Abstract Body: Introduction
Following cardiac injury, neonatal mouse hearts completely regenerate. However, shortly after birth, cardiomyocytes undergo DNA synthesis without cytokinesis. This results in most cardiomyocytes becoming binucleated, undergoing cell cycle arrest, and losing the ability to regenerate the heart. Notably, Aurora B kinase (Aurkb), a key regulator of cytokinesis, sharply declines in cardiomyocytes after birth.

Hypothesis/Aims
A long-standing unanswered question in the field is whether multinucleated cardiomyocytes can bypass mitosis and directly undergo cytokinesis. We aim to characterize the effect of Aurkb on cardiomyocyte proliferation and cytokinesis in vivo.

Methods/Results
To address this, we generated TRE-Aurkb; αMHC-rtTA transgenic mice that express Aurkb in cardiomyocytes upon doxycycline exposure to determine whether forced induction of cytokinesis generates mononucleated cardiomyocytes and restores the endogenous regenerative properties of the myocardium.

Prior to cardiomyocyte binucleation, TRE-Aurkb; αMHC-rtTA mice were treated with doxycycline from P0-P7 and harvested at P7. Neonatal cardiomyocyte-specific Aurkb overexpression increased mitotic phosphohistone H3 (Ser10) positive cardiomyocytes and Aurkb+ cardiomyocytes undergoing cytokinesis.

To assess the effect of inducing Aurkb in P21 heart (a stage when most cardiomyocytes in mice are already binucleated), TRE-Aurkb; αMHC-rtTA mice were treated with doxycycline from P21-P35 and harvested at P35. In contrast to the neonatal cardiomyocytes, overexpression of Aurkb in juvenile cardiomyocytes led to no significant change in mitosis of pH3(Ser10)-positive cardiomyocytes, but increased cardiomyocytes undergoing cytokinesis. This increased total cardiomyocytes and the proportion of mononucleated cardiomyocytes, while decreasing the proportion of binucleated cardiomyocytes.

Conclusion
Collectively, these results demonstrate that Aurkb promotes mitosis and cytokinesis in neonatal cardiomyocytes, and after cardiomyocyte binucleation Aurkb overexpression bypasses mitosis to directly induce cytokinesis. Aurkb-mediated cytokinesis represents a potential strategy to expand cardiomyocyte number to treat heart failure.