Directed cardiomyocyte differentiation from human pluripotent stem cells by modulating Wnt/β-catenin signaling under fully defined conditions

Improving cardiac differentiation of human pluripotent stem cells by targeting ferroptosis

Generation of cardiomyocytes from human pluripotent stem cells (hPSCs) is of high interest for disease modelling and regenerative medicine. hPSCs can provide an unlimited source of patient-specific cardiomyocytes that are otherwise difficult to obtain from individuals. Moreover, the low proliferation rate of adult cardiomyocytes and low viability ex vivo limits the quantity of study material. Most protocols for the differentiation of cardiomyocytes from hPSCs are based on the temporal modulation of the Wnt pathway. However, during the initial stage of GSK-3 inhibition, a substantial number of cells are lost due to detachment. In this study, we aimed to increase the efficiency of generating cardiomyocytes from hPSCs. We identified cell death as a detrimental factor during this initial stage of in vitro cardiomyocyte differentiation. Through pharmacological targeting of different types of cell death, we discovered that ferroptosis was the main cell death type during the first 48 h of the in vitro differentiation procedure. Inhibiting ferroptosis using ferrostatin-1 during cardiomyocyte differentiation resulted in increased robustness and cell yield.

Co-localization of the sodium-glucose co-transporter-2 channel (SGLT-2) with endothelin ETA and ETB receptors in human cardiorenal tissue

Endothelin (ET) receptor antagonists are being investigated in combination with sodium-glucose co-transporter-2 inhibitors (SGLT-2i). These drugs primarily inhibit the SGLT-2 transporter that, in humans, is thought to be mainly restricted to the renal proximal convoluted tubule, resulting in increased glucose excretion favouring improved glycaemic control and diuresis. This action reduces fluid retention with ET receptor antagonists. Studies have suggested SGLT-2 may also be expressed in cardiomyocytes of human heart. To understand the potential of combining the two classes of drugs, our aim was to compare the distribution of ET receptor sub-types in human kidney, with SGLT-2. Secondly, using the same experimental conditions, we determined if SGLT-2 expression could be detected in human heart and whether the transporter co-localised with ET receptors.

METHODS

Immunocytochemistry localised SGLT-2, ETA and ETB receptors in sections of histologically normal kidney, left ventricle from patients undergoing heart transplantation or controls. Primary antisera were visualised using fluorescent microscopy. Image analysis was used to measure intensity compared with background in adjacent control sections.

RESULTS

As expected, SGLT-2 localised to epithelial cells of the proximal convoluted tubules, and co-localised with both ET receptor sub-types. Similarly, ETA receptors predominated in cardiomyocytes; low (compared with kidney but above background) positive staining was also detected for SGLT-2.

DISCUSSION

Whether low levels of SGLT-2 have a (patho)physiological role in cardiomyocytes is not known but results suggest the effect of direct blockade of sodium (and glucose) influx via SGLT-2 inhibition in cardiomyocytes should be explored, with potential for additive effects with ETA antagonists.

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

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

Maturation of human cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) on polycaprolactone and polyurethane nanofibrous mats

Investigating the potential of human cardiomyocytes derived from induced pluripotent stem cells (iPSC-CMs) in in vitro heart models is essential to develop cardiac regenerative medicine. iPSC-CMs are immature with a fetal-like phenotype relative to cardiomyocytes in vivo. Literature indicates methods for enhancing the structural maturity of iPSC-CMs. Among these strategies, nanofibrous scaffolds offer more accurate mimicry of the functioning of cardiac tissue structures in the human body. However, further research is needed on the use of nanofibrous mats to understand their effects on iPSC-CMs. Our research aimed to evaluate the suitability of poly(ε-caprolactone) (PCL) and polyurethane (PU) nanofibrous mats with different elasticities as materials for the maturation of iPSC-CMs. Analysis of cell morphology and orientation and the expression levels of selected genes and proteins were performed to determine the effect of the type of nanofibrous mats on the maturation of iPSC-CMs after long-term (10-day) culture. Understanding the impact of 3D structural properties in in vitro cardiac models on induced pluripotent stem cell-derived cardiomyocyte maturation is crucial for advancing cardiac tissue engineering and regenerative medicine because it can help optimize conditions for obtaining more mature and functional human cardiomyocytes.

Induced pluripotent stem cell (iPSC) modeling validates reduced GBE1 enzyme activity due to a novel variant, p.Ile694Asn, found in a patient with suspected glycogen storage disease IV

Background

Glycogen Storage disease type 4 (GSD4), a rare disease caused by glycogen branching enzyme 1 (GBE1) deficiency, affects multiple organ systems including the muscles, liver, heart, and central nervous system. Here we report a GSD4 patient, who presented with severe hepatosplenomegaly and cardiac ventricular hypertrophy. GBE1 sequencing identified two variants: a known pathogenic missense variant, c.1544G>A (p.Arg515His), and a missense variant of unknown significance (VUS), c.2081T>A (p. Ile694Asn). As a liver transplant alone can exacerbate heart dysfunction in GSD4 patients, a precise diagnosis is essential for liver transplant indication. To characterize the disease-causing variant, we modeled patient-specific GBE1 deficiency using CRISPR/Cas9 genome-edited induced pluripotent stem cells (iPSCs).

Methods

iPSCs from a healthy donor (iPSC-WT) were genome-edited by CRISPR/Cas9 to induce homozygous p.Ile694Asn in GBE1 (iPSC-GBE1-I694N) and differentiated into hepatocytes (iHep) or cardiomyocytes (iCM). GBE1 enzyme activity was measured, and PAS-D staining was performed to analyze polyglucosan deposition in these cells.

Results

iPSCGBE1-I694N differentiated into iHep and iCM exhibited reduced GBE1 protein level and enzyme activity in both cell types compared to iPSCwt. Both iHepGBE1-I694N and iCMGBE1-I694N showed polyglucosan deposits correlating to the histologic patterns of the patient's biopsies.

Conclusions

iPSC-based disease modeling supported a loss of function effect of p.Ile694Asn in GBE1. The modeling of GBE1 enzyme deficiency in iHep and iCM cell lines had multi-organ findings, demonstrating iPSC-based modeling usefulness in elucidating the effects of novel VUS in ultra-rare diseases.

Molecular and cellular neurocardiology in heart disease

This paper updates and builds on a previous White Paper in this journal that some of us contributed to concerning the molecular and cellular basis of cardiac neurobiology of heart disease. Here we focus on recent findings that underpin cardiac autonomic development, novel intracellular pathways and neuroplasticity. Throughout we highlight unanswered questions and areas of controversy. Whilst some neurochemical pathways are already demonstrating prognostic viability in patients with heart failure, we also discuss the opportunity to better understand sympathetic impairment by using patient specific stem cells that provides pathophysiological contextualization to study 'disease in a dish'. Novel imaging techniques and spatial transcriptomics are also facilitating a road map for target discovery of molecular pathways that may form a therapeutic opportunity to treat cardiac dysautonomia.

Biohybrid printing approaches for cardiac pathophysiological studies

Bioengineered hearts, which include single cardiomyocytes, engineered heart tissue, and chamber-like models, generate various biosignals, such as contractility, electrophysiological, and volume-pressure dynamic signals. Monitoring changes in these signals is crucial for understanding the mechanisms of disease progression and developing potential treatments. However, current methodologies face challenges in the continuous monitoring of bioengineered hearts over extended periods and typically require sacrificing the sample post-experiment, thereby limiting in-depth analysis. Thus, a biohybrid system consisting of living and nonliving components was developed. This system primarily features heart tissue alongside nonliving elements designed to support or comprehend its functionality. Biohybrid printing technology has simplified the creation of such systems and facilitated the development of various functional biohybrid systems capable of measuring or even regulating multiple functions, such as pacemakers, which demonstrates its versatility and potential applications. The future of biohybrid printing appears promising, with the ongoing exploration of its capabilities and potential directions for advancement.

Exonuclease editor promotes precision of gene editing in mammalian cells

BACKGROUND

Many efforts have been made to improve the precision of Cas9-mediated gene editing through increasing knock-in efficiency and decreasing byproducts, which proved to be challenging.

RESULTS

Here, we have developed a human exonuclease 1-based genome-editing tool, referred to as exonuclease editor. When compared to Cas9, the exonuclease editor gave rise to increased HDR efficiency, reduced NHEJ repair frequency, and significantly elevated HDR/indel ratio. Robust gene editing precision of exonuclease editor was even superior to the fusion of Cas9 with E1B or DN1S, two previously reported precision-enhancing domains. Notably, exonuclease editor inhibited NHEJ at double strand breaks locally rather than globally, reducing indel frequency without compromising genome integrity. The replacement of Cas9 with single-strand DNA break-creating Cas9 nickase further increased the HDR/indel ratio by 453-fold than the original Cas9. In addition, exonuclease editor resulted in high microhomology-mediated end joining efficiency, allowing accurate and flexible deletion of targeted sequences with extended lengths with the aid of paired sgRNAs. Exonuclease editor was further used for correction of DMD patient-derived induced pluripotent stem cells, where 30.0% of colonies were repaired by HDR versus 11.1% in the control.

CONCLUSIONS

Therefore, the exonuclease editor system provides a versatile and safe genome editing tool with high precision and holds promise for therapeutic gene correction.

MAGIK: A rapid and efficient method to create lineage-specific reporters in human pluripotent stem cells

Precise insertion of fluorescent proteins into lineage-specific genes in human pluripotent stem cells (hPSCs) presents challenges due to low knockin efficiency and difficulties in isolating targeted cells. To overcome these hurdles, we present the modified mRNA (ModRNA)-based Activation for Gene Insertion and Knockin (MAGIK) method. MAGIK operates in two steps: first, it uses a Cas9-2A-p53DD modRNA with a mini-donor plasmid (without a drug selection cassette) to significantly enhance efficiency. Second, a deactivated Cas9 activator modRNA and a 'dead' guide RNA are used to temporarily activate the targeted gene, allowing for live cell sorting of targeted cells. Consequently, MAGIK eliminates the need for drug selection cassettes or labor-intensive single-cell colony screening, expediting precise gene editing. We showed MAGIK can be utilized to insert fluorescent proteins into various genes, including SOX17, NKX6.1, NKX2.5, and PDX1, across multiple hPSC lines. This underscores its robust performance and offers a promising solution for achieving knockin in hPSCs within a significantly shortened time frame.

Sex in cardiovascular disease: Why this biological variable should be considered in in vitro models

Cardiovascular disease (CVD), the world's leading cause of death, exhibits notable epidemiological, clinical, and pathophysiological differences between sexes. Many such differences can be linked back to cardiovascular sexual dimorphism, yet sex-specific in vitro models are still not the norm. A lack of sex reporting and apparent male bias raises the question of whether in vitro CVD models faithfully recapitulate the biology of intended treatment recipients. To ensure equitable treatment for the overlooked female patient population, sex as a biological variable (SABV) inclusion must become commonplace in CVD preclinical research. Here, we discuss the role of sex in CVD and underlying cardiovascular (patho)physiology. We review shortcomings in current SABV practices, describe the relevance of sex, and highlight emerging strategies for SABV inclusion in three major in vitro model types: primary cell, stem cell, and three-dimensional models. Last, we identify key barriers to inclusive design and suggest techniques for overcoming them.

Histone demethylase KDM5 regulates cardiomyocyte maturation by promoting fatty acid oxidation, oxidative phosphorylation, and myofibrillar organization

AIMS

Human pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) provide a platform to identify and characterize factors that regulate the maturation of CMs. The transition from an immature foetal to an adult CM state entails coordinated regulation of the expression of genes involved in myofibril formation and oxidative phosphorylation (OXPHOS) among others. Lysine demethylase 5 (KDM5) specifically demethylates H3K4me1/2/3 and has emerged as potential regulators of expression of genes involved in cardiac development and mitochondrial function. The purpose of this study is to determine the role of KDM5 in iPSC-CM maturation.

METHODS AND RESULTS

KDM5A, B, and C proteins were mainly expressed in the early post-natal stages, and their expressions were progressively downregulated in the post-natal CMs and were absent in adult hearts and CMs. In contrast, KDM5 proteins were persistently expressed in the iPSC-CMs up to 60 days after the induction of myogenic differentiation, consistent with the immaturity of these cells. Inhibition of KDM5 by KDM5-C70 -a pan-KDM5 inhibitor, induced differential expression of 2372 genes, including upregulation of genes involved in fatty acid oxidation (FAO), OXPHOS, and myogenesis in the iPSC-CMs. Likewise, genome-wide profiling of H3K4me3 binding sites by the cleavage under targets and release using nuclease assay showed enriched of the H3K4me3 peaks at the promoter regions of genes encoding FAO, OXPHOS, and sarcomere proteins. Consistent with the chromatin and gene expression data, KDM5 inhibition increased the expression of multiple sarcomere proteins and enhanced myofibrillar organization. Furthermore, inhibition of KDM5 increased H3K4me3 deposits at the promoter region of the ESRRA gene and increased its RNA and protein levels. Knockdown of ESRRA in KDM5-C70-treated iPSC-CM suppressed expression of a subset of the KDM5 targets. In conjunction with changes in gene expression, KDM5 inhibition increased oxygen consumption rate and contractility in iPSC-CMs.

CONCLUSION

KDM5 inhibition enhances maturation of iPSC-CMs by epigenetically upregulating the expressions of OXPHOS, FAO, and sarcomere genes and enhancing myofibril organization and mitochondrial function.

The emerging role of heart-on-a-chip systems in delineating mechanisms of SARS-CoV-2-induced cardiac dysfunction

Coronavirus disease 2019 (COVID-19) has been a major global health concern since its emergence in 2019, with over 680 million confirmed cases as of April 2023. While COVID-19 has been strongly associated with the development of cardiovascular complications, the specific mechanisms by which viral infection induces myocardial dysfunction remain largely controversial as studies have shown that the severe acute respiratory syndrome coronavirus-2 can lead to heart failure both directly, by causing damage to the heart cells, and indirectly, by triggering an inflammatory response throughout the body. In this review, we summarize the current understanding of potential mechanisms that drive heart failure based on in vitro studies. We also discuss the significance of three-dimensional heart-on-a-chip technology in the context of the current and future pandemics.

Advancing Cardiomyocyte Maturation: Current Strategies and Promising Conductive Polymer-Based Approaches

Cardiovascular diseases are a leading cause of mortality and pose a significant burden on healthcare systems worldwide. Despite remarkable progress in medical research, the development of effective cardiovascular drugs has been hindered by high failure rates and escalating costs. One contributing factor is the limited availability of mature cardiomyocytes (CMs) for accurate disease modeling and drug screening. Human induced pluripotent stem cell-derived CMs offer a promising source of CMs; however, their immature phenotype presents challenges in translational applications. This review focuses on the road to achieving mature CMs by summarizing the major differences between immature and mature CMs, discussing the importance of adult-like CMs for drug discovery, highlighting the limitations of current strategies, and exploring potential solutions using electro-mechano active polymer-based scaffolds based on conductive polymers. However, critical considerations such as the trade-off between 3D systems and nutrient exchange, biocompatibility, degradation, cell adhesion, longevity, and integration into wider systems must be carefully evaluated. Continued advancements in these areas will contribute to a better understanding of cardiac diseases, improved drug discovery, and the development of personalized treatment strategies for patients with cardiovascular disorders.

Advancing cardiac regeneration through 3D bioprinting: methods, applications, and future directions

Cardiovascular diseases (CVDs) represent a paramount global mortality concern, and their prevalence is on a relentless ascent. Despite the effectiveness of contemporary medical interventions in mitigating CVD-related fatality rates and complications, their efficacy remains curtailed by an array of limitations. These include the suboptimal efficiency of direct cell injection and an inherent disequilibrium between the demand and availability of heart transplantations. Consequently, the imperative to formulate innovative strategies for cardiac regeneration therapy becomes unmistakable. Within this context, 3D bioprinting technology emerges as a vanguard contender, occupying a pivotal niche in the realm of tissue engineering and regenerative medicine. This state-of-the-art methodology holds the potential to fabricate intricate heart tissues endowed with multifaceted structures and functionalities, thereby engendering substantial promise. By harnessing the prowess of 3D bioprinting, it becomes plausible to synthesize functional cardiac architectures seamlessly enmeshed with the host tissue, affording a viable avenue for the restitution of infarcted domains and, by extension, mitigating the onerous yoke of CVDs. In this review, we encapsulate the myriad applications of 3D bioprinting technology in the domain of heart tissue regeneration. Furthermore, we usher in the latest advancements in printing methodologies and bioinks, culminating in an exploration of the extant challenges and the vista of possibilities inherent to a diverse array of approaches.

Cardiac differentiation of chimpanzee induced pluripotent stem cell lines with different subspecies backgrounds

The comparative analysis between humans and non-human primates is an instrumental approach for elucidating the evolutional traits and disease propensity of humans. However, in primates, cross-species analyses of their developmental events have encountered constraints because of the ethical and technical limitations in available sample collection, sequential monitoring, and manipulations. In an endeavor to surmount these challenges, in recent years, induced pluripotent stem cells (iPSCs) have garnered escalating interest as an in vitro tool for cross-species analyses between humans and non-human primates. Meanwhile, compared to humans, there is less information on in vitro differentiation of non-human primate iPSCs, and their genetic diversity including subspecies may cause different eligibility to in vitro differentiation methods. Therefore, antecedent to embarking on a comparative analysis to humans, it is a prerequisite to develop the efficacious methodologies for in vitro differentiation regardless of the intraspecies genetic background in non-human primates. In this study, we executed the in vitro differentiation of cardiomyocytes from four chimpanzee iPSC lines with different subspecies and individual backgrounds. To induce cardiomyocytes from chimpanzee iPSCs, we evaluated our methodology for in vitro cardiac differentiation of human iPSCs. Eventually, with minor alterations, our cardiac differentiation method was applicable to all chimpanzee iPSC lines tested as assessed by the expression of cardiac marker genes and the beating ability. Hence, our in vitro differentiation method will advance iPSC-based research of chimpanzee cardiac development and also hold possible utility to cross-species analyses among primate species.

Stress-Induced Proteasome Sub-Cellular Translocation in Cardiomyocytes Causes Altered Intracellular Calcium Handling and Arrhythmias

The ubiquitin-proteasome system (UPS) is an essential mechanism responsible for the selective degradation of substrate proteins via their conjugation with ubiquitin. Since cardiomyocytes have very limited self-renewal capacity, as they are prone to protein damage due to constant mechanical and metabolic stress, the UPS has a key role in cardiac physiology and pathophysiology. While altered proteasomal activity contributes to a variety of cardiac pathologies, such as heart failure and ischemia/reperfusion injury (IRI), the environmental cues affecting its activity are still unknown, and they are the focus of this work. Following a recent study by Ciechanover's group showing that amino acid (AA) starvation in cultured cancer cell lines modulates proteasome intracellular localization and activity, we tested two hypotheses in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs, CMs): (i) AA starvation causes proteasome translocation in CMs, similarly to the observation in cultured cancer cell lines; (ii) manipulation of subcellular proteasomal compartmentalization is associated with electrophysiological abnormalities in the form of arrhythmias, mediated via altered intracellular Ca2+ handling. The major findings are: (i) starving CMs to AAs results in proteasome translocation from the nucleus to the cytoplasm, while supplementation with the aromatic amino acids tyrosine (Y), tryptophan (W) and phenylalanine (F) (YWF) inhibits the proteasome recruitment; (ii) AA-deficient treatments cause arrhythmias; (iii) the arrhythmias observed upon nuclear proteasome sequestration(-AA+YWF) are blocked by KB-R7943, an inhibitor of the reverse mode of the sodium-calcium exchanger NCX; (iv) the retrograde perfusion of isolated rat hearts with AA starvation media is associated with arrhythmias. Collectively, our novel findings describe a newly identified mechanism linking the UPS to arrhythmia generation in CMs and whole hearts.

Heart-on-a-Chip Model of Epicardial-Myocardial Interaction in Ischemia Reperfusion Injury

Epicardial cells (EPIs) form the outer layer of the heart and play an important role in development and disease. Current heart-on-a-chip platforms still do not fully mimic the native cardiac environment due to the absence of relevant cell types, such as EPIs. Here, using the Biowire II platform, engineered cardiac tissues with an epicardial outer layer and inner myocardial structure are constructed, and an image analysis approach is developed to track the EPI cell migration in a beating myocardial environment. Functional properties of EPI cardiac tissues improve over two weeks in culture. In conditions mimicking ischemia reperfusion injury (IRI), the EPI cardiac tissues experience less cell death and a lower impact on functional properties. EPI cell coverage is significantly reduced and more diffuse under normoxic conditions compared to the post-IRI conditions. Upon IRI, migration of EPI cells into the cardiac tissue interior is observed, with contributions to alpha smooth muscle actin positive cell population. Altogether, a novel heart-on-a-chip model is designed to incorporate EPIs through a formation process that mimics cardiac development, and this work demonstrates that EPI cardiac tissues respond to injury differently than epicardium-free controls, highlighting the importance of including EPIs in heart-on-a-chip constructs that aim to accurately mimic the cardiac environment.

Telomerase is essential for cardiac differentiation and sustained metabolism of human cardiomyocytes

Telomeres as the protective ends of linear chromosomes, are synthesized by the enzyme telomerase (TERT). Critically short telomeres essentially contribute to aging-related diseases and are associated with a broad spectrum of disorders known as telomeropathies. In cardiomyocytes, telomere length is strongly correlated with cardiomyopathies but it remains ambiguous whether short telomeres are the cause or the result of the disease. In this study, we employed an inducible CRISPRi human induced pluripotent stem cell (hiPSC) line to silence TERT expression enabling the generation of hiPSCs and hiPSC-derived cardiomyocytes with long and short telomeres. Reduced telomerase activity and shorter telomere lengths of hiPSCs induced global transcriptomic changes associated with cardiac developmental pathways. Consequently, the differentiation potential towards cardiomyocytes was strongly impaired and single cell RNA sequencing revealed a shift towards a more smooth muscle cell like identity in the cells with the shortest telomeres. Poor cardiomyocyte function and increased sensitivity to stress directly correlated with the extent of telomere shortening. Collectively our data demonstrates a TERT dependent cardiomyogenic differentiation defect, highlighting the CRISPRi TERT hiPSCs model as a powerful platform to study the mechanisms and consequences of short telomeres in the heart and also in the context of telomeropathies.

A roadmap towards manufacturing extracellular vesicles for cardiac repair

For the past two decades researchers have linked extracellular vesicle (EV)-mediated mechanisms to various physiological and pathological processes in the heart, such as immune response regulation, fibrosis, angiogenesis, and the survival and growth of cardiomyocytes. Although use of EVs has gathered momentum in the cardiac field, several obstacles in both upstream and downstream processes during EV manufacture need to be addressed before clinical success can be achieved. Low EV yields obtained in small-scale cultures deter clinical translation, as mass production is a prerequisite to meet therapeutic doses. Moreover, standardizing EV manufacture is critical given the inherent heterogeneity of EVs and the constraints of current isolation techniques. In this review, we discuss the critical steps for the large-scale manufacturing of high-potency EVs for cardiac therapies.

Far-red and sensitive sensor for monitoring real time H2O2 dynamics with subcellular resolution and in multi-parametric imaging applications

H 2 O 2 is a key oxidant in mammalian biology and a pleiotropic signaling molecule at the physiological level, and its excessive accumulation in conjunction with decreased cellular reduction capacity is often found to be a common pathological marker. Here, we present a red fluorescent Genetically Encoded H 2 O 2 Indicator (GEHI) allowing versatile optogenetic dissection of redox biology. Our new GEHI, oROS-HT, is a chemigenetic sensor utilizing a HaloTag and Janelia Fluor (JF) rhodamine dye as fluorescent reporters. We developed oROS-HT through a structure-guided approach aided by classic protein structures and recent protein structure prediction tools. Optimized with JF 635 , oROS-HT is a sensor with 635 nm excitation and 650 nm emission peaks, allowing it to retain its brightness while monitoring intracellular H 2 O 2 dynamics. Furthermore, it enables multi-color imaging in combination with blue-green fluorescent sensors for orthogonal analytes and low auto-fluorescence interference in biological tissues. Other advantages of oROS-HT over alternative GEHIs are its fast kinetics, oxygen-independent maturation, low pH sensitivity, lack of photo-artifact, and lack of intracellular aggregation. Here, we demonstrated efficient subcellular targeting and how oROS-HT can map inter and intracellular H 2 O 2 diffusion at subcellular resolution. Lastly, we used oROS-HT with other green fluorescence reporters to investigate the transient effect of the anti-inflammatory agent auranofin on cellular redox physiology and calcium levels via multi-parametric, dual-color imaging.

HOIL-1L deficiency induces cell cycle alteration which causes immaturity of skeletal muscle and cardiomyocytes

HOIL-1L deficiency was recently reported to be one of the causes of myopathy and dilated cardiomyopathy (DCM). However, the mechanisms by which myopathy and DCM develop have not been clearly elucidated. Here, we sought to elucidate these mechanisms using the murine myoblast cell line C2C12 and disease-specific human induced pluripotent stem cells (hiPSCs). Myotubes differentiated from HOIL-1L-KO C2C12 cells exhibited deteriorated differentiation and mitotic cell accumulation. CMs differentiated from patient-derived hiPSCs had an abnormal morphology with a larger size and were excessively multinucleated compared with CMs differentiated from control hiPSCs. Further analysis of hiPSC-derived CMs showed that HOIL-1L deficiency caused cell cycle alteration and mitotic cell accumulation. These results demonstrate that abnormal cell maturation possibly contribute to the development of myopathy and DCM. In conclusion, HOIL-1L is an important intrinsic regulator of cell cycle-related myotube and CM maturation and cell proliferation.

CRISPR Activation Reverses Haploinsufficiency and Functional Deficits Caused by TTN Truncation Variants

BACKGROUND

TTN truncation variants (TTNtvs) are the most common genetic lesion identified in individuals with dilated cardiomyopathy, a disease with high morbidity and mortality rates. TTNtvs reduce normal TTN (titin) protein levels, produce truncated proteins, and impair sarcomere content and function. Therapeutics targeting TTNtvs have been elusive because of the immense size of TTN, the rarity of specific TTNtvs, and incomplete knowledge of TTNtv pathogenicity.

METHODS

We adapted CRISPR activation using dCas9-VPR to functionally interrogate TTNtv pathogenicity and develop a therapeutic in human cardiomyocytes and 3-dimensional cardiac microtissues engineered from induced pluripotent stem cell models harboring a dilated cardiomyopathy-associated TTNtv. We performed guide RNA screening with custom TTN reporter assays, agarose gel electrophoresis to quantify TTN protein levels and isoforms, and RNA sequencing to identify molecular consequences of TTN activation. Cardiomyocyte epigenetic assays were also used to nominate DNA regulatory elements to enable cardiomyocyte-specific TTN activation.

RESULTS

CRISPR activation of TTN using single guide RNAs targeting either the TTN promoter or regulatory elements in spatial proximity to the TTN promoter through 3-dimensional chromatin interactions rescued TTN protein deficits disturbed by TTNtvs. Increasing TTN protein levels normalized sarcomere content and contractile function despite increasing truncated TTN protein. In addition to TTN transcripts, CRISPR activation also increased levels of myofibril assembly-related and sarcomere-related transcripts.

CONCLUSIONS

TTN CRISPR activation rescued TTNtv-related functional deficits despite increasing truncated TTN levels, which provides evidence to support haploinsufficiency as a relevant genetic mechanism underlying heterozygous TTNtvs. CRISPR activation could be developed as a therapeutic to treat a large proportion of TTNtvs.

Multi-omic QTL mapping in early developmental tissues reveals phenotypic and temporal complexity of regulatory variants underlying GWAS loci

Most GWAS loci are presumed to affect gene regulation, however, only ∼43% colocalize with expression quantitative trait loci (eQTLs). To address this colocalization gap, we identify eQTLs, chromatin accessibility QTLs (caQTLs), and histone acetylation QTLs (haQTLs) using molecular samples from three early developmental (EDev) tissues. Through colocalization, we annotate 586 GWAS loci for 17 traits by QTL complexity, QTL phenotype, and QTL temporal specificity. We show that GWAS loci are highly enriched for colocalization with complex QTL modules that affect multiple elements (genes and/or peaks). We also demonstrate that caQTLs and haQTLs capture regulatory variations not associated with eQTLs and explain ∼49% of the functionally annotated GWAS loci. Additionally, we show that EDev-unique QTLs are strongly depleted for colocalizing with GWAS loci. By conducting one of the largest multi-omic QTL studies to date, we demonstrate that many GWAS loci exhibit phenotypic complexity and therefore, are missed by traditional eQTL analyses.

Noninvasive Assessment of hiPSC Differentiation toward Cardiomyocytes Using Pretrained Convolutional Neural Networks and the Channel Pruning Algorithm

Human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) offer versatile applications in tissue engineering and drug screening. To facilitate the monitoring of hiPSC cardiac differentiation, a noninvasive approach using convolutional neural networks (CNNs) was explored. HiPSCs were differentiated into cardiomyocytes and analyzed using the quantitative real-time polymerase chain reaction (qRT-PCR). The bright-field images of the cells at different time points were captured to create the dataset. Six pretrained models (AlexNet, GoogleNet, ResNet 18, ResNet 50, DenseNet 121, VGG 19-BN) were employed to identify different stages in differentiation. VGG 19-BN outperformed the other five CNNs and exhibited remarkable performance with 99.2% accuracy, recall, precision, and F1 score and 99.8% specificity. The pruning process was then applied to the optimal model, resulting in a significant reduction of model parameters while maintaining high accuracy. Finally, an automation application using the pruned VGG 19-BN model was developed, facilitating users in assessing the cell status during the myocardial differentiation of hiPSCs.

Unlocking the Future: Pluripotent Stem Cell-Based Lung Repair

The human respiratory system is susceptible to a variety of diseases, ranging from chronic obstructive pulmonary disease (COPD) and pulmonary fibrosis to acute respiratory distress syndrome (ARDS). Today, lung diseases represent one of the major challenges to the health care sector and represent one of the leading causes of death worldwide. Current treatment options often focus on managing symptoms rather than addressing the underlying cause of the disease. The limitations of conventional therapies highlight the urgent clinical need for innovative solutions capable of repairing damaged lung tissue at a fundamental level. Pluripotent stem cell technologies have now reached clinical maturity and hold immense potential to revolutionize the landscape of lung repair and regenerative medicine. Meanwhile, human embryonic (HESCs) and human-induced pluripotent stem cells (hiPSCs) can be coaxed to differentiate into lung-specific cell types such as bronchial and alveolar epithelial cells, or pulmonary endothelial cells. This holds the promise of regenerating damaged lung tissue and restoring normal respiratory function. While methods for targeted genetic engineering of hPSCs and lung cell differentiation have substantially advanced, the required GMP-grade clinical-scale production technologies as well as the development of suitable preclinical animal models and cell application strategies are less advanced. This review provides an overview of current perspectives on PSC-based therapies for lung repair, explores key advances, and envisions future directions in this dynamic field.

HRAS-Mutant Cardiomyocyte Model of Multifocal Atrial Tachycardia

BACKGROUND

Germline HRAS gain-of-function pathogenic variants cause Costello syndrome (CS). During early childhood, 50% of patients develop multifocal atrial tachycardia, a treatment-resistant tachyarrhythmia of unknown pathogenesis. This study investigated how overactive HRAS activity triggers arrhythmogenesis in atrial-like cardiomyocytes (ACMs) derived from human-induced pluripotent stem cells bearing CS-associated HRAS variants.

METHODS

HRAS Gly12 mutations were introduced into a human-induced pluripotent stem cells-ACM reporter line. Human-induced pluripotent stem cells were generated from patients with CS exhibiting tachyarrhythmia. Calcium transients and action potentials were assessed in induced pluripotent stem cell-derived ACMs. Automated patch clamping assessed funny currents. HCN inhibitors targeted pacemaker-like activity in mutant ACMs. Transcriptomic data were analyzed via differential gene expression and gene ontology. Immunoblotting evaluated protein expression associated with calcium handling and pacemaker-nodal expression.

RESULTS

ACMs harboring HRAS variants displayed higher beating rates compared with healthy controls. The hyperpolarization activated cyclic nucleotide gated potassium channel inhibitor ivabradine and the Nav1.5 blocker flecainide significantly decreased beating rates in mutant ACMs, whereas voltage-gated calcium channel 1.2 blocker verapamil attenuated their irregularity. Electrophysiological assessment revealed an increased number of pacemaker-like cells with elevated funny current densities among mutant ACMs. Mutant ACMs demonstrated elevated gene expression (ie, ISL1, TBX3, TBX18) related to intracellular calcium homeostasis, heart rate, RAS signaling, and induction of pacemaker-nodal-like transcriptional programming. Immunoblotting confirmed increased protein levels for genes of interest and suppressed MAPK (mitogen-activated protein kinase) activity in mutant ACMs.

CONCLUSIONS

CS-associated gain-of-function HRASG12 mutations in induced pluripotent stem cells-derived ACMs trigger transcriptional changes associated with enhanced automaticity and arrhythmic activity consistent with multifocal atrial tachycardia. This is the first human-induced pluripotent stem cell model establishing the mechanistic basis for multifocal atrial tachycardia in CS.

Generation of CRISPR/Cas9 edited human induced pluripotent stem cell line carrying the heterozygous p.H695VfsX5 frameshift mutation in the exon 10 of the PKP2 gene

Loss-of-function mutations in the PKP2 gene are associated with arrhythmogenic right ventricular cardiomyopathy (ARVC), a rare cardiac disease associated with a poor prognosis. The search for therapeutics and a better understanding of the molecular mechanisms of the disease require the development of cellular modelling. Using CRISPR/Cas9, we generated a hiPSC line with heterozygous 7-bp deletion in exon 10 of PKP2 (p.H695VfsX5). We demonstrated that hiPSCs were fully pluripotent and showed a high rate of differentiation into cardiomyocytes (iPS-CM). We also showed that PKP2 protein was expressed at the plasma membrane, with an overall decreased expression in iPS-CM indicating haploinsufficiency.

Statins affect human iPSC-derived cardiomyocytes by interfering with mitochondrial function and intracellular acidification

Statins are effective drugs in reducing cardiovascular morbidity and mortality by inhibiting cholesterol synthesis. These effects are primarily beneficial for the patient's vascular system. A significant number of statin users suffer from muscle complaints probably due to mitochondrial dysfunction, a mechanism that has recently been elucidated. This has raised our interest in exploring the effects of statins on cardiac muscle cells in an era where the elderly and patients with poorer functioning hearts and less metabolic spare capacity start dominating our patient population. Here, we investigated the effects of statins on human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-derived CMs). hiPSC-derived CMs were exposed to simvastatin, atorvastatin, rosuvastatin, and cerivastatin at increasing concentrations. Metabolic assays and fluorescent microscopy were employed to evaluate cellular viability, metabolic capacity, respiration, intracellular acidity, and mitochondrial membrane potential and morphology. Over a concentration range of 0.3-100 µM, simvastatin lactone and atorvastatin acid showed a significant reduction in cellular viability by 42-64%. Simvastatin lactone was the most potent inhibitor of basal and maximal respiration by 56% and 73%, respectively, whereas simvastatin acid and cerivastatin acid only reduced maximal respiration by 50% and 42%, respectively. Simvastatin acid and lactone and atorvastatin acid significantly decreased mitochondrial membrane potential by 20%, 6% and 3%, respectively. The more hydrophilic atorvastatin acid did not seem to affect cardiomyocyte metabolism. This calls for further research on the translatability to the clinical setting, in which a more conscientious approach to statin prescribing might be considered, especially regarding the current shift in population toward older patients with poor cardiac function.

Generation of a ISL1 homozygous knockout stem cell line (WAe009-A-1G) by episomal vector-based CRISPR/Cas9 system

The ISL LIM homeobox 1 (ISL1) gene belongs to the LIM/homeodomain transcription factor family and plays a pivotal role in conveying multipotent and proliferative properties of cardiac precursor cells. Mutations in ISL1 are linked to congenital heart disease. To further explore ISL1's role in the human heart, we have created a homozygous ISL1 knockout (ISL1-KO) human embryonic stem cell line using the CRISPR/Cas9 system. Notably, this ISL1-KO cell line retains normal morphology, pluripotency, and karyotype. This resource serves as a valuable tool for investigating ISL1's function in cardiomyocyte differentiation.

Cardiac tissue model of immune-induced dysfunction reveals the role of free mitochondrial DNA and the therapeutic effects of exosomes

Despite tremendous progress in the development of mature heart-on-a-chip models, human cell-based models of myocardial inflammation are lacking. Here, we bioengineered a vascularized heart-on-a-chip with circulating immune cells to model severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-induced acute myocarditis. We observed hallmarks of coronavirus disease (COVID-19)-induced myocardial inflammation, as the presence of immune cells augmented the secretion of proinflammatory cytokines, triggered progressive impairment of contractile function, and altered intracellular calcium transients. An elevation of circulating cell-free mitochondrial DNA (ccf-mtDNA) was measured first in the heart-on-a-chip and then validated in COVID-19 patients with low left ventricular ejection fraction, demonstrating that mitochondrial damage is an important pathophysiological hallmark of inflammation-induced cardiac dysfunction. Leveraging this platform in the context of SARS-CoV-2-induced myocardial inflammation, we established that administration of endothelial cell-derived exosomes effectively rescued the contractile deficit, normalized calcium handling, elevated the contraction force, and reduced the ccf-mtDNA and cytokine release via Toll-like receptor-nuclear factor κB signaling axis.

MicroBundleCompute: Automated segmentation, tracking, and analysis of subdomain deformation in cardiac microbundles

Advancing human induced pluripotent stem cell derived cardiomyocyte (hiPSC-CM) technology will lead to significant progress ranging from disease modeling, to drug discovery, to regenerative tissue engineering. Yet, alongside these potential opportunities comes a critical challenge: attaining mature hiPSC-CM tissues. At present, there are multiple techniques to promote maturity of hiPSC-CMs including physical platforms and cell culture protocols. However, when it comes to making quantitative comparisons of functional behavior, there are limited options for reliably and reproducibly computing functional metrics that are suitable for direct cross-system comparison. In addition, the current standard functional metrics obtained from time-lapse images of cardiac microbundle contraction reported in the field (i.e., post forces, average tissue stress) do not take full advantage of the available information present in these data (i.e., full-field tissue displacements and strains). Thus, we present "MicroBundleCompute," a computational framework for automatic quantification of morphology-based mechanical metrics from movies of cardiac microbundles. Briefly, this computational framework offers tools for automatic tissue segmentation, tracking, and analysis of brightfield and phase contrast movies of beating cardiac microbundles. It is straightforward to implement, runs without user intervention, requires minimal input parameter setting selection, and is computationally inexpensive. In this paper, we describe the methods underlying this computational framework, show the results of our extensive validation studies, and demonstrate the utility of exploring heterogeneous tissue deformations and strains as functional metrics. With this manuscript, we disseminate "MicroBundleCompute" as an open-source computational tool with the aim of making automated quantitative analysis of beating cardiac microbundles more accessible to the community.

Capsid-mediated control of adeno-associated viral transcription determines host range

Adeno-associated virus (AAV) is a member of the genus Dependoparvovirus, which infects a wide range of vertebrate species. Here, we observe that, unlike most primate AAV isolates, avian AAV is transcriptionally silenced in human cells. By swapping the VP1 N terminus from primate AAVs (e.g., AAV8) onto non-mammalian isolates (e.g., avian AAV), we identify a minimal component of the AAV capsid that controls viral transcription and unlocks robust transduction in both human cells and mouse tissue. This effect is accompanied by increased AAV genome chromatin accessibility and altered histone methylation. Proximity ligation analysis reveals that host factors are selectively recruited by the VP1 N terminus of AAV8 but not avian AAV. Notably, these include AAV essential factors implicated in the nuclear factor κB pathway, chromatin condensation, and histone methylation. We postulate that the AAV capsid has evolved mechanisms to recruit host factors to its genome, allowing transcriptional activation in a species-specific manner.

Biosafe cerium oxide nanozymes protect human pluripotent stem cells and cardiomyocytes from oxidative stress

BACKGROUND

Cardiovascular diseases (CVDs) have the highest mortality worldwide. Human pluripotent stem cells (hPSCs) and their cardiomyocyte derivatives (hPSC-CMs) offer a valuable resource for disease modeling, pharmacological screening, and regenerative therapy. While most CVDs are linked to significant over-production of reactive oxygen species (ROS), the effects of current antioxidants targeting excessive ROS are limited. Nanotechnology is a powerful tool to develop antioxidants with improved selectivity, solubility, and bioavailability to prevent or treat various diseases related to oxidative stress. Cerium oxide nanozymes (CeONZs) can effectively scavenge excessive ROS by mimicking the activity of endogenous antioxidant enzymes. This study aimed to assess the nanotoxicity of CeONZs and their potential antioxidant benefits in stressed human embryonic stem cells (hESCs) and their derived cardiomyocytes (hESC-CMs).

RESULTS

CeONZs demonstrated reliable nanosafety and biocompatibility in hESCs and hESC-CMs within a broad range of concentrations. CeONZs exhibited protective effects on the cell viability of hESCs and hESC-CMs by alleviating excessive ROS-induced oxidative stress. Moreover, CeONZs protected hESC-CMs from doxorubicin (DOX)-induced cardiotoxicity and partially ameliorated the insults from DOX in neonatal rat cardiomyocytes (NRCMs). Furthermore, during hESCs culture, CeONZs were found to reduce ROS, decrease apoptosis, and enhance cell survival without affecting their self-renewal and differentiation potential.

CONCLUSIONS

CeONZs displayed good safety and biocompatibility, as well as enhanced the cell viability of hESCs and hESC-CMs by shielding them from oxidative damage. These promising results suggest that CeONZs may be crucial, as a safe nanoantioxidant, to potentially improve the therapeutic efficacy of CVDs and be incorporated into regenerative medicine.

Ultra-fast genetically encoded sensor for precise real-time monitoring of physiological and pathophysiological peroxide dynamics

Hydrogen Peroxide (H2O2) is a central oxidant in redox biology due to its pleiotropic role in physiology and pathology. However, real-time monitoring of H2O2 in living cells and tissues remains a challenge. We address this gap with the development of an optogenetic hydRogen perOxide Sensor (oROS), leveraging the bacterial peroxide binding domain OxyR. Previously engineered OxyR-based fluorescent peroxide sensors lack the necessary sensitivity and response speed for effective real-time monitoring. By structurally redesigning the fusion of Escherichia coli (E. coli) ecOxyR with a circularly permutated green fluorescent protein (cpGFP), we created a novel, green-fluorescent peroxide sensor oROS-G. oROS-G exhibits high sensitivity and fast on-and-off kinetics, ideal for monitoring intracellular H2O2 dynamics. We successfully tracked real-time transient and steady-state H2O2 levels in diverse biological systems, including human stem cell-derived neurons and cardiomyocytes, primary neurons and astrocytes, and mouse brain ex vivo and in vivo. These applications demonstrate oROS's capabilities to monitor H2O2 as a secondary response to pharmacologically induced oxidative stress and when adapting to varying metabolic stress. We showcased the increased oxidative stress in astrocytes via Aβ-putriscine-MAOB axis, highlighting the sensor's relevance in validating neurodegenerative disease models. Lastly, we demonstrated acute opioid-induced generation of H2O2 signal in vivo which highlights redox-based mechanisms of GPCR regulation. oROS is a versatile tool, offering a window into the dynamic landscape of H2O2 signaling. This advancement paves the way for a deeper understanding of redox physiology, with significant implications for understanding diseases associated with oxidative stress, such as cancer, neurodegenerative, and cardiovascular diseases.

Polyoxyethylene tallow amine and glyphosate exert different developmental toxicities on human pluripotent stem cells-derived heart organoid model

The early stage of heart development is highly susceptible to various environmental factors. While the use of animal models has aided in identifying numerous environmental risk factors, the variability between species and the low throughput limit their translational potential. Recently, a type of self-assembling cardiac structures, known as human heart organoids (hHOs), exhibits a remarkable biological consistency with human heart. However, the feasibility of hHOs for assessing cardiac developmental risk factors remains unexplored. Here, we focused on the cardiac developmental effects of core components of Glyphosate-based herbicides (GBHs), the most widely used herbicides, to evaluate the reliability of hHOs for the prediction of possible cardiogenesis toxicity. GBHs have been proven toxic to cardiac development based on multiple animal models, with the mechanism remaining unknown. We found that polyoxyethylene tallow amine (POEA), the most common surfactant in GBHs formulations, played a dominant role in GBHs' heart developmental toxicity. Though there were a few differences in transcriptive features, hHOs exposed to sole POEA and combined POEA and Glyphosate would suffer from both disruption of heart contraction and disturbance of commitment in cardiomyocyte isoforms. By contrast, Glyphosate only caused mild epicardial hyperplasia. This study not only sheds light on the toxic mechanism of GBHs, but also serves as a methodological demonstration, showcasing its effectiveness in recognizing and evaluating environmental risk factors, and deciphering toxic mechanisms.

Wnt dose escalation during the exit from pluripotency identifies tranilast as a regulator of cardiac mesoderm

Wnt signaling is a critical determinant of cell lineage development. This study used Wnt dose-dependent induction programs to gain insights into molecular regulation of stem cell differentiation. We performed single-cell RNA sequencing of hiPSCs responding to a dose escalation protocol with Wnt agonist CHIR-99021 during the exit from pluripotency to identify cell types and genetic activity driven by Wnt stimulation. Results of activated gene sets and cell types were used to build a multiple regression model that predicts the efficiency of cardiomyocyte differentiation. Cross-referencing Wnt-associated gene expression profiles to the Connectivity Map database, we identified the small-molecule drug, tranilast. We found that tranilast synergistically activates Wnt signaling to promote cardiac lineage differentiation, which we validate by in vitro analysis of hiPSC differentiation and in vivo analysis of developing quail embryos. Our study provides an integrated workflow that links experimental datasets, prediction models, and small-molecule databases to identify drug-like compounds that control cell differentiation.

Structural maturation of myofilaments in engineered 3D cardiac microtissues characterized using small angle x-ray scattering

Understanding the structural and functional development of human-induced pluripotent stem-cell-derived cardiomyocytes (hiPSC-CMs) is essential to engineering cardiac tissue that enables pharmaceutical testing, modeling diseases, and designing therapies. Here we use a method not commonly applied to biological materials, small angle x-ray scattering, to characterize the structural development of hiPSC-CMs within three-dimensional engineered tissues during their preliminary stages of maturation. An x-ray scattering experimental method enables the reliable characterization of the cardiomyocyte myofilament spacing with maturation time. The myofilament lattice spacing monotonically decreases as the tissue matures from its initial post-seeding state over the span of 10 days. Visualization of the spacing at a grid of positions in the tissue provides an approach to characterizing the maturation and organization of cardiomyocyte myofilaments and has the potential to help elucidate mechanisms of pathophysiology, and disease progression, thereby stimulating new biological hypotheses in stem cell engineering.

Cardiomyocyte-fibroblast interaction regulates ferroptosis and fibrosis after myocardial injury

Neonatal mouse hearts have transient renewal capacity, which is lost in juvenile and adult stages. In neonatal mouse hearts, myocardial infarction (MI) causes an initial loss of cardiomyocytes. However, it is unclear which type of regulated cell death (RCD) occurs in stressed cardiomyocytes. In the current studies, we induced MI in neonatal and juvenile mouse hearts and showed that ischemic cardiomyocytes primarily undergo ferroptosis, a non-apoptotic and iron-dependent form of RCD. We demonstrated that cardiac fibroblasts (CFs) protect cardiomyocytes from ferroptosis through paracrine effects and direct cell-cell interaction. CFs show strong resistance to ferroptosis due to high ferritin expression. The fibrogenic activity of CFs, typically considered detrimental to heart function, is negatively regulated by paired-like homeodomain 2 (Pitx2) signaling from cardiomyocytes. In addition, Pitx2 prevents ferroptosis in cardiomyocytes by regulating ferroptotic genes. Understanding the regulatory mechanisms of cardiomyocyte survival and death can identify potentially translatable therapeutic strategies for MI.

Graphene-integrated mesh electronics with converged multifunctionality for tracking multimodal excitation-contraction dynamics in cardiac microtissues

Cardiac microtissues provide a promising platform for disease modeling and developmental studies, which require the close monitoring of the multimodal excitation-contraction dynamics. However, no existing assessing tool can track these multimodal dynamics across the live tissue. We develop a tissue-like mesh bioelectronic system to track these multimodal dynamics. The mesh system has tissue-level softness and cell-level dimensions to enable stable embedment in the tissue. It is integrated with an array of graphene sensors, which uniquely converges both bioelectrical and biomechanical sensing functionalities in one device. The system achieves stable tracking of the excitation-contraction dynamics across the tissue and throughout the developmental process, offering comprehensive assessments for tissue maturation, drug effects, and disease modeling. It holds the promise to provide more accurate quantification of the functional, developmental, and pathophysiological states in cardiac tissues, creating an instrumental tool for improving tissue engineering and studies.

PIV-MyoMonitor: an accessible particle image velocimetry-based software tool for advanced contractility assessment of cardiac organoids

Induced pluripotent stem cell (iPSC)-derived cardiac organoids offer a versatile platform for personalized cardiac toxicity assessment, drug screening, disease modeling, and regenerative therapies. While previous image-based contractility analysis techniques allowed the assessment of contractility of two-dimensional cardiac models, they face limitations, including encountering high noise levels when applied to three-dimensional organoid models and requiring expensive equipment. Additionally, they offer fewer functional parameters compared to commercial software. To address these challenges, we developed an open-source, particle image velocimetry-based software (PIV-MyoMonitor) and demonstrated its capacity for accurate contractility analysis in both two- and three-dimensional cardiac models using standard lab equipment. Comparisons with four other open-source software programs highlighted the capability of PIV-MyoMonitor for more comprehensive quantitative analysis, providing 22 functional parameters and enhanced video outputs. We showcased its applicability in drug screening by characterizing the response of cardiac organoids to a known isotropic drug, isoprenaline. In sum, PIV-MyoMonitor enables reliable contractility assessment across various cardiac models without costly equipment or software. We believe this software will benefit a broader scientific community.

Cardiac progenitor cell therapy: mechanisms of action

Heart failure (HF) is an end-stage of many cardiac diseases and one of the main causes of death worldwide. The current management of this disease remains suboptimal. The adult mammalian heart was considered a post-mitotic organ. However, several reports suggest that it may possess modest regenerative potential. Adult cardiac progenitor cells (CPCs), the main players in the cardiac regeneration, constitute, as it may seem, a heterogenous group of cells, which remain quiescent in physiological conditions and become activated after an injury, contributing to cardiomyocytes renewal. They can mediate their beneficial effects through direct differentiation into cardiac cells and activation of resident stem cells but majorly do so through paracrine release of factors. CPCs can secrete cytokines, chemokines, and growth factors as well as exosomes, rich in proteins, lipids and non-coding RNAs, such as miRNAs and YRNAs, which contribute to reparation of myocardium by promoting angiogenesis, cardioprotection, cardiomyogenesis, anti-fibrotic activity, and by immune modulation. Preclinical studies assessing cardiac progenitor cells and cardiac progenitor cells-derived exosomes on damaged myocardium show that administration of cardiac progenitor cells-derived exosomes can mimic effects of cell transplantation. Exosomes may become new promising therapeutic strategy for heart regeneration nevertheless there are still several limitations as to their use in the clinic. Key questions regarding their dosage, safety, specificity, pharmacokinetics, pharmacodynamics and route of administration remain outstanding. There are still gaps in the knowledge on basic biology of exosomes and filling them will bring as closer to translation into clinic.

Differentiation of Pluripotent Stem Cells for Disease Modeling: Learning from Heart Development

Heart disease is a pressing public health problem and the leading cause of death worldwide. The heart is the first organ to gain function during embryogenesis in mammals. Heart development involves cell determination, expansion, migration, and crosstalk, which are orchestrated by numerous signaling pathways, such as the Wnt, TGF-β, IGF, and Retinoic acid signaling pathways. Human-induced pluripotent stem cell-based platforms are emerging as promising approaches for modeling heart disease in vitro. Understanding the signaling pathways that are essential for cardiac development has shed light on the molecular mechanisms of congenital heart defects and postnatal heart diseases, significantly advancing stem cell-based platforms to model heart diseases. This review summarizes signaling pathways that are crucial for heart development and discusses how these findings improve the strategies for modeling human heart disease in vitro.

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

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

Automated fabrication of a scalable heart-on-a-chip device by 3D printing of thermoplastic elastomer nanocomposite and hot embossing

The successful translation of organ-on-a-chip devices requires the development of an automated workflow for device fabrication, which is challenged by the need for precise deposition of multiple classes of materials in micro-meter scaled configurations. Many current heart-on-a-chip devices are produced manually, requiring the expertise and dexterity of skilled operators. Here, we devised an automated and scalable fabrication method to engineer a Biowire II multiwell platform to generate human iPSC-derived cardiac tissues. This high-throughput heart-on-a-chip platform incorporated fluorescent nanocomposite microwires as force sensors, produced from quantum dots and thermoplastic elastomer, and 3D printed on top of a polystyrene tissue culture base patterned by hot embossing. An array of built-in carbon electrodes was embedded in a single step into the base, flanking the microwells on both sides. The facile and rapid 3D printing approach efficiently and seamlessly scaled up the Biowire II system from an 8-well chip to a 24-well and a 96-well format, resulting in an increase of platform fabrication efficiency by 17,5000-69,000% per well. The device's compatibility with long-term electrical stimulation in each well facilitated the targeted generation of mature human iPSC-derived cardiac tissues, evident through a positive force-frequency relationship, post-rest potentiation, and well-aligned sarcomeric apparatus. This system's ease of use and its capacity to gauge drug responses in matured cardiac tissue make it a powerful and reliable platform for rapid preclinical drug screening and development.

Assessing Cardiac Contractility From Single Molecules to Whole Hearts

Fundamentally, the heart needs to generate sufficient force and power output to dynamically meet the needs of the body. Cardiomyocytes contain specialized structures referred to as sarcomeres that power and regulate contraction. Disruption of sarcomeric function or regulation impairs contractility and leads to cardiomyopathies and heart failure. Basic, translational, and clinical studies have adapted numerous methods to assess cardiac contraction in a variety of pathophysiological contexts. These tools measure aspects of cardiac contraction at different scales ranging from single molecules to whole organisms. Moreover, these studies have revealed new pathogenic mechanisms of heart disease leading to the development of novel therapies targeting contractility. In this review, the authors explore the breadth of tools available for studying cardiac contractile function across scales, discuss their strengths and limitations, highlight new insights into cardiac physiology and pathophysiology, and describe how these insights can be harnessed for therapeutic candidate development and translational.

Functional dissection of human cardiac enhancers and noncoding de novo variants in congenital heart disease

Rare coding mutations cause ∼45% of congenital heart disease (CHD). Noncoding mutations that perturb cis-regulatory elements (CREs) likely contribute to the remaining cases, but their identification has been problematic. Using a lentiviral massively parallel reporter assay (lentiMPRA) in human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we functionally evaluated 6,590 noncoding de novo variants (ncDNVs) prioritized from the whole-genome sequencing of 750 CHD trios. A total of 403 ncDNVs substantially affected cardiac CRE activity. A majority increased enhancer activity, often at regions with undetectable reference sequence activity. Of ten DNVs tested by introduction into their native genomic context, four altered the expression of neighboring genes and iPSC-CM transcriptional state. To prioritize future DNVs for functional testing, we used the MPRA data to develop a regression model, EpiCard. Analysis of an independent CHD cohort by EpiCard found enrichment of DNVs. Together, we developed a scalable system to measure the effect of ncDNVs on CRE activity and deployed it to systematically assess the contribution of ncDNVs to CHD.

Hapln1 promotes dedifferentiation and proliferation of iPSC-derived cardiomyocytes by promoting versican-based GDF11 trapping

Hyaluronan and proteoglycan link protein 1 (Hapln1) supports active cardiomyogenesis in zebrafish hearts, but its regulation in mammal cardiomyocytes is unclear. This study aimed to explore the potential regulation of Hapln1 in the dedifferentiation and proliferation of cardiomyocytes and its therapeutic value in myocardial infarction with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) and an adult mouse model of myocardial infarction. HiPSC-CMs and adult mice with myocardial infarction were used as in vitro and in vivo models, respectively. Previous single-cell RNA sequencing data were retrieved for bioinformatic exploration. The results showed that recombinant human Hapln1 (rhHapln1) promotes the proliferation of hiPSC-CMs in a dose-dependent manner. As a physical binding protein of Hapln1, versican interacted with Nodal growth differentiation factor (NODAL) and growth differentiation factor 11 (GDF11). GDF11, but not NODAL, was expressed by hiPSC-CMs. GDF11 expression was unaffected by rhHapln1 treatment. However, this molecule was required for rhHapln1-mediated activation of the transforming growth factor (TGF)-β/Drosophila mothers against decapentaplegic protein (SMAD)2/3 signaling in hiPSC-CMs, which stimulates cell dedifferentiation and proliferation. Recombinant mouse Hapln1 (rmHapln1) could induce cardiac regeneration in the adult mouse model of myocardial infarction. In addition, rmHapln1 induced hiPSC-CM proliferation. In conclusion, Hapln1 can stimulate the dedifferentiation and proliferation of iPSC-derived cardiomyocytes by promoting versican-based GDF11 trapping and subsequent activation of the TGF-β/SMAD2/3 signaling pathway. Hapln1 might be an effective hiPSC-CM dedifferentiation and proliferation agent and a potential reagent for repairing damaged hearts.

Multiplex Single-Cell Bioprinting for Engineering of Heterogeneous Tissue Constructs with Subcellular Spatial Resolution

Tissue development, function, and disease are largely driven by the spatial organization of individual cells and their cell-cell interactions. Precision engineered tissues with single-cell spatial resolution, therefore, have tremendous potential for next generation disease models, drug discovery, and regenerative therapeutics. Despite significant advancements in biofabrication approaches to improve feature resolution, strategies to fabricate tissues with the exact same organization of individual cells in their native cellular microenvironment have remained virtually non-existent to date. Here we report a method to spatially pattern single cells with up to eight cell phenotypes and subcellular spatial precision. As proof-of-concept we first demonstrate the ability to systematically assess the influence of cellular microenvironments on cell behavior by controllably altering the spatial arrangement of cell types in bioprinted precision cell-cell interaction arrays. We then demonstrate, for the first time, the ability to produce high-fidelity replicas of a patient's annotated cancer biopsy with subcellular resolution. The ability to replicate native cellular microenvironments marks a significant advancement for precision biofabricated in-vitro models, where heterogenous tissues can be engineered with single-cell spatial precision to advance our understanding of complex biological systems in a controlled and systematic manner.

Vascularised cardiac spheroids-on-a-chip for testing the toxicity of therapeutics

Microfabricated organ-on-a-chips are rapidly becoming the gold standard for the testing of safety and efficacy of therapeutics. A broad range of designs has emerged, but recreating microvascularised tissue models remains difficult in many cases. This is particularly relevant to mimic the systemic delivery of therapeutics, to capture the complex multi-step processes associated with trans-endothelial transport or diffusion, uptake by targeted tissues and associated metabolic response. In this report, we describe the formation of microvascularised cardiac spheroids embedded in microfluidic chips. Different protocols used for embedding spheroids within vascularised multi-compartment microfluidic chips were investigated first to identify the importance of the spheroid processing, and co-culture with pericytes on the integration of the spheroid within the microvascular networks formed. The architecture of the resulting models, the expression of cardiac and endothelial markers and the perfusion of the system was then investigated. This confirmed the excellent stability of the vascular networks formed, as well as the persistent expression of cardiomyocyte markers such as cTNT and the assembly of striated F-actin, myosin and α-actinin cytoskeletal networks typically associated with contractility and beating. The ability to retain beating over prolonged periods of time was quantified, over 25 days, demonstrating not only perfusability but also functional performance of the tissue model. Finally, as a proof-of-concept of therapeutic testing, the toxicity of one therapeutic associated with cardiac disfunction was evaluated, identifying differences between direct in vitro testing on suspended spheroids and vascularised models.

HAND factors regulate cardiac lineage commitment and differentiation from human pluripotent stem cells

BACKGROUND

Transcription factors HAND1 and HAND2 (HAND1/2) play significant roles in cardiac organogenesis. Abnormal expression and deficiency of HAND1/2 result in severe cardiac defects. However, the function and mechanism of HAND1/2 in regulating human early cardiac lineage commitment and differentiation are still unclear.

METHODS

With NKX2.5eGFP H9 human embryonic stem cells (hESCs), we established single and double knockout cell lines for HAND1 and HAND2, respectively, whose cardiomyocyte differentiation efficiency could be monitored by assessing NKX2.5-eGFP+ cells with flow cytometry. The expression of specific markers for heart fields and cardiomyocyte subtypes was examined by quantitative PCR, western blot and immunofluorescence staining. Microelectrode array and whole-cell patch clamp were performed to determine the electrophysiological characteristics of differentiated cardiomyocytes. The transcriptomic changes of HAND knockout cells were revealed by RNA sequencing. The HAND1/2 target genes were identified and validated experimentally by integrating with HAND1/2 chromatin immunoprecipitation sequencing data.

RESULTS

Either HAND1 or HAND2 knockout did not affect the cardiomyocyte differentiation kinetics, whereas depletion of HAND1/2 resulted in delayed differentiation onset. HAND1 knockout biased cardiac mesoderm toward second heart field progenitors at the expense of first heart field progenitors, leading to increased expression of atrial and outflow tract cardiomyocyte markers, which was further confirmed by the appearance of atrial-like action potentials. By contrast, HAND2 knockout cardiomyocytes had reduced expression of atrial cardiomyocyte markers and displayed ventricular-like action potentials. HAND1/2-deficient hESCs were more inclined to second heart field lineage and its derived cardiomyocytes with atrial-like action potentials than HAND1 single knockout during differentiation. Further mechanistic investigations suggested TBX5 as one of the downstream targets of HAND1/2, whose overexpression partially restored the abnormal cardiomyocyte differentiation in HAND1/2-deficient hESCs.

CONCLUSIONS

HAND1/2 have specific and redundant roles in cardiac lineage commitment and differentiation. These findings not only reveal the essential function of HAND1/2 in cardiac organogenesis, but also provide important information on the pathogenesis of HAND1/2 deficiency-related congenital heart diseases, which could potentially lead to new therapeutic strategies.