OBJECTIVE: Excessive fluoride intake during enamel formation may result in enamel fluorosis and apoptosis is regarded to be involved in the process by an unclear mechanism. We hypothesize that excessive fluoride might cause apoptosis in the ameloblasts and fluoride-induced apoptosis varies with the maturation stages of ameloblasts. METHODS: We set up an in vitro differentiation model of ameloblasts by using retinoic acid (RA) and dexamethasone (DEX) to induce the maturation of mouse ameloblast-like LS8 cells. RESULTS: The mRNA and protein levels of two enamel matrix proteins and two enamel proteinases were downregulated and upregulated, respectively, in the RA/DEX induced cells, indicating RA/DEX induced cells possessed the characteristics of matured ameloblasts. The strengthened endocytosis function and decreased intracellular pH value inside RA/DEX treated ameloblasts confirmed the maturation inducing effect of RA/DEX on ameloblasts. Excessive fluoride inhibited cell proliferation of ameloblasts within 72h. High amounts of fluoride also induced more apoptosis/dead cells and reduced the expression of Bcl-2, but to a different degree in the non-induced cells and RA/DEX induced cells. CONCLUSIONS: We inferred that high doses of fluoride may easily target the transitional/early maturation ameloblasts and cause apoptosis or cell death. Bcl-2 might be involved in this process.
OBJECTIVE: Excessive fluoride intake during enamel formation may result in enamel fluorosis and apoptosis is regarded to be involved in the process by an unclear mechanism. We hypothesize that excessive fluoride might cause apoptosis in the ameloblasts and fluoride-induced apoptosis varies with the maturation stages of ameloblasts. METHODS: We set up an in vitro differentiation model of ameloblasts by using retinoic acid (RA) and dexamethasone (DEX) to induce the maturation of mouse ameloblast-like LS8 cells. RESULTS: The mRNA and protein levels of two enamel matrix proteins and two enamel proteinases were downregulated and upregulated, respectively, in the RA/DEX induced cells, indicating RA/DEX induced cells possessed the characteristics of matured ameloblasts. The strengthened endocytosis function and decreased intracellular pH value inside RA/DEX treated ameloblasts confirmed the maturation inducing effect of RA/DEX on ameloblasts. Excessive fluoride inhibited cell proliferation of ameloblasts within 72h. High amounts of fluoride also induced more apoptosis/dead cells and reduced the expression of Bcl-2, but to a different degree in the non-induced cells and RA/DEX induced cells. CONCLUSIONS: We inferred that high doses of fluoride may easily target the transitional/early maturation ameloblasts and cause apoptosis or cell death. Bcl-2 might be involved in this process.