Runx1 Control of Bone Resorption during Fracture Repair

描述（由申请方提供）：我们生成的初步证据表明，与野生型同窝小鼠相比，Runx 1单倍型不足小鼠骨折愈伤组织中的破骨细胞数量增加。此外，我们发现，破骨细胞前体中Runx 1的靶向缺失导致骨小梁骨量减少25-30%，骨吸收增加40-50%。最后，我们确定Runx 1在体外抑制破骨细胞特异性基因的表达。因此，我们假设Runx 1抑制骨髓前体细胞分化为成熟的破骨细胞，并以这种方式改变骨骼的稳态和修复。我们建议：1.评估Runx 1在骨重建和骨折修复过程中调节破骨细胞的作用。(Aim 1）。我们建议确定是否：（i）Runx 1是体内破骨细胞分化和功能的转录抑制因子，以及（ii）如果有条件地删除Rux 1的前体细胞，但不成熟的破骨细胞会损害骨折愈合。2.定义Runx 1介导的破骨细胞生成抑制的机制。(Aim 2）。我们建议确定（i）Runx 1是否对早期而非晚期破骨细胞分化至关重要;（ii）检查Rux 1介导的破骨细胞生成抑制是否依赖于RANK信号的抑制;（iii）Runx 1通过调节关键基因改变破骨细胞前体谱系定型和分化;（iv）Runx 1调节髓样前体向各种谱系命运的定型。我们提出的实验将提供一个新的和综合的机制洞察破骨细胞分化的转录抑制在骨骼再生和修复。

DESCRIPTION (provided by applicant): We generated preliminary evidence showing that the number of osteoclasts in the fracture calluses of mice haploinsufficient for Runx1 is increased compared to wild type littermates. Furthermore, we found that targeted deletion of Runx1 in osteoclast precursors led to 25-30% decrease in trabecular bone mass and a 40-50% increase in bone resorption. Finally, we determined that Runx1 inhibits the expression of osteoclast specific genes in vitro. Thus, we hypothesized that Runx1 inhibits myeloid precursor cell differentiation into mature osteoclasts and in this way alters skeletal homeostasis and repair. We propose to: 1. Evaluate the role of Runx1 in regulating osteoclasts during bone remodeling and fracture repair. (Aim 1). We propose to determine whether: (i) Runx1 is a transcriptional repressor of osteoclast differentiation and function in vivo and (ii) if conditional deletion of Rux1 in precursors but not mature osteoclasts will impair fracture healing. 2. Define the mechanisms underlying Runx1-mediated inhibition of osteoclastogenesis. (Aim 2). We propose to determine whether (i) Runx1 is critical for early but not late osteoclast differentiation; (ii) examine if Rux1-mediated inhibition of osteoclastogenesis depends on inhibition of RANK-signaling; (iii) Runx1 alters osteoclast precursor lineage commitment and differentiation by regulating critical genes; (iv) Runx1 regulates myeloid precursor commitment towards various lineage fates. Our proposed experiments will provide a novel and integrated mechanistic insight into the transcriptional repression of osteoclast differentiation during skeletal regeneration and repair.