NELL-1, A Cbfa1 DOWNSTREAM TARGET, IN BONE FORMATION

描述（由申请人提供）：Cbfa1介导间充质细胞定向为骨软骨祖细胞谱系，并支持定向成骨细胞的持续分化和功能。然而，决定性的下游介质的Cbfa1，严重影响成骨细胞分化和骨形成尚未被描述。 Ne1（在神经组织中强烈表达的编码表皮生长因子样结构域的蛋白）首先在鸡胚中被鉴定。初步数据显示，体内Nell-1（Ne1样分子-1）与正常和病理性缝线融合相关，而体外Nell-1与成骨细胞分化和矿化增加相关。此外，人Nell-1启动子含有三个成骨细胞特异性顺式作用元件2（OSE 2）的Cbfa1的反应元件，Nell-1过表达小鼠可以在功能上弥补杂合Cbfa1缺陷小鼠膜内骨缺损的某些方面。这些数据导致了这样的假设，即Nell-1是Cbfa 1的中心下游靶点，其支持定向成骨细胞的持续分化和功能，并且正常的膜骨生长和形成需要适当的Nell-1表达。为了验证这一假设，本提案将分析以下内容：1）在成骨细胞形成和功能期间Cbfa1以及Cbfa1通过OSE 2反应元件对Nell-1转录的调节; 2）Nell-1在体内和体外对Cbfa1缺陷的功能补偿;以及3）靶向Nell-1破坏在体内的影响。 如果Nell-1被证明是膜内骨形成的关键介质，它可以进一步帮助理解膜内骨与软骨内骨的发育。此外，由于缝是颅骨膜内骨生长的主要部位，Nell-1与颅骨缝的密切联系也可能影响目前对颅穹窿发育的认识。最后，Nell-1可以作为抑制或诱导膜内骨生长的临床工具非常有用，Nell-1的分泌性质使得这种用途更加可行。通过抗Nell-1策略控制CS患者膜内骨生长的抑制可能为根治性手术颅面重建提供一种侵入性较小、基于生物学的治疗替代方案。此外，Nell-1诱导颅骨成骨细胞分化的能力可在临床上应用于需要膜性骨形成和再生的情况（例如，唇裂或腭裂修复和颅面牵引成骨）。

DESCRIPTION (provided by applicant): Cbfa1 mediates mesenchymal cell commitment to an osteochondroprogenitor lineage and supports continued differentiation and function in committed osteoblasts. However, definitive downstream mediators of Cbfa1 that critically impact osteoblast differentiation and bone formation have yet to be described. Ne1 (a protein strongly expressed in neural tissue encoding epidermal growth factor like domain) was first identified in chicken embryos. The preliminary data shows that Nell-1 (Ne1-like molecule-1) in vivo is associated with normal and pathological suture fusion, while Nell- 1 in vitro is associated with increased osteoblast differentiation and mineralization. Furthermore, the human Nell-1 promoter contains three osteoblast-specific cis-acting element 2 (OSE2) response elements for Cbfa1 and that Nell-1 overexpression mice can functionally compensate for some aspects of intramembranous bone deficiency in heterozygous Cbfa1 deficient mice. These data have led to the hypothesis that Nell-1 is a central downstream target of Cbfa1 that supports continued differentiation and function in committed osteoblasts and proper Nell-1 expression is required for normal membranous bone growth and formation. To test this hypothesis, this proposal will analyze the following: 1) the regulation of Nell-1 transcription by Cbfa1 during osteoblast formation and function and by Cbfa1 through OSE2 response elements; 2) the functional compensation of Cbfa1 deficiency by Nell-1 in vivo and in vitro; and 3) the effects of targeted Nell-1 disruption in vivo. If Nell-1 is proven to be a critical mediator of intramembranous bone formation, it can further aid in understanding the development of intramembranous vs. endochondral bone. In addition, since sutures are major sites of calvarial intramembranous bone growth the close association of Nell-1 with calvarial sutures can also impact present knowledge on cranial vault development. Lastly, Nell-1 can be tremendously useful as a clinical tool to inhibit or induce intramembranous bone growth, with the secretory nature of Nell-1 making this utility even more feasible. Controlled inhibition of intramembranous bone growth by anti-Nell-1 strategies in CS patients may offer a less invasive, biologically based, therapeutic alternative to radical surgical craniofacial reconstruction. In addition, the ability of Nell- 1 to induce calvarial osteoblast differentiation may be clinically applied to situations where membranous bone formation and regeneration are desirable (e.g., cleft lip or cleft palate repair and craniofacial distraction osteogenesis).