Estrogen and inflammation modulate estrogen receptor alpha expression in specific tissues of the temporomandibular joint

Sixteen ovariectomized female rats were divided into two groups such that one group received 17 beta estradiol (E2) and the other was given vehicle (VEH). Groups were then subdivided further, one received injections of saline and the other received Complete Freund's adjuvant (CFA) within the superior joint space of the TMJ. Thus the four groups include no E2/saline, E2/saline, no E2/CFA and E2/CFA. After treatment, the rats were sacrificed, and the TMJ anterior, disc, retrodiscal and synovial tissues were analyzed by western blot and immunocytochemistry. Positive stained cells were counted using a Nikon epifluorescent microscope.The western blot showed that ERalpha protein significantly decreased with inflammation. The number of ERalpha-positive cells in the TMJ was not affected by inflammation or 17 beta-estradiol with exception of the retrodiscal tissue. In the retrodiscal tissue 17 beta-estradiol significantly decreased the number of ERalpha-positive cells but only in a non-inflamed joint.In conclusion, inflammation and 17 beta-estradiol can modulate ERalpha expression in the TMJ but the effects are tissue specific.Epidemiological studies have shown that during their reproductive years, women experience a higher frequency of temporomandibular joint disorders than males with a ratio of = 1.5- 2 [1]. It has been postulated that estrogen could be the primary molecule leading to the higher frequency of TMJ disorders in women. Endogenous estrogen affects the remodeling processes within the TMJ [2,3] possibly by changing the extracellular matrix in the joint [4] or by changing bone volume [2]. Such changes can result in internal derangement of the TMJ. Estrogen modulation of matrix metalloproteinase (MMP) expression has also been observed in the cartilage of the TMJ [5,6]; high levels of MMP have been reported to play a role in TMJ osteoarthritis [7,8]. Moreover, the level of estrogen in the synovial fluid has been correlated to the severity of arthritis in postmenopau