Human iPS cell-derived engineered heart tissue does not affect ventricular arrhythmias in a guinea pig cryo-injury model

Regeneration of Nonhuman Primate Hearts With Human Induced Pluripotent Stem Cell-Derived Cardiac Spheroids

BACKGROUND

The clinical application of human induced pluripotent stem cell-derived cardiomyocytes (CMs) for cardiac repair commenced with the epicardial delivery of engineered cardiac tissue; however, the feasibility of the direct delivery of human induced pluripotent stem cell-derived CMs into the cardiac muscle layer, which has reportedly induced electrical integration, is unclear because of concerns about poor engraftment of CMs and posttransplant arrhythmias. Thus, in this study, we prepared purified human induced pluripotent stem cell-derived cardiac spheroids (hiPSC-CSs) and investigated whether their direct injection could regenerate infarcted nonhuman primate hearts.

METHODS

We performed 2 separate experiments to explore the appropriate number of human induced pluripotent stem cell-derived CMs. In the first experiment, 10 cynomolgus monkeys were subjected to myocardial infarction 2 weeks before transplantation and were designated as recipients of hiPSC-CSs containing 2×107 CMs or the vehicle. The animals were euthanized 12 weeks after transplantation for histological analysis, and cardiac function and arrhythmia were monitored during the observational period. In the second study, we repeated the equivalent transplantation study using more CMs (6×107 CMs).

RESULTS

Recipients of hiPSC-CSs containing 2×107 CMs showed limited CM grafts and transient increases in fractional shortening compared with those of the vehicle (fractional shortening at 4 weeks after transplantation [mean ± SD]: 26.2±2.1%; 19.3±1.8%; P<0.05), with a low incidence of posttransplant arrhythmia. Transplantation of increased dose of CMs resulted in significantly greater engraftment and long-term contractile benefits (fractional shortening at 12 weeks after transplantation: 22.5±1.0%; 16.6±1.1%; P<0.01, left ventricular ejection fraction at 12 weeks after transplantation: 49.0±1.4%; 36.3±2.9%; P<0.01). The incidence of posttransplant arrhythmia slightly increased in recipients of hiPSC-CSs containing 6×107 CMs.

CONCLUSIONS

We demonstrated that direct injection of hiPSC-CSs restores the contractile functions of injured primate hearts with an acceptable risk of posttransplant arrhythmia. Although the mechanism for the functional benefits is not fully elucidated, these findings provide a strong rationale for conducting clinical trials using the equivalent CM products.

Ventricular unloading causes prolongation of the QT interval and induces ventricular arrhythmias in rat hearts

Introduction

Ventricular unloading during prolonged bed rest, mechanical circulatory support or microgravity has repeatedly been linked to potentially life-threatening arrhythmias. It is unresolved, whether this arrhythmic phenotype is caused by the reduction in cardiac workload or rather by underlying diseases or external stimuli. We hypothesized that the reduction in cardiac workload alone is sufficient to impair ventricular repolarization and to induce arrhythmias in hearts.

Methods

Rat hearts were unloaded using the heterotopic heart transplantation. The ECG of unloaded and of control hearts were telemetrically recorded over 56 days resulting in >5 × 106 cardiac cycles in each heart. Long-term electrical remodeling was analyzed using a novel semi-automatic arrhythmia detection algorithm.

Results

56 days of unloading reduced left ventricular weight by approximately 50%. While unloading did not affect average HRs, it markedly prolonged the QT interval by approximately 66% and induced a median tenfold increase in the incidence of ventricular arrhythmias in comparison to control hearts.

Conclusion

The current study provides direct evidence that the previously reported hypertrophic phenotype of repolarization during cardiac unloading translates into an impaired ventricular repolarization and ventricular arrhythmias in vivo. This supports the concept that the reduction in cardiac workload is a causal driver of the development of arrhythmias during ventricular unloading.

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.

Large animal models for cardiac remuscularization studies: A methodological review

Myocardial infarction is the most common cause of heart failure, one of the most fatal non-communicable diseases worldwide. The disease could potentially be treated if the dead, ischemic heart tissues are regenerated and replaced with viable and functional cardiomyocytes. Pluripotent stem cells have proven the ability to derive specific and functional cardiomyocytes in large quantities for therapy. To test the remuscularization hypothesis, the strategy to model the disease in animals must resemble the pathophysiological conditions of myocardial infarction as in humans, to enable thorough testing of the safety and efficacy of the cardiomyocyte therapy before embarking on human trials. Rigorous experiments and in vivo findings using large mammals are increasingly important to simulate clinical reality and increase translatability into clinical practice. Hence, this review focus on large animal models which have been used in cardiac remuscularization studies using cardiomyocytes derived from human pluripotent stem cells. The commonly used methodologies in developing the myocardial infarction model, the choice of animal species, the pre-operative antiarrhythmics prophylaxis, the choice of perioperative sedative, anaesthesia and analgesia, the immunosuppressive strategies in allowing xenotransplantation, the source of cells, number and delivery method are discussed.

Assessing the arrhythmogenic risk of engineered heart tissue patches through in silico application on infarcted ventricle models

BACKGROUND

Post myocardial infarction (MI) ventricles contain fibrotic tissue and may have disrupted electrical properties, both of which predispose to an increased risk of life-threatening arrhythmias. Application of epicardial patches obtained from human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a potential long-term therapy to treat heart failure resulting from post MI remodelling. However, whether the introduction of these patches is anti- or pro-arrhythmic has not been studied.

METHODS

We studied arrhythmic risk using in silico engineered heart tissue (EHT) patch engraftment on human post-MI ventricular models. Two patient models were studied, including one with a large dense scar and one with an apparent channel of preserved viability bordered on both sides by scar. In each heart model a virtual EHT patch was introduced as a layer of viable tissue overlying the scarred area, with hiPSC-CMs electrophysiological properties. The incidence of re-entrant and sustained activation in simulations with and without EHT patches was assessed and the arrhythmia inducibility compared in the context of different EHT patch properties (conduction velocity (CV) and action potential duration (APD)). The impact of the EHT patch on the likelihood of focal ectopic impulse propagation was estimated by assessing the minimum stimulus strength and duration required to generate a propagating impulse in the scar border zone (BZ) with and without patch.

RESULTS

We uncovered two main mechanisms by which ventricular tachycardia (VT) risk could be either augmented or attenuated by the interaction of the patch with the tissue. In the case of isthmus-related VT, our simulations predict that EHT patches can prevent the induction of VT when the, generally longer, hiPSC-CMs APD is reduced towards more physiological values. In the case of large dense scar, we found that, an EHT patch with CV similar to the host myocardium does not promote VT, while EHT patches with lower CV increase the risk of VT, by promoting both non-sustained and sustained re-entry. Finally, our simulations indicate that electrically coupled EHT patches reduce the likelihood of propagation of focal ectopic impulses.

CONCLUSIONS

The introduction of EHT patches as a treatment for heart failure has the potential to augment or attenuate the risk of ventricular arrhythmias, and variations in the anatomic configuration of the substrate, the functional properties of the BZ and the electrophysiologic properties of the patch itself will determine the overall impact. Planning for delivery of this therapy will need to consider the possible impact on arrhythmia.

Assessment of arrhythmia mechanism and burden of the infarcted ventricles following remuscularization with pluripotent stem cell-derived cardiomyocyte patches using patient-derived models

AIMS

Direct remuscularization with pluripotent stem cell-derived cardiomyocytes (PSC-CMs) seeks to address the onset of heart failure post-myocardial infarction (MI) by treating the persistent muscle deficiency that underlies it. However, direct remuscularization with PSC-CMs could potentially be arrhythmogenic. We investigated two possible mechanisms of arrhythmogenesis-focal vs. re-entrant-arising from direct remuscularization with PSC-CM patches in two personalized, human ventricular computer models of post-MI. Moreover, we developed a principled approach for evaluating arrhythmogenicity of direct remuscularization that factors in the VT propensity of the patient-specific post-MI fibrotic substrate and use it to investigate different conditions of patch remuscularization.

METHODS AND RESULTS

Two personalized, human ventricular models of post-MI (P1 and P2) were constructed from late gadolinium enhanced (LGE)-magnetic resonance images (MRIs). In each model, remuscularization with PSC-CM patches was simulated under different treatment conditions that included patch engraftment, patch myofibril orientation, remuscularization site, patch size (thickness and diameter), and patch maturation. To determine arrhythmogenicity of treatment conditions, VT burden of heart models was quantified prior to and after simulated remuscularization and compared. VT burden was quantified based on inducibility (i.e. weighted sum of pacing sites that induced) and severity (i.e. the number of distinct VT morphologies induced). Prior to remuscularization, VT burden was significant in P1 (0.275) and not in P2 (0.0, not VT inducible). We highlight that re-entrant VT mechanisms would dominate over focal mechanisms; spontaneous beats emerging from PSC-CM grafts were always a fraction of resting sinus rate. Moreover, incomplete patch engraftment can be particularly arrhythmogenic, giving rise to particularly aberrant electrical activation and conduction slowing across the PSC-CM patches along with elevated VT burden when compared with complete engraftment. Under conditions of complete patch engraftment, remuscularization was almost always arrhythmogenic in P2 but certain treatment conditions could be anti-arrhythmogenic in P1. Moreover, the remuscularization site was the most important factor affecting VT burden in both P1 and P2. Complete maturation of PSC-CM patches, both ionically and electrotonically, at the appropriate site could completely alleviate VT burden.

CONCLUSION

We identified that re-entrant VT would be the primary VT mechanism in patch remuscularization. To evaluate the arrhythmogenicity of remuscularization, we developed a principled approach that factors in the propensity of the patient-specific fibrotic substrate for VT. We showed that arrhythmogenicity is sensitive to the patient-specific fibrotic substrate and remuscularization site. We demonstrate that targeted remuscularization can be safe in the appropriate individual and holds the potential to non-destructively eliminate VT post-MI in addition to addressing muscle deficiency underlying heart failure progression.

Progress in Bioengineering Strategies for Heart Regenerative Medicine

The human heart has the least regenerative capabilities among tissues and organs, and heart disease continues to be a leading cause of mortality in the industrialized world with insufficient therapeutic options and poor prognosis. Therefore, developing new therapeutic strategies for heart regeneration is a major goal in modern cardiac biology and medicine. Recent advances in stem cell biology and biotechnologies such as human pluripotent stem cells (hPSCs) and cardiac tissue engineering hold great promise for opening novel paths to heart regeneration and repair for heart disease, although these areas are still in their infancy. In this review, we summarize and discuss the recent progress in cardiac tissue engineering strategies, highlighting stem cell engineering and cardiomyocyte maturation, development of novel functional biomaterials and biofabrication tools, and their therapeutic applications involving drug discovery, disease modeling, and regenerative medicine for heart disease.

Novel Optics-Based Approaches for Cardiac Electrophysiology: A Review

Optical techniques for recording and manipulating cellular electrophysiology have advanced rapidly in just a few decades. These developments allow for the analysis of cardiac cellular dynamics at multiple scales while largely overcoming the drawbacks associated with the use of electrodes. The recent advent of optogenetics opens up new possibilities for regional and tissue-level electrophysiological control and hold promise for future novel clinical applications. This article, which emerged from the international NOTICE workshop in 2018, reviews the state-of-the-art optical techniques used for cardiac electrophysiological research and the underlying biophysics. The design and performance of optical reporters and optogenetic actuators are reviewed along with limitations of current probes. The physics of light interaction with cardiac tissue is detailed and associated challenges with the use of optical sensors and actuators are presented. Case studies include the use of fluorescence recovery after photobleaching and super-resolution microscopy to explore the micro-structure of cardiac cells and a review of two photon and light sheet technologies applied to cardiac tissue. The emergence of cardiac optogenetics is reviewed and the current work exploring the potential clinical use of optogenetics is also described. Approaches which combine optogenetic manipulation and optical voltage measurement are discussed, in terms of platforms that allow real-time manipulation of whole heart electrophysiology in open and closed-loop systems to study optimal ways to terminate spiral arrhythmias. The design and operation of optics-based approaches that allow high-throughput cardiac electrophysiological assays is presented. Finally, emerging techniques of photo-acoustic imaging and stress sensors are described along with strategies for future development and establishment of these techniques in mainstream electrophysiological research.

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.

Cardiac Tissue Engineering for the Treatment of Myocardial Infarction

Poor cell engraftment rate is one of the primary factors limiting the effectiveness of cell transfer therapy for cardiac repair. Recent studies have shown that the combination of cell-based therapy and tissue engineering technology can improve stem cell engraftment and promote the therapeutic effects of the treatment for myocardial infarction. This mini-review summarizes the recent progress in cardiac tissue engineering of cardiovascular cells from differentiated human pluripotent stem cells (PSCs), highlights their therapeutic applications for the treatment of myocardial infarction, and discusses the present challenges of cardiac tissue engineering and possible future directions from a clinical perspective.

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.

Substrate Stiffness Influences Structural and Functional Remodeling in Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Novel treatment strategies for cardiac tissue regeneration are heading for the use of engineered cardiac tissue made from induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). Despite the proven cardiogenic phenotype of these cells, a significant lack of structural and functional properties of mature myocytes prevents safe integration into the diseased heart. To date, maturation processes of cardiomyocytes remain largely unknown but may comprise biophysical cues from the immediate cell environment. Mechanosensing is one critical ability of cells to react to environmental changes. Accordingly, the surrounding substrate stiffness, comprised of extracellular matrix (ECM), cells, and growth surface, critically influences the myocyte's physiology, as known from deleterious remodeling processes in fibrotic hearts. Conversely, the mechanical properties during culture of iPSC-CMs may impact on their structural and functional maturation. Here, we tested the hypothesis that the environmental stiffness influences structural and functional properties of iPSC-CMs and investigated the effect of different substrate stiffnesses on cell contractility, excitation-contraction (EC) coupling, and intercellular coupling. Culture surfaces with defined stiffnesses ranging from rigid glass with 25GPa to PDMS of physiological softness were coated with ECM proteins and seeded with murine iPSC-CMs. Using confocal imaging, cardiac protein expression was assessed. Ca²⁺ handling and contractile properties were analyzed on different substrate stiffnesses. Intercellular coupling via gap junctions was investigated by fluorescence recovery after photobleaching (FRAP). Our data revealed greater organization of L-type Ca²⁺ channels and ryanodine receptors and increased EC-coupling gain, demonstrating structural and functional maturation in cells grown on soft surfaces. In addition, increased shortening and altered contraction dynamics revealed increased myofilament Ca²⁺ sensitivity in phase-plane loops. Moreover, connexin 43 expression was significantly increased in iPSC-CMs grown on soft surfaces leading to improved intercellular coupling. Taken together, our results demonstrate that soft surfaces with stiffnesses in the physiological range improve the expression pattern and interaction of cardiac proteins relevant for EC-coupling. In parallel, soft substrates influence contractile properties and improve intercellular coupling in iPSC-CMs. We conclude that the mechanical stiffness of the cell environment plays an important role in driving iPSC-CMs toward further maturation by inducing adaptive responses.

In vivo grafting of large engineered heart tissue patches for cardiac repair

Engineered heart tissue (EHT) strategies, by combining cells within a hydrogel matrix, may be a novel therapy for heart failure. EHTs restore cardiac function in rodent injury models, but more data are needed in clinically relevant settings. Accordingly, an upscaled EHT patch (2.5 cm × 1.5 cm × 1.5 mm) consisting of up to 20 million human induced pluripotent stem cell–derived cardiomyocytes (hPSC-CMs) embedded in a fibrin-based hydrogel was developed. A rabbit myocardial infarction model was then established to test for feasibility and efficacy. Our data showed that hPSC-CMs in EHTs became more aligned over 28 days and had improved contraction kinetics and faster calcium transients. Blinded echocardiographic analysis revealed a significant improvement in function in infarcted hearts that received EHTs, along with reduction in infarct scar size by 35%. Vascularization from the host to the patch was observed at week 1 and stable to week 4, but electrical coupling between patch and host heart was not observed. In vivo telemetry recordings and ex vivo arrhythmia provocation protocols showed that the patch was not pro-arrhythmic. In summary, EHTs improved function and reduced scar size without causing arrhythmia, which may be due to the lack of electrical coupling between patch and host heart.

Next generation of heart regenerative therapies: progress and promise of cardiac tissue engineering

The adult heart is a vital and highly specialized organ of the human body, with limited capability of self-repair and regeneration in case of injury or disease. Engineering biomimetic cardiac tissue to regenerate the heart has been an ambition in the field of tissue engineering, tracing back to the 1990s. Increased understanding of human stem cell biology and advances in process engineering have provided an unlimited source of cells, particularly cardiomyocytes, for the development of functional cardiac muscle, even though pluripotent stem cell-derived cardiomyocytes poorly resemble those of the adult heart. This review outlines key biology-inspired strategies reported to improve cardiomyocyte maturation features and current biofabrication approaches developed to engineer clinically relevant cardiac tissues. It also highlights the potential use of this technology in drug discovery science and disease modeling as well as the current efforts to translate it into effective therapies that improve heart function and promote regeneration.

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.

Human Engineered Heart Tissue Patches Remuscularize the Injured Heart in a Dose-Dependent Manner

Supplemental Digital Content is available in the text.

Human engineered heart tissue (EHT) transplantation represents a potential regenerative strategy for patients with heart failure and has been successful in preclinical models. Clinical application requires upscaling, adaptation to good manufacturing practices, and determination of the effective dose.

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.

The long and winding road of cardiomyocyte maturation

Knowledge about the molecular mechanisms regulating cardiomyocyte (CM) proliferation and differentiation has increased exponentially in recent years. Such insights together with the availability of more efficient protocols for generation of CMs from induced pluripotent stem cells (iPSCs) have raised expectations for new therapeutic strategies to treat congenital and non-congenital heart diseases. However, the poor regenerative potential of the postnatal heart and the incomplete maturation of iPSC-derived CMs represent important bottlenecks for such therapies in future years. CMs undergo dramatic changes at the doorstep between prenatal and postnatal life, including terminal cell cycle withdrawal, change in metabolism, and further specialization of the cellular machinery required for high-performance contraction. Here, we review recent insights into pre- and early postnatal developmental processes that regulate CM maturation, laying specific focus on genetic and metabolic pathways that control transition of CMs from the embryonic and perinatal to the fully mature adult CM state. We recapitulate the intrinsic features of CM maturation and highlight the importance of external factors, such as energy substrate availability and endocrine regulation in shaping postnatal CM development. We also address recent approaches to enhance maturation of iPSC-derived CMs in vitro, and summarize new discoveries that might provide useful tools for translational research on repair of the injured human heart.

Toward Cardiac Regeneration: Combination of Pluripotent Stem Cell-Based Therapies and Bioengineering Strategies

Cardiovascular diseases represent the major cause of morbidity and mortality worldwide. Multiple studies have been conducted so far in order to develop treatments able to prevent the progression of these pathologies. Despite progress made in the last decade, current therapies are still hampered by poor translation into actual clinical applications. The major drawback of such strategies is represented by the limited regenerative capacity of the cardiac tissue. Indeed, after an ischaemic insult, the formation of fibrotic scar takes place, interfering with mechanical and electrical functions of the heart. Hence, the ability of the heart to recover after ischaemic injury depends on several molecular and cellular pathways, and the imbalance between them results into adverse remodeling, culminating in heart failure. In this complex scenario, a new chapter of regenerative medicine has been opened over the past 20 years with the discovery of induced pluripotent stem cells (iPSCs). These cells share the same characteristic of embryonic stem cells (ESCs), but are generated from patient-specific somatic cells, overcoming the ethical limitations related to ESC use and providing an autologous source of human cells. Similarly to ESCs, iPSCs are able to efficiently differentiate into cardiomyocytes (CMs), and thus hold a real regenerative potential for future clinical applications. However, cell-based therapies are subjected to poor grafting and may cause adverse effects in the failing heart. Thus, over the last years, bioengineering technologies focused their attention on the improvement of both survival and functionality of iPSC-derived CMs. The combination of these two fields of study has burst the development of cell-based three-dimensional (3D) structures and organoids which mimic, more realistically, the in vivo cell behavior. Toward the same path, the possibility to directly induce conversion of fibroblasts into CMs has recently emerged as a promising area for in situ cardiac regeneration. In this review we provide an up-to-date overview of the latest advancements in the application of pluripotent stem cells and tissue-engineering for therapeutically relevant cardiac regenerative approaches, aiming to highlight outcomes, limitations and future perspectives for their clinical translation.

Evaluating Novel Targets of Ischemia Reperfusion Injury in Pig Models

Coronary heart diseases are of high relevance for health care systems in developed countries regarding patient numbers and costs. Disappointingly, the enormous effort put into the development of innovative therapies and the high numbers of clinical studies conducted are counteracted by the low numbers of therapies that become clinically effective. Evidently, pre-clinical research in its present form does not appear informative of the performance of treatments in the clinic and, even more relevant, it appears that there is hardly any consent about how to improve the predictive capacity of pre-clinical experiments. According to the steadily increasing relevance that pig models have gained in biomedical research in the recent past, we anticipate that research in pigs can be highly predictive for ischemia-reperfusion injury (IRI) therapies as well. Thus, we here describe the significance of pig models in IRI, give an overview about recent developments in evaluating such models by clinically relevant methods and present the latest insight into therapies applied to pigs under IRI.