Calcium upregulated survivin expression and associated osteogenesis of normal human osteoblasts

Survivin is an antiapoptotic protein expressed in all phases of the normal cell cycle but is at its highest level during the G2/M interphase. This protein has been recently identified in normal human osteoblasts and has raised questions about the regulation of its expression. This study intends to verify if survivin expression could be manipulated by external factors such as calcium ions. Normal human alveolar bone explants recovered from six healthy donors were cultured to 2nd passage. Cells were cultured with essential medium as a control and with medium containing supplemental calcium ions at a concentration of 30 parts per million as a study group. Vitamin D(3) was added to all culture groups at the 5th and 18th days to promote differentiation. Differentiation markers were confirmed by performing mineralization, alkaline phosphatase (ALP), and osteocalcin assays at 7 and 21 days. Cell attachment was measured at 16 h and used as a reference for cell proliferation at 7 days and 21 days. Survivin levels were measured at 16 h, 7 and 21 days. Compared with the control group, the study group presented a significant increase of survivin expression at 16 h (p < 0.01), at 7 days (p < 0.01), and at 21 days (p < 0.05), a significant increase of cell proliferation, ALP activity and mineralization at 7 days (p < 0.05) and 21 days (p < 0.05), and a significant increase in osteocalcin expression only at 21 days (p < 0.01). This study demonstrated that survivin expression could be significantly upregulated by calcium-enhanced normal human osteoblast cultures, which might correlate to subsequent upregulation of cell proliferation and differentiation.