Ezh2 is not required for cardiac regeneration in neonatal mice.

The neonatal mouse heart has the remarkable capacity to regenerate lost myocardium within the first week of life. Neonatal cardiomyocytes re-express fetal genes that control cell proliferation after injury to promote regeneration. The loss of regenerative capacity of the heart one week after birth coincides with repression of a fetal transcriptional program coordinated by epigenetic regulators. The histone methyltransferase enhancer of zeste homolog 2 (Ezh2) is a repressor of fetal cardiac transcriptional programs and suppresses cardiomyocyte cell proliferation, suggesting a potential function in heart regeneration. However, it was recently demonstrated that Ezh2 is dispensable for heart regeneration in the neonatal heart. Here, we provide evidence supporting this finding and demonstrate that Ezh2 deficiency does not affect regeneration of the neonatal heart. We inactivated Ezh2 in differentiating embryonic cardiomyocytes, which led to depletion of histone H3 trimethylated at lysine 27 (H3K27me3). Ezh2 deficiency in cardiomyocytes did not affect clearance of the fibrotic scar in myocardial infarction (MI) and apical resection models of cardiac injury at post-natal day 1 (P1). Similarly, cardiomyocyte-specific loss of Ezh2 did not affect fibrotic scar size after MI or apical resection at P7, suggesting that it does not extend the regenerative time window. Our results demonstrate that Ezh2 is not required for innate neonatal cardiac regeneration.