Effects of Fluoride on ADAM Family Expression in Ameloblasts

Objectives: The ADAM (a disintegrin and metalloproteinase) family of proteinases are important in several biological processes involving cell-cell and cell-matrix interactions, including muscle development and neurogenesis. However, the expression of ADAM family members during amelogenesis is largely unknown. Previously we reported that fluoride decreases the expression of Klk4 and Tgf-β1 during amelogenesis, but the effects of fluoride on ADAMs has not been tested. In this study we demonstrate the expression of Adam9, 15, 17 and 19 in mouse ameloblast-derived LS8 cells in vitro and in mouse ameloblasts in vivo, and evaluate the effect of fluoride on ADAM9 and 17 expression.

Methods: Five-day-old (P5) C57BL/6 pup first molars (secretory stage of enamel development) and molars from P12 pups (maturation stage of development) were harvested (N=6/stage). Enamel organ RNA was extracted and Adam9, 15, 17 and 19 expression levels were quantified by qPCR. Protein localization was evaluated by immunohistochemistry. To assess the effect of NaF on ADAM gene expression, LS8 cells were treated with 0-5 mM of NaF for 24 h followed by qPCR analyses.
Results: The Adam9, 15, 17 and 19 genes were expressed in both P5 and P12 enamel organs. Each ADAM gene assessed had increased expression in the maturation stage compared to the secretory stage (Adam9; P<0.01, Adam15; P<0.01, Adam17; P<0.05, Adam19; P<0.01). In LS8 cells, fluoride exposure (1-5 mM) for 24 h significantly decreased Adam9 and Adam17 mRNA levels compared to controls (0 mM) (regression analysis; P<0.001).
Conclusions: We demonstrate for the first time the expression of Adam9, 15, 17 and 19 in ameloblasts during amelogenesis. The expression was increased in maturation stage compared to secretory stage, and fluoride attenuated Adam9 and Adam17 expression in vitro. These results suggest that ADAMs may play an important role in enamel development and that fluoride may adversely affect ADAM function.