Expression of Retinoic Acid Receptor (RAR) α Protein in the Synovial Membrane from Patients with Osteoarthritis and Rheumatoid Arthritis.

Retinoic acid receptors (RAR) are expressed in inflammatory cells and, through ligand binding, play an important role in cell proliferation and differentiation, as well as in regulation of cytokine and matrix metalloproteinase (MMP) production. Inflammatory cytokines and MMPs play a significant role in cartilage destruction in osteoarthritis (OA) and in joint destruction in rheumatoid arthritis (RA), the prototype of inflammatory arthritis. To determine if RARα is expressed in the synovial membrane (SM) of patients with OA and compare it with RA, SM biopsy samples were used in this study which were from 31 patients with late OA and 14 patients with late RA.