Notch Signaling and Bone Formation

肌肉骨骼医学存在着巨大的未得到满足的临床需求。需要新的战略来 安全促进骨形成在低周转率骨质疏松症、开放性骨质疏松儿童中的应用 骨腱附着处的骨痂、撕脱伤和骨折修复 潜在的恶性肿瘤或血管受损。对分子的基本理解 成骨细胞分化的机制是开发新的治疗方法的关键 解决这些未得到满足的需求。Notch信号作为一种进化上保守的细胞出现 在多细胞生物体中控制细胞命运的通讯机制。在研究最深入的地方 范例，在配体诱导的G-分泌酶切割后，Notch受体激活转录 在哺乳动物中称为RBP-JK的因子，它反过来上调转录的表达 Hes/嘿家族的压抑者。是Hes/嘿家族成员直接监管 细胞系特异性转录因子的表达和/或功能。最近，通过移除Notch 早期肢体的G-分泌酶受体(Notch1和Notch2)或核心成分(早老素1和2) 我们发现了Notch信号在成骨细胞分化中的生理作用。 祖细胞。具体地说，Notch信号的丢失扩大了成骨细胞的数量和数量 附件骨中的松质骨量。重要的是，HES/嘿的特定成员 在Notch缺陷的成骨细胞中，家族减少。此外，我们还发现Hes/嘿蛋白 与Runx2有物理联系，并抑制其活性。因此，我们假设Notch起作用 通过RBP-JK调节成骨祖细胞Hes/Hey水平，而Hes/Hey 蛋白质通过调节Runx2的活性来调节成骨细胞的分化。为了测试这一点 假设，我们将追求三个特定的目标来研究组织中潜在的骨表型- 特定的RBP-JK基因敲除动物，以及Hes/Hey突变动物。我们还将研究 成骨细胞体外分化的关键分子。最后，我们将开始测试 抑制Notch信号作为一种新的骨合成代谢策略。

Tremendous unmet clinical needs exist in musculoskeletal medicine. Novel strategies are required to safely promote bone formation in low turnover osteoporosis, osteoporosis in children with open epiphyses, avulsion injuries at sites of bone-tendon insertion, and fracture repair in the setting of underlying malignancy or vascular compromise. A fundamental understanding of the molecular mechanism governing osteoblast differentiation is essential for developing novel therapeutics to address these unmet needs. Notch signaling has emerged as an evolutionarily conserved cell-cell communication mechanism that controls cell fate in multicellular organisms. In the best-studied paradigms, upon ligand-induced cleavage by g-secretase, Notch receptors activate a transcription factor known as RBP-Jk in mammals, which in turn up-regulates expression of transcription repressors of the Hes/Hey family. It is the Hes/Hey family members that directly regulate the expression and/or function of cell-lineage specific transcription factors. Recently, by removing Notch receptors (Notch1 and 2) or core components of g-secretase (presenilin 1 and 2) in early limb mesenchyme, we discovered a physiological role for Notch signaling in osteoblast differentiation from progenitor cells. Specifically, loss of Notch signaling expands osteoblast numbers and augments trabecular bone mass in the appendicular skeleton. Importantly, specific members of the Hes/Hey family are reduced in Notch-deficient osteoblastic cells. Moreover, we found that Hes/Hey proteins physically associated with Runx2 and inhibited its activity. Thus, we hypothesize that 1) Notch acts through RBP-Jk to regulate Hes/Hey levels in osteoblast progenitors, and that 2) Hes/Hey proteins regulate osteoblast differentiation by modulating Runx2 activity. To test this hypothesis, we will pursue three specific aims to examine the potential bone phenotype in tissue- specific RBP-Jk knockout animals, and Hes/Hey mutant animals. We will also examine the role of the key molecules in osteoblast differentiation in vitro. Finally, we will begin to test the potential of inhibiting Notch signaling as a novel bone anabolic strategy.