Jackson Rebecca A, Kumarasuriyar Arjuna, Nurcombe Victor, Cool Simon M
School of Biomedical Sciences, University of Queensland, Queensland, Australia.
J Cell Physiol. 2006 Dec;209(3):894-904. doi: 10.1002/jcp.20779.
Bone tissue homeostasis relies upon the ability of cells to detect and interpret extracellular signals that direct changes in tissue architecture. This study utilized a four-point bending model to create both fluid shear and strain forces (loading) during the time-dependent progression of MC3T3-E1 preosteoblasts along the osteogenic lineage. Loading was shown to increase cell number, alkaline phosphatase (ALP) activity, collagen synthesis, and the mRNA expression levels of Runx2, osteocalcin (OC), osteopontin, and cyclo-oxygenase-2. However, mineralization in these cultures was inhibited, despite an increase in calcium accumulation, suggesting that loading may inhibit mineralization in order to increase matrix deposition. Loading also increased fibroblast growth factor receptor-3 (FGFR3) expression coincident with an inhibition of FGFR1, FGFR4, FGF1, and extracellular signal-related kinase (ERK)1/2 phosphorylation. To examine whether these loading-induced changes in cell phenotype and FGFR expression could be attributed to the inhibition of ERK1/2 phosphorylation, cells were grown for 25 days in the presence of the MEK1/2 inhibitor, U0126. Significant increases in the expression of FGFR3, ALP, and OC were observed, as well as the inhibition of FGFR1, FGFR4, and FGF1. However, U0126 also increased matrix mineralization, demonstrating that inhibition of ERK1/2 phosphorylation cannot fully account for the changes observed in response to loading. In conclusion, this study demonstrates that preosteoblasts are mechanoresponsive, and that long-term loading, whilst increasing proliferation and differentiation of preosteoblasts, inhibits matrix mineralization. In addition, the increase in FGFR3 expression suggests that it may have a role in osteoblast differentiation.
骨组织稳态依赖于细胞检测和解读细胞外信号的能力，这些信号指导组织结构的变化。本研究利用四点弯曲模型，在MC3T3-E1前成骨细胞沿成骨谱系的时间依赖性进程中产生流体剪切力和应变力（加载）。结果显示，加载可增加细胞数量、碱性磷酸酶（ALP）活性、胶原蛋白合成以及Runx2、骨钙素（OC）、骨桥蛋白和环氧化酶-2的mRNA表达水平。然而，尽管钙积累增加，但这些培养物中的矿化受到抑制，这表明加载可能抑制矿化以增加基质沉积。加载还增加了成纤维细胞生长因子受体-3（FGFR3）的表达，同时抑制了FGFR1、FGFR4、FGF1和细胞外信号调节激酶（ERK）1/2的磷酸化。为了研究这些加载诱导的细胞表型和FGFR表达变化是否可归因于ERK1/2磷酸化的抑制，细胞在MEK1/2抑制剂U0126存在下培养25天。观察到FGFR3、ALP和OC的表达显著增加，同时FGFR1、FGFR4和FGF1受到抑制。然而，U0126也增加了基质矿化，表明抑制ERK1/2磷酸化不能完全解释加载后观察到的变化。总之，本研究表明前成骨细胞具有机械反应性，长期加载虽然增加了前成骨细胞的增殖和分化，但抑制了基质矿化。此外，FGFR3表达的增加表明它可能在成骨细胞分化中起作用。
