Genome editing of isogenic human induced pluripotent stem cells recapitulates long QT phenotype for drug testing

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.

Using induced pluripotent stem cells for drug discovery in arrhythmias

INTRODUCTION

Arrhythmias are disturbances in the normal rhythm of the heart and account for significant cardiovascular morbidity and mortality worldwide. Historically, preclinical research has been anchored in animal models, though physiological differences between these models and humans have limited their clinical translation. The discovery of human induced pluripotent stem cells (iPSC) and subsequent differentiation into cardiomyocyte has led to the development of new in vitro models of arrhythmias with the hope of a new pathway for both exploration of pathogenic variants and novel therapeutic discovery.

AREAS COVERED

The authors describe the latest two-dimensional in vitro models of arrhythmias, several examples of the use of these models in drug development, and the role of gene editing when modeling diseases. They conclude by discussing the use of three-dimensional models in the study of arrythmias and the integration of computational technologies and machine learning with experimental technologies.

EXPERT OPINION

Human iPSC-derived cardiomyocytes models have significant potential to augment disease modeling, drug discovery, and toxicity studies in preclinical development. While there is initial success with modeling arrhythmias, the field is still in its nascency and requires advances in maturation, cellular diversity, and readouts to emulate arrhythmias more accurately.

3D Computational Modeling of Defective Early Endosome Distribution in Human iPSC-Based Cardiomyopathy Models

Intracellular cargo delivery via distinct transport routes relies on vesicle carriers. A key trafficking route distributes cargo taken up by clathrin-mediated endocytosis (CME) via early endosomes. The highly dynamic nature of the endosome network presents a challenge for its quantitative analysis, and theoretical modelling approaches can assist in elucidating the organization of the endosome trafficking system. Here, we introduce a new computational modelling approach for assessment of endosome distributions. We employed a model of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) with inherited mutations causing dilated cardiomyopathy (DCM). In this model, vesicle distribution is defective due to impaired CME-dependent signaling, resulting in plasma membrane-localized early endosomes. We recapitulated this in iPSC-CMs carrying two different mutations, TPM1-L185F and TnT-R141W (MUT), using 3D confocal imaging as well as super-resolution STED microscopy. We computed scaled distance distributions of EEA1-positive vesicles based on a spherical approximation of the cell. Employing this approach, 3D spherical modelling identified a bi-modal segregation of early endosome populations in MUT iPSC-CMs, compared to WT controls. Moreover, spherical modelling confirmed reversion of the bi-modal vesicle localization in RhoA II-treated MUT iPSC-CMs. This reflects restored, homogeneous distribution of early endosomes within MUT iPSC-CMs following rescue of CME-dependent signaling via RhoA II-dependent RhoA activation. Overall, our approach enables assessment of early endosome distribution in cell-based disease models. This new method may provide further insight into the dynamics of endosome networks in different physiological scenarios.

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.

Modeling mutation-specific arrhythmogenic phenotypes in isogenic human iPSC-derived cardiac tissues

Disease modeling using human induced pluripotent stem cells (hiPSCs) from patients with genetic disease is a powerful approach for dissecting pathophysiology and drug discovery. Nevertheless, isogenic controls are required to precisely compare phenotypic outcomes from presumed causative mutations rather than differences in genetic backgrounds. Moreover, 2D cellular models often fail to exhibit authentic disease phenotypes resulting in poor validation in vitro. Here we show that a combination of precision gene editing and bioengineered 3D tissue models can establish advanced isogenic hiPSC-derived cardiac disease models, overcoming these drawbacks. To model inherited cardiac arrhythmias we selected representative N588D and N588K missense mutations affecting the same codon in the hERG potassium channel gene KCNH2, which are reported to cause long (LQTS) and short (SQTS) QT syndromes, respectively. We generated compound heterozygous variants in normal hiPSCs, and differentiated cardiomyocytes (CMs) and mesenchymal cells (MCs) to form 3D cardiac tissue sheets (CTSs). In hiPSC-derived CM monolayers and 3D CTSs, electrophysiological analysis with multielectrode arrays showed prolonged and shortened repolarization, respectively, compared to the isogenic controls. When pharmacologically inhibiting the hERG channels, mutant 3D CTSs were differentially susceptible to arrhythmic events than the isogenic controls. Thus, this strategy offers advanced disease models that can reproduce clinically relevant phenotypes and provide solid validation of gene mutations in vitro.

New drug discovery of cardiac anti-arrhythmic drugs: insights in animal models

Cardiac rhythm regulated by micro-macroscopic structures of heart. Pacemaker abnormalities or disruptions in electrical conduction, lead to arrhythmic disorders may be benign, typical, threatening, ultimately fatal, occurs in clinical practice, patients on digitalis, anaesthesia or acute myocardial infarction. Both traditional and genetic animal models are: In-vitro: Isolated ventricular Myocytes, Guinea pig papillary muscles, Patch-Clamp Experiments, Porcine Atrial Myocytes, Guinea pig ventricular myocytes, Guinea pig papillary muscle: action potential and refractory period, Langendorff technique, Arrhythmia by acetylcholine or potassium. Acquired arrhythmia disorders: Transverse Aortic Constriction, Myocardial Ischemia, Complete Heart Block and AV Node Ablation, Chronic Tachypacing, Inflammation, Metabolic and Drug-Induced Arrhythmia. In-Vivo: Chemically induced arrhythmia: Aconitine antagonism, Digoxin-induced arrhythmia, Strophanthin/ouabain-induced arrhythmia, Adrenaline-induced arrhythmia, and Calcium-induced arrhythmia. Electrically induced arrhythmia: Ventricular fibrillation electrical threshold, Arrhythmia through programmed electrical stimulation, sudden coronary death in dogs, Exercise ventricular fibrillation. Genetic Arrhythmia: Channelopathies, Calcium Release Deficiency Syndrome, Long QT Syndrome, Short QT Syndrome, Brugada Syndrome. Genetic with Structural Heart Disease: Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia, Dilated Cardiomyopathy, Hypertrophic Cardiomyopathy, Atrial Fibrillation, Sick Sinus Syndrome, Atrioventricular Block, Preexcitation Syndrome. Arrhythmia in Pluripotent Stem Cell Cardiomyocytes. Conclusion: Both traditional and genetic, experimental models of cardiac arrhythmias' characteristics and significance help in development of new antiarrhythmic drugs.

The Advantages, Challenges, and Future of Human-Induced Pluripotent Stem Cell Lines in Type 2 Long QT Syndrome

Type 2 long QT syndrome (LQT2) is the second most common subtype of long QT syndrome and is caused by mutations in KCHN2 encoding the rapidly activating delayed rectifier potassium channel vital for ventricular repolarization. Sudden cardiac death is a sentinel event of LQT2. Preclinical diagnosis by genetic testing is potentially life-saving.Traditional LQT2 models cannot wholly recapitulate genetic and phenotypic features; therefore, there is a demand for a reliable experimental model. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) meet this challenge. This review introduces the advantages of the hiPSC-CM model over the traditional model and discusses how hiPSC-CM and gene editing are used to decipher mechanisms of LQT2, screen for cardiotoxicity, and identify therapeutic strategies, thus promoting the realization of precision medicine for LQT2 patients.

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocyte modelling of cardiovascular diseases for natural compound discovery

Cardiovascular disease (CVD) remains the leading cause of death worldwide. Natural compounds extracted from medicinal plants characterized by diverse biological activities and low toxicity or side effects, are increasingly taking center stage in the search for new drugs. Currently, preclinical evaluation of natural products relies mainly on the use of immortalized cell lines of human origin or animal models. Increasing evidence indicates that cardiomyopathy models based on immortalized cell lines do not recapitulate pathogenic phenotypes accurately and a substantial physiological discrepancy between animals and humans casts doubt on the clinical relevance of animal models for these studies. The newly developed human induced pluripotent stem cell (hiPSC) technology in combination with highly-efficient cardiomyocyte differentiation methods provides an ideal tool for modeling human cardiomyopathies in vitro. Screening of drugs, especially screening of natural products, based on these models has been widely used and has shown that evaluation in such models can recapitulate important aspects of the physiological properties of drugs. The purpose of this review is to provide information on the latest developments in this area of research and to help researchers perform screening of natural products using the hiPSC-CM platform.

Modeling long QT syndrome type 2 on-a-chip via in-depth assessment of isogenic gene-edited 3D cardiac tissues

Long QT syndrome (LQTS) is a cardiovascular disease characterized by QT interval prolongation that can lead to sudden cardiac death. Many mutations with heterogeneous mechanisms have been identified in KCNH2, the gene that encodes for hERG (Kv11.1), which lead to onset of LQTS type 2 (LQTS2). In this work, we developed a LQTS2-diseased tissue-on-a-chip model, using 3D coculture of isogenic stem cell-derived cardiomyocytes (CMs) and cardiac fibroblasts (CFs) within an organotypic microfluidic chip technology. Primarily, we created a hiPSC line with R531W mutation in KCNH2 using CRISPR-Cas9 gene-editing technique and characterized the resultant differentiated CMs and CFs. A deficiency in hERG trafficking was identified in KCNH2-edited hiPSC-CMs, revealing a possible mechanism of R531W mutation in LQTS2 pathophysiology. Following creation of a 3D LQTS2 tissue-on-a-chip, the tissues were extensively characterized, through analysis of calcium handling and response to β-agonist. Furthermore, attempted phenotypic rescue via pharmacological intervention of LQTS2 on a chip was investigated.

Clinical Trial in a Dish for Space Radiation Countermeasure Discovery

NASA aims to return humans to the moon within the next five years and to land humans on Mars in a few decades. Space radiation exposure represents a major challenge to astronauts' health during long-duration missions, as it is linked to increased risks of cancer, cardiovascular dysfunctions, central nervous system (CNS) impairment, and other negative outcomes. Characterization of radiation health effects and developing corresponding countermeasures are high priorities for the preparation of long duration space travel. Due to limitations of animal and cell models, the development of novel physiologically relevant radiation models is needed to better predict these individual risks and bridge gaps between preclinical testing and clinical trials in drug development. "Clinical Trial in a Dish" (CTiD) is now possible with the use of human induced pluripotent stem cells (hiPSCs), offering a powerful tool for drug safety or efficacy testing using patient-specific cell models. Here we review the development and applications of CTiD for space radiation biology and countermeasure studies, focusing on progress made in the past decade.

Intersection of stem cell biology and engineering towards next generation in vitro models of human fibrosis

Human fibrotic diseases constitute a major health problem worldwide. Fibrosis involves significant etiological heterogeneity and encompasses a wide spectrum of diseases affecting various organs. To date, many fibrosis targeted therapeutic agents failed due to inadequate efficacy and poor prognosis. In order to dissect disease mechanisms and develop therapeutic solutions for fibrosis patients, in vitro disease models have gone a long way in terms of platform development. The introduction of engineered organ-on-a-chip platforms has brought a revolutionary dimension to the current fibrosis studies and discovery of anti-fibrotic therapeutics. Advances in human induced pluripotent stem cells and tissue engineering technologies are enabling significant progress in this field. Some of the most recent breakthroughs and emerging challenges are discussed, with an emphasis on engineering strategies for platform design, development, and application of machine learning on these models for anti-fibrotic drug discovery. In this review, we discuss engineered designs to model fibrosis and how biosensor and machine learning technologies combine to facilitate mechanistic studies of fibrosis and pre-clinical drug testing.

Translational potential of hiPSCs in predictive modeling of heart development and disease

Congenital heart disease (CHD) represents a major class of birth defects worldwide and is associated with cardiac malformations that often require surgical intervention immediately after birth. Despite the intense efforts from multicentric genome/exome sequencing studies that have identified several genetic variants, the etiology of CHD remains diverse and often unknown. Genetically modified animal models with candidate gene deficiencies continue to provide novel molecular insights that are responsible for fetal cardiac development. However, the past decade has seen remarkable advances in the field of human induced pluripotent stem cell (hiPSC)-based disease modeling approaches to better understand the development of CHD and discover novel preventative therapies. The iPSCs are derived from reprogramming of differentiated somatic cells to an embryonic-like pluripotent state via overexpression of key transcription factors. In this review, we describe how differentiation of hiPSCs to specialized cardiac cellular identities facilitates our understanding of the development and pathogenesis of CHD subtypes. We summarize the molecular and functional characterization of hiPSC-derived differentiated cells in support of normal cardiogenesis, those that go awry in CHD and other heart diseases. We illustrate how stem cell-based disease modeling enables scientists to dissect the molecular mechanisms of cell-cell interactions underlying CHD. We highlight the current state of hiPSC-based studies that are in the verge of translating into clinical trials. We also address limitations including hiPSC-model reproducibility and scalability and differentiation methods leading to cellular heterogeneity. Last, we provide future perspective on exploiting the potential of hiPSC technology as a predictive model for patient-specific CHD, screening pharmaceuticals, and provide a source for cell-based personalized medicine. In combination with existing clinical and animal model studies, data obtained from hiPSCs will yield further understanding of oligogenic, gene-environment interaction, pathophysiology, and management for CHD and other genetic cardiac disorders.

Modelling Diabetic Cardiomyopathy: Using Human Stem Cell-Derived Cardiomyocytes to Complement Animal Models

Diabetes is a global epidemic, with cardiovascular disease being the leading cause of death in diabetic patients. There is a pressing need for an in vitro model to aid understanding of the mechanisms driving diabetic heart disease, and to provide an accurate, reliable tool for drug testing. Human induced-pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have potential as a disease modelling tool. There are several factors that drive molecular changes inside cardiomyocytes contributing to diabetic cardiomyopathy, including hyperglycaemia, lipotoxicity and hyperinsulinemia. Here we discuss these factors and how they can be seen in animal models and utilised in cell culture to mimic the diabetic heart. The use of human iPSC-CMs will allow for a greater understanding of disease pathogenesis and open up new avenues for drug testing.

KCNQ1-deficient and KCNQ1-mutant human embryonic stem cell-derived cardiomyocytes for modeling QT prolongation

Background

The slowly activated delayed rectifier potassium current (I_Ks) mediated by the KCNQ1 gene is one of the main currents involved in repolarization. KCNQ1 mutation can result in long-QT syndrome type 1 (LQT1). I_Ks does not participate in repolarization in mice; thus, no good model is currently available for research on the mechanism of and drug screening for LQT1. In this study, we established a KCNQ1-deficient human cardiomyocyte (CM) model and performed a series of microelectrode array (MEA) detection experiments on KCNQ1-mutant CMs constructed in other studies to explore the pathogenic mechanism of KCNQ1 deletion and mutation and perform drug screening.

Method

KCNQ1 was knocked out in human embryonic stem cell (hESC) H9 line using the CRISPR/cas9 system. KCNQ1-deficient and KCNQ1-mutant hESCs were differentiated into CMs through a chemically defined differentiation protocol. Subsequently, high-throughput MEA analysis and drug intervention were performed to determine the electrophysiological characteristics of KCNQ1-deficient and KCNQ1-mutant CMs.

Results

During high-throughput MEA analysis, the electric field potential and action potential durations in KCNQ1-deficient CMs were significantly longer than those in wild-type CMs. KCNQ1-deficient CMs also showed an irregular rhythm. Furthermore, KCNQ1-deficient and KCNQ1-mutant CMs showed different responses to different drug treatments, which reflected the differences in their pathogenic mechanisms.

Conclusion

We established a human CM model with KCNQ1 deficiency showing a prolonged QT interval and an irregular heart rhythm. Further, we used various drugs to treat KCNQ1-deficient and KCNQ1-mutant CMs, and the three models showed different responses to these drugs. These models can be used as important tools for studying the different pathogenic mechanisms of KCNQ1 mutation and the relationship between the genotype and phenotype of KCNQ1, thereby facilitating drug development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02964-3.

Cellular and Engineered Organoids for Cardiovascular Models

An ensemble of in vitro cardiac tissue models has been developed over the past several decades to aid our understanding of complex cardiovascular disorders using a reductionist approach. These approaches often rely on recapitulating single or multiple clinically relevant end points in a dish indicative of the cardiac pathophysiology. The possibility to generate disease-relevant and patient-specific human induced pluripotent stem cells has further leveraged the utility of the cardiac models as screening tools at a large scale. To elucidate biological mechanisms in the cardiac models, it is critical to integrate physiological cues in form of biochemical, biophysical, and electromechanical stimuli to achieve desired tissue-like maturity for a robust phenotyping. Here, we review the latest advances in the directed stem cell differentiation approaches to derive a wide gamut of cardiovascular cell types, to allow customization in cardiac model systems, and to study diseased states in multiple cell types. We also highlight the recent progress in the development of several cardiovascular models, such as cardiac organoids, microtissues, engineered heart tissues, and microphysiological systems. We further expand our discussion on defining the context of use for the selection of currently available cardiac tissue models. Last, we discuss the limitations and challenges with the current state-of-the-art cardiac models and highlight future directions.

Deciphering Common Long QT Syndrome Using CRISPR/Cas9 in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

From carrying potentially pathogenic genes to severe clinical phenotypes, the basic research in the inherited cardiac ion channel disease such as long QT syndrome (LQTS) has been a significant challenge in explaining gene-phenotype heterogeneity. These have opened up new pathways following the parallel development and successful application of stem cell and genome editing technologies. Stem cell-derived cardiomyocytes and subsequent genome editing have allowed researchers to introduce desired genes into cells in a dish to replicate the disease features of LQTS or replace causative genes to normalize the cellular phenotype. Importantly, this has made it possible to elucidate potential genetic modifiers contributing to clinical heterogeneity and hierarchically manage newly identified variants of uncertain significance (VUS) and more therapeutic options to be tested in vitro. In this paper, we focus on and summarize the recent advanced application of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) combined with clustered regularly interspaced short palindromic repeats/CRISPR-associated system 9 (CRISPR/Cas9) in the interpretation for the gene-phenotype relationship of the common LQTS and presence challenges, increasing our understanding of the effects of mutations and the physiopathological mechanisms in the field of cardiac arrhythmias.

Brugada Syndrome: Different Experimental Models and the Role of Human Cardiomyocytes From Induced Pluripotent Stem Cells

Brugada syndrome (BrS) is an inherited and rare cardiac arrhythmogenic disease associated with an increased risk of ventricular fibrillation and sudden cardiac death. Different genes have been linked to BrS. The majority of mutations are located in the SCN5A gene, and the typical abnormal ECG is an elevation of the ST segment in the right precordial leads V1 to V3. The pathophysiological mechanisms of BrS were studied in different models, including animal models, heterologous expression systems, and human-induced pluripotent stem cell-derived cardiomyocyte models. Currently, only a few BrS studies have used human-induced pluripotent stem cell-derived cardiomyocytes, most of which have focused on genotype-phenotype correlations and drug screening. The combination of new technologies, such as clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 (CRISPR associated protein 9)-mediated genome editing and 3-dimensional engineered heart tissues, has provided novel insights into the pathophysiological mechanisms of the disease and could offer opportunities to improve the diagnosis and treatment of patients with BrS. This review aimed to compare different models of BrS for a better understanding of the roles of human-induced pluripotent stem cell-derived cardiomyocytes in current BrS research and personalized medicine at a later stage.

Ranolazine rescues the heart failure phenotype of PLN-deficient human pluripotent stem cell-derived cardiomyocytes

Phospholamban (PLN) is a key regulator that controls the function of the sarcoplasmic reticulum (SR) and is required for the regulation of cardiac contractile function. Although PLN-deficient mice demonstrated improved cardiac function, PLN loss in humans can result in dilated cardiomyopathy (DCM) or heart failure (HF). The CRISPR-Cas9 technology was used to create a PLN knockout human induced pluripotent stem cell (hiPSC) line in this study. PLN deletion hiPSCs-CMs had enhanced contractility at day 30, but proceeded to a cardiac failure phenotype at day 60, with decreased contractility, mitochondrial damage, increased ROS production, cellular energy metabolism imbalance, and poor Ca²⁺ handling. Furthermore, adding ranolazine to PLN knockout hiPSCs-CMs at day 60 can partially restore Ca²⁺ handling disorders and cellular energy metabolism, alleviating the PLN knockout phenotype of HF, implying that the disorder of intracellular Ca²⁺ transport and the imbalance of cellular energy metabolism are the primary mechanisms for PLN deficiency pathogenesis.

Compact SchCas9 Recognizes the Simple NNGR PAM

Clustered regularly interspaced short palindromic repeat (CRISPR)/SaCas9 is the most popular tool for in vivo genome editing due to its high efficiency and small genome. The authors previously developed four SaCas9 orthologs as genome-editing tools. Here, to expand the targeting scope, they investigate the diversity of protospacer adjacent motifs (PAMs) by screening a list of 16 SaCas9 orthologs, twelve of which display editing activity in mammalian cells. They recognize five types of PAMs: NNGRRT, NNGRRR, NNGRC, NNGA, and NNGR. Importantly, SchCas9 recognizes the simple NNGR PAM, representing the most relaxed PAM preference of compact Cas9s to date. It is further demonstrated that SchCas9 enables efficient genome editing in multiple human cell lines. Altogether, these compact Cas9 tools offer a new option for both basic research and clinical applications.

Engineering Organoids for in vitro Modeling of Phenylketonuria

Phenylketonuria is a recessive genetic disorder of amino-acid metabolism, where impaired phenylalanine hydroxylase function leads to the accumulation of neurotoxic phenylalanine levels in the brain. Severe cognitive and neuronal impairment are observed in untreated/late-diagnosed patients, and even early treated ones are not safe from life-long sequelae. Despite the wealth of knowledge acquired from available disease models, the chronic effect of Phenylketonuria in the brain is still poorly understood and the consequences to the aging brain remain an open question. Thus, there is the need for better predictive models, able to recapitulate specific mechanisms of this disease. Human induced pluripotent stem cells (hiPSCs), with their ability to differentiate and self-organize in multiple tissues, might provide a new exciting in vitro platform to model specific PKU-derived neuronal impairment. In this review, we gather what is known about the impact of phenylalanine in the brain of patients and highlight where hiPSC-derived organoids could contribute to the understanding of this disease.

CRISPR-Mediated Genomic Addition to CPS1 Deficient iPSCs is Insufficient to Restore Nitrogen Homeostasis

CPS1 deficiency is an inborn error of metabolism caused by loss-of-function mutations in the CPS1 gene, catalyzing the initial reaction of the urea cycle. Deficiency typically leads to toxic levels of plasma ammonia, cerebral edema, coma, and death, with the only curative treatment being liver transplantation; due to limited donor availability and the invasiveness and complications of the procedure, however, alternative therapies are needed. Induced pluripotent stem cells offer an alternative cell source to partial or whole liver grafts that theoretically would not require immune suppression regimens and additionally are amenable to genetic modifications. Here, we genetically modified CPS1 deficient patient-derived stem cells to constitutively express human codon optimized CPS1 from the AAVS1 safe harbor site. While edited stem cells efficiently differentiated to hepatocyte-like cells, they failed to metabolize ammonia more efficiently than their unedited counterparts. This unexpected result appears to have arisen in part due to transgene promoter methylation, and thus transcriptional silencing, in undifferentiated cells, impacting their capacity to restore the complete urea cycle function upon differentiation. As pluripotent stem cell strategies are being expanded widely for potential cell therapies, these results highlight the need for strict quality control and functional analysis to ensure the integrity of cell products.

Insights to Heart Development and Cardiac Disease Models Using Pluripotent Stem Cell Derived 3D Organoids

Medical research in the recent years has achieved significant progress due to the increasing prominence of organoid technology. Various developed tissue organoids bridge the limitations of conventional 2D cell culture and animal models by recapitulating in vivo cellular complexity. Current 3D cardiac organoid cultures have shown their utility in modelling key developmental hallmarks of heart organogenesis, but the complexity of the organ demands a more versatile model that can investigate more fundamental parameters, such as structure, organization and compartmentalization of a functioning heart. This review will cover the prominence of cardiac organoids in recent research, unpack current in vitro 3D models of the developing heart and look into the prospect of developing physiologically appropriate cardiac organoids with translational applicability. In addition, we discuss some of the limitations of existing cardiac organoid models in modelling embryonic development of the heart and manifestation of cardiac diseases.

Measuring hypertrophy in neonatal rat primary cardiomyocytes and human iPSC-derived cardiomyocytes

In the heart, left ventricular hypertrophy is initially an adaptive mechanism that increases wall thickness to preserve normal cardiac output and function in the face of coronary artery disease or hypertension. Cardiac hypertrophy develops in response to pressure and volume overload but can also be seen in inherited cardiomyopathies. As the wall thickens, it becomes stiffer impairing the distribution of oxygenated blood to the rest of the body. With complex cellular signalling and transcriptional networks involved in the establishment of the hypertrophic state, several model systems have been developed to better understand the molecular drivers of disease. Immortalized cardiomyocyte cell lines, primary rodent and larger animal models have all helped understand the pathological mechanisms underlying cardiac hypertrophy. Induced pluripotent stem cell-derived cardiomyocytes are also used and have the additional benefit of providing access to human samples with direct disease relevance as when generated from patients suffering from hypertrophic cardiomyopathies. Here, we briefly review in vitro and in vivo model systems that have been used to model hypertrophy and provide detailed methods to isolate primary neonatal rat cardiomyocytes as well as to generate cardiomyocytes from human iPSCs. We also describe how to model hypertrophy in a "dish" using gene expression analysis and immunofluorescence combined with automated high-content imaging.

A Highly Sensitive GFP Activation Assay for Detection of DNA Cleavage in Cells

CRISPR/Cas9 nucleases hold great potential for gene therapy, but they frequently induce unwanted off-target cleavage. We previously developed a GFP activation assay for detection of DNA cleavage in cells. Here, we demonstrate two novel applications of this assay. First, we use this assay to confirm off-target cleavage that cannot be detected by targeted deep sequencing in cells before. Second, we use this approach to detect multiple alternative PAMs recognized by SpCas9. These noncanonical PAMs are associated with low cleavage activity, but targets associated with these PAMs must be considered as potential off-target sites. Taken together, the GFP activation assay is a powerful platform for DNA cleavage detection in cells.

An Episomal CRISPR/Cas12a System for Mediating Efficient Gene Editing

(1) Background: Gene editing technology, as represented by CRISPR is a powerful tool used in biomedical science. However, the editing efficiency of such technologies, especially in induced pluripotent stem cells (iPSCs) and other types of stem cells, is low which hinders its application in regenerative medicine; (2) Methods: A gene-editing system, COE, was designed and constructed based on CRISPR/Cas12a and Orip/EBNA1, and its editing efficiency was evaluated in human embryonic kidney 293T (HEK-293T) cells with flow cytometry and restriction fragment length polymorphism (RFLP) analysis. The COE was nucleofected into iPSCs, then, the editing efficiency was verified by a polymerase chain reaction and Sanger sequencing; (3) Results: With the extension of time, COE enables the generation of up to 90% insertion or deletion rates in HEK-293T cells. Furthermore, the deletion of a 2.5 kb fragment containing Exon 51 of the dystrophin gene (DMD) in iPSCs was achieved with high efficiency; out of 14 clones analyzed, 3 were positive. Additionally, the Exon 51-deleted iPSCs derived from cardiomyocytes had similar expression profiles to those of Duchenne muscular dystrophy (DMD) patient-specific iPSCs. Moreover, there was no residue of each component of the plasmid in the editing cells; (4) Conclusions: In this study, a novel, efficient, and safe gene-editing system, COE, was developed, providing a powerful tool for gene editing.

Cardiotoxicity of Antineoplastic Therapies and Applications of Induced Pluripotent Stem Cell-Derived Cardiomyocytes

The therapeutic landscape for the treatment of cancer has evolved significantly in recent decades, aided by the development of effective oncology drugs. However, many cancer drugs are often poorly tolerated by the body and in particular the cardiovascular system, causing adverse and sometimes fatal side effects that negate the chemotherapeutic benefits. The prevalence and severity of chemotherapy-induced cardiotoxicity warrants a deeper investigation of the mechanisms and implicating factors in this phenomenon, and a consolidation of scientific efforts to develop mitigating strategies. Aiding these efforts is the emergence of induced pluripotent stem cells (iPSCs) in recent years, which has allowed for the generation of iPSC-derived cardiomyocytes (iPSC-CMs): a human-based, patient-derived, and genetically variable platform that can be applied to the study of chemotherapy-induced cardiotoxicity and beyond. After surveying chemotherapy-induced cardiotoxicity and the associated chemotherapeutic agents, we discuss the use of iPSC-CMs in cardiotoxicity modeling, drug screening, and other potential applications. Improvements to the iPSC-CM platform, such as the development of more adult-like cardiomyocytes and ongoing advances in biotechnology, will only enhance the utility of iPSC-CMs in both basic science and clinical applications.

Recent progress of iPSC technology in cardiac diseases

It has been nearly 15 years since the discovery of human-induced pluripotent stem cells (iPSCs). During this time, differentiation methods to targeted cells have dramatically improved, and many types of cells in the human body can be currently generated at high efficiency. In the cardiovascular field, the ability to generate human cardiomyocytes in vitro with the same genetic background as patients has provided a great opportunity to investigate human cardiovascular diseases at the cellular level to clarify the molecular mechanisms underlying the diseases and discover potential therapeutics. Additionally, iPSC-derived cardiomyocytes have provided a powerful platform to study drug-induced cardiotoxicity and identify patients at high risk for the cardiotoxicity; thus, accelerating personalized precision medicine. Moreover, iPSC-derived cardiomyocytes can be sources for cardiac cell therapy. Here, we review these achievements and discuss potential improvements for the future application of iPSC technology in cardiovascular diseases.

Deciphering pathogenicity of variants of uncertain significance with CRISPR-edited iPSCs

Genetic variants play an important role in conferring risk for cardiovascular diseases (CVDs). With the rapid development of next-generation sequencing (NGS), thousands of genetic variants associated with CVDs have been identified by genome-wide association studies (GWAS), but the function of more than 40% of genetic variants is still unknown. This gap of knowledge is a barrier to the clinical application of the genetic information. However, determining the pathogenicity of a variant of uncertain significance (VUS) is challenging due to the lack of suitable model systems and accessible technologies. By combining clustered regularly interspaced short palindromic repeats (CRISPR) and human induced pluripotent stem cells (iPSCs), unprecedented advances are now possible in determining the pathogenicity of VUS in CVDs. Here, we summarize recent progress and new strategies in deciphering pathogenic variants for CVDs using CRISPR-edited human iPSCs.

Pathogenesis and drug response of iPSC-derived cardiomyocytes from two Brugada syndrome patients with different Na v1.5-subunit mutations

Brugada syndrome (BrS) is a complex genetic cardiac ion channel disease that causes a high predisposition to sudden cardiac death. Considering that its heterogeneity in clinical manifestations may result from genetic background, the application of patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) may help to reveal cell phenotype characteristics underlying different genetic variations. Here, to verify and compare the pathogenicity of mutations (SCN5A c.4213G>A andSCN1B c.590C>T) identified from two BrS patients, we generated two novel BrS iPS cell lines that carried missense mutations inSCN5A or SCN1B, compared their structures and electrophysiology, and evaluated the safety of quinidine in patient-specific iPSC-derived CMs. Compared to the control group, BrS-CMs showed a significant reduction in sodium current, prolonged action potential duration, and varying degrees of decreased V_max, but no structural difference. After applying different concentrations of quinidine, drug-induced cardiotoxicity was not observed within 3-fold unbound effective therapeutic plasma concentration (ETPC). The data presented proved that iPSC-CMs with variants in SCN5A c.4213G>A orSCN1B c.590C>T are able to recapitulate single-cell phenotype features of BrS and respond appropriately to quinidine without increasing incidence of arrhythmic events.

Human iPSCs and Genome Editing Technologies for Precision Cardiovascular Tissue Engineering

Induced pluripotent stem cells (iPSCs) originate from the reprogramming of adult somatic cells using four Yamanaka transcription factors. Since their discovery, the stem cell (SC) field achieved significant milestones and opened several gateways in the area of disease modeling, drug discovery, and regenerative medicine. In parallel, the emergence of clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR-Cas9) revolutionized the field of genome engineering, allowing the generation of genetically modified cell lines and achieving a precise genome recombination or random insertions/deletions, usefully translated for wider applications. Cardiovascular diseases represent a constantly increasing societal concern, with limited understanding of the underlying cellular and molecular mechanisms. The ability of iPSCs to differentiate into multiple cell types combined with CRISPR-Cas9 technology could enable the systematic investigation of pathophysiological mechanisms or drug screening for potential therapeutics. Furthermore, these technologies can provide a cellular platform for cardiovascular tissue engineering (TE) approaches by modulating the expression or inhibition of targeted proteins, thereby creating the possibility to engineer new cell lines and/or fine-tune biomimetic scaffolds. This review will focus on the application of iPSCs, CRISPR-Cas9, and a combination thereof to the field of cardiovascular TE. In particular, the clinical translatability of such technologies will be discussed ranging from disease modeling to drug screening and TE applications.

Human Pluripotent Stem-Cell-Derived Models as a Missing Link in Drug Discovery and Development

Human pluripotent stem cells (hPSCs), including human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), have the potential to accelerate the drug discovery and development process. In this review, by analyzing each stage of the drug discovery and development process, we identified the active role of hPSC-derived in vitro models in phenotypic screening, target-based screening, target validation, toxicology evaluation, precision medicine, clinical trial in a dish, and post-clinical studies. Patient-derived or genome-edited PSCs can generate valid in vitro models for dissecting disease mechanisms, discovering novel drug targets, screening drug candidates, and preclinically and post-clinically evaluating drug safety and efficacy. With the advances in modern biotechnologies and developmental biology, hPSC-derived in vitro models will hopefully improve the cost-effectiveness and the success rate of drug discovery and development.

hERG-deficient human embryonic stem cell-derived cardiomyocytes for modelling QT prolongation

Background

Long-QT syndrome type 2 (LQT2) is a common malignant hereditary arrhythmia. Due to the lack of suitable animal and human models, the pathogenesis of LQT2 caused by human ether-a-go-go-related gene (hERG) deficiency is still unclear. In this study, we generated an hERG-deficient human cardiomyocyte (CM) model that simulates ‘human homozygous hERG mutations’ to explore the underlying impact of hERG dysfunction and the genotype–phenotype relationship of hERG deficiency.

Methods

The KCNH2 was knocked out in the human embryonic stem cell (hESC) H9 line using the CRISPR/Cas9 system. Using a chemically defined differentiation protocol, we obtained and verified hERG-deficient CMs. Subsequently, high-throughput microelectrode array (MEA) assays and drug interventions were performed to characterise the electrophysiological signatures of hERG-deficient cell lines.

Results

Our results showed that KCNH2 knockout did not affect the pluripotency or differentiation efficiency of H9 cells. Using high-throughput MEA assays, we found that the electric field potential duration and action potential duration of hERG-deficient CMs were significantly longer than those of normal CMs. The hERG-deficient lines also exhibited irregular rhythm and some early afterdepolarisations. Moreover, we used the hERG-deficient human CM model to evaluate the potency of agents (nifedipine and magnesium chloride) that may ameliorate the phenotype.

Conclusions

We established an hERG-deficient human CM model that exhibited QT prolongation, irregular rhythm and sensitivity to other ion channel blockers. This model serves as an important tool that can aid in understanding the fundamental impact of hERG dysfunction, elucidate the genotype–phenotype relationship of hERG deficiency and facilitate drug development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02346-1.

Patient-specific iPSC-derived cardiomyocytes reveal abnormal regulation of FGF16 in a familial atrial septal defect

AIMS

Congenital heart disease (CHD) frequently occurs in newborns due to abnormal formation of the heart or major blood vessels. Mutations in the GATA4 gene, which encodes GATA binding protein 4, are responsible for atrial septal defect (ASD), a common CHD. This study aims to gain insights into the molecular mechanisms of CHD using human induced pluripotent stem cells (iPSCs) from a family cohort with ASD.

METHODS AND RESULTS

Patient-specific iPSCs possess the same genetic information as the donor and can differentiate into various cell types from all three germ layers in vitro, thus presenting a promising approach for disease modeling and molecular mechanism research. Here, we generated a patient-specific iPSC line (iPSC-G4T280M) from a family cohort carrying a hereditary ASD mutation in GATA4 gene (T280M), as well as a human embryonic stem cell line (ESC-G4T280M) carrying the isogenic T280M mutation using the CRISPR/Cas9 genome editing method. The GATA4-mutant iPSCs and ESCs were then differentiated into cardiomyocytes (CMs) to model GATA4 mutation-associated ASD. We observed an obvious defect in cell proliferation in cardiomyocytes derived from both GATA4T280M-mutant iPSCs (iPSC-G4T280M-CMs) and ESCs (ESC-G4T280M-CMs), while the impaired proliferation ability of iPSC-G4T280M-CMs could be restored by gene correction. Integrated analysis of RNA-Seq and ChIP-Seq data indicated that FGF16 is a direct target of wild-type GATA4. However, the T280M mutation obstructed GATA4 occupancy at the FGF16 promoter region, leading to impaired activation of FGF16 transcription. Overexpression of FGF16 in GATA4-mutant cardiomyocytes rescued the cell proliferation defect. The direct relationship between GATA4T280M and ASD was demonstrated in a human iPSC model for the first time.

CONCLUSIONS

In summary, our study revealed the molecular mechanism of the GATA4T280M mutation in ASD. Understanding the roles of the GATA4-FGF16 axis in iPSC-CMs will shed light on heart development and provide novel insights for the treatment of ASD and other CHD disorders.

Patient-specific induced pluripotent stem cells as “disease-in-a-dish” models for inherited cardiomyopathies and channelopathies – 15 years of research

Among inherited cardiac conditions, a special place is kept by cardiomyopathies (CMPs) and channelopathies (CNPs), which pose a substantial healthcare burden due to the complexity of the therapeutic management and cause early mortality. Like other inherited cardiac conditions, genetic CMPs and CNPs exhibit incomplete penetrance and variable expressivity even within carriers of the same pathogenic deoxyribonucleic acid variant, challenging our understanding of the underlying pathogenic mechanisms. Until recently, the lack of accurate physiological preclinical models hindered the investigation of fundamental cellular and molecular mechanisms. The advent of induced pluripotent stem cell (iPSC) technology, along with advances in gene editing, offered unprecedented opportunities to explore hereditary CMPs and CNPs. Hallmark features of iPSCs include the ability to differentiate into unlimited numbers of cells from any of the three germ layers, genetic identity with the subject from whom they were derived, and ease of gene editing, all of which were used to generate “disease-in-a-dish” models of monogenic cardiac conditions. Functionally, iPSC-derived cardiomyocytes that faithfully recapitulate the patient-specific phenotype, allowed the study of disease mechanisms in an individual-/allele-specific manner, as well as the customization of therapeutic regimen. This review provides a synopsis of the most important iPSC-based models of CMPs and CNPs and the potential use for modeling disease mechanisms, personalized therapy and deoxyribonucleic acid variant functional annotation.

CRISPR: A new paradigm of theranostics

Infectious and hereditary diseases are the primary cause of human mortality globally. Applications of conventional techniques require significant improvement in sensitivity and specificity in therapeutics. However, clustered regularly interspaced short palindromic repeats (CRISPRs) is an innovative genome editing technology which has provided a significant therapeutic tool exhibiting high sensitivity, fast and precise investigation of distinct pathogens in an epidemic. CRISPR technology has also facilitated the understanding of the biology and therapeutic mechanism of cancer and several other hereditary diseases. Researchers have used the CRISPR technology as a theranostic approach for a wide range of diseases causing pathogens including distinct bacteria, viruses, fungi and parasites and genetic mutations as well. In this review article, besides various therapeutic applications of infectious and hereditary diseases we have also explained the structure and mechanism of CRISPR tools and role of CRISPR integrated biosensing technology in provoking diagnostic applications.

Genome editing of hPSCs: Recent progress in hPSC-based disease modeling for understanding disease mechanisms

Generation of proper models for studying human genetic diseases has been hindered until recently by the scarcity of primary cell samples from genetic disease patients and inefficient genetic modification tools. However, recent advances in clustered, regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology and human induced pluripotent stem cells (hiPSCs) have provided an opportunity to explore the function of pathogenic variants and obtain gene-corrected cells for autologous cell therapy. In this chapter, we address recent applications of CRISPR/Cas9 to hiPSCs in genetic diseases, including neurodegenerative, cardiovascular, and rare diseases.

Arrhythmia Mechanisms in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

ABSTRACT

Despite major efforts by clinicians and researchers, cardiac arrhythmia remains a leading cause of morbidity and mortality in the world. Experimental work has relied on combining high-throughput strategies with standard molecular and electrophysiological studies, which are, to a great extent, based on the use of animal models. Because this poses major challenges for translation, the progress in the development of novel antiarrhythmic agents and clinical care has been mostly disappointing. Recently, the advent of human induced pluripotent stem cell-derived cardiomyocytes has opened new avenues for both basic cardiac research and drug discovery; now, there is an unlimited source of cardiomyocytes of human origin, both from healthy individuals and patients with cardiac diseases. Understanding arrhythmic mechanisms is one of the main use cases of human induced pluripotent stem cell-derived cardiomyocytes, in addition to pharmacological cardiotoxicity and efficacy testing, in vitro disease modeling, developing patient-specific models and personalized drugs, and regenerative medicine. Here, we review the advances that the human induced pluripotent stem cell-derived-based modeling systems have brought so far regarding the understanding of both arrhythmogenic triggers and substrates, while also briefly speculating about the possibilities in the future.

Base Editing Mediated Generation of Point Mutations Into Human Pluripotent Stem Cells for Modeling Disease

Human pluripotent stem cells (hPSCs) are a powerful platform for disease modeling and drug discovery. However, the introduction of known pathogenic mutations into hPSCs is a time-consuming and labor-intensive process. Base editing is a newly developed technology that enables facile introduction of point mutations into specific loci within the genome of living cells. Here, we design an all-in-one episomal vector that expresses a single guide RNA (sgRNA) with an adenine base editor (ABE) or a cytosine base editor (CBE). Both ABE and CBE can efficiently introduce mutations into cells, A-to-G and C-to-T, respectively. We introduce disease-specific mutations of long QT syndrome into hPSCs to model LQT1, LQT2, and LQT3. Electrophysiological analysis of hPSC-derived cardiomyocytes (hPSC-CMs) using multi-electrode arrays (MEAs) reveals that edited hPSC-CMs display significant increases in duration of the action potential. Finally, we introduce the novel Brugada syndrome-associated mutation into hPSCs, demonstrating that this mutation can cause abnormal electrophysiology. Our study demonstrates that episomal encoded base editors (epi-BEs) can efficiently generate mutation-specific disease hPSC models.

Drug Development and the Use of Induced Pluripotent Stem Cell-Derived Cardiomyocytes for Disease Modeling and Drug Toxicity Screening

: Over the years, numerous groups have employed human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) as a superb human-compatible model for investigating the function and dysfunction of cardiomyocytes, drug screening and toxicity, disease modeling and for the development of novel drugs for heart diseases. In this review, we discuss the broad use of iPSC-CMs for drug development and disease modeling, in two related themes. In the first theme-drug development, adverse drug reactions, mechanisms of cardiotoxicity and the need for efficient drug screening protocols-we discuss the critical need to screen old and new drugs, the process of drug development, marketing and Adverse Drug reactions (ADRs), drug-induced cardiotoxicity, safety screening during drug development, drug development and patient-specific effect and different mechanisms of ADRs. In the second theme-using iPSC-CMs for disease modeling and developing novel drugs for heart diseases-we discuss the rationale for using iPSC-CMs and modeling acquired and inherited heart diseases with iPSC-CMs.

Base Editing Mediated Generation of Point Mutations Into Human Pluripotent Stem Cells for Modeling Disease

Human pluripotent stem cells (hPSCs) are a powerful platform for disease modeling and drug discovery. However, the introduction of known pathogenic mutations into hPSCs is a time-consuming and labor-intensive process. Base editing is a newly developed technology that enables facile introduction of point mutations into specific loci within the genome of living cells. Here, we design an all-in-one episomal vector that expresses a single guide RNA (sgRNA) with an adenine base editor (ABE) or a cytosine base editor (CBE). Both ABE and CBE can efficiently introduce mutations into cells, A-to-G and C-to-T, respectively. We introduce disease-specific mutations of long QT syndrome into hPSCs to model LQT1, LQT2, and LQT3. Electrophysiological analysis of hPSC-derived cardiomyocytes (hPSC-CMs) using multi-electrode arrays (MEAs) reveals that edited hPSC-CMs display significant increases in duration of the action potential. Finally, we introduce the novel Brugada syndrome-associated mutation into hPSCs, demonstrating that this mutation can cause abnormal electrophysiology. Our study demonstrates that episomal encoded base editors (epi-BEs) can efficiently generate mutation-specific disease hPSC models.

Patient and Disease-Specific Induced Pluripotent Stem Cells for Discovery of Personalized Cardiovascular Drugs and Therapeutics

Human induced pluripotent stem cells (iPSCs) have emerged as an effective platform for regenerative therapy, disease modeling, and drug discovery. iPSCs allow for the production of limitless supply of patient-specific somatic cells that enable advancement in cardiovascular precision medicine. Over the past decade, researchers have developed protocols to differentiate iPSCs to multiple cardiovascular lineages, as well as to enhance the maturity and functionality of these cells. Despite significant advances, drug therapy and discovery for cardiovascular disease have lagged behind other fields such as oncology. We speculate that this paucity of drug discovery is due to a previous lack of efficient, reproducible, and translational model systems. Notably, existing drug discovery and testing platforms rely on animal studies and clinical trials, but investigations in animal models have inherent limitations due to interspecies differences. Moreover, clinical trials are inherently flawed by assuming that all individuals with a disease will respond identically to a therapy, ignoring the genetic and epigenomic variations that define our individuality. With ever-improving differentiation and phenotyping methods, patient-specific iPSC-derived cardiovascular cells allow unprecedented opportunities to discover new drug targets and screen compounds for cardiovascular disease. Imbued with the genetic information of an individual, iPSCs will vastly improve our ability to test drugs efficiently, as well as tailor and titrate drug therapy for each patient.

Modeling Cardiac Disease Mechanisms Using Induced Pluripotent Stem Cell-Derived Cardiomyocytes: Progress, Promises and Challenges

Cardiovascular diseases (CVDs) are a class of disorders affecting the heart or blood vessels. Despite progress in clinical research and therapy, CVDs still represent the leading cause of mortality and morbidity worldwide. The hallmarks of cardiac diseases include heart dysfunction and cardiomyocyte death, inflammation, fibrosis, scar tissue, hyperplasia, hypertrophy, and abnormal ventricular remodeling. The loss of cardiomyocytes is an irreversible process that leads to fibrosis and scar formation, which, in turn, induce heart failure with progressive and dramatic consequences. Both genetic and environmental factors pathologically contribute to the development of CVDs, but the precise causes that trigger cardiac diseases and their progression are still largely unknown. The lack of reliable human model systems for such diseases has hampered the unraveling of the underlying molecular mechanisms and cellular processes involved in heart diseases at their initial stage and during their progression. Over the past decade, significant scientific advances in the field of stem cell biology have literally revolutionized the study of human disease in vitro. Remarkably, the possibility to generate disease-relevant cell types from induced pluripotent stem cells (iPSCs) has developed into an unprecedented and powerful opportunity to achieve the long-standing ambition to investigate human diseases at a cellular level, uncovering their molecular mechanisms, and finally to translate bench discoveries into potential new therapeutic strategies. This review provides an update on previous and current research in the field of iPSC-driven cardiovascular disease modeling, with the aim of underlining the potential of stem-cell biology-based approaches in the elucidation of the pathophysiology of these life-threatening diseases.

Modeling Cardiovascular Diseases with hiPSC-Derived Cardiomyocytes in 2D and 3D Cultures

In the last decade, the generation of cardiac disease models based on human-induced pluripotent stem cells (hiPSCs) has become of common use, providing new opportunities to overcome the lack of appropriate cardiac models. Although much progress has been made toward the generation of hiPSC-derived cardiomyocytes (hiPS-CMs), several lines of evidence indicate that two-dimensional (2D) cell culturing presents significant limitations, including hiPS-CMs immaturity and the absence of interaction between different cell types and the extracellular matrix. More recently, new advances in bioengineering and co-culture systems have allowed the generation of three-dimensional (3D) constructs based on hiPSC-derived cells. Within these systems, biochemical and physical stimuli influence the maturation of hiPS-CMs, which can show structural and functional properties more similar to those present in adult cardiomyocytes. In this review, we describe the latest advances in 2D- and 3D-hiPSC technology for cardiac disease mechanisms investigation, drug development, and therapeutic studies.

CRISPR/Cas9 gene-editing strategies in cardiovascular cells

Cardiovascular diseases are among the main causes of morbidity and mortality in Western countries and considered as a leading public health issue. Therefore, there is a strong need for new disease models to support the development of novel therapeutics approaches. The successive improvement of genome editing tools with zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and more recently with clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9) has enabled the generation of genetically modified cells and organisms with much greater efficiency and precision than before. The simplicity of CRISPR/Cas9 technology made it especially suited for different studies, both in vitro and in vivo, and has been used in multiple studies evaluating gene functions, disease modelling, transcriptional regulation, and testing of novel therapeutic approaches. Notably, with the parallel development of human induced pluripotent stem cells (hiPSCs), the generation of knock-out and knock-in human cell lines significantly increased our understanding of mutation impacts and physiopathological mechanisms within the cardiovascular domain. Here, we review the recent development of CRISPR-Cas9 genome editing, the alternative tools, the available strategies to conduct genome editing in cardiovascular cells with a focus on its use for correcting mutations in vitro and in vivo both in germ and somatic cells. We will also highlight that, despite its potential, CRISPR/Cas9 technology comes with important technical and ethical limitations. The development of CRISPR/Cas9 genome editing for cardiovascular diseases indeed requires to develop a specific strategy in order to optimize the design of the genome editing tools, the manipulation of DNA repair mechanisms, the packaging and delivery of the tools to the studied organism, and the assessment of their efficiency and safety.

Inherited cardiac diseases, pluripotent stem cells, and genome editing combined-the past, present, and future

Research on mechanisms underlying monogenic cardiac diseases such as primary arrhythmias and cardiomyopathies has until recently been hampered by inherent limitations of heterologous cell systems, where mutant genes are expressed in noncardiac cells, and physiological differences between humans and experimental animals. Human-induced pluripotent stem cells (hiPSCs) have proven to be a game changer by providing new opportunities for studying the disease in the specific cell type affected, namely the cardiomyocyte. hiPSCs are particularly valuable because not only can they be differentiated into unlimited numbers of these cells, but they also genetically match the individual from whom they were derived. The decade following their discovery showed the potential of hiPSCs for advancing our understanding of cardiovascular diseases, with key pathophysiological features of the patient being reflected in their corresponding hiPSC-derived cardiomyocytes (the past). Now, recent advances in genome editing for repairing or introducing genetic mutations efficiently have enabled the disease etiology and pathogenesis of a particular genotype to be investigated (the present). Finally, we are beginning to witness the promise of hiPSC in personalized therapies for individual patients, as well as their application in identifying genetic variants responsible for or modifying the disease phenotype (the future). In this review, we discuss how hiPSCs could contribute to improving the diagnosis, prognosis, and treatment of an individual with a suspected genetic cardiac disease, thereby developing better risk stratification and clinical management strategies for these potentially lethal but treatable disorders.

The Emergence of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs) as a Platform to Model Arrhythmogenic Diseases

There is a need for improved in vitro models of inherited cardiac diseases to better understand basic cellular and molecular mechanisms and advance drug development. Most of these diseases are associated with arrhythmias, as a result of mutations in ion channel or ion channel-modulatory proteins. Thus far, the electrophysiological phenotype of these mutations has been typically studied using transgenic animal models and heterologous expression systems. Although they have played a major role in advancing the understanding of the pathophysiology of arrhythmogenesis, more physiological and predictive preclinical models are necessary to optimize the treatment strategy for individual patients. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have generated much interest as an alternative tool to model arrhythmogenic diseases. They provide a unique opportunity to recapitulate the native-like environment required for mutated proteins to reproduce the human cellular disease phenotype. However, it is also important to recognize the limitations of this technology, specifically their fetal electrophysiological phenotype, which differentiates them from adult human myocytes. In this review, we provide an overview of the major inherited arrhythmogenic cardiac diseases modeled using hiPSC-CMs and for which the cellular disease phenotype has been somewhat characterized.