A single-cell comparison of adult and foetal human epicardium defines the age-associated changes in epicardial activity
Ontology highlight
ABSTRACT: Re-activating quiescent adult epicardium represents a potential therapeutic approach for human cardiac regeneration. However, the exact molecular differences between inactive adult and active foetal epicardium are not known. Here, we combined foetal and adult human hearts for the first time using single-cell and single-nuclei RNA sequencing, and compared epicardial cells from both stages. We found a migratory fibroblast-like epicardial population only in the foetal heart and foetal epicardium expressed angiogenic gene programs, while the adult epicardium was solely mesothelial and immune-responsive. Furthermore, we predicted that adult hearts may still receive foetal epicardial paracrine communication, including WNT-signalling with endocardium, reinforcing the validity of regenerative strategies that administer or reactivate epicardial cells in situ. Finally, we explained graft efficacy of our human embryonic stem-cell derived epicardium model, by noting its similarity to human foetal epicardium. Overall, our study defines epicardial programs of regenerative angiogenesis absent in adult hearts, contextualises animal studies, and defines epicardial states required for effective human heart regeneration.
Project description:This study is associated with the GEO accession GSE216019. Abstract from article: Re-activating quiescent adult epicardium represents a potential therapeutic approach for human cardiac regeneration. However, the exact molecular differences between inactive adult and active foetal epicardium are not known. Here, we combined foetal and adult human hearts for the first time using single-cell and single-nuclei RNA sequencing, and compared epicardial cells from both stages. We found a migratory fibroblast-like epicardial population only in the foetal heart and foetal epicardium expressed angiogenic gene programs, while the adult epicardium was solely mesothelial and immune-responsive. Furthermore, we predicted that adult hearts may still receive foetal epicardial paracrine communication, including WNT-signalling with endocardium, reinforcing the validity of regenerative strategies that administer or reactivate epicardial cells in situ. Finally, we explained graft efficacy of our human embryonic stem-cell derived epicardium model, by noting its similarity to human foetal epicardium. Overall, our study defines epicardial programs of regenerative angiogenesis absent in adult hearts, contextualises animal studies, and defines epicardial endpoints required for effective human heart regeneration.
Project description:By contrast with mammals, adult zebrafish have a high capacity to regenerate damaged or lost myocardium through proliferation of spared cardiomyocytes. The epicardial sheet covering the heart is activated by injury and aids muscle regeneration through paracrine effects and as a multipotent cell source, and has received recent attention as a target in cardiac repair strategies. While it is recognized that epicardium is required for muscle regeneration and itself has high regenerative potential, the extent of cellular heterogeneity within epicardial tissue is largely unexplored. In this study, we performed transcriptome analysis on dozens of epicardial lineage cells purified from zebrafish harboring a transgenic reporter for the pan-epicardial gene tcf21. Hierarchical clustering analysis suggested the presence of at least three epicardial cell subsets defined by expression signatures. We validated many new pan-epicardial and epicardial markers by alternative expression assays. Additionally, we explored the function of the scaffolding protein and main component of caveolae, caveolin-1 (cav1), which was present in each epicardial subset. In BAC transgenic zebrafish, cav1 regulatory sequences drove strong expression in ostensibly all epicardial cells and in coronary vascular endothelial cells. Moreover, cav1 mutant zebrafish generated by genome editing showed grossly normal heart development and adult cardiac anatomy, but displayed profound defects in injury-induced cardiomyocyte proliferation and heart regeneration. Our study defines a new platform for the discovery of epicardial lineage markers, genetic tools, and mechanisms of heart regeneration. Deep sequencing of isolated single epicardial cells
Project description:Identification of epicardium-enriched genes in the embryonic heart. The epicardium encapsulates the heart and functions as a source of multipotent progenitor cells and paracrine factors essential for cardiac development and repair. Injury of the adult heart results in re-activation of a developmental gene program in the epicardium, but the transcriptional basis of epicardial gene expression has not been delineated. We established a mouse embryonic heart organ culture and gene expression system that facilitated the identification of epicardial enhancers activated during heart development and injury. Epicardial activation of these enhancers depends on a combinatorial transcriptional code centered on CCAAT/enhancer binding protein (C/EBP) transcription factors. Disruption of C/EBP signaling in the adult epicardium reduced injury-induced neutrophil infiltration and improved cardiac function. These findings reveal a transcriptional basis for epicardial activation and heart injury, providing a platform for enhancing cardiac regeneration. Total RNA obtained from lacZ-positive epicardial cells isolated from the E11.5 Tcf21lacZ hearts compared to total dissociated heart cells
Project description:Unlike the adult mammalian heart, which has limited regenerative capacity, the zebrafish heart can fully regenerate following injury. Reactivation of cardiac developmental programmes is considered key to successfully regenerating the heart, yet the regulatory elements underlying the response triggered upon injury and during development remain elusive. Organ-wide activation of the epicardium is essential for zebrafish heart regeneration and is considered a potential regenerative source to target in the mammalian heart. Here we compared the transcriptome and epigenome of the developing and regenerating zebrafish epicardium by integrating gene expression profiles with open chromatin ATAC-seq data. We identified epicardial enhancer elements with specific activity during development or during adult heart regeneration. By generating gene regulatory networks associated with epicardial development and regeneration, we inferred genetic programmes driving each of these processes, which were largely distinct. We identified Wt1a, Wt1b, and the AP-1 subunits Junbb, Fosab and Fosb as central regulators of the developing network, whereas Hif1ab, Nrf1, Tbx2b and Zbtb7a featured as putative central regulators of the regenerating epicardial network. Targeting hif1ab, nrf1, tbx2b and zbtb7a using CRISPR/Cas9 in injured hearts resulted in elevated epicardial cell numbers infiltrating the wound and excess fibrosis after cryoinjury, illustrating the functional importance of these regulatory factors during zebrafish heart regeneration. Our work reveals striking differences between the regulatory blueprint deployed during epicardial development and regeneration. These findings underline that heart regeneration goes beyond the reactivation of developmental programmes and provide important insights into epicardial regulation.
Project description:By contrast with mammals, adult zebrafish have a high capacity to regenerate damaged or lost myocardium through proliferation of spared cardiomyocytes. The epicardial sheet covering the heart is activated by injury and aids muscle regeneration through paracrine effects and as a multipotent cell source, and has received recent attention as a target in cardiac repair strategies. While it is recognized that epicardium is required for muscle regeneration and itself has high regenerative potential, the extent of cellular heterogeneity within epicardial tissue is largely unexplored. In this study, we performed transcriptome analysis on dozens of epicardial lineage cells purified from zebrafish harboring a transgenic reporter for the pan-epicardial gene tcf21. Hierarchical clustering analysis suggested the presence of at least three epicardial cell subsets defined by expression signatures. We validated many new pan-epicardial and epicardial markers by alternative expression assays. Additionally, we explored the function of the scaffolding protein and main component of caveolae, caveolin-1 (cav1), which was present in each epicardial subset. In BAC transgenic zebrafish, cav1 regulatory sequences drove strong expression in ostensibly all epicardial cells and in coronary vascular endothelial cells. Moreover, cav1 mutant zebrafish generated by genome editing showed grossly normal heart development and adult cardiac anatomy, but displayed profound defects in injury-induced cardiomyocyte proliferation and heart regeneration. Our study defines a new platform for the discovery of epicardial lineage markers, genetic tools, and mechanisms of heart regeneration.
Project description:Adult zebrafish regenerate heart muscle after severe cardiac damage without significant scarring. The epicardium, a mesothelial cell sheet covering the vetebrate heart, is activated by injury and supports muscle regeneration through paracrine effects and as a source of multipotent cells. The understudied cellular heterogeneity of the adult epicardium during heart regeneration has constrained the effort in mobilizing the epicardium for heart repair. To dissect epicardial cell states and the underlying mechanisms that lead to successful heart regeneration in zebrafish, we performed single-cell RNA-sequencing of isolated epicardial cells from the regenerating adult heart and revealed their dynamic cellular heterogeneity. We defined the epithelial and mesenchymal layers of the epicardium and identified a transiently activated epicardial progenitor cell (aEPC) subpopulation that expresses aldh1a2, ptx3a, col12a1b and marcksb. Upon heart amputation injury, aEPCs emerge from the existing epicardial cells, migrate to enclose the wound, and disappear as regeneration progresses. Genetic lineage tracing combined with modified RNA labelling confirmed an epithelial-mesenchymal transition (EMT) process of aEPCs and their differentiations to pdgfrb+ mural cells and pdgfra+hapln1a+ mesenchymal fibroblast-like cells that support heart regeneration. Genetic ablation of aEPCs blocked wound closure of the injured ventricle, suppressed cardiomyocyte proliferation, and disrupted heart regeneration. Our findings define a transient progenitor state of the adult epicardium that is an indispensable driver of zebrafish heart regeneration and identified ptx3a as a regeneration-specific non-ontogenetic regulator of the epicardium.
Project description:The epicardium is a mesothelial layer covering the myocardium and contributes to different cardiac lineage descendants during cardiogenesis. Fine-tuned balanced signaling defines epicardial specification and regulates cell plasticity and cell-fate decisions of epicardial-derived cells (EPCDs) by epicardial-to-mesenchymal transition (EMT). However, powerful tools to investigate epicardial cell function, including markers with pivotal roles in developmental signaling, are still lacking. Here, we recapitulated embryonic epicardiogenesis using human induced pluripotent stem cells (hiPSCs) and identified type II classical cadherin CDH18 as a novel biomarker defining lineage specification in human developing epicardium. The loss of CDH18 led to the onset of EMT and specific differentiation towards cardiac smooth muscle cells. Furthermore, GATA4 regulated epicardial CDH18 expression. These results demonstrate the production and enrichment of hiPSC-derived epicardial cells via the tracing of CDH18 expression, providing a model for investigating epicardial function in human development and disease and enabling new possibilities for regenerative medicine.
Project description:The epicardium, a thin mesothelial tissue layer that encompasses the heart, is a dynamic structure that is essential for cardiac regeneration in species with elevated regenerative capacity like zebrafish. To dissect epicardial cell states and associated pro-regenerative functions, we performed single-cell RNA-sequencing and identified 7 epicardial cell clusters in adult zebrafish, with 3 of these clusters enhanced during regeneration. ECM components encoded by hapln1 paralogs label an enriched epicardial cell type that accumulates and encloses dedifferentiated and proliferating cardiomyocytes during regeneration. Genetic inactivation of hapln1b, or induced genetic depletion of hapln1a-expressing cells, disrupted cardiomyocyte proliferation and heart regeneration. hapln1a+ cells first emerge at the juvenile stage, when they associate with and are required for cardiogenic foci that direct growth of the juvenile heart. Our findings identify a subset of epicardial cells that emerges in post-embryonic animals and sponsors regions of active cardiomyogenesis during heart growth and regeneration
Project description:Identification of epicardium-enriched genes in the embryonic heart. The epicardium encapsulates the heart and functions as a source of multipotent progenitor cells and paracrine factors essential for cardiac development and repair. Injury of the adult heart results in re-activation of a developmental gene program in the epicardium, but the transcriptional basis of epicardial gene expression has not been delineated. We established a mouse embryonic heart organ culture and gene expression system that facilitated the identification of epicardial enhancers activated during heart development and injury. Epicardial activation of these enhancers depends on a combinatorial transcriptional code centered on CCAAT/enhancer binding protein (C/EBP) transcription factors. Disruption of C/EBP signaling in the adult epicardium reduced injury-induced neutrophil infiltration and improved cardiac function. These findings reveal a transcriptional basis for epicardial activation and heart injury, providing a platform for enhancing cardiac regeneration.