TLR4 and obesity due to melanocortin 4 receptor deficiency: Fatty acids may activate Toll-like receptor 4 (TLR4) signaling in adipocytes and macrophages and induce inflammatory signaling (Shi et al., 2006), and mice lacking TLR4 were shown to be protected against high-fat diet-induced obesity and insulin resistance (Poggi et al., 2007; Davis et al., 2008).