The expression of MMP-8 in human odontoblasts and dental pulp cells is down-regulated by TGF-beta 1

Recent findings show that matrix metalloproteinase-8 (MMP-8) is expressed, in addition to neutrophils, by human chondrocytes, cultured fibroblasts, an d endothelial cells. We investigated the expression of MMP-8 in other human mesenchyme-derived cells, odontoblasts, and pulp tissue. Odontoblasts and pulp tissue were collected from extracted human teeth for MMP-8 mRNA analys is with reverse-transcription/polymerase chain-reaction (RT-PCR) and Southe rn blot. The expression, localization, and secretion of MMP-8 protein were studied with Western blot, immunohistochemistry, and immunofluorometric ass ay. The effect of TGF-beta 1 (10 ng/mL) on the expression, secretion, and c oncentration of secreted MMP-8 was studied by odontoblast and pulp tissue c ulture methods (Tjaderhane et al., 1998a). RT-PCR demonstrated MMP-8 mRNA e xpression in native and cultured odontoblasts and pulp tissue and cultured pulp fibroblasts, with a 522-bp transcript comparable with that of bone mar row cells. The specificity of PCR was confirmed with Southern blot. Western blot with MMP-8-specific antibody detected 65- and 50-kDa proteins in nati ve samples, representing latent and active forms of mesenchymal-type MMP-8, and in the conditioned odontoblast culture media, 50-kDa protein was obser ved. TGF-beta down-regulated the MMP-8 mRNA and concentration of secreted p rotein in both cultures. Immunohistochemical staining detected MMP-8 in odo ntoblasts. These findings indicate that mesenchyme-derived cells of the den tin-pulp complex express, synthesize, and activate MMP-8, which may, in con cert with odontoblast-derived gelatinases, participate in organization of d entin organic matrix prior to mineralization.