Automated Video-Based Analysis of Contractility and Calcium Flux in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes Cultured over Different Spatial Scales

Integrated Ca2+ flux and AFM force analysis in human iPSC-derived cardiomyocytes

We developed a new approach for combined analysis of calcium (Ca²⁺) handling and beating forces in contractile cardiomyocytes. We employed human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from dilated cardiomyopathy (DCM) patients carrying an inherited mutation in the sarcomeric protein troponin T (TnT), and isogenic TnT-KO iPSC-CMs generated via CRISPR/Cas9 gene editing. In these cells, Ca²⁺ handling as well as beating forces and -rates using single-cell atomic force microscopy (AFM) were assessed. We report impaired Ca²⁺ handling and reduced contractile force in DCM iPSC-CMs compared to healthy WT controls. TnT-KO iPSC-CMs display no contractile force or Ca²⁺ transients but generate Ca²⁺ sparks. We apply our analysis strategy to Ca²⁺ traces and AFM deflection recordings to reveal maximum rising rate, decay time, and duration of contraction with a multi-step background correction. Our method provides adaptive computing of signal peaks for different Ca²⁺ flux or force levels in iPSC-CMs, as well as analysis of Ca²⁺ sparks. Moreover, we report long-term measurements of contractile force dynamics on human iPSC-CMs. This approach enables deeper and more accurate profiling of disease-specific differences in cardiomyocyte contraction profiles using patient-derived iPSC-CMs.

Elastomer-Grafted iPSC-Derived Micro Heart Muscles to Investigate Effects of Mechanical Loading on Physiology

Mechanical loading plays a critical role in cardiac pathophysiology. Engineered heart tissues derived from human induced pluripotent stem cells (iPSCs) allow rigorous investigations of the molecular and pathophysiological consequences of mechanical cues. However, many engineered heart muscle models have complex fabrication processes and require large cell numbers, making it difficult to use them together with iPSC-derived cardiomyocytes to study the influence of mechanical loading on pharmacology and genotype-phenotype relationships. To address this challenge, simple and scalable iPSC-derived micro-heart-muscle arrays (μHM) have been developed. "Dog-bone-shaped" molds define the boundary conditions for tissue formation. Here, we extend the μHM model by forming these tissues on elastomeric substrates with stiffnesses spanning from 5 to 30 kPa. Tissue assembly was achieved by covalently grafting fibronectin to the substrate. Compared to μHM formed on plastic, elastomer-grafted μHM exhibited a similar gross morphology, sarcomere assembly, and tissue alignment. When these tissues were formed on substrates with different elasticity, we observed marked shifts in contractility. Increased contractility was correlated with increases in calcium flux and a slight increase in cell size. This afterload-enhanced μHM system enables mechanical control of μHM and real-time tissue traction force microscopy for cardiac physiology measurements, providing a dynamic tool for studying pathophysiology and pharmacology.

Muscular Thin Films for Label-Free Mapping of Excitation Propagation in Cardiac Tissue

Muscular thin films (MTFs), have already found a variety of applications in cardiac tissue engineering and in building of lab-on-a-chip systems. Here we present a novel approach to label-free mapping of excitation waves in the cardiomyocyte cell cultures with the use of MTFs. Neonatal rat ventricular cardiomyocytes were cultured on polydimethylsiloxane (PDMS) thin films and observed by means of off-axis illumination. Inflexions of the membrane created by the contraction of cardiomyocytes led to formation of patterns of bright and dark areas on the surface of the membrane. These patterns were recorded and analyzed for the monitoring of the contraction propagation. The method was compared with a standard optical mapping technique based on the use of a Ca²⁺-sensitive fluorescent dye. A good consistency of the results obtained by these two methods was demonstrated. The proposed method is non-toxic and might be of particular interest for the purpose of continuous monitoring in test systems based on human induced pluripotent stem cells.

Microengineered systems with iPSC-derived cardiac and hepatic cells to evaluate drug adverse effects

Hepatic and cardiac drug adverse effects are among the leading causes of attrition in drug development programs, in part due to predictive failures of current animal or in vitro models. Hepatocytes and cardiomyocytes differentiated from human induced pluripotent stem cells (iPSCs) hold promise for predicting clinical drug effects, given their human-specific properties and their ability to harbor genetically determined characteristics that underlie inter-individual variations in drug response. Currently, the fetal-like properties and heterogeneity of hepatocytes and cardiomyocytes differentiated from iPSCs make them physiologically different from their counterparts isolated from primary tissues and limit their use for predicting clinical drug effects. To address this hurdle, there have been ongoing advances in differentiation and maturation protocols to improve the quality and use of iPSC-differentiated lineages. Among these are in vitro hepatic and cardiac cellular microsystems that can further enhance the physiology of cultured cells, can be used to better predict drug adverse effects, and investigate drug metabolism, pharmacokinetics, and pharmacodynamics to facilitate successful drug development. In this article, we discuss how cellular microsystems can establish microenvironments for these applications and propose how they could be used for potentially controlling the differentiation of hepatocytes or cardiomyocytes. The physiological relevance of cells is enhanced in cellular microsystems by simulating properties of tissue microenvironments, such as structural dimensionality, media flow, microfluidic control of media composition, and co-cultures with interacting cell types. Recent studies demonstrated that these properties also affect iPSC differentiations and we further elaborate on how they could control differentiation efficiency in microengineered devices. In summary, we describe recent advances in the field of cellular microsystems that can control the differentiation and maturation of hepatocytes and cardiomyocytes for drug evaluation. We also propose how future research with iPSCs within engineered microenvironments could enable their differentiation for scalable evaluations of drug effects.

RNA is essential for PRC2 chromatin occupancy and function in human pluripotent stem cells

Many chromatin-binding proteins and protein complexes that regulate transcription also bind RNA. One of these, Polycomb repressive complex 2 (PRC2), deposits the H3K27me3 mark of facultative heterochromatin and is required for stem cell differentiation. PRC2 binds RNAs broadly in vivo and in vitro. Yet, the biological importance of this RNA binding remains unsettled. Here, we tackle this question in human induced pluripotent stem cells by using multiple complementary approaches. Perturbation of RNA-PRC2 interaction by RNase A, by a chemical inhibitor of transcription or by an RNA-binding-defective mutant all disrupted PRC2 chromatin occupancy and localization genome wide. The physiological relevance of PRC2-RNA interactions is further underscored by a cardiomyocyte differentiation defect upon genetic disruption. We conclude that PRC2 requires RNA binding for chromatin localization in human pluripotent stem cells and in turn for defining cellular state.

Noninvasive optical coherence tomography imaging of three-dimensional cardiac tissues derived from human induced pluripotent stem cells

Artificial three-dimensional (3D) tissues have the potential to be used in regenerative medicine or in vitro screening. In particular, the fabrication of 3-D cardiac tissues is greatly anticipated. However, hierarchical organization of 3-D tissues is still unknown. In regenerative medicine and drug discovery, noninvasive evaluation methods of 3-D tissues including inside of it play a key role. In this study, we report on noninvasive methods of analyzing bio-fabricated 3-D cardiac tissues using optical coherence tomography (OCT) and image analysis. Three-dimensional cardiac tissues were fabricated by coating of extracellular matrix nanofilms onto a cell surface using a layer-by-layer (LbL) technique. At first, we investigated the relationship between surface beating and its thickness to assess the value of internal analysis. The results showed that the surface beating was influenced by the thickness. Next, we tried to quantitatively evaluate the internal beating of 3-D cardiac tissues. We also confirmed the methods by changing the beating properties through the administration of isoproterenol. Our results demonstrated that the beating properties of 3-D cardiac tissues differed by depth. The results of this study suggest that information on the internal properties of 3-D cardiac tissue was necessary to understand how it functions. The combination of OCT and image analysis can be used to evaluate the internal beating properties, including changes in beating induced by a drug. It is suggested that OCT and image analysis have the potential to be used as noninvasive methods in regenerative medicine and pharmaceutical applications.

Silencing of MYH7 ameliorates disease phenotypes in human iPSC-cardiomyocytes

Allele-specific RNA silencing has been shown to be an effective therapeutic treatment in a number of diseases, including neurodegenerative disorders. Studies of allele-specific silencing in hypertrophic cardiomyopathy (HCM) to date have focused on mouse models of disease. We here examine allele-specific silencing in a human-cell model of HCM. We investigate two methods of silencing, short hairpin RNA (shRNA) and antisense oligonucleotide (ASO) silencing, using a human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model. We used cellular micropatterning devices with traction force microscopy and automated video analysis to examine each strategy's effects on contractile defects underlying disease. We find that shRNA silencing ameliorates contractile phenotypes of disease, reducing disease-associated increases in cardiomyocyte velocity, force, and power. We find that ASO silencing, while better able to target and knockdown a specific disease-associated allele, showed more modest improvements in contractile phenotypes. These findings are the first exploration of allele-specific silencing in a human HCM model and provide a foundation for further exploration of silencing as a therapeutic treatment for MYH7-mutation-associated cardiomyopathy.

Volcano-Shaped Scanning Probe Microscopy Probe for Combined Force-Electrogram Recordings from Excitable Cells

Atomic force microscopy based approaches have led to remarkable advances in the field of mechanobiology. However, linking the mechanical cues to biological responses requires complementary techniques capable of recording these physiological characteristics. In this study, we present an instrument for combined optical, force, and electrical measurements based on a novel type of scanning probe microscopy cantilever composed of a protruding volcano-shaped nanopatterned microelectrode (nanovolcano probe) at the tip of a suspended microcantilever. This probe enables simultaneous force and electrical recordings from single cells. Successful impedance measurements on mechanically stimulated neonatal rat cardiomyocytes in situ were achieved using these nanovolcano probes. Furthermore, proof of concept experiments demonstrated that extracellular field potentials (electrogram) together with contraction displacement curves could simultaneously be recorded. These features render the nanovolcano probe especially suited for mechanobiological studies aiming at linking mechanical stimuli to electrophysiological responses of single cells.

Progressive Myofibril Reorganization of Human Cardiomyocytes on a Dynamic Nanotopographic Substrate

Cardiomyocyte (CM) alignment with striated myofibril organization is developed during early cardiac organogenesis. Previous work has successfully achieved in vitro CM alignment using a variety of biomaterial scaffolds and substrates with static topographic features. However, the cellular processes that occur during the response of CMs to dynamic surface topographic changes, which may provide a model of in vivo developmental progress of CM alignment within embryonic myocardium, remains poorly understood. To gain insights into these cellular processes involved in the response of CMs to dynamic topographic changes, we developed a dynamic topographic substrate that employs a shape memory polymer coated with polyelectrolyte multilayers to produce a flat-to-wrinkle surface transition when triggered by a change in incubation temperature. Using this system, we investigated cellular morphological alignment and intracellular myofibril reorganization in response to the dynamic wrinkle formation. Hence, we identified the progressive cellular processes of human-induced pluripotent stem cell-CMs in a time-dependent manner, which could provide a foundation for a mechanistic model of cardiac myofibril reorganization in response to extracellular microenvironment changes.

Advances in Stem Cell Modeling of Dystrophin-Associated Disease: Implications for the Wider World of Dilated Cardiomyopathy

Familial dilated cardiomyopathy (DCM) is mostly caused by mutations in genes encoding cytoskeletal and sarcomeric proteins. In the pediatric population, DCM is the predominant type of primitive myocardial disease. A severe form of DCM is associated with mutations in the DMD gene encoding dystrophin, which are the cause of Duchenne Muscular Dystrophy (DMD). DMD-associated cardiomyopathy is still poorly understood and orphan of a specific therapy. In the last 5 years, a rise of interest in disease models using human induced pluripotent stem cells (hiPSCs) has led to more than 50 original studies on DCM models. In this review paper, we provide a comprehensive overview on the advances in DMD cardiomyopathy disease modeling and highlight the most remarkable findings obtained from cardiomyocytes differentiated from hiPSCs of DMD patients. We will also describe how hiPSCs based studies have contributed to the identification of specific myocardial disease mechanisms that may be relevant in the pathogenesis of DCM, representing novel potential therapeutic targets.

Cardiac Toxicity From Ethanol Exposure in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Alcohol use prior to and during pregnancy remains a significant societal problem and can lead to developmental fetal abnormalities including compromised myocardia function and increased risk for heart disease later in life. Alcohol-induced cardiac toxicity has traditionally been studied in animal-based models. These models have limitations due to physiological differences from human cardiomyocytes (CMs) and are also not suitable for high-throughput screening. We hypothesized that human-induced pluripotent stem cell-derived CMs (hiPSC-CMs) could serve as a useful tool to study alcohol-induced cardiac defects and/or toxicity. In this study, hiPSC-CMs were treated with ethanol at doses corresponding to the clinically relevant levels of alcohol intoxication. hiPSC-CMs exposed to ethanol showed a dose-dependent increase in cellular damage and decrease in cell viability, corresponding to increased production of reactive oxygen species. Furthermore, ethanol exposure also generated dose-dependent increased irregular Ca2+ transients and contractility in hiPSC-CMs. RNA-seq analysis showed significant alteration in genes belonging to the potassium voltage-gated channel family or solute carrier family, partially explaining the irregular Ca2+ transients and contractility in ethanol-treated hiPSC-CMs. RNA-seq also showed significant upregulation in the expression of genes associated with collagen and extracellular matrix modeling, and downregulation of genes involved in cardiovascular system development and actin filament-based process. These results suggest that hiPSC-CMs can be a novel and physiologically relevant system for the study of alcohol-induced cardiac toxicity.

Single-Cell Determination of Cardiac Microtissue Structure and Function Using Light Sheet Microscopy

Native cardiac tissue is composed of heterogeneous cell populations that work cooperatively for proper tissue function; thus, engineered tissue models have moved toward incorporating multiple cardiac cell types in an effort to recapitulate native multicellular composition and organization. Cardiac tissue models composed of stem cell-derived cardiomyocytes (CMs) require inclusion of non-myocytes to promote stable tissue formation, yet the specific contributions of the supporting non-myocyte population on the parenchymal CMs and cardiac microtissues have to be fully dissected. This gap can be partly attributed to limitations in technologies able to accurately study the individual cellular structure and function that comprise intact three-dimensional (3D) tissues. The ability to interrogate the cell-cell interactions in 3D tissue constructs has been restricted by conventional optical imaging techniques that fail to adequately penetrate multicellular microtissues with sufficient spatial resolution. Light sheet fluorescence microscopy (LSFM) overcomes these constraints to enable single-cell resolution structural and functional imaging of intact cardiac microtissues. Multicellular spatial distribution analysis of heterotypic cardiac cell populations revealed that CMs and cardiac fibroblasts were randomly distributed throughout 3D microtissues. Furthermore, calcium imaging of live cardiac microtissues enabled single-cell detection of CM calcium activity, which showed that functional heterogeneity correlated with spatial location within the tissues. This study demonstrates that LSFM can be utilized to determine single-cell spatial and functional interactions of multiple cell types within intact 3D engineered microtissues, thereby facilitating the determination of structure-function relationships at both tissue-level and single-cell resolution. Impact statement The ability to achieve single-cell resolution by advanced three-dimensional light imaging techniques enables exquisite new investigation of multicellular analyses in native and engineered tissues. In this study, light sheet fluorescence microscopy was used to define structure-function relationships of distinct cell types in engineered cardiac microtissues by determining heterotypic cell distributions and interactions throughout the tissues as well as by assessing regional differences in calcium handing functional properties at the individual cardiomyocyte level.

Maladaptive Contractility of 3D Human Cardiac Microtissues to Mechanical Nonuniformity

Cardiac tissues are able to adjust their contractile behavior to adapt to the local mechanical environment. Nonuniformity of the native tissue mechanical properties contributes to the development of heart dysfunctions, yet the current in vitro cardiac tissue models often fail to recapitulate the mechanical nonuniformity. To address this issue, a 3D cardiac microtissue model is developed with engineered mechanical nonuniformity, enabled by 3D-printed hybrid matrices composed of fibers with different diameters. When escalating the complexity of tissue mechanical environments, cardiac microtissues start to develop maladaptive hypercontractile phenotypes, demonstrated in both contractile motion analysis and force-power analysis. This novel hybrid system could potentially facilitate the establishment of "pathologically-inspired" cardiac microtissue models for deeper understanding of heart pathology due to nonuniformity of the tissue mechanical environment.

Mechanobiology Assays with Applications in Cardiomyocyte Biology and Cardiotoxicity

Cardiomyocytes are the motor units that drive the contraction and relaxation of the heart. Traditionally, testing of drugs for cardiotoxic effects has relied on primary cardiomyocytes from animal models and focused on short-term, electrophysiological, and arrhythmogenic effects. However, primary cardiomyocytes present challenges arising from their limited viability in culture, and tissue from animal models suffers from a mismatch in their physiology to that of human heart muscle. Human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) can address these challenges. They also offer the potential to study not only electrophysiological effects but also changes in cardiomyocyte contractile and mechanical function in response to cardiotoxic drugs. With growing recognition of the long-term cardiotoxic effects of some drugs on subcellular structure and function, there is increasing interest in using hiPSC-CMs for in vitro cardiotoxicity studies. This review provides a brief overview of techniques that can be used to quantify changes in the active force that cardiomyocytes generate and variations in their inherent stiffness in response to cardiotoxic drugs. It concludes by discussing the application of these tools in understanding how cardiotoxic drugs directly impact the mechanobiology of cardiomyocytes and how cardiomyocytes sense and respond to mechanical load at the cellular level.

In Situ Expansion, Differentiation, and Electromechanical Coupling of Human Cardiac Muscle in a 3D Bioprinted, Chambered Organoid

RATIONALE

One goal of cardiac tissue engineering is the generation of a living, human pump in vitro that could replace animal models and eventually serve as an in vivo therapeutic. Models that replicate the geometrically complex structure of the heart, harboring chambers and large vessels with soft biomaterials, can be achieved using 3-dimensional bioprinting. Yet, inclusion of contiguous, living muscle to support pump function has not been achieved. This is largely due to the challenge of attaining high densities of cardiomyocytes-a notoriously nonproliferative cell type. An alternative strategy is to print with human induced pluripotent stem cells, which can proliferate to high densities and fill tissue spaces, and subsequently differentiate them into cardiomyocytes in situ.

OBJECTIVE

To develop a bioink capable of promoting human induced pluripotent stem cell proliferation and cardiomyocyte differentiation to 3-dimensionally print electromechanically functional, chambered organoids composed of contiguous cardiac muscle.

METHODS AND RESULTS

We optimized a photo-crosslinkable formulation of native ECM (extracellular matrix) proteins and used this bioink to 3-dimensionally print human induced pluripotent stem cell-laden structures with 2 chambers and a vessel inlet and outlet. After human induced pluripotent stem cells proliferated to a sufficient density, we differentiated the cells within the structure and demonstrated function of the resultant human chambered muscle pump. Human chambered muscle pumps demonstrated macroscale beating and continuous action potential propagation with responsiveness to drugs and pacing. The connected chambers allowed for perfusion and enabled replication of pressure/volume relationships fundamental to the study of heart function and remodeling with health and disease.

CONCLUSIONS

This advance represents a critical step toward generating macroscale tissues, akin to aggregate-based organoids, but with the critical advantage of harboring geometric structures essential to the pump function of cardiac muscle. Looking forward, human chambered organoids of this type might also serve as a test bed for cardiac medical devices and eventually lead to therapeutic tissue grafting.

Automated single cardiomyocyte characterization by nucleus extraction from dynamic holographic images using a fully convolutional neural network

Human-induced pluripotent stem cell-derived cardiomyocytes (hiPS-CMs) beating can be efficiently characterized by time-lapse quantitative phase imaging (QPIs) obtained by digital holographic microscopy. Particularly, the CM's nucleus section can precisely reflect the associated rhythmic beating pattern of the CM suitable for subsequent beating pattern characterization. In this paper, we describe an automated method to characterize single CMs by nucleus extraction from QPIs and subsequent beating pattern reconstruction and quantification. However, accurate CM's nucleus extraction from the QPIs is a challenging task due to the variations in shape, size, orientation, and lack of special geometry. To this end, we propose a novel fully convolutional neural network (FCN)-based network architecture for accurate CM's nucleus extraction using pixel classification technique and subsequent beating pattern characterization. Our experimental results show that the beating profile of multiple extracted single CMs is less noisy and more informative compared to the whole image slide. Applying this method allows CM characterization at the single-cell level. Consequently, several single CMs are extracted from the whole slide QPIs and multiple parameters regarding their beating profile of each isolated CM are efficiently measured.

Diffraction-based technology for the monitoring of contraction dynamics in 3D and 2D tissue models

We present a novel optical device developed for the monitoring of dynamic behavior in extended 3D-tissue models in various culture environments based on variations in their speckle patterns. The results presented point out the benefit of the technology in terms of detection, accuracy, sensitivity and a reasonable read-out speed as well as reproducibility for the measurements and monitoring of cardiac contractions. We show that the optical read-out technology is suitable for long time monitoring and for drug screening. The method is discussed and compared to other techniques, in particular calcium imaging. The device is flexible and easily adaptable to 2D and 3D-tissue model screenings using different culture environments. The technology can be parallelized for automated read-out of different multi-well-plate formats.

Neuromuscular Activity Induces Paracrine Signaling and Triggers Axonal Regrowth after Injury in Microfluidic Lab-On-Chip Devices

Peripheral nerve injuries, including motor neuron axonal injury, often lead to functional impairments. Current therapies are mostly limited to surgical intervention after lesion, yet these interventions have limited success in restoring functionality. Current activity-based therapies after axonal injuries are based on trial-error approaches in which the details of the underlying cellular and molecular processes are largely unknown. Here we show the effects of the modulation of both neuronal and muscular activity with optogenetic approaches to assess the regenerative capacity of cultured motor neuron (MN) after lesion in a compartmentalized microfluidic-assisted axotomy device. With increased neuronal activity, we observed an increase in the ratio of regrowing axons after injury in our peripheral-injury model. Moreover, increasing muscular activity induces the liberation of leukemia inhibitory factor and glial cell line-derived neurotrophic factor in a paracrine fashion that in turn triggers axonal regrowth of lesioned MN in our 3D hydrogel cultures. The relevance of our findings as well as the novel approaches used in this study could be useful not only after axotomy events but also in diseases affecting MN survival.

Altered microtubule structure, hemichannel localization and beating activity in cardiomyocytes expressing pathologic nuclear lamin A/C

Given the clinical effect of laminopathies, understanding lamin mechanical properties will benefit the treatment of heart failure. Here we report a mechano-dynamic study of LMNA mutations in neonatal rat ventricular myocytes (NRVM) using single cell spectroscopy with Atomic Force Microscopy (AFM) and measured changes in beating force, frequency and contractile amplitude of selected mutant-expressing cells within cell clusters. Furthermore, since beat-to-beat variations can provide clues on the origin of arrhythmias, we analyzed the beating rate variability using a time-domain method which provides a Poincaré plot. Data were further correlated to cell phenotypes. Immunofluorescence and calcium imaging analysis showed that mutant lamin changed NRVMs beating force and frequency. Additionally, we noted an altered microtubule network organization with shorter filament length, and defective hemichannel membrane localization (Connexin 43). These data highlight the interconnection between nucleoskeleton, cytoskeleton and sarcolemmal structures, and the transcellular consequences of mutant lamin protein in the pathogenesis of the cardiac laminopathies.

Human Induced Pluripotent Stem-Cardiac-Endothelial-Tumor-on-a-Chip to Assess Anticancer Efficacy and Cardiotoxicity

Cancer remains a leading health threat in the United States, and cardiovascular drug toxicity is a primary cause to eliminate a drug from FDA approval. As a result, the demand to develop new anticancer drugs without cardiovascular toxicity is high. Human induced pluripotent stem (iPS) cell-derived tissue chips provide potentially a cost-effective preclinical drug testing platform, including potential avenues for personalized medicine. We have developed a three-dimensional microfluidic device that simultaneously cultures tumor cell spheroids with iPS-derived cardiomyocytes (iPS-CMs) and iPS-derived endothelial cells (iPS-EC). The iPS-derived cells include a GCaMP6 fluorescence reporter to allow real-time imaging to monitor intracellular calcium transients. The multiple-chambered tissue chip features electrodes for pacing of the cardiac tissue to assess cardiomyocyte function such as the maximum capture rate and conduction velocity. We measured the inhibition concentration (IC₅₀) of the anticancer drugs, Doxorubicin (0.1 μM) and Oxaliplatin (4.2 μM), on the tissue chip loaded with colon cancer cells (SW620). We simultaneously evaluated the cardiotoxicity of these anticancer drugs by assessing the drug effect on the spontaneous beat frequency and conduction velocity of iPS-derived cardiac tissue. Consistent with in vivo observations, Doxorubicin reduced the spontaneous beating rate and maximum capture rate at or near the IC₅₀ (0.04 and 0.22 μM, respectively), whereas the toxicity of Oxaliplatin was only observed at concentrations beyond the IC₅₀ (33 and 9.9 μM, respectively). Our platform demonstrates the feasibility to simultaneously assess cardiac toxicity and antitumor effects of drugs and could be used to enhance personalized drug testing safety and efficacy. Impact statement Drug development using murine models for preclinical testing is no longer adequate nor acceptable both financially for the pharmaceutical industry as well as for generalized or personalized assessment of safety and efficacy. Innovative solutions using human cells and tissues provide exciting new opportunities. In this study, we report on the creation of a 3D microfluidic device that simultaneously cultures human tumor cell spheroids with cardiomyocytes and endothelial cells derived from the same induced pluripotent stem cell line. The platform provides the opportunity to assess efficacy of anticancer agents while simultaneously screening for potential cardiovascular toxicity in a format conducive for personalized medicine.

Phenotypic Variation Between Stromal Cells Differentially Impacts Engineered Cardiac Tissue Function

IMPACT STATEMENT

Understanding the relationship between parenchymal and supporting cell populations is paramount to recapitulate the multicellular complexity of native tissues. Incorporation of stromal cells is widely recognized to be necessary for the stable formation of stem cell-derived cardiac tissues; yet, the types of stromal cells used have varied widely. This study systematically characterized several stromal populations and found that stromal phenotype and morphology was highly variable depending on cell source and exerted differential impacts on cardiac tissue function and induced pluripotent stem cell-cardiomyocyte phenotype. Therefore, the choice of supporting stromal population can differentially impact the phenotypic or functional performance of engineered cardiac tissues.

An Injectable Conductive Three-Dimensional Elastic Network by Tangled Surgical-Suture Spring for Heart Repair

Designing scaffolds with persistent elasticity and conductivity to mimic microenvironments becomes a feasible way to repair cardiac tissue. Injectable biomaterials for cardiac tissue engineering have demonstrated the ability to restore cardiac function by preventing ventricular dilation, enhancing angiogenesis, and improving conduction velocity. However, limitations are still among them, such as poor mechanical stability, low conductivity, and complicated procedure. Here, we developed thermal plastic poly(glycolic acid) surgical suture and mussel-inspired conductive particle's adhesion into a highly elastic, conductive spring-like coils. The polypyrrole (PPy)-coated biospring acted as an electrode and then was assembled into a solid-state supercapacitor. After being injected through a syringe needle (0.33 mm inner diameter), the tangled coils formed an elastically conductive three-dimensional (3-D) network to modulate cardiac function. We found that cardiomyocytes (CMs) grew along the spring coils' track with elongated morphologies and formed highly oriented sarcomeres. The biospring enhanced the CMs' maturation in synchronous contraction accompanied by high expressions of cardiac-specific proteins, α-actinin, and connexin 43 (cx43). After the elastic, conductive biosprings were injected into the myocardial infarction (MI) area, the left ventricular fractional shortening was improved by about 12.6% and the infarct size was decreased by about 34%. Interestingly, the spring can be utilized as a sensor to measure the CMs' contractile force, which was 1.57 × 10^-3 ± 0.26 × 10^-3 mN (∼4.1 × 10⁶ cells). Accordingly, this study highlights an injectable biospring to form a tangled conductive 3-D network in vivo for MI repair.

Spatiotemporal Characterizations of Spontaneously Beating Cardiomyocytes with Adaptive Reference Digital Image Correlation

We developed an Adaptive Reference-Digital Image Correlation (AR-DIC) method that enables unbiased and accurate mechanics measurements of moving biological tissue samples. We applied the AR-DIC analysis to a spontaneously beating cardiomyocyte (CM) tissue, and could provide correct quantifications of tissue displacement and strain for the beating CMs utilizing physiologically-relevant, sarcomere displacement length-based contraction criteria. The data were further synthesized into novel spatiotemporal parameters of CM contraction to account for the CM beating homogeneity, synchronicity, and propagation as holistic measures of functional myocardial tissue development. Our AR-DIC analyses may thus provide advanced non-invasive characterization tools for assessing the development of spontaneously contracting CMs, suggesting an applicability in myocardial regenerative medicine.

Glial cells influence cardiac permittivity as evidenced through in vitro and in silico models

Excitation-contraction (EC) coupling in the heart has, until recently, been solely accredited to cardiomyocytes. The inherent complexities of the heart make it difficult to examine non-muscle contributions to contraction in vivo, and conventional in vitro models fail to capture multiple features and cellular heterogeneity of the myocardium. Here, we report on the development of a 3D cardiac μTissue to investigate changes in the cellular composition of native myocardium in vitro. Cells are encapsulated within micropatterned gelatin-based hydrogels formed via visible light photocrosslinking. This system enables spatial control of the microarchitecture, perturbation of the cellular composition, and functional measures of EC coupling via video microscopy and a custom algorithm to quantify beat frequency and degree of coordination. To demonstrate the robustness of these tools and evaluate the impact of altered cell population densities on cardiac μTissues, contractility and cell morphology were assessed with the inclusion of exogenous non-myelinating Schwann cells (SCs). Results demonstrate that the addition of exogenous SCs alter cardiomyocyte EC, profoundly inhibiting the response to electrical pacing. Computational modeling of connexin-mediated coupling suggests that SCs impact cardiomyocyte resting potential and rectification following depolarization. Cardiac μTissues hold potential for examining the role of cellular heterogeneity in heart health, pathologies, and cellular therapies.

Mutation-specific differences in arrhythmias and drug responses in CPVT patients: simultaneous patch clamp and video imaging of iPSC derived cardiomyocytes

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited cardiac disease characterized by arrhythmias under adrenergic stress. Mutations in the cardiac ryanodine receptor (RYR2) are the leading cause for CPVT. We characterized electrophysiological properties of CPVT patient-specific induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying different mutations in RYR2 and evaluated effects of carvedilol and flecainide on action potential (AP) and contractile properties of hiPSC-CMs. iPSC-CMs were generated from skin biopsies of CPVT patients carrying exon 3 deletion (E3D) and L4115F mutation in RYR2. APs and contractile movement were recorded simultaneously from the same hiPSC-CMs. Differences in AP properties of ventricular like CMs were seen in CPVT and control CMs: APD90 of both E3D (n = 20) and L4115F (n = 25) CPVT CMs was shorter than in control CMs (n = 15). E3D-CPVT CMs had shortest AP duration, lowest AP amplitude, upstroke velocity and more depolarized diastolic potential than controls. Adrenaline had positive and carvedilol and flecainide negative chronotropic effect in all hiPSC CMs. CPVT CMs had increased amount of delayed after depolarizations (DADs) and early after depolarizations (EADs) after adrenaline exposure. E3D CPVT CMs had the most DADs, EADs, and tachyarrhythmia. Discordant negatively coupled alternans was seen in L4115F CPVT CMs. Carvedilol cured almost all arrhythmias in L4115F CPVT CMs. Both drugs decreased contraction amplitude in all hiPSC CMs. E3D CPVT CMs have electrophysiological properties, which render them more prone to arrhythmias. iPSC-CMs provide a unique platform for disease modeling and drug screening for CPVT. Combining electrophysiological measurements, we can gain deeper insight into mechanisms of arrhythmias.

Instrumented Microphysiological Systems for Real-Time Measurement and Manipulation of Cellular Electrochemical Processes

Recent advancements in electronic materials and subsequent surface modifications have facilitated real-time measurements of cellular processes far beyond traditional passive recordings of neurons and muscle cells. Specifically, the functionalization of conductive materials with ligand-binding aptamers has permitted the utilization of traditional electronic materials for bioelectronic sensing. Further, microfabrication techniques have better allowed microfluidic devices to recapitulate the physiological and pathological conditions of complex tissues and organs in vitro or microphysiological systems (MPS). The convergence of these models with advances in biological/biomedical microelectromechanical systems (BioMEMS) instrumentation has rapidly bolstered a wide array of bioelectronic platforms for real-time cellular analytics. In this review, we provide an overview of the sensing techniques that are relevant to MPS development and highlight the different organ systems to integrate instrumentation for measurement and manipulation of cellular function. Special attention is given to how instrumented MPS can disrupt the drug development and fundamental mechanistic discovery processes.

Effects of Spaceflight on Human Induced Pluripotent Stem Cell-Derived Cardiomyocyte Structure and Function

With extended stays aboard the International Space Station (ISS) becoming commonplace, there is a need to better understand the effects of microgravity on cardiac function. We utilized human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) to study the effects of microgravity on cell-level cardiac function and gene expression. The hiPSC-CMs were cultured aboard the ISS for 5.5 weeks and their gene expression, structure, and functions were compared with ground control hiPSC-CMs. Exposure to microgravity on the ISS caused alterations in hiPSC-CM calcium handling. RNA-sequencing analysis demonstrated that 2,635 genes were differentially expressed among flight, post-flight, and ground control samples, including genes involved in mitochondrial metabolism. This study represents the first use of hiPSC technology to model the effects of spaceflight on human cardiomyocyte structure and function.

Quantification of Contractile Dynamic Complexities Exhibited by Human Stem Cell-Derived Cardiomyocytes Using Nonlinear Dimensional Analysis

Understanding the complexity of biological signals has been gaining widespread attention due to increasing knowledge on the nonlinearity that exists in these systems. Cardiac signals are known to exhibit highly complex dynamics, consisting of high degrees of interdependency that regulate the cardiac contractile functions. These regulatory mechanisms are important to understand for the development of novel in vitro cardiac systems, especially with the exponential growth in deriving cardiac tissue directly from human induced pluripotent stem cells (hiPSCs). This work describes a unique analytical approach that integrates linear amplitude and frequency analysis of physical cardiac contraction, with nonlinear analysis of the contraction signals to measure the signals’ complexity. We generated contraction motion waveforms reflecting the physical contraction of hiPSC-derived cardiomyocytes (hiPSC-CMs) and implemented these signals to nonlinear analysis to compute the capacity and correlation dimensions. These parameters allowed us to characterize the dynamics of the cardiac signals when reconstructed into a phase space and provided a measure of signal complexity to supplement contractile physiology data. Thus, we applied this approach to evaluate drug response and observed that relationships between contractile physiology and dynamic complexity were unique to each tested drug. This illustrated the applicability of this approach in not only characterization of cardiac signals, but also monitoring and diagnostics of cardiac health in response to external stress.

Engineering of human cardiac muscle electromechanically matured to an adult-like phenotype

The application of tissue-engineering approaches to human induced pluripotent stem (hiPS) cells enables the development of physiologically relevant human tissue models for in vitro studies of development, regeneration, and disease. However, the immature phenotype of hiPS-derived cardiomyocytes (hiPS-CMs) limits their utility. We have developed a protocol to generate engineered cardiac tissues from hiPS cells and electromechanically mature them toward an adult-like phenotype. This protocol also provides optimized methods for analyzing these tissues' functionality, ultrastructure, and cellular properties. The approach relies on biological adaptation of cultured tissues subjected to biomimetic cues, applied at an increasing intensity, to drive accelerated maturation. hiPS cells are differentiated into cardiomyocytes and used immediately after the first contractions are observed, when they still have developmental plasticity. This starting cell population is combined with human dermal fibroblasts, encapsulated in a fibrin hydrogel and allowed to compact under passive tension in a custom-designed bioreactor. After 7 d of tissue formation, the engineered tissues are matured for an additional 21 d by increasingly intense electromechanical stimulation. Tissue properties can be evaluated by measuring contractile function, responsiveness to electrical stimuli, ultrastructure properties (sarcomere length, mitochondrial density, networks of transverse tubules), force-frequency and force-length relationships, calcium handling, and responses to β-adrenergic agonists. Cell properties can be evaluated by monitoring gene/protein expression, oxidative metabolism, and electrophysiology. The protocol takes 4 weeks and requires experience in advanced cell culture and machining methods for bioreactor fabrication. We anticipate that this protocol will improve modeling of cardiac diseases and testing of drugs.

Temporal Impact of Substrate Anisotropy on Differentiating Cardiomyocyte Alignment and Functionality

Anisotropic biomaterials can affect cell function by driving cell alignment, which is critical for cardiac engineered tissues. Recent work, however, has shown that pluripotent stem cell-derived cardiomyocytes may self-align over long periods of time. To determine how the degree of biomaterial substrate anisotropy impacts differentiating cardiomyocyte structure and function, we differentiated mouse embryonic stem cells to cardiomyocytes on nonaligned, semialigned, and aligned fibrous substrates and evaluated cell alignment, contractile displacement, and calcium transient synchronicity over time. Although cardiomyocyte gene expression was not affected by fiber alignment, we observed gradient- and threshold-based differences in cardiomyocyte alignment and function. Cardiomyocyte alignment increased with the degree of fiber alignment in a gradient-based manner at early time points and in a threshold-based manner at later time points. Calcium transient synchronization tightly followed cardiomyocyte alignment behavior, allowing highly anisotropic biomaterials to drive calcium transient synchronization within 8 days, while such synchronized cardiomyocyte behavior required 20 days of culture on nonaligned biomaterials. In contrast, cardiomyocyte contractile displacement had no directional preference on day 8 yet became anisotropic in the direction of fiber alignment on aligned fibers by day 20. Biomaterial anisotropy impact on differentiating cardiomyocyte structure and function is temporally dependent. Impact Statement This work demonstrates that biomaterial anisotropy can quickly drive desired pluripotent stem cell-derived cardiomyocyte structure and function. Such an understanding of matrix anisotropy's time-dependent influence on stem cell-derived cardiomyocyte function will have future applications in the development of cardiac cell therapies and in vitro cardiac tissues for drug testing. Furthermore, our work has broader implications concerning biomaterial anisotropy effects on other cell types in which function relies on alignment, such as myocytes and neurons.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

Spatiotemporal imaging documented the maturation of the cardiomyocytes from human induced pluripotent stem cells

OBJECTIVES

Cardiomyocytes derived from human induced pluripotent stem cells are a promising source of cells for regenerative medicine. However, contractions in such derived cardiomyocytes are often irregular and asynchronous, especially at early stages of differentiation. This study aimed to determine the differentiation stage of initiation of synchronized and regular contractions, using spatiotemporal imaging and physiological and genetic analyses.

METHODS

Knock-in human induced pluripotent stem cell lines were established with clustered regularly interspaced short palindromic repeats/clustered regularly interspaced short palindromic repeats-associated protein 9 to analyze cardiac and pacemaker cell maturation. Time-frequency analysis and Ca²⁺ imaging were performed, and the expression of related proteins and specific cardiac/pacemaker mRNAs in contracting embryoid bodies was analyzed at various differentiation stages.

RESULTS

Time-frequency analysis and Ca²⁺ imaging revealed irregular, asynchronous contractions at the early stage of differentiation with altered electrophysiological properties upon differentiation. Genes associated with electrophysiological properties were upregulated after 70 days of culturing in differentiation media, whereas pacemaker genes were initially upregulated during the early stage and downregulated at the later stage.

CONCLUSIONS

A differentiation period >70 days is required for adequate development of cardiac elements including ion channels and gap junctions and for sarcomere maturation.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Adverse Drug-Induced Inotropic Effects in Early Drug Development. Part 1: General Considerations for Development of Novel Testing Platforms

Drug-induced effects on cardiac contractility can be assessed through the measurement of the maximal rate of pressure increase in the left ventricle (LVdP/dt_max) in conscious animals, and such studies are often conducted at the late stage of preclinical drug development. Detection of such effects earlier in drug research using simpler, in vitro test systems would be a valuable addition to our strategies for identifying the best possible drug development candidates. Thus, testing platforms with reasonably high throughput, and affordable costs would be helpful for early screening purposes. There may also be utility for testing platforms that provide mechanistic information about how a given drug affects cardiac contractility. Finally, there could be in vitro testing platforms that could ultimately contribute to the regulatory safety package of a new drug. The characteristics needed for a successful cell or tissue-based testing platform for cardiac contractility will be dictated by its intended use. In this article, general considerations are presented with the intent of guiding the development of new testing platforms that will find utility in drug research and development. In the following article (part 2), specific aspects of using human-induced stem cell-derived cardiomyocytes for this purpose are addressed.

In vitro aged, hiPSC-origin engineered heart tissue models with age-dependent functional deterioration to study myocardial infarction

Deaths attributed to ischemic heart disease increased by 41.7% from 1990 to 2013. This is primarily due to an increase in the aged population, however, research on cardiovascular disease (CVD) has been overlooking aging, a well-documented contributor to CVD. The use of young animals is heavily preferred due to lower costs and ready availability, despite the prominent differences between young and aged heart structure and function. Here we present the first human induced pluripotent stem cell (hiPSC)-derived cardiomyocyte (iCM)-based, in vitro aged myocardial tissue model as an alternative research platform. Within 4 months, iCMs go through accelerated senescence and show cellular characteristics of aging. Furthermore, the model tissues fabricated using aged iCMs, with stiffness resembling that of aged human heart, show functional and pharmacological deterioration specific to aged myocardium. Our novel tissue model with age-appropriate physiology and pathology presents a promising new platform for investigating CVD or other age-related diseases. STATEMENT OF SIGNIFICANCE: In vitro and in vivo models of cardiovascular disease are aimed to provide crucial insight on the pathology and treatment of these diseases. However, the contribution of age-dependent cardiovascular changes is greatly underestimated through the use of young animals and premature cardiomyocytes. Here, we developed in vitro aged cardiac tissue models that mimic the aged heart tissue microenvironment and cellular phenotype and present the first evidence that age-appropriate in vitro disease models can be developed to gain more physiologically-relevant insight on development, progression, and amelioration of cardiovascular diseases.

Reprogramming of Urine-Derived Renal Epithelial Cells into iPSCs Using srRNA and Consecutive Differentiation into Beating Cardiomyocytes

The generation of induced pluripotent stem cells (iPSCs) from patient’s somatic cells and the subsequent differentiation into desired cell types opens up numerous possibilities in regenerative medicine and tissue engineering. Adult cardiomyocytes have limited self-renewal capacity; thus, the efficient, safe, and clinically applicable generation of autologous cardiomyocytes is of great interest for the treatment of damaged myocardium. In this study, footprint-free iPSCs were successfully generated from urine-derived renal epithelial cells through a single application of self-replicating RNA (srRNA). The expression of pluripotency markers and the in vitro as well as in vivo trilineage differentiation were demonstrated. Furthermore, the resulting iPSCs contained no residual srRNA, and the karyotyping analysis demonstrated no detectable anomalies. The cardiac differentiation of these iPSCs resulted in autologous contracting cardiomyocytes after 10 days. We anticipate that the use of urine as a non-invasive cell source to obtain patient cells and the use of srRNA for reprogramming into iPSCs will greatly improve the future production of clinically applicable cardiomyocytes and other cell types. This could allow the regeneration of tissues by generating sufficient quantities of autologous cells without the risk of immune rejection.

Engineering hiPSC cardiomyocyte in vitro model systems for functional and structural assessment

The study of human cardiomyopathies and the development and testing of new therapies has long been limited by the availability of appropriate in vitro model systems. Cardiomyocytes are highly specialized cells whose internal structure and contractile function are sensitive to the local microenvironment and the combination of mechanical and biochemical cues they receive. The complementary technologies of human induced pluripotent stem cell (hiPSC) derived cardiomyocytes (CMs) and microphysiological systems (MPS) allow for precise control of the genetics and microenvironment of human cells in in vitro contexts. These combined systems also enable quantitative measurement of mechanical function and intracellular organization. This review describes relevant factors in the myocardium microenvironment that affect CM structure and mechanical function and demonstrates the application of several engineered microphysiological systems for studying development, disease, and drug discovery.

3D Cardiac Cell Culture: A Critical Review of Current Technologies and Applications

Three-dimensional (3D) cell culture is often mentioned in the context of regenerative medicine, for example, for the replacement of ischemic myocardium with tissue-engineered muscle constructs. Additionally, 3D cell culture is used, although less commonly, in basic research, toxicology, and drug development. These applications have recently benefited from innovations in stem cell technologies allowing the mass-production of hiPSC-derived cardiomyocytes or other cardiovascular cells, and from new culturing methods including organ-on-chip and bioprinting technologies. On the analysis side, improved sensors, computer-assisted image analysis, and data collection techniques have lowered the bar for switching to 3D cell culture models. Nevertheless, 3D cell culture is not as widespread or standardized as traditional cell culture methods using monolayers of cells on flat surfaces. The many possibilities of 3D cell culture, but also its limitations, drawbacks and methodological pitfalls, are less well-known. This article reviews currently used cardiovascular 3D cell culture production methods and analysis techniques for the investigation of cardiotoxicity, in drug development and for disease modeling.

Epigenetic Priming of Human Pluripotent Stem Cell-Derived Cardiac Progenitor Cells Accelerates Cardiomyocyte Maturation

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) exhibit a fetal phenotype that limits in vitro and therapeutic applications. Strategies to promote cardiomyocyte maturation have focused interventions on differentiated hPSC-CMs, but this study tests priming of early cardiac progenitor cells (CPCs) with polyinosinic-polycytidylic acid (pIC) to accelerate cardiomyocyte maturation. CPCs were differentiated from hPSCs using a monolayer differentiation protocol with defined small molecule Wnt temporal modulation, and pIC was added during the formation of early CPCs. pIC priming did not alter the expression of cell surface markers for CPCs (>80% KDR+/PDGFRα+), expression of common cardiac transcription factors, or final purity of differentiated hPSC-CMs (∼90%). However, CPC differentiation in basal medium revealed that pIC priming resulted in hPSC-CMs with enhanced maturity manifested by increased cell size, greater contractility, faster electrical upstrokes, increased oxidative metabolism, and more mature sarcomeric structure and composition. To investigate the mechanisms of CPC priming, RNAseq revealed that cardiac progenitor-stage pIC modulated early Notch signaling and cardiomyogenic transcriptional programs. Chromatin immunoprecipitation of CPCs showed that pIC treatment increased deposition of the H3K9ac activating epigenetic mark at core promoters of cardiac myofilament genes and the Notch ligand, JAG1. Inhibition of Notch signaling blocked the effects of pIC on differentiation and cardiomyocyte maturation. Furthermore, primed CPCs showed more robust formation of hPSC-CMs grafts when transplanted to the NSGW mouse kidney capsule. Overall, epigenetic modulation of CPCs with pIC accelerates cardiomyocyte maturation enabling basic research applications and potential therapeutic uses. Stem Cells 2019;37:910-923.

Targeting HIF-1α in combination with PPARα activation and postnatal factors promotes the metabolic maturation of human induced pluripotent stem cell-derived cardiomyocytes

Immature phenotypes of cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) limit the utility of these cells in clinical application and basic research. During cardiac development, postnatal cardiomyocytes experience high oxygen tension along with a concomitant downregulation of hypoxia-inducible factor 1α (HIF-1α), leading to increased fatty acid oxidation (FAO). We hypothesized that targeting HIF-1α alone or in combination with other metabolic regulators could promote the metabolic maturation of hiPSC-CMs. We examined the effect of HIF-1α inhibition on the maturation of hiPSC-CMs and investigated a multipronged approach to promote hiPSC-CM maturation by combining HIF-1α inhibition with molecules that target key pathways involved in the energy metabolism. Cardiac spheres of highly-enriched hiPSC-CMs were treated with a HIF-1α inhibitor alone or in combination with an agonist of peroxisome proliferator activated receptor α (PPARα) and three postnatal factors (triiodothyronine hormone T3, insulin-like growth factor-1 and dexamethasone). HIF-1α inhibition significantly increased FAO and basal and maximal respiration of hiPSC-CMs. Combining HIF-1α inhibition with PPARα activation and the postnatal factors further increased FAO and improved mitochondrial maturation in hiPSC-CMs. Compared with mock-treated cultures, the cultures treated with the five factors had increased mitochondrial content and contained more cells with mitochondrial distribution throughout the cells, which are features of more mature cardiomyocytes. Consistent with these observations, a number of transcriptional regulators of mitochondrial metabolic processes were upregulated in hiPSC-CMs treated with the five factors. Furthermore, these cells had significantly increased Ca²⁺ transient kinetics and contraction and relaxation velocities, which are functional features for more mature cardiomyocytes. Therefore, targeting HIF-1α in combination with other metabolic regulators significantly improves the metabolic maturation of hiPSC-CMs.

Easy Applied Gelatin-Based Hydrogel System for Long-Term Functional Cardiomyocyte Culture and Myocardium Formation

Harnessing biomaterials for in vitro tissue construction has long been a research focus because of its powerful potentials in tissue engineering and pharmaceutical industry. Myocardium is a critical cardiac tissue with complex multiple muscular layers. Considering the specific characters of native cardiac tissues, it is necessary to design a biocompatible and biomimetic platform for cardiomyocyte culture and myocardium formation with sustained physiological function. In this study, we developed gelatin-based hydrogels chemically cross-linked by genipin, a biocompatible cross-linker, as cell culture scaffolds. Moreover, to achieve and maintain the functionality of myocardium, for instance, well-organized cardiomyocytes and synchronized contractile behavior, we fabricated gelatin-based hydrogels with patterned microstructure using a microcontact printing technique. Furthermore, graphene oxide (GO), with unprecedented physical and chemical properties, has also been incorporated into gelatin for culturing cardiomyocytes. Our results show that micropatterned genipin-cross-linked gelatin hydrogels are very helpful to promote alignment and maturation of neonatal rat ventricular cardiomyocytes. More interestingly, the presence of GO significantly enhances the functional performance of cardiomyocytes, including an increase in contraction amplitude and cardiac gene expression. The cultured cardiomyocytes reach a well-synchronized contraction within 48 h of cell seeding and keep beating for up to 3 months. Our study provides a new and easy-to-use gelatin-based scaffold for improving physiological function of engineered cardiac tissues, exhibiting promising applications in cardiac tissue engineering and drug screening.

User-Friendly and Parallelized Generation of Human Induced Pluripotent Stem Cell-Derived Microtissues in a Centrifugal Heart-on-a-Chip

IMPACT STATEMENT

With the ultimate goal in tissue engineering of approaching in vivo functionality as closely as possible, organ-on-a-chip (OoC) systems provide unprecedented game-changing opportunities by enabling creation of perfused three-dimensional tissues. Most of the recently developed OoC systems, however, require complex handling steps. Hence, a large gap still exists between technology development and collection of valuable biological data in a standardized medium- or high-throughput manner. The system presented here bridges this gap by providing a user-friendly framework for the parallelized creation of multiple physiologically relevant tissues, which could be applicable in every laboratory without additional equipment.

Modelling sarcomeric cardiomyopathies with human cardiomyocytes derived from induced pluripotent stem cells

Cardiomyocytes derived from human induced pluripotent stem cells (iPSCs) provide a unique opportunity to understand the pathophysiological effects of genetic cardiomyopathy mutations. In particular, these cells hold the potential to unmask the effects of mutations on contractile behaviour in vitro, providing new insights into genotype-phenotype relationships. With this goal in mind, several groups have established iPSC lines that contain sarcomeric gene mutations linked to cardiomyopathy in patient populations. Their studies have employed diverse systems and methods for performing mechanical measurements of contractility, ranging from single cell techniques to multicellular tissue-like constructs. Here, we review published results to date within the growing field of iPSC-based sarcomeric cardiomyopathy disease models. We devote special attention to the methods of mechanical characterization selected in each case, and how these relate to the paradigms of classical muscle mechanics. An appreciation of these somewhat subtle paradigms can inform efforts to compare the results of different studies and possibly reconcile discrepancies. Although more work remains to be done to improve and possibly standardize methods for producing, maturing, and mechanically interrogating iPSC-derived cardiomyocytes, the initial results indicate that this approach to modelling cardiomyopathies will continue to provide critical insights into these devastating diseases.

Rapid 3D bioprinting of in vitro cardiac tissue models using human embryonic stem cell-derived cardiomyocytes

There is a great need for physiologically relevant 3D human cardiac scaffolds for both short-term, the development of drug testing platforms to screen new drugs across different genetic backgrounds, and longer term, the replacement of damaged or non-functional cardiac tissue after injury or infarction. In this study, we have designed and printed a variety of scaffolds for in vitro diagnostics using light based Micro-Continuous Optical Printing (μCOP). Human embryonic stem cell-derived cardiomyocyte (hESC-CMs) were directly printed into gelatin hydrogel on glass to determine their viability and ability to align. The incorporation of Green Fluorescent Protein/Calmodulin/M13 Peptide (GCaMP3)-hESC-CMs allowed the ability to continuously monitor calcium transients over time. Normalized fluorescence of GCaMP3-hESCCMs increased by 18 ± 6% and 40 ± 5% when treated with 500 nM and 1 μM of isoproterenol, respectively. Finally, GCaMP3-hESC-CMs were printed across a customizable 3D printed cantilever-based force system. Along with force tracking by visualizing the displacement of the cantilever, calcium transients could be observed in a non-destructive manner, allowing the samples to be examined over several days. Our μCOP-printed cardiac models presented here can be used as a powerful tool for drug screening and to analyze cardiac tissue maturation.

The reduced activity of PP-1α under redox stress condition is a consequence of GSH-mediated transient disulfide formation

Heart failure is the most common cause of morbidity and hospitalization in the western civilization. Protein phosphatases play a key role in the basal cardiac contractility and in the responses to β-adrenergic stimulation with type-1 phosphatase (PP-1) being major contributor. We propose here that formation of transient disulfide bridges in PP-1α might play a leading role in oxidative stress response. First, we established an optimized workflow, the so-called "cross-over-read" search method, for the identification of disulfide-linked species using permutated databases. By applying this method, we demonstrate the formation of unexpected transient disulfides in PP-1α to shelter against over-oxidation. This protection mechanism strongly depends on the fast response in the presence of reduced glutathione. Our work points out that the dimerization of PP-1α involving Cys³⁹ and Cys¹²⁷ is presumably important for the protection of PP-1α active surface in the absence of a substrate. We finally give insight into the electron transport from the PP-1α catalytic core to the surface. Our data suggest that the formation of transient disulfides might be a general mechanism of proteins to escape from irreversible cysteine oxidation and to prevent their complete inactivation.

An Ultrasensitive Calcium Reporter System via CRISPR-Cas9-Mediated Genome Editing in Human Pluripotent Stem Cells

Genetically encoded calcium indicator (GCaMP) proteins have been reported for imaging cardiac cell activity based on intracellular calcium transients. To bring human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) to the clinic, it is critical to evaluate the functionality of CMs. Here, we show that GCaMP6s-expressing hPSCs can be generated and used for CM characterization. By leveraging CRISPR-Cas9 genome editing tools, we generated a knockin cell line that constitutively expresses GCaMP6s, an ultrasensitive calcium sensor protein. We further showed that this clone maintained pluripotency and cardiac differentiation potential. These knockin hPSC-derived CMs exhibited sensitive fluorescence fluctuation with spontaneous contraction. We then compared the fluorescence signal with mechanical contraction signal. The knockin hPSC-derived CMs also showed sensitive response to isoprenaline treatment in a concentration-dependent manner. Therefore, the GCaMP6s knockin hPSC line provides a non-invasive, sensitive, and economic approach to characterize the functionality of hPSC-derived CMs.

Engineering cardiac microphysiological systems to model pathological extracellular matrix remodeling

Many cardiovascular diseases are associated with pathological remodeling of the extracellular matrix (ECM) in the myocardium. ECM remodeling is a complex, multifactorial process that often contributes to declines in myocardial function and progression toward heart failure. However, the direct effects of the many forms of ECM remodeling on myocardial cell and tissue function remain elusive, in part because conventional model systems used to investigate these relationships lack robust experimental control over the ECM. To address these shortcomings, microphysiological systems are now being developed and implemented to establish direct relationships between distinct features in the ECM and myocardial function with unprecedented control and resolution in vitro. In this review, we will first highlight the most prominent characteristics of ECM remodeling in cardiovascular disease and describe how these features can be mimicked with synthetic and natural biomaterials that offer independent control over multiple ECM-related parameters, such as rigidity and composition. We will then detail innovative microfabrication techniques that enable precise regulation of cellular architecture in two and three dimensions. We will also describe new approaches for quantifying multiple aspects of myocardial function in vitro, such as contractility, action potential propagation, and metabolism. Together, these collective technologies implemented as cardiac microphysiological systems will continue to uncover important relationships between pathological ECM remodeling and myocardial cell and tissue function, leading to new fundamental insights into cardiovascular disease, improved human disease models, and novel therapeutic approaches.

Multi-parametric cell profiling with a CMOS quad-modality cellular interfacing array for label-free fully automated drug screening

Cells are complex systems with concurrent multi-physical responses, and cell physiological signals are often encoded with spatiotemporal dynamics and further coupled with multiple cellular activities. However, most existing electronic sensors are only single-modality and cannot capture multi-parametric cellular responses. In this paper, a 1024-pixel CMOS quad-modality cellular interfacing array that enables multi-parametric cell profiling for drug development is presented. The quad-modality CMOS array features cellular impedance characterization, optical detection, extracellular potential recording, and biphasic current stimulation. The fibroblast transparency and surface adhesion are jointly monitored by cellular impedance and optical sensing modalities for comprehensive cell growth evaluation. Simultaneous current stimulation and opto-mechanical monitoring based on cardiomyocytes are demonstrated without any stimulation/sensing dead-zone. Furthermore, drug dose-dependent multi-parametric feature extractions in cardiomyocytes from their extracellular potentials and opto-mechanical signals are presented. The CMOS array demonstrates great potential for fully automated drug screening and drug safety assessments, which may substantially reduce the drug screening time and cost in future new drug development.

Targeted Elimination of Tumorigenic Human Pluripotent Stem Cells Using Suicide-Inducing Virus-like Particles

Sensitization to prodrugs via transgenic expression of suicide genes is a leading strategy for the selective elimination of potentially tumorigenic human pluripotent stem cells (hPSCs) in regenerative medicine, but transgenic modification poses safety risks such as deleterious mutagenesis. We describe here an alternative method of delivering suicide-inducing molecules explicitly to hPSCs using virus-like particles (VLPs) and demonstrate its use in eliminating undifferentiated hPSCs in vitro. VLPs were engineered from Qβ bacteriophage capsids to contain enhanced green fluorescent protein (EGFP) or cytosine deaminase (CD) and to simultaneously display multiple IgG-binding ZZ domains. After labeling with antibodies against the hPSC-specific surface glycan SSEA-5, EGFP-containing particles were shown to specifically bind undifferentiated cells in culture, and CD-containing particles were able to eliminate undifferentiated hPSCs with virtually no cytotoxicity to differentiated cells upon treatment with the prodrug 5-fluorocytosine.