The Role of OPA1 and Interacting Proteins in Mitochondrial Function

Abstract

The cell possesses a number of vital mechanisms to respond to different stressors. Mitochondria are dynamic organelles which undergo constant changes in length, transport and inner membrane structure and curvature. Invaginations of this inner membrane, cristae, have been known to respond to the energetic state of mitochondria, but the regulation of these changes as well as the consequences thereof remain undetermined. We find that Optic Atrophy 1 (OPA1), a protein involved in inner membrane fusion and cristae maintenance during cell death, can respond to the energetic state of mitochondria and the cell. Moreover, OPA1-dependent changes in cristae structure are required for resistance to starvation induced cell death, proper functioning of the electron transport chain, for growth in galactose media and for maintenance of ATP synthase assembly. Interestingly, we demonstrate that select members of the mitochondrial solute carriers (SLC25A) interact with OPA1 and affect the response of OPA1 to substrate levels. Taken together, we propose an SLC25A-dependent role for OPA1 in sensing energy substrate availability and responding to alter cristae, bioenergetics and cellular survival. We also identified KIAA0664 as a novel OPA1-interacting protein, describe its subcellular localization and investigate its role in mitochondrial fusion and in mitochondrial localization. Finally, since both known carriers of mitochondrial glutathione were demonstrated to interact with OPA1, we investigated the role of OPA1 in cellular glutathione redox. OPA1 depleted cells demonstrated both increased total cellular glutathione and a shift in redox to its reduced form. The role of OPA1 in glutathione levels and redox ratios required GTPase activity, but surprisingly not fusion. Since glutathione is a master regulator of reactive oxygen species detoxification, these findings may shed light on the role of OPA1 in ROS-induced cell death pathways.