Runx2 and Axin2 Interactions During Bone Formation

描述(申请人提供)：这个项目探索了颅面发育的两个关键调节因子之间的分子和生理相互作用，即骨修复/再生，以及最佳骨量积累和维持：Runx2和Axin2。Runx2(Cbfa1)是成骨细胞形成和软骨细胞肥大所必需的转录因子。Runx2缺乏症是出生后致命的，而Runx2单倍体缺乏症会导致锁骨颅骨发育不良和骨量减少。唯一已知的至少部分挽救Runx2小鼠的ccd表型的生物学方法是抑制Gsk32。Axin2是一种浓度限制的支架蛋白，它将Gsk32、2-连环蛋白和其他成分组装成2-连环蛋白破坏复合体。Axin2是典型的Wnt信号的负反馈调节因子，可减缓成骨细胞的增殖。有趣的是，Axin2基因敲除小鼠患有颅缝早闭(CS)和高骨小梁密度。在人类中，AXIN2突变与家族性牙齿发育不全有关。因此，Axin2缺乏和Runx2单倍体缺乏导致相反的头面部和骨小梁表型。我们发现，在Runx2缺陷的细胞中，Axin2水平增加。该项目的中心假设是Runx2主动抑制Axin2以增强骨细胞中的Wnt/2-catenin信号。我们的目标是确定Runx2-/-小鼠的成骨祖细胞中规范的Wnt信号是否发生改变，确定Runx2调控Axin2转录的分子机制，并定量评估“双突变”Runx2：Axin2-/-小鼠相对于野生型、Runx2和Axin2-/-小鼠的骨骼表型。 与公共卫生相关：骨骼疾病或损害可困扰任何年龄段的人。每750名活产儿中就有一名与颅面畸形有关，大约每2000名儿童中就有1名患上某种形式的颅突闭锁。在他们的一生中，一半的女性和四分之一的男性可能会遭受与骨质疏松症相关的骨折。本项目探索缝合、骨修复/再生和最佳骨量增加和维持的两个关键调节因子之间的分子相互作用：Runx2和Axin2。这项拟议的项目意义重大，因为Runx2是成骨细胞形成所必需的，而Axin2是Wnt-2-catenin信号通路的关键负调控因子，而Wnt-2-catenin信号通路是新的合成代谢药物的靶标。由于Axin2是2-连环素和LRP5信号的细胞内抑制物，理论上它的活性可能会降低新出现的中和细胞外Wnt/LRP5/6抑制物(如抗硬化素或抗Dkk1抗体)的合成代谢疗法的效率。这项工作将产生集体影响，因为Runx2和Axin2也有助于软骨细胞成熟，是肿瘤抑制因子。

DESCRIPTION (provided by applicant): This project explores the molecular and physiological interactions between two crucial regulators of craniofacial development, bone repair/regeneration, and optimal bone mass accrual and maintenance: Runx2 and Axin2. Runx2 (Cbfa1) is a transcription factor required for osteoblastogenesis and chondrocytes hypertrophy. Runx2-deficiency is postnatally lethal, whereas Runx2-haploinsufficiency causes cleidocranial dysplasia (CCD) and osteopenia. The only known biologic means to at least partially rescue the CCD phenotype in Runx2 mice is by inhibiting Gsk32. Axin2 is the concentration- limiting scaffolding protein that assembles Gsk32, 2-catenin and other components into the 2-catenin destruction complex. Axin2 is a negative feedback regulator of canonical Wnt signaling and slows osteoblast proliferation. Interestingly, Axin2 knockout mice have craniosynostosis (CS) and high trabecular bone mass density. In humans, AXIN2 mutations are linked to familial tooth agenesis. Thus, Axin2-deficiency and Runx2- haploinsufficiency cause opposing craniofacial and trabecular bone phenotypes. We show that Axin2 levels are increased in Runx2-deficient cells. The central hypothesis of this project is that Runx2 actively represses Axin2 to enhance Wnt/ 2-catenin signaling in bone cells. We aim to determine if canonical Wnt signaling is altered in osteoblast progenitors from Runx2-/- mice, define the molecular mechanisms whereby Runx2 regulates Axin2 transcription, and to quantitatively assess the skeletal phenotypes of "double mutant" Runx2: Axin2-/- mice relative to wild type, Runx2 and Axin2-/- mice. PUBLIC HEALTH RELEVANCE: Bone disorders or damage can afflict humans of any age. One in 750 live births is associated with a craniofacial abnormality and approximately 1 in 2000 children develops a form of craniosynostosis. During their lifetimes, half of all women and a quarter of men can expect to suffer an osteoporosis-related fracture. This project explores the molecular interactions between two crucial regulators of suture closure, bone repair/regeneration, and optimal bone mass accrual and maintenance: Runx2 and Axin2. The proposed project is significant because Runx2 is required for osteoblastogenesis and Axin2 is a crucial negative regulator of the Wnt-2-catenin signaling pathway, which is a target for new anabolic agents. Because Axin2 is an intracellular inhibitor of 2-catenin and Lrp5 signaling, its activity could theoretically decrease the efficiency of emerging anabolic therapies that neutralize extracellular Wnt/Lrp5/6 inhibitors (e.g. anti-Sclerostin or anti-Dkk1 antibodies). The work will have collective impact because Runx2 and Axin2 also contribute to chondrocyte maturation and are tumor suppressors.