Fluoride‐stimulated [³H] thymidine uptake in a human osteoblastic osteosarcoma cell line is dependent on transforming growth factor β

Controversy exists regarding the effect of fluoride on human osteoblast proliferation. To learn more of the cellular action of fluoride, we chose the clonal osteoblast cell line HOS TE85 as a model system. In these phenotypically osteoblast‐like cells, sodium fluoride stimulated [³H]thymidine incorporation in a dose‐dependent manner over the concentration range 1 × 10⁻⁵‐2 × 10⁻⁴ M. The fluoride‐induced stimulation of [³H]thymidine uptake was dependent on cell density, being optimal at subconfluent cell numbers. Stimulation of [³H]thymidine uptake was inhibited by anti‐transforming growth factor β but not by antibody to insulin‐like growth factor I or β₂‐microglobulin. Transforming growth factor β was shown to be a biphasic stimulator of [³H]thymidine uptake in HOS TE85, with maximal stimulation occurring at 0.5 nM transforming growth factor β. In the presence of fluoride the cells were more sensitive to stimulation by this growth factor, with maximum effect occurring at 0.1 nM. Fluoride did not increase mRNA for transforming growth factor β following either 8 or 24 h of exposure. We conclude that fluoride activates osteoblast proliferation by modulating the cellular sensitivity to transforming growth factor β, a known stimulator of bone growth.