Integration of TGFb-ALK5 on Wnt signaling and mechanotransduction in bone

描述(申请人提供)：WNT信号是一种强大的骨形成调节器，并被LRP共同受体拮抗剂如硬化剂(Sost)所拮抗。转化生长因子-β(转化生长因子-β)在骨形成中表现出多效性和似乎相互矛盾的作用：转化生长因子-β刺激成骨细胞迁移和增殖，但也抑制成骨细胞的形成。 基质矿化，促进机械劣质编织骨的形成。我们最近证实，转化生长因子通过I型受体Alk5增加Sost的表达，并提出转化生长因子通过增加Wnt共同受体拮抗剂Sost的表达而间接抑制Wnt信号，从而抑制骨量。进一步，我们证明了转化生长因子对SOST的刺激转录效应是由SOST远端增强子元件ECR5介导的，而不是由SOST近端启动子介导的。在这一建议中，(1)我们将检测Alk5缺失或结构性激活对成熟成骨细胞和骨细胞的影响，并检测Alk5缺失或激活对成年小鼠骨骼表型的影响。(2)一旦我们确定了负责调节Alk5对骨骼的影响的细胞类型(成骨细胞或骨细胞)，我们将检测Alk5对Sost和Wnt信号表达的影响，并使用功能丧失或获得的SOST模型，确定Alk5对骨骼表型的调节依赖于Sost的程度。(3)最后，我们将研究Alk5和SOST增强子ECR5在已知负荷诱导的SOST表达减少中的作用。虽然人们已经做出了很多努力来确定单一的促骨因子对骨形成的影响，但我们的建议试图确定转化生长因子和Wnt信号之间的相互作用如何解释转化生长因子对骨骼的分化依赖效应，并开始为药物驱动的骨修复和合成代谢寻找新的药理靶点。

DESCRIPTION (provided by applicant): Wnt signaling is a robust regulator of bone formation, and is antagonized by Lrp co-receptor antagonists like Sclerostin (Sost). Transforming growth factor-beta (TGFß) exhibits pleiotropic and seemingly contradictory effects upon bone formation: TGFß stimulates osteoprogenitor - migration and proliferation, but is also inhibitory to matrix mineralization and promotes formation of mechanically-inferior woven bone. We have recently demonstrated that TGFß increases expression of Sost through the type I receptor Alk5, and propose that TGFß inhibition of bone mass may occur indirectly via inhibition of Wnt signaling by increasing expression of the Wnt co-receptor antagonist Sost. Further, we demonstrated that the stimulatory transcriptional effects of TGFß upon Sost are mediated by the Sost distal enhancer element ECR5, and not the Sost proximal promoter. Within this proposal, (1) we will examine the influence of Alk5 deletion or constitutive activation in mature osteoblasts and osteocytes, and examine the influence of Alk5 deletion or activation upon skeletal phenotype in adult mice. (2) Once we have identified the cell type (osteoblast or osteocyte) responsible for mediating the influence of Alk5 upon the skeleton, we will examine the influence of Alk5 upon expression of Sost and Wnt signaling, and, using Sost models with loss or gain of function, identify the degree to which Alk5 regulation of skeletal phenotype is dependent upon Sost. (3) Finally, we will examine the contribution of Alk5 and the Sost enhancer ECR5 to known load-induced reductions in Sost expression. While much effort has been exerted into identifying the influence of a singular osteotropic factor's influence upon bone formation, our proposal seeks to identify how interplay between TGFß and Wnt signaling may explain the differentiation-dependent effects of TGFß upon the skeleton and begin to identify novel pharmacologic targets for pharmaceutically-driven bone repair and anabolism.