Runx1 Control of Bone Resorption during Fracture Repair

描述(由申请人提供)：我们产生的初步证据表明，与野生型小鼠相比，RUNX1单倍体不足的小鼠骨折愈伤组织中破骨细胞的数量增加。此外，我们发现定向缺失破骨细胞前体中的RUNX1导致骨小梁减少25%-30%，骨吸收增加40%-50%。最后，我们确定RUNX1在体外抑制破骨细胞特异性基因的表达。因此，我们假设RUNX1抑制髓系前体细胞分化为成熟破骨细胞，并通过这种方式改变骨骼的动态平衡和修复。我们建议：1.评价RUNX1在骨重建和骨折修复过程中对破骨细胞的调节作用。(目标1)。我们建议确定：(I)RUNX1是否是体内破骨细胞分化和功能的转录抑制因子，以及(Ii)在前体细胞中有条件地缺失Rux1而不是成熟破骨细胞是否会损害骨折愈合。2.明确RUNX1抑制破骨细胞生成的机制。(目标2)。我们建议确定：(I)RUNX1是否对破骨细胞早期而不是晚期的分化起关键作用；(Ii)检测Rux1介导的对破骨细胞生成的抑制是否依赖于RANK信号的抑制；(Iii)RUNX1通过调节关键基因改变破骨细胞前体的谱系承诺和分化；(Iv)RUNX1调节髓系前体对不同谱系命运的承诺。我们提出的实验将为在骨骼再生和修复过程中转录抑制破骨细胞分化提供一个新颖和完整的机制。

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.