The Hippo-YAP signalling pathway has recently emerged as a promising target to induce cardiac regeneration post myocardial infarction (MI). However, limited understanding of its regulatory mechanisms remains a major obstacle to overcome in order to effectively target this pathway for therapeutic applications. MicroRNAs have been shown to regulate Hippo pathway components in previous studies. In this study, we identified a novel microRNA that effectively regulates the Hippo pathway and induces cardiomyocyte proliferation in vitro and in vivo.
We conducted a bioinformatics study followed by screening analysis using a YAP-luciferase reporter system and identified miR-411 and miR-181a as potential novel Hippo pathway regulators. We used neonatal rat cardiomyocytes (NRCMs) to test the effects of miR-411 and miR-181a expression in vitro. By analysing several cell proliferation markers, we have found that miR-411 significantly induced cardiomyocyte proliferation whilst miR-181a expression did not cause any changes. Additionally, miR-411 could effectively induce YAP activity by reducing its phosphorylation level. We then performed in vivo experiments by overexpressing miR-411 in adult mouse hearts using the nanoparticle polyethylenimine (PEI). Five days post injection, the numbers of Ki-67 and EdU positive nuclei were increased significantly, suggesting that miR-411 can induce proliferation in adult cardiomyocytes in vivo. To test the effect of miR-411 overexpression in a disease model, we subjected adult C57BL/6J mice to MI followed by intramyocardial injection of miR-411/PEI complex. Four weeks after MI, mice injected with miR-411 displayed improved cardiac contractility (ejection fraction) compared to controls. To elucidate the target genes, we analysed expressions of 30 genes predicted as the most likely miR-411 targets in silico. We found that the expression of Foxo1, a known inhibitor of YAP, was significantly decreased in NRCMs and adult mouse heart overexpressing miR-411. These data suggest that miR-411 may increase YAP activity by targeting Foxo1.
In conclusion, miR-411 expression induces cardiomyocyte regeneration and improves cardiac function post-MI by enhancing YAP activity. The mechanism is likely through inhibition of Foxo1 expression.