Expression of MMP-13 (collagenase-3) in long-term cultures of human dental pulp cells

Matrix metalloproteinase-13 (MMP-13 or collagenase-3) is a member of the family of matrix metalloproteinases (MMPs) produced in high amounts by cells with mineralising potential. Human dental pulp has been shown to express high levels of MMP-13 RNA. Objective: Since human dental pulp derived cells (HDPC) are known to possess osteoprogenitor properties, we investigated the pattern of expression of MMP-13 in long-term cultures of those cells under conditions that support mineralisation in vitro. Design: Impacted teeth or teeth extracted for orthodontic purposes were used to obtain dental pulp explants and HDPC were cultured for approximately 5 weeks. Pro- and active MMP-13 levels were determined in the cell culture supernatants by means of enzyme-linked immunosorbent assay (ELISA). Cell growth was evaluated through DNA content and osteogenic differentiation was assessed by alkaline phosphatase (ALP) activity and Alizarin Red staining. Results: Mineralising cultures of HDPC produced significantly higher levels of pro-MMP-13 compared to control cultures. Both pro- and active MMP-13 levels displayed a characteristic peak that was found to coincide with the peak in alkaline phosphataseactivity and the onset of mineralisation. Once mineralisation was firmly established, MMP-13 expression was significantly reduced. Conclusions: Evidence from this study suggests a role for MMP-13 in the transition of human dental pulp cells to a mature mineralising phenotype and points to MMP-13 as a possible marker in HDPC differentiation.