Abstract 3066: Mitochondrial ATP-binding Cassette Protein-1 (mABC1) Plays a Role in Mitochondrial Iron Homeostasis and Cytosolic Iron-Sulfur Protein Assembly
Mitochondria play an important role in regulating cell death and survival. We have shown that overexpression of a novel mitochondrial protein, the mitochondrial ATP-binding cassette protein 1 (mABC1), protects neonatal rat cardiomyocytes (NRCM) against oxidant-induced cell death, however, the primary function of this protein is not known. Since the yeast homolog of mABC1 plays a role in mitochondrial iron homeostasis, we hypothesized that the primary function of mABC1 is to export iron-sulfur (Fe/S) clusters out of mitochondria for subsequent cytosolic Fe/S protein maturation. We took in vitro and in vivo approaches to study this hypothesis. Overexpression of mABC1 using an adenovirus in NRCM resulted in a significant decrease in mitochondrial non-heme iron (67.9±15.7 vs 80.2±19.0 ng/100 μg mitochondrial protein for mABC1 vs GFP transduced cells; P<0.05). When mABC1 levels were downregulated in NRCM using RNA interference, cells displayed a significantly higher non-heme iron levels (50.2±7.4% increase in mABC1- compared to control-siRNA transduced cells; P<0.05). Downregulation of mABC1 was also associated with an impaired xanthine oxidase (a cytosolic Fe/S protein) expression and enzyme activity, while the levels of succinate dehydrogenase (a mitochondrial Fe/S protein) were not altered by mABC1 reduction. Since mitochondrial iron is a source of oxidative stress, we also assessed the effects of mABC1 overexpression on the production of reactive oxygen species (ROS) and showed that ROS production was markedly reduced in cells overexpressing mABC1 compared to the control (71.3±4.7% less fluorescence in mABC1 vs GFP transduced cells; P<0.05). Doxorubicin, an anticancer drug that causes cardiomyopathy in an iron-dependent manner, reduced mABC1 levels and increased cell death, and its cytotoxicity increased with mABC1 knockdown. Finally, transgenic mice overexpressing mABC1 in their hearts were generated and shown to have a significantly lower mitochondrial non-heme iron levels. These results demonstrate that mABC1 plays a role in mitochondrial iron homeostasis and cytosolic iron-sulfur protein assembly. Furthermore, its cytoprotective effects may be through regulating mitochondrial iron, which is a source of ROS and cellular damage.