激活成骨细胞低氧/HIF 通路对骨改建过程的影响及其发生机制

In recent years, it became evident that hypoxia is a major driving force for de novo angiogenesis. Further studies suggest that hypoxia inducible factors (HIFs) and mimicking agents (HMAs) trigger the initiation and promotion of angiogenic-osteogenic cascade events. Such discoveries suggest that innovative strategies can include the application of hypoxia mimicking agents to increase HIF-1 levels, creating this way a hypoxic environment that favours bone repair and regeneration procedures. However, we found that activation of HIFα in osteoblasts through disruption of its degradation pathway produced robust bone mass in development and leads to an imbalance in the bone modeling/remodelling process, similar to osteopetrosis. In this proposal, we will create genetic mouse models engineered with conditional mutagenesis for manipulation of the levels of HIFα in Osteoblasts by disrupting Vhl and for inactivation of HIF-1α in osteoblasts by disrupting Hif-1a respectively, to determine the cellular and molecular effects of gain or loss of HIF function on osteoblast proliferation, survival, fate, differentiation and osteogenic ability during bone development. We will assess the properties of bone produced by osteoblasts lacking Vhl or Hif and reveal the regulaotory roles of the components in bone matrix on osteogenic differentiation of mesenchymal stem cell and osteoclastogenesis involving cell migration, chemotaxis, cell-cell recognition and attachment, as well as changes into a fusion-competent status and activation to bone resorbing osteoclasts. We will screen and expect to discover the regulatory factors of enhancing bone formation or inhibitor of osteoclast, which may be secreted by hyperactive osteoblasts activated HIF? pathway. We expect that the proposed studies will provide important new therapy targets to improve bone reconstruction, exploit novel approaches for patients with difficulty bone diseases.

激活成骨细胞低氧/HIFα通路促进骨形成的有益作用，正引导药用低氧模拟化合物的研发，并呈热点研究内容的发展趋势，但申请者发现，由HIFα通路激活状态下的成骨细胞所形成的骨组织，呈现骨塑建/骨改建过程偏向过量骨形成的"失衡"征象。本课题将以成骨细胞Hif-1α或Vhl基因条件敲除小鼠为对象，深入了解HIFα通路调控成骨细胞增殖、生存、归宿、分化和成骨活性等生物学行为变化的分子机制；评价新生骨组织的构筑特性及其正常程度，揭示骨基质组分微环境变化对骨髓基质干细胞、破骨细胞前体细胞趋化、募集、分化和功能的调节作用及其所涉及的细胞分子生物学事件；筛查成骨细胞因HIFα通路激活而产生的调控骨形成、骨吸收过程的介导因子。这不仅有助于加深骨发生发育、骨塑建/骨改建过程的认识，进一步指导药用低氧模拟化合物的研发与应用，而且有望发现新的调控因子或分子靶点，为提出促进骨修复、防治代谢性骨病的新举措储备科学基础。

继申请者课题组前期研究发现，由HIFα通路激活状态下的成骨细胞所形成的骨组织，呈现骨塑建/骨改建过程偏向过量骨形成的“失衡”征象。本课题将以成骨细胞Hif-1α和Vhl基因条件敲除小鼠为对象，深入了解HIFα通路调控成骨细胞增殖、生存、归宿、分化和成骨活性等生物学行为变化的分子机制；评价新生骨组织的构筑特性，揭示骨基质组分微环境变化对骨髓基质干细胞、破骨细胞前体细胞趋化、募集、分化和功能的调节作用及其所涉及的细胞分子生物学事件；筛查成骨细胞因HIFα通路激活而产生的调控骨形成、骨吸收过程的介导因子。结果表明：成骨细胞低氧/HIFα通路被持续激活的状态下，可通过VEGF/HO-1作用途径促进骨髓基质干细胞成骨性分化，成骨细胞及其演变的骨细胞分化发育进程延迟，骨细胞间、骨细胞与成骨细胞间、骨细胞与骨髓基质干细胞间，通过骨细胞突起所建立的立体网络性信息联系，可因成熟骨细胞量少、骨细胞突起短小而中断，伴随骨细胞Sclerostin、DMP-1表达量降低及其调节信息难以递送等变化，从而引发骨改建过程倾向于骨形成增加的失衡及其骨基质钙化不完全；累积于成骨细胞内的HIF-1α既可通过直接激活作为骨改建过程“藕联因子”的OPG表达，使OPG/RANKL比率上升，从而发挥抑制破骨细胞分化的作用，又可通过促进白细胞介素（IL）-33的形成并释放至骨髓腔，而抑制破骨细胞的生成与分化；应用低氧模拟化合物适度激活细胞低氧/HIFα通路，不仅具有防治骨质疏松、关节假体松动的发生发展及加速骨质疏松性修复的作用，而且可促进难愈性皮肤缺损的修复。另外，关节软骨细胞持续性高表达的HIF-1α及其下游IL-33、15-脂氧合酶-1（15-LO-1）是骨关节炎（OA）的发生发展的重要调节机制之一。这不仅有助于加深骨发生发育、骨塑建/骨改建过程的认识，而且为提出促进骨修复、防治骨关节病损的新举措储备科学基础。