SIRT1 and obesity due to melanocortin 4 receptor deficiency: In addition, CD38 deficiency protect against high-fat-diet-induced obesity through the suppression of adipogenesis- and lipogenesis-related transcriptional factors and target genes such as sterol regulatory element binding protein-1c (SREBP1c), CCAAT/enhancer binding protein (C/EBP), peroxisome proliferator-activated receptor γ (PPARγ) and fatty acid synthase, by Sirt1 activation [95] (Figure 4a).