STAT3 and obesity due to melanocortin 4 receptor deficiency: Serum obesity-related factors (leptin, IL-6) increase the expression of lipoprotein lipase (LPL) in HSCs through STAT3 signaling pathway conduction, which leads to an increase in intracellular free cholesterol content and promotes TLR4 signaling and inhibits the expression of Bambi, stimulates TGF-β induction of HSCs, and accelerates the production of intracellular collagen (Teratani et al., 2019).