Immunohistochemical localization of MMP-2, MMP-9, TIMP-1, and TIMP-2 in the forming rat incisor.

Western blots analyses and gelatin zymography established the presence of matrix metalloproteinase (MMP)-2 and -9 in the forming zone of rat incisor. Light microscope immunohistochemistry carried out on undemineralized material provided evidence for strong MMP-2 staining in the secretory ameloblasts, odontoblasts, in the enamel organ, and in the pulp. A weaker staining was observed in predentin and in the outer part of the forming enamel. Using MMP-9 antibodies, the staining was generally weak, except for the secretory ameloblasts that were positively stained. Electron microscopic immunohistochemistry of undemineralized sections revealed a close association between gold-antibodies complexes and cytoskeletal microfilaments in the cytosol of secretory ameloblasts and odontoblasts, within the rough endoplasmic reticulum and along the plasma membrane. The striking feature of MMP-2 and -9 electron immunostaining was the particularly high labeling in the mantle dentin. By contrast, staining of tissue inhibitors of metalloproteinases (TIMP-1 and -2) was lowest in this region. We suggest that this uneven distribution may have some functional implications.