Human embryonic stem cell-derived cardiomyocytes engraft but do not alter cardiac remodeling after chronic infarction in rats

Human pluripotent stem cell-based cardiac repair: Lessons learned and challenges ahead

The transplantation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and hPSC-derived cardiac progenitors (hPSC-CPs) represents a promising strategy for regenerating hearts damaged by myocardial infarction (MI). After nearly two decades of experience testing these cell populations in various small- and large-animal MI models, multiple clinical trials have recently been initiated. In this review, we consider the principal lessons learned from preclinical experience with hPSC-CMs and -CPs, focusing on three conclusions that have been supported by the majority of reported transplantation studies. First, hPSC-CMs and -CPs stably engraft in injured hearts and partially remuscularize the infarct scar, but more progress is needed to improve graft cell retention and survival. Second, the transplantation of hPSC-CMs and -CPs has been found to improve contractile function in infarcted hearts, but the mechanistic basis for these effects remains incompletely elucidated. Third, the graft tissue formed by these cells can integrate and activate synchronously with host myocardium, but this capacity for electromechanical integration has been associated with an elevated risk of graft-related arrhythmias. Here, we summarize the preclinical evidence supporting these three observations, identify the relevant gaps and barriers to translation, and summarize ongoing efforts to improve the safety and efficacy of hPSC-CM- and -CP-based regenerative therapies.

An Alginate/Gelatin Injectable Hydrogel Containing Au Nanoparticles for Transplantation of Embryonic Mouse Cardiomyocytes in Myocardial Repair

In advancing cardiac tissue engineering (CTE), the development of injectable hydrogels mirroring myocardial properties is pivotal. The designed hydrogels must not only support cardiac cell growth but also have to be conductive to properly promote the functionalities of cardiac cells. Here, a facile approach is developed to incorporate gold nanoparticles (AuNPs) into an injectable hydrogel composed of Alginate (Alg) and Gelatin (Gel). The resultant nanocomposite hydrogel boasts a porous interconnected network and superior conductivity (2.04 × 10-4 S cm-1) compared to the base Alg/Gel hydrogel. Hydrogel hydration and in vitro degradation profiles affirm their suitability as carriers for cardiac cells. Importantly, Alg/Gel+AuNPs hydrogels exhibit no toxicity to mouse Embryonic Cardiac Cells (mECCs) over 7 days, elevating connexin 43 (Cx43) and cardiac troponin T (CTnT) gene expression compared to controls. Then, the Alg/Gel+AuNPs hydrogel is used as a carrier for intramyocardial delivery of mECCs in rats with myocardial infarction. The significant increase in α-Smooth Muscle Actin (α-SMA) and cardiac troponin T (CTnT) expression along with the increase in ejection fraction (EF), smaller infarction size, less fibrosis area confirmed that the hydrogel efficiently promoted the transmission of mechanical and electrical signals between transplanted cells and surrounding tissue.

Emerging Trends and Innovations in the Treatment and Diagnosis of Atherosclerosis and Cardiovascular Disease: A Comprehensive Review towards Healthier Aging

Cardiovascular diseases (CVDs) are classed as diseases of aging, which are associated with an increased prevalence of atherosclerotic lesion formation caused by such diseases and is considered as one of the leading causes of death globally, representing a severe health crisis affecting the heart and blood vessels. Atherosclerosis is described as a chronic condition that can lead to myocardial infarction, ischemic cardiomyopathy, stroke, and peripheral arterial disease and to date, most pharmacological therapies mainly aim to control risk factors in patients with cardiovascular disease. Advances in transformative therapies and imaging diagnostics agents could shape the clinical applications of such approaches, including nanomedicine, biomaterials, immunotherapy, cell therapy, and gene therapy, which are emerging and likely to significantly impact CVD management in the coming decade. This review summarizes the current anti-atherosclerotic therapies' major milestones, strengths, and limitations. It provides an overview of the recent discoveries and emerging technologies in nanomedicine, cell therapy, and gene and immune therapeutics that can revolutionize CVD clinical practice by steering it toward precision medicine. CVD-related clinical trials and promising pre-clinical strategies that would significantly impact patients with CVD are discussed. Here, we review these recent advances, highlighting key clinical opportunities in the rapidly emerging field of CVD medicine.

Long-term engraftment and maturation of autologous iPSC-derived cardiomyocytes in two rhesus macaques

Cellular therapies with cardiomyocytes produced from induced pluripotent stem cells (iPSC-CMs) offer a potential route to cardiac regeneration as a treatment for chronic ischemic heart disease. Here, we report successful long-term engraftment and in vivo maturation of autologous iPSC-CMs in two rhesus macaques with small, subclinical chronic myocardial infarctions, all without immunosuppression. Longitudinal positron emission tomography imaging using the sodium/iodide symporter (NIS) reporter gene revealed stable grafts for over 6 and 12 months, with no teratoma formation. Histological analyses suggested capability of the transplanted iPSC-CMs to mature and integrate with endogenous myocardium, with no sign of immune cell infiltration or rejection. By contrast, allogeneic iPSC-CMs were rejected within 8 weeks of transplantation. This study provides the longest-term safety and maturation data to date in any large animal model, addresses concerns regarding neoantigen immunoreactivity of autologous iPSC therapies, and suggests that autologous iPSC-CMs would similarly engraft and mature in human hearts.

Non-human primate studies for cardiomyocyte transplantation-ready for translation?

Non-human primates (NHP) are valuable models for late translational pre-clinical studies, often seen as a last step before clinical application. The unique similarity between NHPs and humans is often the subject of ethical concerns. However, it is precisely this analogy in anatomy, physiology, and the immune system that narrows the translational gap to other animal models in the cardiovascular field. Cell and gene therapy approaches are two dominant strategies investigated in the research field of cardiac regeneration. Focusing on the cell therapy approach, several xeno- and allogeneic cell transplantation studies with a translational motivation have been realized in macaque species. This is based on the pressing need for novel therapeutic options for heart failure patients. Stem cell-based remuscularization of the injured heart can be achieved via direct injection of cardiomyocytes (CMs) or patch application. Both CM delivery approaches are in the late preclinical stage, and the first clinical trials have started. However, are we already ready for the clinical area? The present review concentrates on CM transplantation studies conducted in NHPs, discusses the main sources and discoveries, and provides a perspective about human translation.

Challenges and perspectives of heart repair with pluripotent stem cell-derived cardiomyocytes

Here we aim at providing a concise but comprehensive overview of the perspectives and challenges of heart repair with pluripotent stem cell-derived cardiomyocytes. This Review comes at a time when consensus has been reached about the lack of relevant proliferative capacity of adult mammalian cardiomyocytes and the lack of new heart muscle formation with autologous cell sources. While alternatives to cell-based approaches will be shortly summarized, the focus lies on pluripotent stem cell-derived cardiomyocyte repair, which entered first clinical trials just 2 years ago. In the view of the authors, these early trials are important but have to be viewed as early proof-of-concept trials in humans that will hopefully provide first answers on feasibility, safety and the survival of allogeneic pluripotent stem cell-derived cardiomyocyte in the human heart. Better approaches have to be developed to make this approach clinically applicable.

Pluripotent stem cell-based cardiac regenerative therapy for heart failure

Cardiac regenerative therapy using human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) is expected to become an alternative to heart transplantation for severe heart failure. It is now possible to produce large numbers of human pluripotent stem cells (hPSCs) and eliminate non-cardiomyocytes, including residual undifferentiated hPSCs, which can cause teratoma formation after transplantation. There are two main strategies for transplanting hPSC-CMs: injection of hPSC-CMs into the myocardium from the epicardial side, and implantation of hPSC-CM patches or engineered heart tissues onto the epicardium. Transplantation of hPSC-CMs into the myocardium of large animals in a myocardial infarction model improved cardiac function. The engrafted hPSC-CMs matured, and microvessels derived from the host entered the graft abundantly. Furthermore, as less invasive methods using catheters, injection into the coronary artery and injection into the myocardium from the endocardium side have recently been investigated. Since transplantation of hPSC-CMs alone has a low engraftment rate, various methods such as transplantation with the extracellular matrix or non-cardiomyocytes and aggregation of hPSC-CMs have been developed. Post-transplant arrhythmias, imaging of engrafted hPSC-CMs, and immune rejection are the remaining major issues, and research is being conducted to address them. The clinical application of cardiac regenerative therapy using hPSC-CMs has just begun and is expected to spread widely if its safety and efficacy are proven in the near future.

Cell Therapy in the Treatment of Coronary Heart Disease

Heart failure is a leading cause of death in patients who have suffered a myocardial infarction. Despite the timely use of modern reperfusion therapies such as thrombolysis, surgical revascularization and balloon angioplasty, they are sometimes unable to prevent the development of significant areas of myocardial damage and subsequent heart failure. Research efforts have focused on developing strategies to improve the functional status of myocardial injury areas. Consequently, the restoration of cardiac function using cell therapy is an exciting prospect. This review describes the characteristics of various cell types relevant to cellular cardiomyoplasty and presents findings from experimental and clinical studies investigating cell therapy for coronary heart disease. Cell delivery methods, optimal dosage and potential treatment mechanisms are discussed.

HLA-Ehigh /HLA-Ghigh /HLA-IIlow Human iPSC-Derived Cardiomyocytes Exhibit Low Immunogenicity for Heart Regeneration

Although human pluripotent stem cells (hPSCs)-derived cardiomyocytes (hPSC-CMs) can remuscularize infarcted hearts and restore post-infarct cardiac function, post-transplant rejection resulting from human leukocyte antigen (HLA) mismatching is an enormous obstacle. It is crucial to identify hypoimmunogenic hPSCs for allogeneic cell therapy. This study is conducted to demonstrate the immune privilege of HLA-Ehigh /HLA-Ghigh /HLA-IIlow human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs). Ischemia-reperfusion surgery is done to create transmural myocardial infarction in rats. At post-infarct 4 days, hPSC-CMs (1.0×107 cells per kg), including human embryonic stem cell-derived cardiomyocytes (hESC-CMs), HLA-Elow/HLA-Glow/HLA-IIhigh hiPSC-CMs, and HLA-Ehigh /HLA-Ghigh /HLA-IIlow hiPSC-CMs, are injected into the infarcted myocardium. Under the treatment of very low dose cyclosporine A (CsA), only HLA-Ehigh /HLA-Ghigh /HLA-IIlow hiPSC-CMs survive in vivo and improved post-infarct cardiac function with infarct size reduction. HLA-Ehigh /HLA-Ghigh /HLA-IIlow hiPSC-CMs activate the SHP-1 signaling pathway of natural killer (NK) cells and cytotoxic T cells to evade attack by NK cells and cytotoxic T cells. Herein, it is demonstrated that using a clinically relevant CsA dose, HLA-Ehigh /HLA-Ghigh /HLA-IIlow hiPSC-CMs repair the infarcted myocardium and restore the post-infarct heart function. HLA-Ehigh /HLA-Ghigh /HLA-IIlow hiPSCs are less immunogenic and may serve as platforms for regeneration medicine.

Cardiac regeneration - Past advancements, current challenges, and future directions

Cardiovascular disease is the leading cause of mortality and morbidity worldwide. Despite improvements in the standard of care for patients with heart diseases, including innovation in pharmacotherapy and surgical interventions, none have yet been proven effective to prevent the progression to heart failure. Cardiac transplantation is the last resort for patients with severe heart failure, but donor shortages remain a roadblock. Cardiac regenerative strategies include cell-based therapeutics, gene therapy, direct reprogramming of non-cardiac cells, acellular biologics, and tissue engineering methods to restore damaged hearts. Significant advancements have been made over the past several decades within each of these fields. This review focuses on the advancements of: 1) cell-based cardiac regenerative therapies, 2) the use of noncoding RNA to induce endogenous cell proliferation, and 3) application of bioengineering methods to promote retention and integration of engrafted cells. Different cell sources have been investigated, including adult stem cells derived from bone marrow and adipose cells, cardiosphere-derived cells, skeletal myoblasts, and pluripotent stem cells. In addition to cell-based transplantation approaches, there have been accumulating interest over the past decade in inducing endogenous CM proliferation for heart regeneration, particularly with the use of noncoding RNAs such as miRNAs and lncRNAs. Bioengineering applications have focused on combining cell-transplantation approaches with fabrication of a porous, vascularized scaffold using biomaterials and advanced bio-fabrication techniques that may offer enhanced retention of transplanted cells, with the hope that these cells would better engraft with host tissue to improve cardiac function. This review summarizes the present status and future challenges of cardiac regenerative therapies.

Cell based dATP delivery as a therapy for chronic heart failure

Transplanted human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) improve ventricular performance when delivered acutely post-myocardial infarction but are ineffective in chronic myocardial infarction/heart failure. 2'-deoxy-ATP (dATP) activates cardiac myosin and potently increases contractility. Here we engineered hPSC-CMs to overexpress ribonucleotide reductase, the enzyme controlling dATP production. In vivo, dATP-producing CMs formed new myocardium that transferred dATP to host cardiomyocytes via gap junctions, increasing their dATP levels. Strikingly, when transplanted into chronically infarcted hearts, dATP-producing grafts increased left ventricular function, whereas heart failure worsened with wild-type grafts or vehicle injections. dATP-donor cells recipients had greater voluntary exercise, improved cardiac metabolism, reduced pulmonary congestion and pathological cardiac hypertrophy, and improved survival. This combination of remuscularization plus enhanced host contractility offers a novel approach to treating the chronically failing heart.

Development of direct cardiac reprogramming for clinical applications

The incidence of cardiovascular diseases is increasing worldwide, and cardiac regenerative therapy has great potential as a new treatment strategy, especially for ischemic heart disease. Direct cardiac reprogramming is a promising new cardiac regenerative therapy that uses defined factors to induce transdifferentiation of endogenous cardiac fibroblasts (CFs) into induced cardiomyocyte-like cells (iCMs). In vivo reprogramming is expected to restore lost cardiac function without necessitating cardiac transplantation by converting endogenous CFs that exist abundantly in cardiac tissues directly into iCMs. Indeed, we and other groups have demonstrated that in vivo cardiac reprogramming improves cardiac contractile function and reduces scar area after acute myocardial infarction (MI). Recently, we demonstrated that in vivo cardiac reprogramming is an innovative cardiac regenerative therapy that not only regenerates the myocardium, but also reverses fibrosis by inducing the quiescence of pro-fibrotic fibroblasts, thereby improving heart failure in chronic MI. In this review, we summarize the recent progresses in in vivo cardiac reprogramming, and discuss its prospects for future clinical applications and the challenges of direct human reprogramming, which has been a longstanding issue.

Advances in 3D Organoid Models for Stem Cell-Based Cardiac Regeneration

The adult human heart cannot regain complete cardiac function following tissue injury, making cardiac regeneration a current clinical unmet need. There are a number of clinical procedures aimed at reducing ischemic damage following injury; however, it has not yet been possible to stimulate adult cardiomyocytes to recover and proliferate. The emergence of pluripotent stem cell technologies and 3D culture systems has revolutionized the field. Specifically, 3D culture systems have enhanced precision medicine through obtaining a more accurate human microenvironmental condition to model disease and/or drug interactions in vitro. In this study, we cover current advances and limitations in stem cell-based cardiac regenerative medicine. Specifically, we discuss the clinical implementation and limitations of stem cell-based technologies and ongoing clinical trials. We then address the advent of 3D culture systems to produce cardiac organoids that may better represent the human heart microenvironment for disease modeling and genetic screening. Finally, we delve into the insights gained from cardiac organoids in relation to cardiac regeneration and further discuss the implications for clinical translation.

Cardiac regeneration: Options for repairing the injured heart

Cardiac regeneration is one of the grand challenges in repairing injured human hearts. Numerous studies of signaling pathways and metabolism on cardiac development and disease pave the way for endogenous cardiomyocyte regeneration. New drug delivery approaches, high-throughput screening, as well as novel therapeutic compounds combined with gene editing will facilitate the development of potential cell-free therapeutics. In parallel, progress has been made in the field of cell-based therapies. Transplantation of human pluripotent stem cell (hPSC)-derived cardiomyocytes (hPSC-CMs) can partially rescue the myocardial defects caused by cardiomyocyte loss in large animals. In this review, we summarize current cell-based and cell-free regenerative therapies, discuss the importance of cardiomyocyte maturation in cardiac regenerative medicine, and envision new ways of regeneration for the injured heart.

Transient secretion of VEGF protein from transplanted hiPSC-CMs enhances engraftment and improves rat heart function post MI

Cell-based therapies offer an exciting and novel treatment for heart repair following myocardial infarction (MI). However, these therapies often suffer from poor cell viability and engraftment rates, which involve many factors, including the hypoxic conditions of the infarct environment. Meanwhile, vascular endothelial growth factor (VEGF) has previously been employed as a therapeutic agent to limit myocardial damage and simultaneously induce neovascularization. This study took an approach to transiently overexpress VEGF protein, in a controlled manner, by transfecting human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) with VEGF mRNA prior to transplantation. The conditioning of iPSC-CMs with VEGF mRNA ultimately led to greater survival rates of the transplanted cells, which promoted a stable vascular network in the grafted region. Furthermore, bulk RNA transcriptomics data and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that phosphoinositide 3-kinase (PI3K)-protein kinase B (Akt) and AGE-RAGE signaling pathways were significantly upregulated in the VEGF-treated iPSC-CMs group. The over-expression of VEGF from iPSC-CMs stimulated cell proliferation and partially attenuated the hypoxic environment in the infarcted area, resulting in reduced ventricular remodeling. This study provides a valuable solution for the survival of transplanted cells in tissue-engineered heart regeneration and may further promote the application of modified mRNA (modRNA) in the field of tissue engineering.

Cardiac Cell Therapy with Pluripotent Stem Cell-Derived Cardiomyocytes: What Has Been Done and What Remains to Do?

PURPOSE OF REVIEW

Exciting pre-clinical data presents pluripotent stem cell-derived cardiomyocytes (PSC-CM) as a novel therapeutic prospect following myocardial infarction, and worldwide clinical trials are imminent. However, despite notable advances, several challenges remain. Here, we review PSC-CM pre-clinical studies, identifying key translational hurdles. We further discuss cell production and characterization strategies, identifying markers that may help generate cells which overcome these barriers.

RECENT FINDINGS

PSC-CMs can robustly repopulate infarcted myocardium with functional, force generating cardiomyocytes. However, current differentiation protocols produce immature and heterogenous cardiomyocytes, creating related issues such as arrhythmogenicity, immunogenicity and poor engraftment. Recent efforts have enhanced our understanding of cardiovascular developmental biology. This knowledge may help implement novel differentiation or gene editing strategies that could overcome these limitations. PSC-CMs are an exciting therapeutic prospect. Despite substantial recent advances, limitations of the technology remain. However, with our continued and increasing biological understanding, these issues are addressable, with several worldwide clinical trials anticipated in the coming years.

Regenerative Neurology and Regenerative Cardiology: Shared Hurdles and Achievements

From the first success in cultivation of cells in vitro, it became clear that developing cell and/or tissue specific cultures would open a myriad of new opportunities for medical research. Expertise in various in vitro models has been developing over decades, so nowadays we benefit from highly specific in vitro systems imitating every organ of the human body. Moreover, obtaining sufficient number of standardized cells allows for cell transplantation approach with the goal of improving the regeneration of injured/disease affected tissue. However, different cell types bring different needs and place various types of hurdles on the path of regenerative neurology and regenerative cardiology. In this review, written by European experts gathered in Cost European action dedicated to neurology and cardiology-Bioneca, we present the experience acquired by working on two rather different organs: the brain and the heart. When taken into account that diseases of these two organs, mostly ischemic in their nature (stroke and heart infarction), bring by far the largest burden of the medical systems around Europe, it is not surprising that in vitro models of nervous and heart muscle tissue were in the focus of biomedical research in the last decades. In this review we describe and discuss hurdles which still impair further progress of regenerative neurology and cardiology and we detect those ones which are common to both fields and some, which are field-specific. With the goal to elucidate strategies which might be shared between regenerative neurology and cardiology we discuss methodological solutions which can help each of the fields to accelerate their development.

Production of functional cardiomyocytes and cardiac tissue from human induced pluripotent stem cells for regenerative therapy

The emergence of human induced pluripotent stem cells (hiPSCs) has revealed the potential for curing end-stage heart failure. Indeed, transplantation of hiPSC-derived cardiomyocytes (hiPSC-CMs) may have applications as a replacement for heart transplantation and conventional regenerative therapies. However, there are several challenges that still must be overcome for clinical applications, including large-scale production of hiPSCs and hiPSC-CMs, elimination of residual hiPSCs, purification of hiPSC-CMs, maturation of hiPSC-CMs, efficient engraftment of transplanted hiPSC-CMs, development of an injection device, and avoidance of post-transplant arrhythmia and immunological rejection. Thus, we developed several technologies based on understanding of the metabolic profiles of hiPSCs and hiPSC derivatives. In this review, we outline how to overcome these hurdles to realize the transplantation of hiPSC-CMs in patients with heart failure and introduce cutting-edge findings and perspectives for future regenerative therapy.

Transplantation of Human Pluripotent Stem Cell-Derived Cardiomyocytes for Cardiac Regenerative Therapy

Cardiovascular disease is the leading cause of death worldwide and bears an immense economic burden. Late-stage heart failure often requires total heart transplantation; however, due to donor shortages and lifelong immunosuppression, alternative cardiac regenerative therapies are in high demand. Human pluripotent stem cells (hPSCs), including human embryonic and induced pluripotent stem cells, have emerged as a viable source of human cardiomyocytes for transplantation. Recent developments in several mammalian models of cardiac injury have provided strong evidence of the therapeutic potential of hPSC-derived cardiomyocytes (hPSC-CM), showing their ability to electromechanically integrate with host cardiac tissue and promote functional recovery. In this review, we will discuss recent developments in hPSC-CM differentiation and transplantation strategies for delivery to the heart. We will highlight the mechanisms through which hPSC-CMs contribute to heart repair, review major challenges in successful transplantation of hPSC-CMs, and present solutions that are being explored to address these limitations. We end with a discussion of the clinical use of hPSC-CMs, including hurdles to clinical translation, current clinical trials, and future perspectives on hPSC-CM transplantation.

Mechanism-Based Cardiac Regeneration Strategies in Mammals

Heart failure in adults is a leading cause of morbidity and mortality worldwide. It can arise from a variety of diseases, with most resulting in a loss of cardiomyocytes that cannot be replaced due to their inability to replicate, as well as to a lack of resident cardiomyocyte progenitor cells in the adult heart. Identifying and exploiting mechanisms underlying loss of developmental cardiomyocyte replicative capacity has proved to be useful in developing therapeutics to effect adult cardiac regeneration. Of course, effective regeneration of myocardium after injury requires not just expansion of cardiomyocytes, but also neovascularization to allow appropriate perfusion and resolution of injury-induced inflammation and interstitial fibrosis, but also reversal of adverse left ventricular remodeling. In addition to overcoming these challenges, a regenerative therapy needs to be safe and easily translatable. Failure to address these critical issues will delay the translation of regenerative approaches. This review critically analyzes current regenerative approaches while also providing a framework for future experimental studies aimed at enhancing success in regenerating the injured heart.

How to repair a broken heart with pluripotent stem cell-derived cardiomyocytes

Heart regeneration addresses a central problem in cardiology, the irreversibility of the loss of myocardium that eventually leads to heart failure. True restoration of heart function can only be achieved by remuscularization, i.e. replacement of lost myocardium by new, force-developing heart muscle. With the availability of principally unlimited human cardiomyocytes from pluripotent stem cells, one option to remuscularize the injured heart is to produce large numbers of cardiomyocytes plus/minus other cardiovascular cell types or progenitors ex vivo and apply them to the heart, either by injection or application as a patch. Exciting progress over the past decade has led to the first clinical applications, but important questions remain. Academic and increasingly corporate activity is ongoing to answer them and optimize the approach to finally develop a true regenerative therapy of heart failure.

Transplantation of Pluripotent Stem Cell-Derived Cardiomyocytes into a Myocardial Infarction Model of Cynomolgus Monkey

Recent evidence has provided exciting proof of concepts for the use of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) for cardiac repair; however, large animal studies, which better reflect human disease, are required for clinical application. Here, we describe how to create myocardial infarction in cynomolgus monkey followed by transplantation of PSC-CMs. This method ensures the establishment of a myocardial infarction model and enables reliable PSC-CM transplantation.

Transplanted microvessels improve pluripotent stem cell-derived cardiomyocyte engraftment and cardiac function after infarction in rats

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer an unprecedented opportunity to remuscularize infarcted human hearts. However, studies have shown that most hiPSC-CMs do not survive after transplantation into the ischemic myocardial environment, limiting their regenerative potential and clinical application. We established a method to improve hiPSC-CM survival by cotransplanting ready-made microvessels obtained from adipose tissue. Ready-made microvessels promoted a sixfold increase in hiPSC-CM survival and superior functional recovery when compared to hiPSC-CMs transplanted alone or cotransplanted with a suspension of dissociated endothelial cells in infarcted rat hearts. Microvessels showed unprecedented persistence and integration at both early (~80%, week 1) and late (~60%, week 4) time points, resulting in increased vessel density and graft perfusion, and improved hiPSC-CM maturation. These findings provide an approach to cell-based therapies for myocardial infarction, whereby incorporation of ready-made microvessels can improve functional outcomes in cell replacement therapies.

A realistic appraisal of the use of embryonic stem cell-based therapies for cardiac repair

Despite the well-documented capacity of embryonic stem cells (ESCs) to differentiate into cardiomyocytes, transplantation of ESCs or ESC-derived cells is plagued by several formidable problems, including graft rejection, arrhythmias, and potential risk of teratomas. Life-long immunosuppression is a disease in itself. Transplantation of human ESC-derived cells in primates causes life-threatening arrhythmias, and the doses used to show efficacy are not clinically relevant. In contemporary clinical research, the margin of tolerance for such catastrophic effects as malignancies is zero, and although the probability of tumours can be reduced by ESC differentiation, it is unlikely to be completely eliminated, particularly when billions of cells are injected. Although ESCs and ESC-derived cells were touted as capable of long-term regeneration, these cells disappear rapidly after transplantation and there is no evidence of long-term engraftment, let alone regeneration. There is, however, mounting evidence that they act via paracrine mechanisms-just like adult cells. To date, no controlled clinical trial of ESC-derived cells in cardiovascular disease has been conducted or even initiated. In contrast, adult cells have been used in thousands of patients with heart disease, with no significant adverse effects and with results that were sufficiently encouraging to warrant Phase II and III trials. Furthermore, induced pluripotent stem cells offer pluripotency similar to ESCs without the need for lifelong immunosuppression. After two decades, the promise that ESC-derived cells would regenerate dead myocardium has not been fulfilled. The most reasonable interpretation of current data is that ESC-based therapies are not likely to have clinical application for heart disease.

In Situ Maturated Early-Stage Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes Improve Cardiac Function by Enhancing Segmental Contraction in Infarcted Rats

The scant ability of cardiomyocytes to proliferate makes heart regeneration one of the biggest challenges of science. Current therapies do not contemplate heart re-muscularization. In this scenario, stem cell-based approaches have been proposed to overcome this lack of regeneration. We hypothesize that early-stage hiPSC-derived cardiomyocytes (hiPSC-CMs) could enhance the cardiac function of rats after myocardial infarction (MI). Animals were subjected to the permanent occlusion of the left ventricle (LV) anterior descending coronary artery (LAD). Seven days after MI, early-stage hiPSC-CMs were injected intramyocardially. Rats were subjected to echocardiography pre-and post-treatment. Thirty days after the injections were administered, treated rats displayed 6.2% human cardiac grafts, which were characterized molecularly. Left ventricle ejection fraction (LVEF) was improved by 7.8% in cell-injected rats, while placebo controls showed an 18.2% deterioration. Additionally, cell-treated rats displayed a 92% and 56% increase in radial and circumferential strains, respectively. Human cardiac grafts maturate in situ, preserving proliferation with 10% Ki67 and 3% PHH3 positive nuclei. Grafts were perfused by host vasculature with no evidence for immune rejection nor ectopic tissue formations. Our findings support the use of early-stage hiPSC-CMs as an alternative therapy to treat MI. The next steps of preclinical development include efficacy studies in large animals on the path to clinical-grade regenerative therapy targeting human patients.

Sarcomere function activates a p53-dependent DNA damage response that promotes polyploidization and limits in vivo cell engraftment

Human cardiac regeneration is limited by low cardiomyocyte replicative rates and progressive polyploidization by unclear mechanisms. To study this process, we engineer a human cardiomyocyte model to track replication and polyploidization using fluorescently tagged cyclin B1 and cardiac troponin T. Using time-lapse imaging, in vitro cardiomyocyte replication patterns recapitulate the progressive mononuclear polyploidization and replicative arrest observed in vivo. Single-cell transcriptomics and chromatin state analyses reveal that polyploidization is preceded by sarcomere assembly, enhanced oxidative metabolism, a DNA damage response, and p53 activation. CRISPR knockout screening reveals p53 as a driver of cell-cycle arrest and polyploidization. Inhibiting sarcomere function, or scavenging ROS, inhibits cell-cycle arrest and polyploidization. Finally, we show that cardiomyocyte engraftment in infarcted rat hearts is enhanced 4-fold by the increased proliferation of troponin-knockout cardiomyocytes. Thus, the sarcomere inhibits cell division through a DNA damage response that can be targeted to improve cardiomyocyte replacement strategies.

Cardiac Tissues From Stem Cells: New Routes to Maturation and Cardiac Regeneration

The ability of human pluripotent stem cells to form all cells of the body has provided many opportunities to study disease and produce cells that can be used for therapy in regenerative medicine. Even though beating cardiomyocytes were among the first cell types to be differentiated from human pluripotent stem cell, cardiac applications have advanced more slowly than those, for example, for the brain, eye, and pancreas. This is, in part, because simple 2-dimensional human pluripotent stem cell cardiomyocyte cultures appear to need crucial functional cues normally present in the 3-dimensional heart structure. Recent tissue engineering approaches combined with new insights into the dialogue between noncardiomyocytes and cardiomyocytes have addressed and provided solutions to issues such as cardiomyocyte immaturity and inability to recapitulate adult heart values for features like contraction force, electrophysiology, or metabolism. Three-dimensional bioengineered heart tissues are thus poised to contribute significantly to disease modeling, drug discovery, and safety pharmacology, as well as provide new modalities for heart repair. Here, we review the current status of 3-dimensional engineered heart tissues.

Cell augmentation strategies for cardiac stem cell therapies

Myocardial infarction (MI) has been the primary cause of death in developed countries, resulting in a major psychological and financial burden for society. Current treatments for acute MI are directed toward rapid restoration of perfusion to limit damage to the myocardium, rather than promoting tissue regeneration and subsequent contractile function recovery. Regenerative cell therapies (CTs), in particular those using multipotent stem cells (SCs), are in the spotlight for treatment post‐MI. Unfortunately, the efficacy of CTs is somewhat limited by their poor long‐term viability, homing, and engraftment to the myocardium. In response, a range of novel SC‐based technologies are in development to provide additional cellular modalities, bringing CTs a step closer to the clinic. In this review, the current landscape of emerging CTs and their augmentation strategies for the treatment post‐MI are discussed. In doing so, we highlight recent advances in cell membrane reengineering via genetic modifications, recombinant protein immobilization, and the utilization of soft biomimetic scaffold interfaces.

Pluripotent Stem Cells for Cardiac Regeneration - Current Status, Challenges, and Future Perspectives

Loss of myocardium permanently impairs cardiac function because the adult mammalian heart has limited regenerative capacity. Strategies to regenerate injured heart tissue include the transplantation of multiple types of stem cells. Among them, pluripotent stem cells (PSCs) are a promising option because of their unlimited self-renewal and unequivocal cardiomyogenic ability. To date, advances in stem cell biology allow generation of relatively homogeneous human PSC-derived cardiomyocytes (CMs). In this regard, preclinical studies of PSC-CM transplantation in rodents and larger animal models have provided convincing proof-of-concept results, triggering clinical studies in multiple countries. However, a few important uncertainties are yet to be addressed, warranting further investigation before clinical implementation of this novel therapy. An overview of the potential of stem cell therapy to provide new CMs for cardiac regeneration is presented.

Cardiomyocyte Induction and Regeneration for Myocardial Infarction Treatment: Cell Sources and Administration Strategies

Occlusion of coronary artery and subsequent damage or death of myocardium can lead to myocardial infarction (MI) and even heart failure-one of the leading causes of deaths world wide. Notably, myocardium has extremely limited regeneration potential due to the loss or death of cardiomyocytes (i.e., the cells of which the myocardium is comprised) upon MI. A variety of stem cells and stem cell-derived cardiovascular cells, in situ cardiac fibroblasts and endogenous proliferative epicardium, have been exploited to provide renewable cellular sources to treat injured myocardium. Also, different strategies, including direct injection of cell suspensions, bioactive molecules, or cell-incorporated biomaterials, and implantation of artificial cardiac scaffolds (e.g., cell sheets and cardiac patches), have been developed to deliver renewable cells and/or bioactive molecules to the MI site for the myocardium regeneration. This article briefly surveys cell sources and delivery strategies, along with biomaterials and their processing techniques, developed for MI treatment. Key issues and challenges, as well as recommendations for future research, are also discussed.

Optical mapping of human embryonic stem cell-derived cardiomyocyte graft electrical activity in injured hearts

BACKGROUND

Human embryonic stem cell-derived cardiomyocytes (hESC-CMs) show tremendous promise for cardiac regeneration, but the successful development of hESC-CM-based therapies requires improved tools to investigate their electrical behavior in recipient hearts. While optical voltage mapping is a powerful technique for studying myocardial electrical activity ex vivo, we have previously shown that intra-cardiac hESC-CM grafts are not labeled by conventional voltage-sensitive fluorescent dyes. We hypothesized that the water-soluble voltage-sensitive dye di-2-ANEPEQ would label engrafted hESC-CMs and thereby facilitate characterization of graft electrical function and integration.

METHODS

We developed and validated a novel optical voltage mapping strategy based on the simultaneous imaging of the calcium-sensitive fluorescent protein GCaMP3, a graft-autonomous reporter of graft activation, and optical action potentials (oAPs) derived from di-2-ANEPEQ, which labels both graft and host myocardium. Cardiomyocytes from three different GCaMP3+ hESC lines (H7, RUES2, or ESI-17) were transplanted into guinea pig models of subacute and chronic infarction, followed by optical mapping at 2 weeks post-transplantation.

RESULTS

Use of a water-soluble voltage-sensitive dye revealed pro-arrhythmic properties of GCaMP3+ hESC-CM grafts from all three lines including slow conduction velocity, incomplete host-graft coupling, and spatially heterogeneous patterns of activation that varied beat-to-beat. GCaMP3+ hESC-CMs from the RUES2 and ESI-17 lines both showed prolonged oAP durations both in vitro and in vivo. Although hESC-CMs partially remuscularize the injured hearts, histological evaluation revealed immature graft structure and impaired gap junction expression at this early timepoint.

CONCLUSION

Simultaneous imaging of GCaMP3 and di-2-ANEPEQ allowed us to acquire the first unambiguously graft-derived oAPs from hESC-CM-engrafted hearts and yielded critical insights into their arrhythmogenic potential and line-to-line variation.

Robust Cardiac Regeneration: Fulfilling the Promise of Cardiac Cell Therapy

PURPOSE

We review the history of cardiac cell therapy, highlighting lessons learned from initial adult stem cell (ASC) clinical trials. We present pluripotent stem cell-derived cardiomyocytes (PSC-CMs) as a leading candidate for robust regeneration of infarcted myocardium but identify several issues that must be addressed before successful clinical translation.

METHODS

We conducted an unstructured literature review of PubMed-listed articles, selecting the most comprehensive and relevant research articles, review articles, clinical trials, and basic or translation articles in the field of cardiac cell therapy. Articles were identified using the search terms adult stem cells, pluripotent stem cells, cardiac stem cell, and cardiac regeneration or from references of relevant articles, Articles were prioritized and selected based on their impact, originality, or potential clinical applicability.

FINDINGS

Since its inception, the ASC therapy field has been troubled by conflicting preclinical data, academic controversies, and inconsistent trial designs. These issues have damaged perceptions of cardiac cell therapy among investors, the academic community, health care professionals, and, importantly, patients. In hindsight, the key issue underpinning these problems was the inability of these cell types to differentiate directly into genuine cardiomyocytes, rendering them unable to replace damaged myocardium. Despite this, beneficial effects through indirect paracrine or immunomodulatory effects remain possible and continue to be investigated. However, in preclinical models, PSC-CMs have robustly remuscularized infarcted myocardium with functional, force-generating cardiomyocytes. Hence, PSC-CMs have now emerged as a leading candidate for cardiac regeneration, and unpublished reports of first-in-human delivery of these cells have recently surfaced. However, the cardiac cell therapy field's history should serve as a cautionary tale, and we identify several translational hurdles that still remain. Preclinical solutions to issues such as arrhythmogenicity, immunogenicity, and poor engraftment rates are needed, and next-generation clinical trials must draw on robust knowledge of mechanistic principles of the therapy.

IMPLICATIONS

The clinical transplantation of functional stem cell-derived heart tissue with seamless integration into native myocardium is a lofty goal. However, considerable advances have been made during the past 2 decades. Currently, PSC-CMs appear to be the best prospect to reach this goal, but several hurdles remain. The history of adult stem cell trials has taught us that shortcuts cannot be taken without dire consequences, and it is essential that progress not be hurried and that a worldwide, cross-disciplinary approach be used to ensure safe and effective clinical translation.

Recent advancements of human iPSC derived cardiomyocytes in drug screening and tissue regeneration

Myocardial infarction together with subsequent heart failures are among the main reasons for death related to cardiovascular diseases (CVD). Restoring cardiac function and replacing scar tissue with healthy regenerated cardiomyocytes (CMs) is a hopeful therapy for heart failure. Human-induced pluripotent stem cell (hiPSC) derived CMs (hiPSC-CMs) offer the advantages of not having significant ethical issues and having negligible immunological rejection compared to other myocardial regeneration methods. hiPSCs can also produce an unlimited number of human CMs, another advantage they have compared with other cell sources for cardiac regeneration. Numerous researchers have focused their work on promoting the functional maturity of hiPSC-CMs, as well as finding out the precise regulatory mechanisms of each differentiation stage together with the economical and practical methods of acquisition and purification. However, the clinical applications of hiPSC-CMs in drug discovery and cardiac regeneration therapy have yet to be achieved. In this review, we present an overview of various methods for improving the differentiation efficiency of hiPSC-CMs and discuss the differences of electrophysiological characteristics between hiPSC-CMs and matured native CMs. We also introduce approaches for obtaining a large quantity of iPSC-CMs, which are needed to achieve biomanufacturing strategies for building biomimetic three-dimensional tissue constructs using combinations of biomaterials and advanced microfabrication techniques. Recent advances in specific iPSC technology-based drug screening platforms and regeneration therapies can suggest future directions for personalized medicine in biomedical applications.

Heart regeneration using pluripotent stem cells

Pluripotent stem cells (PSCs), which include embryonic and induced pluripotent stem cells (ESCs and iPSCs, respectively), have great potential in regenerative medicine for heart diseases due to their virtually unlimited cardiogenic capacity. Many preclinical studies have described the functional benefits after transplantation of PSC-derived cardiomyocytes (PSC-CMs). However, transient ventricular arrhythmias were detected after injection into non-human primates and swine ischemic hearts; as engrafted PSC-CMs form an electrical coupling between host and graft, the immature characteristics of PSC-CMs may serve as an ectopic pacemaker. We are entering a critical time in the development of novel therapies using PSC-CMs, with the recent first clinical trial using human iPSC-CMs (hiPSC-CMs) being launched in Japan. In this review, we summarize the updated knowledge, perspectives, and limitations of PSC-CMs for heart regeneration.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Biodegradable nanofibrous temperature-responsive gelling microspheres for heart regeneration

Myocardial infarction (heart attack) is the number one killer of heart patients. Existing treatments for heart attack do not address the underlying problem of cardiomyocyte (CM) loss and cannot regenerate the myocardium. Introducing exogenous cardiac cells is required for heart regeneration due to the lack of resident progenitor cells and very limited proliferative potential of adult CMs. Poor retention of transplanted cells is the critical bottleneck of heart regeneration. Here, we report the invention of a poly(l-lactic acid)-b-poly(ethylene glycol)-b-poly(N-Isopropylacrylamide) copolymer and its self-assembly into nanofibrous gelling microspheres (NF-GMS). The NF-GMS undergo thermally responsive transition to form not only a 3D hydrogel after injection in vivo, but also exhibit architectural and structural characteristics mimicking the native extracellular matrix (ECM) of nanofibrous proteins and gelling proteoglycans or polysaccharides. By integrating the ECM-mimicking features, injectable form, and the capability of maintaining 3D geometry after injection, the transplantation of hESC-derived CMs carried by NF-GMS led to a striking 10-fold graft size increase over direct CM injection in an infarcted rat model, which is the highest reported engraftment to date. Furthermore, NF-GMS carried CM transplantation dramatically reduced infarct size, enhanced integration of transplanted CMs, stimulated vascularization in the infarct zone, and led to a substantial recovery of cardiac function. The NF-GMS may also serve as advanced injectable and integrative biomaterials for cell/biomolecule delivery in a variety of biomedical applications.

Mending a broken heart: current strategies and limitations of cell-based therapy

The versatility of pluripotent stem cells, attributable to their unlimited self-renewal capacity and plasticity, has sparked a considerable interest for potential application in regenerative medicine. Over the past decade, the concept of replenishing the lost cardiomyocytes, the crux of the matter in ischemic heart disease, with pluripotent stem cell-derived cardiomyocytes (PSC-CM) has been validated with promising pre-clinical results. Nevertheless, clinical translation was hemmed in by limitations such as immature cardiac properties, long-term engraftment, graft-associated arrhythmias, immunogenicity, and risk of tumorigenicity. The continuous progress of stem cell-based cardiac therapy, incorporated with tissue engineering strategies and delivery of cardio-protective exosomes, provides an optimistic outlook on the development of curative treatment for heart failure. This review provides an overview and current status of stem cell-based therapy for heart regeneration, with particular focus on the use of PSC-CM. In addition, we also highlight the associated challenges in clinical application and discuss the potential strategies in developing successful cardiac-regenerative therapy.

A Highly Conductive 3D Cardiac Patch Fabricated Using Cardiac Myocytes Reprogrammed from Human Adipogenic Mesenchymal Stem Cells

PURPOSE

The objective of this study was to bioengineer 3D patches from cardiac myocytes that have been reprogrammed from human adipogenic mesenchymal stem cells (hADMSCs).

METHODS

Human adipogenic mesenchymal stem cells (hADMSCs) were reprogrammed to form cardiac myocytes using transcription factors ETS2 and MESP1. Reprogrammed cardiac myocytes were cultured in a fibrin gel to bioengineer 3D patch patches. The effect of initial plating density (1-25 million cells per patch), time (28-day culture period) and treatment with 1 μM isoproterenol and 1 μM epinephrine were evaluated.

RESULTS

3D patches were fabricated using cardiac myocytes that have been reprogrammed from hADMSCs. Based on optimization studies, it was determined that 10 million cells were needed to bioengineer a single patch, that measured 2 × 2 cm². Furthermore, 3D patches fabricated 10 million cells were stable in culture for up to 28 days. Treatment of 3D patches with 1 μM isoproterenol and 1 μM epinephrine resulted in an increase in the electrical properties, as measured by electrical impulse amplitude and frequency. An increase in the expression of mTOR, KCNV1, GJA5, KCNJ16, CTNNT2, KCNV2, MYO3, FOXO1 and KCND2 was noted in response to treatment of 3D patches with isoproterenol and epinephrine.

CONCLUSION

Based on the results of this study, there is evidence to support the successful fabrication of a highly functional 3D patches with measurable electrical activity using cardiac myocytes reprogrammed from hADMSCs. 3D patches fabricated using optimal conductions described in this study can be used to improve the functional properties of failing hearts. Predominantly, in case of the infarcted hearts with partial loss of electrical activity, the electrical properties of the 3D patches may restore the electrical activity of the heart.

Function Follows Form - A Review of Cardiac Cell Therapy

The investment of nearly 2 decades of clinical investigation into cardiac cell therapy has yet to change cardiovascular practice. Recent insights into the mechanism of cardiac regeneration help explain these results and provide important context in which we can develop next-generation therapies. Non-contractile cells such as bone marrow or adult heart derivatives neither engraft long-term nor induce new muscle formation. Correspondingly, these cells offer little functional benefit to infarct patients. In contrast, preclinical data indicate that transplantation of bona fide cardiomyocytes derived from pluripotent stem cells induces direct remuscularization. This new myocardium beats synchronously with the host heart and induces substantial contractile benefits in macaque monkeys, suggesting that regeneration of contractile myocardium is required to fully recover function. Through a review of the preclinical and clinical trials of cardiac cell therapy, distinguishing the primary mechanism of benefit as either contractile or non-contractile helps appreciate the barriers to cardiac repair and establishes a rational path to optimizing therapeutic benefit.

Current research trends and challenges in tissue engineering for mending broken hearts

Cardiovascular disease (CVD) is among the leading causes of mortality worldwide. The shortage of donor hearts to treat end-stage heart failure patients is a critical problem. An average of 3500 heart transplant surgeries are performed globally, half of these transplants are performed in the US alone. Stem cell therapy is growing rapidly as an alternative strategy to repair or replace the damaged heart tissue after a myocardial infarction (MI). Nevertheless, the relatively poor survival of the stem cells in the ischemic heart is a major challenge to the therapeutic efficacy of stem-cell transplantation. Recent advancements in tissue engineering offer novel biomaterials and innovative technologies to improve upon the survival of stem cells as well as to repair the damaged heart tissue following a myocardial infarction (MI). However, there are several limitations in tissue engineering technologies to develop a fully functional, beating cardiac tissue. Therefore, the main goal of this review article is to address the current advancements and barriers in cardiac tissue engineering to augment the survival and retention of stem cells in the ischemic heart.

Engineering hiPSC cardiomyocyte in vitro model systems for functional and structural assessment

The study of human cardiomyopathies and the development and testing of new therapies has long been limited by the availability of appropriate in vitro model systems. Cardiomyocytes are highly specialized cells whose internal structure and contractile function are sensitive to the local microenvironment and the combination of mechanical and biochemical cues they receive. The complementary technologies of human induced pluripotent stem cell (hiPSC) derived cardiomyocytes (CMs) and microphysiological systems (MPS) allow for precise control of the genetics and microenvironment of human cells in in vitro contexts. These combined systems also enable quantitative measurement of mechanical function and intracellular organization. This review describes relevant factors in the myocardium microenvironment that affect CM structure and mechanical function and demonstrates the application of several engineered microphysiological systems for studying development, disease, and drug discovery.

Pluripotent Stem Cell-Derived Cardiomyocyte Transplantation for Heart Disease Treatment

PURPOSE OF REVIEW

Cardiovascular disease is the leading cause of mortality worldwide. Pluripotent stem cell-derived cardiomyocytes (PSC-CMs) have great potential to treat heart disease, owing to their capacity of engraftment and remuscularization in the host heart after transplantation. In the current review, we provide an overview of PSC-CMs for clinical transplantation.

RECENT FINDINGS

Studies have shown that PSC-CMs can survive, engraft, and form gap junctions after transplantation, with functional benefit. Engrafted PSC-CMs matured gradually in host hearts. Only in a large animal model, transient ventricular arrhythmias were detected, mainly because of the ectopic pacing from the grafted PSC-CMs. Although intense immunosuppression is unavoidable in xenotransplantation, immunosuppression remains necessary for MHC-matched allogenic non-human primate PSC-CMs transplantation. This review offers insights on how PSC-CMs contribute to functional benefit after transplantation to injured non-human primate hearts. We believe that PSC-CM transplantation represents a potentially novel treatment for ischemic heart diseases, provided that several technological and biological limitations can be overcome.

Cardioprotective effects of omega-3 fatty acids and ascorbic acid improve regenerative capacity of embryonic stem cell-derived cardiac lineage cells

One of the major issues in cell therapy of myocardial infarction (MI) is early death of engrafted cells in a harsh oxidative stress environment, which limits the potential therapeutic utility of this strategy in the clinical setting. Increasing evidence implicates beneficial effects of omega-3 fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and ascorbic acid (AA) in cardiovascular diseases, in particular their role in ameliorating fibrosis. In the current study, we aim to assess the cytoprotective role of EPA + DHA and AA in protecting embryonic stem cell (ESC)-derived cardiac lineage cells and amelioration of fibrosis. Herein, we have shown that preincubation of the cells with EPA + DHA + AA prior to H2 O2 treatment attenuated generation of reactive oxygen species (ROS) and enhanced cell viability. Gene expression analysis revealed that preincubation with EPA + DHA + AA followed by H2 O2 treatment, upregulated heme oxygenase-1 (HO-1) along with cardiac markers (GATA4, myosin heavy chain, α isoform [MYH6]), connexin 43 [CX43]) and attenuated oxidative stress-induced upregulation of fibroblast markers (vimentin and collagen type 1 [Col1]). Alterations in gene expression patterns were followed by marked elevation of cardiac troponin (TNNT2) positive cells and reduced numbers of vimentin positive cells. An injection of EPA + DHA + AA-pretreated ESC-derived cardiac lineage cells into the ischemic myocardium of a rat model of MI significantly reduced fibrosis compared to the vehicle group. This study provided evidence that EPA + DHA + AA may be an appropriate preincubation regimen for regenerative purposes. © 2019 BioFactors, 45(3):427-438, 2019.

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.

New Myocyte Formation in the Adult Heart: Endogenous Sources and Therapeutic Implications

Death of adult cardiac myocytes and supportive tissues resulting from cardiovascular diseases such as myocardial infarction is the proximal driver of pathological ventricular remodeling that often culminates in heart failure. Unfortunately, no currently available therapeutic barring heart transplantation can directly replenish myocytes lost from the injured heart. For decades, the field has struggled to define the intrinsic capacity and cellular sources for endogenous myocyte turnover in pursuing more innovative therapeutic strategies aimed at regenerating the injured heart. Although controversy persists to this day as to the best therapeutic regenerative strategy to use, a growing consensus has been reached that the very limited capacity for new myocyte formation in the adult mammalian heart is because of proliferation of existing cardiac myocytes but not because of the activity of an endogenous progenitor cell source of some sort. Hence, future therapeutic approaches should take into consideration the fundamental biology of myocyte renewal in designing strategies to potentially replenish these cells in the injured heart.

Human embryonic stem cell-derived cardiomyocytes restore function in infarcted hearts of non-human primates

Pluripotent stem cell–derived cardiomyocyte grafts can remuscularize substantial amounts of infarcted myocardium and beat in synchrony with the heart, but in some settings cause ventricular arrhythmias. It is unknown whether human cardiomyocytes can restore cardiac function in a physiologically relevant large animal model. Here we show that transplantation of ~750 million cryopreserved human embryonic stem cell–derived cardiomyocytes (hESC-CMs) enhances cardiac function in macaque monkeys with large myocardial infarctions. One month after hESC-CM transplantation, global left ventricular ejection fraction improved 10.6±0.9% vs. 2.5±0.8% in controls, and by 3 months there was an additional 12.4% improvement in treated vs. a 3.5% decline in controls. Grafts averaged 11.6% of infarct size, formed electromechanical junctions with the host heart and by 3 months contained ~99% ventricular myocytes. A subset of animals experienced graft-associated ventricular arrhythmias, shown by electrical mapping to originate from a point-source acting as an ectopic pacemaker. Our data demonstrate that remuscularization of the infarcted macaque heart with human myocardium provides durable improvement in left ventricular function.

Development of a Contractile Cardiac Fiber From Pluripotent Stem Cell Derived Cardiomyocytes

Stem cell therapy has the potential to regenerate cardiac function after myocardial infarction. In this study, we sought to examine if fibrin microthread technology could be leveraged to develop a contractile fiber from human pluripotent stem cell derived cardiomyocytes (hPS-CM). hPS-CM seeded onto fibrin microthreads were able to adhere to the microthread and began to contract seven days after initial seeding. A digital speckle tracking algorithm was applied to high speed video data (>60 fps) to determine contraction behaviour including beat frequency, average and maximum contractile strain, and the principal angle of contraction of hPS-CM contracting on the microthreads over 21 days. At day 7, cells seeded on tissue culture plastic beat at 0.83 ± 0.25 beats/sec with an average contractile strain of 4.23±0.23%, which was significantly different from a beat frequency of 1.11 ± 0.45 beats/sec and an average contractile strain of 3.08±0.19% at day 21 (n = 18, p < 0.05). hPS-CM seeded on microthreads beat at 0.84 ± 0.15 beats/sec with an average contractile strain of 3.56±0.22%, which significantly increased to 1.03 ± 0.19 beats/sec and 4.47±0.29%, respectively, at 21 days (n = 18, p < 0.05). At day 7, 27% of the cells had a principle angle of contraction within 20 degrees of the microthread, whereas at day 21, 65% of hPS-CM were contracting within 20 degrees of the microthread (n = 17). Utilizing high speed calcium transient data (>300 fps) of Fluo-4AM loaded hPS-CM seeded microthreads, conduction velocities significantly increased from 3.69 ± 1.76 cm/s at day 7 to 24.26 ± 8.42 cm/s at day 21 (n = 5-6, p < 0.05). hPS-CM seeded microthreads exhibited positive expression for connexin 43, a gap junction protein, between cells. These data suggest that the fibrin microthread is a suitable scaffold for hPS-CM attachment and contraction. In addition, extended culture allows cells to contract in the direction of the thread, suggesting alignment of the cells in the microthread direction.

Cardiac Regeneration with Human Pluripotent Stem Cell-Derived Cardiomyocytes

Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), which are collectively called pluripotent stem cells (PSCs), have emerged as a promising source for regenerative medicine. Particularly, human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have shown robust potential for regenerating injured heart. Over the past two decades, protocols to differentiate hPSCs into CMs at high efficiency have been developed, opening the door for clinical application. Studies further demonstrated therapeutic effects of hPSC-CMs in small and large animal models and the underlying mechanisms of cardiac repair. However, gaps remain in explanations of the therapeutic effects of engrafted hPSC-CMs. In addition, bioengineering technologies improved survival and therapeutic effects of hPSC-CMs in vivo. While most of the original concerns associated with the use of hPSCs have been addressed, several issues remain to be resolved such as immaturity of transplanted cells, lack of electrical integration leading to arrhythmogenic risk, and tumorigenicity. Cell therapy with hPSC-CMs has shown great potential for biological therapy of injured heart; however, more studies are needed to ensure the therapeutic effects, underlying mechanisms, and safety, before this technology can be applied clinically.