Common regulatory pathways mediate activity of microRNAs inducing cardiomyocyte proliferation

Loss of functional cardiomyocytes is a major determinant of heart failure after myocardial infarction. Previous high throughput screening studies have identified a series of microRNAs that induce cardiomyocyte proliferation and stimulate cardiac regeneration after myocardial infarction. Here we investigate the mechanism of action of the top ten most effective of these miRNAs. Analysis of the transcriptional profile of miRNA-treated cardiomyocytes revealed an involvement of the Hippo-YAP pathway in their action. All the investigated miRNAs activated YAP-mediated transcription, nuclear localization of active YAP and increased expression of YAP responsive genes. In particular, miR-199a-3p, one of the most effective miRNAs, directly downregulated two mRNA targets impinging on the Hippo pathway, the upstream inhibitory kinase TAOK1and the E3 ubiquitin ligase destroying YAP, b-TrCP. Most of the miRNAs that promoted proliferation also modulated the dynamics of the cardiomyocyte actin cytoskeleton. In particular, four miRNAs targeted Cofilin2 and increased the ratio between polymerized F-actin and monomeric G-actin. Cells treated with the most effective miRNAs (including miR-199a-3p) were round-shaped, with formation of gross bundles of actin fibers at the cytoplasm periphery. During mitosis, these miRNA-treated cardiomyocytes displayed disruption of the sarcomeric architecture. Downregulation of Cofilin2 itself was sufficient to promote cardiomyocyte proliferation, activate nuclear translocation of YAP and stimulate transcription of TEAD-responsive genes. Inhibition of F-actin polymerization decreased YAP activation. Collectively, these results indicate that activation of YAP and modulation of the acting cytoskeleton are major components of the pro-proliferative effect of miR-199a-3p and other miRNAs inducing cardiomyocyte proliferation Overall design: Cardiomyocyte transcriptomic profiles of 0-day old wild type (WT) rats were generated by deep sequencing using Illumina Hiseq 2000