Effect of vitamin K2 on osteoblast apoptosis : Vitamin K2 inhibits apoptotic cell death of human osteoblasts induced by Fas, proteasome inhibitor, etoposide, and staurosporine

Abstract Vitamin K 2 is used for the treatment of osteoporosis, but the precise mode of action is still not clear. We investigated the effects of vitamin K 2 on apoptosis of human osteoblasts. Human osteoblastic cell line MG63 cells and human primary osteoblast-like cells obtained from bone fragments in corrective surgery were used as human osteoblasts. Cells were cultured with or without various concentrations of vitamin K 2 and tumor necrosis factor-α (TNF-α). We then determined the proliferative response, expression of Fas and Bcl-2-related proteins, and Fas-mediated apoptosis of these cells induced by anti-Fas immunoglobulin M (IgM). In addition, the effect of vitamin K 2 in osteoblast apoptosis induced by Z-Leu-Leu-Leu-aldehyde (LLL-CHO), etoposide, or staurosporine was also examined. Human osteoblasts did not show spontaneous apoptosis in culture, even in the presence of vitamin K 2 or TNF-α. Furthermore, proliferation of the cells was not influenced by vitamin K 2 or TNF-α. Fas was functionally expressed on human osteoblasts, and the treatment with TNF-α significantly enhanced both Fas expression and Fas-mediated apoptosis of osteoblasts. The addition of vitamin K 2 to the culture resulted in a dose-dependent inhibition of functional Fas expression on osteoblasts, in the presence or absence of TNF-α. Treatment of human osteoblasts with vitamin K 2 clearly suppressed Bax expression of the cells, although the expression of Bcl-2 was not influenced by vitamin K 2 . Fas ligand (FasL) cDNA transformants were cytotoxic against osteoblasts, and the cytotoxicity was increased when osteoblasts were treated with TNF-α. The addition of vitamin K 2 to osteoblasts significantly decreased the cytotoxic effects of FasL cDNA transformants. Furthermore, apoptosis of human osteoblasts induced by LLL-CHO, etoposide, or staurosporine was also clearly suppressed in vitamin K 2 –treated osteoblasts. Our results suggest that vitamin K 2 inhibits apoptotic cell death of osteoblasts and maintains the number of osteoblasts. These actions may explain the therapeutic efficacy of vitamin K 2 in osteoporosis. (J Lab Clin Med 2000;136:181-93)