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

说明(申请人提供)：甲状旁腺激素(PTH)是一种在钙代谢中起主要作用的多肽激素。此外，每日重组甲状旁腺素(1-34，Teriparatide)是FDA批准的唯一治疗合成代谢性骨质疏松的药物。到目前为止，我们还不完全了解Teriparatide合成代谢作用的详细细胞和分子机制。PTH受体在骨细胞中表达，骨细胞中的PTH信号可能对Terparatide刺激净骨生成的能力至关重要。硬化素是一种成骨细胞来源的骨形成抑制因子，其表达受甲状旁腺素下调。硬化素是治疗骨质疏松症的新药靶点，PTH抑制硬化素的作用可能是其抗骨质疏松作用的重要机制之一。本研究旨在研究骨细胞中甲状旁腺素信号导致硬化素下调的分子机制。我们的假设是，IIa类组蛋白脱乙酰酶(HDAC)蛋白在甲状旁腺素受体和硬化素抑制之间的通路中起着重要作用。我们计划使用体外和体内相结合的方法来研究IIa类HDAC在这一途径中的作用。首先，在一种新的骨细胞系中，IIa类HDACs的水平将通过shRNA介导的基因沉默来操纵，该细胞系显示出强大的PTH依赖的skerostin下调。下一步，将进行详细的机制研究，以了解IIa类HDAC如何在从甲状旁腺素到硬化素下调的通路中发挥作用。最后，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来降低体内的硬化素水平。这些研究将提供有关Teriparatide骨合成代谢作用背后的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.