Tomkinson A, Reeve J, Shaw R W, Noble B S
Bone Research Group (Medical Research Council), Cambridge University, United Kingdom.
J Clin Endocrinol Metab. 1997 Sep;82(9):3128-35. doi: 10.1210/jcem.82.9.4200.
Estrogen withdrawal in women leads initially to rapid bone loss caused by increased numbers or activity of osteoclasts. We previously have noted apoptosis of lacunar osteocytes associated with conditions of high bone turnover. Therefore, in this study, we investigated whether the increased bone loss associated with GnRH analogue (GnRH-a)-induced estrogen withdrawal affects osteocyte viability in situ in a way that would be directly contrary to the effect of estrogens on osteoclast viability. Transiliac biopsies were obtained from six premenopausal women, between 30-45 yr old, diagnosed as having endometriosis. Biopsies were taken before and after 24 weeks of GnRH-a therapy. Biopsies were snap-frozen and cryostat sectioned. Osteocyte viability, determined by the presence of lactate dehydrogenase (LDH) activity, was reduced in all but one subject after treatment. Furthermore, in every subject, the proportion of osteocytes showing evidence of DNA fragmentation typical of apoptosis increased, as demonstrated using in situ DNA nick translation (P = 0.008). Gel electrophoresis of extracted DNA and morphological studies of chromatin condensation and nuclear fragmentation confirmed that changes typical of apoptosis were affecting the osteocytes. It was concluded that GnRH-a therapy caused a higher prevalence of dead osteocytes in iliac bone, probably caused by the increase in the observed proportion of osteocytes showing apoptotic changes. The capacity of bone to repair microdamage and to modulate the effects of mechanical strain is currently believed to be dependent on osteocyte viability. Our findings have therefore revealed a possible mechanism whereby estrogen deficiency could lead to increased bone fragility with or without an accompanying net bone loss.
女性体内雌激素撤退最初会导致破骨细胞数量增加或活性增强，从而引发快速骨质流失。我们之前已经注意到，与高骨转换状态相关的骨陷窝骨细胞凋亡现象。因此，在本研究中，我们调查了与促性腺激素释放激素类似物（GnRH-a）诱导的雌激素撤退相关的骨质流失增加，是否会以一种与雌激素对破骨细胞活力的影响直接相反的方式影响原位骨细胞的活力。从6名年龄在30至45岁之间、被诊断患有子宫内膜异位症的绝经前女性身上获取了髂骨活检样本。在GnRH-a治疗24周前后分别进行活检。活检样本经速冻后进行低温切片。通过乳酸脱氢酶（LDH）活性的存在来确定骨细胞活力，并发现除一名受试者外，所有受试者在治疗后骨细胞活力均降低。此外，使用原位DNA缺口平移法显示（P = 0.008），在每个受试者中，显示典型凋亡DNA片段化证据的骨细胞比例均增加。提取DNA的凝胶电泳以及染色质凝聚和核碎裂的形态学研究证实，典型的凋亡变化正在影响骨细胞。得出的结论是，GnRH-a治疗导致髂骨中死亡骨细胞的发生率更高，这可能是由于观察到的显示凋亡变化的骨细胞比例增加所致。目前认为，骨骼修复微损伤和调节机械应变影响的能力取决于骨细胞的活力。因此，我们的研究结果揭示了一种可能的机制，即雌激素缺乏可能导致骨脆性增加，无论是否伴有净骨质流失。
