骨的发育和重建过程中，成骨细胞的骨形成功能与破骨细胞的骨吸收功能协调一致，维持骨的平衡。这两种细胞的功能失调，导致多种骨相关疾病，如骨质疏松症。但分子水平上,骨质疏松症的发病机制还有待进一步研究。前期研究表明，泛素连接酶Smurf2基因敲除小鼠，长骨中骨密度降低，产生类似骨质疏松症的症状，但具体的分子机制不清楚。本项目拟在间充质干细胞、成骨细胞、破骨细胞中条件性敲除Smurf2 基因，鉴定Smurf2影响长骨骨密度的关键细胞群。同时，利用生物化学和分子生物学的方法，结合动物模型表型分析和离体细胞培养，鉴定Smurf2介导的蛋白泛素化底物，研究Smurf2及其泛素化底物对成骨细胞、破骨细胞功能的影响，阐明Smurf2调节长骨中骨密度的分子基础，揭示基因敲除Smurf2导致骨质疏松症的分子机制。此外，Smurf2蛋白可能与Nedd4蛋白家族的其它成员有功能上的重叠，我们将对此进行进一步研究。

Bone development and remodeling is determined by the balance between bone formation by osteoblasts and bone resorption by osteoclasts. Functional dysregulation of osteoblasts and/or osteoclasts contributes to the pathogenesis of skeletal disorders, such as osteoporosis.An improved understanding of osteoblast and osteoclast biology is critical to understand the molecular mechanism of osteoporosis.My recent study found that mice lacking ubiquitin E3 ligase Smurf2 reavealed an osteoporosis-like phenotype, showing markedly reduced bone mass. However,molecular mechanism of Smurf2 in the regulation of bone development and osteoporosis is unknown. We propose to construct conditional Smurf2 knockout mice in mesenchymal stem cells, osteoblasts and osteoclasts to identify the cell population affected by Smurf2. In addition, we will extend these studies to identify the ubiquitination target of Smurf2 and will study the mechanism by which Smurf2 E3 ligases and its substrate regulate the differentiation and function of osteoblasts and/or osteoclasts by a combination of biochemical, molecular and cellular biological approaches and in vivo animal model analysis. We will also broaden our focus to include other Nedd4 E3 ligase proteins that might display overlapping functions with Smurf2.