IGFBP7基因在骨质疏松症骨吸收-骨形成偶联失衡中的效应及机制研究

Excessive reactive oxygen species (ROS) play an important role in an imbalance between bone resorption and bone formation during osteoporosis. Recent studies have revealed that IGFBP7 is associated with ROS, however, its role in osteoporosis is still unclear. We found that the levels of IGFBP7 were related to osteoporosis. Due to the upregulation of IGFBP7 in osteoporotic bone marrow-derived mesenchymal stem cells (BMSCs), the proliferation, osteogenic differentiation, anti-apoptotic abilities of BMSCs were increased. Moreover, the decreased osteoclast differentiation of bone marrow-derived monocytes (BMM) was observed by IGFBP7 overexpression. Meanwhile, increased β-catenin, decreased ROS, and upregulated β-catenin complex and osteoprotegerin (OPG) were also revealed. Accordingly, our hypothesis is that IGFBP7 may reduce the overproduction of ROS, promote the proliferation of osteoporotic BMSCs, and inhibit cell apoptosis through upregulating the expression of β-catenin/FoxO1complex. Moreover, IGFBP7 may reduce the osteoclastogenesis of BMM and increase osteogenesis of BMSCs through upregulating the expression of β-catenin/TCF and OPG. To investigate the effects and mechanisms of IGFBP7 on regulating the imbalance between osteoclastogenesis and osteogenesis, both in vitro and in vivo studies were performed. This study is expected to provide a novel strategy for the prevention and treatment of osteoporosis.

过剩的活性氧（ROS）是造成骨质疏松症骨吸收-骨形成偶联失衡的重要原因。近期研究表明胰岛素样生长因子结合蛋白7（IGFBP7）调控ROS，但其在骨质疏松中的作用仍不清楚。我们前期研究发现：IGFBP7表达与骨质疏松发病存在相关性；IGFBP7可以增加骨髓间充质干细胞（BMSCs）的增殖、抗凋亡和成骨分化，并减弱骨髓来源单核细胞（BMM）的破骨分化，并伴有β-catenin增加、ROS减少。据此我们提出假说：IGFBP7通过上调β-catenin表达，一方面促进β-catenin/FoxO1复合体形成，来减少过剩的ROS，增加BMSCs增殖和抗凋亡；另一方面促进β-catenin/TCF复合体形成，减弱BMM破骨分化，加强BMSCs成骨分化。本研究拟从整体、细胞和分子水平，利用ELISA、基因转染等方法，探讨IGFBP7在骨质疏松发生中的作用和机制，为骨质疏松的防治提供新思路。

IGFBP7可通过Wnt/β-catenin信号通路增强骨髓间充质干细胞的成骨分化并加速大鼠胫骨骨缺损的愈合。体外实验表明：IGFBP7基因在小鼠BMMs破骨分化过程中表达水平逐渐下降。外源性重组IGFBP7蛋白对BMMs活性无显著影响，可呈浓度依赖性抑制RANKL诱导的BMMs的破骨细胞分化。随后我们发现在此过程中，IGFBP7可显著抑制NF-κB信号通路。采用慢病毒/siRNA在BMMs和RAW264.7细胞种过表达/敲低内源性IGFBP7的表达，并通过TRAP染色等实验再次验证了IGFBP7基因对破骨细胞分化以及NF-κB信号通路的抑制作用。IGFBP7也可促进小鼠MC3T3-E1细胞的成骨分化。我们采用OVX诱导的骨质疏松症模型验证IGFBP7对体内破骨细胞分化及骨质疏松性骨丢失的调控作用。结果显示：重组IGFBP7蛋白注射治疗可通过抑制破骨细胞活性、促进成骨细胞活性来减轻骨质疏松性骨丢失。总结来说，这些发现表明IGFBP7可以促进成骨抑制破骨细胞生成，在骨质疏松症中起保护作用。这些发现对了解骨质疏松症等破骨细胞相关疾病的发病机制和开发这些疾病的全新治疗手段具有潜在意义。