Effect of Estrogen on the Tumor Necrosis Factor-alpha-induced Apoptosis and Cytokine Gene Expression in MC3T3-E1 Osteoblast

Keum, Jeong Cheol; Kang, Kyoung Hwa; Kim, Seung Bo

Abstract

INTRODUCTION: Apoptosis is a naturally occurring cell suicide pathway. The absence of a survival factor, such as a particular hormone or growth factor, will induce a cell to initiate its own cell death. This process induced in osteoblast is thought to play a role in the pathophysiology of postmenopausal osteoporosis. Estrogen plays an important role and exerts direct effects on bone cells, but the role in the maintenance of cell survival and apoptosis is poorly understood. Based on the importance of survival factors and cytokines in bone remodeling, some studies suggest that estrogen acts on bone cell by modulation of cytokine production that increases bone resorption. However other studies have not investigated the effect of estrogen on the apoptosis of osteoblast cells.
OBJECTIVE
To understand how estrogens regulate the apoptosis of osteoblast cells, the physiologically active etrogen metabolite 17 beta-estradiol was tested to determine its effects on the well characterized murine osteoblastic cell-line MC3T3-E1.
METHODS
Experiments were designed to identify the effects of estrogen on TNF-alpha induced apoptosis and cytokine gene expression, and collagen synthesis.
RESULTS
1.Within 48 hours of exposure, recombinant murine at 10(-11)M - 10(-10)M TNF-alpha increased the rates of DNA synthesis and 10(-11)~M - 10(-9)M TNF-alpha reduces cell proliferation. 2.Estrogen treatment coordinately increased DNA contents, cell proliferation and collagen synthetic activity. 3.10(-10)M TNF-alpha increased the IL-1beta, IL-6 gene expression. 4.Estrogen attenuated the TNF-alpha- dependent increase in these gene expression. 5.Murine osteoblastic MC3T3-E1 cells underwent apoptosis following removal of serum, or addition of TNF-alpha, as indicated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and DNA fragmentation studies. 6.Estrogen inhibited the apoptosis of osteoblast cells induced by 10(-10)M TNF-alpha but not to the levels observed in those control.
CONCLUSION
This in vitro evidence suggests that estrogen might exert at least part of antiapoptotic inflence on the bone cells.