hiPSC-CM Monolayer Maturation State Determines Drug Responsiveness in High Throughput Pro-Arrhythmia Screen

Induced pluripotent stem cell-derived cardiomyocyte in vitro models: benchmarking progress and ongoing challenges

Recent innovations in differentiating cardiomyocytes from human induced pluripotent stem cells (hiPSCs) have unlocked a viable path to creating in vitro cardiac models. Currently, hiPSC-derived cardiomyocytes (hiPSC-CMs) remain immature, leading many in the field to explore approaches to enhance cell and tissue maturation. Here, we systematically analyzed 300 studies using hiPSC-CM models to determine common fabrication, maturation and assessment techniques used to evaluate cardiomyocyte functionality and maturity and compiled the data into an open-access database. Based on this analysis, we present the diversity of, and current trends in, in vitro models and highlight the most common and promising practices for functional assessments. We further analyzed outputs spanning structural maturity, contractile function, electrophysiology and gene expression and note field-wide improvements over time. Finally, we discuss opportunities to collectively pursue the shared goal of hiPSC-CM model development, maturation and assessment that we believe are critical for engineering mature cardiac tissue.

hiPSC-CM electrophysiology: impact of temporal changes and study parameters on experimental reproducibility

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are frequently used for preclinical cardiotoxicity testing and remain an important tool for confirming model-based predictions of drug effects in accordance with the comprehensive in vitro proarrhythmia assay (CiPA). Despite the considerable benefits hiPSC-CMs provide, concerns surrounding experimental reproducibility have emerged. We investigated the effects of temporal changes and experimental parameters on hiPSC-CM electrophysiology. iCell cardiomyocytes2 were cultured and biosignals were acquired using a microelectrode array (MEA) system (2-14 days). Continuous recordings revealed a 22.6% increase in the beating rate and 7.7% decrease in the field potential duration (FPD) during a 20-min equilibration period. Location-specific differences across a multiwell plate were also observed, with iCell cardiomyocytes2 in the outer rows beating 8.8 beats/min faster than the inner rows. Cardiac endpoints were also impacted by cell culture duration; from 2 to 14 days, the beating rate decreased (-12.7 beats/min), FPD lengthened (+257 ms), and spike amplitude increased (+3.3 mV). Cell culture duration (4-10 days) also impacted cardiomyocyte drug responsiveness (E-4031, nifedipine, isoproterenol). qRT-PCR results suggest that daily variations in cardiac metrics may be linked to the continued maturation of hiPSC-CMs in culture (2-30 days). Daily experiments were also repeated using a second cell line (Cor.4U). Collectively, our study highlights multiple sources of variability to consider and address when performing hiPSC-CM MEA studies. To improve reproducibility and data interpretation, MEA-based studies should establish a standardized protocol and report key experimental conditions (e.g., cell line, culture time, equilibration time, electrical stimulation settings, and raw data values).NEW & NOTEWORTHY We demonstrate that iCell cardiomyocytes2 electrophysiology measurements are impacted by deviations in experimental techniques including electrical stimulation protocols, equilibration time, well-to-well variability, and length of hiPSC-CM culture. Furthermore, our results indicate that hiPSC-CM drug responsiveness changes within the first 2 wk following defrost.

Three-dimensional cardiac models: a pre-clinical testing platform

Major advancements in human pluripotent stem cell (hPSC) technology over recent years have yielded valuable tools for cardiovascular research. Multi-cell type 3-dimensional (3D) cardiac models in particular, are providing complementary approaches to animal studies that are better representatives than simple 2-dimensional (2D) cultures of differentiated hPSCs. These human 3D cardiac models can be broadly divided into two categories; namely those generated through aggregating pre-differentiated cells and those that form self-organizing structures during their in vitro differentiation from hPSCs. These models can either replicate aspects of cardiac development or enable the examination of interactions among constituent cell types, with some of these models showing increased maturity compared with 2D systems. Both groups have already emerged as physiologically relevant pre-clinical platforms for studying heart disease mechanisms, exhibiting key functional attributes of the human heart. In this review, we describe the different cardiac organoid models derived from hPSCs, their generation methods, applications in cardiovascular disease research and use in drug screening. We also address their current limitations and challenges as pre-clinical testing platforms and propose potential improvements to enhance their efficacy in cardiac drug discovery.

Sex-Based Mechanisms of Cardiac Development and Function: Applications for Induced-Pluripotent Stem Cell Derived-Cardiomyocytes

Males and females exhibit intrinsic differences in the structure and function of the heart, while the prevalence and severity of cardiovascular disease vary in the two sexes. However, the mechanisms of this sex-based dimorphism are yet to be elucidated. Sex chromosomes and sex hormones are the main contributors to sex-based differences in cardiac physiology and pathophysiology. In recent years, the advances in induced pluripotent stem cell-derived cardiac models and multi-omic approaches have enabled a more comprehensive understanding of the sex-specific differences in the human heart. Here, we provide an overview of the roles of these two factors throughout cardiac development and explore the sex hormone signaling pathways involved. We will also discuss how the employment of stem cell-based cardiac models and single-cell RNA sequencing help us further investigate sex differences in healthy and diseased hearts.

Bipolar Patient-Specific In Vitro Diagnostic Test Reveals Underlying Cardiac Arrhythmia Phenotype Caused by Calcium Channel Genetic Risk Factor

A common genetic risk factor for bipolar disorder is CACNA1C, a gene that is also critical for cardiac rhythm. The impact of CACNA1C mutations on bipolar patient cardiac rhythm is unknown. Here, we report the cardiac electrophysiological implications of a bipolar disorder-associated genetic risk factor in CACNA1C using patient induced pluripotent stem cell-derived cardiomyocytes. Results indicate that the CACNA1C bipolar disorder-related mutation causes cardiac electrical impulse conduction slowing mediated by impaired intercellular coupling via connexin 43 gap junctions. In vitro gene therapy to restore connexin 43 expression increased cardiac electrical impulse conduction velocity and protected against thioridazine-induced QT prolongation. Patients positive for bipolar disorder CACNA1C genetic risk factors may have elevated proarrhythmic risk for adverse events in response to psychiatric medications that slow conduction or prolong the QT interval. This in vitro diagnostic tool enables cardiac testing specific to patients with psychiatric disorders to determine their sensitivity to off-target effects of psychiatric medications.

Interpretation of field and LEAP potentials recorded from cardiomyocyte monolayers

Multielectrode arrays (MEAs) are the method of choice for electrophysiological characterization of cardiomyocyte monolayers. The field potentials recorded using an MEA are like extracellular electrograms recorded from the myocardium using conventional electrodes. Nevertheless, different criteria are used to interpret field potentials and extracellular electrograms, which hamper correct interpretation and translation to the patient. To validate the criteria for interpretation of field potentials, we used neonatal rat cardiomyocytes to generate monolayers. We recorded field potentials using an MEA and simultaneously recorded action potentials using sharp microelectrodes. In parallel, we recreated our experimental setting in silico and performed simulations. We show that the amplitude of the local RS complex of a field potential correlated with conduction velocity in silico but not in vitro. The peak time of the T wave in field potentials exhibited a strong correlation with APD90 while the steepest upslope correlated well with APD50. However, this relationship only holds when the T wave displayed a biphasic pattern. Next, we simulated local extracellular action potentials (LEAPs). The shape of the LEAP differed markedly from the shape of the local action potential, but the final duration of the LEAP coincided with APD90. Criteria for interpretation of extracellular electrograms should be applied to field potentials. This will provide a strong basis for the analysis of heterogeneity in conduction velocity and repolarization in cultured monolayers of cardiomyocytes. Finally, a LEAP is not a recording of the local action potential but is generated by intracellular current provided by neighboring cardiomyocytes and is superior to field potential duration in estimating APD90.NEW & NOTEWORTHY We present a physiological basis for the interpretation of multielectrode array-derived, extracellular, electrical signals.

In situ monolayer patch clamp of acutely stimulated human iPSC-derived cardiomyocytes promotes consistent electrophysiological responses to SK channel inhibition

Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) represent an in vitro model of cardiac function. Isolated iPSC-CMs, however, exhibit electrophysiological heterogeneity which hinders their utility in the study of certain cardiac currents. In the healthy adult heart, the current mediated by small conductance, calcium-activated potassium (SK) channels (ISK) is atrial-selective. Functional expression of ISK within atrial-like iPSC-CMs has not been explored thoroughly. The present study therefore aimed to investigate atrial-like iPSC-CMs as a model system for the study of ISK. iPSCs were differentiated using retinoic acid (RA) to produce iPSC-CMs which exhibited an atrial-like phenotype (RA-iPSC-CMs). Only 18% of isolated RA-iPSC-CMs responded to SK channel inhibition by UCL1684 and isolated iPSC-CMs exhibited substantial cell-to-cell electrophysiological heterogeneity. This variability was significantly reduced by patch clamp of RA-iPSC-CMs in situ as a monolayer (iPSC-ML). A novel method of electrical stimulation was developed to facilitate recording from iPSC-MLs via In situ Monolayer Patch clamp of Acutely Stimulated iPSC-CMs (IMPASC). Using IMPASC, > 95% of iPSC-MLs could be paced at a 1 Hz. In contrast to isolated RA-iPSC-CMs, 100% of RA-iPSC-MLs responded to UCL1684, with APD50 being prolonged by 16.0 ± 2.0 ms (p < 0.0001; n = 12). These data demonstrate that in conjunction with IMPASC, RA-iPSC-MLs represent an improved model for the study of ISK. IMPASC may be of wider value in the study of other ion channels that are inconsistently expressed in isolated iPSC-CMs and in pharmacological studies.

An In Silico Platform to Predict Cardiotoxicity Risk of Anti-tumor Drug Combination with hiPSC-CMs Based In Vitro Study

OBJECTIVE

Antineoplastic agent-induced systolic dysfunction is a major reason for interruption of anticancer treatment. Although targeted anticancer agents infrequently cause systolic dysfunction, their combinations with chemotherapies remarkably increase the incidence. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide a potent in vitro model to assess cardiovascular safety. However, quantitatively predicting the reduction of ejection fraction based on hiPSC-CMs is challenging due to the absence of the body's regulatory response to cardiomyocyte injury.

METHODS

Here, we developed and validated an in vitro-in vivo translational platform to assess the reduction of ejection fraction induced by antineoplastic drugs based on hiPSC-CMs. The translational platform integrates drug exposure, drug-cardiomyocyte interaction, and systemic response. The drug-cardiomyocyte interaction was implemented as a mechanism-based toxicodynamic (TD) model, which was then integrated into a quantitative system pharmacology-physiological-based pharmacokinetics (QSP-PBPK) model to form a complete translational platform. The platform was validated by comparing the model-predicted and clinically observed incidence of doxorubicin and trastuzumab-induced systolic dysfunction.

RESULTS

A total of 33,418 virtual patients were incorporated to receive doxorubicin and trastuzumab alone or in combination. For doxorubicin, the QSP-PBPK-TD model successfully captured the overall trend of systolic dysfunction incidences against the cumulative doses. For trastuzumab, the predicted incidence interval was 0.31-2.7% for single-agent treatment and 0.15-10% for trastuzumab-doxorubicin sequential treatment, covering the observations in clinical reports (0.50-1.0% and 1.5-8.3%, respectively).

CONCLUSIONS

In conclusion, the in vitro-in vivo translational platform is capable of predicting systolic dysfunction incidence almost merely depend on hiPSC-CMs, which could facilitate optimizing the treatment protocol of antineoplastic agents.

Step-by-step fabrication of heart-on-chip systems as models for cardiac disease modeling and drug screening

Cardiovascular diseases are caused by hereditary factors, environmental conditions, and medication-related issues. On the other hand, the cardiotoxicity of drugs should be thoroughly examined before entering the market. In this regard, heart-on-chip (HOC) systems have been developed as a more efficient and cost-effective solution than traditional methods, such as 2D cell culture and animal models. HOCs must replicate the biology, physiology, and pathology of human heart tissue to be considered a reliable platform for heart disease modeling and drug testing. Therefore, many efforts have been made to find the best methods to fabricate different parts of HOCs and to improve the bio-mimicry of the systems in the last decade. Beating HOCs with different platforms have been developed and techniques, such as fabricating pumpless HOCs, have been used to make HOCs more user-friendly systems. Recent HOC platforms have the ability to simultaneously induce and record electrophysiological stimuli. Additionally, systems including both heart and cancer tissue have been developed to investigate tissue-tissue interactions' effect on cardiac tissue response to cancer drugs. In this review, all steps needed to be considered to fabricate a HOC were introduced, including the choice of cellular resources, biomaterials, fabrication techniques, biomarkers, and corresponding biosensors. Moreover, the current HOCs used for modeling cardiac diseases and testing the drugs are discussed. We finally introduced some suggestions for fabricating relatively more user-friendly HOCs and facilitating the commercialization process.

CRISPRi gene modulation and all-optical electrophysiology in post-differentiated human iPSC-cardiomyocytes

Uncovering gene-phenotype relationships can be enabled by precise gene modulation in human induced pluripotent stem-cell-derived cardiomyocytes (iPSC-CMs) and follow up phenotyping using scalable all-optical electrophysiology platforms. Such efforts towards human functional genomics can be aided by recent CRISPR-derived technologies for reversible gene inhibition or activation (CRISPRi/a). We set out to characterize the performance of CRISPRi in post-differentiated iPSC-CMs, targeting key cardiac ion channel genes, KCNH2, KCNJ2, and GJA1, and providing a multiparametric quantification of the effects on cardiac repolarization, stability of the resting membrane potential and conduction properties using all-optical tools. More potent CRISPRi effectors, e.g., Zim3, and optimized viral delivery led to improved performance on par with the use of CRISPRi iPSC lines. Confirmed mild yet specific phenotype changes when CRISPRi is deployed in non-dividing differentiated heart cells is an important step towards more holistic pre-clinical cardiotoxicity testing and for future therapeutic use in vivo.

hiPSC-CM Electrophysiology: Impact of Temporal Changes and Study Parameters on Experimental Reproducibility

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are frequently used for preclinical cardiotoxicity testing and remain an important tool for confirming model-based predictions of drug effects in accordance with the Comprehensive in Vitro Proarrhythmia Assay (CiPA) initiative. Despite the considerable benefits hiPSC-CMs provide, concerns surrounding experimental reproducibility have emerged. Our study aimed to investigate the effects of temporal changes and experimental parameters on hiPSC-CM electrophysiology. hiPSC-CMs (iCell cardiomyocyte 2 ) were cultured for 14 days and biosignals were acquired using a microelectrode array (MEA) system. Continuous recordings revealed a 22.6% increase in the beating rate and 7.7% decrease in the field potential duration (FPD) during a 20-minute equilibration period. Location specific differences across a multiwell plate were also observed, with hiPSC-CMs in the outer rows beating 8.8 beats per minute (BPM) faster than the inner rows. Cardiac endpoints were also impacted by cell culture duration; from 2-14 days the beating rate decreased (-12.7 BPM), FPD lengthened (+257 ms), and spike amplitude increased (+3.3 mV). Cell culture duration (4-10 days) also impacted hiPSC-CM drug responsiveness (E-4031, nifedipine, isoproterenol). Our study highlights multiple sources of variability that should be considered and addressed when performing hiPSC-CM MEA studies. To improve reproducibility and data interpretation, MEA-based studies should establish a standardized protocol and report key experimental conditions (e.g., culture time, equilibration time, electrical stimulation settings, report raw data values).

New & Noteworthy

We demonstrate that hiPSC-CM electrophysiology measurements are significantly impacted by slight deviations in experimental techniques including electrical stimulation protocols, equilibration time, well-to-well variability, and length of hiPSC-CM culture. Furthermore, our results indicate that hiPSC-CM drug responsiveness changes within the first two weeks following defrost.

Optical Mapping of Cardiomyocytes in Monolayer Derived from Induced Pluripotent Stem Cells

Optical mapping is a powerful imaging technique widely adopted to measure membrane potential changes and intracellular Ca2+ variations in excitable tissues using voltage-sensitive dyes and Ca2+ indicators, respectively. This powerful tool has rapidly become indispensable in the field of cardiac electrophysiology for studying depolarization wave propagation, estimating the conduction velocity of electrical impulses, and measuring Ca2+ dynamics in cardiac cells and tissues. In addition, mapping these electrophysiological parameters is important for understanding cardiac arrhythmia mechanisms. In this review, we delve into the fundamentals of cardiac optical mapping technology and its applications when applied to hiPSC-derived cardiomyocytes and discuss related advantages and challenges. We also provide a detailed description of the processing and analysis of optical mapping data, which is a crucial step in the study of cardiac diseases and arrhythmia mechanisms for extracting and comparing relevant electrophysiological parameters.

High-throughput longitudinal electrophysiology screening of mature chamber-specific hiPSC-CMs using optical mapping

hiPSC-CMs are being considered by the Food and Drug Administration and other regulatory agencies for in vitro cardiotoxicity screening to provide human-relevant safety data. Widespread adoption of hiPSC-CMs in regulatory and academic science is limited by the immature, fetal-like phenotype of the cells. Here, to advance the maturation state of hiPSC-CMs, we developed and validated a human perinatal stem cell-derived extracellular matrix coating applied to high-throughput cell culture plates. We also present and validate a cardiac optical mapping device designed for high-throughput functional assessment of mature hiPSC-CM action potentials using voltage-sensitive dye and calcium transients using calcium-sensitive dyes or genetically encoded calcium indicators (GECI, GCaMP6). We utilize the optical mapping device to provide new biological insight into mature chamber-specific hiPSC-CMs, responsiveness to cardioactive drugs, the effect of GCaMP6 genetic variants on electrophysiological function, and the effect of daily β-receptor stimulation on hiPSC-CM monolayer function and SERCA2a expression.

Reproducibility of drug-induced effects on the contractility of an engineered heart tissue derived from human pluripotent stem cells

Introduction: Engineered heart tissues (EHTs) are three-dimensional culture platforms with cardiomyocytes differentiated from human pluripotent stem cells (hPSCs) and were designed for assaying cardiac contractility. For drug development applications, EHTs must have a stable function and provide reproducible results. We investigated these properties with EHTs made with different tissue casting batches and lines of differentiated hPSC-cardiomyocytes and analyzed them at different times after being fabricated. Methods: A video-optical assay was used for measuring EHT contractile outputs, and these results were compared with results from motion traction analysis of beating hPSC-cardiomyocytes cultured as monolayers in two-dimensional cultures. The reproducibility of induced contractile variations was tested using compounds with known mechanistic cardiac effects (isoproterenol, EMD-57033, omecamtiv mecarbil, verapamil, ranolazine, and mavacamten), or known to be clinically cardiotoxic (doxorubicin, sunitinib). These drug-induced variations were characterized at different electrical pacing rates and variations in intracellular calcium transients were also assessed in EHTs. Results: To ensure reproducibility in experiments, we established EHT quality control criteria based on excitation-contraction coupling and contractile sensitivity to extracellular calcium concentration. In summary, a baseline contractile force of 0.2 mN and excitation-contraction coupling of EHTs were used as quality control criteria to select suitable EHTs for analysis. Overall, drug-induced contractile responses were similar between monolayers and EHTs, where a close relationship was observed between contractile output and calcium kinetics. Contractile variations at multiple time points after adding cardiotoxic compounds were also detectable in EHTs. Discussion: Reproducibility of drug-induced effects in EHTs between experiments and relative to published work on these cellular models was generally observed. Future applications for EHTs may require additional mechanistic criteria related to drug effects and cardiac functional outputs to be measured in regard to specific contexts of use.

Ascorbic acid induces MLC2v protein expression and promotes ventricular-like cardiomyocyte subtype in human induced pluripotent stem cells derived cardiomyocytes

Introduction: The potentially unlimited number of cardiomyocyte (CMs) derived from human induced pluripotent stem cells (hiPSCs) in vitro facilitates high throughput applications like cell transplantation for myocardial repair, disease modelling, and cardiotoxicity testing during drug development. Despite promising progress in these areas, a major disadvantage that limits the use of hiPSC derived CMs (hiPSC-CMs) is their immaturity. Methods: Three hiPSC lines (PCBC-hiPSC, DP3-hiPSCs, and MLC2v-mEGFP hiPSC) were differentiated into CMs (PCBC-CMs, DP3-CMs, and MLC2v-CMs, respectively) with or without retinoic acid (RA). hiPSC-CMs were either maintained up to day 30 of contraction (D30C), or D60C, or purified using lactate acid and used for experiments. Purified hiPSC-CMs were cultured in basal maturation medium (BMM) or BMM supplemented with ascorbic acid (AA) for 14 days. The AA treated and non-treated hiPSC-CMs were characterized for sarcomeric proteins (MLC2v, TNNI3, and MYH7), ion channel proteins (Kir2.1, Nav1.5, Cav1.2, SERCA2a, and RyR), mitochondrial membrane potential, metabolomics, and action potential. Bobcat339, a selective and potent inhibitor of DNA demethylation, was used to determine whether AA promoted hiPSC-CM maturation through modulating DNA demethylation. Results: AA significantly increased MLC2v expression in PCBC-CMs, DP3-CMs, MLC2v-CMs, and RA induced atrial-like PCBC-CMs. AA treatment significantly increased mitochondrial mass, membrane potential, and amino acid and fatty acid metabolism in PCBC-CMs. Patch clamp studies showed that AA treatment induced PCBC-CMs and DP3-CMs adaptation to a ventricular-like phenotype. Bobcat339 inhibited MLC2v protein expression in AA treated PCBC-CMs and DP3-CMs. DNA demethylation inhibition was also associated with reduced TET1 and TET2 protein expressions and reduced accumulation of the oxidative product, 5 hmC, in both PCBC-CMs and DP3-CMs, in the presence of AA. Conclusions: Ascorbic acid induced MLC2v protein expression and promoted ventricular-like CM subtype in hiPSC-CMs. The effect of AA on hiPSC-CM was attenuated with inhibition of TET1/TET2 mediated DNA demethylation.

High throughput screening system for engineered cardiac tissues

Introduction: Three dimensional engineered cardiac tissues (3D ECTs) have become indispensable as in vitro models to assess drug cardiotoxicity, a leading cause of failure in pharmaceutical development. A current bottleneck is the relatively low throughput of assays that measure spontaneous contractile forces exerted by millimeter-scale ECTs typically recorded through precise optical measurement of deflection of the polymer scaffolds that support them. The required resolution and speed limit the field of view to at most a few ECTs at a time using conventional imaging. Methods: To balance the inherent tradeoff among imaging resolution, field of view and speed, an innovative mosaic imaging system was designed, built, and validated to sense contractile force of 3D ECTs seeded on a 96-well plate. Results: The system performance was validated through real-time, parallel contractile force monitoring for up to 3 weeks. Pilot drug testing was conducted using isoproterenol. Discussion: The described tool increases contractile force sensing throughput to 96 samples per measurement; significantly reduces cost, time and labor needed for preclinical cardiotoxicity assay using 3D ECT. More broadly, our mosaicking approach is a general way to scale up image-based screening in multi-well formats.

Aligned Nanofibrous Net Deposited Perpendicularly on Microridges Supports Endothelium Formation and Promotes the Structural Maturation of hiPSC-Derived Cardiomyocytes

Cell alignment widely exists in various in vivo tissues and also plays an essential role in the construction of in vitro models, such as vascular endothelial and myocardial models. Recently, microscale and nanoscale hierarchical topographical structures have been drawing increasing attention for engineering in vitro cell alignment. In the present study, we fabricated a micro-/nanohierarchical substrate based on soft lithography and electrospinning to assess the synergetic effect of both the aligned nanofibrous topographical guidance and the off-ground culture environment provided by the substrate on the endothelium formation and the maturation of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). The morphology, proliferation, and barrier formation of human umbilical vein endothelial cells (HUVECs) as well as the alignment, cardiac-specific proteins, and maturity-related gene expression of hiPSC-CMs on the aligned-nanofiber/microridge (AN-MR) substrate were studied. Compared with the glass slide and the single-aligned nanofiber substrate, the AN-MR substrate enhanced the proliferation, alignment, and cell-cell interaction of HUVECs and improved the length of the sarcomere and maturation-related gene expression of hiPSC-CMs. Finally, the response of hiPSC-CMs on different substrates to two typical cardiac drugs (isoproterenol and E-4031) was tested and analyzed, showing that the hiPSC-CMs on AN-MR substrates were more resistant to drugs than those in other groups, which was related to the higher maturity of the cells. Overall, the proposed micro-/nanohierarchical substrate supports the in vitro endothelium formation and enhances the maturation of hiPSC-CMs, which show great potential to be applied in the construction of in vitro models and tissue engineering.

Proliferation and Maturation: Janus and the Art of Cardiac Tissue Engineering

During cardiac development and morphogenesis, cardiac progenitor cells differentiate into cardiomyocytes that expand in number and size to generate the fully formed heart. Much is known about the factors that regulate initial differentiation of cardiomyocytes, and there is ongoing research to identify how these fetal and immature cardiomyocytes develop into fully functioning, mature cells. Accumulating evidence indicates that maturation limits proliferation and conversely proliferation occurs rarely in cardiomyocytes of the adult myocardium. We term this oppositional interplay the proliferation-maturation dichotomy. Here we review the factors that are involved in this interplay and discuss how a better understanding of the proliferation-maturation dichotomy could advance the utility of human induced pluripotent stem cell-derived cardiomyocytes for modeling in 3-dimensional engineered cardiac tissues to obtain truly adult-level function.

Long-term in vitro recording of cardiac action potentials on microelectrode arrays for chronic cardiotoxicity assessment

The reliable identification of chronic cardiotoxic effects in in vitro screenings is fundamental for filtering out toxic molecular entities before in vivo animal experimentation and clinical trials. Present techniques such as patch-clamp, voltage indicators, and standard microelectrode arrays do not offer at the same time high sensitivity for measuring transmembrane ion currents and low-invasiveness for monitoring cells over long time. Here, we show that optoporation applied to microelectrode arrays enables measuring action potentials from human-derived cardiac syncytia for more than 1 continuous month and provides reliable data on chronic cardiotoxic effects caused by known compounds such as pentamidine. The technique has high potential for detecting chronic cardiotoxicity in the early phases of drug development.

hERG1 channel subunit composition mediates proton inhibition of rapid delayed rectifier potassium current (IKr) in cardiomyocytes derived from hiPSCs

The voltage-gated channel, hERG1, conducts the rapid delayed rectifier potassium current (IKr) and is critical for human cardiac repolarization. Reduced IKr causes long QT syndrome and increases the risk for cardiac arrhythmia and sudden death. At least two subunits form functional hERG1 channels, hERG1a and hERG1b. Changes in hERG1a/1b abundance modulate IKr kinetics, magnitude, and drug sensitivity. Studies from native cardiac tissue suggest that hERG1 subunit abundance is dynamically regulated, but the impact of altered subunit abundance on IKr and its response to external stressors is not well understood. Here, we used a substrate-driven human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) maturation model to investigate how changes in relative hERG1a/1b subunit abundance impact the response of native IKr to extracellular acidosis, a known component of ischemic heart disease and sudden infant death syndrome. IKr recorded from immatured hiPSC-CMs displays a 2-fold greater inhibition by extracellular acidosis (pH 6.3) compared with matured hiPSC-CMs. Quantitative RT-PCR and immunocytochemistry demonstrated that hERG1a subunit mRNA and protein were upregulated and hERG1b subunit mRNA and protein were downregulated in matured hiPSC-CMs compared with immatured hiPSC-CMs. The shift in subunit abundance in matured hiPSC-CMs was accompanied by increased IKr. Silencing hERG1b's impact on native IKr kinetics by overexpressing a polypeptide identical to the hERG1a N-terminal Per-Arnt-Sim domain reduced the magnitude of IKr proton inhibition in immatured hiPSC-CMs to levels comparable to those observed in matured hiPSC-CMs. These data demonstrate that hERG1 subunit abundance is dynamically regulated and determines IKr proton sensitivity in hiPSC-CMs.

Dynamic chromatin landscape encodes programs for perinatal transition of cardiomyocytes

The perinatal period occurring immediately before and after birth is critical for cardiomyocytes because they must change rapidly to accommodate the switch from fetal to neonatal circulation after birth. This transition is a well-orchestrated process, and any perturbation leads to unhealthy cardiomyocytes and heart disease. Despite its importance, little is known about how this transition is regulated and controlled. Here, by mapping the genome-wide chromatin accessibility, transcription-centered long-range chromatin interactions and gene expression in cardiomyocytes undergoing perinatal transition, we discovered two key transcription factors, MEF2 and AP1, that are crucial for driving the phenotypic changes within the perinatal window. Thousands of dynamic regulatory elements were found in perinatal cardiomyocytes and we show these elements mediated the transcriptional reprogramming through an elegant chromatin high-order architecture. We recompiled transcriptional program of induced stem cell-derived cardiomyocytes according to our discovered network, and they showed adult cardiomyocyte-like electrophysiological expression. Our work provides a comprehensive regulatory resource of cardiomyocytes perinatal reprogramming, and aids the gap-filling of cardiac translational research.

A myocardial infarct border-zone-on-a-chip demonstrates distinct regulation of cardiac tissue function by an oxygen gradient

After a myocardial infarction, the boundary between the injured, hypoxic tissue and the adjacent viable, normoxic tissue, known as the border zone, is characterized by an oxygen gradient. Yet, the impact of an oxygen gradient on cardiac tissue function is poorly understood, largely due to limitations of existing experimental models. Here, we engineered a microphysiological system to controllably expose engineered cardiac tissue to an oxygen gradient that mimics the border zone and measured the effects of the gradient on electromechanical function and the transcriptome. The gradient delayed calcium release, reuptake, and propagation; decreased diastolic and peak systolic stress; and increased expression of inflammatory cascades that are hallmarks of myocardial infarction. These changes were distinct from those observed in tissues exposed to uniform normoxia or hypoxia, demonstrating distinct regulation of cardiac tissue phenotypes by an oxygen gradient. Our border-zone-on-a-chip model advances functional and mechanistic insight into oxygen-dependent cardiac tissue pathophysiology.

Animal models and animal-free innovations for cardiovascular research: current status and routes to be explored. Consensus document of the ESC Working Group on Myocardial Function and the ESC Working Group on Cellular Biology of the Heart

Cardiovascular diseases represent a major cause of morbidity and mortality, necessitating research to improve diagnostics, and to discover and test novel preventive and curative therapies, all of which warrant experimental models that recapitulate human disease. The translation of basic science results to clinical practice is a challenging task, in particular for complex conditions such as cardiovascular diseases, which often result from multiple risk factors and comorbidities. This difficulty might lead some individuals to question the value of animal research, citing the translational 'valley of death', which largely reflects the fact that studies in rodents are difficult to translate to humans. This is also influenced by the fact that new, human-derived in vitro models can recapitulate aspects of disease processes. However, it would be a mistake to think that animal models do not represent a vital step in the translational pathway as they do provide important pathophysiological insights into disease mechanisms particularly on an organ and systemic level. While stem cell-derived human models have the potential to become key in testing toxicity and effectiveness of new drugs, we need to be realistic, and carefully validate all new human-like disease models. In this position paper, we highlight recent advances in trying to reduce the number of animals for cardiovascular research ranging from stem cell-derived models to in situ modelling of heart properties, bioinformatic models based on large datasets, and state-of-the-art animal models, which show clinically relevant characteristics observed in patients with a cardiovascular disease. We aim to provide a guide to help researchers in their experimental design to translate bench findings to clinical routine taking the replacement, reduction, and refinement (3R) as a guiding concept.

A comprehensive review of computational and image analysis techniques for quantitative evaluation of striated muscle tissue architecture

Unbiased evaluation of morphology is crucial to understanding development, mechanics, and pathology of striated muscle tissues. Indeed, the ability of striated muscles to contract and the strength of their contraction is dependent on their tissue-, cellular-, and cytoskeletal-level organization. Accordingly, the study of striated muscles often requires imaging and assessing aspects of their architecture at multiple different spatial scales. While an expert may be able to qualitatively appraise tissues, it is imperative to have robust, repeatable tools to quantify striated myocyte morphology and behavior that can be used to compare across different labs and experiments. There has been a recent effort to define the criteria used by experts to evaluate striated myocyte architecture. In this review, we will describe metrics that have been developed to summarize distinct aspects of striated muscle architecture in multiple different tissues, imaged with various modalities. Additionally, we will provide an overview of metrics and image processing software that needs to be developed. Importantly to any lab working on striated muscle platforms, characterization of striated myocyte morphology using the image processing pipelines discussed in this review can be used to quantitatively evaluate striated muscle tissues and contribute to a robust understanding of the development and mechanics of striated muscles.

Enhancing iPSC-CM Maturation Using a Matrigel-Coated Micropatterned PDMS Substrate

Cardiac myocytes isolated from adult heart tissue have a rod-like shape with highly organized intracellular structures. Cardiomyocytes derived from human pluripotent stem cells (iPSC-CMs), on the other hand, exhibit disorganized structure and contractile mechanics, reflecting their pronounced immaturity. These characteristics hamper research using iPSC-CMs. The protocol described here enhances iPSC-CM maturity and function by controlling the cellular shape and environment of the cultured cells. Microstructured silicone membranes function as a cell culture substrate that promotes cellular alignment. iPSC-CMs cultured on micropatterned membranes display an in-vivo-like rod-shaped morphology. This physiological cellular morphology along with the soft biocompatible silicone substrate, which has similar stiffness to the native cardiac matrix, promotes maturation of contractile function, calcium handling, and electrophysiology. Incorporating this technique for enhanced iPSC-CM maturation will help bridge the gap between animal models and clinical care, and ultimately improve personalized medicine for cardiovascular diseases. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Cardiomyocyte differentiation of iPSCs Basic Protocol 2: Purification of differentiated iPSC-CMs using MACS negative selection Basic Protocol 3: Micropatterning on PDMS.

SNTA1 gene rescues ion channel function and is antiarrhythmic in cardiomyocytes derived from induced pluripotent stem cells from muscular dystrophy patients

Background

Patients with cardiomyopathy of Duchenne Muscular Dystrophy (DMD) are at risk of developing life-threatening arrhythmias, but the mechanisms are unknown. We aimed to determine the role of ion channels controlling cardiac excitability in the mechanisms of arrhythmias in DMD patients.

Methods

To test whether dystrophin mutations lead to defective cardiac NaV1.5-Kir2.1 channelosomes and arrhythmias, we generated iPSC-CMs from two hemizygous DMD males, a heterozygous female, and two unrelated control males. We conducted studies including confocal microscopy, protein expression analysis, patch-clamping, non-viral piggy-bac gene expression, optical mapping and contractility assays.

Results

Two patients had abnormal ECGs with frequent runs of ventricular tachycardia. iPSC-CMs from all DMD patients showed abnormal action potential profiles, slowed conduction velocities, and reduced sodium (INa) and inward rectifier potassium (IK1) currents. Membrane NaV1.5 and Kir2.1 protein levels were reduced in hemizygous DMD iPSC-CMs but not in heterozygous iPSC-CMs. Remarkably, transfecting just one component of the dystrophin protein complex (α1-syntrophin) in hemizygous iPSC-CMs from one patient restored channelosome function, INa and IK1 densities, and action potential profile in single cells. In addition, α1-syntrophin expression restored impulse conduction and contractility and prevented reentrant arrhythmias in hiPSC-CM monolayers.

Conclusions

We provide the first demonstration that iPSC-CMs reprogrammed from skin fibroblasts of DMD patients with cardiomyopathy have a dysfunction of the NaV1.5-Kir2.1 channelosome, with consequent reduction of cardiac excitability and conduction. Altogether, iPSC-CMs from patients with DMD cardiomyopathy have a NaV1.5-Kir2.1 channelosome dysfunction, which can be rescued by the scaffolding protein α1-syntrophin to restore excitability and prevent arrhythmias.

Funding

Supported by National Institutes of Health R01 HL122352 grant; 'la Caixa' Banking Foundation (HR18-00304); Fundación La Marató TV3: Ayudas a la investigación en enfermedades raras 2020 (LA MARATO-2020); Instituto de Salud Carlos III/FEDER/FSE; Horizon 2020 - Research and Innovation Framework Programme GA-965286 to JJ; the CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia e Innovación (MCIN) and the Pro CNIC Foundation), and is a Severo Ochoa Center of Excellence (grant CEX2020-001041-S funded by MICIN/AEI/10.13039/501100011033). American Heart Association postdoctoral fellowship 19POST34380706s to JVEN. Israel Science Foundation to OB and MA [824/19]. Rappaport grant [01012020RI]; and Niedersachsen Foundation [ZN3452] to OB; US-Israel Binational Science Foundation (BSF) to OB and TH [2019039]; Dr. Bernard Lublin Donation to OB; and The Duchenne Parent Project Netherlands (DPPNL 2029771) to OB. National Institutes of Health R01 AR068428 to DM and US-Israel Binational Science Foundation Grant [2013032] to DM and OB.

Mutant ANP induces mitochondrial and ion channel remodeling in a human iPSC-derived atrial fibrillation model

Human induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) can model heritable arrhythmias to personalize therapies for individual patients. Although atrial fibrillation (AF) is a leading cause of cardiovascular morbidity and mortality, current platforms to generate iPSC-atrial (a) CMs are inadequate for modeling AF. We applied a combinatorial engineering approach, which integrated multiple physiological cues, including metabolic conditioning and electrical stimulation, to generate mature iPSC-aCMs. Using the patient’s own atrial tissue as a gold standard benchmark, we assessed the electrophysiological, structural, metabolic, and molecular maturation of iPSC-aCMs. Unbiased transcriptomic analysis and inference from gene regulatory networks identified key gene expression pathways and transcription factors mediating atrial development and maturation. Only mature iPSC-aCMs generated from patients with heritable AF carrying the non-ion channel gene (NPPA) mutation showed enhanced expression and function of a cardiac potassium channel and revealed mitochondrial electron transport chain dysfunction. Collectively, we propose that ion channel remodeling in conjunction with metabolic defects created an electrophysiological substrate for AF. Overall, our electro-metabolic approach generated mature human iPSC-aCMs that unmasked the underlying mechanism of the first non-ion channel gene, NPPA, that causes AF. Our maturation approach will allow for the investigation of the molecular underpinnings of heritable AF and the development of personalized therapies.

Tamoxifen treatment ameliorates contractile dysfunction of Duchenne muscular dystrophy stem cell-derived cardiomyocytes on bioengineered substrates

Duchenne muscular dystrophy (DMD) is a progressive genetic myopathy that leads to heart failure from dilated cardiomyopathy by early adulthood. Recent evidence suggests that tamoxifen, a selective estrogen receptor modulator widely used to treat breast cancer, ameliorates DMD cardiomyopathy. However, the mechanism of action of 4-hydroxytamoxifen, the active metabolite of tamoxifen, on cardiomyocyte function remains unclear. To examine the effects of chronic 4-hydroxytamoxifen treatment, we used state-of-the-art human-induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and a bioengineered platform to model DMD. We assessed the beating rate and beating velocity of iPSC-CMs in monolayers and as single cells on micropatterns that promote a physiological cardiomyocyte morphology. We found that 4-hydroxytamoxifen treatment of DMD iPSC-CMs decreased beating rate, increased beating velocity, and ameliorated calcium-handling deficits, leading to prolonged viability. Our study highlights the utility of a bioengineered iPSC-CM platform for drug testing and underscores the potential of repurposing tamoxifen as a therapy for DMD cardiomyopathy.

Chronic Cardiotoxicity Assays Using Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs)

Cardiomyocytes (CMs) differentiated from human induced pluripotent stem cells (hiPSCs) are increasingly used in cardiac safety assessment, disease modeling and regenerative medicine. A vast majority of cardiotoxicity studies in the past have tested acute effects of compounds and drugs; however, these studies lack information on the morphological or physiological responses that may occur after prolonged exposure to a cardiotoxic compound. In this review, we focus on recent advances in chronic cardiotoxicity assays using hiPSC-CMs. We summarize recently published literature on hiPSC-CMs assays applied to chronic cardiotoxicity induced by anticancer agents, as well as non-cancer classes of drugs, including antibiotics, anti-hepatitis C virus (HCV) and antidiabetic drugs. We then review publications on the implementation of hiPSC-CMs-based assays to investigate the effects of non-pharmaceutical cardiotoxicants, such as environmental chemicals or chronic alcohol consumption. We also highlight studies demonstrating the chronic effects of smoking and implementation of hiPSC-CMs to perform genomic screens and metabolomics-based biomarker assay development. The acceptance and wide implementation of hiPSC-CMs-based assays for chronic cardiotoxicity assessment will require multi-site standardization of assay protocols, chronic cardiac maturity marker reproducibility, time points optimization, minimal cellular variation (commercial vs. lab reprogrammed), stringent and matched controls and close clinical setting resemblance. A comprehensive investigation of long-term repeated exposure-induced effects on both the structure and function of cardiomyocytes can provide mechanistic insights and recapitulate drug and environmental cardiotoxicity.

Use of hiPSC-Derived Cardiomyocytes to Rule Out Proarrhythmic Effects of Drugs: The Case of Hydroxychloroquine in COVID-19

In the early phases of the COVID-19 pandemic, drug repurposing was widely used to identify compounds that could improve the prognosis of symptomatic patients infected by SARS-CoV-2. Hydroxychloroquine (HCQ) was one of the first drugs used to treat COVID-19 due to its supposed capacity of inhibiting SARS-CoV-2 infection and replication in vitro. While its efficacy is debated, HCQ has been associated with QT interval prolongation and potentially Torsades de Pointes, especially in patients predisposed to developing drug-induced Long QT Syndrome (LQTS) as silent carriers of variants associated with congenital LQTS. If confirmed, these effects represent a limitation to the at-home use of HCQ for COVID-19 infection as adequate ECG monitoring is challenging. We investigated the proarrhythmic profile of HCQ with Multi-Electrode Arrays after exposure of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from two healthy donors, one asymptomatic and two symptomatic LQTS patients. We demonstrated that: I) HCQ induced a concentration-dependent Field Potential Duration (FPD) prolongation and halted the beating at high concentration due to the combined effect of HCQ on multiple ion currents. II) hiPSC-CMs from healthy or asymptomatic carriers tolerated higher concentrations of HCQ and showed lower susceptibility to HCQ-induced electrical abnormalities regardless of baseline FPD. These findings agree with the clinical safety records of HCQ and demonstrated that hiPSC-CMs potentially discriminates symptomatic vs. asymptomatic mutation carriers through pharmacological interventions. Disease-specific cohorts of hiPSC-CMs may be a valid preliminary addition to assess drug safety in vulnerable populations, offering rapid preclinical results with valuable translational relevance for precision medicine.

Proarrhythmic effects induced by benzethonium chloride and domiphen bromide in vitro and in vivo

Benzethonium chloride (BZT) and domiphen bromide (DMP) are widely used as antimicrobials in drugs, vaccines and industry. However, no cardiac safety data has been developed on both compounds. Previously we reported BZT and DMP as high-affinity human ether-a-go-go related gene (HERG) channel inhibitors with unknown proarrhythmic risk. Here, we investigate the cardiotoxicity of BZT and DMP in vitro and in vivo, aiming to improve the safety-in-use of both antimicrobials. In the present study, human iPSC derived cardiomyocytes (hiPSC-CMs) were generated and rabbit models were used to examine the proarrhythmic potential of BZT and DMP. Our results found that BZT and DMP induced time- and dose-dependent decrease in the contractile parameters of hiPSC-CMs, prolonged FPDc (≥ 0.1 μM), caused tachycardia/fibrillation-like oscillation (0.3-1 μM), ultimately progressing to irreversible arrest of beating (≥ 1 μM). The IC50 values of BZT and DMP derived from normalized beat rate were 0.13 μM and 0.10 μM on hiPSC-CMs at 76 days. Moreover, in vivo rabbit ECG data demonstrated that 12.85 mg/kg BZT and 3.85 mg/kg DMP evoked QTc prolongation, noncomplex arrhythmias and ventricular tachycardias. Our findings support the cardiac safety of 0.01 μM BZT/DMP in vitro and the intravenous infusion of 3.85 mg/kg BZT and 1.28 mg/kg DMP in vivo, whereas higher concentrations of both compounds cause mild to moderate cardiotoxicity that should not be neglected during medical and industrial applications.

High-throughput 3D Spheroid Formation and Effective Cardiomyocyte Differentiation from Human iPS Cells Using the Microfabric Vessels EZSPHERETM

High-throughput 3D spheroid formation from human induced pluripotent stem cells (hiPSCs) can be easily performed using the unique microfabric vessels EZSPHERE, resulting in effective and large scale generation of differentiated cells such as cardiomyocytes or neurons. Such hiPSC-derived cardiomyocytes (hiPSC-CMs) or neurons are very useful in the fields of regenerative medicine or cell-based drug safety tests. Previous studies indicated that 3D spheroids arising from hiPSCs are effectively differentiated into high quality hiPSC-CMs by controlling Wnt signals through utilization of the microfabric vessels EZSPHERE. Here, we describe a simple and highly efficient protocol for generating a large number of uniformly sized hiPSC spheroids and inducing them for cardiac differentiation using the EZSPHERE. This method comprises the collection and dissociation of the spheroids from cardiac differentiation medium, in the middle stage of the whole cardiac differentiation process, and re-seeding the obtained single cells into the EZSPHERE to re-aggregate them into uniform hiPSC-CM spheroids with controlled size. This re-aggregation process promotes non-canonical Wnt signal-related cardiac development and improves the purity and maturity of the hiPSC-CMs generated. Graphic abstract: Overview of cardiac differentiation from iPSCs by spheroid formation and reaggregation using EZSPHERE.

All-Optical and Label-Free Stimulation of Action Potentials in Neurons and Cardiomyocytes by Plasmonic Porous Metamaterials

Optical stimulation technologies are gaining great consideration in cardiology, neuroscience studies, and drug discovery pathways by providing control over cell activity with high spatio-temporal resolution. However, this high precision requires manipulation of biological processes at genetic level concealing its development from broad scale application. Therefore, translating these technologies into tools for medical or pharmacological applications remains a challenge. Here, an all-optical nongenetic method for the modulation of electrogenic cells is introduced. It is demonstrated that plasmonic metamaterials can be used to elicit action potentials by converting near infrared laser pulses into stimulatory currents. The suggested approach allows for the stimulation of cardiomyocytes and neurons directly on commercial complementary metal-oxide semiconductor microelectrode arrays coupled with ultrafast pulsed laser, providing both stimulation and network-level recordings on the same device.

Photobiomodulation therapy preconditioning modifies nitric oxide pathway and oxidative stress in human-induced pluripotent stem cell-derived ventricular cardiomyocytes treated with doxorubicin

Doxorubicin (DOX) is an anthracycline antibiotic that exhibits high heart toxicity. Human-induced pluripotent stem cell-derived ventricular cardiomyocytes (hiPSC-vCMs) are important in vitro models for testing drug cardiotoxicity. Photobiomodulation therapy (PBMT) is a non-invasive therapy that stimulates cells growth and self-repair using light irradiation. This study aimed to investigate the in vitro effects of PBMT preconditioning on cardiotoxicity induced by DOX. HiPSC-vCMs were treated with PBMT for 500 s, followed by the addition of 2 μM DOX. LED irradiation preconditioning parameters were at 660 nm with an irradiance of 10 mW/cm², performing 5 J/cm², followed by 24-h DOX exposure (2 μM). Human iPSC-vCMs treated with 2 μM DOX or irradiated with PBMT composed the second and third groups, respectively. The control group did neither receive PBMT preconditioning nor DOX and was irradiated with a white standard lamp. Cells from all groups were collected to perform mRNA and miRNA expressions quantification. PBMT, when applied before the DOX challenge, restored the viability of hiPSC-vCMs and reduced ROS levels. Although downregulated by DOX, myocardial UCP2 mRNA expression presented marked upregulation after PBMT preconditioning. Expression of eNOS and UCP2 mRNA and NO production were decreased after DOX exposure, and PBMT preconditioning before the DOX challenge reversed these changes. Moreover, our data indicated that PBMT preconditioning lowered the miR-24 expression. Our data suggested that PBMT preconditioning ameliorated in vitro DOX-induced cardiotoxicity on transcription level, restoring NO levels and reducing oxidative stress.

Modeling genetic cardiac channelopathies using induced pluripotent stem cells - Status quo from an electrophysiological perspective

Long QT syndrome (LQTS), Brugada syndrome (BrS), and catecholaminergic polymorphic ventricular tachycardia (CPVT) are genetic diseases of the heart caused by mutations in specific cardiac ion channels and are characterized by paroxysmal arrhythmias, which can deteriorate into ventricular fibrillation. In LQTS3 and BrS different mutations in the SCN5A gene lead to a gain-or a loss-of-function of the voltage-gated sodium channel Nav1.5, respectively. Although sharing the same gene mutation, these syndromes are characterized by different clinical manifestations and functional perturbations and in some cases even present an overlapping clinical phenotype. Several studies have shown that Na⁺ current abnormalities in LQTS3 and BrS can also cause Ca²⁺-signaling aberrancies in cardiomyocytes (CMs). Abnormal Ca²⁺ homeostasis is also the main feature of CPVT which is mostly caused by heterozygous mutations in the RyR2 gene. Large numbers of disease-causing mutations were identified in RyR2 and SCN5A but it is not clear how different variants in the SCN5A gene produce different clinical syndromes and if in CPVT Ca²⁺ abnormalities and drug sensitivities vary depending on the mutation site in the RyR2. These questions can now be addressed by using patient-specific in vitro models of these diseases based on induced pluripotent stem cells (iPSCs). In this review, we summarize different insights gained from these models with a focus on electrophysiological perturbations caused by different ion channel mutations and discuss how will this knowledge help develop better stratification and more efficient personalized therapies for these patients.

A multiscale approach for bridging the gap between potency, efficacy, and safety of small molecules directed at membrane proteins

Membrane proteins constitute a substantial fraction of the human proteome, thus representing a vast source of therapeutic drug targets. Indeed, newly devised technologies now allow targeting "undruggable" regions of membrane proteins to modulate protein function in the cell. Despite the advances in technology, the rapid translation of basic science discoveries into potential drug candidates targeting transmembrane protein domains remains challenging. We address this issue by harmonizing single molecule-based and ensemble-based atomistic simulations of ligand-membrane interactions with patient-derived induced pluripotent stem cell (iPSC)-based experiments to gain insights into drug delivery, cellular efficacy, and safety of molecules directed at membrane proteins. In this study, we interrogated the pharmacological activation of the cardiac Ca2+ pump (Sarcoplasmic reticulum Ca2+-ATPase, SERCA2a) in human iPSC-derived cardiac cells as a proof-of-concept model. The combined computational-experimental approach serves as a platform to explain the differences in the cell-based activity of candidates with similar functional profiles, thus streamlining the identification of drug-like candidates that directly target SERCA2a activation in human cardiac cells. Systematic cell-based studies further showed that a direct SERCA2a activator does not induce cardiotoxic pro-arrhythmogenic events in human cardiac cells, demonstrating that pharmacological stimulation of SERCA2a activity is a safe therapeutic approach targeting the heart. Overall, this novel multiscale platform encompasses organ-specific drug potency, efficacy, and safety, and opens new avenues to accelerate the bench-to-patient research aimed at designing effective therapies directed at membrane protein domains.

Human-induced pluripotent stem cell-derived cardiomyocytes, 3D cardiac structures, and heart-on-a-chip as tools for drug research

Development of new drugs is of high interest for the field of cardiac and cardiovascular diseases, which are a dominant cause of death worldwide. Before being allowed to be used and distributed, every new potentially therapeutic compound must be strictly validated during preclinical and clinical trials. The preclinical studies usually involve the in vitro and in vivo evaluation. Due to the increasing reporting of discrepancy in drug effects in animal and humans and the requirement to reduce the number of animals used in research, improvement of in vitro models based on human cells is indispensable. Primary cardiac cells are difficult to access and maintain in cell culture for extensive experiments; therefore, the human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) became an excellent alternative. This technology enables a production of high number of patient- and disease-specific cardiomyocytes and other cardiac cell types for a large-scale research. The drug effects can be extensively evaluated in the context of electrophysiological responses with a use of well-established tools, such as multielectrode array (MEA), patch clamp, or calcium ion oscillation measurements. Cardiotoxicity, which is a common reason for withdrawing drugs from marketing or rejection at final stages of clinical trials, can be easily verified with a use of hiPSC-CM model providing a prediction of human-specific responses and higher safety of clinical trials involving patient cohort. Abovementioned studies can be performed using two-dimensional cell culture providing a high-throughput and relatively lower costs. On the other hand, more complex structures, such as engineered heart tissue, organoids, or spheroids, frequently applied as co-culture systems, represent more physiological conditions and higher maturation rate of hiPSC-derived cells. Furthermore, heart-on-a-chip technology has recently become an increasingly popular tool, as it implements controllable culture conditions, application of various stimulations and continuous parameters read-out. This paper is an overview of possible use of cardiomyocytes and other cardiac cell types derived from hiPSC as in vitro models of heart in drug research area prepared on the basis of latest scientific reports and providing thorough discussion regarding their advantages and limitations.

Atrial-specific hiPSC-derived cardiomyocytes in drug discovery and disease modeling

The discovery and application of human-induced pluripotent stem cells (hiPSCs) have been instrumental in the investigation of the pathophysiology of cardiovascular diseases. Patient-specific hiPSCs can now be generated, genome-edited, and subsequently differentiated into various cell types and used for regenerative medicine, disease modeling, drug testing, toxicity screening, and 3D tissue generation. Modulation of the retinoic acid signaling pathway has been shown to direct cardiomyocyte differentiation towards an atrial lineage. A variety of studies have successfully differentiated patient-specific atrial cardiac myocytes (hiPSC-aCM) and atrial engineered heart tissue (aEHT) that express atrial specific genes (e.g., sarcolipin and ANP) and exhibit atrial electrophysiological and contractility profiles. Identification of protocols to differentiate atrial cells from patients with atrial fibrillation and other inherited diseases or creating disease models using genetic mutation studies has shed light on the mechanisms of atrial-specific diseases and identified the efficacy of atrial-selective pharmacological compounds. hiPSC-aCMs and aEHTs can be used in drug discovery and drug screening studies to investigate the efficacy of atrial selective drugs on atrial fibrillation models. Furthermore, hiPSC-aCMs can be effective tools in studying the mechanism, pathophysiology and treatment options of atrial fibrillation and its genetic underpinnings. The main limitation of using hiPSC-CMs is their immature phenotype compared to adult CMs. A wide range of approaches and protocols are used by various laboratories to optimize and enhance CM maturation, including electrical stimulation, culture time, biophysical cues and changes in metabolic factors.

In vitro model of ischemic heart failure using human induced pluripotent stem cell-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been used extensively to model inherited heart diseases, but hiPSC-CM models of ischemic heart disease are lacking. Here, our objective was to generate an hiPSC-CM model of ischemic heart disease. To this end, hiPSCs were differentiated into functional hiPSC-CMs and then purified using either a simulated ischemia media or by using magnetic antibody-based purification targeting the nonmyocyte population for depletion from the cell population. Flow cytometry analysis confirmed that each purification approach generated hiPSC-CM cultures that had more than 94% cTnT+ cells. After purification, hiPSC-CMs were replated as confluent syncytial monolayers for electrophysiological phenotype analysis and protein expression by Western blotting. The phenotype of metabolic stress-selected hiPSC-CM monolayers recapitulated many of the functional and structural hallmarks of ischemic CMs, including elevated diastolic calcium, diminished calcium transient amplitude, prolonged action potential duration, depolarized resting membrane potential, hypersensitivity to chemotherapy-induced cardiotoxicity, depolarized mitochondrial membrane potential, depressed SERCA2a expression, reduced maximal oxygen consumption rate, and abnormal response to β1-adrenergic receptor stimulation. These findings indicate that metabolic selection of hiPSC-CMs generated cell populations with phenotype similar to what is well known to occur in the setting of ischemic heart failure and thus provide a opportunity for study of human ischemic heart disease.

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes as an in vitro model in toxicology: strengths and weaknesses for hazard identification and risk characterization

INTRODUCTION

Human induced pluripotent stem cell (iPSC)-derived cardiomyocytes is one of the most widely used cell-based models that resulted from the discovery of how non-embryonic stem cells can be differentiated into multiple cell types. In just one decade, iPSC-derived cardiomyocytes went from a research lab to widespread use in biomedical research and preclinical safety evaluation for drugs and other chemicals.

AREAS COVERED

This manuscript reviews data on toxicology applications of human iPSC-derived cardiomyocytes. We detail the outcome of a systematic literature search on their use (i) in hazard assessment for cardiotoxicity liabilities, (ii) for risk characterization, (iii) as models for population variability, and (iv) in studies of personalized medicine and disease.

EXPERT OPINION

iPSC-derived cardiomyocytes are useful to increase the accuracy, precision, and efficiency of cardiotoxicity hazard identification for both drugs and non-pharmaceuticals, with recent efforts beginning to demonstrate their utility for risk characterization. Notable limitations include the needs to improve the maturation of cells in culture, to better understand their potential use identifying structural cardiotoxicity, and for additional case studies involving population-wide and disease-specific risk characterization. Ultimately, the greatest future benefits are likely for non-pharmaceutical chemicals, filling a critical gap where no routine testing for cardiotoxicity is currently performed.

Dynamic Clamp in Electrophysiological Studies on Stem Cell-Derived Cardiomyocytes-Why and How?

ABSTRACT

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are supposed to be a good human-based model, with virtually unlimited cell source, for studies on mechanisms underlying cardiac development and cardiac diseases, and for identification of drug targets. However, a major drawback of hPSC-CMs as a model system, especially for electrophysiological studies, is their depolarized state and associated spontaneous electrical activity. Various approaches are used to overcome this drawback, including the injection of "synthetic" inward rectifier potassium current (IK1), which is computed in real time, based on the recorded membrane potential ("dynamic clamp"). Such injection of an IK1-like current results in quiescent hPSC-CMs with a nondepolarized resting potential that show "adult-like" action potentials on stimulation, with functional availability of the most important ion channels involved in cardiac electrophysiology. These days, dynamic clamp has become a widely appreciated electrophysiological tool. However, setting up a dynamic clamp system can still be laborious and difficult, both because of the required hardware and the implementation of the dedicated software. In the present review, we first summarize the potential mechanisms underlying the depolarized state of hPSC-CMs and the functional consequences of this depolarized state. Next, we explain how an existing manual patch clamp setup can be extended with dynamic clamp. Finally, we shortly validate the extended setup with atrial-like and ventricular-like hPSC-CMs. We feel that dynamic clamp is a highly valuable tool in the field of cellular electrophysiological studies on hPSC-CMs and hope that our directions for setting up such dynamic clamp system may prove helpful.

Atrial Fibrillation in Inherited Channelopathies

Atrial fibrillation (AF), the common sustained arrhythmia in clinical practice, has major public health implications due to its associated morbidity and increased mortality. The AF epidemic is due to the burgeoning elderly population and the identification of novel risk factors, for example, genetics. Since the diagnosis of AF has a major impact on the clinical assessment and management of patients with inherited arrhythmia syndromes, improved understanding of the cause and pathogenesis of AF has provided important insights into the underlying pathophysiological mechanisms of this common arrhythmia and identified potential mechanism-based therapies.

Optical Mapping in hiPSC-CM and Zebrafish to Resolve Cardiac Arrhythmias

Inherited cardiac arrhythmias contribute substantially to sudden cardiac death in the young. The underlying pathophysiology remains incompletely understood because of the lack of representative study models and the labour-intensive nature of electrophysiological patch clamp experiments. Whereas patch clamp is still considered the gold standard for investigating electrical properties in a cell, optical mapping of voltage and calcium transients has paved the way for high-throughput studies. Moreover, the development of human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) has enabled the study of patient specific cell lines capturing the full genomic background. Nevertheless, hiPSC-CMs do not fully address the complex interactions between various cell types in the heart. Studies using in vivo models, are therefore necessary. Given the analogies between the human and zebrafish cardiovascular system, zebrafish has emerged as a cost-efficient model for arrhythmogenic diseases. In this review, we describe how hiPSC-CM and zebrafish are employed as models to study primary electrical disorders. We provide an overview of the contemporary electrophysiological phenotyping tools and discuss in more depth the different strategies available for optical mapping. We consider the current advantages and disadvantages of both hiPSC-CM and zebrafish as a model and optical mapping as phenotyping tool and propose strategies for further improvement. Overall, the combination of experimental readouts at cellular (hiPSC-CM) and whole organ (zebrafish) level can raise our understanding of the complexity of inherited cardiac arrhythmia disorders to the next level.

Detection of Drug-Induced Torsades de Pointes Arrhythmia Mechanisms Using hiPSC-CM Syncytial Monolayers in a High-Throughput Screening Voltage Sensitive Dye Assay

We validated 3 distinct hiPSC-CM cell lines-each of different purity and a voltage sensitive dye (VSD)-based high-throughput proarrhythmia screening assay as a noncore site in the recently completed CiPA Myocyte Phase II Validation Study. Blinded validation was performed using 12 drugs linked to low, intermediate, or high risk for causing Torsades de Pointes (TdP). Commercially sourced hiPSC-CMs were obtained either from Cellular Dynamics International (CDI, Madison, Wisconsin, iCell Cardiomyoyctes2) or Takara Bio (CLS, Cellartis Cardiomyocytes). A third hiPSC-CM cell line (MCH, Michigan) was generated in house. Each cell type had distinct baseline electrophysiological function (spontaneous beat rate, action potential duration, and conduction velocity) and drug responsiveness. Use of VSD and optical mapping enabled the detection of conduction slowing of sodium channel blockers (quinidine, disopyramide, and mexiletine) and drug-induced TdP-like activation patterns (rotors) for some high- and intermediate-risk compounds. Low-risk compounds did not induce rotors in any cell type tested. These results further validate the utility of hiPSC-CMs for predictive proarrhythmia screening and the utility of VSD technology to detect drug-induced APD prolongation, arrhythmias (rotors), and conduction slowing. Importantly, results indicate that different ratios of cardiomyocytes and noncardiomyocytes have important impact on drug response that may be considered during risk assessment of new drugs. Finally, we present the first blinded CiPA hiPSC-CM validation results to simultaneously detect drug-induced conduction slowing, action potential duration prolongation, action potential triangulation, and drug-induced rotors in a proarrhythmia assay.

Human perinatal stem cell derived extracellular matrix enables rapid maturation of hiPSC-CM structural and functional phenotypes

The immature phenotype of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) is a major limitation to the use of these valuable cells for pre-clinical toxicity testing and for disease modeling. Here we tested the hypothesis that human perinatal stem cell derived extracellular matrix (ECM) promotes hiPSC-CM maturation to a greater extent than mouse cell derived ECM. We refer to the human ECM as Matrix Plus (Matrix Plus) and compare effects to commercially available mouse ECM (Matrigel). hiPSC-CMs cultured on Matrix Plus mature functionally and structurally seven days after thaw from cryopreservation. Mature hiPSC-CMs showed rod-shaped morphology, highly organized sarcomeres, elevated cTnI expression and mitochondrial distribution and function like adult cardiomyocytes. Matrix Plus also promoted mature hiPSC-CM electrophysiological function and monolayers' response to hERG ion channel specific blocker was Torsades de Pointes (TdP) reentrant arrhythmia activations in 100% of tested monolayers. Importantly, Matrix Plus enabled high throughput cardiotoxicity screening using mature human cardiomyocytes with validation utilizing reference compounds recommended for the evolving Comprehensive In Vitro Proarrhythmia Assay (CiPA) coordinated by the Health and Environmental Sciences Institute (HESI). Matrix Plus offers a solution to the commonly encountered problem of hiPSC-CM immaturity that has hindered implementation of these human based cell assays for pre-clinical drug discovery.

Syncytium cell growth increases Kir2.1 contribution in human iPSC-cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) enable cardiotoxicity testing and personalized medicine. However, their maturity is of concern, including relatively depolarized resting membrane potential and more spontaneous activity compared with adult cardiomyocytes, implicating low or lacking inward rectifier potassium current (I_k1). Here, protein quantification confirms Kir2.1 expression in hiPSC-CM syncytia, albeit several times lower than in adult heart tissue. We find that hiPSC-CM culture density influences Kir2.1 expression at the mRNA level (potassium inwardly rectifying channel subfamily J member 2) and at the protein level and its associated electrophysiology phenotype. Namely, all-optical cardiac electrophysiology and pharmacological treatments reveal reduction of spontaneous and irregular activity and increase in action potential upstroke in denser cultures. Blocking I_k1-like currents with BaCl₂ increased spontaneous frequency and blunted action potential upstrokes during pacing in a dose-dependent manner only in the highest-density cultures, in line with I_k1’s role in regulating the resting membrane potential. Our results emphasize the importance of syncytial growth of hiPSC-CMs for more physiologically relevant phenotype and the power of all-optical electrophysiology to study cardiomyocytes in their multicellular setting.

NEW & NOTEWORTHY We identify cell culture density and cell-cell contact as an important factor in determining the expression of a key ion channel at the transcriptional and the protein levels, KCNJ2/Kir2.1, and its contribution to the electrophysiology of human induced pluripotent stem cell-derived cardiomyocytes. Our results indicate that studies on isolated cells, out of tissue context, may underestimate the cellular ion channel properties being characterized.

Cardiac hypertrophy in a dish: a human stem cell based model

Cardiac hypertrophy is an important and independent risk factor for the development of heart failure. To better understand the mechanisms and regulatory pathways involved in cardiac hypertrophy, there is a need for improved in vitro models. In this study, we investigated how hypertrophic stimulation affected human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs). The cells were stimulated with endothelin-1 (ET-1) for 8, 24, 48, 72, or 96 h. Parameters including cell size, ANP-, proBNP-, and lactate concentration were analyzed. Moreover, transcriptional profiling using RNA-sequencing was performed to identify differentially expressed genes following ET-1 stimulation. The results show that the CMs increase in size by approximately 13% when exposed to ET-1 in parallel to increases in ANP and proBNP protein and mRNA levels. Furthermore, the lactate concentration in the media was increased indicating that the CMs consume more glucose, a hallmark of cardiac hypertrophy. Using RNA-seq, a hypertrophic gene expression pattern was also observed in the stimulated CMs. Taken together, these results show that hiPSC-derived CMs stimulated with ET-1 display a hypertrophic response. The results from this study also provide new molecular insights about the underlying mechanisms of cardiac hypertrophy and may help accelerate the development of new drugs against this condition.