Notch Signaling and Bone Formation

描述（由申请人提供）：在肌肉骨骼医学中存在大量未满足的临床需求。需要新的策略来安全地促进低转换性骨质疏松症、开放性骨骺儿童骨质疏松症、骨-肌腱附着部位的撕脱损伤以及潜在恶性肿瘤或血管损伤背景下的骨折修复中的骨形成。对控制成骨细胞分化的分子机制的基本理解对于开发新的治疗方法来解决这些未满足的需求是必不可少的。Notch信号已经成为一种进化上保守的细胞间通讯机制，控制多细胞生物体中的细胞命运。在最好的研究范例中，在配体诱导的裂解？-分泌酶，Notch受体激活转录因子称为RBP-J？在哺乳动物中，其反过来上调Hes/Hey家族的转录抑制子的表达。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，通过去除Notch受体（Notch 1和2）或？分泌酶（早老素1和2）在早期肢体间充质中，我们发现了Notch信号传导在成骨细胞从祖细胞分化的生理作用。具体地说，Notch信号传导的缺失扩大了成骨细胞的数量，并增加了无骨骨架中的小梁骨质量。重要的是，Hes/Hey家族的特定成员在Notch缺陷型成骨细胞中减少。此外，我们发现Hes/Hey蛋白与Runx 2物理结合并抑制其活性。因此，我们假设1）Notch通过RBP-J起作用？2）Hes/Hey蛋白通过调节Runx 2活性调节成骨细胞分化。为了验证这一假设，我们将追求三个具体的目标，以检查潜在的骨表型在组织特异性RBP-J？基因敲除动物和Hes/Hey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信号传导作为一种新的骨合成代谢策略的潜力。公共卫生相关性：肌肉骨骼医学存在大量未满足的临床需求。需要新的策略来安全地促进低转换性骨质疏松症、骨-肌腱附着部位撕裂损伤和骨折修复中的骨形成。该建议旨在了解负责控制出生后骨细胞数量的机制。本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.