Skeletal Functions of Polycystins and TAZ

有缺陷的骨机械感知和骨骼卸载有助于年龄相关性和废用性骨质疏松症。的 骨微环境中成骨细胞对物理力反应的分子机制 维持骨骼内环境稳定的机制知之甚少。我们发现了一种新的机械传感复合物， 成骨细胞由多囊蛋白（PC 1，Pkd 1和PC 2，Pkd 2）和TAZ（转录）之间的相互作用产生 具有PDZ结合基序的共活化剂）。PC 1/PC 2/TAZ复合体的功能是感知和检测机械 进入骨合成代谢反应。小鼠中Pkd 1或Taz的缺失导致骨质减少，其特征为： 成骨细胞介导的骨形成的相互减少和骨髓中脂肪细胞的增加。 缺乏一个拷贝的Pkd 1和TAZ的复合杂合小鼠表现出骨量的累加性减少， 成骨细胞介导的骨形成受损和骨髓脂肪积累增加。PC1 C-ter- PC 1-CTT结合并促进TAZ核转位以共激活Runx 2介导的成骨细胞。 在体外共抑制PPAR γ介导的脂肪形成。使用结构的计算方法- 基于虚拟筛选发现了一种新的激动剂（mechanomimetic），结合到PC 1：PC 2的C-末端尾 螺旋：螺旋相互作用区域，并激活多囊蛋白/TAZ信号传导。这些观察提供了科学的 假设骨骼对负荷的反应是由一个机械感应复合体转导的前提， 成骨细胞由PC 1、PC 2和TAZ之间的相互作用形成。目的1检验Pkd 1/TAZ具有以下功能的假设： 在成熟的成骨细胞中相互依赖的功能，通过骨- 成骨细胞生成和抑制脂肪生成。在这个目标中，我们将研究TAZ的影响， 在体外和体内通过建立具有条件性敲除的小鼠来调节成骨细胞生成和脂肪生成。 成熟成骨细胞中的Taz（TazOc-cko）。我们将进一步测试Taz和Pkd 1之间的遗传相互作用， 建立复合Pkd 1 Oc-cko/Taz Oc-cko小鼠。目的2检验Pkd 1/TAZ复合物介导 Pkd 1和Taz单独及复合应用对成骨细胞在体内外机械载荷下的响应 功能丧失小鼠模型和成骨细胞培养。目标3测试了以下假设： 具有新型“机械模拟物”的PC 1/PC 2/TAZ将通过刺激成骨细胞生成增加骨量， 抑制脂肪生成。我们的影响将是提供一个新的理解的分子机制， 通过在成骨细胞中验证PC 1/PC 2/TAZ机械传感复合物来评估骨骼对负荷的反应。 在这种新的模式中，PC 1-CTT和TAZ在骨内细胞中形成了一个整合的机械感应复合体。 胚细胞谱系差异调节Runx 2依赖性成骨细胞发生和PPARγ介导的脂肪发生 来响应骨骼微环境中的物理提示。多囊蛋白/TAZ复合物也是一种潜在的 治疗骨质疏松症的治疗靶点;和新发现的一流的 mechanomimetic提供了一种化学探针，以测试靶向多囊蛋白/TAZ是否导致骨量增加。

Defective bone mechanosensing and skeletal unloading contribute to age-related and disuse osteoporosis. The molecular mechanisms that transduce the osteoblast response to physical forces in the bone microenvironment to maintain skeletal homeostasis are poorly understood. We discovered a novel mechanosensing complex in osteoblasts created by an interaction between polycystins (PC1, Pkd1 and PC2, Pkd2) and TAZ (transcriptional coactivator with PDZ-binding motif). The PC1/PC2/TAZ complex functions to sense and transduce mechanical loading into anabolic bone responses. Loss of either Pkd1 or Taz in mice results in osteopenia characterized by a reciprocal decrease in osteoblast-mediated bone formation and an increase in adipocytes in bone marrow. Compound heterozygous mice lacking one copy of Pkd1 and TAZ exhibit additive decrements in bone mass, impaired osteoblast-mediated bone formation and enhanced accumulation of bone marrow fat. The PC1 C-ter- minal tail (PC1-CTT) binds to and facilitates TAZ nuclear translocation to co-activate Runx2-mediated osteoblas- togenesis and co-repress PPAR-mediated adipogenesis in vitro. Computational approaches using structure- based virtual screening discovered a novel agonist (mechanomimetic) that binds to the PC1:PC2 C-terminal tail helix: helix interaction region and activates polycystins/TAZ signaling. These observations provide the scientific premise for the hypothesis that skeletal responses to loading are transduced by a mechanosensing complex in osteoblasts formed by interactions between PC1, PC2 and TAZ. Aim 1 tests the hypothesis that Pkd1/TAZ have interdependent functions in mature osteoblasts to regulate bone mass through the reciprocal stimulation of os- teoblastogenesis and inhibition of adipogenesis. In this aim, we will examine the effects of TAZ to differentially regulate osteoblastogenesis and adipogenesis in vitro and in vivo by creating mice with conditional knockout of Taz in mature osteoblasts (TazOc-cko). We will further test for genetic interactions between Taz and Pkd1 by creating compound Pkd1Oc-cko/Taz Oc-cko mice. Aim 2 tests the hypothesis that the Pkd1/TAZ complex mediates the response of osteoblasts to mechanical loading in vivo and in vitro using single and compound Pkd1 and Taz loss-of-function mouse models and osteoblast cultures. Aim 3 tests the hypothesis that activation of the PC1/PC2/TAZ with a novel “mechanomimetic” will increase bone mass by stimulating osteoblastogenesis and inhibiting adipogenesis. Our impact will be to provide a new understanding of the molecular mechanisms medi- ating the skeletal response to loading by validating the PC1/PC2/TAZ mechanosensing complex in osteoblasts. In this new schema, PC1-CTT and TAZ form an integrative mechanosensing complex in cells within the osteo- blast lineage to differentially regulate Runx2-dependent osteoblastogenesis and PPARγ-mediated adipogenesis in response to physical cues in the bone microenvironment. The polycystins/TAZ complex is also a potential therapeutic target for treating osteoporosis caused by skeletal unloading; and the newly discovered first-in-class mechanomimetic provides a chemical probe to test if targeting polycystins/TAZ results in increased bone mass.