Udagawa N, Takahashi N, Katagiri T, Tamura T, Wada S, Findlay D M, Martin T J, Hirota H, Taga T, Kishimoto T, Suda T
Department of Biochemistry, School of Dentistry, Showa University, Tokyo, Japan.
J Exp Med. 1995 Nov 1;182(5):1461-8. doi: 10.1084/jem.182.5.1461.
We reported that interleukin (IL) 6 alone cannot induce osteoclast formation in cocultures of mouse bone marrow and osteoblastic cells, but soluble IL-6 receptor (IL-6R) strikingly triggered osteoclast formation induced by IL-6. In this study, we examined the mechanism of osteoclast formation by IL-6 and related cytokines through the interaction between osteoblastic cells and osteoclast progenitors. When dexamethasone was added to the cocultures, IL-6 could stimulate osteoclast formation without the help of soluble IL-6R. Osteoblastic cells expressed a very low level of IL-6R mRNA, whereas fresh mouse spleen and bone marrow cells, both of which are considered to be osteoclast progenitors, constitutively expressed relatively high levels of IL-6R mRNA. Treatment of osteoblastic cells with dexamethasone induced a marked increase in the expression of IL-6R mRNA. By immunoblotting with antiphosphotyrosine antibody, IL-6 did not tyrosine-phosphorylate a protein with a molecular mass of 130 kD in osteoblastic cells but did so in dexamethasone-pretreated osteoblastic cells. Osteoblastic cells from transgenic mice constitutively expressing human IL-6R could support osteoclast development in the presence of human IL-6 alone in cocultures with normal spleen cells. In contrast, osteoclast progenitors in spleen cells from transgenic mice overexpressing human IL-6R were not able to differentiate into osteoclasts in response to IL-6 in cocultures with normal osteoblastic cells. These results clearly indicate that the ability of IL-6 to induce osteoclast differentiation depends on signal transduction mediated by IL-6R expressed on osteoblastic cells but not on osteoclast progenitors.
我们曾报道，在小鼠骨髓与成骨细胞的共培养体系中，单独的白细胞介素（IL）-6不能诱导破骨细胞形成，但可溶性IL-6受体（IL-6R）能显著触发由IL-6诱导的破骨细胞形成。在本研究中，我们通过成骨细胞与破骨细胞前体细胞之间的相互作用，研究了IL-6及相关细胞因子诱导破骨细胞形成的机制。当在地塞米松加入共培养体系时，IL-6无需可溶性IL-6R的帮助就能刺激破骨细胞形成。成骨细胞表达极低水平的IL-6R mRNA，而新鲜的小鼠脾脏和骨髓细胞，这两者都被认为是破骨细胞前体细胞，组成性地表达相对高水平的IL-6R mRNA。用地塞米松处理成骨细胞可导致IL-6R mRNA表达显著增加。用抗磷酸酪氨酸抗体进行免疫印迹分析显示，IL-6在成骨细胞中不能使分子量为130 kD的蛋白质发生酪氨酸磷酸化，但在地塞米松预处理的成骨细胞中可以。在与正常脾细胞的共培养体系中，组成性表达人IL-6R的转基因小鼠的成骨细胞在单独存在人IL-6的情况下就能支持破骨细胞的发育。相反，在与正常成骨细胞的共培养体系中，过表达人IL-6R的转基因小鼠脾细胞中的破骨细胞前体细胞不能响应IL-6分化为破骨细胞。这些结果清楚地表明，IL-6诱导破骨细胞分化的能力取决于成骨细胞而非破骨细胞前体细胞上表达的IL-6R介导的信号转导。
