LDLR and obesity due to melanocortin 4 receptor deficiency: In genetic animal models, apolipoprotein E-deficient (ApoE-/-) mice and low-density lipoprotein-receptor-deficient (Ldlr-/-) mice are both well-established for studying atherosclerosis, and are also used with a high-fat diet (HFD) to simultaneously induce obesity, liver fibrosis, and atherosclerotic disease [36,37,38,39,40].