Single-cell and spatial heterogeneity landscapes of mature epicardial cells

Tbx18,Wt1,and Tcf21 have been identified as epicardial markers during the early embryonic stage.However,the gene markers of mature epicardial cells remain unclear.Single-cell transcriptomic analysis was performed with the Seurat,Monocle,and CellphoneDB packages in R software with standard procedures.Spatial transcriptomics was performed on chilled Visium Tissue Optimization Slides(10x Genomics)and Visium Spatial Gene Expression Slides(10x Genomics).Spatial transcriptomics analysis was performed with Space Ranger software and R software.Immunofluorescence,whole-mount RNA in situ hybridization and X-gal staining were performed to validate the analysis results.Spatial transcriptomics analysis revealed distinct transcriptional profiles and functions between epicardial tissue and non-epicardial tissue.Several gene markers specific to postnatal epicardial tissue were identified,including Msln,C3,Efemp1,and Upk3b.Single-cell transcriptomic analysis revealed that cardiac cells from wildtype mouse hearts(from embryonic day 9.5 to postnatal day 9)could be categorized into six major cell types,which included epicardial cells.Throughout epicardial development,Wt1,Tbx18,and Upk3b were consistently expressed,whereas genes including Msln,C3,and Efemp1 exhibited increased expression during the mature stages of development.Pseudotime analysis further revealed two epicardial cell fates during maturation.Moreover,Upk3b,Msln,Efemp1,and C3 positive epicardial cells were enriched in extracellular matrix signaling.Our results suggested Upk3b,Efemp1,Msln,C3,and other genes were mature epicardium markers.Extracellular matrix signaling was found to play a critical role in the mature epicardium,thus suggesting potential therapeutic targets for heart regeneration in future clinical practice.

Cardiac cell type-specific responses to injury and contributions to heart regeneration

Heart disease is the leading cause of mortality worldwide.Due to the limited proliferation rate of mature cardiomyocytes,adult mammalian hearts are unable to regenerate damaged cardiac muscle following injury.Instead,injured area is replaced by fibrotic scar tissue,which may lead to irreversible cardiac remodeling and organ failure.In contrast,adult zebrafish and neonatal mammalian possess the capacity for heart regeneration and have been widely used as experimental models.Recent studies have shown that multiple types of cells within the heart can respond to injury with the activation of distinct signaling pathways.Determining the specific contributions of each cell type is essential for our understanding of the regeneration network organization throughout the heart.In this review,we provide an overview of the distinct functions and coordinated cell behaviors of several major cell types including cardiomyocytes,endocardial cells,epicardial cells,fibroblasts,and immune cells.The topic focuses on their specific responses and cellular plasticity after injury,and potential therapeutic applications.

Cholesterol metabolic enzyme Ggpps regulates epicardium development and ventricular wall architecture integrity in mice

During embryonic heart development,the progenitor cells in the epicardium would migrate and differentiate into noncardiomyocytes in myocardium and affect the integrity of ventricular wall,but the underlying mechanism has not been well studied.We have found that myocardium geranylgeranyl diphosphate synthase(Ggpps),a metabolic enzyme for cholesterol biosynthesis,is critical for cardiac cytoarchitecture remodelling during heart development.Here,we further reveal that epicardial Ggpps could also regulate ventricular wall architecture integrity.Epicardium-specific deletion of Ggpps before embryonic day 10.5(E10.5)is embryonic lethal,whereas after E13.5 is survival but with defects in the epicardium and ventricular wall structure.Ggpps deficiency in the epicardium enhances the proliferation of epicardial cells and disrupts cell‒cell contact,which makes epicardial cells easier to invade into ventricular wall.Thus,the fibroblast proliferation and coronary formation in myocardium were found enhanced that might disturb the coronary vasculature remodelling and ventricular wall integrity.These processes might be associated with the activation of YAP signalling,whose nuclear distribution is blocked by Ggpps deletion.In conclusion,our findings reveal a potential link between the cholesterol metabolism and heart epicardium and myocardium development in mammals,which might provide a new view of the cause for congenital heart diseases and potential therapeutic target in pathological cardiac conditions.