Osteocyte apoptosis and regulation of bone resorption with aging

衰老过程中骨细胞凋亡和骨吸收的调节

• 批准号: 9308117
• 负责人: Lilian Irene Plotkin
• 金额: $ 9.79万
• 依托单位: INDIANA UNIV-PURDUE UNIV AT INDIANAPOLIS
• 依托单位国家: 美国
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-04-01 至 2020-02-29
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9308117
• 关键词: Advanced Glycosylation End Products; Aging; Animals; Apoptosis; Apoptotic; Architecture; Area; Bone Resorption; CASP6 gene; Caspase; Cell Death; Cell Survival; Cells; Chemotactic Factors; Connexin 43; Connexins; Cytoplasmic Tail; Development; Duct (organ) structure; Effectiveness; Event; Excision; Exhibits; Gap Junctions; Genetic; Goals; HMGB1 Protein; Human; In Vitro; Individual; Intervention; Lead; Length; Link; Mediating; Mediator of activation protein; MicroRNAs; Mission; Molecular; Mus; Osteoclasts; Osteocytes; Pharmacology; Phenotype; Phosphotransferases; Play; Prevalence; Property; Public Health; Receptor Activation; Recruitment Activity; Regulation; Role; Signal Pathway; Signal Transduction; Skeleton; Surface; Syndrome; System; TLR4 gene; TNFSF11 gene; Tertiary Protein Structure; Testing; Tumor necrosis factor receptor 11b; United States National Institutes of Health; Wild Type Mouse; Work; age effect; bone; bone fragility; bone loss; cortical bone; cytokine; improved; in vivo; inhibitor/antagonist; mouse model; novel; overexpression; permissiveness; prevent; public health relevance; receptor; scaffold; skeletal

DESCRIPTION (provided by applicant): Aging of the skeleton is associated with increased prevalence of osteocyte apoptosis in mice and humans. Work leading to this application shows that the skeletal syndrome that ensues with aging is mimicked by osteocyte specific deletion of the gap junction protein connexin (Cx) 43. Mice lacking Cx43 in osteocytes exhibit increased osteocyte apoptosis and accumulation of empty lacunae, and reduced OPG levels, and Cx43- deficient osteocytes express lower levels of the survival-associated microRNA (miR) miR21. In addition, bones from old mice exhibit reduced Cx43, OPG, and miR21 expression. We showed in vitro that apoptotic osteocytes release high mobility group box protein1 (HMGB1), which reduces OPG expression and increases osteoclast recruitment and differentiation through activation of receptors for advanced glycation end products (RAGE). HMGB1 also activated toll-like receptor 4 (TLR4). However, whether activation of HMGB1 receptors RAGE or TLR4 has a role in the skeletal phenotype of Cx43-deficient or old mice is not known. The mechanism by which HMGB1 is released by apoptotic cells is not known. A potential mechanism could involve opening of Pannexin1 (Pax1) channels in cells undergoing apoptosis. Whether this mechanism operates in osteocytes undergoing apoptosis is not known. The long-term goal of our studies is to improve the management of the adverse skeletal effects of aging by targeting osteocyte apoptosis and resorption. The specific objective of this application is to define the signaling pathways involved in the elevated osteocyte apoptosis and bone resorption in aging. We propose that the bone fragility syndrome that ensues with aging is due to increased osteocyte apoptosis as a consequence of reduced expression of osteocytic Cx43, OPG, and miR21. We hypothesize that low OPG and the consequent increase in the RANKL/OPG ratio acts as a permissive event for osteoclast development; whereas low miR21 reduces anti-apoptotic kinase signaling and activates caspases, with the consequent Panx1 channel opening and HMGB1 release, directing osteoclasts to areas with accumulated apoptotic osteocytes. To test this hypothesis, we will pursue a combination of in vivo and in vitro studies that include the use of novel genetically modified mice, and established and primary osteocytic cells. Aim 1 will examine the role of Cx43/miR21 on osteocyte apoptosis with aging. Aim 2 will investigate the role of HMGB1 in osteoclast recruitment and differentiation in Cx43 deficiency and aging. Aim 3 will explore the consequence of osteocytic Panx1 removal on HMGB1 release and osteoclast recruitment. Successful completion of these studies will provide the molecular basis for the in- creased osteocyte apoptosis in the absence of Cx43 and in old animals. In addition, these studies will establish the molecular link between dying osteocytes and targeted bone resorption. Moreover, they will offer the basis for treatments in which the effect of increased osteocyte apoptosis on osteoclast recruitment are counteracted by targeting the HMGB1-RAGE/TLR4 system.

描述（由申请人提供）：骨骼老化与小鼠和人类骨细胞凋亡发生率增加相关。导致这一应用的工作表明，骨骼综合征，伴随着老化是模仿骨细胞特异性缺失的差距连接蛋白（Cx）43。骨细胞中缺乏Cx43的小鼠表现出骨细胞凋亡增加和空骨陷窝积累，OPG水平降低，Cx43缺陷的骨细胞表达较低水平的存活相关microRNA（miR）miR 21。此外，来自老年小鼠的骨表现出Cx43、OPG和miR 21表达降低。我们发现，在体外，凋亡的骨细胞释放高迁移率族蛋白1（HMGB 1），减少OPG的表达和增加破骨细胞的招聘和分化，通过激活受体的晚期糖基化终产物（AGEs）。HMGB 1还激活Toll样受体4（TLR 4）。然而，HMGB 1受体β 1或TLR 4的激活是否在Cx43缺陷或老年小鼠的骨骼表型中起作用尚不清楚。凋亡细胞释放HMGB 1的机制尚不清楚。一个潜在的机制可能涉及开放的Pannexin 1（Pax 1）通道的细胞凋亡。这种机制是否在骨细胞凋亡中起作用尚不清楚。我们研究的长期目标是通过靶向骨细胞凋亡和骨吸收来改善衰老对骨骼不良影响的管理。本申请的具体目的是确定衰老过程中骨细胞凋亡和骨吸收增加所涉及的信号通路。我们认为，随着年龄的增长，骨脆性综合征是由于骨细胞Cx43，OPG和miR 21表达减少导致骨细胞凋亡增加。我们假设，低OPG和随之而来的RANKL/OPG比值的增加是破骨细胞发育的允许事件;而低miR 21减少抗凋亡激酶信号传导并激活半胱天冬酶，随之而来的是Panx 1通道开放和HMGB 1释放，将破骨细胞引导至凋亡骨细胞聚集的区域。为了验证这一假设，我们将进行体内和体外研究的结合，包括使用新型转基因小鼠，以及建立和原代骨细胞。目的1探讨Cx43/miR 21在衰老过程中骨细胞凋亡中的作用。目的2探讨HMGB 1在Cx43缺陷和衰老过程中破骨细胞募集和分化中的作用。目的3探讨骨细胞Panx 1的去除对HMGB 1释放和破骨细胞募集的影响。这些研究的成功完成将为Cx43缺失和老年动物骨细胞凋亡增加提供分子基础。此外，这些研究将建立死亡骨细胞和靶向骨吸收之间的分子联系。此外，它们将为治疗提供基础，其中通过靶向HMGB 1-β 1/TLR 4系统来抵消骨细胞凋亡增加对破骨细胞募集的影响。