HOPX-associated molecular programs control cardiomyocyte cell states underpinning cardiac structure and function.

Genomic regulation of cardiomyocyte differentiation is central to heart development and function. This study uses genetic loss-of-function human-induced pluripotent stem cell-derived cardiomyocytes to evaluate the genomic regulatory basis of the non-DNA-binding homeodomain protein HOPX. We show that HOPX interacts with and controls cardiac genes and enhancer networks associated with diverse aspects of heart development. Using perturbation studies in vitro, we define how upstream cell growth and proliferation control HOPX transcription to regulate cardiac gene programs. We then use cell, organoid, and zebrafish regeneration models to demonstrate that HOPX-regulated gene programs control cardiomyocyte function in development and disease. Collectively, this study mechanistically links cell signaling pathways as upstream regulators of HOPX transcription to control gene programs underpinning cardiomyocyte identity and function.

Generation of vascularized human cardiac organoids for 3D in vitro modeling.

Here, we provide a protocol for next-generation human cardiac organoid modeling containing markers of vascularized tissues. We describe steps for cardiac differentiation, harvesting cardiac cells, and generating vascularized human cardiac organoids. We then detail downstream analysis of functional parameters and fluorescence labeling of human cardiac organoids. This protocol is useful for high throughput disease modeling, drug discovery, and providing mechanistic insight into cell-cell and cell-matrix interactions. For complete details on the use and execution of this protocol, please refer to Voges et al.1 and Mills et al.2.

Vascular cells improve functionality of human cardiac organoids.

Crosstalk between cardiac cells is critical for heart performance. Here we show that vascular cells within human cardiac organoids (hCOs) enhance their maturation, force of contraction, and utility in disease modeling. Herein we optimize our protocol to generate vascular populations in addition to epicardial, fibroblast, and cardiomyocyte cells that self-organize into in-vivo-like structures in hCOs. We identify mechanisms of communication between endothelial cells, pericytes, fibroblasts, and cardiomyocytes that ultimately contribute to cardiac organoid maturation. In particular, (1) endothelial-derived LAMA5 regulates expression of mature sarcomeric proteins and contractility, and (2) paracrine platelet-derived growth factor receptor ß (PDGFRß) signaling from vascular cells upregulates matrix deposition to augment hCO contractile force. Finally, we demonstrate that vascular cells determine the magnitude of diastolic dysfunction caused by inflammatory factors and identify a paracrine role of endothelin driving dysfunction. Together this study highlights the importance and role of vascular cells in organoid models.

Protocol to transfer epithelial acini between different extracellular matrices and orient fibril organization.

Extracellular matrix (ECM) provides fundamental support for epithelial tissues and controls cell function. The chemistry and mechanical properties of ECM components, including stiffness, elasticity, and fibrillar organization, influence epithelial tissue responses. Here we present a protocol describing the culture and transfer of epithelial acini from Matrigel to collagen gel and an approach to axially align the collagen fibrils by the external gel stretching. This protocol uses the acini of MCF10A cells and needs to be modified for different cell lines. For complete details on the use and execution of this protocol, please refer to Katsuno-Kambe et al. (2021).1.

BET inhibition blocks inflammation-induced cardiac dysfunction and SARS-CoV-2 infection.

Cardiac injury and dysfunction occur in COVID-19 patients and increase the risk of mortality. Causes are ill defined but could be through direct cardiac infection and/or inflammation-induced dysfunction. To identify mechanisms and cardio-protective drugs, we use a state-of-the-art pipeline combining human cardiac organoids with phosphoproteomics and single nuclei RNA sequencing. We identify an inflammatory "cytokine-storm", a cocktail of interferon gamma, interleukin 1ß, and poly(I:C), induced diastolic dysfunction. Bromodomain-containing protein 4 is activated along with a viral response that is consistent in both human cardiac organoids (hCOs) and hearts of SARS-CoV-2-infected K18-hACE2 mice. Bromodomain and extraterminal family inhibitors (BETi) recover dysfunction in hCOs and completely prevent cardiac dysfunction and death in a mouse cytokine-storm model. Additionally, BETi decreases transcription of genes in the viral response, decreases ACE2 expression, and reduces SARS-CoV-2 infection of cardiomyocytes. Together, BETi, including the Food and Drug Administration (FDA) breakthrough designated drug, apabetalone, are promising candidates to prevent COVID-19 mediated cardiac damage.

Sex-Specific Control of Human Heart Maturation by the Progesterone Receptor.

BACKGROUND: Despite in-depth knowledge of the molecular mechanisms controlling embryonic heart development, little is known about the signals governing postnatal maturation of the human heart. METHODS: Single-nucleus RNA sequencing of 54 140 nuclei from 9 human donors was used to profile transcriptional changes in diverse cardiac cell types during maturation from fetal stages to adulthood. Bulk RNA sequencing and the Assay for Transposase-Accessible Chromatin using sequencing were used to further validate transcriptional changes and to profile alterations in the chromatin accessibility landscape in purified cardiomyocyte nuclei from 21 human donors. Functional validation studies of sex steroids implicated in cardiac maturation were performed in human pluripotent stem cell-derived cardiac organoids and mice. RESULTS: Our data identify the progesterone receptor as a key mediator of sex-dependent transcriptional programs during cardiomyocyte maturation. Functional validation studies in human cardiac organoids and mice demonstrate that the progesterone receptor drives sex-specific metabolic programs and maturation of cardiac contractile properties. CONCLUSIONS: These data provide a blueprint for understanding human heart maturation in both sexes and reveal an important role for the progesterone receptor in human heart development.

ß-Catenin drives distinct transcriptional networks in proliferative and nonproliferative cardiomyocytes.

The inability of the adult mammalian heart to regenerate represents a fundamental barrier in heart failure management. By contrast, the neonatal heart retains a transient regenerative capacity, but the underlying mechanisms for the developmental loss of cardiac regenerative capacity in mammals are not fully understood. Wnt/ß-catenin signalling has been proposed as a key cardioregenerative pathway driving cardiomyocyte proliferation. Here, we show that Wnt/ß-catenin signalling potentiates neonatal mouse cardiomyocyte proliferation in vivo and immature human pluripotent stem cell-derived cardiomyocyte (hPSC-CM) proliferation in vitro By contrast, Wnt/ß-catenin signalling in adult mice is cardioprotective but fails to induce cardiomyocyte proliferation. Transcriptional profiling and chromatin immunoprecipitation sequencing of neonatal mouse and hPSC-CMs revealed a core Wnt/ß-catenin-dependent transcriptional network governing cardiomyocyte proliferation. By contrast, ß-catenin failed to re-engage this neonatal proliferative gene network in the adult heart despite partial transcriptional re-activation of a neonatal glycolytic gene programme. These findings suggest that ß-catenin might be repurposed from regenerative to protective functions in the adult heart in a developmental process dependent on the metabolic status of cardiomyocytes.

Centrosome Reduction Promotes Terminal Differentiation of Human Cardiomyocytes.

Centrosome reduction and redistribution of pericentriolar material (PCM) coincides with cardiomyocyte transitions to a post-mitotic and matured state. However, it is unclear whether centrosome changes are a cause or consequence of terminal differentiation. We validated that centrosomes were intact and functional in proliferative human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), consistent with their immature phenotype. We generated acentrosomal hPSC-CMs, through pharmacological inhibition of centriole duplication, and showed that centrosome loss was sufficient to promote post-mitotic transitions and aspects of cardiomyocyte maturation. As Hippo kinases are activated during post-natal cardiac maturation, we pharmacologically activated the Hippo pathway using C19, which was sufficient to trigger centrosome disassembly and relocalization of PCM components to perinuclear membranes. This was due to specific activation of Hippo kinases, as direct inhibition of YAP-TEAD interactions with verteporfin had no effect on centrosome organization. This suggests that Hippo kinase-centrosome remodeling may play a direct role in cardiac maturation.

Enhanced cardiac repair by telomerase reverse transcriptase over-expression in human cardiac mesenchymal stromal cells.

We have previously reported a subpopulation of mesenchymal stromal cells (MSCs) within the platelet-derived growth factor receptor-alpha (PDGFRα)/CD90 co-expressing cardiac interstitial and adventitial cell fraction. Here we further characterise PDGFRα/CD90-expressing cardiac MSCs (PDGFRα + cMSCs) and use human telomerase reverse transcriptase (hTERT) over-expression to increase cMSCs ability to repair the heart after induced myocardial infarction. hTERT over-expression in PDGFRα + cardiac MSCs (hTERT + PDGFRα + cMSCs) modulates cell differentiation, proliferation, survival and angiogenesis related genes. In vivo, transplantation of hTERT + PDGFRα + cMSCs in athymic rats significantly increased left ventricular function, reduced scar size, increased angiogenesis and proliferation of both cardiomyocyte and non-myocyte cell fractions four weeks after myocardial infarction. In contrast, transplantation of mutant hTERT + PDGFRα + cMSCs (which generate catalytically-inactive telomerase) failed to replicate this cardiac functional improvement, indicating a telomerase-dependent mechanism. There was no hTERT + PDGFRα + cMSCs engraftment 14 days after transplantation indicating functional improvement occurred by paracrine mechanisms. Mass spectrometry on hTERT + PDGFRα + cMSCs conditioned media showed increased proteins associated with matrix modulation, angiogenesis, cell proliferation/survival/adhesion and innate immunity function. Our study shows that hTERT can activate pro-regenerative signalling within PDGFRα + cMSCs and enhance cardiac repair after myocardial infarction. An increased understanding of hTERT's role in mesenchymal stromal cells from various organs will favourably impact clinical regenerative and anti-cancer therapies.

Drug Screening in Human PSC-Cardiac Organoids Identifies Pro-proliferative Compounds Acting via the Mevalonate Pathway.

We have previously developed a high-throughput bioengineered human cardiac organoid (hCO) platform, which provides functional contractile tissue with biological properties similar to native heart tissue, including mature, cell-cycle-arrested cardiomyocytes. In this study, we perform functional screening of 105 small molecules with pro-regenerative potential. Our findings reveal surprising discordance between our hCO system and traditional 2D assays. In addition, functional analyses uncovered detrimental effects of many hit compounds. Two pro-proliferative small molecules without detrimental impacts on cardiac function were identified. High-throughput proteomics in hCO revealed synergistic activation of the mevalonate pathway and a cell-cycle network by the pro-proliferative compounds. Cell-cycle reentry in hCO and in vivo required the mevalonate pathway as inhibition of the mevalonate pathway with a statin attenuated pro-proliferative effects. This study highlights the utility of human cardiac organoids for pro-regenerative drug development, including identification of underlying biological mechanisms and minimization of adverse side effects.

Functional screening in human cardiac organoids reveals a metabolic mechanism for cardiomyocyte cell cycle arrest.

The mammalian heart undergoes maturation during postnatal life to meet the increased functional requirements of an adult. However, the key drivers of this process remain poorly defined. We are currently unable to recapitulate postnatal maturation in human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs), limiting their potential as a model system to discover regenerative therapeutics. Here, we provide a summary of our studies, where we developed a 96-well device for functional screening in human pluripotent stem cell-derived cardiac organoids (hCOs). Through interrogation of >10,000 organoids, we systematically optimize parameters, including extracellular matrix (ECM), metabolic substrate, and growth factor conditions, that enhance cardiac tissue viability, function, and maturation. Under optimized maturation conditions, functional and molecular characterization revealed that a switch to fatty acid metabolism was a central driver of cardiac maturation. Under these conditions, hPSC-CMs were refractory to mitogenic stimuli, and we found that key proliferation pathways including ß-catenin and Yes-associated protein 1 (YAP1) were repressed. This proliferative barrier imposed by fatty acid metabolism in hCOs could be rescued by simultaneous activation of both ß-catenin and YAP1 using genetic approaches or a small molecule activating both pathways. These studies highlight that human organoids coupled with higher-throughput screening platforms have the potential to rapidly expand our knowledge of human biology and potentially unlock therapeutic strategies.

Cryoinjury Model for Tissue Injury and Repair in Bioengineered Human Striated Muscle.

Regenerative medicine aims to replace injured tissues to restore normal physiological function. One possibility for achieving this goal is to activate or enhance endogenous regenerative pathways. Therefore, human tissue regeneration models may be useful tools for the discovery and development of novel regenerative therapeutics. In this chapter, we describe methods for the generation of three-dimensional bioengineered striated muscle in vitro and a cryoinjury model that can be applied to these tissues. This technique enables mechanistic in vitro analysis of the endogenous regenerative response of human striated muscle to injury, which is not possible using other in vivo approaches.

Development of a human cardiac organoid injury model reveals innate regenerative potential.

The adult human heart possesses a limited regenerative potential following an ischemic event, and undergoes a number of pathological changes in response to injury. Although cardiac regeneration has been documented in zebrafish and neonatal mouse hearts, it is currently unknown whether the immature human heart is capable of undergoing complete regeneration. Combined progress in pluripotent stem cell differentiation and tissue engineering has facilitated the development of human cardiac organoids (hCOs), which resemble fetal heart tissue and can be used to address this important knowledge gap. This study aimed to characterize the regenerative capacity of immature human heart tissue in response to injury. Following cryoinjury with a dry ice probe, hCOs exhibited an endogenous regenerative response with full functional recovery 2 weeks after acute injury. Cardiac functional recovery occurred in the absence of pathological fibrosis or cardiomyocyte hypertrophy. Consistent with regenerative organisms and neonatal human hearts, there was a high basal level of cardiomyocyte proliferation, which may be responsible for the regenerative capacity of the hCOs. This study suggests that immature human heart tissue has an intrinsic capacity to regenerate.