Molecular mechanisms of mitochondrial metabolic regulation

Project Summary Heart failure, a prominent global health issue, continues to steadily rise in incidence yet has no cure. This condition is distinguished by the heart’s reduced ability to pump blood, largely driven by cardiac bioenergetic abnormalities. As cardiomyocytes rely on mitochondria for 95% of their energy supply, mitochondrial dysfunction characteristically underlies these energetic defects. NAD+ sits at the core of mitochondrial energetics, driving the progression of the tricarboxylic acid cycle in aerobic respiration. Cardiomyocyte failure is linked to NAD+ depletion in the mitochondrial matrix, impairing energy synthesis and sensitizing cells to death. Restoration of mitochondrial function through NAD+ repletion is a powerful therapeutic strategy that has shown early promise in reversing heart failure phenotypes. However, despite the pivotal role of NAD+ in mitochondrial function, a limited understanding exists of the mechanisms governing NAD+ entry into and regulation within the mitochondrial matrix. Notably, recent landmark studies have demonstrated that the mitochondrial matrix cannot independently synthesize NAD+ and have identified the essential transporter responsible for matrix NAD+ import. Yet, little is known about the molecular mechanism of this critical transport process. This project proposes to address this gap in knowledge by exploring the molecular basis of mitochondrial NAD+ import, which will elucidate how mitochondria maintain adequate NAD+ levels and how this process may become dysregulated in disease. Multidisciplinary approaches will be used to investigate fundamental unknowns about the transport mechanism, including the biochemical basis of substrate selectivity and coupling, the key protein features governing transport activity, and the architectural determinants of substrate binding and translocation. Together, this work will shed light on fundamental mechanisms of mitochondrial metabolic regulation and may provide a molecular blueprint for countering mitochondrial dysfunction in the long-term treatment of heart failure.