AKT1 and obesity due to melanocortin 4 receptor deficiency: MUSTN1 knockout mice were protected against HFD-induced obesity, hepatic steatosis, and insulin resistance; and fatty acid binding protein 3 was identified as an interacting protein of MUSTN1, which facilitated preadipocyte proliferation and differentiation by activating the phosphatidylinositol 3 kinase/AKT signaling pathways.