Gene editing to prevent ventricular arrhythmias associated with cardiomyocyte cell therapy

Exploring hiPSC-CM replacement therapy in ischemic hearts

Ischemic heart disease is one of the leading causes of heart failure and death worldwide. The loss of cardiomyocytes following a myocardial infarction drives the remodeling process, which, in most cases, ultimately leads to heart failure. Since the available treatment options only slow down the remodeling process without tackling the causes of heart failure onset (i.e., cardiomyocyte loss and inability of the remaining cardiomyocytes to enter the cell cycle and regenerate the heart), in the last two decades, cardiovascular research focused on finding alternative solutions to regenerate the heart. So far, the investigated approaches include a variety of methods aiming at manipulation of non-coding RNAs, such as long non-coding RNA (lncRNA), circular RNA (circRNA), and microRNA (miRNA), and growth factors to enable the cardiomyocytes to re-enter the cell cycle, direct reprogramming of fibroblasts into cardiomyocytes (CM), and CM replacement therapy, all of them with the main goal to replace the loss of cardiomyocytes and restore the heart function. The development of reprogramming protocols from somatic cells to induced pluripotent stem cells (iPSCs) by Yamanaka and Takahashi, along with advancements in differentiation protocols to generate almost pure populations of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), has fostered optimism in cardiac regenerative medicine. Despite these advancements, critical concerns arose regarding the survival and retention of the engrafted cells, arrhythmogenicity, and immune response. Over time, much effort has been put into enhancing iPSC-CM therapy with different methods, ranging from anti-apoptotic small molecule-based approaches to tissue engineering. In this review, we discuss the evolution of cardiac cell therapy, highlighting recent advancements and the remaining challenges that must be overcome to translate this promising approach into clinical practice.

Pluripotent stem cell-derived cardiomyocyte transplantation: marching from bench to bedside

Cardiovascular diseases such as myocardial infarction, heart failure, and cardiomyopathy, persist as a leading global cause of death. Current treatment options have inherent limitations, particularly in terms of cardiac regeneration due to the limited regenerative capacity of adult human hearts. The transplantation of pluripotent stem cell-derived cardiomyocytes (PSC-CMs) has emerged as a promising and potential solution to address this challenge. This review aims to summarize the latest advancements and prospects of PSC-CM transplantation (PCT), along with the existing constraints, such as immune rejection and engraftment arrhythmias, and corresponding solutions. Encompassing a comprehensive range from fundamental research findings and preclinical experiments to ongoing clinical trials, we hope to offer insights into PCT from bench to bedside.

Designing multicellular cardiac tissue engineering technologies for clinical translation

Cardiovascular diseases remain the leading cause of death worldwide-claiming one-third of all deaths every year. Current two-dimensional in vitro cell culture systems and animal models cannot completely recapitulate the clinical complexity of these diseases in humans. Therefore, there is a dire need for higher fidelity biological systems capable of replicating these phenotypes to inform clinical outcomes and therapeutic development. Cardiac tissue engineering (CTE) strategies have emerged to fulfill this need by the design of in vitro three-dimensional myocardial tissue systems from human pluripotent stem cells. In this way, CTE systems serve as highly controllable human models for a variety of applications-including for physiological and pathological modeling, drug discovery and preclinical testing platforms, and even direct therapeutic interventions in the clinic. Although significant progress has been made in the development of these CTE technologies, critical challenges remain and necessary refinements are required to derive more advanced human heart tissue technologies. In this review, we distill three focus areas for the field to address: I) Generating cardiac muscle cell types and scalable manufacturing methods, II) Engineering tissue structure, function, and analyses, and III) Curating system design for specific application. In each of our focus areas, we emphasize the importance of designing CTE systems capable of mimicking the intricate intercellular connectivity of the human heart and discuss fundamental design considerations that subsequently arise. We conclude by highlighting cutting-edge applications that use CTE technologies for clinical modeling and the direct repair of damaged and diseased hearts.

Population-based computational simulations elucidate mechanisms of focal arrhythmia following stem cell injection

Following a myocardial infarction (MI), a large portion of ventricular cells are replaced by scar, leading to adverse structural remodeling and heart failure. The use of stem cell-derived cardiomyocytes has shown promise in restoring cardiac function in animal models following an MI but leads to rapid focal ventricular tachycardia (VT). The VT in these animals can be variable, and its underlying mechanisms remain unknown. In this study, we used three distinct computational models derived from histological images of post-MI non-human primate ventricles to understand how human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) grafts can affect focal VT individually and synergistically. Specifically, we explored whether grafts could work cooperatively to create new arrhythmia and if geometric features such as graft tortuosity, area, host isolation, and amount of surrounding scar inhibited or enhanced the effect. We observed at least one instance of graft-host excitation (GHE) for eleven of the twenty-five individual grafts examined. Since we used a stochastic population-of-models-based approach to generate graft boundaries, we found that the number of configurations with GHE varied from graft to graft. We also examined grafts in aggregate and found that the high prevalence of GHE when all grafts were included arose from combinations of individually arrhythmogenic grafts (i.e., the overall increase in arrhythmogenicity resulted from graft complementarity rather than graft cooperativity). Further analysis of graft spatial features showed that arrhythmogenic grafts tend to be in areas with high host isolation (i.e., spatially confined regions of surviving myocardium interdigitated with engrafted cells) and when graft area and tortuosity were also high. These insights can aid in the design of novel injection schemes that could result in safer therapy for patients.

At early stages of heart development, the first and second heart fields are a continuum of lateral head mesoderm-derived, cardiogenic cells

Pioneering work in the chicken established that the initial development of the heart consists of two stages: the quick assembly of a beating heart, followed by the recruitment of cells from adjacent tissues to deliver the mature in-and outflow tract. Cells to build the primitive heart were dubbed the first heart field (FHF) cells, cells to be recruited later the second heart field (SHF) cells. The current view is that these cells represent distinct, maybe even pre-determined lineages. However, it is still unclear where exactly FHF and SHF are located at different stages of development, and whether there is a sharp boundary or rather an overlap between the two. It is also unclear whether both FHF cells and SHF cells originate from the lateral head mesoderm (LHM), whether the paraxial head mesoderm (PHM) contributes to the SHF, and where the LHM-PHM boundary might be. To investigate this problem, we exploited the size, ease of access and exquisite anatomy of the chicken embryo and used traditional strategies as well as newly developed transgenic lines to trace the location of cardiogenic fields and boundaries from the time the first heart-markers are expressed to the time SHF cell recruitment ceases. Our work shows that both FHF and SHF stem from the LHM. We also found that FHF and SHF lack a distinct anatomical boundary. Rather, FHF and SHF are a continuum, and the recruitment of cells into the heart is a chance event depending on morphogenetic movements, the position of cells within the moving tissues, the separation of the somatic and splanchnic LHM, and the separation of the heart from the splanchnic subpharyngeal mesoderm during heart-looping. Reconciling our and previous studies we propose that first and second heart field precursors are specified but not determined, thus relying on morphogenetic processes and local environments to realise their cardiogenic potential.

Medium from human iPSC-derived primitive macrophages promotes adult cardiomyocyte proliferation and cardiac regeneration

Heart injury has been characterized by the irreversible loss of cardiomyocytes comprising the contractile tissues of the heart and thus strategies enabling adult cardiomyocyte proliferation are highly desired for treating various heart diseases. Here, we test the ability of human induced pluripotent stem cell-derived primitive macrophages (hiPMs) and their conditioned medium (hiPM-cm) to promote human cardiomyocyte proliferation and enhance cardiac regeneration in adult mice. We find that hiPMs promote human cardiomyocyte proliferation, which is recapitulated by hiPM-cm through the activation of multiple pro-proliferative pathways, and a secreted proteome analysis identifies five proteins participating in this activation. Subsequent in vivo experiments show that hiPM-cm promotes adult cardiomyocyte proliferation in mice. Lastly, hiPM-cm enhances cardiac regeneration and improves contractile function in injured adult mouse hearts. Together, our study demonstrates the efficacy of using hiPM-cm in promoting adult cardiomyocyte proliferation and cardiac regeneration to serve as an innovative treatment for heart disease.

Human Cardiac Microtissues Display Improved Engraftment and Survival in a Porcine Model of Myocardial Infarction

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) constitute a promising therapy for myocardial infarction (MI). The lack of an effective immunosuppressive regimen, combined with single-cell transplantations, results in suboptimal outcomes, such as poor engraftment and compromised therapeutic efficacy. This study aimed to confirm the increased retention of hiPSC-CMs microtissues (CMTs) over single-cell grafts. To ensure the long-term survival of CMTs for potential cardiac applications, CMTs were transplanted in a porcine model of MI using a triple immunosuppression protocol designed to limit immune cell infiltration. Acute evaluation of spherical hiPSC-CMs aggregates and dissociated aggregates followed by the development of a triple immunosuppression protocol were performed in healthy animals. Long-term survival of CMTs was later examined in pigs that underwent a transient coronary occlusion. Two weeks post-MI, the immunosuppression treatment was initiated and on day 28 the animals were transplanted with CMTs and followed for four more weeks. Acutely, CMTs showed superior retention compared to their dissociated counterparts. The immunosuppression regimen led to no organ damage and stable levels of circulating drugs once optimal dose was achieved. Two weeks post-xenotransplantation in healthy pigs, histology revealed that immunosuppressed animals displayed a significant decrease in total cellular infiltrates, particularly in CD3+ T cells. Pigs that underwent coronary occlusion, which later were immunosuppressed and treated with CMTs (5 × 107 cells), showed cell engraftment onto the native myocardium four weeks post-transplantation. This study supports the use of a triple immunosuppression cocktail to ensure long-term survival of CMTs for the treatment of MI.

Engineered heart muscle allografts for heart repair in primates and humans

Cardiomyocytes can be implanted to remuscularize the failing heart1-7. Challenges include sufficient cardiomyocyte retention for a sustainable therapeutic impact without intolerable side effects, such as arrhythmia and tumour growth. We investigated the hypothesis that epicardial engineered heart muscle (EHM) allografts from induced pluripotent stem cell-derived cardiomyocytes and stromal cells structurally and functionally remuscularize the chronically failing heart without limiting side effects in rhesus macaques. After confirmation of in vitro and in vivo (nude rat model) equivalence of the newly developed rhesus macaque EHM model with a previously established Good Manufacturing Practice-compatible human EHM formulation8, long-term retention (up to 6 months) and dose-dependent enhancement of the target heart wall by EHM grafts constructed from 40 to 200 million cardiomyocytes/stromal cells were demonstrated in macaques with and without myocardial infarction-induced heart failure. In the heart failure model, evidence for EHM allograft-enhanced target heart wall contractility and ejection fraction, which are measures for local and global heart support, was obtained. Histopathological and gadolinium-based perfusion magnetic resonance imaging analyses confirmed cell retention and functional vascularization. Arrhythmia and tumour growth were not observed. The obtained feasibility, safety and efficacy data provided the pivotal underpinnings for the approval of a first-in-human clinical trial on tissue-engineered heart repair. Our clinical data confirmed remuscularization by EHM implantation in a patient with advanced heart failure.

Pericellular oxygen dynamics in human cardiac fibroblasts and iPSC-cardiomyocytes in high-throughput plates: insights from experiments and modeling

Adequate oxygen supply is crucial for proper cellular function. The emergence of high-throughput (HT) expansion of human stem-cell-derived cells and HT in vitro cellular assays for drug testing necessitate monitoring and understanding of the oxygenation conditions, yet virtually no data exists for such settings. For metabolically active cells like cardiomyocytes, variations in oxygenation may significantly impact their maturation and function; conversely, electromechanical activity can drive oxygen demands. We used HT label-free optical measurements and computational modeling to gain insights about oxygen availability (peri-cellular oxygen dynamics) in syncytia of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) and human cardiac fibroblasts (cFB) grown in glass-bottom 96-well plates under static conditions. Our experimental results highlight the critical role of cell density and solution height (oxygen delivery path) in peri-cellular oxygen dynamics. The developed 3D reaction-diffusion model with Michaelis-Menten kinetics, trained on the obtained comprehensive data set, revealed that time-variant maximum oxygen consumption rate, Vmax, is needed to faithfully capture the complex peri-cellular oxygen dynamics in the excitable hiPSC-CMs, but not in the cFB. For the latter, accounting for cell proliferation was needed. Interestingly, we found both hypoxic (< 2%) and hyperoxic (> 7%) conditions can easily emerge in these standard HT plates in static culture and that peri-cellular oxygen dynamics evolves with days in culture. Our results and the developed computational model can directly be used to optimize cardiac cell growth in HT plates to achieve desired physiological conditions, important in cellular assays for cardiotoxicity, drug development, personalized medicine and heart regeneration applications.

Cardiomyocytes in Hypoxia: Cellular Responses and Implications for Cell-Based Cardiac Regenerative Therapies

Myocardial infarction (MI) is a severe hypoxic event, resulting in the loss of up to one billion cardiomyocytes (CMs). Due to the limited intrinsic regenerative capacity of the heart, cell-based regenerative therapies, which feature the implantation of stem cell-derived cardiomyocytes (SC-CMs) into the infarcted myocardium, are being developed with the goal of restoring lost muscle mass, re-engineering cardiac contractility, and preventing the progression of MI into heart failure (HF). However, such cell-based therapies are challenged by their susceptibility to oxidative stress in the ischemic environment of the infarcted heart. To maximize the therapeutic benefits of cell-based approaches, a better understanding of the heart environment at the cellular, tissue, and organ level throughout MI is imperative. This review provides a comprehensive summary of the cardiac pathophysiology occurring during and after MI, as well as how these changes define the cardiac environment to which cell-based cardiac regenerative therapies are delivered. This understanding is then leveraged to frame how cell culture treatments may be employed to enhance SC-CMs' hypoxia resistance. In this way, we synthesize both the complex experience of SC-CMs upon implantation and the engineering techniques that can be utilized to develop robust SC-CMs for the clinical translation of cell-based cardiac therapies.

Gene therapy for genetic diseases: challenges and future directions

Genetic diseases constitute the majority of rare human diseases, resulting from abnormalities in an individual's genetic composition. Traditional treatments offer limited relief for these challenging conditions. In contrast, the rapid advancement of gene therapy presents significant advantages by directly addressing the underlying causes of genetic diseases, thereby providing the potential for precision treatment and the possibility of curing these disorders. This review aims to delineate the mechanisms and outcomes of current gene therapy approaches in clinical applications across various genetic diseases affecting different body systems. Additionally, genetic muscular disorders will be examined as a case study to investigate innovative strategies of novel therapeutic approaches, including gene replacement, gene suppression, gene supplementation, and gene editing, along with their associated advantages and limitations at both clinical and preclinical levels. Finally, this review emphasizes the existing challenges of gene therapy, such as vector packaging limitations, immunotoxicity, therapy specificity, and the subcellular localization and immunogenicity of therapeutic cargos, while discussing potential optimization directions for future research. Achieving delivery specificity, as well as long-term effectiveness and safety, will be crucial for the future development of gene therapies targeting genetic diseases.

The Low Tumorigenic Risk and Subtypes of Cardiomyocytes Derived from Human-induced Pluripotent Stem Cells

BACKGROUND

Clinical application of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is a promising approach for the treatment of heart diseases. However, the tumorigenicity of hiPSC-CMs remains a concern for their clinical applications and the composition of the hiPSC-CM subtypes need to be clearly identified.

METHODS

In the present study, hiPSC-CMs were induced from hiPSCs via modulation of Wnt signaling followed by glucose deprivation purification. The structure, function, subpopulation composition, and tumorigenic risk of hiPSC-CMs were evaluated by single-cell RNA sequencing (scRNAseq), whole exome sequencing (WES), and integrated molecular biology, cell biology, electrophysiology, and/or animal experiments.

RESULTS

The high purity of hiPSC-CMs, determined by flow cytometry analysis, was generated. ScRNAseq analysis of differentiation day (D) 25 hiPSC-CMs did not identify the transcripts representative of undifferentiated hiPSCs. WES analysis showed a few newly acquired confidently identified mutations and no mutations in tumor susceptibility genes. Further, no tumor formation was observed after transplanting hiPSC-CMs into NOD-SCID mice for 3 months. Moreover, D25 hiPSC-CMs were composed of subtypes of ventricular-like cells (23.19%) and atrial-like cells (66.45%) in different cell cycle stages or mature levels, based on the scRNAseq analysis. Furthermore, a subpopulation of more mature ventricular cells (3.21%) was identified, which displayed significantly up-regulated signaling pathways related to myocardial contraction and action potentials. Additionally, a subpopulation of cardiomyocytes in an early differentiation stage (3.44%) experiencing nutrient stress-induced injury and heading toward apoptosis was observed.

CONCLUSIONS

This study confirmed the biological safety of hiPSC-CMs and described the composition and expression profile of cardiac subtypes in hiPSC-CMs which provide standards for quality control and theoretical supports for the translational applications of hiPSC-CMs.

The role of cardiomyocyte senescence in cardiovascular diseases: A molecular biology update

Cardiovascular diseases (CVD) are the leading cause of death worldwide, and advanced age is a main contributor to the prevalence of CVD. Cellular senescence is an irreversible state of cell cycle arrest that occurs in old age or after cells encounter various stresses. Senescent cells not only result in the reduction of cellular function, but also produce senescence-associated secretory phenotype (SASP) to affect surrounding cells and tissue microenvironment. There is increasing evidence that the gradual accumulation of senescent cardiomyocytes is causally involved in the decline of cardiovascular system function. To highlight the role of senescent cardiomyocytes in the pathophysiology of age-related CVD, we first introduced that senescent cardiomyoyctes can be identified by structural changes and several senescence-associated biomarkers. We subsequently provided a comprehensive summary of existing knowledge, outlining the compelling evidence on the relationship between senescent cardiomyocytes and age-related CVD phenotypes. In addition, we discussed that the significant therapeutic potential represented by the prevention of accelerated senescent cardiomyocytes, and the current status of some existing geroprotectors in the prevention and treatment of age-related CVD. Together, the review summarized the role of cardiomyocyte senescence in CVD, and explored the molecular knowledge of senescent cardiomyocytes and their potential clinical significance in developing senescent-based therapies, thereby providing important insights into their biology and potential therapeutic exploration.

Left Bundle Branch Area Pacing With or Without Conduction System Capture in Heart Failure Models

BACKGROUND

Left bundle branch area pacing includes left bundle branch pacing (LBBP) and left ventricular septal pacing (LVSP), which is effective in patients with dyssynchronous heart failure (DHF). However, the basic mechanisms are unknown.

OBJECTIVES

This study aimed to compare LBBP with LVSP and explore potential mechanisms underlying the better clinical outcomes of LBBP.

METHODS

A total of 24 beagles were assigned to the following groups: 1) control group; 2) DHF group, left bundle branch ablation followed by 6 weeks of AOO pacing at 200 ppm; 3) LBBP group, DHF for 3 weeks followed by 3 weeks of DOO pacing at 200 ppm; and 4) LVSP with the same interventions in the LBBP group. Metrics of electrocardiogram, echocardiography, hemodynamics, and expression of left ventricular proteins were evaluated.

RESULTS

Compared with LVSP, LBBP had better peak strain dispersion (44.67 ± 1.75 ms vs 55.50 ± 4.85 ms; P < 0.001) and hemodynamic effect (dP/dtmax improvement: 27.16% ± 7.79% vs 11.37% ± 4.73%; P < 0.001), whereas no significant differences in cardiac function were shown. The altered expressions of proteins in the lateral wall vs septum in the DHF group were partially reversed by LBBP and LVSP, which was associated with the contraction and adhesion process, separately.

CONCLUSIONS

The animal study demonstrated that LBBP offered better mechanical synchrony and improved hemodynamics than LVSP, which might be explained by the reversed expression of contraction proteins. These results supported the potential superiority of left bundle branch area pacing with the capture of the conduction system in DHF model.

Transient stabilization of human cardiovascular progenitor cells from human pluripotent stem cells in vitro reflects stage-specific heart development in vivo

AIMS

Understanding the molecular identity of human pluripotent stem cell (hPSC)-derived cardiac progenitors and mechanisms controlling their proliferation and differentiation is valuable for developmental biology and regenerative medicine.

METHODS AND RESULTS

Here, we show that chemical modulation of histone acetyl transferases (by IQ-1) and WNT (by CHIR99021) synergistically enables the transient and reversible block of directed cardiac differentiation progression on hPSCs. The resulting stabilized cardiovascular progenitors (SCPs) are characterized by ISL1pos/KI-67pos/NKX2-5neg expression. In the presence of the chemical inhibitors, SCPs maintain a proliferation quiescent state. Upon small molecules, removal SCPs resume proliferation and concomitant NKX2-5 up-regulation triggers cell-autonomous differentiation into cardiomyocytes. Directed differentiation of SCPs into the endothelial and smooth muscle lineages confirms their full developmental potential typical of bona fide cardiovascular progenitors. Single-cell RNA-sequencing-based transcriptional profiling of our in vitro generated human SCPs notably reflects the dynamic cellular composition of E8.25-E9.25 posterior second heart field of mouse hearts, hallmarked by nuclear receptor sub-family 2 group F member 2 expression. Investigating molecular mechanisms of SCP stabilization, we found that the cell-autonomously regulated retinoic acid and BMP signalling is governing SCP transition from quiescence towards proliferation and cell-autonomous differentiation, reminiscent of a niche-like behaviour.

CONCLUSION

The chemically defined and reversible nature of our stabilization approach provides an unprecedented opportunity to dissect mechanisms of cardiovascular progenitors' specification and reveal their cellular and molecular properties.

In silico evaluation of cell therapy in acute versus chronic infarction: role of automaticity, heterogeneity and Purkinje in human

Human-based modelling and simulation offer an ideal testbed for novel medical therapies to guide experimental and clinical studies. Myocardial infarction (MI) is a common cause of heart failure and mortality, for which novel therapies are urgently needed. Although cell therapy offers promise, electrophysiological heterogeneity raises pro-arrhythmic safety concerns, where underlying complex spatio-temporal dynamics cannot be investigated experimentally. Here, after demonstrating credibility of the modelling and simulation framework, we investigate cell therapy in acute versus chronic MI and the role of cell heterogeneity, scar size and the Purkinje system. Simulations agreed with experimental and clinical recordings from ionic to ECG dynamics in acute and chronic infarction. Following cell delivery, spontaneous beats were facilitated by heterogeneity in cell populations, chronic MI due to tissue depolarisation and slow sinus rhythm. Subsequent re-entrant arrhythmias occurred, in some instances with Purkinje involvement and their susceptibility was enhanced by impaired Purkinje-myocardium coupling, large scars and acute infarction. We conclude that homogeneity in injected ventricular-like cell populations minimises their spontaneous beating, which is enhanced by chronic MI, whereas a healthy Purkinje-myocardium coupling is key to prevent subsequent re-entrant arrhythmias, particularly for large scars.

Toward the latest advancements in cardiac regeneration using induced pluripotent stem cells (iPSCs) technology: approaches and challenges

A novel approach to treating heart failures was developed with the introduction of iPSC technology. Knowledge in regenerative medicine, developmental biology, and the identification of illnesses at the cellular level has exploded since the discovery of iPSCs. One of the most frequent causes of mortality associated with cardiovascular disease is the loss of cardiomyocytes (CMs), followed by heart failure. A possible treatment for heart failure involves restoring cardiac function and replacing damaged tissue with healthy, regenerated CMs. Significant strides in stem cell biology during the last ten years have transformed the in vitro study of human illness and enhanced our knowledge of the molecular pathways underlying human disease, regenerative medicine, and drug development. We seek to examine iPSC advancements in disease modeling, drug discovery, iPSC-Based cell treatments, and purification methods in this article.

Monkey see, monkey do: Tracking iPS-cardiomyocyte survival and maturation in autografts

Induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) therapy has emerged as a highly promising field of heart repair. Lin et al.1 presented compelling evidence on the long-term engraftment and maturation of autologous iPSC-CMs in two rhesus macaques, demonstrating unprecedented cardiac autografting data in large animal models without the need of immunosuppressants.

Electrically Conductive Collagen-PEDOT:PSS Hydrogel Prevents Post-Infarct Cardiac Arrhythmia and Supports hiPSC-Cardiomyocyte Function

Myocardial infarction (MI) causes cell death, disrupts electrical activity, triggers arrhythmia, and results in heart failure, whereby 50-60% of MI-associated deaths manifest as sudden cardiac deaths (SCD). The most effective therapy for SCD prevention is implantable cardioverter defibrillators (ICDs). However, ICDs contribute to adverse remodeling and disease progression and do not prevent arrhythmia. This work develops an injectable collagen-PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) hydrogel that protects infarcted hearts against ventricular tachycardia (VT) and can be combined with human induced pluripotent stem cell (hiPSC)-cardiomyocytes to promote partial cardiac remuscularization. PEDOT:PSS improves collagen gel formation, micromorphology, and conductivity. hiPSC-cardiomyocytes in collagen-PEDOT:PSS hydrogels exhibit near-adult sarcomeric length, improved contractility, enhanced calcium handling, and conduction velocity. RNA-sequencing data indicate enhanced maturation and improved cell-matrix interactions. Injecting collagen-PEDOT:PSS hydrogels in infarcted mouse hearts decreases VT to the levels of healthy hearts. Collectively, collagen-PEDOT:PSS hydrogels offer a versatile platform for treating cardiac injuries.

Advances in Hypertrophic Cardiomyopathy Disease Modelling Using hiPSC-Derived Cardiomyocytes

The advent of human induced pluripotent stem cells (hiPSCs) and their capacity to be differentiated into beating human cardiomyocytes (CMs) in vitro has revolutionized human disease modelling, genotype-phenotype predictions, and therapeutic testing. Hypertrophic cardiomyopathy (HCM) is a common inherited cardiomyopathy and the leading known cause of sudden cardiac arrest in young adults and athletes. On a molecular level, HCM is often driven by single pathogenic genetic variants, usually in sarcomeric proteins, that can alter the mechanical, electrical, signalling, and transcriptional properties of the cell. A deeper knowledge of these alterations is critical to better understanding HCM manifestation, progression, and treatment. Leveraging hiPSC-CMs to investigate the molecular mechanisms driving HCM presents a unique opportunity to dissect the consequences of genetic variants in a sophisticated and controlled manner. In this review, we summarize the molecular underpinnings of HCM and the role of hiPSC-CM studies in advancing our understanding, and we highlight the advances in hiPSC-CM-based modelling of HCM, including maturation, contractility, multiomics, and genome editing, with the notable exception of electrophysiology, which has been previously covered.

Advanced cell and gene therapies in cardiology

We review the evidence for the presence of stem/progenitor cells in the heart and the preclinical and clinical data using diverse cell types for the therapy of cardiac diseases. We highlight the failure of adult stem/progenitor cells to ameliorate heart function in most cardiac diseases, with the possible exception of refractory angina. The use of pluripotent stem cell-derived cardiomyocytes is analysed as a viable alternative therapeutic option but still needs further research at preclinical and clinical stages. We also discuss the use of direct reprogramming of cardiac fibroblasts into cardiomyocytes and the use of extracellular vesicles as therapeutic agents in ischemic and non-ischemic cardiac diseases. Finally, gene therapies and genome editing for the treatment of hereditary cardiac diseases, ablation of genes responsible for atherosclerotic disease, or modulation of gene expression in the heart are discussed.

Gene and stem cell therapy for inherited cardiac arrhythmias

Inherited cardiac arrhythmias are a group of genetic diseases predisposing to sudden cardiac arrest, mainly resulting from variants in genes encoding cardiac ion channels or proteins involved in their regulation. Currently available therapeutic options (pharmacotherapy, ablative therapy and device-based therapy) can not preclude the occurrence of arrhythmia events and/or provide complete protection. With growing understanding of the genetic background and molecular mechanisms of inherited cardiac arrhythmias, advancing insight of stem cell technology, and development of vectors and delivery strategies, gene therapy and stem cell therapy may be promising approaches for treatment of inherited cardiac arrhythmias. Recent years have witnessed impressive progress in the basic science aspects and there is a clear and urgent need to be translated into the clinical management of arrhythmic events. In this review, we present a succinct overview of gene and cell therapy strategies, and summarize the current status of gene and cell therapy. Finally, we discuss future directions for implementation of gene and cell therapy in the therapy of inherited cardiac arrhythmias.

Clinical translation of pluripotent stem cell-based therapies: successes and challenges

The translational stem cell research field has progressed immensely in the past decade. Development and refinement of differentiation protocols now allows the generation of a range of cell types, such as pancreatic β-cells and dopaminergic neurons, from human pluripotent stem cells (hPSCs) in an efficient and good manufacturing practice-compliant fashion. This has led to the initiation of several clinical trials using hPSC-derived cells to replace lost or dysfunctional cells, demonstrating evidence of both safety and efficacy. Here, we highlight successes from some of the hPSC-based trials reporting early signs of efficacy and discuss common challenges in clinical translation of cell therapies.

Strengthening cardiac therapy pipelines using human pluripotent stem cell-derived cardiomyocytes

Advances in hiPSC isolation and reprogramming and hPSC-CM differentiation have prompted their therapeutic application and utilization for evaluating potential cardiovascular safety liabilities. In this perspective, we showcase key efforts toward the large-scale production of hiPSC-CMs, implementation of hiPSC-CMs in industry settings, and recent clinical applications of this technology. The key observations are a need for traceable gender and ethnically diverse hiPSC lines, approaches to reduce cost of scale-up, accessible clinical trial datasets, and transparent guidelines surrounding the safety and efficacy of hiPSC-based therapies.

Stem cell-based therapy in cardiac repair after myocardial infarction: Promise, challenges, and future directions

Stem cells represent an attractive resource for cardiac regeneration. However, the survival and function of transplanted stem cells is poor and remains a major challenge for the development of effective therapies. As two main cell types currently under investigation in heart repair, mesenchymal stromal cells (MSCs) indirectly support endogenous regenerative capacities after transplantation, while induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) functionally integrate into the damaged myocardium and directly contribute to the restoration of its pump function. These two cell types are exposed to a common microenvironment with many stressors in ischemic heart tissue. This review summarizes the research progress on the mechanisms and challenges of MSCs and iPSC-CMs in post-MI heart repair, introduces several randomized clinical trials with 3D-mapping-guided cell therapy, and outlines recent findings related to the factors that affect the survival and function of stem cells. We also discuss the future directions for optimization such as biomaterial utilization, cell combinations, and intravenous injection of engineered nucleus-free MSCs.

Point mutations in RyR2 Ca2+-binding residues of human cardiomyocytes cause cellular remodelling of cardiac excitation contraction-coupling

AIMS

CRISPR/Cas9 gene edits of cardiac ryanodine receptor (RyR2) in human-induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) provide a novel platform for introducing mutations in RyR2 Ca2+-binding residues and examining the resulting excitation contraction (EC)-coupling remodelling consequences.

METHODS AND RESULTS

Ca2+-signalling phenotypes of mutations in RyR2 Ca2+-binding site residues associated with cardiac arrhythmia (RyR2-Q3925E) or not proven to cause cardiac pathology (RyR2-E3848A) were determined using ICa- and caffeine-triggered Ca2+ releases in voltage-clamped and total internal reflection fluorescence-imaged wild type and mutant cardiomyocytes infected with sarcoplasmic reticulum (SR)-targeted ER-GCaMP6 probe. (i) ICa- and caffeine-triggered Fura-2 or ER-GCaMP6 signals were suppressed, even when ICa was significantly enhanced in Q3925E and E3848A mutant cardiomyocytes; (ii) spontaneous beating (Fura-2 Ca2+ transients) persisted in mutant cells without the SR-release signals; (iii) while 5-20 mM caffeine failed to trigger Ca2+-release in voltage-clamped mutant cells, only ∼20% to ∼70% of intact myocytes responded respectively to caffeine; (iv) and 20 mM caffeine transients, however, activated slowly, were delayed, and variably suppressed by 2-APB, FCCP, or ruthenium red.

CONCLUSION

Mutating RyR2 Ca2+-binding residues, irrespective of their reported pathogenesis, suppressed both ICa- and caffeine-triggered Ca2+ releases, suggesting interaction between Ca2+- and caffeine-binding sites. Enhanced transmembrane calcium influx and remodelling of EC-coupling pathways may underlie the persistence of spontaneous beating in Ca2+-induced Ca2+ release-suppressed mutant myocytes.

Cardiac maturation

The heart undergoes a dynamic maturation process following birth, in response to a wide range of stimuli, including both physiological and pathological cues. This process entails substantial re-programming of mitochondrial energy metabolism coincident with the emergence of specialized structural and contractile machinery to meet the demands of the adult heart. Many components of this program revert to a more "fetal" format during development of pathological cardiac hypertrophy and heart failure. In this review, emphasis is placed on recent progress in our understanding of the transcriptional control of cardiac maturation, encompassing the results of studies spanning from in vivo models to cardiomyocytes derived from human stem cells. The potential applications of this current state of knowledge to new translational avenues aimed at the treatment of heart failure is also addressed.

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.

Cellular heterogeneity of pluripotent stem cell-derived cardiomyocyte grafts is mechanistically linked to treatable arrhythmias

Preclinical data have confirmed that human pluripotent stem cell-derived cardiomyocytes (PSC-CMs) can remuscularize the injured or diseased heart, with several clinical trials now in planning or recruitment stages. However, because ventricular arrhythmias represent a complication following engraftment of intramyocardially injected PSC-CMs, it is necessary to provide treatment strategies to control or prevent engraftment arrhythmias (EAs). Here, we show in a porcine model of myocardial infarction and PSC-CM transplantation that EAs are mechanistically linked to cellular heterogeneity in the input PSC-CM and resultant graft. Specifically, we identify atrial and pacemaker-like cardiomyocytes as culprit arrhythmogenic subpopulations. Two unique surface marker signatures, signal regulatory protein α (SIRPA)+CD90-CD200+ and SIRPA+CD90-CD200-, identify arrhythmogenic and non-arrhythmogenic cardiomyocytes, respectively. Our data suggest that modifications to current PSC-CM-production and/or PSC-CM-selection protocols could potentially prevent EAs. We further show that pharmacologic and interventional anti-arrhythmic strategies can control and potentially abolish these arrhythmias.

Gene Expression Profiling of Post Mortem Midbrain of Parkinson's Disease Patients and Healthy Controls

Parkinson's disease (PD) stands as the most prevalent degenerative movement disorder, marked by the degeneration of dopaminergic neurons in the substantia nigra of the midbrain. In this study, we conducted a transcriptome analysis utilizing post mortem mRNA extracted from the substantia nigra of both PD patients and healthy control (CTRL) individuals. Specifically, we acquired eight samples from individuals with PD and six samples from CTRL individuals, with no discernible pathology detected in the latter group. RNA sequencing was conducted using the TapeStation 4200 system from Agilent Technologies. A total of 16,148 transcripts were identified, with 92 mRNAs displaying differential expression between the PD and control groups. Specifically, 33 mRNAs were significantly up-regulated, while 59 mRNAs were down-regulated in PD compared to the controls. The identification of statistically significant signaling pathways, with an adjusted p-value threshold of 0.05, unveiled noteworthy insights. Specifically, the enriched categories included cardiac muscle contraction (involving genes such as ATPase Na+/K+ transporting subunit beta 2 (ATP1B2), solute carrier family 8 member A1 (SLC8A1), and cytochrome c oxidase subunit II (COX2)), GABAergic synapse (involving GABA type A receptor-associated protein-like 1 (GABARAPL1), G protein subunit beta 5 (GNB5), and solute carrier family 38 member 2 (SLC38A2), autophagy (involving GABARAPL1 and tumor protein p53-inducible nuclear protein 2 (TP53INP2)), and Fc gamma receptor (FcγR) mediated phagocytosis (involving amphiphysin (AMPH)). These findings uncover new pathophysiological dimensions underlying PD, implicating genes associated with heart muscle contraction. This knowledge enhances diagnostic accuracy and contributes to the advancement of targeted therapies.

Human Stem Cell-Derived Cardiomyocytes Integrate Into the Heart of Monkeys With Right Ventricular Pressure Overload

Cardiac ventricular pressure overload affects patients with congenital heart defects and can cause cardiac insufficiency. Grafts of stem cell-derived cardiomyocytes are proposed as a complementary treatment to surgical repair of the cardiac defect, aiming to support ventricular function. Here, we report successful engraftment of human induced pluripotent stem cell-derived cardiac lineage cells into the heart of immunosuppressed rhesus macaques with a novel surgical model of right ventricular pressure overload. The human troponin+ grafts were detected in low-dose (2 × 106 cells/kg) and high-dose (10 × 106 cells/kg) treatment groups up to 12 weeks post-injection. Transplanted cells integrated and progressively matched the organization of the surrounding host myocardium. Ventricular tachycardia occurred in five out of 16 animals receiving cells, with episodes of incessant tachycardia observed in two animals; ventricular tachycardia events resolved within 19 days. Our results demonstrate that grafted cardiomyocytes mature and integrate into the myocardium of nonhuman primates modeling right ventricular pressure overload.

Biologically derived epicardial patch induces macrophage mediated pathophysiologic repair in chronically infarcted swine hearts

There are nearly 65 million people with chronic heart failure (CHF) globally, with no treatment directed at the pathologic cause of the disease, the loss of functioning cardiomyocytes. We have an allogeneic cardiac patch comprised of cardiomyocytes and human fibroblasts on a bioresorbable matrix. This patch increases blood flow to the damaged heart and improves left ventricular (LV) function in an immune competent rat model of ischemic CHF. After 6 months of treatment in an immune competent Yucatan mini swine ischemic CHF model, this patch restores LV contractility without constrictive physiology, partially reversing maladaptive LV and right ventricular remodeling, increases exercise tolerance, without inducing any cardiac arrhythmias or a change in myocardial oxygen consumption. Digital spatial profiling in mice with patch placement 3 weeks after a myocardial infarction shows that the patch induces a CD45pos immune cell response that results in an infiltration of dendritic cells and macrophages with high expression of macrophages polarization to the anti-inflammatory reparative M2 phenotype. Leveraging the host native immune system allows for the potential use of immunomodulatory therapies for treatment of chronic inflammatory diseases not limited to ischemic CHF.

Human PSC-derived cardiac cells and their products: therapies for cardiac repair

Despite the dramatic improvements in the management of patients with chronic heart failure which have occurred over the last decades, some of them still exhaust conventional drug-based therapies without being eligible for more aggressive options like heart transplantation or implantation of a left ventricular assist device. Cell therapy has thus emerged as a possible means of filling this niche. Multiple cell types have now been tested both in the laboratory but also in the clinics and it is fair to acknowledge that none of the clinical trials have yet conclusively proven the efficacy of cell-based approaches. These clinical studies, however, have entailed the use of cells from various sources but of non-cardiac lineage origins. Although this might not be the main reason for their failures, the discovery of pluripotent stem cells capable of generating cardiomyocytes now raises the hope that such cardiac-committed cells could be therapeutically more effective. In this review, we will first describe where we currently are with regard to the clinical trials using PSC-differentiated cells and discuss the main issues which remain to be addressed. In parallel, because the capacity of cells to stably engraft in the recipient heart has increasingly been questioned, it has been hypothesized that a major mechanism of action could be the cell-triggered release of biomolecules that foster host-associated reparative pathways. Thus, in the second part of this review, we will discuss the rationale, clinically relevant advantages and pitfalls associated with the use of these PSC "products".

Mature human induced pluripotent stem cell-derived cardiomyocytes promote angiogenesis through alpha-B crystallin

BACKGROUND

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) can be used to treat heart diseases; however, the optimal maturity of hiPSC-CMs for effective regenerative medicine remains unclear. We aimed to investigate the benefits of long-term cultured mature hiPSC-CMs in injured rat hearts.

METHODS

Cardiomyocytes were differentiated from hiPSCs via monolayer culturing, and the cells were harvested on day 28 or 56 (D28-CMs or D56-CMs, respectively) after differentiation. We transplanted D28-CMs or D56-CMs into the hearts of rat myocardial infarction models and examined cell retention and engraftment via in vivo bioluminescence imaging and histological analysis. We performed transcriptomic sequencing analysis to elucidate the genetic profiles before and after hiPSC-CM transplantation.

RESULTS

Upregulated expression of mature sarcomere genes in vitro was observed in D56-CMs compared with D28-CMs. In vivo bioluminescence imaging studies revealed increased bioluminescence intensity of D56-CMs at 8 and 12 weeks post-transplantation. Histological and immunohistochemical analyses showed that D56-CMs promoted engraftment and maturation in the graft area at 12 weeks post-transplantation. Notably, D56-CMs consistently promoted microvessel formation in the graft area from 1 to 12 weeks post-transplantation. Transcriptomic sequencing analysis revealed that compared with the engrafted D28-CMs, the engrafted D56-CMs enriched genes related to blood vessel regulation at 12 weeks post-transplantation. As shown by transcriptomic and western blot analyses, the expression of a small heat shock protein, alpha-B crystallin (CRYAB), was significantly upregulated in D56-CMs compared with D28-CMs. Endothelial cell migration was inhibited by small interfering RNA-mediated knockdown of CRYAB when co-cultured with D56-CMs in vitro. Furthermore, CRYAB overexpression enhanced angiogenesis in the D28-CM grafts at 4 weeks post-transplantation.

CONCLUSIONS

Long-term cultured mature hiPSC-CMs promoted engraftment, maturation and angiogenesis post-transplantation in infarcted rat hearts. CRYAB, which was highly expressed in D56-CMs, was identified as an angiogenic factor from mature hiPSC-CMs. This study revealed the benefits of long-term culture, which may enhance the therapeutic potential of hiPSC-CMs.

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.

Manipulating and studying gene function in human pluripotent stem cell models

Human pluripotent stem cells (hPSCs) are uniquely suited to study human development and disease and promise to revolutionize regenerative medicine. These applications rely on robust methods to manipulate gene function in hPSC models. This comprehensive review aims to both empower scientists approaching the field and update experienced stem cell biologists. We begin by highlighting challenges with manipulating gene expression in hPSCs and their differentiated derivatives, and relevant solutions (transfection, transduction, transposition, and genomic safe harbor editing). We then outline how to perform robust constitutive or inducible loss-, gain-, and change-of-function experiments in hPSCs models, both using historical methods (RNA interference, transgenesis, and homologous recombination) and modern programmable nucleases (particularly CRISPR/Cas9 and its derivatives, i.e., CRISPR interference, activation, base editing, and prime editing). We further describe extension of these approaches for arrayed or pooled functional studies, including emerging single-cell genomic methods, and the related design and analytical bioinformatic tools. Finally, we suggest some directions for future advancements in all of these areas. Mastering the combination of these transformative technologies will empower unprecedented advances in human biology and medicine.

Harnessing developmental cues for cardiomyocyte production

Developmental research has attempted to untangle the exact signals that control heart growth and size, with knockout studies in mice identifying pivotal roles for Wnt and Hippo signaling during embryonic and fetal heart growth. Despite this improved understanding, no clinically relevant therapies are yet available to compensate for the loss of functional adult myocardium and the absence of mature cardiomyocyte renewal that underlies cardiomyopathies of multiple origins. It remains of great interest to understand which mechanisms are responsible for the decline in proliferation in adult hearts and to elucidate new strategies for the stimulation of cardiac regeneration. Multiple signaling pathways have been identified that regulate the proliferation of cardiomyocytes in the embryonic heart and appear to be upregulated in postnatal injured hearts. In this Review, we highlight the interaction of signaling pathways in heart development and discuss how this knowledge has been translated into current technologies for cardiomyocyte production.

When gene editing turns a nasty goddess into a friendly MEDUSA

Marchiano and colleagues interrogate the underlying causes of ventricular arrhythmias occurring after human pluripotent stem cell-cardiomyocyte transplantation. Through stepwise analysis and gene editing of ion channel expression, they mitigate pace-maker-like activity, providing evidence that the automaticity responsible for these rhythmic events can be successfully controlled by appropriate gene edits.