The miR-15 Family Regulates Post-natal Mitotic Arrest of Cardiomyocytes

Rationale—Mammalian cardiomyocytes withdraw from the cell cycle during early post-natal development, which significantly limits the capacity of the adult mammalian heart to regenerate following injury. The regulatory mechanisms which govern cardiomyocyte cell cycle withdrawal and binucleation are poorly understood. Objective—Given the potential of microRNAs (miRNAs) to influence large gene networks and modify complex developmental and disease phenotypes, we searched for miRNAs that were regulated during the postnatal switch to terminal differentiation. Methods and Results—Microarray analysis revealed subsets of miRNAs that were up- or down-regulated in cardiac ventricles from mice at 1- and 10-days of age (P1 and P10). Interestingly, miR-195 (a member of the miR-15 family) was the most highly up-regulated miRNA during this period, with expression levels almost 6-fold higher in P10 ventricles relative to P1. Precocious over-expression of miR-195 in the embryonic heart was associated with ventricular hypoplasia and ventricular septal defects in βMHC-miR-195 transgenic mice. Using global gene profiling and Argonaute-2 immunoprecipitation approaches, we show that miR-195 regulates the expression of a number of cell cycle genes, including checkpoint kinase 1 (Chek1), which we identify as a highly conserved direct target of miR-195. Finally, we demonstrate that knock-down of the miR-15 family in neonatal mice using locked nucleic acid (LNA)-modified antimiRs is associated with an increased number of mitotic cardiomyocytes and de-repression of Chek1. Conclusions—These findings suggest that up-regulation of the miR-15 family during the neonatal period may be an important regulatory mechanism governing cardiomyocyte cell cycle withdrawal and binucleation.