Effect of physical factors on osseointegration

众所周知，适当的咬合力促进种植体周围骨形成，而在无机械应力或过度应力的情况下，骨生长和骨吸收得以发展。已有研究表明，当剪切应力作用于成骨细胞时，细胞内Ca^2+浓度增加，蛋白激酶A激活，环氧合酶2（考克斯-2）基因表达上调，导致成骨细胞分化。本研究旨在从分子水平上阐明骨重建和力学信号转导的适宜应力水平，采用逆转录聚合酶链反应和cDNA微阵列技术检测小鼠成骨样细胞系（MC 3 T3-E1）在压力作用下24小时的基因表达模式。此外，我们还利用基因芯片检测了压力作用下基因表达的变化，当压力作用时，考克斯-2、c-fos和碱性磷酸酶的mRNA表达量与压力值成比例地上调。cDNA微阵列分析显示，促进成骨细胞分化的骨形态发生蛋白4（BMP 4）和BMP 7的表达上调。MC 3 T3-E1细胞的存活率在负荷和去负荷时无明显差异。基因芯片分析表明，挤压力可上调热休克蛋白25 kDa（Hsp 25）的表达。在磁场和微脉冲磁场作用下，MC 3 T3-E1细胞的考克斯-2、c-fos和碱性磷酸酶mRNA表达均上调，提示磁场压力通过上调HSP 25信号通路促进MC 3 T3-E1细胞的分化。这可能是由于钛与免疫细胞的界面是“静态”环境所致。

It is well known that appropriate occlusal force promotes bone formation around implants, whereas bone atorophy and bone resorption develop under no mechanical stress or overstressing. It has been reported that when shear stress loads to osteoblasts, increase of intracellular Ca^<2+> concentration, activation of protein kinase A, and upregulation of cyclooxygenase 2 (Cox-2) gene result in differentiation of osteoblasts. The purpose of this study was to clarify appropriate levels of stress for the bone remodeling and mechanotransduction signaling at molecular levels.We examined pattern of gene expression when compressing force was directly loaded to a mouse osteoblast like cell line (MC3T3-E1) for 24 hours by reverse transcription polymerase chain reaction and cDNA macroarray. Furthermore, we examined change of gene expression under its stress by cDNA microarray.Cox-2, c-fos, and alkaline phosphatase mRNAs were upregulated in proportion to the stress value when compressing force was loaded. The analysis of cDNA macroarray showed that expression of bone morphogenetic protein 4 (BMP4) and BMP7, which promote differentiation of osteoblasts, was upregulated. No differences of survival of MC3T3-E1 cells were observed between loading and unloading of stress. Furthermore, the analysis of cDNA microarray showed that compressing force upregulated expression of heat shock protein 25kDa (Hsp25). And when MC3T3-E1 cells were cultured in magnetic field and micro pulse magnetic field, Cox-2, c-fos, and alkaline phosphatase mRNAs were upregulated.The present study indicates that the compression force promotes differentiation of MC3T3-E1 cells through the signaling pathway upregulating Hsp25.In the study of immune reaction of dendritic cells to titaniumtitanium could not induce the immune reactions easily. It may be caused by the interface of Ti and immune cells which are ‘static' environment.