Disuse Induced Osteocyte Hypoxia

描述(由申请人提供)：骨骼负荷的减少(即，废弃)会导致一系列细胞事件，最终导致局部介导的骨丢失。然而，废用转化为破骨细胞形成和随后的骨吸收的信号通路尚未确定。在我们最初的资金周期中，我们产生的数据证实了我们的普遍假设，即停用会导致骨细胞缺氧。在这一竞争性更新中，我们对骨细胞缺氧如何在生理背景下直接介导破骨细胞活动有了更机械性的理解。具体地说，我们假设废弃诱导的骨桥蛋白(OPN)表达的正常化将抑制废弃诱导的皮质内重构。为了验证这一假设，我们将利用体内(废用性骨量减少的鸟类尺骨模型)和体外(MLO-Y4骨细胞)模型的互补的多学科方法。在一系列特定的目标中，我们将：1)定义骨细胞OPN表达的时间进程，破骨细胞的存在，皮质内和皮质内对急性和慢性停用的吸收容量，2)定义体内间歇性机械加载方案和体外再氧合方案，使骨细胞OPN表达正常化，以响应停用或直接缺氧，3)定义必须启动机械加载和再氧合以使骨细胞OPN表达正常化的时间段，以响应停用或直接缺氧，以及4)通过在慢性停用时叠加每日机械负荷，使骨细胞OPN表达在关键时间窗内正常化。如果没有来自骨细胞的趋化信号(即OPN)，我们认为破骨细胞(或其前体)将不太可能启动皮质内吸收。如果成功，我们预计我们将抑制停用引起的皮质内吸收，从而显著减少与停用相关的组织退化和骨强度损失。如果是这样的话，这些数据将确定一条新的途径，通过它可以直接介导废弃诱导的破骨细胞活动。在我们看来，这一信息的治疗潜力是巨大的，因为抑制废用引起的皮质内吸收的能力可以抵消脊髓损伤、中风、大手术后延长卧床时间或骨折愈合引起的骨脆性和附属健康问题。

DESCRIPTION (provided by applicant): Diminished loading of the skeleton (i.e., disuse) precipitates a series of cellular events culminating in locally mediated bone loss. However, the signaling pathways by which disuse is transduced into osteoclastogenesis and subsequent bone resorption have not been identified. In our initial funding cycle, we generated data that substantiated our general hypothesis that disuse induces osteocyte hypoxia. In this competitive renewal, we progress to a more mechanistic understanding of how osteocyte hypoxia may directly mediate osteoclastic activity within a. physiologic context. Specifically, we hypothesize that normalization of disuse induced osteocyte osteopontin (OPN) expression will inhibit disuse induced intracortical remodeling. To examine this hypothesis, we will implement a multi-disciplinary approach utilizing complementary in vivo (avian ulna model of disuse osteopenia) and in vitro (MLO-Y4 osteocyte) models. In a series of Specific Aims, we will: 1) define the time course of osteocyte OPN expression, osteoclastic presence, intracortical and endocortical resorption volume in response to acute and chronic disuse, 2) define an intermittent in vivo mechanical loading regimen and an in vitro re-oxygenation regimen that normalizes osteocyte OPN expression in response to disuse or direct hypoxia, 3) define the period of time by which mechanical loading and re-oxygenation must be initiated in order to normalize osteocyte OPN expression in response to disuse or direct hypoxia, and 4) normalize osteocyte OPN expression during a critical window of time by superimposing daily mechanical loading upon chronic disuse. Without chemotaxant signals from osteocytes (i.e., OPN), we propose that osteoclasts (or their pre-cursors) will be less likely to initiate intracortical resorption. If successful, we anticipate that we will inhibit disuse induced intracortical resorption and thereby substantially diminish the tissue degradation and loss of bone strength associated with disuse. If so, these data would identify a novel pathway by which disuse induced osteoclastic activity is directly mediated. In our view, the therapeutic potential of this information is substantial as the ability to inhibit disuse induced intracortical resorption could counteract bone fragility and ancillary health issues arising from spinal cord injury, stroke, extended bedrest following major surgery, or fracture healing.