Osteoblast differentiation: Interactions of Wnt, Runx2 and FGF

描述（由申请人提供）：小鼠和人类遗传学研究表明，正常骨发育以及获得正常骨量需要经典Wnt信号传导。典型的Wnt信号传导对骨具有强烈的合成代谢作用。因此，了解经典Wnt信号传导如何诱导骨将阐明可被操纵以增加骨量用于治疗骨质疏松症的途径。由于经典Wnt信号转导增加β-连环蛋白（bcat）的蛋白水平，然后移动到细胞核并诱导基因表达，我们假设bcat与骨特异性转录途径合作，诱导负责Wnt诱导骨形成的基因。值得注意的是，在初步数据中，我们表明成纤维细胞生长因子18（FGF18）的表达需要并直接由经典Wnt信号转导诱导。此外，成骨细胞特异性转录因子Runx2与Wnt依赖性转录因子LEF/TCF结合，从而刺激FGF 18启动子。因此，FGF18表达与骨特异性和Wnt依赖性转录直接相关。鉴于这些与骨的基本途径的直接联系，我们假设诱导FGF18是骨中Wnt信号传导的合成代谢作用所必需的。我们进一步假设Runx2-LEF/TCF转录复合物调节一组诱导成骨细胞分化特定早期阶段的基因。为了验证我们的假设并推进骨疾病的新疗法，我们将追求以下具体目标：1）确定控制Runx2-LEF复合物的组装及其对DNA的亲和力的蛋白质结构域和热力学参数，2）鉴定通过Wnt信号传导和Runx2的会聚而开启（或关闭）的成骨细胞相关基因，和3）使用具有bcat功能等位基因的条件性丧失和获得的小鼠确定在典型Wnt诱导的成骨细胞分化期间对FGF和FGF信号传导的需要。这些研究将提供一个前所未有的观点的分子事件调节成骨细胞基因表达的Wnt和FGF的反应。此外，这些研究将揭示Wnt信号如何诱导骨形成，并与其他转录因子合作调节成骨细胞分化序列中的特定步骤。我们预计，这些研究的完成将为治疗骨质疏松症等骨骼疾病提供新的方法。公共卫生相关性。该应用旨在通过促进我们对骨和骨生成细胞的理解来改善人类健康。这些研究的完成将揭示新的治疗目标和治疗骨质疏松症等骨骼疾病的方法。

DESCRIPTION (provided by applicant): Studies of mouse and human genetics show that canonical Wnt signaling is required for normal bone development as well as acquisition of normal bone mass. Canonical Wnt signaling is strongly anabolic for bone. Consequently, understanding how canonical Wnt signaling induces bone will illuminate pathways that can be manipulated to increase bone mass for the treatment of osteoporosis. Because canonical Wnt signaling increases the protein levels of beta-catenin (bcat), which then moves to the nucleus and induces gene expression, we hypothesized that bcat cooperates with bone-specific transcription pathways to induce genes responsible for Wnt- induced bone formation. Significantly, in preliminary data we show that fibroblast growth factor 18 (FGF18) expression requires and is directly induced by canonical Wnt signaling. Moreover, the osteoblast-specific transcription factor, Runx2, binds to the Wnt-dependent transcription factor LEF/TCF and thereby stimulates the FGF18 promoter. Thus, FGF18 expression is directly linked to bone-specific and Wnt-dependent transcription. Given these direct links to the essential pathways of bone, we hypothesize that induction of FGF18 is required for the anabolic effects of Wnt signaling in bone. We further hypothesize that the Runx2-LEF/TCF transcription complex regulates a set of genes that induce a specific early stage of osteoblast differentiation. To test our hypotheses and advance new therapies for bone disease we will pursue the following specific aims: 1) determine the protein domains and thermodynamic parameters that govern assembly of the Runx2-LEF complex and its affinity for DNA, 2) identify osteoblast-relevant genes that are turned on (or off) by the convergence of Wnt signaling and Runx2, and 3) using mice with conditional loss and gain of function alleles for bcat define the requirement for FGFs and FGF signaling during canonical Wnt-induced osteoblast differentiation. These studies will provide an unprecedented view of the molecular events regulating osteoblast gene expression in respose to Wnt and FGF. Additionally, these studies will unravel how Wnt signaling induces formation of bone and in cooperation with other transcription factors regulates specific steps in the sequence of osteoblast differentiation. We anticipate that the completion of these studies will suggest new way to treating bone diseases like osteoporosis. PUBLIC HEALTH RELEVANCE. This application aims to improve human health by advancing our understanding of the bone and bone producing cells. The completion of these studies will reveal new therapeutic targets and ways for treating bone disease like osteoporosis.