Analysis of the mechanism of bone destruction by neutrophils

在这项研究中，我们研究了类风湿关节炎中性粒细胞是否在体内和体外破坏钙化骨的可能性。氨基二膦酸盐（ABP）是一种破骨细胞骨吸收抑制剂，用于抑制胶原诱导关节炎（CIA）的破骨细胞活性。经ABP处理的CIA小鼠出现了严重的CIA骨破坏，在发现骨破坏的区域，许多中性粒细胞沿破坏的骨表面排列。部分中性粒细胞破裂，细胞内颗粒散在破坏骨上和骨内。骨衬里细胞在该区域不再被检测到。在这一区域也检测到一些破骨细胞。然而，这些破骨细胞脱离骨表面，没有褶皱的边界和清晰的区域，这表明破骨细胞没有吸收骨的能力。此外，在破坏的骨基质中未检测到胶原纤维。这些结果强烈提示中性粒细胞直接破坏钙化骨的可能性。因此，我们下一步将类风湿关节炎患者的中性粒细胞与骨碎片共培养，从超微结构水平研究骨基质的变化。与中性粒细胞共培养的骨碎片中典型的胶原纤维消失。在这种培养体系中，胶原纤维的破坏被添加MMP或弹性酶抑制剂所抑制。这些结果表明，中性粒细胞通过其固有的蛋白酶如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.