不同速率的手术辅助前颌骨扩展(SARMP)对BMP/Smad信号通路相关因子表达影响的研究

Maxillary hypoplasia can be classified as sagittal or transversal deficiency. Corticotomy has been applied to treat maxillary transversal deficiency (Surgically Assisted Rapid Maxillary Expansion, SARME) at present. BMP/Smad signal pathway is one of the most vital process in osteoblast differentiation and bone formation，which involves a serial osteogenic factors’ expression, including BMP-2, Runx2 and Osterix. OPG/RANKL/RANK system plays an essential role in the interaction between osteoblasts and osteoclasts. The up-regulation of RANKL serves as the sign of Osteoclasts process. The aim of this study was to establish the miniature swine model of Surgically Assisted Rapid Maxillary Protraction (SARMP), and to increase premaxillary bone mass with different distraction rate (0.6mm/d, 1.2 mm/d, 1.8 mm/d, 2.4 mm/d). Osseous tissue samples were collected at different distraction periods. Mechanical strength tests, including bone density measurement and three-point bending test, as well as histology detections, including Hematoxylin and Eosin staining, Masson's trichrome method and Sirius red stain, were used to evaluate the distraction effect. To analyze the relation between distraction rate and BMP/Smad signal pathway related factors’ expression, reverse transcription polymerase chain reaction (RT-PCR) was used for determination of the gene expression of BMP-2, Runx2, Osterix and RANKL during distraction osteogenesis in different rate and time points, and protein levels of BMP-2, Runx2 and Osterix were measured with ELISA method.

上颌发育不足包括矢状向或横向发育不足，骨皮质切开术已被用来治疗上颌横向发育不足。BMP/Smad信号通路是促进成骨细胞分化及新骨形成最重要的通路之一，其涉及多种因子的表达包括BMP-2、Runx2和Osterix。OPG/RANKL系统是成骨与破骨细胞之间相互作用的信号通道，RANKL上调表示骨破坏过程加强。本研究在小型猪上建立手术辅助的前颌骨扩展模型(SARMP)，通过断离前颌骨骨皮质，以四种速率进行矢状向牵张，在不同时间取新骨样本，用骨密度测试和三点弯曲实验对新骨机械强度进行测试，HE染色、三色染色及天狼猩红染色观察组织学变化，探讨该技术的可行性及最佳牵张速率；用PCR法检测不同牵张速率及牵张不同时期骨组织BMP-2、Runx2、Osterix和RANKL mRNA的表达变化，用ELISA方法检测相关蛋白表达，以研究牵张速率对BMP/Smad信号通路的影响以及骨形成与吸收的动态变化规律

上颌骨前段牵张成骨的临床应用兴起较晚，相关研究尚不完善，且缺乏成熟的动物模型。本实验旨在建立上颌骨前段牵张成骨小型猪模型，比较不同固定期新骨形成情况。. 实验采用10只10月龄雌性巴马小型猪作为实验动物，行单侧（5只）及双侧（5只）上颌骨前段截骨术，术后间歇期5天，牵张期7天，以0.8mm/天的速率进行牵张，分别于固定期2、4、8、12周处死，截取上颌骨标本，进行大体观察。结果显示：7只小型猪对麻醉及手术的耐受性较好，3只小型猪（单侧1只，双侧2只）于术中或术后死亡，4只小型猪一侧加力杆于术后折断（单侧1只，双侧3只），将该侧作为手术对照侧。牵张侧上颌骨前段平均被牵开4.9mm；牵张侧腭侧牵张区被新骨充满，手术对照侧腭侧截骨间隙愈合，双侧颊侧骨板均有部分吸收。. 将上颌骨标本进行显微CT扫描，测量牵张侧及手术对照侧腭侧新骨骨密度值及骨小梁结构参数。结果显示：新骨骨密度随固定时间延长而升高，骨小梁结构参数值随固定期延长呈规律性变化，固定期12周时，牵张侧新骨相关测量值与空白对照组及手术对照组最相近。. 取术区组织进行大体观察并行HE染色、Masson染色。结果显示：固定 4周时，牵张区两侧为疏松的、网状骨小梁，中间为纤维组织；固定8周时，牵张区主要由网状的骨小梁组成；固定12周时，牵张区主要由板状骨和编织骨组成，可见规则的哈弗氏管；牵张区新骨未见软骨组织。. 分别于术前、间歇期末、牵张期末、固定期1周、固定期2周时，应用酶联免疫吸附方法测定对牵张组及对照组小型猪血清BMP-2含量进行测定。结果显示，牵张组血清BMP-2浓度整体高于对照组,间歇期末牵张组血清BMP-2浓度增高，在牵张期末进一步增高达到峰值；随后在固定期一周时其浓度迅速降低，对照组各时间点血清BMP-2浓度无显著性变化。. 综上，小型猪能较好的耐受手术及牵张过程，牵张新骨形成质量随固定时间的延长而增高，固定期12周时，新骨质量达到较为成熟稳定的状态，BMP-2在牵张成骨愈合早期发挥了重要作用，牵张力可以促进内源性BMP-2的表达。