Efficient differentiation of human induced pluripotent stem cells generates cardiac cells that provide protection following myocardial infarction in the rat

Progress in preclinical research on induced pluripotent stem cell therapy for acute myocardial infarction

Induced pluripotent stem cells (iPSCs) are obtained by introducing exogenous genes or adding chemicals to the culture medium to induce somatic cell differentiation. Similarly to embryonic stem cells, iPSCs have the ability to differentiate into all three embryonic cell lines. iPSCs can differentiate into cardiac muscle cells through two-dimensional differentiation methods such as monolayer cell culture and co-culture, or through embryoid body and scaffold-based three-dimensional differentiation methods. In addition, the process of iPSCs differentiation into cardiac muscle cells also requires activation or inhibition of specific signaling pathways,such as Wnt, BMP, Notch signaling pathways to mimic the development of the heart in vivo. In recent years, suspension culturing in bioreactors has been shown to produce large number of iPSCs derived cardiac muscle cells (iPSC-CMs). Before transplantation, it is necessary to purify iPSC-CMs through metabolic regulation or cell sorting to eliminate undifferentiated iPSCs, which may lead to teratoma formation. The transplantation methods for iPSC-CMs are mainly injection of cell suspension and transplantation of cell patches into the infarcted myocardium. Animal studies have shown that transplantation of iPSC-CMs into the infarcted myocardium can improve cardiac function. This article reviews the progress in preclinical studies on iPSC-CMs therapy for acute myocardial infarction and discusses the limitations and challenges of its clinical application to provide references for further clinical research and application.

The Structural and the Functional Aspects of Intercellular Communication in iPSC-Cardiomyocytes

Recent advances in the technology of producing novel cardiomyocytes from induced pluripotent stem cells (iPSC-cardiomyocytes) fuel new hope for future clinical applications. The use of iPSC-cardiomyocytes is particularly promising for the therapy of cardiac diseases such as myocardial infarction, where these cells could replace scar tissue and restore the functionality of the heart. Despite successful cardiogenic differentiation, medical applications of iPSC-cardiomyocytes are currently limited by their pronounced immature structural and functional phenotype. This review focuses on gap junction function in iPSC-cardiomyocytes and portrays our current understanding around the structural and the functional limitations of intercellular coupling and viable cardiac graft formation involving these novel cardiac muscle cells. We further highlight the role of the gap junction protein connexin 43 as a potential target for improving cell–cell communication and electrical signal propagation across cardiac tissue engineered from iPSC-cardiomyocytes. Better insight into the mechanisms that promote functional intercellular coupling is the foundation that will allow the development of novel strategies to combat the immaturity of iPSC-cardiomyocytes and pave the way toward cardiac tissue regeneration.

Cardiomyocyte Death and Genome-Edited Stem Cell Therapy for Ischemic Heart Disease

Massive death of cardiomyocytes is a major feature of cardiovascular diseases. Since the regenerative capacity of cardiomyocytes is limited, the regulation of their death has been receiving great attention. The cell death of cardiomyocytes is a complex mechanism that has not yet been clarified, and it is known to appear in various forms such as apoptosis, necrosis, etc. In ischemic heart disease, the apoptosis and necrosis of cardiomyocytes appear in two types of programmed forms (intrinsic and extrinsic pathways) and they account for a large portion of cell death. To repair damaged cardiomyocytes, diverse stem cell therapies have been attempted. However, despite the many positive effects, the low engraftment and survival rates have clearly limited the application of stem cells in clinical therapy. To solve these challenges, the introduction of the desired genes in stem cells can be used to enhance their capacity and improve their therapeutic efficiency. Moreover, as genome engineering technologies have advanced significantly, safer and more stable delivery of target genes and more accurate deletion of genes have become possible, which facilitates the genetic modification of stem cells. Accordingly, stem cell therapy for damaged cardiac tissue is expected to further improve. This review describes myocardial cell death, stem cell therapy for cardiac repair, and genome-editing technologies. In addition, we introduce recent stem cell therapies that incorporate genome-editing technologies in the myocardial infarction model. Graphical Abstract.

Cardiac Progenitor Cells

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

Engineered cardiac tissue microsphere production through direct differentiation of hydrogel-encapsulated human pluripotent stem cells

Engineered cardiac tissues that can be directly produced from human induced pluripotent stem cells (hiPSCs) in scalable, suspension culture systems are needed to meet the demands of cardiac regenerative medicine. Here, we demonstrate successful production of functional cardiac tissue microspheres through direct differentiation of hydrogel encapsulated hiPSCs. To form the microspheres, hiPSCs were suspended within the photocrosslinkable biomaterial, PEG-fibrinogen (25 million cells/mL), and encapsulated at a rate of 420,000 cells/minute using a custom microfluidic system. Even at this high cell density and rapid production rate, high intra-batch and batch-to-batch reproducibility was achieved. Following microsphere formation, hiPSCs maintained high cell viability and continued to grow within and beyond the original PEG-fibrinogen matrix. These initially soft microspheres (<250 Pa) supported efficient cardiac differentiation; spontaneous contractions initiated by differentiation day 8, and the microspheres contained >75% cardiomyocytes (CMs). CMs responded appropriately to pharmacological stimuli and exhibited 1:1 capture up to 6.0 Hz when electrically paced. Over time, cells formed cell-cell junctions and aligned myofibril fibers; engineered cardiac microspheres were maintained in culture over 3 years. The capability to rapidly generate uniform cardiac microsphere tissues is critical for advancing downstream applications including biomanufacturing, multi-well plate drug screening, and injection-based regenerative therapies.

Engineering and Assessing Cardiac Tissue Complexity

Cardiac tissue engineering is very much in a current focus of regenerative medicine research as it represents a promising strategy for cardiac disease modelling, cardiotoxicity testing and cardiovascular repair. Advances in this field over the last two decades have enabled the generation of human engineered cardiac tissue constructs with progressively increased functional capabilities. However, reproducing tissue-like properties is still a pending issue, as constructs generated to date remain immature relative to native adult heart. Moreover, there is a high degree of heterogeneity in the methodologies used to assess the functionality and cardiac maturation state of engineered cardiac tissue constructs, which further complicates the comparison of constructs generated in different ways. Here, we present an overview of the general approaches developed to generate functional cardiac tissues, discussing the different cell sources, biomaterials, and types of engineering strategies utilized to date. Moreover, we discuss the main functional assays used to evaluate the cardiac maturation state of the constructs, both at the cellular and the tissue levels. We trust that researchers interested in developing engineered cardiac tissue constructs will find the information reviewed here useful. Furthermore, we believe that providing a unified framework for comparison will further the development of human engineered cardiac tissue constructs displaying the specific properties best suited for each particular application.

A Concise Review on Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Personalized Regenerative Medicine

The induced pluripotent stem cells (iPSCs) are derived from somatic cells by using reprogramming factors such as Oct4, Sox2, Klf4, and c-Myc (OSKM) or Oct4, Sox2, Nanog and Lin28 (OSNL). They resemble embryonic stem cells (ESCs) and have the ability to differentiate into cell lineage of all three germ-layer, including cardiomyocytes (CMs). The CMs can be generated from iPSCs by inducing embryoid bodies (EBs) formation and treatment with activin A, bone morphogenic protein 4 (BMP4), and inhibitors of Wnt signaling. However, these iPSC-derived CMs are a heterogeneous population of cells and require purification and maturation to mimic the in vivo CMs. The matured CMs can be used for various therapeutic purposes in regenerative medicine by cardiomyoplasty or through the development of tissue-engineered cardiac patches. In recent years, significant advancements have been made in the isolation of iPSC and their differentiation, purification, and maturation into clinically usable CMs. Newer small molecules have also been identified to substitute the reprogramming factors for iPSC generation as well as for direct differentiation of somatic cells into CMs without an intermediary pluripotent state. This review provides a concise update on the generation of iPSC-derived CMs and their application in personalized cardiac regenerative medicine. It also discusses the current limitations and challenges in the application of iPSC-derived CMs. Graphical abstract.

Cardiac repair in a murine model of myocardial infarction with human induced pluripotent stem cell-derived cardiomyocytes

Background

Cellular replacement strategies using human induced pluripotent stem cells (iPSCs) and their cardiac derivatives are emerging as novel treatments for post-myocardial infarction (MI) heart failure (HF); however, the mechanism of recovery of heart function is not very clear. The purpose of this study was to investigate the efficiency of using highly purified human induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) for myocardial repair in a mouse model of MI and to clarify the mechanism of recovery of heart function.

Methods

Animals modelling MI were randomly assigned to receive direct intramyocardial injection of culture medium (MI group) or 4 × 10⁵ iPS-CMs (cell group) at the infarct border zone. Left ventricle (LV) performance was assessed with serial cardiac electrophysiology and was measured 1, 2 and 4 weeks post-MI. Invasive LV pressure measurement was measured at 4 weeks and was followed by sacrifice for histological examination.

Results

Compared to the MI group, the left ventricle ejection fraction (LVEF), left ventricular internal diameter in end-diastole (LVIDd) and end-systole (LVIDs) and maximal positive and negative pressure derivative (±dP/dt) were significantly improved in the iPS-CM group at 4 weeks post-MI. Histological examination revealed a very limited number of iPS-CMs 4 weeks after transplantation. Nonetheless, there was a significant enhancement of angiogenesis and a reduction in apoptosis of native cardiomyocyte after iPS-CM transplantation.

Conclusions

Our results demonstrate that transplantation of human iPS-CMs can improve heart function via paracrine action in a mouse model of myocardial infarction.

Transplantation of human induced pluripotent stem cell-derived cardiomyocytes improves myocardial function and reverses ventricular remodeling in infarcted rat hearts

Background

Human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have shed great light on cardiac regenerative medicine and specifically myocardial repair in heart failure patients. However, the treatment efficacy and the survival of iPSC-CMs in vivo after transplantation have yielded inconsistent results.

Objectives

The objective of this study was to evaluate the ability of human iPSC-CMs to improve myocardial function in a rat postinfarction heart failure model.

Methods

Eight-week-old male Sprague-Dawley rats were randomly selected to receive an intramyocardial injection of 5% albumin solution with or without 1 × 10⁷ human iPSC-CMs 10 days after undergoing left anterior descending (LAD) coronary artery ligation. Cyclosporine A and methylprednisolone were administered before iPSC-CM injection and until the rats were killed to prevent graft rejection. Cardiac function was evaluated by echocardiography. The survival of grafted cardiomyocytes was confirmed by observing the fluorescent cell tracer Vybrant™ CM-DiI or expression of the enhanced green fluorescent protein (eGFP) in transplanted cells, or survival was demonstrated by polymerase chain reaction (PCR)-based detection of human mitochondrial DNA. Sirius red stain was used to evaluate the fibrosis ratio. Hematoxylin-eosin staining was used to observe the formation of teratomas.

Results

Four weeks after intramyocardial injection of iPSC-CMs, animals undergoing iPSC-CM transplantation had lower mortality than the control group. Animals injected with cell-free solution (control group) demonstrated significant left ventricular (LV) functional deterioration, whereas grafting of iPSC-CMs attenuated this remodeling process. In the control group, the ejection fraction deteriorated by 10.11% (from 46.36 to 41.67%), and fractional shortening deteriorated by 9.23% (from 24.37 to 22.12%) by 4 weeks. In the iPSC-CM injection group, the ejection fraction improved by 18.86% (from 44.09 to 52.41%), and fractional shortening improved by 23.69% (from 23.08 to 28.54%). Cell labeling, tracking, and molecular biology techniques indicated that the grafted cardiomyocytes survived in the rat heart 1 month after iPSC-CM transplantation. Myocardial fibrosis was also attenuated in the iPSC-CM treatment group.

Conclusions

Human iPSC-CM grafts survived in infarcted rat hearts and restored myocardial function 4 weeks after transplantation. Cell replacement therapy also reversed ventricular remodeling, indicating the potential of iPSC-CMs for cardiac repair strategies.

Electronic supplementary material

The online version of this article (10.1186/s13287-020-01602-0) contains supplementary material, which is available to authorized users.

Human embryonic stem cell-derived cardiomyocyte therapy in mouse permanent ischemia and ischemia-reperfusion models

Background

Ischemic heart diseases are still a threat to human health. Human pluripotent stem cell-based transplantation exhibits great promise in cardiovascular disease therapy, including heart ischemia. The purpose of this study was to compare the efficacy of human embryonic stem cell-derived cardiomyocyte (ESC-CM) therapy in two heart ischemia models, namely, permanent ischemia (PI) and myocardial ischemia reperfusion (IR).

Methods

Human embryonic stem cell-derived cardiomyocytes were differentiated from engineered human embryonic stem cells (ESC-Rep) carrying green fluorescent protein (GFP), herpes simplex virus-1 thymidine kinase (HSVtk), and firefly luciferase (Fluc). Two different heart ischemia models were generated by the ligation of the left anterior descending artery (LAD), and ESC-Rep-derived cardiomyocytes (ESC-Rep-CMs) were transplanted into the mouse hearts. Cardiac function was analyzed to evaluate the outcomes of ESC-Rep-CM transplantation. Bioluminescence signal analysis was performed to assess the cell engraftment. Finally, the inflammation response was analyzed by real-time PCR and ELISA.

Results

Cardiac function was significantly improved in the PI group with ESC-Rep-CM injection compared to the PBS-injected control, as indicated by increased left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS), as well as reduced fibrotic area. However, minimal improvement by ESC-Rep-CM injection was detected in the IR mouse model. We observed similar engraftment efficiency between PI and IR groups after ESC-Rep-CM injection. However, the restricted inflammation was observed after the injection of ESC-Rep-CMs in the PI group, but not in the IR group. Transplantation of ESC-Rep-CMs can partially preserve the heart function via regulating the inflammation response in the PI model, while little improvement of cardiac function in the IR model may be due to the less dynamic inflammation response by the mild heart damage.

Conclusions

Our findings identified the anti-inflammatory effect of ESC-CMs as a possible therapeutic mechanism to improve cardiac function in the ischemic heart.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1271-4) contains supplementary material, which is available to authorized users.

Changing Metabolism in Differentiating Cardiac Progenitor Cells-Can Stem Cells Become Metabolically Flexible Cardiomyocytes?

The heart is a metabolic omnivore and the adult heart selects the substrate best suited for each circumstance, with fatty acid oxidation preferred in order to fulfill the high energy demand of the contracting myocardium. The fetal heart exists in an hypoxic environment and obtains the bulk of its energy via glycolysis. After birth, the "fetal switch" to oxidative metabolism of glucose and fatty acids has been linked to the loss of the regenerative phenotype. Various stem cell types have been used in differentiation studies, but most are cultured in high glucose media. This does not change in the majority of cardiac differentiation protocols. Despite the fact that metabolic state affects marker expression and cellular function and activity, the substrate composition is currently being overlooked. In this review we discuss changes in cardiac metabolism during development, the various protocols used to differentiate progenitor cells to cardiomyocytes, what is known about stem cell metabolism and how consideration of metabolism can contribute toward maturation of stem cell-derived cardiomyocytes.

Applications of genetically engineered human pluripotent stem cell reporters in cardiac stem cell biology

The advent of human pluripotent stem cells (hPSCs) has benefited many fields, from regenerative medicine to disease modeling, with an especially profound effect in cardiac research. Coupled with other novel technologies in genome engineering, hPSCs offer a great opportunity to delineate human cardiac lineages, investigate inherited cardiovascular diseases, and assess the safety and efficacy of cell-based therapies. In this review, we provide an overview of methods for generating genetically engineered hPSC reporters and a succinct synopsis of a variety of hPSC reporters, with a particular focus on their applications in cardiac stem cell biology.

Comparison of Non-human Primate versus Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Treatment of Myocardial Infarction

Non-human primates (NHPs) can serve as a human-like model to study cell therapy using induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). However, whether the efficacy of NHP and human iPSC-CMs is mechanistically similar remains unknown. To examine this, RNU rats received intramyocardial injection of 1 × 107 NHP or human iPSC-CMs or the same number of respective fibroblasts or PBS control (n = 9-14/group) at 4 days after 60-min coronary artery occlusion-reperfusion. Cardiac function and left ventricular remodeling were similarly improved in both iPSC-CM-treated groups. To mimic the ischemic environment in the infarcted heart, both cultured NHP and human iPSC-CMs underwent 24-hr hypoxia in vitro. Both cells and media were collected, and similarities in transcriptomic as well as metabolomic profiles were noted between both groups. In conclusion, both NHP and human iPSC-CMs confer similar cardioprotection in a rodent myocardial infarction model through relatively similar mechanisms via promotion of cell survival, angiogenesis, and inhibition of hypertrophy and fibrosis.

Effect of stem cell niche elasticity/ECM protein on the self-beating cardiomyocyte differentiation of induced pluripotent stem (iPS) cells at different stages

Stem cell-based myocardial regeneration therapies have emerged as alternative strategies to heart transplantation for serious heart diseases, but autologous beating mature cardiomyocytes are not available. Here we investigated the effect of culture substrates on the cardiomyocyte differentiation of induced pluripotent stem cells (iPSs) in vitro by separately evaluating the following continuous three steps: (1) cardiac marker gene expression, (2) contractile gene expression and self-beating, and (3) beating duration. To this end, we used iPS cells to study the cardiac differentiation, and neonatal rat cardiomyocytes (NCMs) to study beating behavior. These cells were cultured on substrates with different natures, i.e., an elastic substrate (Es) with the modulus of 9, 20, or 180 kPa, and hard tissue culture polystyrene dishes (TCPS) coated with collagen type I (Col), gelatin (Gel), or fibronectin (FN). The results revealed that the effective niches in each step were very different. The cardiac marker gene (GATA4, Tbx5, MEF2C) expression of iPSs at the 1st step was very high on the TCPS coated with FN or Gel, whereas on the FN-coated Es (especially with the 9 kPa modulus), the undifferentiated marker gene (Nanog) expression of iPSs was maintained. The expression of the contractile genes α-MHC, TnC1, and TnT2 and the self-beating (the 2nd step) of the NCMs were high on FN-coated TCPS and Col-coated Es. The 3rd step (beating duration) of the NCMs was effective on the Es, and at 21 days both the iPSs and NCMs stopped beating on the TCPS but were still beating on the Es. Overall, cardiac differentiation 'preferred' ECM-rigid culture substrates, and beating-behavior 'preferred' Col-soft culture substrates. These results are important for understanding and designing cardiac differentiation niches for regenerative medicine, and they suggest that a single culture substrate is not suitable for preparing self-beating cardiomyocytes.

STATEMENT OF SIGNIFICANCE

The transplantation of beating cardiomyocytes (BCMs) is expected to be made more effective for serious heart diseases. The identification of the appropriate engineering processes and suitable culture substrates for inducing stem cell differentiation into BCMs is thus indispensable. The differentiation can be divided into three major processes, the cardiac differentiation step, the beating-induction step and the beating-duration step. A protocol with the higher efficiency in all of the steps must be useful. In this study, we separately evaluated the effect of culture substrates at each three step. We clarified that the biological and the physical properties of the culture substrates required at these steps were different. We found useful criteria for effective cardiac cell niche systems design.

Extracellular vesicles from human-induced pluripotent stem cell-derived mesenchymal stromal cells (hiPSC-MSCs) protect against renal ischemia/reperfusion injury via delivering specificity protein (SP1) and transcriptional activating of sphingosine kinase 1 and inhibiting necroptosis

Renal ischemia-reperfusion is a main cause of acute kidney injury (AKI), which is associated with high mortality. Here we show that extracellular vesicles (EVs) secreted from hiPSC-MSCs play a critical role in protection against renal I/R injury. hiPSC-MSCs-EVs can fuse with renal cells and deliver SP1 into target cells, subsequently active SK1 expression and increase S1P formation. Chromatin immunoprecipitation (ChIP) analyses and luciferase assay were used to confirm SP1 binds directly to the SK1 promoter region and promote promoter activity. Moreover, SP1 inhibition (MIT) or SK1 inhibition (SKI-II) completely abolished the renal protective effect of hiPSC-MSCs-EVs in rat I/R injury mode. However, pre-treatment of necroptosis inhibitor Nec-1 showed no difference with the administration of hiPSC-MSCs-EVs only. We then generated an SP1 knockout hiPSC-MSC cell line by CRISPR/Cas9 system and found that SP1 knockout failed to show the protective effect of hiPSC-MSCs-EVs unless restoring the level of SP1 by Ad-SP1 in vitro and in vivo. In conclusion, this study describes an anti-necroptosis effect of hiPSC-MSCs-EVs against renal I/R injury via delivering SP1 into target renal cells and intracellular activating the expression of SK1 and the generation of S1P. These findings suggest a novel mechanism for renal protection against I/R injury, and indicate a potential therapeutic approach for a variety of renal diseases and renal transplantation.

Stem cells and heart disease - Brake or accelerator?

After two decades of intensive research and attempts of clinical translation, stem cell based therapies for cardiac diseases are not getting closer to clinical success. This review tries to unravel the obstacles and focuses on underlying mechanisms as the target for regenerative therapies. At present, the principal outcome in clinical therapy does not reflect experimental evidence. It seems that the scientific obstacle is a lack of integration of knowledge from tissue repair and disease mechanisms. Recent insights from clinical trials delineate mechanisms of stem cell dysfunction and gene defects in repair mechanisms as cause of atherosclerosis and heart disease. These findings require a redirection of current practice of stem cell therapy and a reset using more detailed analysis of stem cell function interfering with disease mechanisms. To accelerate scientific development the authors suggest intensifying unified computational data analysis and shared data knowledge by using open-access data platforms.

Transplantation of purified iPSC-derived cardiomyocytes in myocardial infarction

Background

Induced pluripotent stem cells (iPSC) can be differentiated into cardiomyocytes and represent a possible autologous cell source for myocardial repair. We analyzed the engraftment and functional effects of murine iPSC-derived cardiomyocytes (iPSC-CMs) in a murine model of myocardial infarction.

Methods and results

To maximize cardiomyocyte yield and purity a genetic purification protocol was applied. Murine iPSCs were genetically modified to express a Zeocin^™ resistance gene under control of the cardiac-specific α-myosin heavy chain (α-MHC, MYH6) promoter. Thus, CM selection was performed during in vitro differentiation. iPSC-CM aggregates (“cardiac bodies”, CBs) were transplanted on day 14 after LAD ligation into the hearts of previously LAD-ligated mice (800 CBs/animal; 2-3x10⁶ CMs). Animals were treated with placebo (PBS, n = 14) or iPSC-CMs (n = 35). Myocardial remodeling and function were evaluated by magnetic resonance imaging (MRI), conductance catheter (CC) analysis and histological morphometry. In vitro and in vivo differentiation was investigated. Follow up was 28 days (including histological assessment and functional analysis). iPSC-CM purity was >99%. Transplanted iPSC-CMs formed mature grafts within the myocardium, expressed cardiac markers and exhibited sarcomeric structures. Intramyocardial transplantation of iPSC-CMs significantly improved myocardial remodeling and left ventricular function 28 days after LAD-ligation.

Conclusions

We conclude that iPSCs can effectively be differentiated into cardiomyocytes and genetically enriched to high purity. iPSC derived cardiomyocytes engraft within the myocardium of LAD-ligated mice and contribute to improve left ventricular function.

Usage of Human Mesenchymal Stem Cells in Cell-based Therapy: Advantages and Disadvantages

The use of human mesenchymal stem cells (hMSCs) in cell-based therapy has attracted extensive interest in the field of regenerative medicine, and it shows applications to numerous incurable diseases. hMSCs show several superior properties for therapeutic use compared to other types of stem cells. Different cell types are discussed in terms of their advantages and disadvantages, with focus on the characteristics of hMSCs. hMSCs can proliferate readily and produce differentiated cells that can substitute for the targeted affected tissue. To maximize the therapeutic effects of hMSCs, a substantial number of these cells are essential, requiring extensive ex vivo cell expansion. However, hMSCs have a limited lifespan in an in vitro culture condition. The senescence of hMSCs is a double-edged sword from the viewpoint of clinical applications. Although their limited cell proliferation potency protects them from malignant transformation after transplantation, senescence can alter various cell functions including proliferation, differentiation, and migration, that are essential for their therapeutic efficacy. Numerous trials to overcome the limited lifespan of mesenchymal stem cells are discussed.

Efficient and robust differentiation of endothelial cells from human induced pluripotent stem cells via lineage control with VEGF and cyclic AMP

Blood vessels are essential components for many tissues and organs. Thus, efficient induction of endothelial cells (ECs) from human pluripotent stem cells is a key method for generating higher tissue structures entirely from stem cells. We previously established an EC differentiation system with mouse pluripotent stem cells to show that vascular endothelial growth factor (VEGF) is essential to induce ECs and that cyclic adenosine monophosphate (cAMP) synergistically enhances VEGF effects. Here we report an efficient and robust EC differentiation method from human pluripotent stem cell lines based on a 2D monolayer, serum-free culture. We controlled the direction of differentiation from mesoderm to ECs using stage-specific stimulation with VEGF and cAMP combined with the elimination of non-responder cells at early EC stage. This "stimulation-elimination" method robustly achieved very high efficiency (>99%) and yield (>10 ECs from 1 hiPSC input) of EC differentiation, with no purification of ECs after differentiation. We believe this method will be a valuable technological basis broadly for regenerative medicine and 3D tissue engineering.

Exosomes Generated From iPSC-Derivatives: New Direction for Stem Cell Therapy in Human Heart Diseases

Cardiovascular disease (CVD) is the leading cause of death in modern society. The adult heart innately lacks the capacity to repair and regenerate the damaged myocardium from ischemic injury. Limited understanding of cardiac tissue repair process hampers the development of effective therapeutic solutions to treat CVD such as ischemic cardiomyopathy. In recent years, rapid emergence of induced pluripotent stem cells (iPSC) and iPSC-derived cardiomyocytes presents a valuable opportunity to replenish the functional cells to the heart. The therapeutic effects of iPSC-derived cells have been investigated in many preclinical studies. However, the underlying mechanisms of iPSC-derived cell therapy are still unclear, and limited engraftment of iPSC-derived cardiomyocytes is well known. One facet of their mechanism is the paracrine effect of the transplanted cells. Microvesicles such as exosomes secreted from the iPSC-derived cardiomyocytes exert protective effects by transferring the endogenous molecules to salvage the injured neighboring cells by regulating apoptosis, inflammation, fibrosis, and angiogenesis. In this review, we will focus on the current advances in the exosomes from iPSC derivatives and discuss their therapeutic potential in the treatment of CVD.

A molecular roadmap of definitive erythropoiesis from human induced pluripotent stem cells

Human induced pluripotent stem cells (hiPSCs) are being considered for use in understanding haematopoietic disorders and as a potential source of in vitro manufactured red cells. Here, we show that hiPSCs are able to recapitulate various stages of developmental erythropoiesis. We show that primitive erythroblasts arise first, express CD31⁺ with CD235a⁺ , embryonic globins and red cell markers, but fail to express the hallmark red cell transcripts of adult erythropoiesis. When hiPSC-derived CD45⁺ CD235a^- haematopoietic progenitors are isolated on day 12 and further differentiated on OP9 stroma, they selectively express CD36⁺ and CD235a⁺ , adult erythroid transcripts for transcription factors (e.g., BCL11A, KLF1) and fetal/adult globins (HBG1/2, HBB). Importantly, hiPSC- and cord-derived CD36⁺ CD235a⁺ erythroblasts show a striking homology by transcriptome array profiling (only 306 transcripts with a 2Log fold change >1·5- or 2·8-fold). Phenotypic and transcriptome profiling of CD45⁺ CD117⁺ CD235a⁺ pro-erythroblasts and terminally differentiated erythroblasts is also provided, including evidence of a HbF (fetal) to HbA (adult) haemoglobin switch and enucleation, that mirrors their definitive erythroblast cord-derived counterparts. These findings provide a molecular roadmap of developmental erythropoiesis from hiPSC sources at several critical stages, but also helps to inform on their use for clinical applications and modelling human haematopoietic disease.

Clinical potential of human-induced pluripotent stem cells : Perspectives of induced pluripotent stem cells

The recent establishment of induced pluripotent stem (iPS) cells promises the development of autologous cell therapies for degenerative diseases, without the ethical concerns associated with human embryonic stem (ES) cells. Initially, iPS cells were generated by retroviral transduction of somatic cells with core reprogramming genes. To avoid potential genotoxic effects associated with retroviral transfection, more recently, alternative non-viral gene transfer approaches were developed. Before a potential clinical application of iPS cell-derived therapies can be planned, it must be ensured that the reprogramming to pluripotency is not associated with genome mutagenesis or epigenetic aberrations. This may include direct effects of the reprogramming method or "off-target" effects associated with the reprogramming or the culture conditions. Thus, a rigorous safety testing of iPS or iPS-derived cells is imperative, including long-term studies in model animals. This will include not only rodents but also larger mammalian model species to allow for assessing long-term stability of the transplanted cells, functional integration into the host tissue, and freedom from undifferentiated iPS cells. Determination of the necessary cell dose is also critical; it is assumed that a minimum of 1 billion transplantable cells is required to achieve a therapeutic effect. This will request medium to long-term in vitro cultivation and dozens of cell divisions, bearing the risk of accumulating replication errors. Here, we review the clinical potential of human iPS cells and evaluate which are the most suitable approaches to overcome or minimize risks associated with the application of iPS cell-derived cell therapies.

In Vivo Dynamic Metabolic Changes After Transplantation of Induced Pluripotent Stem Cells for Ischemic Injury

This study aimed to investigate in vivo dynamic metabolic changes after transplantation of induced pluripotent stem cells (iPSCs) and iPSC-derived enriched cardiomyocytes (iPSC-CMs) in a rat model of ischemic injury.

METHODS

Serial ¹⁸F-FDG PET, echocardiographic, immunohistochemical, and immunofluorescence studies were performed after transplantation of iPSCs and iPSC-CMs and compared with embryonic stem cells (ESCs), ESC-CMs, and a phosphate-buffered saline control group of rats with myocardial infarction.

RESULTS

Increased glucose metabolism in periinfarct areas and improved myocardial function were observed in the stem cell transplantation groups compared with the control group, and serial immunofluorescence and immunohistochemical results exhibited the survival and migration of stem cells during the study period.

CONCLUSION

Serial ¹⁸F-FDG PET and echocardiographic imaging studies demonstrated the dynamic metabolic changes and recovery of myocardial function after stem cell transplantation. ¹⁸F-FDG PET could be a potential approach to evaluating spatiotemporal dynamic metabolic changes in vivo after transplantation of iPSCs or iPSC-CMs for ischemic injury.

Therapeutic use of stem cells for cardiovascular disease

Stem cell treatments are a desirable therapeutic option to regenerate myocardium and improve cardiac function after myocardial infarction. Several different types of cells have been explored, each with their own benefits and limitations. Induced pluripotent stem cells possess an embryonic-like state and therefore have a high proliferative capacity, but they also pose a risk of teratoma formation. Mesenchymal stem cells have been investigated from both bone marrow and adipose tissue. Their immunomodulatory characteristics may permit the use of allogeneic cells as universal donor cells in the future. Lastly, studies have consistently shown that cardiac stem cells are better able to express markers of cardiogenesis compared to other cell types, as well improve cardiac function. The ideal source of stem cells depends on multiple factors such as the ease of extraction/isolation, effectiveness of engraftment, ability to differentiate into cardiac lineages and effect on cardiac function. Although multiple studies highlight the benefits and limitations of each cell type and reinforce the successful potential use of these cells to regenerate damaged myocardium, more studies are needed to directly compare cells from various sources. It is interesting to note that research using stem cell therapies is also expanding to treat other cardiovascular diseases including non-ischemic cardiomyopathies.

Long noncoding RNAs: Novel molecules in cardiovascular biology, disease and regeneration

Remarkable breakthroughs made in genomic technologies have facilitated the discovery of thousands of novel transcripts that do not template protein synthesis. Numerous RNAs termed as long noncoding RNAs (lncRNAs) generated from this pervasive transcription function vividly in gene regulatory networks and a variety of biological and cellular processes. Here, we make a brief description of the known and putative functions of lncRNAs in cardiovascular biology and disease. The association between lncRNAs and stem cells mediated cardiomyocytes differentiation and neovascularization is discussed then. It will provide a new clue for further studies on these novel molecules in cardiovascular disease and bring bright prospects for their future applications in cardiac regenerative medicine.

Robust Generation of Cardiomyocytes from Human iPS Cells Requires Precise Modulation of BMP and WNT Signaling

Various strategies have been published enabling cardiomyocyte differentiation of human induced pluripotent stem (iPS) cells. However the complex nature of signaling pathways involved as well as line-to-line variability compromises the application of a particular protocol to robustly obtain cardiomyocytes from multiple iPS lines. Hence it is necessary to identify optimized protocols with alternative combinations of specific growth factors and small molecules to enhance the robustness of cardiac differentiation. Here we focus on systematic modulation of BMP and WNT signaling to enhance cardiac differentiation. Moreover, we improve the efficacy of cardiac differentiation by enrichment via lactate. Using our protocol we show efficient derivation of cardiomyocytes from multiple human iPS lines. In particular we demonstrate cardiomyocyte differentiation within 15 days with an efficiency of up to 95 % as judged by flow cytometry staining against cardiac troponin T. Cardiomyocytes derived were functionally validated by alpha-actinin staining, transmission electron microscopy as well as electrophysiological analysis. We expect our protocol to provide a robust basis for scale-up production of functional iPS cell-derived cardiomyocytes that can be used for cell replacement therapy and disease modeling.

Mapping Human Pluripotent-to-Cardiomyocyte Differentiation: Methylomes, Transcriptomes, and Exon DNA Methylation "Memories"

The directed differentiation of human cardiomyocytes (CMs) from pluripotent cells provides an invaluable model for understanding mechanisms of cell fate determination and offers considerable promise in cardiac regenerative medicine. Here, we utilize a human embryonic stem cell suspension bank, produced according to a good manufacturing practice, to generate CMs using a fully defined and small molecule-based differentiation strategy. Primitive and cardiac mesoderm purification was used to remove non-committing and multi-lineage populations and this significantly aided the identification of key transcription factors, lncRNAs, and essential signaling pathways that define cardiomyogenesis. Global methylation profiles reflect CM development and we report on CM exon DNA methylation "memories" persisting beyond transcription repression and marking the expression history of numerous developmentally regulated genes, especially transcription factors.

Electrical effects of stem cell transplantation for ischaemic cardiomyopathy: friend or foe?

Despite advances in other realms of cardiac care, the mortality attributable to ischaemic cardiomyopathy has only marginally decreased over the last 10 years. These findings highlight the growing realization that current pharmacological and device therapies rarely reverse disease progression and rationalize a focus on novel means to reverse, repair and re-vascularize damaged hearts. As such, multiple candidate cell types have been used to regenerate damaged hearts either directly (through differentiation to form new tissue) or indirectly (via paracrine effects). Emerging literature suggests that robust engraftment of electrophysiolgically heterogeneous tissue from transplanted cells comes at the cost of a high incidence of ventricular arrhythmias. Similar electrophysiological studies of haematological stem cells raised early concerns that transplant of depolarized, inexcitable cells that also induce paracrine-mediated electrophysiological remodelling may be pro-arrhythmic. However, meta-analyses suggest that patients receiving haematological stem cells paradoxically may experience a decrease in ventricular arrhythmias, an observation potentially related to the extremely poor long-term survival of injected cells. Finally, early clinical and preclinical data from technologies capable of differentiating to a mature cardiomyocyte phenotype (such as cardiac-derived stem cells) suggests that these cells are not pro-arrhythmic although they too lack robust long-term engraftment. These results highlight the growing understanding that as next generation cell therapies are developed, emphasis should also be placed on understanding possible anti-arrhythmic contributions of transplanted cells while vigilance is needed to predict and treat the inadvertent effects of regenerative cell therapies on the electrophysiological stability of the ischaemic cardiomyopathic heart.

Bioengineering Human Myocardium on Native Extracellular Matrix

RATIONALE

More than 25 million individuals have heart failure worldwide, with ≈4000 patients currently awaiting heart transplantation in the United States. Donor organ shortage and allograft rejection remain major limitations with only ≈2500 hearts transplanted each year. As a theoretical alternative to allotransplantation, patient-derived bioartificial myocardium could provide functional support and ultimately impact the treatment of heart failure.

OBJECTIVE

The objective of this study is to translate previous work to human scale and clinically relevant cells for the bioengineering of functional myocardial tissue based on the combination of human cardiac matrix and human induced pluripotent stem cell-derived cardiomyocytes.

METHODS AND RESULTS

To provide a clinically relevant tissue scaffold, we translated perfusion-decellularization to human scale and obtained biocompatible human acellular cardiac scaffolds with preserved extracellular matrix composition, architecture, and perfusable coronary vasculature. We then repopulated this native human cardiac matrix with cardiomyocytes derived from nontransgenic human induced pluripotent stem cells and generated tissues of increasing 3-dimensional complexity. We maintained such cardiac tissue constructs in culture for 120 days to demonstrate definitive sarcomeric structure, cell and matrix deformation, contractile force, and electrical conduction. To show that functional myocardial tissue of human scale can be built on this platform, we then partially recellularized human whole-heart scaffolds with human induced pluripotent stem cell-derived cardiomyocytes. Under biomimetic culture, the seeded constructs developed force-generating human myocardial tissue and showed electrical conductivity, left ventricular pressure development, and metabolic function.

CONCLUSIONS

Native cardiac extracellular matrix scaffolds maintain matrix components and structure to support the seeding and engraftment of human induced pluripotent stem cell-derived cardiomyocytes and enable the bioengineering of functional human myocardial-like tissue of multiple complexities.

Modeling Viral Infectious Diseases and Development of Antiviral Therapies Using Human Induced Pluripotent Stem Cell-Derived Systems

The recent biotechnology breakthrough of cell reprogramming and generation of induced pluripotent stem cells (iPSCs), which has revolutionized the approaches to study the mechanisms of human diseases and to test new drugs, can be exploited to generate patient-specific models for the investigation of host–pathogen interactions and to develop new antimicrobial and antiviral therapies. Applications of iPSC technology to the study of viral infections in humans have included in vitro modeling of viral infections of neural, liver, and cardiac cells; modeling of human genetic susceptibility to severe viral infectious diseases, such as encephalitis and severe influenza; genetic engineering and genome editing of patient-specific iPSC-derived cells to confer antiviral resistance.

Molecular imaging of stem cells for the treatment of acute myocardial infarction

Stem cell therapy has a unique potential and promises hope for the treatment of acute myocardial infarction. Preclinical studies have identified barriers to clinical translation, one of which involves the monitoring of transplanted cells and the elucidation of their fates in vivo. Molecular imaging may help the solutions for these challenges. In this review, we illustrate the mechanisms by which molecular imaging enables insights into and the development of stem cell therapy.

Heart Regeneration with Embryonic Cardiac Progenitor Cells and Cardiac Tissue Engineering

Myocardial infarction (MI) is the leading cause of death worldwide. Recent advances in stem cell research hold great potential for heart tissue regeneration through stem cell-based therapy. While multiple cell types have been transplanted into MI heart in preclinical studies or clinical trials, reduction of scar tissue and restoration of cardiac function have been modest. Several challenges hamper the development and application of stem cell-based therapy for heart regeneration. Application of cardiac progenitor cells (CPCs) and cardiac tissue engineering for cell therapy has shown great promise to repair damaged heart tissue. This review presents an overview of the current applications of embryonic CPCs and the development of cardiac tissue engineering in regeneration of functional cardiac tissue and reduction of side effects for heart regeneration. We aim to highlight the benefits of the cell therapy by application of CPCs and cardiac tissue engineering during heart regeneration.

How to mend a broken heart: adult and induced pluripotent stem cell therapy for heart repair and regeneration

The recently developed ability to differentiate primary adult stem cells and induced pluripotent stem cells (iPSCs) into cardiomyocytes is providing unprecedented opportunities to produce an unlimited supply of cardiomyocytes for use in patients with heart disease. Here, we examine the evidence for the preclinical use of such cells for successful heart regeneration. We also describe advances in the identification of new cardiac molecular and cellular targets to induce proliferation of cardiomyocytes for heart regeneration. Such new advances are paving the way for a new innovative drug development process for the treatment of heart disease.

Comparison of human induced pluripotent stem-cell derived cardiomyocytes with human mesenchymal stem cells following acute myocardial infarction

INTRODUCTION

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have recently been shown to express key cardiac proteins and improve in vivo cardiac function when administered following myocardial infarction. However, the efficacy of hiPSC-derived cell therapies, in direct comparison to current, well-established stem cell-based therapies, is yet to be elucidated. The goal of the current study was to compare the therapeutic efficacy of human mesenchymal stem cells (hMSCs) with hiPSC-CMs in mitigating myocardial infarction (MI).

METHODS

Male athymic nude hyrats were subjected to permanent ligation of the left-anterior-descending (LAD) coronary artery to induce acute MI. Four experimental groups were studied: 1) control (non-MI), 2) MI, 3) hMSCs (MI+MSC), and 4) hiPSC-CMs (MI+hiPSC-derived cardiomyocytes). The hiPSC-CMs and hMSCs were labeled with superparamagnetic iron oxide (SPIO) in vitro to track the transplanted cells in the ischemic heart by high-field cardiac MRI. These cells were injected into the ischemic heart 30-min after LAD ligation. Four-weeks after MI, cardiac MRI was performed to track the transplanted cells in the infarct heart. Additionally, echocardiography (M-mode) was performed to evaluate the cardiac function. Immunohistological and western blot studies were performed to assess the cell tracking, engraftment and cardiac fibrosis in the infarct heart tissues.

RESULTS

Echocardiography data showed a significantly improved cardiac function in the hiPSC-CMs and hMSCs groups, when compared to MI. Immunohistological studies showed expression of connexin-43, α-actinin and myosin heavy chain in engrafted hiPSC-CMs. Cardiac fibrosis was significantly decreased in hiPSC-CMs group when compared to hMSCs or MI groups. Overall, this study demonstrated improved cardiac function with decreased fibrosis with both hiPSC-CMs and hMSCs groups when compared with MI group.

Neuregulin-1β induces mature ventricular cardiac differentiation from induced pluripotent stem cells contributing to cardiac tissue repair

Stem cell-derived cardiomyocytes (CMs) are often electrophysiologically immature and heterogeneous, which represents a major barrier to their in vitro and in vivo application. Therefore, the purpose of this study was to examine whether Neuregulin-1β (NRG-1β) treatment could enhance in vitro generation of mature "working-type" CMs from induced pluripotent stem (iPS) cells and assess the regenerative effects of these CMs on cardiac tissue after acute myocardial infarction (AMI). With that purpose, adult mouse fibroblast-derived iPS from α-MHC-GFP mice were derived and differentiated into CMs through NRG-1β and/or dimethyl sulfoxide (DMSO) treatment. Cardiac specification and maturation of the iPS was analyzed by gene expression array, quantitative real-time polymerase chain reaction, immunofluorescence, electron microscopy, and patch-clamp techniques. In vivo, the iPS-derived CMs or culture medium control were injected into the peri-infarct region of hearts after coronary artery ligation, and functional and histology changes were assessed from 1 to 8 weeks post-transplantation. On differentiation, the iPS displayed early and robust in vitro cardiogenesis, expressing cardiac-specific genes and proteins. More importantly, electrophysiological studies demonstrated that a more mature ventricular-like cardiac phenotype was achieved when cells were treated with NRG-1β and DMSO compared with DMSO alone. Furthermore, in vivo studies demonstrated that iPS-derived CMs were able to engraft and electromechanically couple to heart tissue, ultimately preserving cardiac function and inducing adequate heart tissue remodeling. In conclusion, we have demonstrated that combined treatment with NRG-1β and DMSO leads to efficient differentiation of iPS into ventricular-like cardiac cells with a higher degree of maturation, which are capable of preserving cardiac function and tissue viability when transplanted into a mouse model of AMI.

Databases and collaboration require standards for human stem cell research

Stem cell research is at an important juncture: despite significant potential for human health and several countries with key initiatives to expedite commercialization, there are gaps in capturing and exploiting the results of past and current research. Here, we propose a concerted plan that could be taken to foster a more collaborative approach and ensure that all research efforts can be leveraged across the community. The creation of a definitive centralized database repository, or at least harmonized data repositories, for stem cell groups in academia and industry, enabling secure selective sharing of data when needed, could provide the core structure that is sought globally and protect intellectual property. The development of minimum information about stem cell experiments (MIASCE) could be key to this development.

Clinical Potentials of Cardiomyocytes Derived from Patient-Specific Induced Pluripotent Stem Cells

The lack of appropriate human cardiomyocyte-based experimental platform has largely hindered the study of cardiac diseases and the development of therapeutic strategies. To date, somatic cells isolated from human subjects can be reprogramed into induced pluripotent stem cells (iPSCs) and subsequently differentiated into functional cardiomyocytes. This powerful reprogramming technology provides a novel in vitro human cell-based platform for the study of human hereditary cardiac disorders. The clinical potential of using iPSCs derived from patients with inherited cardiac disorders for therapeutic studies have been increasingly highlighted. In this review, the standard procedures for generating patient-specific iPSCs and the latest commonly used cardiac differentiation protocols will be outlined. Furthermore, the progress and limitations of current applications of iPSCs and iPSCs-derived cardiomyocytes in cell replacement therapy, disease modeling, drug-testing and toxicology studies will be discussed in detail.

The case for induced pluripotent stem cell-derived cardiomyocytes in pharmacological screening

The current drug screening models are deficient, particularly in detecting cardiac side effects. Human stem cell-derived cardiomyocytes could aid both early cardiotoxicity detection and novel drug discovery. Work over the last decade has generated human embryonic stem cells as potentially accurate sources of human cardiomyocytes, but ethical constraints and poor efficacy in establishing cell lines limit their use. Induced pluripotent stem cells do not require the use of human embryos and have the added advantage of producing patient-specific cardiomyocytes, allowing both generic and disease- and patient-specific pharmacological screening, as well as drug development through disease modelling. A critical question is whether sufficient standards have been achieved in the reliable and reproducible generation of 'adult-like' cardiomyocytes from human fibroblast tissue to progress from validation to safe use in practice and drug discovery. This review will highlight the need for a new experimental system, assess the validity of human induced pluripotent stem cell-derived cardiomyocytes and explore what the future may hold for their use in pharmacology.

Pluripotent Stem Cell Therapy in Ischemic Cardiovascular Disease

Stem cell therapy has been viewed as a promising therapeutic strategy in ischemic cardiovascular disease for almost a decade. Although many progenitor/stem cells obtained from patients have been investigated, and are alleged to be suitable for autologous transplantation, their therapeutic application has been limited by their inability to yield a sufficient number of stem cells, as well as impaired regeneration capacity from ageing and cardiovascular risk factors. Pluripotent stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have the capacity for functional multi-lineage differentiation and properties of self-renewal and immortality, and can generate clinically relevant amounts of stem cells. The regeneration capacity of these cells is not affected by ageing. Patient-specific pluripotent stem cells, iPSCs, can be established by epigenetically reprogramming somatic fibroblasts. iPSCs and iPSC-derived stem cells share similar phenotypes and gene expressions of ESCs and ESC-derived stem cells. Transplantation of pluripotent stem cell-derived endothelial cells, mural cells, cardiomyocytes, or cardiovascular progenitor cells contribute to neovascularization and cardiomyogenesis with better limb perfusion and recovery of myocardial contractility in the preclinical studies. Several strategies have been developed to enhance the efficacy of reprogramming and engrafting, and improve graft survival, proliferation, and electromechanical coupling by tissue engineering. However, the therapeutic application of ESCs and derivatives is limited by ethical concerns. Before wide clinical application of these cells in regeneration therapy occurs, substantial effort should be undertaken to discover the most promising cell type and derivatives, the best protocol regarding cell preparation, reprogramming and differentiation, and the most efficacious methods to avoid adverse effects.

KEY WORDS

Embryonic stem cells; Induced pluripotent stem cells; Limb ischemia; Myocardial infarction.

A promising approach to iPSC-based cell therapy for diabetic wound treatment: direct lineage reprogramming

Successful reprogramming of somatic cells into induced pluripotent stem cells (iPSCs) has ushered in a new era of regenerative medicine. Several studies on iPSCs have corroborated their immense promise and potential for use in cell therapy and disease modeling. However, several shortcomings need to be overcome before they can be used in clinical therapy. Investigation of iPSC fate and physiology in vivo and ultimately, the feasibility of their application in cell transplantation therapy, requires more in-depth studies in living subjects. One recently established alternative approach to reprogramming involves the direct conversion of a terminally differentiated somatic cell of one type into another, without dedifferentiating into a pluripotent state. This direct lineage reprogramming strategy is significantly faster, has the potential to generate an enriched population of a specific subtype of cells, and hence, has wide implications in regenerative cell therapy. Here, we review recent advances in iPSC technology and summarize the research on the generation of patient-specific induced cell types using direct lineage conversion. Specifically, we focus on the scope of application of this approach in autologous cell replacement therapy for diabetic wound treatment.

Advances in understanding the cell types and approaches used for generating induced pluripotent stem cells

Successfully reprogramming somatic cells to a pluripotent state generates induced pluripotent stem (iPS) cells (or iPSCs), which have extensive self-renewal capacity like embryonic stem cells (ESCs). iPSCs can also generate daughter cells that can further undergo differentiation into various lineages or terminally differentiate to reach their final functional state. The discovery of how to produce iPSCs opened a new field of stem cell research with both intellectual and therapeutic benefits. The huge potential implications of disease-specific or patient-specific iPSCs have impelled scientists to solve problems hindering their applications in clinical medicine, especially the issues of convenience and safety. To determine the range of tissue types amenable to reprogramming as well as their particular characteristics, cells from three embryonic germ layers have been assessed, and the advantages that some tissue origins have over fibroblast origins concerning efficiency and accessibility have been elucidated. To provide safe iPSCs in an efficient and convenient way, the delivery systems and combinations of inducing factors as well as the chemicals used to generate iPSCs have also been significantly improved in addition to the efforts on finding better donor cells. Currently, iPSCs can be generated without c-Myc and Klf4 oncogenes, and non-viral delivery integration-free chemically mediated reprogramming methods have been successfully employed with relatively satisfactory efficiency. This paper will review recent advances in iPS technology by highlighting tissue origin and generation of iPSCs. The obstacles that need to be overcome for clinical applications of iPSCs are also discussed.

Human embryonic stem cells vs human induced pluripotent stem cells for cardiac repair

Human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) have the capacity to differentiate into any specialized cell type, including cardiomyocytes. Therefore, hESC-derived and hiPSC-derived cardiomyocytes (hESC-CMs and hiPSC-CMs, respectively) offer great potential for cardiac regenerative medicine. Unlike some organs, the heart has a limited ability to regenerate, and dysfunction resulting from significant cardiomyocyte loss under pathophysiological conditions, such as myocardial infarction (MI), can lead to heart failure. Unfortunately, for patients with end-stage heart failure, heart transplantation remains the main alternative, and it is insufficient, mainly because of the limited availability of donor organs. Although left ventricular assist devices are progressively entering clinical practice as a bridge to transplantation and even as an optional therapy, cell replacement therapy presents a plausible alternative to donor organ transplantation. During the past decade, multiple candidate cells were proposed for cardiac regeneration, and their mechanisms of action in the myocardium have been explored. The purpose of this article is to critically review the comprehensive research involving the use of hESCs and hiPSCs in MI models and to discuss current controversies, unresolved issues, challenges, and future directions.

Regulatory T cells enhance mesenchymal stem cell survival and proliferation following autologous cotransplantation in ischemic myocardium

OBJECTIVES

We sought to investigate if autologous freshly isolated regulatory T cells (Tregs) provide a protective and supportive role when cotransplanted with mesenchymal stem cells (MSCs).

METHODS

In a porcine model of chronic ischemia, autologous MSCs were isolated and expanded ex vivo for 4 weeks. Autologous Treg cells were freshly isolated from 100 mL peripheral blood and purified by fluorescence-activated cell sorting. MSCs and Treg cells were then cotransplanted into the chronic ischemic myocardium of Yorkshire pigs by direct intramyocardial injection (1.2 × 10(8) MSCs plus an average of 1.5 million Treg cells in 25 injection sites). Animals were killed 6 weeks postinjection to study the fate of the cells and compare the effect of combined MSCs + Treg cells transplantation versus MSCs alone.

RESULTS

The coinjection of MSCs along with Tregs was safe and no deleterious side effects were observed. Six weeks after injection of the cell combination, spherical MSCs clusters with thin layer capsules were found in the injected areas. In animals treated with MSCs only, the MSC clusters were less organized and not encapsulated. Immunofluorescent staining showed CD25+ cells among the CD90+ (MSC marker) cells, suggesting that the injected Treg cells remained present locally, and survived. Factor VIII+ cells were also prevalent suggesting new angiogenesis. We found no evidence that coinjections were associated with the generation of cardiac myocytes.

CONCLUSIONS

The cotransplantation of Treg cells with MSCs dramatically increased the MSC survival rate, proliferation, and augmented their role in angiogenesis, which suggests a new way for future clinical application of cell-based therapy.

Chemically defined generation of human cardiomyocytes

Existing methods for human induced pluripotent stem cell (hiPSC) cardiac differentiation are efficient but require complex, undefined medium constituents that hinder further elucidation of the molecular mechanisms of cardiomyogenesis. Using hiPSCs derived under chemically defined conditions on synthetic matrices, we systematically developed an optimized cardiac differentiation strategy, using a chemically defined medium consisting of just three components: the basal medium RPMI 1640, L-ascorbic acid 2-phosphate and rice-derived recombinant human albumin. Along with small molecule-based induction of differentiation, this protocol produced contractile sheets of up to 95% TNNT2(+) cardiomyocytes at a yield of up to 100 cardiomyocytes for every input pluripotent cell and was effective in 11 hiPSC lines tested. This chemically defined platform for cardiac specification of hiPSCs will allow the elucidation of cardiomyocyte macromolecular and metabolic requirements and will provide a minimal system for the study of maturation and subtype specification.

Pluripotent stem cell derived cardiomyocytes for cardiac repair

OPINION STATEMENT

The adult mammalian heart has limited capacity for regeneration, and any major injury such as a myocardial infarction results in the permanent loss of up to 1 billion cardiomyocytes. The field of cardiac cell therapy aims to replace these lost contractile units with de novo cardiomyocytes to restore lost systolic function and prevent progression to heart failure. Arguably, the ideal cell for this application is the human cardiomyocyte itself, which can electromechanically couple with host myocardium and contribute active systolic force. Pluripotent stem cells from human embryonic or induced pluripotent lineages are attractive sources for cardiomyocytes, and preclinical investigation of these cells is in progress. Recent work has focused on the efficient generation and purification of cardiomyocytes, tissue engineering efforts, and examining the consequences of cell transplantation from mechanical, vascular, and electrical standpoints. Here we discuss historical and contemporary aspects of pluripotent stem cell-based cardiac cell therapy, with an emphasis on recent preclinical studies with translational goals.

Human induced pluripotent stem cell derived erythroblasts can undergo definitive erythropoiesis and co-express gamma and beta globins

Human induced pluripotent stem cells (hiPSCs), like embryonic stem cells, are under intense investigation for novel approaches to model disease and for regenerative therapies. Here, we describe the derivation and characterization of hiPSCs from a variety of sources and show that, irrespective of origin or method of reprogramming, hiPSCs can be differentiated on OP9 stroma towards a multi-lineage haemo-endothelial progenitor that can contribute to CD144(+) endothelium, CD235a(+) erythrocytes (myeloid lineage) and CD19(+) B lymphocytes (lymphoid lineage). Within the erythroblast lineage, we were able to demonstrate by single cell analysis (flow cytometry), that hiPSC-derived erythroblasts express alpha globin as previously described, and that a sub-population of these erythroblasts also express haemoglobin F (HbF), indicative of fetal definitive erythropoiesis. More notably however, we were able to demonstrate that a small sub-fraction of HbF positive erythroblasts co-expressed HbA in a highly heterogeneous manner, but analogous to cord blood-derived erythroblasts when cultured using similar methods. Moreover, the HbA expressing erythroblast population could be greatly enhanced (44·0 ± 6·04%) when a defined serum-free approach was employed to isolate a CD31(+) CD45(+) erythro-myeloid progenitor. These findings demonstrate that hiPSCs may represent a useful alternative to standard sources of erythrocytes (RBCs) for future applications in transfusion medicine.

Excision of viral reprogramming cassettes by Cre protein transduction enables rapid, robust and efficient derivation of transgene-free human induced pluripotent stem cells

Integrating viruses represent robust tools for cellular reprogramming; however, the presence of viral transgenes in induced pluripotent stem cells (iPSCs) is deleterious because it holds the risk of insertional mutagenesis leading to malignant transformation. Here, we combine the robustness of lentiviral reprogramming with the efficacy of Cre recombinase protein transduction to derive iPSCs devoid of transgenes. By genome-wide analysis and targeted differentiation towards the cardiomyocyte lineage, we show that transgene-free iPSCs are superior to iPSCs before Cre transduction. Our study provides a simple, rapid and robust protocol for the generation of clinical-grade iPSCs suitable for disease modeling, tissue engineering and cell replacement therapies.