Li Bing-Yan, Tong Jian, Zhang Zeng-Li
Radiation Medical and Public School of Soochow University, Suzhou 215123, China.
Sheng Li Xue Bao. 2006 Dec 25;58(6):573-6.
It is well known that estrogen can inhibit bone absorption, decrease bone turnover and preserve bone mass. Some studies indicated that the effect of estrogen on calcium and bone is relative to vitamin D system, while others also reported that this effect of estrogen is independent of vitamin D. The genomic effect of 1alpha, 25(OH)(2)D(3)is mediated by the nuclear vitamin D receptor (VDR) in a ligand-dependent manner. Hypocalcemia, hyperparathyroidism and osteomalacia are developed in VDR gene knockout mice. To determine whether the effect of estrogen on calcium and bone is dependent on VDR, this study examined the effect of exogenous estrogen on calcium and bone homeostasis in VDR gene knockout mice. Male and female wild type (WT) and VDR gene knockout heterozygous mice were mated each other and the genotyping of their offsprings were determined by PCR. At age of 21-day, WT and knockout mice were weaned and treated by one of three different regimens: (1) WT-vehicle group: the WT mice were injected with normal saline; (2) VDR KO-vehicle group: the VDR gene knockout mice were injected with normal saline; (3) VDR KO-E group: the VDR gene knockout mice were subcutaneously injected with estradiol, 0.2 mug per mouse, once daily for 1 month. The bone mineral density (BMD) of mice was measured using dual-energy X-ray absorptiometry. All mice were sacrificed at age of 50-day. Blood was taken by heart puncture under anesthesia and serum calcium was measured by autoanalyser.Tibiae were removed, fixed and embedded with the methylmethacrylate (MMA), and undecalcified sections were cut. These sections were stained for mineral with the von Kossa staining procedure and counterstained with toluidine blue. Static histomorphometric analyses were performed on those stained sections. The results showed that the serum calcium level was (2.10+/-0.37) mmol/L in the VDR KO-vehicle mice and rose to (2.80+/-0.41) mmol/L in the VDR KO-E mice although it was still lower than WT-vehicle mice [(3.10+/-0.48) mmol/L]. BMD and mineralized trabeculer volume were increased significantly in VDR KO-E group compared with that in VDR KO-vehicle group. These results suggest that exogenous estrogen can improve calcium absorption and skeletal mineralization in a VDR-independent manner.
众所周知，雌激素可抑制骨吸收，降低骨转换并维持骨量。一些研究表明，雌激素对钙和骨骼的作用与维生素D系统有关，而另一些研究也报道雌激素的这种作用独立于维生素D。1α,25(OH)₂D₃的基因组效应由核维生素D受体（VDR）以配体依赖的方式介导。VDR基因敲除小鼠会出现低钙血症、甲状旁腺功能亢进和骨软化症。为了确定雌激素对钙和骨骼的作用是否依赖于VDR，本研究检测了外源性雌激素对VDR基因敲除小鼠钙和骨稳态的影响。雄性和雌性野生型（WT）及VDR基因敲除杂合小鼠相互交配，通过聚合酶链反应（PCR）确定其后代的基因分型。在21日龄时，WT和基因敲除小鼠断奶，并采用三种不同方案之一进行处理：（1）WT-溶剂组：WT小鼠注射生理盐水；（2）VDR KO-溶剂组：VDR基因敲除小鼠注射生理盐水；（3）VDR KO-E组：VDR基因敲除小鼠皮下注射雌二醇，每只小鼠0.2μg，每日一次，共1个月。使用双能X线吸收法测量小鼠的骨密度（BMD）。所有小鼠在50日龄时处死。在麻醉下通过心脏穿刺取血，用自动分析仪测量血清钙。取出胫骨，固定并用甲基丙烯酸甲酯（MMA）包埋，切取不脱钙切片。这些切片用冯·科萨染色法进行矿物质染色，并用甲苯胺蓝复染。对这些染色切片进行静态组织形态计量学分析。结果显示，VDR KO-溶剂组小鼠的血清钙水平为（2.10±0.37）mmol/L，VDR KO-E组小鼠的血清钙水平升至（2.80±0.41）mmol/L，尽管仍低于WT-溶剂组小鼠[（3.10±0.48）mmol/L]。与VDR KO-溶剂组相比，VDR KO-E组的BMD和矿化骨小梁体积显著增加。这些结果表明，外源性雌激素可通过不依赖VDR的方式改善钙吸收和骨骼矿化。
