Setd4 controlled quiescent c-Kit(+) cells contribute to cardiac neovascularization of capillaries beyond activation

Blood vessels in the adult mammal exist in a highly organized and stable state. In the ischemic heart, limited expansion capacity of the myocardial vascular bed cannot satisfy demands for oxygen supply and the myocardium eventually undergoes irreversible damage. The predominant contribution of endogenous c-Kit(+) cells is understood to be in the development and homeostasis of cardiac endothelial cells, which suggests potential for their targeting in treatments for cardiac ischemic injury. Quiescent cells in other tissues are known to contribute to the long-term maintenance of a cell pool, preserve proliferation capacity and, upon activation, facilitate tissue homeostasis and regeneration in response to tissue injury. Here, we present evidence of a Setd4-expressing quiescent c-Kit(+) cell population in the adult mouse heart originating from embryonic stages. Conditional knock-out of Setd4 in c-Kit-CreER(T2);Setd4(f/f);Rosa26(TdTomato) mice induced an increase in vascular endothelial cells of capillaries in both neonatal and adult mice. We show that Setd4 regulates quiescence of c-Kit(+) cells by the PI3K-Akt-mTOR signaling pathway via H4K20me3 catalysis. In myocardial infarction injured mice, Setd4 knock-out resulted in attenuated cardiomyocyte apoptosis, decreased infarction size and improved cardiac function. Lineage tracing in Setd4-Cre;Rosa26(mT/mG) mice showed that Setd4(+) cells contribute to each cardiac lineage. Overall, Setd4 epigenetically controls c-Kit(+) cell quiescence in the adult heart by facilitating heterochromatin formation via H4K20me3. Beyond activation, endogenous quiescent c-Kit(+) cells were able to improve cardiac function in myocardial infarction injured mice via the neovascularization of capillaries.