Abstract 3621: MicroRNA-21 Enhances AKT Activity and Reduces Myocyte Apoptosis and Ischemic Heart Failure Through Suppression of PTEN
MicroRNAs are posttranscriptional regulators of gene expression, which are involved in organogenesis and pathogenesis. Others and we have previously reported that miR-21 is highly upregulated during cardiac hypertrophy and carcinogenesis. We also showed that overexpression of miR-21 in a transgenic mouse model does not induce nor inhibit cardiac hypertrophy, but does ameliorate signs of pressure overload-induced heart failure. Similarly, when subjected to permanent coronary artery occlusion, the transgenic hearts vs. wild type littermates exhibited less apoptosis and fibrosis (2 vs. 20 fold), higher ejection fraction (52±2 vs. 36±2 %), lower left ventricular end diastolic pressure (13±3 vs. 22±6 mm Hg), and smaller left ventricular end diastolic volume (4.57±0.5 vs. 5.35±0.3 mm). The objective of this study was to identify the targets of miR-21 that mediate its protective effects. Phosphatase and tensin homolog (PTEN), a negative regulator of the AKT pathway, has been established as a target of miR-21 in cancer cells. We confirmed that overexpression of miR-21 in cardiac myocytes completely inhibited hypoxia-induced PTEN expression, whereas, knockdown of miR-21 enhanced its expression (4±0.7 fold). As a result, overexpression of miR-21 reduced mitochondrial damage during hypoxia (80±12 %). Similarly, ischemia-induced PTEN expression in the heart was completely suppressed in the miR-21 transgenic model. To examine the consequence of inhibiting PTEN expression, on activation of AKT, we overexpressed miR-21 in myocytes before stimulating them with insulin. This resulted in a robust amplification of insulin-induced AKT phosphorylation of Serine-473 (20±7 fold) and threonine-308 (5±1 fold), whereas it had no effect or phospho-Erk1/2. To verify whether this effect was indeed mediated through suppression of PTEN, we enriched the cells with exogenous PTEN that lacks the miR-21-targeted site, before providing them with miR-21 or insulin. This treatment resulted in complete inhibition of miR-21-insulin-stimulated AKT phosphorylation. In conclusion, overexpression of miR-21 in myocytes is anti-apoptotic through suppression of PTEN and, thereby, sensitization of the AKT pathway to receptor stimulation.