小GTPase蛋白Rab5介导AKT-mTOR通路促进骨质疏松症的成骨功能及保护机制研究

Osteoporosis and its induced fractures have become a serious social health problem, the key mechanism is the balance between osteogenesis and osteoclastic absorption.The previous studies show that activating AKT-mTOR signaling can promote osteogenesis. Our previous study found that there was a strong interaction between Rab5 and mTOR protein during muscular regenesis. At the same time, we found that the endogenous Rab5 in clinical samples decreased when the age of osteoporosis patients increased, similar to the phenomenon of calcium loss. Preliminary experiments showed that Rab5 was up-regulated during osteogenic differentiation; knocking down Rab5 inhibited phosphorylation of AKT, thereby hindering osteogenic differentiation; in vivo studies in mice also confirmed that knockdown of Rab5 prevented the development of the skull. However, it remains unclear about the mechanism of Rab5 on osteoblasts and whether Rab5 can treat osteoporosis. This led to the hypothesis that Rab5 is a protective factor in osteoblast formation and Rab5 can delay and/or treat osteoporosis through the AKT-mTOR pathway. In this study, firstly we will detect the Rab5 levels in clinical specimens and osteoporosis mice. Secondly, we will establish osteogenic cell models and study the effect of Rab5 knocking down and overexpression on the osteogenesis. We will further investigate the effect of Rab5 on AKT-mTOR signaling; Finally, we will use the osteoporosis animal models to test Rab5 for the protection and treatment of osteoporosis. This study can broaden the molecular mechanism of bone metabolism regulation and provide the experimental and theoretical basis for the treatment of osteoporosis.

骨质疏松症及其引起的骨折已成为严重的社会健康问题，关健机制为成骨形成和破骨吸收的平衡。已证实激活AKT-mTOR可促进成骨。细胞预实验发现Rab5和mTOR蛋白有明确相互作用，同时发现临床标本内源性Rab5随着骨质疏松程度加重而下调，类似于钙质丢失。预实验显示，Rab5在成骨过程中表达上调；敲降Rab5抑制AKT磷酸化，阻碍成骨分化；小鼠siRNA研究也证实敲降Rab5延缓颅骨发育。但是Rab5如何通过AKT信号作用成骨，是否可治疗骨质疏松症，尚不明确。由此提出假说：Rab5是骨松症成骨的保护因子，Rab5通过AKT-mTOR通路可以延缓并治疗骨质疏松症。本课题组首先检测临床骨松标本和骨松小鼠Rab5水平；其次通过细胞成骨模型，敲降和过表达Rab5研究对成骨影响；最后采用骨松动物模型，研究体内使用Rab5对骨松的治疗作用。本研究将为Rab5治疗骨质疏松症提供实验基础和理论依据。

中国是世界上老龄人口最多的国家，骨质疏松症及其所引起的骨折已成为严重的社会问题。成骨分化和破骨吸收之间的平衡对于骨的稳态维持至关重要。作为成骨的重要信号分子之一，AKT的活性和调控细胞内体的小G蛋白Rab5密切相关。课题组前期研究发现临床标本中内源性Rab5随着患者年龄上升出现显著下降。进一步实验显示Rab5在成骨分化中表达上调，同时磷酸化AKT活性增强；敲降Rab5则明显抑制AKT磷酸化，进而阻碍成骨分化进程；小鼠体内研究也证实敲降Rab5阻碍颅骨发育。利用骨特异性敲除Rab5的转基因鼠建立动物骨松模型，研究Rab5对骨质疏松症的调控作用，进一步探索Rab5和AKT信号通路的蛋白分子发现成骨分化过程中，各种信号分子存在相互作用的密切联系；Rab5通过细胞内体来调控AKT通路的细胞学机制深入挖掘将为骨松治疗带来一定的价值和临床意义；。我们希望借助以上研究来阐明调控骨代谢的分子机制，为骨质疏松症的治疗开发提供实验基础和理论依据。