IL6 and obesity due to melanocortin 4 receptor deficiency: However, obesity can also increase bone reabsorption through the increased release of pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6), which stimulate the formation and activity of osteoclasts through the receptor activator of the nuclear factor kappa-beta ligand (RANKL)/(RANK)/Osteoprotegerin (OPG) pathway [7,8,9].