MOLECULAR MECHANISMS OF THE SKELETAL EFFECTS OF ESTROGEN IN OLD AGE

雌激素对老年骨骼影响的分子机制

• 批准号: 7094994
• 负责人: STAVROS C. MANOLAGAS
• 金额: $ 21.49万
• 依托单位: UNIV OF ARKANSAS FOR MED SCIS
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-01 至 2011-05-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7094994
• 关键词: aging; animal old age; antioxidants; apoptosis; biological signal transduction; bone density; bone imaging /visualization /scanning; cellular pathology; computed axial tomography; cytokine; developmental genetics; estrogen receptors; estrogens; female; free radical oxygen; genetically modified animals; glutathione; laboratory mouse; mitogen activated protein kinase; molecular pathology; nuclear factor kappa beta; osteoblasts; osteoclasts; osteoporosis; oxidative stress; tissue /cell culture

Estrogen loss increases osteoclastogenesis, decreases osteoclast and increases osteoblast apoptosis, and causes loss of bone by decreasing anti-oxidant defense in these cell types. In addition, an age-dependent decrease in bone strength and mass in ovary-intact C57BL/6 mice is temporally associated with an agedependent increase in the prevalence of osteoblast apoptosis, decreased glutathione reductase (GSR) activity and corresponding increases in the production of reactive oxygen species (ROS) in the bone marrow and the phosphorylation of p66shc in vertebrae. Based on this evidence, it is hypothesized that increased ROS levels with advancing age is a fundamental mechanism of the age-dependent decline of bone strength and mass, and loss of estrogens exaggerates the adverse effects of aging on bone by decreasing defense against ROS, thereby, contributing perpetually to the loss of bone mass and strength that persists for decades after menopause, and is associated with old age. Estrogens enhance defense against ROS by modulating the activity of anti-oxidant enzymes, attenuating ROS-mediated induction of cytokines, and modulating signaling cascades that have been implicated in the defense against oxidative stress, apoptosis, and aging. All these effects are mediated by extranuclear (nongenotropic) actions of the ER on cytoplasmic kinases and result in changes in the birth and lifespan of osteoblasts, osteoclasts, and osteocytes. To test these interrelated hypotheses, in vitro studies are proposed to investigate whether the effects of estrogens on osteoblast and osteoclast apoptosis, as well as on osteoclastogenesis, are, at least in part, a direct consequence of the ability of these hormones to: a) antagonize the actions of ROS by increasing the levels of glutathione; and/or b) counteract ROS-activated signals on cytoplasmic kinases, and/or downstream transcription factors and the resulting upregulation of cytokines. Further, the role of oxidative stress in the molecular and cellular mechanism responsible for the loss of bone strength and mass associated with aging and the extent to which estrogen deficiency and the resulting attenuation of defense against oxidative stress in osteoblasts or osteoclasts contributes to these changes will be studied in mice over-expressing GSR in osteoblasts or osteoclasts. Finally, mice in which ERa will be deleted from osteoblasts or osteoclasts by means of CreXLoxP recombination; mice heterozygotes for an ERa knock-in mutant which cannot bind to ERE; and mice over-expressing an ERa mutant, which is incapable of membrane localization and prevents kinase-mediated signaling of the endogenous receptor, will be used to examine whether the antioxidant actions of estrogens on osteoblasts and osteoclasts in vivo are ER-dependent and nongenotropic. This work should help us understand how women become increasingly more susceptible to fractures as they grow old. Moreover, it mav lead to the discovery of more effective treatments or even a cure for osteoporosis.

雌激素损失增加破骨细胞生成，减少破骨细胞并增加成骨细胞的细胞凋亡，并增加 通过减少这些细胞类型的抗氧化剂防御来导致骨骼丧失。另外，依赖年龄 卵巢INTACT C57BL/6小鼠的骨强度和质量的降低在时间上与年龄相关 成骨细胞凋亡的患病率增加，谷胱甘肽还原酶（GSR）降低 骨髓中活性氧（ROS）产生的活性和相应增加 以及椎骨中p66SHC的磷酸化。基于这些证据，假设增加 随着年龄的增长，ROS水平是骨骼强度下降的基本机制 和质量以及雌激素的丧失通过减少防御来夸大骨骼对骨骼的不利影响 反对ROS，从而永远导致骨骼质量和力量的损失，这持续存在 绝经后的几十年，与老年有关。雌激素通过 调节抗氧化剂酶的活性，减弱ROS介导的细胞因子的诱导和 调节与氧化应激，凋亡的防御相关的信号传导级联 和老化。所有这些作用均由ER对细胞质的核外（非核）作用介导 激酶并导致成骨细胞，破骨细胞和骨细胞的出生和寿命变化。测试 提出了这些相互关联的假设的体外研究，以研究雌激素的影响是否 在成骨细胞和破骨细胞凋亡以及破骨细胞生成上，至少部分是直接的 这些激素能够以下能力的结果：a）通过增加水平来拮抗ROS的作用 谷胱甘肽；和/或b）在细胞质激酶和/或下游抵抗ROS激活的信号 转录因子和导致细胞因子的上调。此外，氧化应激在 分子和细胞机制，导致骨骼强度损失与衰老相关的质量 以及雌激素缺乏以及防御氧化应激的防御衰减的程度 在成骨细胞或破骨细胞中，将在过度表达GSR的小鼠中研究这些变化 成骨细胞或破骨细胞。最后，从成骨细胞或破骨细胞中删除的时代的老鼠 Crexloxp重组的手段；小鼠的杂合子，用于ERA敲入突变体，该突变体无法结合 eere;和过表达ERA突变体的小鼠，该突变体无能力被膜定位并防止 内源性受体的激酶介导的信号传导将用于检查抗氧化剂是否是否 雌激素对体内成骨细胞和破骨细胞的作用是ER依赖性和非核酸的。这项工作 应该帮助我们了解妇女如何随着骨折的年龄而越来越容易受到骨折的影响。 此外，它会导致发现更有效的治疗方法，甚至可以治愈骨质疏松症。