Project Summary: It is widely accepted that mitochondrial metabolism contributes to the development and progression of non- alcoholic fatty liver disease (NAFLD), but the mechanisms of this process are poorly understood. Hepatocellular mitochondria are unique in their ability and requirement to support biosynthetic, catabolic, and substrate trafficking pathways. These functions are mediated by anaplerosis, non-oxidative pathways of the TCA cycle that allow its intermediates to produce and recycle substrates. The downstream pathways that require anaplerosis (e.g., gluconeogenesis and urea cycle function) are energetically costly. They are also notably dysregulated by obesity and insulin resistance, but it is unknown how mitochondrial anaplerotic function impinges on the progress of liver disease. It is suspected that changes in anaplerotic pathways of liver mitochondria alter apparent mitochondrial function, redox state, and antioxidant capacity. This project tests the hypothesis that the equilibrium between anaplerosis and downstream pathways impinge on antioxidant capacity by modulating redox-mediated reactions in liver. Hence, seemingly unrelated intermediary metabolism may have secondary effects on mitochondrial function and contribute to factors like oxidative stress and inflammation in NAFLD. To test the hypothesis, we will use state-of-the-art stable isotope tracer methods, NMR and MS to evaluate metabolic flux, and conditional knockout mice to establish mechanism. Emphasis is placed on identifying how TCA cycle intermediates modulate antioxidant function and the role of metabolic compartmentation. In the process, we will develop new tools and concepts that can be tested and applied against human disease.