The role of class II histone deacetylases in PTH signaling in osteocytes

描述（申请人提供）：甲状旁腺激素（PTH）是一种肽激素，在钙代谢中起主要作用。此外，每日重组形式的甲状旁腺激素（1-34，特立帕肽）是唯一获得fda批准的合成代谢骨质疏松症治疗药物。到目前为止，我们还没有完全了解特立帕肽合成代谢作用的详细细胞和分子机制。甲状旁腺激素受体在骨细胞中表达，骨细胞中的甲状旁腺激素信号可能对特立帕肽刺激净骨生成的能力至关重要。硬化蛋白是一种骨细胞来源的成骨细胞骨形成抑制剂，其表达受甲状旁腺激素的下调。硬化蛋白是治疗骨质疏松的新药物靶点，甲状旁腺激素抑制硬化蛋白可能是特立帕肽治疗效果的重要机制。本研究旨在研究骨细胞中PTH信号导致硬化蛋白下调的分子机制。我们的假设是IIa类组蛋白去乙酰化酶（HDAC）蛋白在PTH受体和硬化蛋白抑制之间的通路中起重要作用。我们计划通过体外和体内结合的方法来研究IIa类hdac在这一途径中的作用。首先，将在一种新型骨细胞细胞系中使用shrna介导的基因沉默来控制IIa类hdac的水平，该细胞系显示出强劲的pth依赖性硬化蛋白下调。接下来，将进行详细的机制研究，以了解IIa类hdac如何在从甲状旁腺激素到硬化蛋白下调的途径中起作用。最后，我们将对骨细胞中缺乏IIa类hdac的小鼠进行研究，以确定PTH是否需要IIa类hdac来降低体内的硬化蛋白水平。这些研究将提供关于特立帕肽骨合成代谢作用下骨细胞信号通路的关键数据。此外，对这些途径的更好理解可能会导致骨质疏松症新疗法的发展。

DESCRIPTION (provided by applicant): Parathyroid hormone (PTH) is a peptide hormone with a major role in calcium metabolism. In addition, a daily recombinant form of PTH (1-34, teriparatide) is the only FDA-approved anabolic osteoporosis treatment. To date, we do not fully understand the detailed cellular and molecular mechanism of teriparatide's anabolic effect. PTH receptors are expressed in osteocytes, and PTH signaling in osteocytes is likely to be vital for the ability of teriparatide to stimulate net bone production. Sclerostin is an osteocyte-derived inhibitor of bone formation by osteoblasts whose expression is down-regulated by PTH. Sclerostin is a novel drug target for osteoporosis, and sclerostin inhibition by PTH is likely to b an important mechanism underlying the teriparatide treatment effect. This proposal aims to study the molecular mechanisms whereby PTH signaling in osteocytes leads to sclerostin down-regulation. Our hypothesis is that class IIa histone deacetylase (HDAC) proteins play an essential role in the pathway between the PTH receptor and sclerostin inhibition. We plan to study the role of class IIa HDACs in this pathway using a combination of in vitro and in vivo approaches. First, levels of class IIa HDACs will be manipulated using shRNA-mediated gene silencing in a novel osteocytes cell line which displays robust PTH-dependent sclerostin down-regulation. Next, detailed mechanistic studies will be performed to understand how class IIa HDACs function in the pathway leading from PTH to sclerostin down-regulation. Finally, mice lacking class IIa HDACs in osteocytes will be studied to determine if class IIa HDACs are required for PTH to reduce sclerostin levels in vivo. These studies will provide key data regarding the signaling pathways in osteocytes underlying teriparatide's osteoanabolic effect. In addition, an improved understanding of these pathways may lead to the development of novel therapies for osteoporosis.