Parikka V, Lehenkari P, Sassi M L, Halleen J, Risteli J, Härkönen P, Väänänen H K
Institute of Biomedicine, Department of Anatomy and Medicity Research Laboratory, University of Turku, FIN-20520 Turku, Finland.
Endocrinology. 2001 Dec;142(12):5371-8. doi: 10.1210/endo.142.12.8533.
Decreased E2 levels after menopause cause bone loss through increased penetrative resorption. The reversal effect of E2 substitution therapy is well documented in vivo, although the detailed mechanism of action is not fully understood. To study the effects of E2 on bone resorption, we developed a novel in vitro bone resorption assay in which degradation of inorganic and organic matrix could be measured separately. E2 treatment significantly decreased the depth of resorption pits, although the area resorbed was not changed. Electron microscopy further revealed that the resorption pits were filled with nondegraded collagen, suggesting that E2 disturbed the organic matrix degradation. Two major groups of proteinases, matrix metalloproteinases (MMPs) and cysteine proteinases, have been suggested to participate in organic matrix degradation by osteoclasts. We show here that MMP-9 released a cross-linked carboxyl-terminal telopeptide of type I collagen from bone collagen, and cathepsin K released another C-terminal fragment, the C-terminal cross-linked peptide of type I collagen. E2 significantly inhibited the release of the C-terminal cross-linked peptide of type I collagen into the culture medium without affecting the release of cross-linked carboxyl-terminal telopeptide of type I collagen in osteoclast cultures. These results suggest that organic matrix degradation is initiated by MMPs and continued by cysteine proteases; the latter event is regulated by E2.
绝经后雌激素（E2）水平降低通过增加穿透性骨吸收导致骨质流失。E2替代疗法的逆转作用在体内已有充分记录，尽管其详细作用机制尚未完全明确。为了研究E2对骨吸收的影响，我们开发了一种新型的体外骨吸收测定法，可分别测量无机和有机基质的降解情况。E2处理显著降低了吸收陷窝的深度，尽管吸收面积未改变。电子显微镜进一步显示，吸收陷窝内充满了未降解的胶原蛋白，这表明E2干扰了有机基质的降解。已有研究表明，两组主要的蛋白酶，即基质金属蛋白酶（MMPs）和半胱氨酸蛋白酶，参与破骨细胞对有机基质的降解。我们在此表明，MMP-9从骨胶原蛋白中释放出I型胶原蛋白的交联羧基末端肽段，组织蛋白酶K释放出另一个C末端片段，即I型胶原蛋白的C末端交联肽段。在破骨细胞培养中，E2显著抑制I型胶原蛋白C末端交联肽段释放到培养基中，而不影响I型胶原蛋白交联羧基末端肽段的释放。这些结果表明，有机基质的降解由MMPs启动，由半胱氨酸蛋白酶继续进行；后者受E2调节。
