Sørensen M G, Henriksen K, Dziegiel M H, Tankó L B, Karsdal M A
Nordic Bioscience A/S, Herlev, Denmark.
DNA Cell Biol. 2006 Aug;25(8):475-83. doi: 10.1089/dna.2006.25.475.
Estrogen deficiency arising with the menopause promotes marked acceleration of bone resorption, which can be restored by hormone replacement therapy. The inhibitory effects of estrogen seem to involve indirect cytokine- mediated effects via supporting bone marrow cells, but direct estrogen-receptor mediated effects on the bone-resorbing osteoclasts have also been proposed. Little information is available on whether estrogens modulate human osteoclastogenesis or merely inhibit the functional activity of osteoclasts. To clarify whether estrogens directly modulate osteoclastic activities human CD14+ monocytes were cultured in the presence of M-CSF and RANKL to induce osteoclast differentiation. Addition of 0.1-10 nM 17beta-estradiol to differentiating osteoclasts resulted in a dose-dependent reduction in tartrate resistant acid phosphatase (TRACP) activity reaching 60% at 0.1 nM. In addition, 17beta-estradiol inhibited bone resorption, as measured by the release of the C-terminal crosslinked telopeptide (CTX), by 60% at 0.1 nM, but had no effect on the overall cell viability. In contrast to the results obtained with differentiating osteoclasts, addition of 17beta-estradiol (0.001-10 nM) to mature osteoclasts did not affect bone resorption or TRACP activity. We investigated expression of the estrogen receptors, using immunocytochemistry and Western blotting. We found that ER-alpha is expressed in osteoclast precursors, whereas ER- beta is expressed at all stages, indicating that the inhibitory effect of estrogen on osteoclastogenesis is mediated by ER-alpha for the major part. In conclusion, these results suggest that the in vivo effects of estrogen are mediated by reduction of osteoclastogenesis rather than direct inhibition of the resorptive activity of mature osteoclasts.
绝经后出现的雌激素缺乏会促使骨吸收显著加速，而激素替代疗法可使其恢复。雌激素的抑制作用似乎涉及通过支持骨髓细胞产生的间接细胞因子介导效应，但也有人提出雌激素受体对骨吸收破骨细胞有直接介导效应。关于雌激素是调节人类破骨细胞生成还是仅仅抑制破骨细胞的功能活性，目前所知甚少。为了阐明雌激素是否直接调节破骨细胞活性，将人类CD14+单核细胞在M-CSF和RANKL存在的情况下培养以诱导破骨细胞分化。向正在分化的破骨细胞中添加0.1 - 10 nM的17β-雌二醇会导致抗酒石酸酸性磷酸酶（TRACP）活性呈剂量依赖性降低，在0.1 nM时达到60%。此外，17β-雌二醇抑制骨吸收，以C端交联端肽（CTX）的释放来衡量，在0.1 nM时抑制60%，但对总体细胞活力没有影响。与在正在分化的破骨细胞中获得的结果相反，向成熟破骨细胞中添加17β-雌二醇（0.001 - 10 nM）对骨吸收或TRACP活性没有影响。我们使用免疫细胞化学和蛋白质印迹法研究了雌激素受体的表达。我们发现ER-α在破骨细胞前体中表达，而ER-β在所有阶段都有表达，这表明雌激素对破骨细胞生成的抑制作用主要由ER-α介导。总之，这些结果表明雌激素在体内的作用是通过减少破骨细胞生成来介导的，而不是直接抑制成熟破骨细胞的吸收活性。
