Tensile Stress Induces Bone Morphogenetic Protein 4 in Preosteoblastic and Fibroblastic Cells, Which Later Differentiate into Osteoblasts Leading to Osteogenesis in the Mouse Calvariae in Organ Culture
作者:Mika Ikegame、Osamu Ishibashi、Tatsuya Yoshizawa、Junko Shimomura、Toshihisa Komori、Hidehiro Ozawa、Hiroyuki Kawashima
DOI:10.1359/jbmr.2001.16.1.24
日期:——
Mechanical stress is an important factor controlling bone remodeling, which maintains proper bone morphology and functions. However, the mechanism by which mechanical stress is transduced into biological stimuli remains unclear. Therefore, the purpose of this study is to examine how gene expression changes with osteoblast differentiation and which cells differentiate into osteoblasts. Tensile stress was applied to the cranial suture of neonatal mouse calvaria in a culture by means of helical springs. The suture was extended gradually, displaying a marked increase in cell number including osteoblasts. A histochemical study showed that this osteoblast differentiation began in the neighborhood of the existing osteoblasts, which can be seen by 3 h. The site of osteoblast differentiation moved with time toward the center of the suture, which resulted in an extension of osteoid. Scattered areas of the extended osteoid were calcified by 48 h. Reverse‐transcription polymerase chain reaction (RT‐PCR) revealed that tensile stress increased bone morphogenetic protein 4 (BMP‐4) gene expression by 6 h and it remained elevated thereafter. This was caused by the induction of the gene in preosteoblastic cells in the neighborhood of osteoblasts and adjacent spindle‐shaped fibroblastic cells. These changes were evident as early as 3 h and continued moving toward the center of the suture. The expression of Cbfa1/Osf‐2, an osteoblast‐specific transcription factor, followed that of BMP‐4 and those cells positive with these genes appeared to differentiate into osteoblasts. These results suggest that BMP‐4 may play a pivotal role by acting as an autocrine and a paracrine factor for recruiting osteoblasts in tensile stress‐induced osteogenesis.
机械应力是控制骨重建的重要因素,它维持骨骼的正常形态和功能。然而,机械应力如何转化为生物应激信号的机制仍不清楚。因此,本研究的目的是探讨成骨细胞分化过程中基因表达如何变化,以及哪些细胞分化成成骨细胞。通过螺旋弹簧在培养环境下对新生小鼠颅骨骨缝施加拉应力。骨缝逐渐展开,细胞数量(包括成骨细胞)明显增加。组织化学研究表明,这种成骨细胞分化始于现有成骨细胞的周围,3h 时就可以看出。成骨细胞分化部位随时间向骨缝中心移动,导致类骨质延伸。延伸的类骨质分散区域在 48h 时可矿化。反转录‐聚合酶链反应(RT‐PCR) 揭示拉应力在 6h 时增加了骨形态发生蛋白 4 ( BMP‐4)的基因表达,此后它一直保持在高水平。这是由于在成骨细胞周围的成骨前体细胞和相邻的梭形纤维母细胞中诱导了基因。这些变化早在3h 时就很明显并持续向骨缝中心移动。成骨细胞特异转录因子 Cbfa1/Osf‐2 的表达紧随 BMP‐4 的表达, 这些基因阳性的细胞似乎分化成成骨细胞。这些结果提示,BMP‐4 可能在拉应力诱导的成骨中起关键作用,因为它通过内分泌和旁分泌方式募集成骨细胞。