Sirtuin/FOXO Signaling in the Regulation of Bone Mass

描述（由申请人提供）：成人或衰老骨骼中的骨稳态受到涉及氧化应激防御能力下降和/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个分子也被导致寿命延长的信号级联所共享。在骨骼和任何其他组织中，各种代谢反应和外源性药物产生ROS，可以破坏细胞成分。细胞通过一种机制来抵消ROS的不利影响，这种机制包括去磷酸化和随后激活一系列普遍存在的转录因子，即FOXOs。fox01是三个FOXO同源物之一，调控细胞分化，促进细胞存活或凋亡；也增加了模型生物系统的寿命。细胞命运对fox01去磷酸化的反应取决于Sirtuins。Sirtuins是一种nadd依赖性蛋白去乙酰化酶，可减轻应激诱导的细胞凋亡，延长果蝇、蠕虫和哺乳动物的寿命。哺乳动物的同系物SIRT1使fox01去乙酰化，从而将foxo依赖性反应从细胞死亡转向细胞存活。我们发现FOXO1和SIRT1对成骨细胞和成骨细胞前体具有直接的抗凋亡或增殖作用。它们也在破骨细胞中表达。fox01的sirt1依赖性去乙酰化是其抗凋亡作用所必需的。最重要的是，fox01单倍体不足会降低成年小鼠的骨量并损害骨微结构。从成骨细胞中删除fox01导致成骨细胞数量减少，但不影响破骨细胞数量。相反，表达SIRT1的转基因小鼠表现出骨中FOXO1去乙酰化增强，脊柱和股骨骨量增加，成骨细胞增加，破骨细胞数量减少。最后，fox01与Wnt信号通路的关键组分¿-catenin物理结合，形成一个功能复合物。氧化应激增加fox01介导的抗氧化酶转录；并减弱成骨细胞谱系中-连环蛋白介导的转录的抗破骨和成骨作用。在本提案将要进行的研究中，我们将验证SIRT1/FOXO1信号被激活以响应生理水平的氧化应激以保护骨量和保持骨稳态的假设。该途径与-catenin之间的相互作用可能增强fox01介导的转录和/或调节-catenin的抗破骨细胞特性。在这个提议中，我们将确定fox01在成骨细胞功能中的作用。我们还将阐明SIRT1本身或作为fox01信号激活剂在骨中的作用。最后，我们将研究fox01是否调控¿-catenin的抗破骨细胞作用。这些研究将首次提供在Sirtuin/FOXO系统控制下调节氧化应激、寿命和骨骼稳态的途径之间的联系。旨在恢复FOXO去乙酰化和磷酸化的治疗方式可能形成一种新的骨质疏松症治疗方法的基础。公共卫生相关性。在骨骼和任何其他组织中，各种代谢反应和外源性药物产生活性氧（ROS），可以破坏细胞成分。细胞通过涉及nad依赖性蛋白去乙酰化酶SIRT1和转录因子FOXO1的机制抵消ROS的不利影响；它们都能延长苍蝇、蠕虫或哺乳动物的寿命。我们将验证SIRT1/FOXO1信号被激活以响应生理水平的氧化应激以保护骨量和保持骨稳态的假设。该途径与2-catenin之间的相互作用可能增强fox01介导的转录并调节2-catenin的抗破骨细胞特性。

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.