TNF and rheumatoid arthritis: TNFα, the key player and current therapeutic target in RA, stimulates ATX expression in synovial fibroblasts in vitro [82] and LPA induces proliferation, migration and secretion of proinflammatory cytokines IL-6 and IL-8 in synovial fibroblasts, providing mechanistic insights for the implication of ATX/LPA/LPAR signaling in RA [82,83].