Abstract 342: Upregulation Of Mir-21 During Cardiac Hypertrophy Induces Down-regulation Of An Inhibitor Of The Ras-MAPK Pathway, Sprouty 2

Abstract

MicroRNA (miRNA) are ~22 ribonucleotides-long, with a potential to recognize multiple mRNA targets guided by sequence complimentarity. This class of molecules is functionally versatile, with the capacity to specifically inhibit translation, as well as, induce mRNA degradation, through targeting the 3′ untranslated regions. The levels of individual miRNA vary under different developmental, biological, or pathological conditions, thus, implicating them in normal and pathological cellular attributes. We have previously reported a miRNA signature that distinguishes pressure-overload compensatory hypertrophy by recapitulating the neonatal pattern. In that model we found that miR-21 is one of the highest differentially expressed miRNA (~8x). Thus, we hypothesized that miR-21 may contribute to the development of hypertrophy by inducing down-regulation of antagonizing genes. To experimentally test the effect of miR-21 on cardiac myocytes, we generated adenoviruses harboring primary miR-21 or, uniquely, anti-miR-21 sequences. These viruses were used to infect cultured myocytes. Interestingly, overexpression of miR-21 resulted in extensive, dose-dependent, branching (sprouting) of the cells. Computational predictions by ’TargetScanS’ identified Sprouty 1 and 2 as potential targets. Subsequently, we confirmed down-regulation of sprouty by over-expression of miR-21. Conversely, knocking down miR-21, using anti-miR-21, resulted in enhanced expression of sprouty during growth-induced conditions. Immunocytochemical staining shows that it is localized to sarcomeric structures and the nucleus. Sprouty is a known inhibitor of the Ras-MAPK signaling pathway and is, concordantly, downregulated in many forms of cancer. Notably, sprouty also negatively regulates ureteric and tracheal branching during morphogenesis. In heart, sprouty has been suggested to control myocyte size and vascularization during mechanical stress-induced ventricular remodeling. Thus, we propose that upregulation of miR-21 during cardiac hypertrophy, induces down-regulation of sprouty, which results in activation of the Ras-MAPK pathway. Moreover, down-regulation of sprouty is necessary for the increased myocyte branching observed during hypertrophy.