ER-Α Enhances and ER-Β Represses Estrogen-induced MMPs in TMJ Fibrochondrocytes

Objectives: In determining the potential contributions of female hormones to temporomandibular joint (TMJ) diseases, we have previously localized estrogen receptors (ERs) -α and -β in the mouse TMJ disc fibrocartilage (Wang, et al., J Dent Res, 2006), and shown that β-estradiol induces specific MMPs and contributes to degradation of the extracellular matrix in this tissue (Hashem, et al., Arthritis Res Ther, 2006). The objective of this study was to identify which of these two estrogen receptors are involved in the induction of MMPs by estrogen in TMJ disc cells.

Methods: ER-α or -β was either overexpressed using plasmid cDNA transfections or suppressed by siRNA transfections into early passage mouse TMJ disc fibrochondrocytes. After 16-hour recovery and 4-hour serum starvation, cells were maintained in serum-free media in the presence or absence of 0.1 ng/ml β-estradiol for 48-hours. Total RNA, cell lysate, and conditioned media were retrieved and assayed for ERs and MMP-9, -13 and -14 using qRT-PCR, gelatin substrate-zymography, Western blots, or immunocytochemistry.

Results: Overexpression or suppression of ER-α or -β did not alter the levels of constitutively expressed MMP-9, -13 and -14 in disc fibrochondrocytes. However, ER-α overexpression enhanced β-estradiol-induced MMP-9, -13 and -14 expression in these cells relative to cells transfected with the control vector. In contrast, the induction of these MMPs by β-estradiol was repressed in cells overexpressing ER-β. Consistent with these findings, downregulation of ER-α diminished, whereas suppression of ER-β augmented MMP induction by β-estradiol in disc fibrochondrocytes.

Conclusions: Activation by β-estradiol of ER-α or ER-β results in the reciprocal regulation of MMP-9, -13 and -14 in TMJ disc cells. These findings suggest that the ratio of ER-α to ER-β may be important in determining the net matrix degradative phentoype of disc cells in response to estrogen.

(Supported by NIH RO1 DE018455)