| Objective To investigate the effects of tumor necrosis factor-a (TNF-a) on the expression of osteoprotegerin (OPG) in mouse marrow stromal cell and in human osteoblast-like cell lines, as well as the signal transduction pathway of TNF-a on the expression of OPG in both cell lines.Methods: Cell cultures were used to observe the morphologic characteristics of MBA-1. The expressions of OPG mRNA and OPG protein were measured by RT-PCR, Western and Northern blot in MBA-1 cells and in human osteoblastic-like MG-63 cells treated by TNF-a with different concentrations and at different time-course of cultures.Results: (1) MBA-1 cells are characterized by adherent fibroblastoid appearance, with large volume, multinucleoli(4 ~ 8). They partly behave the osteblastic phenotypes, such as the expression of type 1 collage and alkaline phosphatase. (2) TNF-a downregulates the expression of OPG in MBA-1 cells, but not in a dose- and time-dependent manner. 17 3 -estradiol can suppress the downregulation of TNF-a on the exppresion of OPG, whereas pyrrodine dithiocarbamate (PDTC) (a specific inhibitor of nuclear factor-B) has no effects on its downregulation. (3) TNF-a upregulates the expression of nuclear protein p65 of MG-63 cells in a dose- and time- dependent manner. Both of 17 3 -E2 and PDTC can abrogate the expression induced by TNF- a . (4) TNF-a supresses the mRNA and protein expression of OPG in MG-63 cells, but not in a dose-dependent manner.Conclusion: MBA-1 cell is a kind of osteoblast precursors with partly osteoblastic phenotypes. TNF-a may enhance osteoclastic bone resorption and bone loss by decreasing the expression of OPG in bone marrow stromal cells and osteoblastic cells. The mechanism involved in the therapeutc action of estrogen in postmenopausalosteoporosis may associated with the suppression of OPG expression by estrogen. The signaling pathway that regulates OPG expression by TNF-a is not involved in the activation of nuclear factor-B.
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