Sirtuin/FOXO Signaling in the Regulation of Bone Mass

描述(由申请人提供)：成人或老化骨骼的骨骼动态平衡受到机制的干扰，包括对氧化应激的防御能力降低和/或活性氧物种(ROS)的产生增加。值得注意的是，调节有机体对氧化应激反应的几个分子也被导致寿命延长的信号级联信号所共享。在骨骼和任何其他组织中，各种新陈代谢反应和外源性因素产生的ROS可以破坏细胞成分。细胞通过去磷酸化和随后激活一系列被称为FOXO的普遍存在的转录因子来抵消ROS的不利影响。Foxo1是FOXO的三个同系物之一，它调节细胞分化，促进细胞存活或凋亡，并在模型生物系统中延长寿命。FOXO1去磷酸化反应的细胞命运取决于sirtuins。Sirtuins是一种NAD依赖的蛋白脱乙酰酶，可以减弱应激诱导的细胞凋亡，延长苍蝇、蠕虫和哺乳动物的寿命。哺乳动物同系物SIRT1去乙酰化FOXO1，从而将FOXO依赖的反应从细胞死亡转移到细胞生存。我们发现FOXO1和SIRT1对成骨细胞和成骨前体细胞具有直接的抗凋亡或增殖作用。它们也在破骨细胞中表达。FOXO1的抗凋亡作用需要依赖于SIRT1的脱乙酰基。最重要的是，FOXO1单倍体功能不全会降低成年小鼠的骨量，并损害骨的微结构。从成骨细胞中删除FOXO1会导致成骨细胞数量减少，而不会影响破骨细胞数量。相反，表达SIRT1的转基因小鼠表现出骨中FOXO1的脱乙酰化增强，脊柱和股骨的骨量增加，成骨细胞增加，但破骨细胞数量减少。最后，FOXO1在物理上与Wnt信号通路的关键成分-连环蛋白结合，形成一个功能复合体。氧化应激增加FOXO1介导的抗氧化酶的转录；并减弱成骨细胞系细胞中连环蛋白介导的转录的抗破骨和成骨作用。在这项计划中将要进行的研究中，我们将测试SIRT1/FOXO1信号被激活的假设，以响应生理水平的氧化应激，以保护骨量和维持骨稳态。该途径与β-catenin之间的相互作用可能增强FOXO1介导的转录和/或调节β-catenin的抗破骨细胞生成特性。在这项提案中，我们将确定FOXO1在成骨细胞功能中的作用。我们还将阐明SIRT1本身或作为FOXO1信号激活剂在骨骼中的作用。最后，我们将研究FOXO1是否调节？-catenin的抗破骨作用。这些研究将首次提供在Sirtuin/FOXO系统控制下调节氧化应激、寿命和骨骼动态平衡的途径之间的联系。旨在恢复FOXO脱乙酰化和磷酸化的治疗方式可能形成一种新的骨质疏松治疗方法的基础。与公共卫生相关。在骨骼和任何其他组织中，各种新陈代谢反应和外源物质会产生活性氧物种(ROS)，从而破坏细胞成分。细胞通过涉及NAD依赖的蛋白脱乙酰酶SIRT1和转录因子FOXO1的机制来抵消ROS的不利影响；这两种机制都延长了苍蝇、蠕虫或哺乳动物的寿命。我们将验证SIRT1/FOXO1信号被激活的假设，以响应生理水平的氧化应激，以保护骨量和维持骨稳态。该途径与2-连环蛋白的相互作用可能增强FOXO1介导的转录，并调节2-连环蛋白的抗破骨细胞生成特性。

DESCRIPTION (provided by applicant): Bone homeostasis in the adult or aging skeleton, is perturbed by mechanisms that involve decreased defense against oxidative stress and/or increased production of Reactive Oxygen Species (ROS). Remarkably, several molecules that regulate the organism's response to oxidative stress are also shared by signaling cascades that lead to prolongation of lifespan. In bone, and in any other tissue, a variety of metabolic reactions and exogenous agents generate ROS that can damage cellular constituents. Cells counteract the adverse effects of ROS by mechanisms that involve dephosphorylation and subsequent activation of a family of ubiquitous transcription factors known as FOXOs. FOXO1, one of the three FOXO homologs, regulates cell differentiation, promotes either cell survival or apoptosis; and also increases lifespan in model biologic systems. Cellular fate in response to FOXO1 dephosphorylation depends on Sirtuins. Sirtuins are NAD-dependent protein deacetylases which attenuate stress-induced apoptosis and extend lifespan in flies, worms and mammals. The mammalian homolog SIRT1, deacetylates FOXO1, thus shifting FOXO-dependent responses away from cell death and towards cell survival. We have found that FOXO1 and SIRT1 exert direct anti-apoptotic or proliferative effects on osteoblasts and osteoblast precursors. They are also expressed in osteoclasts. SIRT1-dependent deacetylation of FOXO1 is required for its anti-apoptotic effects. Most importantly, FOXO1 haploinsufficiency decreases bone mass and compromises bone microarchitecture in adult mice. Deletion of FOXO1 from osteoblasts results in reduction in osteoblast numbers without affecting osteoclast numbers. Conversely, transgenic mice expressing SIRT1 show enhanced deacetylation of FOXO1 in bone, increased bone mass in the spine and femur and increased osteoblast but decreased osteoclast numbers. Finally, FOXO1 physically associates with ¿-catenin, a key component of the Wnt signaling pathway, to form a functional complex. Oxidative stress increases FOXO1-mediated transcription of anti-oxidant enzymes; and attenuates both the anti-osteoclastogenic and the osteoblastogenic effects of ¿-catenin-mediated transcription in cells of the osteoblastic lineage. In studies to be conducted in this proposal, we will test the hypothesis that SIRT1/FOXO1 signaling is activated in response to physiological levels of oxidative stress to protect bone mass and preserve bone homeostasis. An interaction between this pathway and ¿-catenin may enhance FOXO1-mediated transcription and/or regulate the anti-osteoclastogenic properties of ¿-catenin. In this proposal we will determine the role of FOXO1 in osteoblast function. We will also elucidate the role of SIRT1 by itself or as an activator of FOXO1 signaling in bone. Finally, we will examine whether FOXO1 regulates the anti-osteoclastogenic actions of ¿-catenin. These studies will provide for the first time a link between pathways that regulate oxidative stress, longevity and skeletal homeostasis under the control of the Sirtuin/FOXO system. Treatment modalities aimed at restoring FOXO deacetylation and phosphorylation may form the basis for a novel approach to osteoporosis therapy. PUBLIC HEALTH RELEVANCE. In bone, and in any other tissue, a variety of metabolic reactions and exogenous agents generate Reactive Oxygen Species (ROS) that can damage cellular constituents. Cells counteract the adverse effects of ROS by mechanisms that involve the NAD-dependent protein deacetylase SIRT1 and the transcription factor FOXO1; both of which extend lifespan in flies, worms or mammals. We will test the hypothesis that SIRT1/FOXO1 signaling is activated in response to physiological levels of oxidative stress to protect bone mass and preserve bone homeostasis. An interaction between this pathway and 2-catenin may enhance FOXO1-mediated transcription and regulate the anti-osteoclastogenic properties of 2-catenin.