Osteoblast differentiation: Interactions of Wnt, Runx2 and FGF

描述(申请人提供)：对小鼠和人类遗传学的研究表明，规范的Wnt信号是正常骨骼发育和获得正常骨量所必需的。规范的Wnt信号对骨骼具有强烈的合成代谢作用。因此，了解规范的Wnt信号如何诱导骨将阐明可用于治疗骨质疏松症的增加骨量的途径。由于典型的Wnt信号增加了β-连环蛋白(BCAT)的蛋白水平，然后BCAT移动到细胞核并诱导基因表达，我们假设BCAT与骨特异的转录途径合作，诱导与Wnt诱导成骨有关的基因。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规范的Wnt信号诱导。此外，成骨细胞特异性转录因子Runx2与Wnt依赖的转录因子Lef/Tcf结合，从而刺激FGF18启动子。因此，FGF18的表达与骨特异性和Wnt依赖的转录直接相关。鉴于这些与骨的基本途径的直接联系，我们假设，骨中Wnt信号的合成代谢效应需要诱导FGF18。我们进一步假设Runx2-Lef/Tcf转录复合体调控一组诱导成骨细胞分化的特定早期阶段的基因。为了检验我们的假设并推进骨疾病的新疗法，我们将追求以下特定目标：1)确定控制Runx2-Lef复合体的组装及其与DNA的亲和力的蛋白质结构域和热力学参数；2)确定通过Wnt信号和Runx2的融合而开启(或关闭)的成骨细胞相关基因；以及3)使用BCAT功能等位基因的条件性丧失和获得来确定在Wnt诱导的典型成骨细胞分化过程中对FGFs和成纤维细胞生长因子信号的需求。这些研究将为调控成骨细胞基因表达的分子事件提供一个前所未有的视角。此外，这些研究还将揭示Wnt信号如何诱导骨的形成，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。与公共卫生相关。这项应用旨在通过促进我们对骨和骨生成细胞的了解来改善人类健康。这些研究的完成将揭示治疗骨质疏松症等骨病的新的治疗目标和方法。

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.