Abstract 64: Meis1 Is a Key Regulator of Postnatal Cardiomyocyte Cell Cycle Arrest

Abstract

Heart failure is a costly and deadly disease affecting over 5 million Americans. The inability of the adult mammalian heart to regenerate following injury lies at core of the pathophysiology of heart failure. We recently showed that the neonatal mammalian heart is capable of complete regeneration following resection of the entire ventricular apex. Moreover, our preliminary data indicate that the neonatal mouse heart is also capable of complete regeneration following ischemic myocardial infarction. In both these types of injury, the regenerative response is associated with robust proliferation of cardiomyocytes without significant hypertrophy or fibrosis. Genetic fate mapping studies demonstrated that the majority of newly formed cardiomyocytes originated from pre-existing cardiomyocytes. In an effort to determine the mechanism of cardiomyocytes cell cycle arrest after the first week of life, we performed a gene array after cardiac injury at multiple post-natal timepoints. This enabled us to identify Meis1 as a potential regulator of neonatal cardiomyocyte proliferation. Meis1, which belongs to the TALE family of homeodomain transcription factors, is required for normal hematopoiesis and cardiac development. While Meis1 has been extensively studied in the hematopoietic system, little is known about its role in the heart. Our results indicate that Meis1 expression and nuclear localization in the post-natal cardiomyocytes coincides with cell cycle arrest. To further explore this pattern, we generated a cardiomyocyte-specific Meis1 knockout mouse, and showed that loss of Meis1 results in robust cardiomyocyte proliferation in the adult heart. Moreover, we identified p16 and p21; two synergistic cyclin dependent kinase inhibitors that induce arrest at all three cell cycle checkpoints, as potential targets for transcriptional activation by Meis1. These results identify Meis1 as a key regulator of post-natal cardiomyocyte cell cycle arrest, and a potential therapeutic target for cardiac regeneration.