Osteocyte integrity and bone remodeling

描述（由申请人提供）：骨中细胞和基质的更替通过骨重塑发生，其中吸收去除和成骨细胞填充取代已达到其功能寿命的致密骨的微观区域。这种转换过程中的不平衡会导致骨质量受损和脆性增加。骨重塑如何以骨骼区域为目标一直不清楚。我们发现疲劳后抑制骨细胞凋亡可阻止破骨细胞吸收的激活，首次证明骨细胞凋亡是微损伤靶向骨吸收激活的控制步骤。我们还发现骨细胞凋亡和破骨细胞骨吸收之间的时空关系，这些关系先前在骨支架微损伤重塑以及卵巢切除和废用诱导的骨吸收中建立。最后，我们发现微损伤区域附近的存活骨细胞似乎也对局部微损伤有反应，并可能潜在地分泌调节因子来帮助协调破骨细胞的反应。在目前的研究中，我们将采用实时PCR、免疫组织化学和组织形态学相结合的方法在大鼠尺疲劳模型中进行体内实验，以确定微损伤周围的凋亡和非凋亡骨细胞向破骨细胞发出信号并激活骨重塑的调控过程。我们还将通过使用泛半胱天冬酶抑制剂抑制骨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主要调节因子的骨细胞表达，这是a)破骨细胞分化的既定要求，b)已证明骨细胞表达或对骨细胞的影响。对骨细胞样细胞的补充体外研究将用于使用特定阻断方法来测试因果关系，以确定单个信号细胞因子在连接凋亡和促破骨细胞的途径中的作用。在第二系列研究中，我们将使用大鼠尺骨疲劳模型来确定骨细胞凋亡在微损伤周围骨吸收的激活和进展中的重要性。最后，我们将通过在小鼠模型中使用泛半胱天冬酶抑制剂抑制雌激素停药和停用的骨细胞凋亡，来测试骨细胞凋亡是否是响应各种重塑刺激启动骨吸收的“共同最终途径”。公共卫生相关性。维持骨质量和防止骨组织脆弱依赖于骨重塑，其中破骨细胞移除和成骨细胞替换已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，以及绝经后骨质疏松症和废用性骨质疏松症的增加和骨质流失，反过来取决于骨内骨细胞的调节死亡（凋亡）。这些发现表明，骨细胞凋亡可能是多种重塑刺激下控制骨吸收的“共同最终途径”，也表明这种凋亡可能是调节衰老和骨质疏松症中破骨细胞活性的新治疗靶点。

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.