IGF1对地塞米松抑制干细胞成骨分化的影响及机制研究

Glucocorticoid-induced osteoporosis (GIOP) is prevalent in clinical parctice. The causes of GIOP were regarded to be related with the suppression of osteogenic differentiation in mesenchymal stem cells (MSCs) induced by glucocorticoid, such as dexamethasone. But the exact mechanism remains unclear. It is reported that the expression level and function of insulin-like growth factor 1 (IGF1) can be inhibited by DEX. Although bone morphogenetic protein 9 (BMP9) is perceived as one of the most potent osteogenic inducer, our previous studies confirmed that the osteogenic capacity of BMP9 could be affected by some cytokines. For example, IGF1 enhanced osteogenic differentiation of MSCs induced by BMP9 significantly. Moreover, osteogenic differentiation induced by BMP9 was inhibited by DEX dramatically. And over-expression of IGF1 could attenuate the inhibitory effect of DEX on osteogenic differentiation. This function may be related to the expression of cyclooxygenase-2 (COX-2). Therefore, we speculated that the interaction between DEX and IGF1 may be one of the important pathogenesis of GIOP. In this project, we employed several molecular biological methods (including over-expression, RNA-interference and conditional gene knockout), and IGF1 conditional knockout mice model. Our project is proposed to determine whether IGF1 could rescue the inhibitory effect of DEX on osteogenic differentiation of MSCs in vitro and in vivo, and explore its possible molecular mechanisms. This project will provide new ideas for clinical prevention and treatment of GIOP through greater understanding of the pathogenesis of the GIOP.

糖皮质激素性骨质疏松症(GIOP)临床上十分常见，发病原因与地塞米松(DEX)等糖皮质激素抑制骨髓间充质干细胞成骨分化有关，但确切机制仍不清楚。DEX能抑制胰岛素样生长因子1(IGF1)的表达与功能。课题组在证实IGF1能明显增强骨形态发生蛋白9（BMP9）诱导干细胞成骨分化的基础上，进一步研究发现DEX能显著抑制BMP9诱导的干细胞成骨分化，当过表达IGF1时能明显减弱DEX的抑制作用。因此，我们推测DEX与IGF1的相互作用是GIOP的重要发病机制之一。本课题拟进一步利用过表达、RNA干扰和基因敲除等分子生物学技术，建立IGF1条件敲除动物模型，通过体外和体内实验，明确IGF1能否逆转DEX对骨髓间充质干细胞成骨分化的抑制作用以及可能的分子机制。本研究将丰富对GIOP发病机制的认识，为临床预防和治疗GIOP提供新思路。

糖皮质激素性骨质疏松症（GIOP）作为最常见的继发性骨质疏松，易发生椎体和股骨近端骨折，严重威胁着人类的健康。本项目通过骨形态发生蛋白9（BMP9）诱导间充质干细胞（MSCs）成骨分化作为体外成骨模型，以裸鼠异位成骨作为体内模型，探究以地塞米松（DEX）为代表的糖皮质激素对成骨分化的影响，并初步探索了胰岛素样生长因子1（IGF-1）在此过程中发挥的作用，以及相关分子机制。研究表明，高浓度（＞100nM）地塞米松可抑制间充质干细胞成骨指标（RUNX2、OSX和OPN等）的表达、碱性磷酸酶（ALP）活性及钙盐沉积。体内研究表明地塞米松抑制骨样组织的形成，并促进脂肪细胞填充。而IGF-1与地塞米松联用后，IGF-1阻断了地塞米松对MSCs的成骨抑制作用，体内实验表明IGF-1可阻断地塞米松对骨样组织形成的抑制。在机制探究中，我们发现IGF-1使AKT的磷酸化增强，而PI3K的特异性抑制剂LY294002可阻断IGF-1的逆转效果，提示IGF-1可能通过PI3K/AKT信号通路发挥作用。我们进一步发现环氧合酶2（COX-2）也参与了IGF-1的逆转过程，使用COX-2特异性抑制剂NS398或沉默也可减弱IGF-1对地塞米松抑制成骨的逆转作用，且LY294002的联用可抑制COX-2的表达，提示PI3K/AKT的下游可能是COX-2。通过本项目，我们发现IGF-1可能通过PI3K/AKT/COX-2通路逆转地塞米松对MSCs成骨分化的抑制，为GIOP的预防和治疗提供了理论依据。受本研究项目的支持，课题组已发表10篇SCI论文,还有1篇SCI论文正在审稿。同时，我们发现全反式维甲酸（ATRA）与IGF-1有相似的逆转地塞米松抑制成骨分化的作用，且效果更强，我们拟进行下一个相关课题的自然科学基金申请并探讨ATRA与IGF-1在此过程中的关系。