The liver has been proposed as a primary source of circulating DPP4.133 Within the liver, DPP4 is expressed in both hepatocytes and nonparenchymal cells, yet obesity only increases Dpp4 expression in hepatocytes.134 Analysis by Baumeier et al135 calculated by total weight predicted that in mice, the majority of DPP4 protein release came from the liver. Here, DPP4 is linked to obesity due to melanocortin 4 receptor deficiency.