Human Odontoblast Culture Method: The Expression of Collagen and Matrix Metalloproteinases (MMPs)

Studies on mature human odontoblasts have suffered for the lack of in vitro models. We recently introduced a human odontoblast and pulp tissue organ culture method, in which the odontoblasts are cultured in the pulp chamber after removal of the pulp tissue, and the pulp tissue can be cultured separately (Tjaderhane et al., 1998a). With this method, we have studied the effects of growth factors on the expression of collagen and extracellular matrix (ECM)-degrading enzymes, matrix metalloproteinases (MMPs), in mature human odontoblasts. TGF-β1 was selected because of its ability to regulate the response of the dentin-pulp complex to external irritation. The effect of TGF-β1 (10 ng/mL) on proal(I) collagen mRNA was analyzed by quantitative PCR, and type I procollagen propeptide (PINP) was analyzed from conditioned culture media with RIA. Odontoblast media were also assayed for respective type III procollagen propeptide (PIIINP). TGF-β had a negligible effect on collagen mRNA expression or protein synthesis, indicating that TGF-β alone does not markedly induce dentin matrix formation per se in the human dentin-pulp complex (Palosaari et al., 2001). However, TGF-β1 seems to regulate MMP expression in mature human odontoblasts differentially. A strong down-regulation of MMP-8 (Palosaari et al., 2000), a modest down-regulation of MMP-20 (Tjaderhane et al., 2000), and considerable up-regulation of MMP-9, with no apparent effect on MMP-2 expression (Tjaderhane et al., 1998b), indicate that growth factors may affect the matrix synthesis by controlling the expression and activity of MMPs instead of collagen synthesis. The altered expression of MMPs may result in altered ECM formation, which in turn may contribute to the formation of atubular reparative dentin.