Background: Several microRNAs (miRs) have been shown to regulate gene expression in the heart, and dysregulation of their expression has been linked to cardiac disease. miR-378 is strongly expressed in the mammalian heart but so far has been studied predominantly in cancer, in which it regulates cell survival and tumor growth.
Methods and results: Here, we report tight control of cardiomyocyte hypertrophy through miR-378. In isolated primary cardiomyocytes, miR-378 was found to be both necessary and sufficient to repress cardiomyocyte hypertrophy. Bioinformatic prediction suggested that factors of the mitogen-activated protein kinase (MAPK) pathway are enriched among miR-378 targets. Using mRNA and protein expression analysis along with luciferase assays, we validated 4 key components of the MAPK pathway as targets of miR-378: MAPK1 itself, insulin-like growth factor receptor 1, growth factor receptor-bound protein 2, and kinase suppressor of ras 1. RNA interference with these targets prevented the prohypertrophic effect of antimiR-378, suggesting their functional relation with miR-378. Because miR-378 significantly decreases in cardiac disease, we sought to compensate for its loss through adeno-associated virus-mediated, cardiomyocyte-targeted expression of miR-378 in an in vivo model of cardiac hypertrophy (pressure overload by thoracic aortic constriction). Restoration of miR-378 levels significantly attenuated thoracic aortic constriction-induced cardiac hypertrophy and improved cardiac function.
Conclusions: Our data identify miR-378 as a regulator of cardiomyocyte hypertrophy, which exerts its activity by suppressing the MAPK signaling pathway on several distinct levels. Restoration of disease-associated loss of miR-378 through cardiomyocyte-targeted adeno-associated virus-miR-378 may prove to be an effective therapeutic strategy in myocardial disease.
Keywords: cardiomyocytes; gene therapy; hypertrophy; microRNA.