BMI1 stress-related functions contribute to the redox-dependent fate of adult cardiac progenitors

The accumulation of reactive oxygen species (ROS) is linked to several cardiovascular pathologies; it is also associated with cell cycle exit by nenonatal cardiomyocytes, a key limiting factor in the regenerative capacity of the adult mammalian heart. BMI1 is a component of the polycomb complex 1, which is linked to adult multipotent progenitors, and is also an important partner in DNA repair and redox regulation. Here we show that high BMI1 expression is associated with a cardiac Sca1+ progenitor subpopulation with low ROS levels. In homeostasis, BMI1 represses cell-fate genes, including a cardiogenic differentiation program. Persistent oxidative damage nonetheless modified BMI1 activity in vivo, by derepressing canonical target genes in favor of their antioxidant and anticlastogenic functions. This derepression induced cardiac progenitor proliferation and differentiation, and thus increased its contribution to mature cardiac progeny. This redox-mediated mechanism is not restricted to damage situations, and we report ROS-associated differentiation of cardiac progenitors in steady state. These findings demonstrate how redox status influences the adult cardiac progenitor response, and identifies a redox-mediated BMI1 function with potential implications in adult cardiac turnover.