Abstract 636: Cytoprotective Role of Mitochondrial ATP-Binding Cassette Protein-2
The molecular mechanisms that lead to myocardial cell death in ischemic heart disease are not totally understood; however, mitochondria are thought to play an important role in this process. We recently showed that a novel mitochondrial protein, mitochondrial ATP-binding cassette protein 1 (mABC1), plays a role in protection against oxidative stress. mABC1 belongs to the ABC family of proteins, and thus far, eight mitochondrial ABC proteins have been identified in mammalian and yeast cells. One member of this family, mABC2, shares significant sequence homology with mABC1, however, its function is not known. A yeast homolog of mABC2 was recently shown to play a novel role in cellular resistance to oxidative stress. Based on these observations, we hypothesized that mABC2 also plays a key role in protection of cells against oxidative stress. We studied this hypothesis by modulating the levels of mABC2 in tissue culture via overexpression and RNA interference (RNAi). To assess the effects of overexpression and downregulation of mABC2, mitochondrial membrane potential was measured by flow cytometry of tetramethylrhodamine ethyl ester (TMRE)-loaded cells. Treatment with mABC2 RNAi increased cell death (93±1% vs. 76±2% survival for control siRNA and mABC2 siRNA, respectively; P < 0.05), while overexpression resulted in protection against cell death in the presence of hydroge peroxide (73±2% vs. 90±1% survival for green fluorescent protein (GFP) transfected cells+H2O2 and mABC2+H2O2, respectively; P < 0.05). Furthermore, dog hearts subjected to ischemia displayed higher levels of mABC2 protein, suggesting a role for this protein in ischemic injury. Similar results were obtained in explanted hearts of patients with ischemic cardiomyopathy (normalized band intensity of 1.00±0.15 vs 1.97±0.18 for control and ischemic cardiomyopathy, respectively). These results support the notion that mABC2 protein plays an important role in cellular protection against oxidative stress, and identifies mABC2 as a novel target for cardioprotective therapeutics.