Pannexin-1 and P2X7-Receptor Are Required for Apoptotic Osteocytes in Fatigued Bone to Trigger RANKL Production in Neighboring Bystander Osteocytes.
Pannexin-1 and P2X7-Receptor Are Required for Apoptotic Osteocytes in Fatigued Bone to Trigger RANKL Production in Neighboring Bystander Osteocytes.
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DOI：
10.1002/jbmr.2740
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发表时间：
2016-04
期刊：
影响因子：
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通讯作者：
Schaffler MB
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作者：
Cheung WY;Fritton JC;Morgan SA;Seref-Ferlengez Z;Basta-Pljakic J;Thi MM;Suadicani SO;Spray DC;Majeska RJ;Schaffler MB
在动物模型中，骨细胞凋亡是微损伤后诱导皮质内骨重建所必需的，但凋亡的骨细胞如何向邻近的“旁观者”细胞发出信号以启动重建过程尚不清楚。细胞凋亡已显示打开泛连接蛋白-1（Panx 1）通道以释放ATP作为吞噬细胞的“找到我”信号。为了解决凋亡骨细胞是否使用这种信号传导机制，我们采用大鼠尺骨疲劳负荷模型，可重复地将微损伤引入小鼠皮质骨，并测量野生型（WT，C57 Bl/6）小鼠和Panx 1遗传缺陷小鼠（Panx 1 KO）中骨细胞凋亡，RANKL表达和骨吸收的后续变化。小鼠尺骨负荷产生的线性微裂纹在数量和位置上与大鼠模型相当。WT小鼠在负荷后3天显示微损伤部位骨细胞凋亡和RANKL表达增加，在第14天皮质内重塑和皮质内隧道增加。疲劳时，Panx 1 KO小鼠表现出与WT小鼠相同的微损伤和骨细胞凋亡水平。然而，他们没有上调RANKL在旁观者骨细胞或启动吸收。Panx 1在ATP释放中与P2 X7 R相互作用;因此，我们检查了P2 X7 R缺陷小鼠和用P2 X7 R拮抗剂Brilliant Blue G（BBG）处理的WT小鼠，以测试ATP作为find-me信号的可能作用。尽管疲劳负荷后骨细胞凋亡正常升高，但P2 X7 RKO小鼠未能上调骨细胞中的RANKL或诱导骨吸收。类似地，用BBG治疗疲劳的C57 Bl/6小鼠模仿了Panx 1 KO和P2 X7 RKO小鼠的行为; BBG对疲劳骨中的骨细胞凋亡没有影响，但完全阻止了旁观者骨细胞RANKL表达的增加，并使再吸收的激活减弱了50%以上。这些结果表明，激活Panx 1和P2 X7 R是疲劳骨中凋亡骨细胞触发邻近旁观者骨细胞产生RANKL所必需的，并暗示ATP是介导该过程的重要信号。
Osteocyte apoptosis is required to induce intracortical bone remodeling following microdamage in animal models, but how apoptotic osteocytes signal neighboring “bystander” cells to initiate the remodeling process is unknown. Apoptosis has been shown to open pannexin-1 (Panx1) channels to release ATP as a “find-me” signal for phagocytic cells. To address whether apoptotic osteocytes use this signaling mechanism, we adapted the rat ulnar fatigue-loading model to reproducibly introduce microdamage into mouse cortical bone and measured subsequent changes in osteocyte apoptosis, RANKL expression and osteoclastic bone resorption in wild type (WT, C57Bl/6) mice and in mice genetically deficient in Panx1 (Panx1KO). Mouse ulnar-loading produced linear microcracks comparable in number and location to the rat model. WT mice showed increased osteocyte apoptosis and RANKL expression at microdamage sites at 3 days after loading, and increased intracortical remodeling and endocortical tunneling at day 14. With fatigue, Panx1KO mice exhibited levels of microdamage and osteocyte apoptosis identical to WT mice. However, they did not upregulate RANKL in bystander osteocytes or initiate resorption. Panx1 interacts with P2X7R in ATP release; thus we examined P2X7R-deficient mice and WT mice treated with P2X7R antagonist Brilliant Blue G (BBG) to test the possible role of ATP as a find-me signal. P2X7RKO mice failed to upregulate RANKL in osteocytes or induce resorption despite normally elevated osteocyte apoptosis after fatigue loading. Similarly, treatment of fatigued C57Bl/6 mice with BBG mimicked behavior of both Panx1KO and P2X7RKO mice; BBG had no effect on osteocyte apoptosis in fatigued bone, but completely prevented increases in bystander osteocyte RANKL expression and attenuated activation of resorption by more than 50 percent. These results indicate that activation of Panx1 and P2X7R are required for apoptotic osteocytes in fatigued bone to trigger RANKL production in neighboring bystander osteocytes and implicate ATP as an essential signal mediating this process.