Group for Bone Biology and Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, CH-3010 Bern, Switzerland.
Bone. 2011 Nov;49(5):1090-100. doi: 10.1016/j.bone.2011.08.003. Epub 2011 Aug 16.
Inflammatory cytokines such as tumor necrosis factor-alpha (TNFα) are potent stimulators of osteoclast formation and bone resorption and are frequently associated with pathologic bone metabolism. The cytokine exerts specific effects on its target cells and constitutes a part of the cellular microenvironment. Previously, TNFα was demonstrated to inhibit the development of osteoclasts in vitro via an osteoblast-mediated pathway. In the present study, the molecular mechanisms of the inhibition of osteoclastogenesis were investigated in co-cultures of osteoblasts and bone marrow cells (BMC) and in cultures of macrophage-colony stimulating factor (M-CSF) dependent, non-adherent osteoclast progenitor cells (OPC) grown with M-CSF and receptor activator of NF-κB ligand (RANKL). Granulocyte-macrophage colony stimulating factor (GM-CSF), a known inhibitor of osteoclastogenesis was found to be induced in osteoblasts treated with TNFα and the secreted protein accumulated in the supernatant. Dexamethasone (Dex), an anti-inflammatory steroid, caused a decrease in GM-CSF expression, leading to partial recovery of osteoclast formation. Flow cytometry analysis revealed that in cultures of OPC, supplemented with 10% conditioned medium (CM) from osteoblasts treated with TNFα/1,25(OH)(2)D(3), expression of RANK and CD11c was suppressed. The decrease in RANK expression may be explained by the finding, that GM-CSF and the CM from wt osteoblasts were found to suppress the expression of c-Fos, Fra-1, and Nfatc-1. The failure of OPC to develop into CD11c(+) dendritic cells suggests that cell development is not deviated to an alternative differentiation pathway, but rather, that the monocytes are maintained in an undifferentiated, F4/80(+), state. The data further implies possible interactions among inflammatory cytokines. GM-CSF induced by TNFα acts on early hematopoietic precursors, inhibiting osteoclastogenesis while acting as the growth factor for M-CSF independent inflammatory macrophages. These in turn may condition a microenvironment enhancing osteoclast differentiation and bone resorption upon migration of the OPC from circulation to the bone/bone marrow compartment.
炎症细胞因子，如肿瘤坏死因子-α（TNFα），是破骨细胞形成和骨吸收的有效刺激物，常与病理性骨代谢有关。该细胞因子对其靶细胞具有特异性作用，并构成细胞微环境的一部分。先前已经证明 TNFα 通过成骨细胞介导的途径在体外抑制破骨细胞的发育。在本研究中，在成骨细胞和骨髓细胞（BMC）的共培养物以及巨噬细胞集落刺激因子（M-CSF）依赖性、非贴壁破骨细胞前体细胞（OPC）的培养物中研究了抑制破骨细胞发生的分子机制，这些 OPC 在 M-CSF 和核因子-κB 配体受体激活剂（RANKL）的作用下生长。已知抑制破骨细胞发生的粒细胞-巨噬细胞集落刺激因子（GM-CSF）在 TNFα 处理的成骨细胞中被诱导产生，并且分泌的蛋白在上清液中积累。抗炎类固醇地塞米松（Dex）导致 GM-CSF 表达减少，从而部分恢复破骨细胞形成。流式细胞术分析显示，在补充了来自经 TNFα/1,25(OH)2D3 处理的成骨细胞的 10%条件培养基（CM）的 OPC 培养物中，RANK 和 CD11c 的表达受到抑制。RANK 表达的减少可能是由于发现 GM-CSF 和来自 wt 成骨细胞的 CM 抑制了 c-Fos、Fra-1 和 Nfatc-1 的表达。OPC 未能发育为 CD11c+树突状细胞表明细胞发育没有偏离到替代分化途径，而是单核细胞保持未分化状态，F4/80+。数据进一步暗示了炎症细胞因子之间可能存在相互作用。TNFα 诱导的 GM-CSF 作用于早期造血前体，抑制破骨细胞发生，同时作为 M-CSF 非依赖性炎症巨噬细胞的生长因子。反过来，这些细胞因子可能会在 OPC 从循环迁移到骨/骨髓腔室时，调节微环境，增强破骨细胞分化和骨吸收。
