RXFP1 Mediates Induction of MMPs by Relaxin in Mouse TMJ-Fibrochondrocytes

Objectives: In determining the potential contribution of female hormones to temporomandibular joint diseases (TMJD), we have demonstrated that relaxin induces tissue-degrading enzymes of the matrix metalloproteinase (MMP) family in TMJ discs. The mechanisms for the induction of these MMPs by relaxin have not been determined, but may involve one or both of the two known receptors of relaxin, relaxin family peptide (RXFP) -1 and -2 receptors. Since our recent studies have demonstrated the presence of RXFP1 and RXFP2 in TMJ fibrochondrocytes, in this study we determined the precise contributions of these receptors to the induction of MMP-9 (92 kDa gelatinase) and -13 (collagenase 3) in mouse TMJ fibrochondrocytes. Methods: RXFP1 and RXFP2 were suppressed or overexpressed in early passage fibrochondrocytes by receptor specific siRNA or plasmid cDNA, respectively. After 16-hour recovery, the cells were maintained in the presence or absence of 0.1 ng/ml relaxin for 48-hours. Total RNA, cell lysate, and conditioned media were retrieved and analyzed using qRT-PCR, Western blots and gelatin substrate zymography. Results: siRNA or cDNA transfections of RXFP1 and RXFP2 resulted in knockdown or overexpression, respectively, of these receptors. Relaxin treatment of RXFP1 knocked-down cells showed diminished induction of MMP-9 and -13 by relaxin, whereas overexpression of RXFP1 resulted in increased induction of MMP-9 and -13 by relaxin compared to control cells. In contrast, knockdown or overexpression of RXFP2 resulted in no or minimal changes in the levels of relaxin-induced MMP-9 and -13. Conclusions: The relaxin receptor RXFP1 mediates relaxin's induction of MMP-9 and -13 in mouse TMJ fibrochondrocytes. These findings and those showing the presence of relaxin receptors in TMJ fibrocartilaginous cells demonstrate that the TMJ disc is a target tissue for the matrix remodeling activities of relaxin. Supported by NIH/NIDCR RO1 DE018455, DE007057, AADR, and University of Michigan School of Dentistry.