Rhee Samuel T, Buchman Steven R
Section of Plastic Surgery, University of Michigan Medical Center, Ann Arbor, MI, USA.
Ann Plast Surg. 2005 Aug;55(2):207-15. doi: 10.1097/01.sap.0000164576.10754.aa.
Craniofacial distraction osteogenesis (DO) is an evolving reconstructive technique with expanding applications for the treatment of bony deficiencies of the facial skeleton. Mechanical force has been known to play a fundamental role in modulating sustained osteogenic response and therefore is believed to function as a critical regulator of DO. We hypothesize that key clustering components of an integrin-mediated signaling pathway, including c-Src (pp60), are necessary for mediating the response to mechanical force. The specific aim of this study is to demonstrate up-regulation of a key focal adhesion molecule, c-Src, selectively in new bone formation subject to the mechanical forces of distraction and to demonstrate a lack of that same up-regulation in new bone formation associated with simple fracture healing. An additional specific aim is to demonstrate colocalization of c-Src expression and bone morphogenetic protein (BMP 2/4) expression during mandibular DO. Using a rat model of mandibular DO, c-Src and BMP 2/4 expression were evaluated in critical size defects, subcritical size defects, and mandibles undergoing gradual distraction. Osseous regeneration was observed in the course of gradual distraction; this process was associated with increased expression of c-Src. Furthermore, the presence of BMP 2/4 closely approximated c-Src expression spatially and temporally, suggesting a link between cytoplasmic focal adhesion activation and the resultant nuclear regulation of osteogenic protein expression. In significant contradistinction, minimal c-Src expression was found in the subcritical-sized defects where the fractures healed secondarily but where no gradual distraction was performed. Instead, the new bone formation inherent in the secondarily healed subcritical-sized defects demonstrated expected BMP 2/4 expression but was devoid of an up-regulation of c-Src. Finally, as expected, minimal expression of both c-Src and BMP was found in fibrous nonunion specimens. C-src expression was observed during gradual distraction; furthermore, minimal c-Src expression was visualized during subacute and critical-size defect fracture healing. C-Src expression also closely approximated BMP expression during DO. These findings that c-Src expression is found primarily only during conditions of cyclic distraction forces strongly implicates that mechanical force during gradual distraction is associated with c-Src expression. These results provide in vivo support for previous in vitro evidence that mechanical force profoundly influences osseous regeneration during distraction osteogenesis by means of a c-Src dependent mechanotransduction pathway, resulting in increased expression of osteogenic proteins, including BMP 2/4.
颅面骨牵引成骨术（DO）是一种不断发展的重建技术，在治疗面部骨骼骨缺损方面的应用日益广泛。已知机械力在调节持续性成骨反应中起基本作用，因此被认为是骨牵引成骨术的关键调节因子。我们假设整合素介导的信号通路的关键聚集成分，包括c-Src（pp60），是介导对机械力反应所必需的。本研究的具体目的是证明在受牵引机械力作用的新骨形成中，关键粘着斑分子c-Src选择性上调，并证明在与单纯骨折愈合相关的新骨形成中不存在同样的上调。另一个具体目的是证明在下颌骨牵引成骨过程中c-Src表达与骨形态发生蛋白（BMP 2/4）表达的共定位。使用下颌骨牵引成骨的大鼠模型，在临界尺寸缺损、亚临界尺寸缺损以及逐渐牵引的下颌骨中评估c-Src和BMP 2/4的表达。在逐渐牵引过程中观察到骨再生；这个过程与c-Src表达增加有关。此外，BMP 2/4的存在在空间和时间上与c-Src表达密切相关，表明细胞质粘着斑激活与成骨蛋白表达的核调控之间存在联系。与之形成显著对比的是，在亚临界尺寸缺损中发现c-Src表达极少，这些缺损骨折二期愈合但未进行逐渐牵引。相反，二期愈合的亚临界尺寸缺损中固有的新骨形成显示出预期的BMP 2/4表达，但c-Src没有上调。最后，正如预期的那样，在纤维性骨不连标本中发现c-Src和BMP的表达都极少。在逐渐牵引过程中观察到c-src表达；此外，在亚急性和临界尺寸缺损骨折愈合过程中可见极少的c-Src表达。在牵引成骨过程中，C-Src表达也与BMP表达密切相关。这些发现表明c-Src表达主要仅在周期性牵张力条件下出现，这强烈暗示逐渐牵引过程中的机械力与c-Src表达有关。这些结果为先前的体外证据提供了体内支持，即机械力通过依赖c-Src的机械转导途径深刻影响牵引成骨过程中的骨再生，导致包括BMP 2/4在内的成骨蛋白表达增加。
