SFRP1 and obesity due to melanocortin 4 receptor deficiency: Next, we chose to look at how Arg1 mRNA was impacted in Sfrp1−/− mice fed a high fat diet (HFD) and our findings reveal that the expression of the Arg1 is also significantly elevated in response to diet-induced obesity (DIO) in the mammary gland of Sfrp1−/− mice (Fig. 1D).