Relaxin and Estrogen Receptor Expression in TMJ and Meniscus Fibrocartilages

Temporomandibular joint disorders have a high female to male preponderance and occur primarily in women of reproductive age. We have shown that relaxin stimulates matrix metalloproteinase (MMP) expression that is potentiated by β-estradiol priming in rabbit TMJ fibrocartilaginous cells, resulting in matrix loss. Objectives: To compare expression of estrogen receptors (EsR) -α and -β, and relaxin receptors (LGR7, LGR8) in cells from mouse TMJ disc (TMJ) and knee meniscus (MEN) fibrocartilages and determine the effects of relaxin on the levels of receptors expressed in these fibrochondrocytes. Methods: Fibrochondrocytes, isolated from TMJ, MEN and positive control pubic symphyseal (PS) fibrocartilages were maintained in α-MEM supplemented with FBS until confluent. Total RNA and protein were obtained, and analyzed for expression of the receptors by RT-PCR, qRT-PCR, and Western blots. Additionally, cells cultured in serum-free medium (α-MEM+0.2%LAH) were treated with relaxin (0-100 ng/ml) with or without 0.1 ng/ml β-estradiol or 10 ng/ml progesterone and changes in relaxin receptor message and protein were determined. Results: TMJ fibrochondroctyes had significantly greater EsR-α (>2.8-fold), EsR-β (>2.2-fold), and LGR7 (>3.75-fold) gene levels than those from MEN. These findings were also confirmed at the protein level. PS cells showed the highest level of expression for all four receptors. Relaxin (10πg/ml) treatment led to 2-fold upregulation of EsR-α, EsR-β, and relaxin receptor gene expression; β-estradiol priming enhanced this stimulation while progesterone attenuated these effects. Conclusion: This study shows for the first time the differential expression of relaxin and estrogen receptors that are highly expressed in TMJ and PS fibrocartilage but not in MEN fibrocartilage. Since these hormones contribute to the induction of MMPs and subsequent tissue degradation, the findings may provide an explanation for the distinct gender and age distributions for TMDs as opposed to that of other joints. (Supported by NIH/NIDCR grants DE11993 and DE00458 to SK).