Estrogen receptor regulation of bone metabolism in adult mice

雌激素受体对成年小鼠骨代谢的调节

• 批准号: 9130741
• 负责人: Sundeep Khosla
• 金额: $ 20.98万
• 依托单位: MAYO CLINIC ROCHESTER
• 依托单位国家: 美国
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-09-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9130741
• 关键词: Address; Adult; Affect; Aging; Apoptosis; Apoptotic; Back; Bone Resorption; Bone remodeling; Cells; Conceptions; Data; Estrogen Receptor alpha; Estrogen Receptor beta; Estrogen Receptors; Estrogens; Experimental Models; Extracellular Signal Regulated Kinases; Financial compensation; Health; Human; In Vitro; Knockout Mice; Laboratories; Mediating; Modeling; Mus; Osteoblasts; Osteoclasts; Osteocytes; Ovariectomy; Pathway interactions; Population; Postmenopause; Prevention; RNA Splicing; Regulation; Risk; Role; Skeletal Development; Skeleton; Source; Structure; TRANCE protein; Testing; Uterus; Variant; Weight; Woman; bone; bone age; bone loss; bone mass; bone metabolism; bone turnover; cell type; insight; mature animal; mouse model; new therapeutic target; novel; prevent; progenitor; receptor; skeletal; substantia spongiosa

DESCRIPTION (provided by applicant): Despite the importance of estrogen (E) in regulating bone metabolism and age-related bone loss, there remain fundamental, unanswered questions regarding E action on bone. A more complete understanding of E regulation of bone turnover is important because even though E treatment of postmenopausal women is declining due to well publicized non-skeletal risks, understanding the mechanisms by which E regulates bone metabolism is likely to identify novel therapeutic targets. Existing mouse models with cell-specific deletion of estrogen receptor (ER)α have provided significant mechanistic insights, but an important limitation of all current models is that they have involved ER deletion from conception onwards, making it impossible to distinguish the effects of E on skeletal development from those on the adult skeleton. To address this issue, we have developed an experimental model in which we can selectively delete ERα in the adult mouse. In preliminary studies in which ERα was globally deleted in adult mice while holding circulating E levels constant, we surprisingly found no bone loss or increase in bone resorption despite marked decreases in uterine weight to levels observed following ovariectomy. These data establish a unique approach to define the role of ERα in regulating bone turnover in the adult skeleton, and also point to a potential compensatory mechanism in bone that has been largely ignored. We hypothesize that this mechanism involves ERß, and in Aim 1, we will globally delete both ERα and ERß following skeletal maturity and determine whether the absence of bone loss we observed following ERα deletion alone in the adult mouse was due to ERß compensation. A second important, unresolved question is that when E is withdrawn in the adult mouse (or human), which cell type is crucial for triggering bone loss? In Aim 2 we will test the hypothesis that this crucial cell is the osteocyte, and that deletion of both ERα and ERß in the osteocyte will be required to trigger bone loss in the adult mouse. The existing evidence in support of this hypothesis is that 1) the osteocyte is increasingly recognized as the "master regulator" of bone remodeling; 2) prevention of osteocyte apoptosis also prevents the increase in bone resorption following ovariectomy; and 3) both ERα and ERß activate extracellular signal- related kinases that mediate the anti-apoptotic effects of E on osteocytes. A competing hypothesis to the osteocyte being the crucial cell triggering bone remodeling following E deficiency is that the key cell is, in fact, the osteoclast. Thus, mice with ERα deletion in osteoclasts from conception onwards have increased bone turnover and reduced bone mass. In order to definitively resolve this issue, in Aim 3 we will delete ERα and/or ERß in osteoclasts in the adult mouse and compare this to osteocyte-specific deletion of these receptors in Aim 2. Moreover, embedded within Aims 2 and 3 will be analyses of highly enriched populations of osteocytes, osteoclast progenitors, and osteoblasts that are performed without in vitro culture, thereby providing important mechanistic insights into E action on bone.

描述（由申请人提供）：尽管雌激素(E)在调节骨代谢和与年龄相关的骨质流失方面具有重要作用，但关于E对骨骼的作用仍然存在根本的、未解之谜。更全面地了解E对骨转换的调节是很重要的，因为尽管由于众所周知的非骨骼风险，绝经后妇女的E治疗正在减少，但了解E调节骨代谢的机制可能会确定新的治疗靶点。雌激素受体(ER)α细胞特异性缺失的现有小鼠模型已经提供了重要的机制见解，但所有现有模型的一个重要限制是，它们从受孕开始就涉及ER缺失，因此无法区分E对骨骼发育的影响与对成年骨骼的影响。为了解决这个问题，我们开发了一个实验模型，我们可以选择性地删除成年小鼠的ERα。在初步研究中，在保持循环E水平不变的情况下，在成年小鼠中全面删除ERα，我们惊讶地发现，尽管子宫重量明显减少到卵巢切除术后的水平，但没有骨丢失或骨吸收增加。这些数据建立了一种独特的方法来定义ERα在调节成人骨骼中骨转换中的作用，并且还指出了在很大程度上被忽视的骨的潜在代偿机制。我们假设这种机制涉及ERß，在Aim 1中，我们将在骨骼成熟后全面删除ERα和ERß，并确定我们在成年小鼠中单独删除ERα后观察到的骨质丢失是否由于ERß补偿。第二个重要但尚未解决的问题是，当成年小鼠（或人类）体内的E消失时，哪种细胞类型对引发骨质流失至关重要？在Aim 2中，我们将测试这个关键细胞是骨细胞的假设，并且骨细胞中ERα和ERß的缺失将需要触发成年小鼠的骨质流失。支持这一假设的现有证据是：1)骨细胞越来越被认为是骨重塑的“总调节器”；2)防止骨细胞凋亡也可以防止卵巢切除术后骨吸收的增加；3) ERα和ERß均激活细胞外信号相关激酶，介导E对骨细胞的抗凋亡作用。关于骨细胞是E缺乏后引发骨重塑的关键细胞的另一种假说是，关键细胞实际上是破骨细胞。因此，从受孕开始，破骨细胞ERα缺失的小鼠骨转换增加，骨量减少。为了明确解决这个问题，在Aim 3中，我们将删除成年小鼠破骨细胞中的ERα和/或ERß，并将其与Aim 2中骨细胞特异性删除这些受体进行比较。此外，在目标2和目标3中，将分析高度富集的骨细胞、破骨细胞祖细胞和成骨细胞，这些都是在没有体外培养的情况下进行的，从而为E对骨的作用提供重要的机制见解。