SIRT1 and obesity due to melanocortin 4 receptor deficiency: Additionally, these in vivo obesity models exhibited a significant decrease in adipose tissue fat oxidation genes, markers of mitochondrial biogenesis and thermogenesis, including peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α), carnitine palmitoyltransferase-1 (CPT1), uncoupling protein-1 and -2 (UCP -1 and -2), Sirt1 and mitofusin (MFN) -1 and -2 [8].