Project Summary Mitochondrial energy production in the heart is crucial for proper cardiac function due to its high energy demand. Cardiolipin is a phospholipid localized in the inner mitochondrial membrane that is necessary for mitochondrial energy production via oxidative phosphorylation. Consisting of two head-groups and four acyl-chains, there are tremendous numbers of molecular species of cardiolipin with varying acyl chain compositions. Among them, the heart enriches linoleic acid (LA)-cardiolipin. It has been suggested that the cardiac form of cardiolipin may be patho- and physiologically significant in cardiac function by facilitating energy production. Genetic disorders of enzymes in cardiolipin metabolism with the reduced LA-cardiolipin in the heart are accompanied by cardiomyopathy and mitochondrial dysfunction. Also, disturbed cardiolipin profiles are observed in several cardiac failures. However, the importance of correct cardiolipin acylation is not fully understood. The goal of this study is to determine the mechanisms underlying the specific regulation of cardiac cardiolipin by reconciling three hotly debated cardiolipin acylation theories: 1) LA-cardiolipin is dependent on an enzyme Tafazzin that remodels cardiolipin with acquired preference for LA; 2) IMM protein environment controls cardiolipin acylation, and; 3) tissue-specific lipid pools drive cardiolipin diversity. The contribution of each theory needs to be determined in the context of cardiac specific LA-cardiolipin. Cardiomyocytes may draw from all three to enrich LA-cardiolipin. I will test my central hypotheses that LA-cardiolipin optimizes cardiac bioenergetics and that cardiomyocytes have an integrated system to generate and dominantly maintain LA-cardiolipin. I will determine the significance/preference of LA-cardiolipin in cardiac energy production (Aim 1), characterize the contributions of the cardiac IMM protein environment in LA-cardiolipin control (Aim 2), and identify the cardiac LA-pool and pathway that concentrates LA in cardiolipin (Aim 3). This study will provide a fundamental understanding of a cardiac-specific mitochondrial lipid. Also, characterizing this heart-specific system will expand our knowledge of basic cardiac biology and energy metabolism. Performing this study in conjunction with the proposed career development plan, including solid mentorship and training, as well as institutional support, will develop my research-related and professional skills. This will enable my transition toward the achievement of my career goal to become an independent investigator who conducts phospholipid studies with multi-directional skill sets and expertise.