Regulation of matrix metalloproteinase-13 and tissue inhibitor of matrix metalloproteinase-1 gene expression by WNT3A and bone morphogenetic protein-2 in osteoblastic differentiation

During bone remodeling, degradation of skeletal connective tissue is regulated, at least in part, by the balance between matrix metalloproteinases ( MMPs) and tissue inhibitors of matrix metalloproteinase (TIMPs), their natural inhibitors. Recently, the Wnt signaling pathway has been demonstrated to play a crucial role in the regulation of bone formation. Here, we investigated a potential role for Wnt signaling and functional cross-talk with bone morphogenetic protein (BMP)-2 in mRNA expression of MMPs, TIMPs and bone matrix proteins in pluripotent C2C12 cells. To assess the functional contribution of Wnt signaling, we have generated C2C12 cell lines stably over-expressing Wnt3a or Wnt5a, and then treated these cells with BMP-2 for 24 h. In these cultures, MMP-13 mRNA expression was induced by BMP-2 in Wnt3a over-expressing C2C12 (Wnt3a-C2C12) cells but not in either Wnt5a over-expressing C2C12 (Wnt5aC2C12) cells or vehicle-transfected C2C12 cells. MMP-13 mRNA was induced in these cells by addition of BMP-2 for 12 h and the enhancement lasted up to 48 h. These effects were observed in a dose-dependent manner. Enzymatic activity of MMP-13 also induced in Wnt3a- C2C12 cells by addition of BMP-2. However, membrane type-1 matrix metalloproteinase (MT1- MMP) and MMP-2 mRNA expression was not affected by either Wnt3a or BMP-2. In contrast, TIMP-1 mRNA expression was suppressed by BMP-2 in Wnt3a-C2C12 cells but not in Wnt5a-C2C12 cells. Our results show that expression of MMP-13 and TIMP-1 is regulated by Wnt signaling combined with BMP-2 in osteoblastic differentiation, and this signaling may in part mediate MMP-13 and TIMP-1 production during bone formation and/or remodeling.