牙本质是牙齿的重要矿化组织之一，DSP在牙本质生成中发挥重要作用。本课题组前期研究发现：大部分DSP蛋白并不是以全长蛋白发挥生物学功能，而是被酶切为小片段发挥生物学功能；被酶切后的DSP蛋白N端和C端片段在前期牙本质和矿化牙本质呈相反分布模式；MMP9可以在体外酶切体系和体内小鼠牙齿中酶切DSP蛋白。在前期研究基础上，本课题拟解决以下科学问题：（1）DSP被MMP9酶切的特异性氨基酸位点；（2）全段DSP蛋白被酶切成片段蛋白是否为其功能活化过程，DSP蛋白N端和C端片段是否分别发挥抑制矿化和促进矿化的功能；（3）细胞内活性MMP9是否有细胞内活化和细胞外活化后内吞两种来源。本项目拟使用多种分子生物学、组织学等技术并结合使用转基因动物模型，进一步揭示牙本质生成的分子机制，为治疗牙本质生成缺陷相关疾病奠定理论基础，同时也为牙本质再生提供实验依据和线索。

Dentin is a major mineralized tissue of tooth. Heterogeneous mutations of the dentin sialoprotein (DSP) domain in humans are associated with hereditary dentin defects, including dentinogenesis imperfecta type II (DGI-II) and dentin dysplasia type II (DD-II). Our preliminary data showed that, similar to dentin sialophosphoprotein (DSPP), most full-length DSP protein is processed into NH2-terminal and COOH-terminal fragments in odontoblasts. NH2-terminal and COOH-terminal fragments are separately strongly immuno-distributed in predentin and mineralized dentin; Matrix metalloproteinase 9 (MMP9) processed full-length DSP into three fragment products and is also able to cleave DSP in mouse teeth. Based on our preliminary data, we will solve the following scientific questions: (1) the specific site of DSP protein cleaved by MMP9; (2) whether the processing of DSP by MMP9 is an activation step of DSP function and the respective effects of DSP NH2-terminal and COOH-terminal fragments on dentinogenesis; (3) whether pro-MMP9 is activated by other proteinases both inside and outside of odontoblasts. In this study, multiple molecular biological and histological techniques combined with transgenic mouse models will be used. We will unveil the molecular mechanisms underlying dentinogenesis, provide theoretical basis for the future treatment of hereditary dentin defects, and provide experimental evidences and clues for future dentin regeneration.