Project description:Despite extensive studies on endogenous heart regeneration within the past 20 years, the players involved in initiating early regeneration events are far from clear. Here, we assessed the function of neutrophils, the first-responder cells to tissue damage, during heart regeneration. We detected rapid neutrophil mobilization to the injury site after ventricular amputation, peaking at 1-day post-amputation (dpa) and resolving by 3 dpa. Further analyses indicated neutrophil mobilization coincides with peak epicardial cell proliferation and recruited neutrophils associated with activated, expanding epicardial cells at 1 dpa. Neutrophil depletion inhibited myocardial regeneration and significantly reduced epicardial cell expansion, proliferation, and activation. To explore the molecular mechanism of neutrophils on the epicardial regenerative response, we performed scRNA-seq analysis of 1 dpa neutrophils and identified enrichment of the FGF and ERK signaling pathways. Pharmacological inhibition of FGF signaling indicated its’ requirement for epicardial cell expansion, while neutrophil depletion blocked ERK signaling activation in epicardial cells. Altogether, our studies revealed that neutrophils quickly induce epicardial cells, which later accumulate at the injury site and contribute to 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: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: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:The main goal of this study was to examine the presence and specific transcriptomic profile of epicardial adipose tissue (eAT) in zebrafish. We assessed how cold treatment affects the epicardial adipose tissue. Additional we provided some key differences between human, mouse and zebrafish epicardial adipose tissue.
Project description:The epicardium is a mesothelial tissue layer that envelops the heart. Cardiac injury activates dynamic gene expression programs in epicardial tissue, which in the case of zebrafish enables subsequent regeneration through paracrine and vascularizing effects. To identify tissue regeneration enhancer elements (TREEs) that control injury-induced epicardial gene expression during heart regeneration, we profiled transcriptomes and chromatin accessibility in epicardial cells purified from regenerating zebrafish hearts. We identified hundreds of candidate TREEs, defined by increased chromatin accessibility of non-coding elements near genes with increased expression during regeneration. Several of these candidate TREEs were incorporated into stable transgenic lines, with 5 of 6 elements directing injury-induced epicardial expression but not ontogenetic expression in hearts of larval animals. Whereas two independent TREEs linked to the gene gnai3 showed similar functional features of gene regulation in transgenic lines, two independent ncam1a-linked TREEs directed distinct spatiotemporal domains of epicardial gene expression. Thus, multiple TREEs linked to a regeneration gene can possess either matching or complementary regulatory controls. Our study provides a new resource and principles for understanding the regulation of epicardial genetic programs during heart regeneration.
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:In the adult heart, the epicardium becomes activated after injury, contributing to cardiac healing by secretion of paracrine factors. Here we analyzed by single-cell RNA sequencing combined with RNA in situ hybridization and lineage tracing of WT1+ cells the cellular composition, location, and hierarchy of epicardial stromal cells (EpiSC) in comparison to activated myocardial fibroblasts/stromal cells in infarcted mouse hearts. We identified 11 transcriptionally distinct EpiSC populations, that can be classified in three groups each containing a cluster of proliferating cells. Two groups expressed cardiac specification makers and sarcomeric proteins suggestive of cardiomyogenic potential. Transcripts of HIF-1α and HIF-responsive genes were enriched in EpiSC consistent with the epicardium being a hypoxic niche. Expression of paracrine factors was not limited to WT1+ cells but was a general feature of activated cardiac stromal cells. Our findings provide the cellular framework by which myocardial ischemia may trigger in EpiSC the formation of cardioprotective/regenerative responses.
Project description: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.