Cell-based therapy for heart failure: skeletal myoblasts

Engineering of MSCs sheet for the prevention of myocardial ischemia and for left ventricle remodeling

Tissue engineering combines cell biology and material science to construct tissues or organs for disease modeling, drug testing, and regenerative medicine. The cell sheet is a newly developed tissue engineering technology that has brought about scaffold-free tissue and shows great application potential. In this review, we summarized recent progress and future possibilities in preclinical research into and clinical applications of cell sheets fabricated by differing cell types from various sources for cardiac tissue repair, and the manufacturing strategies and promising application potential of 3D cell-dense tissue constructed from cell sheets. Special attention was paid to the mechanisms of mesenchymal stem cell (MSC) sheets in the prevention of myocardial ischemia and left ventricle remodeling. Comparing MSCs sheets with other types of cell sheets and 3D cardiac tissues, engineering tissues' potential safety and effectiveness concerns were also discussed.

Cardiomyocytes induced from hiPSCs by well-defined compounds have therapeutic potential in heart failure by secreting PDGF-BB

Recent studies have suggested that transplant of hiPS-CMs is a promising approach for treating heart failure. However, the optimally clinical benefits have been hampered by the immature nature of the hiPS-CMs, and the hiPS-CMs-secreted proteins contributing to the repair of cardiomyocytes remain largely unidentified. Here, we established a saponin⁺ compound optimally induced system to generate hiPS-CMs with stable functional attributes in vitro and transplanted in heart failure mice. Our study showed enhanced therapeutic effects of optimally induced hiPS-CMs by attenuating cardiac remodeling and dysfunction, these beneficial effects were concomitant with reduced cardiomyocytes death and increased angiogenesis. Moreover, the optimally induced hiPS-CMs could gathering to the injured heart and secret an abundant PDGF-BB. The reparative effect of the optimally induced hiPS-CMs in the hypoxia-injured HCMs was mimicked by PDGF-BB but inhibited by PDGF-BB neutralizing antibody, which was accompanied by the changed expression of p-PI3K and p-Akt proteins. It is highly possible that the PI3K/Akt pathway is regulated by the PDGF-BB secreted from the compound induced hiPS-CMs to achieve a longer lasting myocardial repair effect compared with the standard induced hiPS-CMs. Taken together, our data strongly implicate that the compound induced hiPS-CMs promote the recovery of injured hearts via paracrine action. In this process, the paracrine factor PDGF-BB derived from the compound induced hiPS-CMs reduces isoproterenol-induced adverse cardiac remodeling, which is associated with improved cardiac function, and these effects are mediated by the PI3K/Akt pathway, suggesting that the optimally induced hiPS-CMs may serve as a new promising cell therapy for clinical applications.

Analyzing Impetus of Regenerative Cellular Therapeutics in Myocardial Infarction

Both vasculature and myocardium in the heart are excessively damaged following myocardial infarction (MI), hence therapeutic strategies for treating MI hearts should concurrently aim for true cardiac repair by introducing new cardiomyocytes to replace lost or injured ones. Of them, mesenchymal stem cells (MSCs) have long been considered a promising candidate for cell-based therapy due to their unspecialized, proliferative differentiation potential to specific cell lineage and, most importantly, their capacity of secreting beneficial paracrine factors which further promote neovascularization, angiogenesis, and cell survival. As a consequence, the differentiated MSCs could multiply and replace the damaged tissues to and turn into tissue- or organ-specific cells with specialized functions. These cells are also known to release potent anti-fibrotic factors including matrix metalloproteinases, which inhibit the proliferation of cardiac fibroblasts, thereby attenuating fibrosis. To achieve the highest possible therapeutic efficacy of stem cells, the other interventions, including hydrogels, electrical stimulations, or platelet-derived biomaterials, have been supplemented, which have resulted in a narrow to broad range of outcomes. Therefore, this article comprehensively analyzed the progress made in stem cells and combinatorial therapies to rescue infarcted myocardium.

Injected Human Muscle Precursor Cells Overexpressing PGC-1α Enhance Functional Muscle Regeneration after Trauma

While many groups demonstrated new muscle tissue formation after muscle precursor cell (MPC) injection, the capacity of these cells to heal muscle damage, for example, sphincter in stress urinary incontinence, in long-term is still limited. Therefore, the first goal of our project was to optimize the functional regenerative potential of hMPC by genetic modification to overexpress human peroxisome proliferator-activated receptor gamma coactivator 1-alpha (hPGC-1α), key regulator of exercise-mediated adaptation. Moreover, we aimed at establishing a feasible methodology for noninvasive PET visualization of implanted cells and their microenvironment in muscle crush injury model. PGC-1α-bioengineered muscles showed enhanced marker expression for myogenesis (α-actinin, MyHC, and Desmin), vascularization (VEGF), neuronal (ACHE), and mitochondrial (COXIV) activity. Consistently, use of hPGC-1α_hMPCs produced significantly increased contractile force one to three weeks postinjury. PET imaging showed distinct differences in radiotracer signals ([¹⁸F]Fallypride and [¹¹C]Raclopride (both targeting dopamine 2 receptors (D2R)) and [⁶⁴Cu]NODAGA-RGD (targeting neovascularization)) between GFP_hMPCs and hD2R_hPGC-1α_hMPCs. After muscle harvesting, inflammation levels were in parallel to radiotracer uptake amount, with significantly lower uptake in hPGC-1α overexpressing samples. In summary, we facilitated early functional muscle tissue regeneration, introducing a novel approach to improve skeletal muscle regeneration. Besides successful tracking of hMPCs in muscle crush injuries, we showed that in high-inflammation areas, the specificity of radioligands might be significantly reduced, addressing a possible bottleneck of neovascularization PET imaging.

Optimizing stem cells for cardiac repair: Current status and new frontiers in regenerative cardiology

Cell therapy has the potential to improve healing of ischemic heart, repopulate injured myocardium and restore cardiac function. The tremendous hope and potential of stem cell therapy is well understood, yet recent trials involving cell therapy for cardiovascular diseases have yielded mixed results with inconsistent data thereby readdressing controversies and unresolved questions regarding stem cell efficacy for ischemic cardiac disease treatment. These controversies are believed to arise by the lack of uniformity of the clinical trial methodologies, uncertainty regarding the underlying reparative mechanisms of stem cells, questions concerning the most appropriate cell population to use, the proper delivery method and timing in relation to the moment of infarction, as well as the poor stem cell survival and engraftment especially in a diseased microenvironment which is collectively acknowledged as a major hindrance to any form of cell therapy. Indeed, the microenvironment of the failing heart exhibits pathological hypoxic, oxidative and inflammatory stressors impairing the survival of transplanted cells. Therefore, in order to observe any significant therapeutic benefit there is a need to increase resilience of stem cells to death in the transplant microenvironment while preserving or better yet improving their reparative functionality. Although stem cell differentiation into cardiomyocytes has been observed in some instance, the prevailing reparative benefits are afforded through paracrine mechanisms that promote angiogenesis, cell survival, transdifferentiate host cells and modulate immune responses. Therefore, to maximize their reparative functionality, ex vivo manipulation of stem cells through physical, genetic and pharmacological means have shown promise to enable cells to thrive in the post-ischemic transplant microenvironment. In the present work, we will overview the current status of stem cell therapy for ischemic heart disease, discuss the most recurring cell populations employed, the mechanisms by which stem cells deliver a therapeutic benefit and strategies that have been used to optimize and increase survival and functionality of stem cells including ex vivo preconditioning with drugs and a novel “pharmaco-optimizer” as well as genetic modifications.

An in silico prediction tool for the expansion culture of human skeletal muscle myoblasts

Regenerative therapy using autologous skeletal myoblasts requires a large number of cells to be prepared for high-level secretion of cytokines and chemokines to induce good regeneration of damaged regions. However, myoblast expansion culture is hindered by a reduction in growth rate owing to cellular quiescence and differentiation, therefore optimization is required. We have developed a kinetic computational model describing skeletal myoblast proliferation and differentiation, which can be used as a prediction tool for the expansion process. In the model, myoblasts migrate, divide, quiesce and differentiate as observed during in vitro culture. We assumed cell differentiation initiates following cell-cell attachment for a defined time period. The model parameter values were estimated by fitting to several predetermined experimental datasets. Using an additional experimental dataset, we confirmed validity of the developed model. We then executed simulations using the developed model under several culture conditions and quantitatively predicted that non-uniform cell seeding had adverse effects on the expansion culture, mainly by reducing the existing ratio of proliferative cells. The proposed model is expected to be useful for predicting myoblast behaviours and in designing efficient expansion culture conditions for these cells.

Implantation of autologous muscle-derived stem cells in treatment of fecal incontinence: results of an experimental pilot study

Background

The aim of this study is to present results of the implantation of autologous myoblasts into the external anal sphincter (EAS) in ten patients with fecal incontinence.

Methods

After anatomical and functional assessment of the patients’ EAS, a vastus lateralis muscle open biopsy was performed. Stem cells were extracted from the biopsy specimens and cultured in vitro. Cell suspensions were then administered to the EAS. Patients were scheduled for follow-up visits in 6-week intervals. Total follow-up was 12 months.

Results

All biopsy and cell implantation procedures were performed without complications. Nine of the patients completed a full 12-month follow-up. There was subjective improvement in six patients (66.7 %). In manometric examinations 18 weeks after implantation, squeeze anal pressures and high-pressure zone length increased in all patients, with particularly significant sphincter function recovery in five patients (55.6 %). Electromyographic (EMG) examination showed an increase in signal amplitude in all patients, detecting elevated numbers of propagating action potentials. Twelve months after implantation two patients experienced deterioration of continence, which was also reflected in the deterioration of manometric and EMG parameters. The remaining four patients (44.4 %) still described their continence as better than before implantation and retained satisfactory functional examination parameters.

Conclusions

Implantation of autologous myoblasts gives good short-term results not only in a subjective assessment, but also in objective functional tests. It seems that this promising technology can improve the quality of life of patients with fecal incontinence, but further study is required to achieve better and more persistent results.

External physical and biochemical stimulation to enhance skeletal muscle bioengineering

PURPOSE OF REVIEW

Cell based muscle tissue engineering carries the potential to revert the functional loss of muscle tissue caused by disease and trauma. Although muscle tissue can be bioengineered using various precursor cells, major limitations still remain.

RECENT FINDINGS

In the last decades several cellular pathways playing a crucial role in muscle tissue regeneration have been described. These pathways can be influenced by external stimuli and they not only orchestrate the regenerative process after physiologic wear and muscle trauma, but also play an important part in aging and maintaining the stem cell niche, which is required to maintain long-term muscle function.

SUMMARY

In this review article we will highlight possible new avenues using external physical and biochemical stimulation in order to optimize muscle bioengineering.

Exogenous connexin43-expressing autologous skeletal myoblasts ameliorate mechanical function and electrical activity of the rabbit heart after experimental infarction

Acute myocardial infarction is one of the major causes of mortality worldwide. For regeneration of the rabbit heart after experimentally induced infarction we used autologous skeletal myoblasts (SMs) due to their high proliferative potential, resistance to ischaemia and absence of immunological and ethical concerns. The cells were characterized with muscle-specific and myogenic markers. Cell transplantation was performed by injection of cell suspension (0.5 ml) containing approximately 6 million myoblasts into the infarction zone. The animals were divided into four groups: (i) no injection; (ii) sham injected; (iii) injected with wild-type SMs; and (iv) injected with SMs expressing connexin43 fused with green fluorescent protein (Cx43EGFP). Left ventricular ejection fraction (LVEF) was evaluated by 2D echocardiography in vivo before infarction, when myocardium has stabilized after infarction, and 3 months after infarction. Electrical activity in the healthy and infarction zones of the heart was examined ex vivo in Langendorff-perfused hearts by optical mapping using di-4-ANEPPS, a potential sensitive fluorescent dye. We demonstrate that SMs in the coculture can couple electrically not only to abutted but also to remote acutely isolated allogenic cardiac myocytes through membranous tunnelling tubes. The beneficial effect of cellular therapy on LVEF and electrical activity was observed in the group of animals injected with Cx43EGFP-expressing SMs. L-type Ca(2+) current amplitude was approximately fivefold smaller in the isolated SMs compared to healthy myocytes suggesting that limited recovery of LVEF may be related to inadequate expression or function of L-type Ca(2+) channels in transplanted differentiating SMs.

Long-term follow-up after autologous skeletal myoblast transplantation in ischaemic heart disease

OBJECTIVES

Short-term follow-up after autologous skeletal myoblasts (ASM) transplantation (Tx) (Myoblast Autologous Grafting in Ischaemic Cardiomyopathy (MAGIC) Phase II Study) for the treatment of ischaemic cardiomyopathy revealed improved left ventricular (LV) remodelling. Our study reports the longest long-term worldwide follow-up of a single-centre cohort, focusing on the safety and efficacy of ASM-Tx.

METHODS

The multicentre MAGIC Phase II Study involved 120 patients and was conducted between 2004 and 2006. Out of the 120 patients involved in the entire study, the cohort treated at our institution contained 7 patients only. These 7 patients received ASM-Tx (injection volume: 400 million cells, n = 2 low dosage; 800 million cells, n = 2 high dosage) or placebo (n = 3) injections, in addition to coronary artery bypass grafting (CABG). After closure of the MAGIC registry, we conducted a long-term follow-up for our 7-patient cohort. The mean follow-up was 72.0 ± 5.3 months. The follow-up was complete for echo data, implanted cardioverter defibrillator (ICD) report, clinical investigation and New York Heart Association (NYHA) class.

RESULTS

At final follow-up, all the patients were alive, and 5 were in NYHA class 1 or 2. There were 6 hospitalizations for congestive heart failure during the follow-up (1 patient from each group). One patient (placebo group) was treated twice for ventricular fibrillation by the ICD. The LV ejection fraction remained stable in all the three groups (31.1 ± 3.9% preoperative vs 29.4 ± 4.4% at final follow-up). The LV volumes were reduced in the high-dosage group, remained unchanged in the low-dosage group and deteriorated in the placebo group.

CONCLUSIONS

Our long-term data confirm the findings of the MAGIC study. The LV function did not improve, but the long-term LV volumes in the high-dosage group were reduced. During the follow-up, there were also no additional arrhythmogenic incidences. Our data could imply that CABG in combination with ASM-Tx is safe and has beneficial therapeutic effects in the long-term. However, due to the small patient number, the clinical impact is limited.

Characterisation of nuclear architectural alterations during in vitro differentiation of human stem cells of myogenic origin

Cell differentiation is based on a synchronised orchestra of complex pathways of intrinsic and extrinsic signals that manifest in the induced expression of specific transcription factors and pivotal genes within the nucleus. One cannot ignore the epigenetic status of differentiating cells, comprising not only histones and DNA modifications but also the spatial and temporal intranuclear chromatin organisation, which is an important regulator of nuclear processes. In the present study, we investigated the nuclear architecture of human primary myoblasts and myocytes in an in vitro culture, with reference to global changes in genomic expression. Repositioning of the chromosomal centromeres, along with alterations in the nuclear shape and volume, was observed as a consequence of myotube formation. Moreover, the microarray data showed that during in vitro myogenesis cells tend to silence rather than induce gene expression. The creation of a chromosome map marked with gene expression changes that were at least 2-fold confirmed the observation. Additionally, almost all of the chromosomal centromeres in the differentiated cells preferentially localised near the nuclear periphery when compared to the undifferentiated cells. The exceptions were chromosomes 7 and 11, in which we were unable to confirm the centromere repositioning. In our opinion, this is the first reported observation of the movement of chromosomal centromeres along differentiating myogenic cells. Based on these data we can conclude that the myogenic differentiation with global gene expression changes is accompanied by the spatial repositioning of chromosomes and chromatin remodelling, which are important processes that regulate cell differentiation.

Muscle Precursor Cells for the Restoration of Irreversibly Damaged Sphincter Function

Multiple modalities, including injectable bulking agents and surgery, have been used to treat stress urinary incontinence. However, none of these methods is able to fully restore normal striated sphincter muscle function. In this study, we explored the possibility of achieving functional recovery of the urinary sphincter muscle using autologous muscle precursor cells (MPCs) as an injectable, cell-based therapy. A canine model of striated urinary sphincter insufficiency was created by microsurgically removing part of the sphincter muscle in 24 dogs. Autologous MPCs were obtained, expanded in culture, and injected into the damaged sphincter muscles of 12 animals. The animals were followed for up to 6 months after injection, and urodynamic studies, functional organ bath studies, ultrastructural and histological examinations were performed. Animals receiving MPC injections demonstrated sphincter pressures of approximately 80% of normal values, while the pressures in the control animals without cells dropped and remained at 20% of normal values. Histological analysis indicated that the implanted cells survived and formed tissue, including new innervated muscle fibers, within the injected region of the sphincter. These results indicate that autologous muscle precursor cells may be able to restore otherwise irreversibly damaged urinary sphincter function clinically.

Alteration of cardiac progenitor cell potency in GRMD dogs

Among the animal models of Duchenne muscular dystrophy (DMD), the Golden Retriever muscular dystrophy (GRMD) dog is considered the best model in terms of size and pathological onset of the disease. As in human patients presenting with DMD or Becker muscular dystrophies (BMD), the GRMD is related to a spontaneous X-linked mutation of dystrophin and is characterized by myocardial lesions. In this respect, GRMD is a useful model to explore cardiac pathogenesis and for the development of therapeutic protocols. To investigate whether cardiac progenitor cells (CPCs) isolated from healthy and GRMD dogs may differentiate into myocardial cell types and to test the feasibility of cell therapy for cardiomyopathies in a preclinical model of DMD, CPCs were isolated from cardiac biopsies of healthy and GRMD dogs. Gene profile analysis revealed an active cardiac transcription network in both healthy and GRMD CPCs. However, GRMD CPCs showed impaired self-renewal and cardiac differentiation. Population doubling and telomerase analyses highlighted earlier senescence and proliferation impairment in progenitors isolated from GRMD cardiac biopsies. Immunofluorescence analysis revealed that only wt CPCs showed efficient although not terminal cardiac differentiation, consistent with the upregulation of cardiac-specific proteins and microRNAs. Thus, the pathological condition adversely influences the cardiomyogenic differentiation potential of cardiac progenitors. Using PiggyBac transposon technology we marked CPCs for nuclear dsRed expression, providing a stable nonviral gene marking method for in vivo tracing of CPCs. Xenotransplantation experiments in neonatal immunodeficient mice revealed a valuable contribution of CPCs to cardiomyogenesis with homing differences between wt and dystrophic progenitors. These results suggest that cardiac degeneration in dystrophinopathies may account for the progressive exhaustion of local cardiac progenitors and shed light on cardiac stemness in physiological and pathological conditions. Furthermore, we provide essential information that canine CPCs may be used to alleviate cardiac involvement in a large preclinical model of DMD.

Isolation of myogenic stem cells from cultures of cryopreserved human skeletal muscle

We demonstrate that subpopulations of adult human skeletal muscle-derived stem cells, myogenic endothelial cells (MECs), and perivascular stem cells (PSCs) can be simultaneously purified by fluorescence-activated cell sorting (FACS) from cryopreserved human primary skeletal muscle cell cultures (cryo-hPSMCs). For FACS isolation, we utilized a combination of cell lineage markers: the myogenic cell marker CD56, the endothelial cell marker UEA-1 receptor (UEA-1R), and the perivascular cell marker CD146. MECs expressing all three cell lineage markers (CD56(+)UEA-1R(+)CD146(+)/CD45(-)) and PSCs expressing only CD146 (CD146(+)/CD45(-)CD56(-)UEA-1R(-)) were isolated by FACS. To evaluate their myogenic capacities, the sorted cells, with and without expansion in culture, were transplanted into the cardiotoxin-injured skeletal muscles of immunodeficient mice. The purified MECs exhibited the highest regenerative capacity in the injured mouse muscles among all cell fractions tested, while PSCs remained superior to myoblasts and the unpurified primary skeletal muscle cells. Our findings show that both MECs and PSCs retain their high myogenic potentials after in vitro expansion, cryopreservation, and FACS sorting. The current study demonstrates that myogenic stem cells are prospectively isolatable from long-term cryopreserved primary skeletal muscle cell cultures. We emphasize the potential application of this new approach to extract therapeutic stem cells from human muscle cells cryogenically banked for clinical purposes.

Experience from experimental cell transplantation therapy of myocardial infarction: what have we learned?

During the past 15 years, our research group has transplanted fetal/neonatal cardiomyocytes, mesenchymal stem cells, and embryonic stem cell-derived cardiomyocytes into infarcted myocardium in a rat myocardial infarction model. Our experimental data demonstrated that cell transplantation therapy provides a potential approach for the treatment of injured myocardium after myocardial infarction based on the reported positive effects upon histological appearance and left ventricular function. However, the underlying mechanisms of the benefits from cell transplantation therapy remain unclear and may involve replacement of scar tissue by transplanted cells, induced neoangiogenesis and paracrine effects of factors released by the transplanted cells. In this review, we summarize our experiences from experimental cell transplantation therapy in a rat myocardial infarction model and discuss the controversies and questions that need to be addressed in future studies.

Cardiac regeneration

The heart is a pump that is comprised of cardiac myocytes and other cell types and whose proper function is critical to quality of life. The ability to trigger regeneration of heart muscle following injury eludes adult mammals, a deficiency of great clinical impact. Major research efforts are attempting to change this through advances in cell therapy or activating endogenous regenerative mechanisms that exist only early in life. In contrast with mammals, lower vertebrates like zebrafish demonstrate an impressive natural capacity for cardiac regeneration throughout life. This review will cover recent progress in the field of heart regeneration with a focus on endogenous regenerative capacity and its potential manipulation.

Trichostatin a promotes cardiomyocyte differentiation of rat mesenchymal stem cells after 5-azacytidine induction or during coculture with neonatal cardiomyocytes via a mechanism independent of histone deacetylase inhibition

This study was to investigate the effect of trichostatin A (TSA), a histone deacetylase (HDAC) inhibitor, on cardiac differentiation of bone marrow mesenchymal stem cells (MSCs) in vitro. Rat MSCs were isolated and divided into six groups: 1) control; 2) 5-azacytidine treatment (5-aza, 10 μM); 3) treatment with TSA (100, 300, and 500 nM); 4) treatment with 5-aza followed by incubation with TSA; 5) coculture with neonatal cardiomyocytes (CMs); and 6) treatment with TSA then coculture with CMs. HDAC activity was significantly inhibited in TSA-treated cells with the maximal inhibition after 24 h of exposure to TSA at 300 nM. No changes in HDAC activity were observed in control, 5-aza-treated, or coculture groups. Following 7 days of differentiation, the expression of early cardiac transcription factors GATA-4, NKx2.5, MEF2c, and cardiac troponin T (cTnT) was increased by 6-8 times in the cells in 5-aza-treated, coculture, or TSA-treated groups over control as determined using real-time PCR, immunofluorescence staining, and Western blotting. However, the percent cTnT-positive cells were dramatically different with 0.7% for control, 10% for 5-aza-treated, 25% for coculture, and 4% for TSA-treated group (500 nM). TSA treatment of the cells pretreated with 5-aza or cocultured with CMs dramatically increased the expression of GATA-4, NKx2.5, and MEF2c by 35-50 times over control. The cTnT protein expression was also significantly increased by over threefold by TSA treatment (500 nM) in both 5-aza-treated and coculture group over control. The percent cTnT-positive cells in both 5-aza-pre-treated and coculture groups were significantly increased by TSA treatment after 1 week of differentiation by up to 92.6% (from 10.3% to 19.8%) and 23.9% (from 24.5% to 30.2%), respectively. These data suggested that TSA enhanced the cardiac differentiation of MSCs after 5-aza induction or during coculture with CMs through a mechanism beyond the inhibition of HDAC activity.

Stem cell research in cell transplantation: sources, geopolitical influence, and transplantation

If the rapidly progressing field of stem cell research reaches its full potential, successful treatments and enhanced understanding of many diseases are the likely results. However, the full potential of stem cell science will only be reached if all possible avenues can be explored and on a worldwide scale. Until 2009, the US had a highly restrictive policy on obtaining cells from human embryos and fetal tissue, a policy that pushed research toward the use of adult-derived cells. Currently, US policy is still in flux, and retrospective analysis does show the US lagging behind the rest of the world in the proportional increase in embryonic/fetal stem cell research. The majority of US studies being on either a limited number of cell lines, or on cells derived elsewhere (or funded by other sources than Federal) rather than on freshly isolated embryonic or fetal material. Neural, mesenchymal, and the mixed stem cell mononuclear fraction are the most commonly investigated types, which can generally be classified as adult-derived stem cells, although roughly half of the neural stem cells are fetal derived. Other types, such as embryonic and fat-derived stem cells, are increasing in their prominence, suggesting that new types of stem cells are still being pursued. Sixty percent of the reported stem cell studies involved transplantation, of which over three quarters were allogeneic transplants. A high proportion of the cardiovascular systems articles were on allogeneic transplants in a number of different species, including several autologous studies. A number of pharmaceutical grade stem cell products have also recently been tested and reported on. Stem cell research shows considerable promise for the treatment of a number of disorders, some of which have entered clinical trials; over the next few years it will be interesting to see how these treatments progress in the clinic.

Preclinical and clinical studies on application of human myoblasts in regeneration of the postinfarction heart

Principal definitions of stem cell subdivisions as well as of the physiology of the renewal of their descendants have been elucidated in recent years. Regeneration mechanisms have been outlined using as an example the intestinal villus niche. Sources of stem cells for preclinical studies and the main conclusions from clinical trials have been developed in the vast majority in the 21st century. Meta-analyses and summaries have been focused so far on bone marrow stem cells and muscle-derived stem cells, which have been most often tried to date. Polish clinical trials on postinfarcted hearts have been consistent with the world literature regarding the major conclusions for myocardial regeneration. The controversies include possible side effects of stem cell applications. The necessity for genetic modification of the stem cells, which are mainly myoblasts, has been justified by the results of recently performed trials, initial examples including transfections of proangiogenic factors into human primary myoblast suspensions.

Bcl-2 Expression Enhances Myoblast Sheet Transplantation Therapy for Acute Myocardial Infarction

Myoblast sheet transplantation is a promising novel treatment modality for heart failure after an ischemic insult. However, low supply of blood and nutrients may compromise sheet survival. The aim of this study was to investigate the effect of mitochondria-protective Bcl-2-modified myoblasts in cell sheet transplantation therapy. In the Bcl-2-expressing rat L6 myoblast sheets (L6-Bcl2), increased expression of myocyte markers and angiogenic mediators was evident compared to wild-type (L6-WT) sheets. The L6-Bcl2 sheets demonstrated significant resistance to apoptotic stimuli, and their differentiation capacity in vitro was increased. We evaluated the therapeutic effect of Bcl-2-modified myoblast sheets in a rat model of acute myocardial infarction (AMI). Sixty-four Wistar rats were divided into four groups. One group underwent AMI ( n = 22), another AMI and L6-WT sheet transplantation ( n = 17), and a third AMI and L6-Bcl2 sheet transplantation ( n = 20). Five rats underwent a sham operation. Echocardiography was performed after 3, 10, and 28 days. Samples for histological analysis were collected at the end of the study. After AMI, the Bcl-2-expressing sheets survived longer on the infarcted myocardium, and significantly improved cardiac function. L6-Bcl2 sheet transplantation reduced myocardial fibrosis and increased vascular density in infarct and border areas. Moreover, the number of c-kit-positive and proliferating cells in the myocardium was increased in the L6-Bcl2 group. In conclusion, Bcl-2 prolongs survival of myoblast sheets, increases production of proangiogenic paracrine mediators, and enhances the therapeutic efficacy of cell sheet transplantation.