牙本质涎磷蛋白对下颌骨髁突软骨作用的机理研究

Dentin sialophosphoprotein (DSPP) is one kind of non-collagenous protein which has been recently found to be expressed in the mandibular condylar cartilage, our previous work demonstrated that Dspp knockout mice have mandibular condylar cartialge phenotypes: the mandibular condylar cartilage become thinner accampany with decreased amount of mandibular condylar cartialge cells and extracellular matrix disorders cause of the loss-of-function of DSPP. Further study of heterozygous Dspp konckout mice showed that longstanding functioal defect of DSPP may lead to a mandibular condylar cartilage defect which resmbles temporomandibular joint osteoarthritis (TMJ OA). To further explore the mechanism of DSPP function on mandibular condylar cartilage, we will investigate the project in vitro and in vivo: 1. To isolate and culture the mandibular condylar cartilage cells from Dspp knockout mice and WT mice and examine its function on the proliferation, apoptosis，differentiation of mandibular condylar cartilage, and then select the possible signaling pathways of DSPP on mandibular condylar cartilage cells; 2. Comparing with WT mice, we will observe the phenotypic changes of mandibular condylar cartilage of the Dspp knockout mice and analyze the potential mechanism of DSPP plays on the mandibular condylar cartilage at early stage. 3. Comparing the heterozygous Dspp knockout mice with WT mice, we will try to observe the direct relationship of longstanding functional defect of DSPP and temporomandibular joint osteoarthritis (TMJ OA) and to explore the relevant mechanism. Based on the above works, we will try to explain the mechanism of DSPP functions on mandibular condylar cartilage cell. This work will also provide a theoretical basis for regulating the mandibular condylar cartilage development and performing the TMJ OA treatment on the target of DSPP.

颞下颌关节骨关节炎（TMJ OA）主要是髁突软骨的进行性破坏，牙本质涎磷蛋白(DSPP)是一种非胶原蛋白，近年来发现其在下颌骨髁突软骨中表达。我们的前期研究发现：DSPP功能丧失会导致下颌骨髁突软骨变薄、细胞数目减少、细胞外基质合成异常。Dspp基因敲除小鼠模型证实：长期DSPP功能缺陷会导致髁突软骨出现类似TMJ OA的表现。为了进一步阐明DSPP对下颌骨髁突软骨作用的机理，我们将通过体内及体外两个角度进行研究：1.体外观察DSPP对下颌骨髁突软骨细胞增殖、调亡、分化、功能的作用，筛选DSPP调控髁突软骨细胞的信号通路；2.探讨DSPP早期功能缺失对髁突软骨形成的影响及其调控机理；3.利用Dspp基因敲除杂合子小鼠模型，观察DSPP长期功能缺陷与TMJ OA的发生、发展关系，并分析其相关机制。通过上述研究，阐述DSPP作为靶点调控髁突软骨发育的作用机制，为TMJ OA发现治疗新靶点。

牙本质涎磷蛋白(DSPP)是一种在牙本质中含量最多的非胶原蛋白。最初认为DSPP是牙本质特异性蛋白质，近年来发现其在软骨及骨等组织中也广泛表达。这种蛋白质在同一组织中存在形式多样，不同组织中又存在明显差异。我们的前期研究发现：DSPP功能丧失会导致下颌骨髁突软骨变薄、细胞数目减少、细胞外基质合成异常。说明DSPP参与软骨发育及维持，推测其长期功能缺陷可能会导致颞下颌关节骨关节炎。为阐明DSPP对软骨作用,DSPP缺失或缺陷与疾病发生发展关系。我们：①应用Dspp KO/D452A-Tg小鼠（表达外源性的突变 D452A-DSPP）、Dspp KO/normal-Tg小鼠（表达外源性的正常DSPP），Dspp KO/DSP-Tg小鼠、Dspp KO小鼠，WT小鼠作对比实验。通过研究我们发现，全长DSPP，DSP片段在髁突软骨发育均起重要作用，说明DSPP的翻译后修饰过程在下颌骨髁突软骨发育过程中起重要作用；②应用WT小鼠明确DSPP在股骨头软骨中分布表达特点。对比Dspp KO小鼠及WT小鼠，发现DSPP调控股骨头软骨细胞增殖，影响软骨骨化过程，调控软骨下骨矿化状态；③比对Dspp-/- KO小鼠，Dspp+/- KO小鼠及WT小鼠表型，明确Dspp基因敲除杂合子小鼠（Dspp+/- KO小鼠）具有颞下颌关节骨关节炎（TMJ OA）的表现。证实长期DSPP功能缺陷会导致髁突出现类似TMJ OA的表现，该病理变化与软骨基质代谢紊乱及破骨细胞活性增强密切相关。本课题研究表明，DSPP是一种非常重要的软骨及骨细胞外基质蛋白，其翻译后修饰过程复杂多样，在生理条件下调控软骨细胞增殖，影响软骨下骨矿化。DSPP表达缺陷会导致软骨破坏，软骨下骨矿化降低、骨赘形成等颞下颌关节骨关节炎表现。