Abstract 14187: Mitochondrial Iron Accumulation Leads to Cardiomyocyte Death and its Levels are Directly Sensed in the Cytoplasm
Background: Maintaining mitochondrial iron balance is critical for normal cardiac function. We showed earlier that deletion of ATP-binding cassette B8 (ABCB8) protein which facilitates mitochondrial iron export results in mitochondrial iron accumulation, oxidative stress, dysfunction of cytosolic iron-sulfur (Fe/S) cluster proteins, and spontaneous development of cardiomyopathy in mice. Given the complex phenotype, it remains unexplored which of these processes are responsible for cytotoxicity with ABCB8 deletion. This study has characterized the effects of mitochondrial iron accumulation due to ABCB8 knockdown (KD) or knockout (KO) on cellular survival, and potential communication between the mitochondria and cytoplasm in sensing iron levels.
Results: To reverse mitochondrial iron accumulation with ABCB8 KD, we treated cells with various iron chelators, or with siRNA against mitoferrin-2 (MFRN2), the primary mitochondrial iron importer in cardiomyocytes. Both iron chelators and MFRN2 siRNA reversed mitochondrial iron accumulation, ROS production and cell death resulting from ABCB8 KD, suggesting that mitochondrial iron overload mediates cytotoxicity of ABCB8 deletion. To determine if the defect in cytosolic Fe/S proteins was primarily due to mitochondrial iron deregulation or was secondary to increased oxidative stress, we measured cytosolic Fe/S protein activity with iron chelators, MFRN2 siRNA, or antioxidant treatments. Neither MFRN2 siRNA nor various antioxidants were able to reverse inactivation of cytosolic Fe/S proteins with ABCB8 KD. However, iron chelator treatment rescued Fe/S protein activities in ABCB8 KD cells. Similarly, iron chelators reversed mitochondrial iron accumulation and restored activity of cytosolic Fe/S proteins in hearts from ABCB8 KO mice. Thus, the defect in maturation of cytosolic Fe/S proteins is independent of the oxidative stress, but is a direct effect of mitochondrial iron overload.
Conclusions: Cytotoxicity of ABCB8 KD and the defect in cytosolic Fe/S cluster maturation are due to mitochondrial iron accumulation, but not the associated oxidative stress. Moreover, our results suggest that mitochondrial iron is sensed in the cytoplasm and influences maturation of cytosolic Fe/S proteins.
- © 2013 by American Heart Association, Inc.