Atomic force mechanobiology of pluripotent stem cell-derived cardiomyocytes

Guidelines for assessing maternal cardiovascular physiology during pregnancy and postpartum

Maternal mortality rates are at an all-time high across the world and are set to increase in subsequent years. Cardiovascular disease is the leading cause of death during pregnancy and postpartum, especially in the United States. Therefore, understanding the physiological changes in the cardiovascular system during normal pregnancy is necessary to understand disease-related pathology. Significant systemic and cardiovascular physiological changes occur during pregnancy that are essential for supporting the maternal-fetal dyad. The physiological impact of pregnancy on the cardiovascular system has been examined in both experimental animal models and in humans. However, there is a continued need in this field of study to provide increased rigor and reproducibility. Therefore, these guidelines aim to provide information regarding best practices and recommendations to accurately and rigorously measure cardiovascular physiology during normal and cardiovascular disease-complicated pregnancies in human and animal models.

Integrated machine learning and multimodal data fusion for patho-phenotypic feature recognition in iPSC models of dilated cardiomyopathy

Integration of multiple data sources presents a challenge for accurate prediction of molecular patho-phenotypic features in automated analysis of data from human model systems. Here, we applied a machine learning-based data integration to distinguish patho-phenotypic features at the subcellular level for dilated cardiomyopathy (DCM). We employed a human induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM) model of a DCM mutation in the sarcomere protein troponin T (TnT), TnT-R141W, compared to isogenic healthy (WT) control iPSC-CMs. We established a multimodal data fusion (MDF)-based analysis to integrate source datasets for Ca2+ transients, force measurements, and contractility recordings. Data were acquired for three additional layer types, single cells, cell monolayers, and 3D spheroid iPSC-CM models. For data analysis, numerical conversion as well as fusion of data from Ca2+ transients, force measurements, and contractility recordings, a non-negative blind deconvolution (NNBD)-based method was applied. Using an XGBoost algorithm, we found a high prediction accuracy for fused single cell, monolayer, and 3D spheroid iPSC-CM models (≥92 ± 0.08 %), as well as for fused Ca2+ transient, beating force, and contractility models (>96 ± 0.04 %). Integrating MDF and XGBoost provides a highly effective analysis tool for prediction of patho-phenotypic features in complex human disease models such as DCM iPSC-CMs.

Interferometric Biosensor for High Sensitive Label-Free Recording of HiPS Cardiomyocytes Contraction in Vitro

Heart disease remains a leading cause of global mortality, underscoring the need for advanced technologies to study cardiovascular diseases and develop effective treatments. We introduce an innovative interferometric biosensor for high-sensitivity and label-free recording of human induced pluripotent stem cell (hiPSC) cardiomyocyte contraction in vitro. Using an optical cavity, our device captures interference patterns caused by the contraction-induced displacement of a thin flexible membrane. First, we demonstrate the capability to quantify spontaneous contractions and discriminate between contraction and relaxation phases. We calculate a contraction-induced vertical membrane displacement close to 40 nm, which implies a traction stress of 34 ± 4 mN/mm2. Finally, we investigate the effects of a drug compound on contractility amplitude, revealing a significant reduction in contractile forces. The label-free and high-throughput nature of our biosensor may enhance drug screening processes and drug development for cardiac treatments. Our interferometric biosensor offers a novel approach for noninvasive and real-time assessment of cardiomyocyte contraction.

Cell Migration Assays and Their Application to Wound Healing Assays-A Critical Review

In recent years, cell migration assays (CMAs) have emerged as a tool to study the migration of cells along with their physiological responses under various stimuli, including both mechanical and bio-chemical properties. CMAs are a generic system in that they support various biological applications, such as wound healing assays. In this paper, we review the development of the CMA in the context of its application to wound healing assays. As such, the wound healing assay will be used to derive the requirements on CMAs. This paper will provide a comprehensive and critical review of the development of CMAs along with their application to wound healing assays. One salient feature of our methodology in this paper is the application of the so-called design thinking; namely we define the requirements of CMAs first and then take them as a benchmark for various developments of CMAs in the literature. The state-of-the-art CMAs are compared with this benchmark to derive the knowledge and technological gap with CMAs in the literature. We will also discuss future research directions for the CMA together with its application to wound healing assays.

Defective Biomechanics and Pharmacological Rescue of Human Cardiomyocytes with Filamin C Truncations

Actin-binding filamin C (FLNC) is expressed in cardiomyocytes, where it localizes to Z-discs, sarcolemma, and intercalated discs. Although FLNC truncation variants (FLNCtv) are an established cause of arrhythmias and heart failure, changes in biomechanical properties of cardiomyocytes are mostly unknown. Thus, we investigated the mechanical properties of human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs) carrying FLNCtv. CRISPR/Cas9 genome-edited homozygous FLNCKO-/- hiPSC-CMs and heterozygous knock-out FLNCKO+/- hiPSC-CMs were analyzed and compared to wild-type FLNC (FLNCWT) hiPSC-CMs. Atomic force microscopy (AFM) was used to perform micro-indentation to evaluate passive and dynamic mechanical properties. A qualitative analysis of the beating traces showed gene dosage-dependent-manner "irregular" peak profiles in FLNCKO+/- and FLNCKO-/- hiPSC-CMs. Two Young's moduli were calculated: E1, reflecting the compression of the plasma membrane and actin cortex, and E2, including the whole cell with a cytoskeleton and nucleus. Both E1 and E2 showed decreased stiffness in mutant FLNCKO+/- and FLNCKO-/- iPSC-CMs compared to that in FLNCWT. The cell adhesion force and work of adhesion were assessed using the retraction curve of the SCFS. Mutant FLNC iPSC-CMs showed gene dosage-dependent decreases in the work of adhesion and adhesion forces from the heterozygous FLNCKO+/- to the FLNCKO-/- model compared to FLNCWT, suggesting damaged cytoskeleton and membrane structures. Finally, we investigated the effect of crenolanib on the mechanical properties of hiPSC-CMs. Crenolanib is an inhibitor of the Platelet-Derived Growth Factor Receptor α (PDGFRA) pathway which is upregulated in FLNCtv hiPSC-CMs. Crenolanib was able to partially rescue the stiffness of FLNCKO-/- hiPSC-CMs compared to control, supporting its potential therapeutic role.

Characterizing induced pluripotent stem cells and derived cardiomyocytes: insights from nano scale mass measurements and mechanical properties

Our study reveals that the nano-mechanical measures of elasticity and cell mass change significantly through induced pluripotent stem cell (iPSC) differentiation to cardiomyocytes, providing a reliable method to evaluate such processes. The findings support the importance of identifying these properties, and highlight the potential of AFM for comprehensive characterization of iPSC at the nanoscale.

Noninvasive Quantification of Contractile Dynamics in Cardiac Cells, Spheroids, and Organs-on-a-Chip Using High-Frequency Ultrasound

Cell-based models that mimic in vivo heart physiology are poised to make significant advances in cardiac disease modeling and drug discovery. In these systems, cardiomyocyte (CM) contractility is an important functional metric, but current measurement methods are inaccurate and low-throughput or require complex setups. To address this need, we developed a standalone noninvasive, label-free ultrasound technique operating at 40-200 MHz to measure the contractile kinetics of cardiac models, ranging from single adult CMs to 3D microtissue constructs in standard cell culture formats. The high temporal resolution of 1000 fps resolved the beat profile of single mouse CMs paced at up to 9 Hz, revealing limitations of lower speed optical based measurements to resolve beat kinetics or characterize aberrant beats. Coupling of ultrasound with traction force microscopy enabled the measurement of the CM longitudinal modulus and facile estimation of adult mouse CM contractile forces of 2.34 ± 1.40 μN, comparable to more complex measurement techniques. Similarly, the beat rate, rhythm, and drug responses of CM spheroid and microtissue models were measured, including in configurations without optical access. In conclusion, ultrasound can be used for the rapid characterization of CM contractile function in a wide range of commonly studied configurations ranging from single cells to 3D tissue constructs using standard well plates and custom microdevices, with applications in cardiac drug discovery and cardiotoxicity evaluation.

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

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

Single-Cell Analysis of Contractile Forces in iPSC-Derived Cardiomyocytes: Paving the Way for Precision Medicine in Cardiovascular Disease

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold enormous potential in cardiac disease modeling, drug screening, and regenerative medicine. Furthermore, patient-specific iPSC-CMS can be tested for personalized medicine. To provide a deeper understanding of the contractile force dynamics of iPSC-CMs, we employed Atomic Force Microscopy (AFM) as an advanced detection tool to distinguish the characteristics of force dynamics at a single cell level. We measured normal (vertical) and lateral (axial) force at different pacing frequencies. We found a significant correlation between normal and lateral force. We also observed a significant force-frequency relationship for both types of forces. This work represents the first demonstration of the correlation of normal and lateral force from individual iPSC-CMs. The identification of this correlation is relevant because it validates the comparison across systems and models that can only account for either normal or lateral force. These findings enhance our understanding of iPSC-CM properties, thereby paving the way for the development of therapeutic strategies in cardiovascular medicine.

Effects of targeted lung cancer drugs on cardiomyocytes studied by atomic force microscopy

The epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKIs) has become one of the important targeted drugs for the treatment of non-small cell lung cancer (NSCLC). But the cardiac adverse events (AEs) related to the EGFR-TKI treatment occur frequently. And the cases of TKI-associated cardiac AEs remain poorly understood. In order to study the effects of EGFR-TKIs on cardiomyocytes, atomic force microscopy (AFM) was used to measure and analyze the physical properties of cardiomyocytes under the actions of three drugs (gefitinib, afatinib and osimertinib) with different concentrations. By comparing the height, adhesion, Young's modulus, the amplitude and the time of the contraction and relaxation process, it was found that the changes of the mechanical properties of cells were well correlated with the symptoms of AEs, such as cardiomyocyte hypertrophy, QT prolongation, atrial fibrillation, ejection fraction reductions, and cardiac failure. In addition, osimertinib has the most obvious effect on cardiomyocytes at a low concentration, and gefitinib has the greatest effect with the increase of concentration, while afatinib has the least effect on cardiomyocytes. This provides a new method for screening drugs and exploring the principle of action in the process of cancer treatment at the cellular level.

Ultrathin and Flexible Bioelectronic Arrays for Functional Measurement of iPSC-Cardiomyocytes under Cardiotropic Drug Administration and Controlled Microenvironments

Emerging heart-on-a-chip technology is a promising tool to establish in vitro cardiac models for therapeutic testing and disease modeling. However, due to the technical complexity of integrating cell culture chambers, biosensors, and bioreactors into a single entity, a microphysiological system capable of reproducing controlled microenvironmental cues to regulate cell phenotypes, promote iPS-cardiomyocyte maturity, and simultaneously measure the dynamic changes of cardiomyocyte function in situ is not available. This paper reports an ultrathin and flexible bioelectronic array platform in 24-well format for higher-throughput contractility measurement under candidate drug administration or defined microenvironmental conditions. In the array, carbon black (CB)-PDMS flexible strain sensors were embedded for detecting iPSC-CM contractility signals. Carbon fiber electrodes and pneumatic air channels were integrated to provide electrical and mechanical stimulation to improve iPSC-CM maturation. Performed experiments validate that the bioelectronic array accurately reveals the effects of cardiotropic drugs and identifies mechanical/electrical stimulation strategies for promoting iPSC-CM maturation.

Genome Editing Technology: A New Frontier for the Treatment and Prevention of Cardiovascular Diseases

Over the past two decades, genome-editing technique has proven to be a robust editing method that revolutionizes the field of biomedicine. At the genetic level, it can be efficiently utilized to generate various disease-resistance models to elucidate the mechanism of human diseases. It also develops an outstanding tool and enables the generation of genetically modified organisms for the treatment and prevention of various diseases. The versatile and novel CRISPR/Cas9 system mitigates the challenges of various GETs such as ZFNs, and TALENs. For this reason, it has become a ground-breaking technology potentially employed to manipulate the desired gene of interest. Interestingly, this system has been broadly utilized due to its tremendous applications for treating and preventing tumors and various rare disorders; however, its applications for treating CVDs remain in infancy. More recently, two newly developed GETs, such as base editing and prime editing, have further broadened the accuracy range to treat CVDs under consideration. Furthermore, recently emerged CRISPR tools have been potentially applied in vivo and in vitro to treat CVDs. To the best of our knowledge, we strongly enlightened the applications of the CRISPR/Cas9 system that opened a new window in the field of cardiovascular research and, in detail, discussed the challenges and limitations of CVDs.

Actin-microtubule cytoskeletal interplay mediated by MRTF-A/SRF signaling promotes dilated cardiomyopathy caused by LMNA mutations

Mutations in the lamin A/C gene (LMNA) cause dilated cardiomyopathy associated with increased activity of ERK1/2 in the heart. We recently showed that ERK1/2 phosphorylates cofilin-1 on threonine 25 (phospho(T25)-cofilin-1) that in turn disassembles the actin cytoskeleton. Here, we show that in muscle cells carrying a cardiomyopathy-causing LMNA mutation, phospho(T25)-cofilin-1 binds to myocardin-related transcription factor A (MRTF-A) in the cytoplasm, thus preventing the stimulation of serum response factor (SRF) in the nucleus. Inhibiting the MRTF-A/SRF axis leads to decreased α-tubulin acetylation by reducing the expression of ATAT1 gene encoding α-tubulin acetyltransferase 1. Hence, tubulin acetylation is decreased in cardiomyocytes derived from male patients with LMNA mutations and in heart and isolated cardiomyocytes from Lmna^{p.H222P/H222P} male mice. In Atat1 knockout mice, deficient for acetylated α-tubulin, we observe left ventricular dilation and mislocalization of Connexin 43 (Cx43) in heart. Increasing α-tubulin acetylation levels in Lmna^{p.H222P/H222P} mice with tubastatin A treatment restores the proper localization of Cx43 and improves cardiac function. In summary, we show for the first time an actin-microtubule cytoskeletal interplay mediated by cofilin-1 and MRTF-A/SRF, promoting the dilated cardiomyopathy caused by LMNA mutations. Our findings suggest that modulating α-tubulin acetylation levels is a feasible strategy for improving cardiac function.

Molecular and electrophysiological evaluation of human cardiomyocyte subtypes to facilitate generation of composite cardiac models

Paucity of physiologically relevant cardiac models has limited the widespread application of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes in drug development. Here, we performed comprehensive characterization of hiPSC-derived cardiomyocyte subtypes from 2D and 3D cultures and established a novel 3D model to study impulse initiation and propagation. Directed differentiation approaches were used to generate sinoatrial nodal (SANCM), atrial (ACM) and ventricular cardiomyocytes (VCM). Single cell RNA sequencing established that the protocols yield distinct cell populations in line with expected identities, which was also confirmed by electrophysiological characterization. In 3D EHT cultures of all subtypes, we observed prominent expression of stretch-responsive genes such as NPPA. Response to rate modulating drugs noradrenaline, carbachol and ivabradine were comparable in single cells and EHTs. Differences in the speed of impulse propagation between the subtypes were more pronounced in EHTs compared with 2D monolayers owing to a progressive increase in conduction velocities in atrial and ventricular cardiomyocytes, in line with a more mature phenotype. In a novel binary EHT model of pacemaker-atrial interface, the SANCM end of the tissue consistently paced the EHTs under baseline conditions, which was inhibited by ivabradine. Taken together, our data provide comprehensive insights into molecular and electrophysiological properties of hiPSC-derived cardiomyocyte subtypes, facilitating the creation of next generation composite cardiac models for drug discovery, disease modeling and cell-based regenerative therapies.

Atomic Force Microscopy (AFM) Applications in Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is an inherited heart muscle disorder characterized by progressive replacement of cardiomyocytes by fibrofatty tissue, ventricular dilatation, cardiac dysfunction, arrhythmias, and sudden cardiac death. Interest in molecular biomechanics for these disorders is constantly growing. Atomic force microscopy (AFM) is a well-established technic to study the mechanobiology of biological samples under physiological and pathological conditions at the cellular scale. However, a review which described all the different data that can be obtained using the AFM (cell elasticity, adhesion behavior, viscoelasticity, beating force, and frequency) is still missing. In this review, we will discuss several techniques that highlight the potential of AFM to be used as a tool for assessing the biomechanics involved in ACM. Indeed, analysis of genetically mutated cells with AFM reveal abnormalities of the cytoskeleton, cell membrane structures, and defects of contractility. The higher the Young’s modulus, the stiffer the cell, and it is well known that abnormal tissue stiffness is symptomatic of a range of diseases. The cell beating force and frequency provide information during the depolarization and repolarization phases, complementary to cell electrophysiology (calcium imaging, MEA, patch clamp). In addition, original data is also presented to emphasize the unique potential of AFM as a tool to assess fibrosis in cardiac tissue.

Microengineered platforms for characterizing the contractile function of in vitro cardiac models

Emerging heart-on-a-chip platforms are promising approaches to establish cardiac cell/tissue models in vitro for research on cardiac physiology, disease modeling and drug cardiotoxicity as well as for therapeutic discovery. Challenges still exist in obtaining the complete capability of in situ sensing to fully evaluate the complex functional properties of cardiac cell/tissue models. Changes to contractile strength (contractility) and beating regularity (rhythm) are particularly important to generate accurate, predictive models. Developing new platforms and technologies to assess the contractile functions of in vitro cardiac models is essential to provide information on cell/tissue physiologies, drug-induced inotropic responses, and the mechanisms of cardiac diseases. In this review, we discuss recent advances in biosensing platforms for the measurement of contractile functions of in vitro cardiac models, including single cardiomyocytes, 2D monolayers of cardiomyocytes, and 3D cardiac tissues. The characteristics and performance of current platforms are reviewed in terms of sensing principles, measured parameters, performance, cell sources, cell/tissue model configurations, advantages, and limitations. In addition, we highlight applications of these platforms and relevant discoveries in fundamental investigations, drug testing, and disease modeling. Furthermore, challenges and future outlooks of heart-on-a-chip platforms for in vitro measurement of cardiac functional properties are discussed.

Aminophylline Induces Two Types of Arrhythmic Events in Human Pluripotent Stem Cell-Derived Cardiomyocytes

Cardiac side effects of some pulmonary drugs are observed in clinical practice. Aminophylline, a methylxanthine bronchodilator with documented proarrhythmic action, may serve as an example. Data on the action of aminophylline on cardiac cell electrophysiology and contractility are not available. Hence, this study was focused on the analysis of changes in the beat rate and contraction force of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) and HL-1 cardiomyocytes in the presence of increasing concentrations of aminophylline (10 µM-10 mM in hPSC-CM and 8-512 µM in HL-1 cardiomyocytes). Basic biomedical parameters, namely, the beat rate (BR) and contraction force, were assessed in hPSC-CMs using an atomic force microscope (AFM). The beat rate changes under aminophylline were also examined on the HL-1 cardiac muscle cell line via a multielectrode array (MEA). Additionally, calcium imaging was used to evaluate the effect of aminophylline on intracellular Ca2+ dynamics in HL-1 cardiomyocytes. The BR was significantly increased after the application of aminophylline both in hPSC-CMs (with 10 mM aminophylline) and in HL-1 cardiomyocytes (with 256 and 512 µM aminophylline) in comparison with controls. A significant increase in the contraction force was also observed in hPSC-CMs with 10 µM aminophylline (a similar trend was visible at higher concentrations as well). We demonstrated that all aminophylline concentrations significantly increased the frequency of rhythm irregularities (extreme interbeat intervals) both in hPSC-CMs and HL-1 cells. The occurrence of the calcium sparks in HL-1 cardiomyocytes was significantly increased with the presence of 512 µM aminophylline. We conclude that the observed aberrant cardiomyocyte response to aminophylline suggests an arrhythmogenic potential of the drug. The acquired data represent a missing link between the arrhythmic events related to the aminophylline/theophylline treatment in clinical practice and describe cellular mechanisms of methylxanthine arrhythmogenesis. An AFM combined with hPSC-CMs may serve as a robust platform for direct drug effect screening.

Heart-on-Chip for Combined Cellular Dynamics Measurements and Computational Modeling Towards Clinical Applications

Organ-on-chip or micro-engineered three-dimensional cellular or tissue models are increasingly implemented in the study of cardiovascular pathophysiology as alternatives to traditional in vitro cell culture. Drug induced cardiotoxicity is a key issue in drug development pipelines, but the current in vitro and in vivo studies suffer from inter-species differences, high costs, and lack of reliability and accuracy in predicting cardiotoxicity. Microfluidic heart-on-chip devices can impose a paradigm shift to the current tools. They can not only recapitulate cardiac tissue level functionality and the communication between cells and extracellular matrices but also allow higher throughput studies conducive to drug screening especially with their added functionalities or sensors that extract disease-specific phenotypic, genotypic, and electrophysiological information in real-time. Such electrical and mechanical components can tailor the electrophysiology and mechanobiology of the experiment to better mimic the in vivo condition as well. Recent advancements and challenges are reviewed in the fabrication, functionalization and sensor assisted mechanical and electrophysiological measurements, numerical and computational modeling of cardiomyocytes' behavior, and the clinical applications in drug screening and disease modeling. This review concludes with the current challenges and perspectives on the future of such organ-on-chip platforms.

Micro/nanoengineered technologies for human pluripotent stem cells maintenance and differentiation

Human pluripotent stem cells (hPSCs) are a promising source of cells for cell replacement-based therapies as well as modeling human development and diseases in vitro. However, achieving fate control of hPSC with a high yield and specificity remains challenging. The fate specification of hPSCs is regulated by biochemical and biomechanical cues in their environment. Driven by this knowledge, recent exciting advances in micro/nanoengineering have been leveraged to develop a broad range of tools for the generation of extracellular biomechanical and biochemical signals that determine the behavior of hPSCs. In this review, we summarize such micro/nanoengineered technologies for controlling hPSC fate and highlight the role of biochemical and biomechanical cues such as substrate rigidity, surface topography, and cellular confinement in the hPSC-based technologies that are on the horizon.

Maturation of Stem Cell-Derived Cardiomyocytes: Foe in Translation Medicine

With the in-depth study of heart development, many human cardiomyocytes (CMs) have been generated in a laboratory environment. CMs derived from pluripotent stem cells (PSCs) have been widely used for a series of applications such as laboratory studies, drug toxicology screening, cardiac disease models, and as an unlimited resource for cell-based cardiac regeneration therapy. However, the low maturity of the induced CMs significantly impedes their applicability. Scientists have been committed to improving the maturation of CMs to achieve the purpose of heart regeneration in the past decades. In this review, we take CMs maturation as the main object of discussion, describe the characteristics of CMs maturation, summarize the key regulatory mechanism of regulating maturation and address the approaches to promote CMs maturation. The maturation of CM is gradually improving due to the incorporation of advanced technologies and is expected to continue.

Tools for studying and modulating (cardiac muscle) cell mechanics and mechanosensing across the scales

Cardiomyocytes generate force for the contraction of the heart to pump blood into the lungs and body. At the same time, they are exquisitely tuned to the mechanical environment and react to e.g. changes in cell and extracellular matrix stiffness or altered stretching due to reduced ejection fraction in heart disease, by adapting their cytoskeleton, force generation and cell mechanics. Both mechanical sensing and cell mechanical adaptations are multiscale processes. Receptor interactions with the extracellular matrix at the nanoscale will lead to clustering of receptors and modification of the cytoskeleton. This in turn alters mechanosensing, force generation, cell and nuclear stiffness and viscoelasticity at the microscale. Further, this affects cell shape, orientation, maturation and tissue integration at the microscale to macroscale. A variety of tools have been developed and adapted to measure cardiomyocyte receptor-ligand interactions and forces or mechanics at the different ranges, resulting in a wealth of new information about cardiomyocyte mechanobiology. Here, we take stock at the different tools for exploring cardiomyocyte mechanosensing and cell mechanics at the different scales from the nanoscale to microscale and macroscale.

A micromachined force sensing apparatus and method for human engineered cardiac tissue and induced pluripotent stem cell characterization

Induced pluripotent stem cell derived-cardiomyocytes (iPSC-CMs) have great potential for cell therapy, drug assessment, and for understanding the pathophysiology and genetic underpinnings of cardiac diseases. Contraction forces are one of the most important characteristics of cardiac function and are predictors of healthy and diseased states. Cantilever techniques, such as atomic force microscopy, measure the vertical force of a single cell, while systems designed to more closely resemble the physical heart function, such as engineered cardiac tissue held by end-posts, measure the axial force. One important question is how do these two force measurements correlate? By establishing a correlation of the axial and vertical force, we will be one step closer in being able to use single cell iPSC-CMs as models. A novel micromachined sensor for measuring force contractions of engineered tissue has been developed. Using this novel sensor, a correlation between axial force and vertical force is experimentally established. This finding supports the use of vertical measurements as an alternative to tissue measurements.

Real-Time Monitoring of Changes in Cardiac Contractility Using Silicon Cantilever Arrays Integrated with Strain Sensors

This paper proposes the use of sensor-integrated silicon cantilever arrays to measure drug-induced cardiac toxicity in real time. The proposed cantilever sensors, unlike the conventional electrophysiological methods, aim to evaluate cardiac toxicity by measuring the contraction force of the cardiomyocytes corresponding to the target drugs. The surface of the silicon cantilever consists of microgrooves to maximize the alignment and the contraction force of the cardiomyocytes. This type of surface pattern also helps in the maturation of the cardiomyocytes by increasing the sarcomere length. The preliminary characterization of the cantilever sensors was performed on the cantilever surface, with the cardiomyocytes seeded with a density of 1000 cells/mm², and the cardiac contractility was measured as a function of the culture days. The change in the contraction force of the cardiomyocytes due to the drug concentration was successfully measured through the integrated strain sensor in the culture media. The reliability of the sensor-integrated cantilevers and the feasibility of their mass production ensure that they meet the practical requirements in the medical applications.

Recent Advances in CRISPR/Cas9-Based Genome Editing Tools for Cardiac Diseases

In the past two decades, genome editing has proven its value as a powerful tool for modeling or even treating numerous diseases. After the development of protein-guided systems such as zinc finger nucleases (ZFNs) and transcription activator-like effector nucleases (TALENs), which for the first time made DNA editing an actual possibility, the advent of RNA-guided techniques has brought about an epochal change. Based on a bacterial anti-phage system, the CRISPR/Cas9 approach has provided a flexible and adaptable DNA-editing system that has been able to overcome several limitations associated with earlier methods, rapidly becoming the most common tool for both disease modeling and therapeutic studies. More recently, two novel CRISPR/Cas9-derived tools, namely base editing and prime editing, have further widened the range and accuracy of achievable genomic modifications. This review aims to provide an overview of the most recent developments in the genome-editing field and their applications in biomedical research, with a particular focus on models for the study and treatment of cardiac diseases.

Mechanical activities of self-beating cardiomyocyte aggregates under mechanical compression

Since the discovery of synchronous pulsations in cardiomyocytes (CMs), electrical communication between CMs has been emphasized; however, recent studies suggest the possibility of mechanical communication. Here, we demonstrate that spherical self-beating CM aggregates, termed cardiac spheroids (CSs), produce enhanced mechanical energy under mechanical compression and work cooperatively via mechanical communication. For single CSs between parallel plates, compression increased both beating frequency and beating energy. Contact mechanics revealed a scaling law on the beating energy, indicating that the most intensively stressed cells in the compressed CSs predominantly contributed to the performance of mechanical work against mechanical compression. For pairs of CSs between parallel plates, compression immediately caused synchronous beating with mechanical coupling. Compression tended to strengthen and stabilize the synchronous beating, although some irregularity and temporary arrest were observed. These results suggest that mechanical compression is an indispensable control parameter when evaluating the activities of CMs and their aggregates.

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

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

Monitoring Contractile Cardiomyocytes via Impedance Using Multipurpose Thin Film Ruthenium Oxide Electrodes

A ruthenium oxide (RuOx) electrode was used to monitor contractile events of human pluripotent stem cells-derived cardiomyocytes (hPSC-CMs) through electrical impedance spectroscopy (EIS). Using RuOx electrodes presents an advantage over standard thin film Pt electrodes because the RuOx electrodes can also be used as electrochemical sensor for pH, O₂, and nitric oxide, providing multisensory functionality with the same electrode. First, the EIS signal was validated in an optically transparent well-plate setup using Pt wire electrodes. This way, visual data could be recorded simultaneously. Frequency analyses of both EIS and the visual data revealed almost identical frequency components. This suggests both the EIS and visual data captured the similar events of the beating of (an area of) hPSC-CMs. Similar EIS measurement was then performed using the RuOx electrode, which yielded comparable signal and periodicity. This mode of operation adds to the versatility of the RuOx electrode's use in in vitro studies.

Human Induced Pluripotent Stem Cells as a Disease Model System for Heart Failure

PURPOSE OF REVIEW

Heart failure is among the most prevalent disease complexes overall and is associated with high morbidity and mortality. The underlying aetiology is manifold including coronary artery disease, genetic alterations and mutations, viral infections, adverse immune responses, and cardiac toxicity. To date, no specific therapies have been developed despite notable efforts. This can especially be attributed to hurdles in translational research, mainly due to the lack of proficient models of heart failure limited translation of therapeutic approaches from bench to bedside.

RECENT FINDINGS

Human induced pluripotent stem cells (hiPSCs) are rising in popularity, granting the ability to divide infinitely, to hold human, patient-specific genome, and to differentiate into any human cell, including cardiomyocytes (hiPSC-CMs). This brings magnificent promise to cardiological research, providing the possibility to recapitulate cardiac diseases in a dish. Advances in yield, maturity, and in vivo resemblance due to straightforward, low-cost protocols, high-throughput approaches, and complex 3D cultures have made this tool widely applicable. In recent years, hiPSC-CMs have been used to model a wide variety of cardiac diseases, bringing along the possibility to not only elucidate molecular mechanisms but also to test novel therapeutic approaches in the dish. Within the last decade, hiPSC-CMs have been exponentially employed to model heart failure. Constant advancements are aiming at improvements of differentiation protocols, hiPSC-CM maturity, and assays to elucidate molecular mechanisms and cellular functions. However, hiPSC-CMs are remaining relatively immature, and in vitro models can only partially recapitulate the complex interactions in vivo. Nevertheless, hiPSC-CMs have evolved as an essential model system in cardiovascular research.

Advances in Multidimensional Cardiac Biosensing Technologies: From Electrophysiology to Mechanical Motion and Contractile Force

Cardiovascular disease is currently a leading killer to human, while drug-induced cardiotoxicity remains the main cause of the withdrawal and attrition of drugs. Taking clinical correlation and throughput into account, cardiomyocyte is perfect as in vitro cardiac model for heart disease modeling, drug discovery, and cardiotoxicity assessment by accurately measuring the physiological multiparameters of cardiomyocytes. Remarkably, cardiomyocytes present both electrophysiological and biomechanical characteristics due to the unique excitation-contraction coupling, which plays a significant role in studying the cardiomyocytes. This review mainly focuses on the recent advances of biosensing technologies for the 2D and 3D cardiac models with three special properties: electrophysiology, mechanical motion, and contractile force. These high-performance multidimensional cardiac models are popular and effective to rebuild and mimic the heart in vitro. To help understand the high-quality and accurate physiologies, related detection techniques are highly demanded, from microtechnology to nanotechnology, from extracellular to intracellular recording, from multiple cells to single cell, and from planar to 3D models. Furthermore, the characteristics, advantages, limitations, and applications of these cardiac biosensing technologies, as well as the future development prospects should contribute to the systematization and expansion of knowledge.

hiPSC-Derived Cardiac Tissue for Disease Modeling and Drug Discovery

Relevant, predictive normal, or disease model systems are of vital importance for drug development. The difference between nonhuman models and humans could contribute to clinical trial failures despite ideal nonhuman results. As a potential substitute for animal models, human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) provide a powerful tool for drug toxicity screening, modeling cardiovascular diseases, and drug discovery. Here, we review recent hiPSC-CM disease models and discuss the features of hiPSC-CMs, including subtype and maturation and the tissue engineering technologies for drug assessment. Updates from the international multisite collaborators/administrations for development of novel drug discovery paradigms are also summarized.

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.

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.

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.

Cardiomyocyte mechanodynamics under conditions of actin remodelling

The mechanical performance of cardiomyocytes (CMs) is an important indicator of their maturation state and of primary importance for the development of therapies based on cardiac stem cells. As the mechanical analysis of adherent cells at high-throughput remains challenging, we explore the applicability of real-time deformability cytometry (RT-DC) to probe cardiomyocytes in suspension. RT-DC is a microfluidic technology allowing for real-time mechanical analysis of thousands of cells with a throughput exceeding 1000 cells per second. For CMs derived from human-induced pluripotent stem cells, we determined a Young's modulus of 1.25 ± 0.08 kPa which is in close range to previous reports. Upon challenging the cytoskeleton with cytochalasin D (CytoD) to induce filamentous actin depolymerization, we distinguish three different regimes in cellular elasticity. Transitions are observed below 10 nM and above 103 nM and are characterized by a decrease in Young's modulus. These regimes can be linked to cytoskeletal and sarcomeric actin contributions by CM contractility measurements at varying CytoD concentrations, where we observe a significant reduction in pulse duration only above 103 nM while no change is found for compound exposure at lower concentrations. Comparing our results to mechanical cell measurements using atomic force microscopy, we demonstrate for the first time to our knowledge, the feasibility of using a microfluidic technique to measure mechanical properties of large samples of adherent cells while linking our results to the composition of the cytoskeletal network. This article is part of a discussion meeting issue 'Single cell ecology'.

Human Induced Pluripotent Stem-Cell-Derived Cardiomyocytes as Models for Genetic Cardiomyopathies

In the last few decades, many pathogenic or likely pathogenic genetic mutations in over hundred different genes have been described for non-ischemic, genetic cardiomyopathies. However, the functional knowledge about most of these mutations is still limited because the generation of adequate animal models is time-consuming and challenging. Therefore, human induced pluripotent stem cells (iPSCs) carrying specific cardiomyopathy-associated mutations are a promising alternative. Since the original discovery that pluripotency can be artificially induced by the expression of different transcription factors, various patient-specific-induced pluripotent stem cell lines have been generated to model non-ischemic, genetic cardiomyopathies in vitro. In this review, we describe the genetic landscape of non-ischemic, genetic cardiomyopathies and give an overview about different human iPSC lines, which have been developed for the disease modeling of inherited cardiomyopathies. We summarize different methods and protocols for the general differentiation of human iPSCs into cardiomyocytes. In addition, we describe methods and technologies to investigate functionally human iPSC-derived cardiomyocytes. Furthermore, we summarize novel genome editing approaches for the genetic manipulation of human iPSCs. This review provides an overview about the genetic landscape of inherited cardiomyopathies with a focus on iPSC technology, which might be of interest for clinicians and basic scientists interested in genetic 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.

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.

Shear Modulus Measurement by Quantitative Phase Imaging and Correlation with Atomic Force Microscopy

Many approaches have been developed to characterize cell elasticity. Among these, atomic force microscopy (AFM) combined with modeling has been widely used to characterize cellular compliance. However, such approaches are often limited by the difficulties associated with using a specific instrument and by the complexity of analyzing the measured data. More recently, quantitative phase imaging (QPI) has been applied to characterize cellular stiffness by using an effective spring constant. This metric was further correlated to mass distribution (disorder strength) within the cell. However, these measurements are difficult to compare to AFM-derived measurements of Young's modulus. Here, we describe, to our knowledge, a new way of analyzing QPI data to directly retrieve the shear modulus. Our approach enables label-free measurement of cellular mechanical properties that can be directly compared to values obtained from other rheological methods. To demonstrate the technique, we measured shear modulus and phase disorder strength using QPI, as well as Young's modulus using AFM, across two breast cancer cell-line populations dosed with three different concentrations of cytochalasin D, an actin-depolymerizing toxin. Comparison of QPI-derived and AFM moduli shows good agreement between the two measures and further agrees with theory. Our results suggest that QPI is a powerful tool for cellular biophysics because it allows for optical quantitative measurements of cell mechanical properties.

Analysis of time-course drug response in rat cardiomyocytes cultured on a pattern of islands

We previously reported the kinetics analysis of cardiomyocyte beating using scanning electrochemical microscopy (SECM). In this study, a stage-top incubator and a capillary micropipette (MP) for delivering drugs were assembled with an SECM instrument, and the responses of rat cardiomyocytes were analyzed under a culture environment after drug stimulation. When adenosine triphosphate (ATP) was delivered to synchronously beating cardiomyocytes, the beating acceleration effect of ATP was counteracted by the synchronously beating network in the culture dish. In contrast, cardiomyocytes cultured on a pattern of islands in a culture dish showed fluctuations in the duration of beating upon the addition of ATP. We also examined the effect of the cardiotoxic agent astemizole on cardiomyocytes and successfully detected motion fluctuations. Therefore, drug stimulation via MPs and beating measurement by SECM are effective routes for the evaluation of drug candidates through the analysis of time-course beating motion fluctuations of the cardiomyocytes.

Modeling cardiac complexity: Advancements in myocardial models and analytical techniques for physiological investigation and therapeutic development in vitro

Cardiomyopathies, heart failure, and arrhythmias or conduction blockages impact millions of patients worldwide and are associated with marked increases in sudden cardiac death, decline in the quality of life, and the induction of secondary pathologies. These pathologies stem from dysfunction in the contractile or conductive properties of the cardiomyocyte, which as a result is a focus of fundamental investigation, drug discovery and therapeutic development, and tissue engineering. All of these foci require in vitro myocardial models and experimental techniques to probe the physiological functions of the cardiomyocyte. In this review, we provide a detailed exploration of different cell models, disease modeling strategies, and tissue constructs used from basic to translational research. Furthermore, we highlight recent advancements in imaging, electrophysiology, metabolic measurements, and mechanical and contractile characterization modalities that are advancing our understanding of cardiomyocyte physiology. With this review, we aim to both provide a biological framework for engineers contributing to the field and demonstrate the technical basis and limitations underlying physiological measurement modalities for biologists attempting to take advantage of these state-of-the-art techniques.

Biochemical Stimulation of Immune Cells and Measurement of Mechanical Responses Using Atomic Force Microscopy

This manuscript details methods to ligate cell-surface receptors on live cells with precise spatiotemporal control using an atomic force microscope (AFM) to deliver ligands. This approach can be used to image cellular responses upon activating T cell receptors when the AFM is mounted on an optical microscope. Moreover, the AFM measures forces generated by the cell during the contact. Using AFM to trigger cellular responses adds an important capability to the field of mechanobiology. We describe how to incorporate anti-CD3 antibodies or other molecules onto an AFM cantilever and how to use AFM to activate T cells. © 2019 by John Wiley & Sons, Inc.

Programmed assembly of synthetic protocells into thermoresponsive prototissues

Although several new types of synthetic cell-like entities are now available, their structural integration into spatially interlinked prototissues that communicate and display coordinated functions remains a considerable challenge. Here we describe the programmed assembly of synthetic prototissue constructs based on the bio-orthogonal adhesion of a spatially confined binary community of protein-polymer protocells, termed proteinosomes. The thermoresponsive properties of the interlinked proteinosomes are used collectively to generate prototissue spheroids capable of reversible contractions that can be enzymatically modulated and exploited for mechanochemical transduction. Overall, our methodology opens up a route to the fabrication of artificial tissue-like materials capable of collective behaviours, and addresses important emerging challenges in bottom-up synthetic biology and bioinspired engineering.

Effect of Substrate Stiffness on Mechanical Coupling and Force Propagation at the Infarct Boundary

Heterogeneous intercellular coupling plays a significant role in mechanical and electrical signal transmission in the heart. Although many studies have investigated the electrical signal conduction between myocytes and nonmyocytes within the heart muscle tissue, there are not many that have looked into the mechanical counterpart. This study aims to investigate the effect of substrate stiffness and the presence of cardiac myofibroblasts (CMFs) on mechanical force propagation across cardiomyocytes (CMs) and CMFs in healthy and heart-attack-mimicking matrix stiffness conditions. The contractile forces generated by the CMs and their propagation across the CMFs were measured using a bio-nanoindenter integrated with fluorescence microscopy for fast calcium imaging. Our results showed that softer substrates facilitated stronger and further signal transmission. Interestingly, the presence of the CMFs attenuated the signal propagation in a stiffness-dependent manner. Stiffer substrates with CMFs present attenuated the signal ∼24-32% more compared to soft substrates with CMFs, indicating a synergistic detrimental effect of increased matrix stiffness and increased CMF numbers after myocardial infarction on myocardial function. Furthermore, the beating pattern of the CMF movement at the CM-CMF boundary also depended on the substrate stiffness, thereby influencing the waveform of the propagation of CM-generated contractile forces. We performed computer simulations to further understand the occurrence of different force transmission patterns and showed that cell-matrix focal adhesions assembled at the CM-CMF interfaces, which differs depending on the substrates stiffness, play important roles in determining the efficiency and mechanism of signal transmission. In conclusion, in addition to substrate stiffness, the degree and type of cell-cell and cell-matrix interactions, affected by the substrate stiffness, influence mechanical signal conduction between myocytes and nonmyocytes in the heart muscle tissue.

Biomechanical Characterization at the Cell Scale: Present and Prospects

The rapidly growing field of mechanobiology demands for robust and reproducible characterization of cell mechanical properties. Recent achievements in understanding the mechanical regulation of cell fate largely rely on technological platforms capable of probing the mechanical response of living cells and their physico–chemical interaction with the microenvironment. Besides the established family of atomic force microscopy (AFM) based methods, other approaches include optical, magnetic, and acoustic tweezers, as well as sensing substrates that take advantage of biomaterials chemistry and microfabrication techniques. In this review, we introduce the available methods with an emphasis on the most recent advances, and we discuss the challenges associated with their implementation.

Post-Translational Modifications and Diastolic Calcium Leak Associated to the Novel RyR2-D3638A Mutation Lead to CPVT in Patient-Specific hiPSC-Derived Cardiomyocytes

Background: Sarcoplasmic reticulum Ca²⁺ leak and post-translational modifications under stress have been implicated in catecholaminergic polymorphic ventricular tachycardia (CPVT), a highly lethal inherited arrhythmogenic disorder. Human induced pluripotent stem cells (hiPSCs) offer a unique opportunity for disease modeling. Objective: The aims were to obtain functional hiPSC-derived cardiomyocytes from a CPVT patient harboring a novel ryanodine receptor (RyR2) mutation and model the syndrome, drug responses and investigate the molecular mechanisms associated to the CPVT syndrome. Methods: Patient-specific cardiomyocytes were generated from a young athletic female diagnosed with CPVT. The contractile, intracellular Ca²⁺ handling and electrophysiological properties as well as the RyR2 macromolecular remodeling were studied. Results: Exercise stress electrocardiography revealed polymorphic ventricular tachycardia when treated with metoprolol and marked improvement with flecainide alone. We found abnormal stress-induced contractile and electrophysiological properties associated with sarcoplasmic reticulum Ca²⁺ leak in CPVT hiPSC-derived cardiomyocytes. We found inadequate response to metoprolol and a potent response of flecainide. Stabilizing RyR2 with a Rycal compound prevents those abnormalities specifically in CPVT hiPSC-derived cardiomyocytes. The RyR2-D3638A mutation is located in the conformational change inducing-central core domain and leads to RyR2 macromolecular remodeling including depletion of PP2A and Calstabin2. Conclusion: We identified a novel RyR2-D3638A mutation causing 3D conformational defects and aberrant biophysical properties associated to RyR2 macromolecular complex post-translational remodeling. The molecular remodeling is for the first time revealed using patient-specific hiPSC-derived cardiomyocytes which may explain the CPVT proband’s resistance. Our study promotes hiPSC-derived cardiomyocytes as a suitable model for disease modeling, testing new therapeutic compounds, personalized medicine and deciphering underlying molecular mechanisms.

Simultaneous AFM Investigation of the Single Cardiomyocyte Electro-Chemo-Mechanics During Excitation-Contraction Coupling

The cardiac excitation-contraction coupling is the cellular process through which the heart absolves its blood pumping function, and it is directly affected when cardiac pathologies occur. Cardiomyocytes are the functional units in which this complex biomolecular process takes place: they can be represented as a two-stage electro-chemo and chemo-mechanical transducer, along which each stage can be probed and monitored via appropriate micro/nanotechnology-based tools. Atomic force microscopy (AFM), with its unique nanoresolved force sensitivity and versatile modes of extracting sample properties, can represent a key instrument to study time-dependent heart mechanics and topography at the single cell level. In this work, we show how the integrative possibilities of AFM allowed us to implement an in vitro system which can monitor cardiac electrophysiology, intracellular calcium dynamics, and single cell mechanics. We believe this single cell-sensitive and integrated system will unlock improved, fast, and reliable cardiac in vitro tests in the future.

AFM nano-mechanical study of the beating profile of hiPSC-derived cardiomyocytes beating bodies WT and DM1

Myotonic Dystrophy type 1 (DM1) is the most common form of muscular dystrophy in adults, characterized by a variety of multisystemic features and associated with cardiac anomalies. Among cardiac phenomena, conduction defects, ventricular arrhythmias, and dilated cardiomyopathy represent the main cause of sudden death in DM1 patients. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) represent a powerful in vitro model for molecular, biochemical, and physiological studies of disease in the target cells. Here, we used an Atomic Force Microscope (AFM) to measure the beating profiles of a large number of cells, organized in CM clusters (Beating Bodies, BBs), obtained from wild type (WT) and DM1 patients. We monitored the evolution over time of the frequency and intensity of the beating. We determined the variations between different BBs and over various areas of a single BB, caused by morphological and biomechanical variations. We exploited the AFM tip to apply a controlled force over the BBs, to carefully assess the biomechanical reaction of the different cell clusters over time, both in terms of beating frequency and intensity. Our measurements demonstrated differences between the WT and DM1 clusters highlighting, for the DM1 samples, an instability which was not observed in WT cells. We measured differences in the cellular response to the applied mechanical stimulus in terms of beating synchronicity over time and cell tenacity, which are in good agreement with the cellular behavior in vivo. Overall, the combination of hiPSC-CMs with AFM characterization can become a new tool to study the collective movements of cell clusters in different conditions and can be extended to the characterization of the BB response to chemical and pharmacological stimuli.