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

描述（由申请人提供）：Wnt信号传导是骨形成的稳健调节剂，并且被Lrp共受体拮抗剂如硬化蛋白（Sost）拮抗。转化生长因子-β（TGF β）对骨形成表现出多效性和似乎矛盾的作用：TGF β刺激骨祖细胞迁移和增殖，但也抑制骨形成。 基质矿化并促进机械性下编织骨的形成。我们最近已经证明，TGF β通过I型受体Alk5增加Sost的表达，并提出TGF β对骨量的抑制可能通过增加Wnt共受体拮抗剂Sost的表达来抑制Wnt信号传导而间接发生。此外，我们证明了TGF β对Sost的刺激性转录作用是由Sost远端增强子元件ECR 5介导的，而不是Sost近端启动子。在这个提议中，（1）我们将检查Alk5缺失或组成性激活对成熟成骨细胞和骨细胞的影响，并检查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介导Alk5对骨骼影响的细胞类型（成骨细胞或骨细胞），我们将检查Alk5对Sost和Wnt信号传导表达的影响，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ECR 5对已知负荷诱导的Sost表达减少的贡献。虽然已经付出了很多努力来确定单一的骨形成因子的影响的影响，我们的建议，以确定如何TGF β 1和Wnt信号之间的相互作用可以解释分化依赖性的作用，TGF β 1对骨骼和开始，以确定新的药理学目标，为药物驱动的骨修复和骨愈合。

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.