Notch Signaling and Bone Formation

描述(由申请人提供)：肌肉骨骼医学存在巨大的未得到满足的临床需求。需要新的策略来安全地促进低周转率骨质疏松症、有开放骨骺的儿童的骨质疏松症、骨腱附着点的撕脱损伤以及潜在恶性肿瘤或血管受损的骨折修复。基本了解成骨细胞分化的分子机制对于开发新的治疗方法来解决这些未得到满足的需求是至关重要的。Notch信号作为一种进化保守的细胞间通讯机制，控制着多细胞生物体中细胞的命运。在研究得最好的范例中，当配体被β-分泌酶诱导切割时，Notch受体激活一种被称为RBP-J？的转录因子。在哺乳动物中，这反过来又上调Hes/嘿家族转录抑制物的表达。正是Hes/Hey家族成员直接调控细胞系特异性转录因子的表达和/或功能。最近，通过去除早期肢体间充质中的Notch受体(Notch1和Notch2)或β-分泌酶的核心成分(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。具体地说，Notch信号的丢失扩大了成骨细胞的数量，增加了附件骨中的骨小梁数量。重要的是，Hes/嘿家族的特定成员在Notch缺陷的成骨细胞中减少。此外，我们发现Hes/Hey蛋白与Runx2物理上相关，并抑制其活性。因此，我们假设1)Notch通过RBP-J？2)Hes/Hey蛋白通过调节Runx2活性来调节成骨细胞的分化。为了验证这一假设，我们将追求三个具体目标来检查组织特异性RBP-J？基因敲除动物和Hes/嘿突变动物。我们还将研究关键分子在体外成骨细胞分化中的作用。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的潜力。公共卫生相关性：肌肉骨骼医学存在巨大的未得到满足的临床需求。需要新的策略来安全地促进低周转率骨质疏松症、骨腱附着点撕裂伤和骨折修复中的骨形成。这项建议旨在了解在出生后生活中负责控制骨细胞数量的机制。本研究的研究结果将为开发新型骨增强药物提供分子框架。

DESCRIPTION (provided by applicant): 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 ?-secretase, Notch receptors activate a transcription factor known as RBP-J? 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 ?-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-J? 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-J? 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. PUBLIC HEALTH RELEVANCE: Tremendous unmet clinical needs exist in musculoskeletal medicine. Novel strategies are required to safely promote bone formation in low turnover osteoporosis, tearing injuries at sites of bone-tendon insertion, and bone fracture repair. This proposal is designed to understand the mechanism responsible for controlling the number of bone cells in postnatal life. Research results from this study will provide a molecular framework for developing novel bone-enhancing pharmaceutics.