Oxytocin promotes epicardial cell activation and heart regeneration after cardiac injury

Cardiovascular disease (CVD) is one of the leading causes of mortality worldwide, and frequently leads to massive heart injury and the loss of billions of cardiac muscle cells and associated vasculature. Critical work in the last two decades demonstrated that these lost cells can be partially regenerated by the epicardium, the outermost mesothelial layer of the heart, in a process that highly recapitulates its role in heart development. Upon cardiac injury, mature epicardial cells activate and undergo an epithelial-mesenchymal transition (EMT) to form epicardial-derived progenitor cells (EpiPCs), multipotent progenitors that can differentiate into several important cardiac lineages, including cardiomyocytes and vascular cells. In mammals, this process alone is insufficient for significant regeneration, but it may be possible to prime it by administering specific reprogramming factors, leading to enhanced EpiPC function. Here, we show that oxytocin (OXT), a hypothalamic neuroendocrine peptide, induces epicardial cell proliferation, EMT, and migration in a mature-like model of human induced pluripotent stem cell (hiPSC)-derived epicardial cells. In addition, we demonstrate that OXT is released from the brain into the bloodstream after cardiac cryoinjury in zebrafish, eliciting significant epicardial activation and promoting heart regeneration. Oxytocin signaling is also critical for proper epicardium and myocardium development in zebrafish embryos. The above processes are significantly impaired when OXT signaling is inhibited chemically and genetically through RNA interference. Mechanistically, RNA sequencing analyses suggest that the transforming growth factor beta (TGF-β) pathway is the primary mediator of OXT-induced epicardial activation. Our research reveals for the first time a primarily brain-controlled mechanism that induces cellular reprogramming and regeneration of the injured heart, a finding that could yield significant translational advances for the treatment of CVD.