Malaval L, Gupta A K, Liu F, Delmas P D, Aubin J E
INSERM U403, Hôpital Edouard Herriot, Lyon, France.
J Bone Miner Res. 1998 Feb;13(2):175-84. doi: 10.1359/jbmr.1998.13.2.175.
Cytokines of the interleukin 6 (IL-6) subfamily are a group of factors produced by osteoblasts and acting through the same transducing element, membrane protein gp130. We have previously shown that exogenous (added to the culture medium) leukemia inhibitory factor (LIF) inhibits bone nodule formation and expression of osteoblast-associated genes in fetal rat calvaria (RC) cell cultures and that dexamethasone (Dex) increases the ID50 of LIF. To investigate the respective roles of IL-6-related cytokines and receptors in osteprogenitor differentiation, and their regulatory interplay with Dex, we used reverse transcribed polymerase chain reaction, bioassay, and blocking antibody techniques to assess the time courses of LIF, IL-6, LIF transmembrane receptor, IL-6 receptor, and gp130 expression in RC cell cultures grown with and without Dex. The levels of the mRNAs for IL-6, LIF, and gp130 decreased concomitantly with the formation of bone nodules. Dex treatment, which stimulates bone nodule formation, reduced the expression of LIF and IL-6 mRNAs and IL-6 bioactivity in the culture medium. LIF treatment strongly stimulated the expression of IL-6. Incubation with anti-LIF antibodies increased the number of nodules, while an antibody blocking IL-6 activity had little or no effect on nodule numbers and did not antagonize the action of exogenous LIF, indicating that IL-6 does not mediate the action of LIF in this system. Moreover, although exogenously added IL-6 was active in the cultures as noted by a reduction of nodule mineralization, it had no effect on nodule numbers, i.e., on osteoprogenitor differentiation, in the presence or absence of Dex. In conclusion, IL-6, LIF, and their receptors are expressed throughout the time-course of osteogenesis in RC cell cultures. However, only LIF, but not IL-6, appears to play a significant role in autocrine regulation of osteoblastic differentiation in this system. The antagonist action of Dex on the effects of exogenously added LIF, as well as the bone-promoting action of Dex in RC cell cultures, could be exerted partly through the down-regulation of the expression of endogenous LIF.
白细胞介素6（IL-6）亚家族的细胞因子是由成骨细胞产生并通过相同转导元件膜蛋白gp130发挥作用的一组因子。我们先前已经表明，外源性（添加到培养基中）白血病抑制因子（LIF）在胎鼠颅骨（RC）细胞培养物中抑制骨结节形成和成骨细胞相关基因的表达，并且地塞米松（Dex）增加LIF的半数抑制浓度（ID50）。为了研究IL-6相关细胞因子和受体在成骨祖细胞分化中的各自作用，以及它们与Dex的调节相互作用，我们使用逆转录聚合酶链反应、生物测定和阻断抗体技术来评估在添加和不添加Dex的情况下RC细胞培养物中LIF、IL-6、LIF跨膜受体、IL-6受体和gp130表达的时间进程。IL-6、LIF和gp130的mRNA水平随着骨结节的形成而同时下降。刺激骨结节形成的Dex处理降低了培养基中LIF和IL-6 mRNA的表达以及IL-6生物活性。LIF处理强烈刺激IL-6的表达。用抗LIF抗体孵育增加了结节数量，而阻断IL-6活性的抗体对结节数量几乎没有影响，并且不拮抗外源性LIF的作用，这表明在该系统中IL-6不介导LIF的作用。此外，尽管如通过结节矿化减少所表明的那样，外源性添加的IL-6在培养物中具有活性，但在存在或不存在Dex的情况下，它对结节数量即对成骨祖细胞分化没有影响。总之，IL-6、LIF及其受体在RC细胞培养物成骨过程的整个时间进程中均有表达。然而，在该系统中，似乎只有LIF而非IL-6在成骨细胞分化的自分泌调节中起重要作用。Dex对外源性添加LIF作用的拮抗作用以及Dex在RC细胞培养物中的促骨作用可能部分是通过下调内源性LIF的表达来实现的。
