Kurokouchi K, Jacobs C R, Donahue H J
Department of Orthopaedics and Rehabilitation and Cellular and Molecular Physiology, Musculoskeletal Research Laboratory, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA.
J Biol Chem. 2001 Apr 20;276(16):13499-504. doi: 10.1074/jbc.M003795200. Epub 2000 Nov 28.
Fluid flow plays an important role in load-induced bone remodeling. However, the molecular mechanism of flow-induced signal transduction in osteoblasts remains unclear. In endothelial cells, fluid flow alters activation of NF-kappaB resulting in changes in expression of cell adhesion molecules. To test the hypothesis that fluid flow alters NF-kappaB activation and expression of cell adhesion molecules in osteoblastic cells, we examined the effect of oscillating fluid flow (OFF) on tumor necrosis factor (TNF)-alpha-induced NF-kappaB activation in rat osteoblast-like UMR106 cells. We found that OFF inhibits NF-kappaB-DNA binding activities, especially TNF-alpha-induced p50-p65 heterodimer NF-kappaB activation and TNF-alpha-induced intercellular adhesion molecule-1 mRNA expression. The inhibitory effects of OFF on both TNF-alpha-induced NF-kappaB activation and intercellular adhesion molecule-1 mRNA expression were shear stress-dependent and also increased with OFF exposure duration, indicating that OFF has potent effects on mechanotransduction pathways. OFF also inhibited TNF-alpha-induced IkappaBalpha degradation and TNF-alpha-induced IkappaB kinase (IKK) activity in a shear stress-dependent manner. These results demonstrate that IKK is an initial target molecule for OFF effects on osteoblastic cells. Thus, OFF inhibits TNF-alpha-induced IKK activation, leading to a decrease in phosphorylation and degradation of inhibitory IkappaBalpha, which in turn results in the decrease of TNF-alpha-induced NF-kappaB activation and potentially the transcription of target genes.
流体流动在负荷诱导的骨重塑中起着重要作用。然而，流体流动诱导成骨细胞信号转导的分子机制仍不清楚。在内皮细胞中，流体流动会改变核因子κB（NF-κB）的激活，从而导致细胞黏附分子表达的变化。为了验证流体流动会改变成骨细胞中NF-κB激活和细胞黏附分子表达这一假说，我们研究了振荡流体流动（OFF）对大鼠成骨样UMR106细胞中肿瘤坏死因子（TNF）-α诱导的NF-κB激活的影响。我们发现OFF抑制NF-κB与DNA的结合活性，尤其是TNF-α诱导的p50-p65异二聚体NF-κB激活以及TNF-α诱导的细胞间黏附分子-1 mRNA表达。OFF对TNF-α诱导的NF-κB激活和细胞间黏附分子-1 mRNA表达的抑制作用均依赖于剪切应力，并且也随着OFF暴露时间的延长而增强，这表明OFF对机械转导通路具有显著影响。OFF还以剪切应力依赖的方式抑制TNF-α诱导的IκBα降解和TNF-α诱导的IκB激酶（IKK）活性。这些结果表明IKK是OFF对成骨细胞作用的初始靶分子。因此，OFF抑制TNF-α诱导的IKK激活，导致抑制性IκBα的磷酸化和降解减少，进而导致TNF-α诱导的NF-κB激活以及潜在的靶基因转录减少。
