MMP-1 (collagenase-1) and MMP-13 (collagenase-3) differentially regulate markers of osteoblastic differentiation in osteogenic cells.

Previous studies have demonstrated an inverse relationship between constitutive or stimulated collagenase expression and osteoblastic phenotype of osteogenic cells. However, the direct effects of cell-secreted collagenases on osteoblastic differentiation, and the precise contributions of the key collagenolytic MMPs, MMP-1 and -13 to the modulation of specific osteoblastic markers have not been elucidated. Early passage osteogenic human periodontal ligament (PDL) cells were exposed to exogenous collagenase-1 in the presence and absence of dexamethasone. Alternatively, endogenous collagenases were modulated by transfecting the cells with cDNA or siRNA to MMP-1 and/or -13. Specific osteoblastic markers and collagenase expression and activity were then assayed. Increasing concentrations of exogenous collagenase or endogenous MMP-1 and -13 produced a dose-dependent decrease in AP activity. Conversely, a dose-dependent increase in AP activity was observed with increasing concentrations of MMP-1 or MMP-13 siRNA. Overexpression of MMP-1 resulted in a significant decrease in Runx2, osteonectin (ON), osteopontin (OP), bone sialoprotein (BSP) and osteocalcin (OC), but an increase in osterix (Osx) mRNA levels. In contrast, knockdown of MMP-1 caused a significant increase in Runx2, ON, OP, BSP and OC levels and a decrease in Osx levels. MMP-13 overexpression resulted in diminished levels of Osx, OP and BSP, while its knockdown caused a significant increase in Osx and OP levels and a significant decrease in ON levels. The accretion of matrix molecules including collagen I(alpha1) in cell-matrix extracts paralleled the changes in their respective mRNAs. Simultaneous suppression of both MMP-1 and -13 resulted in significant increases in all osteoblastic markers assayed. MMP-1 and -13 differentially regulate osteoblastic markers and their combined suppression is important for the elaboration of an osteoblastic phenotype in PDL cells.