Project Summary Mitochondrial diseases are heterogeneous genetic disorders caused by the impairment of the oxidative phosphorylation (OXPHOS) system, affecting tissues that are heavily energy dependent, and often manifesting with neuromuscular symptoms accompanied by a variety of additional clinical features. Although the energetic defects arising from genetic errors in mitochondrial and nuclear DNA are often known, many aspects of mitochondrial disease pathogenesis are yet to be elucidated. As a consequence, because of the lack of defined metabolic targets, no proven effective treatments or cures are available. Our published studies indicate that a dramatic metabolic remodeling occurs in vivo in a mouse model of mitochondrial disease. We found that a starvation-like response promotes muscle protein breakdown and amino acid catabolism to support a compensatory energy-generating oxidative flux. In this flux, glutamate is oxidized through the TCA cycle and allows for OXPHOS-independent substrate-level ADP phosphorylation. At the same time, lipid utilization through -oxidation is downregulated and therefore this maladaptive process results in muscle wasting and lipid accumulation. Importantly, in preliminary studies leading to this application, we have discovered that skeletal muscle from mitochondrial patients affected by Myoclonus Epilepsy and Ragged Red Fibers (MERRF) encephalomyopathy show similar compensatory metabolic responses. We also find that the hypothalamic–pituitary–adrenal axis is altered leading to increased glucocorticoid levels, which can play a role in muscle protein and lipid dyshomeostasis. Our findings suggest that this metabolic shift towards preferred utilization of amino acids over lipids for energetic purposes underlies maladaptive effects, contributing to disease pathogenesis. In aim 1 of this pilot study, we will provide proof of principle that metabolic rewiring caused by OXPHOS defects are common features in animal models and human patients with mitochondrial diseases. We will also test the hypothesis that energy substrate supplementation can provide beneficial metabolic modulation in patient-derived muscle cells. Furthermore, in aim 2, we will test an innovative metabolic therapy in a mouse model of mitochondrial disease by glucocorticoid signal inhibition with or without metabolic supplementation with dimethyl-alpha ketoglutarate.