Li Yan, Li Aimin, Strait Karen, Zhang Hongying, Nanes Mark S, Weitzmann M Neale
Division of Endocrinology and Metabolism and Lipids, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
J Bone Miner Res. 2007 May;22(5):646-55. doi: 10.1359/jbmr.070121.
Endogenous TNFalpha prevents the attainment of maximum achievable peak bone mass in vivo. In vitro, TNFalpha suppresses BMP-2- and TGFbeta-mediated Smad activation through induction of NF-kappaB. Consistently, pharmacological suppression of NF-kappaB augments osteoblast differentiation and mineralization in vitro.
Osteoporosis is a major health threat. Traditional therapeutic strategies have centered on anti-catabolic drugs that block bone resorption. Recently focus has shifted to anabolic agents that actively rebuild lost bone mass. Future strategies may involve elevating peak bone mass to delay osteoporosis development. Recent in vitro studies show that TNFalpha represses osteoblast differentiation and mineralization; however, the mechanisms are poorly understood and the impact of basal TNFalpha concentrations on the acquisition of peak bone mass in vivo is unknown.
We examined peak BMD, bone volume, and bone turnover makers in mice deficient in TNFalpha or its receptors. We further examined the effect of TNFalpha on Smad-induced signaling by TGFbeta and BMP-2 in vitro using a Smad responsive reporter. The effect of TNFalpha-induced NF-kappaB signaling on Smad signaling and on in vitro osteoblast mineralization was examined using specific NF-kappaB inhibitors and activators, and effects of TNFalpha-induced NF-kappaB signaling on BMP-2-induced Runx2 mRNA were examined using RT-PCR.
Mice null for TNFalpha or its p55 receptor had significantly increased peak bone mass, resulting exclusively from elevated bone formation. In vitro, TNFalpha potently suppressed Smad signaling induced by TGFbeta and BMP-2, downregulated BMP-2-mediated Runx2 expression, and inhibited mineralization of osteoblasts. These effects were mimicked by overexpression of NF-kappaB and prevented by pharmacological NF-kappaB suppression.
Our data suggest that TNFalpha and NF-kappaB antagonists may represent novel anabolic agents for the maximization of peak basal bone mass and/or the amelioration of pathological bone loss.
内源性肿瘤坏死因子α（TNFα）可阻止体内达到最大可实现的峰值骨量。在体外，TNFα通过诱导核因子κB（NF-κB）抑制骨形态发生蛋白2（BMP-2）和转化生长因子β（TGFβ）介导的Smad激活。同样，NF-κB的药理学抑制可增强体外成骨细胞的分化和矿化。
骨质疏松症是对健康的重大威胁。传统治疗策略主要集中在阻断骨吸收的抗分解代谢药物上。最近，重点已转向积极重建丢失骨量的合成代谢药物。未来的策略可能包括提高峰值骨量以延缓骨质疏松症的发展。最近的体外研究表明，TNFα可抑制成骨细胞的分化和矿化；然而，其机制尚不清楚，基础TNFα浓度对体内峰值骨量获取的影响也未知。
我们检测了缺乏TNFα或其受体的小鼠的峰值骨密度、骨体积和骨转换标志物。我们还使用Smad反应性报告基因在体外进一步检测了TNFα对TGFβ和BMP-2诱导的Smad信号传导的影响。使用特异性NF-κB抑制剂和激活剂检测TNFα诱导的NF-κB信号传导对Smad信号传导和体外成骨细胞矿化的影响，并使用逆转录聚合酶链反应（RT-PCR）检测TNFα诱导的NF-κB信号传导对BMP-2诱导的Runx2信使核糖核酸（mRNA）的影响。
TNFα或其p55受体缺失型小鼠的峰值骨量显著增加，这完全是由于骨形成增加所致。在体外，TNFα强烈抑制TGFβ和BMP-2诱导的Smad信号传导，下调BMP-2介导的Runx2表达，并抑制成骨细胞的矿化。这些作用可通过NF-κB的过表达模拟，并可通过NF-κB的药理学抑制来预防。
我们的数据表明，TNFα和NF-κB拮抗剂可能代表新型合成代谢药物，可使基础峰值骨量最大化和/或改善病理性骨丢失。
