Abstract 59: Antimir Therapy Ameliorates HIF1-mediated Loss of SERCA2 and Cardiac Contractility

Abstract

Ischemic heart disease is a major precipitant of heart failure in the developed world. Hypoxia inducible factor 1 (HIF1) is a highly oxygen-sensitive protein and the principal regulator of hypoxia-related signaling including changes in metabolism and angiogenesis. To more fully understand the role of HIF1 in the heart, our lab has developed a transgenic mouse model in which a stable form of HIF-1alpha can be inducibly expressed under normoxic conditions in cardiomyocytes. Upon HIF1 induction, genes associated with calcium signaling are downregulated and metabolism is shifted toward glycolysis. Strikingly, these mice also show a rapid decrease in cardiac contractility and concurrent loss of SERCA2 protein expression (up to 90%) within one week. SERCA2a (sarcoplasmic/endoplasmic reticulum calcium ATPase 2) is the ATP-dependent calcium pump required for calcium re-uptake during excitation-contraction coupling in the heart and its dysfunction has been implicated in heart failure. To extend the physiological significance of these findings, we examined ischemic heart tissue from WT mice subjected to ligation of the left anterior descending (LAD) artery to mimic myocardial infarction. At one day and 3 days post-ligation, we observed an increase in transcripts needed for glycolysis and decreased abundance of transcripts from the genes for proteins that regulate excitation-contraction including the ryanodine receptor, phospholamban and SERCA2. We also observed that while SERCA2 transcript decreased in HIF1 transgenic hearts, it did not fully account for the observed protein loss. Microarray analysis found miR-29c to be substantially upregulated and a potential regulator of SERCA2 expression. Subsequent in vitro analysis confirmed miR-29c reduced SERCA2 expression by 20-30% and could be modulated with an anti-sense inhibitor. In vivo administration of the antimir to miR-29c also improved cardiac contractility and SERCA2 expression in HIF1 transgenic mice. These results suggest that a HIF1 regulated microRNA, miR-29c, contributes to loss of SERCA2 in hypoxia and can be therapeutically targeted to improve cardiac function.