Abstract 392: MicroRNA Plays an Essential Role in the Development of Cardiac Hypertrophy
MicroRNA (miR) are non-coding, ~21 nucleotide-long, RNA molecules that regulate gene expression post-transcription. A given miR will down-regulate an array of genes through specifically targeting the 3′UTR. MiR has recently been implicated in regulating development, growth, differentiation, survival, and proliferation, in a variety of species ranging from plants to human. In addition to normal cellular processes, it is also involved in the development of many forms of cancer. We predicted that miR might be involved in the development of cardiac hypertrophy. First, to identify miR that may be differentially regulated during hypertrophy, we preformed miR microarray analysis (with 340 mouse miR sequences identified to-date) on RNA isolated from the hearts of mice subjected to transverse aortic banding or a sham operation, for 1, 7, and 14 d (n=3, each). After 1 day, with no significant change in heart/body wt, 2 miRs were down-regulated and 3 were up-regulated (p<0.05). After 7 days, with ~30% increase in heart/body wt, 9 were down-regulated and 10 were up-regulated (p<0.05). Fourteen-day results are pending. Of those miR, the skeletal and cardiac specific, miR-1, but not miR-133a/b, was down-regulated (0.56±0.036) by day 1 post-banding, as confirmed by Northern blot analysis, and persisted through day 7. MiR-1 is highly conserved and its expression parallels myocyte differentiation. Our results also confirm its higher expression in the adult vs. neonatal heart. Second, to test the potential role of miR-1 in cardiac hypertrophy, we cloned miR-1 stem-loop precursor into recombinant adenovirus, for delivery to cardiac myocytes. The Sanger Institute, miR-1 predicted targets, include Ras GTPase-activating protein and cyclin-dependent kinase 9, both of which are essential for hypertrophic growth. Our data show that over-expression of miR-1 completely inhibited growth-induced up-regulation of both those targets, in addition to protein synthesis. Thus, we propose that microRNA play an essential regulatory role in the development of cardiac hypertrophy, wherein down-regulation of muscle-specific miR-1 is necessary for the relief of its growth-related target genes from its repressive influence.