Sato M, Yasui N, Nakase T, Kawahata H, Sugimoto M, Hirota S, Kitamura Y, Nomura S, Ochi T
Department of Orthopaedic Surgery, Osaka University Medical School, Suita, Japan.
J Bone Miner Res. 1998 Aug;13(8):1221-31. doi: 10.1359/jbmr.1998.13.8.1221.
Distraction osteogenesis is a recently advanced principle of bone lengthening in which a bone separated by osteotomy is subjected to slow progressive distraction using an external fixation device. Appropriate mechanical tension-stress is believed not to break the callus but rather to stimulate osteogenesis. To study the molecular features of this process, the expression and localization of the mRNAs encoding osteopontin (OPN), osteocalcin (OC), matrix Gla protein (MGP), osteonectin (ON), and collagen type I and I during distraction osteogenesis were examined by in situ hybridization and Northern blot analysis. The process can be divided into three distinct phases: the lag phase for 7 days between osteotomy and the beginning of distraction, the distraction phase for 21 days, and the consolidation phase for several weeks. The histologic and molecular events taking place during the lag phase were similar to those observed in fracture healing. The osteotomy site was surrounded by external callus consisting of hyaline cartilage. As distraction started at the rate of 0.25 mm/12 h, the cartilaginous callus was elongated, deformed, and eventually separated into proximal and distal segments. The chondrocytes were stretched along the tension vector and became fibroblast-like in shape. Although morphologically these cells were distinguishable from osteogenic cells, they expressed OPN, OC, and alkaline phosphatase mRNAs. As distraction advanced, the cartilaginous callus was progressively replaced by bony callus by endochondral ossification and thereafter new bone was formed directly by intramembranous ossification. OPN mRNA was detected in preosteoblasts and osteoblasts at the boundary between fibrous tissue and new bone. ON, MGP, and OC mRNAs appeared early in the differentiation stage. The variety of cell types expressing mRNA encoding bone matrix proteins in distraction osteogenesis was much greater than that detected in the embryonic bone formation and fracture healing process. Moreover, the levels of OPN, ON, MGP, and OC mRNA expression markedly increased during the distraction phase. These results suggested that mechanical tension-stress modulates cell shape and phenotype, and stimulates the expression of the mRNA for bone matrix proteins.
牵张成骨是一种最近发展起来的骨延长原理，即通过截骨分离的骨利用外固定装置进行缓慢的渐进性牵张。适当的机械张应力据信不会破坏骨痂，反而会刺激成骨。为了研究这一过程的分子特征，通过原位杂交和Northern印迹分析检测了在牵张成骨过程中编码骨桥蛋白（OPN）、骨钙素（OC）、基质Gla蛋白（MGP）、骨连接蛋白（ON）以及I型和I型胶原蛋白的mRNA的表达和定位。该过程可分为三个不同阶段：截骨与牵张开始之间的7天延迟期、21天的牵张期以及数周的巩固期。延迟期发生的组织学和分子事件与骨折愈合中观察到的相似。截骨部位被由透明软骨组成的外骨痂包围。当以0.25毫米/12小时的速度开始牵张时，软骨痂被拉长、变形，最终分为近端和远端节段。软骨细胞沿张力向量伸展并变成成纤维细胞样形状。尽管在形态上这些细胞与成骨细胞可区分，但它们表达OPN、OC和碱性磷酸酶mRNA。随着牵张的进行，软骨痂通过软骨内成骨逐渐被骨痂替代，此后新骨通过膜内成骨直接形成。在纤维组织与新骨之间的边界处，前成骨细胞和成骨细胞中检测到OPN mRNA。ON、MGP和OC mRNA在分化阶段早期出现。在牵张成骨过程中表达编码骨基质蛋白mRNA的细胞类型种类比在胚胎骨形成和骨折愈合过程中检测到的要多得多。此外，在牵张期OPN、ON、MGP和OC mRNA表达水平显著增加。这些结果表明机械张应力调节细胞形状和表型，并刺激骨基质蛋白mRNA的表达。
