| Abstract |
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 (Wnt5a-C2C12) 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.
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