Estrogen receptors and estrogen responsive genes in the pathogenesis of osteoporosis

雌激素在维持骨密度和预防骨质疏松症中发挥重要作用，但雌激素通过雌激素受体（er）在骨中的作用机制尚不清楚。在本研究中，我们产生了erα显性阴性的大鼠，它不仅抑制erα的作用，而且抑制erβ的作用。我们观察到转基因雌性大鼠去卵巢后，即使给予17β -雌二醇（E2），骨密度（BMD）仍保持下降，而E2完全阻止了窝鼠骨密度的下降，提示雌激素对卵巢切除引起的骨质流失的预防是通过内质网途径介导的。然后，我们从转基因大鼠及其野生型幼崽中分离出原代成骨细胞。利用基因芯片分析，我们发现在转基因大鼠的成骨细胞中，细胞周期蛋白D2的mRNA水平较低。17 -雌二醇处理后，野生型成骨细胞中d型细胞周期蛋白（包括cyclin D2和cyclin D3）的蛋白水平升高，但不包括cyclin D1，从而激活细胞周期蛋白依赖性激酶4和6 （Cdk4/6）活性，促进细胞生长。此外，我们还发现了雌激素应答通路包括Efp和EBAG9通路。特别是，我们揭示了Efp作为泛素连接酶在细胞周期调控中的分子机制。这些基因在骨质疏松症中的功能分析正在进行中。我们还发现骨密度与参与骨代谢的人类基因（如VDP、IL-6、TNFalpa、Klotho、BNP、TNFR1、LRP5/6）中的每个SNP之间存在关联。

Estrogen plays important roles in maintaining bone density and protecting against osteoporosis, but the underlying mechanisms of estrogen action via estrogen receptors (ERs) in bone remain to be clarified. In the present study, we have generated rats harboring a dominant negative ERalpha, which inhibits the actions of not only ERalpha but also ERbeta. We observed bone mineral density (BMD) of the transgenic female rats, after ovariectomized, remained decreased even if 17beta-estradiol (E2) was administrated, whereas, in contrast, the decrease of littermate BMD was completely prevented by E2, suggesting that the prevention from the ovariectomy-induced bone loss by estrogen is mediated by ER pathways. We then isolated primary osteoblasts derived from transgenic rats and from their wild-type littermates. Utilizing cDNA microarray analysis, we found that mRNA level of cyclin D2 was lower in the osteoblasts from the transgenic rats. The protein levels of D-type cyclins including cyclin D2 and cyclin D3 but not cyclin D1 were elevated in wild-type osteoblasts with 17beta-estradiol treatment, resulting in the activation of cyclin-dependent kinases 4 and 6 (Cdk4/6) activities and the promotion of cell growth. Besides, we identified estrogen responsive pathways including Efp and EBAG9 pathways. Especially, we have revealed the molecular mechanism of Efp action as ubiquitin ligase in the cell cycle control. Functional analyzes of these genes in osteoporosis are underway. We have also shown associations between BMD and each SNP in human genes involved in the bone metabolism such as VDP, IL-6, TNFalpa, Klotho, BNP, TNFR1, LRP5/6.