Division of Endocrinology and Metabolism, Asan Medical Center, University of Ulsan College of Medicine, 388-1 Poongnap2-Dong, Seoul, Republic of Korea.
Biochem Biophys Res Commun. 2012 Jul 20;424(1):170-5. doi: 10.1016/j.bbrc.2012.06.100. Epub 2012 Jun 23.
Although recent clinical studies have suggested a possible role for sclerostin, a secreted Wnt antagonist, in the pathogenesis of postmenopausal osteoporosis, the detailed mechanisms how estrogen deficiency regulates sclerostin expression have not been well-elucidated. Bilateral ovariectomy or a sham operation in female C57BL/6 mice and BALB/c nude mice was performed when they were seven weeks of age. The C57BL/6 mice were intraperitoneally injected with phosphate-buffered serum (PBS), 5 μg/kg β-estradiol five times per week for three weeks, or 10 mg/kg TNF-α blocker three times per week for three weeks. Bony sclerostin expression was assessed by immunohistochemistry staining in their femurs. The activity and expression of myocyte enhancer factors 2 (MEF2), which is essential for the transcriptional activation of sclerostin, in rat UMR-106 osteosarcoma cells were determined by luciferase reporter assay and western blot analysis, respectively. Bony sclerostin expression was stimulated by estrogen deficiency and it was reversed by estradiol supplementation. When the UMR-106 cells were treated with well-known, estrogen-regulated cytokines, only TNF-α, but not IL-1 and IL-6, increased the MEF2 activity. Consistently, TNF-α also increased the nuclear MEF2 expression. Furthermore, the TNF-α blocker prevented the stimulation of bony sclerostin expression by ovariectomy. We also found that there was no difference in sclerostin expression between ovariectomized nude mice and sham-operated nude mice. In conclusion, these results suggest that TNF-α originating from T cells may be at least in part responsible for stimulating the sclerostin expression observed in an estrogen-deficient condition.
尽管最近的临床研究表明，一种分泌型 Wnt 拮抗剂骨硬化蛋白（Sclerostin）可能在绝经后骨质疏松症的发病机制中起作用，但雌激素缺乏如何调节骨硬化蛋白表达的详细机制尚未完全阐明。当 7 周龄的雌性 C57BL/6 小鼠和 BALB/c 裸鼠接受双侧卵巢切除术或假手术时，将磷酸盐缓冲液（PBS）、每周 5 次、每次 5μg/kgβ-雌二醇或每周 3 次、每次 10mg/kgTNF-α 阻滞剂腹腔内注射。通过免疫组织化学染色检测其股骨中的骨硬化蛋白表达。通过荧光素酶报告测定和 Western blot 分析分别确定大鼠 UMR-106 骨肉瘤细胞中肌细胞增强因子 2（MEF2）的活性和表达，MEF2 对骨硬化蛋白的转录激活至关重要。雌激素缺乏刺激骨硬化蛋白表达，而雌激素补充可逆转这种作用。当 UMR-106 细胞用已知的雌激素调节细胞因子处理时，只有 TNF-α而不是 IL-1 和 IL-6 增加 MEF2 活性。一致地，TNF-α也增加了核 MEF2 的表达。此外，TNF-α 阻滞剂可防止卵巢切除术引起的骨硬化蛋白表达增加。我们还发现，去卵巢裸鼠和假手术裸鼠之间的骨硬化蛋白表达没有差异。总之，这些结果表明，源自 T 细胞的 TNF-α可能至少部分负责刺激雌激素缺乏状态下观察到的骨硬化蛋白表达。
