PTHrP协同压应力促进正畸牙移动的机制及应用基础研究

Slow orthodontic tooth movement (OTM)leading to lengthy treatment duration, not only frustrates patients, but also considerably increases risks of complications including white-spot lesion, root resorption and gingival recession. However,to date no molecule/medicine has been developed as atisfactory OTM accelerator for clinical use.Undoutedly, it remains a hot pursuit in orthodontic biomechanics research, with great social and economic significance. In our previous studies, we have reported, for the first time, that human periodontal ligament(PDL) cells express up-regulated parathyroid hormone related peptide(PTHrP) under compressive stress, both in vitro and in vivo. PTHrP is well known as the local simulator for PTH, and like PTH, it can promote bone resorption upon continuous delivery. Notably, PTHrP is essential for initiation of bone resorption in tooth eruption. Taken together, we reasonably hypothesize that PTHrP may play a pivotal role in the "compressive stress-PDL-bone resorption" axis in OTM, and local administration of PTHrP may accelerate OTM. In the present project, we are going to address this hypothesis through the following experimentations.(1)To elucidate the role of PTHrP in the "compressive stress-PDL-bone resorption" axis ,the PDL tissue model is to be established and loaded with static compressive stress for 24 h. The conditional media is to be used for co-culture of osteoblasts and osteoclast precursors. The PTHrP-PTHR1 signaling is to be enhanced or suppressed, with recombinant PTHrP or PTH/PTHrP antagonist respectively.Formation of TRAP+ osteoclasts and expression of RANKL/OPG in osteoblast are to be investigated.(2)To observe the effects of local administration of PTHrP to accelerate OTM, the rat OTM model is to be established. During mesialization of the upper first molar with NiTi coil spring, biodegradable thermosensitive PEG-PCL-PEG(PECE) hydrogel loaded with recombinant PTHrP is to be injected at the compressive periodontium, resulting in controlled continuous release of the factor. The rate of OTM, TRAP+ osteoclast number and the expression of PTHrP, RANKL/OPG, etc., are to be investigated, with the vehicle treated OTM group serving as the control. (3) To further verify the acceleratory effects of local continuous release of PTHrP on OTM , the beagle OTM model is to be established, with the upper first premolar extracted and the second premolar mesialized using NiTi coil spring. The PTHrP-loaded PECE hydrogel is to be injected at the compressive periodontium, and the rate of OTM, TRAP+ osteoclast number and expression of PTHrP, RANKL/OPG ,etc. are to be investigated. In summary, this project is to elucidate the pivotal role of PTHrP in "compressive stress-PDL-bone resorption" , the kernel biological axis, in OTM , and to testify the paradigm of local administration of PTHrP to accelerate OTM in synergy with compressive stress.

加速正畸牙移动（orthodontic tooth movement，OTM），缩短正畸疗程，具有广泛临床需求，是正畸生物力学领域研究热点。申请人在前期研究中首次报道压应力作用下牙周膜细胞PTHrP表达上调。此外，PTHrP通过促进骨吸收在牙萌出中发挥核心作用。由此，我们提出应用PTHrP促进骨吸收，加速OTM的科学假说。本项目拟：1）利用已建立的"压应力-牙周膜组织模型"，增强或阻断PTHrP-PTHR1信号通路，观察对破骨细胞生成和RANKL/OPG表达的影响。2）建立大鼠OTM模型，在压力侧牙周组织局部注射可降解"水凝胶-PTHrP"缓释制剂。检测OTM速率、牙周组织改建、破骨细胞数及RANKL/OPG表达的改变。3）建立Beagle犬OTM模型，进一步验证压力侧牙周组织注射PTHrP加速OTM的效果。综上，本项目有望阐明PTHrP协同压应力促进OTM的机制，并初步建立其应用体系。

摘要：安全有效地加速正畸牙移动，缩短正畸疗程，具有广泛的临床需求，也一直是正畸生物力学领域的研究热点。甲状旁腺激素（parathyroid hormone，PTH）一直是研究热点，但其加速牙移动的最适作用方式、机制等尚未被完全阐明。并且与甲状旁腺激素具有高度相似性的甲状旁腺激素相关蛋白(parathyroid hormone related protein，PTHrP)也被用于口腔领域的研究，并被认为可能是一个新的加速正畸牙移动的分子调控靶点，但其加速正畸牙移动的效应尚未见明确报道。本研究探究了其在体内体外对骨改建发挥的作用。实验一中通过对建立的聚乳酸-乙醇酸共聚物与人牙周膜细胞的3D培养系统施加静压力，并观察不同药物处理后破骨相关因子的表达，得到PTHrP可促进持续压应力下牙周膜细胞破骨因子表达。实验二中，对不同组别的人牙周膜细胞进行成骨诱导，观察成骨分化相关因子及增殖相关指标，得到外源性或自身表达的PTHrP抑制人牙周膜细胞成骨向分化，对其增殖没有明显影响。实验三在体内做了进一步的验证，制备安全有效的水温敏凝胶缓释体系及在Wistar大鼠口内建立经典的上颌牙移动模型，通过不同的药物处理后比较牙移动情况及组织学变化，得到PTH和PTHrP能够同时促进破骨细胞介导的骨吸收和成骨细胞介导的骨形成，即通过加快骨改建来加速正畸牙移动，并且局部持续释放的PTH能够减少正畸牙移动后的复发，其机制与局部骨改建进程加快相关。体内外实验均表明PTH和PTHrP能够促进骨改建加速正畸牙移动，为以后加速正畸牙移动提供了新思路。