Osteocyte integrity and bone remodeling

描述(申请人提供)：骨中细胞和基质的周转通过骨性重塑发生，其中吸收去除，成骨细胞填充取代已达到其功能寿命结束的致密骨的微观区域。这一转换过程中的不平衡可能会导致骨骼质量受损和脆性增加。骨重建是如何以骨区域为靶点的，长期以来一直不清楚。我们发现，抑制疲劳后的骨细胞凋亡可以阻止破骨细胞吸收的激活，这首次证明了骨细胞凋亡是激活微损伤的靶向性骨吸收的控制步骤。我们还发现，以前为骨微损伤重塑而建立的骨细胞凋亡与破骨细胞性骨吸收之间的空间和时间关系，也适用于卵巢切除和停用引起的骨吸收。最后，我们发现微损伤区域附近存活的骨细胞似乎也对局灶性微损伤有反应，并可能潜在地分泌有助于协调破骨反应的调节因子。在目前的研究中，我们将结合实时定量聚合酶链式反应、免疫组织化学和组织形态计量学的方法，在体内建立大鼠尺骨疲劳模型，以确定微损伤周围的凋亡和非凋亡性骨细胞向破骨细胞发出信号并激活骨重建的调控过程。我们还将通过使用泛半胱氨酸氨基转移酶抑制剂来抑制骨细胞的凋亡，从而确定骨细胞来源的信号中哪些依赖于骨细胞的凋亡。我们将侧重于骨吸收的主要调节因子的骨细胞表达，即a)破骨细胞分化的既定要求，以及b)已通过骨细胞表达或对骨细胞产生影响。对骨样细胞的补充性体外研究将用特定的阻断方法来检验因果关系，以确定单个信号细胞因子在连接凋亡细胞和支持破骨细胞的通路中的作用。在第二系列研究中，我们将使用大鼠尺骨疲劳模型来建立骨细胞凋亡在微损伤周围骨吸收的激活与进展中的重要性。最后，我们将通过使用泛半胱氨酸天冬氨酸氨基转移酶抑制剂抑制雌激素撤除和停用小鼠模型中的骨细胞凋亡，来测试骨细胞凋亡是否是在不同重塑刺激下启动骨吸收的“共同的最终途径”。与公共卫生相关。保持骨质量和预防骨组织脆性依赖于骨重建，在骨重建中，破骨细胞移除，成骨细胞取代已达到其功能寿命结束的骨的微观区域。我们最近的发现表明，这种重塑以及绝经后和废用性骨质疏松症中更新换代和骨丢失的增加，反过来又依赖于骨内骨细胞的调节死亡(细胞凋亡)。这些发现表明，骨细胞凋亡可能是控制骨吸收的一条共同的最终途径，以响应不同的重塑刺激，并提示这种凋亡可能是调节衰老和骨质疏松中破骨细胞活性的一个新的治疗靶点。

DESCRIPTION (provided by applicant): Turnover of cells and matrix in bone occur through osteonal remodeling, wherein resorption removes and osteoblastic infilling replaces microscopic regions of compact bone that have reached the end of their functional life. Imbalances in this turnover process can lead to impaired bone quality and increased fragility. How bone remodeling targets area of bone has long been unclear. We found that inhibiting osteocyte apoptosis after fatigue prevents activation of osteoclastic resorption, demonstrating for the first time that osteocyte apoptosis is a controlling step in the activation of targeted bone resorption of microdamage. We also discovered that the spatial and temporal relationships between osteocyte apoptosis and osteoclastic bone resorption previously established for remodeling of microdamage in bone hold as well for resorption induced by ovariectomy and disuse. Finally, we found that the surviving osteocytes near areas of microdamage also appear to respond to the focal microinury and may potentially secrete regulatory factors that help coordinate the osteoclastic response. In the current studies, we will use a combination of real-time PCR, immunohistochemical and histomorphometry approaches in the rat ulnar fatigue model in vivo to determine the regulatory processes by which apoptotic and non-apoptotic osteocytes surrounding microdamage signal to osteoclasts and activate bone remodeling. We will also determine which among the osteocyte derived signals is dependent upon osteocyte apoptosis by using a pan-caspase inhibitor to suppress the apoptosis. We will focus on osteocyte expression of major regulators of bone resorption that are a) an established requirements for osteoclastic differentiation and b) have demonstrated expression by, or effects on, osteocytes. Complementary in vitro studies on osteocyte-like cells will be used to test causal relationships using specific blocking approaches to determine roles of individual signaling cytokines within the pathway linking apoptotic and pro-osteoclastogenic cells. In the second series of studies, we will use the rat ulnar fatigue model to establish the importance of osteocyte apoptosis in the activation versus progression of bone resorption around microdamage. Finally, we will test whether osteocyte apoptosis is a 'common final pathway' for initiation of bone resorption in response to diverse remodeling stimuli, by using a pan-caspase inhibitor to suppress osteocyte apoptosis in mouse models for estrogen withdrawal and disuse. PUBLIC HEALTH RELEVANCE. Maintaining bone quality and preventing bone tissue fragility depends upon bone remodeling, wherein osteoclasts remove and osteoblasts replace microscopic regions of bone that have reached the end of their functional life. Our recent discoveries indicate that this remodeling, as well as the increased turnover and bone loss in postmenopausal and disuse osteoporoses, in turn, depends of the regulated death (apoptosis) of osteocytes within the bone. These findings suggest that osteocyte apoptosis may be a 'common final pathway' controlling bone resorption in response to diverse remodeling stimuli, and also suggest that this apoptosis could represent a novel therapeutic target for modulating osteoclastic activity in aging and osteoporosis.