MECHANISMS OF INHIBITING BONE FORMATION THROUGH ANTAGONISM

描述（由申请人提供）：一个重要的研究领域是识别和表征促进骨形成的关键分子和途径。目前用于全身治疗骨质疏松症的最有前途的合成代谢剂是甲状旁腺激素（PTH），最近已经表明骨形成的负调节剂硬化素（sost）是PTH的直接靶点，这表明sost调节可能在PTH依赖性骨形成中起重要作用。这是非常重要的生物医学意义，因为在人类中失去Sost会导致两种严重的骨发育不良：硬化症（MIM 269500）和货车Buchem（VB）病（MIM 239100），两者的特征都是骨质增生，因此将Sost定位为治疗骨丢失的理想新靶点。我们最近发现，在转基因小鼠中过度表达人Sost会导致骨质减少，而表达模拟VB等位基因的转基因的小鼠则不受影响。通过结合跨物种序列比较，然后在体外和体内增强子测定，我们已经确定了一个高度保守的元素，ECR 5，作为成骨细胞/骨细胞增强子在体外和体内的功能。此外，我们已经在体外表明，ECR 5是PTH-响应性的，并且PTH-介导的sost抑制需要ECR 5远端增强子，独立于近端sost启动子。由于调节调节骨形成的蛋白质的表达具有重要的生物医学意义，并且由于sost在调节成骨细胞活性和骨形成中的作用得到充分证实，因此我们研究的首要目标是了解涉及骨形成或“骨拮抗剂”的负调节剂的激素调节和信号转导途径。特别是，我们感兴趣的是阐明转录机制，其中sost表达在骨生成，骨模式和骨代谢过程中调制。我们假设，这种拮抗剂是在严格的转录控制下，从几个信号传导途径，已知是至关重要的骨稳态，如PTH-和BMP-的信号，并优先上调或下调所需的肌细胞增强因子2（Mef 2）家族的成员，以介导其效应子功能，通过微调其转录水平。公共卫生相关性：超过2500万美国人患有骨质疏松症。随着我们的寿命越来越长，老龄化人口面临着更大的骨质流失风险，从而增加了经济负担和对能够替代流失骨量的合成代谢疗法的医疗需求。一个重要的研究领域是识别和表征促进骨形成的关键分子和途径。最近，sost已被确定为两个严重的骨质增生症的基因，其特征在于增加骨密度：硬化症和货车Buchem病，从而定位sost作为一个理想的新的目标，为治疗骨丢失。由于调节蛋白质的表达，调节骨形成是非常重要的生物医学意义，因为有充分的证据证明的作用，sost在调节成骨细胞的活性和骨形成，我们的研究的首要目标是了解转录调控机制，控制sost表达在骨生成，骨形成和骨代谢。

DESCRIPTION (provided by applicant): An important area of research is the identification and characterization of key molecules and pathways that promote bone formation, de novo. Currently the most promising anabolic agent used for the systemic treatment of osteoporosis is parathyroid hormone (PTH) and recently it has been shown that sclerostin (sost), a negative regulator of bone formation, is a direct target of PTH, suggesting that sost regulation may play an important role in PTH-dependent bone formation. This is of great biomedical importance since loss of Sost in humans causes two severe bone dysplasias: sclerosteosis (MIM 269500) and Van Buchem (VB) disease (MIM 239100), both characterized by hyperostosis and thus positioning sost as an ideal new target for the treatment of bone loss. We have recently shown that over-expressing human Sost in transgenic mice results in osteopenia, while mice expressing a transgene that mimics the VB allele, are unaffected. Through a combination of cross-species sequence comparisons followed by in vitro and in vivo enhancer assays, we have identified a highly-conserved element, ECR5 that functions as an osteoblast/osteocyte enhancer in vitro and in vivo. Further, we have shown in vitro that ECR5 is PTH-responsive, and that PTH- mediated suppression of sost requires the ECR5 distal enhancer, independently of the proximal sost promoter. Since modulating expression of proteins that regulate bone formation is of great biomedical importance and because of the well-documented role of sost in regulating osteoblast activity and bone formation, the overarching goal of our research is to understand the hormonal regulation and signal transduction pathways involving negative regulators of bone formation or `bone- antagonists'. In particular, we are interested in elucidating the transcriptional mechanisms by which sost expression is modulated during osteogenesis, bone patterning, and bone metabolism. We hypothesize that this antagonist is under tight transcriptional control from several signaling pathways known to be critical during bone homeostasis, such as the PTH- and BMP- signaling, and is preferentially up-regulated or down-regulated as needed by members of the Myocyte Enhancer Factor 2 (Mef2) family to mediate its effector function via fine-tuning of its transcript levels. PUBLIC HEALTH RELEVANCE: Over 25 million Americans suffer from osteoporosis. As we continue to live longer, the aging population is at greater risk of bone loss, and thus increasing the economic burden and the medical need for anabolic therapies capable of replacing lost bone mass. An important area of research is the identification and characterization of key molecules and pathways that promote bone formation, de novo. Recently, sost has been identified as the gene responsible for two severe hyperostoses characterized by increased bone mineral density: sclerosteosis and Van Buchem disease, thus positioning sost as an ideal new target for the treatment of bone loss. Since modulating the expression of proteins that regulate bone formation is of great biomedical importance and because of the well-documented role of sost in regulating osteoblast activity and bone formation, the overarching goal of our research is to understand the transcriptional regulation mechanisms that control sost expression during osteogenesis, bone patterning, and bone metabolism.