LEP and rheumatoid arthritis: In particular, leptin was found to induce expression of IL-6 and IL-8 in synovial fibroblasts in patients with RA, via activation of JAK2/STAT3, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), and AP-1 signaling pathways (Muraoka et al., 2013; Yang et al., 2013), representing a new therapeutic target in the treatment of RA.