PROJECT SUMMARY Diabetes is a leading cause of peripheral arterial disease (PAD), a cardiovascular complication characterized by blood vessel regression, ischemia, mitochondrial dysfunction and limb myopathy. Classic angiogenic regulators such as Vegfa, which have been a major focus of therapeutic interventions have proved to be inefficient clinically. Consequently, pharmacological treatment of PAD has remained an unmet medical need, leading to limb amputations in nearly 200,000 patients every year. Rehabilitative exercise has emerged as an effective clinical strategy for managing PAD by virtue of its stimulatory effects on oxidative metabolism and vascularization in the limb musculature. However, a common limitation of physical therapy is that majority of PAD patients, especially ones with diabetes, cannot exercise due to severe leg pain or other cardiovascular complications. Therefore, characterizing molecular regulation of metabolic and vascular remodeling in exercise and diabetes may present novel targets for treating PAD. In this study, we will investigate the role of nuclear receptor estrogen-related receptor alpha (ERR) in regulating metabolic capacity, vascular supply and exercise capacity in murine models of exercise, diabetes and ischemia. We will also investigate mechanisms regulating ERR expression and activity in the skeletal muscles. We hypothesize that (I) ERR is responsible for exercise-mediated metabolic and vascular remodeling in the skeletal muscle, (II) overexpression of ERR in the skeletal muscles of diabetic mice mitigates diabetic PAD-like pathology in absence of exercise, and (III) HIFs regulate ERR expression and signaling in the skeletal muscle. The hypothesis will be tested in three aims. In Aim 1, we will investigate the role of ERR in regulating metabolic and vascular characteristics of the limb musculature at baseline and in response to exercise. In Aim 2, we will investigate whether ERR activation can mitigate PAD-like pathology in diabetic mice. In Aim 3, we will investigate the function of hypoxia-inducible factors (HIFs) in the regulation of ERR expression and activity in the skeletal muscle. For these studies, we will use muscle-specific targeting of ERR in transgenic mice, as well as intramuscular AAV9-ERR delivery to examine effect on exercise, diabetes and ischemic adaptations. In addition, we will use cellular mechanistic approach to further elucidate metabolic and paracrine angiogenic regulation by muscle ERR, as well as regulation of ERR by HIFs. We expect our work to demonstrate that ERR is a central regulator of muscle metabolic and vascular capacity in exercise, diabetes and ischemia, and highlight ERR as a potential therapeutic candidate for treating diabetes-associated PAD.