乳蛋白是构成牛奶营养品质的主要物质基础，乳蛋白含量是奶业核心竞争力的重要标志。乳蛋白含量偏低已成为我国奶业发展路上不可忽视的重大问题。近年来，研究表明G蛋白偶联受体对乳蛋白合成具有重要的调控作用。本课题组前期研究发现GPR109A在奶牛乳腺上皮细胞中有表达，并可能具有调控乳蛋白合成的作用。本项目拟通过分析乳腺组织GPR109A水平与奶牛乳蛋白含量的关系，首先明确两者的相关性，进而分别以奶牛乳腺上皮细胞、乳腺组织块泌乳模型、GPR109A敲除鼠以及乳腺上皮细胞GPR109A条件性敲除鼠为对象，研究GPR109A对乳蛋白合成的调控作用及机制；最后在奶牛体内进行验证。预期研究结果不仅能够阐明GPR109A参与乳蛋白合成调控的机制，而且将为通过人工干预手段提高乳蛋白含量提供实验依据，因而具有重要的学术价值和实践意义。

Milk protein is the main substance determining the nutritional quality of cow's milk. Low nutritional quality of cow's milk has increasingly become a several challenge faced by the healthy development of dairy industry in china. Recent evidences have demonstrated that G protein-coupled receptors play an important role in the synthesis of milk protein. In previous study, we found that GPR109A is expressed in mammary epithelial cells from cow, and may regulate the synthesis of milk protein. To identify the role of GPR109A in the regulation of milk protein synthesis, we will firstly explore the relationship between the expression level of GPR109A and the contents of protein in cow. Then, the effect of GPR109A on the synthesis of milk protein, the relative signaling pathway and integrity of tight junctions will be investigated on mammary epithelial cells and cultured mammary tissues of cow. Moreover, the GPR109A knockout mice and GPR109A conditional knockout mice (selective deletion of GPR109A in mammary epithelial cells) will also be applied to study the effect and mechanism of GPR109A on milk protein synthesis. Finally, the effect of GPR109A on the synthesis of milk protein will be also investigated by the in vivo experiments in cow. The main purpose of this project is to reveal the potential mechanisms involved in the synthesis of milk protein. These results will also provide the fundamental data for the development new strategies to improve the nutritional quality of cow's milk.