Effect of Calcium Sulfate on Osteopontin Expression in U-2 Osteosarcoma Cells

Calcium sulfate has been used for bone regeneration in oral medicine. Osteopontin, a marker molecule of osteoblasts, plays multiple roles in bone formation. However, the effect of calcium sulfate on osteopontin expression in osteoblasts remains unclear. In this study, U-2 osteosarcoma (U-20S) osteoblast-like cells were cultured in medium containing 0, 0.5, 1, or 10 μM calcium sulfate hemihydrate for 6 days. The messenger (m) RNA and protein expressions of osteopontin were respectively analyzed by reverse-transcription polymerase chain reaction (RT-PCR) and Western blotting. In the in vitro culture for 1-2 days, there was no effect on the proliferation of cells, suggesting that calcium sulfate at up to 10μM is biocompatible. RT-PCR results showed that a lower concentration of calcium sulfate (＜ 1μM) upregulated the osteopontin mRNA level of U-2OS cells. However, the protein expression of osteopontin was downregulated as the concentration of calcium sulfate increased in cultured U-2OS osteoblastic cells. Dissolved •Ca(superscript 2+) and SO(superscript 2- subscript 4) from calcium sulfate hemihydrates may alter the structure of secreted osteopontin, which then was not recognizable by the antibody in the Western blot analysis. In summary, calcium sulfate can regulate the mRNA and protein expressions of osteopontin. Controlling the degradation of calcium sulfate implants is important for regulating bone formation. This study provides additional information to help dentists understand the effects of calcium sulfate on bone formation and use calcium sulfate more efficiently in treating bone defects.