Automated analysis of contractile force and Ca2+ transients in engineered heart tissue

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

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

Nonclinical evaluation of chronic cardiac contractility modulation on 3D human engineered cardiac tissues

INTRODUCTION

Cardiac contractility modulation (CCM) is a medical device-based therapy delivering non-excitatory electrical stimulations to the heart to enhance cardiac function in heart failure (HF) patients. The lack of human in vitro tools to assess CCM hinders our understanding of CCM mechanisms of action. Here, we introduce a novel chronic (i.e., 2-day) in vitro CCM assay to evaluate the effects of CCM in a human 3D microphysiological system consisting of engineered cardiac tissues (ECTs).

METHODS

Cryopreserved human induced pluripotent stem cell-derived cardiomyocytes were used to generate 3D ECTs. The ECTs were cultured, incorporating human primary ventricular cardiac fibroblasts and a fibrin-based gel. Electrical stimulation was applied using two separate pulse generators for the CCM group and control group. Contractile properties and intracellular calcium were measured, and a cardiac gene quantitative PCR screen was conducted.

RESULTS

Chronic CCM increased contraction amplitude and duration, enhanced intracellular calcium transient amplitude, and altered gene expression related to HF (i.e., natriuretic peptide B, NPPB) and excitation-contraction coupling (i.e., sodium-calcium exchanger, SLC8).

CONCLUSION

These data represent the first study of chronic CCM in a 3D ECT model, providing a nonclinical tool to assess the effects of cardiac electrophysiology medical device signals complementing in vivo animal studies. The methodology established a standardized 3D ECT-based in vitro testbed for chronic CCM, allowing evaluation of physiological and molecular effects on human cardiac tissues.

A highly versatile biopolymer-based platform for the maturation of human pluripotent stem cell-derived cardiomyocytes enables functional analysis in vitro and 3D printing of heart patches

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) represent a valuable tool for in vitro modeling of the cardiac niche and possess great potential in tissue engineering applications. However, conventional polystyrene-based cell culture substrates have adverse effects on cardiomyocytes in vitro due to the stress applied by a stiff substrate on contractile cells. Ultra-high viscosity alginates offer a unique versatility as tunable substrates for cardiac cell cultures due to their biocompatibility, flexible biofunctionalization, and stability. In this work, we analyzed the effect of alginate substrates on hPSC-CM maturity and functionality. Alginate substrates in high-throughput compatible culture formats fostered a more mature gene expression and enabled the simultaneous assessment of chronotropic and inotropic effects upon beta-adrenergic stimulation. Furthermore, we produced 3D-printed alginate scaffolds with differing mechanical properties and plated hPSC-CMs on the surface of these to create Heart Patches for tissue engineering applications. These exhibited synchronous macro-contractions in concert with more mature gene expression patterns and extensive intracellular alignment of sarcomeric structures. In conclusion, the combination of biofunctionalized alginates and human cardiomyocytes represents a valuable tool for both in vitro modeling and regenerative medicine, due to its beneficial effects on cardiomyocyte physiology, the possibility to analyze cardiac contractility, and its applicability as Heart Patches.

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

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

Automated Dual-Mode Cell Monitoring To Simultaneously Explore Calcium Dynamics and Contraction-Relaxation Kinetics within Drug-Treated Stem Cell-Derived Cardiomyocytes

This manuscript proposes a new dual-mode cell imaging system for studying the relationships between calcium dynamics and the contractility process of cardiomyocytes derived from human-induced pluripotent stem cells. Practically, this dual-mode cell imaging system provides simultaneously both live cell calcium imaging and quantitative phase imaging based on digital holographic microscopy. Specifically, thanks to the development of a robust automated image analysis, simultaneous measurements of both intracellular calcium, a key player of excitation-contraction coupling, and the quantitative phase image-derived dry mass redistribution, reflecting the effective contractility, namely, the contraction and relaxation processes, were achieved. Practically, the relationships between calcium dynamics and the contraction-relaxation kinetics were investigated in particular through the application of two drugs─namely, isoprenaline and E-4031─known to act precisely on calcium dynamics. Specifically, this new dual-mode cell imaging system enabled us to establish that calcium regulation can be divided into two phases, an early phase influencing the occurrence of the relaxation process followed by a late phase, which although not having a significant influence on the relaxation process affects significantly the beat frequency. In combination with cutting-edge technologies allowing the generation of human stem cell-derived cardiomyocytes, this dual-mode cell monitoring approach therefore represents a very promising technique, particularly in the fields of drug discovery and personalized medicine, to identify compounds likely to act more selectively on specific steps that compose the cardiomyocyte contractility.

[Toward Regulatory Acceptance of MPS-Cardiac Safety Assessment as an Example]

Microphysiological system (MPS) are "Cell/tissue culture systems that reproduce in vivo organ functions in vitro by placing organ compartments that mimic the physiological environment of various organs such as the liver, small intestine, and lungs in micro-spaces." The MPS are attracting attention around the world as tools to improve human predictability in drug discovery research. In the U.S., in 2012, the NIH (National Institutes of Health) allocated a large budget to academia for research development of MPS. In Japan, the National Institute of Advanced Industrial Science and Technology and the NIHS (National Institute of Health Sciences) have been playing a central role in commercialization, performance evaluation, and standardization of MPS devices developed by academia for the liver, small intestine, kidney, and BBB as target organs/tissues in the AMED-MPS project that started in 2017. Pharmaceutical companies are beginning to utilize MPS in drug discovery research. However, MPS have only just been raised as a topic of discussion between regulatory authorities and pharmaceutical companies, and it will be necessary to overcome many barriers before data obtained by MPS can be included in drug approval documents and be widely accepted administratively. In this review, I would like to introduce cardiac safety evaluation as a concrete example to show what paths MPS should take to gain regulatory approval. In addition, I would like also to introduce human 3D heart tissue, which was developed in NIHS, as a cardiac MPS.

In vitro circulation model driven by tissue-engineered dome-shaped cardiac tissue

The heart is an essential organ for animals and humans. With the increased availability of pluripotent stem cells, the use of three-dimensional cardiac tissues consisting of cultured cardiomyocytes in in vitro drug evaluation has been widely studied. Several models have been proposed for the realization of the pump function, which is the original function of the heart. However, there are no models that simulate the human circulatory system using cultured cardiac tissue. This study shows that a dome-shaped cardiac tissue fabricated using the cell sheet stacking technique can achieve a heart-like pump function and circulate culture medium, there by mimicking the human circulatory system. Firstly, human induced pluripotent stem cells were differentiated into autonomously beating cardiomyocytes, and cardiomyocyte cell sheets were created using temperature-responsive culture dishes. A cardiomyocyte sheet and a human dermal fibroblast sheet were stacked using a cell sheet manipulator. This two-layered cell sheet was then inflated to create a dome-shaped cardiac tissue with a base diameter of 8 mm. The volume of the dome-shaped cardiac tissue changed according to the autonomous beating. The stroke volume increased with the culture period and reached 21 ± 8.9 μL (n = 6) on day 21. It also responded to β-stimulant and extracellular calcium concentrations. Internal pressure fluctuations were also recorded under isovolumetric conditions by dedicated culture devices. The peak heights of pulsatile pressure were 0.33 ± 0.048 mmHg (n = 3) under a basal pressure of 0.5 mmHg on day 19. When the tissue was connected to a flow path that had check valves applied, it drove a directional flow with an average flow rate of approximately 1 μL/s. Furthermore, pressure-volume (P-V) diagrams were created from the simultaneous measurement of changes in pressure and volume under three conditions of fluidic resistance. In conclusion, this cardiac model can potentially be used for biological pumps that drive multi-organ chips and for more accurate in vitro drug evaluation using P-V diagrams.

A Change of Heart: Human Cardiac Tissue Engineering as a Platform for Drug Development

PURPOSE OF REVIEW

Human cardiac tissue engineering holds great promise for early detection of drug-related cardiac toxicity and arrhythmogenicity during drug discovery and development. We describe shortcomings of the current drug development pathway, recent advances in the development of cardiac tissue constructs as drug testing platforms, and the challenges remaining in their widespread adoption.

RECENT FINDINGS

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) have been used to develop a variety of constructs including cardiac spheroids, microtissues, strips, rings, and chambers. Several ambitious studies have used these constructs to test a significant number of drugs, and while most have shown proper negative inotropic and arrhythmogenic responses, few have been able to demonstrate positive inotropy, indicative of relative hPSC-CM immaturity. Several engineered human cardiac tissue platforms have demonstrated native cardiac physiology and proper drug responses. Future studies addressing hPSC-CM immaturity and inclusion of patient-specific cell lines will further advance the utility of such models for in vitro drug development.

Live-Cell Imaging of the Contractile Velocity and Transient Intracellular Ca2+ Fluctuations in Human Stem Cell-Derived Cardiomyocytes

Live-cell imaging techniques are essential for acquiring vital physiological and pathophysiological knowledge to understand and treat heart disease. For live-cell imaging of transient alterations of [Ca2+]i in human cardiomyocytes, we engineered human-induced pluripotent stem cells carrying a genetically-encoded Ca2+-indicator (GECI). To monitor sarcomere shortening and relaxation in cardiomyocytes in real-time, we generated a α-cardiac actinin (ACTN2)-copepod (cop) green fluorescent protein (GFP+)-human-induced pluripotent stem cell line by using the CRISPR-Cas9 and a homology directed recombination approach. The engineered human-induced pluripotent stem cells were differentiated in transgenic GECI-enhanced GFP+-cardiomyocytes and ACTN2-copGFP+-cardiomyocytes, allowing real-time imaging of [Ca2+]i transients and live recordings of the sarcomere shortening velocity of ACTN2-copGFP+-cardiomyocytes. We developed a video analysis software tool to quantify various parameters of sarcoplasmic Ca2+ fluctuations recorded during contraction of cardiomyocytes and to calculate the contraction velocity of cardiomyocytes in the presence and absence of different drugs affecting cardiac function. Our cellular and software tool not only proved the positive and negative inotropic and lusitropic effects of the tested cardioactive drugs but also quantified the expected effects precisely. Our platform will offer a human-relevant in vitro alternative for high-throughput drug screenings, as well as a model to explore the underlying mechanisms of cardiac diseases.

Comprehensive analyses of the inotropic compound omecamtiv mecarbil in rat and human cardiac preparations

Omecamtiv mecarbil (OM), a myosin activator, was reported to induce complex concentration- and species-dependent effects on contractile function and clinical studies indicated a low therapeutic index with diastolic dysfunction at concentrations above 1 µM. To further characterize effects of OM in a human context and under different preload conditions, we constructed a setup that allows isometric contractility analyses of human induced pluripotent stem cell (hiPSC)-derived engineered heart tissues (EHTs). The results were compared to effects of OM on the very same EHTs measured under auxotonic conditions. OM induced a sustained, concentration-dependent increase in time-to-peak under all conditions (maximally 2-3 fold). Peak force, in contrast, was increased by OM only in human, but not rat EHTs and only under isometric conditions, varied between hiPSC lines and showed a biphasic concentration-dependency with maximal effects at 1 µM. Relaxation time tended to fall under auxotonic and strongly increase under isometric conditions, again with biphasic concentration-dependency. Diastolic tension concentration-dependently increased under all conditions. The latter was reduced by an inhibitor of the mitochondrial sodium calcium exchanger (CGP-37157). OM induced increases in mitochondrial oxidation in isolated cardiomyocytes, indicating that OM, an inotrope that does not increase intracellular and mitochondrial Ca²⁺, can induce mismatch between an increase in ATP and ROS production and unstimulated mitochondrial redox capacity. Taken together, we developed a novel setup well suitable for isometric measurements of EHTs. The effects of OM on contractility and diastolic tension are complex with concentration-, time-, species- and loading-dependent differences. Effects on mitochondrial function require further studies.

"Ryanopathies" and RyR2 dysfunctions: can we further decipher them using in vitro human disease models?

The regulation of intracellular calcium (Ca²⁺) homeostasis is fundamental to maintain normal functions in many cell types. The ryanodine receptor (RyR), the largest intracellular calcium release channel located on the sarco/endoplasmic reticulum (SR/ER), plays a key role in the intracellular Ca²⁺ handling. Abnormal type 2 ryanodine receptor (RyR2) function, associated to mutations (ryanopathies) or pathological remodeling, has been reported, not only in cardiac diseases, but also in neuronal and pancreatic disorders. While animal models and in vitro studies provided valuable contributions to our knowledge on RyR2 dysfunctions, the human cell models derived from patients’ cells offer new hope for improving our understanding of human clinical diseases and enrich the development of great medical advances. We here discuss the current knowledge on RyR2 dysfunctions associated with mutations and post-translational remodeling. We then reviewed the novel human cellular technologies allowing the correlation of patient’s genome with their cellular environment and providing approaches for personalized RyR-targeted therapeutics.

Engineered models of the human heart: Directions and challenges

Human heart (patho)physiology is now widely studied using human pluripotent stem cells, but the immaturity of derivative cardiomyocytes has largely limited disease modeling to conditions associated with mutations in cardiac ion channel genes. Recent advances in tissue engineering and organoids have, however, created new opportunities to study diseases beyond "channelopathies." These synthetic cardiac structures allow quantitative measurement of contraction, force, and other biophysical parameters in three-dimensional configurations, in which the cardiomyocytes in addition become more mature. Multiple cardiac-relevant cell types are also often combined to form organized cardiac tissue mimetic constructs, where cell-cell, cell-extracellular matrix, and paracrine interactions can be mimicked. In this review, we provide an overview of some of the most promising technologies being implemented specifically in personalized heart-on-a-chip models and explore their applications, drawbacks, and potential for future development.

Depressed β-adrenergic inotropic responsiveness and intracellular calcium handling abnormalities in Duchenne Muscular Dystrophy patients' induced pluripotent stem cell-derived cardiomyocytes

Duchenne muscular dystrophy (DMD), caused by mutations in the dystrophin gene, is an X-linked disease affecting male and rarely adult heterozygous females, resulting in death by the late 20s to early 30s. Previous studies reported depressed left ventricular function in DMD patients which may result from deranged intracellular Ca2+ -handling. To decipher the mechanism(s) underlying the depressed LV function, we tested the hypothesis that iPSC-CMs generated from DMD patients feature blunted positive inotropic response to β-adrenergic stimulation. To test the hypothesis, [Ca2+ ]i transients and contractions were recorded from healthy and DMD-CMs. While in healthy CMs (HC) isoproterenol caused a prominent positive inotropic effect, DMD-CMs displayed a blunted inotropic response. Next, we tested the functionality of the sarcoplasmic reticulum (SR) by measuring caffeine-induced Ca2+ release. In contrast to HC, DMD-CMs exhibited reduced caffeine-induced Ca2+ signal amplitude and recovery time. In support of the depleted SR Ca2+ stores hypothesis, in DMD-CMs the negative inotropic effects of ryanodine and cyclopiazonic acid were smaller than in HC. RNA-seq analyses demonstrated that in DMD CMs the RNA-expression levels of specific subunits of the L-type calcium channel, the β1-adrenergic receptor (ADRβ1) and adenylate cyclase were down-regulated by 3.5-, 2.8- and 3-fold, respectively, which collectively contribute to the depressed β-adrenergic responsiveness.

In vitro and In silico Models to Study SARS-CoV-2 Infection: Integrating Experimental and Computational Tools to Mimic "COVID-19 Cardiomyocyte"

The rapid dissemination of SARS-CoV-2 has made COVID-19 a tremendous social, economic, and health burden. Despite the efforts to understand the virus and treat the disease, many questions remain unanswered about COVID-19 mechanisms of infection and progression. Severe Acute Respiratory Syndrome (SARS) infection can affect several organs in the body including the heart, which can result in thromboembolism, myocardial injury, acute coronary syndromes, and arrhythmias. Numerous cardiac adverse events, from cardiomyocyte death to secondary effects caused by exaggerated immunological response against the virus, have been clinically reported. In addition to the disease itself, repurposing of treatments by using "off label" drugs can also contribute to cardiotoxicity. Over the past several decades, animal models and more recently, stem cell-derived cardiomyocytes have been proposed for studying diseases and testing treatments in vitro. In addition, mechanistic in silico models have been widely used for disease and drug studies. In these models, several characteristics such as gender, electrolyte imbalance, and comorbidities can be implemented to study pathophysiology of cardiac diseases and to predict cardiotoxicity of drug treatments. In this Mini Review, we (1) present the state of the art of in vitro and in silico cardiomyocyte modeling currently in use to study COVID-19, (2) review in vitro and in silico models that can be adopted to mimic the effects of SARS-CoV-2 infection on cardiac function, and (3) provide a perspective on how to combine some of these models to mimic "COVID-19 cardiomyocytes environment.".

Multiparametric Mechanistic Profiling of Inotropic Drugs in Adult Human Primary Cardiomyocytes

Effects of non-cardiac drugs on cardiac contractility can lead to serious adverse events. Furthermore, programs aimed at treating heart failure have had limited success and this therapeutic area remains a major unmet medical need. The challenges in assessing drug effect on cardiac contractility point to the fundamental translational value of the current preclinical models. Therefore, we sought to develop an adult human primary cardiomyocyte contractility model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic effect (sarcomere shortening) and generating multi-parameter data to profile different mechanisms of action based on cluster analysis of a set of 12 contractility parameters. We report that 17 positive and 9 negative inotropes covering diverse mechanisms of action exerted concentration-dependent increases and decreases in sarcomere shortening, respectively. Interestingly, the multiparametric readout allowed for the differentiation of inotropes operating via distinct mechanisms. Hierarchical clustering of contractility transient parameters, coupled with principal component analysis, enabled the classification of subsets of both positive as well as negative inotropes, in a mechanism-related mode. Thus, human cardiomyocyte contractility model could accurately facilitate informed mechanistic-based decision making, risk management and discovery of molecules with the most desirable pharmacological profile for the correction of heart failure.

Force and Calcium Transients Analysis in Human Engineered Heart Tissues Reveals Positive Force-Frequency Relation at Physiological Frequency

Force measurements in ex vivo and engineered heart tissues are well established. Analysis of calcium transients (CaT) is complementary to force, and the combined analysis is meaningful to the study of cardiomyocyte biology and disease. This article describes a model of human induced pluripotent stem cell cardiomyocyte-derived engineered heart tissues (hiPSC-CM EHTs) transduced with the calcium sensor GCaMP6f followed by sequential analysis of force and CaT. Average peak analysis demonstrated the temporal sequence of the CaT preceding the contraction twitch. The pharmacological relevance of the test system was demonstrated with inotropic indicator compounds. Force-frequency relationship was analyzed in the presence of ivabradine (300 nM), which reduced spontaneous frequency and unmasked a positive correlation of force and CaT at physiological human heart beating frequency with stimulation frequency between 0.75 and 2.5 Hz (force +96%; CaT +102%). This work demonstrates the usefulness of combined force/CaT analysis and demonstrates a positive force-frequency relationship in hiPSC-CM EHTs.

•

Analysis of calcium transients and force in engineered heart tissues

•

Accurate replications of drug effects on calcium transients and force analysis

•

Positive force- and calcium transients-frequency relationship

•

Reverse correlation between omecamtiv mecarbil's inotropic effect and frequency

Human Heart Cardiomyocytes in Drug Discovery and Research: New Opportunities in Translational Sciences

In preclinical drug development, accurate prediction of drug effects on the human heart is critically important, whether in the context of cardiovascular safety or for the purpose of modulating cardiac function to treat heart disease. Current strategies have significant limitations, whereby, cardiotoxic drugs can escape detection or potential life-saving therapies are abandoned due to false positive toxicity signals. Thus, new and more reliable translational approaches are urgently needed to help accelerate the rate of new therapy development. Renewed efforts in the recovery of human donor hearts for research and in cardiomyocyte isolation methods, are providing new opportunities for preclinical studies in adult primary cardiomyocytes. These cells exhibit the native physiological and pharmacological properties, overcoming the limitations presented by artificial cellular models, animal models and have great potential for providing an excellent tool for preclinical drug testing. Adult human primary cardiomyocytes have already shown utility in assessing drug-induced cardiotoxicity risk and helping in the identification of new treatments for cardiac diseases, such as heart failure and atrial fibrillation. Finally, strategies with actionable decision-making trees that rely on data derived from adult human primary cardiomyocytes will provide the holistic insights necessary to accurately predict human heart effects of drugs.

Disease modeling of a mutation in α-actinin 2 guides clinical therapy in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease accompanied by structural and contractile alterations. We identified a rare c.740C>T (p.T247M) mutation in ACTN2, encoding α-actinin 2 in a HCM patient, who presented with left ventricular hypertrophy, outflow tract obstruction, and atrial fibrillation. We generated patient-derived human-induced pluripotent stem cells (hiPSCs) and show that hiPSC-derived cardiomyocytes and engineered heart tissues recapitulated several hallmarks of HCM, such as hypertrophy, myofibrillar disarray, hypercontractility, impaired relaxation, and higher myofilament Ca²⁺ sensitivity, and also prolonged action potential duration and enhanced L-type Ca²⁺ current. The L-type Ca²⁺ channel blocker diltiazem reduced force amplitude, relaxation, and action potential duration to a greater extent in HCM than in isogenic control. We translated our findings to patient care and showed that diltiazem application ameliorated the prolonged QTc interval in HCM-affected son and sister of the index patient. These data provide evidence for this ACTN2 mutation to be disease-causing in cardiomyocytes, guiding clinical therapy in this HCM family. This study may serve as a proof-of-principle for the use of hiPSC for personalized treatment of cardiomyopathies.

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.

Modeling Hypertrophic Cardiomyopathy: Mechanistic Insights and Pharmacological Intervention

Hypertrophic cardiomyopathy (HCM) is a prevalent and complex cardiovascular disease where cardiac dysfunction often associates with mutations in sarcomeric genes. Various models based on tissue explants, isolated cardiomyocytes, skinned myofibrils, and purified actin/myosin preparations have uncovered disease hallmarks, enabling the development of putative therapeutics, with some reaching clinical trials. Newly developed human pluripotent stem cell (hPSC)-based models could be complementary by overcoming some of the inconsistencies of earlier systems, whilst challenging and/or clarifying previous findings. In this article we compare recent progress in unveiling multiple HCM mechanisms in different models, highlighting similarities and discrepancies. We explore how insight is facilitating the design of new HCM therapeutics, including those that regulate metabolism, contraction and heart rhythm, providing a future perspective for treatment of HCM.

Cardiovascular disease models: A game changing paradigm in drug discovery and screening

Cardiovascular disease is the leading cause of death worldwide. Although investment in drug discovery and development has been sky-rocketing, the number of approved drugs has been declining. Cardiovascular toxicity due to therapeutic drug use claims the highest incidence and severity of adverse drug reactions in late-stage clinical development. Therefore, to address this issue, new, additional, replacement and combinatorial approaches are needed to fill the gap in effective drug discovery and screening. The motivation for developing accurate, predictive models is twofold: first, to study and discover new treatments for cardiac pathologies which are leading in worldwide morbidity and mortality rates; and second, to screen for adverse drug reactions on the heart, a primary risk in drug development. In addition to in vivo animal models, in vitro and in silico models have been recently proposed to mimic the physiological conditions of heart and vasculature. Here, we describe current in vitro, in vivo, and in silico platforms for modelling healthy and pathological cardiac tissues and their advantages and disadvantages for drug screening and discovery applications. We review the pathophysiology and the underlying pathways of different cardiac diseases, as well as the new tools being developed to facilitate their study. We finally suggest a roadmap for employing these non-animal platforms in assessing drug cardiotoxicity and safety.

Human iPS Cell-Derived Patient Tissues and 3D Cell Culture Part 2: Spheroids, Organoids, and Disease Modeling

Human induced pluripotent stem cells (HiPSCs) provide several advantages for drug discovery, but principally they provide a source of clinically relevant tissue. Furthermore, the use of HiPSCs cultured in three-dimensional (3D) systems, as opposed to traditional two-dimensional (2D) culture approaches, better represents the complex tissue architecture in vivo. The use of HiPSCs in 3D spheroid and organoid culture is now growing, but particularly when using myocardial, intestinal enteric nervous system, and retinal cell lines. However, organoid cell culture is perhaps making the most notable impact in research and drug discovery, in which 3D neuronal cell cultures allow direct modeling of cortical cell layering and neuronal circuit activity. Given the specific degeneration seen in discrete neuronal circuitry in Alzheimer’s disease (AD) and Parkinson’s disease (PD), HiPSC culture systems are proving to be a major advance. In the present review, the second part of a two-part review, we discuss novel methods in which 3D cell culture systems (principally organoids) are now being used to provide insights into disease mechanisms. (The use of HiPSCs in target identification was reviewed in detail in Part 1.)

Piezo-bending actuators for isometric or auxotonic contraction analysis of engineered heart tissue

Engineered heart tissue (EHT) has proven as valuable tool for disease modelling, drug safety screening, and cardiac repair. Especially in combination with the stem cell technology, these in vitro models of the human heart have generated interest not only of basic cardiovascular researchers but also of regulatory authorities responsible for drug safety. A main limitation of 3D-based assays for evaluating cardiotoxicity is their limited throughput. We integrated piezo-bending actuators in a 24-well system for the generation of strip-like rat and human EHT attached to hollow, elastic silicone posts. Muscle contractions of EHTs induced a measurable electrical current in the piezo-bending actuators that could be analysed for contraction amplitude, frequency, and contraction and relaxation kinetics. Compared with the standard video-optical analysis of contractile activity, the new system allows for (a) the analysis of several tissues in parallel, (b) switching between auxotonic and isometric contractions by inserting a stiff metal post in the silicone post opposing the piezo actuator, (c) continuous measurement over days with low data volume (megabyte), (d) automated measurement without the necessity of adjustment of tissue position for video-optical analysis, (e) reduced complexity and costs, (f) high sensitivity of contraction detection, (g) calculation of absolute contraction force, and (h) suitability for variable tissue geometries. The new set-up for contraction analysis based on piezo-bending actuators is a promising new method for the parallel screening of EHT for pharmacological drug effects and other applications of muscle tissue engineering (e.g., skeletal muscle engineering or cardiac repair).

Functional abnormalities in induced Pluripotent Stem Cell-derived cardiomyocytes generated from titin-mutated patients with dilated cardiomyopathy

Aims

Dilated cardiomyopathy (DCM), a myocardial disorder that can result in progressive heart failure and arrhythmias, is defined by ventricular chamber enlargement and dilatation, and systolic dysfunction. Despite extensive research, the pathological mechanisms of DCM are unclear mainly due to numerous mutations in different gene families resulting in the same outcome—decreased ventricular function. Titin (TTN)—a giant protein, expressed in cardiac and skeletal muscles, is an important part of the sarcomere, and thus TTN mutations are the most common cause of adult DCM. To decipher the basis for the cardiac pathology in titin-mutated patients, we investigated the hypothesis that induced Pluripotent Stem Cell (iPSC)-derived cardiomyocytes (iPSC-CM) generated from patients, recapitulate the disease phenotype. The hypothesis was tested by 3 Aims: (1) Investigate key features of the excitation-contraction-coupling machinery; (2) Investigate the responsiveness to positive inotropic interventions; (3) Investigate the proteome profile of the AuP cardiomyocytes using mass-spectrometry (MS).

Methods and results

iPSC were generated from the patients' skin fibroblasts. The major findings were: (1) Sarcomeric organization analysis in mutated iPSC-CM showed defects in assembly and maintenance of sarcomeric structure. (2) Mutated iPSC-CM exhibited diminished inotropic and lusitropic responses to β-adrenergic stimulation with isoproterenol, increased [Ca²⁺]_out and angiotensin-II. Additionally, mutated iPSC-CM displayed prolonged recovery in response to caffeine. These findings may result from defective or lack of interactions of the sarcomeric components with titin through its kinase domain which is absent in the mutated cells.

Conclusions

These findings show that the mutated cardiomyocytes from DCM patients recapitulate abnormalities of the inherited cardiomyopathies, expressed as blunted inotropic response.

The Application of Induced Pluripotent Stem Cells in Cardiac Disease Modeling and Drug Testing

In recent decades, cardiovascular diseases have become the greatest health threat to human beings, and thus it is particularly important to explore the subtle underlying pathogenesis of cardiovascular diseases. Although many molecular pathways have been explored to be essential in the development of cardiovascular diseases, their clinical significances are still uncertain. With the emergence of induced pluripotent stem cells (iPSCs), a unique platform for cardiovascular diseases has been established to model cardiovascular diseases on specific genetic background in vitro. This review summarizes current progresses of iPSCs in cardiovascular disease modeling and drug testing. This review highlighted iPSC-based cardiovascular disease modeling and drug testing. The technical advances in iPSC-based researches and various clinically relevant applications are discussed. With further intensive research, iPSC technology will shape the future of clinical translational research in cardiovascular diseases.

Contractile Work Contributes to Maturation of Energy Metabolism in hiPSC-Derived Cardiomyocytes

Energy metabolism is a key aspect of cardiomyocyte biology. Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a promising tool for biomedical application, but they are immature and have not undergone metabolic maturation related to early postnatal development. To assess whether cultivation of hiPSC-CMs in 3D engineered heart tissue format leads to maturation of energy metabolism, we analyzed the mitochondrial and metabolic state of 3D hiPSC-CMs and compared it with 2D culture. 3D hiPSC-CMs showed increased mitochondrial mass, DNA content, and protein abundance (proteome). While hiPSC-CMs exhibited the principal ability to use glucose, lactate, and fatty acids as energy substrates irrespective of culture format, hiPSC-CMs in 3D performed more oxidation of glucose, lactate, and fatty acid and less anaerobic glycolysis. The increase in mitochondrial mass and DNA in 3D was diminished by pharmacological reduction of contractile force. In conclusion, contractile work contributes to metabolic maturation of hiPSC-CMs.

•

Higher mitochondrial mass, protein, and DNA content in 3D versus 2D hiPSC-CMs

•

Similarity of mitochondrial proteomes between 3D hiPSC-CMs and adult human heart

•

Preference for oxidative metabolism in favor of anaerobic glycolysis in 3D hiPSC-CMs

Passive Stretch Induces Structural and Functional Maturation of Engineered Heart Muscle as Predicted by Computational Modeling

The ability to differentiate human pluripotent stem cells (hPSCs) into cardiomyocytes (CMs) makes them an attractive source for repairing injured myocardium, disease modeling, and drug testing. Although current differentiation protocols yield hPSC-CMs to >90% efficiency, hPSC-CMs exhibit immature characteristics. With the goal of overcoming this limitation, we tested the effects of varying passive stretch on engineered heart muscle (EHM) structural and functional maturation, guided by computational modeling. Human embryonic stem cells (hESCs, H7 line) or human induced pluripotent stem cells (IMR-90 line) were differentiated to hPSC-derived cardiomyocytes (hPSC-CMs) in vitro using a small molecule based protocol. hPSC-CMs were characterized by troponin⁺ flow cytometry as well as electrophysiological measurements. Afterwards, 1.2 × 10⁶ hPSC-CMs were mixed with 0.4 × 10⁶ human fibroblasts (IMR-90 line) (3:1 ratio) and type-I collagen. The blend was cast into custom-made 12-mm long polydimethylsiloxane reservoirs to vary nominal passive stretch of EHMs to 5, 7, or 9 mm. EHM characteristics were monitored for up to 50 days, with EHMs having a passive stretch of 7 mm giving the most consistent formation. Based on our initial macroscopic observations of EHM formation, we created a computational model that predicts the stress distribution throughout EHMs, which is a function of cellular composition, cellular ratio, and geometry. Based on this predictive modeling, we show cell alignment by immunohistochemistry and coordinated calcium waves by calcium imaging. Furthermore, coordinated calcium waves and mechanical contractions were apparent throughout entire EHMs. The stiffness and active forces of hPSC-derived EHMs are comparable with rat neonatal cardiomyocyte-derived EHMs. Three-dimensional EHMs display increased expression of mature cardiomyocyte genes including sarcomeric protein troponin-T, calcium and potassium ion channels, β-adrenergic receptors, and t-tubule protein caveolin-3. Passive stretch affects the structural and functional maturation of EHMs. Based on our predictive computational modeling, we show how to optimize cell alignment and calcium dynamics within EHMs. These findings provide a basis for the rational design of EHMs, which enables future scale-up productions for clinical use in cardiovascular tissue engineering. Stem Cells 2018;36:265-277.

Engineered Microenvironments for Maturation of Stem Cell Derived Cardiac Myocytes

Through the use of stem cell-derived cardiac myocytes, tissue-engineered human myocardial constructs are poised for modeling normal and diseased physiology of the heart, as well as discovery of novel drugs and therapeutic targets in a human relevant manner. This review highlights the recent bioengineering efforts to recapitulate microenvironmental cues to further the maturation state of newly differentiated cardiac myocytes. These techniques include long-term culture, co-culture, exposure to mechanical stimuli, 3D culture, cell-matrix interactions, and electrical stimulation. Each of these methods has produced various degrees of maturation; however, a standardized measure for cardiomyocyte maturation is not yet widely accepted by the scientific community.

MUSCLEMOTION: A Versatile Open Software Tool to Quantify Cardiomyocyte and Cardiac Muscle Contraction In Vitro and In Vivo

Supplemental Digital Content is available in the text.

Rationale:

There are several methods to measure cardiomyocyte and muscle contraction, but these require customized hardware, expensive apparatus, and advanced informatics or can only be used in single experimental models. Consequently, data and techniques have been difficult to reproduce across models and laboratories, analysis is time consuming, and only specialist researchers can quantify data.

Objective:

Here, we describe and validate an automated, open-source software tool (MUSCLEMOTION) adaptable for use with standard laboratory and clinical imaging equipment that enables quantitative analysis of normal cardiac contraction, disease phenotypes, and pharmacological responses.

Methods and Results:

MUSCLEMOTION allowed rapid and easy measurement of movement from high-speed movies in (1) 1-dimensional in vitro models, such as isolated adult and human pluripotent stem cell-derived cardiomyocytes; (2) 2-dimensional in vitro models, such as beating cardiomyocyte monolayers or small clusters of human pluripotent stem cell-derived cardiomyocytes; (3) 3-dimensional multicellular in vitro or in vivo contractile tissues, such as cardiac “organoids,” engineered heart tissues, and zebrafish and human hearts. MUSCLEMOTION was effective under different recording conditions (bright-field microscopy with simultaneous patch-clamp recording, phase contrast microscopy, and traction force microscopy). Outcomes were virtually identical to the current gold standards for contraction measurement, such as optical flow, post deflection, edge-detection systems, or manual analyses. Finally, we used the algorithm to quantify contraction in in vitro and in vivo arrhythmia models and to measure pharmacological responses.

Conclusions:

Using a single open-source method for processing video recordings, we obtained reliable pharmacological data and measures of cardiac disease phenotype in experimental cell, animal, and human models.

Investigating the cardiac pathology of SCO2-mediated hypertrophic cardiomyopathy using patients induced pluripotent stem cell-derived cardiomyocytes

Mutations in SCO2 are among the most common causes of COX deficiency, resulting in reduced mitochondrial oxidative ATP production capacity, often leading to hypertrophic cardiomyopathy (HCM). To date, none of the recent pertaining reports provide deep understanding of the SCO2 disease pathophysiology. To investigate the cardiac pathology of the disease, we were the first to generate induced pluripotent stem cell (iPSC)-derived cardiomyocytes (iPSC-CMs) from SCO2-mutated patients. For iPSC generation, we reprogrammed skin fibroblasts from two SCO2 patients and healthy controls. The first patient was a compound heterozygote to the common E140K mutation, and the second was homozygote for the less common G193S mutation. iPSC were differentiated into cardiomyocytes through embryoid body (EB) formation. To test the hypothesis that the SCO2 mutation is associated with mitochondrial abnormalities, and intracellular Ca²⁺ -overload resulting in functional derangements and arrhythmias, we investigated in SCO2-mutated iPSC-CMs (compared to control cardiomyocytes): (i) the ultrastructural changes; (ii) the inotropic responsiveness to β-adrenergic stimulation, increased [Ca²⁺ ]_o and angiotensin-II (AT-II); and (iii) the Beat Rate Variability (BRV) characteristics. In support of the hypothesis, we found in the mutated iPSC-CMs major ultrastructural abnormalities and markedly attenuated response to the inotropic interventions and caffeine, as well as delayed afterdepolarizations (DADs) and increased BRV, suggesting impaired SR Ca²⁺ handling due to attenuated SERCA activity caused by ATP shortage. Our novel results show that iPSC-CMs are useful for investigating the pathophysiological mechanisms underlying the SCO2 mutation syndrome.

Toward improved myocardial maturity in an organ-on-chip platform with immature cardiac myocytes

In vitro studies of cardiac physiology and drug response have traditionally been performed on individual isolated cardiomyocytes or isotropic monolayers of cells that may not mimic desired physiological traits of the laminar adult myocardium. Recent studies have reported a number of advances to Heart-on-a-Chip platforms for the fabrication of more sophisticated engineered myocardium, but cardiomyocyte immaturity remains a challenge. In the anisotropic musculature of the heart, interactions between cardiac myocytes, the extracellular matrix (ECM), and neighboring cells give rise to changes in cell shape and tissue architecture that have been implicated in both development and disease. We hypothesized that engineered myocardium fabricated from cardiac myocytes cultured in vitro could mimic the physiological characteristics and gene expression profile of adult heart muscle. To test this hypothesis, we fabricated engineered myocardium comprised of neonatal rat ventricular myocytes with laminar architectures reminiscent of that observed in the mature heart and compared their sarcomere organization, contractile performance characteristics, and cardiac gene expression profile to that of isolated adult rat ventricular muscle strips. We found that anisotropic engineered myocardium demonstrated a similar degree of global sarcomere alignment, contractile stress output, and inotropic concentration-response to the β-adrenergic agonist isoproterenol. Moreover, the anisotropic engineered myocardium exhibited comparable myofibril related gene expression to muscle strips isolated from adult rat ventricular tissue. These results suggest that tissue architecture serves an important developmental cue for building in vitro model systems of the myocardium that could potentially recapitulate the physiological characteristics of the adult heart. Impact statement With the recent focus on developing in vitro Organ-on-Chip platforms that recapitulate tissue and organ-level physiology using immature cells derived from stem cell sources, there is a strong need to assess the ability of these engineered tissues to adopt a mature phenotype. In the present study, we compared and contrasted engineered tissues fabricated from neonatal rat ventricular myocytes in a Heart-on-a-Chip platform to ventricular muscle strips isolated from adult rats. The results of this study support the notion that engineered tissues fabricated from immature cells have the potential to mimic mature tissues in an Organ-on-Chip platform.

Manufacturing Cell Therapies Using Engineered Biomaterials

Emerging manufacturing processes to generate regenerative advanced therapies can involve extensive genomic and/or epigenomic manipulation of autologous or allogeneic cells. These cell engineering processes need to be carefully controlled and standardized to maximize safety and efficacy in clinical trials. Engineered biomaterials with smart and tunable properties offer an intriguing tool to provide or deliver cues to retain stemness, direct differentiation, promote reprogramming, manipulate the genome, or select functional phenotypes. This review discusses the use of engineered biomaterials to control human cell manufacturing. Future work exploiting engineered biomaterials has the potential to generate manufacturing processes that produce standardized cells with well-defined critical quality attributes appropriate for clinical testing.

Engineering Cardiac Muscle Tissue: A Maturating Field of Research

Twenty years after the initial description of a tissue engineered construct, 3-dimensional human cardiac tissues of different kinds are now generated routinely in many laboratories. Advances in stem cell biology and engineering allow for the generation of constructs that come close to recapitulating the complex structure of heart muscle and might, therefore, be amenable to industrial (eg, drug screening) and clinical (eg, cardiac repair) applications. Whether the more physiological structure of 3-dimensional constructs provides a relevant advantage over standard 2-dimensional cell culture has yet to be shown in head-to-head-comparisons. The present article gives an overview on current strategies of cardiac tissue engineering with a focus on different hydrogel methods and discusses perspectives and challenges for necessary steps toward the real-life application of cardiac tissue engineering for disease modeling, drug development, and cardiac repair.

Nebivolol Desensitizes Myofilaments of a Hypertrophic Cardiomyopathy Mouse Model

Background: Hypertrophic cardiomyopathy (HCM) patients often present with diastolic dysfunction and a normal to supranormal systolic function. To counteract this hypercontractility, guideline therapies advocate treatment with beta-adrenoceptor and Ca²⁺ channel blockers. One well established pathomechanism for the hypercontractile phenotype frequently observed in HCM patients and several HCM mouse models is an increased myofilament Ca²⁺ sensitivity. Nebivolol, a commonly used beta-adrenoceptor antagonist, has been reported to lower maximal force development and myofilament Ca²⁺ sensitivity in rabbit and human heart tissues. The aim of this study was to evaluate the effect of nebivolol in cardiac muscle strips of an established HCM Mybpc3 mouse model. Furthermore, we investigated actions of nebivolol and epigallocatechin-gallate, which has been shown to desensitize myofilaments for Ca²⁺ in mouse and human HCM models, in cardiac strips of HCM patients with a mutation in the most frequently mutated HCM gene MYBPC3.

Methods and Results: Nebivolol effects were tested on contractile parameters and force-Ca²⁺ relationship of skinned ventricular muscle strips isolated from Mybpc3-targeted knock-in (KI), wild-type (WT) mice and cardiac strips of three HCM patients with MYBPC3 mutations. At baseline, KI strips showed no difference in maximal force development compared to WT mouse heart strips. Neither 1 nor 10 μM nebivolol had an effect on maximal force development in both genotypes. 10 μM nebivolol induced myofilament Ca²⁺ desensitization in WT strips and to a greater extent in KI strips. Neither 1 nor 10 μM nebivolol had an effect on Ca²⁺ sensitivity in cardiac muscle strips of three HCM patients with MYBPC3 mutations, whereas epigallocatechin-gallate induced a right shift in the force-Ca²⁺ curve.

Conclusion: Nebivolol induced a myofilament Ca²⁺ desensitization in both WT and KI strips, which was more pronounced in KI muscle strips. In human cardiac muscle strips of three HCM patients nebivolol had no effect on myofilament Ca²⁺ sensitivity.

Contractile force generation by 3D hiPSC-derived cardiac tissues is enhanced by rapid establishment of cellular interconnection in matrix with muscle-mimicking stiffness

Engineering 3D human cardiac tissues is of great importance for therapeutic and pharmaceutical applications. As cardiac tissue substitutes, extracellular matrix-derived hydrogels have been widely explored. However, they exhibit premature degradation and their stiffness is often orders of magnitude lower than that of native cardiac tissue. There are no reports on establishing interconnected cardiomyocytes in 3D hydrogels at physiologically-relevant cell density and matrix stiffness. Here we bioengineer human cardiac microtissues by encapsulating human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) in chemically-crosslinked gelatin hydrogels (1.25 × 10⁸/mL) with tunable stiffness and degradation. In comparison to the cells in high stiffness (16 kPa)/slow degrading hydrogels, hiPSC-CMs in low stiffness (2 kPa)/fast degrading and intermediate stiffness (9 kPa)/intermediate degrading hydrogels exhibit increased intercellular network formation, α-actinin and connexin-43 expression, and contraction velocity. Only the 9 kPa microtissues exhibit organized sarcomeric structure and significantly increased contractile stress. This demonstrates that muscle-mimicking stiffness together with robust cellular interconnection contributes to enhancement in sarcomeric organization and contractile function of the engineered cardiac tissue. This study highlights the importance of intercellular connectivity, physiologically-relevant cell density, and matrix stiffness to best support 3D cardiac tissue engineering.

Turning Potential Into Action: Using Pluripotent Stem Cells to Understand Heart Development and Function in Health and Disease

Pluripotent stem cells hold enormous potential for regenerative therapies, however their ability to provide insight into early human development and the origins of disease could arguably provide an even greater outcome. This is primarily due to their contribution to the establishment of a powerful knowledge base of human development, something which all researchers and clinicians can potentially benefit from. Modeling human heart development and disease using pluripotent stem cells has already provided many important insights into cardiogenesis and cardiovascular disease mechanisms however, it is important to be aware of the complexities of this model system. Thorough contemplation of experimental models and specialized techniques is required to provide high‐quality evidence of the intricacies of both normal early development, and when this process goes awry in disease states. Stem Cells Translational Medicine2017;6:1452–1457

I-Wire Heart-on-a-Chip I: Three-dimensional cardiac tissue constructs for physiology and pharmacology

Engineered 3D cardiac tissue constructs (ECTCs) can replicate complex cardiac physiology under normal and pathological conditions. Currently, most measurements of ECTC contractility are either made isometrically, with fixed length and without control of the applied force, or auxotonically against a variable force, with the length changing during the contraction. The "I-Wire" platform addresses the unmet need to control the force applied to ECTCs while interrogating their passive and active mechanical and electrical characteristics. A six-well plate with inserted PDMS casting molds containing neonatal rat cardiomyocytes cultured with fibrin for 13-15days is mounted on the motorized mechanical stage of an inverted microscope equipped with a fast sCMOS camera. A calibrated flexible probe provides strain load of the ECTC via lateral displacement, and the microscope detects the deflections of both the probe and the ECTC. The ECTCs exhibited longitudinally aligned cardiomyocytes with well-developed sarcomeric structure, recapitulated the Frank-Starling force-tension relationship, and demonstrated expected transmembrane action potentials, electrical and mechanical restitutions, and responses to both β-adrenergic stimulation and blebbistatin. The I-Wire platform enables creation and mechanical and electrical characterization of ECTCs, and hence can be valuable in the study of cardiac diseases, drug screening, drug development, and the qualification of cells for tissue-engineered regenerative medicine.

STATEMENT OF SIGNIFICANCE

There is a growing interest in creating engineered heart tissue constructs for basic cardiac research, applied research in cardiac pharmacology, and repair of damaged hearts. We address an unmet need to characterize fully the performance of these tissues with our simple "I-Wire" assay that allows application of controlled forces to three-dimensional cardiac fiber constructs and measurement of both the electrical and mechanical properties of the construct. The advantage of I-Wire over other approaches is that the constructs being measured are truly three-dimensional, rather than a single layer of cells grown within a microfluidic device. We anticipate that the I-Wire will be extremely useful for the evaluation of myocardial constructs created using cardiomyocytes derived from human induced pluripotent stem cells.

Analysis of Calcium Transients and Uniaxial Contraction Force in Single Human Embryonic Stem Cell-Derived Cardiomyocytes on Microstructured Elastic Substrate with Spatially Controlled Surface Chemistries

The mechanical activity of cardiomyocytes is the result of a process called excitation-contraction coupling (ECC). A membrane depolarization wave induces a transient cytosolic calcium concentration increase that triggers activation of calcium-sensitive contractile proteins, leading to cell contraction and force generation. An experimental setup capable of acquiring simultaneously all ECC features would have an enormous impact on cardiac drug development and disease study. In this work, we develop a microengineered elastomeric substrate with tailor-made surface chemistry to measure simultaneously the uniaxial contraction force and the calcium transients generated by single human cardiomyocytes in vitro. Microreplication followed by photocuring is used to generate an array consisting of elastomeric micropillars. A second photochemical process is employed to spatially control the surface chemistry of the elastomeric pillar. As result, human embryonic stem cell-derived cardiomyocytes (hESC-CMs) can be confined in rectangular cell-adhesive areas, which induce cell elongation and promote suspended cell anchoring between two adjacent micropillars. In this end-to-end conformation, confocal fluorescence microscopy allows simultaneous detection of calcium transients and micropillar deflection induced by a single-cell uniaxial contraction force. Computational finite elements modeling (FEM) and 3D reconstruction of the cell-pillar interface allow force quantification. The platform is used to follow calcium dynamics and contraction force evolution in hESC-CMs cultures over the course of several weeks. Our results show how a biomaterial-based platform can be a versatile tool for in vitro assaying of cardiac functional properties of single-cell human cardiomyocytes, with applications in both in vitro developmental studies and drug screening on cardiac cultures.

Systematic Characterization of Dynamic Parameters of Intracellular Calcium Signals

Dynamic processes, such as intracellular calcium signaling, are hallmark of cellular biology. As real-time imaging modalities become widespread, a need for analytical tools to reliably characterize time-series data without prior knowledge of the nature of the recordings becomes more pressing. The goal of this study is to develop a signal-processing algorithm for MATLAB that autonomously computes the parameters characterizing prominent single transient responses (TR) and/or multi-peaks responses (MPR). The algorithm corrects for signal contamination and decomposes experimental recordings into contributions from drift, TRs, and MPRs. It subsequently provides numerical estimates for the following parameters: time of onset after stimulus application, activation time (time for signal to increase from 10 to 90% of peak), and amplitude of response. It also provides characterization of the (i) TRs by quantifying their area under the curve (AUC), response duration (time between 1/2 amplitude on ascent and descent of the transient), and decay constant of the exponential decay region of the deactivation phase of the response, and (ii) MPRs by quantifying the number of peaks, mean peak magnitude, mean periodicity, standard deviation of periodicity, oscillatory persistence (time between first and last discernable peak), and duty cycle (fraction of period during which system is active) for all the peaks in the signal, as well as coherent oscillations (i.e., deterministic spikes). We demonstrate that the signal detection performance of this algorithm is in agreement with user-mediated detection and that parameter estimates obtained manually and algorithmically are correlated. We then apply this algorithm to study how metabolic acidosis affects purinergic (P2) receptor-mediated calcium signaling in osteoclast precursor cells. Our results reveal that acidosis significantly attenuates the amplitude and AUC calcium responses at high ATP concentrations. Collectively, our data validated this algorithm as a general framework for comprehensively analyzing dynamic time-series.

Direct Production of Human Cardiac Tissues by Pluripotent Stem Cell Encapsulation in Gelatin Methacryloyl

Direct stem cell encapsulation and cardiac differentiation within supporting biomaterial scaffolds are critical for reproducible and scalable production of the functional human tissues needed in regenerative medicine and drug-testing applications. Producing cardiac tissues directly from pluripotent stem cells rather than assembling tissues using pre-differentiated cells can eliminate multiple cell-handling steps that otherwise limit the potential for process automation and production scale-up. Here we asked whether our process for forming 3D developing human engineered cardiac tissues using poly(ethylene glycol)-fibrinogen hydrogels can be extended to widely used and printable gelatin methacryloyl (GelMA) hydrogels. We demonstrate that low-density GelMA hydrogels can be formed rapidly using visible light (<1 min) and successfully employed to encapsulate human induced pluripotent stem cells while maintaining high cell viability. Resulting constructs had an initial stiffness of approximately 220 Pa, supported tissue growth and dynamic remodeling, and facilitated high-efficiency cardiac differentiation (>70%) to produce spontaneously contracting GelMA human engineered cardiac tissues (GEhECTs). GEhECTs initiated spontaneous contractions on day 8 of differentiation, with synchronicity, frequency, and velocity of contraction increasing over time, and displayed developmentally appropriate temporal changes in cardiac gene expression. GEhECT-dissociated cardiomyocytes displayed well-defined and aligned sarcomeres spaced at 1.85 ± 0.1 μm and responded appropriately to drug treatments, including the β-adrenergic agonist isoproterenol and antagonist propranolol, as well as to outside pacing up to 3.0 Hz. Overall results demonstrate that GelMA is a suitable biomaterial for the production of developing cardiac tissues and has the potential to be employed in scale-up production and bioprinting of GEhECTs.

Real-Time Force and Frequency Analysis of Engineered Human Heart Tissue Derived from Induced Pluripotent Stem Cells Using Magnetic Sensing

Engineered heart tissues made from human pluripotent stem cell-derived cardiomyocytes have been used for modeling cardiac pathologies, screening new therapeutics, and providing replacement cardiac tissue. Current methods measure the functional performance of engineered heart tissue by their twitch force and beating frequency, typically obtained by optical measurements. In this article, we describe a novel method for assessing twitch force and beating frequency of engineered heart tissue using magnetic field sensing, which enables multiple tissues to be measured simultaneously. The tissues are formed as thin structures suspended between two silicone posts, where one post is rigid and another is flexible and contains an embedded magnet. When the tissue contracts it causes the flexible post to bend in proportion to its twitch force. We measured the bending of the post using giant magnetoresistive (GMR) sensors located underneath a 24-well plate containing the tissues. We validated the accuracy of the readings from the GMR sensors against optical measurements. We demonstrated the utility and sensitivity of our approach by testing the effects of three concentrations of isoproterenol and verapamil on twitch force and beating frequency in real-time, parallel experiments. This system should be scalable beyond the 24-well format, enabling greater automation in assessing the contractile function of cardiomyocytes in a tissue-engineered environment.

Cardiac Meets Skeletal: What's New in Microfluidic Models for Muscle Tissue Engineering

In the last few years microfluidics and microfabrication technique principles have been extensively exploited for biomedical applications. In this framework, organs-on-a-chip represent promising tools to reproduce key features of functional tissue units within microscale culture chambers. These systems offer the possibility to investigate the effects of biochemical, mechanical, and electrical stimulations, which are usually applied to enhance the functionality of the engineered tissues. Since the functionality of muscle tissues relies on the 3D organization and on the perfect coupling between electrochemical stimulation and mechanical contraction, great efforts have been devoted to generate biomimetic skeletal and cardiac systems to allow high-throughput pathophysiological studies and drug screening. This review critically analyzes microfluidic platforms that were designed for skeletal and cardiac muscle tissue engineering. Our aim is to highlight which specific features of the engineered systems promoted a typical reorganization of the engineered construct and to discuss how promising design solutions exploited for skeletal muscle models could be applied to improve cardiac tissue models and vice versa.

The myocardial regenerative potential of three-dimensional engineered cardiac tissues composed of multiple human iPS cell-derived cardiovascular cell lineages

Human induced pluripotent stem cells (hiPSCs) are a robust source for cardiac regenerative therapy due to their potential to support autologous and allogeneic transplant paradigms. The in vitro generation of three-dimensional myocardial tissue constructs using biomaterials as an implantable hiPSC-derived myocardium provides a path to realize sustainable myocardial regeneration. We generated engineered cardiac tissues (ECTs) from three cellular compositions of cardiomyocytes (CMs), endothelial cells (ECs), and vascular mural cells (MCs) differentiated from hiPSCs. We then determined the impact of cell composition on ECT structural and functional properties. In vitro force measurement showed that CM+EC+MC ECTs possessed preferential electromechanical properties versus ECTs without vascular cells indicating that incorporation of vascular cells augmented tissue maturation and function. The inclusion of MCs facilitated more mature CM sarcomeric structure, preferential alignment, and activated multiple tissue maturation pathways. The CM+EC+MC ECTs implanted onto infarcted, immune tolerant rat hearts engrafted, displayed both host and graft-derived vasculature, and ameliorated myocardial dysfunction. Thus, a composition of CMs and multiple vascular lineages derived from hiPSCs and incorporated into ECTs promotes functional maturation and demonstrates myocardial replacement and perfusion relevant for clinical translation.

Concise Review: Measuring Physiological Responses of Human Pluripotent Stem Cell Derived Cardiomyocytes to Drugs and Disease

Cardiomyocytes from human pluripotent stem cells (hPSC) are of growing interest as models to understand mechanisms underlying genetic disease, identify potential drug targets and for safety pharmacology as they may predict human relevant effects more accurately and inexpensively than animals or other cell models. Crucial to their optimal use are accurate methods to quantify cardiomyocyte phenotypes accurately and reproducibly. Here, we review current methods for determining biophysical parameters of hPSC‐derived cardiomyocytes (hPSC‐CMs) that recapitulate disease and drug responses. Even though hPSC‐CMs as currently available are immature, various biophysical methods are nevertheless already providing useful insights into the biology of the human heart and its maladies. Advantages and limitations of assays currently available looking toward applications of hPSC‐CMs are described with examples of how they have been used to date. This will help guide the choice of biophysical method to characterize healthy cardiomyocytes and their pathologies in vitro. Stem Cells2016;34:2008–2015

Comparison of the effects of a truncating and a missense MYBPC3 mutation on contractile parameters of engineered heart tissue

Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by left ventricular hypertrophy, diastolic dysfunction and myocardial disarray. The most frequently mutated gene is MYBPC3, encoding cardiac myosin-binding protein-C (cMyBP-C). We compared the pathomechanisms of a truncating mutation (c.2373_2374insG) and a missense mutation (c.1591G>C) in MYBPC3 in engineered heart tissue (EHT). EHTs enable to study the direct effects of mutants without interference of secondary disease-related changes. EHTs were generated from Mybpc3-targeted knock-out (KO) and wild-type (WT) mouse cardiac cells. MYBPC3 WT and mutants were expressed in KO EHTs via adeno-associated virus. KO EHTs displayed higher maximal force and sensitivity to external [Ca(2+)] than WT EHTs. Expression of WT-Mybpc3 at MOI-100 resulted in ~73% cMyBP-C level but did not prevent the KO phenotype, whereas MOI-300 resulted in ≥95% cMyBP-C level and prevented the KO phenotype. Expression of the truncating or missense mutation (MOI-300) or their combination with WT (MOI-150 each), mimicking the homozygous or heterozygous disease state, respectively, failed to restore force to WT level. Immunofluorescence analysis revealed correct incorporation of WT and missense, but not of truncated cMyBP-C in the sarcomere. In conclusion, this study provides evidence in KO EHTs that i) haploinsufficiency affects EHT contractile function if WT cMyBP-C protein levels are ≤73%, ii) missense or truncating mutations, but not WT do not fully restore the disease phenotype and have different pathogenic mechanisms, e.g. sarcomere poisoning for the missense mutation, iii) the direct impact of (newly identified) MYBPC3 gene variants can be evaluated.

Miniaturized iPS-Cell-Derived Cardiac Muscles for Physiologically Relevant Drug Response Analyses

Tissue engineering approaches have the potential to increase the physiologic relevance of human iPS-derived cells, such as cardiomyocytes (iPS-CM). However, forming Engineered Heart Muscle (EHM) typically requires >1 million cells per tissue. Existing miniaturization strategies involve complex approaches not amenable to mass production, limiting the ability to use EHM for iPS-based disease modeling and drug screening. Micro-scale cardiospheres are easily produced, but do not facilitate assembly of elongated muscle or direct force measurements. Here we describe an approach that combines features of EHM and cardiospheres: Micro-Heart Muscle (μHM) arrays, in which elongated muscle fibers are formed in an easily fabricated template, with as few as 2,000 iPS-CM per individual tissue. Within μHM, iPS-CM exhibit uniaxial contractility and alignment, robust sarcomere assembly, and reduced variability and hypersensitivity in drug responsiveness, compared to monolayers with the same cellular composition. μHM mounted onto standard force measurement apparatus exhibited a robust Frank-Starling response to external stretch, and a dose-dependent inotropic response to the β-adrenergic agonist isoproterenol. Based on the ease of fabrication, the potential for mass production and the small number of cells required to form μHM, this system provides a potentially powerful tool to study cardiomyocyte maturation, disease and cardiotoxicology in vitro.

Induced pluripotent stem cells: at the heart of cardiovascular precision medicine

The advent of human induced pluripotent stem cell (hiPSC) technology has revitalized the efforts in the past decade to realize more fully the potential of human embryonic stem cells for scientific research. Adding to the possibility of generating an unlimited amount of any cell type of interest, hiPSC technology now enables the derivation of cells with patient-specific phenotypes. Given the introduction and implementation of the large-scale Precision Medicine Initiative, hiPSC technology will undoubtedly have a vital role in the advancement of cardiovascular research and medicine. In this Review, we summarize the progress that has been made in the field of hiPSC technology, with particular emphasis on cardiovascular disease modelling and drug development. The growing roles of hiPSC technology in the practice of precision medicine will also be discussed.

Combining patient proteomics and in vitro cardiomyocyte phenotype testing to identify potential mediators of heart failure with preserved ejection fraction

BACKGROUND

Heart failure with ejection fraction (HFpEF) is a syndrome resulting from several co-morbidities in which specific mediators are unknown. The platelet proteome responds to disease processes. We hypothesize that the platelet proteome will change composition in patients with HFpEF and may uncover mediators of the syndrome.

METHODS AND RESULTS

Proteomic changes were assessed in platelets from hospitalized subjects with symptoms of HFpEF (n = 9), the same subjects several weeks later without symptoms (n = 7) and control subjects (n = 8). Mass spectrometry identified 6102 proteins with five scans with peptide probabilities of ≥0.85. Of the 6102 proteins, 165 were present only in symptomatic subjects, 78 were only found in outpatient subjects and 157 proteins were unique to the control group. The S100A8 protein was identified consistently in HFpEF samples when compared with controls. We validated the fining that plasma S100A8 levels are increased in subjects with HFpEF (654 ± 391) compared to controls (352 ± 204) in an external cohort (p = 0.002). Recombinant S100A8 had direct effects on the electrophysiological and calcium handling profile in human induced pluripotent stem cell-derived cardiomyocytes.

CONCLUSIONS

Platelets may harbor proteins associated with HFpEF. S100A8 is present in the platelets of subjects with HFpEF and increased in the plasma of the same subjects. We further established a bedside-to-bench translational system that can be utilized as a secondary screen to ascertain whether the biomarkers may be an associated finding or causal to the disease process. S100A8 has been linked with other cardiovascular disease such as atherosclerosis and risk for myocardial infarction, stroke, or death. This is the first report on association of S100A8 with HFpEF.