We also show that hCPCs, after preconditioning of both hypoxic and ERK inhibition, are capable of differentiating into smooth muscle cells (SMCs) and cardiomyocytes (CMs), but not endothelial cells (ECs), as demonstrated by the strong expression of α-SMA, Nkx2.5, and cTnT, respectively. From our results, we conclude that the functional bioactivity of patient-derived hCPCs and their ability to differentiate into SMCs and CMs can be effi ciently increased under specifically defined culture conditions such as shortterm hypoxic preconditioning and ERK inhibition.

Nestin expression in end-stage disease in dystrophin-deficient heart: implications for regeneration from endogenous cardiac stem cells

Nestin(+) cardiac stem cells differentiate into striated cells following myocardial infarct. Transplantation of exogenous stem cells into myocardium of a murine model for Duchenne muscular dystrophy (DMD) increased proliferation of endogenous nestin(+) stem cells and resulted in the appearance of nestin(+) striated cells. This correlated with, and may be responsible for, prevention of dilated cardiomyopathy. We examined nestin(+) stem cells in the myocardium of dystrophin/utrophin-deficient (mdx/utrn(-/-)) mice, a model for DMD. We found that 92% of nestin(+) interstitial cells expressed Flk-1, a marker present on cardiac progenitor cells that differentiate into the cardiac lineage, and that a subset expressed Sca-1, present on adult cardiac cells that become cardiomyocytes. Nestin(+) interstitial cells maintained expression of Flk-1 but lost Sca-1 expression with age and were present in lower numbers in dystrophin-deficient heart than in wild-type heart. Unexpectedly, large clusters of nestin(+) striated cells ranging in size from 20 to 250 cells and extending up to 500 μm were present in mdx/utrn(-/-) heart near the end stage of disease. These cells were also present in dystrophin-deficient mdx/utrn(+/-) and mdx heart but not wild-type heart. Nestin(+) striated cells expressed cardiac troponin I, desmin, and Connexin 43 and correlated with proinflammatory CD68(+) macrophages. Elongated nestin(+) interstitial cells with striations were observed that did not express Flk-1 or the late cardiac marker cardiac troponin I but strongly expressed the early cardiac marker desmin. Nestin was also detected in endothelial and smooth muscle cells. These data indicate that new cardiomyocytes form in dystrophic heart, and nestin(+) interstitial cells may generate them in addition to other cells of the cardiac lineage.

Injection of vessel-derived stem cells prevents dilated cardiomyopathy and promotes angiogenesis and endogenous cardiac stem cell proliferation in mdx/utrn-/- but not aged mdx mouse models for duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy. DMD patients lack dystrophin protein and develop skeletal muscle pathology and dilated cardiomyopathy (DCM). Approximately 20% succumb to cardiac involvement. We hypothesized that mesoangioblast stem cells (aorta-derived mesoangioblasts [ADMs]) would restore dystrophin and alleviate or prevent DCM in animal models of DMD. ADMs can be induced to express cardiac markers, including Nkx2.5, cardiac tropomyosin, cardiac troponin I, and α-actinin, and adopt cardiomyocyte morphology. Transplantation of ADMs into the heart of mdx/utrn(-/-) mice prior to development of DCM prevented onset of cardiomyopathy, as measured by echocardiography, and resulted in significantly higher CD31 expression, consistent with new vessel formation. Dystrophin-positive cardiomyocytes and increased proliferation of endogenous Nestin(+) cardiac stem cells were detected in ADM-injected heart. Nestin(+) striated cells were also detected in four of five mdx/utrn(-/-) hearts injected with ADMs. In contrast, when ADMs were injected into the heart of aged mdx mice with advanced fibrosis, no functional improvement was detected by echocardiography. Instead, ADMs exacerbated some features of DCM. No dystrophin protein, increase in CD31 expression, or increase in Nestin(+) cell proliferation was detected following ADM injection in aged mdx heart. Dystrophin was observed following transplantation of ADMs into the hearts of young mdx mice, however, suggesting that pathology in aged mdx heart may alter the fate of donor stem cells. In summary, ADMs delay or prevent development of DCM in dystrophin-deficient heart, but timing of stem cell transplantation may be critical for achieving benefit with cell therapy in DMD cardiac muscle.

Cardiac aging: from molecular mechanisms to significance in human health and disease

Cardiovascular diseases (CVDs) are the major causes of death in the western world. The incidence of cardiovascular disease as well as the rate of cardiovascular mortality and morbidity increase exponentially in the elderly population, suggesting that age per se is a major risk factor of CVDs. The physiologic changes of human cardiac aging mainly include left ventricular hypertrophy, diastolic dysfunction, valvular degeneration, increased cardiac fibrosis, increased prevalence of atrial fibrillation, and decreased maximal exercise capacity. Many of these changes are closely recapitulated in animal models commonly used in an aging study, including rodents, flies, and monkeys. The application of genetically modified aged mice has provided direct evidence of several critical molecular mechanisms involved in cardiac aging, such as mitochondrial oxidative stress, insulin/insulin-like growth factor/PI3K pathway, adrenergic and renin angiotensin II signaling, and nutrient signaling pathways. This article also reviews the central role of mitochondrial oxidative stress in CVDs and the plausible mechanisms underlying the progression toward heart failure in the susceptible aging hearts. Finally, the understanding of the molecular mechanisms of cardiac aging may support the potential clinical application of several "anti-aging" strategies that treat CVDs and improve healthy cardiac aging.

Canine models of Duchenne muscular dystrophy and their use in therapeutic strategies

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder in which the loss of dystrophin causes progressive degeneration of skeletal and cardiac muscle. Potential therapies that carry substantial risk, such as gene- and cell-based approaches, must first be tested in animal models, notably the mdx mouse and several dystrophin-deficient breeds of dogs, including golden retriever muscular dystrophy (GRMD). Affected dogs have a more severe phenotype, in keeping with that of DMD, so may better predict disease pathogenesis and treatment efficacy. Various phenotypic tests have been developed to characterize disease progression in the GRMD model. These biomarkers range from measures of strength and joint contractures to magnetic resonance imaging. Some of these tests are routinely used in clinical veterinary practice, while others require specialized equipment and expertise. By comparing serial measurements from treated and untreated groups, one can document improvement or delayed progression of disease. Potential treatments for DMD may be broadly categorized as molecular, cellular, or pharmacologic. The GRMD model has increasingly been used to assess efficacy of a range of these therapies. A number of these studies have provided largely general proof-of-concept for the treatment under study. Others have demonstrated efficacy using the biomarkers discussed. Importantly, just as symptoms in DMD vary among patients, GRMD dogs display remarkable phenotypic variation. Though confounding statistical analysis in preclinical trials, this variation offers insight regarding the role that modifier genes play in disease pathogenesis. By correlating functional and mRNA profiling results, gene targets for therapy development can be identified.

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.

Engineered fetal cardiac graft preserves its cardiomyocyte proliferation within postinfarcted myocardium and sustains cardiac function

The goal of cellular cardiomyoplasty is to replace damaged myocardium by healthy myocardium achieved by host myocardial regeneration and/or transplantation of donor cardiomyocytes (CMs). In the case of CM transplantation, studies suggest that immature CMs may be the optimal cell type to survive and functionally integrate into damaged myocardium. In the present study, we tested the hypothesis that active proliferation of immature CMs contributes graft survival and functional recovery of recipient myocardium. We constructed engineered cardiac tissue from gestational day 14 rat fetal cardiac cells (EFCT) or day 3 neonatal cardiac cells (ENCT). Culture day 7 EFCTs or ENCTs were implanted onto the postinfarct adult left ventricle (LV). CM proliferation rate of EFCT was significantly higher than that of ENCT at 3 days and 8 weeks after the graft implantation, whereas CM apoptosis rate remained the same in both groups. Echocardiogram showed that ENCT implantation sustained LV contraction, whereas EFCT implantation significantly increased the LV contraction at 8 weeks versus sham group (p < 0.05, analysis of variance). These results suggest that active CM proliferation may play a critical role in immature donor CM survival and the functional recovery of damaged recipient myocardium.

Experimental models of duchenne muscular dystrophy: relationship with cardiovascular disease

Almost every boy that has Duchenne Muscular Dystrophy (DMD) will develop cardiac problems. Whereas, it used to be respiratory problems that was the main cause of death in these DMD boys; with the advent of better respiratory care it is now the cardiac involvement that is becoming the most common cause of their death. Once the heart is affected, there is progressive deterioration in the function of the heart over time. The main problem is the death of the cardiomyocytes. The cause of the cardiomyocyte death is due to the loss of dystrophin, this makes the sarcolemma more susceptible to damage, and leads to a cascade of calcium influx, calcium activated proteases and ultimately the death of the cardiomyocyte. The dead cardiomyocytes are replaced by fibrotic tissue, which results in a dilated cardiomyopathy (DCM) developing, which begins in the base of the left ventricle and progresses to involve the entire left ventricle. The treatments used for the DMD cardiomyopathy are based on ones designed for other forms of cardiac weakness and include ACE-inhibitors and β-blockers. New therapies based around the pathophysiology in DMD are now being introduced. This review will look at the pathophysiology of the cardiac problems in DMD and how the various animal models that are available can be used to design new treatment options for DMD boys.

Assessment of human MAPCs for stem cell transplantation and cardiac regeneration after myocardial infarction in SCID mice

OBJECTIVE

Clinical studies suggest that transplantation of total bone marrow (BM) after myocardial infarction (MI) is feasible and potentially effective. However, focusing on a defined BM-derived stem cell type may enable a more specific and optimized treatment. Multilineage differentiation potential makes BM-derived multipotent adult progenitor cells (MAPCs) a promising stem cell pool for regenerative purposes. We analyzed the cardioregenerative potential of human MAPCs in a murine model of myocardial infarction.

MATERIALS AND METHODS

Human MAPCs were selected by negative depletion of CD45(+)/glycophorin(+) BM cells and plated on fibronectin-coated dishes. In vitro, stem cells were analyzed by reverse transcription polymerase chain reaction. In vivo, we transplanted human MAPCs (5 × 10(5)) by intramyocardial injection after MI in severe combined immunodeficient (SCID) beige mice. Six and 30 days after the surgical procedure, pressure-volume relationships were investigated in vivo. Heart tissues were analyzed immunohistochemically.

RESULTS

Reverse transcription polymerase chain reaction experiments on early human MAPC passages evidenced an expression of Oct-4, a stem cell marker indicating pluripotency. In later passages, cardiac markers (Nkx2.5, GATA4, MLC-2v, MLC-2a, ANP, cTnT, cTnI,) and smooth muscle cell markers (SMA, SM22α) were expressed. Transplantation of human MAPCs into the ischemic border zone after MI resulted in an improved cardiac function at day 6 (ejection fraction, 26% vs 20%) and day 30 (ejection fraction, 30% vs 23%). Confirmation of human MAPC marker vimentin in immunohistochemistry demonstrated that human MAPC integrated in the peri-infarct region. The proliferation marker Ki67 was absent in immunohistochemistry and teratoma formation was not found, indicating no tumorous potential of transplanted human MAPCs in the tumor-sensitive SCID model.

CONCLUSIONS

Transplantation of human MAPCs after MI ameliorates myocardial function, which may be explained by trophic effects of human MAPCs. Lack of evidence of tumorous potential in the tumor-sensitive SCID model indicates that human MAPCs may deliver an effective and safe stem cell pool for potential treatment of ischemic heart disease.

Interrogating functional integration between injected pluripotent stem cell-derived cells and surrogate cardiac tissue

Myocardial infarction resulting in irreversible loss of cardiomyocytes (CMs) remains a leading cause of heart failure. Although cell transplantation has modestly improved cardiac function, major challenges including increasing cell survival, engraftment, and functional integration with host tissue, remain. Embryonic stem cells (ESCs), which can be differentiated into cardiac progenitors (CPs) and CMs, represent a candidate cell source for cardiac cell therapy. However, it is not known what specific cell type or condition is the most appropriate for transplantation. This problem is exasperated by the lack of efficient and predictive strategies to screen the large numbers of parameters that may impact cell transplantation. We used a cardiac tissue model, engineered heart tissue (EHT), and quantitative molecular and electrophysiological analyses, to test transplantation conditions and specific cell populations for their potential to functionally integrate with the host tissue. In this study, we validated our analytical platform using contractile mouse neonatal CMs (nCMs) and noncontractile cardiac fibroblasts (cFBs), and screened for the integration potential of ESC-derived CMs and CPs (ESC-CMs and -CPs). Consistent with previous in vivo studies, cFB injection interfered with electrical signal propagation, whereas injected nCMs improved tissue function. Purified bioreactor-generated ESC-CMs exhibited a diminished capacity for electrophysiological integration; a result correlated with lower (compared with nCMs) connexin 43 expression. ESC-CPs, however, appeared able to appropriately mature and integrate into EHT, enhancing the amplitude of tissue contraction. Our results support the use of EHT as a model system to accelerate development of cardiac cell therapy strategies.

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

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

Human embryonic stem cells and cardiac repair

The muscle lost after a myocardial infarction is replaced with noncontractile scar tissue, often initiating heart failure. Whole-organ cardiac transplantation is the only currently available clinical means of replacing the lost muscle, but this option is limited by the inadequate supply of donor hearts. Thus, cell-based cardiac repair has attracted considerable interest as an alternative means of ameliorating cardiac injury. Because of their tremendous capacity for expansion and unquestioned cardiac potential, pluripotent human embryonic stem cells (hESCs) represent an attractive candidate cell source for obtaining cardiomyocytes and other useful mesenchymal cell types for such therapies. Human embryonic stem cell-derived cardiomyocytes exhibit a committed cardiac phenotype and robust proliferative capacity, and recent testing in rodent infarct models indicates that they can partially remuscularize injured hearts and improve contractile function. Although the latter successes give good reason for optimism, considerable challenges remain in the successful application of hESCs to cardiac repair, including the need for preparations of high cardiac purity, improved methods of delivery, and approaches to overcome immune rejection and other causes of graft cell death. This review will describe the phenotype of hESC-derived cardiomyocytes and preclinical experience with these cells and will consider strategies to overcoming the aforementioned challenges.

Enhanced proliferation of monolayer cultures of embryonic stem (ES) cell-derived cardiomyocytes following acute loss of retinoblastoma

Background

Cardiomyocyte (CM) cell cycle analysis has been impeded because of a reliance on primary neonatal cultures of poorly proliferating cells or chronic transgenic animal models with innate compensatory mechanisms.

Methodology/Principal Findings

We describe an in vitro model consisting of monolayer cultures of highly proliferative embryonic stem (ES) cell-derived CM. Following induction with ascorbate and selection with puromycin, early CM cultures are >98% pure, and at least 85% of the cells actively proliferate. During the proliferative stage, cells express high levels of E2F3a, B-Myb and phosphorylated forms of retinoblastoma (Rb), but with continued cultivation, cells stop dividing and mature functionally. This developmental transition is characterized by a switch from slow skeletal to cardiac TnI, an increase in binucleation, cardiac calsequestrin and hypophosphorylated Rb, a decrease in E2F3, B-Myb and atrial natriuretic factor, and the establishment of a more negative resting membrane potential. Although previous publications suggested that Rb was not necessary for cell cycle control in heart, we find following acute knockdown of Rb that this factor actively regulates progression through the G1 checkpoint and that its loss promotes proliferation at the expense of CM maturation.

Conclusions/Significance

We have established a unique model system for studying cardiac cell cycle progression, and show in contrast to previous reports that Rb actively regulates both cell cycle progression through the G1 checkpoint and maturation of heart cells. We conclude that this in vitro model will facilitate the analysis of cell cycle control mechanisms of CMs.

Origins and fates of cardiovascular progenitor cells

Multipotent cardiac progenitor cells are found in the fetal and adult heart of many mammalian species including humans and form as intermediates during the differentiation of embryonic stem cells. Despite similar biological properties, the molecular identities of these different cardiac progenitor cell populations appear to be distinct. Elucidating the origins and lineage relationships of these cell populations will accelerate clinical applications such as drug screening and cell therapy as well as shedding light on the pathogenic mechanisms underlying cardiac diseases.

Dystrophin deficiency in Drosophila reduces lifespan and causes a dilated cardiomyopathy phenotype

A number of studies have been conducted recently on the model organism Drosophila to determine the function of genes involved in human disease, including those implicated in neurological disorders, cancer and metabolic and cardiovascular diseases. The simple structure and physiology of the Drosophila heart tube together with the available genetics provide a suitable in vivo assay system for studying cardiac gene functions. In our study, we focus on analysis of the role of dystrophin (Dys) in heart physiology. As in humans, the Drosophila dys gene encodes multiple isoforms, of which the large isoforms (DLPs) and a truncated form (Dp117) are expressed in the adult heart. Here, we show that the loss of dys function in the heart leads to an age-dependent disruption of the myofibrillar organization within the myocardium as well as to alterations in cardiac performance. dys RNAi-mediated knockdown in the mesoderm also shortens lifespan. Knockdown of all or deletion of the large isoforms increases the heart rate by shortening the diastolic intervals (relaxation phase) of the cardiac cycle. Morphologically, loss of the large DLPs isoforms causes a widening of the cardiac tube and a lower fractional shortening, a phenotype reminiscent of dilated cardiomyopathy. The dilated dys mutant phenotype was reversed by expressing a truncated mammalian form of dys (Dp116). Our results illustrate the utility of Drosophila as a model system to study dilated cardiomyopathy and other muscular-dystrophy-associated phenotypes.

Stem cell differentiation: cardiac repair

Cellular transplantation has been employed for several years to deliver donor cardiomyocytes to normal and injured hearts. Recent reports of a variety of stem cells with apparent cardiomyogenic potential have raised the possibility of cell transplantation-based therapeutic interventions for heart disease. Here we review the preclinical studies demonstrating that intracardiac transplantation of skeletal myoblasts, cardiomyocytes and cardiomyogenic stem cells is feasible. In addition, recent clinical studies of skeletal myoblast and adult stem cell transplantation for heart disease are discussed.

The art of cobbling a running pump--will human embryonic stem cells mend broken hearts?

The heart is one of the least regenerative organs in the body, and highly vulnerable to the increasing incidence of cardiovascular diseases in an aging world population. Cell-based approaches aimed at cardiac repair have recently caused great public excitement. But clinical trials of patients' own skeletal myoblasts or bone marrow cells for transplantation have been disappointing. Human embryonic stem cells (hESCs) form bona fide cardiomyocytes in vitro which are readily generated in mass culture and are being tested in animal models of heart damage. The early results, while encouraging, underscore that much remains to be done. This review focuses on the many challenges that remain before hESCs-mediated repair of the human heart becomes a reality.

The bone marrow--cardiac axis of myocardial regeneration

Congestive heart failure remains the leading cause of morbidity and mortality in the developed world. Current therapies do not address the underlying pathophysiology of this disease, namely, the progressive loss of functional cardiomyocytes. The notion of repairing or regenerating lost myocardium via cell-based therapies remains highly appealing. The recent identification of adult stem cells, including both cardiac stem/progenitor cells and bone marrow stem cells, has triggered an explosive interest in using these cells for physiologically relevant cardiomyogenesis. Enthusiasm for cardiac regeneration via cell therapy has further been fueled by the many encouraging reports in both animals and human studies. Further intensive research in basic science and clinical arenas are needed to make this next great frontier in cardiovascular regenerative medicine a reality. In this review, we focus on the role of bone marrow-derived stem cells and cardiac stem/progenitor cells in cardiomyocyte homeostasis and myocardial repair and regeneration, as well as provide a brief overview of current clinical trials using cell-based therapeutic approaches in patients with heart disease.

Stem Cell Therapy: A Hope for Dying Hearts

The restoration of functional myocardium following heart failure still remains a formidable challenge among researchers. Irreversible damage caused by myocardial infarction is followed by left ventricular remodeling. The current pharmacologic and interventional strategies fail to regenerate dead myocardium and are usually insufficient to meet the challenge caused by necrotic cardiac myocytes. There is growing evidence, suggesting that the heart has the ability to regenerate through the activation of resident cardiac stem cells or through the recruitment of a stem cell population from other tissues such as bone marrow. These new findings belie the earlier conception about the poor regenerating ability of myocardial tissue. Stem cell therapy is a promising new approach for myocardial repair. However, it has been limited by the paucity of cell sources for functional human cardiomyocytes. Moreover, cells isolated from different sources exhibit idiosyncratic characteristics including modes of isolation, ease of expansion in culture, proliferative ability, characteristic markers, etc., which are the basis for several technical manipulations to achieve successful engraftment. Clinical trials show some evidence for the successful integration of stem cells of extracardiac origin in adult human heart with an improved functional outcome. This may be attributed to the discrepancies in the methods of detection, study subject selection (early or late post transplantation), presence of inflammation, and false identification of infiltrating leukocytes. This review discusses these issues in a comprehensive manner so that their physiological significance in animal as well as in human studies can be better understood.

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.

Cardiovascular therapeutic aspects of cell therapy and stem cells

The recent advancements in stem cell biology, molecular and cell biology, and tissue engineering have paved the way to the development of a new biomedical discipline: regenerative medicine. The heart represents an attractive candidate for this emerging discipline since these emerging technologies could be used to potentially treat a variety of myocardial disorders. Here we describe our efforts in using stem cell and cell therapy strategies to restore the myocardial electromechanical properties. Specifically, our research has focused on the potential role of human embryonic stem cells (hESC) for myocardial regeneration (for the treatment of heart failure) and on using genetically engineered cell grafts to modify the myocardial electrophysiological properties (for the treatment of cardiac arrhythmias). The recently described hESC lines are unique pluripotent cell lines that can be propagated in the undifferentiated state in culture and coaxed to differentiate into cell derivatives of all three germ layers, including cardiomyocytes. The current article describes this unique cardiomyocyte differentiating system and details the molecular, ultrastructural, and functional properties of the generated hESC-derived cardiomyocytes (hESC-CMs). The ability of the hESC-CMs to integrate structurally and functionally with host cardiomyocytes in both in vitro and in vivo studies will be described as well as their ability to restore the myocardial electromechanical function in animal models of diseased hearts. We will next present detailed in vitro, in vivo, and computer simulation studies performed in our laboratory testing the hypothesis that cell grafts, engineered to express specific ion channels, can be used to modify the myocardial electrophysiological properties of cardiac tissue. The potential and drawbacks of this novel approach for the treatment of both tachyarrhythmias (using cell grafts expressing potassium channels) and bradyarrhythmias (using hESC coaxed to differentiate into pacemaking cells or conducting tissue) will be described.

Cell-based approaches for cardiac repair

Many forms of cardiovascular disease are associated with cardiomyocyte loss via necrosis and/or apoptosis. The cumulative loss of contractile cells ultimately results in diminished cardiac function. Numerous approaches have been employed to reduce the rate of cardiomyocyte loss, or alternatively, to repopulate the heart with new cardiomyocytes. Strategies aimed at repopulating the heart include cardiomyocyte cell therapy, myogenic stem cell therapy, and cell cycle activation therapy. All three approaches are based on the assumption that the de novo cardiomyocytes will participate in a functional syncytium with the surviving myocardium. This review will discuss the current status of interventions aimed at repopulating the heart with functional cardiomyocytes.

Plasticity and cardiovascular applications of multipotent adult progenitor cells

Cardiovascular disease is the leading cause of death worldwide, which has encouraged the search for new therapies that enable the treatment of patients in palliative and curative ways. In the past decade, the potential benefit of transplantation of cells that are able to substitute for the injured tissue has been studied with several cell populations, such as stem cells. Some of these cell populations, such as myoblasts and bone marrow cells, are already being used in clinical trials. The laboratory of CM Verfaillie has studied primitive progenitors, termed multipotent adult progenitor cells, which can be isolated from adult bone marrow. These cells can differentiate in vitro at the single-cell level into functional cells that belong to the three germ layers and contribute to most, if not all, somatic cell types after blastocyst injection. This remarkably broad differentiation potential makes this particular cell population a candidate for transplantation in tissues in need of regeneration. Here, we focus on the regenerative capacity of multipotent adult progenitor cells in several ischemic mouse models, such as acute and chronic myocardial infarction and limb ischemia.

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.

Myocardial regeneration strategies using human embryonic stem cell-derived cardiomyocytes

Regenerative medicine is a new biomedicine discipline that takes advantage of the recent advancements in the fields of stem cell biology, molecular biology, and tissue engineering to derive tissue substitutes, in an attempt to replace or modify the function of diseased organs. The heart represents an attractive candidate for these emerging technologies since adult cardiac tissue has limited regenerative capacity. Consequentially, myocardial cell replacement therapy has emerged as a novel therapeutic paradigm for restoration of the myocardial electromechanical function. This innovative strategy has been significantly hampered, however, by the paucity of cell sources for human cardiomyocytes. The recent establishment of the human embryonic stem cell (hESC) lines may provide a possible solution for this cell-sourcing problem. These unique pluripotent cell lines can be propagated in the undifferentiated state in culture and coaxed to differentiate into cell derivatives of all three germ layers, including cardiomyocytes. This review will describe the hESC system, their differentiation into cardiomyocytes, and the structural and functional characterization of these cardiac lineage derivatives. The potential applications of this unique differentiating system in several research areas will be discussed with special emphasis on the steps required to fully harness their unique potential in the emerging field of cardiovascular regenerative medicine.

Effects of cardiac patches engineered with bone marrow-derived mononuclear cells and PGCL scaffolds in a rat myocardial infarction model

Little is known about the cardioprotective effects against heart failure (HF), the effects on differentiation of bone marrow-derived mononuclear cell (BMMNC), and the biocompatibility of BMMNC-seeded biodegradable poly-glycolide-co-caprolactone (PGCL) scaffolds in a myocardial infarction (MI) animal model. This study hypothesized that implantation of a BMMNC-seeded PGCL scaffold into the epicardial surface in a rat MI model would be biocompatible, induce BMMNC migration into infarcted myocardium, and effectively improve left ventricular (LV) systolic dysfunction. One week after the implantation of a BMMNC-seeded PGCL scaffold, BMMMC showed migration into the epicardial region. Four weeks after implantation, augmented neovascularization was observed in infarcted areas and in infarct border zones. Some BMMNCs exhibited the presence of alpha-MHC and troponin I, markers of differentiation into cardiomyocytes. In echocardiographic examinations, BMMNC-seeded PGCL scaffold and non-cell-seeded simple PGCL scaffold groups effectively reduced progressive LV dilatation and preserved LV systolic function as compared to control rat MI groups. Thus, BMMNC-seeded PGCL scaffolding influences BMMNC migration, differentiation to cardiomyocytes, and induction of neovascularization, ultimately effectively lessening LV remodeling and progressive LV systolic dysfunction. PGCL scaffolding can be considered as an effective treatment alternative in MI-induced advanced HF.

Cardiac regeneration: repopulating the heart

Many forms of pediatric and adult heart disease result from a deficiency in cardiomyocyte number. Through repopulation of the heart with new cardiomyocytes (that is, induction of regenerative cardiac growth), cardiac disease potentially can be reversed, provided that the newly formed myocytes structurally and functionally integrate in the preexisting myocardium. A number of approaches have been utilized to effect regenerative growth of the myocardium in experimental animals. These include interventions aimed at enhancing the ability of cardiomyocytes to proliferate in response to cardiac injury, as well as transplantation of cardiomyocytes or myogenic stem cells into diseased hearts. Here we review efforts to induce myocardial regeneration. We also provide a critical review of techniques currently used to assess cardiac regeneration and functional integration of de novo cardiomyocytes.

Transplanted Neonatal Cardiomyocytes as a Potential Biological Pacemaker in Pigs with Complete Atrioventricular Block

BACKGROUND

Sinus node dysfunction and severe heart block are major indications for electronic pacemaker implantation. The aim of the present study was to investigate the feasibility of an alternative approach by using spontaneously excitable cell grafts to serve as a biological pacemaker.

METHODS

Enzymatically isolated neonatal atrial cardiomyocytes (including sinus nodal cells) were grafted into the free wall of the left ventricle of 5 male pigs. In the control group (n = 4), the medium was used for injecting. Three weeks after the transplantation the pigs underwent catheter ablation of the atrioventricular (AV) node. Microelectrode technique was used to record the transmembrane action potential of myocytes from cell- and medium-injected preparations. Immunohistochemistry was used to verify the grafted cells and the establishment of the gap junctions between donor and host cardiomyocytes.

RESULTS

After the creation of complete AV-block, a higher average idioventricular rate was observed in cell-grafted pigs than that in control pigs (89 +/- 13 vs. 30 +/- 11 bpm, P < 0.05). Administering isoprenaline caused a significant increase in the idioventricular rate from 89 +/- 13 to 120 +/- 18 bpm in the cell-grafted animals (P < 0.05). Microelectrode recordings showed that the spontaneously beating rate was significantly higher in the cell-implanted than that in the control preparations (82 +/- 17 vs. 33 +/- 13 bpm, P < 0.05). Furthermore, the immunofluorescence microscopy identified the DAPI-labeled donor cells, and the connexin-43 and N-cadherin positive junctions between them and host cardiomyocytes.

CONCLUSION

Grafted neonatal atrial cardiomyocytes are able to survive and integrate into the host myocardium, and show a pacing function that can be modulated by autonomic agents.

Regeneration of dystrophin-expressing myocytes in the mdx heart by skeletal muscle stem cells

Cell transplantation holds promise as a potential treatment for cardiac dysfunction. Our group has isolated populations of murine skeletal muscle-derived stem cells (MDSCs) that exhibit stem cell-like properties. Here, we investigated the fate of MDSCs after transplantation into the hearts of dystrophin-deficient mdx mice, which model Duchenne muscular dystrophy (DMD). Transplanted MDSCs generated large grafts consisting primarily of numerous dystrophin-positive myocytes and, to a lesser degree, dystrophin-negative non-myocytes that expressed an endothelial phenotype. Most of the dystrophin-positive myocytes expressed a skeletal muscle phenotype and did not express a cardiac phenotype. However, some donor myocytes, located at the graft-host myocardium border, were observed to express cardiac-specific markers. More than half of these donor cells that exhibited a cardiac phenotype still maintained a skeletal muscle phenotype, demonstrating a hybrid state. Sex-mismatched donors and hosts revealed that many donor-derived cells that acquired a cardiac phenotype did so through fusion with host cardiomyocytes. Connexin43 gap junctions were not expressed by donor-derived myocytes in the graft. Scar tissue formation in the border region may inhibit the fusion and gap junction connections between donor and host cells. This study demonstrates that MDSC transplantation warrants further investigation as a potential therapy for cardiac dysfunction in DMD.

Cardiac repair by embryonic stem-derived cells

Cell transplantation approaches offer the potential to promote regenerative growth of diseased hearts. It is well established that donor cardiomyocytes stably engraft into recipient hearts when injected directly into the myocardial wall. Moreover, the transplanted donor cardiomyocytes participate in a functional syncytium with the host myocardium. Thus, transplantation of donor cardiomyocytes resulted in at least partial restoration of lost muscle mass. It is also well established that embryonic stem (ES) cells differentiate into cells of ecto-, endo-, and mesodermal lineages when cultured under appropriate conditions in vitro. Robust cardiomyogenic differentiation was frequently observed in spontaneously differentiating ES cultures. Cellular, molecular and physiologic analyses indicated that ES-derived cells were bona fide cardiomyocytes, with in vitro characteristics typical for cells obtained from early stages of cardiac development. Thus, ES-derived cardiomyocytes constitute a viable source of donor cells for cell transplantation therapies.

Cardiac tissue engineering: regeneration of the wounded heart

New solutions are needed to regenerate hearts damaged by myocardial infarction, to overcome bad prognosis of patients with heart failure, and to address the shortage of heart donors. In the past few years, cardiac tissue engineering has emerged as a new and ambitious approach that combines knowledge from material chemistry with cell biology and medicine. In this short review, we present an overview on the most promising materials and cell-therapy strategies used in the past few years for the regeneration of the wounded heart.

Cardiac remodeling and failure: from molecules to man (Part III)

Given the lack of a unified theory of heart failure, future research efforts will be required to unify and synthesize our current understanding of the multiple mechanisms that control remodeling in the failing heart. Matrix remodeling and the associated activation of inflammatory cytokines and MMPs have emerged as key pathways in the development of heart failure. As such, attempts to understand the integrated control of ECM homeostasis with the bioactivation of inflammatory cytokines may be of particular relevance to the development of effective anti-remodeling approaches. Notably, the implantation of isolated populations of cells in failing myocardium has a profound and consistent anti-remodeling effect that limits the progression to CHF. These observations were consistently identified in numerous studies using diverse experimental animal models and varied cell types. Accordingly, multicenter clinical trials are underway, and the preliminary data in patients with CHF are encouraging. Despite the enormous promise of cell transplantation to restore and regenerate failing myocardium, the mechanisms underlying these profound biological effects are not understood. An improved understanding of the myocardial response to cell implantation, particularly on parameters of matrix remodeling, may help unify our current understanding of the progression of heart failure and optimize the development of this technique for its evolving therapeutic use. The following review outlines recent advances in medical and surgical approaches to control the remodeling process that underlies the progression of heart failure.

Stimulation of P19CL6 with multiple reagents induces pulsating particles in vivo

OBJECTIVE

Injection of stem cells into ischaemic areas of the heart is expected to be an effective method for myocardial regeneration. The embryogenic carcinoma (EC) cell line P19CL6 is known to differentiate into cardiomyocytes when cultured with dimethyl sulfoxide (DMSO) and is expected to be a promising source for regenerative therapy in cardiac disease. To establish a high-yield method of cardiomyocyte differentiation, P19CL6 cells were double-stimulated with 5-azacytidine. Double stimulation-induced cardiomyocytes were also transplanted into ectopic sites in mice and their function evaluated.

METHODS AND RESULTS

To induce differentiation under adherent conditions, P19CL6 cells were incubated in growth medium with 10 microM 5-azacytidine for 24 h. After 5-azacytidine treatment, P19CL6 cells were incubated with 1% DMSO for nine days until they began to pulsate. Prior to transplantation, cells were treated again with 5-azacytidine. Differentiated cells were injected into the greater omentum, para-aorta region of the retroperitoneum and peri-femoral artery of adult BALB/c nude mice. Nine days after transplantation, irregularly pulsating tissues at a rate slower than the host heart were observed in the transplanted sites. Light microscopy showed formation of cardiac muscle tissues originating from P19CL6 cells. Differentiated cardiomyocytes were positive for cardiac troponin I, cadherin and alpha-smooth muscle actin, and the expressions of Csx/Nkx2.5 and GATA4 mRNAs were up-regulated. Electron microscopy demonstrated components specific to cardiomyocytes, such as Z-bands, desmosomes, fasciae adherens, myofibrils and mitochondria, which confirmed successful heterotopic cardiac muscle differentiation from P19CL6 cells.

CONCLUSION

This study demonstrated high-yield cardiac muscle differentiation of P19CL6 by 5-azacytidine and DMSO double stimulation and successful formation of cardiac muscle-like tissue by ectopic transplantation of cardiomyocytes derived from P19CL6 into the retroperitoneal area as well as into the peripheral vessel area.

Biological pacemaker created by fetal cardiomyocyte transplantation

BACKGROUND

The aim of this study was to investigate the feasibility of an alternative approach to electronic pacemaker by using spontaneously excitable cell grafts as a biological pacemaker in a large animal model of complete atrioventricular block.

METHODS AND RESULTS

Dissociated male human atrial cardiomyocytes including sinus nodal cells were grafted into the free wall of the left ventricle in five female pigs. Three weeks after the injection of cell-grafted solution/control medium the pigs underwent catheter ablation of the atrioventricular node (AV-node). After complete AV block was created, the idioventricular beat rate was more rapid in cell-grafted pigs than that in control pigs (86+/-21 vs. 30+/-10 bpm; P<0.001). Administering of isoprenalin significantly increased idioventricular rate from 86+/-21 to 117+/-18 bpm in the cell-grafted animals (P<0.01). Electrophysiological mapping studies demonstrated that the idioventricular rhythm originated from the cell-injection site. Polymerase chain reaction verifying the existence of SRY DNA in the cell injection site indicated that the grafted male cells were survived. Furthermore, the connexin-43 and N-cadherin positive junctions between donor cardiomyocytes and host cells were identified.

CONCLUSION

Xenografted fetal human atrial cardiomyocytes are able to survive and integrate into the host myocardium, and show a pacing function that can be modulated by autonomic agents.

[Cell transplantation in heart failure management]

Heart failure is becoming a major issue for public health in western countries and the effect of currently available therapies is limited. Therefore cell transplantation was developed as an alternative strategy to improve cardiac structure and function. This review describes the multiple cell types and clinical trials considered for use in this indication. Most studies have been developed in models of post-ischemic heart failure. The transplantation of fetal or neonatal cardiomyocytes has proven to be functionally successful, but ethical as well as immunological and technical reasons make their clinical use limited. Recent reports, however, suggested that adult autologous cardiomyocytes could be prepared from stem cells present in various tissues (bone marrow, vessels, adult heart itself, adipose tissue). Alternatively, endothelial progenitors originating from bone marrow or peripheral blood could promote the neoangiogenesis within the scar tissue. Hematopietic stem cells prepared from bone marrow or peripheral blood have been proposed but their differentiation ability seems limited. Finally, the transplantation of skeletal muscle cells (myoblasts) in the infarcted area improved myocardial function, in correlation with the development of skeletal muscle tissue in various animal models. The latter results paved the way for the development of a first phase I clinical trial of myoblast transplantation in patients with severe post-ischemic heart failure. It required the scale-up of human cell production according to good manufacturing procedures, started in june 2000 in Paris and was terminated in november 2001, and was followed by several others. The results were encouraging and prompted the onset of a blinded, multicentric phase II clinical trial for skeletal muscle cells transplantation. Meanwhile, phase I clinical trials also evaluate the safeness and efficacy of various cell types originating from the bone marrow or the peripheral blood. However, potential side effects related to the biological properties of the cells or the delivery procedures are being reported. High quality clinical trials supported by strong pre-clinical data will help to evaluate the role of cell therapy as a potential treatment for heart failure.

Efficient cardiomyogenic differentiation of embryonic stem cell by fibroblast growth factor 2 and bone morphogenetic protein 2

BACKGROUND

Despite the pluripotency of embryonic stem (ES) cells, the specific control of their cardiomyogenic differentiation remains difficult. The aim of the present study was to investigate whether growth factors may efficiently enhance the in vitro cardiac differentiation of ES cells.

METHODS AND RESULTS

Recombinant growth factors at various concentrations or their inhibitors were added according to various schedules during the cardiomyogenic differentiation of ES cells. Cardiomyogenic differentiation was assessed by mRNA and protein expressions of several cardiomyocyte-specific genes. Basic fibroblast growth factor-2 (FGF-2) and/or bone morphogenetic protein-2 (BMP-2) efficiently enhanced the cardiomyogenic differentiation, but only when they were added at the optimal concentration (1.0 ng/ml in FGF-2 and 0.2 ng/ml in BMP-2; relatively lower than expected in both cases) for the first 3 days. Inhibition of FGF-2 and/or BMP-2 drastically suppressed the cardiomyogenic differentiation.

CONCLUSION

FGF-2 and BMP-2 play a crucial role in early cardiomyogenesis. The achievement of efficient cardiac differentiation using both growth factors may facilitate ES cell-derived cell therapy for heart diseases as well as contribute to developmental studies of the heart.

Skeletal myoblast for cell therapy

After a decade of experimental work, skeletal myoblast transplantation has now entered the clinical arena as a potentially new means of improving the function of the failing heart. Because of the apparent lack of connections between the engrafted myoblasts and the host cardiomyocytes, it is likely that the functional benefits of myogenic cell transplantation are more related to limitation of adverse post-infarction remodelling and/or paracrine effects on recipient tissue rather than to a synchronous contribution of the graft to systolic pump function. As the initial clinical studies have primarily documented the feasibility of the procedure, it is now critical to assess whether the functional benefits observed in the laboratory setting translate into meaningful improvements in cardiac contractility and ultimate patient outcomes. Only randomised trials will allow us to satisfactorily address efficacy. These trials should also clarify the potentially pro-arrhythmic risk of myoblast engraftment, which might be related to the heterogeneous electrical properties between donor and recipient cells. In parallel, additional experimental studies are still warranted to address some key issues including the means of optimising post-transplantation myoblast survival, the development of less invasive cell transfer delivery technologies, the role of myoblast transplantation in non-ischemic heart failure settings and the comparative effects of skeletal myoblasts compared with other potential forms of cell therapy such as bone marrow-derived and embryonic stem cells.