Notch Signaling and Bone Formation

肌肉骨骼医学中存在大量未满足的临床需求。需要新的战略， 安全地促进低转换骨质疏松症的骨形成，开放性骨质疏松症儿童 骨骺、骨-肌腱附着点处的撕脱损伤以及 潜在的恶性肿瘤或血管损伤。对分子的基本理解 控制成骨细胞分化的机制对于开发新的治疗方法至关重要， 解决这些未满足的需求。Notch信号已经作为进化上保守的细胞-细胞 在多细胞生物中控制细胞命运的通讯机制。在研究最多的 在一些范例中，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，其反过来上调转录的表达， Hes/Hey家族的阻遏物。是Hes/Hey家族成员直接调节 细胞系特异性转录因子的表达和/或功能。最近，通过删除Notch 受体（Notch 1和2）或g-分泌酶的核心成分（早老素1和2）在早期肢体 在间充质中，我们发现Notch信号在成骨细胞分化中的生理作用， 祖细胞具体地说，Notch信号传导的缺失扩大了成骨细胞的数量， 骨小梁骨质量在approxial骨骼。重要的是，Hes/Hey的特定成员 在Notch缺陷型成骨细胞中家族减少。此外，我们发现Hes/Hey蛋白 与Runx 2物理相关并抑制其活性。因此，我们假设1）Notch行为 通过RBP-Jk调节成骨细胞祖细胞中Hes/Hey水平，2）Hes/Hey 蛋白质通过调节Runx 2活性来调节成骨细胞分化。为了验证这一 假设，我们将追求三个具体目标，以检查组织中潜在的骨表型- 特异性RBP-Jk敲除动物和Hes/Hey突变动物。我们亦会研究 体外成骨细胞分化的关键分子。最后，我们将开始测试 抑制Notch信号传导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.