Contractile Defect Caused by Mutation in MYBPC3 Revealed under Conditions Optimized for Human PSC-Cardiomyocyte Function

Automatic motion estimation with applications to hiPSC-CMs

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are an effective tool for studying cardiac function and disease, and hold promise for screening drug effects on human tissue. Understanding alterations in motion patterns within these cells is crucial for comprehending how the administration of a drug or the onset of a disease can impact the rhythm of the human heart. However, quantifying motion accurately and efficiently from optical measurements using microscopy is currently time consuming. In this work, we present a unified framework for performing motion analysis on a sequence of microscopically obtained images of tissues consisting of hiPSC-CMs. We provide validation of our developed software using a synthetic test case and show how it can be used to extract displacements and velocities in hiPSC-CM microtissues. Finally, we show how to apply the framework to quantify the effect of an inotropic compound. The described software system is distributed as a python package that is easy to install, well tested and can be integrated into any python workflow.

Enhancing Maturation and Translatability of Human Pluripotent Stem Cell-Derived Cardiomyocytes through a Novel Medium Containing Acetyl-CoA Carboxylase 2 Inhibitor

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) constitute an appealing tool for drug discovery, disease modeling, and cardiotoxicity screening. However, their physiological immaturity, resembling CMs in the late fetal stage, limits their utility. Herein, we have developed a novel, scalable cell culture medium designed to enhance the maturation of hPSC-CMs. This medium facilitates a metabolic shift towards fatty acid utilization and augments mitochondrial function by targeting Acetyl-CoA carboxylase 2 (ACC2) with a specific small molecule inhibitor. Our findings demonstrate that this maturation protocol significantly advances the metabolic, structural, molecular and functional maturity of hPSC-CMs at various stages of differentiation. Furthermore, it enables the creation of cardiac microtissues with superior structural integrity and contractile properties. Notably, hPSC-CMs cultured in this optimized maturation medium display increased accuracy in modeling a hypertrophic cardiac phenotype following acute endothelin-1 induction and show a strong correlation between in vitro and in vivo target engagement in drug screening efforts. This approach holds promise for improving the utility and translatability of hPSC-CMs in cardiac disease modeling and drug discovery.

Generation of induced pluripotent stem cells from an individual with early onset and severe hypertrophic cardiomyopathy linked to MYBPC3: c.772G > A mutation

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in the MYPBC3 gene, which encodes the cardiac myosin-binding protein C (cMyBP-C). Most pathogenic variants in MYPBC3 are either nonsense mutations or result in frameshifts, suggesting that the primary disease mechanism involves reduced functional cMyBP-C protein levels within sarcomeres. However, a subset of MYPBC3 variants are missense mutations, and the molecular mechanisms underlying their pathogenicity remain elusive. Upon in vitro differentiation into cardiomyocytes, induced pluripotent stem cells (iPSCs) derived from HCM patients represent a valuable resource for disease modeling. In this study, we generated two iPSC lines from peripheral blood mononuclear cells (PBMCs) of a female with early onset and severe HCM linked to the MYBPC3: c.772G > A variant. Although this variant was initially classified as a missense mutation, recent studies indicate that it interferes with splicing and results in a frameshift. The generated iPSC lines exhibit a normal karyotype and display hallmark characteristics of pluripotency, including the ability to undergo trilineage differentiation. These novel iPSCs expand the existing repertoire of MYPBC3-mutated cell lines, broadening the spectrum of resources for exploring how diverse mutations induce HCM. They additionally offer a platform to study potential secondary genetic elements contributing to the pronounced disease severity observed in this individual.

Micro-Engineered Heart Tissues On-Chip with Heterotypic Cell Composition Display Self-Organization and Improved Cardiac Function

Advanced in vitro models that recapitulate the structural organization and function of the human heart are highly needed for accurate disease modeling, more predictable drug screening, and safety pharmacology. Conventional 3D Engineered Heart Tissues (EHTs) lack heterotypic cell complexity and culture under flow, whereas microfluidic Heart-on-Chip (HoC) models in general lack the 3D configuration and accurate contractile readouts. In this study, an innovative and user-friendly HoC model is developed to overcome these limitations, by culturing human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs), endothelial (ECs)- and smooth muscle cells (SMCs), together with human cardiac fibroblasts (FBs), underflow, leading to self-organized miniaturized micro-EHTs (µEHTs) with a CM-EC interface reminiscent of the physiological capillary lining. µEHTs cultured under flow display enhanced contractile performance and conduction velocity. In addition, the presence of the EC layer altered drug responses in µEHT contraction. This observation suggests a potential barrier-like function of ECs, which may affect the availability of drugs to the CMs. These cardiac models with increased physiological complexity, will pave the way to screen for therapeutic targets and predict drug efficacy.

Independent compartmentalization of functional, metabolic, and transcriptional maturation of hiPSC-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) recapitulate numerous disease and drug response phenotypes, but cell immaturity may limit their accuracy and fidelity as a model system. Cell culture medium modification is a common method for enhancing maturation, yet prior studies have used complex media with little understanding of individual component contribution, which may compromise long-term hiPSC-CM viability. Here, we developed high-throughput methods to measure hiPSC-CM maturation, determined factors that enhanced viability, and then systematically assessed the contribution of individual maturation medium components. We developed a medium that is compatible with extended culture. We discovered that hiPSC-CM maturation can be sub-specified into electrophysiological/EC coupling, metabolism, and gene expression and that induction of these attributes is largely independent. In this work, we establish a defined baseline for future studies of cardiomyocyte maturation. Furthermore, we provide a selection of medium formulae, optimized for distinct applications and priorities, that promote measurable attributes of maturation.

Myosin inhibitor reverses hypertrophic cardiomyopathy in genotypically diverse pediatric iPSC-cardiomyocytes to mirror variant correction

Pathogenic variants in MYH7 and MYBPC3 account for the majority of hypertrophic cardiomyopathy (HCM). Targeted drugs like myosin ATPase inhibitors have not been evaluated in children. We generate patient and variant-corrected iPSC-cardiomyocytes (CMs) from pediatric HCM patients harboring single variants in MYH7 (V606M; R453C), MYBPC3 (G148R) or digenic variants (MYBPC3 P955fs, TNNI3 A157V). We also generate CMs harboring MYBPC3 mono- and biallelic variants using CRISPR editing of a healthy control. Compared with isogenic and healthy controls, variant-positive CMs show sarcomere disorganization, higher contractility, calcium transients, and ATPase activity. However, only MYH7 and biallelic MYBPC3 variant-positive CMs show stronger myosin-actin binding. Targeted myosin ATPase inhibitors show complete rescue of the phenotype in variant-positive CMs and in cardiac Biowires to mirror isogenic controls. The response is superior to verapamil or metoprolol. Myosin inhibitors can be effective in genotypically diverse HCM highlighting the need for myosin inhibitor drug trials in pediatric HCM.

Advances in Hypertrophic Cardiomyopathy Disease Modelling Using hiPSC-Derived Cardiomyocytes

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

A safety screening platform for individualized cardiotoxicity assessment

Cardiotoxicity remains a major cause of drug withdrawal, partially due to lacking predictability of animal models. Additionally, risk of cardiotoxicity following treatment of cancer patients is treatment limiting. It is unclear which patients will develop heart failure following therapy. Human pluripotent stem cell (hPSC)-derived cardiomyocytes present an unlimited cell source and may offer individualized solutions to this problem. We developed a platform to predict molecular and functional aspects of cardiotoxicity. Our platform can discriminate between the different cardiotoxic mechanisms of existing and novel anthracyclines Doxorubicin, Aclarubicin, and Amrubicin. Doxorubicin and Aclarubicin unlike Amrubicin substantially affected the transcriptome, mitochondrial membrane integrity, contractile force and transcription factor availability. Cardiomyocytes recovered fully within two or three weeks, corresponding to the intermittent clinical treatment regimen. Our system permits the study of hPSC-cardiomyocyte recovery and the effects of accumulated dose after multiple dosing, allowing individualized cardiotoxicity evaluation, which effects millions of cancer patients treated annually.

Engineered cocultures of iPSC-derived atrial cardiomyocytes and atrial fibroblasts for modeling atrial fibrillation

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia treatable with antiarrhythmic drugs; however, patient responses remain highly variable. Human induced pluripotent stem cell-derived atrial cardiomyocytes (iPSC-aCMs) are useful for discovering precision therapeutics, but current platforms yield phenotypically immature cells and are not easily scalable for high-throughput screening. Here, primary adult atrial, but not ventricular, fibroblasts induced greater functional iPSC-aCM maturation, partly through connexin-40 and ephrin-B1 signaling. We developed a protein patterning process within multiwell plates to engineer patterned iPSC-aCM and atrial fibroblast coculture (PC) that significantly enhanced iPSC-aCM structural, electrical, contractile, and metabolic maturation for 6+ weeks compared to conventional mono-/coculture. PC displayed greater sensitivity for detecting drug efficacy than monoculture and enabled the modeling and pharmacological or gene editing treatment of an AF-like electrophysiological phenotype due to a mutated sodium channel. Overall, PC is useful for elucidating cell signaling in the atria, drug screening, and modeling AF.

Critical contribution of mitochondria in the development of cardiomyopathy linked to desmin mutation

BACKGROUND

Beyond the observed alterations in cellular structure and mitochondria, the mechanisms linking rare genetic mutations to the development of heart failure in patients affected by desmin mutations remain unclear due in part, to the lack of relevant human cardiomyocyte models.

METHODS

To shed light on the role of mitochondria in these mechanisms, we investigated cardiomyocytes derived from human induced pluripotent stem cells carrying the heterozygous DESE439K mutation that were either isolated from a patient or generated by gene editing. To increase physiological relevance, cardiomyocytes were either cultured on an anisotropic micropatterned surface to obtain elongated and aligned cardiomyocytes, or as a cardiac spheroid to create a micro-tissue. Moreover, when applicable, results from cardiomyocytes were confirmed with heart biopsies of suddenly died patient of the same family harboring DESE439K mutation, and post-mortem heart samples from five control healthy donors.

RESULTS

The heterozygous DESE439K mutation leads to dramatic changes in the overall cytoarchitecture of cardiomyocytes, including cell size and morphology. Most importantly, mutant cardiomyocytes display altered mitochondrial architecture, mitochondrial respiratory capacity and metabolic activity reminiscent of defects observed in patient's heart tissue. Finally, to challenge the pathological mechanism, we transferred normal mitochondria inside the mutant cardiomyocytes and demonstrated that this treatment was able to restore mitochondrial and contractile functions of cardiomyocytes.

CONCLUSIONS

This work highlights the deleterious effects of DESE439K mutation, demonstrates the crucial role of mitochondrial abnormalities in the pathophysiology of desmin-related cardiomyopathy, and opens up new potential therapeutic perspectives for this disease.

Nongenetic Optical Modulation of Pluripotent Stem Cells Derived Cardiomyocytes Function in the Red Spectral Range

Optical stimulation in the red/near infrared range recently gained increasing interest, as a not-invasive tool to control cardiac cell activity and repair in disease conditions. Translation of this approach to therapy is hampered by scarce efficacy and selectivity. The use of smart biocompatible materials, capable to act as local, NIR-sensitive interfaces with cardiac cells, may represent a valuable solution, capable to overcome these limitations. In this work, a far red-responsive conjugated polymer, namely poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]] (PCPDTBT) is proposed for the realization of photoactive interfaces with cardiomyocytes derived from pluripotent stem cells (hPSC-CMs). Optical excitation of the polymer turns into effective ionic and electrical modulation of hPSC-CMs, in particular by fastening Ca2+ dynamics, inducing action potential shortening, accelerating the spontaneous beating frequency. The involvement in the phototransduction pathway of Sarco-Endoplasmic Reticulum Calcium ATPase (SERCA) and Na+ /Ca2+ exchanger (NCX) is proven by pharmacological assays and is correlated with physical/chemical processes occurring at the polymer surface upon photoexcitation. Very interestingly, an antiarrhythmogenic effect, unequivocally triggered by polymer photoexcitation, is also observed. Overall, red-light excitation of conjugated polymers may represent an unprecedented opportunity for fine control of hPSC-CMs functionality and can be considered as a perspective, noninvasive approach to treat arrhythmias.

Advancing Treatments for Feline Hypertrophic Cardiomyopathy: The Role of Animal Models and Targeted Therapeutics

Feline HCM is the most common cardiovascular disease in cats, leading to devastating outcomes, including congestive heart failure (CHF), arterial thromboembolism (ATE), and sudden death. Evidence demonstrating long-term survival benefit with currently available therapies is lacking. Therefore, it is imperative to explore intricate genetic and molecular pathways that drive HCM pathophysiology to inspire the development of novel therapeutics. Several clinical trials exploring new drug therapies are currently underway, including those investigating small molecule inhibitors and rapamycin. This article outlines the key work performed using cellular and animal models that has led to and continues to guide the development of new innovative therapeutic strategies.

Mass production of lumenogenic human embryoid bodies and functional cardiospheres using in-air-generated microcapsules

Organoids are engineered 3D miniature tissues that are defined by their organ-like structures, which drive a fundamental understanding of human development. However, current organoid generation methods are associated with low production throughputs and poor control over size and function including due to organoid merging, which limits their clinical and industrial translation. Here, we present a microfluidic platform for the mass production of lumenogenic embryoid bodies and functional cardiospheres. Specifically, we apply triple-jet in-air microfluidics for the ultra-high-throughput generation of hollow, thin-shelled, hydrogel microcapsules that can act as spheroid-forming bioreactors in a cytocompatible, oil-free, surfactant-free, and size-controlled manner. Uniquely, we show that microcapsules generated by in-air microfluidics provide a lumenogenic microenvironment with near 100% efficient cavitation of spheroids. We demonstrate that upon chemical stimulation, human pluripotent stem cell-derived spheroids undergo cardiomyogenic differentiation, effectively resulting in the mass production of homogeneous and functional cardiospheres that are responsive to external electrical stimulation. These findings drive clinical and industrial adaption of stem cell technology in tissue engineering and drug testing.

An Unbiased Screen Identified the Hsp70-BAG3 Complex as a Regulator of Myosin-Binding Protein C3

Variants in the gene myosin-binding protein C3 (MYBPC3) account for approximately 50% of familial hypertrophic cardiomyopathy (HCM), leading to reduced levels of myosin-binding protein C3 (MyBP-C), the protein product made by gene MYBPC3. Elucidation of the pathways that regulate MyBP-C protein homeostasis could uncover new therapeutic strategies. Toward this goal, we screened a library of 2,426 bioactive compounds and identified JG98, an allosteric modulator of heat shock protein 70 that inhibits interaction with Bcl-2-associated athanogene (BAG) domain co-chaperones. JG98 reduces MyBP-C protein levels. Furthermore, genetic reduction of BAG3 phenocopies treatment with JG-98 by reducing MYBP-C protein levels.. Thus, an unbiased compound screen identified the heat shock protein 70-BAG3 complex as a regulator of MyBP-C stability.

Speckle-Tracking Strain Analysis for Mapping Spatiotemporal Contractility of Induced Pluripotent Stem Cell (iPSC)-Derived Cardiomyocytes

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) hold tremendous potential for cardiovascular disease modeling, drug screening, personalized medicine, and pathophysiology studies. The availability of a robust protocol and functional assay for studying phenotypic behavior of hiPSC-CMs is essential for establishing an in vitro disease model. Many heart diseases manifest due to changes in the mechanical strain of cardiac tissue. Therefore, non-invasive evaluation of the contractility properties of hiPSC-CMs remains crucial to gain an insight into the pathogenesis of cardiac diseases. Speckle tracking-based strain analysis is an efficient non-invasive method that uses video microscopy and image analysis of beating hiPSC-CMs for quantitative evaluation of mechanical contractility properties. This article presents step-by-step protocols for extracting quantitative contractility properties of an hiPSC-CM system obtained from five members of a family, of whom three were affected by DiGeorge syndrome, using speckle tracking-based strain analysis. The hiPSCs from the family members were differentiated and purified into hiPSC-CMs using metabolic selection. Time-lapse images of hiPSC-CMs were acquired using high-spatial-resolution and high-time-resolution phase-contrast video microscopy. Speckled images were characterized by evaluating the cross-correlation coefficient, speckle size, speckle contrast, and speckle quality of the images. The optimum parameters of the speckle tracking algorithm were determined by performing sensitivity analysis concerning computation time, effective mapping area, average contraction velocity, and strain. Furthermore, the hiPSC-CM response to adrenaline was evaluated to validate the sensitivity of the strain analysis algorithm. Then, we applied speckle tracking-based strain analysis to characterize the dynamic behavior of patient-specific hiPSC-CMs from the family members affected/unaffected by DiGeorge syndrome. Here, we report an efficient and manipulation-free method to analyze the contraction displacement vector and velocity field, contraction-relaxation strain rate, and contractile cycles. Implementation of this method allows for quantitative analysis of the contractile phenotype characteristics of hiPSC-CMs to distinguish possible cardiac manifestation of DiGeorge syndrome. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Differentiation of iPSCs into iPSC-derived cardiomyocytes (iPSC-CMs) and metabolic selection of differentiated iPSC-CMs Support Protocol 1: Culture, maintenance, and expansion of human iPSCs Support Protocol 2: Immunohistochemistry of iPSC-CMs Basic Protocol 2: Time-lapse speckle imaging of iPSC-CMs and speckle quality characterization Support Protocol 3: Enhancement of local contrast of videos by applying contrast limited adaptive histogram equalization (CLAHE) to all frames Support Protocol 4: Evaluation of average speckle size Support Protocol 5: Evaluation of average speckle contrast Support Protocol 6: Determination of relative peak height, Pc(x), of consecutive images acquired from video microscopy of iPSC-CMs Basic Protocol 3: Speckle tracking-based analysis of beating iPSC-CMs Support Protocol 7: Validation of sensitivity of the speckle tracking analysis for mapping the contractility of iPSC-CMs Basic Protocol 4: Data extraction, visualization, and mapping of contractile cycles of iPSC-CMs.

Biomechanical Impact of Pathogenic MYBPC3 Truncation Variant Revealed by Dynamically Tuning In Vitro Afterload

Engineered cardiac microtissues were fabricated using pluripotent stem cells with a hypertrophic cardiomyopathy associated c. 2827 C>T; p.R943x truncation variant in myosin binding protein C (MYBPC3+/-). Microtissues were mounted on iron-incorporated cantilevers, allowing manipulations of cantilever stiffness using magnets, enabling examination of how in vitro afterload affects contractility. MYPBC3+/- microtissues developed augmented force, work, and power when cultured with increased in vitro afterload when compared with isogenic controls in which the MYBPC3 mutation had been corrected (MYPBC3+/+(ed)), but weaker contractility when cultured with lower in vitro afterload. After initial tissue maturation, MYPBC3+/- CMTs exhibited increased force, work, and power in response to both acute and sustained increases of in vitro afterload. Together, these studies demonstrate that extrinsic biomechanical challenges potentiate genetically-driven intrinsic increases in contractility that may contribute to clinical disease progression in patients with HCM due to hypercontractile MYBPC3 variants.

iPSC-Based Modeling of Variable Clinical Presentation in Hypertrophic Cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiac disease and a frequent cause of heart failure and sudden cardiac death. Our understanding of the genetic bases and pathogenic mechanisms underlying HCM has improved significantly in the recent past, but the combined effect of various pathogenic gene variants and the influence of genetic modifiers in disease manifestation are very poorly understood. Here, we set out to investigate genotype-phenotype relationships in 2 siblings with an extensive family history of HCM, both carrying a pathogenic truncating variant in the MYBPC3 gene (p.Lys600Asnfs*2), but who exhibited highly divergent clinical manifestations.

METHODS

We used a combination of induced pluripotent stem cell (iPSC)-based disease modeling and CRISPR (clustered regularly interspersed short palindromic repeats)/Cas9 (CRISPR-associated protein 9)-mediated genome editing to generate patient-specific cardiomyocytes (iPSC-CMs) and isogenic controls lacking the pathogenic MYBPC3 variant.

RESULTS

Mutant iPSC-CMs developed impaired mitochondrial bioenergetics, which was dependent on the presence of the mutation. Moreover, we could detect altered excitation-contraction coupling in iPSC-CMs from the severely affected individual. The pathogenic MYBPC3 variant was found to be necessary, but not sufficient, to induce iPSC-CM hyperexcitability, suggesting the presence of additional genetic modifiers. Whole-exome sequencing of the mutant carriers identified a variant of unknown significance in the MYH7 gene (p.Ile1927Phe) uniquely present in the individual with severe HCM. We finally assessed the pathogenicity of this variant of unknown significance by functionally evaluating iPSC-CMs after editing the variant.

CONCLUSIONS

Our results indicate that the p.Ile1927Phe variant of unknown significance in MYH7 can be considered as a modifier of HCM expressivity when found in combination with truncating variants in MYBPC3. Overall, our studies show that iPSC-based modeling of clinically discordant subjects provides a unique platform to functionally assess the effect of genetic modifiers.

Automated assessment of human engineered heart tissues using deep learning and template matching for segmentation and tracking

The high rate of drug withdrawal from the market due to cardiovascular toxicity or lack of efficacy, the economic burden, and extremely long time before a compound reaches the market, have increased the relevance of human in vitro models like human (patient-derived) pluripotent stem cell (hPSC)-derived engineered heart tissues (EHTs) for the evaluation of the efficacy and toxicity of compounds at the early phase in the drug development pipeline. Consequently, the EHT contractile properties are highly relevant parameters for the analysis of cardiotoxicity, disease phenotype, and longitudinal measurements of cardiac function over time. In this study, we developed and validated the software HAARTA (Highly Accurate, Automatic and Robust Tracking Algorithm), which automatically analyzes contractile properties of EHTs by segmenting and tracking brightfield videos, using deep learning and template matching with sub-pixel precision. We demonstrate the robustness, accuracy, and computational efficiency of the software by comparing it to the state-of-the-art method (MUSCLEMOTION), and by testing it with a data set of EHTs from three different hPSC lines. HAARTA will facilitate standardized analysis of contractile properties of EHTs, which will be beneficial for in vitro drug screening and longitudinal measurements of cardiac function.

cMyBP-C ablation in human engineered cardiac tissue causes progressive Ca2+-handling abnormalities

Truncation mutations in cardiac myosin binding protein C (cMyBP-C) are common causes of hypertrophic cardiomyopathy (HCM). Heterozygous carriers present with classical HCM, while homozygous carriers present with early onset HCM that rapidly progress to heart failure. We used CRISPR-Cas9 to introduce heterozygous (cMyBP-C+/-) and homozygous (cMyBP-C-/-) frame-shift mutations into MYBPC3 in human iPSCs. Cardiomyocytes derived from these isogenic lines were used to generate cardiac micropatterns and engineered cardiac tissue constructs (ECTs) that were characterized for contractile function, Ca2+-handling, and Ca2+-sensitivity. While heterozygous frame shifts did not alter cMyBP-C protein levels in 2-D cardiomyocytes, cMyBP-C+/- ECTs were haploinsufficient. cMyBP-C-/- cardiac micropatterns produced increased strain with normal Ca2+-handling. After 2 wk of culture in ECT, contractile function was similar between the three genotypes; however, Ca2+-release was slower in the setting of reduced or absent cMyBP-C. At 6 wk in ECT culture, the Ca2+-handling abnormalities became more pronounced in both cMyBP-C+/- and cMyBP-C-/- ECTs, and force production became severely depressed in cMyBP-C-/- ECTs. RNA-seq analysis revealed enrichment of differentially expressed hypertrophic, sarcomeric, Ca2+-handling, and metabolic genes in cMyBP-C+/- and cMyBP-C-/- ECTs. Our data suggest a progressive phenotype caused by cMyBP-C haploinsufficiency and ablation that initially is hypercontractile, but progresses to hypocontractility with impaired relaxation. The severity of the phenotype correlates with the amount of cMyBP-C present, with more severe earlier phenotypes observed in cMyBP-C-/- than cMyBP-C+/- ECTs. We propose that while the primary effect of cMyBP-C haploinsufficiency or ablation may relate to myosin crossbridge orientation, the observed contractile phenotype is Ca2+-mediated.

Cardiomyocyte Apoptosis Is Associated with Contractile Dysfunction in Stem Cell Model of MYH7 E848G Hypertrophic Cardiomyopathy

Missense mutations in myosin heavy chain 7 (MYH7) are a common cause of hypertrophic cardiomyopathy (HCM), but the molecular mechanisms underlying MYH7-based HCM remain unclear. In this work, we generated cardiomyocytes derived from isogenic human induced pluripotent stem cells to model the heterozygous pathogenic MYH7 missense variant, E848G, which is associated with left ventricular hypertrophy and adult-onset systolic dysfunction. MYH7E848G/+ increased cardiomyocyte size and reduced the maximum twitch forces of engineered heart tissue, consistent with the systolic dysfunction in MYH7E848G/+ HCM patients. Interestingly, MYH7E848G/+ cardiomyocytes more frequently underwent apoptosis that was associated with increased p53 activity relative to controls. However, genetic ablation of TP53 did not rescue cardiomyocyte survival or restore engineered heart tissue twitch force, indicating MYH7E848G/+ cardiomyocyte apoptosis and contractile dysfunction are p53-independent. Overall, our findings suggest that cardiomyocyte apoptosis is associated with the MYH7E848G/+ HCM phenotype in vitro and that future efforts to target p53-independent cell death pathways may be beneficial for the treatment of HCM patients with systolic dysfunction.

Cardiomyocyte apoptosis contributes to contractile dysfunction in stem cell model of MYH7 E848G hypertrophic cardiomyopathy

Missense mutations in myosin heavy chain 7 ( MYH7 ) are a common cause of hyper-trophic cardiomyopathy (HCM), but the molecular mechanisms underlying MYH7 -based HCM remain unclear. In this work, we generated cardiomyocytes derived from isogenic human induced pluripotent stem cells to model the heterozygous pathogenic MYH7 missense variant, E848G, which is associated with left ventricular hypertrophy and adultonset systolic dysfunction. MYH7 E848G/+ increased cardiomyocyte size and reduced the maximum twitch forces of engineered heart tissue, consistent with the systolic dysfunction in MYH7 E848G HCM patients. Interestingly, MYH7 E848G/+ cardiomyocytes more frequently underwent apoptosis that was associated with increased p53 activity relative to controls. However, genetic ablation of TP53 did not rescue cardiomyocyte survival or restore engineered heart tissue twitch force, indicating MYH7 E848G/+ cardiomyocyte apoptosis and contractile dysfunction are p53-independent. Overall, our findings suggest that cardiomyocyte apoptosis plays an important role in the MYH7 E848G/+ HCM phenotype in vitro and that future efforts to target p53-independent cell death pathways may be beneficial for the treatment of HCM patients with systolic dysfunction.

Cardiac calcium regulation in human induced pluripotent stem cell cardiomyocytes: Implications for disease modeling and maturation

Human induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) are based on ground-breaking technology that has significantly impacted cardiovascular research. They provide a renewable source of human cardiomyocytes for a variety of applications including in vitro disease modeling and drug toxicity testing. Cardiac calcium regulation plays a critical role in the cardiomyocyte and is often dysregulated in cardiovascular disease. Due to the limited availability of human cardiac tissue, calcium handling and its regulation have most commonly been studied in the context of animal models. hiPSC-CMs can provide unique insights into human physiology and pathophysiology, although a remaining limitation is the relative immaturity of these cells compared to adult cardiomyocytes Therefore, this field is rapidly developing techniques to improve the maturity of hiPSC-CMs, further establishing their place in cardiovascular research. This review briefly covers the basics of cardiomyocyte calcium cycling and hiPSC technology, and will provide a detailed description of our current understanding of calcium in hiPSC-CMs.

Adaptation of cardiomyogenesis to the generation and maturation of cardiomyocytes from human pluripotent stem cells

The advent of methods for efficient generation and cardiac differentiation of pluripotent stem cells opened new avenues for disease modelling, drug testing, and cell therapies of the heart. However, cardiomyocytes (CM) obtained from such cells demonstrate an immature, foetal-like phenotype that involves spontaneous contractions, irregular morphology, expression of embryonic isoforms of sarcomere components, and low level of ion channels. These and other features may affect cellular response to putative therapeutic compounds and the efficient integration into the host myocardium after in vivo delivery. Therefore, novel strategies to increase the maturity of pluripotent stem cell-derived CM are of utmost importance. Several approaches have already been developed relying on molecular changes that occur during foetal and postnatal maturation of the heart, its electromechanical activity, and the cellular composition. As a better understanding of these determinants may facilitate the generation of efficient protocols for in vitro acquisition of an adult-like phenotype by immature CM, this review summarizes the most important molecular factors that govern CM during embryonic development, postnatal changes that trigger heart maturation, as well as protocols that are currently used to generate mature pluripotent stem cell-derived cardiomyocytes.

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

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

Human pluripotent stem cell-derived cardiomyocytes align under cyclic strain when guided by cardiac fibroblasts

The myocardium is a mechanically active tissue typified by anisotropy of the resident cells [cardiomyocytes (CMs) and cardiac fibroblasts (cFBs)] and the extracellular matrix (ECM). Upon ischemic injury, the anisotropic tissue is replaced by disorganized scar tissue, resulting in loss of coordinated contraction. Efforts to re-establish tissue anisotropy in the injured myocardium are hampered by a lack of understanding of how CM and/or cFB structural organization is affected by the two major physical cues inherent in the myocardium: ECM organization and cyclic mechanical strain. Herein, we investigate the singular and combined effect of ECM (dis)organization and cyclic strain in a two-dimensional human in vitro co-culture model of the myocardial microenvironment. We show that (an)isotropic ECM protein patterning can guide the orientation of CMs and cFBs, both in mono- and co-culture. Subsequent application of uniaxial cyclic strain-mimicking the local anisotropic deformation of beating myocardium-causes no effect when applied parallel to the anisotropic ECM. However, when cultured on isotropic substrates, cFBs, but not CMs, orient away from the direction of cyclic uniaxial strain (strain avoidance). In contrast, CMs show strain avoidance via active remodeling of their sarcomeres only when co-cultured with at least 30% cFBs. Paracrine signaling or N-cadherin-mediated communication between CMs and cFBs was no contributing factor. Our findings suggest that the mechanoresponsive cFBs provide structural guidance for CM orientation and elongation. Our study, therefore, highlights a synergistic mechanobiological interplay between CMs and cFBs in shaping tissue organization, which is of relevance for regenerating functionally organized myocardium.

Embedded 3D printing of dilute particle suspensions into dense complex tissue fibers using shear thinning xanthan baths

In order to fabricate functional organoids and microtissues, a high cell density is generally required. As such, the placement of cell suspensions in molds or microwells to allow for cell concentration by sedimentation is the current standard for the production of organoids and microtissues. Even though molds offer some level of control over the shape of the resulting microtissue, this control is limited as microtissues tend to compact towards a sphere after sedimentation of the cells. 3D bioprinting on the other hand offers complete control over the shape of the resulting structure. Even though the printing of dense cell suspensions in the ink has been reported, extruding dense cellular suspensions is challenging and generally results in high shear stresses on the cells and a poor shape fidelity of the print. As such, additional materials such as hydrogels are added in the bioink to limit shear stresses, and to improve shape fidelity and resolution. The maximum cell concentration that can be incorporated in a hydrogel-based ink before the ink's rheological properties are compromised, is significantly lower than the concentration in a tissue equivalent. Additionally, the hydrogel components often interfere with cellular self-assembly processes. To circumvent these limitations, we report a simple and inexpensive xanthan bath based embedded printing method to 3D print dense functional linear tissues using dilute particle suspensions consisting of cells, spheroids, hydrogel beads, or combinations thereof. Using this method, we demonstrated the self-organization of functional cardiac tissue fibers with a layer of epicardial cells surrounding a body of cardiomyocytes.

Prospects for remodeling the hypertrophic heart with myosin modulators

Hypertrophic cardiomyopathy (HCM) is a complex but relatively common genetic disease that usually arises from pathogenic variants that disrupt sarcomere function and lead to variable structural, hypertrophic, and fibrotic remodeling of the heart which result in substantial adverse clinical outcomes including arrhythmias, heart failure, and sudden cardiac death. HCM has had few effective treatments with the potential to ameliorate disease progression until the recent advent of inhibitory myosin modulators like mavacamten. Preclinical investigations and clinical trials utilizing this treatment targeted to this specific pathophysiological mechanism of sarcomere hypercontractility in HCM have confirmed that myosin modulators can alter disease expression and attenuate hypertrophic remodeling. Here, we summarize the state of hypertrophic remodeling and consider the arguments for and against salutary HCM disease modification using targeted myosin modulators. Further, we consider critical unanswered questions for future investigative and therapeutic avenues in HCM disease modification. We are at the precipice of a new era in understanding and treating HCM, with the potential to target agents toward modifying disease expression and natural history of this most common inherited disease of the heart.

Contraction pressure analysis using optical imaging in normal and MYBPC3-mutated hiPSC-derived cardiomyocytes grown on matrices with tunable stiffness

Current in vivo disease models and analysis methods for cardiac drug development have been insufficient in providing accurate and reliable predictions of drug efficacy and safety. Here, we propose a custom optical flow-based analysis method to quantitatively measure recordings of contracting cardiomyocytes on polydimethylsiloxane (PDMS), compatible with medium-throughput systems. Movement of the PDMS was examined by covalently bound fluorescent beads on the PDMS surface, differences caused by increased substrate stiffness were compared, and cells were stimulated with β-agonist. We further validated the system using cardiomyocytes treated with endothelin-1 and compared their contractions against control and cells incubated with receptor antagonist bosentan. After validation we examined two MYBPC3-mutant patient-derived cell lines. Recordings showed that higher substrate stiffness resulted in higher contractile pressure, while beating frequency remained similar to control. β-agonist stimulation resulted in both higher beating frequency as well as higher pressure values during contraction and relaxation. Cells treated with endothelin-1 showed an increased beating frequency, but a lower contraction pressure. Cells treated with both endothelin-1 and bosentan remained at control level of beating frequency and pressure. Lastly, both MYBPC3-mutant lines showed a higher beating frequency and lower contraction pressure. Our validated method is capable of automatically quantifying contraction of hiPSC-derived cardiomyocytes on a PDMS substrate of known shear modulus, returning an absolute value. Our method could have major benefits in a medium-throughput setting.

Physiological calcium combined with electrical pacing accelerates maturation of human engineered heart tissue

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have wide potential application in basic research, drug discovery, and regenerative medicine, but functional maturation remains challenging. Here, we present a method whereby maturation of hiPSC-CMs can be accelerated by simultaneous application of physiological Ca2+ and frequency-ramped electrical pacing in culture. This combination produces positive force-frequency behavior, physiological twitch kinetics, robust β-adrenergic response, improved Ca2+ handling, and cardiac troponin I expression within 25 days. This study provides insights into the role of Ca2+ in hiPSC-CM maturation and offers a scalable platform for translational and clinical research.

Software Tool for Automatic Quantification of Sarcomere Length and Organization in Fixed and Live 2D and 3D Muscle Cell Cultures In Vitro

Sarcomeres are the structural units of the contractile apparatus in cardiac and skeletal muscle cells. Changes in sarcomere characteristics are indicative of changes in the sarcomeric proteins and function during development and disease. Assessment of sarcomere length, alignment, and organization provides insight into disease and drug responses in striated muscle cells and models, ranging from cardiomyocytes and skeletal muscle cells derived from human pluripotent stem cells to adult muscle cells isolated from animals or humans. However, quantification of sarcomere length is typically time consuming and prone to user-specific selection bias. Automated analysis pipelines exist but these often require either specialized software or programming experience. In addition, these pipelines are often designed for only one type of cell model in vitro. Here, we present an easy-to-implement protocol and software tool for automated sarcomere length and organization quantification in a variety of striated muscle in vitro models: Two dimensional (2D) cardiomyocytes, three dimensional (3D) cardiac microtissues, isolated adult cardiomyocytes, and 3D tissue engineered skeletal muscles. Based on an existing mathematical algorithm, this image analysis software (SotaTool) automatically detects the direction in which the sarcomere organization is highest over the entire image and outputs the length and organization of sarcomeres. We also analyzed videos of live cells during contraction, thereby allowing measurement of contraction parameters like fractional shortening, contraction time, relaxation time, and beating frequency. In this protocol, we give a step-by-step guide on how to prepare, image, and automatically quantify sarcomere and contraction characteristics in different types of in vitro models and we provide basic validation and discussion of the limitations of the software tool. © 2022 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Staining and analyzing static hiPSC-CMs with SotaTool Alternate Protocol: Sample preparation, acquisition, and quantification of fractional shortening in live reporter hiPSC lines Support Protocol 1: Finding the image resolution Support Protocol 2: Advanced analysis settings Support Protocol 3: Finding sarcomere length in non-aligned cells.

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.

Contractility analysis of human engineered 3D heart tissues by an automatic tracking technique using a standalone application

The use of Engineered Heart Tissues (EHT) as in vitro model for disease modeling and drug screening has increased, as they provide important insight into the genetic mechanisms, cardiac toxicity or drug responses. Consequently, this has highlighted the need for a standardized, unbiased, robust and automatic way to analyze hallmark physiological features of EHTs. In this study we described and validated a standalone application to analyze physiological features of EHTs in an automatic, robust, and unbiased way, using low computational time. The standalone application “EHT Analysis” contains two analysis modes (automatic and manual) to analyzes the contractile properties and the contraction kinetics of EHTs from high speed bright field videos. As output data, the graphs of displacement, contraction force and contraction kinetics per file will be generated together with the raw data. Additionally, it also generates a summary file containing all the data from the analyzed files, which facilitates and speeds up the post analysis. From our study we highlight the importance of analyzing the axial stress which is the force per surface area (μN/mm²). This allows to have a readout overtime of tissue compaction, axial stress and leave the option to calculate at the end point of an experiment the physiological cross-section area (PSCA). We demonstrated the utility of this tool by analyzing contractile properties and compaction over time of EHTs made out of a double reporter human pluripotent stem cell (hPSC) line (NKX2.5^EGFP/+-COUP-TFII^mCherry/+) and different ratios of human adult cardiac fibroblasts (HCF). Our standalone application “EHT Analysis” can be applied for different studies where the physiological features of EHTs needs to be analyzed under the effect of a drug compound or in a disease model.

Improved Atrial Differentiation of Human Pluripotent Stem Cells by Activation of Retinoic Acid Receptor Alpha (RARα)

Human pluripotent stem cell (hPSC)-derived cardiomyocytes have proven valuable for modeling disease and as a drug screening platform. Here, we depict an optimized protocol for the directed differentiation of hPSCs toward cardiomyocytes with an atrial identity by modulating the retinoic acid signaling cascade in spin embryoid bodies. The crucial steps of the protocol, including hPSC maintenance, embryoid body (EB) differentiation, the induction of cardiac mesoderm, direction toward the atrial phenotype, as well as molecular and functional characterization of the cardiomyocytes, are described. Atrial cardiomyocytes (AMs) can be generated within 14 days. Most importantly, we show that induction of the specific retinoic acid receptor alpha (RARα) increased the efficiency of atrial differentiation to 72% compared with 45% after modulating the retinoic acid (RA) pathway with all-trans RA (atRA). In contrast, the induction of RARβ signaling only had a minor impact on the efficiency of atrial differentiation (from about 45% to 50%). Similarly, the total yield of AM per EB of 5000 hPSCs was increased from 10,350 (2.07 per hPSC) to 16,120 (3.22 per hPSC) while selectively modulating RARα signaling. For further purification of the AMs, we describe a metabolic selection procedure that enhanced the AM percentage to more than 90% without compromising the AM yield (15,542 per EB, equal to 3.11 per hPSC) or functionality of the AMs as evaluated by RNAseq, immunostaining, and optical action potential measurement. Cardiomyocytes with distinct atrial and ventricular properties can be applied for selective pharmacology, such as the development of novel atrial-specific anti-arrhythmic agents, and disease modeling, including atrial fibrillation, which is the most common heart rhythm disorder. Moreover, fully characterized and defined cardiac subtype populations are of the utmost importance for potential cell-based therapeutic approaches.

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.

Fluidic circuit board with modular sensor and valves enables stand-alone, tubeless microfluidic flow control in organs-on-chips

Organs-on-chips are a unique class of microfluidic in vitro cell culture models, in which the in vivo tissue microenvironment is mimicked. Unfortunately, their widespread use is hampered by their operation complexity and incompatibility with end-user research settings. To address these issues, many commercial and non-commercial platforms have been developed for semi-automated culture of organs-on-chips. However, these organ-on-chip culture platforms each represent a closed ecosystem, with very little opportunity to interchange and integrate components from different platforms or to develop new ones. The translational organ-on-chip platform (TOP) is a multi-institutional effort to develop an open platform for automated organ-on-chip culture and integration of components from various developers. Central to TOP is the fluidic circuit board (FCB), a microfluidic plate with the form factor of a typical well plate. The FCB enables microfluidic control of multiple components like sensors or organ-on-chip devices through an interface based on openly available standards. Here, we report an FCB to integrate commercial and in-house developed components forming a stand-alone flow control system for organs-on-chips. The control system is able to achieve constant and pulsatile flow recirculation through a connected organ-on-chip device. We demonstrate that this system is able to automatically perfuse a heart-on-chip device containing co-cultures of cardiac tissues derived from human pluripotent stem cell-derived cardiomyocytes and monolayers of endothelial cells for five days. Altogether, we conclude that open technology platforms allow the integration of components from different sources to form functional and fit-for-purpose organ-on-chip systems. We anticipate that open platforms will play a central role in catalyzing and maturing further technological development of organ-on-chip culture systems.

From engineered heart tissue to cardiac organoid

The advent of human pluripotent stem cells (hPSCs) presented a new paradigm to employ hPSC-derived cardiomyocytes (hPSC-CMs) in drug screening and disease modeling. However, hPSC-CMs differentiated in conventional two-dimensional systems are structurally and functionally immature. Moreover, these differentiation systems generate predominantly one type of cell. Since the heart includes not only CMs but other cell types, such monolayer cultures have limitations in simulating the native heart. Accordingly, three-dimensional (3D) cardiac tissues have been developed as a better platform by including various cardiac cell types and extracellular matrices. Two advances were made for 3D cardiac tissue generation. One type is engineered heart tissues (EHTs), which are constructed by 3D cell culture of cardiac cells using an engineering technology. This system provides a convenient real-time analysis of cardiac function, as well as a precise control of the input/output flow and mechanical/electrical stimulation. The other type is cardiac organoids, which are formed through self-organization of differentiating cardiac lineage cells from hPSCs. While mature cardiac organoids are more desirable, at present only primitive forms of organoids are available. In this review, we discuss various models of hEHTs and cardiac organoids emulating the human heart, focusing on their unique features, utility, and limitations.

Microphysiological stem cell models of the human heart

Models of heart disease and drug responses are increasingly based on human pluripotent stem cells (hPSCs) since their ability to capture human heart (dys-)function is often better than animal models. Simple monolayer cultures of hPSC-derived cardiomyocytes, however, have shortcomings. Some of these can be overcome using more complex, multi cell-type models in 3D. Here we review modalities that address this, describe efforts to tailor readouts and sensors for monitoring tissue- and cell physiology (exogenously and in situ) and discuss perspectives for implementation in industry and academia.

A New Versatile Platform for Assessment of Improved Cardiac Performance in Human-Engineered Heart Tissues

Cardiomyocytes derived from human pluripotent stem cells (hPSC-CMs) hold a great potential as human in vitro models for studying heart disease and for drug safety screening. Nevertheless, their associated immaturity relative to the adult myocardium limits their utility in cardiac research. In this study, we describe the development of a platform for generating three-dimensional engineered heart tissues (EHTs) from hPSC-CMs for the measurement of force while under mechanical and electrical stimulation. The modular and versatile EHT platform presented here allows for the formation of three tissues per well in a 12-well plate format, resulting in 36 tissues per plate. We compared the functional performance of EHTs and their histology in three different media and demonstrated that tissues cultured and maintained in maturation medium, containing triiodothyronine (T3), dexamethasone, and insulin-like growth factor-1 (TDI), resulted in a higher force of contraction, sarcomeric organization and alignment, and a higher and lower inotropic response to isoproterenol and nifedipine, respectively. Moreover, in this study, we highlight the importance of integrating a serum-free maturation medium in the EHT platform, making it a suitable tool for cardiovascular research, disease modeling, and preclinical drug testing.

Recent Advances in Modeling Mitochondrial Cardiomyopathy Using Human Induced Pluripotent Stem Cells

Around one third of patients with mitochondrial disorders develop a kind of cardiomyopathy. In these cases, severity is quite variable ranging from asymptomatic status to severe manifestations including heart failure, arrhythmias, and sudden cardiac death. ATP is primarily generated in the mitochondrial respiratory chain via oxidative phosphorylation by utilizing fatty acids and carbohydrates. Genes in both the nuclear and the mitochondrial DNA encode components of this metabolic route and, although mutations in these genes are extremely rare, the risk to develop cardiac symptoms is significantly higher in this patient cohort. Additionally, infants with cardiovascular compromise in mitochondrial deficiency display a worse late survival compared to patients without cardiac symptoms. At this point, the mechanisms behind cardiac disease progression related to mitochondrial gene mutations are poorly understood and current therapies are unable to substantially restore the cardiac performance and to reduce the disease burden. Therefore, new strategies are needed to uncover the pathophysiological mechanisms and to identify new therapeutic options for mitochondrial cardiomyopathies. Here, human induced pluripotent stem cell (iPSC) technology has emerged to provide a suitable patient-specific model system by recapitulating major characteristics of the disease in vitro, as well as to offer a powerful platform for pre-clinical drug development and for the testing of novel therapeutic options. In the present review, we summarize recent advances in iPSC-based disease modeling of mitochondrial cardiomyopathies and explore the patho-mechanistic insights as well as new therapeutic approaches that were uncovered with this experimental platform. Further, we discuss the challenges and limitations of this technology and provide an overview of the latest techniques to promote metabolic and functional maturation of iPSC-derived cardiomyocytes that might be necessary for modeling of mitochondrial disorders.

Conditional immortalization of human atrial myocytes for the generation of in vitro models of atrial fibrillation

The lack of a scalable and robust source of well-differentiated human atrial myocytes constrains the development of in vitro models of atrial fibrillation (AF). Here we show that fully functional atrial myocytes can be generated and expanded one-quadrillion-fold via a conditional cell-immortalization method relying on lentiviral vectors and the doxycycline-controlled expression of a recombinant viral oncogene in human foetal atrial myocytes, and that the immortalized cells can be used to generate in vitro models of AF. The method generated 15 monoclonal cell lines with molecular, cellular and electrophysiological properties resembling those of primary atrial myocytes. Multicellular in vitro models of AF generated using the immortalized atrial myocytes displayed fibrillatory activity (with activation frequencies of 6-8 Hz, consistent with the clinical manifestation of AF), which could be terminated by the administration of clinically approved antiarrhythmic drugs. The conditional cell-immortalization method could be used to generate functional cell lines from other human parenchymal cells, for the development of in vitro models of human disease.

Mass-Spectrometry-Based Functional Proteomic and Phosphoproteomic Technologies and Their Application for Analyzing Ex Vivo and In Vitro Models of Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disease thought to be principally caused by mutations in sarcomeric proteins. Despite extensive genetic analysis, there are no comprehensive molecular frameworks for how single mutations in contractile proteins result in the diverse assortment of cellular, phenotypic, and pathobiological cascades seen in HCM. Molecular profiling and system biology approaches are powerful tools for elucidating, quantifying, and interpreting dynamic signaling pathways and differential macromolecule expression profiles for a wide range of sample types, including cardiomyopathy. Cutting-edge approaches combine high-performance analytical instrumentation (e.g., mass spectrometry) with computational methods (e.g., bioinformatics) to study the comparative activity of biochemical pathways based on relative abundances of functionally linked proteins of interest. Cardiac research is poised to benefit enormously from the application of this toolkit to cardiac tissue models, which recapitulate key aspects of pathogenesis. In this review, we evaluate state-of-the-art mass-spectrometry-based proteomic and phosphoproteomic technologies and their application to in vitro and ex vivo models of HCM for global mapping of macromolecular alterations driving disease progression, emphasizing their potential for defining the components of basic biological systems, the fundamental mechanistic basis of HCM pathogenesis, and treating the ensuing varied clinical outcomes seen among affected patient cohorts.

A simple protocol to produce mature human-induced pluripotent stem cell-derived cardiomyocytes

When cultured under typical conditions, human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are structurally and functionally immature. We have previously demonstrated that culture of hiPSC-CMs in maturation medium containing fatty acids, in combination with culture on micropatterned surfaces, produces cells that demonstrate a more mature phenotype compared to standard approaches. Here, we show in detail the steps needed to produce mature hiPSC-CMs. Compared with many approaches, our protocol is relatively simple and can be easily adapted to new laboratories.

For complete details on the use and execution of this protocol, please refer to Knight et al. (2021).

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Two-step protocol to increase maturity of stem cell-derived cardiomyocytes

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Improves sarcomeric organization, contractile function, and metabolic behavior

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Improved cardiomyocyte maturation suppresses baseline hypertrophy

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Simple protocol which most labs should be able to implement

Human Induced Pluripotent Stem Cell as a Disease Modeling and Drug Development Platform-A Cardiac Perspective

A comprehensive understanding of the pathophysiology and cellular responses to drugs in human heart disease is limited by species differences between humans and experimental animals. In addition, isolation of human cardiomyocytes (CMs) is complicated because cells obtained by biopsy do not proliferate to provide sufficient numbers of cells for preclinical studies in vitro. Interestingly, the discovery of human-induced pluripotent stem cell (hiPSC) has opened up the possibility of generating and studying heart disease in a culture dish. The combination of reprogramming and genome editing technologies to generate a broad spectrum of human heart diseases in vitro offers a great opportunity to elucidate gene function and mechanisms. However, to exploit the potential applications of hiPSC-derived-CMs for drug testing and studying adult-onset cardiac disease, a full functional characterization of maturation and metabolic traits is required. In this review, we focus on methods to reprogram somatic cells into hiPSC and the solutions for overcome immaturity of the hiPSC-derived-CMs to mimic the structure and physiological properties of the adult human CMs to accurately model disease and test drug safety. Finally, we discuss how to improve the culture, differentiation, and purification of CMs to obtain sufficient numbers of desired types of hiPSC-derived-CMs for disease modeling and drug development platform.

Retinoic acid signaling in heart development: Application in the differentiation of cardiovascular lineages from human pluripotent stem cells

Retinoic acid (RA) signaling plays an important role during heart development in establishing anteroposterior polarity, formation of inflow and outflow tract progenitors, and growth of the ventricular compact wall. RA is also utilized as a key ingredient in protocols designed for generating cardiac cell types from pluripotent stem cells (PSCs). This review discusses the role of RA in cardiogenesis, currently available protocols that employ RA for differentiation of various cardiovascular lineages, and plausible transcriptional mechanisms underlying this fate specification. These insights will inform further development of desired cardiac cell types from human PSCs and their application in preclinical and clinical research.

Physiologic biomechanics enhance reproducible contractile development in a stem cell derived cardiac muscle platform

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) allow investigations in a human cardiac model system, but disorganized mechanics and immaturity of hPSC-CMs on standard two-dimensional surfaces have been hurdles. Here, we developed a platform of micron-scale cardiac muscle bundles to control biomechanics in arrays of thousands of purified, independently contracting cardiac muscle strips on two-dimensional elastomer substrates with far greater throughput than single cell methods. By defining geometry and workload in this reductionist platform, we show that myofibrillar alignment and auxotonic contractions at physiologic workload drive maturation of contractile function, calcium handling, and electrophysiology. Using transcriptomics, reporter hPSC-CMs, and quantitative immunofluorescence, these cardiac muscle bundles can be used to parse orthogonal cues in early development, including contractile force, calcium load, and metabolic signals. Additionally, the resultant organized biomechanics facilitates automated extraction of contractile kinetics from brightfield microscopy imaging, increasing the accessibility, reproducibility, and throughput of pharmacologic testing and cardiomyopathy disease modeling.

Investigations of human cardiac disease involving human pluripotent stem cell-derived cardiomyocytes are limited by the disorganized presentation of biomechanical cues resulting in cell immaturity. Here the authors develop a platform of micron-scale 2D cardiac muscle bundles to precisely deliver physiologic cues, improving reproducibility and throughput.

Recent progress of iPSC technology in cardiac diseases

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

Interplay of Genotype and Substrate Stiffness in Driving the Hypertrophic Cardiomyopathy Phenotype in iPSC-Micro-Heart Muscle Arrays

INTRODUCTION

In clinical and animal studies, Hypertrophic Cardiomyopathy (HCM) shares many similarities with non-inherited cardiac hypertrophy induced by pressure overload (hypertension). This suggests a potential role for mechanical stress in priming tissues with mutation-induced changes in the sarcomere to develop phenotypes associated with HCM, including hypercontractility and aberrant calcium handling. Here, we tested the hypothesis that heterozygous loss of function of Myosin Binding Protein C (MYBCP3 +/- , mutations in which account for almost 50% of inherited HCM) combines with environmental stiffness to drive HCM phenotypes.

METHODS

We differentiated isogenic control (WTC) and MYBPC3 +/- iPSC into cardiomyocytes using small molecule manipulation of Wnt signaling, and then purified them using lactate media. The purified cardiomyocytes were seeded into "dog bone" shaped stencil molds to form micro-heart muscle arrays (μHM). To mimic changes in myocardial stiffness stemming from pressure overload, we varied the rigidity of the substrates μHM contract against. Stiffness levels ranged from those corresponding to fetal (5 kPa), healthy (15 kPa), pre-fibrotic (30 kPa) to fibrotic (65 kPa) myocardium. Substrates were embedded with a thin layer of fluorescent beads to track contractile force, and parent iPSC were engineered to express the genetic calcium indicator, GCaMP6f. High speed video microscopy and image analysis were used to quantify calcium handling and contractility of μHM.

RESULTS

Substrate rigidity triggered physiological adaptation for both genotypes. However, MYBPC3 +/- μHM showed a lower tolerance to substrate stiffness with the peak traction on 15 kPa, while WTC μHM had peak traction on 30 kPa. MYBPC3 +/- μHM exhibited hypercontractility, which was exaggerated by substrate rigidity. MYBPC3 +/- μHM hypercontractility was associated with longer rise times for calcium uptake and force development, along with higher overall Ca2+ intake.

CONCLUSION

We found MYBPC3 +/- mutations cause iPSC-μHM to exhibit hypercontractility, and also a lower tolerance for mechanical stiffness. Understanding how genetics work in combination with mechanical stiffness to trigger and/or exacerbate pathophysiology may lead to more effective therapies for HCM.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s12195-021-00684-x).