PROJECT SUMMARY Regulation of OXPHOS assembly in skeletal muscles The skeletal musculature is by far the largest organ in animals, accounting for about half the body weight of humans and up to 75% of the body mass of insects. In order to provide the energy required for contraction of muscles, skeletal muscles tend to be highly enriched with mitochondria. Accordingly, mitochondrial disorders frequently present with myopathy as a prominent clinical feature. While the factors responsible for increasing overall mitochondrial mass during myogenesis have been well-characterized, relatively little is known about the specific factors that assist with assembling the oxidative phosphorylation (OXPHOS) complexes in muscles. The broad and long-term objective of my research group is to discover and elucidate the mechanism(s) by which various proteins regulate OXPHOS assembly in skeletal muscles. Apoptosis Inducing Factor (AIF) is a nuclear- encoded oxidoreductase that is largely localized to the mitochondrial intermembrane space. Mutations in AIF cause major alterations in the OXPHOS system and is associated with muscle atrophy in humans. However, the precise mechanism by which AIF exerts its bioenergetics functions has not been resolved. The rising number of pathogenic AIF variants underscores the importance of AIF in human pathophysiology and has made seeking therapeutic options difficult, as it is a major reason for the highly pleiotropic nature of AIF mutations. Therefore, elucidating the mechanism by which AIF regulates OXPHOS assembly in muscles is significant, and is a crucial unmet need, as it will allow the development of therapeutic strategies that exploit various functional properties of AIF to treat specific pathological mutations of the protein in muscles. Accordingly, we have established a genetically tractable system for studying AIF’s function in Drosophila flight muscles. Based on our findings discussed elsewhere in this proposal, we have formulated the following central hypothesis to be tested: AIF is a key signaling hub that regulates OXPHOS assembly through its effect on stabilizing the mitochondrial intermembrane space bridging (MIB) supercomplex, reactive oxygen species (ROS) formation and interaction with other proteins. We will test our hypothesis via three specific aims. First, we will dissect the mechanism by which AIF regulates OXPHOS biogenesis via the MIB supercomplex (Aim 1) and elucidate how ROS signaling impinges on the AIF bioenergetics phenotypes (Aim 2). Finally, we will define and functionally characterize the AIF interactome (Aim 3). We will be using blue native polyacrylamide gel electrophoresis (BN-PAGE), in-gel OXPHOS activity assays, Western blots, RNA-seq, genetics, transmission electron microscopy, and a range of physiology and cell biology assays to address these questions. Altogether, we envisage that the ease of isolating copious amounts of mitochondria from Drosophila flight muscles, extensive arsenal of tools for genetic analyses, relatively short generation time, and limited gene redundancy in Drosophila are assets that should make it feasible to elucidate the mechanism by which AIF regulates OXPHOS assembly.

PROJECT NARRATIVE These studies will lead to fundamental new insights into the mechanism by which AIF regulates OXPHOS assembly in muscles. In addition, these studies have the potential to identify novel regulators of OXPHOS assembly that interact with AIF to regulate muscle bioenergetics. This may open up therapeutic opportunities for muscle diseases linked to mutations in AIF.