Osteocyte Integrity and Bone Remodeling

描述（由申请人提供）：骨中细胞和基质的更新通过骨细胞重塑发生，其中吸收作用消除，成骨细胞填充取代了已经达到其功能寿命终点的密质骨的微观区域。这种周转过程的不平衡可能导致骨质受损和脆性增加。骨重建如何靶向骨区域长期以来一直不清楚。我们发现，在疲劳后抑制骨细胞凋亡可以防止骨细胞再吸收的激活，首次证明骨细胞凋亡是微损伤靶向骨再吸收激活的控制步骤。我们还发现，骨细胞凋亡和osteocytes骨吸收之间的空间和时间的关系，以前建立的骨微损伤的重塑，以及卵巢切除术和废用引起的骨吸收。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，并可能分泌有助于协调骨细胞反应的调节因子。在目前的研究中，我们将使用实时PCR，免疫组织化学和组织形态计量学方法相结合，在体内的大鼠尺骨疲劳模型，以确定调节过程中，周围的微损伤信号的破骨细胞和激活骨重建的凋亡和非凋亡的骨细胞。我们还将通过使用泛半胱天冬酶抑制剂来抑制细胞凋亡来确定骨细胞来源的信号中哪一个依赖于骨细胞凋亡。我们将重点关注骨吸收的主要调节因子的骨细胞表达，这些调节因子是a）骨细胞分化的既定要求和B）已证实的骨细胞表达或对骨细胞的影响。骨细胞样细胞的补充体外研究将用于测试因果关系，使用特定的阻断方法来确定单个信号细胞因子在连接凋亡和促破骨细胞生成细胞的途径中的作用。在第二个系列的研究中，我们将使用大鼠尺骨疲劳模型，以建立骨细胞凋亡的重要性，在活化与周围微损伤骨吸收的进展。最后，我们将测试骨细胞凋亡是否是一个“共同的最终途径”启动骨吸收在不同的重塑刺激，通过使用泛半胱天冬酶抑制剂抑制骨细胞凋亡的雌激素戒断和废用小鼠模型。公共卫生相关性。维持骨质量和防止骨组织脆性取决于骨重建，其中破骨细胞去除并且成骨细胞替换已经达到其功能寿命终点的骨的微观区域。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增加的周转和骨丢失，反过来又取决于骨内骨细胞的调节性死亡（凋亡）。这些研究结果表明，骨细胞凋亡可能是一个“共同的最终途径”控制骨吸收在不同的重塑刺激，也表明这种凋亡可能代表一种新的治疗靶点，用于调节骨细胞活性的老化和骨质疏松症。

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.