Skeletal Functions of Polycystins and TAZ

骨机械感知缺陷和骨骼卸载导致年龄相关性和废用性骨质疏松症。这个 骨微环境中成骨细胞对物理力反应的分子机制 人们对维持骨骼内环境平衡知之甚少。我们发现了一种新型的机械传感复合体 多囊蛋白(PC1、PKD1和PC2、PKD2)与TAZ(转录因子)相互作用所产生的成骨细胞 带有PDZ结合基序的辅活化子)。PC1/PC2/TAZ复合体具有感知和传递机械力的功能 加载到合成代谢的骨骼反应中。在小鼠中，PKD1或Taz的丢失会导致骨量减少，其特征是 成骨细胞介导的骨形成减少和骨髓中脂肪细胞的增加。 缺乏一个PKD1和TAZ拷贝的复合杂合子小鼠表现出骨量的相加减少， 成骨细胞介导的骨形成受损，骨髓脂肪堆积增加。PC1 C-TER- Minal Tail(PC1-CTT)结合并促进TAZ核转位，共同激活Runx2介导的成骨细胞- PPAR介导的体外成脂和共抑制作用。使用结构的计算方法- 基于虚拟筛选发现了一种新的与PC1：PC2 C末端尾巴结合的激动剂(机械模拟) 螺旋：螺旋相互作用区，激活多囊蛋白/TAZ信号。这些观察结果提供了科学依据 假设骨骼对负荷的反应是由一个机械传感复合体传递的前提 PC1、PC2和TAZ相互作用形成成骨细胞。目的1检验PKD1/TAZ的假设 成熟成骨细胞中相互依赖的功能，通过相互刺激OS-2来调节骨量。 成骨细胞发生和抑制脂肪生成。在这一目标中，我们将研究TAZ对不同 建立条件性基因敲除的小鼠在体外和体内调节成骨细胞发生和脂肪形成 成骨细胞中的Taz(TazOc-CKO)。我们将进一步测试Taz和PKD1之间的遗传相互作用 建立复合Pkd10c-CKO/Taz Oc-CKO小鼠。目的2验证PKD1/TAZ复合体介导的假说 单一和复合PKD_1和Taz在体内外对成骨细胞机械负荷的响应 功能丧失的小鼠模型和成骨细胞培养。AIM 3测试了一种假说，即激活 PC1/PC2/TAZ是一种新型的“机械仿生体”，可通过刺激成骨细胞的形成增加骨量 抑制脂肪生成。我们的影响将是提供一个新的理解分子机制的医学。 通过验证成骨细胞中的PC1/PC2/TAZ机械传感复合体来验证骨骼对负荷的反应。 在这个新的方案中，PC1-CTT和TAZ在骨内的细胞内形成了一个整合的机械传感复合体。 差异调控Runx2依赖的成骨细胞生成和PPARγ介导的脂肪生成的原始细胞系 对骨骼微环境中的物理线索做出反应。多囊蛋白/TAZ复合体也是一种潜在的 治疗骨骼卸载所致骨质疏松症的治疗靶点；新发现的一流 机械仿生提供了一种化学探针来测试靶向多囊蛋白/TAZ是否会导致骨量增加。

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.