TNFSF11 and rheumatoid arthritis: In addition, bone and extracellular metabolic pathways are also involved in pathogenesis: activated fibroblasts produce receptor activator of NF-κB ligand (RANKL), which promotes differentiation of osteoclast precursors into bone-resorbing osteoclasts, leading to bone erosion in Rheumatoid Arthritis (RA) (7).