PPARGC1A and obesity due to melanocortin 4 receptor deficiency: Obesity- and diabetes-induced type I to type II fiber transition and decreases of oxidative capacity of skeletal muscle has been explained by down-regulation of peroxisome proliferator-activated receptor γ, coactivator-1α (PGC-1α) and peroxisome proliferator-activated receptor δ (PPARδ) [4,9,14].