Wiren K M, Chapman Evans A, Zhang X-W
Veterans Affairs Medical Center, 3710 SW Veterans Hospital Road, Portland, Oregon 97201, USA.
J Endocrinol. 2002 Dec;175(3):683-94. doi: 10.1677/joe.0.1750683.
Significant levels of estrogen and androgens circulate in men and women, and both play an important role in bone metabolism. While it is well established that either estrogen or androgen replacement therapy is effective at ameliorating bone loss associated with hypogonadism, recent evidence nevertheless suggests that estrogen and androgens have distinct molecular actions on the skeleton. In this study, we have employed normal rat calvarial osteoblast cultures to characterize relative expression profiles of estrogen (ERalpha and ERbeta) and androgen receptors (AR) during osteoblast differentiation. Normal osteoblast cultures can proceed through in vitro differentiation with distinct stages of proliferation, matrix maturation and mineralization in the appropriate differentiation medium containing ascorbic acid. Expression profiles of AR, ERalpha and ERbeta in primary cultures during osteoblast differentiation were characterized both by semi-quantitative relative RT-PCR and by Western analysis. In cultures induced to differentiate by growth in the presence of ascorbic acid, the expression profile for each receptor was unique during the course of differentiation. ERalpha levels were elevated during matrix maturation and then declined during mineralization. ERbeta expression was relatively constant throughout differentiation, exhibiting more constitutive expression. In contrast, AR levels were lowest during proliferation, and then increased throughout differentiation with highest levels in the most mature mineralizing cultures. Since steroid hormone action is generally mediated by specific cognate receptors, these results suggest that androgen actions may target cells during the mineralization stage of osteoblast differentiation, while estrogen action through either receptor isoform is more likely to affect osteoblasts earlier during matrix maturation. Interestingly, sex steroid receptor expression profiles did not exhibit the same patterns of regulation if osteoblast cultures were grown without ascorbic acid in medium that did not support extracellular matrix deposition. Thus, sex steroids may distinctly influence skeletal health by differential modulation of function during osteoblast differentiation.
雌激素和雄激素在男性和女性体内均有显著水平的循环，且二者在骨代谢中均发挥重要作用。虽然雌激素或雄激素替代疗法可有效改善与性腺功能减退相关的骨质流失，这一点已得到充分证实，但最近的证据表明，雌激素和雄激素对骨骼具有不同的分子作用。在本研究中，我们利用正常大鼠颅骨成骨细胞培养物来表征成骨细胞分化过程中雌激素（雌激素受体α和雌激素受体β）和雄激素受体（AR）的相对表达谱。正常成骨细胞培养物可在含有抗坏血酸的合适分化培养基中经历体外分化，具有增殖、基质成熟和矿化的不同阶段。通过半定量相对逆转录聚合酶链反应（RT-PCR）和蛋白质免疫印迹分析对原代培养物中成骨细胞分化过程中AR、雌激素受体α和雌激素受体β的表达谱进行了表征。在抗坏血酸存在下生长诱导分化的培养物中，每种受体的表达谱在分化过程中都是独特的。雌激素受体α水平在基质成熟期间升高，然后在矿化期间下降。雌激素受体β表达在整个分化过程中相对恒定，表现出更多的组成性表达。相比之下，AR水平在增殖期间最低，然后在整个分化过程中升高，在最成熟的矿化培养物中水平最高。由于类固醇激素作用通常由特定的同源受体介导，这些结果表明雄激素作用可能在成骨细胞分化的矿化阶段靶向细胞，而通过任一受体亚型的雌激素作用更可能在基质成熟早期影响成骨细胞。有趣的是，如果成骨细胞培养物在不支持细胞外基质沉积的培养基中无抗坏血酸生长，性类固醇受体表达谱则不会表现出相同的调控模式。因此，性类固醇可能通过在成骨细胞分化过程中对功能的差异调节来显著影响骨骼健康。
