Malaval L, Gupta A K, Aubin J E
Medical Research Council Group in Periodontal Physiology, University of Toronto, Ontario, Canada.
Endocrinology. 1995 Apr;136(4):1411-8. doi: 10.1210/endo.136.4.7895651.
Leukemia inhibitory factor (LIF) is a pleiotropic cytokine with both anabolic and catabolic effects on bone tissue. To investigate the effect of LIF on bone formation in the absence of a resorption cycle, we used fetal rat calvaria cell cultures and quantified bone nodule production, which provides a colony assay to analyze the effects of factors on osteoprogenitor differentiation and bone formation. In these cultures, dexamethasone (Dex) stimulates bone nodule formation. In dose-response experiments, LIF inhibited bone nodule formation by cells cultured with (+Dex; ID50 = 250 U/ml) or without (-Dex; ID50 = 30 U/ml) 10(-8) M Dex. Residual nodules were small and poorly mineralized. Continuous exposure to LIF (500 U/ml) up to day 25 did not affect either the growth rate or saturation density of the cultures, but decreased alkaline phosphatase activity and bone nodule production, with greater inhibition in -Dex cultures. Exposure to LIF (500 U/ml) for 3 days early during nodule formation (about day 10) reduced bone nodule numbers to the same extent as continuous treatment in -Dex cultures and significantly, but less markedly, in +Dex cultures; earlier and later pulses had no effect. Northern blot analysis of expression of messenger RNAs of bone related proteins in cultures pulsed (-Dex) at various stages of development showed marked inhibition of alkaline phosphatase, bone sialoprotein, and osteocalcin; slight inhibition of type I collagen; early stimulation of osteopontin; and no effect on Secreted Protein, Acidic and Rich in Cysteine/osteonectin. These results suggest that LIF is an inhibitor of bone nodule formation in these cultures, acting at a stage when late osteoprogenitors and/or early osteoblasts are present, and that Dex may modulate the effects of LIF by shifting effective doses to higher concentrations.
白血病抑制因子（LIF）是一种对骨组织具有合成代谢和分解代谢作用的多效性细胞因子。为了研究在没有吸收周期的情况下LIF对骨形成的影响，我们使用了胎鼠颅骨细胞培养物并对骨结节生成进行了定量，这提供了一种集落测定法来分析各种因素对骨祖细胞分化和骨形成的影响。在这些培养物中，地塞米松（Dex）刺激骨结节形成。在剂量反应实验中，LIF抑制了与10^(-8) M Dex一起培养（+Dex；半数抑制浓度 = 250 U/ml）或不与Dex一起培养（-Dex；半数抑制浓度 = 30 U/ml）的细胞形成骨结节。残留的结节较小且矿化程度低。持续暴露于LIF（500 U/ml）直至第25天对培养物的生长速率或饱和密度均无影响，但降低了碱性磷酸酶活性和骨结节生成，在-Dex培养物中的抑制作用更强。在结节形成早期（约第10天）暴露于LIF（500 U/ml）3天，骨结节数量减少的程度与-Dex培养物中的持续处理相同，在+Dex培养物中也有显著但不太明显的减少；更早和更晚的脉冲处理则没有效果。对在不同发育阶段进行脉冲处理（-Dex）的培养物中骨相关蛋白信使RNA表达的Northern印迹分析显示，碱性磷酸酶、骨唾液蛋白和骨钙素受到明显抑制；I型胶原受到轻微抑制；骨桥蛋白受到早期刺激；对富含半胱氨酸的酸性分泌蛋白/骨连接素没有影响。这些结果表明，LIF在这些培养物中是骨结节形成的抑制剂，作用于晚期骨祖细胞和/或早期成骨细胞存在的阶段，并且Dex可能通过将有效剂量转移到更高浓度来调节LIF的作用。
