Production of Matrix-degrading Enzymes and Inhibition of Osteoclast-like Cell Differentiation by Fibroblast-like Cells from the Periodontal Ligament of Human Primary Teeth

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Abstract
Clinically, the most apparent difference between the primary and permanent dentitions is the physiologic loss of the primary tooth by root resorption. Root resorption is associated with loss of integrity of the periodontal ligament (PDL), followed by recruitment of resorptive cells that remove root structure. We therefore cultured primary dentition PDL fibroblasts (PPDL cells) to investigate in vitro their production of matrix metalloproteinases (MMPs) and tissue inhibitors of MMP (TIMPs), and the effects of soluble factors produced by these cells on osteoclast-like cell differentiation. These studies demonstrate that PPDL cells in vitro have a heterogeneous morphology, and they constitutively synthesize 92-kDa gelatinase, 72-kDa gelatinase, and 53/57-kDa procollagenase as well as TIMP-1, -2, and a third inhibitor of matrix metalloproteinase, as determined by substrate gel zymography and immunoblot analysis. Compared with PDL cells from the permanent dentition, PPDL cells generally produced a greater amount of collagenase but similar amounts of the gelatinases and inhibitors. PPDL cells were treated with pro-inflammatory cytokines to determine their effect on the expression of matrix-degrading enzymes and inhibitors. Interleukin-la and tumor necrosis factor-a enhanced the constitutive expression of proteinases but not that of inhibitors in PPDL cells. Conditioned media from PPDL cell lines inhibited the differentiation of osteoclastlike cells in mouse bone marrow cultures. These findings indicate that PPDL cells may modulate the cascade of root resorption both by their regulated production of proteinases and inhibitors and by synthesis of unknown soluble factor(s) that may regulate osteoclast development.

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