Regenerative and non-regenerative transcriptional states of the human epicardium: from foetus to adult and back again

Epicardial activation appears to be required for cardiac regeneration. Although reverting quiescent adult epicardium to an active neonatal or foetal state will likely represent a key therapeutic approach for human cardiac regeneration, the exact molecular differences between human adult and foetal epicardium are not understood. We used single-cell RNA sequencing to compare epicardial cells from both foetal and adult hearts. We found two foetal epicardial cell types, mesothelial and fibroblast-like, with only the mesothelial population present in adults. We also identified foetal-specific epicardial genes associated with regeneration and angiogenesis, and found that adult epicardium may be primed for immune and inflammatory responses. We predict that restoring the foetal epicardial state in human hearts would increase adult angiogenic potential. Finally, we demonstrated that human embryonic stem-cell derived epicardium is a valid model for the foetal epicardium and for investigating epicardial-mediated cardiac regeneration in humans. Our study defines regenerative programs in human foetal epicardium that are absent in the adult, brings human context to animal studies, and provides a roadmap for directing the epicardium in human heart regeneration.