晚期糖基化终末产物（AGEs）在失重性骨质疏松发生中的作用及可能机制

For now, the mechanism of microgravity induced-bone loss is not clear yet, while it had many similarities with ageing or diabetes induced- osteoporosis. As we know, the hyperglycemia induced by the ageing and diabetes can make the accumulation of advanced glycation end products (AGEs) in bone matrix, and further induce the osteoporosis. Since it has been reported that the blood glucose of astronauts were increased during spaceflight, we speculate this increased blood glucose may also result in the AGEs accumulation in bone matrix and an imbalanced interaction with its receptor RAGE, which meanwhile may affect the mechanosensitivity of osteocytes and lead to the osteoporosis. In this study, the tail-suspension model was used to simulate microgravity, the blood glucose and the biomarkers of bone metabolism, AGEs and RAGE will be detected, to investigate the changes of matrix AGEs and its role in bone remodeling under the simulated microgravity. Meanwhile, under the determined AGEs concentration, the signaling molecules, the expression of RAGE, HMGB-1, IGF-1, bone formation/resorption biomarkers, and the activity of Wnt/β-catenin signaling pathway will be detected in the MLO-Y4 osteocyte-like cell line, to briefly investigate the effects of AGEs accumulation on the osteocytes function and their mechanical response under the simulated microgravity. These studies may clarify the role and the potential mechanism of AGEs in the microgravity induced-bone loss, and provide a new clue of mechano-biology for studying microgravity-induced osteoporosis.

失重性骨丢失机制尚不明确，其与老年性及糖尿病致骨质疏松表现有相似之处。老龄化及糖尿病引起血糖升高会导致晚期糖基化终末产物AGEs在骨组织积聚，诱导骨质疏松发生。基于航天员也有血糖升高的现象，推测模拟失重效应下可能引起AGEs在骨基质中积聚并与其受体RAGE作用失衡，影响骨细胞力学敏感性，导致失重性骨丢失。本项目拟利用大鼠尾吊模型模拟微重力效应，检测血糖、骨代谢、骨质量等指标与AGEs含量间的关系，在组织层面上研究模拟微重力效应下骨基质AGEs的变化及AGEs对骨重建的作用。同时在确定的AGEs浓度条件下，检测MLO-Y4骨细胞系内信号分子、RAGE、HMGB-1、IGF-1、骨形成/吸收标志物等的基因及蛋白表达，以及Wnt/β-catenin通路活性，在细胞层面初探模拟微重力效应下AGEs对骨细胞功能及其力学敏感性作用的机制，为寻找失重性骨丢失的发生机制提供力学生物学新线索。

晚期糖基化终末产物AGEs是糖尿病和老年性骨质疏松的发病机理之一。然而AGEs是否是失重性骨丢失的发生机制，目前国内外尚未见报道。本课题从两方面进行研究：首先利用尾吊大鼠模型模拟微重力效应，检测了大鼠血清及不同结构和部位骨基质中AGEs的积聚变化，血清中血糖和胰岛素等生化指标，骨吸收及骨生成标记物的基因和蛋白表达，后肢骨微观结构参数和骨微观力学性能。结果显示，模拟微重力效应引起的血糖应激性升高在一定程度上导致血清和骨基质中AGEs发生积聚，积聚的AGEs会通过扰乱骨代谢活动破坏骨重建过程，进而使骨微观结构恶化。另一方面，本课题还以骨细胞（MLO-Y4）为实验对象，在不影响细胞增殖和活性的高、低两种AGEs浓度孵育下对细胞施加流体剪切力，检测早期信号分子释放、细胞骨架的聚合情况，并检测了RAGE、Wnt/β-catenin通路关键因子及骨代谢指标的mRNA及蛋白的表达。结果显示，sAGEs对骨细胞力学敏感性产生不利影响，特别是高浓度AGEs可能导致骨细胞处于病理状态，使黏着斑过度增加，降低骨细胞对外部机械负荷的响应，导致早期力学信号分子NO和PGE2对流体剪切应力过度响应，Wnt/β-catenin信号通路的力学响应受抑制，进而最终影响骨细胞对骨重建过程的调控能力。本项目的开展为探索失重性骨丢失机制提供了新的线索，为寻找有效对抗措施提供新的研究靶点。