Center for Biochemistry, Medical Faculty, University of Cologne, Cologne, Germany.
J Bone Miner Res. 2012 Nov;27(11):2399-412. doi: 10.1002/jbmr.1682.
Numerous biochemical studies have pointed to an essential role of annexin A5 (AnxA5), annexin A6 (AnxA6), and collagen X in matrix vesicle-mediated biomineralization during endochondral ossification and in osteoarthritis. By binding to the extracellular matrix protein collagen X and matrix vesicles, annexins were proposed to anchor matrix vesicles in the extracellular space of hypertrophic chondrocytes to initiate the calcification of cartilage. However, mineralization appears to be normal in mice lacking AnxA5 and AnxA6, whereas collagen X-deficient mice show only subtle alterations in the growth plate organization. We hypothesized that the simultaneous lack of AnxA5, AnxA6, and collagen X in vivo induces more pronounced changes in the growth plate development and the initiation of mineralization. In this study, we generated and analyzed mice deficient for AnxA5, AnxA6, and collagen X. Surprisingly, mice were viable, fertile, and showed no obvious abnormalities. Assessment of growth plate development indicated that the hypertrophic zone was expanded in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) newborns, whereas endochondral ossification and mineralization were not affected in 13-day- and 1-month-old mutants. In peripheral quantitative computed tomography, no changes in the degree of biomineralization were found in femora of 1-month- and 1-year-old mutants even though the diaphyseal circumference was reduced in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mice. The percentage of naive immature IgM(+) /IgM(+) B cells and peripheral T-helper cells were increased in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mutants, and activated splenic T cells isolated from Col10a1(-/-) mice secreted elevated levels of IL-4 and GM-CSF. Hence, collagen X is needed for hematopoiesis during endochondral ossification and for the immune response, but the interaction of annexin A5, annexin A6, and collagen X is not essential for physiological calcification of growth plate cartilage. Therefore, annexins and collagen X may rather fulfill functions in growth plate cartilage not directly linked to the mineralization process.
许多生化研究指出，膜联蛋白 A5（AnxA5）、膜联蛋白 A6（AnxA6）和胶原 X 在软骨内骨化和骨关节炎中基质小泡介导的生物矿化过程中具有重要作用。通过与细胞外基质蛋白胶原 X 和基质小泡结合，膜联蛋白被认为将基质小泡锚定在肥大软骨细胞的细胞外空间中，从而启动软骨的钙化。然而，在缺乏 AnxA5 和 AnxA6 的小鼠中，矿化似乎是正常的，而胶原 X 缺陷小鼠仅在生长板组织中显示出细微的改变。我们假设体内同时缺乏 AnxA5、AnxA6 和胶原 X 会导致生长板发育和矿化起始的更明显变化。在这项研究中，我们生成并分析了缺乏 AnxA5、AnxA6 和胶原 X 的小鼠。令人惊讶的是，这些小鼠是存活的、可育的，并且没有明显的异常。生长板发育的评估表明，在 Col10a1(-/-) 和 AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) 新生小鼠中，肥大区扩大，而 13 天和 1 个月龄的突变体的软骨内骨化和矿化不受影响。在周围定量计算机断层扫描中，即使在 Col10a1(-/-) 和 AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) 小鼠的骨干直径减小的情况下，1 个月和 1 岁突变体的股骨中也未发现生物矿化程度的变化。Col10a1(-/-) 和 AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) 突变体中幼稚的未成熟 IgM(+) /IgM(+) B 细胞和外周辅助性 T 细胞的百分比增加，并且从 Col10a1(-/-) 小鼠分离的激活的脾 T 细胞分泌升高水平的 IL-4 和 GM-CSF。因此，胶原 X 对于软骨内骨化期间的造血以及免疫反应是必需的，但是膜联蛋白 A5、膜联蛋白 A6 和胶原 X 的相互作用对于生长板软骨的生理矿化不是必需的。因此，膜联蛋白和胶原 X 可能在与矿化过程没有直接联系的生长板软骨中发挥作用。
