Development of a Bmi1 + Cardiac Mouse Progenitor Immortalized Model to Unravel the Relationship with Its Protective Vascular Endothelial Niche.

The adult mammalian heart has been demonstrated to be endowed with low but real turnover capacity, especially for cardiomyocytes, the key functional cell type. The source, however, of that turnover capacity remains controversial. In this regard, we have defined and characterized a resident multipotent cardiac mouse progenitor population, Bmi1 +DR (for Bmi1 + Damage-Responsive cells). Bmi1 +DR is one of the cell types with the lowest ROS (Reactive Oxygen Species) levels in the adult heart, being particularly characterized by their close relationship with cardiac vessels, most probably involved in the regulation of proliferation/maintenance of Bmi1 +DR. This was proposed to work as their endothelial niche. Due to the scarcity of Bmi1 +DR cells in the adult mouse heart, we have generated an immortalization/dis-immortalization model using Simian Vacuolating Virus 40-Large Antigen T (SV40-T) to facilitate their in vitro characterization. We have obtained a heterogeneous population of immortalized Bmi1 +DR cells ( Bmi1 +DR IMM ) that was validated attending to different criteria, also showing a comparable sensitivity to strong oxidative damage. Then, we concluded that the Bmi1 -DR IMM population is an appropriate model for primary Bmi1 +DR in vitro studies. The co-culture of Bmi1 +DR IMM cells with endothelial cells protects them against oxidative damage, showing a moderate depletion in non-canonical autophagy and also contributing with a modest metabolic regulation.