Fakhry Ali, Ratisoontorn Chootima, Vedhachalam Charulatha, Salhab Imad, Koyama Eiki, Leboy Phoeby, Pacifici Maurizio, Kirschner Richard E, Nah Hyun-Duck
Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, 4010 Locust Street, Philadelphia, PA 19104, USA.
Bone. 2005 Feb;36(2):254-66. doi: 10.1016/j.bone.2004.10.003.
Systemically administered fibroblast growth factors (FGFs) show anabolic effects on bone formation in animals, whereas in vitro cell culture studies have demonstrated that FGFs block mineralized bone nodule formation. These apparently contradictory outcomes indicate that the nature of FGF action is complex and that the biological effect of FGFs may depend on the differentiation stage of osteoblasts, interaction with other cytokines, or the length and mode of exposure to factors. Thus, we have utilized primary calvarial bone cell populations at different maturation phases to determine their responses to 2, FGF-9, and BMP-2, the factors expressed in bone. FGF-2 and FGF-9 stimulated proliferation of the cell populations consisting of more mature osteoblasts, but not those with undifferentiated precursor cells. Continuous treatment with FGF-2/-9 inhibited expression of several osteoblast marker genes and mineralization. However, brief pretreatment with FGF-2/-9 or sequential treatment with FGF-2/-9 followed by BMP-2 led to marked stimulation of mineralization, suggesting that FGFs enhance the intrinsic osteogenic potential. Furthermore, FGF-2 and FGF-9 increased expression of other osteogenic factors BMP-2 and TGFbeta-1. Meanwhile, blocking endogenous FGF signaling, using a virally transduced dominant-negative FGF receptor (FgfR), resulted in drastically reduced expression of the BMP-2 gene, demonstrating for the first time that endogenous FGF/FgfR signaling is a positive upstream regulator of the BMP-2 gene in calvarial osteoblasts. In contrast, expression of a BMP antagonist noggin was inhibited by FGF-2 and FGF-9. Thus, collective data from this study suggest that FGF/FgfR signaling enhances the intrinsic osteogenic potential by selectively expanding committed osteogenic cell populations as well as inversely regulating BMP-2 and noggin gene expression.
全身给药的成纤维细胞生长因子（FGFs）对动物的骨形成具有合成代谢作用，而体外细胞培养研究表明FGFs可阻断矿化骨结节的形成。这些明显相互矛盾的结果表明FGF作用的性质很复杂，并且FGFs的生物学效应可能取决于成骨细胞的分化阶段、与其他细胞因子的相互作用，或接触因子的时长和方式。因此，我们利用处于不同成熟阶段的原代颅骨细胞群体来确定它们对FGF-2、FGF-9和BMP-2（在骨中表达的因子）的反应。FGF-2和FGF-9刺激了由更成熟的成骨细胞组成的细胞群体的增殖，但未刺激含有未分化前体细胞的细胞群体的增殖。用FGF-2/-9持续处理会抑制几种成骨细胞标记基因的表达和矿化。然而，用FGF-2/-9进行短暂预处理或先用FGF-2/-9再用BMP-2进行序贯处理会显著刺激矿化，这表明FGFs增强了内在的成骨潜能。此外，FGF-2和FGF-9增加了其他成骨因子BMP-2和TGFβ-1的表达。同时，使用病毒转导的显性负性FGF受体（FgfR）阻断内源性FGF信号传导，导致BMP-2基因的表达大幅降低，首次证明内源性FGF/FgfR信号传导是颅骨成骨细胞中BMP-2基因的正向上游调节因子。相比之下，FGF-2和FGF-9抑制了BMP拮抗剂头蛋白（noggin）的表达。因此，本研究的综合数据表明，FGF/FgfR信号传导通过选择性地扩大定向成骨细胞群体以及反向调节BMP-2和头蛋白基因表达来增强内在的成骨潜能。
