Analysis of the mechanism of bone destruction by neutrophils

在这项研究中，我们调查的可能性是否中性粒细胞在类风湿性关节炎可以破坏钙化骨在体内和体外。氨基二膦酸盐（ABP）是一种骨吸收抑制剂，用于抑制胶原诱导性关节炎（CIA）中破骨细胞的活性。在用ABP处理的CIA小鼠中观察到CIA中的严重骨破坏。在检测到骨破坏的区域，许多中性粒细胞沿着破坏的骨表面排列。部分中性粒细胞破裂，胞内颗粒散在。在该区域不再检测到骨衬细胞。在该区域也检测到一些破骨细胞。但破骨细胞从骨表面脱落，边缘无皱褶，无明显区带，表明破骨细胞无吸收骨的能力。此外，在破坏的骨基质中未检测到胶原纤维。这些结果有力地证明了中性粒细胞直接破坏钙化骨的可能性。因此，我们接下来将类风湿关节炎患者的中性粒细胞与骨碎片共培养，从超微结构水平观察骨基质的变化。与中性粒细胞共培养的骨碎片中典型的胶原纤维消失。胶原纤维的破坏在这个培养系统中被抑制的MMP或弹性蛋白酶的抑制剂的加入。提示中性粒细胞通过其自身的蛋白酶如MMP和弹性蛋白酶破坏骨基质。

In this study, we investigated the possibility whether neutrophils in rheumatoid arthritis could destruct calcified bone in vivo and in vitro. Aminobisphosphonate (ABP), an inhibitor of osteoclastic bone resorption, was used to inhibit osteoclast activity in collagen-induced arthritis (CIA). Severe bone destruction in CIA was observed in the CIA mice treated with ABP. In the areawhere bone destruction was detected, many neutrophils were aligned along the destructed bone surface. Some of neutrophils were ruptured and scattered intracellular granules on and in the destructed bone. Bone lining cells were no longer deteted in this region. Some osteoclasts were also detected in this region. However, these osteoclast detached from bone surface and had no ruffled borders and clear zones, which indicated that osteoclast had no capacity to resorb bone. Furthermore, no collagen fibers were detected in the destructed bone matrix. These results strongly suggeted the possibility that neutrophils directly destructed calcified bone. Therefore, we next cocultured neutrophils from rheumatoid arthritis patients and bone fragments and investigated the changes of bone matrix ay the ultrastructural level. Typical collagen fibers in the bone fragments cocultured with neutrophils were disappeared. Destruction of collagen fibers in this culture system was inhibited by the addition of the inhibitors of MMP or elastase. These results indicated that neutrophils destructed bone matrix by their intrinsic proteases such as MMP and elastase.