INS and obesity due to melanocortin 4 receptor deficiency: 3T3-L1 fibroblasts are widely used in studies on adipogenesis and energy metabolism, because in the presence of 1.0 μM dexamethasone, 0.5 mM methyl-isobutyl-xanthine, or 1.0 μg/mL insulin they can differentiate into mature adipocytes, with specific physiological and morphological characteristics, allowing exploration of the mechanisms underlying obesity and its possible treatment [24].