We investigated the expression of estrogen receptors (ER) and the presence of estradiol in human synovial tissues from subjects without arthritis and patients with traumatic arthritis, osteoarthritis, and rheumatoid arthritis.
Synovial tissues were immunostained using ER-D5 monoclonal antibody (Mab) directed toward an ER related protein (p29), ER-ICA Mab directed toward nuclear ER, and antiestradiol serum. Fluorescent estradiol was used to demonstrate specific estradiol binding to ER.
(1) p29 was present predominantly in hyperplastic synovial lining cells and smooth muscles of blood vessels. (2) Exogenous estradiol bound to synoviocytes and sublining macrophage-like cells in the inflamed synovium. (3) Endogenous estradiol was also detected in hyperplastic lining cells and macrophage-like cells in arthritic synovium.
Our study demonstrated the expression of ER in arthritic synovium and suggested that estrogen modulates local inflammation in various joint diseases via synoviocytes as well as sublining macrophage-like cells.