Strategies for Improving the Maturity of Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Unveiling the Heart's Hidden Enemy: Dynamic Insights into Polystyrene Nanoplastic-Induced Cardiotoxicity Based on Cardiac Organoid-on-a-Chip

Exposure to micro- and nanoplastics (MNPs) has been implicated in potential cardiotoxicity. However, in vitro models based on cardiomyocyte cell lines lack crucial cardiac characteristics, while interspecies differences in animal models compromise the reliability of the conclusions. In addition, current research has predominantly focused on single-time point exposures to MNPs, neglecting comparative analyses of cardiac injury across early and late stages. Moreover, there remains a large gap in understanding the susceptibility to MNPs under pathological conditions. To address these limitations, this study integrated cardiac organoids (COs) and organ-on-a-chip (OoC) technology to develop the cardiac organoid-on-a-chip (COoC), which was validated for cardiotoxicity evaluation through multiple dimensions. Based on COoC, we conducted a dynamic observation of the cardiac damage caused by short- and long-term exposure to polystyrene nanoplastics (PS-NPs). Oxidative stress, inflammation, disruption of calcium ion homeostasis, and mitochondrial dysfunction were confirmed as the potential mechanisms of PS-NP-induced cardiotoxicity and the crucial events in the early stages, while cardiac fibrosis emerged as a prominent feature in late stages. Notably, low-dose exposure exacerbated myocardial infarction symptoms under pathological states, despite no significant cardiotoxicity shown in healthy models. In conclusion, these findings further deepened our understanding of PS-NP-induced cardiotoxic effects and introduced a promising in vitro platform for assessing cardiotoxicity.

Simultaneous electromechanical monitoring in engineered heart tissues using a mesoscale framework

Engineered heart tissues (EHTs) generated from human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent powerful platforms for human cardiac research, especially in drug testing and disease modeling. Here, we report a flexible, three-dimensional electronic framework that enables real-time, spatiotemporal analysis of electrophysiologic and mechanical signals in EHTs under physiological loading conditions for dynamic, noninvasive, longer-term assessments. These electromechanically monitored EHTs support multisite measurements throughout the tissue under baseline conditions and in response to stimuli. Demonstrations include uses in tracking physiological responses to pharmacologically active agents and in capturing electrophysiological characteristics of reentrant arrhythmias. This platform facilitates precise analysis of signal location and conduction velocity in human cardiomyocyte tissues, as the basis for a broad range of advanced cardiovascular studies.

Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) for modeling cardiac arrhythmias: strengths, challenges and potential solutions

Ion channels and cytoskeletal proteins in the cardiac dyad play a critical role in maintaining excitation-contraction (E-C) coupling and provide cardiac homeostasis. Functional changes in these dyad proteins, whether induced by genetic, epigenetic, metabolic, therapeutic, or environmental factors, can disrupt normal cardiac electrophysiology, leading to abnormal E-C coupling and arrhythmias. Animal models and heterologous cell cultures provide platforms to elucidate the pathogenesis of arrhythmias for basic cardiac research; however, these traditional systems do not truly reflect human cardiac electro-pathophysiology. Notably, patients with the same genetic variants of inherited channelopathies (ICC) often exhibit incomplete penetrance and variable expressivity which underscores the need to establish patient-specific disease models to comprehend the mechanistic pathways of arrhythmias and determine personalized therapies. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) inherit the genetic background of the patient and reflect the electrophysiological characteristics of the native cardiomyocytes. Thus, iPSC-CMs provide an innovative and translational pivotal platform in cardiac disease modeling and therapeutic screening. In this review, we will examine how patient-specific iPSC-CMs historically evolved to model arrhythmia syndromes in a dish, and their utility in understanding the role of specific ion channels and their functional characteristics in causing arrhythmias. We will also examine how CRISPR/Cas9 have enabled the establishment of patient-independent and variant-induced iPSC-CMs-based arrhythmia models. Next, we will examine the limitations of using human iPSC-CMs with respect to in vitro arrhythmia modeling that stems from variations in iPSCs or toxicity due to gene editing on iPSC or iPSC-CMs and explore how such hurdles are being addressed. Importantly, we will also discuss how novel 3D iPSC-CM models can better capture in vitro characteristics and how all-optical platforms provide non-invasive and high- throughput electrophysiological data that is useful for stratification of emerging arrhythmogenic variants and drug discovery. Finally, we will examine strategies to improve iPSC-CM maturity, including powerful gene editing and optogenetic tools that can introduce/modify specific ion channels in iPSC-CMs and tailor cellular and functional characteristics. We anticipate that an elegant synergy of iPSCs, novel gene editing, 3D- culture models, and all-optical platforms will offer a high-throughput template to faithfully recapitulate in vitro arrhythmogenic events necessary for personalized arrhythmia monitoring and drug screening process.

Advances in induced pluripotent stem cell-derived cardiac myocytes: technological breakthroughs, key discoveries and new applications

A transformation is underway in precision and patient-specific medicine. Rapid progress has been enabled by multiple new technologies including induced pluripotent stem cell-derived cardiac myocytes (iPSC-CMs). Here, we delve into these advancements and their future promise, focusing on the efficiency of reprogramming techniques, the fidelity of differentiation into the cardiac lineage, the functional characterization of the resulting cardiac myocytes, and the many applications of in silico models to understand general and patient-specific mechanisms controlling excitation-contraction coupling in health and disease. Furthermore, we explore the current and potential applications of iPSC-CMs in both research and clinical settings, underscoring the far-reaching implications of this rapidly evolving field.

Chamber-specific contractile responses of atrial and ventricular hiPSC-cardiomyocytes to GPCR and ion channel targeting compounds: A microphysiological system for cardiac drug development

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) have found utility for conducting in vitro drug screening and disease modelling to gain crucial insights into pharmacology or disease phenotype. However, diseases such as atrial fibrillation, affecting >33 M people worldwide, demonstrate the need for cardiac subtype-specific cells. Here, we sought to investigate the base characteristics and pharmacological differences between commercially available chamber-specific atrial or ventricular hiPSC-CMs seeded onto ultra-thin, flexible PDMS membranes to simultaneously measure contractility in a 96 multi-well format. We investigated the effects of GPCR agonists (acetylcholine and carbachol), a Ca2+ channel agonist (S-Bay K8644), an HCN channel antagonist (ivabradine) and K+ channel antagonists (4-AP and vernakalant). We observed differential effects between atrial and ventricular hiPSC-CMs on contractile properties including beat rate, beat duration, contractile force and evidence of arrhythmias at a range of concentrations. As an excerpt of the compound analysis, S-Bay K8644 treatment showed an induced concentration-dependent transient increase in beat duration of atrial hiPSC-CMs, whereas ventricular cells showed a physiological increase in beat rate over time. Carbachol treatment produced marked effects on atrial cells, such as increased beat duration alongside a decrease in beat rate over time, but only minimal effects on ventricular cardiomyocytes. In the context of this chamber-specific pharmacology, we not only add to contractile characterization of hiPSC-CMs but propose a multi-well platform for medium-throughput early compound screening. Overall, these insights illustrate the key pharmacological differences between chamber-specific cardiomyocytes and their application on a multi-well contractility platform to gain insights for in vitro cardiac liability studies and disease modelling.

Physiological stress improves stem cell modeling of dystrophic cardiomyopathy

Heart failure contributes to Duchenne muscular dystrophy (DMD), which arises from mutations that ablate dystrophin, rendering the plasma membrane prone to disruption. Cardiomyocyte membrane breakdown in patients with DMD yields a serum injury profile similar to other types of myocardial injury with the release of creatine kinase and troponin isoforms. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are highly useful but can be improved. We generated hiPSC-CMs from a patient with DMD and subjected these cells to equibiaxial mechanical strain to mimic in vivo stress. Compared to healthy cells, DMD hiPSC-CMs demonstrated greater susceptibility to equibiaxial strain after 2 h at 10% strain. We generated an aptamer-based profile of proteins released from hiPSC-CMs both at rest and subjected to strain and identified a strong correlation in the mechanical stress-induced proteome from hiPSC-CMs and serum from patients with DMD. We exposed hiPSC-CMs to recombinant annexin A6, a protein resealing agent, and found reduced biomarker release in DMD and control hiPSC-CMs subjected to strain. Thus, the application of mechanical strain to hiPSC-CMs produces a model that reflects an in vivo injury profile, providing a platform to assess pharmacologic intervention.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization

AIMS

Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition from an immature foetal to an adult CM state entails coordinated regulation of the expression of genes involved in myofibril formation and oxidative phosphorylation (OXPHOS) among others. Lysine demethylase 5 (KDM5) specifically demethylates H3K4me1/2/3 and has emerged as potential regulators of expression of genes involved in cardiac development and mitochondrial function. The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

METHODS AND RESULTS

KDM5A, B, and C proteins were mainly expressed in the early post-natal stages, and their expressions were progressively downregulated in the post-natal CMs and were absent in adult hearts and CMs. In contrast, KDM5 proteins were persistently expressed in the iPSC-CMs up to 60 days after the induction of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor, induced differential expression of 2372 genes, including upregulation of genes involved in fatty acid oxidation (FAO), OXPHOS, and myogenesis in the iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the cleavage under targets and release using nuclease assay showed enriched of the H3K4me3 peaks at the promoter regions of genes encoding FAO, OXPHOS, and sarcomere proteins. Consistent with the chromatin and gene expression data, KDM5 inhibition increased the expression of multiple sarcomere proteins and enhanced myofibrillar organization. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene and increased its RNA and protein levels. Knockdown of ESRRA in KDM5-C70-treated iPSC-CM suppressed expression of a subset of the KDM5 targets. In conjunction with changes in gene expression, KDM5 inhibition increased oxygen consumption rate and contractility in iPSC-CMs.

CONCLUSION

KDM5 inhibition enhances maturation of iPSC-CMs by epigenetically upregulating the expressions of OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

Induced pluripotent stem cells (iPSCs): molecular mechanisms of induction and applications

The induced pluripotent stem cell (iPSC) technology has transformed in vitro research and holds great promise to advance regenerative medicine. iPSCs have the capacity for an almost unlimited expansion, are amenable to genetic engineering, and can be differentiated into most somatic cell types. iPSCs have been widely applied to model human development and diseases, perform drug screening, and develop cell therapies. In this review, we outline key developments in the iPSC field and highlight the immense versatility of the iPSC technology for in vitro modeling and therapeutic applications. We begin by discussing the pivotal discoveries that revealed the potential of a somatic cell nucleus for reprogramming and led to successful generation of iPSCs. We consider the molecular mechanisms and dynamics of somatic cell reprogramming as well as the numerous methods available to induce pluripotency. Subsequently, we discuss various iPSC-based cellular models, from mono-cultures of a single cell type to complex three-dimensional organoids, and how these models can be applied to elucidate the mechanisms of human development and diseases. We use examples of neurological disorders, coronavirus disease 2019 (COVID-19), and cancer to highlight the diversity of disease-specific phenotypes that can be modeled using iPSC-derived cells. We also consider how iPSC-derived cellular models can be used in high-throughput drug screening and drug toxicity studies. Finally, we discuss the process of developing autologous and allogeneic iPSC-based cell therapies and their potential to alleviate human diseases.

Far-red and sensitive sensor for monitoring real time H2O2 dynamics with subcellular resolution and in multi-parametric imaging applications

H2O2 is a key oxidant in mammalian biology and a pleiotropic signaling molecule at the physiological level, and its excessive accumulation in conjunction with decreased cellular reduction capacity is often found to be a common pathological marker. Here, we present a red fluorescent Genetically Encoded H2O2 Indicator (GEHI) allowing versatile optogenetic dissection of redox biology. Our new GEHI, oROS-HT, is a chemigenetic sensor utilizing a HaloTag and Janelia Fluor (JF) rhodamine dye as fluorescent reporters. We developed oROS-HT through a structure-guided approach aided by classic protein structures and recent protein structure prediction tools. Optimized with JF635, oROS-HT is a sensor with 635 nm excitation and 650 nm emission peaks, allowing it to retain its brightness while monitoring intracellular H2O2 dynamics. Furthermore, it enables multi-color imaging in combination with blue-green fluorescent sensors for orthogonal analytes and low auto-fluorescence interference in biological tissues. Other advantages of oROS-HT over alternative GEHIs are its fast kinetics, oxygen-independent maturation, low pH sensitivity, lack of photo-artifact, and lack of intracellular aggregation. Here, we demonstrated efficient subcellular targeting and how oROS-HT can map inter and intracellular H2O2 diffusion at subcellular resolution. Lastly, we used oROS-HT with other green fluorescence reporters to investigate the transient effect of the anti-inflammatory agent auranofin on cellular redox physiology and calcium levels via multi-parametric, dual-color imaging.

Dapagliflozin prevents ERK activation and SGLT2-dependent endoglin upregulation in a mechanically provoked cardiac injury model

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) are rapidly gaining ground in the treatment of heart failure (HF) with reduced ejection fraction (HFrEF) and acute myocardial infarction (AMI) by an unknown mechanism. Upregulation of Na+/H+ exchanger 1 (NHE1), SGLT1, and Ca2+/calmodulin-dependent protein kinase II (CaMKII) in the diseased hearts was found to be attenuated by prolonged SGLT2i treatment. Unfortunately, dapagliflozin is not well understood as to how Na+/Ca2+ homeostasis is affected in cardiomyocytes. In this study, we aimed to investigate whether mechanical stretch in cardiomyocytes upregulate SGLT2, resulted to loss of Na+/Ca2+ homeostasis via ERK and eNOS signaling. AMI (+) and AMI (-) serum levels were estimated using ELISA assays of TGFβ-1 or endoglin (CD105). Human cardiomyocyte cell line AC16 was subjected to different stresses: 5% mild and 25% aggressive, at 1 Hz for 24 h. Immunofluorescence assays were used to estimate troponin I, CD105, SGLT1/2, eNOSS633, and ERK1/2T202/Y204 levels was performed for 5% (mild), and 25% elongation for 24 h. AMI (+) serum showed increased TGFβ1 and CD105 compared to AMI (-) patients. In consistent, troponin I, CD105, SGLT1/2, eNOSS633 and ERK1/2T202/Y204 were upregulated after 25% of 24 h cyclic stretch. Dapagliflozin addition caused SGLT2 inhibition, which significantly decreased troponin I, CD105, SGLT1/2, eNOSS633, and ERK1/2T202/Y204 under 25% cyclic stretching. In summary, SGLT2 may have sensed mechanical stretch in a way similar to cardiac overloading as in vivo. By blocking SGLT2 in stretched cardiomyocytes, the AMI biomarkers (CD105, troponin I and P-ERK) were decreased, potentially to rescue eNOS production to maintain normal cellular function. This discovery of CD105 and SGLT2 increase in mechanically stretched cardiomyocytes suggests that SGLT2 may conceive a novel role in direct or indirect sensing of mechanical stretch, prompting the possibility of an in vitro cardiac overloaded cell model, an alternative to animal heart model.

3D Aligned Nanofiber Scaffold Fabrication with Trench-Guided Electrospinning for Cardiac Tissue Engineering

Constructing three-dimensional (3D) aligned nanofiber scaffolds is significant for the development of cardiac tissue engineering, which is promising in the field of drug discovery and disease mechanism study. However, the current nanofiber scaffold preparation strategy, which mainly includes manual assembly and hybrid 3D printing, faces the challenge of integrated fabrication of morphology-controllable nanofibers due to its cross-scale structural feature. In this research, a trench-guided electrospinning (ES) strategy was proposed to directly fabricate 3D aligned nanofiber scaffolds with alternative ES and a direct ink writing (DIW) process. The electric field effect of DIW poly(dimethylsiloxane) (PDMS) side walls on guiding whipping ES nanofibers was investigated to construct trench design rules. It was found that the width/height ratio of trenches greatly affected the nanofiber alignment, and the trench width/height ratio of 1.5 provided the nanofiber alignment degree over 60%. As a proof of principle, 3D nanofiber scaffolds with controllable porosity (60-80%) and alignment (30-60%) were fabricated. The effect of the scaffolds was verified by culturing human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), which resulted in the uniform 3D distribution of aligned hiPSC-CMs with ∼1000 μm thickness. Therefore, this printing strategy shows great potential for the efficient engineered tissue construction.

Advances in ion channel high throughput screening: where are we in 2023?

INTRODUCTION

Automated Patch Clamp (APC) technology has become an integral element in ion channel research, drug discovery and development pipelines to overcome the use of the highly time-consuming manual patch clamp (MPC) procedures. This automated technology offers increased throughput and promises a new model in obtaining ion channel recordings, which has significant relevance to the development of novel therapies and safety profiling of candidate therapeutic compounds.

AREAS COVERED

This article reviews the recent innovations in APC technology, including platforms, and highlights how they have facilitated usage in both industry and academia. The review also provides an overview of the ion channel research endeavors and how APC platforms have contributed to the understanding of ion channel research, pharmacological tools and therapeutics. Furthermore, the authors provide their opinion on the challenges and goals for APC technology going forward to accelerate academic research and drug discovery across a host of therapeutic areas.

EXPERT OPINION

It is clear that APC technology has progressed drug discovery programs, specifically in the field of neuroscience and cardiovascular research. The challenge for the future is to keep pace with fundamental research and improve translation of the large datasets obtained.

Harnessing human genetics and stem cells for precision cardiovascular medicine

Human induced pluripotent stem cell (iPSC) platforms are valuable for biomedical and pharmaceutical research by providing tissue-specific human cells that retain patients' genetic integrity and display disease phenotypes in a dish. Looking forward, combining iPSC phenotyping platforms with genomic and screening technologies will continue to pave new directions for precision medicine, including genetic prediction, visualization, and treatment of heart disease. This review summarizes the recent use of iPSC technology to unpack the influence of genetic variants in cardiovascular pathology. We focus on various state-of-the-art genomic tools for cardiovascular therapies-including the expansion of genetic toolkits for molecular interrogation, in vitro population studies, and function-based drug screening-and their current applications in patient- and genome-edited iPSC platforms that are heralding new avenues for cardiovascular research.

Far-red and sensitive sensor for monitoring real time H2O2 dynamics with subcellular resolution and in multi-parametric imaging applications

H2O2 is a key oxidant in mammalian biology and a pleiotropic signaling molecule at the physiological level, and its excessive accumulation in conjunction with decreased cellular reduction capacity is often found to be a common pathological marker. Here, we present a red fluorescent Genetically Encoded H2O2 Indicator (GEHI) allowing versatile optogenetic dissection of redox biology. Our new GEHI, oROS-HT, is a chemigenetic sensor utilizing a HaloTag and Janelia Fluor (JF) rhodamine dye as fluorescent reporters. We developed oROS-HT through a structure-guided approach aided by classic protein structures and recent protein structure prediction tools. Optimized with JF635, oROS-HT is a sensor with 635 nm excitation and 650 nm emission peaks, allowing it to retain its brightness while monitoring intracellular H2O2 dynamics. Furthermore, it enables multi-color imaging in combination with blue-green fluorescent sensors for orthogonal analytes and low auto-fluorescence interference in biological tissues. Other advantages of oROS-HT over alternative GEHIs are its fast kinetics, oxygen-independent maturation, low pH sensitivity, lack of photo-artifact, and lack of intracellular aggregation. Here, we demonstrated efficient subcellular targeting and how oROS-HT can map inter and intracellular H2O2 diffusion at subcellular resolution. Lastly, we used oROS-HT with the green fluorescent calcium indicator Fluo-4 to investigate the transient effect of the anti-inflammatory agent auranofin on cellular redox physiology and calcium levels via multi-parametric, dual-color imaging.

Simulated microgravity improves maturation of cardiomyocytes derived from human induced pluripotent stem cells

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) possess tremendous potential for basic research and translational application. However, these cells structurally and functionally resemble fetal cardiomyocytes, which is a major limitation of these cells. Microgravity can significantly alter cell behavior and function. Here we investigated the effect of simulated microgravity on hiPSC-CM maturation. Following culture under simulated microgravity in a random positioning machine for 7 days, 3D hiPSC-CMs had increased mitochondrial content as detected by a mitochondrial protein and mitochondrial DNA to nuclear DNA ratio. The cells also had increased mitochondrial membrane potential. Consistently, simulated microgravity increased mitochondrial respiration in 3D hiPSC-CMs, as indicated by higher levels of maximal respiration and ATP content, suggesting improved metabolic maturation in simulated microgravity cultures compared with cultures under normal gravity. Cells from simulated microgravity cultures also had improved Ca2+ transient parameters, a functional characteristic of more mature cardiomyocytes. In addition, these cells had improved structural properties associated with more mature cardiomyocytes, including increased sarcomere length, z-disc length, nuclear diameter, and nuclear eccentricity. These findings indicate that microgravity enhances the maturation of hiPSC-CMs at the structural, metabolic, and functional levels.

A data-driven computational model for engineered cardiac microtissues

Engineered heart tissues (EHTs) present a potential solution to some of the current challenges in the treatment of heart disease; however, the development of mature, adult-like cardiac tissues remains elusive. Mechanical stimuli have been observed to improve whole-tissue function and cardiomyocyte (CM) maturation, although our ability to fully utilize these mechanisms is hampered, in part, by our incomplete understanding of the mechanobiology of EHTs. In this work, we leverage experimental data, produced by a mechanically tunable experimental setup, to introduce a tissue-specific computational modeling pipeline of EHTs. Our new modeling pipeline generates simulated, image-based EHTs, capturing ECM and myofibrillar structure as well as functional parameters estimated directly from experimental data. This approach enables the unique estimation of EHT function by data-based estimation of CM active stresses. We use this experimental and modeling pipeline to study different mechanical environments, where we contrast the force output of the tissue with the computed active stress of CMs. We show that the significant differences in measured experimental forces can largely be explained by the levels of myofibril formation achieved by the CMs in the distinct mechanical environments, with active stress showing more muted variations across conditions. The presented model also enables us to dissect the relative contributions of myofibrils and extracellular matrix to tissue force output, a task difficult to address experimentally. These results highlight the importance of tissue-specific modeling to augment EHT experiments, providing deeper insights into the mechanobiology driving EHT function. STATEMENT OF SIGNIFICANCE: Engineered heart tissues (EHTs) have the potential to revolutionize the way heart disease is treated. However, developing mature cardiomyocytes (CM) in these tissues remains a challenge due, in part, to our incomplete understanding of the fundamental biomechanical mechanisms that drive EHT development. This work integrates the experimental data of an EHT platform developed to study the influence of mechanics in CM maturation with computational biomechanical models. This approach is used to augment conclusions obtained in-vitro - by measuring quantities such as cell stress and strain - and to dissect the relevance of each component in the whole tissue performance. Our results show how a combination of specialized in-silico and in-vitro approaches can help us better understand the mechanobiology of EHTs.

Activation of AMPK promotes cardiac differentiation by stimulating the autophagy pathway

Autophagy, a critical catabolic process for cell survival against different types of stress, has a role in the differentiation of various cells, such as cardiomyocytes. Adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) is an energy-sensing protein kinase involved in the regulation of autophagy. In addition to its direct role in regulating autophagy, AMPK can also influence other cellular processes by regulating mitochondrial function, posttranslational acetylation, cardiomyocyte metabolism, mitochondrial autophagy, endoplasmic reticulum stress, and apoptosis. As AMPK is involved in the control of various cellular processes, it can influence the health and survival of cardiomyocytes. This study investigated the effects of an AMPK inducer (Metformin) and an autophagy inhibitor (Hydroxychloroquine) on the differentiation of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs). The results showed that autophagy was upregulated during cardiac differentiation. Furthermore, AMPK activation increased the expression of CM-specific markers in hPSC-CMs. Additionally, autophagy inhibition impaired cardiomyocyte differentiation by targeting autophagosome-lysosome fusion. These results indicate the significance of autophagy in cardiomyocyte differentiation. In conclusion, AMPK might be a promising target for the regulation of cardiomyocyte generation by in vitro differentiation of pluripotent stem cells.

Comparing the signaling and transcriptome profiling landscapes of human iPSC-derived and primary rat neonatal cardiomyocytes

The inaccessibility of human cardiomyocytes significantly hindered years of cardiovascular research efforts. To overcome these limitations, non-human cell sources were used as proxies to study heart function and associated diseases. Rodent models became increasingly acceptable surrogates to model the human heart either in vivo or through in vitro cultures. More recently, due to concerns regarding animal to human translation, including cross-species differences, the use of human iPSC-derived cardiomyocytes presented a renewed opportunity. Here, we conducted a comparative study, assessing cellular signaling through cardiac G protein-coupled receptors (GPCRs) in rat neonatal cardiomyocytes (RNCMs) and human induced pluripotent stem cell-derived cardiomyocytes. Genetically encoded biosensors were used to explore GPCR-mediated nuclear protein kinase A (PKA) and extracellular signal-regulated kinase 1/ 2 (ERK1/2) activities in both cardiomyocyte populations. To increase data granularity, a single-cell analytical approach was conducted. Using automated high content microscopy, our analyses of nuclear PKA and ERK_1/2 signaling revealed distinct response clusters in rat and human cardiomyocytes. In line with this, bulk RNA-seq revealed key differences in the expression patterns of GPCRs, G proteins and downstream effector expression levels. Our study demonstrates that human stem cell-derived models of the cardiomyocyte offer distinct advantages for understanding cellular signaling in the heart.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization

Rationale

Human pluripotent stem cell-derived CMs (iPSC-CMs) are a valuable tool for disease modeling, cell therapy and to reconstruct the CM maturation process and identify, characterize factors that regulate maturation. The transition from immature fetal to adult CM entails coordinated regulation of the mature gene programming, which is characterized by the induction of myofilament and OXPHOS gene expression among others. Recent studies in Drosophila , C. elegans, and C2C12 myoblast cell lines have implicated the histone H3K4me3 demethylase KDM5 and its homologs, as a potential regulator of developmental gene program and mitochondrial function. We speculated that KDM5 may potentiate the maturation of iPSC-CMs by targeting a conserved epigenetic program that encompass mitochondrial OXPHOS and other CM specific maturation genes.

Objectives

The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

Methods and Results

Immunoblot analysis revealed that KDM5A, B, and C expression was progressively downregulated in postnatal cardiomyocytes and absent in adult hearts and CMs. Additionally, KDM5 proteins were found to be persistently expressed in iPSC-CMs up to 60 days after the onset of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor-resulted in differential regulation of 2,372 genes including upregulation of Fatty acid oxidation (FAO), OXPHOS, and myogenic gene programs in iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the CUT&RUN assay revealed enriched H3K4me3 peaks at the promoter regions of FAO, OXPHOS, and sarcomere genes. Consistent with the chromatin and gene expression data, KDM5 inhibition led to increased expression of multiple sarcomere proteins, enhanced myofibrillar organization and improved calcium handling. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene, which is known to regulate OXPHOS and cardiomyocyte maturation, and resulted in its increased RNA and protein levels. Finally, KDM5 inhibition increased baseline, peak, and spare oxygen consumption rates in iPSC-CMs.

Conclusions

KDM5 regulates the maturation of iPSC-CMs by epigenetically regulating the expression of ESRRA, OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

PAPP-A-Specific IGFBP-4 Proteolysis in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

The insulin-like growth factors IGF-I and IGF-II-as well as their binding proteins (IGFBPs), which regulate their bioavailability-are involved in many pathological and physiological processes in cardiac tissue. Pregnancy-associated plasma protein A (PAPP-A) is a metalloprotease that preferentially cleaves IGFBP-4, releasing IGF and activating its biological activity. Previous studies have shown that PAPP-A-specific IGFBP-4 proteolysis is involved in the pathogenesis of cardiovascular diseases, such as ischemia, heart failure, and acute coronary syndrome. However, it remains unclear whether PAPP-A-specific IGFBP-4 proteolysis participates in human normal cardiomyocytes. Here, we report PAPP-A-specific IGFBP-4 proteolysis occurring in human cardiomyocytes derived from two independent induced pluripotent cell lines (hiPSC-CMs), detected both on the cell surface and in the cell secretome. PAPP-A was measured by fluoroimmune analysis (FIA) in a conditioned medium of hiPSC-CMs and was detected in concentrations of up to 4.3 ± 1.33 ng/mL and 3.8 ± 1.1 ng/mL. The level of PAPP-A-specific IGFBP-4 proteolysis was determined as the concentration of NT-IGFBP-4 proteolytic fragments using FIA for a proteolytic neo-epitope-specific assay. We showed that PAPP-A-specific IGFBP-4 proteolysis is IGF-dependent and inhibited by EDTA and 1,10-phenanthroline. Therefore, it may be concluded that PAPP-A-specific IGFBP-4 proteolysis functions in human normal cardiomyocytes, and hiPSC-CMs contain membrane-bound and secreted forms of proteolytically active PAPP-A.

Microfluidic Liver-on-a-Chip for Preclinical Drug Discovery

Drug discovery is an expensive, long, and complex process, usually with a high degree of uncertainty. In order to improve the efficiency of drug development, effective methods are demanded to screen lead molecules and eliminate toxic compounds in the preclinical pipeline. Drug metabolism is crucial in determining the efficacy and potential side effects, mainly in the liver. Recently, the liver-on-a-chip (LoC) platform based on microfluidic technology has attracted widespread attention. LoC systems can be applied to predict drug metabolism and hepatotoxicity or to investigate PK/PD (pharmacokinetics/pharmacodynamics) performance when combined with other artificial organ-on-chips. This review discusses the liver physiological microenvironment simulated by LoC, especially the cell compositions and roles. We summarize the current methods of constructing LoC and the pharmacological and toxicological application of LoC in preclinical research. In conclusion, we also discussed the limitations of LoC in drug discovery and proposed a direction for improvement, which may provide an agenda for further research.

Administration of stem cells against cardiovascular diseases with a focus on molecular mechanisms: Current knowledge and prospects

Cardiovascular diseases (CVDs) are a serious global concern for public and human health. Despite the emergence of significant therapeutic advances, it is still the leading cause of death and disability worldwide. As a result, extensive efforts are underway to develop practical therapeutic approaches. Stem cell-based therapies could be considered a promising strategy for the treatment of CVDs. The efficacy of stem cell-based therapeutic approaches is demonstrated through recent laboratory and clinical studies due to their inherent regenerative properties, proliferative nature, and their capacity to differentiate into different cells such as cardiomyocytes. These properties could improve cardiovascular functioning leading to heart regeneration. The two most common types of stem cells with the potential to cure heart diseases are induced pluripotent stem cells (iPSCs) and mesenchymal stem cells (MSCs). Several studies have demonstrated the use, efficacy, and safety of MSC and iPSCs-based therapies for the treatment of CVDs. In this study, we explain the application of stem cells, especially iPSCs and MSCs, in the treatment of CVDs with a focus on cellular and molecular mechanisms and then discuss the advantages, disadvantages, and perspectives of using this technology in the treatment of these diseases.

A review on qualifications and cost effectiveness of induced pluripotent stem cells (IPSCs)-induced cardiomyocytes in drug screening tests

Human induced pluripotent stem cells (hIPSCs) have initiated a higher degree of successes in disease modelling, preclinical evaluation of drug therapy and pharmaco-toxicological testing. Since the discovery of iPSCs in 2006, many advanced techniques have been introduced to differentiate iPSCs to cardiomyocytes, which have been progressively improved. The disease models from iPSC-induced cardiomyocytes (iPSC-CM) have been successfully helping to study a variety of cardiac diseases such as long QT syndrome, drug-induced long QT, different cardiomyopathies related to mutations in mitochondria or desmosomal proteins and other rare genetic diseases. IPSC-CMs have also been used to screen the role of chemicals in cardiovascular drug discovery and individualisation of drug dosages. In this review, the quality of current procedures for characterisation and maturation of iPSC-CM lines will be discussed. Also, we will focus on time efficiency and cost of standard differentiation methods after reprogramming.

iPSC-Derived Airway Epithelial Cells: Progress, Promise, and Challenges

Induced pluripotent stem cells (iPSCs) generated from somatic cell sources are pluripotent and capable of indefinite expansion in vitro. They provide an unlimited source of cells that can be differentiated into lung progenitor cells for potential clinical use in pulmonary regenerative medicine. This review gives a comprehensive overview of recent progress toward the use of iPSCs to generate proximal and distal airway epithelial cells and mix lung organoids. Furthermore, their potential applications and future challenges for the field are discussed, with a focus on the technological hurdles that must be cleared before stem cell therapeutics can be used for clinical treatment.

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.

Culture impact on the transcriptomic programs of primary and iPSC-derived human alveolar type 2 cells

Dysfunction of alveolar epithelial type 2 cells (AEC2s), the facultative progenitors of lung alveoli, is implicated in pulmonary disease pathogenesis, highlighting the importance of human in vitro models. However, AEC2-like cells in culture have yet to be directly compared to their in vivo counterparts at single-cell resolution. Here, we performed head-to-head comparisons among the transcriptomes of primary (1°) adult human AEC2s, their cultured progeny, and human induced pluripotent stem cell-derived AEC2s (iAEC2s). We found each population occupied a distinct transcriptomic space with cultured AEC2s (1° and iAEC2s) exhibiting similarities to and differences from freshly purified 1° cells. Across each cell type, we found an inverse relationship between proliferative and maturation states, with preculture 1° AEC2s being most quiescent/mature and iAEC2s being most proliferative/least mature. Cultures of either type of human AEC2s did not generate detectable alveolar type 1 cells in these defined conditions; however, a subset of iAEC2s cocultured with fibroblasts acquired a transitional cell state described in mice and humans to arise during fibrosis or following injury. Hence, we provide direct comparisons of the transcriptomic programs of 1° and engineered AEC2s, 2 in vitro models that can be harnessed to study human lung health and disease.

Modeling the human heart ex vivo-current possibilities and strive for future applications

The high organ specification of the human heart is inversely proportional to its functional recovery after damage. The discovery of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) has accelerated research in human heart regeneration and physiology. Nevertheless, due to the immaturity of iPSC-CMs, they are far from being an representative model of the adult heart physiology. Therefore, number of laboratories strive to obtain a heart tissues by engineering methods by structuring iPSC-CMs into complex and advanced platforms. By using the iPSC-CMs and arranging them in 3D cultures it is possible to obtain a human heart muscle with physiological capabilities potentially similar to the adult heart, while remaining in vitro. Here, we attempt to describe existing examples of heart muscle either in vitro or ex vivo models and discuss potential options for the further development of such structures. This will be a crucial step for ultimate derivation of complete heart tissue-mimicking organs and their future use in drug development, therapeutic approaches testing, pre-clinical studies, and clinical applications. This review particularly aims to compile available models of advanced human heart tissue for scientists considering which model would best fit their research needs.

Cardiac ultrastructure inspired matrix induces advanced metabolic and functional maturation of differentiated human cardiomyocytes

The vast potential of human induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) in preclinical models of cardiac pathologies, precision medicine, and drug screening remains to be fully realized because hiPSC-CMs are immature without adult-like characteristics. Here, we present a method to accelerate hiPSC-CM maturation on a substrate, cardiac mimetic matrix (CMM), mimicking adult human heart matrix ligand chemistry, rigidity, and submicron ultrastructure, which synergistically mature hiPSC-CMs rapidly within 30 days. hiPSC-CMs matured on CMM exhibit systemic transcriptomic maturation toward an adult heart state, are aligned with high strain energy, metabolically rely on oxidative phosphorylation and fatty acid oxidation, and display enhanced redox handling capability, efficient calcium handling, and electrophysiological features of ventricular myocytes. Endothelin-1-induced pathological hypertrophy is mitigated on CMM, highlighting the role of a native cardiac microenvironment in withstanding hypertrophy progression. CMM is a convenient model for accelerated development of ventricular myocytes manifesting highly specialized cardiac-specific functions.

Human Induced Pluripotent Stem Cells for Studying Mitochondrial Diseases in the Heart

Mitochondrial dysfunction is known to contribute to a range of diseases, and primary mitochondrial defects strongly impact high-energy organs such as the heart. Platforms for high-throughput and human-relevant assessment of mitochondrial diseases are currently lacking, hindering the development of targeted therapies. In the past decade, human induced pluripotent stem cells (iPSCs) have become a promising technology for drug discovery in basic and clinical research. In particular, human iPSC-derived cardiomyocytes (iPSC-CMs) offer a unique tool to study a wide range of mitochondrial functions and possess the potential to become a key translational asset for mitochondrial drug development. This review summarizes mitochondrial functions and recent therapeutic discoveries, advancements, and limitations of using iPSC-CMs to study mitochondrial diseases of the heart with an emphasis on cardiac applications.

Modeling hypertrophic cardiomyopathy with human cardiomyocytes derived from induced pluripotent stem cells

One of the obstacles in studying the pathogenesis of hypertrophic cardiomyopathy (HCM) is the poor availability of myocardial tissue samples at the early stages of disease development. This has been addressed by the advent of induced pluripotent stem cells (iPSCs), which allow us to differentiate patient-derived iPSCs into cardiomyocytes (iPSC-CMs) in vitro. In this review, we summarize different approaches to establishing iPSC models and the application of genome editing techniques in iPSC. Because iPSC-CMs cultured at the present stage are immature in structure and function, researchers have attempted several methods to mature iPSC-CMs, such as prolonged culture duration, and mechanical and electrical stimulation. Currently, many researchers have established iPSC-CM models of HCM and employed diverse methods for performing measurements of cellular morphology, contractility, electrophysiological property, calcium handling, mitochondrial function, and metabolism. Here, we review published results in humans to date within the growing field of iPSC-CM models of HCM. Although there is no unified consensus, preliminary results suggest that this approach to modeling disease would provide important insights into our understanding of HCM pathogenesis and facilitate drug development and safety testing.

Interpenetrating polymer network hydrogels as bioactive scaffolds for tissue engineering

Tissue engineering, after decades of exciting progress and monumental breakthroughs, has yet to make a significant impact on patient health. It has become apparent that a dearth of biomaterial scaffolds that possess the material properties of human tissue while remaining bioactive and cytocompatible has been partly responsible for this lack of clinical translation. Herein, we propose the development of interpenetrating polymer network hydrogels as materials that can provide cells with an adhesive extracellular matrix-like 3D microenvironment while possessing the mechanical integrity to withstand physiological forces. These hydrogels can be synthesized from biologically-derived or synthetic polymers, the former polymer offering preservation of adhesion, degradability, and microstructure and the latter polymer offering tunability and superior mechanical properties. We review critical advances in the enhancement of mechanical strength, substrate-scale stiffness, electrical conductivity, and degradation in IPN hydrogels intended as bioactive scaffolds in the past five years. We also highlight the exciting incorporation of IPN hydrogels into state-of-the-art tissue engineering technologies, such as organ-on-a-chip and bioprinting platforms. These materials will be critical in the engineering of functional tissue for transplant, disease modeling, and drug screening.

Systematic transcriptomic and phenotypic characterization of human and murine cardiac myocyte cell lines and primary cardiomyocytes reveals serious limitations and low resemblances to adult cardiac phenotype

BACKGROUND

Cardiac cell lines and primary cells are widely used in cardiovascular research. Despite increasing number of publications using these models, comparative characterization of these cell lines has not been performed, therefore, their limitations are undetermined. We aimed to compare cardiac cell lines to primary cardiomyocytes and to mature cardiac tissues in a systematic manner.

METHODS AND RESULTS

Cardiac cell lines (H9C2, AC16, HL-1) were differentiated with widely used protocols. Left ventricular tissue, neonatal primary cardiomyocytes, and human induced pluripotent stem cell-derived cardiomyocytes served as reference tissue or cells. RNA expression of cardiac markers (e.g. Tnnt2, Ryr2) was markedly lower in cell lines compared to references. Differentiation induced increase in cardiac- and decrease in embryonic markers however, the overall transcriptomic profile and annotation to relevant biological processes showed consistently less pronounced cardiac phenotype in all cell lines in comparison to the corresponding references. Immunocytochemistry confirmed low expressions of structural protein sarcomeric alpha-actinin, troponin I and caveolin-3 in cell lines. Susceptibility of cell lines to sI/R injury in terms of viability as well as mitochondrial polarization differed from the primary cells irrespective of their degree of differentiation.

CONCLUSION

Expression patterns of cardiomyocyte markers and whole transcriptomic profile, as well as response to sI/R, and to hypertrophic stimuli indicate low-to-moderate similarity of cell lines to primary cells/cardiac tissues regardless their differentiation. Low resemblance of cell lines to mature adult cardiac tissue limits their potential use. Low translational value should be taken into account while choosing a particular cell line to model cardiomyocytes.

Cardiac Remodeling and Repair: Recent Approaches, Advancements, and Future Perspective

The limited ability of mammalian adult cardiomyocytes to proliferate following an injury to the heart, such as myocardial infarction, is a major factor that results in adverse fibrotic and myocardial remodeling that ultimately leads to heart failure. The continued high degree of heart failure-associated morbidity and lethality requires the special attention of researchers worldwide to develop efficient therapeutics for cardiac repair. Recently, various strategies and approaches have been developed and tested to extrinsically induce regeneration and restoration of the myocardium after cardiac injury have yielded encouraging results. Nevertheless, these interventions still lack adequate success to be used for clinical interventions. This review highlights and discusses both cell-based and cell-free therapeutic approaches as well as current advancements, major limitations, and future perspectives towards developing an efficient therapeutic method for cardiac repair.

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.

Analysis of the response of human iPSC-derived cardiomyocyte tissue to ICaL block. A combined in vitro and in silico approach

The high incidence of cardiac arrythmias underlines the need for the assessment of pharmacological therapies. In this field of drug efficacy, as in the field of drug safety highlighted by the Comprehensive in Vitro Proarrhythmia Assay initiative, new pillars for research have become crucial: firstly, the integration of in-silico experiments, and secondly the evaluation of fully integrated biological systems, such as human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). In this study, we therefore aimed to combine in-vitro experiments and in-silico simulations to evaluate the antiarrhythmic effect of L-type calcium current (I_CaL) block in hiPSC-CMs. For this, hiPSC-CM preparations were cultured and an equivalent virtual tissue was modeled. Re-entry patterns of electrical activation were induced and several biomarkers were obtained before and after I_CaL block. The virtual hiPSC-CM simulations were also reproduced using a tissue composed of adult ventricular cardiomyocytes (hAdultV-CMs). The analysis of phases, currents and safety factor for propagation showed an increased size of the re-entry core when I_CaL was blocked as a result of depressed cellular excitability. The bigger wavefront curvature yielded reductions of 12.2%, 6.9%, and 4.2% in the frequency of the re-entry for hiPSC-CM cultures, virtual hiPSC-CM, and hAdultV-CM tissues, respectively. Furthermore, I_CaL block led to a 47.8% shortening of the vulnerable window for re-entry in the virtual hiPSC-CM tissue and to re-entry vanishment in hAdultV-CM tissue. The consistent behavior between in-vitro and in-silico hiPSC-CMs and between in-silico hiPSC-CMs and hAdultV-CMs evidences that virtual hiPSC-CM tissues are suitable for assessing cardiac efficacy, as done in the present study through the analysis of I_CaL block.

Organ-on-chip applications in drug discovery: an end user perspective

Organ-on-chip (OoC) systems are in vitro microfluidic models that mimic the microstructures, functions and physiochemical environments of whole living organs more accurately than two-dimensional models. While still in their infancy, OoCs are expected to bring ground-breaking benefits to a myriad of applications, enabling more human-relevant candidate drug efficacy and toxicity studies, and providing greater insights into mechanisms of human disease. Here, we explore a selection of applications of OoC systems. The future directions and scope of implementing OoCs across the drug discovery process are also discussed.

A deep learning algorithm to translate and classify cardiac electrophysiology

The development of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) has been a critical in vitro advance in the study of patient-specific physiology, pathophysiology, and pharmacology. We designed a new deep learning multitask network approach intended to address the low throughput, high variability, and immature phenotype of the iPSC-CM platform. The rationale for combining translation and classification tasks is because the most likely application of the deep learning technology we describe here is to translate iPSC-CMs following application of a perturbation. The deep learning network was trained using simulated action potential (AP) data and applied to classify cells into the drug-free and drugged categories and to predict the impact of electrophysiological perturbation across the continuum of aging from the immature iPSC-CMs to the adult ventricular myocytes. The phase of the AP extremely sensitive to perturbation due to a steep rise of the membrane resistance was found to contain the key information required for successful network multitasking. We also demonstrated successful translation of both experimental and simulated iPSC-CM AP data validating our network by prediction of experimental drug-induced effects on adult cardiomyocyte APs by the latter.

Production of Cardiomyocytes by microRNA-Mediated Reprogramming in Optimized Reprogramming Media

There are currently no effective treatments to regenerate the heart after cardiac injury. Following cardiac injury, heart muscle cells, also known as cardiomyocytes, die in large numbers. The adult mammalian heart does not have the ability to replace these dead cardiomyocytes. In their place, fibroblasts invade the injury zone and generate a scar. The scar impairs cardiac function. An important approach to cardiac regeneration is direct cardiac reprogramming, whereby cardiac fibroblasts within the scar are directly converted into functional cardiomyocytes. Several laboratories have achieved direct cardiac reprogramming via overexpression of the cardiac transcription factors. In contrast, we utilize a combination of four miRNAs (miR-1, miR-133, miR-208, miR-499) that we call miR Combo. One common issue regarding direct cardiac reprogramming strategies is low efficiency. Recently, we have demonstrated that the efficiency of direct cardiac reprogramming is enhanced in the chemically defined reprogramming media.

Disease Modeling and Disease Gene Discovery in Cardiomyopathies: A Molecular Study of Induced Pluripotent Stem Cell Generated Cardiomyocytes

The in vitro modeling of cardiac development and cardiomyopathies in human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs) provides opportunities to aid the discovery of genetic, molecular, and developmental changes that are causal to, or influence, cardiomyopathies and related diseases. To better understand the functional and disease modeling potential of iPSC-differentiated CMs and to provide a proof of principle for large, epidemiological-scale disease gene discovery approaches into cardiomyopathies, well-characterized CMs, generated from validated iPSCs of 12 individuals who belong to four sibships, and one of whom reported a major adverse cardiac event (MACE), were analyzed by genome-wide mRNA sequencing. The generated CMs expressed CM-specific genes and were highly concordant in their total expressed transcriptome across the 12 samples (correlation coefficient at 95% CI =0.92 ± 0.02). The functional annotation and enrichment analysis of the 2116 genes that were significantly upregulated in CMs suggest that generated CMs have a transcriptomic and functional profile of immature atrial-like CMs; however, the CMs-upregulated transcriptome also showed high overlap and significant enrichment in primary cardiomyocyte (p-value = 4.36 × 10⁻⁹), primary heart tissue (p-value = 1.37 × 10⁻⁴¹) and cardiomyopathy (p-value = 1.13 × 10⁻²¹) associated gene sets. Modeling the effect of MACE in the generated CMs-upregulated transcriptome identified gene expression phenotypes consistent with the predisposition of the MACE-affected sibship to arrhythmia, prothrombotic, and atherosclerosis risk.

Cardiac Regeneration: the Heart of the Issue

Purpose of Review

The regenerative capacity of the heart is insufficient to compensate for the pathological loss of cardiomyocytes during a large injury, such as a myocardial infarction. Therapeutic options for patients after cardiac infarction are limited: treatment with drugs that only treat the symptoms or extraordinary measures, such as heart transplantation. Cell therapies offer a promising strategy for cardiac regeneration. In this brief review, the major issues in these areas are discussed, and possible directions for future research are indicated.

Recent Findings

Cardiac regeneration can be obtained by at least two strategies: the first is direct to generate an ex vivo functional myocardial tissue that replaces damaged tissue; the second approach aims to stimulate endogenous mechanisms of cardiac repair. However, current cell therapies are still hampered by poor translation into actual clinical applications.

Summary

In this scenario, recent advancements in cell biology and biomaterial-based technologies can play a key role to design effective therapeutic approaches.

Stem cell-based approaches in cardiac tissue engineering: controlling the microenvironment for autologous cells

Cardiovascular disease is one of the leading causes of mortality worldwide. Cardiac tissue engineering strategies focusing on biomaterial scaffolds incorporating cells and growth factors are emerging as highly promising for cardiac repair and regeneration. The use of stem cells within cardiac microengineered tissue constructs present an inherent ability to differentiate into cell types of the human heart. Stem cells derived from various tissues including bone marrow, dental pulp, adipose tissue and umbilical cord can be used for this purpose. Approaches ranging from stem cell injections, stem cell spheroids, cell encapsulation in a suitable hydrogel, use of prefabricated scaffold and bioprinting technology are at the forefront in the field of cardiac tissue engineering. The stem cell microenvironment plays a key role in the maintenance of stemness and/or differentiation into cardiac specific lineages. This review provides a detailed overview of the recent advances in microengineering of autologous stem cell-based tissue engineering platforms for the repair of damaged cardiac tissue. A particular emphasis is given to the roles played by the extracellular matrix (ECM) in regulating the physiological response of stem cells within cardiac tissue engineering platforms.

Investigation into the difference in mitochondrial-cytosolic calcium coupling between adult cardiomyocyte and hiPSC-CM using a novel multifunctional genetic probe

Ca2+ cycling plays a critical role in regulating cardiomyocyte (CM) function under both physiological and pathological conditions. Mitochondria have been implicated in Ca2+ handling in adult cardiomyocytes (ACMs). However, little is known about their role in the regulation of Ca2+ dynamics in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). In the present study, we developed a multifunctional genetically encoded Ca2+ probe capable of simultaneously measuring cytosolic and mitochondrial Ca2+ in real time. Using this novel probe, we determined and compared mitochondrial Ca2+ activity and the coupling with cytosolic Ca2+ dynamics in hiPSC-CMs and ACMs. Our data showed that while ACMs displayed a highly coordinated beat-by-beat response in mitochondrial Ca2+ in sync with cytosolic Ca2+, hiPSC-CMs showed high cell-wide variability in mitochondrial Ca2+ activity that is poorly coordinated with cytosolic Ca2+. We then revealed that mitochondrial-sarcoplasmic reticulum (SR) tethering, as well as the inter-mitochondrial network connection, is underdeveloped in hiPSC-CM compared to ACM, which may underlie the observed spatiotemporal decoupling between cytosolic and mitochondrial Ca2+ dynamics. Finally, we showed that knockdown of mitofusin-2 (Mfn2), a protein tethering mitochondria and SR, led to reduced cytosolic-mitochondrial Ca2+ coupling in ACMs, albeit to a lesser degree compared to hiPSC-CMs, suggesting that Mfn2 is a potential engineering target for improving mitochondrial-cytosolic Ca2+ coupling in hiPSC-CMs. Physiological relevance: The present study will advance our understanding of the role of mitochondria in Ca2+ handling and cycling in CMs, and guide the development of hiPSC-CMs for healing injured hearts.

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.

Clinical Trial in a Dish: Using Patient-Derived Induced Pluripotent Stem Cells to Identify Risks of Drug-Induced Cardiotoxicity

Drug-induced cardiotoxicity is a significant clinical issue, with many drugs in the market being labeled with warnings on cardiovascular adverse effects. Treatments are often prematurely halted when cardiotoxicity is observed, which limits their therapeutic potential. Moreover, cardiotoxicity is a major reason for abandonment during drug development, reducing available treatment options for diseases and creating a significant financial burden and disincentive for drug developers. Thus, it is important to minimize the cardiotoxic effects of medications that are in use or in development. To this end, identifying patients at a higher risk of developing cardiovascular adverse effects for the drug of interest may be an effective strategy. The discovery of human induced pluripotent stem cells has enabled researchers to generate relevant cell types that retain a patient's own genome and examine patient-specific disease mechanisms, paving the way for precision medicine. Combined with the rapid development of pharmacogenomic analysis, the ability of induced pluripotent stem cell-derivatives to recapitulate patient-specific drug responses provides a powerful platform to identify subsets of patients who are particularly vulnerable to drug-induced cardiotoxicity. In this review, we will discuss the current use of patient-specific induced pluripotent stem cells in identifying populations who are at risk to drug-induced cardiotoxicity and their potential applications in future precision medicine practice. Graphic Abstract: A graphic abstract is available for this article.

Engineering and Assessing Cardiac Tissue Complexity

Cardiac tissue engineering is very much in a current focus of regenerative medicine research as it represents a promising strategy for cardiac disease modelling, cardiotoxicity testing and cardiovascular repair. Advances in this field over the last two decades have enabled the generation of human engineered cardiac tissue constructs with progressively increased functional capabilities. However, reproducing tissue-like properties is still a pending issue, as constructs generated to date remain immature relative to native adult heart. Moreover, there is a high degree of heterogeneity in the methodologies used to assess the functionality and cardiac maturation state of engineered cardiac tissue constructs, which further complicates the comparison of constructs generated in different ways. Here, we present an overview of the general approaches developed to generate functional cardiac tissues, discussing the different cell sources, biomaterials, and types of engineering strategies utilized to date. Moreover, we discuss the main functional assays used to evaluate the cardiac maturation state of the constructs, both at the cellular and the tissue levels. We trust that researchers interested in developing engineered cardiac tissue constructs will find the information reviewed here useful. Furthermore, we believe that providing a unified framework for comparison will further the development of human engineered cardiac tissue constructs displaying the specific properties best suited for each particular application.

The Potential Properties of Natural Compounds in Cardiac Stem Cell Activation: Their Role in Myocardial Regeneration

Cardiovascular diseases (CVDs), which include congenital heart disease, rhythm disorders, subclinical atherosclerosis, coronary heart disease, and many other cardiac disorders, cause about 30% of deaths globally; representing one of the main health problems worldwide. Among CVDs, ischemic heart diseases (IHDs) are one of the major causes of morbidity and mortality in the world. The onset of IHDs is essentially due to an unbalance between the metabolic demands of the myocardium and its supply of oxygen and nutrients, coupled with a low regenerative capacity of the heart, which leads to great cardiomyocyte (CM) loss; promoting heart failure (HF) and myocardial infarction (MI). To date, the first strategy recommended to avoid IHDs is prevention in order to reduce the underlying risk factors. In the management of IHDs, traditional therapeutic options are widely used to improve symptoms, attenuate adverse cardiac remodeling, and reduce early mortality rate. However, there are no available treatments that aim to improve cardiac performance by replacing the irreversible damaged cardiomyocytes (CMs). Currently, heart transplantation is the only treatment being carried out for irreversibly damaged CMs. Hence, the discovery of new therapeutic options seems to be necessary. Interestingly, recent experimental evidence suggests that regenerative stem cell medicine could be a useful therapeutic approach to counteract cardiac damage and promote tissue regeneration. To this end, researchers are tasked with answering one main question: how can myocardial regeneration be stimulated? In this regard, natural compounds from plant extracts seem to play a particularly promising role. The present review will summarize the recent advances in our knowledge of stem cell therapy in the management of CVDs; focusing on the main properties and potential mechanisms of natural compounds in stimulating and activating stem cells for myocardial regeneration.

Purification of Pluripotent Stem Cell-Derived Cardiomyocytes Using CRISPR/Cas9-Mediated Integration of Fluorescent Reporters

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes have become critically important for the detailed study of cardiac development, disease modeling, and drug screening. However, directed differentiation of hiPSCs into cardiomyocytes often results in mixed populations of cardiomyocytes and other cell types, which may confound experiments that require pure populations of cardiomyocytes. Here, we detail the use of a CRISPR/Cas9 genome editing strategy to develop cardiomyocyte-specific reporters that allow for the isolation of hiPSC-derived cardiomyocytes and chamber-specific myocytes. Moreover, we describe a cardiac differentiation protocol to derive cardiomyocytes from hiPSCs, as well as a strategy to use fluorescence-activated cell sorting to isolate pure populations of fluorescently labeled cardiomyocytes for downstream applications.