TLR4 and obesity due to melanocortin 4 receptor deficiency: Petersen et al. [49] found that the proliferation of Desulfovibrio and the loss of Clostridia were the key features of obesity, and Desulfovibrio was capable of producing lipopolysaccharide in the blood to activate TLR4-dependent (Toll-like receptor 4) signaling and aggravate inflammation and insulin resistance.