TNFRSF9 and obesity due to melanocortin 4 receptor deficiency: To determine if the protective effect of 4-1BB deficiency against obesity-induced atrophic response in skeletal muscle is associated with oxidative metabolic response, we examined the expression of genes associated with mitochondrial biogenesis and oxidative metabolism in skeletal muscle of WT and 4-1BB-deficient obese mice fed an HFD.