GLP-1对营养变迁动物模型骨髓干细胞分化方向的调控作用与机制

。A rapid nutrition transition over the past few decades in developing country has been implicated in an increasing epidemic of dyslipidemia,insulin resistance and metabolic syndrome. However the effects of nutrition transition on bone metabolism are not clearly undersood. The slow progress partially imputed to be lack of appropriate animal models and methods. Catch-up growth mice, an new animal model of nutrition transition, was observed a decrease in bone formation, associated with an increased bone marrow fat. Since adipocytes and osteoblasts are closely related through a common progenitor mesenchymal stem cells(MSCs),and some adipocyte differentiation regulators decline osteoblast differentiation, an increase in marrow adipose tissue is often accompanied by a decrease in bone formation. The gut peptide GLP-1, is a crucial factor in the regulation of nutrient intake, activates the GLP-1R, result in regulating adipocyte proliferation and differentiation. Recent studies have established that GLP-1 regulates bone formation in addition to its suppressive effect on glucagon secretion. We hypothesized that GLP-1 could modulate osteogenesis and adipogenesis in MSCs. The impaired GLP-1 secretion caused by catch-up growth may play a important role in differentiation balance between preadipocyte and preosteoblast. GLP-1 could be a useful intervention for improving the imbalance. In order to verify this assumption, we'll observe the relationship among GLP-1 level, bone marrow fat deposits and bone metabolism. Then we'll study the changes between osteogenesis and adipogenesis and lineage-determining marker genes expression at catch-up growth model with or without GLP-1 treatment. To further exploring the mechanism of GLP-1 , We'll investigate the roles of Wnt\β-catenin signaling in MSCs fifferentiation and determine whether GLP-1 activates Wnt signaling through GLP-1 receptor and Wnt signaling plays key roles in GLP-1 mediated functions. We believe that these studies may open new directions for the understanding the crosstalk among nutrient intake , adipose tissue and bone metabolism,which lead to discovery of novel therapeutic approaches for the osteoporosis.

关于营养变迁对骨代谢的影响，以前由于缺乏合适的动物模型和研究手段，一直知之甚少。本课题组在近年新建立的营养变迁模型-追赶生长小鼠的骨髓中发现脂肪异常增加的同时，骨形成能力下降，提示其骨髓干细胞（MSCs）成脂、成骨分化平衡发生了改变。鉴于GLP-1是营养变化时体内调节糖脂代谢的关键激素，结合其在脂肪细胞分化中的重要调控作用以及对骨形成的有益影响，申请人推测：GLP-1具有调控MSCs分化方向的作用，营养变迁所引起的GLP-1分泌障碍是导致MSCs分化失衡的原因，GLP-1的干预能够予以改善。为验证此假设，我们以追赶生长小鼠模型为基础，首次对GLP-1调控MSCs成脂与成骨分化的作用进行研究，并通过建立体外营养变迁细胞模型，运用基因干扰及纯化技术在不同层面探讨GLP-1调控MSCs的靶点与信号通路。本研究可望阐明营养摄入与骨代谢、脂肪代谢之间相互影响机制，并建立新的研究方法。

骨质疏松的发生与营养摄入密切相关，以往由于缺乏合适的动物模型和研究手段，营养变迁对骨代谢的影响及其机制目前尚未知晓。本研究在前期建立的追赶生长模型上的研究发现低营养基础上的迅速营养提升对骨代谢有着不利的影响，主要表现为骨形成能力的下降。同时，我们发现营养变迁导致GLP-1水平下降，继而机体内发生特征性的脂肪堆积，不仅发生在肝脏、骨骼肌等部位，并且在骨髓中也出现明显的脂肪组织增多。介导骨形成的成骨细胞和骨髓来源的脂肪细胞均来源于多潜能的骨髓间充质干细胞（MSCs），二者间存在此消彼长的相互作用。因此通过本项目旨在研究追赶生长小鼠骨形成能力下降的原因，与GLP-1水平的相关性，及与MSCs成脂、成骨定向分化的影响与作用机制。.通过本研究发现：.1)追赶生长动物模型小鼠表现出内脏型肥胖、脂质异位沉积、肠促胰素分泌低下和骨形成能力下降的特征性改变。证实营养的变迁通过影响肠道GLP-1的分泌水平导致糖、脂代谢紊乱，同时会对骨代谢产生不利影响。.2)在不同GLP-1水平下，骨髓干细胞成脂、成骨分化能力发生改变，与细胞分化有关的各指标发生趋向于成脂分化的改变，此改变进而引起骨代谢发生成骨活力下降的不利变化。在外源性补充GLP-1受体激动剂后，上述改变都得到显著地改善。证实追赶生长模型存在骨髓干细胞成脂、成骨分化失衡，且与GLP-1明显相关。.3)通过与Wnt\β-catenin信号通路之间相互作用的研究证实，GLP-1能够干预在骨髓干细胞早期定向分化，尤其在机体发生营养改变后，其作用更为显著，证实GLP-1在骨髓干细胞成脂、成骨分化过程中具有调控作用，合理的干预将有利于纠正骨髓干细胞的分化失衡。.本研究以追赶生长这一动物模型为基础，通过体内和体外研究，以营养变迁—GLP-1—MSCs定向分化—Wnt/β-catenin信号通路为轴线，在不同层面对营养变迁致GLP-1水平改变在骨髓干细胞定向分化中的作用与机制进行了探讨，结果部分阐明了，营养变迁发生后骨质疏松发病率持续增加的致病机制。并且通过本研究，在营养摄入、骨代谢与脂肪代谢三者中建立一个相互作用的桥梁，为探讨膳食营养变迁与骨代谢的相互关系建立新的动物和细胞研究方法。其预期结果将对骨质疏松的早期合理化营养干预提供理论支持，为临床更优化的多效应综合治疗措施提供新的思路与作用靶点。