Extracellular Matrix in Regulation of Contractile System in Cardiomyocytes

Focal Adhesion's Role in Cardiomyocytes Function: From Cardiomyogenesis to Mechanotransduction

Mechanotransduction refers to the ability of cells to sense mechanical stimuli and convert them into biochemical signals. In this context, the key players are focal adhesions (FAs): multiprotein complexes that link intracellular actin bundles and the extracellular matrix (ECM). FAs are involved in cellular adhesion, growth, differentiation, gene expression, migration, communication, force transmission, and contractility. Focal adhesion signaling molecules, including Focal Adhesion Kinase (FAK), integrins, vinculin, and paxillin, also play pivotal roles in cardiomyogenesis, impacting cell proliferation and heart tube looping. In fact, cardiomyocytes sense ECM stiffness through integrins, modulating signaling pathways like PI3K/AKT and Wnt/β-catenin. Moreover, FAK/Src complex activation mediates cardiac hypertrophic growth and survival signaling in response to mechanical loads. This review provides an overview of the molecular and mechanical mechanisms underlying the crosstalk between FAs and cardiac differentiation, as well as the role of FA-mediated mechanotransduction in guiding cardiac muscle responses to mechanical stimuli.

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

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

Maturation of induced pluripotent stem cell-derived cardiomyocytes and its therapeutic effect on myocardial infarction in mouse

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have an irreplaceable role in the treatment of myocardial infarction (MI), which can be injected into the transplanted area with new cardiomyocytes (Cardiomyocytes, CMs), and improve myocardial function. However, the immaturity of the structure and function of iPSC-CMs is the main bottleneck at present. Since collagen participates in the formation of extracellular matrix (ECM), we synthesized nano colloidal gelatin (Gel) with collagen as the main component, and confirmed that the biomaterial has good biocompatibility and is suitable for cellular in vitro growth. Subsequently, we combined the PI3K/AKT/mTOR pathway inhibitor BEZ-235 with Gel and found that the two combined increased the sarcomere length and action potential amplitude (APA) of iPSC-CMs, and improved the Ca²⁺ processing ability, the maturation of mitochondrial morphological structure and metabolic function. Not only that, Gel can also prolong the retention rate of iPSC-CMs in the myocardium and increase the expression of Cx43 and angiogenesis in the transplanted area of mature iPSC-CMs, which also provides a reliable basis for the subsequent treatment of mature iPSC-CMs.

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BEZ-235 + Gel promotes the maturation of sarcomere structure in iPSC-CMs.

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BEZ-235 + Gel promotes electrophysiological maturation of iPSC-CMs.

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BEZ-235 + Gel increases mitochondrial respiration in iPSC-CMs.

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Gel loaded with mature iPSC-CMs enhanced angiogenesis and gap junction formation at the injection site.

Modulation of the miR-122/Sirt-6/ACE2 axis on experimentally-induced myocardial infarction

Myocardial infarction (MI) is a progressive myocardial necrosis that can lead to a number of life-threatening complications. MiRNAs have a crucial role in the pathogenesis of many cardiovascular diseases. Remarkably, miR-122 targets the sirtuin-6 (Sirt-6) gene, which is an essential regulator of cardiovascular function and is considered a partial angiotensin converting enzyme 2 (ACE2) activator. Modulation of this axis is supposed to contribute to MI pathogenesis. The current study aims to investigate the cardioprotective effects of xanthenone through targeting the miR-122/Sirt-6/ACE2 axis on experimentally-induced MI in rats. Xanthenone was administered for 14 days and isoprenaline was injected in the last 2 days of the experiment. Xanthenone treatment resulted in a significant downregulation of miR-122, which further upregulated Sirt-6 and thus activated the adenosine monophosphate-activated protein kinase (AMPK). AMPK increases ACE2 levels and results in a decrease in the level of its substrate angiotensin II resulting in the normalization of the inflammatory cytokines and the cardiac biomarkers. Finally, by targeting the miR-122/Sirt-6/AMPK/ACE2 axis, xanthenone has the potential to be a promising cardioprotective agent against MI.

Collagen type XIX regulates cardiac extracellular matrix structure and ventricular function

The cardiac extracellular matrix plays essential roles in homeostasis and injury responses. Although the role of fibrillar collagens have been thoroughly documented, the functions of non-fibrillar collagen members remain underexplored. These include a distinct group of non-fibrillar collagens, termed, fibril-associated collagens with interrupted triple helices (FACITs). Recent reports of collagen type XIX (encoded by Col19a1) expression in adult heart and evidence of its enhanced expression in cardiac ischemia suggest important functions for this FACIT in cardiac ECM structure and function. Here, we examined the cellular source of collagen XIX in the adult murine heart and evaluated its involvement in ECM structure and ventricular function. Immunodetection of collagen XIX in fractionated cardiovascular cell lineages revealed fibroblasts and smooth muscle cells as the primary sources of collagen XIX in the heart. Based on echocardiographic and histologic analyses, Col19a1 null (Col19a1N/N) mice exhibited reduced systolic function, thinning of left ventricular walls, and increased cardiomyocyte cross-sectional areas-without gross changes in myocardial collagen content or basement membrane morphology. Col19a1N/N cardiac fibroblasts had augmented expression of several enzymes involved in the synthesis and stability of fibrillar collagens, including PLOD1 and LOX. Furthermore, second harmonic generation-imaged ECM derived from Col19a1N/N cardiac fibroblasts, and transmission electron micrographs of decellularized hearts from Col19a1N/N null animals, showed marked reductions in fibrillar collagen structural organization. Col19a1N/N mice also displayed enhanced phosphorylation of focal adhesion kinase (FAK), signifying de-repression of the FAK pathway-a critical mediator of cardiomyocyte hypertrophy. Collectively, we show that collagen XIX, which had a heretofore unknown role in the mammalian heart, participates in the regulation of cardiac structure and function-potentially through modulation of ECM fibrillar collagen structural organization. Further, these data suggest that this FACIT may modify ECM superstructure via acting at the level of the fibroblast to regulate their expression of collagen synthetic and stabilization enzymes.

Bizonal cardiac engineered tissues with differential maturation features in a mid-throughput multimodal bioreactor

Functional three-dimensional (3D) engineered cardiac tissue (ECT) models are essential for effective drug screening and biological studies. Application of physiological cues mimicking those typical of the native myocardium is known to promote the cardiac maturation and functionality in vitro. Commercially available bioreactors can apply one physical force type at a time and often in a restricted loading range. To overcome these limitations, a millimetric-scale microscope-integrated bioreactor was developed to deliver multiple biophysical stimuli to ECTs. In this study, we showed that the single application of auxotonic loading (passive) generated a bizonal ECT with a unique cardiac maturation pattern. Throughout the statically cultured constructs and in the ECT region exposed to high passive loading, cardiomyocytes predominantly displayed a round morphology and poor contractility ability. The ECT region with a low passive mechanical stimulation instead showed both rat- and human-origin cardiac cell maturation and organization, as well as increased ECT functionality.

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Mid-throughput culture platform to engineer reproducible 3D cardiac in vitro models

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3D culture under multiphysical stimuli mimicking the in vivo heart environment

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Passive loading leads to bizonal constructs with different cardiac maturation stages

Human Engineered Heart Tissue Models for Disease Modeling and Drug Discovery

The emergence of human induced pluripotent stem cells (hiPSCs) and efficient differentiation of hiPSC-derived cardiomyocytes (hiPSC-CMs) induced from diseased donors have the potential to recapitulate the molecular and functional features of the human heart. Although the immaturity of hiPSC-CMs, including the structure, gene expression, conduct, ion channel density, and Ca²⁺ kinetics, is a major challenge, various attempts to promote maturation have been effective. Three-dimensional cardiac models using hiPSC-CMs have achieved these functional and morphological maturations, and disease models using patient-specific hiPSC-CMs have furthered our understanding of the underlying mechanisms and effective therapies for diseases. Aside from the mechanisms of diseases and drug responses, hiPSC-CMs also have the potential to evaluate the safety and efficacy of drugs in a human context before a candidate drug enters the market and many phases of clinical trials. In fact, novel drug testing paradigms have suggested that these cells can be used to better predict the proarrhythmic risk of candidate drugs. In this review, we overview the current strategies of human engineered heart tissue models with a focus on major cardiac diseases and discuss perspectives and future directions for the real application of hiPSC-CMs and human engineered heart tissue for disease modeling, drug development, clinical trials, and cardiotoxicity tests.

miR-431-5p Regulates Apoptosis of Cardiomyocytes After Acute Myocardial Infarction via Targeting Selenoprotein T

Acute myocardial infarction (AMI) represents the acute manifestation of coronary artery disease. In recent years, microRNAs (miRNAs) have been extensively studied in AMI. This study focused on the role of miR-431-5p in AMI and its effect on cardiomyocyte apoptosis after AMI. The expression of miR-431-5p was analyzed by quantitative real-time PCR (qRT-PCR). By interfering with miR-431-5p in hypoxia-reoxygenation (H/R)-induced HL-1 cardiomyocytes, the effect of miR-431-5p on cardiomyocyte apoptosis after AMI was examined. The interaction between miR-431-5p and selenoprotein T (SELT) mRNA was verified by dual-luciferase reporter assay. Cell apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay and flow cytometry. Cell viability was examined by 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay. The results of qRT-PCR showed that the expression of miR-431-5p in AMI myocardial tissues and H/R-induced HL-1 cardiomyocytes was significantly increased. After interfering with miR-431-5p, the expression of SELT in HL-1 cells was up-regulated, cell apoptosis was decreased, cell viability was increased, and lactate dehydrogenase (LDH) activity was decreased. The dual-luciferase reporter assay confirmed the targeting relationship between miR-431-5p and SELT1 3’ untranslated region (UTR). In H/R-induced HL-1 cells, the simultaneous silencing of SELT and miR-431-5p resulted in a decrease of Bcl-2 expression, an increase of Bax expression, and an increase of cleaved-caspase 3 expression compared with silencing miR-431-5p alone. Also, cell viability was decreased, while LDH activity was increased by the simultaneous silencing of SELT and miR-431-5p. Interfering miR-431-5p protected cardiomyocytes from AMI injury via restoring the expression of SELT, providing new ideas for the treatment of AMI.

Chronic Ethanol Exposure Induces Deleterious Changes in Cardiomyocytes Derived from Human Induced Pluripotent Stem Cells

Chronic alcohol consumption in adults can induce cardiomyopathy, arrhythmias, and heart failure. In newborns, prenatal alcohol exposure can increase the risk of congenital heart diseases. Understanding biological mechanisms involved in the long-term alcohol exposure-induced cardiotoxicity is pivotal to the discovery of therapeutic strategies. In this study, cardiomyocytes derived from human pluripotent stem cells (hiPSC-CMs) were treated with clinically relevant doses of ethanol for various durations up to 5 weeks. The treated cells were characterized for their cellular properties and functions, and global proteomic profiling was conducted to understand the molecular changes associated with long-term ethanol exposure. Increased cell death, oxidative stress, deranged Ca²⁺ handling, abnormal action potential, altered contractility, and suppressed structure development were observed in ethanol-treated cells. Many dysregulated proteins identified by global proteomic profiling were involved in apoptosis, heart contraction, and extracellular collagen matrix. In addition, several signaling pathways including the Wnt and TGFβ signaling pathways were affected due to long-term ethanol treatment. Therefore, chronic ethanol treatment of hiPSC-CMs induces cardiotoxicity, impairs cardiac functions, and alters protein expression and signaling pathways. This study demonstrates the utility of hiPSC-CMs as a novel model for chronic alcohol exposure study and provides the molecular mechanisms associated with long-term alcohol exposure in human cardiomyocytes.

Key Roles of RGD-Recognizing Integrins During Cardiac Development, on Cardiac Cells, and After Myocardial Infarction

Cardiac cells interact with the extracellular matrix (ECM) proteins through integrin mechanoreceptors that control many cellular events such as cell survival, apoptosis, differentiation, migration, and proliferation. Integrins play a crucial role in cardiac development as well as in cardiac fibrosis and hypertrophy. Integrins recognize oligopeptides present on ECM proteins and are involved in three main types of interaction, namely with collagen, laminin, and the oligopeptide RGD (Arg-Gly-Asp) present on vitronectin and fibronectin proteins. To date, the specific role of integrins recognizing the RGD has not been addressed. In this review, we examine their role during cardiac development, their role on cardiac cells, and their upregulation during pathological processes such as heart fibrosis and hypertrophy. We also examine their role in regenerative and angiogenic processes after myocardial infarction (MI) in the peri-infarct area. Specific targeting of these integrins may be a way of controlling some of these pathological events and thereby improving medical outcomes.

Integrins in cardiac hypertrophy: lessons learned from culture systems

Heart growth and pathological changes are accompanied by extracellular matrix‐dependent alterations in integrins and integrin‐associated proteins, suggesting their role in heart development and disease. Most of our knowledge on the involvement of integrins in heart pathology is provided by the in vivo experiments, including cardiac hypertrophy models. However, in vivo studies are limited by the complex organization of heart tissue and fail to discern cell types and particular integrins implicated in hypertrophic signalling. This problem is being addressed by isolated cardiomyocyte primary cultures, which have been successfully used in different in vitro disease models. This review aimed to analyse the general approaches to studying integrins and integrin‐associated signalling pathways in cardiac hypertrophy focusing on the in vitro systems. The lessons learned from culture experiments on the models of hypertrophy induced by stretch, stimulating factors, and/or extracellular matrix components are summarized, demonstrating the major involvement of integrin‐mediated signalling in cardiac hypertrophic response and its apparent crosstalk with signal pathways induced by stretch or hypertrophy stimulating factors. The benefits and perspectives of using cardiomyocyte primary culture as a hypertrophy model are discussed.

Maturation strategies and limitations of induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cells (iPSCs) have the ability to differentiate into cardiomyocytes (CMs). They are not only widely used in cardiac pharmacology screening, human heart disease modeling, and cell transplantation-based treatments, but also the most promising source of CMs for experimental and clinical applications. However, their use is largely restricted by the immature phenotype of structure and function, which is similar to embryonic or fetal CMs and has certain differences from adult CMs. In order to overcome this critical issue, many studies have explored and revealed new strategies to induce the maturity of iPSC-CMs. Therefore, this article aims to review recent induction methods of mature iPSC-CMs, related mechanisms, and limitations.

Evaluation of laser induced sarcomere micro-damage: Role of damage extent and location in cardiomyocytes

Whereas it is evident that a well aligned and regular sarcomeric structure in cardiomyocytes is vital for heart function, considerably less is known about the contribution of individual elements to the mechanics of the entire cell. For instance, it is unclear whether altered Z-disc elements are the reason or the outcome of related cardiomyopathies. Therefore, it is crucial to gain more insight into this cellular organization. This study utilizes femtosecond laser-based nanosurgery to better understand sarcomeres and their repair upon damage. We investigated the influence of the extent and the location of the Z-disc damage. A single, three, five or ten Z-disc ablations were performed in neonatal rat cardiomyocytes. We employed image-based analysis using a self-written software together with different already published algorithms. We observed that cardiomyocyte survival associated with the damage extent, but not with the cell area or the total number of Z-discs per cell. The cell survival is independent of the damage position and can be compensated. However, the sarcomere alignment/orientation is changing over time after ablation. The contraction time is also independent of the extent of damage for the tested parameters. Additionally, we observed shortening rates between 6–7% of the initial sarcomere length in laser treated cardiomyocytes. This rate is an important indicator for force generation in myocytes. In conclusion, femtosecond laser-based nanosurgery together with image-based sarcomere tracking is a powerful tool to better understand the Z-disc complex and its force propagation function and role in cellular mechanisms.

Molecular Regulators of Cellular Mechanoadaptation at Cell-Material Interfaces

Diverse essential cellular behaviors are determined by extracellular physical cues that are detected by highly orchestrated subcellular interactions with the extracellular microenvironment. To maintain the reciprocity of cellular responses and mechanical properties of the extracellular matrix, cells utilize a variety of signaling pathways that transduce biophysical stimuli to biochemical reactions. Recent advances in the micromanipulation of individual cells have shown that cellular responses to distinct physical and chemical features of the material are fundamental determinants of cellular mechanosensation and mechanotransduction. In the process of outside-in signal transduction, transmembrane protein integrins facilitate the formation of focal adhesion protein clusters that are connected to the cytoskeletal architecture and anchor the cell to the substrate. The linkers of nucleoskeleton and cytoskeleton molecular complexes, collectively termed LINC, are critical signal transducers that relay biophysical signals between the extranuclear cytoplasmic region and intranuclear nucleoplasmic region. Mechanical signals that involve cytoskeletal remodeling ultimately propagate into the nuclear envelope comprising the nuclear lamina in assistance with various nuclear membrane proteins, where nuclear mechanics play a key role in the subsequent alteration of gene expression and epigenetic modification. These intracellular mechanical signaling cues adjust cellular behaviors directly associated with mechanohomeostasis. Diverse strategies to modulate cell-material interfaces, including alteration of surface rigidity, confinement of cell adhesive region, and changes in surface topology, have been proposed to identify cellular signal transduction at the cellular and subcellular levels. In this review, we will discuss how a diversity of alterations in the physical properties of materials induce distinct cellular responses such as adhesion, migration, proliferation, differentiation, and chromosomal organization. Furthermore, the pathological relevance of misregulated cellular mechanosensation and mechanotransduction in the progression of devastating human diseases, including cardiovascular diseases, cancer, and aging, will be extensively reviewed. Understanding cellular responses to various extracellular forces is expected to provide new insights into how cellular mechanoadaptation is modulated by manipulating the mechanics of extracellular matrix and the application of these materials in clinical aspects.

Non-coding RNAs in Cardiac Intercellular Communication

Intercellular communication allows for molecular information to be transferred from cell to cell, in order to maintain tissue or organ homeostasis. Alteration in the process due to changes, either on the vehicle or the cargo information, may contribute to pathological events, such as cardiac pathological remodeling. Extracellular vesicles (EVs), namely exosomes, are double-layer vesicles secreted by cells to mediate intercellular communication, both locally and systemically. EVs can carry different types of cargo, including non-coding RNAs (ncRNAs), which, are major regulators of physiological and pathological processes. ncRNAs transported in EVs are functionally active and trigger a cascade of processes in the recipient cells. Upon cardiac injury, exosomal ncRNAs can derive from and target different cardiac cell types to initiate cellular and molecular remodeling events such as hypertrophic growth, cardiac fibrosis, endothelial dysfunction, and inflammation, all contributing to cardiac dysfunction and, eventually, heart failure. Exosomal ncRNAs are currently accepted as crucial players in the process of cardiac pathological remodeling and alterations in their presence profile in EVs may attenuate cardiac dysfunction, suggesting that exosomal ncRNAs are potential new therapeutic targets. Here, we review the current research on the role of ncRNAs in intercellular communication, in the context of cardiac pathological remodeling.

TRPC Channels in Cardiac Plasticity

The heart flexibly changes its structure in response to changing environments and oxygen/nutrition demands of the body. Increased and decreased mechanical loading induces hypertrophy and atrophy of cardiomyocytes, respectively. In physiological conditions, these structural changes of the heart are reversible. However, chronic stresses such as hypertension or cancer cachexia cause irreversible remodeling of the heart, leading to heart failure. Accumulating evidence indicates that calcium dyshomeostasis and aberrant reactive oxygen species production cause pathological heart remodeling. Canonical transient receptor potential (TRPC) is a nonselective cation channel subfamily whose multimodal activation or modulation of channel activity play important roles in a plethora of cellular physiology. Roles of TRPC channels in cardiac physiology have been reported in pathological cardiac remodeling. In this review, we summarize recent findings regarding the importance of TRPC channels in flexible cardiac remodeling (i.e., cardiac plasticity) in response to environmental stresses and discuss questions that should be addressed in the near future.

Suppression of β1-Adrenoceptor Autoantibodies is Involved in the Antiarrhythmic Effects of Omega-3 Fatty Acids in Male and Female Hypertensive Rats

The arrhythmogenic potential of β1-adrenoceptor autoantibodies (β1-AA), as well as antiarrhythmic properties of omega-3 in heart diseases, have been reported while underlying mechanisms are poorly understood. We aimed to test our hypothesis that omega-3 (eicosapentaenoic acid-EPA, docosahexaenoic acid-DHA) may inhibit matrix metalloproteinase (MMP-2) activity to prevent cleavage of β1-AR and formation of β1-AA resulting in attenuation of pro-arrhythmic connexin-43 (Cx43) and protein kinase C (PKC) signaling in the diseased heart. We have demonstrated that the appearance and increase of β1-AA in blood serum of male and female 12-month-old spontaneously hypertensive rats (SHR) was associated with an increase of inducible ventricular fibrillation (VF) comparing to normotensive controls. In contrast, supplementation of hypertensive rats with omega-3 for two months suppressed β1-AA levels and reduced incidence of VF. Suppression of β1-AA was accompanied by a decrease of elevated myocardial MMP-2 activity, preservation of cardiac cell membrane integrity and Cx43 topology. Moreover, omega-3 abrogated decline in expression of total Cx43 as well as its phosphorylated forms at serine 368 along with PKC-ε, while decreased pro-fibrotic PKC-δ levels in hypertensive rat heart regardless the sex. The implication of MMP-2 in the action of omega-3 was also demonstrated in cultured cardiomyocytes in which desensitization of β1-AR due to permanent activation of β1-AR with isoproterenol was prevented by MMP-2 inhibitor or EPA. Collectively, these data support the notion that omega-3 via suppression of β1-AA mechanistically controlled by MMP-2 may attenuate abnormal of Cx43 and PKC-ε signaling; thus, abolish arrhythmia substrate and protect rats with an advanced stage of hypertension from malignant arrhythmias.