Modeling Human Cardiac Hypertrophy in Stem Cell-Derived Cardiomyocytes

Role of chemical groups in regulating membrane tension of mBMSCs under stretch stimulation

As a crucial mechanobiological regulator, the tension of the cell membrane plays a vital role in governing cellular adhesion, proliferation, and differentiation processes. Additionally, it displayed a dynamic response to mechanical microenvironmental changes. This research systematically examines the mechanoresponsive behaviors of mouse bone marrow mesenchymal stem cells (mBMSCs) that are cultured on poly(dimethylsiloxane) (PDMS) substrates which are functionalized with methyl (-CH3), amino (-NH2), and carboxyl (-COOH) groups. Under both static and stretching conditions, it is found that compared with the -CH3 surface, static culture on the -NH2 and -COOH functionalized surfaces significantly promotes the proliferation of mBMSCs and upregulates the expression of extracellular matrix adhesion-related genes, especially focal adhesion kinase (FAK) and integrin β1. Morphometric analysis reveals that there are concomitant increases in the cell spreading area and the number of pseudopods on these modified surfaces. Mechanical stretching stimulation not only amplifies these cellular responses but also leads to more uniform FAK distribution. The assessment by atomic force microscopy (AFM) shows that both chemical functionalization (-NH2/-COOH) and stretch stimulation reduce the deformability of the cell membrane, and the -NH2 modification exhibits a greater membrane-stiffening effect than -COOH.

Toxicity of long term exposure to low dose polystyrene microplastics and nanoplastics in human iPSC-derived cardiomyocytes

Microplastics and nanoplastics (MNPs) are widespread environmental pollutants with potential risks to human health including cardiovascular effects. However, the impact of MNPs on the heart, particularly in human-relevant cardiac models, remains poorly understood. In this study, we investigated the long term effects of polystyrene (PS) MNPs-1 μm (PS-1) and 0.05 μm (PS-0.05) in human iPSC-derived cardiomyocytes (hiPSC-CMs). PS MNPs exposure reduced myocyte viability in a time- and dose-dependent manner. At a low dose of 0.1 μg/L, both PS-0.05 and PS-1 suppressed myocyte contractility, reduced Ca2+ transient amplitude, and altered contraction and Ca2+ transient dynamics. In hypertrophic hiPSC-CMs, PS-0.05 exposure exacerbated hypertrophy, increasing cell size and proBNP expression, a marker of myocyte hypertrophy. The mechanism of PS MNPs-induced cardiotoxicity likely involved mitochondrial dysfunction, as indicated by decreased mitochondrial membrane potential, increased mitochondrial ROS, and elevated intracellular ROS levels. This is the first study to assess the long term impact of low dose MNPs in human cardiomyocytes, providing crucial insight into the potential cardiac toxicity of MNPs and their implications for human heart health.

Differential impact of substrates on myosin heavy and light chain expression in human stem cell-derived cardiomyocytes at single-cell level

To fully exploit the potential of human pluripotent stem cell-derived cardiomyocytes, ideally they should acquire a mature, adult ventricular-like phenotype. Predominant expression of the β-isoform of myosin heavy chain (β-MyHC) and the ventricular isoform of myosin regulatory light chain 2 (MLC2v) is a marker of human adult cardiac ventricle. Yet predominant co-expression of these isoforms is rarely reported by current culture protocols. Here, we assessed the impact of different substrates on β-MyHC and MLC2v expression in single human embryonic stem cell-derived CMs (hESC-CMs). As substrates, surface materials with differing stiffness as defined by Young's modulus were combined with either laminin, a single-component coating, or Matrigel, a multi-component coating including growth factors. Semi-quantitative single-cell immunofluorescence analysis demonstrated that surfaces with supraphysiological stiffness in combination with laminin are sufficient for promotion of predominant β-MyHC expression, but not for predominant MLC2v expression in hESC-CMs. Accordingly, mechanical stimuli likely promote expression of β-MyHC in these cultures. Culture on matrices with a lower stiffness than glass in combination with growth factor-containing Matrigel led to only moderate increases in MLC2v expression, possibly more dependent on growth factors, suggesting different regulation of expression. Integrin-related downstream signal transducers, integrin-linked and cardiac troponin I-interacting kinase, as well as modulation of intracellular Ca2+-concentration and epigenetic signaling did not affect MyHC/MLC2 isoform expression. The data indicate that expression of adult ventricular markers β-MyHC and MLC2v depends on different stimuli like substrate stiffness and growth factors. To conclude, multiple stimuli appear to be necessary to promote an adult ventricular phenotype.

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.

The sinoatrial node extracellular matrix promotes pacemaker phenotype and protects automaticity in engineered heart tissues from cyclic strain

The composite material-like extracellular matrix (ECM) in the sinoatrial node (SAN) supports the native pacemaking cardiomyocytes (PCMs). To test the roles of SAN ECM in the PCM phenotype and function, we engineered reconstructed-SAN heart tissues (rSANHTs) by recellularizing porcine SAN ECMs with hiPSC-derived PCMs. The hiPSC-PCMs in rSANHTs self-organized into clusters resembling the native SAN and displayed higher expression of pacemaker-specific genes and a faster automaticity compared with PCMs in reconstructed-left ventricular heart tissues (rLVHTs). To test the protective nature of SAN ECMs under strain, rSANHTs and rLVHTs were transplanted onto the murine thoracic diaphragm to undergo constant cyclic strain. All strained-rSANHTs preserved automaticity, whereas 66% of strained-rLVHTs lost their automaticity. In contrast to the strained-rLVHTs, PCMs in strained-rSANHTs maintained high expression of key pacemaker genes (HCN4, TBX3, and TBX18). These findings highlight the promotive and protective roles of the composite SAN ECM and provide valuable insights for pacemaking tissue engineering.

Efficacy of exon-skipping therapy for DMD cardiomyopathy with mutations in actin binding domain 1

Exon-skipping therapy is a promising treatment strategy for Duchenne muscular dystrophy (DMD), which is caused by loss-of-function mutations in the DMD gene encoding dystrophin, leading to progressive cardiomyopathy. In-frame deletion of exons 3-9 (Δ3-9), manifesting a very mild clinical phenotype, is a potential targeted reading frame for exon-skipping by targeting actin-binding domain 1 (ABD1); however, the efficacy of this approach for DMD cardiomyopathy remains uncertain. In this study, we compared three isogenic human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) expressing Δ3-9, frameshifting Δ3-7, or intact DMD. RNA sequencing revealed a resemblance in the expression patterns of mechano-transduction-related genes between Δ3-9 and wild-type samples. Furthermore, we observed similar electrophysiological properties between Δ3-9 and wild-type hiPSC-CMs; Δ3-7 hiPSC-CMs showed electrophysiological alterations with accelerated CaMKII activation. Consistently, Δ3-9 hiPSC-CMs expressed substantial internally truncated dystrophin protein, resulting in maintaining F-actin binding and desmin retention. Antisense oligonucleotides targeting exon 8 efficiently induced skipping exons 8-9 to restore functional dystrophin and electrophysiological parameters in Δ3-7 hiPSC-CMs, bringing the cell characteristics closer to those of Δ3-9 hiPSC-CMs. Collectively, exon-skipping targeting ABD1 to convert the reading frame to Δ3-9 may become a promising therapy for DMD cardiomyopathy.

Bridging the Translational Gap in Heart Failure Research: Using Human iPSC-derived Cardiomyocytes to Accelerate Therapeutic Insights

Heart failure (HF) remains a leading cause of death worldwide, with increasing prevalence and burden. Despite extensive research, a cure for HF remains elusive. Traditionally, the study of HF's pathogenesis and therapies has relied heavily on animal experimentation. However, these models have limitations in recapitulating the full spectrum of human HF, resulting in challenges for clinical translation. To address this translational gap, research employing human cells, especially cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs), offers a promising solution. These cells facilitate the study of human genetic and molecular mechanisms driving cardiomyocyte dysfunction and pave the way for research tailored to individual patients. Further, engineered heart tissues combine hiPSC-CMs, other cell types, and scaffold-based approaches to improve cardiomyocyte maturation. Their tridimensional architecture, complemented with mechanical, chemical, and electrical cues, offers a more physiologically relevant environment. This review explores the advantages and limitations of conventional and innovative methods used to study HF pathogenesis, with a primary focus on ischemic HF due to its relative ease of modeling and clinical relevance. We emphasize the importance of a collaborative approach that integrates insights obtained in animal and hiPSC-CMs-based models, along with rigorous clinical research, to dissect the mechanistic underpinnings of human HF. Such an approach could improve our understanding of this disease and lead to more effective treatments.

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.

An Experimental and Numerical Investigation of Cardiac Tissue-Patch Interrelation

Tissue engineered cardiac patches have great potential as a regenerative therapy for myocardial infarction. Yet, the mutual interaction of cardiac patches with healthy tissue has not been completely understood. Here, we investigated the impact of acellular and cellular patches on a beating two-dimensional (2D) cardiac cell layer, and the effect of the beating of this layer on the cells encapsulated in the patch. We cultured human-induced pluripotent stem cell-derived cardiomyocytes (iCMs) on a coverslip and placed gelatin methacryloyl hydrogel alone or with encapsulated iCMs to create acellular and cellular patches, respectively. When the acellular patch was placed on the cardiac cell layer, the beating characteristics and Ca+2 handling properties reduced, whereas placing the cellular patch restored these characteristics. To better understand the effects of the cyclic contraction and relaxation induced by the beating cardiac cell layer on the patch placed on top of it, a simulation model was developed, and the calculated strain values were in agreement with the values measured experimentally. Moreover, this dynamic culture induced by the beating 2D iCM layer on the iCMs encapsulated in the cellular patch improved their beating velocity and frequency. Additionally, the encapsulated iCMs were observed to be coupled with the underlying beating 2D iCM layer. Overall, this study provides a detailed investigation on the mutual relationship of acellular/cellular patches with the beating 2D iCM layer, understanding of which would be valuable for developing more advanced cardiac patches.

The Microenvironment of the Pathogenesis of Cardiac Hypertrophy

Pathological cardiac hypertrophy is a key risk factor for the development of heart failure and predisposes individuals to cardiac arrhythmia and sudden death. While physiological cardiac hypertrophy is adaptive, hypertrophy resulting from conditions comprising hypertension, aortic stenosis, or genetic mutations, such as hypertrophic cardiomyopathy, is maladaptive. Here, we highlight the essential role and reciprocal interactions involving both cardiomyocytes and non-myocardial cells in response to pathological conditions. Prolonged cardiovascular stress causes cardiomyocytes and non-myocardial cells to enter an activated state releasing numerous pro-hypertrophic, pro-fibrotic, and pro-inflammatory mediators such as vasoactive hormones, growth factors, and cytokines, i.e., commencing signaling events that collectively cause cardiac hypertrophy. Fibrotic remodeling is mediated by cardiac fibroblasts as the central players, but also endothelial cells and resident and infiltrating immune cells enhance these processes. Many of these hypertrophic mediators are now being integrated into computational models that provide system-level insights and will help to translate our knowledge into new pharmacological targets. This perspective article summarizes the last decades' advances in cardiac hypertrophy research and discusses the herein-involved complex myocardial microenvironment and signaling components.

Molecular and cellular evidence for the impact of a hypertrophic cardiomyopathy-associated RAF1 variant on the structure and function of contractile machinery in bioartificial cardiac tissues

Noonan syndrome (NS), the most common among RASopathies, is caused by germline variants in genes encoding components of the RAS-MAPK pathway. Distinct variants, including the recurrent Ser257Leu substitution in RAF1, are associated with severe hypertrophic cardiomyopathy (HCM). Here, we investigated the elusive mechanistic link between NS-associated RAF1S257L and HCM using three-dimensional cardiac bodies and bioartificial cardiac tissues generated from patient-derived induced pluripotent stem cells (iPSCs) harboring the pathogenic RAF1 c.770 C > T missense change. We characterize the molecular, structural, and functional consequences of aberrant RAF1-associated signaling on the cardiac models. Ultrastructural assessment of the sarcomere revealed a shortening of the I-bands along the Z disc area in both iPSC-derived RAF1S257L cardiomyocytes and myocardial tissue biopsies. The aforementioned changes correlated with the isoform shift of titin from a longer (N2BA) to a shorter isoform (N2B) that also affected the active force generation and contractile tensions. The genotype-phenotype correlation was confirmed using cardiomyocyte progeny of an isogenic gene-corrected RAF1S257L-iPSC line and was mainly reversed by MEK inhibition. Collectively, our findings uncovered a direct link between a RASopathy gene variant and the abnormal sarcomere structure resulting in a cardiac dysfunction that remarkably recapitulates the human disease.

Robust generation of human-chambered cardiac organoids from pluripotent stem cells for improved modelling of cardiovascular diseases

BACKGROUND

Tissue organoids generated from human pluripotent stem cells are valuable tools for disease modelling and to understand developmental processes. While recent progress in human cardiac organoids revealed the ability of these stem cell-derived organoids to self-organize and intrinsically formed chamber-like structure containing a central cavity, it remained unclear the processes involved that enabled such chamber formation.

METHODS

Chambered cardiac organoids (CCOs) differentiated from human embryonic stem cells (H7) were generated by modulation of Wnt/ß-catenin signalling under fully defined conditions, and several growth factors essential for cardiac progenitor expansion. Transcriptomic profiling of day 8, day 14 and day 21 CCOs was performed by quantitative PCR and single-cell RNA sequencing. Endothelin-1 (EDN1) known to induce oxidative stress in cardiomyocytes was used to induce cardiac hypertrophy in CCOs in vitro. Functional characterization of cardiomyocyte contractile machinery was performed by immunofluorescence staining and analysis of brightfield and fluorescent video recordings. Quantitative PCR values between groups were compared using two-tailed Student's t tests. Cardiac organoid parameters comparison between groups was performed using two-tailed Mann-Whitney U test when sample size is small; otherwise, Welch's t test was used. Comparison of calcium kinetics parameters derived from the fluorescent data was performed using two-tailed Student's t tests.

RESULTS

Importantly, we demonstrated that a threshold number of cardiac progenitor was essential to line the circumference of the inner cavity to ensure proper formation of a chamber within the organoid. Single-cell RNA sequencing revealed improved maturation over a time course, as evidenced from increased mRNA expression of cardiomyocyte maturation genes, ion channel genes and a metabolic shift from glycolysis to fatty acid ß-oxidation. Functionally, CCOs recapitulated clinical cardiac hypertrophy by exhibiting thickened chamber walls, reduced fractional shortening, and increased myofibrillar disarray upon treatment with EDN1. Furthermore, electrophysiological assessment of calcium transients displayed tachyarrhythmic phenotype observed as a consequence of rapid depolarization occurring prior to a complete repolarization.

CONCLUSIONS

Our findings shed novel insights into the role of progenitors in CCO formation and pave the way for the robust generation of cardiac organoids, as a platform for future applications in disease modelling and drug screening in vitro.

Transcriptomics reveal stretched human pluripotent stem cell-derived cardiomyocytes as an advantageous hypertrophy model

Left ventricular hypertrophy, characterized by hypertrophy of individual cardiomyocytes, is an adaptive response to an increased cardiac workload that eventually leads to heart failure. Previous studies using neonatal rat ventricular myocytes (NRVMs) and animal models have revealed several genes and signaling pathways associated with hypertrophy and mechanical load. However, these models are not directly applicable to humans. Here, we studied the effect of cyclic mechanical stretch on gene expression of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) using RNA sequencing. hiPSC-CMs showed distinct hypertrophic changes in gene expression at the level of individual genes and in biological processes. We also identified several differentially expressed genes that have not been previously associated with cardiomyocyte hypertrophy and thus serve as attractive targets for future studies. When compared to previously published data attained from stretched NRVMs and human embryonic stem cell-derived cardiomyocytes, hiPSC-CMs displayed a smaller number of changes in gene expression, but the differentially expressed genes revealed more pronounced enrichment of hypertrophy-related biological processes and pathways. Overall, these results establish hiPSC-CMs as a valuable in vitro model for studying human cardiomyocyte hypertrophy.

Cyclic Stretching Induces Maturation of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes through Nuclear-Mechanotransduction

BACKGROUND

During cardiogenesis, cardiac cells receive various stimuli, such as biomechanical and chemical cues, from the surrounding microenvironment, and these signals induce the maturation of heart cells. Mechanical force, especially tensile force in the heart, is one of the key stimuli that induce cardiomyocyte (CM) maturation through mechanotransduction, a process through which physical cues are transformed into biological responses. However, the effects and mechanisms of tensile force on cell maturation are poorly studied.

METHODS

In this study, we developed a cyclic stretch system that mimics the mechanical environment of the heart by loading tensile force to human-induced pluripotent stem cell (hiPSC)-derived CMs. hiPSC-CMs cultured with the cyclic stretch system analyzed morphological change, immunofluorescent staining, expression of maturation markers in mRNA, and beating properties compared to static cultures.

RESULTS

hiPSC-CMs cultured with the cyclic stretch system showed increased cell alignment, sarcomere length and expression of maturation markers in mRNA, such as TNNI3, MYL2 and TTN, compared to static cultures. Especially, the expression of genes related to nuclear mechanotransduction, such as Yap1, Lamin A/C, plectin, and desmin, was increased in the cyclically stretched hiPSC-CMs. Furthermore, the volume of the nucleus was increased by as much as 120% in the cyclic stretch group.

CONCLUSION

These results revealed that nuclear mechanotransduction induced by tensile force is involved in CM maturation. Together, these findings provide novel evidence suggesting that nuclear mechanotransduction induced by tensile force is involved in the regulation of cardiac maturation.

Tissue-engineered heart chambers as a platform technology for drug discovery and disease modeling

Current drug screening approaches are incapable of fully detecting and characterizing drug effectiveness and toxicity of human cardiomyocytes. The pharmaceutical industry uses mathematical models, cell lines, and in vivo models. Many promising drugs are abandoned early in development, and some cardiotoxic drugs reach humans leading to drug recalls. Therefore, there is an unmet need to have more reliable and predictive tools for drug discovery and screening applications. Biofabrication of functional cardiac tissues holds great promise for developing a faithful 3D in vitro disease model, optimizing drug screening efficiencies enabling precision medicine. Different fabrication techniques including molding, pull spinning and 3D bioprinting were used to develop tissue-engineered heart chambers. The big challenge is to effectively organize cells into tissue with structural and physiological features resembling native tissues. Some advancements have been made in engineering miniaturized heart chambers that resemble a living pump for drug screening and disease modeling applications. Here, we review the currently developed tissue-engineered heart chambers and discuss challenges and prospects.

Identification of critical genes and molecular pathways in COVID-19 myocarditis and constructing gene regulatory networks by bioinformatic analysis

BACKGROUND

There is growing evidence of a strong relationship between COVID-19 and myocarditis. However, there are few bioinformatics-based analyses of critical genes and the mechanisms related to COVID-19 Myocarditis. This study aimed to identify critical genes related to COVID-19 Myocarditis by bioinformatic methods, explore the biological mechanisms and gene regulatory networks, and probe related drugs.

METHODS

The gene expression data of GSE150392 and GSE167028 were obtained from the Gene Expression Omnibus (GEO), including cardiomyocytes derived from human induced pluripotent stem cells infected with SARS-CoV-2 in vitro and GSE150392 from patients with myocarditis infected with SARS-CoV-2 and the GSE167028 gene expression dataset. Differentially expressed genes (DEGs) (adjusted P-Value <0.01 and |Log2 Fold Change| ≥2) in GSE150392 were assessed by NetworkAnalyst 3.0. Meanwhile, significant modular genes in GSE167028 were identified by weighted gene correlation network analysis (WGCNA) and overlapped with DEGs to obtain common genes. Functional enrichment analyses were performed by using the "clusterProfiler" package in the R software, and protein-protein interaction (PPI) networks were constructed on the STRING website (https://cn.string-db.org/). Critical genes were identified by the CytoHubba plugin of Cytoscape by 5 algorithms. Transcription factor-gene (TF-gene) and Transcription factor-microRibonucleic acid (TF-miRNA) coregulatory networks construction were performed by NetworkAnalyst 3.0 and displayed in Cytoscape. Finally, Drug Signatures Database (DSigDB) was used to probe drugs associated with COVID-19 Myocarditis.

RESULTS

Totally 850 DEGs (including 449 up-regulated and 401 down-regulated genes) and 159 significant genes in turquoise modules were identified from GSE150392 and GSE167028, respectively. Functional enrichment analysis indicated that common genes were mainly enriched in biological processes such as cell cycle and ubiquitin-protein hydrolysis. 6 genes (CDK1, KIF20A, PBK, KIF2C, CDC20, UBE2C) were identified as critical genes. TF-gene interactions and TF-miRNA coregulatory network were constructed successfully. A total of 10 drugs, (such as Etoposide, Methotrexate, Troglitazone, etc) were considered as target drugs for COVID-19 Myocarditis.

CONCLUSIONS

Through bioinformatics method analysis, this study provides a new perspective to explore the pathogenesis, gene regulatory networks and provide drug compounds as a reference for COVID-19 Myocarditis. It is worth highlighting that critical genes (CDK1, KIF20A, PBK, KIF2C, CDC20, UBE2C) may be potential biomarkers and treatment targets of COVID-19 Myocarditis for future study.

Genetically Encoded ATP Biosensors for Direct Monitoring of Cellular ATP Dynamics

Adenosine 5'-triphosphate, or ATP, is the primary molecule for storing and transferring energy in cells. ATP is mainly produced via oxidative phosphorylation in mitochondria, and to a lesser extent, via glycolysis in the cytosol. In general, cytosolic glycolysis is the primary ATP producer in proliferative cells or cells subjected to hypoxia. On the other hand, mitochondria produce over 90% of cellular ATP in differentiated cells under normoxic conditions. Under pathological conditions, ATP demand rises to meet the needs of biosynthesis for cellular repair, signaling transduction for stress responses, and biochemical processes. These changes affect how mitochondria and cytosolic glycolysis function and communicate. Mitochondria undergo remodeling to adapt to the imbalanced demand and supply of ATP. Otherwise, a severe ATP deficit will impair cellular function and eventually cause cell death. It is suggested that ATP from different cellular compartments can dynamically communicate and coordinate to adapt to the needs in each cellular compartment. Thus, a better understanding of ATP dynamics is crucial to revealing the differences in cellular metabolic processes across various cell types and conditions. This requires innovative methodologies to record real-time spatiotemporal ATP changes in subcellular regions of living cells. Over the recent decades, numerous methods have been developed and utilized to accomplish this task. However, this is not an easy feat. This review evaluates innovative genetically encoded biosensors available for visualizing ATP in living cells, their potential use in the setting of human disease, and identifies where we could improve and expand our abilities.

Chronic Cardiotoxicity Assays Using Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hiPSC-CMs)

Cardiomyocytes (CMs) differentiated from human induced pluripotent stem cells (hiPSCs) are increasingly used in cardiac safety assessment, disease modeling and regenerative medicine. A vast majority of cardiotoxicity studies in the past have tested acute effects of compounds and drugs; however, these studies lack information on the morphological or physiological responses that may occur after prolonged exposure to a cardiotoxic compound. In this review, we focus on recent advances in chronic cardiotoxicity assays using hiPSC-CMs. We summarize recently published literature on hiPSC-CMs assays applied to chronic cardiotoxicity induced by anticancer agents, as well as non-cancer classes of drugs, including antibiotics, anti-hepatitis C virus (HCV) and antidiabetic drugs. We then review publications on the implementation of hiPSC-CMs-based assays to investigate the effects of non-pharmaceutical cardiotoxicants, such as environmental chemicals or chronic alcohol consumption. We also highlight studies demonstrating the chronic effects of smoking and implementation of hiPSC-CMs to perform genomic screens and metabolomics-based biomarker assay development. The acceptance and wide implementation of hiPSC-CMs-based assays for chronic cardiotoxicity assessment will require multi-site standardization of assay protocols, chronic cardiac maturity marker reproducibility, time points optimization, minimal cellular variation (commercial vs. lab reprogrammed), stringent and matched controls and close clinical setting resemblance. A comprehensive investigation of long-term repeated exposure-induced effects on both the structure and function of cardiomyocytes can provide mechanistic insights and recapitulate drug and environmental cardiotoxicity.

From engineered heart tissue to cardiac organoid

The advent of human pluripotent stem cells (hPSCs) presented a new paradigm to employ hPSC-derived cardiomyocytes (hPSC-CMs) in drug screening and disease modeling. However, hPSC-CMs differentiated in conventional two-dimensional systems are structurally and functionally immature. Moreover, these differentiation systems generate predominantly one type of cell. Since the heart includes not only CMs but other cell types, such monolayer cultures have limitations in simulating the native heart. Accordingly, three-dimensional (3D) cardiac tissues have been developed as a better platform by including various cardiac cell types and extracellular matrices. Two advances were made for 3D cardiac tissue generation. One type is engineered heart tissues (EHTs), which are constructed by 3D cell culture of cardiac cells using an engineering technology. This system provides a convenient real-time analysis of cardiac function, as well as a precise control of the input/output flow and mechanical/electrical stimulation. The other type is cardiac organoids, which are formed through self-organization of differentiating cardiac lineage cells from hPSCs. While mature cardiac organoids are more desirable, at present only primitive forms of organoids are available. In this review, we discuss various models of hEHTs and cardiac organoids emulating the human heart, focusing on their unique features, utility, and limitations.

Mechanical control of nuclear import by Importin-7 is regulated by its dominant cargo YAP

Mechanical forces regulate multiple essential pathways in the cell. The nuclear translocation of mechanoresponsive transcriptional regulators is an essential step for mechanotransduction. However, how mechanical forces regulate the nuclear import process is not understood. Here, we identify a highly mechanoresponsive nuclear transport receptor (NTR), Importin-7 (Imp7), that drives the nuclear import of YAP, a key regulator of mechanotransduction pathways. Unexpectedly, YAP governs the mechanoresponse of Imp7 by forming a YAP/Imp7 complex that responds to mechanical cues through the Hippo kinases MST1/2. Furthermore, YAP behaves as a dominant cargo of Imp7, restricting the Imp7 binding and the nuclear translocation of other Imp7 cargoes such as Smad3 and Erk2. Thus, the nuclear import process is an additional regulatory layer indirectly regulated by mechanical cues, which activate a preferential Imp7 cargo, YAP, which competes out other cargoes, resulting in signaling crosstalk.

The translation of mechanical cues into gene expression changes is dependent on the nuclear import of mechanoresponsive transcriptional regulators. Here the authors identify that Importin-7 drives the nuclear import of one such regulator YAP while YAP then controls Importin-7 response to mechanical cues and restricts Importin-7 binding to other cargoes.

Multi-Omics Characterization of a Human Stem Cell-Based Model of Cardiac Hypertrophy

Cardiac hypertrophy is an important and independent risk factor for the development of cardiac myopathy that may lead to heart failure. The mechanisms underlying the development of cardiac hypertrophy are yet not well understood. To increase the knowledge about mechanisms and regulatory pathways involved in the progression of cardiac hypertrophy, we have developed a human induced pluripotent stem cell (hiPSC)-based in vitro model of cardiac hypertrophy and performed extensive characterization using a multi-omics approach. In a series of experiments, hiPSC-derived cardiomyocytes were stimulated with Endothelin-1 for 8, 24, 48, and 72 h, and their transcriptome and secreted proteome were analyzed. The transcriptomic data show many enriched canonical pathways related to cardiac hypertrophy already at the earliest time point, e.g., cardiac hypertrophy signaling. An integrated transcriptome–secretome analysis enabled the identification of multimodal biomarkers that may prove highly relevant for monitoring early cardiac hypertrophy progression. Taken together, the results from this study demonstrate that our in vitro model displays a hypertrophic response on both transcriptomic- and secreted-proteomic levels. The results also shed novel insights into the underlying mechanisms of cardiac hypertrophy, and novel putative early cardiac hypertrophy biomarkers have been identified that warrant further investigation to assess their potential clinical relevance.

Reverse re-modelling chronic heart failure by reinstating heart rate variability

Heart rate variability (HRV) is a crucial indicator of cardiovascular health. Low HRV is correlated with disease severity and mortality in heart failure. Heart rate increases and decreases with each breath in normal physiology termed respiratory sinus arrhythmia (RSA). RSA is highly evolutionarily conserved, most prominent in the young and athletic and is lost in cardiovascular disease. Despite this, current pacemakers either pace the heart in a metronomic fashion or sense activity in the sinus node. If RSA has been lost in cardiovascular disease current pacemakers cannot restore it. We hypothesized that restoration of RSA in heart failure would improve cardiac function. Restoration of RSA in heart failure was assessed in an ovine model of heart failure with reduced ejection fraction. Conscious 24 h recordings were made from three groups, RSA paced (n = 6), monotonically paced (n = 6) and heart failure time control (n = 5). Real-time blood pressure, cardiac output, heart rate and diaphragmatic EMG were recorded in all animals. Respiratory modulated pacing was generated by a proprietary device (Ceryx Medical) to pace the heart with real-time respiratory modulation. RSA pacing substantially increased cardiac output by 1.4 L/min (20%) compared to contemporary (monotonic) pacing. This increase in cardiac output led to a significant decrease in apnoeas associated with heart failure, reversed cardiomyocyte hypertrophy, and restored the T-tubule structure that is essential for force generation. Re-instating RSA in heart failure improves cardiac function through mechanisms of reverse re-modelling; the improvement observed is far greater than that seen with current contemporary therapies. These findings support the concept of re-instating RSA as a regime for patients who require a pacemaker.

Systematic transcriptomic and phenotypic characterization of human and murine cardiac myocyte cell lines and primary cardiomyocytes reveals serious limitations and low resemblances to adult cardiac phenotype

BACKGROUND

Cardiac cell lines and primary cells are widely used in cardiovascular research. Despite increasing number of publications using these models, comparative characterization of these cell lines has not been performed, therefore, their limitations are undetermined. We aimed to compare cardiac cell lines to primary cardiomyocytes and to mature cardiac tissues in a systematic manner.

METHODS AND RESULTS

Cardiac cell lines (H9C2, AC16, HL-1) were differentiated with widely used protocols. Left ventricular tissue, neonatal primary cardiomyocytes, and human induced pluripotent stem cell-derived cardiomyocytes served as reference tissue or cells. RNA expression of cardiac markers (e.g. Tnnt2, Ryr2) was markedly lower in cell lines compared to references. Differentiation induced increase in cardiac- and decrease in embryonic markers however, the overall transcriptomic profile and annotation to relevant biological processes showed consistently less pronounced cardiac phenotype in all cell lines in comparison to the corresponding references. Immunocytochemistry confirmed low expressions of structural protein sarcomeric alpha-actinin, troponin I and caveolin-3 in cell lines. Susceptibility of cell lines to sI/R injury in terms of viability as well as mitochondrial polarization differed from the primary cells irrespective of their degree of differentiation.

CONCLUSION

Expression patterns of cardiomyocyte markers and whole transcriptomic profile, as well as response to sI/R, and to hypertrophic stimuli indicate low-to-moderate similarity of cell lines to primary cells/cardiac tissues regardless their differentiation. Low resemblance of cell lines to mature adult cardiac tissue limits their potential use. Low translational value should be taken into account while choosing a particular cell line to model cardiomyocytes.

Measuring hypertrophy in neonatal rat primary cardiomyocytes and human iPSC-derived cardiomyocytes

In the heart, left ventricular hypertrophy is initially an adaptive mechanism that increases wall thickness to preserve normal cardiac output and function in the face of coronary artery disease or hypertension. Cardiac hypertrophy develops in response to pressure and volume overload but can also be seen in inherited cardiomyopathies. As the wall thickens, it becomes stiffer impairing the distribution of oxygenated blood to the rest of the body. With complex cellular signalling and transcriptional networks involved in the establishment of the hypertrophic state, several model systems have been developed to better understand the molecular drivers of disease. Immortalized cardiomyocyte cell lines, primary rodent and larger animal models have all helped understand the pathological mechanisms underlying cardiac hypertrophy. Induced pluripotent stem cell-derived cardiomyocytes are also used and have the additional benefit of providing access to human samples with direct disease relevance as when generated from patients suffering from hypertrophic cardiomyopathies. Here, we briefly review in vitro and in vivo model systems that have been used to model hypertrophy and provide detailed methods to isolate primary neonatal rat cardiomyocytes as well as to generate cardiomyocytes from human iPSCs. We also describe how to model hypertrophy in a "dish" using gene expression analysis and immunofluorescence combined with automated high-content imaging.

How Localized Z-Disc Damage Affects Force Generation and Gene Expression in Cardiomyocytes

The proper function of cardiomyocytes (CMs) is highly related to the Z-disc, which has a pivotal role in orchestrating the sarcomeric cytoskeletal function. To better understand Z-disc related cardiomyopathies, novel models of Z-disc damage have to be developed. Human pluripotent stem cell (hPSC)-derived CMs can serve as an in vitro model to better understand the sarcomeric cytoskeleton. A femtosecond laser system can be applied for localized and defined damage application within cells as single Z-discs can be removed. We have investigated the changes in force generation via traction force microscopy, and in gene expression after Z-disc manipulation in hPSC-derived CMs. We observed a significant weakening of force generation after removal of a Z-disc. However, no significant changes of the number of contractions after manipulation were detected. The stress related gene NF-kB was significantly upregulated. Additionally, α-actinin (ACTN2) and filamin-C (FLNc) were upregulated, pointing to remodeling of the Z-disc and the sarcomeric cytoskeleton. Ultimately, cardiac troponin I (TNNI3) and cardiac muscle troponin T (TNNT2) were significantly downregulated. Our results allow a better understanding of transcriptional coupling of Z-disc damage and the relation of damage to force generation and can therefore finally pave the way to novel therapies of sarcomeric disorders.

Selenoprotein DIO2 Is a Regulator of Mitochondrial Function, Morphology and UPRmt in Human Cardiomyocytes

Members of the fetal-gene-program may act as regulatory components to impede deleterious events occurring with cardiac remodeling, and constitute potential novel therapeutic heart failure (HF) targets. Mitochondrial energy derangements occur both during early fetal development and in patients with HF. Here we aim to elucidate the role of DIO2, a member of the fetal-gene-program, in pluripotent stem cell (PSC)-derived human cardiomyocytes and on mitochondrial dynamics and energetics, specifically. RNA sequencing and pathway enrichment analysis was performed on mouse cardiac tissue at different time points during development, adult age, and ischemia-induced HF. To determine the function of DIO2 in cardiomyocytes, a stable human hPSC-line with a DIO2 knockdown was made using a short harpin sequence. Firstly, we showed the selenoprotein, type II deiodinase (DIO2): the enzyme responsible for the tissue-specific conversion of inactive (T4) into active thyroid hormone (T3), to be a member of the fetal-gene-program. Secondly, silencing DIO2 resulted in an increased reactive oxygen species, impaired activation of the mitochondrial unfolded protein response, severely impaired mitochondrial respiration and reduced cellular viability. Microscopical 3D reconstruction of the mitochondrial network displayed substantial mitochondrial fragmentation. Summarizing, we identified DIO2 to be a member of the fetal-gene-program and as a key regulator of mitochondrial performance in human cardiomyocytes. Our results suggest a key position of human DIO2 as a regulator of mitochondrial function in human cardiomyocytes.

Recent Advances in Maturation of Pluripotent Stem Cell-Derived Cardiomyocytes Promoted by Mechanical Stretch

Stem cells have significant potential use in tissue regeneration, especially for treating cardiac diseases because of their multi-directional differentiation capability. By mimicking the in vivo physiological environment of native cardiomyocytes during their development and maturation, researchers have been able to induce pluripotent stem cell-derived cardiomyocytes (PSC-CMs) at high purity. However, the phenotype of these PSC-CMs is immature compared with that of adult cardiomyocytes. Various strategies have been explored to improve the maturity of PSC-CMs, such as long-term culturing, mechanical stimuli, chemical stimuli, and combinations of these strategies. Among these strategies, mechanical stretch as a key mechanical stimulus plays an important role in PSC-CM maturation. In this review, the optimal parameters of mechanical stretch, the effects of mechanical stretch on maturation of PSC-CMs, underlying molecular mechanisms as well as existing problems are discussed. Mechanical stretch is a powerful approach to promote the maturation of SC-CMs in terms of morphology, structure, and functionality. Nonetheless, further research efforts are needed to reach a satisfactory standard for clinical applications of PSC-CMs in treating cardiac diseases.

The CR9 element is a novel mechanical load-responsive enhancer that regulates natriuretic peptide genes expression

Enhancers regulate gene expressions in a tissue- and pathology-specific manner by altering its activities. Plasma levels of atrial and brain natriuretic peptides, encoded by the Nppa and Nppb, respectively, and synthesized predominantly in cardiomyocytes, vary depending on the severity of heart failure. We previously identified the noncoding conserved region 9 (CR9) element as a putative Nppb enhancer at 22-kb upstream from the Nppb gene. However, its regulatory mechanism remains unknown. Here, we therefore investigated the mechanism of CR9 activation in cardiomyocytes using different kinds of drugs that induce either cardiac hypertrophy or cardiac failure accompanied by natriuretic peptides upregulation. Chronic treatment of mice with either catecholamines or doxorubicin increased CR9 activity during the progression of cardiac hypertrophy to failure, which is accompanied by proportional increases in Nppb expression. Conversely, for cultured cardiomyocytes, doxorubicin decreased CR9 activity and Nppb expression, while catecholamines increased both. However, exposing cultured cardiomyocytes to mechanical loads, such as mechanical stretch or hydrostatic pressure, upregulate CR9 activity and Nppb expression even in the presence of doxorubicin. Furthermore, the enhancement of CR9 activity and Nppa and Nppb expressions by either catecholamines or mechanical loads can be blunted by suppressing mechanosensing and mechanotransduction pathways, such as muscle LIM protein (MLP) or myosin tension. Finally, the CR9 element showed a more robust and cell-specific response to mechanical loads than the -520-bp BNP promoter. We concluded that the CR9 element is a novel enhancer that responds to mechanical loads by upregulating natriuretic peptides expression in cardiomyocytes.

Piezo1 Mechanosensitive Ion Channel Mediates Stretch-Induced Nppb Expression in Adult Rat Cardiac Fibroblasts

In response to stretch, cardiac tissue produces natriuretic peptides, which have been suggested to have beneficial effects in heart failure patients. In the present study, we explored the mechanism of stretch-induced brain natriuretic peptide (Nppb) expression in cardiac fibroblasts. Primary adult rat cardiac fibroblasts subjected to 4 h or 24 h of cyclic stretch (10% 1 Hz) showed a 6.6-fold or 3.2-fold (p < 0.05) increased mRNA expression of Nppb, as well as induction of genes related to myofibroblast differentiation. Moreover, BNP protein secretion was upregulated 5.3-fold in stretched cardiac fibroblasts. Recombinant BNP inhibited TGFβ1-induced Acta2 expression. Nppb expression was >20-fold higher in cardiomyocytes than in cardiac fibroblasts, indicating that cardiac fibroblasts were not the main source of Nppb in the healthy heart. Yoda1, an agonist of the Piezo1 mechanosensitive ion channel, increased Nppb expression 2.1-fold (p < 0.05) and significantly induced other extracellular matrix (ECM) remodeling genes. Silencing of Piezo1 reduced the stretch-induced Nppb and Tgfb1 expression in cardiac fibroblasts. In conclusion, our study identifies Piezo1 as mediator of stretch-induced Nppb expression, as well as other remodeling genes, in cardiac fibroblasts.

Cardiovascular microphysiological systems (CVMPS) for safety studies - a pharma perspective

The integrative responses of the cardiovascular (CV) system are essential for maintaining blood flow to provide oxygenation, nutrients, and waste removal for the entire body. Progress has been made in independently developing simple in vitro models of two primary components of the CV system, namely the heart (using induced pluripotent stem-cell derived cardiomyocytes) and the vasculature (using endothelial cells and smooth muscle cells). These two in vitro biomimics are often described as immature and simplistic, and typically lack the structural complexity of native tissues. Despite these limitations, they have proven useful for specific "fit for purpose" applications, including early safety screening. More complex in vitro models offer the tantalizing prospect of greater refinement in risk assessments. To this end, efforts to physically link cardiac and vascular components to mimic a true CV microphysiological system (CVMPS) are ongoing, with the goal of providing a more holistic and integrated CV response model. The challenges of building and implementing CVMPS in future pharmacological safety studies are many, and include a) the need for more complex (and hence mature) cell types and tissues, b) the need for more realistic vasculature (within and across co-modeled tissues), and c) the need to meaningfully couple these two components to allow for integrated CV responses. Initial success will likely come with simple, bioengineered tissue models coupled with fluidics intended to mirror a vascular component. While the development of more complex integrated CVMPS models that are capable of differentiating safe compounds and providing mechanistic evaluations of CV liabilities may be feasible, adoption by pharma will ultimately hinge on model efficiency, experimental reproducibility, and added value above current strategies.

Cardiac hypertrophy in a dish: a human stem cell based model

Cardiac hypertrophy is an important and independent risk factor for the development of heart failure. To better understand the mechanisms and regulatory pathways involved in cardiac hypertrophy, there is a need for improved in vitro models. In this study, we investigated how hypertrophic stimulation affected human induced pluripotent stem cell (iPSC)-derived cardiomyocytes (CMs). The cells were stimulated with endothelin-1 (ET-1) for 8, 24, 48, 72, or 96 h. Parameters including cell size, ANP-, proBNP-, and lactate concentration were analyzed. Moreover, transcriptional profiling using RNA-sequencing was performed to identify differentially expressed genes following ET-1 stimulation. The results show that the CMs increase in size by approximately 13% when exposed to ET-1 in parallel to increases in ANP and proBNP protein and mRNA levels. Furthermore, the lactate concentration in the media was increased indicating that the CMs consume more glucose, a hallmark of cardiac hypertrophy. Using RNA-seq, a hypertrophic gene expression pattern was also observed in the stimulated CMs. Taken together, these results show that hiPSC-derived CMs stimulated with ET-1 display a hypertrophic response. The results from this study also provide new molecular insights about the underlying mechanisms of cardiac hypertrophy and may help accelerate the development of new drugs against this condition.

H3K27ac acetylome signatures reveal the epigenomic reorganization in remodeled non-failing human hearts

BACKGROUND

H3K27ac histone acetylome changes contribute to the phenotypic response in heart diseases, particularly in end-stage heart failure. However, such epigenetic alterations have not been systematically investigated in remodeled non-failing human hearts. Therefore, valuable insight into cardiac dysfunction in early remodeling is lacking. This study aimed to reveal the acetylation changes of chromatin regions in response to myocardial remodeling and their correlations to transcriptional changes of neighboring genes.

RESULTS

We detected chromatin regions with differential acetylation activity (DARs; Padj. < 0.05) between remodeled non-failing patient hearts and healthy donor hearts. The acetylation level of the chromatin region correlated with its RNA polymerase II occupancy level and the mRNA expression level of its adjacent gene per sample. Annotated genes from DARs were enriched in disease-related pathways, including fibrosis and cell metabolism regulation. DARs that change in the same direction have a tendency to cluster together, suggesting the well-reorganized chromatin architecture that facilitates the interactions of regulatory domains in response to myocardial remodeling. We further show the differences between the acetylation level and the mRNA expression level of cell-type-specific markers for cardiomyocytes and 11 non-myocyte cell types. Notably, we identified transcriptome factor (TF) binding motifs that were enriched in DARs and defined TFs that were predicted to bind to these motifs. We further showed 64 genes coding for these TFs that were differentially expressed in remodeled myocardium when compared with controls.

CONCLUSIONS

Our study reveals extensive novel insight on myocardial remodeling at the DNA regulatory level. Differences between the acetylation level and the transcriptional level of cell-type-specific markers suggest additional mechanism(s) between acetylome and transcriptome. By integrating these two layers of epigenetic profiles, we further provide promising TF-encoding genes that could serve as master regulators of myocardial remodeling. Combined, our findings highlight the important role of chromatin regulatory signatures in understanding disease etiology.

Sophocarpine ameliorates cardiac hypertrophy through activation of autophagic responses

Mounting evidences indicate that autophagy is an essential homeostatic mechanism to maintain the global cardiac structure function. Sophocarpine (SOP), a major bioactive compound derived from the natural plant Sophora flavescens. However, the role of SOP in cardiac hypertrophy remain to be fully elucidated. In the present study, we tested the hypothesis that SOP protects against Ang II-induced cardiac hypertrophy by mediating the regulation of autophagy. The results demonstrated that SOP attenuated the Ang II-induced cardiac hypertrophy, as assessed by measurements of echocardiography parameters, the ratios of heart weight/body weight and left ventricle weight/body weight, histopathological staining, cross-sectional cardiomyocyte area, and the expression levels of cardiac hypertrophic markers. The anti-hypertrophic effect of SOP was mediated by activating autophagy-related pathway, as revealed by reversal of the increased autophagy marker protein expression. These findings reveal a novel mechanism of SOP attenuating cardiac hypertrophy via activating autophagy-related signaling pathways.

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

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

Selenium and outcome in heart failure

Aims

Severe deficiency of the essential trace element selenium can cause myocardial dysfunction although the mechanism at cellular level is uncertain. Whether, in clinical practice, moderate selenium deficiency is associated with worse symptoms and outcome in patients with heart failure is unknown.

Methods and results

BIOSTAT‐CHF is a multinational, prospective, observational cohort study that enrolled patients with worsening heart failure. Serum concentrations of selenium were measured by inductively coupled plasma mass spectrometry. Primary endpoint was a composite of all‐cause mortality and hospitalization for heart failure; secondary endpoint was all‐cause mortality. To investigate potential mechanisms by which selenium deficiency might affect prognosis, human cardiomyocytes were cultured in absence of selenium, and mitochondrial function and oxidative stress were assessed. Serum selenium concentration (deficiency) was <70 μg/L in 485 (20.4%) patients, who were older, more often women, had worse New York Heart Association class, more severe signs and symptoms of heart failure and poorer exercise capacity (6‐min walking test) and quality of life (Kansas City Cardiomyopathy Questionnaire). Selenium deficiency was associated with higher rates of the primary endpoint [hazard ratio (HR) 1.23; 95% confidence interval (CI) 1.06–1.42] and all‐cause mortality (HR 1.52; 95% CI 1.26–1.86). In cultured human cardiomyocytes, selenium deprivation impaired mitochondrial function and oxidative phosphorylation, and increased intracellular reactive oxygen species levels.

Conclusions

Selenium deficiency in heart failure patients is independently associated with impaired exercise tolerance and a 50% higher mortality rate, and impaired mitochondrial function in vitro, in human cardiomyocytes. Clinical trials are needed to investigate the effect of selenium supplements in patients with heart failure, especially if they have low plasma concentrations of selenium.

The role of cathepsin D in the pathophysiology of heart failure and its potentially beneficial properties: a translational approach

Aims

Cathepsin D is a ubiquitous lysosomal protease that is primarily secreted due to oxidative stress. The role of circulating cathepsin D in heart failure (HF) is unknown. The aim of this study is to determine the association between circulating cathepsin D levels and clinical outcomes in patients with HF and to investigate the biological settings that induce the release of cathepsin D in HF.

Methods and results

Cathepsin D levels were studied in 2174 patients with HF from the BIOSTAT‐CHF index study. Results were validated in 1700 HF patients from the BIOSTAT‐CHF validation cohort. The primary combined outcome was all‐cause mortality and/or HF hospitalizations. Human pluripotent stem cell‐derived cardiomyocytes were subjected to hypoxic, pro‐inflammatory signalling and stretch conditions. Additionally, cathepsin D expression was inhibited by targeted short hairpin RNAs (shRNA). Higher levels of cathepsin D were independently associated with diabetes mellitus, renal failure and higher levels of interleukin‐6 and N‐terminal pro‐B‐type natriuretic peptide (P < 0.001 for all). Cathepsin D levels were independently associated with the primary combined outcome [hazard ratio (HR) per standard deviation (SD): 1.12; 95% confidence interval (CI) 1.02–1.23], which was validated in an independent cohort (HR per SD: 1.23, 95% CI 1.09–1.40). In vitro experiments demonstrated that human stem cell‐derived cardiomyocytes released cathepsin D and troponin T in response to mechanical stretch. ShRNA‐mediated silencing of cathepsin D resulted in increased necrosis, abrogated autophagy, increased stress‐induced metabolism, and increased release of troponin T from human stem cell‐derived cardiomyocytes under stress.

Conclusions

Circulating cathepsin D levels are associated with HF severity and poorer outcome, and reduced levels of cathepsin D may have detrimental effects with therapeutic potential in HF.

MiR-21, MiR-29a, GATA4, and MEF2c Expression Changes in Endothelin-1 and Angiotensin II Cardiac Hypertrophy Stimulated Isl-1+Sca-1+c-kit+ Porcine Cardiac Progenitor Cells In Vitro

Cost- and time-intensive porcine translational disease models offer great opportunities to test drugs and therapies for pathological cardiac hypertrophy and can be supported by porcine cell culture models that provide further insights into basic disease mechanisms. Cardiac progenitor cells (CPCs) residing in the adult heart have been shown to differentiate in vitro into cardiomyocytes and could contribute to cardiac regeneration. Therefore, it is important to evaluate their changes on the cellular level caused by disease. We successfully isolated Isl1⁺Sca1⁺cKit⁺ porcine CPCs (pCPCs) from pig hearts and stimulated them with endothelin-1 (ET-1) and angiotensin II (Ang II) in vitro. We also performed a cardiac reprogramming transfection and tested the same conditions. Our results show that undifferentiated Isl1⁺Sca1⁺cKit⁺ pCPCs were significantly upregulated in GATA4, MEF2c, and miR-29a gene expressions and in BNP and MCP-1 protein expressions with Ang II stimulation, but they showed no significant changes in miR-29a and MCP-1 when stimulated with ET-1. Differentiated Isl1⁺Sca1⁺cKit⁺ pCPCs exhibited significantly higher levels of MEF2c, GATA4, miR-29a, and miR-21 as well as Cx43 and BNP with Ang II stimulation. pMx-MGT-transfected Isl1⁺Sca1⁺cKit⁺ pCPCs showed significant elevations in MEF2c, GATA4, and BNP expressions when stimulated with ET-1. Our model demonstrates that in vitro stimulation leads to successful Isl1⁺Sca1⁺cKit⁺ pCPC hypertrophy with upregulation of cardiac remodeling associated genes and profibrotic miRNAs and offers great possibilities for further investigations of disease mechanisms and treatment.

Disease-inspired tissue engineering: Investigation of cardiovascular pathologies

Once focused exclusively on the creation of tissues to repair or replace diseased or damaged organs, the field of tissue engineering has undergone an important evolution in recent years. Namely, tissue engineering techniques are increasingly being applied to intentionally generate pathological conditions. Motivated in part by the wide gap between 2D cultures and animal models in the current disease modeling continuum, disease-inspired tissue-engineered platforms have numerous potential applications, and may serve to advance our understanding and clinical treatment of various diseases. This review will focus on recent progress toward generating tissue-engineered models of cardiovascular diseases, including cardiac hypertrophy, fibrosis, and ischemia reperfusion injury, atherosclerosis, and calcific aortic valve disease, with an emphasis on how these disease-inspired platforms can be used to decipher disease etiology. Each pathology is discussed in the context of generating both disease-specific cells as well as disease-specific extracellular environments, with an eye toward future opportunities to integrate different tools to yield more complex and physiologically relevant culture platforms. Ultimately, the development of effective disease treatments relies upon our ability to develop appropriate experimental models; as cardiovascular diseases are the leading cause of death worldwide, the insights yielded by improved in vitro disease modeling could have substantial ramifications for public health and clinical care.

Excision of the expanded GAA repeats corrects cardiomyopathy phenotypes of iPSC-derived Friedreich's ataxia cardiomyocytes

Friedreich's ataxia is caused by large homozygous, intronic expansions of GAA repeats in the frataxin (FXN) gene, resulting in severe downregulation of its expression. Pathogenic repeats are located in intron one, hence patients express unaffected FXN protein, albeit in low quantities. Although FRDA symptoms typically afflict the nervous system, hypertrophic cardiomyopathy is the predominant cause of death. Our studies were conducted using cardiomyocytes differentiated from induced pluripotent stem cells derived from control individuals, FRDA patients, and isogenic cells corrected by zinc finger nucleases-mediated excision of pathogenic expanded GAA repeats. This correction of the FXN gene removed the primary trigger of the transcription defect, upregulated frataxin expression, reduced pathological lipid accumulation observed in patient cardiomyocytes, and reversed gene expression signatures of FRDA cardiomyocytes. Transcriptome analyses revealed hypertrophy-specific expression signatures unique to FRDA cardiomyocytes, and emphasized similarities between unaffected and ZFN-corrected FRDA cardiomyocytes. Thus, the iPSC-derived FRDA cardiomyocytes exhibit various molecular defects characteristic for cellular models of cardiomyopathy that can be corrected by genome editing of the expanded GAA repeats. These results underscore the utility of genome editing in generating isogenic cellular models of FRDA and the potential of this approach as a future therapy for this disease.

Closer to Nature Through Dynamic Culture Systems

Mechanics in the human body are required for normal cell function at a molecular level. It is now clear that mechanical stimulations play significant roles in cell growth, differentiation, and migration in normal and diseased cells. Recent studies have led to the discovery that normal and cancer cells have different mechanosensing properties. Here, we discuss the application and the physiological and pathological meaning of mechanical stimulations. To reveal the optimal conditions for mimicking an in vivo microenvironment, we must, therefore, discern the mechanotransduction occurring in cells.

Hypertrophy of human embryonic stem cell-derived cardiomyocytes supported by positive feedback between Ca2+ and diacylglycerol signals

Human embryonic stem cell-derived cardiomyocytes develop pronounced hypertrophy in response to angiotensin-2, endothelin-1, and a selected mix of three fatty acids. All three of these responses are accompanied by increases in both basal cytoplasmic Ca2+ and diacylglycerol, quantified with the Ca2+ sensor Fluo-4 and a FRET-based diacylglycerol sensor expressed in these cardiomyocytes. The heart glycoside, ouabain (30 nM), and a recently developed inhibitor of diacylglycerol lipases, DO34 (1 μM), cause similar hypertrophy responses, and both responses are accompanied by equivalent increases of basal Ca2+ and diacylglycerol. These results together suggest that basal Ca2+ and diacylglycerol form a positive feedback signaling loop that promotes execution of cardiac growth programs in these human myocytes. Given that basal Ca2+ in myocytes depends strongly on the Na+ gradient, we also tested whether nanomolar ouabain concentrations might stimulate Na+/K+ pumps, as described by others, and thereby prevent hypertrophy. However, stimulatory effects of nanomolar ouabain (1.5 nM) were not verified on Na+/K+ pump currents in stem cell-derived myocytes, nor did nanomolar ouabain block hypertrophy induced by endothelin-1. Thus, low-dose ouabain is not a "protective" intervention under the conditions of these experiments in this human myocyte model. To summarize, the major aim of this study has been to characterize the progression of hypertrophy in human embryonic stem cell-derived cardiac myocytes in dependence on diacylglycerol and Na+ gradient changes, developing a case that positive feedback coupling between these mechanisms plays an important role in the initiation of hypertrophy programs.

On the existence of endocytosis driven by membrane phase separations

Large endocytic responses can occur rapidly in diverse cell types without dynamins, clathrin, or actin remodeling. Our experiments suggest that membrane phase separations are crucial with more ordered plasma membrane domains being internalized. Not only do these endocytic processes rely on coalescence of membrane domains, they are promoted by participation of membrane proteins in such domains, one important regulatory influence being palmitoylation. Membrane actin cytoskeleton in general resists membrane phase transitions, and its remodeling may play many roles. Besides membrane 'caging' and 'pinching' roles, typically ascribed to clathrin and dynamins, cytoskeleton remodeling may modify local membrane tension and buckling, as well as the presence and location of actin- and tension-free membrane patches. Endocytosis that depends on membrane phase separations becomes activated in metabolic stress and in response to Ca and PI3 kinase signaling. Internalized membrane traffics normally, and the secretory pathway eventually resupplies membrane to the plasmalemma or directs internalized membrane to other locations, including the extracellular space as exosomes. We describe here that endocytosis driven by membrane phase transitions is regulated by the same signaling mechanisms that regulate macropinocytosis, and it may play diverse roles in cells from nutrient assimilation to membrane recycling, cell migration, and the initiation of quiescent or hibernating cell states. Membrane ordering and phase separations have been shown to promote endocytosis in diverse cell types, including fibroblasts, myocytes, glial cells, and immune cells. We propose that clathrin/dynamin-independent endocytosis represents a continuum of related mechanisms with variable but universal dependence on membrane ordering and actin remodeling. This article is part of a Special Issue entitled: Molecular biophysics of membranes and membrane proteins.

Concise Review: The Current State of Human In Vitro Cardiac Disease Modeling: A Focus on Gene Editing and Tissue Engineering

Until recently, in vivo and ex vivo experiments were the only means to determine factors and pathways involved in disease pathophysiology. After the generation of characterized human embryonic stem cell lines, human diseases could readily be studied in an extensively controllable setting. The introduction of human‐induced pluripotent stem cells, a decade ago, allowed the investigation of hereditary diseases in vitro. In the field of cardiology, diseases linked to known genes have successfully been studied, revealing novel disease mechanisms. The direct effects of various mutations leading to hypertrophic cardiomyopathy, dilated cardiomyopathy, arrythmogenic cardiomyopathy, or left ventricular noncompaction cardiomyopathy are discovered as a result of in vitro disease modeling. Researchers are currently applying more advanced techniques to unravel more complex phenotypes, resulting in state‐of‐the‐art models that better mimic in vivo physiology. The continued improvement of tissue engineering techniques and new insights into epigenetics resulted in more reliable and feasible platforms for disease modeling and the development of novel therapeutic strategies. The introduction of CRISPR‐Cas9 gene editing granted the ability to model diseases in vitro independent of induced pluripotent stem cells. In addition to highlighting recent developments in the field of human in vitro cardiomyopathy modeling, this review also aims to emphasize limitations that remain to be addressed; including residual somatic epigenetic signatures induced pluripotent stem cells, and modeling diseases with unknown genetic causes. Stem Cells Translational Medicine2019;8:66–74