Upstream Requirements for the Regulation of Mitochondrial Bioenergetics by the Mitochondrial Acyl Carrier Protein

PROJECT SUMMARY Recent advances in cell biology have implicated metabolism in diseases ranging from cancer to heart failure. The cellular hubs of metabolism, mitochondria, are often called the “powerhouses of the cell,” and have become an attractive therapeutic target for these common diseases. Patients suffering from mitochondrial disease also stand to benefit from mitochondrially-targeted therapeutics. However, currently, our ability to influence mitochondrial function therapeutically is limited. Uncovering how mitochondria regulate energy production in normal conditions will provide the groundwork for the development of future treatment strategies. The mitochondrial acyl carrier protein (mtACP) sits at the intersection of nutrient inputs and energy expenditure in the mitochondria. The acylated form of mtACP both serves as a source for citric acid cycle (TCA) enzyme activation via lipoylation, as well as a stabilization factor in electron transport chain assembly, controlling the two major arms of mitochondrial oxidative metabolism. Despite its central role in oxidative metabolism, how acyl-mtACP is formed in the mitochondria is poorly defined. Acyl-mtACP formation relies on a 4’- phosphopantetheine (4’-PP) modification, followed by the addition of 2-carbon units from malonyl-CoA decarboxylation via de novo mitochondrial fatty acid synthesis (mtFAS). The enzyme responsible for mtACP 4’- phosphopantethenylation in vivo is not known, and the subcellular compartment where this occurs is undefined yet has major implications for the regulation of this process. Finally, the carbon substrate of mtFAS is highly disputed. The carbon source for mtACP acylation has huge implications for the regulation of mtACP and therefore mitochondrial oxidative metabolism. Our preliminary analyses indicate that mtACP is 4’- phosphopantetheinylated in the mitochondria by the only known mammalian PPTase: AASDHPPT, and that mitochondrial acetyl-CoA provides carbon for acylation of mtACP by mtFAS. The experiments in this proposal will definitively explain how mtACP is activated (4’-PP) and how the acylation substrate (malonyl-CoA) is generated, thus providing a clearer picture of upstream regulation of mtACP in mammalian mitochondria. Understanding the key enzymes in mtACP activation and their activity in cells will provide the foundation for future studies that seek to modulate mtACP activity in patients with mitochondrial dysfunction. The proposed study will be conducted as part of the applicant’s training in a joint MD-PhD program through Michigan State University College of Human Medicine and the Van Andel Insitute. The Van Andel Insitute provides PhD training in a small and collaborative environment with world-class scientists and state-of-the art facilities. The applicant will receive mentorship from leading experts in the field of metabolism, metabolomics, and cell biology, as well as complete support for continued clinical activity, collaboration across scientific disciplines, and professional development throughout the degree program.