Sirtuin/FOXO Signaling in the Regulation of Bone Mass

描述（由申请人提供）：成人或老化骨骼中的骨稳态受到涉及对氧化应激的防御降低和/或活性氧（ROS）产生增加的机制的干扰。值得注意的是，调节生物体对氧化应激反应的几种分子也被导致寿命延长的信号级联共享。在骨和任何其他组织中，各种代谢反应和外源性试剂产生可损伤细胞成分的ROS。细胞通过涉及去磷酸化和随后激活称为FOXO的普遍存在的转录因子家族的机制来抵消ROS的不利影响。FOXO 1是三种FOXO同源物之一，调节细胞分化，促进细胞存活或凋亡;并且还增加模型生物系统的寿命。响应FOXO 1去磷酸化的细胞命运取决于Sirtuins。Sirtuins是NAD依赖的蛋白质脱乙酰酶，其减弱应激诱导的细胞凋亡并延长苍蝇、蠕虫和哺乳动物的寿命。哺乳动物同源物SIRT 1使FOXO 1脱乙酰基，从而使FOXO依赖性反应从细胞死亡转向细胞存活。我们已经发现FOXO 1和SIRT 1对成骨细胞和成骨细胞前体细胞发挥直接的抗凋亡或增殖作用。它们也在破骨细胞中表达。FOXO 1的SIRT 1依赖性脱乙酰化是其抗凋亡作用所必需的。最重要的是，FOXO 1单倍不足降低了成年小鼠的骨量并损害了骨微结构。从成骨细胞中缺失FOXO 1导致成骨细胞数量减少而不影响破骨细胞数量。相反，表达SIRT 1的转基因小鼠显示骨骼中FOXO 1的脱乙酰化增强，脊柱和股骨中的骨量增加，成骨细胞增加，但破骨细胞数量减少。最后，FOXO 1与Wnt信号通路的关键组分--连环蛋白物理结合，形成功能复合物。氧化应激增加FOXO 1介导的抗氧化酶的转录;并减弱成骨细胞谱系细胞中连环蛋白介导的转录的抗破骨细胞生成和成骨细胞生成作用。在本提案中进行的研究中，我们将测试SIRT 1/FOXO 1信号转导响应于生理水平的氧化应激而被激活以保护骨量和保持骨稳态的假设。这一途径和<$-连环蛋白之间的相互作用可能会增强FOXO 1介导的转录和/或调节<$-连环蛋白的抗破骨细胞生成特性。在这个建议中，我们将确定FOXO 1在成骨细胞功能中的作用。我们还将阐明SIRT 1本身或作为FOXO 1信号传导激活剂在骨中的作用。最后，我们将研究FOXO 1是否调节<$-连环蛋白的抗破骨细胞生成作用。这些研究将首次提供调节氧化应激，长寿和骨骼稳态的Sirtuin/FOXO系统的控制下的途径之间的联系。旨在恢复FOXO去乙酰化和磷酸化的治疗方式可能成为骨质疏松症治疗新方法的基础。公共卫生相关性。在骨和任何其他组织中，各种代谢反应和外源性试剂产生可损伤细胞成分的活性氧（ROS）。细胞通过涉及NAD依赖性蛋白脱乙酰酶SIRT 1和转录因子FOXO 1的机制抵消ROS的不利影响;这两者都延长了苍蝇，蠕虫或哺乳动物的寿命。我们将检验SIRT 1/FOXO 1信号转导在生理水平的氧化应激反应中被激活以保护骨量和保持骨稳态的假设。该途径与2-连环蛋白之间的相互作用可能增强FOXO 1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.