Direct comparison of mononucleated and binucleated cardiomyocytes reveals molecular mechanisms underlying distinct proliferative competencies

The mammalian heart is incapable of regenerating a sufficient number of cardiomyocytes to ameliorate the loss of contractile muscle after acute myocardial injury, often resulting in heart failure. Several reports have demonstrated that mononucleated (MoNuc) cardiomyocytes are more responsive to pro-proliferative stimuli than are binucleated (BiNuc) cardiomyocytes. However, techniques to isolate and characterize these two different cardiomyocyte populations have been lacking. We have developed a novel fluorescence associated cell sorting method to isolate highly enriched populations of MoNuc and BiNuc cardiomyocytes at various times of development. Transcriptome analysis reveals an underlying biological signature that defines the differences between MoNucs and BiNucs, including a central role for the E2f/Rb transcriptional network in establishing the divergent ability of these two populations to re-enter and complete the cell cycle. Moreover, inducing binucleation by genetically blocking the ability of cardiomyocytes to complete cytokinesis leads to a reduction in E2f target gene expression, linking the E2f pathway with nucleation. These data identify key molecular differences between MoNuc and BiNuc mammalian cardiomyocytes that can be used to leverage cardiomyocyte proliferation for promoting injury repair in the heart.