Interestingly, Ctsd, the gene encoding cathepsin D which is a critical lysosomal enzyme associated with lipid metabolism and obesity [32, 33], was significantly increased in CD11b+CD45hi cells of WD-fed mice comparing that of CD-fed mice (FC = 1.38) (Additional file 1: Figure S5B, C). This evidence concerns the gene CTSD and obesity due to melanocortin 4 receptor deficiency.