甲状旁腺激素对正畸牙移动所致牙根吸收的影响及其分子机制研究

Orthodontically induced inflammatory root resorption (OIIRR) is an unavoidable adverse reaction of orthodontic treatment. However, there have been no available approaches for clinical protection and repair of root resorption. Cementoblasts are in charge of forming new cementum, and play a crucial role in repair of root resorption. Cementoblasts share phenotypic features with osteoblasts in terms of cell origin, appearance, function and signaling. Parathyroid hormone (PTH), as a clinical osteoporosis-treating medicine, exerts anabolic effects on osteoblasts through activating Wnt signal pathway and other growth factors like IGF-1 and FGF-2. Previous studies also revealed that intermittent PTH administration could activate osteogenic/cementogenic differentiation of periodontal ligament cells and facilitate periodontal repair, and PTH-related protein played an important role in cementum formation and tooth development. The potential prospect of application of PTH in repair of OIIRR has drawn researchers' attention. Our previous studies have indicated that intermittent PTH administration may facilitate the repair process of OIIRR, and might act directly on cementoblasts through binding to the receptor PTH1R, and stimulate functional activity of cementoblasts subsequently. However, the specific molecular and cellular mechanisms behind this possible anabolic effect of PTH have not been reported. The present research tend to establish a rat model of OIIRR and cementoblast culture system with intermittent PTH administration, and with the detection technology of micro-CT, histomorphometry, molecular biology, gene microarray, RNA interference, precursor-mRNA transinfection, to investigate the effect of PTH on OIIRR repair and biological behavior of cementoblasts and the underlying molecular mechanisms behind the anabolic effect of PTH on cementoblasts, furthermore, the present study will explore special role of microRNAs in the regulation mechanism of cementoblasts by PTH. The results of the present research will reveal the effect of PTH on OIIRR repair and the molecular mechanisms behind the anabolic effect of PTH on cementoblasts, which would provide scientific evidence for the clinical application of PTH in treatment of OIIRR.

牙移动导致的牙根吸收是正畸治疗中不可避免的不良反应。甲状旁腺激素(PTH)作为治疗骨质疏松的临床药物,通过刺激成骨细胞的功能活动促进新骨的形成，其在促进牙根修复方面的潜在价值也逐渐受到人们的关注。我们的前期研究结果显示PTH可能对正畸牙根吸收的修复有促进作用，可能直接作用于成牙骨质细胞介导牙根吸收的修复，但其分子作用机制尚不清楚。本课题拟通过建立正畸牙根吸收的动物模型和成牙骨质细胞的体外培养，分别间歇性给予PTH，采用分子生物学、基因芯片、RNA干扰等实验技术，重点研究PTH对正畸牙移动所致牙根吸收的修复及成牙骨质细胞生物学行为的影响及其分子生物学机制，以及microRNAs在PTH调控成牙骨质细胞的分子机制中所发挥的特殊作用。本项目研究的开展将为揭示PTH对牙根吸收的修复作用与机制及其潜在治疗价值提供科学依据。

牙根吸收是正畸治疗牙移动过程中常见的不良反应。其往往造成牙根组织的不可逆缺失，严重者可导致牙齿松动甚至脱落，使患者的咀嚼功能下降、生活质量降低。然而，牙根吸收发生发展的具体机制尚不明确，且缺乏有效的预防和治疗措施。相关研究已成为正畸临床医师和学者关注及探究的热点之一。甲状旁腺激素PTH是人体重要的钙磷代谢调节剂。有研究表明：间歇性PTH可以促进骨形成，而持续性PTH则能够加速骨吸收。但PTH对牙根吸收的修复作用尚不清楚。本项目中，我们运用由PTH氨基端第1至第34个氨基酸组成的主要功能片段（PTH（1-34），以下简称PTH），来探究其对成牙骨质细胞和牙根外层细胞性牙骨质的影响。首先，我们证实成牙骨质细胞表达I型PTH受体（PTHR1），说明成牙骨质细胞可作为PTH作用的靶细胞。接下来，我们分别建立了间歇性PTH体内和体外给药模型，并发现间歇性PTH可以促进细胞性牙骨质的形成、提高成牙骨质细胞的成牙骨活性，且进一步证明了PKA-ERK1/2通路参与调控这一生物过程。在此基础上，我们采用四点弯曲加力仪对成牙骨质细胞进行机械应力加载、采用正畸拉簧近中移动大鼠上颌第一磨牙，以更好地模拟正畸治疗中的牙齿受力状态。实验结果证明，间歇性PTH能够缓解机械应力导致的成牙骨向抑制作用、增强牙移动过程中的骨改建活动，而ephrinB2/EphB4双向调节通路是其重要的作用机制之一。鉴于甲状旁腺激素相关蛋白PTHrP与PTH存在结构上的相似性和功能上的关联性，我们同时开展了关于PTHrP是否参与骨改建过程的研究。结果显示，PTHrP表达于牙齿发育时的牙囊周围，其通过调节经典Wnt/β-catenin通路抑制牙囊细胞的成骨向分化，且使得牙齿萌出过程中的破骨活动显著，从而有助于牙齿的萌出。本项目研究结果揭示了间歇性PTH对牙根吸收的修复作用和一些具体机制，为临床预防和治疗牙根吸收提供了新的思路。