Effect of transmembrane proteoglycans in human periodontal ligament fibroblasts

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Basic fibroblast growth factor (bFGF, FGF-2) is one of the potent mitogens for periodontal ligament (PDL) cells. However, the role of bFGF on the matrix metalloproteinase (MMP) -3 expression in PDL cells is unknown. In this study, the effect of bFGF on MMP-3 expression in PDL cells and the mechanism of this process were examined.Human PDL cells were exposed to bFGF at various concentrations (0.01 - 10 ng/ml) in monolayer cultures. bFGF increased [3H]-thymidine incorporation and suppressed proteoglycan synthesis concentration-dependently. However, similar concentration ranges of bFGF increased the release of the cell-associated proteoglycans into the medium. Furthermore, bFGF increased MMP-3 mRNA levels concentration-dependently as examined by reverse transcription-polymerase chain reaction. Induction of MMP-3 after the stimulation with bFGF was observed as early as 12 h with maximal at 24 h. Thereafter the MMP-3 mRNA level gradually decreased until 72 h. Cycloheximide blocked the induction of MMP-3 by bFGF, indicating the requirement of de novo protein synthesis for this stimulation. Furthermore, MMP-3 expression induced by bFGF was abrogated by U0126, a specific inhibitor of MEK1/2 and ERK1/2 in mitogen-activated protein (MAP) kinase pathway, not by PD98059, a specific inhibitor of MEK1. In addition, bFGF up-regulated the phosphorylated ERK1/2 in 5 min with the maximal at 20 min as examined by Western blotting, and U0126 inhibited the ERK1/2 phosphorylation induced by bFGF.These findings suggest that bFGF induces MMP-3 expression in PDL cells through the activation of the MEK2 in MAP kinase pathway. bFGF stimulation on MMP-3 synthesis may be involved in the control of the cell-associated proteoglycans in PDL cells during periodontal regeneration and degradation.