Expansion and patterning of cardiovascular progenitors derived from human pluripotent stem cells

Mending a broken heart: current strategies and limitations of cell-based therapy

The versatility of pluripotent stem cells, attributable to their unlimited self-renewal capacity and plasticity, has sparked a considerable interest for potential application in regenerative medicine. Over the past decade, the concept of replenishing the lost cardiomyocytes, the crux of the matter in ischemic heart disease, with pluripotent stem cell-derived cardiomyocytes (PSC-CM) has been validated with promising pre-clinical results. Nevertheless, clinical translation was hemmed in by limitations such as immature cardiac properties, long-term engraftment, graft-associated arrhythmias, immunogenicity, and risk of tumorigenicity. The continuous progress of stem cell-based cardiac therapy, incorporated with tissue engineering strategies and delivery of cardio-protective exosomes, provides an optimistic outlook on the development of curative treatment for heart failure. This review provides an overview and current status of stem cell-based therapy for heart regeneration, with particular focus on the use of PSC-CM. In addition, we also highlight the associated challenges in clinical application and discuss the potential strategies in developing successful cardiac-regenerative therapy.

Stem cell therapy of myocardial infarction: a promising opportunity in bioengineering

Myocardial infarction (MI) is a life-threatening disease resulting from irreversible death of cardiomyocytes (CMs) and weakening of the heart blood-pumping function. Stem cell-based therapies have been studied for MI treatment over the last two decades with promising outcome. In this review, we critically summarize the past work in this field to elucidate the advantages and disadvantages of treating MI using pluripotent stem cells (PSCs) including both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), adult stem cells, and cardiac progenitor cells. The main advantage of the latter is their cytokine production capability to modulate immune responses and control the progression of healing. However, human adult stem cells have very limited (if not 'no') capacity to differentiate into functional CMs in vitro or in vivo. In contrast, PSCs can be differentiated into functional CMs although the protocols for the cardiac differentiation of PSCs are mainly for adherent cells under 2D culture. Derivation of PSC-CMs in 3D, allowing for large-scale production of CMs via modulation of the Wnt/β-catenin signal pathway with defined chemicals and medium, may be desired for clinical translation. Furthermore, the technology of purification and maturation of the PSC-CMs may need further improvements to eliminate teratoma formation after in vivo implantation of the PSC-CMs for treating MI. In addition, in vitro derived PSC-CMs may have mechanical and electrical mismatch with the patient's cardiac tissue, which causes arrhythmia. This supports the use of PSC-derived cells committed to cardiac lineage without beating for implantation to treat MI. In this case, the PSC derived cells may utilize the mechanical, electrical, and chemical cues in the heart to further differentiate into mature/functional CMs in situ. Another major challenge facing stem cell therapy of MI is the low retention/survival of stem cells or their derivatives (e.g., PSC-CMs) in the heart for MI treatment after injection in vivo. This may be resolved by using biomaterials to engineer stem cells for reduced immunogenicity, immobilization of the cells in the heart, and increased integration with the host cardiac tissue. Biomaterials have also been applied in the derivation of CMs in vitro to increase the efficiency and maturation of differentiation. Collectively, a lot has been learned from the past failure of simply injecting intact stem cells or their derivatives in vivo for treating MI, and bioengineering stem cells with biomaterials is expected to be a valuable strategy for advancing stem cell therapy towards its widespread application for treating MI in the clinic.

Towards chamber specific heart-on-a-chip for drug testing applications

Modeling of human organs has long been a task for scientists in order to lower the costs of therapeutic development and understand the pathological onset of human disease. For decades, despite marked differences in genetics and etiology, animal models remained the norm for drug discovery and disease modeling. Innovative biofabrication techniques have facilitated the development of organ-on-a-chip technology that has great potential to complement conventional animal models. However, human organ as a whole, more specifically the human heart, is difficult to regenerate in vitro, in terms of its chamber specific orientation and its electrical functional complexity. Recent progress with the development of induced pluripotent stem cell differentiation protocols, made recapitulating the complexity of the human heart possible through the generation of cells representative of atrial & ventricular tissue, the sinoatrial node, atrioventricular node and Purkinje fibers. Current heart-on-a-chip approaches incorporate biological, electrical, mechanical, and topographical cues to facilitate tissue maturation, therefore improving the predictive power for the chamber-specific therapeutic effects targeting adult human. In this review, we will give a summary of current advances in heart-on-a-chip technology and provide a comprehensive outlook on the challenges involved in the development of human physiologically relevant heart-on-a-chip.

Cardiac progenitors and paracrine mediators in cardiogenesis and heart regeneration

The mammalian hearts have the least regenerative capabilities among tissues and organs. As such, heart regeneration has been and continues to be the ultimate goal in the treatment against acquired and congenital heart diseases. Uncovering such a long-awaited therapy is still extremely challenging in the current settings. On the other hand, this desperate need for effective heart regeneration has developed various forms of modern biotechnologies in recent years. These involve the transplantation of pluripotent stem cell-derived cardiac progenitors or cardiomyocytes generated in vitro and novel biochemical molecules along with tissue engineering platforms. Such newly generated technologies and approaches have been shown to effectively proliferate cardiomyocytes and promote heart repair in the diseased settings, albeit mainly preclinically. These novel tools and medicines give somehow credence to breaking down the barriers associated with re-building heart muscle. However, in order to maximize efficacy and achieve better clinical outcomes through these cell-based and/or cell-free therapies, it is crucial to understand more deeply the developmental cellular hierarchies/paths and molecular mechanisms in normal or pathological cardiogenesis. Indeed, the morphogenetic process of mammalian cardiac development is highly complex and spatiotemporally regulated by various types of cardiac progenitors and their paracrine mediators. Here we discuss the most recent knowledge and findings in cardiac progenitor cell biology and the major cardiogenic paracrine mediators in the settings of cardiogenesis, congenital heart disease, and heart regeneration.

Spatiotemporal Control of Morphogen Delivery to Pattern Stem Cell Differentiation in Three-Dimensional Hydrogels

Morphogens are biological molecules that alter cellular identity and behavior across both space and time. During embryonic development, morphogen spatial localization can be confined to small volumes in a single tissue or permeate throughout an entire organism, and the temporal effects of morphogens can range from fractions of a second to several days. In most cases, morphogens are presented as a gradient to adjacent cells within tissues to pattern cell fate. As such, to appropriately model development and build representative multicellular architectures in vitro, it is vital to recapitulate these gradients during stem cell differentiation. However, the ability to control morphogen presentation within in vitro systems remains challenging. Here, we describe an innovative platform using channels patterned within thick, three-dimensional hydrogels that deliver multiple morphogens to embedded cells, thereby demonstrating exquisite control over both spatial and temporal variations in morphogen presentation. This generalizable approach should have broad utility for researchers interested in patterning in vitro tissue structures. © 2019 by John Wiley & Sons, Inc.

Cardiac Progenitor Cells from Stem Cells: Learning from Genetics and Biomaterials

Cardiac Progenitor Cells (CPCs) show great potential as a cell resource for restoring cardiac function in patients affected by heart disease or heart failure. CPCs are proliferative and committed to cardiac fate, capable of generating cells of all the cardiac lineages. These cells offer a significant shift in paradigm over the use of human induced pluripotent stem cell (iPSC)-derived cardiomyocytes owing to the latter’s inability to recapitulate mature features of a native myocardium, limiting their translational applications. The iPSCs and direct reprogramming of somatic cells have been attempted to produce CPCs and, in this process, a variety of chemical and/or genetic factors have been evaluated for their ability to generate, expand, and maintain CPCs in vitro. However, the precise stoichiometry and spatiotemporal activity of these factors and the genetic interplay during embryonic CPC development remain challenging to reproduce in culture, in terms of efficiency, numbers, and translational potential. Recent advances in biomaterials to mimic the native cardiac microenvironment have shown promise to influence CPC regenerative functions, while being capable of integrating with host tissue. This review highlights recent developments and limitations in the generation and use of CPCs from stem cells, and the trends that influence the direction of research to promote better application of CPCs.

Expression of miRNAs from the Imprinted DLK1/DIO3 Locus Signals the Osteogenic Potential of Human Pluripotent Stem Cells

Substantial variations in differentiation properties have been reported among human pluripotent cell lines (hPSC), which could affect their utility and clinical safety. We characterized the variable osteogenic capacity observed between different human pluripotent stem cell lines. By focusing on the miRNA expression profile, we demonstrated that the osteogenic differentiation propensity of human pluripotent stem cell lines could be associated with the methylation status and the expression of miRNAs from the imprinted DLK1/DIO3 locus. More specifically, quantitative analysis of the expression of six different miRNAs of that locus prospectively identified human embryonic stem cells and human-induced pluripotent stem cells with differential osteogenic differentiation capacities. At the molecular and functional levels, we showed that these miRNAs modulated the expression of the activin receptor type 2B and the downstream signal transduction, which impacted osteogenesis. In conclusion, miRNAs of the imprinted DLK1/DIO3 locus appear to have both a predictive value and a functional impact in determining the osteogenic fate of human pluripotent stem cells.

Cardiac differentiation of pluripotent stem cells and implications for modeling the heart in health and disease

Cellular models comprising cardiac cell types derived from human pluripotent stem cells are valuable for studying heart development and disease. We discuss transcriptional differences that define cellular identity in the heart, current methods for generating different cardiomyocyte subtypes, and implications for disease modeling, tissue engineering, and regenerative medicine.

Unlocking Personalized Biomedicine and Drug Discovery with Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes: Fit for Purpose or Forever Elusive?

In recent decades, drug development costs have increased by approximately a hundredfold, and yet about 1 in 7 licensed drugs are withdrawn from the market, often due to cardiotoxicity. This review considers whether technologies using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) could complement existing assays to improve discovery and safety while reducing socioeconomic costs and assisting with regulatory guidelines on cardiac safety assessments. We draw on lessons from our own work to suggest a panel of 12 drugs that will be useful in testing the suitability of hiPSC-CM platforms to evaluate contractility. We review issues, including maturity versus complexity, consistency, quality, and cost, while considering a potential need to incorporate auxiliary approaches to compensate for limitations in hiPSC-CM technology. We give examples on how coupling hiPSC-CM technologies with Cas9/CRISPR genome engineering is starting to be used to personalize diagnosis, stratify risk, provide mechanistic insights, and identify new pathogenic variants for cardiovascular disease.

Chromatin compartment dynamics in a haploinsufficient model of cardiac laminopathy

Mutations in A-type nuclear lamins cause dilated cardiomyopathy, which is postulated to result from dysregulated gene expression due to changes in chromatin organization into active and inactive compartments. To test this, we performed genome-wide chromosome conformation analyses in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) with a haploinsufficient mutation for lamin A/C. Compared with gene-corrected cells, mutant hiPSC-CMs have marked electrophysiological and contractile alterations, with modest gene expression changes. While large-scale changes in chromosomal topology are evident, differences in chromatin compartmentalization are limited to a few hotspots that escape segregation to the nuclear lamina and inactivation during cardiogenesis. These regions exhibit up-regulation of multiple noncardiac genes including CACNA1A, encoding for neuronal P/Q-type calcium channels. Pharmacological inhibition of the resulting current partially mitigates the electrical alterations. However, chromatin compartment changes do not explain most gene expression alterations in mutant hiPSC-CMs. Thus, global errors in chromosomal compartmentation are not the primary pathogenic mechanism in heart failure due to lamin A/C haploinsufficiency.

Transcriptional regulation of the cardiac conduction system

The rate and rhythm of heart muscle contractions are coordinated by the cardiac conduction system (CCS), a generic term for a collection of different specialized muscular tissues within the heart. The CCS components initiate the electrical impulse at the sinoatrial node, propagate it from atria to ventricles via the atrioventricular node and bundle branches, and distribute it to the ventricular muscle mass via the Purkinje fibre network. The CCS thereby controls the rate and rhythm of alternating contractions of the atria and ventricles. CCS function is well conserved across vertebrates from fish to mammals, although particular specialized aspects of CCS function are found only in endotherms (mammals and birds). The development and homeostasis of the CCS involves transcriptional and regulatory networks that act in an embryonic-stage-dependent, tissue-dependent, and dose-dependent manner. This Review describes emerging data from animal studies, stem cell models, and genome-wide association studies that have provided novel insights into the transcriptional networks underlying CCS formation and function. How these insights can be applied to develop disease models and therapies is also discussed.

Canonical Wnt5b Signaling Directs Outlying Nkx2.5+ Mesoderm into Pacemaker Cardiomyocytes

Pacemaker cardiomyocytes that create the sinoatrial node are essential for the initiation and maintenance of proper heart rhythm. However, illuminating developmental cues that direct their differentiation has remained particularly challenging due to the unclear cellular origins of these specialized cardiomyocytes. By discovering the origins of pacemaker cardiomyocytes, we reveal an evolutionarily conserved Wnt signaling mechanism that coordinates gene regulatory changes directing mesoderm cell fate decisions, which lead to the differentiation of pacemaker cardiomyocytes. We show that in zebrafish, pacemaker cardiomyocytes derive from a subset of Nkx2.5+ mesoderm that responds to canonical Wnt5b signaling to initiate the cardiac pacemaker program, including activation of pacemaker cell differentiation transcription factors Isl1 and Tbx18 and silencing of Nkx2.5. Moreover, applying these developmental findings to human pluripotent stem cells (hPSCs) notably results in the creation of hPSC-pacemaker cardiomyocytes, which successfully pace three-dimensional bioprinted hPSC-cardiomyocytes, thus providing potential strategies for biological cardiac pacemaker therapy.

Identification of Cardiomyocyte-Fated Progenitors from Human-Induced Pluripotent Stem Cells Marked with CD82

Here, we find that human-induced pluripotent stem cell (hiPSC)-derived cardiomyocyte (CM)-fated progenitors (CFPs) that express a tetraspanin family glycoprotein, CD82, almost exclusively differentiate into CMs both in vitro and in vivo. CD82 is transiently expressed in late-stage mesoderm cells during hiPSC differentiation. Purified CD82⁺ cells gave rise to CMs under nonspecific in vitro culture conditions with serum, as well as in vivo after transplantation to the subrenal space or injured hearts in mice, indicating that CD82 successfully marks CFPs. CD82 overexpression in mesoderm cells as well as in undifferentiated hiPSCs increased the secretion of exosomes containing β-catenin and reduced nuclear β-catenin protein, suggesting that CD82 is involved in fated restriction to CMs through Wnt signaling inhibition. This study may contribute to the understanding of CM differentiation mechanisms and to cardiac regeneration strategies.

Genetic variation in GNB5 causes bradycardia by augmenting the cholinergic response via increased acetylcholine-activated potassium current (I K,ACh)

Mutations in GNB5, encoding the G-protein β5 subunit (Gβ5), have recently been linked to a multisystem disorder that includes severe bradycardia. Here, we investigated the mechanism underlying bradycardia caused by the recessive p.S81L Gβ5 variant. Using CRISPR/Cas9-based targeting, we generated an isogenic series of human induced pluripotent stem cell (hiPSC) lines that were either wild type, heterozygous or homozygous for the GNB5 p.S81L variant. These were differentiated into cardiomyocytes (hiPSC-CMs) that robustly expressed the acetylcholine-activated potassium channel [I(KACh); also known as I_K,ACh]. Baseline electrophysiological properties of the lines did not differ. Upon application of carbachol (CCh), homozygous p.S81L hiPSC-CMs displayed an increased acetylcholine-activated potassium current (I _K,ACh) density and a more pronounced decrease of spontaneous activity as compared to wild-type and heterozygous p.S81L hiPSC-CMs, explaining the bradycardia in homozygous carriers. Application of the specific I(KACh) blocker XEN-R0703 resulted in near-complete reversal of the phenotype. Our results provide mechanistic insights and proof of principle for potential therapy in patients carrying GNB5 mutations.This article has an associated First Person interview with the first author of the paper.

Transcriptomic analysis of 3D Cardiac Differentiation of Human Induced Pluripotent Stem Cells Reveals Faster Cardiomyocyte Maturation Compared to 2D Culture

Human induced pluripotent stem cells (hiPSCs) represent an almost limitless source of cells for disease modelling and drug screening applications. Here we established an efficient and robust 3D platform for cardiomyocyte (CMs) production from hiPSCs, solely through small-molecule-based temporal modulation of the Wnt signalling, which generates more than 90% cTNT⁺ cells. The impact of performing the differentiation process in 3D conditions as compared to a 2D culture system, was characterized by transcriptomic analysis by using data collected from sequential stages of 2D and 3D culture. We highlight that performing an initial period of hiPSC aggregation before cardiac differentiation primed hiPSCs towards an earlier mesendoderm lineage differentiation, via TGF-β/Nodal signaling stabilization. Importantly, it was also found that CMs in the 3D microenvironment mature earlier and show an improved communication system, which we suggested to be responsible for a higher structural and functional maturation of 3D cardiac aggregates.

Comprehensive proteogenomic analysis of human embryonic and induced pluripotent stem cells

Although the concepts of somatic cell reprogramming and human‐induced pluripotent stem cells (hiPSCs) generation have undergone several analyses to validate the usefulness of these cells in research and clinic, it remains still controversial whether the hiPSCs are equivalent to human embryonic stem cells (hESCs), pointing to the need of further characterization for a more comprehensive understanding of pluripotency. Most of the experimental evidence comes from the transcriptome analysis, while a little is available on protein data, and even less is known about the post‐translational modifications. Here, we report a combined strategy of mass spectrometry and gene expression profiling for proteogenomic analysis of reprogrammed and embryonic stem cells. The data obtained through this integrated, multi‐“omics” approach indicate that a small, but still significant, number of distinct pathways is enriched in reprogrammed versus embryonic stem cells, supporting the view that pluripotency is an extremely complex, multifaceted phenomenon, with peculiarities that are characteristic of each cell type.

Upstairs, Downstairs: Atrial and Ventricular Cardiac Myocytes from Human Pluripotent Stem Cells

Cardiomyocyte creation by human pluripotent stem cells (hPSCs) has generated opportunities for heart repair, disease modeling, and drug development. In this issue of Cell Stem Cell,Lee et al. (2017) report prospective markers of atrial versus ventricular myocyte formation from hPSCs and their use in directed differentiation of cardiac sub-lineages.

Non-contact monitoring of extra-cellular field potentials with a multi-electrode array

Developing tools to enable non-invasive, high-throughput electrophysiology measurements of large functional-networks of electrogenic cells used as in vitro disease models for the heart and brain remains an outstanding challenge for preclinical drug discovery, where failures are costly and can prove to be fatal during clinical trials. Here we demonstrate, for the first time, that it is possible to perform non-contact monitoring of extra-cellular field potentials with a multi-electrode array (MEA). To do this preliminary demonstration we built a prototype with a custom mechanical stage to micro-position cells grown on conventional glass coverslips over the recording surface of a MEA sensor. The prototype can monitor extra-cellular fields generated by multi-cellular networks in a non-contact configuration, enabling a single MEA sensor to probe different cultures in succession, without fouling or degrading its sensitive electronic surface. This first demonstration with easy to culture cardiomyocyte cells and a prototype device points to the exciting possibility for instrument development leading to more efficient and cost-effective drug screening paradigms for cardiovascular and neurological diseases.

Spatiotemporal control and modeling of morphogen delivery to induce gradient patterning of stem cell differentiation using fluidic channels

The process of cell differentiation in a developing embryo is influenced by numerous factors, including various biological molecules whose presentation varies dramatically over space and time. These morphogens regulate cell fate based on concentration profiles, thus creating discrete populations of cells and ultimately generating large, complex tissues and organs. Recently, several in vitro platforms have attempted to recapitulate the complex presentation of extrinsic signals found in nature. However, it has been a challenge to design versatile platforms that can dynamically control morphogen gradients over extended periods of time. To address some of these issues, we introduce a platform using channels patterned in hydrogels to deliver multiple morphogens to cells in a 3D scaffold, thus creating a spectrum of cell phenotypes based on the resultant morphogen gradients. The diffusion coefficient of a common small molecule morphogen, retinoic acid (RA), was measured within our hydrogel platform using Raman spectroscopy and its diffusion in our platform's geometry was modeled using finite element analysis. The predictive model of spatial gradients was validated in a cell-free hydrogel, and temporal control of morphogen gradients was then demonstrated using a reporter cell line that expresses green fluorescent protein in the presence of RA. Finally, the utility of this approach for regulating cell phenotype was demonstrated by generating opposing morphogen gradients to create a spectrum of mesenchymal stem cell differentiation states.

A Human iPSC Double-Reporter System Enables Purification of Cardiac Lineage Subpopulations with Distinct Function and Drug Response Profiles

The diversity of cardiac lineages contributes to the heterogeneity of human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs). Here, we report the generation of a hiPSC TBX5^Clover2 and NKX2-5^TagRFP double reporter to delineate cardiac lineages and isolate lineage-specific subpopulations. Molecular analyses reveal that four different subpopulations can be isolated based on the differential expression of TBX5 and NKX2-5, TBX5+NKX2-5+, TBX5+NKX2-5-, TBX5-NKX2-5+, and TBX5-NKX2-5-, mimicking the first heart field, epicardial, second heart field, and endothelial lineages, respectively. Genetic and functional characterization indicates that each subpopulation differentiates into specific cardiac cells. We further identify CORIN as a cell-surface marker for isolating the TBX5+NKX2-5+ subpopulation and demonstrate the use of lineage-specific CMs for precise drug testing. We anticipate that this tool will facilitate the investigation of cardiac lineage specification and isolation of specific cardiac subpopulations for drug screening, tissue engineering, and disease modeling.

Amniotic membrane as novel scaffold for human iPSC-derived cardiomyogenesis

Recent approaches of using decellularized organ matrices for cardiac tissue engineering prompted us to culture human-induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (CMs) on the human amniotic membrane (hAM). Since hAM has been used lately to patch diseased hearts in patients and has shown anti-inflammatory and anti-fibrotic benefits, it qualifies as a cardiac compatible and clinically relevant heart tissue scaffold. The aim of this study was to test the ability of the hAM to support attachment, differentiation, and maturation of hiPSC-derived CMs in vitro. hAMs were prepared from term placenta. An in-house generated hiPSC line was used for CM derivation. hiPSC-derived cardiac progenitors were cultured on the surface of cryopreserved hAMs and in the presence of cytokines promoting cardiac differentiation. CMs grown on hAM and popular basement membrane matrix (BMM) Matrigel™ were compared for the following aspects of cardiac development: the morphology of cardiomyocytes with respect to shape and cellular alignments, levels of cardiac-related gene transcript expression, functionality in terms of spontaneous calcium fluxes and mitochondrial densities and distributions. hAM is biocompatible with hiPSC-derived CMs. hAM increased cardiac transcription regulator and myofibril protein transcript expression, accelerated intracellular calcium transients, and enhanced cellular mitochondrial complexity of its cardiomyocytes in comparison to cardiomyocytes differentiated on Matrigel™. Our data suggests that hAM supports differentiation and improves cardiomyogenesis in comparison to Matrigel™. hAMs are natural, easily and largely available. The method of preparing hAM cardiac sheets described here is simple with potential for clinical transplantation. Graphical abstract A An outline of the differentiation protocol with stage-specific growth factors and culture media used. B Cell fates from pluripotent stem cells to cardiomyocytes during differentiation on the amniotic membrane. C-FPhotomicrographs of cells at various stages of differentiation. Scale bars represent 100 μm.

Attenuation of doxorubicin-induced cardiotoxicity in a human in vitro cardiac model by the induction of the NRF-2 pathway

Dose-dependent cardiotoxicity is the leading adverse reaction seen in cancer patients treated with doxorubicin. Currently, dexrazoxane is the only approved drug that can partially protect against this toxicity in patients, however, its administration is restricted to those patients receiving a high cumulative dose of anthracyclines. Investigations into the mechanisms of cardiotoxicity and efforts to improve cardioprotective strategies have been hindered by the limited availability of a phenotypically relevant in vitro adult human cardiac model system. Here, we adapted a readily reproducible, functional 3D human multi-cell type cardiac system to emulate patient responses seen with doxorubicin and dexrazoxane. We show that administration of two NRF2 gene inducers namely the semi-synthetic triterpenoid Bardoxolone methyl, and the isothiocyanate sulfurophane, result in cardioprotection against doxorubicin toxicity comparable to dexrazoxane as evidenced by an increase in cell viability and a decrease in the production of reactive oxygen species. We further show a synergistic attenuation of cardiotoxicity when the NRF2 inducers and dexrazoxane are used in tandem. Taken together, our data indicate that the 3D spheroid is a suitable model to investigate drug induced cardiotoxicity and we reveal an essential role of the NRF2 pathway in cardioprotection providing a novel pharmacological mechanism and intervention route towards the alleviation of doxorubicin-induced toxicity.

Regenerating the field of cardiovascular cell therapy

The retraction of >30 falsified studies by Anversa et al. has had a disheartening impact on the cardiac cell therapeutics field. The premise of heart muscle regeneration by the transdifferentiation of bone marrow cells or putative adult resident cardiac progenitors has been largely disproven. Over the past 18 years, a generation of physicians and scientists has lost years chasing these studies, and patients have been placed at risk with little scientific grounding. Funding agencies invested hundreds of millions of dollars in irreproducible work, and both academic institutions and the scientific community ignored troubling signals over a decade of questionable work. Our collective retrospective analysis identifies preventable problems at the level of the editorial and peer-review process, funding agencies and academic institutions. This Perspective provides a chronology of the forces that led to this scientific debacle, integrating direct knowledge of the process. We suggest a science-driven path forward that includes multiple novel approaches to the problem of heart muscle regeneration.

Cell population balance of cardiovascular spheroids derived from human induced pluripotent stem cells

Stem cell-derived cardiomyocytes and vascular cells can be used for a variety of applications such as studying human heart development and modelling human disease in culture. In particular, protocols based on modulation of Wnt signaling were able to produce high quality of cardiomyocytes or vascular cells from human pluripotent stem cells (hPSCs). However, the mechanism behind the development of 3D cardiovascular spheroids into either vascular or cardiac cells has not been well explored. Hippo/Yes-associated protein (YAP) signaling plays important roles in the regulation of organogenesis, but its impact on cardiovascular differentiation has been less evaluated. In this study, the effects of seeding density and a change in YAP signaling on 3D cardiovascular spheroids patterning from hPSCs were evaluated. Compared to 2D culture, 3D cardiovascular spheroids exhibited higher levels of sarcomeric striations and higher length-to-width ratios of α-actinin⁺ cells. The spheroids with high seeding density exhibited more α-actinin⁺ cells and less nuclear YAP expression. The 3D cardiovascular spheroids were also treated with different small molecules, including Rho kinase inhibitor (Y27632), Cytochalasin D, Dasatinib, and Lysophosphatidic acid to modulate YAP localization. Nuclear YAP inhibition resulted in lower expression of active β-catenin, vascular marker, and MRTF, the transcription factor mediated by RhoGTPases. Y27632 also promoted the gene expression of MMP-2/-3 (matrix remodeling) and Notch-1 (Notch signaling). These results should help our understanding of the underlying effects for the efficient patterning of cardiovascular spheroids after mesoderm formation from hPSCs.

Population and Single-Cell Analysis of Human Cardiogenesis Reveals Unique LGR5 Ventricular Progenitors in Embryonic Outflow Tract

The morphogenetic process of mammalian cardiac development is complex and highly regulated spatiotemporally by multipotent cardiac stem/progenitor cells (CPCs). Mouse studies have been informative for understanding mammalian cardiogenesis; however, similar insights have been poorly established in humans. Here, we report comprehensive gene expression profiles of human cardiac derivatives from multipotent CPCs to intermediates and mature cardiac cells by population and single-cell RNA-seq using human embryonic stem cell-derived and embryonic/fetal heart-derived cardiac cells micro-dissected from specific heart compartments. Importantly, we discover a uniquely human subset of cono-ventricular region-specific CPCs, marked by LGR5. At 4 to 5 weeks of fetal age, the LGR5⁺ population appears to emerge specifically in the proximal outflow tract of human embryonic hearts and thereafter promotes cardiac development and alignment through expansion of the ISL1⁺TNNT2⁺ intermediates. The current study contributes to a deeper understanding of human cardiogenesis, which may uncover the putative origins of certain human congenital cardiac malformations.

Derivation of Intestinal Organoids from Human Induced Pluripotent Stem Cells for Use as an Infection System

Intestinal human organoids (iHOs) provide an effective system for studying the intestinal epithelium and its interaction with various stimuli. By using combinations of different signaling factors, human induced pluripotent stem cells (hIPSCs) can be driven to differentiate down the intestinal lineage. Here, we describe the process for this differentiation, including the derivation of hindgut from hIPSCs, embedding hindgut into a pro-intestinal culture system and passaging the resulting iHOs. We then describe how to carry out microinjections to introduce bacteria to the apical side of the intestinal epithelial cells (IECs).

A hPSC-based platform to discover gene-environment interactions that impact human β-cell and dopamine neuron survival

Common disorders, including diabetes and Parkinson’s disease, are caused by a combination of environmental factors and genetic susceptibility. However, defining the mechanisms underlying gene-environment interactions has been challenging due to the lack of a suitable experimental platform. Using pancreatic β-like cells derived from human pluripotent stem cells (hPSCs), we discovered that a commonly used pesticide, propargite, induces pancreatic β-cell death, a pathological hallmark of diabetes. Screening a panel of diverse hPSC-derived cell types we extended this observation to a similar susceptibility in midbrain dopamine neurons, a cell type affected in Parkinson’s disease. We assessed gene-environment interactions using isogenic hPSC lines for genetic variants associated with diabetes and Parkinson’s disease. We found GSTT1^−/− pancreatic β-like cells and dopamine neurons were both hypersensitive to propargite-induced cell death. Our study identifies an environmental chemical that contributes to human β-cell and dopamine neuron loss and validates a novel hPSC-based platform for determining gene-environment interactions.

Diseases such as diabetes and Parkinson's manifest based on interactions between genes and environment. Here, the authors find among a panel of cell types that propargite, a common pesticide, induces pancreatic β-cell and dopamine neuron death and that loss of the gene GSTT1 confers hypersensitivity.

Systems-Wide Approaches in Induced Pluripotent Stem Cell Models

Human induced pluripotent stem cells (iPSCs) provide a renewable supply of patient-specific and tissue-specific cells for cellular and molecular studies of disease mechanisms. Combined with advances in various omics technologies, iPSC models can be used to profile the expression of genes, transcripts, proteins, and metabolites in relevant tissues. In the past 2 years, large panels of iPSC lines have been derived from hundreds of genetically heterogeneous individuals, further enabling genome-wide mapping to identify coexpression networks and elucidate gene regulatory networks. Here, we review recent developments in omics profiling of various molecular phenotypes and the emergence of human iPSCs as a systems biology model of human diseases.

Geometry-Dependent Arrhythmias in Electrically Excitable Tissues

Little is known about how individual cells sense the macroscopic geometry of their tissue environment. Here, we explore whether long-range electrical signaling can convey information on tissue geometry to individual cells. First, we studied an engineered electrically excitable cell line. Cells grown in patterned islands of different shapes showed remarkably diverse firing patterns under otherwise identical conditions, including regular spiking, period-doubling alternans, and arrhythmic firing. A Hodgkin-Huxley numerical model quantitatively reproduced these effects, showing how the macroscopic geometry affected the single-cell electrophysiology via the influence of gap junction-mediated electrical coupling. Qualitatively similar geometry-dependent dynamics were observed in human induced pluripotent stem cell (iPSC)-derived cardiomyocytes. The cardiac results urge caution in translating observations of arrhythmia in vitro to predictions in vivo, where the tissue geometry is very different. We study how to extrapolate electrophysiological measurements between tissues with different geometries and different gap junction couplings.

Scalable Cardiac Differentiation of Pluripotent Stem Cells Using Specific Growth Factors and Small Molecules

The envisioned routine application of human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) for therapies and industry-compliant screening approaches will require efficient and highly reproducible processes for the mass production of well-characterized CM batches.On their way toward beating CMs, hPSCs initially undergo an epithelial-to-mesenchymal transition into a primitive-streak (PS)-like population that later gives rise to all endodermal and mesodermal lineages, including cardiovascular progenies (CVPs). CVPs are multipotent and possess the capability to give rise to all major cell types of the heart, including CMs, endothelial cells, cardiac fibroblasts, and smooth muscle cells. This article provides an historical overview and describes the stepwise development of protocols that typically result in the appearance of beating CMs within 7-12 days of hPSC differentiation.We describe the development of directed and closely controlled cardiomyogenic differentiation, which now enables the induction of >90% CM purity without further lineage enrichment. Although secreted lineage specifiers (revealed from developmental biology) were initially used, we outline the advantages of chemical pathway modulators, as defined by more recent screening approaches. Subsequently, we discuss the use of defined culture media for upscaling the production of hPSC-CMs in controlled bioreactors and how this, in principle, unlimited source of human CMs can be used to progress heart regeneration and stimulate the drug discovery pipeline. Graphical Abstract.

Embryonic Tbx3+ cardiomyocytes form the mature cardiac conduction system by progressive fate restriction

A small network of spontaneously active Tbx3+ cardiomyocytes forms the cardiac conduction system (CCS) in adults. Understanding the origin and mechanism of development of the CCS network are important steps towards disease modeling and the development of biological pacemakers to treat arrhythmias. We found that Tbx3 expression in the embryonic mouse heart is associated with automaticity. Genetic inducible fate mapping revealed that Tbx3+ cells in the early heart tube are fated to form the definitive CCS components, except the Purkinje fiber network. At mid-fetal stages, contribution of Tbx3+ cells was restricted to the definitive CCS. We identified a Tbx3+ population in the outflow tract of the early heart tube that formed the atrioventricular bundle. Whereas Tbx3+ cardiomyocytes also contributed to the adjacent Gja5+ atrial and ventricular chamber myocardium, embryonic Gja5+ chamber cardiomyocytes did not contribute to the Tbx3+ sinus node or to atrioventricular ring bundles. In conclusion, the CCS is established by progressive fate restriction of a Tbx3+ cell population in the early developing heart, which implicates Tbx3 as a useful tool for developing strategies to study and treat CCS diseases.

A human iPSC line capable of differentiating into functional macrophages expressing ZsGreen: a tool for the study and in vivo tracking of therapeutic cells

We describe the production of a human induced pluripotent stem cell (iPSC) line, SFCi55-ZsGr, that has been engineered to express the fluorescent reporter gene, ZsGreen, in a constitutive manner. The CAG-driven ZsGreen expression cassette was inserted into the AAVS1 locus and a high level of expression was observed in undifferentiated iPSCs and in cell lineages derived from all three germ layers including haematopoietic cells, hepatocytes and neurons. We demonstrate efficient production of terminally differentiated macrophages from the SFCi55-ZsGreen iPSC line and show that they are indistinguishable from those generated from their parental SFCi55 iPSC line in terms of gene expression, cell surface marker expression and phagocytic activity. The high level of ZsGreen expression had no effect on the ability of macrophages to be activated to an M(LPS + IFNγ), M(IL10) or M(IL4) phenotype nor on their plasticity, assessed by their ability to switch from one phenotype to another. Thus, targeting of the AAVS1 locus in iPSCs allows for the production of fully functional, fluorescently tagged human macrophages that can be used for in vivo tracking in disease models. The strategy also provides a platform for the introduction of factors that are predicted to modulate and/or stabilize macrophage function.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Pluripotent Stem Cell-Derived Cardiomyocytes as a Platform for Cell Therapy Applications: Progress and Hurdles for Clinical Translation

Cardiovascular diseases are the leading cause of morbidity and mortality worldwide. Regenerative therapy has been applied to restore lost cardiac muscle and cardiac performance. Induced pluripotent stem cells (iPSCs) can provide an unlimited source of cardiomyocytes and therefore play a key role in cardiac regeneration. Despite initial encouraging results from pre-clinical studies, progress toward clinical applications has been hampered by issues such as tumorigenesis, arrhythmogenesis, immune rejection, scalability, low graft-cell survival, and poor engraftment. Here, we review recent developments in iPSC research on regenerating injured heart tissue, including novel advances in cell therapy and potential strategies to overcome current obstacles in the field.

Human pluripotent stem cell models of cardiac disease: from mechanisms to therapies

It is now a decade since human induced pluripotent stem cells (hiPSCs) were first described. The reprogramming of adult somatic cells to a pluripotent state has become a robust technology that has revolutionised our ability to study human diseases. Crucially, these cells capture all the genetic aspects of the patient from which they were derived. Combined with advances in generating the different cell types present in the human heart, this has opened up new avenues to study cardiac disease in humans and investigate novel therapeutic approaches to treat these pathologies. Here, we provide an overview of the current state of the field regarding the generation of cardiomyocytes from human pluripotent stem cells and methods to assess them functionally, an essential requirement when investigating disease and therapeutic outcomes. We critically evaluate whether treatments suggested by these in vitro models could be translated to clinical practice. Finally, we consider current shortcomings of these models and propose methods by which they could be further improved.

Engineering Scalable Manufacturing of High-Quality Stem Cell-Derived Cardiomyocytes for Cardiac Tissue Repair

Recent advances in the differentiation and production of human pluripotent stem cell (hPSC)-derived cardiomyocytes (CMs) have stimulated development of strategies to use these cells in human cardiac regenerative therapies. A prerequisite for clinical trials and translational implementation of hPSC-derived CMs is the ability to manufacture safe and potent cells on the scale needed to replace cells lost during heart disease. Current differentiation protocols generate fetal-like CMs that exhibit proarrhythmogenic potential. Sufficient maturation of these hPSC-derived CMs has yet to be achieved to allow these cells to be used as a regenerative medicine therapy. Insights into the native cardiac environment during heart development may enable engineering of strategies that guide hPSC-derived CMs to mature. Specifically, considerations must be made in regard to developing methods to incorporate the native intercellular interactions and biomechanical cues into hPSC-derived CM production that are conducive to scale-up.

Human Pluripotent Stem Cell-Derived Atrial and Ventricular Cardiomyocytes Develop from Distinct Mesoderm Populations

The ability to direct the differentiation of human pluripotent stem cells (hPSCs) to the different cardiomyocyte subtypes is a prerequisite for modeling specific forms of cardiovascular disease in vitro and for developing novel therapies to treat them. Here we have investigated the development of the human atrial and ventricular lineages from hPSCs, and we show that retinoic acid signaling at the mesoderm stage of development is required for atrial specification. Analyses of early developmental stages revealed that ventricular and atrial cardiomyocytes derive from different mesoderm populations that can be distinguished based on CD235a and RALDH2 expression, respectively. Molecular and electrophysiological characterization of the derivative cardiomyocytes revealed that optimal specification of ventricular and atrial cells is dependent on induction of the appropriate mesoderm. Together these findings provide new insights into the development of the human atrial and ventricular lineages that enable the generation of highly enriched, functional cardiomyocyte populations for therapeutic applications.

NKX2-5 regulates human cardiomyogenesis via a HEY2 dependent transcriptional network

Congenital heart defects can be caused by mutations in genes that guide cardiac lineage formation. Here, we show deletion of NKX2-5, a critical component of the cardiac gene regulatory network, in human embryonic stem cells (hESCs), results in impaired cardiomyogenesis, failure to activate VCAM1 and to downregulate the progenitor marker PDGFRα. Furthermore, NKX2-5 null cardiomyocytes have abnormal physiology, with asynchronous contractions and altered action potentials. Molecular profiling and genetic rescue experiments demonstrate that the bHLH protein HEY2 is a key mediator of NKX2-5 function during human cardiomyogenesis. These findings identify HEY2 as a novel component of the NKX2-5 cardiac transcriptional network, providing tangible evidence that hESC models can decipher the complex pathways that regulate early stage human heart development. These data provide a human context for the evaluation of pathogenic mutations in congenital heart disease.

A gene regulatory network, including the transcription factor Nkx2-5, regulates cardiac development. Here, the authors show that on deletion of NKX2-5 from human embryonic stem cells, there is impaired cardiomyogenesis and changes in action potentials, and that this is regulated via HEY2.

Applications of genetically engineered human pluripotent stem cell reporters in cardiac stem cell biology

The advent of human pluripotent stem cells (hPSCs) has benefited many fields, from regenerative medicine to disease modeling, with an especially profound effect in cardiac research. Coupled with other novel technologies in genome engineering, hPSCs offer a great opportunity to delineate human cardiac lineages, investigate inherited cardiovascular diseases, and assess the safety and efficacy of cell-based therapies. In this review, we provide an overview of methods for generating genetically engineered hPSC reporters and a succinct synopsis of a variety of hPSC reporters, with a particular focus on their applications in cardiac stem cell biology.

Can Human Pluripotent Stem Cell-Derived Cardiomyocytes Advance Understanding of Muscular Dystrophies?

Muscular dystrophies (MDs) are clinically and molecularly a highly heterogeneous group of single-gene disorders that primarily affect striated muscles. Cardiac disease is present in several MDs where it is an important contributor to morbidity and mortality. Careful monitoring of cardiac issues is necessary but current management of cardiac involvement does not effectively protect from disease progression and cardiac failure. There is a critical need to gain new knowledge on the diverse molecular underpinnings of cardiac disease in MDs in order to guide cardiac treatment development and assist in reaching a clearer consensus on cardiac disease management in the clinic. Animal models are available for the majority of MDs and have been invaluable tools in probing disease mechanisms and in pre-clinical screens. However, there are recognized genetic, physiological, and structural differences between human and animal hearts that impact disease progression, manifestation, and response to pharmacological interventions. Therefore, there is a need to develop parallel human systems to model cardiac disease in MDs. This review discusses the current status of cardiomyocytes (CMs) derived from human induced pluripotent stem cells (hiPSC) to model cardiac disease, with a focus on Duchenne muscular dystrophy (DMD) and myotonic dystrophy (DM1). We seek to provide a balanced view of opportunities and limitations offered by this system in elucidating disease mechanisms pertinent to human cardiac physiology and as a platform for treatment development or refinement.

The long non-coding RNA uc.4 influences cell differentiation through the TGF-beta signaling pathway

In a previous study, we screened thousands of long non-coding RNAs (lncRNAs) to assess their potential relationship with congenital heart disease (CHD). In this study, uc.4 attracted our attention because of its high level of evolutionary conservation and its antisense orientation to the CASZ1 gene, which is vital for heart development. We explored the function of uc.4 in cells and in zebrafish, and describe a potential mechanism of action. P19 cells were used to investigate the function of uc.4. We studied the effect of uc.4 overexpression on heart development in zebrafish. The overexpression of uc.4 influenced cell differentiation by inhibiting the TGF-beta signaling pathway and suppressed heart development in zebrafish, resulting in cardiac malformation. Taken together, our findings show that uc.4 is involved in heart development, thus providing a potential therapeutic target for CHD.

Cardiac Progenitor Cells in Basic Biology and Regenerative Medicine

Major cardiovascular events including myocardial infarction (MI) continue to dominate morbidity rates in the developed world. Although multiple device therapies and various pharmacological agents have been shown to improve patient care and reduce mortality rates, clinicians and researchers alike still lack a true panacea to regenerate damaged cardiac tissue. Over the previous two to three decades, cardiovascular stem cell therapies have held great promise. Several stem cell-based approaches have now been shown to improve ventricular function and are documented in preclinical animal models as well as phase I and phase II clinical trials. More recently, the cardiac progenitor cell has begun to gain momentum as an ideal candidate for stem cell therapy in heart disease. Here, we will highlight the most recent advances in cardiac stem/progenitor cell biology in regard to both the basics and applied settings.

Automated fabrication of photopatterned gelatin hydrogels for organ-on-chips applications

Organ-on-chip platforms aim to improve preclinical models for organ-level responses to novel drug compounds. Heart-on-a-chip assays in particular require tissue engineering techniques that rely on labor-intensive photolithographic fabrication or resolution-limited 3D printing of micropatterned substrates, which limits turnover and flexibility of prototyping. We present a rapid and automated method for large scale on-demand micropatterning of gelatin hydrogels for organ-on-chip applications using a novel biocompatible laser-etching approach. Fast and automated micropatterning is achieved via photosensitization of gelatin using riboflavin-5'phosphate followed by UV laser-mediated photoablation of the gel surface in user-defined patterns only limited by the resolution of the 15 μm wide laser focal point. Using this photopatterning approach, we generated microscale surface groove and pillar structures with feature dimensions on the order of 10-30 μm. The standard deviation of feature height was 0.3 μm, demonstrating robustness and reproducibility. Importantly, the UV-patterning process is non-destructive and does not alter gelatin micromechanical properties. Furthermore, as a quality control step, UV-patterned heart chip substrates were seeded with rat or human cardiac myocytes, and we verified that the resulting cardiac tissues achieved structural organization, contractile function, and long-term viability comparable to manually patterned gelatin substrates. Start-to-finish, UV-patterning shortened the time required to design and manufacture micropatterned gelatin substrates for heart-on-chip applications by up to 60% compared to traditional lithography-based approaches, providing an important technological advance enroute to automated and continuous manufacturing of organ-on-chips.

Strategies for directing cells into building functional hearts and parts

This review presents the current state-of-the-art, emerging directions and future trends to direct cells for building functional heart parts.

Human Pluripotent Stem Cell Differentiation into Functional Epicardial Progenitor Cells

Human pluripotent stem cells (hPSCs) are widely used to study cardiovascular cell differentiation and function. Here, we induced differentiation of hPSCs (both embryonic and induced) to proepicardial/epicardial progenitor cells that cover the heart during development. Addition of retinoic acid (RA) and bone morphogenetic protein 4 (BMP4) promoted expression of the mesodermal marker PDGFRα, upregulated characteristic (pro)epicardial progenitor cell genes, and downregulated transcription of myocardial genes. We confirmed the (pro)epicardial-like properties of these cells using in vitro co-culture assays and in ovo grafting of hPSC-epicardial cells into chick embryos. Our data show that RA + BMP4-treated hPSCs differentiate into (pro)epicardial-like cells displaying functional properties (adhesion and spreading over the myocardium) of their in vivo counterpart. The results extend evidence that hPSCs are an excellent model to study (pro)epicardial differentiation into cardiovascular cells in human development and evaluate their potential for cardiac regeneration.

Haploinsufficiency for the Six2 gene increases nephron progenitor proliferation promoting branching and nephron number

The regulation of final nephron number in the kidney is poorly understood. Cessation of nephron formation occurs when the self-renewing nephron progenitor population commits to differentiation. Transcription factors within this progenitor population, such as SIX2, are assumed to control expression of genes promoting self-renewal such that homozygous Six2 deletion results in premature commitment and an early halt to kidney development. In contrast, Six2 heterozygotes were assumed to be unaffected. Using quantitative morphometry, we found a paradoxical 18% increase in ureteric branching and final nephron number in Six2 heterozygotes, despite evidence for reduced levels of SIX2 protein and transcript. This was accompanied by a clear shift in nephron progenitor identity with a distinct subset of downregulated progenitor genes such as Cited1 and Meox1 while other genes were unaffected. The net result was an increase in nephron progenitor proliferation, as assessed by elevated EdU (5-ethynyl-2'-deoxyuridine) labeling, an increase in MYC protein, and transcriptional upregulation of MYC target genes. Heterozygosity for Six2 on an Fgf20-/- background resulted in premature differentiation of the progenitor population, confirming that progenitor regulation is compromised in Six2 heterozygotes. Overall, our studies reveal a unique dose response of nephron progenitors to the level of SIX2 protein in which the role of SIX2 in progenitor proliferation versus self-renewal is separable.

Induced pluripotent stem-cell-derived cardiomyocytes: cardiac applications, opportunities, and challenges

Chronic diseases are the primary cause of mortality worldwide, accounting for 67% of deaths. One of the major challenges in developing new treatments is the lack of understanding of the exact underlying biological and molecular mechanisms. Chronic cardiovascular diseases are the single most common cause of death worldwide, and sudden deaths due to cardiac arrhythmias account for approximately 50% of all such cases. Traditional genetic screening for genes involved in cardiac disorders is labourious and frequently fails to detect the mutation that explains or causes the disorder. However, when mutations are identified, human induced pluripotent stem cells (hiPSCs) derived from affected patients make it possible to address fundamental research questions directly relevant to human health. As such, hiPSC technology has recently been used to model human diseases and patient-specific hiPSC-derived cardiomyocytes (hiPSC-CMs) thus offer a unique opportunity to investigate potential disease-causing genetic variants in their natural environment. The purpose of this review is to present the current state of knowledge regarding hiPSC-CMs, including their potential, limitations, and challenges and to discuss future prospects.