Substrate Stiffness Influences Structural and Functional Remodeling in Induced Pluripotent Stem Cell-Derived Cardiomyocytes

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.

Current Status of Cardiac Regenerative Therapy Using Induced Pluripotent Stem Cells

Heart failure (HF) is a life-threatening disorder and is treated by drug therapies and surgical interventions such as heart transplantation and left ventricular assist device (LVAD). However, these treatments can lack effectiveness in the long term and are associated with issues such as donor shortage in heart transplantation, and infection, stroke, or gastrointestinal bleeding in LVADs. Therefore, alternative therapeutic strategies are still needed. In this respect, stem cell therapy has been introduced for the treatment of HF and numerous preclinical and clinical studies are employing a range of stem cell varieties. These stem cells, such as embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), have been shown to improve cardiac function and attenuate left ventricular remodeling. IPSCs, which have a capacity for unlimited proliferation and differentiation into cardiomyocytes, are a promising cell source for myocardial regeneration therapy. In this review, we discuss the following topics: (1) what are iPSCs; (2) the limitations and solutions for the translation of iPSC-CMs practically; and (3) the current therapeutic clinical trials.

A data-driven computational model for engineered cardiac microtissues

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

Recent advances in regulating the proliferation or maturation of human-induced pluripotent stem cell-derived cardiomyocytes

In the last decade, human-induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM)-based cell therapy has drawn broad attention as a potential therapy for treating injured hearts. However, mass production of hiPSC-CMs remains challenging, limiting their translational potential in regenerative medicine. Therefore, multiple strategies including cell cycle regulators, small molecules, co-culture systems, and epigenetic modifiers have been used to improve the proliferation of hiPSC-CMs. On the other hand, the immaturity of these proliferative hiPSC-CMs could lead to lethal arrhythmias due to their limited ability to functionally couple with resident cardiomyocytes. To achieve functional maturity, numerous methods such as prolonged culture, biochemical or biophysical stimulation, in vivo transplantation, and 3D culture approaches have been employed. In this review, we summarize recent approaches used to promote hiPSC-CM proliferation, and thoroughly review recent advances in promoting hiPSC-CM maturation, which will serve as the foundation for large-scale production of mature hiPSC-CMs for future clinical applications.

Heart-derived collagen promotes maturation of engineered heart tissue

Although the extracellular matrix (ECM) plays essential roles in heart tissue engineering, the optimal ECM components for heart tissue organization have not previously been elucidated. Here, we focused on the main ECM component, fibrillar collagen, and analyzed the effects of collagens on heart tissue engineering, by comparing the use of porcine heart-derived collagen and other organ-derived collagens in generating engineered heart tissue (EHT). We demonstrate that heart-derived collagen induces better contraction and relaxation of human induced pluripotent stem cell-derived EHT (hiPSC-EHT) and that hiPSC-EHT with heart-derived collagen exhibit more mature profiles than those with collagens from other organs. Further, we found that collagen fibril formation and gel stiffness influence the contraction, relaxation, and maturation of hiPSC-EHT, suggesting the importance of collagen types III and type V, which are relatively abundant in the heart. Thus, we demonstrate the effectiveness of organ-specific collagens in tissue engineering and drug discovery.

Building blocks of microphysiological system to model physiology and pathophysiology of human heart

Microphysiological systems (MPS) are drawing increasing interest from academia and from biomedical industry due to their improved capability to capture human physiology. MPS offer an advanced in vitro platform that can be used to study human organ and tissue level functions in health and in diseased states more accurately than traditional single cell cultures or even animal models. Key features in MPS include microenvironmental control and monitoring as well as high biological complexity of the target tissue. To reach these qualities, cross-disciplinary collaboration from multiple fields of science is required to build MPS. Here, we review different areas of expertise and describe essential building blocks of heart MPS including relevant cardiac cell types, supporting matrix, mechanical stimulation, functional measurements, and computational modelling. The review presents current methods in cardiac MPS and provides insights for future MPS development with improved recapitulation of human physiology.

The Utilisation of Hydrogels for iPSC-Cardiomyocyte Research

Cardiac fibroblasts' (FBs) and cardiomyocytes' (CMs) behaviour and morphology are influenced by their environment such as remodelling of the myocardium, thus highlighting the importance of biomaterial substrates in cell culture. Biomaterials have emerged as important tools for the development of physiological models, due to the range of adaptable properties of these materials, such as degradability and biocompatibility. Biomaterial hydrogels can act as alternative substrates for cellular studies, which have been particularly key to the progression of the cardiovascular field. This review will focus on the role of hydrogels in cardiac research, specifically the use of natural and synthetic biomaterials such as hyaluronic acid, polydimethylsiloxane and polyethylene glycol for culturing induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). The ability to fine-tune mechanical properties such as stiffness and the versatility of biomaterials is assessed, alongside applications of hydrogels with iPSC-CMs. Natural hydrogels often display higher biocompatibility with iPSC-CMs but often degrade quicker, whereas synthetic hydrogels can be modified to facilitate cell attachment and decrease degradation rates. iPSC-CM structure and electrophysiology can be assessed on natural and synthetic hydrogels, often resolving issues such as immaturity of iPSC-CMs. Biomaterial hydrogels can thus provide a more physiological model of the cardiac extracellular matrix compared to traditional 2D models, with the cardiac field expansively utilising hydrogels to recapitulate disease conditions such as stiffness, encourage alignment of iPSC-CMs and facilitate further model development such as engineered heart tissues (EHTs).

Optimization of 3D printing and in vitro characterization of alginate/gelatin lattice and angular scaffolds for potential cardiac tissue engineering

Background: Engineering cardiac tissue that mimics the hierarchical structure of cardiac tissue remains challenging, raising the need for developing novel methods capable of creating structures with high complexity. Three-dimensional (3D)-printing techniques are among promising methods for engineering complex tissue constructs with high precision. By means of 3D printing, this study aims to develop cardiac constructs with a novel angular structure mimicking cardiac architecture from alginate (Alg) and gelatin (Gel) composite. The 3D-printing conditions were optimized and the structures were characterized in vitro, with human umbilical vein endothelial cells (HUVECs) and cardiomyocytes (H9c2 cells), for potential cardiac tissue engineering. Methods: We synthesized the composites of Alg and Gel with varying concentrations and examined their cytotoxicity with both H9c2 cells and HUVECs, as well as their printability for creating 3D structures of varying fibre orientations (angular design). The 3D-printed structures were characterized in terms of morphology by both scanning electron microscopy (SEM) and synchrotron radiation propagation-based imaging computed tomography (SR-PBI-CT), and elastic modulus, swelling percentage, and mass loss percentage as well. The cell viability studies were conducted via measuring the metabolic activity of the live cells with MTT assay and visualizing the cells with live/dead assay kit. Results: Among the examined composite groups of Alg and Gel, two combinations with ratios of 2 to 1 and 3 to 1 (termed as Alg2Gel1 and Alg3Gel1) showed the highest cell survival; they accordingly were used to fabricate two different structures: a novel angular and a conventional lattice structure. Scaffolds made of Alg3Gel1 showed higher elastic modulus, lower swelling percentage, less mass loss, and higher cell survival compared to that of Alg2Gel1. Although the viability of H9c2 cells and HUVECs on all scaffolds composed of Alg3Gel1 was above 99%, the group of the constructs with the angular design maintained significantly more viable cells compared to other investigated groups. Conclusion: The group of angular 3D-ptinted constructs has illustrated promising properties for cardiac tissue engineering by providing high cell viability for both endothelial and cardiac cells, high mechanical strength as well as appropriate swelling, and degradation properties during 21 days of incubation. Statement of Significance: 3D-printing is an emerging method to create complex constructs with high precision in a large scale. In this study, we have demonstrated that 3D-printing can be used to create compatible constructs from the composite of Alg and Gel with endothelial cells and cardiac cells. Also, we have demonstrated that these constructs are able to enhance the viability of cardiac and endothelial cells via creating a 3D structure mimicking the alignment and orientation of the fibers in the native heart.

Does Enhanced Structural Maturity of hiPSC-Cardiomyocytes Better for the Detection of Drug-Induced Cardiotoxicity?

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) are currently used following the Comprehensive in vitro Proarrhythmic Assay (CiPA) initiative and subsequent recommendations in the International Council for Harmonization (ICH) guidelines S7B and E14 Q&A, to detect drug-induced cardiotoxicity. Monocultures of hiPSC-CMs are immature compared to adult ventricular cardiomyocytes and might lack the native heterogeneous nature. We investigated whether hiPSC-CMs, treated to enhance structural maturity, are superior in detecting drug-induced changes in electrophysiology and contraction. This was achieved by comparing hiPSC-CMs cultured in 2D monolayers on the current standard (fibronectin matrix, FM), to monolayers on a coating known to promote structural maturity (CELLvo™ Matrix Plus, MM). Functional assessment of electrophysiology and contractility was made using a high-throughput screening approach involving the use of both voltage-sensitive fluorescent dyes for electrophysiology and video technology for contractility. Using 11 reference drugs, the response of the monolayer of hiPSC-CMs was comparable in the two experimental settings (FM and MM). The data showed no functionally relevant differences in electrophysiology between hiPSC-CMs in standard FM and MM, while contractility read-outs indicated an altered amplitude of contraction but not changes in time course. RNA profiling for cardiac proteins shows similarity of the RNA expression across the two forms of 2D culture, suggesting that cell-to-matrix adhesion differences may explain account for differences in contraction amplitude. The results support the view that hiPSC-CMs in both 2D monolayer FM and MM that promote structural maturity are equally effective in detecting drug-induced electrophysiological effects in functional safety studies.

Membrane remodelling triggers maturation of excitation-contraction coupling in 3D-shaped human-induced pluripotent stem cell-derived cardiomyocytes

The prospective use of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) for cardiac regenerative medicine strongly depends on the electro-mechanical properties of these cells, especially regarding the Ca2+-dependent excitation-contraction (EC) coupling mechanism. Currently, the immature structural and functional features of hiPSC-CM limit the progression towards clinical applications. Here, we show that a specific microarchitecture is essential for functional maturation of hiPSC-CM. Structural remodelling towards a cuboid cell shape and induction of BIN1, a facilitator of membrane invaginations, lead to transverse (t)-tubule-like structures. This transformation brings two Ca2+ channels critical for EC coupling in close proximity, the L-type Ca2+ channel at the sarcolemma and the ryanodine receptor at the sarcoplasmic reticulum. Consequently, the Ca2+-dependent functional interaction of these channels becomes more efficient, leading to improved spatio-temporal synchronisation of Ca2+ transients and higher EC coupling gain. Thus, functional maturation of hiPSC-cardiomyocytes by optimised cell microarchitecture needs to be considered for future cardiac regenerative approaches.

Acute effects of cardiac contractility modulation stimulation in conventional 2D and 3D human induced pluripotent stem cell-derived cardiomyocyte models

Cardiac contractility modulation (CCM) is a medical device therapy whereby non-excitatory electrical stimulations are delivered to the myocardium during the absolute refractory period to enhance cardiac function. We previously evaluated the effects of the standard CCM pulse parameters in isolated rabbit ventricular cardiomyocytes and 2D human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) monolayers, on flexible substrate. In the present study, we sought to extend these results to human 3D microphysiological systems to develop a robust model to evaluate various clinical CCM pulse parameters in vitro. HiPSC-CMs were studied in conventional 2D monolayer format, on stiff substrate (i.e., glass), and as 3D human engineered cardiac tissues (ECTs). Cardiac contractile properties were evaluated by video (i.e., pixel) and force-based analysis. CCM pulses were assessed at varying electrical ‘doses’ using a commercial pulse generator. A robust CCM contractile response was observed for 3D ECTs. Under comparable conditions, conventional 2D monolayer hiPSC-CMs, on stiff substrate, displayed no contractile response. 3D ECTs displayed enhanced contractile properties including increased contraction amplitude (i.e., force), and accelerated contraction and relaxation slopes under standard acute CCM stimulation. Moreover, 3D ECTs displayed enhanced contractility in a CCM pulse parameter-dependent manner by adjustment of CCM pulse delay, duration, amplitude, and number relative to baseline. The observed acute effects subsided when the CCM stimulation was stopped and gradually returned to baseline. These data represent the first study of CCM in 3D hiPSC-CM models and provide a nonclinical tool to assess various CCM device signals in 3D human cardiac tissues prior to in vivo animal studies. Moreover, this work provides a foundation to evaluate the effects of additional cardiac medical devices in 3D ECTs.

Distress-Mediated Remodeling of Cardiac Connexin-43 in a Novel Cell Model for Arrhythmogenic Heart Diseases

Gap junctions and their expression pattern are essential to robust function of intercellular communication and electrical propagation in cardiomyocytes. In healthy myocytes, the main cardiac gap junction protein connexin-43 (Cx43) is located at the intercalated disc providing a clear direction of signal spreading across the cardiac tissue. Dislocation of Cx43 to lateral membranes has been detected in numerous cardiac diseases leading to slowed conduction and high propensity for the development of arrhythmias. At the cellular level, arrhythmogenic diseases are associated with elevated levels of oxidative distress and gap junction remodeling affecting especially the amount and sarcolemmal distribution of Cx43 expression. So far, a mechanistic link between sustained oxidative distress and altered Cx43 expression has not yet been identified. Here, we propose a novel cell model based on murine induced-pluripotent stem cell-derived cardiomyocytes to investigate subcellular signaling pathways linking cardiomyocyte distress with gap junction remodeling. We tested the new hypothesis that chronic distress, induced by rapid pacing, leads to increased reactive oxygen species, which promotes expression of a micro-RNA, miR-1, specific for the control of Cx43. Our data demonstrate that Cx43 expression is highly sensitive to oxidative distress, leading to reduced expression. This effect can be efficiently prevented by the glutathione peroxidase mimetic ebselen. Moreover, Cx43 expression is tightly regulated by miR-1, which is activated by tachypacing-induced oxidative distress. In light of the high arrhythmogenic potential of altered Cx43 expression, we propose miR-1 as a novel target for pharmacological interventions to prevent the maladaptive remodeling processes during chronic distress in the heart.