Abstract 105: The Novel Heart-specific Ring-finger Protein 207 Regulates Energy Metabolism in Cardiomyocytes

Abstract

Background: Ring-finger proteins constitute a large protein family in the human genome and play essential roles in various biological processes. However, little is known about heart-specific Ring-finger proteins and those relations with cardiac functions. We performed the comprehensive analysis of the expression profiles of various kinds of Ring-finger proteins and found that Ring-finger protein 207 (RNF207) was largely expressed in the heart. The purpose of our study was to elucidate a role of RNF207 in the heart. Methods and Results: First, we confirmed that RNF207 was predominantly expressed in the heart at the mRNA and protein level. Next, we examined whether the expression of RNF207 changed in transverse aortic constriction (TAC) model mice and coronary ischemic heart failure model mice . 4 weeks after TAC, mRNA level of RNF207 was significantly decreased to approximately 40% of that in sham mice. Moreover, we found that the protein level of RNF207 in the mice with heart failure was significantly reduced to around 70% of that in sham mice. Considering the well-known facts that the heart is a high-energy demanding organ and that the levels of ATP in cardiomyocytes are reduced in those model mice, we hypothesized that RNF207 got involved in cardiac energy metabolism. To investigate the hypothesis, we depleted RNF207 in rat neonatal cardiomyocytes (RNC) and performed metabolomic analysis. Metabolomic analysis revealed that ATP concentration and NADH/NAD + ratio were significantly lower and mitochondrial function was significantly reduced in RNF207 depleted RNC, compared to control NRC. Next, to elucidate the molecular mechanism by which RNF207 had effect on cardiac energy metabolism, we explored RNF207-associated proteins by mass spectrometric analysis. We identified voltage-dependent anion channel 1 (VDAC1) as a RNF207-associated protein. It has been shown that mitochondrial protein VDAC1 plays a crucial role in mitochondrial functions, such as energy metabolism. We confirmed that RNF207 directly interacted with VDAC1 by in vitro binding assay. Our results strongly indicate that RNF207 functions as a regulator of cardiac energy metabolism. Conclusion: RNF207 is a novel heart-specific protein and regulates energy metabolism in cardiomyocytes.