Study on direct action of estrogen on mature osteoclasts

雌激素缺乏，由绝经后卵巢切除引起，导致病理性骨丢失，这可以通过雌激素替代治疗来预防。虽然人们认为雌激素预防骨丢失的主要作用是通过抑制破骨细胞性骨吸收，但这种作用的确切机制尚不清楚，主要是由于获得纯化的功能性破骨细胞的技术困难。在整个研究过程中，我们使用了最近发展起来的两种独特的高纯度哺乳动物破骨细胞的分离方法：一种是在塑料碟子上进行纯化，以获得大量的破骨细胞用于分子生物学分析；另一种是在细胞悬液中分离破骨细胞，以评估破骨细胞的骨吸收活性。在一定生理浓度的雌激素(10^&lt；-12&gt；-10^&lt；-10&gt；M)中，雌激素抑制破骨细胞性骨吸收活性。在相同的浓度范围内，雌激素还降低了在破骨细胞中大量和特异表达的组织蛋白酶K和参与破骨细胞质子产生的碳酸氢酶II的mRNA水平。此外，雌激素以剂量和时间依赖的方式诱导破骨细胞凋亡。ICI1164、384和他莫昔芬分别完全和部分阻断雌激素抑制破骨细胞性骨吸收和诱导破骨细胞凋亡的作用。最后，我们检测到雌激素受体(ERA)的mRNA表达，但没有检测到BRB的表达。这些数据表明，雌激素对绝经后骨质疏松症的保护作用部分是通过直接降低破骨细胞性骨吸收的关键酶和通过雌激素受体介导的机制直接诱导破骨细胞凋亡来实现的。

Estrogen deficiency, cause by either menopause ovariectomy, results in pathological bone loss, which can be prevented by estrogen replacement therapy. Although it is believed that estrogen's main action in preventing bone loss is through inhibition of osteoclastic bone resorption, the precise mechanism of such effect is not clear, largely due to technical difficulties in obtaining purified functional osteoclasts. Throughout this study, we used two unique isolation methods of highly purified mammalian osteoclasts, which were recently developed by us : one is the purification on plastic dished to get a large number of osteoclasts for molecular biological analyzes, and the other is the isolation of osteoclasts in cell suspension for estimation of osteoclastic bone-resorbing activity. In a range of physiological concentrations of estrogen (10^<-12>-10^<-10>M), estrogen inhibited osteoclastic bone resorbing activity. In the same concentration range, estrogen also reduced mRNA levels of cathepsin K,which is abundantly and specifically expressed in osteoclasts, and of carbonic anhydrase II,that is involved in proton production in osteoclasts. Furthermore, estrogen induced osteoclast apoptosis in a dose-and time-dependent manner. ICI1164,384 and tamoxifen, as pure and partial antagonists, respectively, completely and partially blocked the effect of estrogen on both inhibition of osteoclastic bone resorption and induction of osteoclast apoptosis. Finally, we detected the mRNA expression of estrogen reccptor (ERA), but not BRb. Thses data suggest that the protective effects of estrogen against postmenopausal osteoporosis are mediated in part by the direct reduction of key enzymes for osteoclastic bone resorption and the direct induction of osteoclast apoptosis via estrogen receptor-mediated mechanisms.