SIRT1 and obesity due to melanocortin 4 receptor deficiency: On the other hand, Sirt1/dSir2 can regulate lipid metabolism and obesity via some target histones, transcription factors, co-regulators, and metabolic enzymes, such as peroxisome proliferator-activated receptor g (PPARg) coactivator-1 (PGC-1), which is a key regulator of thermogenesis in brown adipose tissue; and controls mitochondrial fatty acid oxidation.