TLR4 and obesity due to melanocortin 4 receptor deficiency: Studies examining the role of Fet A in obesity have shown that free fatty acid (FFA)-induced insulin resistance is dependent on the presence of both Fet A and TLR4, where Fet A serves as an adaptor for FFA to stimulate TLR4 signaling that results in the release of pro-inflammatory cytokines through the TLR4-NF kB pathway [15].