Ernst M, Schmid C, Froesch E R
Department of Medicine, University Hospital of Zurich, Switzerland.
Proc Natl Acad Sci U S A. 1988 Apr;85(7):2307-10. doi: 10.1073/pnas.85.7.2307.
Estrogens play a crucial role in the development of postmenopausal osteoporosis. However, the mechanism by which estrogens exert their effects on bone is unknown. To examine possible direct effects of 17 beta-estradiol on bone-forming cells, we used pure rat osteoblast-like cells in vitro as a model. Osteoblast-like cells prepared from calvaria of newborn rats were cultured serum-free in methylcellulose-containing medium for 21 days. Osteoblast-like cells proliferate selectively into clonally derived cell clusters of spherical morphology. 17 beta-Estradiol at concentrations of 0.1 nM and 1 nM enhanced osteoblast-like cell proliferation by 41% and 68% above vehicle-treated controls. The biologically inactive stereoisomer 17 alpha-estradiol (same concentrations) had no effect. Moreover, the antiestrogen tamoxifen abolished the stimulation of osteoblast-like cell proliferation by 17 beta-estradiol. After 21 days of culture, RNA was prepared and analyzed in a dot-hybridization assay for the abundance of pro alpha 1(I) collagen mRNA. Steady-state mRNA levels were increased in cultures treated with 17 beta-estradiol in a dose-dependent manner with maximal stimulation at 1 nM and 10 nM. At the same concentrations, the percentage of synthesized protein (labeled by [3H]proline pulse) that was digestible by collagenase was increased, indicating that 17 beta-estradiol acts at pretranslational levels to enhance synthesis of bone collagen. These data show that the osteoblast is a direct target for 17 beta-estradiol.
雌激素在绝经后骨质疏松症的发展过程中起着关键作用。然而，雌激素对骨骼发挥作用的机制尚不清楚。为了研究17β - 雌二醇对成骨细胞可能的直接作用，我们使用体外培养的纯大鼠成骨样细胞作为模型。从新生大鼠颅骨制备的成骨样细胞在含甲基纤维素的无血清培养基中培养21天。成骨样细胞选择性增殖形成球形形态的克隆衍生细胞簇。浓度为0.1 nM和1 nM的17β - 雌二醇使成骨样细胞增殖比溶媒处理的对照组分别提高了41%和68%。生物活性无的立体异构体17α - 雌二醇（相同浓度）则无作用。此外，抗雌激素他莫昔芬消除了17β - 雌二醇对成骨样细胞增殖的刺激作用。培养21天后，制备RNA并通过点杂交分析检测I型前胶原α1（proα1(I)）mRNA的丰度。用17β - 雌二醇处理的培养物中，稳态mRNA水平呈剂量依赖性增加，在1 nM和10 nM时刺激作用最大。在相同浓度下，可被胶原酶消化的合成蛋白（用[3H]脯氨酸脉冲标记）的百分比增加，表明17β - 雌二醇在翻译前水平起作用以增强骨胶原的合成。这些数据表明成骨细胞是17β - 雌二醇的直接作用靶点。
