Divergent cell cycle kinetics of midgestation ventricular cells entail a higher engraftment efficiency after cell transplantation.

Cardiac progenitor cells (CPCs) in the primary and secondary heart fields contribute to the formation of all major cell types in the mammalian heart. While some CPCs remain undifferentiated in midgestation and postnatal hearts, very little is known about their proliferation and differentiation potential. In this study, using an Nkx2.5 cell lineage-restricted reporter mouse model, we provide evidence that Nkx2.5(+) CPCs and cardiomyocytes can be readily distinguished from nonmyocyte population using a combination of Nkx2.5 and sarcomeric myosin staining of dispersed ventricular cell preparations. Assessment of cell number and G1/S transit rates during ventricular development indicates that the proliferative capacity of Nkx2.5(+) cell lineage gradually decreases despite a progressive increase in Nkx2.5(+) cell number. Notably, midgestation ventricles (E11.5) contain a larger number of CPCs (∼2-fold) compared with E14.5 ventricles, and the embryonic CPCs retain cardiomyogenic differentiation potential. The proliferation rates are consistently higher in embryonic CPCs compared with myocyte population in both E11.5 and E14.5 ventricles. Results from two independent cell transplantation models revealed that E11.5 ventricular cells with a higher percentage of proliferating CPCs can form larger grafts compared with E14.5 ventricular cells. Furthermore, transplantation of embryonic ventricular cells did not cause any undesirable side effects such as arrhythmias. These data underscore the benefits of donor cell developmental staging in myocardial repair.